JP3736452B2 - Solder foil - Google Patents

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Publication number
JP3736452B2
JP3736452B2 JP2001385444A JP2001385444A JP3736452B2 JP 3736452 B2 JP3736452 B2 JP 3736452B2 JP 2001385444 A JP2001385444 A JP 2001385444A JP 2001385444 A JP2001385444 A JP 2001385444A JP 3736452 B2 JP3736452 B2 JP 3736452B2
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JP
Japan
Prior art keywords
solder
particles
foil
solder foil
balls
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.)
Expired - Fee Related
Application number
JP2001385444A
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Japanese (ja)
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JP2002301588A (en
Inventor
太佐男 曽我
英恵 下川
寿治 石田
哲也 中塚
正英 岡本
一真 三浦
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Hitachi Ltd
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Hitachi Ltd
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Priority to JP2001385444A priority Critical patent/JP3736452B2/en
Publication of JP2002301588A publication Critical patent/JP2002301588A/en
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Publication of JP3736452B2 publication Critical patent/JP3736452B2/en
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    • H01L2924/15311—Connection portion the connection portion being formed only on the surface of the substrate opposite to the die mounting surface being a ball array, e.g. BGA
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
    • H01L2924/151—Die mounting substrate
    • H01L2924/156—Material
    • H01L2924/15786—Material with a principal constituent of the material being a non metallic, non metalloid inorganic material
    • H01L2924/15787—Ceramics, e.g. crystalline carbides, nitrides or oxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
    • H01L2924/161—Cap
    • H01L2924/1615—Shape
    • H01L2924/16152—Cap comprising a cavity for hosting the device, e.g. U-shaped cap
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
    • H01L2924/181—Encapsulation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/19—Details of hybrid assemblies other than the semiconductor or other solid state devices to be connected
    • H01L2924/1901—Structure
    • H01L2924/1904—Component type
    • H01L2924/19041—Component type being a capacitor

Abstract

PROBLEM TO BE SOLVED: To provide fresh solder and a method for manufacturing the solder, or electronic apparatus using this solder and a method for manufacturing the apparatus, and also to provide solder connection in temperature hierarchical connection necessary in the method manufacturing the electronic apparatus, more particularly the solder connection on a high-temperature side. SOLUTION: This solder foil is formed by rolling a solder material containing Cu particles 2 as metallic particles and Sn particles 3 as solder particles. The Cu is in the state of the particles and the Sn is in a state 4 of embedding the spacings among the Cu particles. The surfaces of the Cu particles are covered by Cu6Sn5 when the particles are caused to reflow. The electronic apparatus connected by using this foil is provided.

Description

【０００１】
【発明の属する技術分野】
電子装置および電子機器の製造において、特に、 Sn-Ag-Cu 系 Pb フリーはんだ等に対する高温側の温度階層接続を必要とするはんだ接続に適用して有効なはんだ箔の技術に関する。
【０００２】
【従来の技術】
Sn-Pb系はんだにおいては、高温系はんだとしてPbリッチのPb-5Sn(融点：314〜310℃)、Pb-10Sn(融点：302〜275℃)等を330℃近傍の温度ではんだ付けし、その後、このはんだ付け部を溶かさないで、低温系はんだのSn-37Pb共晶(融点：183℃)で接続する温度階層接続が可能であった。これらのはんだは、柔軟で変形性に富み、このため破壊し易いSiチップ等を熱膨張係数の異なる基板に接合することができた。このような温度階層接続は、チップをダイボンドするタイプの半導体装置や、チップをフリップチップ接続するＢＧＡ，ＣＳＰなどの半導体装置などで適用されている。即ち、半導体装置内部で使用するはんだと、半導体装置自身を基板に接続するはんだとは温度階層接続されていることを意味する。
【０００３】
【発明が解決しようとする課題】
現在、あらゆる分野において鉛フリー化が進んでいる。
【０００４】
Pbフリーはんだの主流はSn-Ag共晶系(融点：221℃)、Sn-Ag-Cu共晶系(融点：221〜217℃)、Sn-Cu共晶系(融点：227℃)になるが、表面実装におけるはんだ付け温度は部品の耐熱性から低いことが望ましいが、信頼性確保のためぬれ性を確保する必要性から、均熱制御に優れた炉を用いても、基板内の温度ばらつきを考慮すると、一番低い温度で可能なSn-Ag-Cu共晶系で235〜245℃くらいが実情である。従って、このはんだ付け温度に耐えられる階層用はんだとしては、融点が少なくても250℃以上である必要がある。現状で、これらのはんだと組合せて使用できる高温側の温度階層用Pbフリーはんだはない。最も可能性のある組成として、Sn-5Sb(融点：240〜232℃)はあるが、溶けてしまうので温度階層用にはならない。
【０００５】
また、高温系のはんだとしてAu-20Sn(融点：280℃)は知られているが、硬く、コスト高のために使用が狭い範囲に限定される。特に、熱膨張係数の異なる材料へのSiチップの接続、大型チップの接続では、Au-20Snはんだは硬いため、Siチップを破壊させる可能性が高いため使用されていない。
【０００６】
本発明の目的は、電子装置および電子機器の製造において、温度階層接続における低温側はんだ接続が、特に、 Sn-Ag-Cu 系 Pb フリーはんだを使用する場合に、高温側の Pb フリーはんだとして使用するはんだ箔を提供することにある。
【０００７】
【課題を解決するための手段】
上記目的を達成するために、本願において開示される発明のうち、代表的なものの概要を簡単に説明すれば、次の通りである。
Cu 、 Ag 、 Au または Al の第１の粒子 ( 体積比率５０％〜７４％ ) と、 Sn または In の第２の粒子とを分散混入したはんだ材料を、前記第２の粒子の融点より低い温度で、および真空中、還元性雰囲気中もしくは不活性雰囲気中で加圧して前記はんだ材料に塑性流動を起こさせて複合材料の塊に成形し、前記複合材料の塊をロール圧延して形成したはんだ箔である。このはんだ箔は、リフロー時に、前記第２の粒子の融点以上の温度で、溶融した前記第２の粒子の金属が前記第１の粒子の金属の表面部と化合物を形成することを特徴とする。
前記第１の粒子の粒径は１０〜４０μｍ、または３〜１０μｍである。また、前記はんだ箔の厚さが８０μｍから１５０μｍ、または１５０μｍから２５０μｍである。また、前記第１の粒子よりも熱膨張係数が小さい材料の第３の粒子として、インバー系、シリカ、アルミナ、 AlN 、 SiC の粒子を含むこともある。また、圧延率が１５％から２０％である。
【０００８】
【発明の実施の形態】
以下、本発明の実施の形態について説明する。
Cu等の金属ボールとSn系はんだボールとを約50%づつ配合して圧延すると、Cu粒子同志が接触し、Snはその隙間に入り込んだ複合はんだが得られる。この箔をチップと基板間に挟んで加圧、リフローすると複合はんだ部はCuボール間がCu-Sn化合物で連結され、該複合はんだ部とチップ及び基板間はCuボールとチップ電極との化合物、Cuボールと基板端子との化合物形成により、280℃の高温でも接合強度を確保する鉛フリー化した温度階層構造となる。これにより、鉛フリーはんだにおいて、温度階層を設けた接続方法を提供することができる。
温度階層接続を考えると、既に接続した高温側のはんだは、一部が溶融しても、他の残りの部分が溶融しなければ、後付けのはんだ接続時のプロセスにおいて耐えられる強度を十分に確保できる。我々は、金属ボール（Cu、Ag、Au、表面処理したAl、Zn-Al系はんだ等)とはんだボールとを分散混入したはんだ材料について研究を進めている。このはんだ材料により接続しておけば、例えば、後付けのはんだ接続時のプロセスであるSn-Ag-Cu系はんだによるリフロー炉(max 250℃)を通したとしても、接続部分におけるSnの部分は溶けるが、Cuボール間、Cuボールとチップ間、Cuボールと基板間は融点の高い金属間化合物(Cu6Sn5)で接続されているため、リフロー炉(max 250℃)の設定温度では接続は保たれ十分な接続強度を確保することができる。すなわち、Sn-Ag-Cu系はんだに対する温度階層接続を実現することが出来る。なお、この金属間化合物形成の効果はCu-Snに限らず、Ni-Sn(Ni3Sn4)、Ag-Sn(Ag3Sn)等の化合物、Au-Snでも同様である。また、はんだはSnの代わりにInでも同様である。合金層成長速度の違いはあるが、拡散により形成された合金層の融点は高く、形成されれば280℃で溶ける
ものではない。
【０００９】
このはんだ材料による接続は、完全にはCu同志が拘束されていない状態なので、例えばダイボンド接続に用いても上下、左右に対するある程度の自由度があり、Cuとはんだの中間段階の機械的特性が期待でき、温度サイクル試験でもSnによる耐熱疲労性とCu粒子（ボール）によるクラック進展防止による高信頼性が期待できる。
【００１０】
しかしながら、Cuボールとはんだボールとを混合した複合ペーストでは、本来、Sn系はんだはCu上にはぬれ拡がりが少ない性質を持つこと、かつ、Cuをぬらさなければならない部分が多く、Cuボールを完全にぬらせるとは限らないこと、更には、Cuとはんだボールとが最初は架橋状態で拘束されているので、はんだが溶けてもその部分が空間となって残るため、ボイドになる確率が高いこと等が我々の研究が進むにつれて明らかとなってきた。このため、このペースト方式は必然的にボイドが多くなるプロセスとなってしまい、接続用途によっては不向きな材料となってしまう。電子部品を実装する際にボイドが抜ければ良いが、例えばSiチップのダイボンド、パワーモジュール接合などは面と面とを接続するような形態であるので構造的にボイドが抜けにくい。ボイドが残存すると、ボイドを原因とするクラックの発生や、必要な熱拡散の阻害などの問題を引き起こしてしまう。
【００１１】
そこで、我々は、このはんだ材料を予め圧延し易い形状の型に入れて真空中、還元性雰囲気中もしくは不活性雰囲気中で、全体を均一に圧縮し、Sn系はんだボールを金属ボール間に塑性流動させ、隙間をはんだ（塑性変形後のＳｎ系はんだ）で充填した複合成型体とし、これを圧延することで得られるはんだ箔を用いることとした。
【００１２】
例えば、この複合成型体をSiチップなどのダイボンド用のはんだ箔に圧延して作製した場合、Cu-Cu等の金属ボール間は圧縮により接触しダイボンド時には金属ボール間は容易に金属間化合物を形成し、全体が高融点の金属で有機的につながれ、280℃でも強度を確保することを確認できた。当然のこととして、接続部分において空隙は真空中で圧縮されて埋まっているので、ボイドの少ない接続が可能である。窒素中での低温ホットプレスを用いると、Cuボール及びSn系はんだボールの粒径が大きい場合(約40μm)、Ｓｎ系はんだは97%以上の空隙充填率を示すことを確認した。また、箔表面を適度な膜厚のSnめっきを施すことで、酸化が著しい材料でも酸化を防止することはできる。
【００１３】
Cu箔リード同志をこのはんだで接合し、張り合わせたラップ型継手を270℃で50mm/minの引張速度で、せん断引張試験を行ったところ、約0.3kgf/mm2の値が得られたことにより、高温での強度は十分確保していることも確認した。
【００１４】
本方式ははんだ材料内部の空間を金属ボールで予め埋めてしまう方式であり、その分、ボイドは少なく、従来のはんだ箔の場合と同レベルまたはそれ以下のボイド率となることが予想される（大きなボイドはでき難い構造である。）。従って、本方式によるはんだでは、大面積ゆえにボイドレス化が重要課題であった、例えばSiのダイボンド、パワーモジュール接合等に対して好適な鉛フリー材料（鉛を積極的に含んでいない）となる。すなわち、温度階層接続などに好適な高信頼の高温鉛フリー材料を提供することが出来る。
【００１５】
更に、ペースト方式では酸化しやすいためフラックスレス化が困難であったが、これにより解決することもできる。すなわち、フラックス残さを嫌う分野においては、ペースト方式で接続した後、フラックスの洗浄が必要であったが、フラックスレス化により洗浄レス化が可能になる。
【００１６】
この他、望ましい融点を持つ硬い、剛性の強いはんだ、例えばAu-20Sn,Au-(50〜55)Sn(融点：309〜370℃),Au-12Ge(融点：356℃)等の場合でも、これらを金属ボールとして使用し、さらに軟らかい、弾性のあるゴム粒子をSn,In等の軟らかいはんだボールとともに分散混入させることにより、金属ボールに使用するはんだの固相線温度が約280℃以上をもつことで、高温での接続強度を有し、変形に対しては粒子間にある軟らかいSnもしくはInもしくはゴムが緩和することができ、これらのはんだの弱点を補完する新たな効果が期待できる。
【００１７】
以下、図面を参照して本発明の実施の形態を詳細に説明する。なお、発明の実施の形態を説明するための全図において、同一機能を有するものは同一符号を付け、その繰り返しの説明は省略する。
【００１８】
図１は複合ボール（金属ボール、はんだボール）で作る複合体金属の製作工程の概略を示し、(a)は真空ホットプレスのカーボン治具１中に金属ボールであるCuボール２と、はんだボールであるSnボール３を入れた状態で、(b)は真空ホットプレス後のはんだが塑性流動した後の複合ボール塊の断面形状モデルで、SnとCuは「海島構造」に変形している。(c)はその複合ボール塊を更にロール５で圧延し、はんだ箔を作製しているモデルである。
【００１９】
図では、10〜40μmのCuボールと10〜40μmのSnボールとを体積比でCuボールが50〜60%になるように配合した。Cuボールに対しては更に微細粒を入れて、最密充填配合(例えば、三輪茂雄；粉体工学通論、P39、1981/2/5、日刊工業新聞社)することによりCuボール間の接触を多くすることは可能である。最密充填ならば理論上Cuの体積比率は約74%になり、はんだは26%になる。また、10μm以下の微細粒にしても可能であり、合金層のネットワークが細かくなり、高密度で、ファインな接続に向いている。一例として3〜8μmのCu ボールと10〜40μm のSnボールの場合、3〜10μmのCu ボールと10〜40μm のSnボールの場合、あるいは5〜15μmのCu ボールと10〜40μm のSnボールの場合、箔のはんだ充填密度は下がるが、接続は良好な結果が得られている。なお、Cu ボールおよびSnボール等の径（大きさ）については、必ずしもすべての粒子が開示された大きさに含まれるというものではなく、発明の効果に影響のない範囲において、開示された大きさよりも、大きい又は小さいボールが含まれていても良いことは言うまでもない．これらのボールは窒素中で混合され、図１（a）に示すカーボン治具でできた圧力容器の中に入れる。真空引きした後、時間をかけて周囲から均一に圧力をかけていくと、Snのみが塑性変形しながらCuボール間の隙間を埋めていく。Snの融点は232℃であるが、室温でも時間をかけることで流動させることは可能である。室温で隅々まで流動させることが出来ない場合、若干（100〜150℃）、温度を上げることで、容易に可能となる。この工程ではCuとSnとは反応しない程、界面での拘束がないので自由度が上がりSnは変形（流動）し易くなる。そして、この真空ホットプレス等で形成された複合ボール塊は、更にロール５で圧延されはんだ箔を得る。圧延することで、よりCuボール間の隙間がなくなり、結果としてボイドの少ないはんだ箔を形成することが出来る。なお、前述の複合ボール塊は、この場合、150μm（±10μm）厚さのはんだ箔作製を目的としているので、それに近い形状の型に予めしておくことが圧延率を下げられることから望ましい。圧延率を上げると、Cu同志の接触部が増えるので、接触面積向上による拘束が増す。従って、温度サイクル等の変形に対応する柔軟性を持たすことを考慮すると、接触部を少なくすることが望ましく、最終的な圧延率は20%以下が好ましい。さらに圧延率は15〜20％がより好ましい。
【００２０】
なお、形成したはんだ箔で、Cu等が露出している場合は、更にSnを0.5〜2μmの厚さにめっきすることで、露出部のCuの酸化を防止することが好ましい。
【００２１】
作りやすさ、配合時に均一分散し易いこと、扱い易さ等の点ではCuボール及びはんだボールは球状であることが好ましいが、必ずしも球状である必要はない。Cuボール表面の凹凸が激しいもの、棒状、針状、繊維状、角状であるもの、樹枝状で合っても良く、また、これらを組合せたものでも良く、接合後にCu同志が絡み合えば良い。ただし、上記の圧縮によりCu同志で拘束されすぎて自由度がきかなくなると、はんだ付け時にクッション性なくなり、接続不良が生じ易くなるのであれば、ボール状よりもCuボールは表面に凹凸が激しいもの、棒状、針状、繊維状、角状であるもの、樹枝状のもの、またはこれらを組合せたものが好ましい。そして、図２に示すように、Cu２、Sn３ボール以外に、耐熱性の軟らかい弾性体であるメタライズした(無電解Niめっき-Auめっき、もしくは無電解Niめっき-はんだめっき)プラスチックボール(ゴム)６を分散させ低ヤング率化してクッション性を確保することも出来る。図２(a)は圧延前、(b)は圧延後を示す。樹脂ボール径は理想的には10μm以下、望ましくは1μmレベルが良い。例えば0.5〜5μmが望ましい。配合量としては体積で数%でも効果がある。
本明細書において「金属」「はんだ」について「粒子」「ボール」と２つの用語を用いているが、両者は、上記説明からわかるようにほぼ同意義で用いている。強いて区別をつけるとすれば、「粒子」は「ボール」を包括したやや広い意味で用いている。
【００２２】
次に、他の金属ボールの例としてAlを使用する場合を説明する。
【００２３】
高融点の金属は一般に硬いが、低コストで柔らかい金属として純Alがある。純Al(99.99%)は柔らかい（Hv17）が、通常はSnにぬれにくい。従って、Ni-Auめっき、もしくはNi-Snめっき等を施すことが好ましい。Al表面にスパッター等で薄くAuを被覆しても良い。柔かい純Alの微細粒を作るのが爆発等の安全性の問題で困難を伴うが、不活性雰囲気で製造し、即、表面にNi-Auめっきを施すことで、大気中にAlを接触させないことで安全性を確保できる。なお、Al粒子は多少の酸化膜を形成しても、めっき処理で除去できるので問題はない。更には、圧延工程でもAlの酸化膜は破壊され易いのでAlの新生面がでるので、接続にはそれほど影響されない。なお、Al表面へのメタライズとしてこれらに限定されるものでなく、はんだ箔を作製後、該はんだがCu、Ni等に対してぬれて、高温で接合強度を確保することが必要である。このため、Al粒子とNiめっきCu板間、及びAl粒子とSiチップのNiめっき間でAｌ粒子上のメタライズとNiとのSn化合物形成で連結することが必要である。
【００２４】
複合ボール塊を得るに当たって、Alは真空中であって特に高温で拡散し易いので、Ag入りのSnはんだを使用する等でAlとの化合物を形成することができる。Ag以外にAlに反応し易いようにSnの中に微量のZn、Cu、Ni、Sb等を入れてAl接続用のはんだとすることでも良い。Snの中に微量のAg、Zn、Cu、Ni、Sb等を入れる場合は、Al表面へのメタライズは不要であり、コスト上でのメリットは大きい。
【００２５】
Al表面を完全にぬらす場合と、まだら状にぬらすこともできる。これはメタライズの領域と関係し、まだらにメタライズを形成するか全体に形成するかによる。まだら状にすれば応力がかかった場合、変形時に拘束が小さくなることから変形し易く、かつ、ぬれていない部分は摩擦損出としてエネルギーを吸収してくれるので、変形能に優れた材料となる。当然、接合強度は確保する。
【００２６】
Alをボール状にする代わりに、20〜40μm位のAl線にSn、Ni-Sn、Au等のめっきを施し、切断して粒状、棒状にしたものを使用することも可能である。なお、ボール状のAl粒子は窒素中でアトマイズ法などで低コストで多量に製造することが可能である。
【００２７】
次にAuボールについて説明する。
【００２８】
