JP2012036490A - Gold-coated copper wire for ball bonding - Google Patents

Gold-coated copper wire for ball bonding Download PDF

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Publication number
JP2012036490A
JP2012036490A JP2010180617A JP2010180617A JP2012036490A JP 2012036490 A JP2012036490 A JP 2012036490A JP 2010180617 A JP2010180617 A JP 2010180617A JP 2010180617 A JP2010180617 A JP 2010180617A JP 2012036490 A JP2012036490 A JP 2012036490A
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JP
Japan
Prior art keywords
wire
copper
palladium
mass
gold
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
JP2010180617A
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Japanese (ja)
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JP4919364B2 (en
Inventor
Mitsuo Takada
満生 高田
Tsutomu Yamashita
勉 山下
Hiroyuki Amano
裕之 天野
Noriaki Harada
紀明 原田
Hiroyuki Shigyo
裕之 執行
Yoshifumi Nonaka
義文 野中
Takeshi Kuwabara
岳 桑原
Junichi Okazaki
純一 岡崎
Hirofumi Yanai
博文 梁井
Yukihiro Yanaga
幸弘 彌永
Rina Honda
里奈 本田
Yoshiyuki Imaizumi
欣之 今泉
Shigeru Saito
茂 斉藤
Masaaki Kurita
昌昭 栗田
Hiroshi Matsuo
寛 松尾
Akihide Funaki
明秀 船木
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Tanaka Denshi Kogyo KK
Original Assignee
Tanaka Denshi Kogyo KK
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Publication date
Application filed by Tanaka Denshi Kogyo KK filed Critical Tanaka Denshi Kogyo KK
Priority to JP2010180617A priority Critical patent/JP4919364B2/en
Publication of JP2012036490A publication Critical patent/JP2012036490A/en
Application granted granted Critical
Publication of JP4919364B2 publication Critical patent/JP4919364B2/en
Expired - Fee Related legal-status Critical Current
Anticipated expiration legal-status Critical

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Abstract

PROBLEM TO BE SOLVED: To form a stable melting ball by suppressing wear of diamond die by reducing deposition of Pd powder at continuous wire drawing and further reducing eccentricity on axis, in a palladium-coated copper bonding wire.SOLUTION: A coated copper wire for ball bonding with a wire diameter of 10-25 μm is composed of a core material composed of high-purity copper or copper alloy, an intermediate layer comprising palladium with a purity of 99 mass% or more, and an ultra-thin surface layer formed on the intermediate layer as an upper layer, having a film thickness of 1-9 nm, and composed of gold, silver, copper or an alloy whose purity is 99.9 mass% or more and whose hardness and melting point are lower than those of palladium of the intermediate layer as an upper layer. The palladium is coated as the surface layer to improve lubricating property, so that breaking of wire at drawing wire due to deposition of palladium powder in a Figure 3 is prevented, and eccentricity on axis is suppressed.

Description

本発明は、半導体素子上の電極と回路配線基板の配線とをボールボンディングで接続するために用いられる被覆銅ワイヤに関する。   The present invention relates to a coated copper wire used for connecting an electrode on a semiconductor element and a wiring of a circuit wiring board by ball bonding.

現在、半導体素子上の電極と外部端子との間をボールボンディングで接合するボンディングワイヤとして、線径１５〜３０μｍ程度の金線が主に使用されている。しかしながら、近年の金地金価格の高騰によってこれまでの高純度４N系（純度が９９．９９質量％以上）の金線に替わり、１０〜２５μｍ程度の銅線の利用が注目されており、特に、高密度実装上の要請から、より小径の１０〜２０μｍ程度の銅（Cu）ワイヤが求められ始めている。   At present, gold wires having a wire diameter of about 15 to 30 μm are mainly used as bonding wires for bonding electrodes on semiconductor elements and external terminals by ball bonding. However, due to the recent rise in gold bullion prices, the use of copper wires of about 10 to 25 μm has attracted attention in place of conventional high-purity 4N-based (purity of 99.99% by mass or more), Due to demands for high-density mounting, a copper (Cu) wire having a smaller diameter of about 10 to 20 μm has been demanded.

この銅線も金線と同様の利用分野が考えられており、例えば、実装構造では、現行のリードフレームを使用したQFP（Quad Flat Packaging）に加え、基板、ポリイミドテープ等を使用するBGA（Ball Grid Array）、CSP（Chip Scale Packaging ）等の新しい形態への応用が検討され、ループ性、接合性、量産使用性等をより向上したボールボンディングで接合するボンディングワイヤが求められている。   This copper wire is considered to be used in the same fields as gold wires. For example, in the mounting structure, in addition to QFP (Quad Flat Packaging) using the current lead frame, BGA (Ball) using a substrate, polyimide tape, etc. Application to new forms such as Grid Array (CSP) and Chip Scale Packaging (CSP) has been studied, and bonding wires are required to be bonded by ball bonding with improved loop characteristics, bonding characteristics, mass-use usability, and the like.

他方、銅線ボンディングワイヤの接合相手となる電極などの材質も金線の場合と同様であって、シリコン基板上の配線、電極材料としては、従来のアルミニウム（Al）に加えて、より微細配線に好適な高純度の銅（Cu）が実用化されている。また、リードフレーム上には銀（Ag）メッキ、金（Au）メッキ、ニッケル（Ni）メッキ上のパラジウム（Pd）メッキ等が施されており、また、樹脂基板、テープ等の上には、銅（Cu）配線が施され、その上に金（Au）等の貴金属元素及びその合金の皮膜が施されている場合が多い。こうした種々の接合相手に応じて、銅（Cu）ワイヤの接合性、接合信頼性を向上することが求められる。   On the other hand, the material of the electrode, etc., to which the copper wire bonding wire is joined is the same as that of the gold wire, and the wiring on the silicon substrate and the electrode material are finer wiring in addition to the conventional aluminum (Al) High-purity copper (Cu) suitable for the above has been put into practical use. In addition, silver (Ag) plating, gold (Au) plating, palladium (Pd) plating on nickel (Ni) plating, etc. are applied on the lead frame, and on the resin substrate, tape, etc. In many cases, copper (Cu) wiring is provided, and a film of a noble metal element such as gold (Au) and an alloy thereof is provided thereon. It is required to improve the bondability and bonding reliability of copper (Cu) wires according to these various bonding partners.

当初の銅（Cu）ワイヤは、高純度３N〜６N系（純度が９９．９質量％以上〜純度９９．９９９９質量％以上。）の銅（Cu）線の使用が考えられた、しかし、銅線は酸化され易い欠点がある。このため、CuやCu-Sn等の芯材の外周に０．００２〜０．５μｍのPd、Pd-Ni、Pd-Co等の被覆層を設けて、耐食性並びに硬度を改良する提案がなされている（特許文献１）。
また、銅ボンディングワイヤの表面酸化を防ぐ方法として、金、銀、白金、パラジウム、ニッケル、コバルト、クロム、チタンなどの貴金属や耐食性金属で銅を被覆したボンディングワイヤが提案されている（特許文献２、特許文献３参照。）。 The original copper (Cu) wire was considered to be a copper (Cu) wire having a high purity of 3N to 6N (purity of 99.9 mass% or more to purity 99.9999 mass% or more). The wire has the disadvantage of being easily oxidized. For this reason, a proposal has been made to improve the corrosion resistance and hardness by providing a coating layer of Pd, Pd—Ni, Pd—Co, etc. of 0.002 to 0.5 μm on the outer periphery of a core material such as Cu or Cu—Sn. (Patent Document 1).
Further, as a method for preventing the surface oxidation of the copper bonding wire, a bonding wire in which copper is coated with a noble metal such as gold, silver, platinum, palladium, nickel, cobalt, chromium, titanium, or a corrosion-resistant metal has been proposed (Patent Document 2). , See Patent Document 3).

このうち、パラジウム（Pd）を被覆した銅（Cu）ワイヤは、還元性の窒素雰囲気中で溶融ボールを形成すると安定した真球ボールを形成するが、ダイス寿命が短いので、表層に０．０２μｍ（２０ｎｍ：特許文献３の段落００２０〜００２１参照。）の金（Au）メッキをして用いている。
他方、セカンドボンドを接合して引きちぎった後のボールアップに際して、銅（Cu）又は銅合金の芯材の酸化による不都合を回避するため、銅（Cu）にリン（P）を添加し、表層に０．０１５μｍ（１５ｎｍ：特許文献４、段落００２６、表１の実施例８参照。）の金（Au）メッキをすることで、良好な真球状のボールを形成できる被覆ワイヤも開発されている。しかし、これらのワイヤは、後記するように「軸上偏芯」が発生するという新たな問題があることが判明した。 Of these, copper (Cu) wire coated with palladium (Pd) forms a stable spherical ball when a molten ball is formed in a reducing nitrogen atmosphere. However, since the die life is short, the surface layer is 0.02 μm. (20 nm: see paragraphs 0020 to 0021 of Patent Document 3) Gold (Au) plating is used.
On the other hand, in order to avoid inconvenience due to oxidation of the core material of copper (Cu) or copper alloy at the time of ball up after joining and tearing the second bond, phosphorus (P) is added to copper (Cu) and the surface layer is added. A coated wire capable of forming a good spherical ball by gold (Au) plating of 0.015 μm (15 nm: see Patent Document 4, paragraph 0026, Example 8 in Table 1) has also been developed. However, it has been found that these wires have a new problem that “on-axis eccentricity” occurs as described later.

実開昭６０−１６０５５４号公報Japanese Utility Model Publication No. 60-160554 特開昭６２−９７３６０号公報JP-A-62-97360 特開２００５−１６７０２０号公報JP 2005-167020 A 特許第４２０３４５９号公報Japanese Patent No. 4203459 特許第４３４９６４１号公報Japanese Patent No. 4349641

改森信吾ほか、「ハイブリッドボンディングワイヤーの開発」“SEIテクニカルレビュー”第１６９号−４７，２００６年７月Shingo Kaimori et al., “Development of Hybrid Bonding Wire”, “SEI Technical Review” No. 169-47, July 2006

従来（２００７年当時）のワイヤボンディングにおける銅（Cu)ワイヤや銅（Cu）芯材にパラジウム（Pd）を被覆したワイヤの線径は３０μｍオーダーのものが主体であって、ボンディングパッド間のピッチはそれに応じて広いものであった。しかし、近年は高密度実装の進展に伴ってボンディングワイヤの細線化と共に微細なパッドとパッド間のファインピッチ化が進められ、ボンディングワイヤに形成される溶融ボールが真球であること、及び溶融ボールがパッドに対して圧着した形状が真円であることが強く求められるようになっている。
これらの条件が満たされないと、接合された溶融ボールが微細化されたパッド上に収まらず、また接合信頼性が確保されないからであるが、ここでこれらの材質のボンディングワイヤにおいて、溶融ボールの「軸上偏芯」という新たな問題が取り上げられるようになってきた。
「軸上偏芯」は、ボンディングワイヤ先端に形成される溶融ボールの形状が真球か否かというボール形状ではなく、形成された溶融ボールがボンディングワイヤの中心線上からずれる現象をいい、その形状が真球であるか、否かによらず発生し、著しい不具合の原因となる。
すなわち、「軸上偏芯」が発生すると接合されるパッドに対して接合する位置がずれて定まらず、設定されたファインピッチに収まらないのみか、接合の信頼性も得られない。また、「軸上偏芯」の程度の大小のみでなく、その大きさにバラツキがあれば、そのバラツキの幅、程度に応じてパッドの接合面積やピッチを定めなければならない。
無論、この「軸上偏芯」の発生したボンディングワイヤを用いて溶融ボールをパッドに対してボンディングして接合すること自体が困難であり、このため、本発明は「軸上偏芯」の抑制及びそのバラツキの低減を本発明の課題とする。
また、これらのパラジウム（Pd）被覆銅ワイヤにおいて、その伸線加工に伴って、ワイヤ表面にパラジウム（Pd）粉が堆積し、ワイヤ断線が発生すると共にダイヤモンドダイスの磨耗が著しく進行して、銅（Cu）のみの無被覆ワイヤの場合の５分の一以下のダイス寿命となることが新たな問題となり、本発明はこれらワイヤの伸線加工時のパラジウム（Pd）粉の発生、堆積の解消とダイス磨耗を低減する被覆銅ワイヤの提供をも課題とする。 The wire diameter of copper (Cu) wire and copper (Cu) core material coated with palladium (Pd) in conventional (at the time of 2007) wire bonding is mainly 30 μm, and the pitch between bonding pads Was broad accordingly. However, in recent years, along with the progress of high-density packaging, the bonding wire has been made finer and the fine pitch between the pads has been reduced, and the molten ball formed on the bonding wire is a true sphere, and the molten ball It is strongly demanded that the shape that is pressed against the pad is a perfect circle.
If these conditions are not satisfied, the bonded molten ball will not fit on the miniaturized pad, and the bonding reliability will not be ensured, but here in the bonding wire of these materials, The new problem of “axial eccentricity” has been taken up.
“On-axis eccentricity” is not the ball shape of whether the shape of the molten ball formed at the tip of the bonding wire is a true sphere, but the phenomenon that the formed molten ball deviates from the center line of the bonding wire. This occurs regardless of whether or not the ball is a true sphere, and causes a significant defect.
In other words, when “on-axis eccentricity” occurs, the bonding position with respect to the pads to be bonded is shifted and is not fixed, and it does not fit within the set fine pitch, or the bonding reliability cannot be obtained. In addition to the magnitude of the “axial eccentricity”, if there is a variation in the size, the bonding area and pitch of the pads must be determined according to the width and degree of the variation.
Of course, it is difficult to bond the molten ball to the pad using the bonding wire in which the “on-axis eccentricity” occurs, and therefore, the present invention suppresses the “on-axis eccentricity”. It is an object of the present invention to reduce the variation.
Also, in these palladium (Pd) coated copper wires, with the wire drawing process, palladium (Pd) powder accumulates on the wire surface, wire breakage occurs, and diamond die wear progresses remarkably. A new problem is that the die life is less than one-fifth of the case of uncoated wires made only of (Cu), and the present invention eliminates the generation and deposition of palladium (Pd) powder during wire drawing of these wires. Another object is to provide a coated copper wire that reduces die wear.

前記した、銅（Cu）ワイヤの「軸上偏芯」の抑制、バラツキ低減とワイヤ伸線時のパラジウム（Pd）粉の堆積及びダイス磨耗の低減という、本発明の課題はそれぞれワイヤの構成上相互に関連する。
溶融ボールの真球性の不良は、溶融ボールが形成される段階で酸化することに起因すると考えられる。事実、線径２５μｍのパラジウム（Pd）被覆銅ワイヤの表面層として２０ｎｍ厚さの金（Au）層を形成したワイヤに大気中で溶融ボールを形成すると、即座に溶融ボールが槍状となるが、不活性ガスや不活性ガスと還元性ガスの混合ガス中で溶融ボールを形成する場合には真球性の高い溶融ボールが形成される。
一方、軸上偏芯は、同じく径２５μｍのパラジウム（Pd）被覆銅ワイヤの表面層として２０ｎｍ厚さの金（Au）層を形成したワイヤは、還元性雰囲気中でも溶融ボールを形成すると軸上偏芯が発生するが、表面層の金（Au）被覆がない場合には、不活性ガスや不活性ガスと還元性ガスの混合ガス中で軸上偏芯は発生しない。
このことから、溶融ボールの真球性と軸上偏芯の発生とは其のメカニズムが異なると考えられる。
詳しいメカニズムは判明していないが、軸上偏芯については、表面層の金（Au）は展延性が高いため、第２ボンディング（２nd接合）後にワイヤを引きちぎる際にワイヤ切断部の金（Au）表面層のみが大きく延伸し、中間層のパラジウム（Pd）や芯材の銅（Cu）はこの伸びに追従できないため、金（Au）表面層とパラジウム（Pd）中間層の境界面で金（Au）表面層の不均一な突出構造が出現する。そして、次の溶融ボール形成時にこの構造のために溶融時の温度の伝わり方の不均一さ、不均一な溶融の進行を伴ってその結果軸上偏芯が発生すると考えている。また、一方で溶融ボールの形状自体は酸化されない雰囲気下では溶融状態の表面張力の作用が働くため、真球状の溶融ボールが形成されると考えられる。
この課題について、本発明者らが研究した結果、パラジウム（Ｐｄ）被覆銅ワイヤにおいて、パラジウム（Ｐｄ）被覆層の上に金（Ａｕ）等のパラジウム（Ｐｄ）よりも展延性があり、かつ低融点の金属からなる９ｎｍ以下の極く薄い表面被覆層を設けることによって「軸上偏芯」が発生しなくなることを見出した。 As described above, the problems of the present invention, such as suppression of “on-axis eccentricity” of copper (Cu) wire, reduction of variation, accumulation of palladium (Pd) powder during wire drawing, and reduction of die wear, are respectively related to the wire configuration. Interrelated.
It is considered that the poor spherical nature of the molten ball is caused by oxidation at the stage where the molten ball is formed. In fact, when a molten ball is formed in the air on a wire in which a gold (Au) layer having a thickness of 20 nm is formed as a surface layer of a palladium (Pd) -coated copper wire having a wire diameter of 25 μm, the molten ball immediately becomes bowl-shaped. In the case where the molten ball is formed in an inert gas or a mixed gas of an inert gas and a reducing gas, a highly spherical ball is formed.
On the other hand, on-axis eccentricity is the same as the surface layer of a palladium (Pd) -coated copper wire having a diameter of 25 μm, but when a gold (Au) layer having a thickness of 20 nm is formed in a reducing atmosphere, Although a core is generated, if there is no gold (Au) coating on the surface layer, on-axis eccentricity does not occur in an inert gas or a mixed gas of an inert gas and a reducing gas.
From this, it is considered that the mechanism of the sphericity of the molten ball and the occurrence of axial eccentricity are different.
Although the detailed mechanism is not known, for axial eccentricity, the gold (Au) of the surface layer is highly malleable. ) Only the surface layer stretches greatly, and palladium (Pd) in the intermediate layer and copper (Cu) in the core material cannot follow this elongation, so gold at the interface between the gold (Au) surface layer and the palladium (Pd) intermediate layer (Au) A non-uniform protruding structure of the surface layer appears. In addition, it is considered that due to this structure at the time of the next molten ball formation, on-axis eccentricity occurs as a result of non-uniformity in how the temperature is transmitted during melting and non-uniform melting. On the other hand, since the action of surface tension in the molten state works in an atmosphere where the shape of the molten ball itself is not oxidized, it is considered that a true spherical molten ball is formed.
As a result of the present inventors' study on this problem, the palladium (Pd) -coated copper wire is more malleable and lower than palladium (Pd) such as gold (Au) on the palladium (Pd) coating layer. It has been found that “on-axis eccentricity” does not occur by providing a very thin surface coating layer of 9 nm or less made of a melting point metal.

本発明者らは、次に伸線加工中のパラジウム（Pd）被覆銅ワイヤの断線とダイスの異常磨耗を抑制することについて、パラジウムを被覆した銅ワイヤにおいては伸線加工中にパラジウム粉がワイヤに堆積することに伴って特徴的な断線が発生することに気が付き、このパラジウム粉の発生を制御することによってダイス磨耗を抑制できると考えた。
一般的な銅（Cu）ワイヤの伸線加工に伴う破断モードは、図１（かぶり）に示すように線材表面にかぶりの打痕点ないし薄片が連続した後で破断したり、酸化物やカーボンなどの異物が線材中に混入して図２（異物）に示すように伸線中にそのカッピー（cuppy）欠陥箇所から破断する。これに対して、パラジウム（Pd）被覆銅ワイヤは、伸線加工中にダイヤモンドダイスの案内口でパラジウム（Pd）が削り取られてワイヤに堆積していくという現象を伴う。
そして、このパラジウム（Pd）堆積量がある程度の量まで蓄積されると、伸線加工中ワイヤの引き抜き力が増大するため、銅（Cu）ワイヤが摩擦抵抗力に耐えられなくなって、図３（堆積）に示すように引きちぎられるような態様で断線する。また、この断線モードは、一般的な銅（Cu）ボンディングワイヤではほとんど確認されたことがない。パラジウム粉は、数μｍ以下の細かい粒子からなっており、また、パラジウムは硬いことから、伸線加工中に研磨剤のような作用をし、ダイヤモンドダイスを磨耗させる要因となっていると考えられる。このことから、パラジウム粉の堆積が伸線加工中の断線を引き起こしている主原因であり、結果的にダイヤモンドダイスの異常磨耗の原因にもなっていると考えられる。 Next, the inventors of the present invention are concerned with suppressing the disconnection of the palladium (Pd) -coated copper wire during wire drawing and the abnormal wear of the die. We noticed that a characteristic disconnection occurred as it deposited on the surface, and thought that die wear could be suppressed by controlling the generation of this palladium powder.
As shown in Fig. 1 (fogging), the break mode that accompanies the general copper (Cu) wire drawing process is that the surface of the wire rod breaks after the dents or flakes are continuous, or the oxide or carbon As shown in FIG. 2 (foreign matter), foreign matter such as is mixed in the wire and breaks from the cuppy defect portion during drawing. On the other hand, palladium (Pd) -coated copper wire is accompanied by a phenomenon in which palladium (Pd) is scraped off at the guide port of a diamond die during wire drawing and is deposited on the wire.
When the amount of accumulated palladium (Pd) is accumulated to some extent, the drawing force of the wire is increased during wire drawing, so that the copper (Cu) wire cannot withstand the frictional resistance, and FIG. The wire is broken in such a manner that it is torn off as shown in (deposition). Moreover, this disconnection mode has hardly been confirmed with a general copper (Cu) bonding wire. Palladium powder is composed of fine particles of several μm or less, and since palladium is hard, it acts as an abrasive during wire drawing and is considered to be a factor that wears the diamond die. . From this, it is considered that the accumulation of palladium powder is the main cause of wire breakage during wire drawing, resulting in abnormal wear of the diamond die.

本発明者らの研究によればパラジウム被覆銅ワイヤの表面にさらに金（Au）被覆を形成したボンディングワイヤの場合には、このような伸線加工中のパラジウム粉の堆積現象や断線は起こらないばかりか、ダイヤモンドダイスの異常な磨耗も生じていない。
このことは、パラジウム（Pd）は、金（Au）と比較して潤滑液の濡れ性が悪いのに対して、その上に表面層として金層を形成することによって、パラジウムよりも潤滑液との濡れ性が改善されることによると考えられる。また、金（Au）自体がパラジウム（Pd）中間層全体を覆っているため、展延性のよい金層が介在することにより加工性を向上しているとも考えられるが、後述するように、金層の厚さは極めて薄く（１〜９ｎｍ）てよいことから、潤滑性などの表面の改質効果が大きいとも考えられる。
このような伸線加工中の破断モードは、連続伸線工程において最終のボンディングワイヤ径が細くなればなるほど多く発生し、また、伸線工程の断面減少率を大きくすればするほど多く発生する。さらに、最終伸線速度が６００ｍ／分以下であれば伸線加工中にワイヤの振動が生じにくいので断線頻度は少なくなる。 According to the research of the present inventors, in the case of a bonding wire in which a gold (Au) coating is further formed on the surface of a palladium-coated copper wire, such a deposition phenomenon or disconnection of palladium powder during wire drawing does not occur. Not only does the diamond die wear abnormally.
This is because palladium (Pd) is poor in wettability of the lubricating liquid compared to gold (Au), but by forming a gold layer as a surface layer thereon, the lubricating liquid is more effective than palladium. This is considered to be due to the improvement of the wettability. In addition, since gold (Au) itself covers the entire palladium (Pd) intermediate layer, it is considered that the workability is improved by interposing a gold layer having good extensibility. Since the thickness of the layer may be extremely thin (1 to 9 nm), it is considered that the surface modification effect such as lubricity is large.
Such breaking modes during wire drawing occur more frequently as the final bonding wire diameter becomes smaller in the continuous wire drawing process, and more frequently as the cross-sectional reduction rate in the wire drawing process increases. Furthermore, if the final wire drawing speed is 600 m / min or less, the wire vibration is less likely to occur during wire drawing, so the frequency of wire disconnection is reduced.

