JP2011235315A - Pb-FREE SOLDER ALLOY HAVING ZN AS MAIN COMPONENT - Google Patents
Pb-FREE SOLDER ALLOY HAVING ZN AS MAIN COMPONENT Download PDFInfo
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本発明は、Ｐｂを含まない、いわゆるＰｂフリーのはんだ合金に関するものであり、特に高温用として好適なＺｎを主成分とするＰｂフリーはんだ合金に関する。 The present invention relates to a so-called Pb-free solder alloy containing no Pb, and more particularly to a Pb-free solder alloy mainly composed of Zn suitable for high temperatures.
パワートランジスタ素子のダイボンディングを始めとして、各種電子部品の組立工程におけるはんだ付では高温はんだ付が行われ、３００℃程度の比較的高温の融点を有するはんだ合金が使用されている。この時使用される高温用はんだ合金としては、Ｐｂ−５質量％Ｓｎ合金に代表されるＰｂ系はんだ合金が従来から主に用いられている。 Starting with die bonding of power transistor elements, high temperature soldering is performed in soldering in the assembly process of various electronic components, and a solder alloy having a relatively high melting point of about 300 ° C. is used. As the high-temperature solder alloy used at this time, a Pb-based solder alloy represented by a Pb-5 mass% Sn alloy has been mainly used conventionally.
しかし、近年では環境汚染に対する配慮からＰｂの使用を制限する動きが強くなり、例えばＲｏｈｓ指令などで規制対象物質になっている。こうした動きに対応して、電子部品などの組立の分野においても、Ｐｂを含まないはんだ合金が求められている。 However, in recent years, there has been a strong movement to limit the use of Pb from the viewpoint of environmental pollution, and it has become a regulated substance under the RoHS directive, for example. Corresponding to such a movement, a solder alloy containing no Pb is also required in the field of assembling electronic components and the like.
Ｐｂを含まない中低温用（約１４０℃〜２３０℃）のはんだ合金に関しては、Ｓｎを主成分とするものが既に実用化されている。例えば、特許文献１には、Ｓｎを主成分とし、Ａｇを１.０〜４.０質量％、Ｃｕを２.０質量％以下、Ｎｉを０.５質量％以下、Ｐを０.２質量％以下含有するＰｂフリーはんだ合金が記載されている。また、特許文献２には、Ａｇを０.５〜３.５質量％、Ｃｕを０.５〜２.０質量％含有し、残部がＳｎからなるＰｂフリーはんだ合金が記載されている。 As for a solder alloy for medium and low temperatures (about 140 ° C. to 230 ° C.) not containing Pb, a solder alloy containing Sn as a main component has already been put into practical use. For example, in Patent Document 1, Sn is the main component, Ag is 1.0 to 4.0 mass%, Cu is 2.0 mass% or less, Ni is 0.5 mass% or less, and P is 0.2 mass%. % Pb-free solder alloy is described. Patent Document 2 describes a Pb-free solder alloy containing 0.5 to 3.5% by mass of Ag, 0.5 to 2.0% by mass of Cu, and the balance being Sn.
一方、Ｐｂを含まない高温用のはんだに関しても、各種の研究開発がなされている。しかしながら、従来のＰｂ系はんだ合金を代替できるような十分な特性を有するＰｂフリーはんだ合金はまだ提案されていない。 On the other hand, various research and development have been conducted on high-temperature solder that does not contain Pb. However, a Pb-free solder alloy having sufficient characteristics that can replace the conventional Pb-based solder alloy has not yet been proposed.
例えば、Ｂｉ系はんだ合金に関しては、特許文献３に、Ｂｉを３０〜８０質量％含み、溶融温度が３５０〜５００℃であるＢｉ／Ａｇはんだ合金が開示されている。しかし、このはんだ合金の液相線温度は４００〜７００℃と高く、接合時の作業温度も４００〜７００℃以上になると推測される。一般的な電子部品や基板の材料として多用されている熱可塑性樹脂や熱硬化性樹脂などの作業温度は４００℃未満、望ましくは３７０℃以下であることから、上記の作業温度は接合される電子部品や基板が耐えうる温度を超えていると考えられる。 For example, regarding Bi-based solder alloys, Patent Document 3 discloses a Bi / Ag solder alloy containing 30 to 80% by mass of Bi and having a melting temperature of 350 to 500 ° C. However, it is estimated that the liquidus temperature of this solder alloy is as high as 400 to 700 ° C., and the working temperature at the time of joining is 400 to 700 ° C. or higher. The working temperature of thermoplastic resins and thermosetting resins that are widely used as materials for general electronic components and substrates is less than 400 ° C., preferably 370 ° C. or less. It is considered that the temperature that a component or board can withstand is exceeded.