複合ボール塊を得るに当たって、AuボールについてはSn系はんだは容易にぬれるので短時間の接続ならばメタライズの必要はない。但し、はんだ付け時間が長いと、Snが顕著に拡散し、脆いAu-Sn化合物の形成に不安が残る。このため、柔らかい構造とするにはAu拡散の少ないInめっきなども有力であり、Ni、Ni-Au等をバリアにしても良い。バリア層は極力薄くすることで、Auボールが変形し易くなる。Auとの合金層成長が抑えられるメタライズ構成であれば、他の構成でも良い。圧延までは温度を抑えることで拡散を抑えられる。ダイボンドで短時間で接合させる場合、粒界に生ずる合金層は薄いので、バリアを設けなくてもAuの柔軟性による効果は大いに期待できる。AuボールとInはんだボールの組み合わせも可能である。
【００２９】
次にAｇボールについて説明する。
【００３０】
Agボールについても、Cuボール同様であるが、Ag3Sn化合物の機械的性質は悪くはないので、通常プロセスでAg粒子間を化合物で連結することも可能である。Cu等の中に混ぜた使用も可能である。
【００３１】
次に金属ボールとして合金材料を使用する場合を説明する。
【００３２】
合金系の代表例としてZn-Al系、Au-Sn系等がある。Zn-Al系はんだの融点は330〜370℃の範囲が主で、Sn-Ag-Cu、Sn-Ag、Sn-Cu系はんだとの階層接続を行うには適した温度域にあり、これらを金属ボールに使用することが出来る。Zn-Al系の代表例として、Zn-Al-Mg、Zn-Al-Mg-Ga、Zn-Al-Ge、Zn-Al-Mg-Ge、更にはこれらにSn、In、Ag、Cu、Au、Ni等のいずれか一つ以上を含有したものを含む。
【００３３】
しかしながら、Zn-Al系は酸化が激しいこと、はんだの剛性が高いこと等のため、Siを接合した場合Siチップに割れを起こす恐れが指摘されており（清水他：「ダイアタッチ向けPbフリーはんだ用Zn-Ai-Mg-Ga合金」Mate99,1999-2）、単に複合ボール塊の金属ボールとして使用するとこれらの課題を解決しなければならない。
【００３４】
そこで、これらの課題をクリアする必要から、はんだの剛性を下げるために、Ni-はんだめっきもしくはAuめっきを施した耐熱性のプラスチックボールをSnボールとZn-Al系ボールとともに均一に分散させて、ヤング率の低減を図った。Snボールは全体の10〜50%混入すると、Zn-Al系はんだ間に溶融したSnが入り込む。この場合、一部はZn-Alボール同志が接合されるが、他の部分は主に析出した低温の柔らかいSn-Zn相や、溶解しないSnが存在する。変形はこのSn、Sn-Zn相とプラスチックボールのゴムが分担する。
【００３５】
実際にこのはんだ箔を用いて接続する場合、例えばダイボンドした場合もその後に一部Sn層を残すことにより、Snにより変形を吸収することができる。プラスチックボールとSn層との複合作用により、更に剛性を緩和することが期待できる。なお、この場合も、Zn-Al系はんだの固相線温度は280℃以上を確保しているので、高温での強度上の問題はない。
【００３６】
プラスチックボールはZn-Al系ボールに比べて径を小さくし、均一に分散させることが望ましい。変形時に柔らかい弾性を有する1μmレベルのプラスチックボールが変形すれば、熱衝撃緩和、機械的衝撃緩和の効果は大きい。プラスチックボールとして市販品の耐熱性のものがある。Zn-Al系はんだのボール間にプラスチックボールがほぼ均一に入るので、接続時の短時間の溶融ではこの分散は大きくくずれない。この耐熱樹脂は熱分解温度が約300℃なので、更に耐熱性のある材料が望ましいが、時間の短いダイボンドの場合は問題はない。
【００３７】
前述のように、真空中でホットプレスで成型する場合、Snめっきしたプラスチックボール上のSnが溶けない温度(Snの融点：232℃)で均等に圧縮させることで、塑性流動させる。このとき、Zn-Alボールは余り変形しない。均一な圧縮により空間をプラスチックボール、Sn等で均一に充填し、約150μmに圧延し、はんだ箔を作製する。ダイボンドで使用するときは、ロールに巻いて連続工程で供給することができる。
【００３８】
Zn-Alは酸化され易いので、保管時のことも考慮すると、表面にCu置換のSnめっきを施すことが望ましい。このSn、Cuは例えばダイボンド時にZn-Al系はんだに溶解する。Snが表面に存在することで、例えば、Cu電極上のNi-Auめっき上への接続が容易となる。Siチップ側も例えば、Ti-Ni-Auメタライズに対しても同様に容易に接合できる。200℃以上の高温下においては、NiとSnとの合金層(Ni3Sn4)の成長速度はCu-Sn以上に大であることから、化合物形成が不十分のために接合ができないようなことはない。
【００３９】
場合によっては、Zn-Al系はんだボールとプラスチックボールとで複合ボール塊を構成しても良い。
【００４０】
なお、Zn-Al系はんだに、固相線温度が280℃レベルを確保するレベルまで、Sn、In量を多く加える階層接続は可能である。Sn、In等を多く入れると、一部、Zn-Snの共晶等の低い相が部分的に生成されるが、接合強度は骨格となっているZn-Al系の固相が担っているので、高温での強度上の問題はない。
【００４１】
ところで、Zn-Al系はんだにCuで置換したSnめっきを施すと、Zn-Al系はんだの液相線温度以上に温度を上げることで、Snは容易にぬれ拡がり、薄いCuを固溶しながらZn-Al系はんだに溶解する。Snは多い(5％以上)とZn-Al の中には固溶できず、粒界に低温のSn-Zn相を析出してくる。意図的にSn相を多数分散析出させることで、変形はSn-Zn相で、接合強度はZn-Al系の固相で分担させることができる。従って、Zn-Al系はんだボールにSnめっきを施し、ボールに固溶できないSn相を意図的に残すことにより、変形をSn層で吸収させ、Zn-Alの剛性を緩和させることもできる。すなわち、接続した部分のはんだの剛性を緩和させることができ、接続不良が少なくなる。
【００４２】
図３は前述のはんだ箔11を用いてAl2O3基板13上のW-Cuめっきメタライズ(Niめっきでも良い)14にSiチップ８をダイボンドする一例を示す。はんだ箔11の代表例として、金属ボールがCｕで、はんだがSnの組合せがある。Cuは比較的に軟らかく、Snとの反応が活発で、金属間化合物(Cu6Sn5)の機械的性質は優れているので、厚く成長しても脆さは出にくい。万一、化合物成長が顕著でその弊害が現れる場合、Sn中にCu等を微量添加して合金層成長速度を抑えることは可能である。またはCu上にNi、Ni-Au等の薄いNiめっきを施すことで合金層成長を抑えることは可能である。ここでは、短時間のはんだ付け時にCuボール間を金属間化合物で確実に連結することが重要であり、反応を活発にすることが望まれるので、成長過剰が問題になることはない。それよりも、Snとチップ及びSnと基板との接続において、Snのぬれ性、ぬれ拡がり性の向上が重要である。このため、Sn中に微量のCu、Bi添加による流動性の向上、表面張力の低減によるぬれ性改良の効果が期待できる。他方、界面との強度向上のため、Ni、Ag、Zn等の微量添加の効果も期待できる。なお、Snの融点向上にはSnの代わりにSn-Sb(5〜10％)にすることで、Cu-Sn化合物、Ni-Sn化合物形成ではんだ中のSb濃度が増して、246℃にはんだの融点を向上させることができる。
【００４３】
他の代表例として、Cuよりも更に軟らかい純Alボールの場合、温度サイクルに対する変形能に優れる。課題はAlボールとチップ、基板のメタライズとの反応である。Al表面にNiめっきもしくはNi-Auフラッシュめっきを施すことでAlボール間及びAlボールとNiめっきのチップ間、Niめっきの基板間も同様にSnによる接合強度は確保される。NiとSn間の金属間化合物は通常はNi3Sn4であり、200℃以上ではCu-Snの成長速度より速いので反応不足の心配はない。CuとNiが同時に介在する個所では一部に（NiCu）3Sn4の混合した合金層が形成されることもある。Alボールにはんだが直接反応できるように、Sn中にAg、Ni、Zn、Ti等を微量添加することにより、Alボール間の接続も接続条件しだいで可能である。
【００４４】
Auのボールに対しても同様な対応が可能である。Auは柔軟でSnとの化合物を形成し易いので、コストの面を除くと有力な組成である。但し、Snが多い系での化合物は融点が低いので、280℃以上の融点を持つためには、Snが55%以下の組成比であるAuSn、AuSn2の化合物とする必要がある。このため、はんだ付け温度を高くして、接合部はSnが少ない構成にすることが必要であることから、Siチップ側のメタライズに、例えば、Cr-Ni-Snを設けることにより、Au-Sn、AuSnの形成が容易になる。Auボールにコスト低減等を考慮し、Cu、Al、Agボール等を混ぜることも可能である。
【００４５】
Agボールも同様に有力候補であり、高融点のAg3Sn化合物の形成で280℃でも溶けない連結接続が可能となる。
【００４６】
次に、硬くて、融点の低いZn-Al系ボールへの適用例を示す。Zn-Al系は融点と脆さの点で、一般にAl:3〜5%の範囲に落ち着き、更に融点を下げるためMg、Ge、Ga等を入れ、更にSn、Inの添加で主に固相線温度を下げる。そして、ぬれ性、強度確保なため、Cu、Ag、Ni等を入れる場合もある。これらの融点は280〜360℃レベルである。例えば、Zn-4Al-2Mg-1Ag-10Snの場合、はんだボールとしてSnボールを混合すると、両者が溶融してもSnはZn-Al系ボールに一部が固溶する程度で、残りの大部分はSnのままである。また、この場合、はんだに固溶できない余分なSn、In等を粒子の状態で良く分散させてはんだ中に孤立分散させることができるので、同様な効果が期待できる。Zn-Al系ボールにSnめっきを厚く施すこともSnを孤立分散させる一つの解である。
【００４７】
Zn-Al系ボールの場合、はんだ付け時に全体が溶融するので、表面張力の作用などによる表面形状が自然の形状になりやすい等の特徴がある。また、Zn-Al系は表面酸化が激しいので、予熱過程を含めて酸化させない工夫が必要になる。箔として使用する場合、表面にCu(0〜0.2μm)-Sn(1μm)めっきを施すことで、酸化防止の効果がある。なお、Zn-Al系ボール間にSnが存在することで、温度サイクル時の変形に対し、Snが緩衝材の役目を果たすが、それでも不充分の場合、微細なSnめっきプラスチックボールのゴムを分散混合することで更に変形性、耐衝撃性を向上させることができ、ヤング率は低下し、耐熱疲労性も向上させることができる。
【００４８】
同様に硬く、かつ融点の低い合金系として、Au-Sn系等があるが、同様な対応が可能である。
【００４９】
使用したAl2O3基板13にはW(焼結)-Cuめっき(3μm)38(もしくはW-Niめっき)を施した電極が形成されている。セラミック基板として他にムライト、ガラスセラミック、ALN等がある。接続時にフラックスを使用する場合、もしくは予熱段階から不活性雰囲気、あるいは還元雰囲気で使用できるならば、Cu電極のままで良い。
【００５０】
使用したSiチップ８のサイズは5mm□であり、はんだ箔11のサイズは4mm□×t(厚さ)0.15であるが、チップ寸法の制約はなく、大型チップでも可能である。
後工程の２次リフローに対して、化合物層が高温での強度を確保し、その後の熱疲労に対してはSn系はんだ主に寄与し、一部、応力的に厳しい個所では部分的に弾性結合した個所が最大限の効果を発揮し、(一部耐えれないところは破壊するが、)弾性結合がない場合に比べ寿命は向上する。従って、化合物層で強く拘束されたイメージはなく、はんだ中で一部の化合物がネットワーク状に形成すれば良い。大きな歪、応力がかかるチップ周辺部では接合界面で化合物を形成させることで、強固な接続のため破壊が起こりにくくなる。他方、同じ周辺部位置のはんだ箔中央はネットワーク結合が少ないと、最外周部にかかる応力、歪ははんだ箔中央のSnにかかることで、上下の界面部にかかるストレスが緩和できる。
【００５１】
まず、Al2O3基板13は真空吸引により架台に固定され、Siチップ８も真空吸引９により取付治具となる抵抗加熱体ツール7に保持される。そして、抵抗加熱体ツール7を下降させるなどしてSiチップ８をはんだ箔11を介してAl2O3基板１３と接触させ、加熱（max 380℃）、加圧（初期に2kgf）により5秒間保持する。なお、温度測定用熱電対16はツールのチップが接触する近くに埋め込んであり、温度コントロールができる構成となっている。
【００５２】
また、はんだ箔11の温度はその融点に達すると、瞬時にはんだ箔のSnなどが溶け、金属ボール間接合に圧力が加わり溶け始める。そこで、金属ボール間接合のつぶれ防止のため、設定温度に達すると抵抗加熱体ツール７をはんだ箔11を加圧した時の位置を起点とし、その位置からはんだ箔厚さに対して約10%(max20%)以下にし、チップからのはんだのはみ出し量を制御している。はんだ箔の厚さは熱疲労寿命に影響するので、80〜150μm位にするのが一般的である。この、はんだ厚さと、チップ寸法に対するはんだ箔の寸法で、つぶれ量を制御することになる。
しかし、本方式はＣｕが半分入って、しかもネットワーク状に連結されているので熱伝導に優れるので、200〜250μmでも熱的には従来より優れる。
【００５３】
Al2O3基板13の予熱15は約100℃とした。急激な温度上昇、下降は継手に大きなストレスをかけるので、予熱は熱衝撃を緩和させる意味でも重要である。
【００５４】
抵抗加熱体によるダイボンドの場合、接続時のはんだ箔11の酸化を防止するため、局所的に周囲から窒素10を吹き付ける機構としている。また、Siチップ８を吸着する抵抗加熱体ツール７の周囲にも窒素10を吹き付け、常に接合部が50〜100ppmレベルの酸素純度に保たれるようにするのが良い。
【００５５】
このはんだ箔であれば、水素炉もしくは窒素等の不活性雰囲気炉でmax270℃前後でSiチップ等のダイボンド、パワーモジュール等の接合も可能である。炉を使用する場合、max温度はSnの場合260℃から350℃までも可能であるが、化合物の形成状態を考慮した条件選定が必要である。
【００５６】
図４は抵抗加熱体によるダイボンド、及び水素炉もしくは窒素等の不活性雰囲気炉によるダイボンドした代表的な接合部の断面モデルを示す。このようにダイボンドされたチップの上面からワイヤボンド等により基板の端子に繋ぎ、キャップでチップを封止したり、樹脂で封止して、さらには基板の周囲に小型のチップ部品等を接続し(この場合の接続も端子に合った箔を、予めチップ部品の電極等に仮付けしたものを基板に接続させたり、または熱圧着したものを同時にリフロー炉で接続することも可能である)、基板の裏面側等から外部接続端子(通常はSn-3Ag-0.5Cu等のはんだで接合される)をとることにより、モジュールが出来あがる。
【００５７】
Cuボール2同志、Cuボールとチップ側のメタライズ44(例えばCr-Ni-Au；Auは大変薄いので実質はCu-Sn-Ni間での合金層の形成)、Cuボールと基板側のメタライズ42（例えばAg-Pd導体にNiめっき；Cu-Sn-Ni間での合金層の形成）、とはそれぞれ合金層がしっかり形成され、連結状態を確保する。チップ側のメタライズの組合せは多様であるが、はんだのSnと反応するのはCuかNiが大部分である。表面層に主に酸化防止のためAuが使用される場合があるが、0.1μmレベル以下でSnに固溶し、合金層形成には関与しない。他方、基板側も同様に下地は各種あるが、Snとの反応層はチップ同様NiもしくはCuである。特殊な場合としてAg、Ag-Pt、Ag-Pd、Au-Pd等の厚膜導体等もある。パワーもののダイボンドでは熱伝導の面で、ボイドがあると特性に大きく影響を及ぼすため、ボイドレス化が最重要視される。はんだペーストの場合はフラックスの反応、溶剤の揮発等によりガス量は多いため、ガスが逃げ易い継手構造、例えば細長い端子、小型のSiチップのダイボンド等に適用される。従って、中、大型のSiチップのダイボンドでは、不活性雰囲気で、フラックスレスではんだ箔を用いた抵抗加熱体によるダイボンド、もしくは水素炉もしくは窒素等の不活性雰囲気炉によるダイボンドの使用が一般的である。なお、本発明で作られたはんだ箔中に内蔵するボイドはCu粒径が小さくなると多くなる傾向があるが、構造上粒径以下に細かく分散するため、これまでの大きなボイドのイメージはなく、特性への影響も少ないことが予想される。粒径が3〜8μmのCu粒子、Sn粒子を用いた場合、箔でのはんだ充填率は約80%であった(ボイド率20%)。この箔をSnめっきCu板に挟んで窒素雰囲気中でダイボンダーで加圧接合すると、CuボールとCu板間はしっかりとCu6Sn5の金属間化合物が形成され、しかも、余分なSnははんだ内部のミクロの空間部(ボイド)に吸収されて、良好な接合部が得られることが分かった。断面観察結果でも、接合前の箔の充填率に比べ、接合後の充填率は向上していることが確認された。これより、従来の課題であったボイドの問題は、本方式においてはそれほどの問題にはならないことが分かった。なお、Cu粒子径を3μmレベルもしくはそれ以下に微細化すると、はんだ付け温度が300℃以上の高い温度で接続したり、高温での保持時間が長いとSnとの反応は活発のため、Cu粒子の形は崩れ、Cu-Sn化合物の連結になることもありうるが、耐高温強度等の特性自体は変わらない。特に反応を抑えたい場合は化学Ni/Auめっき(高温でも化合物が厚く形成されにくい)等を施したり、Ag粒子等を使用することも可能である。Cu粒子が30μm レベルの粗大な場合、ボイド率は3%以下であり、しかも分散したボイドであることから特性には影響しないボイドと言える。
【００５８】
ところで、上記実施例に示した工程で作製したはんだ箔はリールに巻いて切断工程を含めて連続供給できる。従って、温度階層を必要とする部品の封止部、端子接続部の接続に使用する場合は、パンチング加工、レーザ加工等でその形状に合わせたものを用いることができる。そして、その部品の封止部、端子接続部をパルス方式の加圧型ヒートツールで窒素雰囲気下で加熱、加圧することでフラックスレスで接続することができる。予熱時の酸化防止、ぬれ性を確保するため、Snめっきされたはんだ箔が望ましい。ピッチが粗く、端子数が少ない部品の接続などははんだ箔の載置、部品端子の位置決め、パルス電流による抵抗加熱電極による加圧接続などが容易でやり易い。
【００５９】
図５(a)はフラックスを用いないで、窒素雰囲気中でパルス加熱による抵抗加熱体でチップ8と中継基板36の間に、図５(c)に示すような前述したはんだ箔３９を載せてダイボンドした後、Au線のワイヤボンド35で、チップ上の端子と中継基板36上の端子とを繋ぎ、NiめっきしたAl等のキャップ23と中継基板36の間に箔を載せ、窒素雰囲気中で抵抗加熱体でフラックスレスで封止を行ったBGA、CSPタイプのチップキャリアの断面である。はんだ箔は被接合体に仮固着して接合することもできる。なお、中継基板３６は図示しないスルーホールにより上下間の電気的接続、すなわちチップ８と外部接続端子との電気的接続を確保している。本構造は、通常のモジュール構造の代表例であり、図示はしてないが中継基板３６上には抵抗、コンデンサー等のチップ部品が搭載されても良い。なお、高出力チップの場合、放熱の効率から熱伝導性に優れるAlN中継基板を使用することが好ましい。このモジュールの外部接続端子のはんだ組成はSn-3Ag-0.5Cuで、端子ピッチが広い場合はボールで供給され、ピッチが狭い場合はペーストで形成される。また、Cu端子もしくはNi-Auめっき端子のままの場合もある。モジュールはこの後、プリント基板上に搭載され、Sn-3Ag-0.5Cuはんだ(融点：217〜221℃)ペーストで他の部品と同時に、max240℃でリフロー接続されるが、前述の通り、このリフロー温度でははんだ箔自体の接合は確保されるので、高信頼にプリント基板上に接続することが出来る。すなわち、モジュール実装における接続とプリント基板上の接続とは温度階層接続を実現することが出来る。外部接続端子の形態はさまざまであるが、いずれにせよはんだ箔を用いることで外部接続端子とプリント基板との接続に対して温度階層接続を実現することが出来る。なお、本構造は、基板上に半導体チップをはんだ箔よりダイボンド接続し、半導体チップの端子と基板上の端子とをワイヤボンデングにより接続し、基板の裏面に外部接続端子となるはんだボールを形成した、いわゆるＢＧＡタイプの半導体装置についても適用出来ることは言うまでもない。この場合、チップの搭載面には樹脂モールドが施される。なお、接続部の外周部のぬれ性をより良くするため、パルス加熱による抵抗加熱体で接続後、更に窒素炉もしくは水素炉等でリフローをすることで良好な継手が形成できる。
【００６０】
図５(b)は、図５（a）に示した構造において窒素雰囲気中でNiめっきしたAlフィン23を、中継基板43に箔を載せ、抵抗加熱体でフラックスレスで封止を行った例である。
【００６１】
図５(b)左はCuボール,Snボールで作ってパンチングで切り抜いたはんだ箔２４で、図５(b)右は窒素雰囲気中でパルス加熱による抵抗加圧体41で、はんだ箔40(左図のB-B′断面)とNiめっきしたAlフィン23を加熱して中継基板上の端子部(Ni-Auフラシュ42)に封止するモデルの断面である。図５(b)右の状態で接続した後は図５(a)の接合部24の形状になる。このはんだ箔も前述同様、図５（C）にしめすようなものを用いた。
【００６２】
なお、水素等の還元雰囲気炉でのフラックスレスのリフロー接続も可能である。また、長期間の絶縁性を確保できるロジンベースのフラックスの場合、腐食の問題はないので洗浄レスのリフロー接続も製品によっては使用が可能である。
【００６３】
ところで、リフローの課題は高融点の金属ボールを用いる場合、はんだ箔の両面で拡散接続をし易くするため、はんだ箔と接続される側とが接触している状態を作ることがポイントであり、加圧して接触させることが好ましいこととなる。従って、仮り付け工程もしくは加圧工程があるプロセスを採用することが好ましい。例えば、リード、部品の電極部に予め圧接等で固着して供給しておくことと良い。なお、Zn-Al系の場合は全てが溶けるタイプなので、その不安はない。
【００６４】
図６はパワーモジュール接続に適用した例である。Siチップ8は10mm□レベルの寸法を対象にする場合が多い。このため、従来は軟らかいPbリッチ系高温系はんだが使われてきた。Pbフリー化になるとSn-3.5Ag(221℃)、Sn-0.7Cu(227℃)もしくはSn-5Sb(235℃)がある。Sbは環境に対する負荷の問題が有ることを考えると、Sn-3.5Ag、 Sn-0.7Cu以外はないのが実情である。Zn-Al系は硬いので、そのままではSiチップ割れを起こす可能性が大である。
【００６５】
この場合のはんだは階層接続用高温はんだと言うよりは、高発熱のため、従来のSn-5Sb等でも信頼性を確保できないため、Pb-5Sn系を使ってきた経緯がある。高Pbはんだに代わるPbフリーのソフトソルダーはないので、本案がその代替となる。車では230℃レベルに達する状態はまれに起こる程度が、要求仕様として示されている。更には、260℃のリフローに耐えられることも要求されている。この複合はんだは260℃のリフロー時にSnは溶けるが金属間化合物がネットワークで連結されているため、高温での強度は確保されている。なお、220℃レベルの高温に曝す機会がある車等において、高温での瞬時部分溶融防止にはSn系はんだとしてSn-(5〜7)%Sbはんだ(融点：236〜243℃)ボールを使用することで、SnとCuボール間の反応、Snと基板端子(Cu,Ni)との反応でSb濃度が10%以上になり、下限温度をSn(232℃)以上の245℃レベルに上昇させることができる。このため、220℃になっても部分溶融の心配はなくなる。なお、280℃での本方式のせん断強度は１Ｎ／mm2(0.1kgf／mm2)以上を確保している。
他方、Sn-Ag-Cu系はんだはSn-Pb共晶と異なり、強度が高く剛性が強く変形性に劣ることにより、素子、部品等への悪影響が言われている。このため、柔軟性のあるSn-In系、Sn-Cu-In系、Sn-(0〜1)Ag-Cu、Sn-(0〜1)Ag-Cu-In系等のはんだを用いることで、はんだの融点は200℃レベルに多少下がっても、はんだ自体が変形に対応してくれるので、耐衝撃性が要求される携帯用機器等の実装用の階層はんだとしての応用が期待できる。当然ながら、２次のはんだ付け時に必要な強度はネットワーク状に発達したCuとの化合物連結で高温強度を確保し、特に、最大応力、歪がかかるチップ、部品等の最外周部では基板の界面部ではCuボールとの化合物形成で、界面近傍での破壊を阻止し、はんだ内部で破壊するようなネットワーク形成が望ましい構成である。