ところで、前記の課題はそれぞれ相互に関連し、「軸上偏芯」の抑制という面からは前記したようにパラジウム被覆銅ワイヤにおいて、金（Au）層を表面層として形成することは「軸上偏芯」発生の原因ともなっているのであり、一方、伸線加工工程におけるパラジウム粉発生を伴う断線やダイス磨耗の抑制という面から、このパラジウム（Pd）中間層の表面に金（Au）被覆層が必要となることがわかった。
そもそもパラジウム（Pd）被覆銅ワイヤにおいて最上層に金（Au）被覆を行うことは、前述の先行技術文献５（特許第４３４９６４１号公報）にもあるようにワイヤボンディングの第二ボンディング（２nd接合）後の切断されたワイヤ端面を被覆して酸化を防止するものであった。
このため、銅、パラジウムよりもいち早く溶融して、被覆効果を発揮する厚さとして、０．００５〜０．１μｍ（５〜１００ｎｍ）とし、これと合金化するパラジウム中間層の厚さを０．００５〜０．２μｍとし、表皮層の厚さが中間層の厚さよりも薄い、としている。
また、前述の特許文献３（特開２００５−１６７０２０号公報）によれば、銅ワイヤにパラジウム層を形成することによって伸線性を向上し、ダイス磨耗を低減できること、さらにパラジウム層の上に金表皮層を被覆層よりも薄く形成することによってこれらの効果が向上することが記載されている。
該金表皮層の膜厚については、その実験例４で０．０２μｍ（２０ｎｍ）であるが、ワイヤ径の０．００２倍以下、より好ましくは０．００１倍以下の厚さであって、使用ワイヤ径が１５〜４０μｍであるから、１５〜４０ｎｍとなるが、段落００２１に、溶融ボールの真球性との関係でその厚さが厚いと溶融ボールが槍状になり、良好なボールが形成されないことが挙げられており、上記の厚さが上限となるが、一方、「伸線性」からは下限が想定されるもののその記載はなく、また、本発明の課題とする「軸上偏芯」に関して言及はない。 By the way, the above-mentioned problems are related to each other, and from the viewpoint of suppressing “on-axis eccentricity”, as described above, forming a gold (Au) layer as a surface layer in a palladium-coated copper wire is “on-axis On the other hand, the surface of this palladium (Pd) intermediate layer is covered with a gold (Au) coating layer from the viewpoint of suppressing disconnection and die wear associated with the generation of palladium powder in the wire drawing process. It turns out that is necessary.
In the first place, the gold (Au) coating on the uppermost layer of the palladium (Pd) coated copper wire is performed by the second bonding (2nd bonding) of the wire bonding as described in the above-mentioned prior art document 5 (Patent No. 4349641). The later cut wire end face was covered to prevent oxidation.
For this reason, it is 0.005-0.1 micrometer (5-100 nm) as thickness which melt | dissolves earlier than copper and palladium, and exhibits a coating effect, and the thickness of the palladium intermediate | middle layer alloyed with this is 0.00. 005 to 0.2 μm, and the thickness of the skin layer is thinner than the thickness of the intermediate layer.
Further, according to the above-mentioned Patent Document 3 (Japanese Patent Laid-Open No. 2005-167020), by forming a palladium layer on a copper wire, wire drawing can be improved, die wear can be reduced, and a gold skin on the palladium layer. It is described that these effects are improved by forming the layer thinner than the covering layer.
The film thickness of the gold skin layer is 0.02 μm (20 nm) in Experimental Example 4, but it is 0.002 times or less of the wire diameter, more preferably 0.001 times or less. Since the wire diameter is 15 to 40 μm, it is 15 to 40 nm. However, in paragraph 0021, when the thickness is thick in relation to the true sphericity of the molten ball, the molten ball becomes bowl-shaped and a good ball is formed. The above thickness is the upper limit, but the lower limit is assumed from the “drawability”, but there is no description thereof. Is not mentioned.

本発明においては、これらの課題を両立して達成することが求められる。
前記したように「軸上偏芯」に関して、金表面層の厚さは、線径２５μｍのパラジウム（Ｐｄ）被覆銅ワイヤに対して金表面層厚さ２０ｎｍでは解決せず、後述するように９ｎｍ以下の厚さとして始めて達成できた。
また、Pd粉発生を伴う、伸線加工時の断線、ダイヤモンドダイスの磨耗低減の課題は、金表面層の厚さが、１ｎｍ以上あれば達成できる。
すなわち、本発明は、パラジウム被覆銅ワイヤにおいて、最上層として厚さの範囲が１〜９ｎｍの金層を形成することによって上記課題を達成する。
さらにこれらのメカニズムから、最表面の金（Au）の働きは、その展延性がパラジウムよりも高いこと、及びパラジウムよりも融点が低いという性質によって達成できたものであり、同様の性質を備えた金属が適用可能であることが解る。具体的には、このような金属として、銀（Ag）や銅（Cu）の単体金属や金（Au）、銀（Ag）、銅（Cu）、あるいはパラジウム（Pd）と組み合わせてこれらの性質を持たせた合金が考えられる。 In the present invention, it is required to achieve both of these problems.
As described above, regarding the “axial eccentricity”, the thickness of the gold surface layer cannot be solved with a gold surface layer thickness of 20 nm with respect to a palladium (Pd) -coated copper wire having a wire diameter of 25 μm. The following thickness was achieved for the first time.
Further, the problem of wire breakage during wire drawing and diamond die wear reduction accompanied by generation of Pd powder can be achieved if the gold surface layer has a thickness of 1 nm or more.
That is, this invention achieves the said subject by forming the gold | metal layer whose thickness range is 1-9 nm as an uppermost layer in a palladium covering copper wire.
Furthermore, from these mechanisms, the action of gold (Au) on the outermost surface can be achieved by the property that its extensibility is higher than palladium and its melting point is lower than that of palladium. It can be seen that metals are applicable. Specifically, these metals are used in combination with simple metals such as silver (Ag) and copper (Cu), gold (Au), silver (Ag), copper (Cu), and palladium (Pd). An alloy with a slag can be considered.

本発明のボールボンディング用被覆銅ワイヤの具体的構成は、次のとおりである。
（１） 銅（Cu）又は銅合金からなる芯材、パラジウム（Pd）からなる中間被覆層（以下、中間層という。）、及び表面被覆層（以下、表面層という。）からなる、連続伸線加工されたワイヤ径１０〜２５μｍのボールボンディング用被覆銅ワイヤであって、
該パラジウム（Pd）中間層の膜厚がワイヤ径の０．００１〜０．０２倍であり、
該表面層が中間層のパラジウム（Pd）の融点よりも低融点であって、かつ硬さの低い、金（Au）、銀（Ag）又は銅（Cu）からなる膜厚１〜９ｎｍの被覆層であるボールボンディング用銅被覆ワイヤである。
（２） さらに、上記表面層の膜厚が上記中間層の１／８以下であり、
（３） 上記ワイヤ径が１０〜２０μｍであって、表面層の膜厚が２〜７ｎｍであり、
（４） 上記パラジウム（Pd）中間層が湿式メッキにより形成されたものであり、
（５） 上記表面層が室温下のスパッタリング法により形成されたものであり、
（６） 上記中間層が純度９９質量％以上のパラジウム（Pd）であり、
（７） 上記表面層が純度９９．９９質量％以上の金（Au）、純度９９．９９以上の銀（Ag）、又は純度９９．９９質量％以上の銅（Cu）であり、
（８） 上記芯材が純度９９．９質量％以上の銅（Cu）であり、
（９） 上記芯材が０．５〜９９質量ｐｐｍのジルコニウム（Zr）、スズ（Sn）、バナジウム（V）、ホウ素（B）、チタン（Ti）の少なくとも一種を含み、残部が純度９９．９９質量％以上の銅（Cu）からなり、
（１０）芯材が０．５〜９９質量ｐｐｍのジルコニウム（Zr）、スズ（Sn）、バナジウム（V）、ホウ素（B）、チタン（Ti）の少なくとも一種を含み、１〜５００質量ｐｐｍのリン（P）と残部が純度９９．９９質量％以上の銅（Cu）からなり、
（１１）芯材が１〜８０質量ｐｐｍのリン（P）と残部が純度９９．９９質量％以上の銅（Cu）からなる、ことを特徴とするボールボンディング用被覆銅ワイヤである。 The specific configuration of the coated copper wire for ball bonding of the present invention is as follows.
(1) Continuous stretching comprising a core material made of copper (Cu) or a copper alloy, an intermediate coating layer (hereinafter referred to as an intermediate layer) made of palladium (Pd), and a surface coating layer (hereinafter referred to as a surface layer). Wire-coated copper wire for ball bonding having a wire diameter of 10 to 25 μm,
The film thickness of the palladium (Pd) intermediate layer is 0.001 to 0.02 times the wire diameter,
A coating having a thickness of 1 to 9 nm made of gold (Au), silver (Ag) or copper (Cu), wherein the surface layer has a melting point lower than that of palladium (Pd) of the intermediate layer and has a low hardness It is a copper-coated wire for ball bonding that is a layer.
(2) Furthermore, the film thickness of the surface layer is 1/8 or less of the intermediate layer,
(3) The wire diameter is 10 to 20 μm, and the film thickness of the surface layer is 2 to 7 nm.
(4) The palladium (Pd) intermediate layer is formed by wet plating,
(5) The surface layer is formed by a sputtering method at room temperature,
(6) The intermediate layer is palladium (Pd) having a purity of 99% by mass or more,
(7) The surface layer is gold (Au) having a purity of 99.99 mass% or more, silver (Ag) having a purity of 99.99 or more, or copper (Cu) having a purity of 99.99 mass% or more,
(8) The core material is copper (Cu) having a purity of 99.9% by mass or more,
(9) The core material contains at least one of 0.5 to 99 mass ppm of zirconium (Zr), tin (Sn), vanadium (V), boron (B), and titanium (Ti), and the balance is 99. It consists of 99% by mass of copper (Cu),
(10) The core material contains 0.5 to 99 mass ppm of zirconium (Zr), tin (Sn), vanadium (V), boron (B), titanium (Ti), and 1 to 500 mass ppm. Phosphorus (P) and the balance consists of copper (Cu) with a purity of 99.99% by mass or more,
(11) A coated copper wire for ball bonding, characterized in that the core material is composed of phosphorus (P) having a purity of 1 to 80 mass ppm and the balance being copper (Cu) having a purity of 99.99 mass% or more.

本発明によれば、ワイヤ径１０〜２５μｍに対して金（Au）などからなる表面層の膜厚が１〜９ｎｍと極めて薄いため、溶融ボールの真球性に影響を与えることがなく、パラジウム（Pd）被覆銅ワイヤと同様に扱うことができると共に、軸上偏芯を抑制し、さらにパラジウム（Pd）粉の堆積を伴う、伸線加工時の断線やダイヤモンドダイスの異常磨耗を大幅（１／５以下）に抑制することができた。
また、軸上偏芯は抑制され、そのバラツキも小さいため、ファインピッチのボンディングパッドに対応することが可能であり、更にボンディングの接合信頼性が著しく向上し、
今後の電子デバイスにおける微細化に伴う要請に対応することができる。 According to the present invention, since the film thickness of the surface layer made of gold (Au) or the like is as extremely thin as 1 to 9 nm with respect to the wire diameter of 10 to 25 μm, the sphericity of the molten ball is not affected. (Pd) Can be handled in the same way as a coated copper wire, suppresses on-axis eccentricity, and further causes breakage during wire drawing and abnormal wear of diamond dies accompanied by accumulation of palladium (Pd) powder (1 / 5 or less).
In addition, since the eccentricity on the axis is suppressed and its variation is small, it can be used for fine pitch bonding pads, and the bonding reliability of bonding is significantly improved.
It is possible to meet the demands associated with miniaturization in future electronic devices.

図１は、銅ボンディングワイヤの代表的な欠陥例であるかぶり欠陥により破断した状態を示す。FIG. 1 shows a state in which the copper bonding wire is broken by a fogging defect, which is a typical defect example of a copper bonding wire. 図２は、銅ボンディングワイヤの代表的な欠陥例である異物欠陥により破断した状態を示す。FIG. 2 shows a state in which the copper bonding wire is broken by a foreign substance defect which is a typical defect example of the copper bonding wire. 図３は、銅ボンディングワイヤに対するPd粉の堆積により破断した状態を示す。FIG. 3 shows a state in which the copper bonding wire is broken by the deposition of Pd powder.

本発明の被覆銅ワイヤで、表面層の理論的な膜厚の上限は９ｎｍであり、より好ましくは７ｎｍ以下である。ここで、「理論的な膜厚」とは、これらの極めて薄い被覆層を全表面にわたって直接測定することは極めて困難であるため、連続伸線前の湿式めっきやスパッタリングによって形成した被覆層の膜厚から、伸線加工後の値を比例計算して求めたものを明細書において「理論的な」膜厚と表現した。この「理論的な膜厚」を求める比例定数は、ボンディングワイヤとしての連続伸線加工の終了後の線径を連続伸線加工開始前の線径で除した値である。
表面層の膜厚は薄ければ薄いほど、表面層の膜厚に起因した軸上偏芯とそのバラツキを低く抑えることができるが、ダイヤモンドダイスに対する潤滑作用など、前記のダイスの異常磨耗に対する効果がなくなるため、１ｎｍを下限とする。
好ましくは、この値は２ｎｍ以上であり、より好ましくは４ｎｍである。
ダイヤモンドダイスの伸線磨耗や異常磨耗を避けるため、連続伸線は水溶液中で冷却し、かつ、一定速度（連続伸線の最終伸線速度が３０〜６００ｍ／分）で行うことが好ましい。伸線速度がこの範囲を超えて速すぎると、伸線加工中のワイヤに振動が発生し、断線しやすくなる。なお、ダイヤモンドダイスと金（Au）との摩擦抵抗を下げるため、市販の界面活性剤を添加した金属潤滑液を水やアルコール等の希釈液で希釈して使用するほか、エチルアルコール、メチルアルコール又はイソプロピルアルコールだけを含有した水溶液なども用いることができる。 In the coated copper wire of the present invention, the upper limit of the theoretical film thickness of the surface layer is 9 nm, more preferably 7 nm or less. Here, “theoretical film thickness” means that it is very difficult to directly measure these extremely thin coating layers over the entire surface, so the coating layer film formed by wet plating or sputtering before continuous drawing. The value obtained by proportionally calculating the value after wire drawing from the thickness was expressed as “theoretical” film thickness in the specification. The proportional constant for obtaining the “theoretical film thickness” is a value obtained by dividing the wire diameter after the end of continuous wire drawing as a bonding wire by the wire diameter before the start of continuous wire drawing.
The thinner the surface layer, the lower the axial eccentricity and variations caused by the thickness of the surface layer, but the effect on abnormal wear of the die, such as the lubrication action on the diamond die, etc. Therefore, 1 nm is set as the lower limit.
Preferably, this value is 2 nm or more, more preferably 4 nm.
In order to avoid the wire wear and abnormal wear of the diamond die, it is preferable that the continuous wire drawing is cooled in an aqueous solution and performed at a constant speed (the final wire drawing speed of continuous wire drawing is 30 to 600 m / min). If the wire drawing speed exceeds this range and is too fast, vibration will occur in the wire being drawn, making it easier to break. In addition, in order to reduce the frictional resistance between the diamond die and gold (Au), a metal lubricant added with a commercially available surfactant is used by diluting with a diluent such as water or alcohol. An aqueous solution containing only isopropyl alcohol can also be used.

表面層は、断面方向の付きまわり性の均一性からは湿式めっきが最もよいが、めっき析出物中に不純物を取り込みやすいので、これを回避するため乾式めっきを採用してもよい。
めっき層中に不純物を取り込むと、溶融ボール形成のスパーク放電時に溶融ボールの形状に影響を及ぼす。乾式めっきは付きまわり性及び中間層との接合性の観点から、真空蒸着よりもスパッタリング法によるコーティングがよい。スパッタリング法によりコーティングされた金（Au）等の被覆層は、一旦イオン化されているため、純度９９．９質量％以上であっても硬質となり、付きまわり性がよい。
金（Au）などの表面層は、冷間の連続伸線加工で相対的に更に硬質となるパラジウム（Pd）析出物の微細な接合界面内部まで入り込み、冷間伸線加工中にしっかり接合される。
なお、スパッタリング法によりコーティングされた本発明の極めて薄い金（Au）などの表面層は、断面方向から観察すると方向によって厚みが最大６倍程度の差が生じる場合もあるが、溶融ボールに軸上偏芯やそのバラツキは見られない。これは、本発明における金（Au）などの表面層の平均的な膜厚が９ｎｍ以下と薄い場合には、第二ボンド後の切断部における金（Au）表面層の異常な伸びが発生しにくいため、スパーク放電時の不均一な溶融が生じないためと思われる。また、これら表面層の膜厚が極めて薄いことから、このような幾何学的な不均一さがあっても、溶融ボール形成時の表面張力が勝って真球状の溶融ボールとなるものとも考えられる。 For the surface layer, wet plating is the best in terms of uniformity of throwing power in the cross-sectional direction. However, since it is easy to incorporate impurities into the plating deposit, dry plating may be employed to avoid this.
Incorporation of impurities into the plating layer affects the shape of the molten ball during spark discharge in forming the molten ball. In dry plating, coating by sputtering is better than vacuum deposition from the viewpoint of throwing power and bondability with an intermediate layer. Since the coating layer such as gold (Au) coated by the sputtering method is once ionized, even if the purity is 99.9% by mass or more, it is hard and has good throwing power.
Surface layers such as gold (Au) penetrate into the fine joint interface of palladium (Pd) precipitates, which become relatively harder during continuous cold drawing, and are firmly joined during cold drawing. The
It should be noted that the surface layer such as gold (Au) of the present invention coated by the sputtering method may have a maximum thickness difference of about 6 times depending on the direction when observed from the cross-sectional direction. There is no eccentricity or variation. This is because when the average film thickness of the surface layer such as gold (Au) in the present invention is as thin as 9 nm or less, abnormal elongation of the gold (Au) surface layer at the cut portion after the second bond occurs. This is probably because non-uniform melting during spark discharge does not occur. In addition, since the thickness of these surface layers is extremely thin, even if there is such geometrical non-uniformity, it is considered that the surface tension at the time of forming the molten ball wins and a true spherical molten ball is formed. .

本発明の表面層の金（Au）、銀（Ag）、又は銅（Cu）の純度は９９．９質量％以上あれば十分であるが、９９．９９質量％以上あればより好ましい。あるいは、これらの純金属やこれらの純度の金属からなる合金（Au-Ag、Ag-Cu、Au-Cu）に微量添加元素（例えば、Mg、Si、P、Ti、V、Cr、Mn、Co、Ni、Cu、Zn、Ga、Ｇe、Y、Zr、Nb、Rh、Pd、Ag、In、Sn、Sｂ、希土類元素）を意図的に添加、含有させることができる。 The purity of gold (Au), silver (Ag), or copper (Cu) in the surface layer of the present invention is sufficient if it is 99.9% by mass or more, more preferably 99.99% by mass or more. Alternatively, a small amount of additive elements (for example, Mg, Si, P, Ti, V, Cr, Mn, Co) are added to these pure metals or alloys (Au-Ag, Ag-Cu, Au-Cu) made of these pure metals. Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Rh, Pd, Ag, In, Sn, Sb, and rare earth elements) can be intentionally added and contained.

本発明の銅（Cu）芯材は、還元性窒素雰囲気中で真球状の溶融ボールが形成可能な銅（Cu）又は銅合金からなる。銅合金としては、例えば、P、Au、Pd、Ptなどを含有させたものが考えられる。
他方、銅（Cu）の純度が９９質量％以下になると、不純物が含有して連続伸線加工中に断線しやすくなるために、９９．９９９質量％オーダーのものが好適である。ここで、「銅（Cu）の純度００．９９９質量％以上」とは、銅（Cu）以外の金属の不純物元素が０．００１質量％未満であることをいい、銅（Cu）中に存在する酸素、窒素や炭素などのガス状元素を除いたものをいう。 The copper (Cu) core material of the present invention is made of copper (Cu) or a copper alloy capable of forming a true spherical molten ball in a reducing nitrogen atmosphere. As the copper alloy, for example, an alloy containing P, Au, Pd, Pt or the like can be considered.
On the other hand, when the purity of copper (Cu) is 99% by mass or less, impurities are contained and the wire is easily broken during continuous wire drawing. Here, “the purity of copper (Cu) is 0.0999% by mass or more” means that the impurity element of metal other than copper (Cu) is less than 0.001% by mass, and is present in copper (Cu). It excludes gaseous elements such as oxygen, nitrogen and carbon.

なお、本発明の銅（Cu）芯材は、リン（P）が存在することが好ましい。リン（P）は微量でも銅ワイヤの再結晶温度を上昇させ、ワイヤ自体の強度を向上する効果があるからである。また、芯材に所定量のリン（P）が含まれると、第一ボンディングにおいて溶融した銅ボールが凝固していく過程で、銅（Cu）ボールの脱酸作用をする。銅（Cu）の純度９９．９９９質量％以上であれば、リン（P）は１質量ｐｐｍ以上の範囲で脱酸作用をし、５００質量ｐｐｍ以下の範囲であれば、溶融ボールが圧着時に加工硬化してAlパッドを破壊する不良は発生しづらい。このようにリン（P）の脱酸効果により、銅（Cu）の酸化が防止できる。     The copper (Cu) core material of the present invention preferably contains phosphorus (P). This is because even if the amount of phosphorus (P) is small, the recrystallization temperature of the copper wire is raised and the strength of the wire itself is improved. Further, when a predetermined amount of phosphorus (P) is contained in the core material, the copper (Cu) ball is deoxidized in the process of solidifying the molten copper ball in the first bonding. If the purity of copper (Cu) is 99.999% by mass or more, phosphorus (P) deoxidizes in the range of 1 ppm by mass or more, and if it is in the range of 500 ppm by mass or less, the molten ball is processed during compression bonding Defects that harden and destroy the Al pad are unlikely to occur. Thus, oxidation of copper (Cu) can be prevented by the deoxidation effect of phosphorus (P).