また、特許文献４には、Ｂｉを含む共昌合金と２元共昌合金を加え、更に添加元素を加えることによって、液相線温度の調整とばらつきの減少が可能な生産方法が開示されている。しかしながら、液相線の温度調整のみで４元系以上の多元系はんだになり、更にＢｉの脆弱な機械的特性については有効な改善がされていない。 Further, Patent Document 4 discloses a production method capable of adjusting the liquidus temperature and reducing variation by adding a Kyochang alloy containing Bi and a binary Kyochang alloy and further adding additional elements. Yes. However, only by adjusting the temperature of the liquidus line, it becomes a multi-component solder of quaternary or higher, and further, Bi is not improved effectively with respect to fragile mechanical characteristics.
Ｚｎ系はんだ合金についても、同様に、実用的な高温用のＰｂフリーはんだ材料は存在しない。Ｚｎ系はんだの場合、Ｚｎ自身の還元性が強く自ら酸化してしまうため、濡れ性が非常に悪いことが大きな問題の一つである。 Similarly, there is no practical high-temperature Pb-free solder material for Zn-based solder alloys. In the case of a Zn-based solder, the reducibility of Zn itself is strong and it oxidizes by itself, so that the wettability is one of the major problems.
例えば、特許文献５には、Ａｌを１〜９質量％、Ｇｅを０.０５〜１質量％含み、残部がＺｎ及び不可避不純物からなる高温はんだ付け用のＺｎ合金など、数種のＺｎ系はんだ合金が記載されている。これらのＺｎ系はんだ合金は、ＺｎにＡｌを添加することにより融点を下げたＺｎ−Ａｌ合金を基本とし、これにＧｅ又はＭｇの添加、更にはＳｎ又はＩｎの添加により、融点を一層下げる効果があることが記載されている。 For example, Patent Document 5 discloses several types of Zn-based solders such as a Zn alloy for high-temperature soldering containing 1 to 9% by mass of Al, 0.05 to 1% by mass of Ge, and the balance being Zn and inevitable impurities. Alloys are described. These Zn-based solder alloys are based on a Zn-Al alloy whose melting point is lowered by adding Al to Zn, and the effect of further lowering the melting point by adding Ge or Mg, and further by adding Sn or In. It is described that there is.
しかし、上記特許文献５に記載されたＺｎ系はんだ合金は、その組成の範囲内では合金の加工性が十分とは言えず、最も加工性が要求されるワイヤーへの加工は困難な場合が多い。しかも、濡れ性に関しては、上記のごとくＺｎは酸化し易く、ＣｕやＮｉなどに容易に接合できない。例えば、Ｃｕ基板やＮｉを最上層に有するＣｕ基板などに接合した場合、接合ができても車載用などのように厳しい環境下で使用し続けることは困難である。ＧｅやＳｎが添加されても酸化したＺｎは還元できず、濡れ性を向上させることはできない。 However, the Zn-based solder alloy described in Patent Document 5 cannot be said to have sufficient workability of the alloy within the range of the composition, and it is often difficult to process the wire that requires the highest workability. . Moreover, regarding wettability, Zn is easily oxidized as described above, and cannot be easily joined to Cu, Ni, or the like. For example, when bonded to a Cu substrate or a Cu substrate having Ni as the uppermost layer, it is difficult to continue using the device in a severe environment such as in-vehicle use even if the bonding is possible. Even if Ge or Sn is added, oxidized Zn cannot be reduced and wettability cannot be improved.