【００６６】
そこで、ここではCuボールとSnボールのはんだ箔を使用する。10〜30μmの軟Cuボールと10〜30μmのSnボールを重量比で約１：１に混合して、真空中もしくは還元雰囲気中でSnをCuボール間に塑性流動させ、更に圧延してはんだ箔を作製する。または、3〜8μmの軟Cuボールと3〜8μmのSnボールを重量比で約１：１に混合して、真空中もしくは還元雰囲気中でSnをCuボール間に塑性流動させ、更に圧延してはんだ箔を作製してもよい。この箔を必要な寸法に切りだし、NiめっきしたCuリード51とSiチップとの間、Siチップ８とNiめっき46を施したCuデイスク板(もしくはMoデイスク板)48との間、Cuデイスク板48とWメタライズ上にNiめっき49を施したアルミナ絶縁基板50との間、及び同上のアルミナ絶縁基板50と電気Niめっき46を施したCuベース板49間に、該はんだ箔を搭載し、280℃の水素炉で一括してリフロー接続した。これにより、Cuボール間、CuボールとCuリード間、Cuボールとチップ間、CuボールとNiめっきCu板間、CuボールとNiめっきアルミナ絶縁基板間、CuボールとNiめっきCuベース間等のCuとNi金属間化合物による接合がなされる。これで接続したものは、既に、耐高温の金属間化合物(Cuの場合はCu6Sn5、Niの場合はNi3Sn4)で連結されるので、260℃（260℃〜280℃でも可）で強度を保持し、後工程のリフローで問題になることはない。この継手を温度サイクル試験、パワーサイクル試験にかけても、これまでの高Pb入りはんだと同等な寿命を有することを確認できた。
【００６７】
更に、Snめっきされたプラスチックボールのゴムを分散させることで低ヤング率化により、より耐熱衝撃性を向上させることができ、より大型Ｓｉチップの接合を可能にする。なお、パルス加熱方式のダイボンダーで窒素を吹き付け、max 350℃、５秒間（5〜10秒間でも可）で加圧接合する方式でも実装が可能である。また、パルス加熱方式で仮付けし、界面での接触を確実にした後、水素炉で一括してリフローすることで、外周部のぬれ確保、接合界面の接続を確実にすることが可能である。なお、チップ周辺部はスムーズなフィレットを形成することが望ましいので、はんだ箔の外周部にSnだけの層を設けることも可能である。
【００６８】
Cuボールの代わりに、Zn-Al系(Zn-Al-Mg、Zn-Al-Ge、Zn-Al-Mg-Ge、Zn-Al-Mg-Ga等)はんだボールにSn、In等のボール、更にはSnめっきされたプラスチックボールのゴムを分散混入した圧延箔を用いた結果、同様に耐温度サイクル性、耐衝撃性を緩和し、高信頼性を確保することができる。Zn-Al系はんだのみでは硬く(約Hv120〜160)、剛性が高いので大型Siチップは、容易に破壊する恐れがある。そこで、一部、ボール周辺に軟らかい低温のSnの層、Inの層が存在することにより、また、ゴムがボールの周囲に分散することにより、変形させる効果がでて剛性を低下させ、信頼性を向上させることができる。
【００６９】
また、低熱膨張フィラー(SiO2、AlN、インバー等)にNiめっき、Ni-Auめっきした粒子を混入することで、Si等に熱膨張係数が近づき、作用する応力が小さくなり長寿命化が期待できる。
【００７０】
図７は携帯電話等に使用される信号処理用に使われる高周波用ＲＦ(Radio Frequency)モジュールをプリント基板に実装した例を示す。
【００７１】
この種の形態は熱伝導性に優れた中継基板に素子裏面をダイボンドし、ワイヤボンドで中継基板の端子部にひきまわされる方式が一般的である。数個のチップと周囲にＲ，Ｃ等のチップ部品を配し、ＭＣＭ(マルチ・チップ・モジュール)化している例が多い。従来のＨＩＣ(Hybrid IC)、パワーＭＯＳＩＣ等は代表例である。モジュール基板材料としてSi薄膜基板、低熱膨張係数で高熱伝導のAlN基板、低熱膨張係数のガラスセラミック基板、熱膨張係数がGaAsに近いAl2O3基板、高耐熱性で熱伝導を向上させたインバー等のメタルコア有機基板等がある。
【００７２】
図７(a)はSiのモジュール基板29 上にSiチップ8を実装した例である。Siのモジュール基板29上ではR、C等は薄膜で形成できるのでより高密度実装が可能であり、主にSiチップ8のみフリップチップ実装される。プリント基板22への実装はQFP-LSI型で柔らかいCu系リード20を介して行う。リード20とSi基板29との接続は本案の切断したはんだ箔17を用いて、加圧、加熱して行う。その後、シリコーン等の柔らかい樹脂19で最後に保護、補強を行う。Siチップのはんだバンプ18 をSn-3Ag(融点：221℃)で構成し中継基板29に接続する。プリント基板22へはSn-Ag-Cu系Pbフリーはんだ21により接続する。はんだバンプ18は、Sn-Ag-Cu系Pbフリーはんだ21のリフロー時に再溶融してもプリント基板22への実装におけるSiチップ８の自重により変化することは殆どなく、かつSi-Siの接続のため応力的負担はなく、信頼性上問題はない。プリント基板22への実装が終わった後で、Siチップ８上には保護のためシリコンゲル12等をコートすることも可能である。
【００７３】
また、他の方法としてSiチップ８のはんだバンプ18をAuのボールバンプにして、中継基板29上に形成する端子にSnめっきを施すと、熱圧着によりAu-Sn接合を得ることができ、プリント基板22への実装における250℃のリフロー温度では溶けることはなく、従って、温度階層接続が可能であり、リフローに十分耐えられる接合となる。
【００７４】
はんだ箔17による接続は、前述の如く、Cuなどの金属ボール間に形成される金属間化合物により接合が保たれており、プリント基板22への実装における250℃のリフロー温度においても強度を確保することが出来る。これによって今までの大きな課題であった温度階層をつけた鉛フリー接続を実現することが出来る。
【００７５】
なお、Si基板に代えて、AlN基板、ガラスセラミック基板、Al2O3基板等の厚膜基板を用いた場合、R、C等のチップ部品の搭載は機能素子を作る上で必要である。他方、厚膜ペーストでレーザートリミングによるR、C形成方法もある。厚膜ペーストによるR、Cの場合、上記Si基板と同様な実装方式が可能である。
【００７６】
図７(b)はGaAsチップ8を熱伝導性、機械的特性に優れるAl2O3モジュール基板29を用いたモジュールをAlフィン23のケースで絶縁封止した場合である。 GaAsとAl2O3とは熱膨張係数が近いのでフリップチップ実装は信頼性上問題はない。これらのチップ部品の端子接続は端子面積が□0.6mm以上であれば、はんだ厚t；0.05〜0.10の箔とし端子数の少ない素子、チップ部品に仮付けして、あるいは基板側の端子に仮付けして、個別に抵抗加熱体で窒素雰囲気の加圧接続で、あるいは還元雰囲気もしくは不活性雰囲気のリフローでの接続が可能である。また、はんだ厚t；0.15〜0.25の箔を用いることも可能である。高出力対応には、ここでは示してないが、チップ搭載法としては本案の箔を用い(チップ裏面8)、ダイボンドし、端子はワイヤボンドする方法が一般的である。
【００７７】
Alフィン接続の場合はフィンの周囲を取り巻く形状の箔を用い、窒素雰囲気で抵抗加熱体で加圧接続する。図７(c)は左側が端子接続の例で、右側はAlフィン23の例であり、共に該はんだ箔27をモジュール基板の端子28とフィン接続部の端子間に挟んで接合する。この時、はんだ箔は予め基板かフィンのどちらかに仮付けしておくと良い。Alの場合は端子部はNiめっき等が施されている。
【００７８】
図７(d)はインバー等のCの有機基板32に実装する段取りのモデルである。発熱チップは低熱膨張で耐熱性に優れるメタルコアのポリイミド等の有機基板、高密度実装に対応したビルドアップ基板等を使用すれば、GaAsチップを直接に搭載することが可能である。高発熱チップの場合、ダミーの端子を設け、直接熱がメタルに伝導させることも可能である。
【００７９】
なお、本案の素子への実施例として、ＲＦモジュールを取り上げたが、各種移動体通信機用のバンドパスフィルタとして使用されているＳＡＷ(弾性表面波)素子構造、ＰＡ(高周波電力増幅器)モジュール、他のモジュール、素子等に対しても同様に応用できる。また、製品分野としては、携帯電話、ノートパソコン等に限らずデジタル化時代を迎え、新たな家電品等に使用できるモジュール実装品を含む。
【００８０】
図８はRFモジュール実装への応用を更に具体化したものである。図８(a)はモジュールの断面図であり、図８(b)は上面に部材23を透かしてみた平面図のモデルである。実際の構造は、電波を発生する約□２mmチップ8のMOSFET素子がマルチバンド化に対応するため、数個フェースアップ接続で搭載されており、更に周辺には効率良く電波を発生させる高周波回路がR,Cチップ部品52等で形成されている。
チップ部品も小型化され、1005等が使用されていて、モジュールの縦横寸法も７×１４程度で高密度実装されている。ここでは、はんだの機能面のみを考慮し、代表して素子を１個、チップ部品を１個搭載したモデルの例で示す。なお、後述するようにチップ8、チップ部品52はAl2O3基板13にはんだ接続されている。チップ8の端子はAl2O3基板13の有する電極にワイヤボンデングにより接続され、さらにスルーホール59、厚膜導体61を介して基板裏面の外部接続部となる厚膜電極60と電気的に接続される。チップ部品52は基板13の有する電極と半田接続され、さらにスルーホール59、配線61を介して基板裏面の外部接続部となる厚膜電極60と電気的に接続される。図示はしていないが、チップやチップ部品と接続する基板の有する電極62とスルーホール59とは配線により電気的に接続されている。モジュール全体を覆う部材(Alフィン)23とAl2O3基板13とは、かしめなどにより接合される。また、本モジュールは、プリント基板などに対して外部接続部となる厚膜電極60とのはんだ接続により実装されるものであり、温度階層接続が必要となるものである。
【００８１】
図９は図８に示す構造においてはんだ箔を使用したSi(もしくはGaAs)チップのダイボンドを前提とした４つのプロセスを示すフローチャート図である。(1)、(2)のプロセスは1005等の小型のR、Cチップ部品に対して、作業性から従来のAgペーストを選択する方式で、(1)は基板表面が清浄な状態でフラックスレスで窒素雰囲気で短時間ではんだ箔を用いてダイボンドした後、ワイヤボンドし、その後、Agペーストでチップ部品を接続する方式である。(2)は先にAgペーストでチップ部品を接続する方式であり、樹脂硬化のために炉を用いると基板表面が汚れ、後工程のワイヤボンドに影響を及ぼす恐れがあるので、その場合は洗浄してワイヤボンドすることになる。(3)は、同じく高温側の温度階層性を確保するため、接合原理ははんだ箔と同様であるが、小型のチップ部品に対しては作業性に優れる金属ボールとはんだボールとの混合ペーストで供給する方式であり、印刷でも、デイスペンサーでも可能である。リフロー後洗浄し、高出力Siチップには極力ボイドレス化が要求されるので、ボイドレス化に適しているはんだ箔のダイボンドを行い、最後にワイヤボンドを行う。なお、(3)の工程で先にダイボンド、ワイヤボンドを行えば、フラックスの洗浄工程を省くことも可能である。(4)は先にダイボンド、ワイヤボンドする方式で、後工程で二つの考え方がある。一つは、後工程で、チップ部品を一個づつ窒素雰囲気でフラックスレスで接続する方式である。この方式は時間がかかる欠点がある。そこで、もう一つは、(4)に示したプロセスで、チップ部品に対して、フラックスを用いて仮付け程度にし、後でリフローで一括接続する方式である。具体的には、ダイボンド、ワイヤボンドした後、例えばCuボールとSnボールで構成され、表面に約1μmのSnめっきを施した複合はんだ箔(予めチップ部品にはNiめっきされている場合がほとんどで、その場合はSnめっきは不要である)を、ほぼ電極寸法に切断し、部品の電極部に加圧加熱(フラックスを用いても良い)により仮固着させ、仮固着した該部品をAl2O3基板上のW-Ni-Auめっき電極部に熱圧着ではんだが塑性変形する程度に仮固着させることが好ましい。なお、個々の部品を一個づつ、窒素雰囲気下でパルスの抵抗加熱体で300〜350℃で5秒間押しつければ、確実に金属間化合物が形成され、連結されて、260℃以上の高温でも強度を保つことは言うまでもない。そして、リフロー炉(max270〜320℃)に通せば、圧着している部分はCu、Niともに合金層の連結で繋がれる。この連結は完全である必要はなく、どこかで繋がれていれば、強度は小さくても高温時に問題になることはない。
【００８２】
小型チップ部品は、素子ほどは高温にならないが、長期に使用した場合、Agペーストの劣化が問題になる場合には、本発明の構成要素のはんだを用いることにより、高信頼性を確保できる。課題は小型のチップ部品に対して、1個づつ確実に熱圧着で固着すると手間がかかることである。
【００８３】
図８（C）は、前述のモジュールをプリント基板22にはんだ接続した例であり、モジュールのほか、電子部品52やＢＧＡタイプの半導体装置が半田接続されている。半導体装置は、半導体チップ8を中継基板43上に前述のはんだ箔によりフェースアップの状態で接続し、半導体チップ8の端子と中継基板43の有する端子とをワイヤボンデイング35により接続したものであり、その周りはレジン58により樹脂封止されている。また中継基板43の下側にははんだボールバンプ21が形成されている。はんだボールバンプ21には、例えばSn-2.5Ag-0.5Cuのはんだが用いられる。なお、はんだボール３０としては、Sn-(1〜2.5)Ag-0.5Cuが望ましく、例えばSn-1.0Ag-0.5Cuを用いても良い。また、その裏面にも電子部品が半田接続されており、いわゆる両面実装の例となっている。
【００８４】
実装の形態としては、まず、プリント基板上の電極部分に、例えばSn-3Ag-0.5Cuはんだ(融点：217〜221℃)ペーストを印刷する。そして、まず、電子部品54の搭載面側から半田接続を行うために、電子部品54を搭載し、max240℃でリフロー接続することで実現する。次に、電子部品、モジュール、半導体装置を搭載し、max240℃でリフロー接続することで両面実装を実現する。このように、先に耐熱性のある軽い部品をリフローし、後で、耐熱性のない、重い部品を接続するのが一般的である。後でリフロー接続する場合、最初に接続した側のはんだを再溶融させないことが理想である。
【００８５】
前述の通り、この場合もプリント基板への実装時のリフロー温度では、モジュール内の接続に用いたはんだ箔自体の接合は確保されるので、モジュールや半導体装置を高信頼にプリント基板上に接続することが出来る。すなわち、半導体装置やモジュー内の接続とプリント基板上の接続との温度階層接続を実現することが出来る。なお、プリント基板の両面を同一のはんだにより接続したが、電子部品54として1005等の重量のない小型部品においては、電子部品、モジュール、半導体装置のリフロー接続においてはんだが溶融したとしても、それ自体が軽いため重力よりも表面張力の作用が勝り、落下することはない。従って、最悪のケースを考えた場合、基板の端子との金属間化合物はできずに単にSnで接合されただけでも問題は起きない。なお、モジュール内において実装した小型部品に対しては、Cu,Snを混合したはんだ箔を仮固着する方式より、Cu,Snを混合したはんだペーストを使用する組合せが生産性を考慮すると望ましい。
【００８６】
次に、モータドライバーIC等の高出力チップの樹脂パッケージへの適用例を示す。図１０(a)はリードフレーム65と熱拡散板64とを張り合わせてかしめた平面図で、かしめ個所63は２個所である。図１０(b)はパッケージの断面図であり、図１０(c)はその一部の拡大である。3Wレベルの発熱チップ8からの熱ははんだ47を介してヘッダの熱拡散板(Cu系の低膨張複合材)64に伝わる。リード材は例えば42Alloy系の材料で構成する。
【００８７】
図１１はパッケージの工程図を示す。まず、リードフレームと熱拡散板（ヒートシンク）をかしめ接合する。そして、かしめ接合された熱拡散板６４上にはんだ(箔)４７を介して半導体チップ８をダイボンド接続する。ダイボンド接続された半導体チップ８は、さらに図示するように、リード５６と金線３５などによりワイヤボンデングされる。その後、樹脂モールドされ、ダム57切断後、Sn系はんだめっきが施される。そして、リード切断成形され、熱拡散板の切断が行われ完成する。Siチップ8の裏面の電極は、Cr-Ni-Au、Cr-Cu-Au、Ti-Pt-Au、Ti-Ni-Au等の一般に使用されるメタライズであれば可能である。Auが多い場合も、Au-Snの融点の高いAuリッチ側の化合物が形成されれば良い。チップのダイボンドは窒素を吹き付けて、パルスの抵抗加熱体で、初期加圧2kgf、350℃で5秒間で行った。はんだ厚の制御は初期加圧時の位置(70μm膜厚)から10μm下がったところでセットされ、耐熱疲労性向上のため、機構上、膜厚を確保するシステムになっている。上記以外に、初期加圧１kgf、350℃で5〜10秒間で行った。はんだ厚の制御は初期加圧時の位置(150μm膜厚) から10μm下がったところでセットされても同様であった。高出力チップのため、ボイド率低減が重要であり、目標の５％以下を達成できた。該はんだはCuボールが均一に分散された状態で入っているため、構造的に大きなボイドが発生し難くなっている。厳しい熱疲労に対しても、Sn、Sn系はんだ自体の耐熱疲労性は優れており、かつ変形性にも優れている。更には、Cu粒子間、Cu粒子と電極間でネットワーク上に金属間化合物が形成されるので、260℃以上の高温でも強度を確保する。Cu粒子間等が強く結合し過ぎると(Cu粒子間等で合金層形成面が多い)、拘束され自由度がなくなり、強い弾性体結合になるので、素子等に対して良くはない。適度の結合が存在する。特に、チップ周辺部において、従来はんだでは応力集中する接合界面近傍で破壊して、はんだ内部では破壊が起こり難い状況であった。本方式では接合界面はCuボールとの反応で界面破壊が起こり難く、はんだ内部で破壊できるネットワーク形成にすることが可能である。ダイボンド、ワイヤボンド後、樹脂モールドされ、ダム57切断され、リードにはSn-Bi、Sn-Ag、Sn-Cu系のPbフリーはんだめっきが2〜8μm施される。更に、リード切断成形され、不要な部分の熱拡散板を切断して完成する。
【００８８】
図１２は一般的なプラスチックパッケージに適用した例である。Siチップ裏面が42Alloyのタブ66上にはんだ箔67（導電ペースト67）でを介して接着されている。素子はワイヤボンド35を通してリード56に繋がれ、樹脂58でモールドされる。その後、リードにはPbフリー化に対応したSn-Bi系のめっきが施される。従来はプリント基板実装に対して、融点；183℃のSn-37Pb共晶はんだが使用できたので、max220℃でリフロー接続ができた。Pbフリー化になるとSn-3Ag-0.5Cu(融点；217〜221℃)でリフロー接続を行うことになるので、max240℃となり、最高温度が約20℃高くなる。このため、Siチップ8と42Alloyのタブ66の接続に、従来の耐熱性の導電ペーストもしくは接着剤を使用すると高温での接着力は低下し、その後の信頼性に影響することが予想される。そこで、導電ペーストの代わりに該はんだ箔を使用することで、max270〜350℃での高温での強度を確保するので、Pbフリーはんだによる階層接続が可能となる。このプラスチックパッケージへの応用は、Siチップとタブとを接続するプラスチックパッケージ構造すべてに適用できる。構造上、Gull Wingタイプ、Flatタイプ、J-Leadタイプ、Butt-Leedタイプ。Leadlessタイプがある。
【００８９】
図１３は複合はんだ箔にする前段階のモデル構造の一例である。3〜15μmレベルのSnめっきしたCuなどの金属繊維69(高い温度での成型、圧延する場合はCuとSnとの反応を抑えるためNi/Au等の表面処理を施しても良い)を一列に敷いて、その上にSnなどのはんだボール及びSnめっきしたCuなどの金属ボールとを適切な配合(約50%)に混ぜたものを、成型、圧延して150〜250μmレベルに加工した箔を作る。この中に、更に低ヤング率化のためSnめっきした耐熱性のプラスチックボール、もしくは金属ボールの一部としてCu/Snめっきされた低熱膨張のシリカ、インバー等を加えても良い。成型、圧延した段階では、柔かいはんだボールは金属ボール、金属繊維の隙間に入り『海島構造』の海の形を形成する。金属繊維径は上記3〜15μmにこだわるものでなく、箔の中央部で核になり、被接合体との接合界面では金属ボールが主要な役目を果たす。連続圧延等において金属繊維をその方向に向けることで、作業はやり易くなる。 なお、金属繊維の代わりに細線化、低膨張化が可能なカーボン繊維にCu(もしくはCu/はんだ)めっきしたもの、他にセラミック、ガラス、インバー等の繊維にNi/Au、Ni/はんだ、Cu(もしくはCu/はんだ)めっき等も可能である。
【００９０】
図１３は箔の核となる金属繊維を一列に並べた例であるが、図１４はクロスに並べたもの(角度は自由)で安定した構造になる。クロスの隙間にSnなどのはんだボール及びSnめっきしたCuなどの金属ボールとを適切な配合(約50%)に混ぜたものを入れ込んだものであり、応用は図１３と同様に可能である。
【００９１】
図１５は金網状の繊維71を用いた場合の箔の断面であり、奥行き方向に伸びた金網断面を×印70で示した。図１５(a)は金網とはんだで構成された箔である。金網のメッシュを細かくするには限界があり、現状の市販品の最小メッシュは325で、通過する粒径は44μmと大きく、網を形成する線径も太いので、接合界面での接触部面積が小さい(化合物形成域)ので、高温での強度確保に課題がある。そこで金網70,71の隙間に、Snなどのはんだボール及びSnめっきしたCuなどの金属ボール2とを適切な配合(約50%)に混ぜたものを充填して作製した箔の断面を図１５(b)に示す。はんだ72は隙間に入り込んだ構造になる。高温時の強度確保が必要な場合はCuボールを多目に配合し、被接合体との界面での化合物形成に重点をおき、継手の熱疲労を重視する場合ははんだを多目に配合することで、はんだの耐熱疲労性に重点をおく制御が可能である。なお、充填する金属ボールはボールに限定するものでなく、後述の繊維等は有力である。金属ボールとはんだとの配合比率も、金属の形状、接触状態等にも関係し、大きく異なる可能性がある。
【００９２】
図１６は紙を作るように細長い金属繊維73をランダムに平坦化して、骨組を作り両側にSnなどのはんだボール68及びSnめっきしたCuなどの金属ボール2とを適切な配合(約50%)に混ぜたものを充填した状態のモデルである。図１６(a)は平面図で、図１６(b)は断面図である。
【００９３】
図１７は金属ボールの代わりに短冊金属繊維、あるいは低膨張化が可能なカーボン繊維にCu(もしくはCu/はんだ)めっきしたもの、他にセラミック、ガラス、インバー等の繊維にNi/Au、Ni/はんだ、Cu(もしくはCu/はんだ)めっき短冊繊維等が可能である。短冊繊維にすることではんだの配合量を大幅に増やすことができる。また、隙間に金属ボールを混ぜて化合物形成によるネットワークを強化することも可能である。金属ボールだけでは拘束され、剛体構造になるが、このように短冊状繊維を分散することで変形性と弾力性に富む構造が期待でき、ダイボンド時、あるいは熱疲労に対しても良い性能が得られるものと考える。短冊の長さは、箔の厚さを200μmとすれば1/10以下が望ましい。一例として、径；１〜5μm、長さ；5〜15μmレベルの範囲にあることが望ましい。
以上本発明者によってなされた発明を実施形態に基づき具体的に説明したが、本発明は上記実施形態に限定されるものではなく、その要旨を逸脱しない範囲で種々変更可能であることはいうまでもない。
また、上記実施例において開示した観点の代表的なものは次の通りである。
金属の粒子とはんだの粒子を含むはんだ材料を圧延して形成したはんだ箔である。Snなどのめっき層を有する金属の粒子を含むはんだ材料を圧延して形成したはんだ箔である。
金属の粒子とはんだの粒子を含むはんだ材料を圧延するはんだ箔の製造方法である。Snなどのめっき層を有する金属の粒子を含むはんだ材料を圧延するはんだ箔の製造方法である。
上記はんだ箔であって、例えば金属の粒子がCuの粒子であり、はんだの粒子がSnの粒子であるものである。