本発明の中間層は、パラジウム（Pd）から構成される。パラジウム（Pd）の融点（１，５５４℃）は、芯材の銅（Cu）の融点（１，０８５℃）よりも高い。このため、芯材の銅（Cu）や銅合金が球状の溶融ボールを形成していく最初の溶融段階でパラジウム（Pd）が薄皮となって溶融ボールの側面からの酸化を防止すると考えられる。
本発明の中間層の金属の純度は、第二ボンドの接合強度を確保するため、純度９９質量以上のパラジウム（Pd）が必要である。中間層が厚いと銅ボールが合金化して硬くなり、このためチップ割れが起きやすくなる傾向にあるので、芯材を被覆する膜厚を線径の０．０１倍を上限とした。逆に、中間層の膜厚が薄いと、第二ボンドの接合強度が低下するので芯材の線径の０．００１倍を下限とした。
また、高温放置試験による信頼性の評価結果から、パラジウム（Pd）の中間層はある程度の厚さが必要である。これらのことから、銅（Cu）等の芯材を被覆するパラジウム（Pd）からなる中間層の理論的な最終膜厚を線径の０．００１〜０．０２倍とした。好ましくは、線径の０．００２〜０．０１倍の範囲である。 The intermediate layer of the present invention is composed of palladium (Pd). The melting point (1,554 ° C.) of palladium (Pd) is higher than the melting point (1,085 ° C.) of copper (Cu) as the core material. For this reason, it is considered that palladium (Pd) is thinned to prevent oxidation from the side surface of the molten ball in the first melting stage in which the core material copper (Cu) or copper alloy forms a spherical molten ball.
As for the purity of the metal of the intermediate layer of the present invention, palladium (Pd) having a purity of 99 mass or more is required in order to ensure the bonding strength of the second bond. If the intermediate layer is thick, the copper ball is alloyed and hardened, so that chip cracking tends to occur. Therefore, the upper limit of the film thickness covering the core material is 0.01 times the wire diameter. On the contrary, when the film thickness of the intermediate layer is thin, the bonding strength of the second bond decreases, so 0.001 times the wire diameter of the core material is set as the lower limit.
Further, from the result of the reliability evaluation by the high temperature storage test, the intermediate layer of palladium (Pd) needs to have a certain thickness. From these facts, the theoretical final film thickness of the intermediate layer made of palladium (Pd) covering the core material such as copper (Cu) was set to 0.001 to 0.02 times the wire diameter. Preferably, it is in the range of 0.002 to 0.01 times the wire diameter.

パラジウム（Pd）中間層の形成方法には、乾式めっきや湿式めっきを採用することができる、乾式めっきとして、スパッタリング法、イオンプレーティング法、真空蒸着などいずれでもよい。不純物の混入を避けるためには乾式めっきが好ましいが、断面が均一な円環形状を得るには付きまわりのよい、湿式めっきがよい。不純物が混入していても中間層は溶融ボール形成時のスパーク放電の影響を受けないので、溶融ボールの軸上偏芯には影響を与えない。   As the method for forming the palladium (Pd) intermediate layer, dry plating or wet plating can be employed. As the dry plating, any of sputtering, ion plating, vacuum deposition, and the like may be used. In order to avoid mixing of impurities, dry plating is preferable, but in order to obtain an annular shape with a uniform cross section, wet plating with good circulation is preferable. Even if impurities are mixed in, the intermediate layer is not affected by the spark discharge at the time of forming the molten ball, so it does not affect the on-axis eccentricity of the molten ball.

湿式めっきによりパラジウム（Pd）中間層を形成する前処理としてエッチングを行う場合、芯材の銅（Cu）又は銅合金は純度が高いので、塩素や臭素等のハロゲンイオン、あるいはイオウの混入を防ぐため、エッチングは燐酸浴や硝酸浴が好ましい。電解エッチング浴としては、０．１規定の硝酸と２規定の硝酸アンモニウム又は硝酸カリウム溶液、６０％燐酸水溶液などがあり、化学エッチング浴としては、燐酸４５、氷酢酸４５及び硝酸１０のエッチング浴、燐酸１０及び硝酸１のエッチング浴などがある。一方、乾式エッチングとしては、真空中におけるアルゴンイオンやヘリウムイオンなどの希ガスによるマグネトロンスパッタリングがある。パラジウム（Pd）中間層をマグネトロンスパッタする場合は、芯材との拡散を防ぐため室温で行うのがよい。   When etching is performed as a pretreatment to form a palladium (Pd) intermediate layer by wet plating, the copper (Cu) or copper alloy of the core material is high in purity, thus preventing contamination by halogen ions such as chlorine and bromine, or sulfur. Therefore, the etching is preferably a phosphoric acid bath or a nitric acid bath. Examples of the electrolytic etching bath include 0.1 N nitric acid, 2 N ammonium nitrate or potassium nitrate solution, 60% phosphoric acid aqueous solution, and the like. And nitric acid 1 etching bath. On the other hand, dry etching includes magnetron sputtering using a rare gas such as argon ions or helium ions in a vacuum. When magnetron sputtering is performed on the palladium (Pd) intermediate layer, it is preferable to carry out at room temperature in order to prevent diffusion with the core material.

本発明で使用する銅（Cu）は純度が高いので、パラジウム（Pd）の電解めっき浴もハロゲンイオンや硫酸イオンを含まないアンモニア性水溶液やシアン系水溶液のものが好ましい。また、高分子化合物や金属塩の光沢剤は溶融ボールの真球性に悪影響を与えるので、膜成分としては含まないことが好ましい。銅（Cu）等の芯材に電解めっきされた膜は、その後の連続伸線によって強圧縮加工されるので、膜性状は膜成分ほど重要ではない。膜成分にイオウ（S）が存在すると、溶融ボール形成時に銅（Cu）に混入して溶融ボールを硬化させるおそれがあるからである。パラジウム（Pd）電解めっき浴としては、パラジウムｐ−ソルト（Pd（NH3）2(NO2)２）、亜硝酸アンモニウム及び硝酸カリウム、又はパラジウムｐ−ソルト（Pd（NH3）2（NO2）２）、硝酸アンモニウム及びアンモニア水の弱アルカリ性アンモニア性水溶液、Pd（NH3）２（COO）2及び（NH４）2HPO4の中性アンモニア性水溶液などが採用できる。パラジウムｐ−ソルトを用いた浴では、PHが高いほど、析出物の粒径が大きくなる傾向にある。
パラジウム（Pd）を乾式めっきする場合、スパッタ膜等の異常析出を防ぐため、銅（Cu）の純度は９９．９９質量％よりも９９．９９９質量％程度のものが好ましい。 Since copper (Cu) used in the present invention has a high purity, an electrolytic plating bath of palladium (Pd) is preferably an ammoniacal aqueous solution or a cyanic aqueous solution not containing halogen ions or sulfate ions. In addition, since a polymer compound or a metal salt brightener adversely affects the sphericity of a molten ball, it is preferably not included as a film component. Since the film electroplated on a core material such as copper (Cu) is subjected to strong compression processing by subsequent continuous drawing, the film properties are not as important as the film components. This is because if the film component contains sulfur (S), it may be mixed with copper (Cu) during the formation of the molten ball to cure the molten ball. The palladium (Pd) electrolytic plating bath includes palladium p-salt (Pd (NH 3 ) 2 (NO 2 ) 2 ), ammonium nitrite and potassium nitrate, or palladium p-salt (Pd (NH 3 ) 2 (NO 2 ) 2. ), A weak alkaline aqueous ammoniacal solution of ammonium nitrate and ammonia, and a neutral aqueous ammoniacal solution of Pd (NH 3 ) 2 (COO) 2 and (NH 4 ) 2 HPO 4 . In the bath using palladium p-salt, the particle size of the precipitate tends to increase as the PH increases.
When palladium (Pd) is dry-plated, the purity of copper (Cu) is preferably about 99.999% by mass rather than 99.99% by mass in order to prevent abnormal deposition of a sputtered film or the like.

なお、溶融ボールの形成時に金（Au）表面被覆層が銅（Cu）芯材に溶け込むタイミングを調整するため、パラジウム（Pd）めっきをする前にパラジウム（Pd）や金（Au）やニッケル（Ni）等の市販のストライクめっき（極薄めっき）を施すことができる。 In order to adjust the timing at which the gold (Au) surface coating layer melts into the copper (Cu) core during the formation of the molten ball, palladium (Pd), gold (Au), nickel ( Commercial strike plating (ultra-thin plating) such as Ni) can be applied.

アーク放電による溶融ボールの形成において、各被覆層中の金属の融点は非常に重要である。ボンディングワイヤの大部分は、高純度の銅（Cu）又は銅合金の芯材が占めるので、銅（Cu）の融点（約１，０８５℃）や銅合金の融点が基準になる。芯材の高純度の銅（Cu）や銅合金は、還元性雰囲気中のアーク放電によって完全な真球形状となることが知られている。また、パラジウム（Pd）で被覆した高純度銅（Cu）の芯材も非酸化性雰囲気中でアーク放電によって真球形状となることが知られている。パラジウム（Ｐｄ）の融点（約１，５５５℃）は銅（Ｃｕ）の融点（約１，０８５℃）よりも高いので、非酸化性雰囲気中で銅（Ｃｕ）が真球形状となるのに引きずられて真球形状となるものと考えられる。
しかし、不安定なアーク放電によって最初に溶融するのは表面層なので、溶融ボールの形成には表面被覆層の影響が最も重要となる。高純度の金（Ａｕ）や銀（Ａｇ）のボンディングワイヤは雰囲気を問わずアーク放電により溶融ボールを形成すると真球状の溶融ボールが得られるにもかかわらず、高純度の金（Ａｕ）や銀（Ａｇ）を高純度銅（Ｃｕ）の芯材に直接被覆したボンディングワイヤは、槍状になってしまい、真球形状のボールが得られない。金（Ａｕ）の融点（約１，０６４℃）や銀（Ａｇ）の融点（約９６２℃）は、芯材の銅（Ｃｕ）の融点（約１，０８５度）よりも低いので、銅（Ｃｕ）が球状の溶融ボールを形成していく段階で、低融点の金（Ａｕ）表面被覆層が芯材の銅（Ｃｕ）よりも早く早期に融解してワイヤ端面をすばやく包むが、芯材の銅（Ｃｕ）中への拡散も生じて銅（Ｃｕ）の融解を不均一に促進するものと考えられる。 In forming a molten ball by arc discharge, the melting point of the metal in each coating layer is very important. Since most of the bonding wires are occupied by high-purity copper (Cu) or a copper alloy core material, the melting point of copper (Cu) (about 1,085 ° C.) or the melting point of the copper alloy is used as a reference. It is known that high purity copper (Cu) or a copper alloy as a core material becomes a perfect spherical shape by arc discharge in a reducing atmosphere. Further, it is known that a core material of high-purity copper (Cu) coated with palladium (Pd) also becomes a spherical shape by arc discharge in a non-oxidizing atmosphere. Since the melting point of palladium (Pd) (about 1,555 ° C.) is higher than the melting point of copper (Cu) (about 1,085 ° C.), copper (Cu) becomes a spherical shape in a non-oxidizing atmosphere. It is thought that it becomes a true spherical shape by being dragged.
However, since the surface layer is first melted by the unstable arc discharge, the influence of the surface coating layer is most important for the formation of the molten ball. High-purity gold (Au) or silver (Ag) bonding wires can be used to form high-purity gold (Au) or silver, regardless of the atmosphere. A bonding wire obtained by directly coating (Ag) on a core material of high-purity copper (Cu) has a bowl shape, and a spherical ball cannot be obtained. Since the melting point of gold (Au) (about 1,064 ° C.) and the melting point of silver (Ag) (about 962 ° C.) are lower than the melting point of copper (Cu) of the core material (about 1,085 ° C.), copper ( In the stage where Cu) forms a spherical molten ball, the low melting point gold (Au) surface coating layer melts earlier and earlier than copper (Cu) of the core material and wraps the wire end face quickly. It is considered that diffusion of copper into copper (Cu) also occurs and promotes the melting of copper (Cu) nonuniformly.

ボンディングワイヤの軸上偏芯量は、前記したように金（Ａｕ）等の表面層の膜厚が厚いほど大きく起こりやすい。また、金（Ａｕ）等の純度はできるだけ高いことが展延性の良い超極薄膜で芯材を全面被覆する上から望ましい。湿式めっきの場合には金（Ａｕ）の析出と同時にカリウム（Ｋ）やナトリウム（Ｎａ）塩などの不純物が巻き込まれやすいので、９９．９質量％以上の純度の高いものが望ましい。光沢剤等の他の金属成分や高分子成分がメッキ液中に混入していると、１ｎｍ未満の膜厚まで連続伸線したときに全面被覆することが難しくなり、超極薄膜が破れやすくなる。超極薄の表面層は、いずれの場合も完全な円輪形状でないが、表面層の厚みが１ｎｍ以上あれば十分である。   As described above, the on-axis eccentricity of the bonding wire is likely to increase as the film thickness of the surface layer such as gold (Au) increases. Further, it is desirable that the purity of gold (Au) or the like is as high as possible from the viewpoint of covering the entire core material with a super-thin film having good spreadability. In the case of wet plating, impurities such as potassium (K) and sodium (Na) salts are easily involved at the same time as the deposition of gold (Au), so that a high purity of 99.9% by mass or more is desirable. When other metal components such as brighteners and polymer components are mixed in the plating solution, it becomes difficult to cover the entire surface when continuously drawn to a film thickness of less than 1 nm, and the ultra-thin film is easily broken. . The ultra-thin surface layer is not a perfect annular shape in any case, but it is sufficient that the thickness of the surface layer is 1 nm or more.

パラジウム（Ｐｄ）中間層の湿式メッキは、レべリング剤や光沢剤などが含まれていないことが好ましいが、レべリング剤等が含まれていない場合は不規則な粒状に析出する傾向にある。また、パラジウム（Ｐｄ）の乾式メッキは高純度の銅（Ｃｕ）の芯材の結晶面に沿って層状に析出する傾向にある。しかし、本発明においては、ダイヤモンドダイスは、パラジウム（Ｐｄ）中間層と直接接触することはなく金（Ａｕ）等の表面層と接触して伸線加工されているので、連続伸線加工中にパラジウム（Ｐｄ）粉がダイヤモンドダイスの入り口に堆積することがなく、ワイヤが断線することはない。このため１５μｍの線径のパラジウム（Ｐｄ）を被覆した細い銅（Ｃｕ）ワイヤであっても、金（Ａｕ）表面層を形成しないボンディングワイヤと比較して、５倍以上のダイヤモンドダイスのダイス寿命がある。本発明の表面層は極めて薄いが全面被覆されており、１ｎｍ以上の厚みであれば連続伸線途中で破れることがないからである。   The wet plating of the palladium (Pd) intermediate layer preferably does not contain a leveling agent or a brightening agent, but if it does not contain a leveling agent or the like, it tends to precipitate in irregular particles. is there. Further, palladium (Pd) dry plating tends to deposit in layers along the crystal plane of a high purity copper (Cu) core material. However, in the present invention, the diamond die is not in direct contact with the palladium (Pd) intermediate layer, but is drawn in contact with the surface layer of gold (Au) or the like. Palladium (Pd) powder is not deposited at the entrance of the diamond die, and the wire is not broken. For this reason, even if it is a thin copper (Cu) wire coated with palladium (Pd) having a wire diameter of 15 μm, the die life of the diamond die is more than five times that of a bonding wire that does not form a gold (Au) surface layer. There is. This is because the surface layer of the present invention is extremely thin but is entirely covered, and if it has a thickness of 1 nm or more, it is not broken during continuous wire drawing.

高純度の金（Ａｕ）等の表面層を乾式メッキによって形成する場合、付きまわりを改善するため、乾式メッキ中にワイヤを軸中心に回転させながら移動したり、乾式メッキ中にワイヤを往復させて移動したり、ワイヤの両側から乾式メッキしたりして、高純度の金（Ａｕ）を中間被覆層上により均一な膜厚で析出させることができる。高純度の金（Ａｕ）等の表面層は、展延性が良いので、ダイヤモンドダイスのダイス穴形状にしたがって最終線径まで連続伸線加工することができ、パラジウム（Ｐｄ）中間層がダイヤモンドダイスと直接接触することはない。ワイヤの表面は金（Ａｕ）等が全面的に被覆されているので、連続伸線加工中に金（Ａｕ）等の表面層と中間層との界面の隙間は埋められ、パラジウム（Ｐｄ）中間層の湿式メッキに異常析出等があっても表面層を突き破って析出するようなことはない。 When a surface layer of high-purity gold (Au) or the like is formed by dry plating, the wire is moved while rotating around the axis during dry plating, or the wire is reciprocated during dry plating in order to improve throwing power. The high-purity gold (Au) can be deposited on the intermediate coating layer with a more uniform film thickness by moving the electrode or dry-plating from both sides of the wire. Since the surface layer of high-purity gold (Au) or the like has good spreadability, it can be continuously drawn to the final wire diameter according to the die hole shape of the diamond die, and the palladium (Pd) intermediate layer is made of a diamond die. There is no direct contact. Since the surface of the wire is entirely covered with gold (Au) or the like, the gap at the interface between the surface layer of gold (Au) or the like and the intermediate layer is filled during the continuous wire drawing process, and the palladium (Pd) intermediate Even if there is abnormal deposition or the like in the wet plating of the layer, it does not break through the surface layer and deposit.

以下、具体的に実施例について説明する。始めに、各実施例の共通項目を説明する。
中間層とは芯材の銅（Ｃｕ）と金（Ａｕ）や銀（Ａｇ）などの最表面層と芯材との間に形成された被覆層である。また、表面層は、前記の中間層の外側に形成された最表面層である。
芯材の銅（Ｃｕ）は、以下のＡ〜Ｆの６種類の純度の成分組成を原材料として用いた。
なお、原材料には不純物としてケイ素（Ｓｉ）、鉄（Ｆｅ）、銀（Ａｇ）、マグネシウム（Ｍｇ）、マンガン（Ｍｎ）、硫黄（Ｓ）、鉛（Ｐｂ）などが含有していることが考えられる。
Ａ：９９．９質量％銅（Ｃｕ）
Ｂ：９９．９５質量％銅（Ｃｕ）
Ｃ：９９．９９質量％銅（Ｃｕ）
Ｄ：９９．９９９質量％銅（Ｃｕ）
Ｅ： ５０質量ｐｐｍリン（Ｐ）と残部９９．９質量％銅（Ｃｕ）からなる合金
Ｆ：４５０質量ｐｐｍリン（Ｐ）と残部９９．９質量％銅（Ｃｕ）からなる合金
上記原材料は、溶解、鋳造し、圧延、伸線して線径５００μｍまで加工し、線径５００μｍで芯材の銅（Ｃｕ）にPd中間層の被覆を施し、その後、Ａｕなどの表面層を形成した。
次に各層の形成方法について説明する。
Pd中間層の形成方法が湿式メッキと記載あるものは、日本エレクトロプレイティング・エンジニヤース株式会社（略称「ＥＥＪＡ」という。）製のパラジウムメッキ液ＡＤＰ−７００（公称純度９９．９％）を使用して、湿式の電解メッキにより被覆した。
Pd中間層の形成方法が乾式メッキと記載あるものは、田中貴金属工業株式会社製の純度９９．９質量％のパラジウム（Ｐｄ）金属ターゲットを用いて、真空度７．０×１０−１Ｐａ，スパッタ電力３００〜１０００Ｗで、マグネトロンスパッタ法により被覆した。
Ａｕ表面層の形成方法が湿式メッキと記載あるものは、ＥＥＪＡ製シアン系金メッキ液テンヘ゜レックス２０４Ａを用い、めっき温度：５０℃で、湿式の電解メッキにより被覆した。
Ａｕ表面層の形成方法が乾式メッキと記載あるものは、田中貴金属工業株式会社製の純度９９．９質量％の金（Ａｕ）金属ターゲットを用いて、真空度７．０×１０−１Ｐａ，スパッタ電力２００〜５００Ｗで、マグネトロンスパッタ法により被覆した。
また、表面層の組成がＡｕ以外のものは、各合金組成の金属ターゲットを作製して、真空度７．０×１０−１Ｐａ，スパッタ電力５００Ｗで、マグネトロンスパッタ法により被覆した。
〔実施例１〕 Hereinafter, specific examples will be described. First, common items of each embodiment will be described.
The intermediate layer is a coating layer formed between the core material such as copper (Cu) and gold (Au) or silver (Ag) as the core material and the core material. The surface layer is the outermost surface layer formed outside the intermediate layer.
As the core material, copper (Cu) was used as a raw material with the following six component compositions of purity A to F.
The raw material may contain silicon (Si), iron (Fe), silver (Ag), magnesium (Mg), manganese (Mn), sulfur (S), lead (Pb), etc. as impurities. It is done.
A: 99.9 mass% copper (Cu)
B: 99.95 mass% copper (Cu)
C: 99.99 mass% copper (Cu)
D: 99.999 mass% copper (Cu)
E: Alloy consisting of 50 mass ppm phosphorus (P) and the balance 99.9 mass% copper (Cu) F: Alloy consisting of 450 massppm phosphorus (P) and the balance 99.9 mass% copper (Cu) The above raw materials are: Melting, casting, rolling and drawing were performed to a wire diameter of 500 μm, and a core material copper (Cu) was coated with a Pd intermediate layer with a wire diameter of 500 μm, and then a surface layer such as Au was formed.
Next, a method for forming each layer will be described.
The Pd intermediate layer forming method is described as wet plating using palladium plating solution ADP-700 (nominal purity 99.9%) manufactured by Nippon Electroplating Engineers Co., Ltd. (abbreviated as “EEJA”). Then, it was coated by wet electrolytic plating.
The method for forming the Pd intermediate layer is described as dry plating, using a palladium (Pd) metal target having a purity of 99.9% by mass made by Tanaka Kikinzoku Kogyo Co., Ltd., with a degree of vacuum of 7.0 × 10 −1 Pa, The film was coated by a magnetron sputtering method at a sputtering power of 300 to 1000 W.
When the formation method of the Au surface layer is described as wet plating, it was coated by wet electrolytic plating at a plating temperature of 50 ° C. using a cyan gold plating solution Tenhelex 204A manufactured by EEJA.
The method for forming the Au surface layer is described as dry plating, using a gold (Au) metal target with a purity of 99.9% by mass made by Tanaka Kikinzoku Kogyo Co., Ltd., with a degree of vacuum of 7.0 × 10 −1 Pa, The film was coated by a magnetron sputtering method with a sputtering power of 200 to 500 W.
Further, when the surface layer composition was other than Au, a metal target having each alloy composition was prepared and coated by a magnetron sputtering method at a vacuum degree of 7.0 × 10 −1 Pa and a sputtering power of 500 W.
[Example 1]

実験番号No.４は、Pd中間層によるＰｄ被覆を行なわず、実験番号１、２、５および７は湿式メッキでPd中間層の被覆を行なった。また、実験番号３、６および８は乾式メッキで中間Ｐｄ被覆を行なった。その直後、実験番号Ｎｏ１〜８の表面層としてＡｕ極薄層を形成した。その後は連続伸線加工を行い、表１に記載する線径１３〜２５μｍまで連続伸線加工を行い、その後に窒素ガス不活性雰囲気で伸び率が４〜１０％となる条件で熱処理し、製品スプールに巻き取った。Pd中間層およびＡｕ表面層の最終的な膜厚は表１に記載するとおりである。 Experiment No. 4 did not perform Pd coating with the Pd intermediate layer, and Experiment Nos. 1, 2, 5 and 7 performed the Pd intermediate layer coating by wet plating. In Experiment Nos. 3, 6 and 8, intermediate Pd coating was performed by dry plating. Immediately thereafter, an Au ultrathin layer was formed as the surface layer of Experiment Nos. 1 to 8. After that, continuous wire drawing is performed, wire drawing is performed to a wire diameter of 13 to 25 μm shown in Table 1, and then heat treatment is performed in a nitrogen gas inert atmosphere under conditions where the elongation is 4 to 10%. I wound it up on a spool. The final film thicknesses of the Pd intermediate layer and the Au surface layer are as shown in Table 1.