更に、Ｚｎ−Ａｌ合金には、凝固する際の収縮が大きいと言う問題がある。即ち、Ａｌの凝固収縮率（＋は収縮、−は膨張）が＋６.４〜＋６.８％、Ｚｎの凝固収縮率が＋４.９〜＋６.９％であるため、溶融したＺｎ−Ａｌ合金が凝固する時には５〜７％程度収縮する。これに加え、凝固後の冷却時に２７７℃付近で相変態が起き、更に収縮をしてしまうことが推測される。この現象によって、接合した電子部品の割れや剥がれなどの問題が生じることが考えられる。 Furthermore, the Zn—Al alloy has a problem that the shrinkage during solidification is large. That is, the solidification shrinkage rate of Al (+ is shrinkage,-is expansion) is +6.4 to + 6.8%, and the solidification shrinkage rate of Zn is +4.9 to + 6.9%. When it solidifies, it shrinks about 5-7%. In addition to this, it is presumed that phase transformation occurs near 277 ° C. during cooling after solidification and further shrinks. This phenomenon may cause problems such as cracking and peeling of the joined electronic components.
本発明は、電子部品の組立などで用いるのに好適な３００℃〜４００℃程度の融点を有し、濡れ性、接合性、信頼性に優れ、Ｐｂを含まず且つＺｎを主成分とする、高温用のＰｂフリーＺｎ系はんだ合金を提供することを目的とする。 The present invention has a melting point of about 300 ° C. to 400 ° C. suitable for use in the assembly of electronic components, etc., has excellent wettability, bondability, and reliability, does not contain Pb, and contains Zn as a main component. An object is to provide a high-temperature Pb-free Zn-based solder alloy.
本発明者は、Ｚｎを主成分とするＰｂフリーはんだ合金の加工性を向上させることを検討し、Ｚｎと共晶合金となる元素としてＢｉに注目した。即ち、Ｚｎ−Ｂｉ系状態図によれば、ＢｉはＺｎと共晶合金を作り、更に液相温度は４１６℃高めではあるものの、固相温度は２５４.５℃であるから実質的にリフロー温度に耐えうる温度であると考えられる。更に、液相温度と固相温度の差が約１６０℃あり、凝固時にＺｎの収縮によって生じる応力をＢｉよって緩和できることを見出し、本発明を完成したものである。 The present inventor studied improving the workability of a Pb-free solder alloy containing Zn as a main component, and paid attention to Bi as an element that becomes a eutectic alloy with Zn. That is, according to the Zn-Bi phase diagram, Bi forms a eutectic alloy with Zn, and although the liquidus temperature is 416 ° C higher, the solidus temperature is 254.5 ° C, so the reflow temperature is substantially increased. It is considered that the temperature can withstand. Further, the present inventors have found that the difference between the liquid phase temperature and the solid phase temperature is about 160 ° C., and that stress caused by Zn shrinkage during solidification can be relaxed by Bi.
即ち、本発明が提供するＰｂフリーＺｎ系はんだ合金は、Ｐｂを含まず、Ｚｎを主成分とし、ＢｉとＳｎを含む３元系のはんだ合金であって、第２元素であるＢｉを０.１〜８.０質量％、第３元素であるＳｎを０.３〜１０.０質量％含有し、残部がＺｎであることを特徴とする。 That is, the Pb-free Zn-based solder alloy provided by the present invention is a ternary solder alloy that does not contain Pb, contains Zn as a main component, and contains Bi and Sn, and Bi as the second element is reduced to 0. 1 to 8.0% by mass, the third element of Sn is contained in an amount of 0.3 to 10.0% by mass, and the balance is Zn.
また、本発明が提供する他のＰｂフリーＺｎ系はんだ合金は、Ｐｂを含まず、Ｚｎを主成分とし、ＢｉとＳｎとＰを含む４元系のはんだ合金であって、第２元素であるＢｉを０.１〜８.０質量％、第３元素であるＳｎを０.３〜１０.０質量、及び第４元素であるＰを０.５００質量％以下含有し、残部がＺｎであることを特徴とする。 Further, another Pb-free Zn-based solder alloy provided by the present invention is a quaternary solder alloy that does not contain Pb, contains Zn as a main component, and contains Bi, Sn, and P, and is a second element. It contains 0.1 to 8.0% by mass of Bi, 0.3 to 10.0% by mass of Sn as the third element, and 0.50% by mass or less of P as the fourth element, with the balance being Zn. It is characterized by that.