CuとSnを有するをはんだに圧力を加えて形成したはんだ箔であって、Cuは粒子の状態であり、Snは該Cu粒子の間を埋める状態であるものである。
前記はんだ箔であって、該はんだ箔をリフローさせるとCu粒子の表面の少なくとも一部はCu６Sn５により覆われるものである。
前記はんだ箔であって、Cu粒子と塑性変形後のSnは該はんだ箔をリフローさせるとCu６Sn５を含む化合物により結合されるものである。
前記はんだ箔であって、Cu粒子の粒径は１０〜４０μmであるものである。
前記はんだ箔であって、Cu粒子の粒径は３〜１０μmであるものである。
前記はんだ箔であって、前記Cu粒子の表面にNiめっきもしくはNi/Auめっき層を有するものである。
前記はんだ箔であって、該箔の少なくともCuが露出している部分をSnめっきするものである。
前記はんだ箔であって、該はんだ箔の厚さが８０μmから１５０μmであるものである。
前記はんだ箔であって、該はんだ箔の厚さが１５０μmから２５０μmであるものである。
前記はんだ箔であって、プラスチック粒子を有するものである。
前記はんだ箔であって、前記Cuよりも熱膨張係数が小さい他の粒子を有するものである。
前記はんだ箔であって、前記Cuよりも熱膨張係数が小さい他の粒子はインバー系、シリカ、アルミナ、AlN(窒化アルミニウム)、SiCの粒子であるものである。なお、インバー(合金)とは、Fe（鉄）にNi(ニッケル)を34〜36％合金したもので、線膨張係数が小さい。
前記はんだ箔であって、さらにInの粒子を含むものである。
前記はんだ箔であって、Cu粒子とSn粒子を真空中、還元性雰囲気中もしくは不活性雰囲気中で混合し、その後圧力をかけることにより箔状にしたものである。
前記はんだ箔であって、圧延率が１５％から２０％であるものである。
前記はんだ箔であって、金属繊維とはんだ粒子を含む材料を圧延して形成したものである。
Cuの金属繊維とSnの粒子を含むはんだ材料を圧延して形成したはんだ箔である。
前記はんだ箔であって、該はんだ材料のうち、該Cuの金属繊維は短冊状であるものである。
Al、Au、Agのいずれかの粒子とSnの粒子を含むはんだ材料を圧延して形成したはんだ箔である。
Zn−Al系合金、Au−Sn系合金の粒子とSnの粒子を含むはんだ材料を圧延して形成したはんだ箔である。
また、はんだにぬれる単体金属、合金、化合物もしくはこれらの混合物を含む金属ボールと、Sn、Inのどちらか一つ以上を含むはんだボールとを混合して、隙間を埋めて圧入充填後、圧延したことを特徴とするはんだ箔である。
また、はんだにぬれる単体金属、合金、化合物もしくはこれらの混合物を含む金属ボールと、Sn、Inのどちらか一つ以上を含むはんだボールとを混合して、均等圧がかけられる予め圧延し易い型に入れ、隙間のないように均等に圧入させて埋め込んだ後、該複合体を圧延して作製したはんだ箔である。
また、前記記載のはんだ箔であって、該はんだは、Sn、In以外にAg、Bi、Cu、Zn、Ni、Pd、Au、Sb等のいずれか一つ以上を含むものである。
また、前記記載のはんだ箔であって、前記金属ボールがCu、Cu合金、Cu6Sn5化合物、Ag、Ag-Sn化合物、Au、Au-Sn化合物、Al、Al-Ag化合物、Aｌ-Au化合物、Zn-Al系はんだ、もしくはこれらの混合物を含むボールであるものである。
また、前記記載のはんだ箔であって、該圧延箔、もしくははんだ複合材にSnめっき、もしくはSnにBi、In、Ag、Au、Cu、Ni、Pdのいずれか一つ以上を含有しためっきを施したものである。
また、前記記載のはんだ箔であって、該単体金属、合金、化合物もしくはこれらの混合物を含む金属ボールがぬれない場合は、表面をNi、Ni-Au、Cu、Ag、Sn、Au等のめっき、もしくはこれらの複合めっき、もしくはこれらに更にSn系のめっき等のはんだにぬれるメタライズを施したものである。
また、前記記載のはんだ箔であって、該単体金属、合金、化合物もしくはこれらの混合物を含む金属ボールの最密充填を考慮した粒度分布であるはんだ箔である。
また、前記記載のはんだ箔であって、複合はんだの剛性低減のため、表面にはんだがぬれるメタライズを施したプラスチックボールを分散させたものである。
また、前記記載のはんだ箔であって、複合はんだの熱膨張係数低減のため、単体金属、合金、化合物もしくはこれらの混合物を含む金属よりも低熱膨張係数を有する粒子であり、表面にはんだをぬらすためのメタライズ、もしくはその上にSn、In等のはんだめっきを施して、分散させたものである。
また、前記記載のはんだ箔であって、低熱膨張係数を有する粒子として、インバー系、シリカ、アルミナ、AlN、SiC等であるものである。
また、前記記載のはんだ箔であって、該プラスチックボール素材として、ポリイミド系樹脂、耐熱エポキシ系樹脂、シリコーン系樹脂、各種ポリマービーズもしくはこれらを変成したもの、もしくはこれらを混合したものである。
また、前記記載のはんだ箔であって、帯、線、ボール、塊状であるものである。
また、前記記載のはんだ箔であって、前記金属ボールの代わりに金属繊維もしくは銅めっきしたカーボン、ガラス、セラミック等の繊維を用いたもの、もしくは該金属繊維の中に該金属ボールを分散混合したものを用いたものである。
また、前記記載のはんだ箔であって、前記金属ボールの代わりに金属繊維もしくは銅めっきしたカーボン、ガラス、セラミック等の繊維をクロスに重ねたこと、もしくは該クロスの繊維と該金属ボールを分散したものを用いたものである。
また、前記記載のはんだ箔であって、前記金属ボールの代わりに金属繊維もしくは銅めっきしたカーボン、ガラス、セラミック等の繊維を網状にしたものを用いたもの、もしくは該網に該金属ボールを分散したものである。
また、前記記載のはんだ箔であって、該繊維の径として１〜２０μm、望ましくは３〜１５μmであるものである。
また、前記記載のはんだ箔であって、該金属ボールの代わりに金属短繊維もしくは銅めっきしたカーボン、ガラス、セラミック等の短繊維を用いたこと、もしくは該短繊維に該金属ボールを分散したものを用いたものである。
また、前記記載のはんだ箔であって、該短繊維の径として１〜１０μm、望ましくは１〜５μm、アスペクト比(長さ／径)：２〜５であるものである。
第一の電子装置と、第二の電子装置と、第三の電子装置を有する電子装置であって、該第一の電子装置と該第二電子装置は、前記はんだ箔により接続され、該第二の電子装置と該第三の電子装置は該第一のはんだと異なるはんだにより接続されているものである。
半導体チップと、該半導体チップが配置されるタブと、外部との接続端子となるリードとを備え、該半導体チップの有する電極と該リードとがワイヤボンデングにより接続された半導体装置であって、該半導体チップと該タブは前記はんだ箔により接続されているものである。
第一の電子部品と、第二の電子部品と、第三の電子部品を有する電子装置であって、該第一の電子部品と該第二の電子部品は、金属の粒子とはんだの粒子を含む材料を圧延して形成したはんだ箔である第一のはんだを用いて接続され、該第二の電子部品と該第三の電子部品は該第一のはんだと異なる融点を有する第二のはんだを用いて接続されているものである。
第一の電子部品と、第二の電子部品と、第三の電子部品を有する電子装置であって、該第一の電子部品と該第二の電子部品は、金属の粒子とはんだの粒子を有するをはんだ材料に圧力を加えることにより、該金属は粒子の状態で、該はんだ粒子は該金属の粒子の間を埋めた状態となる第一のはんだを用いて接続され、該第二の電子部品と該第三の電子部品は該第一のはんだと異なる融点を有する第二のはんだを用いて接続されているものである。
前記電子装置であって、前記第一のはんだにおけるはんだの粒子はSnであるものである。
第一の電子装置と、第二の電子装置と、第三の電子装置を有する電子装置であって、該第一の電子装置と該第二の電子装置は、Snめっき層を有する金属の粒子を含むはんだ材料を圧延して形成したはんだ箔である第一のはんだを用いて接続され、該第二の電子部品と該第三の電子部品は該第一のはんだと異なる融点を有する第二のはんだを用いて接続されているものである。
第一の電子部品と、第二の電子部品と、第三の電子部品を有する電子装置であって、該第一の電子部品と該第二の電子部品は、Snめっき層を有する金属の粒子に圧力を加えることにより、該金属は粒子の状態であり、該Snは該金属の粒子の間を埋めた状態となる第一のはんだを用いて接続され、該第二の電子部品と該第三の電子部品は該第一のはんだと異なる融点を有する第二のはんだを用いて接続されているものである。
前記電子装置であって、前記第一のはんだにおける金属の粒子はCuであるものである。
前記電子装置であって、前記第一のはんだにおける金属の粒子はAl、Au、Agのいずれかの粒子であるものである。
前記電子装置であって、前記第二のはんだの融点は前記第一のはんだの金属の粒子の融点よりも低いものである。
前記電子装置であって、前記第一のはんだに含まれるSnが融解すると、前記Cu粒子は該Snと反応し、該Cu粒子はCu６Sn５を含む化合物により結合されるものである。
前記電子装置であって、前記金属の粒子の径は１０〜４０μmであるものである。
前記電子装置であって、該第一のはんだの厚さが８０μmから１５０μmであるものである。
前記電子装置であって、さらに前記第一のはんだはプラスチック粒子を有するものである。
前記電子装置であって、さらに前記第一のはんだは前記金属の粒子より熱膨張係数が小さい他の粒子を有するものである。
前記電子装置であって、前記第二のはんだはSn−Ag−Cu系鉛フリーはんだであるものである。
第一の電子部品と第二の電子部品を有する電子装置であって、該第一の電子部品と該第二の電子部品ははんだ接続部により接続されており、該はんだ接続部は、金属の粒子と該金属の粒子の間を埋めているSn部分を有するものである。
前記電子装置であって、前記金属の粒子は該金属とSnにより形成される化合物により結びついているものである。
半導体チップと、該半導体チップが配置されるタブと、外部との接続端子となるリードとを備え、該半導体チップの有する電極と該リードとがワイヤボンデングにより接続された半導体装置であって、該半導体チップと該タブは金属の粒子とはんだの粒子とを混合したはんだ箔を用いて接続されてものである。
半導体チップと、該半導体チップが配置されるタブと、外部との接続端子となるリードとを備え、該半導体チップの有する電極と該リードとがワイヤボンデングにより接続された半導体装置であって、該半導体チップと該タブは金属の粒子とはんだの粒子を有するをはんだ材料に圧力を加えることにより、該金属は粒子の状態で、該はんだ粒子は該金属の粒子の間を埋めた状態となる第一のはんだを用いて接続されているものである。
半導体チップと、該半導体チップが配置されるタブと、外部との接続端子となるリードとを備え、該半導体チップの有する電極と該リードとがワイヤボンデングにより接続された半導体装置であって、該半導体チップと該タブは金属の粒子と該金属の粒子の間を埋めているSn部分を有する接続部により接続されているものである。
前記半導体装置であって、前記金属の粒子は該金属とSnにより形成される化合物により結びついているものである。
基板と該基板に実装されている受動部品および半導体チップを有するモジュールであって、該半導体チップの電極と該基板の電極はワイヤにより接続され、ワイヤボンディング接続されない該半導体チップの面と該基板は金属の粒子と該金属の粒子の間を埋めているSn部分を有する接続部により接続されているものである。
前記モジュールであって、前記受動部品と前記基板も金属の粒子と該金属の粒子の間を埋めているSn部分を有する接続部により接続されているものである。
前記モジュールであって、前記基板は前記半導体チップが実装される部分にスルーホールを有し、該スルーホールの内部も金属の粒子と該金属の粒子の間を埋めているはんだにより充填されているものである。
【００９４】
【発明の効果】
本願において開示される発明のうち代表的なものによって得られる効果を簡単に説明すれば、下記のとおりである。
（１）全く新規なはんだ接続による電子機器および電子機器の製造方法を提供することができる。
（２）電子機器の製造方法において必要となる温度階層接続におけるはんだ接続、特に高温側のはんだ接続を提供することができる。
（３）全く新規なはんだおよびその製造方法を提供することができる。
【図面の簡単な説明】
【図１】 複合ボールで作る複合体金属の製作工程の図
【図２】 弾性体のプラスチックボールを分散させた状態の圧延前、後の断面モデルの図
【図３】 ダイボンドプロセスの一例を示す断面モデルの図
【図４】 Cu、Sn配合はんだ箔によるダイボンド接続部の断面モデルの図
【図５】 LSI、キャップを基板に接続する断面モデルの図
【図６】 パワーモジュールの断面モデルの図
【図７】 モジュールをプリント基板に実装した断面モデルの図
【図８】 RFモジュール実装の断面のモデル図
【図９】 RFモジュール実装のプロセスを示すフローチャート図
【図１０】高出力樹脂パッケージの平面、断面モデル図
【図１１】高出力樹脂パッケージのプロセスを示すフローチャート図
【図１２】プラスチックパッケージの断面モデル図
【図１３】金属繊維を用いて配合したモデルの平面図、断面図
【図１４】クロス金属繊維を用いたモデルの平面図
【図１５】金網繊維を用いたモデルの断面図
【図１６】細長い金属繊維をランダムに置いて平坦化した平面図、断面図
【図１７】短冊金属、非金属繊維を用いたモデルの断面
【符号の説明】
1.カーボン治具 2.Cuボール
3.Snボール 4.Sn
5.ロール 6.プラスチックボール
7.抵抗加熱体ツール 8.Siチップ
9.真空吸引穴 10.窒素
11.はんだ箔 12.シリコーンゲル
13.Al2O3基板 14.W(焼結)-Cuめっき電極
15.予熱用ヒータ 16.窒素
17.Cu,Sn混合箔 18.バンプ
19.軟らかい樹脂 20.リード
21.はんだボールバンプ 22.プリント基板
23.Alフィン 24.フィンとの接合部
25.リードとの接合部 26.リード
27.はんだ箔 28.基板の端子
29.モジュール基板 30.端子
31.Cu 32.有機基板
33.Cuスルーホール導体 34.Ag-Pd導体
35.ワイヤボンド 36.AlN中継基板
37.接続端子 38.Cr-Cu-Au
39.ダイボンド 40.はんだ箔
41.加圧体 42.Ni-Auめっきメタライズ
43.中継基板 44.Cr-Ni-Auメタライズ
45.化学Niめっき 46.電気Niめっき
47.はんだ 48.Cuデイスク
49.Cuベース 50. Al2O3絶縁基板
51.Cuリード 52.チップ部品
53.Cuパッド 54.TQFP-LSI
55.Sn-Ag-Cu系はんだ 56.リード
57.ダム切断部
58.樹脂 59.スルーホール
60.W-Ni-Au厚膜電極 61.W-Ni(もしくはAg-Pd、Ag)厚膜導体
62.Auめっき電極 63.かしめ部分
64.熱拡散板（ヘッダ） 65.リードフレーム
66.タブ 67.導電ペースト
68.はんだ 69.繊維
70.Cu網(横断面) 71.Cu網(長手断面)
72.はんだ(海) 73.細長い繊維
74.短冊繊維[0001]
BACKGROUND OF THE INVENTION
  In the manufacture of electronic devices and electronic equipment, Sn-Ag-Cu system Pb Solder foil effective when applied to solder connections that require a high-temperature side layer connection to free solder, etc.Related to technology.
[0002]
[Prior art]
In Sn-Pb solder, Pb-rich Pb-5Sn (melting point: 314 to 310 ° C), Pb-10Sn (melting point: 302 to 275 ° C), etc. are soldered at a temperature around 330 ° C as high-temperature solder, After that, it was possible to perform a temperature hierarchical connection in which the soldered portion was not melted and was connected with a low-temperature solder Sn-37Pb eutectic (melting point: 183 ° C.). These solders were flexible and highly deformable, so that it was possible to join Si chips that were easily broken to substrates with different thermal expansion coefficients. Such a temperature hierarchy connection is applied to a semiconductor device of a type in which a chip is die-bonded or a semiconductor device such as a BGA or CSP in which a chip is flip-chip connected. That is, the solder used inside the semiconductor device and the solder that connects the semiconductor device itself to the substrate are connected in a temperature hierarchy.
[0003]
[Problems to be solved by the invention]
Currently, lead-free technology is progressing in all fields.
[0004]
The mainstream of Pb-free solder is Sn-Ag eutectic (melting point: 221 ° C), Sn-Ag-Cu eutectic (melting point: 221-217 ° C), Sn-Cu eutectic (melting point: 227 ° C) However, it is desirable that the soldering temperature in surface mounting is low due to the heat resistance of the components. However, because of the need to ensure wettability to ensure reliability, the temperature inside the board can be maintained even if a furnace with excellent soaking control is used. Considering the variation, the actual situation is the Sn-Ag-Cu eutectic system, which is possible at the lowest temperature, around 235-245 ° C. Therefore, the solder for a layer that can withstand this soldering temperature needs to be 250 ° C. or higher even if the melting point is at least. Currently, there is no Pb-free solder for the high temperature side that can be used in combination with these solders. The most possible composition is Sn-5Sb (melting point: 240 to 232 ° C.), but since it melts, it is not suitable for the temperature class.
[0005]
Further, Au-20Sn (melting point: 280 ° C.) is known as a high-temperature solder, but it is hard and is limited to a narrow range due to high cost. In particular, when connecting Si chips to materials with different thermal expansion coefficients or connecting large chips, Au-20Sn solder is not used because it is likely to break the Si chip because it is hard.
[0006]
  The purpose of the present invention is toIn the manufacture of electronic devices and electronic equipment, the low temperature side solder connection in the temperature hierarchy connection is particularly Sn-Ag-Cu system Pb When using free solder, Pb The object is to provide a solder foil for use as free solder.
[0007]
[Means for Solving the Problems]
  In order to achieve the above object, the outline of typical ones of the inventions disclosed in the present application will be briefly described as follows.
  Cu , Ag , Au Or Al First particles of ( Volume ratio 50% ~ 74% ) When, Sn Or In The solder material in which the second particles are dispersed and mixed is pressed at a temperature lower than the melting point of the second particles and in a vacuum, in a reducing atmosphere or in an inert atmosphere to cause plastic flow in the solder material. It is a solder foil formed by rolling up and forming a lump of composite material by rolling. The solder foil is characterized in that, during reflow, the molten metal of the second particles forms a compound with the metal surface portion of the first particles at a temperature equal to or higher than the melting point of the second particles. .