次に、実験番号１〜８の８種類のワイヤを用いてワイヤボンディングした。ボンディングワイヤの接続には、市販の自動ワイヤボンダ（（株）Ｋ＆Ｓ社製の超音波熱圧着ワイヤボンダ「ＭＡＸｕｍ Ｕｌｔｒａ（商品名）」を使用し、ボール／ステッチ接合を行った。溶融ボールはＭAXｕｍ ｐｌｕｓ Ｃｏｐｐｅｒ Ｋｉｔ（商品名）を用いて、流量０．５（ｌ／ｍｉｎ）で４体積％水素と残部窒素からなる混合ガスを使用して、ガス雰囲気中でアーク放電によりワイヤ先端にボールを形成した。
以上のボンディングワイヤをシリコン基板上の０．８μｍアルミニウム（Ａｌ−０．５％Ｃｕ）電極膜に接合し、ワイヤ他端を４μｍの銀（Ａｇ）メッキした２００℃のリードフレーム（材質は４２アロイ、板厚は１５０μｍ））上にステッチ接合した。キャピラリーはＳＰＴ社製を使用し、溶融ボールに関するワイヤボンダの設定値は、ＥＦＯ Ｆｉｒｅ ＭｏｄｅをＢａｌｌ Ｓｉｚｅとし、ＦＡＢ Ｓｉｚｅは実際の溶融ボール径がワイヤ径の２倍となるように調整した。
アルミニウム（Ａｌ−０．５％Ｃｕ）電極膜のダメージは、ボールボンディング直後に割れが発生していないかを、１９６個の電極膜で確認した。ボールボンディングされた状態でアルミニウム（Ａｌ）電極膜を上部から観察し、圧着されたボール周辺の電極膜に割れや盛り上がりのダメージが入っている個数を数え、０〜５個を○、６〜１０個を△、１１個以上を×とした。
第二ボンディング性は、上記のアルミニウム（Ａｌ−０．５％Ｃｕ）電極膜は使用せずに、ワイヤ両端を４μｍの銀（Ａｇ）メッキした２００℃のリードフレーム（材質は４２アロイ、板厚は１５０μｍ））上にボール／ステッチ接合した。３，９２０本のワイヤをボンディングし、不圧着回数が０〜３本を○、４〜２０本を△、２１以上を×とした。
軸上偏芯の観察は、２００９年頃からワイヤボンディングマシンを使い、連続的に溶融ボールを圧着せずに、裏返した状態で形成する方法が一般的となり、軸上偏芯は容易に観察することが可能になった。例えば、（株）Ｋ＆Ｓ社製の超音波熱圧着ワイヤボンダ「ＭＡＸｕｍ Ｕｌｔｒａ（商品名）」を使用した場合、ループパラメータをＦＡＢモードとすることで実施することが可能となったため、今回はこの方法を用いて、４μｍの銀（Ａｇ）メッキした２００℃のリードフレーム上へ連続ボンディングし、アルミニウム（Ａｌ−０．５％Ｃｕ）電極膜は使用しなかった。なお、その他のワイヤボンディングに関する設定値は、上記のアルミニウム（Ａｌ−０．５％Ｃｕ）電極膜のダメージ評価と同様に行なった。判定は、接合前の溶融ボール形状を１００個観察して、軸上偏芯と寸法精度が良好であるか等を判定した。ワイヤに対するボール位置の芯ずれが５μｍ以上ある個数を測定し、１０個以上である場合に×印、５〜９個である場合に△印、２〜４個であれば実用上の大きな問題はないと判断して○印、芯ずれが１個以下である場合は、ボール形成は良好であるため◎印で表記した。
その結果を表１に示す。 Next, wire bonding was performed using eight kinds of wires of experiment numbers 1 to 8. Bonding wires were connected using a commercially available automatic wire bonder (ultrasonic thermocompression wire bonder “MAXum Ultra (trade name)” manufactured by K & S Co., Ltd.) and ball / stitch bonding was performed. Using a Kit (trade name), a ball was formed at the tip of the wire by arc discharge in a gas atmosphere using a mixed gas consisting of 4% by volume hydrogen and the balance nitrogen at a flow rate of 0.5 (l / min).
The above bonding wire is bonded to a 0.8 μm aluminum (Al-0.5% Cu) electrode film on a silicon substrate, and the other end of the wire is plated with 4 μm silver (Ag) at 200 ° C. (42 alloy) The plate thickness was 150 μm)). The capillaries manufactured by SPT were used, and the wire bonder set value for the molten ball was adjusted so that EFO Fire Mode was Ball Size, and FAB Size was adjusted so that the actual molten ball diameter was twice the wire diameter.
The damage to the aluminum (Al-0.5% Cu) electrode film was confirmed with 196 electrode films to determine whether cracks occurred immediately after ball bonding. The aluminum (Al) electrode film is observed from the upper side in a ball-bonded state, and the number of cracks and bulging damages on the electrode film around the pressure-bonded ball is counted. The number was Δ and the number of 11 or more was ×.
The second bonding property is that the above-mentioned aluminum (Al-0.5% Cu) electrode film is not used, but a lead frame at 200 ° C. in which both ends of the wire are plated with 4 μm of silver (Ag) (material is 42 alloy, plate thickness) Is 150 μm)). 3,920 wires were bonded, the number of non-bonding times was 0-3, ○, 4-20 were Δ, and 21 or more were X.
For the observation of on-axis eccentricity, it has become common to use a wire bonding machine from around 2009 to form the melted ball upside down without continuously crimping the molten ball. Became possible. For example, when the ultrasonic thermocompression wire bonder “MAXum Ultra (trade name)” manufactured by K & S Co., Ltd. is used, it has become possible to implement by setting the loop parameter to the FAB mode. In addition, continuous bonding was performed on a lead frame at 200 ° C. plated with 4 μm of silver (Ag), and an aluminum (Al-0.5% Cu) electrode film was not used. The other set values for wire bonding were performed in the same manner as the damage evaluation of the aluminum (Al-0.5% Cu) electrode film. The determination was made by observing 100 molten ball shapes before joining to determine whether the on-axis eccentricity and the dimensional accuracy were good. The number of balls with a misalignment of 5 μm or more with respect to the wire is measured. When the number is 10 or more, × mark, when it is 5 to 9, Δ mark, 2 to 4 When it was determined that there was no circle, and when the misalignment was 1 or less, the ball formation was good, so that it was marked with ◎.
The results are shown in Table 1.

表１から明らかなとおり、銅（Ｃｕ）からなる芯材にパラジウム（Ｐｄ）中間層を形成し、Ａｕ表面層が被覆されたボンディングワイヤは、実験番号１，２，５，６，７，８のようにパラジウム（Ｐｄ）中間層の膜厚がワイヤ径の０．００１倍以上であれば第二ボンディング性が良好であり、実験番号３〜８のようにパラジウム（Ｐｄ）中間層の膜厚がワイヤ径の０．０２倍未満であればＡｌ電極膜のダメージは良好であった。
上記より、銅（Ｃｕ）からなる芯材に、ワイヤ径の０．００１以上〜０．０２倍未満の厚みでパラジウム（Ｐｄ）中間層を形成し、さらにＡｕ表面層が形成されたボンディングワイヤはボンディングワイヤとして実用に耐えることが確認された。
なお後記するが、実験番号５〜８はダイスライフの評価も行い問題ないことが確認された。
〔実施例２〕 As is apparent from Table 1, bonding wires in which a palladium (Pd) intermediate layer is formed on a core material made of copper (Cu) and an Au surface layer is coated are shown in Experiment Nos. 1, 2, 5, 6, 7, 8 If the film thickness of the palladium (Pd) intermediate layer is 0.001 times the wire diameter or more, the second bonding property is good, and the film thickness of the palladium (Pd) intermediate layer is as in Experiment Nos. 3-8. If the wire diameter is less than 0.02 times the wire diameter, the damage of the Al electrode film was good.
From the above, a bonding wire in which a palladium (Pd) intermediate layer is formed on a core material made of copper (Cu) with a thickness of 0.001 to less than 0.02 times the wire diameter, and further an Au surface layer is formed. It has been confirmed that it can withstand practical use as a bonding wire.
As will be described later, in Experiment Nos. 5 to 8, the die life was evaluated and it was confirmed that there was no problem.
[Example 2]

実験番号No.９〜３８および比較例１〜６を、表２−１および表２−２に示す。
所定の銅（Ｃｕ）を用い、溶解、鋳造し、圧延、伸線して線径５００μｍまで加工し、線径５００μｍで芯材の銅（Ｃｕ）にPd中間層を施し、Ａｕ表面層を形成した。Pd中間層およびＡｕ表面層の形成方法および最終的な厚みは表２−１および表２−２に記載した。その後、連続伸線加工を行い、表に掲げた最終線径とした。その後、窒素ガス不活性雰囲気で伸び率が４〜１０％となる条件で熱処理し、製品スプールに巻き取り、各種の評価を行った。評価は、実施例１と同様に、Ａｌ電極膜ダメージ、第二ボンディング性、軸上偏芯について行った。次に、ダイスライフ評価について説明する。 Experimental numbers No. 9 to 38 and Comparative Examples 1 to 6 are shown in Table 2-1 and Table 2-2.
Using predetermined copper (Cu), melting, casting, rolling and wire drawing to process the wire diameter to 500μm, applying Pd intermediate layer to core copper (Cu) with wire diameter of 500μm to form Au surface layer did. The formation method and final thickness of the Pd intermediate layer and Au surface layer are shown in Tables 2-1 and 2-2. Thereafter, continuous wire drawing was performed to obtain the final wire diameter listed in the table. Then, it heat-processed on nitrogen gas inert atmosphere on the conditions which become 4 to 10% of elongation rate, wound up on the product spool, and performed various evaluation. In the same manner as in Example 1, the evaluation was performed on the Al electrode film damage, the second bonding property, and the on-axis eccentricity. Next, dice life evaluation will be described.

前記したように、伸線加工中に発生するＰｄ粉の堆積が、断線を引き起こしている主原因であり、結果的にダイス磨耗の原因にもなっていると考えられる。発明者らは、Ｐｄ粉の堆積が増えると、断線頻度が増えると共にダイス磨耗も早くなり、逆にＰｄ粉の堆積が減ると、断線が減少し、ダイス磨耗が遅くなることを見出した。このように断線とダイス磨耗に一定の関係が認められたが、断線は製造ロット間の差が大きくなり、評価方法としてばらつきも多いため、ダイス磨耗を評価することで、Ｐｄ粉の堆積の良し悪しを判定することにした。
ダイス磨耗はダイスライフという評価方法で行った。ダイスライフ評価は、伸線用ダイスを用いて、最終伸線で実施した。使用したダイスは、一般的な天然ダイヤモンド製で、伸線加工の最終リダクションは７％を用い、評価は最終線径で実施した。また、伸線速度は３００ｍ／分で行い、伸線加工中はダイスに一般的なＣｕ線加工用の界面活性剤が添加された潤滑液を用いて、伸線用キャプスタンおよび伸線用ダイスに常温の潤滑液をシャワー方式で濡らしながら行った。
具体的には、伸線加工開始時に線径を測定し、次に、伸線１万ｍ毎に線径測定し、伸線加工時の線径と比較して線径が初めて０．０８μｍ増加した時点までの伸線加工長さをダイスライフと定義し、ダイスライフが４万ｍ未満を×、４万ｍ以上〜８万ｍ未満を△、８万ｍ以上〜１５万ｍ未満○、１５万ｍ以上を◎とした。
なお、本評価方法による、線径１８μｍで芯材の銅（Ｃｕ）に０．１μｍの湿式めっきでPd中間層を施し、Ａｕ表面層を形成しなかったワイヤについて評価した結果、ダイスライフは３万ｍであり、×と判定されたが、実験番号５〜８のダイスライフはいずれも１５万ｍ以上となり◎であった。 As described above, it is considered that the accumulation of Pd powder generated during wire drawing is the main cause of wire breakage, and as a result, die wear. The inventors have found that when the deposition of Pd powder increases, the frequency of disconnection increases and the die wear increases, and conversely, when the deposition of Pd powder decreases, the disconnection decreases and the die wear slows. In this way, a certain relationship was found between the disconnection and die wear, but the disconnection increases the difference between production lots, and there are many variations in the evaluation method. Therefore, by evaluating the die wear, the Pd powder accumulation is good. I decided to judge evil.
The die wear was performed by an evaluation method called die life. The die life evaluation was performed at the final wire drawing using a wire drawing die. The dies used were made of general natural diamond, the final reduction of the wire drawing was 7%, and the evaluation was carried out with the final wire diameter. Further, the drawing speed is 300 m / min, and during drawing, a capstan for drawing and a drawing die are used by using a lubricating liquid in which a surfactant for general Cu wire processing is added to the die. It was carried out while wetting a normal temperature lubricating liquid with a shower method.
Specifically, the wire diameter is measured at the start of wire drawing, then the wire diameter is measured every 10,000 m, and the wire diameter is increased by 0.08 μm for the first time compared to the wire diameter at the time of wire drawing. The wire drawing length to the point of time is defined as the die life, the die life is less than 40,000 m, x is from 40,000 m to less than 80,000 m, 80,000 m to less than 150,000 m, 15 More than 10,000 m was marked ◎.
In addition, as a result of evaluating the wire in which the Pd intermediate layer was formed by wet plating of 0.1 μm on the core material copper (Cu) with the wire diameter of 18 μm and the Au surface layer was not formed by this evaluation method, the die life was 3 Although it was determined to be x, the dice life of Experiment Nos. 5 to 8 was all 150,000 m or more.

始めに表２−１および表２−２のサンプルについて、実施例１と同様にＡｌ電極膜ダメージと第二ボンディング性について評価を行ったが、いずれも○であり良好な結果が得られた。
次に、表２−１の実施例のサンプル作製条件と評価結果について説明する。表２−１より、銅（Ｃｕ）または銅（Ｃｕ）とリン（Ｐ）の合金からなる芯材に、パラジウム（Ｐｄ）を中間層とし、さらにＡｕ表面層が１．２ｎｍ〜８．７ｎｍ被覆されたボンディングワイヤは、ボンディングワイヤの生産および機能において実用に耐えることが確認された。
最後に、表２−２に比較例のサンプル作製条件と評価結果を記す。比較例１および２のように、Ａｕ表面層が０．６ｎｍと非常に薄いものは、ダイスライフが悪く、ボンディングワイヤの生産において実用に耐えない結果であった。一方、比較例３〜６のように、Ａｕ表面層が１３ｎｍ〜２０ｎｍと厚いものは、溶融ボールが軸上偏芯するため、ボンディングワイヤの機能において実用に耐えない結果であった。
〔実施例３〕 First, the samples of Table 2-1 and Table 2-2 were evaluated for Al electrode film damage and second bonding properties in the same manner as in Example 1. Both were good and good results were obtained.
Next, sample preparation conditions and evaluation results of the examples in Table 2-1 will be described. From Table 2-1, a core material made of copper (Cu) or an alloy of copper (Cu) and phosphorus (P) has palladium (Pd) as an intermediate layer, and an Au surface layer covers 1.2 nm to 8.7 nm. It was confirmed that the bonded wire was practical in terms of bonding wire production and function.
Finally, Table 2-2 shows the sample preparation conditions and evaluation results of the comparative example. As in Comparative Examples 1 and 2, when the Au surface layer was as thin as 0.6 nm, the die life was poor and the results were not practical in the production of bonding wires. On the other hand, as in Comparative Examples 3 to 6, when the Au surface layer was as thick as 13 to 20 nm, the molten ball was eccentric on the axis, so that the bonding wire function was not practical.
Example 3

実験番号No.３９〜４３は、表３に示すに示す所定の銅（Ｃｕ）を用い、溶解、鋳造し、圧延、伸線して線径５００μｍまで加工し、線径５００μｍで芯材の銅（Ｃｕ）にPd中間層を施し、各種組成の表面層を形成した。Pd中間層および表面層の形成方法および最終的な厚みを表３に挙げる。その後、連続伸線加工を行い、窒素ガス不活性雰囲気で伸び率が４〜１０％となる条件で熱処理し、製品スプールに巻き取り、実施例２と同様な方法で評価を実施した。
なお、表面層は、９９．９９質量％以上の金（Ａｕ）および９９．９９質量％以上の銀（Ａｇ）および９９．９９質量％のＰｄ（パラジウム）および９９．９９質量％のＣｕ（銅）を、原材料として調合して溶解してターゲットを作製して乾式メッキにより形成した。 Experiment Nos. 39 to 43 use the predetermined copper (Cu) shown in Table 3 and melt, cast, roll and wire the wire to a wire diameter of 500 μm, and the wire diameter is 500 μm. A Pd intermediate layer was applied to (Cu) to form surface layers having various compositions. The formation methods and final thicknesses of the Pd intermediate layer and surface layer are listed in Table 3. Thereafter, continuous wire drawing was performed, heat treatment was performed in a nitrogen gas inert atmosphere under conditions where the elongation was 4 to 10%, the product was wound around a product spool, and evaluation was performed in the same manner as in Example 2.
The surface layer is composed of 99.99% by mass or more of gold (Au), 99.99% by mass or more of silver (Ag), 99.99% by mass of Pd (palladium), and 99.99% by mass of Cu (copper). ) Was prepared and dissolved as a raw material to prepare a target, which was formed by dry plating.

実験番号N0.３９〜４３について、実施例１と同様にＡｌ電極膜ダメージと第二ボンディング性について評価を行ったが、いずれも○であり良好な結果が得られた。つまり、再表面層が銀（Ａｇ）や銅（Ｃｕ）であっても、実施例程度の厚みであれば良好に使用できることが確認できた。
また、実験番号No.３９〜４３について、実施例２と同様に溶融ボールの軸上偏芯、ダイスライフの評価を行ったが、いずれも○以上の判定となり、良好な結果が確認された。
従って、表面層は金（Ａｕ）だけでなく、金（Ａｕ）と銀（Ａｇ）とパラジウム（Ｐｄ）と銅（Ｃｕ）を単体または組み合わせてできる加工性の良い合金組成であれば、良好に使用できることが確認できた。


〔実施例４〕 For the experiment numbers N0.39 to 43, the Al electrode film damage and the second bonding property were evaluated in the same manner as in Example 1. Both were good and good results were obtained. That is, even if the resurface layer is silver (Ag) or copper (Cu), it can be confirmed that it can be used satisfactorily as long as the thickness is about the same as that of the example.
In addition, for the experiment numbers No. 39 to 43, the on-axis eccentricity of the molten ball and the evaluation of the die life were performed in the same manner as in Example 2. Both were judged as “good” or better, and good results were confirmed.
Therefore, if the surface layer is not only gold (Au) but also an alloy composition with good workability made of gold (Au), silver (Ag), palladium (Pd), and copper (Cu) alone or in combination, it is good. It was confirmed that it could be used.


Example 4

実験番号No.４４〜５５は、下記および表４に示すに示す所定の銅（Ｃｕ）を用い、溶解、鋳造し、圧延、伸線して線径５００μｍまで加工し、線径５００μｍで芯材の銅（Ｃｕ）にPd中間層を施し、Ａｕ表面層を形成した。実施例２と同様な方法で評価を実施した。
Ｄ１：２０質量ｐｐｍジルコニウム（Ｚｒ）が添加された、残部がＤの銅（Ｃｕ）合金
Ｅ２：１０質量ｐｐｍバナジウム（Ｖ）と２０質量ｐｐｍジルコニウム（Ｚｒ）が添加された、残部がＥの銅（Ｃｕ）合金
Ｄ３：２０質量ｐｐｍジルコニウム（Ｚｒ）が添加された、残部がＤの銅（Ｃｕ）合金
Ｄ４：４０質量ｐｐｍスズ（Ｓｎ）が添加された、残部がＤの銅（Ｃｕ）合金
Ｄ５：３０質量ｐｐｍホウ素（Ｂ）が添加された、残部がＤの銅（Ｃｕ）合金
Ｄ６：１０質量ｐｐｍチタン（Ｔｉ）が添加された、残部がＤの銅（Ｃｕ）合金 Experiment Nos. 44 to 55 are made of the prescribed copper (Cu) shown below and shown in Table 4, and are melted, cast, rolled and drawn to be processed to a wire diameter of 500 μm. Pd intermediate layer was applied to copper (Cu) to form an Au surface layer. Evaluation was performed in the same manner as in Example 2.
D1: 20 mass ppm zirconium (Zr) added, balance D copper (Cu) alloy E2: 10 mass ppm vanadium (V) and 20 mass ppm zirconium (Zr) added, balance copper E (Cu) alloy D3: 20 mass ppm zirconium (Zr) added, balance D copper (Cu) alloy D4: 40 mass ppm tin (Sn) added, balance D copper (Cu) alloy D5: 30 mass ppm boron (B) added, balance D copper (Cu) alloy D6: 10 mass ppm titanium (Ti) added, balance D copper (Cu) alloy

実験番号Ｎｏ４４〜５５について、実施例１と同様にＡｌ電極膜ダメージと第二ボンディング性について評価を行ったが、いずれも○であり問題は無かった。また、実験番号No.４４〜４７について、実施例２と同様に溶融ボールの軸上偏芯、ダイスライフの評価を行ったが、いずれも○であり良好な結果が得られた。
従って、芯材の銅（Ｃｕ）に数十ｐｐｍの範囲で、ジルコニウム（Ｚｒ）、バナジウム（Ｖ）、スズ（Ｓｎ）、ホウ素（Ｂ）、チタン（Ｔｉ）の元素を添加したボンディングワイヤは、生産および機能として良好に使用できることが確認できた。 About experiment number No44-55, although Al electrode film damage and 2nd bondability were evaluated similarly to Example 1, all were (circle) and there was no problem. For Experiment Nos. 44 to 47, the on-axis eccentricity of the molten ball and the die life were evaluated in the same manner as in Example 2, and both were good and good results were obtained.
Therefore, the bonding wire in which the elements of zirconium (Zr), vanadium (V), tin (Sn), boron (B), and titanium (Ti) are added to the core material copper (Cu) within a range of several tens of ppm, It was confirmed that it can be used well as production and function.

実験番号N0.３９〜４３について、実施例１と同様にＡｌ電極膜ダメージと第二ボンディング性について評価を行ったが、いずれも○であり良好な結果が得られた。つまり、最表面層が銀（Ａｇ）や銅（Ｃｕ）であっても、実施例程度の厚みであれば良好に使用できることが確認できた。
また、実験番号No.３９〜４３について、実施例２と同様に溶融ボールの軸上偏芯、ダイスライフの評価を行ったが、いずれも○以上の判定となり、良好な結果が確認された。
従って、表面層は金（Ａｕ）だけでなく、金（Ａｕ）と銀（Ａｇ）とパラジウム（Ｐｄ）と銅（Ｃｕ）を単体または組み合わせてできる加工性の良い合金組成であれば、良好に使用できることが確認できた。

For the experiment numbers N0.39 to 43, the Al electrode film damage and the second bonding property were evaluated in the same manner as in Example 1. Both were good and good results were obtained. That is, even if the outermost surface layer was silver (Ag) or copper (Cu), it could be confirmed that it could be used satisfactorily as long as the thickness was about the example.
In addition, for the experiment numbers No. 39 to 43, the on-axis eccentricity of the molten ball and the evaluation of the die life were performed in the same manner as in Example 2. Both were judged as “good” or better, and good results were confirmed.
Therefore, if the surface layer is not only gold (Au) but also an alloy composition with good workability made of gold (Au), silver (Ag), palladium (Pd), and copper (Cu) alone or in combination, it is good. It was confirmed that it could be used.