本発明によれば、濡れ性、接合性、信頼性等に優れ、且つ３００℃程度のリフロー温度に十分耐え、パワートランジスタ素子のダイボンディング等の各種電子部品の組立工程でのはんだ付に好適な高温用のＰｂフリーＺｎ系はんだ合金を提供することができる。 According to the present invention, it is excellent in wettability, bondability, reliability, etc., sufficiently withstands a reflow temperature of about 300 ° C., and suitable for soldering in assembly processes of various electronic components such as die bonding of power transistor elements. A high-temperature Pb-free Zn-based solder alloy can be provided.
本発明による第１のＰｂフリーＺｎ系はんだ合金は、Ｐｂを含まず、Ｚｎを主成分とし、ＢｉとＳｎを含む３元系のはんだ合金である。第２元素のＢｉは、Ｚｎ−Ｂｉ系状態図から明らかなように、Ｚｎと共晶合金を作り、液相温度と固相温度の差が約１６０℃あり、固相温度が２５４.５℃であるから、実質的にリフロー温度に耐えることができる。 The first Pb-free Zn-based solder alloy according to the present invention is a ternary solder alloy that does not contain Pb, contains Zn as a main component, and contains Bi and Sn. As is apparent from the Zn-Bi phase diagram, the second element Bi forms a eutectic alloy with Zn, the difference between the liquid phase temperature and the solid phase temperature is about 160 ° C, and the solid phase temperature is 254.5 ° C. Therefore, it can withstand substantially the reflow temperature.
更に、Ｂｉは凝固する際に膨張するという珍しい性質を有する。即ち、Ｚｎの凝固収縮率（＋は収縮、−は膨張）が＋４.９〜＋６.９％であるのに対し、Ｂｉの凝固収縮率は−３.２〜−３.４％である。このＢｉの凝固膨張により、Ｚｎ合金の凝固時の収縮によって発生する応力を大きく緩和することができる。これによって、電子部品の割れや剥がれなどの問題を解決できるだけでなく、はんだ合金の加工性も向上する。 Furthermore, Bi has the unusual property of expanding when it solidifies. That is, the solidification shrinkage rate of Zn (+ is shrinkage and − is expansion) is +4.9 to + 6.9%, whereas Bi is solidification shrinkage rate of −3.2 to −3.4%. By this solidification expansion of Bi, the stress generated by the shrinkage at the time of solidification of the Zn alloy can be greatly relieved. This not only solves problems such as cracking and peeling of electronic components, but also improves the workability of the solder alloy.
上記第１のＰｂフリーＺｎ系はんだ合金において、第２元素であるＢｉの添加量は０.１〜８.０質量％とする。この範囲内であれば、上記した熱応力緩和特性の向上と共に、加工性の向上、濡れ性の向上のいずれかの１つ以上の効果が期待できる。ただし、Ｂｉの添加量が０.１質量％未満では上記したＢｉの効果が現れず、８.０質量％を超えるとＺｎリッチ相及びＢｉリッチ相のそれぞれの結晶粒が大きく成長してしまい、加工性が低下するなどの問題が生じる。 In the first Pb-free Zn-based solder alloy, the addition amount of Bi as the second element is set to 0.1 to 8.0 mass%. Within this range, one or more effects of improving workability and wettability can be expected along with improvement of the above-described thermal stress relaxation characteristics. However, if the amount of Bi added is less than 0.1% by mass, the above-described effect of Bi does not appear, and if it exceeds 8.0% by mass, each crystal grain of the Zn-rich phase and Bi-rich phase grows greatly, Problems such as deterioration of workability occur.
しかしばがら、Ｚｎ−Ｂｉ合金は液相温度が４１６℃程度であり、高温用はんだとして若干高めである。そこで、このＺｎ−Ｂｉ合金の液相温度を下げるために、第３元素としてＳｎを添加する。例えば、Ｓｎを１０質量％添加すれば、液相温度を３９０℃以下にすることができる。しかし、必ずしも液相温度を４００℃以下にする必要はなく、電子部品や基板の接合時の条件によっては液相温度が４００℃を超えても接合できる場合があり、そのような場合はＳｎを過剰に添加する必要はない。 However, the Zn—Bi alloy has a liquidus temperature of about 416 ° C., which is slightly higher as a high-temperature solder. Therefore, Sn is added as the third element in order to lower the liquidus temperature of this Zn—Bi alloy. For example, if Sn is added in an amount of 10% by mass, the liquidus temperature can be reduced to 390 ° C. or lower. However, it is not always necessary to set the liquidus temperature to 400 ° C. or lower, and depending on the conditions at the time of joining electronic components and substrates, bonding may be possible even if the liquidus temperature exceeds 400 ° C. It is not necessary to add excessively.