  The particle diameter of the first particles is 10 to 40 μm, or 3 to 10 μm. The solder foil has a thickness of 80 μm to 150 μm, or 150 μm to 250 μm. In addition, as the third particles of a material having a smaller thermal expansion coefficient than the first particles, Invar, silica, alumina, AlN , SiC May also be included. The rolling rate is 15% to 20%.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
When metal balls such as Cu and Sn-based solder balls are mixed and rolled at about 50%, Cu particles come into contact with each other, and Sn can be obtained as a composite solder that enters the gap. When this foil is sandwiched between the chip and the substrate and reflowed, the composite solder portion is connected between the Cu balls with a Cu-Sn compound, and between the composite solder portion and the chip and the substrate is a compound of a Cu ball and a chip electrode, By forming a compound between the Cu ball and the substrate terminal, a lead-free temperature hierarchical structure is obtained that ensures bonding strength even at high temperatures of 280 ° C. Thereby, the connection method which provided the temperature hierarchy in lead free solder can be provided.
Considering the temperature hierarchy connection, if the solder on the high-temperature side that has already been connected partially melts, but the other remaining parts do not melt, sufficient strength can be secured in the process of soldering later. it can. We are researching solder materials in which metal balls (Cu, Ag, Au, surface-treated Al, Zn-Al solder, etc.) and solder balls are mixed. If it is connected with this solder material, for example, even if it is passed through a reflow furnace (max 250 ° C) with Sn-Ag-Cu solder, which is a process at the time of soldering, the Sn part in the connecting part will melt However, since the Cu balls, the Cu balls and the chip, and the Cu balls and the substrate are connected by an intermetallic compound (Cu6Sn5) with a high melting point, the connection is sufficiently maintained at the set temperature of the reflow furnace (max 250 ° C). High connection strength can be ensured. That is, a temperature hierarchy connection to the Sn—Ag—Cu solder can be realized. The effect of this intermetallic compound formation is not limited to Cu-Sn, but is similar to compounds such as Ni-Sn (Ni3Sn4) and Ag-Sn (Ag3Sn), and Au-Sn. Also, the same solder can be used for In instead of Sn. Although there is a difference in the growth rate of the alloy layer, the melting point of the alloy layer formed by diffusion is high, and if formed, it melts at 280 ° C
It is not a thing.
[0009]
Since the connection with this solder material is not completely constrained by Cu, for example, even when used for die bonding, there is a certain degree of freedom in the vertical and horizontal directions, and mechanical properties at the intermediate stage between Cu and solder are expected. Even in temperature cycle tests, heat fatigue resistance due to Sn and high reliability by preventing crack growth due to Cu particles (balls) can be expected.
[0010]
However, in composite pastes that are a mixture of Cu balls and solder balls, Sn-based solder originally has the property of less wetting and spreading on Cu, and there are many parts that must be wetted with Cu. In addition, Cu and solder balls are initially constrained in a cross-linked state, so even if the solder melts, the part remains as a space, so there is a high probability of becoming a void. This has become clear as our research progresses. For this reason, this paste method inevitably becomes a process in which voids increase, and it becomes a material unsuitable for connection applications. It is sufficient that voids are removed when mounting electronic components. However, for example, die bonding of a Si chip, power module bonding, and the like are structured such that surfaces are connected to each other, so that voids are difficult to remove structurally. If voids remain, problems such as generation of cracks due to voids and inhibition of necessary thermal diffusion are caused.
[0011]
Therefore, we put this solder material in a mold that is easy to roll in advance, compress it uniformly in a vacuum, in a reducing atmosphere or in an inert atmosphere, and plasticize Sn solder balls between metal balls. The composite molded body was made to flow and filled with solder (Sn-based solder after plastic deformation), and a solder foil obtained by rolling this was used.
[0012]
For example, when this composite molded product is rolled into a die-bonding solder foil such as a Si chip, the metal balls such as Cu-Cu are brought into contact by compression and an intermetallic compound is easily formed between the metal balls during die bonding. As a result, it was confirmed that the whole was organically connected with a high melting point metal, and the strength was secured even at 280 ° C. As a matter of course, since the gap is compressed and filled in the connection portion in the vacuum, a connection with less voids is possible. Using a low temperature hot press in nitrogen, it was confirmed that when the particle size of the Cu balls and Sn solder balls is large (about 40 μm), the Sn solder shows a void filling rate of 97% or more. Further, by subjecting the foil surface to Sn plating with an appropriate film thickness, it is possible to prevent oxidation even in materials that are significantly oxidized.
[0013]
A copper foil lead was joined with this solder, and a laminated lap joint was subjected to a shear tensile test at 270 ° C and a tensile speed of 50 mm / min. About 0.3 kgf / mm2It was also confirmed that the strength at high temperature was sufficiently secured by obtaining the value of.
[0014]
This method is a method in which the space inside the solder material is prefilled with metal balls, so that there are few voids, and it is expected that the void rate will be the same level or lower than that of the conventional solder foil ( Large voids are difficult to make.) Therefore, the solder according to the present method is a lead-free material (not actively containing lead) suitable for, for example, Si die bonding, power module bonding, and the like, where voidlessness has been an important issue due to its large area. That is, it is possible to provide a highly reliable high-temperature lead-free material suitable for temperature hierarchical connection and the like.
[0015]
Furthermore, since it is easy to oxidize in the paste method, it has been difficult to make it fluxless, but this can also be solved. That is, in the field where the flux residue is disliked, it is necessary to clean the flux after the connection by the paste method.
[0016]
In addition, even in the case of a hard and rigid solder having a desirable melting point, such as Au-20Sn, Au- (50 to 55) Sn (melting point: 309 to 370 ° C.), Au-12Ge (melting point: 356 ° C.), By using these as metal balls and dispersing soft and elastic rubber particles together with soft solder balls such as Sn and In, the solidus temperature of the solder used for the metal balls has about 280 ° C or more. Thus, it has high-temperature connection strength, and soft Sn or In or rubber between the particles can be relaxed against deformation, and a new effect that complements the weaknesses of these solders can be expected.
[0017]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment of the invention, and the repetitive description thereof is omitted.
[0018]
FIG. 1 shows an outline of a production process of a composite metal made of composite balls (metal balls, solder balls). (A) shows a Cu ball 2 which is a metal ball in a carbon jig 1 of a vacuum hot press, and a solder ball. (B) is a cross-sectional model of the composite ball lump after the plastic hot-flow of the solder after vacuum hot pressing, and Sn and Cu are deformed into a “sea-island structure”. (c) is a model in which the composite ball lump is further rolled with a roll 5 to produce a solder foil.
[0019]
In the figure, 10 to 40 μm Cu balls and 10 to 40 μm Sn balls were mixed so that the volume ratio of Cu balls was 50 to 60%. For Cu balls, further fine particles are added, and close contact packing (for example, Shigeo Miwa; Powder Engineering, P39, 1981/2/5, Nikkan Kogyo Shimbun) makes contact between Cu balls. It is possible to do more. In the case of close-packing, the theoretical volume ratio of Cu is about 74%, and the solder is 26%. Also, it is possible to make fine grains of 10 μm or less, and the alloy layer network is fine, suitable for high density and fine connection. For example, in the case of 3 to 8 μm Cu ball and 10 to 40 μm Sn ball, in the case of 3 to 10 μm Cu ball and 10 to 40 μm Sn ball, or in the case of 5 to 15 μm Cu ball and 10 to 40 μm Sn ball Although the solder filling density of the foil is lowered, the connection is good. Note that the diameters (sizes) of Cu balls, Sn balls, etc. are not necessarily included in the disclosed sizes, and are within the range that does not affect the effects of the invention. However, it goes without saying that large or small balls may be included. These balls are mixed in nitrogen and placed in a pressure vessel made of a carbon jig shown in FIG. After evacuation, when pressure is applied uniformly from the surroundings over time, only Sn fills the gaps between the Cu balls while plastically deforming. Although Sn has a melting point of 232 ° C., it can be flowed by taking time even at room temperature. If it is not possible to flow to every corner at room temperature, it can be easily achieved by raising the temperature slightly (100 to 150 ° C.). In this process, Cu and Sn do not react so much that there is no constraint at the interface, so the degree of freedom increases and Sn is likely to deform (flow). And the composite ball lump formed by this vacuum hot press or the like is further rolled with a roll 5 to obtain a solder foil. By rolling, there are no more gaps between the Cu balls, and as a result, a solder foil with fewer voids can be formed. In this case, the above-mentioned composite ball lump is intended to produce a solder foil having a thickness of 150 μm (± 10 μm). Therefore, it is desirable to prepare a mold having a shape close to that in advance because the rolling rate can be reduced. Increasing the rolling rate increases the number of contact areas between Cu, which increases the restraint due to improved contact area. Therefore, in view of having flexibility corresponding to deformation such as a temperature cycle, it is desirable to reduce the contact portion, and the final rolling rate is preferably 20% or less. Further, the rolling rate is more preferably 15 to 20%.
[0020]
In addition, when Cu etc. are exposed by the formed solder foil, it is preferable to prevent the oxidation of Cu of an exposed part by further plating Sn to the thickness of 0.5-2 micrometers.