本発明は、半導体素子上の電極と回路配線基板の配線とをボールボンディングで接続するために用いられる被覆銅ワイヤに関する。   The present invention relates to a coated copper wire used for connecting an electrode on a semiconductor element and a wiring of a circuit wiring board by ball bonding.

現在、半導体素子上の電極と外部端子との間をボールボンディングで接合するボンディングワイヤとして、線径１５〜３０μｍ程度の金線が主に使用されている。しかしながら、近年の金地金価格の高騰によってこれまでの高純度４N系（純度が９９．９９質量％以上）の金線に替わり、１０〜２５μｍ程度の銅線の利用が注目されており、特に、高密度実装上の要請から、より小径の１０〜２０μｍ程度の銅（Cu）ワイヤが求められ始めている。   At present, gold wires having a wire diameter of about 15 to 30 μm are mainly used as bonding wires for bonding electrodes on semiconductor elements and external terminals by ball bonding. However, due to the recent rise in gold bullion prices, the use of copper wires of about 10 to 25 μm has attracted attention in place of conventional high-purity 4N-based (purity of 99.99% by mass or more), Due to demands for high-density mounting, a copper (Cu) wire having a smaller diameter of about 10 to 20 μm has been demanded.

この銅線も金線と同様の利用分野が考えられており、例えば、実装構造では、現行のリードフレームを使用したQFP（Quad Flat Packaging）に加え、基板、ポリイミドテープ等を使用するBGA（Ball Grid Array）、CSP（Chip Scale Packaging ）等の新しい形態への応用が検討され、ループ性、接合性、量産使用性等をより向上したボールボンディングで接合するボンディングワイヤが求められている。   This copper wire is considered to be used in the same fields as gold wires. For example, in the mounting structure, in addition to QFP (Quad Flat Packaging) using the current lead frame, BGA (Ball) using a substrate, polyimide tape, etc. Application to new forms such as Grid Array (CSP) and Chip Scale Packaging (CSP) has been studied, and bonding wires are required to be bonded by ball bonding with improved loop characteristics, bonding characteristics, mass-use usability, and the like.

他方、銅線ボンディングワイヤの接合相手となる電極などの材質も金線の場合と同様であって、シリコン基板上の配線、電極材料としては、従来のアルミニウム（Al）に加えて、より微細配線に好適な高純度の銅（Cu）が実用化されている。また、リードフレーム上には銀（Ag）メッキ、金（Au）メッキ、ニッケル（Ni）メッキ上のパラジウム（Pd）メッキ等が施されており、また、樹脂基板、テープ等の上には、銅（Cu）配線が施され、その上に金（Au）等の貴金属元素及びその合金の皮膜が施されている場合が多い。こうした種々の接合相手に応じて、銅（Cu）ワイヤの接合性、接合信頼性を向上することが求められる。   On the other hand, the material of the electrode, etc., to which the copper wire bonding wire is joined is the same as that of the gold wire, and the wiring on the silicon substrate and the electrode material are finer wiring in addition to the conventional aluminum (Al) High-purity copper (Cu) suitable for the above has been put into practical use. In addition, silver (Ag) plating, gold (Au) plating, palladium (Pd) plating on nickel (Ni) plating, etc. are applied on the lead frame, and on the resin substrate, tape, etc. In many cases, copper (Cu) wiring is provided, and a film of a noble metal element such as gold (Au) and an alloy thereof is provided thereon. It is required to improve the bondability and bonding reliability of copper (Cu) wires according to these various bonding partners.

当初の銅（Cu）ワイヤは、高純度３N〜６N系（純度が９９．９質量％以上〜純度９９．９９９９質量％以上。）の銅（Cu）線の使用が考えられた、しかし、銅線は酸化され易い欠点がある。このため、CuやCu-Sn等の芯材の外周に０．００２〜０．５μｍのPd、Pd-Ni、Pd-Co等の被覆層を設けて、耐食性並びに硬度を改良する提案がなされている（特許文献１）。
また、銅ボンディングワイヤの表面酸化を防ぐ方法として、金、銀、白金、パラジウム、ニッケル、コバルト、クロム、チタンなどの貴金属や耐食性金属で銅を被覆したボンディングワイヤが提案されている（特許文献２、特許文献３参照。）。 The original copper (Cu) wire was considered to be a copper (Cu) wire having a high purity of 3N to 6N (purity of 99.9 mass% or more to purity 99.9999 mass% or more). The wire has the disadvantage of being easily oxidized. For this reason, a proposal has been made to improve the corrosion resistance and hardness by providing a coating layer of Pd, Pd—Ni, Pd—Co, etc. of 0.002 to 0.5 μm on the outer periphery of a core material such as Cu or Cu—Sn. (Patent Document 1).
Further, as a method for preventing the surface oxidation of the copper bonding wire, a bonding wire in which copper is coated with a noble metal such as gold, silver, platinum, palladium, nickel, cobalt, chromium, titanium, or a corrosion-resistant metal has been proposed (Patent Document 2). , See Patent Document 3).

このうち、パラジウム（Pd）を被覆した銅（Cu）ワイヤは、還元性の窒素雰囲気中で溶融ボールを形成すると安定した真球ボールを形成するが、ダイス寿命が短いので、表層に０．０２μｍ（２０ｎｍ：特許文献３の段落００２０〜００２１参照。）の金（Au）メッキをして用いている。
他方、セカンドボンドを接合して引きちぎった後のボールアップに際して、銅（Cu）又は銅合金の芯材の酸化による不都合を回避するため、銅（Cu）にリン（P）を添加し、表層に０．０１５μｍ（１５ｎｍ：特許文献４、段落００２６、表１の実施例８参照。）の金（Au）メッキをすることで、良好な真球状のボールを形成できる被覆ワイヤも開発されている。しかし、これらのワイヤは、後記するように「軸上偏芯」が発生するという新たな問題があることが判明した。 Of these, copper (Cu) wire coated with palladium (Pd) forms a stable spherical ball when a molten ball is formed in a reducing nitrogen atmosphere. However, since the die life is short, the surface layer is 0.02 μm. (20 nm: see paragraphs 0020 to 0021 of Patent Document 3) Gold (Au) plating is used.
On the other hand, in order to avoid inconvenience due to oxidation of the core material of copper (Cu) or copper alloy at the time of ball up after joining and tearing the second bond, phosphorus (P) is added to copper (Cu) and the surface layer is added. A coated wire capable of forming a good spherical ball by gold (Au) plating of 0.015 μm (15 nm: see Patent Document 4, paragraph 0026, Example 8 in Table 1) has also been developed. However, it has been found that these wires have a new problem that “on-axis eccentricity” occurs as described later.

実開昭６０−１６０５５４号公報Japanese Utility Model Publication No. 60-160554 特開昭６２−９７３６０号公報JP-A-62-97360 特開２００５−１６７０２０号公報JP 2005-167020 A 特許第４２０３４５９号公報Japanese Patent No. 4203459 特許第４３４９６４１号公報Japanese Patent No. 4349641

改森信吾ほか、「ハイブリッドボンディングワイヤーの開発」“SEIテクニカルレビュー”第１６９号−４７，２００６年７月Shingo Kaimori et al., “Development of Hybrid Bonding Wire”, “SEI Technical Review” No. 169-47, July 2006

従来（２００７年当時）のワイヤボンディングにおける銅（Cu)ワイヤや銅（Cu）芯材にパラジウム（Pd）を被覆したワイヤの線径は３０μｍオーダーのものが主体であって、ボンディングパッド間のピッチはそれに応じて広いものであった。しかし、近年は高密度実装の進展に伴ってボンディングワイヤの細線化と共に微細なパッドとパッド間のファインピッチ化が進められ、ボンディングワイヤに形成される溶融ボールが真球であること、及び溶融ボールがパッドに対して圧着した形状が真円であることが強く求められるようになっている。
これらの条件が満たされないと、接合された溶融ボールが微細化されたパッド上に収まらず、また接合信頼性が確保されないからであるが、ここでこれらの材質のボンディングワイヤにおいて、溶融ボールの「軸上偏芯」という新たな問題が取り上げられるようになってきた。
「軸上偏芯」は、ボンディングワイヤ先端に形成される溶融ボールの形状が真球か否かというボール形状ではなく、形成された溶融ボールがボンディングワイヤの中心線上からずれる現象をいい、その形状が真球であるか、否かによらず発生し、著しい不具合の原因となる。
すなわち、「軸上偏芯」が発生すると接合されるパッドに対して接合する位置がずれて定まらず、設定されたファインピッチに収まらないのみか、接合の信頼性も得られない。また、「軸上偏芯」の程度の大小のみでなく、その大きさにバラツキがあれば、そのバラツキの幅、程度に応じてパッドの接合面積やピッチを定めなければならない。
無論、この「軸上偏芯」の発生したボンディングワイヤを用いて溶融ボールをパッドに対してボンディングして接合すること自体が困難であり、このため、本発明は「軸上偏芯」の抑制及びそのバラツキの低減を本発明の課題とする。
また、これらのパラジウム（Pd）被覆銅ワイヤにおいて、その伸線加工に伴って、ワイヤ表面にパラジウム（Pd）粉が堆積し、ワイヤ断線が発生すると共にダイヤモンドダイスの磨耗が著しく進行して、銅（Cu）のみの無被覆ワイヤの場合の５分の一以下のダイス寿命となることが新たな問題となり、本発明はこれらワイヤの伸線加工時のパラジウム（Pd）粉の発生、堆積の解消とダイス磨耗を低減する被覆銅ワイヤの提供をも課題とする。 The wire diameter of copper (Cu) wire and copper (Cu) core material coated with palladium (Pd) in conventional (at the time of 2007) wire bonding is mainly 30 μm, and the pitch between bonding pads Was broad accordingly. However, in recent years, along with the progress of high-density packaging, the bonding wire has been made finer and the fine pitch between the pads has been reduced, and the molten ball formed on the bonding wire is a true sphere, and the molten ball It is strongly demanded that the shape that is pressed against the pad is a perfect circle.
If these conditions are not satisfied, the bonded molten ball will not fit on the miniaturized pad, and the bonding reliability will not be ensured, but here in the bonding wire of these materials, The new problem of “axial eccentricity” has been taken up.
“On-axis eccentricity” is not the ball shape of whether the shape of the molten ball formed at the tip of the bonding wire is a true sphere, but the phenomenon that the formed molten ball deviates from the center line of the bonding wire. This occurs regardless of whether or not the ball is a true sphere, and causes a significant defect.
In other words, when “on-axis eccentricity” occurs, the bonding position with respect to the pads to be bonded is shifted and is not fixed, and it does not fit within the set fine pitch, or the bonding reliability cannot be obtained. In addition to the magnitude of the “axial eccentricity”, if there is a variation in the size, the bonding area and pitch of the pads must be determined according to the width and degree of the variation.
Of course, it is difficult to bond the molten ball to the pad using the bonding wire in which the “on-axis eccentricity” occurs, and therefore, the present invention suppresses the “on-axis eccentricity”. It is an object of the present invention to reduce the variation.
Also, in these palladium (Pd) coated copper wires, with the wire drawing process, palladium (Pd) powder accumulates on the wire surface, wire breakage occurs, and diamond die wear progresses remarkably. A new problem is that the die life is less than one-fifth of the case of uncoated wires made only of (Cu), and the present invention eliminates the generation and deposition of palladium (Pd) powder during wire drawing of these wires. Another object is to provide a coated copper wire that reduces die wear.

前記した、銅（Cu）ワイヤの「軸上偏芯」の抑制、バラツキ低減とワイヤ伸線時のパラジウム（Pd）粉の堆積及びダイス磨耗の低減という、本発明の課題はそれぞれワイヤの構成上相互に関連する。
溶融ボールの真球性の不良は、溶融ボールが形成される段階で酸化することに起因すると考えられる。事実、線径２５μｍのパラジウム（Pd）被覆銅ワイヤの表面層として２０ｎｍ厚さの金（Au）層を形成したワイヤに大気中で溶融ボールを形成すると、即座に溶融ボールが槍状となるが、不活性ガスや不活性ガスと還元性ガスの混合ガス中で溶融ボールを形成する場合には真球性の高い溶融ボールが形成される。
一方、軸上偏芯は、同じく径２５μｍのパラジウム（Pd）被覆銅ワイヤの表面層として２０ｎｍ厚さの金（Au）層を形成したワイヤは、還元性雰囲気中でも溶融ボールを形成すると軸上偏芯が発生するが、表面層の金（Au）被覆がない場合には、不活性ガスや不活性ガスと還元性ガスの混合ガス中で軸上偏芯は発生しない。
このことから、溶融ボールの真球性と軸上偏芯の発生とは其のメカニズムが異なると考えられる。
詳しいメカニズムは判明していないが、軸上偏芯については、表面層の金（Au）は展延性が高いため、第２ボンディング（２nd接合）後にワイヤを引きちぎる際にワイヤ切断部の金（Au）表面層のみが大きく延伸し、中間層のパラジウム（Pd）や芯材の銅（Cu）はこの伸びに追従できないため、金（Au）表面層とパラジウム（Pd）中間層の境界面で金（Au）表面層の不均一な突出構造が出現する。そして、次の溶融ボール形成時にこの構造のために溶融時の温度の伝わり方の不均一さ、不均一な溶融の進行を伴ってその結果軸上偏芯が発生すると考えている。また、一方で溶融ボールの形状自体は酸化されない雰囲気下では溶融状態の表面張力の作用が働くため、真球状の溶融ボールが形成されると考えられる。
この課題について、本発明者らが研究した結果、パラジウム（Ｐｄ）被覆銅ワイヤにおいて、パラジウム（Ｐｄ）被覆層の上に金（Ａｕ）等のパラジウム（Ｐｄ）よりも展延性があり、かつ低融点の金属からなる９ｎｍ以下の極く薄い表面被覆層を設けることによって「軸上偏芯」が発生しなくなることを見出した。 As described above, the problems of the present invention, such as suppression of “on-axis eccentricity” of copper (Cu) wire, reduction of variation, accumulation of palladium (Pd) powder during wire drawing, and reduction of die wear, are respectively related to the wire configuration. Interrelated.
It is considered that the poor spherical nature of the molten ball is caused by oxidation at the stage where the molten ball is formed. In fact, when a molten ball is formed in the air on a wire in which a gold (Au) layer having a thickness of 20 nm is formed as a surface layer of a palladium (Pd) -coated copper wire having a wire diameter of 25 μm, the molten ball immediately becomes bowl-shaped. In the case where the molten ball is formed in an inert gas or a mixed gas of an inert gas and a reducing gas, a highly spherical ball is formed.
On the other hand, on-axis eccentricity is the same as the surface layer of a palladium (Pd) -coated copper wire having a diameter of 25 μm, but when a gold (Au) layer having a thickness of 20 nm is formed in a reducing atmosphere, Although a core is generated, if there is no gold (Au) coating on the surface layer, on-axis eccentricity does not occur in an inert gas or a mixed gas of an inert gas and a reducing gas.
From this, it is considered that the mechanism of the sphericity of the molten ball and the occurrence of axial eccentricity are different.
Although the detailed mechanism is not known, for axial eccentricity, the gold (Au) of the surface layer is highly malleable. ) Only the surface layer stretches greatly, and palladium (Pd) in the intermediate layer and copper (Cu) in the core material cannot follow this elongation, so gold at the interface between the gold (Au) surface layer and the palladium (Pd) intermediate layer (Au) A non-uniform protruding structure of the surface layer appears. In addition, it is considered that due to this structure at the time of the next molten ball formation, on-axis eccentricity occurs as a result of non-uniformity in how the temperature is transmitted during melting and non-uniform melting. On the other hand, since the action of surface tension in the molten state works in an atmosphere where the shape of the molten ball itself is not oxidized, it is considered that a true spherical molten ball is formed.
As a result of the present inventors' study on this problem, the palladium (Pd) -coated copper wire is more malleable and lower than palladium (Pd) such as gold (Au) on the palladium (Pd) coating layer. It has been found that “on-axis eccentricity” does not occur by providing a very thin surface coating layer of 9 nm or less made of a melting point metal.

本発明者らは、次に伸線加工中のパラジウム（Pd）被覆銅ワイヤの断線とダイスの異常磨耗を抑制することについて、パラジウムを被覆した銅ワイヤにおいては伸線加工中にパラジウム粉がワイヤに堆積することに伴って特徴的な断線が発生することに気が付き、このパラジウム粉の発生を制御することによってダイス磨耗を抑制できると考えた。
一般的な銅（Cu）ワイヤの伸線加工に伴う破断モードは、図１（かぶり）に示すように線材表面にかぶりの打痕点ないし薄片が連続した後で破断したり、酸化物やカーボンなどの異物が線材中に混入して図２（異物）に示すように伸線中にそのカッピー（cuppy）欠陥箇所から破断する。これに対して、パラジウム（Pd）被覆銅ワイヤは、伸線加工中にダイヤモンドダイスの案内口でパラジウム（Pd）が削り取られてワイヤに堆積していくという現象を伴う。
そして、このパラジウム（Pd）堆積量がある程度の量まで蓄積されると、伸線加工中ワイヤの引き抜き力が増大するため、銅（Cu）ワイヤが摩擦抵抗力に耐えられなくなって、図３（堆積）に示すように引きちぎられるような態様で断線する。また、この断線モードは、一般的な銅（Cu）ボンディングワイヤではほとんど確認されたことがない。パラジウム粉は、数μｍ以下の細かい粒子からなっており、また、パラジウムは硬いことから、伸線加工中に研磨剤のような作用をし、ダイヤモンドダイスを磨耗させる要因となっていると考えられる。このことから、パラジウム粉の堆積が伸線加工中の断線を引き起こしている主原因であり、結果的にダイヤモンドダイスの異常磨耗の原因にもなっていると考えられる。 Next, the inventors of the present invention are concerned with suppressing the disconnection of the palladium (Pd) -coated copper wire during wire drawing and the abnormal wear of the die. We noticed that a characteristic disconnection occurred as it deposited on the surface, and thought that die wear could be suppressed by controlling the generation of this palladium powder.
As shown in Fig. 1 (fogging), the break mode that accompanies the general copper (Cu) wire drawing process is that the surface of the wire rod breaks after the dents or flakes are continuous, or the oxide or carbon As shown in FIG. 2 (foreign matter), foreign matter such as is mixed in the wire and breaks from the cuppy defect portion during drawing. On the other hand, palladium (Pd) -coated copper wire is accompanied by a phenomenon in which palladium (Pd) is scraped off at the guide port of a diamond die during wire drawing and is deposited on the wire.
When the amount of accumulated palladium (Pd) is accumulated to some extent, the drawing force of the wire is increased during wire drawing, so that the copper (Cu) wire cannot withstand the frictional resistance, and FIG. The wire is broken in such a manner that it is torn off as shown in (deposition). Moreover, this disconnection mode has hardly been confirmed with a general copper (Cu) bonding wire. Palladium powder is composed of fine particles of several μm or less, and since palladium is hard, it acts as an abrasive during wire drawing and is considered to be a factor that wears the diamond die. . From this, it is considered that the accumulation of palladium powder is the main cause of wire breakage during wire drawing, resulting in abnormal wear of the diamond die.

本発明者らの研究によればパラジウム被覆銅ワイヤの表面にさらに金（Au）被覆を形成したボンディングワイヤの場合には、このような伸線加工中のパラジウム粉の堆積現象や断線は起こらないばかりか、ダイヤモンドダイスの異常な磨耗も生じていない。
このことは、パラジウム（Pd）は、金（Au）と比較して潤滑液の濡れ性が悪いのに対して、その上に表面層として金層を形成することによって、パラジウムよりも潤滑液との濡れ性が改善されることによると考えられる。また、金（Au）自体がパラジウム（Pd）中間層全体を覆っているため、展延性のよい金層が介在することにより加工性を向上しているとも考えられるが、後述するように、金層の厚さは極めて薄く（１〜９ｎｍ）てよいことから、潤滑性などの表面の改質効果が大きいとも考えられる。
このような伸線加工中の破断モードは、連続伸線工程において最終のボンディングワイヤ径が細くなればなるほど多く発生し、また、伸線工程の断面減少率を大きくすればするほど多く発生する。さらに、最終伸線速度が６００ｍ／分以下であれば伸線加工中にワイヤの振動が生じにくいので断線頻度は少なくなる。 According to the research of the present inventors, in the case of a bonding wire in which a gold (Au) coating is further formed on the surface of a palladium-coated copper wire, such a deposition phenomenon or disconnection of palladium powder during wire drawing does not occur. Not only does the diamond die wear abnormally.
This is because palladium (Pd) is poor in wettability of the lubricating liquid compared to gold (Au), but by forming a gold layer as a surface layer thereon, the lubricating liquid is more effective than palladium. This is considered to be due to the improvement of the wettability. In addition, since gold (Au) itself covers the entire palladium (Pd) intermediate layer, it is considered that the workability is improved by interposing a gold layer having good extensibility. Since the thickness of the layer may be extremely thin (1 to 9 nm), it is considered that the surface modification effect such as lubricity is large.
Such breaking modes during wire drawing occur more frequently as the final bonding wire diameter becomes smaller in the continuous wire drawing process, and more frequently as the cross-sectional reduction rate in the wire drawing process increases. Furthermore, if the final wire drawing speed is 600 m / min or less, the wire vibration is less likely to occur during wire drawing, so the frequency of wire disconnection is reduced.

ところで、前記の課題はそれぞれ相互に関連し、「軸上偏芯」の抑制という面からは前記したようにパラジウム被覆銅ワイヤにおいて、金（Au）層を表面層として形成することは「軸上偏芯」発生の原因ともなっているのであり、一方、伸線加工工程におけるパラジウム粉発生を伴う断線やダイス磨耗の抑制という面から、このパラジウム（Pd）中間層の表面に金（Au）被覆層が必要となることがわかった。
そもそもパラジウム（Pd）被覆銅ワイヤにおいて最上層に金（Au）被覆を行うことは、前述の先行技術文献５（特許第４３４９６４１号公報）にもあるようにワイヤボンディングの第二ボンディング（２nd接合）後の切断されたワイヤ端面を被覆して酸化を防止するものであった。
このため、銅、パラジウムよりもいち早く溶融して、被覆効果を発揮する厚さとして、０．００５〜０．１μｍ（５〜１００ｎｍ）とし、これと合金化するパラジウム中間層の厚さを０．００５〜０．２μｍとし、表皮層の厚さが中間層の厚さよりも薄い、としている。
また、前述の特許文献３（特開２００５−１６７０２０号公報）によれば、銅ワイヤにパラジウム層を形成することによって伸線性を向上し、ダイス磨耗を低減できること、さらにパラジウム層の上に金表皮層を被覆層よりも薄く形成することによってこれらの効果が向上することが記載されている。
該金表皮層の膜厚については、その実験例４で０．０２μｍ（２０ｎｍ）であるが、ワイヤ径の０．００２倍以下、より好ましくは０．００１倍以下の厚さであって、使用ワイヤ径が１５〜４０μｍであるから、１５〜４０ｎｍとなるが、段落００２１に、溶融ボールの真球性との関係でその厚さが厚いと溶融ボールが槍状になり、良好なボールが形成されないことが挙げられており、上記の厚さが上限となるが、一方、「伸線性」からは下限が想定されるもののその記載はなく、また、本発明の課題とする「軸上偏芯」に関して言及はない。 By the way, the above-mentioned problems are related to each other, and from the viewpoint of suppressing “on-axis eccentricity”, as described above, forming a gold (Au) layer as a surface layer in a palladium-coated copper wire is “on-axis On the other hand, the surface of this palladium (Pd) intermediate layer is covered with a gold (Au) coating layer from the viewpoint of suppressing disconnection and die wear associated with the generation of palladium powder in the wire drawing process. It turns out that is necessary.
In the first place, the gold (Au) coating on the uppermost layer of the palladium (Pd) coated copper wire is performed by the second bonding (2nd bonding) of the wire bonding as described in the above-mentioned prior art document 5 (Patent No. 4349641). The later cut wire end face was covered to prevent oxidation.
For this reason, it is 0.005-0.1 micrometer (5-100 nm) as thickness which melt | dissolves earlier than copper and palladium, and exhibits a coating effect, and the thickness of the palladium intermediate | middle layer alloyed with this is 0.00. 005 to 0.2 μm, and the thickness of the skin layer is thinner than the thickness of the intermediate layer.
Further, according to the above-mentioned Patent Document 3 (Japanese Patent Laid-Open No. 2005-167020), by forming a palladium layer on a copper wire, wire drawing can be improved, die wear can be reduced, and a gold skin on the palladium layer. It is described that these effects are improved by forming the layer thinner than the covering layer.
The film thickness of the gold skin layer is 0.02 μm (20 nm) in Experimental Example 4, but it is 0.002 times or less of the wire diameter, more preferably 0.001 times or less. Since the wire diameter is 15 to 40 μm, it is 15 to 40 nm. However, in paragraph 0021, when the thickness is thick in relation to the true sphericity of the molten ball, the molten ball becomes bowl-shaped and a good ball is formed. The above thickness is the upper limit, but the lower limit is assumed from the “drawability”, but there is no description thereof. Is not mentioned.