Ｓｎを添加することによる更に別の効果として、１つは、Ｚｎ−Ｓｎの固相温度が１９９℃であって、液相温度と固相温度の差が大きいため、凝固時に発生する残留応力を緩和する効果である。もう１つの効果は、ＳｎはＺｎより酸化され難いため、Ｓｎを添加することで濡れ性が向上する効果がある。 Another effect of adding Sn is that the solid-state temperature of Zn—Sn is 199 ° C. and the difference between the liquid-phase temperature and the solid-phase temperature is large. It is a mitigating effect. Another effect is that Sn is less likely to be oxidized than Zn, so that the addition of Sn has the effect of improving wettability.
第３元素であるＳｎの添加量は、０.３〜１０質量％の範囲とする。０.３質量％未満では上記したＳｎの添加効果が現れず、逆に１０質量％を超えるとリフロー時に液相の割合が多くなりすぎるため、基板等に接合した電子部品を固定し続けることが困難になるという不都合がある。 The addition amount of Sn as the third element is in the range of 0.3 to 10% by mass. If the amount is less than 0.3% by mass, the above-mentioned effect of adding Sn does not appear. Conversely, if the amount exceeds 10% by mass, the liquid phase is too high at the time of reflow. There is an inconvenience that it becomes difficult.
次に、本発明による第２のＰｂフリーＺｎ系はんだ合金は、上記第１のＰｂフリーＺｎ系はんだ合金に更にＰを添加したもの、即ち、Ｐｂを含まず、Ｚｎを主成分とし、ＢｉとＳｎとＰを含む４元系のはんだ合金である。 Next, a second Pb-free Zn-based solder alloy according to the present invention is obtained by further adding P to the first Pb-free Zn-based solder alloy, that is, containing no Pb, containing Zn as a main component, Bi and It is a quaternary solder alloy containing Sn and P.
第４元素としてＰを添加することによって、濡れ性を更に向上させることができる。即ち、Ｐは自らが酸化して気化するため、接合時にはんだ表面の酸化膜の除去に大きく役立つ。特にＺｎを主成分とするはんだ合金は酸化しやすいため、Ｐの添加による効果は極めて顕著である。 By adding P as the fourth element, the wettability can be further improved. That is, since P is oxidized and vaporized by itself, it is very useful for removing the oxide film on the solder surface during bonding. In particular, since a solder alloy containing Zn as a main component is easily oxidized, the effect of addition of P is extremely remarkable.
上記第２のＰｂフリーＺｎ系はんだ合金において、第２元素であるＢｉ及び第３元素であるＳｎの添加量は、上記第１のＰｂフリーＺｎ系はんだ合金の場合と同様である。即ち、第２元素であるＢｉの添加量は０.１〜８.０質量％、第３元素であるＳｎの添加量は０.３〜１０.０質量とする。更に第４元素であるＰの添加量は、０.５００質量％を超えるとＰが偏析して加工性が低下し、接合性や信頼性を低下させる場合があるため、０.５００質量％以下とする。 In the second Pb-free Zn-based solder alloy, the addition amounts of Bi as the second element and Sn as the third element are the same as in the case of the first Pb-free Zn-based solder alloy. That is, the addition amount of Bi as the second element is 0.1 to 8.0 mass%, and the addition amount of Sn as the third element is 0.3 to 10.0 mass. Furthermore, if the addition amount of P, which is the fourth element, exceeds 0.50% by mass, P is segregated and the workability is lowered, which may lower the bondability and reliability. And
尚、上記第１のＰｂフリーＺｎ系はんだ合金で接合時に十分な濡れ性が得られる場合には、更にＰを添加して４元系とした上記第２のＰｂフリーＺｎ系はんだ合金を用いなくてもよい。例えば、電子部品等はメタライズ層を有するが、最上層として濡れ性向上のためＡｕ、Ａｇなどのメタライズ層を形成することで既に十分な濡れ性が確保されている場合などには、Ｐを添加して更なる濡れ性の向上を図る必要はなく、第１のＰｂフリーＺｎ系はんだ合金を用いて接合することができる。 In addition, when sufficient wettability is obtained at the time of joining with the first Pb-free Zn-based solder alloy, the second Pb-free Zn-based solder alloy, which is a quaternary system by further adding P, is not used. May be. For example, electronic parts have a metallized layer, but P is added when sufficient wettability has already been secured by forming a metallized layer such as Au or Ag to improve wettability as the uppermost layer. Thus, there is no need to further improve the wettability, and the first Pb-free Zn-based solder alloy can be used for bonding.