[0021]
The Cu ball and the solder ball are preferably spherical in terms of ease of production, easy uniform dispersion at the time of blending, ease of handling, and the like, but they are not necessarily spherical. Cu balls with a rough surface, sticks, needles, fibers, horns, dendrites may be combined, or a combination of these. . However, if the above-mentioned compression is too constrained by Cu and the degree of freedom is not sufficient, the cushioning property will be lost during soldering, and if the connection is prone to poor connection, the Cu ball will have more irregularities on the surface than the ball shape. A rod-like shape, a needle-like shape, a fibrous shape, an angular shape, a dendritic shape, or a combination thereof is preferable. As shown in FIG. 2, in addition to Cu2 and Sn3 balls, plasticized ball (rubber) 6 which is a heat-resistant soft elastic body (electroless Ni plating-Au plating or electroless Ni plating-solder plating) 6 Can be dispersed to lower the Young's modulus to ensure cushioning properties. FIG. 2 (a) shows before rolling and (b) shows after rolling. The diameter of the resin ball is ideally 10 μm or less, preferably 1 μm. For example, 0.5 to 5 μm is desirable. Even if the amount is several percent by volume, it is effective.
In this specification, the terms “metal” and “solder” are used in two terms, “particle” and “ball”. If it is strongly distinguished, “particle” is used in a slightly broad sense including “ball”.
[0022]
Next, the case where Al is used as an example of another metal ball will be described.
[0023]
High melting point metals are generally hard, but there is pure Al as a soft metal at low cost. Pure Al (99.99%) is soft (Hv17), but usually hard to get wet with Sn. Therefore, it is preferable to perform Ni—Au plating, Ni—Sn plating, or the like. The Al surface may be thinly coated with Au by sputtering or the like. Making fine particles of soft pure Al is difficult due to safety problems such as explosions, but it is manufactured in an inert atmosphere, and Ni-Au plating is immediately applied to the surface, so that Al does not contact with the atmosphere Safety can be ensured. In addition, even if some Al oxide forms an oxide film, since it can be removed by plating, there is no problem. Furthermore, since the Al oxide film is easily broken even in the rolling process, a new surface of Al is formed, so that the connection is not affected so much. The metallization on the Al surface is not limited to these, and it is necessary to secure the bonding strength at a high temperature after the solder foil is produced and the solder is wetted with Cu, Ni or the like. For this reason, it is necessary to connect between the Al particles and the Ni-plated Cu plate and between the Al particles and the Ni plating of the Si chip by forming the Sn compound of the metallization on the Al particles and Ni.
[0024]
In obtaining the composite ball lump, Al is easily diffused at a high temperature in a vacuum, so that a compound with Al can be formed by using Sn solder containing Ag. In addition to Ag, a small amount of Zn, Cu, Ni, Sb or the like may be put into Sn so that it can easily react with Al, and it may be used as a solder for Al connection. When a small amount of Ag, Zn, Cu, Ni, Sb, or the like is added to Sn, metallization on the Al surface is unnecessary, and the cost advantage is great.
[0025]
When the Al surface is completely wetted, it can be mottled. This is related to the area of metallization, and depends on whether the metallization is formed mottled or entirely. If stress is applied if it is mottled, it becomes easy to deform because the constraint becomes small at the time of deformation, and the part that is not wet absorbs energy as friction loss, so it becomes a material with excellent deformability . Of course, the bonding strength is secured.
[0026]
Instead of Al in the form of a ball, it is also possible to use a 20-40 μm Al wire plated with Sn, Ni—Sn, Au, etc. and cut into a granular or rod shape. Ball-like Al particles can be produced in large quantities at low cost by the atomizing method in nitrogen.
[0027]
Next, the Au ball will be described.
[0028]
In obtaining a composite ball lump, the Sn-based solder is easily wetted with respect to the Au ball, so there is no need for metallization for a short time connection. However, when the soldering time is long, Sn diffuses remarkably, and there remains anxiety about the formation of a brittle Au—Sn compound. For this reason, in order to obtain a soft structure, In plating with a small amount of Au diffusion is also effective, and Ni, Ni—Au or the like may be used as a barrier. By making the barrier layer as thin as possible, the Au ball is easily deformed. Other configurations may be used as long as the metallized configuration can suppress the growth of the alloy layer with Au. Diffusion can be suppressed by suppressing the temperature until rolling. When bonding by die bonding in a short time, since the alloy layer generated at the grain boundary is thin, the effect of the flexibility of Au can be greatly expected without providing a barrier. A combination of Au balls and In solder balls is also possible.
[0029]
Next, the Ag ball will be described.
[0030]
The Ag balls are the same as the Cu balls, but the mechanical properties of the Ag3Sn compound are not bad, so it is possible to connect the Ag particles with the compound by a normal process. It can also be used mixed with Cu or the like.
[0031]
Next, the case where an alloy material is used as the metal ball will be described.
[0032]
Typical examples of the alloy system include Zn-Al system and Au-Sn system. The melting point of Zn-Al solder is mainly in the range of 330 to 370 ° C, and it is in a temperature range suitable for hierarchical connection with Sn-Ag-Cu, Sn-Ag, Sn-Cu solder. Can be used for metal balls. Typical examples of Zn-Al system include Zn-Al-Mg, Zn-Al-Mg-Ga, Zn-Al-Ge, Zn-Al-Mg-Ge, and Sn, In, Ag, Cu, Au Including those containing at least one of Ni and the like.
[0033]
However, it has been pointed out that Zn-Al may be cracked in the Si chip when bonded to Si due to the fact that it is highly oxidized and the rigidity of the solder is high (Shimizu et al .: “Pb-free solder for die attach” Zn-Ai-Mg-Ga alloy "Mate99, 1999-2), if simply used as a metal ball of a composite ball lump, these problems must be solved.
[0034]
Therefore, since it is necessary to clear these issues, in order to reduce the rigidity of the solder, heat-resistant plastic balls with Ni-solder plating or Au plating are uniformly dispersed together with Sn balls and Zn-Al balls, The Young's modulus was reduced. When 10-50% of the Sn ball is mixed, molten Sn enters between the Zn-Al solder. In this case, Zn-Al balls are partly joined together, but the other part is mainly precipitated low-temperature soft Sn-Zn phase and undissolved Sn. The deformation is shared by the Sn, Sn-Zn phase and plastic ball rubber.
[0035]
When actually connecting using this solder foil, for example, even when die bonding is performed, deformation can be absorbed by Sn by leaving a part of the Sn layer after that. It can be expected that the rigidity is further relaxed by the combined action of the plastic ball and the Sn layer. In this case as well, since the solidus temperature of the Zn—Al solder is secured at 280 ° C. or higher, there is no problem in strength at high temperatures.
[0036]
It is desirable that plastic balls have a smaller diameter than Zn-Al balls and are uniformly dispersed. If a plastic ball of 1 μm level that has soft elasticity at the time of deformation is deformed, the effects of thermal shock relaxation and mechanical shock relaxation are great. There are commercially available heat-resistant plastic balls. Since plastic balls are almost uniformly inserted between the balls of Zn-Al solder, this dispersion will not be greatly affected by melting in a short time during connection. Since this heat-resistant resin has a thermal decomposition temperature of about 300 ° C., a heat-resistant material is desirable, but there is no problem in the case of a die bond with a short time.
[0037]
As described above, when hot-pressing in vacuum, plastic flow is achieved by uniformly compressing Sn on a Sn-plated plastic ball at a temperature at which Sn does not melt (melting point of Sn: 232 ° C.). At this time, the Zn-Al ball does not deform much. The space is uniformly filled with plastic balls, Sn, etc. by uniform compression, and rolled to about 150 μm to produce a solder foil. When used in die bonding, it can be wound in a roll and supplied in a continuous process.
[0038]
Since Zn-Al is easily oxidized, it is desirable to apply Cu-substituted Sn plating to the surface in consideration of storage. For example, Sn and Cu are dissolved in a Zn-Al solder at the time of die bonding. The presence of Sn on the surface facilitates connection to, for example, Ni—Au plating on a Cu electrode. The Si chip side can be similarly easily joined to, for example, Ti—Ni—Au metallization. At high temperatures of 200 ° C or higher, the growth rate of the alloy layer of Ni and Sn (Ni3Sn4) is higher than that of Cu-Sn. .
[0039]
In some cases, a composite ball lump may be composed of a Zn-Al solder ball and a plastic ball.
[0040]
In addition, it is possible to make a hierarchical connection in which a large amount of Sn and In is added to the Zn—Al solder to a level at which the solidus temperature is as high as 280 ° C. When a large amount of Sn, In, etc. is added, a low phase such as a Zn-Sn eutectic is partially generated, but the bonding strength is borne by the Zn-Al solid phase which is the skeleton. Therefore, there is no problem in strength at high temperatures.
[0041]
By the way, when Sn plating substituted with Cu is applied to Zn-Al solder, by increasing the temperature above the liquidus temperature of Zn-Al solder, Sn easily wets and spreads while thin Cu dissolves. Dissolves in Zn-Al solder. When Sn is large (5% or more), it cannot be dissolved in Zn—Al, and a low temperature Sn—Zn phase is precipitated at the grain boundary. By intentionally dispersing and precipitating a large number of Sn phases, the deformation can be shared by the Sn—Zn phase and the bonding strength can be shared by the Zn—Al solid phase. Therefore, by applying Sn plating to a Zn—Al solder ball and intentionally leaving an Sn phase that cannot be dissolved in the ball, deformation can be absorbed by the Sn layer and the rigidity of Zn—Al can be reduced. That is, the rigidity of the solder at the connected portion can be relaxed, and connection failures are reduced.
[0042]
FIG. 3 shows an example in which the Si chip 8 is die-bonded to the W—Cu plating metallization (or Ni plating) 14 on the Al 2 O 3 substrate 13 using the solder foil 11 described above. A typical example of the solder foil 11 is a combination in which the metal ball is Cu and the solder is Sn. Cu is relatively soft, reacts actively with Sn, and the mechanical properties of the intermetallic compound (Cu6Sn5) are excellent. In the unlikely event that compound growth is remarkable and its adverse effects appear, it is possible to suppress the alloy layer growth rate by adding a small amount of Cu or the like into Sn. Alternatively, it is possible to suppress the growth of the alloy layer by applying a thin Ni plating such as Ni or Ni—Au on Cu. Here, it is important to securely connect the Cu balls with an intermetallic compound at the time of soldering for a short time, and since it is desired to activate the reaction, excessive growth does not become a problem. Rather, it is more important to improve the wettability and wettability of Sn in the connection between Sn and the chip and Sn and the substrate. For this reason, the effect of improving the fluidity by adding a small amount of Cu and Bi to Sn and improving the wettability by reducing the surface tension can be expected. On the other hand, in order to improve the strength with the interface, the effect of adding trace amounts of Ni, Ag, Zn, etc. can be expected. In order to improve the melting point of Sn, Sn-Sb (5 to 10%) is used instead of Sn, so that the Sb concentration in the solder increases due to the formation of Cu-Sn compounds and Ni-Sn compounds. The melting point of can be improved.
[0043]
As another representative example, in the case of a pure Al ball that is softer than Cu, the deformability with respect to the temperature cycle is excellent. The problem is the reaction between the Al ball, the chip, and the metallization of the substrate. By applying Ni plating or Ni-Au flash plating to the Al surface, the bonding strength by Sn is similarly secured between Al balls, between Al balls and Ni-plated chips, and between Ni-plated substrates. The intermetallic compound between Ni and Sn is usually Ni3Sn4, and since it is faster than the growth rate of Cu-Sn above 200 ° C, there is no worry of lack of reaction. An alloy layer in which (NiCu) 3Sn4 is mixed may be formed in a part where Cu and Ni are present at the same time. By adding a small amount of Ag, Ni, Zn, Ti or the like into Sn so that the solder can directly react with the Al balls, connection between the Al balls can be made depending on the connection conditions.
[0044]
A similar approach is possible for Au balls. Since Au is flexible and can easily form a compound with Sn, it has a powerful composition except for cost. However, since the compound in a system with a large amount of Sn has a low melting point, in order to have a melting point of 280 ° C. or higher, it is necessary to use AuSn and AuSn 2 compounds having a composition ratio of Sn of 55% or less. For this reason, it is necessary to increase the soldering temperature and to form a structure with less Sn in the joint. Therefore, by providing, for example, Cr-Ni-Sn on the Si chip metallization, Au-Sn , AuSn can be easily formed. In consideration of cost reduction etc., it is possible to mix Cu, Al, Ag balls, etc. with Au balls.
[0045]
Similarly, Ag balls are promising candidates, and the formation of a high melting point Ag3Sn compound enables connection that does not melt even at 280 ° C.
[0046]
Next, an application example to a hard Zn-Al ball having a low melting point will be described. Zn-Al system generally has a melting point and brittleness, Al generally settles in the range of 3 to 5%, and Mg, Ge, Ga, etc. are added to further lower the melting point, and Sn and In are added mainly to form a solid phase. Reduce line temperature. In order to ensure wettability and strength, Cu, Ag, Ni, or the like may be added. Their melting points are on the level of 280-360 ° C. For example, in the case of Zn-4Al-2Mg-1Ag-10Sn, when Sn balls are mixed as solder balls, even if both are melted, Sn is only partly dissolved in the Zn-Al ball, and most of the rest Remains Sn. Further, in this case, the same effect can be expected because extra Sn, In and the like that cannot be dissolved in the solder can be well dispersed in the form of particles and can be isolated and dispersed in the solder. Thick Sn plating on Zn-Al balls is one solution to isolate and disperse Sn.
[0047]
In the case of a Zn-Al ball, since the whole is melted during soldering, the surface shape due to the action of surface tension tends to become a natural shape. In addition, since Zn-Al system undergoes severe surface oxidation, it is necessary to devise a technique that does not oxidize, including the preheating process. When used as a foil, Cu (0 to 0.2 μm) -Sn (1 μm) plating is applied to the surface to provide an antioxidant effect. In addition, Sn serves as a buffer material against deformation during temperature cycling due to the presence of Sn between Zn-Al balls, but if that is still insufficient, fine Sn-plated plastic ball rubber is dispersed. By mixing, the deformability and impact resistance can be further improved, the Young's modulus can be lowered, and the heat fatigue resistance can also be improved.
[0048]
Similarly, there are Au—Sn and the like as an alloy system that is hard and has a low melting point, but the same measures can be taken.
[0049]
The Al2O3 substrate 13 used is formed with an electrode subjected to W (sintered) -Cu plating (3 μm) 38 (or W-Ni plating). Other ceramic substrates include mullite, glass ceramic, and ALN. If a flux is used at the time of connection, or if it can be used in an inert atmosphere or a reducing atmosphere from the preheating stage, the Cu electrode may be used.
[0050]
The size of the Si chip 8 used is 5 mm □, and the size of the solder foil 11 is 4 mm □ × t (thickness) 0.15, but there is no restriction on the chip size, and a large chip can be used.
The compound layer ensures high-temperature strength against secondary reflow in the subsequent process, contributes to the Sn-based solder mainly for the subsequent thermal fatigue, and is partially elastic in places where stress is severe. The jointed part exerts the maximum effect, and the life is improved compared to the case where there is no elastic joint (although the part that cannot be tolerated is broken). Therefore, there is no image strongly constrained by the compound layer, and a part of the compound may be formed in a network form in the solder. By forming a compound at the bonding interface at the periphery of the chip where large strain and stress are applied, destruction is unlikely to occur due to strong connection. On the other hand, if there is little network coupling at the center of the solder foil at the same peripheral position, the stress and strain applied to the outermost peripheral portion are applied to Sn at the center of the solder foil, and the stress applied to the upper and lower interface portions can be alleviated.
[0051]
First, the Al 2 O 3 substrate 13 is fixed to the gantry by vacuum suction, and the Si chip 8 is also held by the resistance heating tool 7 serving as an attachment jig by the vacuum suction 9. Then, the Si heater 8 is brought into contact with the Al2O3 substrate 13 through the solder foil 11 by lowering the resistance heating tool 7 and held for 5 seconds by heating (max 380 ° C.) and pressurization (initially 2 kgf). The temperature measuring thermocouple 16 is embedded near the tool tip so that the temperature can be controlled.
[0052]
Further, when the temperature of the solder foil 11 reaches its melting point, Sn of the solder foil is instantaneously melted and pressure is applied to the bonding between the metal balls to start melting. Therefore, in order to prevent the metal ball joint from collapsing, when the set temperature is reached, the resistance heating tool 7 starts from the position when the solder foil 11 is pressed, and from that position, the solder foil thickness is about 10%. (max 20%) or less, and the amount of solder protruding from the chip is controlled. Since the thickness of the solder foil affects the thermal fatigue life, it is generally set to about 80 to 150 μm. The amount of crushing is controlled by the solder thickness and the size of the solder foil relative to the chip size.
However, since this method contains half Cu and is connected in a network form, it is excellent in heat conduction. Therefore, even if it is 200 to 250 μm, it is thermally superior to the conventional one.
[0053]
The preheating 15 of the Al2O3 substrate 13 was about 100 ° C. Since rapid temperature rise and fall places great stress on the joint, preheating is also important in terms of mitigating thermal shock.
[0054]
In the case of die bonding using a resistance heating body, a mechanism is used in which nitrogen 10 is locally blown from the surroundings in order to prevent oxidation of the solder foil 11 during connection. Also, nitrogen 10 may be blown around the resistance heating tool 7 that adsorbs the Si chip 8 so that the bonded portion is always kept at an oxygen purity of 50 to 100 ppm.
[0055]
With this solder foil, die bonds such as Si chips, power modules, etc. can be joined at about 270 ° C. in an inert atmosphere furnace such as a hydrogen furnace or nitrogen. In the case of using a furnace, the maximum temperature can be 260 ° C to 350 ° C in the case of Sn, but it is necessary to select the conditions in consideration of the formation state of the compound.
[0056]
FIG. 4 shows a cross-sectional model of a typical joint portion die-bonded by a resistance heater and die-bonded by an inert atmosphere furnace such as a hydrogen furnace or nitrogen. The upper surface of the die-bonded chip is connected to the terminal of the substrate by wire bonding or the like, and the chip is sealed with a cap or sealed with resin, and further, small chip components are connected around the substrate. (In this case, it is also possible to connect the foil suitable for the terminal, which is temporarily attached to the electrode of the chip component, etc., to the substrate, or to connect the thermocompression bonded at the same time in the reflow furnace), Modules are completed by taking external connection terminals (usually joined with solder such as Sn-3Ag-0.5Cu) from the back side of the board.