本発明においては、これらの課題を両立して達成することが求められる。
前記したように「軸上偏芯」に関して、金表面層の厚さは、線径２５μｍのパラジウム（Ｐｄ）被覆銅ワイヤに対して金表面層厚さ２０ｎｍでは解決せず、後述するように９ｎｍ以下の厚さとして始めて達成できた。
また、Pd粉発生を伴う、伸線加工時の断線、ダイヤモンドダイスの磨耗低減の課題は、金表面層の厚さが、１ｎｍ以上あれば達成できる。
すなわち、本発明は、パラジウム被覆銅ワイヤにおいて、最上層として厚さの範囲が１〜９ｎｍの金層を形成することによって上記課題を達成する。
さらにこれらのメカニズムから、最表面の金（Au）の働きは、その展延性がパラジウムよりも高いこと、及びパラジウムよりも融点が低いという性質によって達成できたものであり、同様の性質を備えた金属が適用可能であることが解る。具体的には、このような金属として、銀（Ag）や銅（Cu）の単体金属や金（Au）、銀（Ag）、銅（Cu）、あるいはパラジウム（Pd）と組み合わせてこれらの性質を持たせた合金が考えられる。 In the present invention, it is required to achieve both of these problems.
As described above, regarding the “axial eccentricity”, the thickness of the gold surface layer cannot be solved with a gold surface layer thickness of 20 nm with respect to a palladium (Pd) -coated copper wire having a wire diameter of 25 μm. The following thickness was achieved for the first time.
Further, the problem of wire breakage during wire drawing and diamond die wear reduction accompanied by generation of Pd powder can be achieved if the gold surface layer has a thickness of 1 nm or more.
That is, this invention achieves the said subject by forming the gold | metal layer whose thickness range is 1-9 nm as an uppermost layer in a palladium covering copper wire.
Furthermore, from these mechanisms, the action of gold (Au) on the outermost surface can be achieved by the property that its extensibility is higher than palladium and its melting point is lower than that of palladium. It can be seen that metals are applicable. Specifically, these metals are used in combination with simple metals such as silver (Ag) and copper (Cu), gold (Au), silver (Ag), copper (Cu), and palladium (Pd). An alloy with a slag can be considered.

本発明のボールボンディング用被覆銅ワイヤの具体的構成は、次のとおりである。
（１） 銅（Cu）又は銅合金からなる芯材、パラジウム（Pd）からなる中間被覆層（以下、中間層という。）、及び表面被覆層（以下、表面層という。）からなる、連続伸線加工されたワイヤ径１０〜２５μｍのボールボンディング用被覆銅ワイヤであって、
該パラジウム（Pd）中間層の膜厚がワイヤ径の０．００１〜０．０２倍であり、
該表面層が中間層のパラジウム（Pd）の融点よりも低融点であって、かつ硬さの低い、金（Au）、銀（Ag）又は銅（Cu）からなる膜厚１〜９ｎｍの被覆層であるボールボンディング用銅被覆ワイヤである。
（２） さらに、上記表面層の膜厚が上記中間層の１／８以下であり、
（３） 上記ワイヤ径が１０〜２０μｍであって、表面層の膜厚が２〜７ｎｍであり、
（４） 上記パラジウム（Pd）中間層が湿式メッキにより形成されたものであり、
（５） 上記表面層が室温下のスパッタリング法により形成されたものであり、
（６） 上記中間層が純度９９質量％以上のパラジウム（Pd）であり、
（７） 上記表面層が純度９９．９９質量％以上の金（Au）、純度９９．９９以上の銀（Ag）、又は純度９９．９９質量％以上の銅（Cu）であり、
（８） 上記芯材が純度９９．９質量％以上の銅（Cu）であり、
（９） 上記芯材が０．５〜９９質量ｐｐｍのジルコニウム（Zr）、スズ（Sn）、バナジウム（V）、ホウ素（B）、チタン（Ti）の少なくとも一種を含み、残部が純度９９．９９質量％以上の銅（Cu）からなり、
（１０）芯材が０．５〜９９質量ｐｐｍのジルコニウム（Zr）、スズ（Sn）、バナジウム（V）、ホウ素（B）、チタン（Ti）の少なくとも一種を含み、１〜５００質量ｐｐｍのリン（P）と残部が純度９９．９９質量％以上の銅（Cu）からなり、
（１１）芯材が１〜８０質量ｐｐｍのリン（P）と残部が純度９９．９９質量％以上の銅（Cu）からなる、ことを特徴とするボールボンディング用被覆銅ワイヤである。 The specific configuration of the coated copper wire for ball bonding of the present invention is as follows.
(1) Continuous stretching comprising a core material made of copper (Cu) or a copper alloy, an intermediate coating layer (hereinafter referred to as an intermediate layer) made of palladium (Pd), and a surface coating layer (hereinafter referred to as a surface layer). Wire-coated copper wire for ball bonding having a wire diameter of 10 to 25 μm,
The film thickness of the palladium (Pd) intermediate layer is 0.001 to 0.02 times the wire diameter,
A coating having a thickness of 1 to 9 nm made of gold (Au), silver (Ag) or copper (Cu), wherein the surface layer has a melting point lower than that of palladium (Pd) of the intermediate layer and has a low hardness It is a copper-coated wire for ball bonding that is a layer.
(2) Furthermore, the film thickness of the surface layer is 1/8 or less of the intermediate layer,
(3) The wire diameter is 10 to 20 μm, and the film thickness of the surface layer is 2 to 7 nm.
(4) The palladium (Pd) intermediate layer is formed by wet plating,
(5) The surface layer is formed by a sputtering method at room temperature,
(6) The intermediate layer is palladium (Pd) having a purity of 99% by mass or more,
(7) The surface layer is gold (Au) having a purity of 99.99 mass% or more, silver (Ag) having a purity of 99.99 or more, or copper (Cu) having a purity of 99.99 mass% or more,
(8) The core material is copper (Cu) having a purity of 99.9% by mass or more,
(9) The core material contains at least one of 0.5 to 99 mass ppm of zirconium (Zr), tin (Sn), vanadium (V), boron (B), and titanium (Ti), and the balance is 99. It consists of 99% by mass of copper (Cu),
(10) The core material contains 0.5 to 99 mass ppm of zirconium (Zr), tin (Sn), vanadium (V), boron (B), titanium (Ti), and 1 to 500 mass ppm. Phosphorus (P) and the balance consists of copper (Cu) with a purity of 99.99% by mass or more,
(11) A coated copper wire for ball bonding, characterized in that the core material is composed of phosphorus (P) having a purity of 1 to 80 mass ppm and the balance being copper (Cu) having a purity of 99.99 mass% or more.

本発明によれば、ワイヤ径１０〜２５μｍに対して金（Au）などからなる表面層の膜厚が１〜９ｎｍと極めて薄いため、溶融ボールの真球性に影響を与えることがなく、パラジウム（Pd）被覆銅ワイヤと同様に扱うことができると共に、軸上偏芯を抑制し、さらにパラジウム（Pd）粉の堆積を伴う、伸線加工時の断線やダイヤモンドダイスの異常磨耗を大幅（１／５以下）に抑制することができた。
また、軸上偏芯は抑制され、そのバラツキも小さいため、ファインピッチのボンディングパッドに対応することが可能であり、更にボンディングの接合信頼性が著しく向上し、
今後の電子デバイスにおける微細化に伴う要請に対応することができる。 According to the present invention, since the film thickness of the surface layer made of gold (Au) or the like is as extremely thin as 1 to 9 nm with respect to the wire diameter of 10 to 25 μm, the sphericity of the molten ball is not affected. (Pd) Can be handled in the same way as a coated copper wire, suppresses on-axis eccentricity, and further causes breakage during wire drawing and abnormal wear of diamond dies accompanied by accumulation of palladium (Pd) powder (1 / 5 or less).
In addition, since the eccentricity on the axis is suppressed and its variation is small, it can be used for fine pitch bonding pads, and the bonding reliability of bonding is significantly improved.
It is possible to meet the demands associated with miniaturization in future electronic devices.

図１は、銅ボンディングワイヤの代表的な欠陥例であるかぶり欠陥により破断した状態を示す。FIG. 1 shows a state in which the copper bonding wire is broken by a fogging defect, which is a typical defect example of a copper bonding wire. 図２は、銅ボンディングワイヤの代表的な欠陥例である異物欠陥により破断した状態を示す。FIG. 2 shows a state in which the copper bonding wire is broken by a foreign substance defect which is a typical defect example of the copper bonding wire. 図３は、銅ボンディングワイヤに対するPd粉の堆積により破断した状態を示す。FIG. 3 shows a state in which the copper bonding wire is broken by the deposition of Pd powder.

本発明の被覆銅ワイヤで、表面層の理論的な膜厚の上限は９ｎｍであり、より好ましくは７ｎｍ以下である。ここで、「理論的な膜厚」とは、これらの極めて薄い被覆層を全表面にわたって直接測定することは極めて困難であるため、連続伸線前の湿式めっきやスパッタリングによって形成した被覆層の膜厚から、伸線加工後の値を比例計算して求めたものを明細書において「理論的な」膜厚と表現した。この「理論的な膜厚」を求める比例定数は、ボンディングワイヤとしての連続伸線加工の終了後の線径を連続伸線加工開始前の線径で除した値である。
表面層の膜厚は薄ければ薄いほど、表面層の膜厚に起因した軸上偏芯とそのバラツキを低く抑えることができるが、ダイヤモンドダイスに対する潤滑作用など、前記のダイスの異常磨耗に対する効果がなくなるため、１ｎｍを下限とする。
好ましくは、この値は２ｎｍ以上であり、より好ましくは４ｎｍである。
ダイヤモンドダイスの伸線磨耗や異常磨耗を避けるため、連続伸線は水溶液中で冷却し、かつ、一定速度（連続伸線の最終伸線速度が３０〜６００ｍ／分）で行うことが好ましい。伸線速度がこの範囲を超えて速すぎると、伸線加工中のワイヤに振動が発生し、断線しやすくなる。なお、ダイヤモンドダイスと金（Au）との摩擦抵抗を下げるため、市販の界面活性剤を添加した金属潤滑液を水やアルコール等の希釈液で希釈して使用するほか、エチルアルコール、メチルアルコール又はイソプロピルアルコールだけを含有した水溶液なども用いることができる。 In the coated copper wire of the present invention, the upper limit of the theoretical film thickness of the surface layer is 9 nm, more preferably 7 nm or less. Here, “theoretical film thickness” means that it is very difficult to directly measure these extremely thin coating layers over the entire surface, so the coating layer film formed by wet plating or sputtering before continuous drawing. The value obtained by proportionally calculating the value after wire drawing from the thickness was expressed as “theoretical” film thickness in the specification. The proportional constant for obtaining the “theoretical film thickness” is a value obtained by dividing the wire diameter after the end of continuous wire drawing as a bonding wire by the wire diameter before the start of continuous wire drawing.
The thinner the surface layer, the lower the axial eccentricity and variations caused by the thickness of the surface layer, but the effect on abnormal wear of the die, such as the lubrication action on the diamond die, etc. Therefore, 1 nm is set as the lower limit.
Preferably, this value is 2 nm or more, more preferably 4 nm.
In order to avoid the wire wear and abnormal wear of the diamond die, it is preferable that the continuous wire drawing is cooled in an aqueous solution and performed at a constant speed (the final wire drawing speed of continuous wire drawing is 30 to 600 m / min). If the wire drawing speed exceeds this range and is too fast, vibration will occur in the wire being drawn, making it easier to break. In addition, in order to reduce the frictional resistance between the diamond die and gold (Au), a metal lubricant added with a commercially available surfactant is used by diluting with a diluent such as water or alcohol. An aqueous solution containing only isopropyl alcohol can also be used.

表面層は、断面方向の付きまわり性の均一性からは湿式めっきが最もよいが、めっき析出物中に不純物を取り込みやすいので、これを回避するため乾式めっきを採用してもよい。
めっき層中に不純物を取り込むと、溶融ボール形成のスパーク放電時に溶融ボールの形状に影響を及ぼす。乾式めっきは付きまわり性及び中間層との接合性の観点から、真空蒸着よりもスパッタリング法によるコーティングがよい。スパッタリング法によりコーティングされた金（Au）等の被覆層は、一旦イオン化されているため、純度９９．９質量％以上であっても硬質となり、付きまわり性がよい。
金（Au）などの表面層は、冷間の連続伸線加工で相対的に更に硬質となるパラジウム（Pd）析出物の微細な接合界面内部まで入り込み、冷間伸線加工中にしっかり接合される。
なお、スパッタリング法によりコーティングされた本発明の極めて薄い金（Au）などの表面層は、断面方向から観察すると方向によって厚みが最大６倍程度の差が生じる場合もあるが、溶融ボールに軸上偏芯やそのバラツキは見られない。これは、本発明における金（Au）などの表面層の平均的な膜厚が９ｎｍ以下と薄い場合には、第二ボンド後の切断部における金（Au）表面層の異常な伸びが発生しにくいため、スパーク放電時の不均一な溶融が生じないためと思われる。また、これら表面層の膜厚が極めて薄いことから、このような幾何学的な不均一さがあっても、溶融ボール形成時の表面張力が勝って真球状の溶融ボールとなるものとも考えられる。 For the surface layer, wet plating is the best in terms of uniformity of throwing power in the cross-sectional direction. However, since it is easy to incorporate impurities into the plating deposit, dry plating may be employed to avoid this.
Incorporation of impurities into the plating layer affects the shape of the molten ball during spark discharge in forming the molten ball. In dry plating, coating by sputtering is better than vacuum deposition from the viewpoint of throwing power and bondability with an intermediate layer. Since the coating layer such as gold (Au) coated by the sputtering method is once ionized, even if the purity is 99.9% by mass or more, it is hard and has good throwing power.
Surface layers such as gold (Au) penetrate into the fine joint interface of palladium (Pd) precipitates, which become relatively harder during continuous cold drawing, and are firmly joined during cold drawing. The
It should be noted that the surface layer such as gold (Au) of the present invention coated by the sputtering method may have a maximum thickness difference of about 6 times depending on the direction when observed from the cross-sectional direction. There is no eccentricity or variation. This is because when the average film thickness of the surface layer such as gold (Au) in the present invention is as thin as 9 nm or less, abnormal elongation of the gold (Au) surface layer at the cut portion after the second bond occurs. This is probably because non-uniform melting during spark discharge does not occur. In addition, since the thickness of these surface layers is extremely thin, even if there is such geometrical non-uniformity, it is considered that the surface tension at the time of forming the molten ball wins and a true spherical molten ball is formed. .

本発明の表面層の金（Au）、銀（Ag）、又は銅（Cu）の純度は９９．９質量％以上あれば十分であるが、９９．９９質量％以上あればより好ましい。あるいは、これらの純金属やこれらの純度の金属からなる合金（Au-Ag、Ag-Cu、Au-Cu）に微量添加元素（例えば、Mg、Si、P、Ti、V、Cr、Mn、Co、Ni、Cu、Zn、Ga、Ｇe、Y、Zr、Nb、Rh、Pd、Ag、In、Sn、Sｂ、希土類元素）を意図的に添加、含有させることができる。 The purity of gold (Au), silver (Ag), or copper (Cu) in the surface layer of the present invention is sufficient if it is 99.9% by mass or more, more preferably 99.99% by mass or more. Alternatively, a small amount of additive elements (for example, Mg, Si, P, Ti, V, Cr, Mn, Co) are added to these pure metals or alloys (Au-Ag, Ag-Cu, Au-Cu) made of these pure metals. Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Rh, Pd, Ag, In, Sn, Sb, and rare earth elements) can be intentionally added and contained.

本発明の銅（Cu）芯材は、還元性窒素雰囲気中で真球状の溶融ボールが形成可能な銅（Cu）又は銅合金からなる。銅合金としては、例えば、P、Au、Pd、Ptなどを含有させたものが考えられる。
他方、銅（Cu）の純度が９９質量％以下になると、不純物が含有して連続伸線加工中に断線しやすくなるために、９９．９９９質量％オーダーのものが好適である。ここで、「銅（Cu）の純度００．９９９質量％以上」とは、銅（Cu）以外の金属の不純物元素が０．００１質量％未満であることをいい、銅（Cu）中に存在する酸素、窒素や炭素などのガス状元素を除いたものをいう。 The copper (Cu) core material of the present invention is made of copper (Cu) or a copper alloy capable of forming a true spherical molten ball in a reducing nitrogen atmosphere. As the copper alloy, for example, an alloy containing P, Au, Pd, Pt or the like can be considered.
On the other hand, when the purity of copper (Cu) is 99% by mass or less, impurities are contained and the wire is easily broken during continuous wire drawing. Here, “the purity of copper (Cu) is 0.0999% by mass or more” means that the impurity element of metal other than copper (Cu) is less than 0.001% by mass, and is present in copper (Cu). It excludes gaseous elements such as oxygen, nitrogen and carbon.

なお、本発明の銅（Cu）芯材は、リン（P）が存在することが好ましい。リン（P）は微量でも銅ワイヤの再結晶温度を上昇させ、ワイヤ自体の強度を向上する効果があるからである。また、芯材に所定量のリン（P）が含まれると、第一ボンディングにおいて溶融した銅ボールが凝固していく過程で、銅（Cu）ボールの脱酸作用をする。銅（Cu）の純度９９．９９９質量％以上であれば、リン（P）は１質量ｐｐｍ以上の範囲で脱酸作用をし、５００質量ｐｐｍ以下の範囲であれば、溶融ボールが圧着時に加工硬化してAlパッドを破壊する不良は発生しづらい。このようにリン（P）の脱酸効果により、銅（Cu）の酸化が防止できる。     The copper (Cu) core material of the present invention preferably contains phosphorus (P). This is because even if the amount of phosphorus (P) is small, the recrystallization temperature of the copper wire is raised and the strength of the wire itself is improved. Further, when a predetermined amount of phosphorus (P) is contained in the core material, the copper (Cu) ball is deoxidized in the process of solidifying the molten copper ball in the first bonding. If the purity of copper (Cu) is 99.999% by mass or more, phosphorus (P) deoxidizes in the range of 1 ppm by mass or more, and if it is in the range of 500 ppm by mass or less, the molten ball is processed during compression bonding Defects that harden and destroy the Al pad are unlikely to occur. Thus, oxidation of copper (Cu) can be prevented by the deoxidation effect of phosphorus (P).

本発明の中間層は、パラジウム（Pd）から構成される。パラジウム（Pd）の融点（１，５５４℃）は、芯材の銅（Cu）の融点（１，０８５℃）よりも高い。このため、芯材の銅（Cu）や銅合金が球状の溶融ボールを形成していく最初の溶融段階でパラジウム（Pd）が薄皮となって溶融ボールの側面からの酸化を防止すると考えられる。
本発明の中間層の金属の純度は、第二ボンドの接合強度を確保するため、純度９９質量以上のパラジウム（Pd）が必要である。中間層が厚いと銅ボールが合金化して硬くなり、このためチップ割れが起きやすくなる傾向にあるので、芯材を被覆する膜厚を線径の０．０１倍を上限とした。逆に、中間層の膜厚が薄いと、第二ボンドの接合強度が低下するので芯材の線径の０．００１倍を下限とした。
また、高温放置試験による信頼性の評価結果から、パラジウム（Pd）の中間層はある程度の厚さが必要である。これらのことから、銅（Cu）等の芯材を被覆するパラジウム（Pd）からなる中間層の理論的な最終膜厚を線径の０．００１〜０．０２倍とした。好ましくは、線径の０．００２〜０．０１倍の範囲である。 The intermediate layer of the present invention is composed of palladium (Pd). The melting point (1,554 ° C.) of palladium (Pd) is higher than the melting point (1,085 ° C.) of copper (Cu) as the core material. For this reason, it is considered that palladium (Pd) is thinned to prevent oxidation from the side surface of the molten ball in the first melting stage in which the core material copper (Cu) or copper alloy forms a spherical molten ball.
As for the purity of the metal of the intermediate layer of the present invention, palladium (Pd) having a purity of 99 mass or more is required in order to ensure the bonding strength of the second bond. If the intermediate layer is thick, the copper ball is alloyed and hardened, so that chip cracking tends to occur. Therefore, the upper limit of the film thickness covering the core material is 0.01 times the wire diameter. On the contrary, when the film thickness of the intermediate layer is thin, the bonding strength of the second bond decreases, so 0.001 times the wire diameter of the core material is set as the lower limit.
Further, from the result of the reliability evaluation by the high temperature storage test, the intermediate layer of palladium (Pd) needs to have a certain thickness. From these facts, the theoretical final film thickness of the intermediate layer made of palladium (Pd) covering the core material such as copper (Cu) was set to 0.001 to 0.02 times the wire diameter. Preferably, it is in the range of 0.002 to 0.01 times the wire diameter.

パラジウム（Pd）中間層の形成方法には、乾式めっきや湿式めっきを採用することができる、乾式めっきとして、スパッタリング法、イオンプレーティング法、真空蒸着などいずれでもよい。不純物の混入を避けるためには乾式めっきが好ましいが、断面が均一な円環形状を得るには付きまわりのよい、湿式めっきがよい。不純物が混入していても中間層は溶融ボール形成時のスパーク放電の影響を受けないので、溶融ボールの軸上偏芯には影響を与えない。   As the method for forming the palladium (Pd) intermediate layer, dry plating or wet plating can be employed. As the dry plating, any of sputtering, ion plating, vacuum deposition, and the like may be used. In order to avoid mixing of impurities, dry plating is preferable, but in order to obtain an annular shape with a uniform cross section, wet plating with good circulation is preferable. Even if impurities are mixed in, the intermediate layer is not affected by the spark discharge at the time of forming the molten ball, so it does not affect the on-axis eccentricity of the molten ball.