原料として、それぞれ純度９９.９重量％以上のＺｎ、Ｂｉ、Ｓｎ及びＰを準備した。大きな薄片やバルク状の原料については、溶解後の合金においてサンプリング場所による組成のバラツキがなく、均一になるように留意しながら、切断及び粉砕等を行い、３ｍｍ以下の大きさに細かくした。これらの各原料から所定量を秤量し、高周波溶解炉用グラファイトるつぼに入れた。尚、Ｐは溶融し難く、また酸化して揮発しやすいうえ、第２類の危険物であり、そのまま添加すると発火してしまうため、予めＡｌ又はＢｉと合金を作ってから砕いて再溶解させた。 As raw materials, Zn, Bi, Sn and P each having a purity of 99.9% by weight or more were prepared. Large flakes and bulk-shaped raw materials were cut and pulverized into fine pieces of 3 mm or less while paying attention to make the composition uniform in the alloy after melting without any variation in the sampling location. A predetermined amount of each of these raw materials was weighed and placed in a graphite crucible for a high-frequency melting furnace. In addition, P is difficult to melt and easily oxidizes and volatilizes, and is a second kind of hazardous material. If added as it is, it will ignite. Therefore, after making an alloy with Al or Bi in advance, it is crushed and re-dissolved. It was.
上記各原料の入ったるつぼを高周波溶解炉に入れ、酸化を抑制するために窒素を原料１ｋｇ当たり０.７リットル／分以上の流量で流しながら、溶解炉の電源を入れて原料を加熱溶融させた。金属が溶融しはじめたら混合棒でよく攪拌し、局所的な組成のばらつきが生じないように均一に混合した。十分溶融したことを確認した後、高周波電源を切って速やかにるつぼを取り出し、るつぼ内の溶湯を鋳型に流し込み、はんだ母合金を作製した。鋳型には、はんだ合金の製造の際に一般的に使用している形状と同様のものを使用した。 Put the crucible containing the above raw materials into a high-frequency melting furnace, and turn on the melting furnace to heat and melt the raw materials while flowing nitrogen at a flow rate of 0.7 liter / min or more per kg of raw materials in order to suppress oxidation. It was. When the metal began to melt, it was thoroughly stirred with a mixing rod and mixed uniformly so as not to cause local compositional variations. After confirming sufficient melting, the high frequency power supply was turned off and the crucible was quickly removed, and the molten metal in the crucible was poured into the mold to produce a solder mother alloy. A mold having the same shape as that generally used in the manufacture of solder alloys was used.
このようにして、各原料の混合比率を変えることにより試料１〜２０のＺｎ系はんだ母合金を作製した。これらの試料１〜２０の各はんだ母合金の組成をＩＣＰ発光分光分析器（ＳＨＩＭＡＺＵ Ｓ−８１００）を用いて分析し、その分析結果をはんだ組成として下記の表１に示した。 Thus, the Zn type solder mother alloy of samples 1-20 was produced by changing the mixing ratio of each raw material. The composition of each solder mother alloy of Samples 1 to 20 was analyzed using an ICP emission spectroscopic analyzer (SHIMAZU S-8100), and the analysis results are shown in Table 1 below as the solder composition.