[0057]
Two Cu balls, metallization 44 on the Cu ball and the chip side (for example, Cr—Ni—Au; Au is very thin, so the actual formation of an alloy layer between Cu and Sn—Ni), metallization on the Cu ball and the substrate side 42 (For example, Ni plating on an Ag—Pd conductor; formation of an alloy layer between Cu—Sn—Ni) means that an alloy layer is firmly formed and a connected state is secured. There are various combinations of metallization on the chip side, but most of Cu or Ni reacts with solder Sn. Au may be used for the surface layer mainly to prevent oxidation, but it dissolves in Sn at a level of 0.1 μm or less and does not participate in the formation of the alloy layer. On the other hand, there are various bases on the substrate side as well, but the reaction layer with Sn is Ni or Cu like the chip. Special cases include thick film conductors such as Ag, Ag-Pt, Ag-Pd, and Au-Pd. In power die bonds, voids are considered to be the most important factor because there is a significant effect on the characteristics of voids in terms of heat conduction. In the case of solder paste, the amount of gas is large due to flux reaction, solvent volatilization, etc., and therefore, it is applied to a joint structure in which gas easily escapes, for example, a long and narrow terminal, a die bond of a small Si chip, and the like. Therefore, in die bonding of medium and large Si chips, it is common to use die bonding with a resistance heating body using a solder foil without flux in an inert atmosphere, or die bonding with an inert atmosphere furnace such as a hydrogen furnace or nitrogen. is there. In addition, the voids incorporated in the solder foil made according to the present invention tend to increase as the Cu particle size decreases, but because of the fine dispersion to the particle size or less on the structure, there is no image of large voids so far, Expected to have little impact on properties. When Cu particles and Sn particles having a particle diameter of 3 to 8 μm were used, the solder filling ratio in the foil was about 80% (void ratio 20%). When this foil is sandwiched between Sn-plated Cu plates and pressure bonded with a die bonder in a nitrogen atmosphere, a Cu6Sn5 intermetallic compound is firmly formed between the Cu balls and the Cu plate, and the extra Sn is microscopic inside the solder. It was found that a good joint can be obtained by being absorbed by the space (void). The cross-sectional observation result also confirmed that the filling rate after joining was improved as compared with the filling rate of the foil before joining. From this, it has been found that the problem of voids, which has been a problem in the past, is not so much a problem in this method. If the Cu particle diameter is refined to 3 μm level or less, the reaction with Sn is active when the soldering temperature is connected at a high temperature of 300 ° C or higher, or the holding time at a high temperature is long. The shape of the material may collapse and become a Cu—Sn compound linkage, but the properties such as high temperature resistance remain unchanged. In particular, when it is desired to suppress the reaction, chemical Ni / Au plating (a compound is difficult to be formed thick even at high temperatures) or the like, or Ag particles or the like can be used. When the Cu particles are coarse at the 30 μm level, the void ratio is 3% or less, and since it is a dispersed void, it can be said that the void does not affect the characteristics.
[0058]
By the way, the solder foil produced in the process shown in the above embodiment can be continuously supplied by winding it on a reel including the cutting process. Therefore, when using it for the sealing part of a part which requires a temperature hierarchy, and the connection of a terminal connection part, what was match | combined with the shape by punching processing, laser processing, etc. can be used. And the sealing part and the terminal connection part of the component can be connected without flux by heating and pressurizing in a nitrogen atmosphere with a pulse-type pressurizing heat tool. In order to prevent oxidation during preheating and ensure wettability, a Sn-plated solder foil is desirable. Connection of components with a small pitch and a small number of terminals is easy and easy, such as mounting of solder foil, positioning of component terminals, and pressure connection with resistance heating electrodes using pulse current.
[0059]
FIG. 5 (a) shows the above-described solder foil 39 as shown in FIG. 5 (c) placed between the chip 8 and the relay substrate 36 by a resistance heating element by pulse heating in a nitrogen atmosphere without using a flux. After die bonding, a wire bond 35 of Au wire connects the terminal on the chip and the terminal on the relay substrate 36, and a foil is placed between the Ni-plated Al cap 23 and the relay substrate 36 in a nitrogen atmosphere. It is a cross section of a BGA and CSP type chip carrier that is sealed without flux with a resistance heating element. The solder foil can also be temporarily bonded to the object to be joined. Note that the relay substrate 36 secures an electrical connection between the upper and lower sides, that is, an electrical connection between the chip 8 and the external connection terminals by a through hole (not shown). This structure is a typical example of a normal module structure, and although not shown, chip parts such as resistors and capacitors may be mounted on the relay substrate 36. In the case of a high-power chip, it is preferable to use an AlN relay substrate that is excellent in thermal conductivity from the efficiency of heat dissipation. The solder composition of the external connection terminals of this module is Sn-3Ag-0.5Cu. When the terminal pitch is wide, it is supplied by a ball, and when the pitch is narrow, it is formed by a paste. In some cases, Cu terminals or Ni-Au plated terminals remain. The module is then mounted on a printed circuit board and Sn-3Ag-0.5Cu solder (melting point: 217-221 ° C) paste is reflow-connected at a maximum of 240 ° C at the same time as other components. Since the bonding of the solder foil itself is secured at the temperature, it can be connected to the printed circuit board with high reliability. That is, the connection in module mounting and the connection on the printed circuit board can realize a temperature hierarchy connection. Although the form of the external connection terminal is various, in any case, by using the solder foil, the temperature hierarchy connection can be realized for the connection between the external connection terminal and the printed circuit board. In this structure, the semiconductor chip is die-bonded on the substrate with solder foil, the terminal of the semiconductor chip and the terminal on the substrate are connected by wire bonding, and the solder ball that becomes the external connection terminal is formed on the back surface of the substrate Needless to say, the present invention can also be applied to a so-called BGA type semiconductor device. In this case, a resin mold is applied to the chip mounting surface. In addition, in order to improve the wettability of the outer peripheral part of a connection part, a good joint can be formed by reflowing in a nitrogen furnace or a hydrogen furnace after connecting with a resistance heating body by pulse heating.
[0060]
FIG. 5 (b) shows an example in which the Al fin 23 plated with Ni in a nitrogen atmosphere in the structure shown in FIG. 5 (a) is placed on a relay substrate 43 and sealed with a resistance heating element in a fluxless manner. It is.
[0061]
5 (b) is a solder foil 24 made of Cu balls and Sn balls and cut by punching. FIG. 5 (b) is a resistance pressurizing body 41 by pulse heating in a nitrogen atmosphere. This is a cross section of a model in which a Ni-plated Al fin 23 is heated and sealed to a terminal portion (Ni-Au flash 42) on a relay substrate by BB 'cross section in the figure. After the connection in the right state in FIG. 5B, the shape of the joint 24 in FIG. 5A is obtained. The solder foil shown in FIG. 5C was also used as described above.
[0062]
A fluxless reflow connection in a reducing atmosphere furnace such as hydrogen is also possible. Also, in the case of a rosin-based flux that can ensure long-term insulation, there is no problem of corrosion, so a cleaning-less reflow connection can be used depending on the product.
[0063]
By the way, when using a high melting point metal ball, the problem of reflow is to make a state where the solder foil and the side to be connected are in contact with each other in order to facilitate diffusion connection on both sides of the solder foil. It is preferable to press and contact. Therefore, it is preferable to employ a process having a temporary attaching step or a pressurizing step. For example, it is preferable to fix and supply the lead and the electrode part of the component by pressure contact or the like in advance. In the case of Zn-Al type, all are soluble, so there is no concern.
[0064]
FIG. 6 shows an example applied to power module connection. In many cases, the Si chip 8 is intended for dimensions of 10 mm □ level. For this reason, soft Pb-rich high-temperature solder has been used in the past. When it becomes Pb-free, there are Sn-3.5Ag (221 ° C), Sn-0.7Cu (227 ° C) or Sn-5Sb (235 ° C). Considering that there is a problem of environmental load on Sb, there is no actual situation other than Sn-3.5Ag and Sn-0.7Cu. Since Zn-Al is hard, there is a high possibility of causing Si chip cracking.
[0065]
The solder in this case has a history of using the Pb-5Sn system because it cannot generate high reliability even with conventional Sn-5Sb or the like because of high heat generation rather than a high-temperature solder for hierarchical connection. There is no Pb-free soft solder to replace high Pb solder, so this is an alternative. The required specification shows the degree to which the condition of reaching the 230 ° C level rarely occurs in a car. Furthermore, it is required to withstand reflow at 260 ° C. This composite solder melts Sn when reflowed at 260 ° C, but intermetallic compounds are connected by a network, so that strength at high temperatures is secured. In cars where there is an opportunity to be exposed to high temperatures of 220 ° C, Sn- (5-7)% Sb solder (melting point: 236-243 ° C) balls are used as Sn solder to prevent instantaneous partial melting at high temperatures. By doing so, the reaction between Sn and Cu balls, the reaction between Sn and the substrate terminal (Cu, Ni), the Sb concentration becomes 10% or more, and the lower limit temperature is raised to the 245 ° C level above Sn (232 ° C) be able to. For this reason, there is no worry of partial melting even at 220 ° C. The shear strength of this method at 280 ° C is 1N / mm2 (0.1kgf / mm2) The above is secured.
On the other hand, Sn—Ag—Cu based solder, unlike Sn—Pb eutectic, is said to have an adverse effect on elements, components, etc. due to its high strength, high rigidity and poor deformability. For this reason, by using flexible Sn-In, Sn-Cu-In, Sn- (0-1) Ag-Cu, Sn- (0-1) Ag-Cu-In solders, etc. Even if the melting point of the solder is slightly lowered to the 200 ° C. level, the solder itself can cope with the deformation, so that it can be expected to be applied as a hierarchical solder for mounting a portable device or the like that requires impact resistance. Of course, the strength required for secondary soldering ensures high-temperature strength by connecting the compound with Cu, which has developed into a network, especially at the outermost periphery of chips, components, etc. where the maximum stress or strain is applied. In this part, it is desirable to form a network that forms a compound with the Cu ball to prevent breakage near the interface and break inside the solder.
[0066]
Therefore, Cu ball and Sn ball solder foils are used here. 10-30μm soft Cu balls and 10-30μm Sn balls are mixed in a weight ratio of about 1: 1, Sn is plastically flowed between Cu balls in vacuum or in a reducing atmosphere, and further rolled to solder foil Is made. Alternatively, 3 to 8 μm soft Cu balls and 3 to 8 μm Sn balls are mixed at a weight ratio of about 1: 1, and Sn is plastically flowed between the Cu balls in a vacuum or reducing atmosphere, and further rolled. A solder foil may be produced. This foil is cut to the required dimensions, between the Cu lead 51 plated with Ni and the Si chip, between the Si chip 8 and the Cu disk plate (or Mo disk plate) 48 with Ni plating 46, and the Cu disk plate. The solder foil is mounted between the alumina insulating substrate 50 provided with Ni plating 49 on 48 and W metallization, and between the alumina insulating substrate 50 and the Cu base plate 49 provided with electric Ni plating 46, 280 Reflow connection was performed at once in a hydrogen furnace at ℃. This allows Cu between Cu balls, between Cu balls and Cu leads, between Cu balls and chips, between Cu balls and Ni-plated Cu plates, between Cu balls and Ni-plated alumina insulating substrates, between Cu balls and Ni-plated Cu bases, etc. And Ni intermetallic compound. The connected parts are already connected with a high-temperature resistant intermetallic compound (Cu6Sn5 for Cu and Ni3Sn4 for Ni), so the strength is maintained at 260 ° C (260 ° C to 280 ° C is acceptable). There is no problem in the reflow of the post process. Even if this joint was subjected to a temperature cycle test and a power cycle test, it was confirmed that the joint had a life equivalent to that of the conventional high Pb-containing solder.
[0067]
Furthermore, by dispersing the Sn-plated plastic ball rubber, the thermal shock resistance can be further improved by lowering the Young's modulus, and a larger Si chip can be joined. Note that mounting is also possible by a method in which nitrogen is blown with a pulse heating type die bonder and pressure bonding is performed at a maximum of 350 ° C. for 5 seconds (or 5 to 10 seconds). In addition, it is possible to ensure the wetness of the outer peripheral part and ensure the connection of the bonding interface by tacking with the pulse heating method, ensuring contact at the interface, and then reflowing in a hydrogen furnace all at once. . In addition, since it is desirable to form a smooth fillet around the chip, it is possible to provide a layer of only Sn on the outer periphery of the solder foil.
[0068]
Instead of Cu balls, Zn-Al (Zn-Al-Mg, Zn-Al-Ge, Zn-Al-Mg-Ge, Zn-Al-Mg-Ga, etc.) solder balls such as Sn, In, Furthermore, as a result of using a rolled foil in which Sn-plated plastic ball rubber is dispersed and mixed, temperature cycle resistance and impact resistance can be similarly reduced, and high reliability can be ensured. Zn-Al solder alone is hard (about Hv120-160) and has high rigidity, so there is a risk that large Si chips will be easily destroyed. Therefore, the soft low-temperature Sn layer and In layer exist around the ball, and the rubber is dispersed around the ball. Can be improved.
[0069]
In addition, by mixing Ni-plated or Ni-Au-plated particles into low thermal expansion fillers (SiO2, AlN, Invar, etc.), the thermal expansion coefficient approaches that of Si, etc., and the stress that acts is reduced, and a longer life can be expected. .
[0070]
FIG. 7 shows an example in which a high frequency RF (Radio Frequency) module used for signal processing used in a cellular phone or the like is mounted on a printed circuit board.
[0071]
This type of configuration is generally a method in which the back surface of an element is die-bonded to a relay substrate having excellent thermal conductivity, and the wire is bonded to a terminal portion of the relay substrate. There are many examples in which several chips and chip parts such as R, C, etc. are arranged around them to form an MCM (multi-chip module). Conventional HICs (Hybrid ICs), power MOSICs, etc. are representative examples. Si thin film substrate as module substrate material, AlN substrate with low thermal expansion coefficient and high thermal conductivity, glass ceramic substrate with low thermal expansion coefficient, Al2O3 substrate with thermal expansion coefficient close to GaAs, metal core such as Invar with high heat resistance and improved thermal conductivity There are organic substrates.
[0072]
FIG. 7A shows an example in which the Si chip 8 is mounted on the Si module substrate 29. On the Si module substrate 29, R, C, etc. can be formed as a thin film, so that higher-density mounting is possible, and only the Si chip 8 is mainly flip-chip mounted. Mounting on the printed circuit board 22 is performed via a soft Cu-based lead 20 of the QFP-LSI type. The connection between the lead 20 and the Si substrate 29 is performed by pressurizing and heating using the solder foil 17 cut in this proposal. Thereafter, protection and reinforcement are finally performed with a soft resin 19 such as silicone. The solder bump 18 of the Si chip is composed of Sn-3Ag (melting point: 221 ° C.) and connected to the relay substrate 29. The printed circuit board 22 is connected by Sn-Ag-Cu Pb-free solder 21. Even if the solder bump 18 is remelted during reflow of the Sn-Ag-Cu-based Pb-free solder 21, it hardly changes due to the weight of the Si chip 8 when mounted on the printed circuit board 22, and the connection of Si-Si Therefore, there is no stress burden and there is no problem in reliability. After the mounting on the printed circuit board 22 is finished, it is possible to coat the Si chip 8 with a silicon gel 12 or the like for protection.
[0073]
As another method, if the solder bumps 18 of the Si chip 8 are changed to Au ball bumps and Sn plating is applied to the terminals formed on the relay substrate 29, Au-Sn bonding can be obtained by thermocompression bonding. It does not melt at a reflow temperature of 250 ° C. in mounting on the substrate 22, and therefore, a temperature hierarchy connection is possible and the joint can sufficiently withstand reflow.
[0074]
As described above, the connection by the solder foil 17 is maintained by the intermetallic compound formed between the metal balls such as Cu, and ensures the strength even at the reflow temperature of 250 ° C. when mounted on the printed circuit board 22. I can do it. This makes it possible to realize a lead-free connection with a temperature hierarchy, which has been a major issue until now.
[0075]
When a thick film substrate such as an AlN substrate, a glass ceramic substrate, or an Al2O3 substrate is used in place of the Si substrate, mounting of chip parts such as R and C is necessary for making a functional element. On the other hand, there is a method of forming R and C by laser trimming with a thick film paste. In the case of R and C by thick film paste, the same mounting method as that of the Si substrate is possible.
[0076]
FIG. 7B shows a case where a module using an Al 2 O 3 module substrate 29 having excellent thermal conductivity and mechanical properties is insulated and sealed in a case of an Al fin 23 for the GaAs chip 8. Since GaAs and Al2O3 have similar thermal expansion coefficients, flip chip mounting has no problem in reliability. For terminal connection of these chip components, if the terminal area is □ 0.6mm or more, solder with a solder thickness t: 0.05 to 0.10 foil and a small number of terminals, temporarily attached to the chip component, or temporarily to the terminal on the board side In addition, it is possible to individually connect with a resistance heating body by pressure connection in a nitrogen atmosphere, or by reflow in a reducing atmosphere or an inert atmosphere. It is also possible to use a foil having a solder thickness t; 0.15 to 0.25. Although not shown here for high output, a chip mounting method using the foil of the present proposal (chip back surface 8), die bonding, and wire bonding of terminals is general.
[0077]
In the case of Al fin connection, foil having a shape surrounding the periphery of the fin is used, and pressure connection is made with a resistance heating body in a nitrogen atmosphere. In FIG. 7C, the left side is an example of terminal connection, and the right side is an example of an Al fin 23, both of which are joined by sandwiching the solder foil 27 between the terminal 28 of the module substrate and the terminal of the fin connection portion. At this time, the solder foil is preferably temporarily attached to either the substrate or the fin. In the case of Al, the terminal portion is plated with Ni or the like.
[0078]
FIG. 7 (d) shows a setup model to be mounted on a C organic substrate 32 such as Invar. The heat generating chip can be directly mounted with a GaAs chip by using an organic substrate such as a metal core polyimide having low thermal expansion and excellent heat resistance, or a build-up substrate corresponding to high-density mounting. In the case of a high heat generating chip, a dummy terminal can be provided to directly conduct heat to the metal.
[0079]
In addition, although the RF module was taken up as an example to the element of this proposal, SAW (surface acoustic wave) element structure used as a band pass filter for various mobile communication devices, PA (high frequency power amplifier) module, The present invention can be similarly applied to other modules and elements. The product field includes not only mobile phones and laptop computers, but also module-mounted products that can be used for new home appliances in the age of digitalization.
[0080]
FIG. 8 is a more specific example of application to RF module mounting. 8A is a cross-sectional view of the module, and FIG. 8B is a model of a plan view in which the member 23 is seen through the upper surface. The actual structure is that about □ 2mm chip 8 MOSFET elements that generate radio waves are equipped with multiple face-up connections to support multi-band, and there are high-frequency circuits that efficiently generate radio waves in the periphery. R, C chip parts 52 and the like are formed.
The chip parts are also miniaturized, 1005 and the like are used, and the module has a vertical and horizontal dimension of about 7 × 14 and is mounted with high density. Here, considering only the functional aspect of solder, a model in which one element and one chip component are mounted is shown as a representative. As will be described later, the chip 8 and the chip component 52 are solder-connected to the Al 2 O 3 substrate 13. The terminal of the chip 8 is connected to the electrode of the Al2O3 substrate 13 by wire bonding, and is further electrically connected to the thick film electrode 60 serving as the external connection portion on the back surface of the substrate through the through hole 59 and the thick film conductor 61. . The chip component 52 is solder-connected to the electrode of the substrate 13 and is further electrically connected to the thick film electrode 60 serving as an external connection portion on the back surface of the substrate through the through hole 59 and the wiring 61. Although not shown, the electrode 62 and the through hole 59 of the substrate connected to the chip or chip component are electrically connected by wiring. The member (Al fin) 23 covering the entire module and the Al 2 O 3 substrate 13 are joined by caulking or the like. In addition, this module is mounted by solder connection with a thick film electrode 60 serving as an external connection portion on a printed circuit board or the like, and requires a temperature hierarchy connection.