湿式めっきによりパラジウム（Pd）中間層を形成する前処理としてエッチングを行う場合、芯材の銅（Cu）又は銅合金は純度が高いので、塩素や臭素等のハロゲンイオン、あるいはイオウの混入を防ぐため、エッチングは燐酸浴や硝酸浴が好ましい。電解エッチング浴としては、０．１規定の硝酸と２規定の硝酸アンモニウム又は硝酸カリウム溶液、６０％燐酸水溶液などがあり、化学エッチング浴としては、燐酸４５、氷酢酸４５及び硝酸１０のエッチング浴、燐酸１０及び硝酸１のエッチング浴などがある。一方、乾式エッチングとしては、真空中におけるアルゴンイオンやヘリウムイオンなどの希ガスによるマグネトロンスパッタリングがある。パラジウム（Pd）中間層をマグネトロンスパッタする場合は、芯材との拡散を防ぐため室温で行うのがよい。   When etching is performed as a pretreatment to form a palladium (Pd) intermediate layer by wet plating, the copper (Cu) or copper alloy of the core material is high in purity, thus preventing contamination by halogen ions such as chlorine and bromine, or sulfur. Therefore, the etching is preferably a phosphoric acid bath or a nitric acid bath. Examples of the electrolytic etching bath include 0.1 N nitric acid, 2 N ammonium nitrate or potassium nitrate solution, 60% phosphoric acid aqueous solution, and the like. And nitric acid 1 etching bath. On the other hand, dry etching includes magnetron sputtering using a rare gas such as argon ions or helium ions in a vacuum. When magnetron sputtering is performed on the palladium (Pd) intermediate layer, it is preferable to carry out at room temperature in order to prevent diffusion with the core material.

本発明で使用する銅（Cu）は純度が高いので、パラジウム（Pd）の電解めっき浴もハロゲンイオンや硫酸イオンを含まないアンモニア性水溶液やシアン系水溶液のものが好ましい。また、高分子化合物や金属塩の光沢剤は溶融ボールの真球性に悪影響を与えるので、膜成分としては含まないことが好ましい。銅（Cu）等の芯材に電解めっきされた膜は、その後の連続伸線によって強圧縮加工されるので、膜性状は膜成分ほど重要ではない。膜成分にイオウ（S）が存在すると、溶融ボール形成時に銅（Cu）に混入して溶融ボールを硬化させるおそれがあるからである。パラジウム（Pd）電解めっき浴としては、パラジウムｐ−ソルト（Pd（NH3）2(NO2)２）、亜硝酸アンモニウム及び硝酸カリウム、又はパラジウムｐ−ソルト（Pd（NH3）2（NO2）２）、硝酸アンモニウム及びアンモニア水の弱アルカリ性アンモニア性水溶液、Pd（NH3）２（COO）2及び（NH４）2HPO4の中性アンモニア性水溶液などが採用できる。パラジウムｐ−ソルトを用いた浴では、PHが高いほど、析出物の粒径が大きくなる傾向にある。
パラジウム（Pd）を乾式めっきする場合、スパッタ膜等の異常析出を防ぐため、銅（Cu）の純度は９９．９９質量％よりも９９．９９９質量％程度のものが好ましい。 Since copper (Cu) used in the present invention has a high purity, an electrolytic plating bath of palladium (Pd) is preferably an ammoniacal aqueous solution or a cyanic aqueous solution not containing halogen ions or sulfate ions. In addition, since a polymer compound or a metal salt brightener adversely affects the sphericity of a molten ball, it is preferably not included as a film component. Since the film electroplated on a core material such as copper (Cu) is subjected to strong compression processing by subsequent continuous drawing, the film properties are not as important as the film components. This is because if the film component contains sulfur (S), it may be mixed with copper (Cu) during the formation of the molten ball to cure the molten ball. The palladium (Pd) electrolytic plating bath includes palladium p-salt (Pd (NH 3 ) 2 (NO 2 ) 2 ), ammonium nitrite and potassium nitrate, or palladium p-salt (Pd (NH 3 ) 2 (NO 2 ) 2. ), A weak alkaline aqueous ammoniacal solution of ammonium nitrate and ammonia, and a neutral aqueous ammoniacal solution of Pd (NH 3 ) 2 (COO) 2 and (NH 4 ) 2 HPO 4 . In the bath using palladium p-salt, the particle size of the precipitate tends to increase as the PH increases.
When palladium (Pd) is dry-plated, the purity of copper (Cu) is preferably about 99.999% by mass rather than 99.99% by mass in order to prevent abnormal deposition of a sputtered film or the like.

なお、溶融ボールの形成時に金（Au）表面被覆層が銅（Cu）芯材に溶け込むタイミングを調整するため、パラジウム（Pd）めっきをする前にパラジウム（Pd）や金（Au）やニッケル（Ni）等の市販のストライクめっき（極薄めっき）を施すことができる。 In order to adjust the timing at which the gold (Au) surface coating layer melts into the copper (Cu) core during the formation of the molten ball, palladium (Pd), gold (Au), nickel ( Commercial strike plating (ultra-thin plating) such as Ni) can be applied.

アーク放電による溶融ボールの形成において、各被覆層中の金属の融点は非常に重要である。ボンディングワイヤの大部分は、高純度の銅（Cu）又は銅合金の芯材が占めるので、銅（Cu）の融点（約１，０８５℃）や銅合金の融点が基準になる。芯材の高純度の銅（Cu）や銅合金は、還元性雰囲気中のアーク放電によって完全な真球形状となることが知られている。また、パラジウム（Pd）で被覆した高純度銅（Cu）の芯材も非酸化性雰囲気中でアーク放電によって真球形状となることが知られている。パラジウム（Ｐｄ）の融点（約１，５５５℃）は銅（Ｃｕ）の融点（約１，０８５℃）よりも高いので、非酸化性雰囲気中で銅（Ｃｕ）が真球形状となるのに引きずられて真球形状となるものと考えられる。
しかし、不安定なアーク放電によって最初に溶融するのは表面層なので、溶融ボールの形成には表面被覆層の影響が最も重要となる。高純度の金（Ａｕ）や銀（Ａｇ）のボンディングワイヤは雰囲気を問わずアーク放電により溶融ボールを形成すると真球状の溶融ボールが得られるにもかかわらず、高純度の金（Ａｕ）や銀（Ａｇ）を高純度銅（Ｃｕ）の芯材に直接被覆したボンディングワイヤは、槍状になってしまい、真球形状のボールが得られない。金（Ａｕ）の融点（約１，０６４℃）や銀（Ａｇ）の融点（約９６２℃）は、芯材の銅（Ｃｕ）の融点（約１，０８５度）よりも低いので、銅（Ｃｕ）が球状の溶融ボールを形成していく段階で、低融点の金（Ａｕ）表面被覆層が芯材の銅（Ｃｕ）よりも早く早期に融解してワイヤ端面をすばやく包むが、芯材の銅（Ｃｕ）中への拡散も生じて銅（Ｃｕ）の融解を不均一に促進するものと考えられる。 In forming a molten ball by arc discharge, the melting point of the metal in each coating layer is very important. Since most of the bonding wires are occupied by high-purity copper (Cu) or a copper alloy core material, the melting point of copper (Cu) (about 1,085 ° C.) or the melting point of the copper alloy is used as a reference. It is known that high purity copper (Cu) or a copper alloy as a core material becomes a perfect spherical shape by arc discharge in a reducing atmosphere. Further, it is known that a core material of high-purity copper (Cu) coated with palladium (Pd) also becomes a spherical shape by arc discharge in a non-oxidizing atmosphere. Since the melting point of palladium (Pd) (about 1,555 ° C.) is higher than the melting point of copper (Cu) (about 1,085 ° C.), copper (Cu) becomes a spherical shape in a non-oxidizing atmosphere. It is thought that it becomes a true spherical shape by being dragged.
However, since the surface layer is first melted by the unstable arc discharge, the influence of the surface coating layer is most important for the formation of the molten ball. High-purity gold (Au) or silver (Ag) bonding wires can be used to form high-purity gold (Au) or silver, regardless of the atmosphere. A bonding wire obtained by directly coating (Ag) on a core material of high-purity copper (Cu) has a bowl shape, and a spherical ball cannot be obtained. Since the melting point of gold (Au) (about 1,064 ° C.) and the melting point of silver (Ag) (about 962 ° C.) are lower than the melting point of copper (Cu) of the core material (about 1,085 ° C.), copper ( In the stage where Cu) forms a spherical molten ball, the low melting point gold (Au) surface coating layer melts earlier and earlier than copper (Cu) of the core material and wraps the wire end face quickly. It is considered that diffusion of copper into copper (Cu) also occurs and promotes the melting of copper (Cu) nonuniformly.

ボンディングワイヤの軸上偏芯量は、前記したように金（Ａｕ）等の表面層の膜厚が厚いほど大きく起こりやすい。また、金（Ａｕ）等の純度はできるだけ高いことが展延性の良い超極薄膜で芯材を全面被覆する上から望ましい。湿式めっきの場合には金（Ａｕ）の析出と同時にカリウム（Ｋ）やナトリウム（Ｎａ）塩などの不純物が巻き込まれやすいので、９９．９質量％以上の純度の高いものが望ましい。光沢剤等の他の金属成分や高分子成分がメッキ液中に混入していると、１ｎｍ未満の膜厚まで連続伸線したときに全面被覆することが難しくなり、超極薄膜が破れやすくなる。超極薄の表面層は、いずれの場合も完全な円輪形状でないが、表面層の厚みが１ｎｍ以上あれば十分である。   As described above, the on-axis eccentricity of the bonding wire is likely to increase as the film thickness of the surface layer such as gold (Au) increases. Further, it is desirable that the purity of gold (Au) or the like is as high as possible from the viewpoint of covering the entire core material with a super-thin film having good spreadability. In the case of wet plating, impurities such as potassium (K) and sodium (Na) salts are easily involved at the same time as the deposition of gold (Au), so that a high purity of 99.9% by mass or more is desirable. When other metal components such as brighteners and polymer components are mixed in the plating solution, it becomes difficult to cover the entire surface when continuously drawn to a film thickness of less than 1 nm, and the ultra-thin film is easily broken. . The ultra-thin surface layer is not a perfect annular shape in any case, but it is sufficient that the thickness of the surface layer is 1 nm or more.

パラジウム（Ｐｄ）中間層の湿式メッキは、レべリング剤や光沢剤などが含まれていないことが好ましいが、レべリング剤等が含まれていない場合は不規則な粒状に析出する傾向にある。また、パラジウム（Ｐｄ）の乾式メッキは高純度の銅（Ｃｕ）の芯材の結晶面に沿って層状に析出する傾向にある。しかし、本発明においては、ダイヤモンドダイスは、パラジウム（Ｐｄ）中間層と直接接触することはなく金（Ａｕ）等の表面層と接触して伸線加工されているので、連続伸線加工中にパラジウム（Ｐｄ）粉がダイヤモンドダイスの入り口に堆積することがなく、ワイヤが断線することはない。このため１５μｍの線径のパラジウム（Ｐｄ）を被覆した細い銅（Ｃｕ）ワイヤであっても、金（Ａｕ）表面層を形成しないボンディングワイヤと比較して、５倍以上のダイヤモンドダイスのダイス寿命がある。本発明の表面層は極めて薄いが全面被覆されており、１ｎｍ以上の厚みであれば連続伸線途中で破れることがないからである。   The wet plating of the palladium (Pd) intermediate layer preferably does not contain a leveling agent or a brightening agent, but if it does not contain a leveling agent or the like, it tends to precipitate in irregular particles. is there. Further, palladium (Pd) dry plating tends to deposit in layers along the crystal plane of a high purity copper (Cu) core material. However, in the present invention, the diamond die is not in direct contact with the palladium (Pd) intermediate layer, but is drawn in contact with the surface layer of gold (Au) or the like. Palladium (Pd) powder is not deposited at the entrance of the diamond die, and the wire is not broken. For this reason, even if it is a thin copper (Cu) wire coated with palladium (Pd) having a wire diameter of 15 μm, the die life of the diamond die is more than five times that of a bonding wire that does not form a gold (Au) surface layer. There is. This is because the surface layer of the present invention is extremely thin but is entirely covered, and if it has a thickness of 1 nm or more, it is not broken during continuous wire drawing.

高純度の金（Ａｕ）等の表面層を乾式メッキによって形成する場合、付きまわりを改善するため、乾式メッキ中にワイヤを軸中心に回転させながら移動したり、乾式メッキ中にワイヤを往復させて移動したり、ワイヤの両側から乾式メッキしたりして、高純度の金（Ａｕ）を中間被覆層上により均一な膜厚で析出させることができる。高純度の金（Ａｕ）等の表面層は、展延性が良いので、ダイヤモンドダイスのダイス穴形状にしたがって最終線径まで連続伸線加工することができ、パラジウム（Ｐｄ）中間層がダイヤモンドダイスと直接接触することはない。ワイヤの表面は金（Ａｕ）等が全面的に被覆されているので、連続伸線加工中に金（Ａｕ）等の表面層と中間層との界面の隙間は埋められ、パラジウム（Ｐｄ）中間層の湿式メッキに異常析出等があっても表面層を突き破って析出するようなことはない。 When a surface layer of high-purity gold (Au) or the like is formed by dry plating, the wire is moved while rotating around the axis during dry plating, or the wire is reciprocated during dry plating in order to improve throwing power. The high-purity gold (Au) can be deposited on the intermediate coating layer with a more uniform film thickness by moving the electrode or dry-plating from both sides of the wire. Since the surface layer of high-purity gold (Au) or the like has good spreadability, it can be continuously drawn to the final wire diameter according to the die hole shape of the diamond die, and the palladium (Pd) intermediate layer is made of a diamond die. There is no direct contact. Since the surface of the wire is entirely covered with gold (Au) or the like, the gap at the interface between the surface layer of gold (Au) or the like and the intermediate layer is filled during the continuous wire drawing process, and the palladium (Pd) intermediate Even if there is abnormal deposition or the like in the wet plating of the layer, it does not break through the surface layer and deposit.

以下、具体的に実施例について説明する。始めに、各実施例の共通項目を説明する。
中間層とは芯材の銅（Ｃｕ）と金（Ａｕ）や銀（Ａｇ）などの最表面層と芯材との間に形成された被覆層である。また、表面層は、前記の中間層の外側に形成された最表面層である。
芯材の銅（Ｃｕ）は、以下のＡ〜Ｆの６種類の純度の成分組成を原材料として用いた。
なお、原材料には不純物としてケイ素（Ｓｉ）、鉄（Ｆｅ）、銀（Ａｇ）、マグネシウム（Ｍｇ）、マンガン（Ｍｎ）、硫黄（Ｓ）、鉛（Ｐｂ）などが含有していることが考えられる。
Ａ：９９．９質量％銅（Ｃｕ）
Ｂ：９９．９５質量％銅（Ｃｕ）
Ｃ：９９．９９質量％銅（Ｃｕ）
Ｄ：９９．９９９質量％銅（Ｃｕ）
Ｅ： ５０質量ｐｐｍリン（Ｐ）と残部９９．９質量％銅（Ｃｕ）からなる合金
Ｆ：４５０質量ｐｐｍリン（Ｐ）と残部９９．９質量％銅（Ｃｕ）からなる合金
上記原材料は、溶解、鋳造し、圧延、伸線して線径５００μｍまで加工し、線径５００μｍで芯材の銅（Ｃｕ）にPd中間層の被覆を施し、その後、Ａｕなどの表面層を形成した。
次に各層の形成方法について説明する。
Pd中間層の形成方法が湿式メッキと記載あるものは、日本エレクトロプレイティング・エンジニヤース株式会社（略称「ＥＥＪＡ」という。）製のパラジウムメッキ液ＡＤＰ−７００（公称純度９９．９％）を使用して、湿式の電解メッキにより被覆した。
Pd中間層の形成方法が乾式メッキと記載あるものは、田中貴金属工業株式会社製の純度９９．９質量％のパラジウム（Ｐｄ）金属ターゲットを用いて、真空度７．０×１０−１Ｐａ，スパッタ電力３００〜１０００Ｗで、マグネトロンスパッタ法により被覆した。
Ａｕ表面層の形成方法が湿式メッキと記載あるものは、ＥＥＪＡ製シアン系金メッキ液テンヘ゜レックス２０４Ａを用い、めっき温度：５０℃で、湿式の電解メッキにより被覆した。
Ａｕ表面層の形成方法が乾式メッキと記載あるものは、田中貴金属工業株式会社製の純度９９．９質量％の金（Ａｕ）金属ターゲットを用いて、真空度７．０×１０−１Ｐａ，スパッタ電力２００〜５００Ｗで、マグネトロンスパッタ法により被覆した。
また、表面層の組成がＡｕ以外のものは、各合金組成の金属ターゲットを作製して、真空度７．０×１０−１Ｐａ，スパッタ電力５００Ｗで、マグネトロンスパッタ法により被覆した。
〔実施例１〕 Hereinafter, specific examples will be described. First, common items of each embodiment will be described.
The intermediate layer is a coating layer formed between the core material such as copper (Cu) and gold (Au) or silver (Ag) as the core material and the core material. The surface layer is the outermost surface layer formed outside the intermediate layer.
As the core material, copper (Cu) was used as a raw material with the following six component compositions of purity A to F.
The raw material may contain silicon (Si), iron (Fe), silver (Ag), magnesium (Mg), manganese (Mn), sulfur (S), lead (Pb), etc. as impurities. It is done.
A: 99.9 mass% copper (Cu)
B: 99.95 mass% copper (Cu)
C: 99.99 mass% copper (Cu)
D: 99.999 mass% copper (Cu)
E: Alloy consisting of 50 mass ppm phosphorus (P) and the balance 99.9 mass% copper (Cu) F: Alloy consisting of 450 massppm phosphorus (P) and the balance 99.9 mass% copper (Cu) The above raw materials are: Melting, casting, rolling and drawing were performed to a wire diameter of 500 μm, and a core material copper (Cu) was coated with a Pd intermediate layer with a wire diameter of 500 μm, and then a surface layer such as Au was formed.
Next, a method for forming each layer will be described.
The Pd intermediate layer forming method is described as wet plating using palladium plating solution ADP-700 (nominal purity 99.9%) manufactured by Nippon Electroplating Engineers Co., Ltd. (abbreviated as “EEJA”). Then, it was coated by wet electrolytic plating.
The method for forming the Pd intermediate layer is described as dry plating, using a palladium (Pd) metal target having a purity of 99.9% by mass made by Tanaka Kikinzoku Kogyo Co., Ltd., with a degree of vacuum of 7.0 × 10 −1 Pa, The film was coated by a magnetron sputtering method at a sputtering power of 300 to 1000 W.
When the formation method of the Au surface layer is described as wet plating, it was coated by wet electrolytic plating at a plating temperature of 50 ° C. using a cyan gold plating solution Tenhelex 204A manufactured by EEJA.
The method for forming the Au surface layer is described as dry plating, using a gold (Au) metal target with a purity of 99.9% by mass made by Tanaka Kikinzoku Kogyo Co., Ltd., with a degree of vacuum of 7.0 × 10 −1 Pa, The film was coated by a magnetron sputtering method with a sputtering power of 200 to 500 W.
Further, when the surface layer composition was other than Au, a metal target having each alloy composition was prepared and coated by a magnetron sputtering method at a vacuum degree of 7.0 × 10 −1 Pa and a sputtering power of 500 W.
[Example 1]

実験番号No.４は、Pd中間層によるＰｄ被覆を行なわず、実験番号１、２、５および７は湿式メッキでPd中間層の被覆を行なった。また、実験番号３、６および８は乾式メッキで中間Ｐｄ被覆を行なった。その直後、実験番号Ｎｏ１〜８の表面層としてＡｕ極薄層を形成した。その後は連続伸線加工を行い、表１に記載する線径１３〜２５μｍまで連続伸線加工を行い、その後に窒素ガス不活性雰囲気で伸び率が４〜１０％となる条件で熱処理し、製品スプールに巻き取った。Pd中間層およびＡｕ表面層の最終的な膜厚は表１に記載するとおりである。 Experiment No. 4 did not perform Pd coating with the Pd intermediate layer, and Experiment Nos. 1, 2, 5 and 7 performed the Pd intermediate layer coating by wet plating. In Experiment Nos. 3, 6 and 8, intermediate Pd coating was performed by dry plating. Immediately thereafter, an Au ultrathin layer was formed as the surface layer of Experiment Nos. 1 to 8. After that, continuous wire drawing is performed, wire drawing is performed to a wire diameter of 13 to 25 μm shown in Table 1, and then heat treatment is performed in a nitrogen gas inert atmosphere under conditions where the elongation is 4 to 10%. I wound it up on a spool. The final film thicknesses of the Pd intermediate layer and the Au surface layer are as shown in Table 1.