次に、上記試料１〜２０の各はんだ母合金を圧延機でシート状に加工し、Ｚｎ系はんだ合金の加工性を評価した。また、シート状の各Ｚｎ系はんだ合金について、下記の方法により濡れ性（接合性）の評価及びヒートサイクル試験を行った。尚、はんだの濡れ性ないし接合性等の評価は、はんだ形状に依存しないためワイヤー、ボール、ペーストなどの形状で評価してもよいが、本実施例においてはシートの形状で評価した。得られた結果を下記表２に示した。 Next, each solder mother alloy of Samples 1 to 20 was processed into a sheet shape with a rolling mill, and the workability of the Zn-based solder alloy was evaluated. Each sheet-like Zn-based solder alloy was subjected to wettability (joinability) evaluation and heat cycle test by the following methods. The evaluation of solder wettability or bondability does not depend on the shape of the solder, so it may be evaluated by the shape of a wire, ball, paste, or the like, but in this example, it was evaluated by the shape of a sheet. The obtained results are shown in Table 2 below.
＜はんだ合金の加工性＞
上記はんだ母合金（厚さ５ｍｍの板状インゴット）を、圧延機を用いて厚さ０.１０ｍｍまで圧延した。その際インゴットの送り速度を調整しながら圧延し、その後スリッター加工により２５ｍｍの幅に裁断した。このようにしてシート状に加工した後、得られたシートのＺｎ系はんだ合金を観察して、傷やクラックがなかった場合を○、シート１０ｍ当たり割れやクラックが１〜３箇所あった場合を△、４箇所以上あった場合を×とした。
<Processability of solder alloy>
The solder mother alloy (a plate-like ingot having a thickness of 5 mm) was rolled to a thickness of 0.10 mm using a rolling mill. At that time, it was rolled while adjusting the feed speed of the ingot, and then cut into a width of 25 mm by slitting. After processing into a sheet shape in this way, the Zn-based solder alloy of the obtained sheet was observed, ○ when there were no scratches or cracks, and when there were 1 to 3 cracks or cracks per 10 m of the sheet (Triangle | delta) was set to x when there were four or more places.
＜濡れ性（接合性）の評価＞
上記のごとくシート状に加工した各Ｚｎ系はんだ合金を、濡れ性試験機（装置名：雰囲気制御式濡れ性試験機）を用いて評価した。即ち、濡れ性試験機のヒーター部に２重のカバーをして、ヒーター部の周囲４箇所から窒素を１２リットル／分の流量でながしながら、ヒーター設定温度を各試料の融点より約１０℃高い温度にして加熱した。設定したヒーター温度が安定した後、Ｃｕ基板（板厚：約０.７０ｍｍ）をヒーター部にセッティングして２５秒間加熱した。
<Evaluation of wettability (bondability)>
Each Zn-based solder alloy processed into a sheet as described above was evaluated using a wettability tester (device name: atmosphere control type wettability tester). In other words, a double cover is applied to the heater section of the wettability tester, and the heater set temperature is about 10 ° C. higher than the melting point of each sample while flowing nitrogen from four locations around the heater section at a flow rate of 12 liters / minute. Heated to temperature. After the set heater temperature was stabilized, a Cu substrate (plate thickness: about 0.70 mm) was set in the heater section and heated for 25 seconds.
次に、シート状のＺｎ系はんだ合金をＣｕ基板の上に載せ、２５秒間加熱した。加熱が完了した後、Ｃｕ基板をヒーター部から取り上げ、横の窒素雰囲気が保たれている場所に移して冷却した。十分に冷却した後、大気中に取り出して接合部分を確認した。Ｃｕ基板に接合できなかった場合を×、接合できたが濡れ広がりが悪かった場合（はんだが盛り上がった状態）を△、接合でき且つ濡れ広がりが良好な場合（はんだが薄く濡れ広がった状態）を○とした。 Next, a sheet-like Zn-based solder alloy was placed on the Cu substrate and heated for 25 seconds. After the heating was completed, the Cu substrate was picked up from the heater part, moved to a place where a horizontal nitrogen atmosphere was maintained, and cooled. After sufficiently cooling, it was taken out into the atmosphere and a joint portion was confirmed. X when the bonding to the Cu substrate was not possible, △ when the bonding was successful but the wetting spread was poor (the state where the solder was raised), and when the bonding was successful and the wetting and spreading was favorable (the state where the solder was thinly spreading) ○.
＜ヒートサイクル試験＞
はんだ接合の信頼性を評価するためにヒートサイクル試験を行った。尚、この試験は、上記濡れ性の評価においてＺｎ系はんだ合金がＣｕ基板に接合できた試料（濡れ性の評価が○及び△の試料）を用いて行った。
<Heat cycle test>
A heat cycle test was conducted to evaluate the reliability of solder joints. This test was performed using a sample in which the Zn-based solder alloy was able to be bonded to the Cu substrate in the evaluation of the wettability (samples having a wettability evaluation of ◯ and Δ).
即ち、Ｚｎ系はんだ合金が接合されたＣｕ基板に対して、−４０℃の冷却と１５０℃の加熱を１サイクルとして、これを５００サイクルまで繰り返した。その後、はんだ合金が接合されたＣｕ基板を樹脂に埋め込み、断面研磨を行い、ＳＥＭ（装置名：ＨＩＴＡＣＨＩ Ｓ−４８００）により接合面の観察を行った。接合面に剥がれが生じるか又ははんだにクラックが入った場合を×、そのような不良がなく、初期状態と同様の接合面を保っていた場合を○とした。 That is, with respect to the Cu substrate to which the Zn-based solder alloy was bonded, cooling at −40 ° C. and heating at 150 ° C. were taken as one cycle, and this was repeated up to 500 cycles. Thereafter, the Cu substrate to which the solder alloy was bonded was embedded in the resin, the cross-section was polished, and the bonded surface was observed by SEM (device name: HITACHI S-4800). The case where peeling occurred on the joint surface or the solder cracked was evaluated as x, and the case where there was no such defect and the same joint surface as in the initial state was maintained was evaluated as ◯.
上記の結果から分かるように、本発明による試料１〜１２の各Ｚｎ系はんだ合金は、各評価項目において全て良好な特性を示している。即ち、シートに加工しても傷やクラックの発生は無く、濡れ性も非常に良好であり、Ｃｕ基板に瞬時に濡れ広がった。特にＰを添加した試料７〜試料１２は濡れ広がりがよく、試料がＣｕ基板に接触した瞬間にはんだが基板上に薄く濡れ広がったうえ、非常に光沢のあるはんだ表面であり、接合時に酸化が進行していないことが目視でも確認できた。 As can be seen from the above results, each of the Zn-based solder alloys of Samples 1 to 12 according to the present invention exhibits good characteristics in each evaluation item. That is, no scratches or cracks were generated even when processed into a sheet, the wettability was very good, and the Cu substrate wetted and spread instantaneously. In particular, Samples 7 to 12 to which P is added have good wetting and spreading, and at the moment when the sample comes into contact with the Cu substrate, the solder thinly spreads on the substrate and is a very shiny solder surface, which is oxidized at the time of joining. It was confirmed visually that it was not progressing.
更に、試料１〜２０のＺｎ系はんだ合金は、ヒートサイクル試験においても５００回まで割れなどが発生せず、良好な接合性と信頼性を示し、Ｂｉの残留応力緩和効果が大きく寄与していることが推察される。以上の結果より、本発明のＺｎ系はんだ合金が非常に優れていることを確認できた。 Furthermore, the Zn-based solder alloys of Samples 1 to 20 do not generate cracks or the like up to 500 times even in the heat cycle test, exhibit good bondability and reliability, and the residual stress relaxation effect of Bi greatly contributes. It is inferred. From the above results, it was confirmed that the Zn-based solder alloy of the present invention was very excellent.
一方、比較例である試料１３〜試料２０のＺｎ系はんだ合金は、少なくともいずれかの特性において好ましくない結果であった。即ち、加工性の評価においては全ての試料において傷やクラックが発生し、ヒートサイクル試験では３００回で全て不良が発生した。これらの結果は、上記本発明の試料１〜９との対比から、はんだの残留応力が一因であると推測することができる。 On the other hand, the Zn-based solder alloys of Sample 13 to Sample 20, which are comparative examples, were undesirable in at least any of the characteristics. That is, in the evaluation of workability, scratches and cracks occurred in all the samples, and in the heat cycle test, all defects occurred in 300 times. From these comparisons with the samples 1 to 9 of the present invention, it can be inferred that the residual stress of the solder is one factor.
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