次に、実験番号１〜８の８種類のワイヤを用いてワイヤボンディングした。ボンディングワイヤの接続には、市販の自動ワイヤボンダ（（株）Ｋ＆Ｓ社製の超音波熱圧着ワイヤボンダ「ＭＡＸｕｍ Ｕｌｔｒａ（商品名）」を使用し、ボール／ステッチ接合を行った。溶融ボールはＭAXｕｍ ｐｌｕｓ Ｃｏｐｐｅｒ Ｋｉｔ（商品名）を用いて、流量０．５（ｌ／ｍｉｎ）で４体積％水素と残部窒素からなる混合ガスを使用して、ガス雰囲気中でアーク放電によりワイヤ先端にボールを形成した。
以上のボンディングワイヤをシリコン基板上の０．８μｍアルミニウム（Ａｌ−０．５％Ｃｕ）電極膜に接合し、ワイヤ他端を４μｍの銀（Ａｇ）メッキした２００℃のリードフレーム（材質は４２アロイ、板厚は１５０μｍ））上にステッチ接合した。キャピラリーはＳＰＴ社製を使用し、溶融ボールに関するワイヤボンダの設定値は、ＥＦＯ Ｆｉｒｅ ＭｏｄｅをＢａｌｌ Ｓｉｚｅとし、ＦＡＢ Ｓｉｚｅは実際の溶融ボール径がワイヤ径の２倍となるように調整した。
アルミニウム（Ａｌ−０．５％Ｃｕ）電極膜のダメージは、ボールボンディング直後に割れが発生していないかを、１９６個の電極膜で確認した。ボールボンディングされた状態でアルミニウム（Ａｌ）電極膜を上部から観察し、圧着されたボール周辺の電極膜に割れや盛り上がりのダメージが入っている個数を数え、０〜５個を○、６〜１０個を△、１１個以上を×とした。
第二ボンディング性は、上記のアルミニウム（Ａｌ−０．５％Ｃｕ）電極膜は使用せずに、ワイヤ両端を４μｍの銀（Ａｇ）メッキした２００℃のリードフレーム（材質は４２アロイ、板厚は１５０μｍ））上にボール／ステッチ接合した。３，９２０本のワイヤをボンディングし、不圧着回数が０〜３本を○、４〜２０本を△、２１以上を×とした。
軸上偏芯の観察は、２００９年頃からワイヤボンディングマシンを使い、連続的に溶融ボールを圧着せずに、裏返した状態で形成する方法が一般的となり、軸上偏芯は容易に観察することが可能になった。例えば、（株）Ｋ＆Ｓ社製の超音波熱圧着ワイヤボンダ「ＭＡＸｕｍ Ｕｌｔｒａ（商品名）」を使用した場合、ループパラメータをＦＡＢモードとすることで実施することが可能となったため、今回はこの方法を用いて、４μｍの銀（Ａｇ）メッキした２００℃のリードフレーム上へ連続ボンディングし、アルミニウム（Ａｌ−０．５％Ｃｕ）電極膜は使用しなかった。なお、その他のワイヤボンディングに関する設定値は、上記のアルミニウム（Ａｌ−０．５％Ｃｕ）電極膜のダメージ評価と同様に行なった。判定は、接合前の溶融ボール形状を１００個観察して、軸上偏芯と寸法精度が良好であるか等を判定した。ワイヤに対するボール位置の芯ずれが５μｍ以上ある個数を測定し、１０個以上である場合に×印、５〜９個である場合に△印、２〜４個であれば実用上の大きな問題はないと判断して○印、芯ずれが１個以下である場合は、ボール形成は良好であるため◎印で表記した。
その結果を表１に示す。 Next, wire bonding was performed using eight kinds of wires of experiment numbers 1 to 8. Bonding wires were connected using a commercially available automatic wire bonder (ultrasonic thermocompression wire bonder “MAXum Ultra (trade name)” manufactured by K & S Co., Ltd.) and ball / stitch bonding was performed. Using a Kit (trade name), a ball was formed at the tip of the wire by arc discharge in a gas atmosphere using a mixed gas consisting of 4% by volume hydrogen and the balance nitrogen at a flow rate of 0.5 (l / min).
The above bonding wire is bonded to a 0.8 μm aluminum (Al-0.5% Cu) electrode film on a silicon substrate, and the other end of the wire is plated with 4 μm silver (Ag) at 200 ° C. (42 alloy) The plate thickness was 150 μm)). The capillaries manufactured by SPT were used, and the wire bonder set value for the molten ball was adjusted so that EFO Fire Mode was Ball Size, and FAB Size was adjusted so that the actual molten ball diameter was twice the wire diameter.
The damage to the aluminum (Al-0.5% Cu) electrode film was confirmed with 196 electrode films to determine whether cracks occurred immediately after ball bonding. The aluminum (Al) electrode film is observed from the upper side in a ball-bonded state, and the number of cracks and bulging damages on the electrode film around the pressure-bonded ball is counted. The number was Δ and the number of 11 or more was ×.
The second bonding property is that the above-mentioned aluminum (Al-0.5% Cu) electrode film is not used, but a lead frame at 200 ° C. in which both ends of the wire are plated with 4 μm of silver (Ag) (material is 42 alloy, plate thickness) Is 150 μm)). 3,920 wires were bonded, the number of non-bonding times was 0-3, ○, 4-20 were Δ, and 21 or more were X.
For the observation of on-axis eccentricity, it has become common to use a wire bonding machine from around 2009 to form the melted ball upside down without continuously crimping the molten ball. Became possible. For example, when the ultrasonic thermocompression wire bonder “MAXum Ultra (trade name)” manufactured by K & S Co., Ltd. is used, it has become possible to implement by setting the loop parameter to the FAB mode. In addition, continuous bonding was performed on a lead frame at 200 ° C. plated with 4 μm of silver (Ag), and an aluminum (Al-0.5% Cu) electrode film was not used. The other set values for wire bonding were performed in the same manner as the damage evaluation of the aluminum (Al-0.5% Cu) electrode film. The determination was made by observing 100 molten ball shapes before joining to determine whether the on-axis eccentricity and the dimensional accuracy were good. The number of balls with a misalignment of 5 μm or more with respect to the wire is measured. When the number is 10 or more, × mark, when it is 5 to 9, Δ mark, 2 to 4 When it was determined that there was no circle, and when the misalignment was 1 or less, the ball formation was good, so that it was marked with ◎.
The results are shown in Table 1.

表１から明らかなとおり、銅（Ｃｕ）からなる芯材にパラジウム（Ｐｄ）中間層を形成し、Ａｕ表面層が被覆されたボンディングワイヤは、実験番号１，２，５，６，７，８のようにパラジウム（Ｐｄ）中間層の膜厚がワイヤ径の０．００１倍以上であれば第二ボンディング性が良好であり、実験番号３〜８のようにパラジウム（Ｐｄ）中間層の膜厚がワイヤ径の０．０２倍未満であればＡｌ電極膜のダメージは良好であった。
上記より、銅（Ｃｕ）からなる芯材に、ワイヤ径の０．００１以上〜０．０２倍未満の厚みでパラジウム（Ｐｄ）中間層を形成し、さらにＡｕ表面層が形成されたボンディングワイヤはボンディングワイヤとして実用に耐えることが確認された。
なお後記するが、実験番号５〜８はダイスライフの評価も行い問題ないことが確認された。
〔実施例２〕 As is apparent from Table 1, bonding wires in which a palladium (Pd) intermediate layer is formed on a core material made of copper (Cu) and an Au surface layer is coated are shown in Experiment Nos. 1, 2, 5, 6, 7, 8 If the film thickness of the palladium (Pd) intermediate layer is 0.001 times the wire diameter or more, the second bonding property is good, and the film thickness of the palladium (Pd) intermediate layer is as in Experiment Nos. 3-8. If the wire diameter is less than 0.02 times the wire diameter, the damage of the Al electrode film was good.
From the above, a bonding wire in which a palladium (Pd) intermediate layer is formed on a core material made of copper (Cu) with a thickness of 0.001 to less than 0.02 times the wire diameter, and further an Au surface layer is formed. It has been confirmed that it can withstand practical use as a bonding wire.
As will be described later, in Experiment Nos. 5 to 8, the die life was evaluated and it was confirmed that there was no problem.
[Example 2]

実験番号No.９〜３２および比較例１〜６を、表２−１および表２−２に示す。
所定の銅（Ｃｕ）を用い、溶解、鋳造し、圧延、伸線して線径５００μｍまで加工し、線径５００μｍで芯材の銅（Ｃｕ）にPd中間層を施し、Ａｕ表面層を形成した。Pd中間層およびＡｕ表面層の形成方法および最終的な厚みは表２−１および表２−２に記載した。その後、連続伸線加工を行い、表に掲げた最終線径とした。その後、窒素ガス不活性雰囲気で伸び率が４〜１０％となる条件で熱処理し、製品スプールに巻き取り、各種の評価を行った。評価は、実施例１と同様に、Ａｌ電極膜ダメージ、第二ボンディング性、軸上偏芯について行った。次に、ダイスライフ評価について説明する。 Experimental numbers No. 9 to 32 and Comparative Examples 1 to 6 are shown in Table 2-1 and Table 2-2.
Using predetermined copper (Cu), melting, casting, rolling and wire drawing to process the wire diameter to 500μm, applying Pd intermediate layer to core copper (Cu) with wire diameter of 500μm to form Au surface layer did. The formation method and final thickness of the Pd intermediate layer and Au surface layer are shown in Tables 2-1 and 2-2. Thereafter, continuous wire drawing was performed to obtain the final wire diameter listed in the table. Then, it heat-processed on nitrogen gas inert atmosphere on the conditions which become 4 to 10% of elongation rate, wound up on the product spool, and performed various evaluation. In the same manner as in Example 1, the evaluation was performed on the Al electrode film damage, the second bonding property, and the on-axis eccentricity. Next, dice life evaluation will be described.

前記したように、伸線加工中に発生するＰｄ粉の堆積が、断線を引き起こしている主原因であり、結果的にダイス磨耗の原因にもなっていると考えられる。発明者らは、Ｐｄ粉の堆積が増えると、断線頻度が増えると共にダイス磨耗も早くなり、逆にＰｄ粉の堆積が減ると、断線が減少し、ダイス磨耗が遅くなることを見出した。このように断線とダイス磨耗に一定の関係が認められたが、断線は製造ロット間の差が大きくなり、評価方法としてばらつきも多いため、ダイス磨耗を評価することで、Ｐｄ粉の堆積の良し悪しを判定することにした。
ダイス磨耗はダイスライフという評価方法で行った。ダイスライフ評価は、伸線用ダイスを用いて、最終伸線で実施した。使用したダイスは、一般的な天然ダイヤモンド製で、伸線加工の最終リダクションは７％を用い、評価は最終線径で実施した。また、伸線速度は３００ｍ／分で行い、伸線加工中はダイスに一般的なＣｕ線加工用の界面活性剤が添加された潤滑液を用いて、伸線用キャプスタンおよび伸線用ダイスに常温の潤滑液をシャワー方式で濡らしながら行った。
具体的には、伸線加工開始時に線径を測定し、次に、伸線１万ｍ毎に線径測定し、伸線加工時の線径と比較して線径が初めて０．０８μｍ増加した時点までの伸線加工長さをダイスライフと定義し、ダイスライフが４万ｍ未満を×、４万ｍ以上〜８万ｍ未満を△、８万ｍ以上〜１５万ｍ未満○、１５万ｍ以上を◎とした。
なお、本評価方法による、線径１８μｍで芯材の銅（Ｃｕ）に０．１μｍの湿式めっきでPd中間層を施し、Ａｕ表面層を形成しなかったワイヤについて評価した結果、ダイスライフは３万ｍであり、×と判定されたが、実験番号５〜８のダイスライフはいずれも１５万ｍ以上となり◎であった。 As described above, it is considered that the accumulation of Pd powder generated during wire drawing is the main cause of wire breakage, and as a result, die wear. The inventors have found that when the deposition of Pd powder increases, the frequency of disconnection increases and the die wear increases, and conversely, when the deposition of Pd powder decreases, the disconnection decreases and the die wear slows. In this way, a certain relationship was found between the disconnection and die wear, but the disconnection increases the difference between production lots, and there are many variations in the evaluation method. Therefore, by evaluating the die wear, the Pd powder accumulation is good. I decided to judge evil.
The die wear was performed by an evaluation method called die life. The die life evaluation was performed at the final wire drawing using a wire drawing die. The dies used were made of general natural diamond, the final reduction of the wire drawing was 7%, and the evaluation was carried out with the final wire diameter. Further, the drawing speed is 300 m / min, and during drawing, a capstan for drawing and a drawing die are used by using a lubricating liquid in which a surfactant for general Cu wire processing is added to the die. It was carried out while wetting a normal temperature lubricating liquid with a shower method.
Specifically, the wire diameter is measured at the start of wire drawing, then the wire diameter is measured every 10,000 m, and the wire diameter is increased by 0.08 μm for the first time compared to the wire diameter at the time of wire drawing. The wire drawing length to the point of time is defined as the die life, the die life is less than 40,000 m, x is from 40,000 m to less than 80,000 m, 80,000 m to less than 150,000 m, 15 More than 10,000 m was marked ◎.
In addition, as a result of evaluating the wire in which the Pd intermediate layer was formed by wet plating of 0.1 μm on the core material copper (Cu) with the wire diameter of 18 μm and the Au surface layer was not formed by this evaluation method, the die life was 3 Although it was determined to be x, the dice life of Experiment Nos. 5 to 8 was all 150,000 m or more.

始めに表２−１および表２−２のサンプルについて、実施例１と同様にＡｌ電極膜ダメージと第二ボンディング性について評価を行ったが、いずれも○であり良好な結果が得られた。
次に、表２−１の実施例のサンプル作製条件と評価結果について説明する。表２−１より、銅（Ｃｕ）または銅（Ｃｕ）とリン（Ｐ）の合金からなる芯材に、パラジウム（Ｐｄ）を中間層とし、さらにＡｕ表面層が１．２ｎｍ〜８．７ｎｍ被覆されたボンディングワイヤは、ボンディングワイヤの生産および機能において実用に耐えることが確認された。
最後に、表２−２に比較例のサンプル作製条件と評価結果を記す。比較例１および２のように、Ａｕ表面層が０．６ｎｍと非常に薄いものは、ダイスライフが悪く、ボンディングワイヤの生産において実用に耐えない結果であった。一方、比較例３〜６のように、Ａｕ表面層が１３ｎｍ〜２０ｎｍと厚いものは、溶融ボールが軸上偏芯するため、ボンディングワイヤの機能において実用に耐えない結果であった。
〔実施例３〕 First, the samples of Table 2-1 and Table 2-2 were evaluated for Al electrode film damage and second bonding properties in the same manner as in Example 1. Both were good and good results were obtained.
Next, sample preparation conditions and evaluation results of the examples in Table 2-1 will be described. From Table 2-1, a core material made of copper (Cu) or an alloy of copper (Cu) and phosphorus (P) has palladium (Pd) as an intermediate layer, and an Au surface layer covers 1.2 nm to 8.7 nm. It was confirmed that the bonded wire was practical in terms of bonding wire production and function.
Finally, Table 2-2 shows the sample preparation conditions and evaluation results of the comparative example. As in Comparative Examples 1 and 2, when the Au surface layer was as thin as 0.6 nm, the die life was poor and the results were not practical in the production of bonding wires. On the other hand, as in Comparative Examples 3 to 6, when the Au surface layer was as thick as 13 to 20 nm, the molten ball was eccentric on the axis, so that the bonding wire function was not practical.
Example 3

実験番号No.３９〜４３は、表３に示すに示す所定の銅（Ｃｕ）を用い、溶解、鋳造し、圧延、伸線して線径５００μｍまで加工し、線径５００μｍで芯材の銅（Ｃｕ）にPd中間層を施し、各種組成の表面層を形成した。Pd中間層および表面層の形成方法および最終的な厚みを表３に挙げる。その後、連続伸線加工を行い、窒素ガス不活性雰囲気で伸び率が４〜１０％となる条件で熱処理し、製品スプールに巻き取り、実施例２と同様な方法で評価を実施した。
なお、表面層は、９９．９９質量％以上の金（Ａｕ）および９９．９９質量％以上の銀（Ａｇ）および９９．９９質量％のＰｄ（パラジウム）および９９．９９質量％のＣｕ（銅）を、原材料として調合して溶解してターゲットを作製して乾式メッキにより形成した。 Experiment Nos. 39 to 43 use the predetermined copper (Cu) shown in Table 3 and melt, cast, roll and wire the wire to a wire diameter of 500 μm, and the wire diameter is 500 μm. A Pd intermediate layer was applied to (Cu) to form surface layers having various compositions. The formation methods and final thicknesses of the Pd intermediate layer and surface layer are listed in Table 3. Thereafter, continuous wire drawing was performed, heat treatment was performed in a nitrogen gas inert atmosphere under conditions where the elongation was 4 to 10%, the product was wound around a product spool, and evaluation was performed in the same manner as in Example 2.
The surface layer is composed of 99.99% by mass or more of gold (Au), 99.99% by mass or more of silver (Ag), 99.99% by mass of Pd (palladium), and 99.99% by mass of Cu (copper). ) Was prepared and dissolved as a raw material to prepare a target, which was formed by dry plating.

実験番号N0.３９〜４３について、実施例１と同様にＡｌ電極膜ダメージと第二ボンディング性について評価を行ったが、いずれも○であり良好な結果が得られた。つまり、再表面層が銀（Ａｇ）や銅（Ｃｕ）であっても、実施例程度の厚みであれば良好に使用できることが確認できた。
また、実験番号No.３９〜４３について、実施例２と同様に溶融ボールの軸上偏芯、ダイスライフの評価を行ったが、いずれも○以上の判定となり、良好な結果が確認された。
従って、表面層は金（Ａｕ）だけでなく、金（Ａｕ）と銀（Ａｇ）とパラジウム（Ｐｄ）と銅（Ｃｕ）を単体または組み合わせてできる加工性の良い合金組成であれば、良好に使用できることが確認できた。


〔実施例４〕 For the experiment numbers N0.39 to 43, the Al electrode film damage and the second bonding property were evaluated in the same manner as in Example 1. Both were good and good results were obtained. That is, even if the resurface layer is silver (Ag) or copper (Cu), it can be confirmed that it can be used satisfactorily as long as the thickness is about the same as that of the example.
In addition, for the experiment numbers No. 39 to 43, the on-axis eccentricity of the molten ball and the evaluation of the die life were performed in the same manner as in Example 2. Both were judged as “good” or better, and good results were confirmed.
Therefore, if the surface layer is not only gold (Au) but also an alloy composition with good workability made of gold (Au), silver (Ag), palladium (Pd), and copper (Cu) alone or in combination, it is good. It was confirmed that it could be used.


Example 4

実験番号No.４４〜５５は、下記および表４に示すに示す所定の銅（Ｃｕ）を用い、溶解、鋳造し、圧延、伸線して線径５００μｍまで加工し、線径５００μｍで芯材の銅（Ｃｕ）にPd中間層を施し、Ａｕ表面層を形成した。実施例２と同様な方法で評価を実施した。
Ｄ１：２０質量ｐｐｍジルコニウム（Ｚｒ）が添加された、残部がＤの銅（Ｃｕ）合金
Ｅ２：１０質量ｐｐｍバナジウム（Ｖ）と２０質量ｐｐｍジルコニウム（Ｚｒ）が添加された、残部がＥの銅（Ｃｕ）合金
Ｄ３：２０質量ｐｐｍジルコニウム（Ｚｒ）が添加された、残部がＤの銅（Ｃｕ）合金
Ｄ４：４０質量ｐｐｍスズ（Ｓｎ）が添加された、残部がＤの銅（Ｃｕ）合金
Ｄ５：３０質量ｐｐｍホウ素（Ｂ）が添加された、残部がＤの銅（Ｃｕ）合金
Ｄ６：１０質量ｐｐｍチタン（Ｔｉ）が添加された、残部がＤの銅（Ｃｕ）合金 Experiment Nos. 44 to 55 are made of the prescribed copper (Cu) shown below and shown in Table 4, and are melted, cast, rolled and drawn to be processed to a wire diameter of 500 μm. Pd intermediate layer was applied to copper (Cu) to form an Au surface layer. Evaluation was performed in the same manner as in Example 2.
D1: 20 mass ppm zirconium (Zr) added, balance D copper (Cu) alloy E2: 10 mass ppm vanadium (V) and 20 mass ppm zirconium (Zr) added, balance copper E (Cu) alloy D3: 20 mass ppm zirconium (Zr) added, balance D copper (Cu) alloy D4: 40 mass ppm tin (Sn) added, balance D copper (Cu) alloy D5: 30 mass ppm boron (B) added, balance D copper (Cu) alloy D6: 10 mass ppm titanium (Ti) added, balance D copper (Cu) alloy

実験番号Ｎｏ４４〜５５について、実施例１と同様にＡｌ電極膜ダメージと第二ボンディング性について評価を行ったが、いずれも○であり問題は無かった。また、実験番号No.４４〜４７について、実施例２と同様に溶融ボールの軸上偏芯、ダイスライフの評価を行ったが、いずれも○であり良好な結果が得られた。
従って、芯材の銅（Ｃｕ）に数十ｐｐｍの範囲で、ジルコニウム（Ｚｒ）、バナジウム（Ｖ）、スズ（Ｓｎ）、ホウ素（Ｂ）、チタン（Ｔｉ）の元素を添加したボンディングワイヤは、生産および機能として良好に使用できることが確認できた。
About experiment number No44-55, although Al electrode film damage and 2nd bondability were evaluated similarly to Example 1, all were (circle) and there was no problem. For Experiment Nos. 44 to 47, the on-axis eccentricity of the molten ball and the die life were evaluated in the same manner as in Example 2, and both were good and good results were obtained.
Therefore, the bonding wire in which the elements of zirconium (Zr), vanadium (V), tin (Sn), boron (B), and titanium (Ti) are added to the core material copper (Cu) within a range of several tens of ppm, It was confirmed that it can be used well as production and function.

Claims (8)

銅（Ｃｕ）または銅合金からなる芯材、パラジウム（Ｐｄ）からなる中間層および表面層が被覆された線径が１０〜２５μｍのボールボンディング用被覆銅ワイヤにおいて、
前記中間層は、ワイヤ径の０．００１〜０．０２倍の膜厚のパラジウム（Ｐｄ）被覆層であり、
前記表面層は、中間層のパラジウム（Ｐｄ）よりも低融点で、かつ展延性の金属又は合金からなり、ダイヤモンドダイスにより最終膜厚が１〜９ｎｍまで連続伸線された、最上層の被覆層であることを特徴とするボールボンディング用被覆銅ワイヤ。 In a coated copper wire for ball bonding having a wire diameter of 10 to 25 μm coated with a core material made of copper (Cu) or a copper alloy, an intermediate layer made of palladium (Pd), and a surface layer,
The intermediate layer is a palladium (Pd) coating layer having a thickness of 0.001 to 0.02 times the wire diameter,
The surface layer is made of a malleable metal or alloy having a melting point lower than that of the intermediate layer palladium (Pd), and is continuously drawn to a final film thickness of 1 to 9 nm by a diamond die. A coated copper wire for ball bonding, characterized in that: 上記表面層の厚さが１〜８ｎｍであることを特徴とする請求項１記載のボールボンディング用被覆銅ワイヤ。   2. The coated copper wire for ball bonding according to claim 1, wherein the surface layer has a thickness of 1 to 8 nm. 上記表面層の厚さが２〜７ｎｍであることを特徴とする請求項１記載のボールボンディング用被覆銅ワイヤ。     2. The coated copper wire for ball bonding according to claim 1, wherein the surface layer has a thickness of 2 to 7 nm. 前記表面層が９９．９９質量％以上の金（Au）、純度９９．９質量％以上のパラジウム（Pd）を１〜３０質量％及び残部が純度９９．９９質量％以上の金（Au）からなるAu-Pd合金、純度９９．９９質量％以上の銀（Ag）を１〜４０質量％以上及び残部純度９９．９９質量％以上の金（Au）からなるAu-Ag合金又は純度９９．９９質量％以上の銀（Ag）を１〜３０質量％、純度９９．９質量％以上のパラジウム（Pd）を１〜１５質量％及び残部純度９９．９９質量％以上の金（Au）からなるAu-Ag-Pd合金である請求項１記載のボールボンディング用被覆銅ワイヤ。   The surface layer is made of gold (Au) having a purity of 99.99% by mass or more, 1-30% by mass of palladium (Pd) having a purity of 99.9% by mass or more, and the balance being gold (Au) having a purity of 99.99% by mass or more. Au-Pd alloy, Au-Ag alloy consisting of 1-40 mass% or more of gold (Au) with a purity of 99.99 mass% or more and a purity of 99.99 mass% or more, or a purity of 99.99 mass%. Au composed of 1 to 30% by mass of silver (Ag) of not less than 1% by mass, 1 to 15% by mass of palladium (Pd) having a purity of not less than 99.9% by mass and the balance of 99.99% by mass or more of gold (Au). The coated copper wire for ball bonding according to claim 1, which is a -Ag-Pd alloy. 前記表面層が純度９９．９９９質量％以上の銅（Cu）又は１〜５００質量ｐｐｍリン（P）及び残部が純度９９．９９９質量％以上の銅（Cu）からなるCu-P合金である請求項１記載のボールボンディング用被覆銅ワイヤ。     The surface layer is a Cu-P alloy having a purity of 99.999% by mass or more of copper (Cu) or 1 to 500 ppm by mass of phosphorus (P) and the balance of 99.999% by mass or more of copper (Cu). Item 2. A coated copper wire for ball bonding according to item 1. 前記表面層が室温でマグネトロンスパッタリングにより形成されたものである、請求項１記載のボールボンディング用被覆銅ワイヤ。   The coated copper wire for ball bonding according to claim 1, wherein the surface layer is formed by magnetron sputtering at room temperature. 前記中間層が湿式メッキにより形成されたパラジウム（Pd）である請求項１記載のボールボンディング用被覆銅ワイヤ。   The coated copper wire for ball bonding according to claim 1, wherein the intermediate layer is palladium (Pd) formed by wet plating. 前記連続伸線の最終伸線速度が３０ｍ／分〜６００ｍ／分であることを特徴とする請求項１記載のボールボンディング用被覆銅ワイヤ。
2. The coated copper wire for ball bonding according to claim 1, wherein the final wire drawing speed of the continuous wire drawing is 30 m / min to 600 m / min.
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