[0081]
FIG. 9 is a flowchart showing four processes on the premise of die bonding of a Si (or GaAs) chip using a solder foil in the structure shown in FIG. Processes (1) and (2) select a conventional Ag paste from the viewpoint of workability for small R and C chip parts such as 1005, and (1) is flux-free with a clean substrate surface. In this method, die bonding is performed using a solder foil in a nitrogen atmosphere in a short time, wire bonding is performed, and then chip components are connected with Ag paste. (2) is a method of connecting chip parts with Ag paste first, and using a furnace to cure the resin may contaminate the substrate surface and affect wire bonding in the subsequent process. Then, wire bonding will occur. (3) is the same as the soldering foil in order to ensure the same temperature hierarchy on the high temperature side, but for small chip components, it is a mixed paste of metal balls and solder balls that excels in workability. This is a supply method, and can be printed or dispensed. Cleaning after reflow and high-power Si chips are required to be voided as much as possible, so die bonding of solder foil suitable for voiding is performed, and finally wire bonding is performed. If die bonding and wire bonding are performed in the step (3), the flux cleaning step can be omitted. (4) is a method of die-bonding and wire-bonding first, and there are two ways of thinking in the subsequent process. One is a method in which chip components are connected one after another in a nitrogen atmosphere without flux in a subsequent process. This method has the disadvantage of taking time. Therefore, the other is a method in which, in the process shown in (4), the chip parts are temporarily attached to the chip parts by using flux, and then connected together by reflow later. Specifically, after die bonding and wire bonding, for example, a composite solder foil composed of, for example, Cu balls and Sn balls and having a surface plated with Sn plating of about 1 μm (mostly chip parts are pre-plated with Ni. In this case, Sn plating is not necessary), cut to approximately the electrode dimensions, temporarily fixed to the electrode part of the component by pressure heating (a flux may be used), and the temporarily fixed component on the Al2O3 substrate It is preferable that the solder is temporarily fixed to the W-Ni-Au plating electrode portion of the solder so that the solder is plastically deformed by thermocompression bonding. In addition, if you press individual parts one by one with a resistance heating element of pulse in a nitrogen atmosphere at 300 to 350 ° C for 5 seconds, an intermetallic compound is formed and connected, and the strength is high even at a high temperature of 260 ° C or higher. Needless to say, keep it. And if it passes through a reflow furnace (max 270-320 degreeC), the part currently crimped | bonded will be connected by connection of an alloy layer with Cu and Ni. This connection does not need to be perfect, and if it is connected somewhere, even if the strength is small, there is no problem at high temperatures.
[0082]
The small chip component does not reach a temperature as high as the element, but when used for a long period of time, when deterioration of the Ag paste becomes a problem, high reliability can be ensured by using the solder of the component of the present invention. The problem is that it takes time and effort to securely fix small chip components one by one by thermocompression.
[0083]
FIG. 8C shows an example in which the above-described module is soldered to the printed circuit board 22. In addition to the module, an electronic component 52 and a BGA type semiconductor device are soldered. In the semiconductor device, the semiconductor chip 8 is connected to the relay substrate 43 in a face-up state with the above-described solder foil, and the terminals of the semiconductor chip 8 and the terminals of the relay substrate 43 are connected by wire bonding 35. The periphery is sealed with resin 58 by resin 58. A solder ball bump 21 is formed on the lower side of the relay substrate 43. For the solder ball bump 21, for example, Sn-2.5Ag-0.5Cu solder is used. The solder balls 30 are preferably Sn- (1 to 2.5) Ag-0.5Cu, and for example, Sn-1.0Ag-0.5Cu may be used. Also, an electronic component is soldered to the back surface, which is an example of so-called double-sided mounting.
[0084]
As a mounting form, first, for example, Sn-3Ag-0.5Cu solder (melting point: 217 to 221 ° C.) paste is printed on the electrode portion on the printed circuit board. First, in order to perform solder connection from the mounting surface side of the electronic component 54, the electronic component 54 is mounted and reflow connection is performed at a maximum of 240 ° C. Next, double-sided mounting is realized by mounting electronic components, modules, and semiconductor devices and performing reflow connection at max. Thus, it is common to first reflow light parts with heat resistance and then connect heavy parts without heat resistance later. When reflow connection is made later, it is ideal not to remelt the solder on the side to which the connection is made first.
[0085]
As described above, in this case as well, the reflow temperature at the time of mounting on the printed circuit board ensures the bonding of the solder foil itself used for connection in the module, so the module and the semiconductor device are connected to the printed circuit board with high reliability. I can do it. That is, it is possible to realize a temperature hierarchy connection between the connection in the semiconductor device or module and the connection on the printed circuit board. In addition, although both sides of the printed circuit board are connected by the same solder, even if the solder melts in the reflow connection of the electronic component, module, or semiconductor device in the small component such as 1005 as the electronic component 54 itself Because of its light weight, the surface tension is more effective than gravity and it does not fall. Therefore, when considering the worst case, no intermetallic compound is formed with the terminal of the substrate, and no problem arises even if it is simply joined with Sn. For small parts mounted in a module, a combination of using a solder paste mixed with Cu and Sn is more preferable than a method of temporarily fixing a solder foil mixed with Cu and Sn in consideration of productivity.
[0086]
Next, an application example of a high output chip such as a motor driver IC to a resin package will be described. FIG. 10 (a) is a plan view in which the lead frame 65 and the heat diffusing plate 64 are bonded together, and there are two caulking locations 63. FIG. FIG. 10B is a cross-sectional view of the package, and FIG. 10C is an enlarged view of a part thereof. Heat from the 3 W level heat generating chip 8 is transferred to the header heat diffusion plate (Cu-based low expansion composite material) 64 through the solder 47. The lead material is made of, for example, 42 Alloy type material.
[0087]
FIG. 11 shows a process chart of the package. First, a lead frame and a heat diffusion plate (heat sink) are caulked and joined. Then, the semiconductor chip 8 is die-bonded via solder (foil) 47 onto the heat diffusion plate 64 that has been crimped. The die-bonded semiconductor chip 8 is wire bonded with leads 56 and gold wires 35 as shown in the drawing. Thereafter, resin molding is performed, and after dam 57 is cut, Sn-based solder plating is performed. Then, lead cutting is performed, and the thermal diffusion plate is cut and completed. The electrode on the back surface of the Si chip 8 can be a metallization generally used such as Cr—Ni—Au, Cr—Cu—Au, Ti—Pt—Au, Ti—Ni—Au. Even when there is a large amount of Au, a compound on the Au rich side having a high melting point of Au—Sn may be formed. The die bond of the chip was performed by blowing nitrogen and using a pulse resistance heating body at an initial pressure of 2 kgf and 350 ° C. for 5 seconds. The control of the solder thickness is set when it is 10 μm lower than the initial pressurization position (70 μm film thickness), and it is a system that ensures the film thickness due to the mechanism to improve thermal fatigue resistance. In addition to the above, initial pressurization was performed at 1 kgf and 350 ° C. for 5 to 10 seconds. The control of the solder thickness was the same even when the solder thickness was set 10 μm below the initial pressurization position (150 μm film thickness). Because of the high output chip, it was important to reduce the void ratio, and the target of 5% or less was achieved. Since the solder is contained in a state where Cu balls are uniformly dispersed, it is difficult for structurally large voids to be generated. Even for severe thermal fatigue, Sn and Sn-based solder itself have excellent heat fatigue resistance and excellent deformability. Furthermore, since an intermetallic compound is formed on the network between the Cu particles and between the Cu particles and the electrode, the strength is ensured even at a high temperature of 260 ° C. or higher. If the Cu particles and the like are too strongly bonded (the Cu layer has a large number of alloy layer forming surfaces), they are constrained and the degree of freedom is lost, resulting in strong elastic bonding. Moderate binding exists. In particular, in the peripheral portion of the chip, the conventional solder breaks in the vicinity of the joint interface where the stress is concentrated, and the breakage hardly occurs inside the solder. In this method, it is possible to form a network in which the interface of the joint is less likely to break by reaction with the Cu ball and can be broken inside the solder. After die bonding and wire bonding, resin molding is performed, and the dam 57 is cut, and Sn—Bi, Sn—Ag, Sn—Cu Pb-free solder plating is applied to the leads at 2 to 8 μm. Furthermore, lead cutting is performed, and the heat diffusion plate at an unnecessary portion is cut to complete.
[0088]
FIG. 12 shows an example applied to a general plastic package. The back surface of the Si chip is bonded onto a tab 66 of 42Alloy via a solder foil 67 (conductive paste 67). The element is connected to the lead 56 through the wire bond 35 and molded with the resin 58. Thereafter, the lead is plated with Sn-Bi based on Pb-free. Conventionally, Sn-37Pb eutectic solder with a melting point of 183 ° C could be used for printed circuit board mounting, so reflow connection was possible at a maximum of 220 ° C. When Pb-free is used, reflow connection is performed with Sn-3Ag-0.5Cu (melting point: 217-221 ° C), so the maximum temperature is 240 ° C, and the maximum temperature is about 20 ° C higher. For this reason, when a conventional heat-resistant conductive paste or adhesive is used to connect the Si chip 8 and the tab 66 of the 42 Alloy, the adhesive strength at high temperatures is lowered, and it is expected that the reliability thereafter will be affected. Therefore, by using the solder foil in place of the conductive paste, the strength at a high temperature of max 270 to 350 ° C. is secured, so that hierarchical connection by Pb-free solder is possible. This plastic package application can be applied to all plastic package structures that connect the Si chip and the tab. Structurally, Gull Wing type, Flat type, J-Lead type, Butt-Leed type. There is a Leadless type.
[0089]
FIG. 13 shows an example of a model structure at the previous stage of making a composite solder foil. 3-15μm level Sn-plated Cu or other metal fiber 69 (If forming or rolling at high temperature, surface treatment such as Ni / Au may be applied to suppress reaction between Cu and Sn) Lay the foil mixed with an appropriate blending (about 50%) with a solder ball such as Sn and a metal ball such as Sn-plated Cu on it, and then processed it into a 150 to 250 μm level foil create. In order to further lower the Young's modulus, heat-resistant plastic balls plated with Sn, or Cu / Sn-plated low thermal expansion silica or invar may be added as a part of the metal balls. At the stage of molding and rolling, the soft solder ball enters the gap between the metal ball and the metal fiber to form a sea shape of “sea-island structure”. The metal fiber diameter is not limited to the above 3 to 15 μm, and becomes a nucleus at the center of the foil, and metal balls play a major role at the bonding interface with the object to be bonded. By directing the metal fiber in that direction in continuous rolling or the like, the work becomes easy. Carbon fibers that can be thinned and reduced in expansion instead of metal fibers are plated with Cu (or Cu / solder), and other fibers such as ceramic, glass, invar, Ni / Au, Ni / solder, Cu (Or Cu / solder) plating is also possible.
[0090]
FIG. 13 shows an example in which the metal fibers that form the core of the foil are arranged in a line, but FIG. 14 shows a stable structure in which the metal fibers are arranged in a cross (the angle is free). A mixture of a solder ball such as Sn and a metal ball such as Sn-plated Cu in an appropriate composition (about 50%) is inserted in the gap of the cloth, and the application is possible as in FIG. .
[0091]
FIG. 15 is a cross section of the foil in the case of using the wire net-like fibers 71, and the cross section of the metal net extending in the depth direction is indicated by a cross 70. FIG. 15A shows a foil composed of a wire mesh and solder. There is a limit to making the mesh of the metal mesh finer, the smallest mesh of the current commercial product is 325, the passing particle size is as large as 44 μm, and the wire diameter forming the mesh is thick, so the contact area at the joint interface is large Since it is small (compound formation region), there is a problem in securing strength at high temperatures. Accordingly, FIG. 15 shows a cross section of a foil prepared by filling a gap between the metal meshes 70 and 71 with a solder ball such as Sn and a metal ball 2 such as Sn-plated Cu mixed in an appropriate composition (about 50%). Shown in (b). The solder 72 has a structure that enters the gap. When strength is required at high temperatures, Cu balls are compounded in many cases, emphasizing the formation of compounds at the interface with the joints, and when emphasizing the thermal fatigue of joints, solder is compounded in many cases. Therefore, it is possible to control with emphasis on the thermal fatigue resistance of the solder. In addition, the metal ball to be filled is not limited to the ball, and fibers and the like described later are powerful. The compounding ratio of the metal balls and the solder may also be greatly different depending on the shape of the metal, the contact state, and the like.
[0092]
FIG. 16 shows an appropriate blending (about 50%) of elongated metal fibers 73 that are randomly flattened to make paper, and a framework is formed and solder balls 68 such as Sn and metal balls 2 such as Sn plated Cu are formed on both sides. It is a model in a state filled with the mixture. FIG. 16A is a plan view, and FIG. 16B is a cross-sectional view.
[0093]
FIG. 17 shows a strip metal fiber instead of a metal ball, or a carbon fiber capable of low expansion plated with Cu (or Cu / solder), and other fibers such as ceramic, glass, invar, Ni / Au, Ni / Solder, Cu (or Cu / solder) plated strip fibers, etc. are possible. The amount of solder can be greatly increased by using strip fibers. It is also possible to reinforce the network by compound formation by mixing metal balls in the gap. The metal ball is constrained and becomes a rigid structure, but by dispersing the strip-like fibers in this way, a structure with excellent deformability and elasticity can be expected, and good performance can be obtained during die bonding or thermal fatigue. I think that The length of the strip is preferably 1/10 or less if the thickness of the foil is 200 μm. As an example, it is desirable that the diameter is in the range of 1 to 5 μm and the length is in the range of 5 to 15 μm.
Although the invention made by the present inventor has been specifically described based on the embodiment, the present invention is not limited to the embodiment described above, and various modifications can be made without departing from the scope of the invention. Nor.
The representative aspects disclosed in the above embodiments are as follows.
It is a solder foil formed by rolling a solder material containing metal particles and solder particles. This is a solder foil formed by rolling a solder material containing metal particles having a plating layer such as Sn.
This is a method for producing a solder foil in which a solder material containing metal particles and solder particles is rolled. This is a method for producing a solder foil in which a solder material containing metal particles having a plating layer such as Sn is rolled.
In the solder foil, for example, metal particles are Cu particles, and solder particles are Sn particles.
A solder foil having Cu and Sn formed by applying pressure to solder, where Cu is in a particle state and Sn is in a state of filling between the Cu particles.
When the solder foil is reflowed, at least a part of the surface of the Cu particles is covered with Cu6Sn5.
In the solder foil, Cu particles and Sn after plastic deformation are bonded by a compound containing Cu6Sn5 when the solder foil is reflowed.
It is the said solder foil, Comprising: The particle size of Cu particle | grains is 10-40 micrometers.
It is the said solder foil, Comprising: The particle size of Cu particle | grains is 3-10 micrometers.
The solder foil has a Ni plating or Ni / Au plating layer on the surface of the Cu particles.
It is the said solder foil, Comprising: At least the part which Cu has exposed is plated with Sn.
The solder foil having a thickness of 80 μm to 150 μm.
The solder foil having a thickness of 150 μm to 250 μm.
The solder foil has plastic particles.
The solder foil has other particles having a smaller coefficient of thermal expansion than Cu.
The other particles of the solder foil whose thermal expansion coefficient is smaller than that of the Cu are Invar, silica, alumina, AlN (aluminum nitride), and SiC particles. Invar (alloy) is an alloy of 34% to 36% of Ni (nickel) to Fe (iron), and has a small linear expansion coefficient.
The solder foil further contains In particles.
The solder foil is obtained by mixing Cu particles and Sn particles in a vacuum, in a reducing atmosphere or in an inert atmosphere, and then applying pressure to form a foil.
The solder foil has a rolling rate of 15% to 20%.
The solder foil is formed by rolling a material containing metal fibers and solder particles.
This is a solder foil formed by rolling a solder material containing Cu metal fibers and Sn particles.
It is the said solder foil, Comprising: The metal fiber of this Cu is a strip shape among this solder material.
This is a solder foil formed by rolling a solder material containing particles of any one of Al, Au, and Ag and Sn particles.
This is a solder foil formed by rolling a solder material containing particles of Zn-Al alloy, Au-Sn alloy and Sn.
Also, a metal ball containing a single metal, an alloy, a compound or a mixture thereof wetted by solder and a solder ball containing one or more of Sn and In are mixed, filled in a gap, press-fitted and rolled. It is the solder foil characterized by this.
Also, a metal ball containing a single metal, alloy, compound or mixture thereof wetted by solder and a solder ball containing one or more of Sn and In are mixed and pre-rolled molds that are applied with uniform pressure. It is a solder foil produced by rolling the composite body after being embedded and filled in evenly with no gaps.
In the solder foil described above, the solder contains one or more of Ag, Bi, Cu, Zn, Ni, Pd, Au, Sb and the like in addition to Sn and In.
Further, in the solder foil described above, the metal ball is Cu, Cu alloy, Cu6Sn5 compound, Ag, Ag-Sn compound, Au, Au-Sn compound, Al, Al-Ag compound, Al-Au compound, Zn -Balls containing Al solder or a mixture thereof.
Further, the solder foil described above, Sn plating to the rolled foil or solder composite, or plating containing any one or more of Bi, In, Ag, Au, Cu, Ni, Pd in Sn It has been applied.
Further, in the case of the solder foil described above, when the metal ball containing the single metal, alloy, compound or mixture thereof is not wetted, the surface is plated with Ni, Ni-Au, Cu, Ag, Sn, Au, etc. Or, these composite platings, or further metallized so as to be wetted by solder such as Sn-based plating.
Further, the solder foil described above is a solder foil having a particle size distribution in consideration of close-packing of metal balls containing the single metal, alloy, compound or mixture thereof.
Further, in the solder foil described above, in order to reduce the rigidity of the composite solder, plastic balls having metallized surfaces on which the solder is wet are dispersed.
The solder foil is a particle having a lower coefficient of thermal expansion than a metal including a single metal, an alloy, a compound or a mixture thereof for reducing the thermal expansion coefficient of the composite solder, and wets the solder on the surface. For this purpose, or solder plating such as Sn or In on the metallization for dispersion.
In the solder foil described above, the particles having a low thermal expansion coefficient are Invar, silica, alumina, AlN, SiC, or the like.
Also, in the above-described solder foil, the plastic ball material is a polyimide resin, a heat-resistant epoxy resin, a silicone resin, various polymer beads, modified ones thereof, or a mixture thereof.
Moreover, it is a solder foil of the above-mentioned description, Comprising: It is a strip | belt, a line | wire, a ball | bowl, and lump shape.
Also, the solder foil as described above, wherein metal fibers or copper-plated carbon, glass, ceramic or other fibers are used instead of the metal balls, or the metal balls are dispersed and mixed in the metal fibers Things are used.
Further, in the solder foil described above, a metal fiber or copper-plated carbon, glass, ceramic, or other fiber is stacked on the cloth instead of the metal ball, or the cloth fiber and the metal ball are dispersed. Things are used.
Also, the solder foil described above, wherein the metal balls are replaced with metal fibers or copper-plated carbon, glass, ceramic or other fibers, or the metal balls are dispersed in the mesh It is a thing.
Moreover, it is a solder foil of the said description, Comprising: It is 1-20 micrometers as a diameter of this fiber, Preferably it is 3-15 micrometers.
Also, the solder foil as described above, wherein short metal fibers or copper-plated short fibers such as carbon, glass and ceramic are used instead of the metal balls, or the metal balls are dispersed in the short fibers Is used.
Moreover, it is a solder foil of the said description, Comprising: It is 1-10 micrometers as a diameter of this short fiber, Preferably it is 1-5 micrometers, Aspect ratio (length / diameter): 2-5.
An electronic device having a first electronic device, a second electronic device, and a third electronic device, wherein the first electronic device and the second electronic device are connected by the solder foil, The second electronic device and the third electronic device are connected by a solder different from the first solder.
A semiconductor device comprising a semiconductor chip, a tab on which the semiconductor chip is disposed, and a lead serving as a connection terminal to the outside, wherein the electrode of the semiconductor chip and the lead are connected by wire bonding, The semiconductor chip and the tab are connected by the solder foil.
An electronic device having a first electronic component, a second electronic component, and a third electronic component, wherein the first electronic component and the second electronic component include metal particles and solder particles. A second solder having a melting point different from that of the first solder, wherein the second electronic component and the third electronic component are connected using a first solder which is a solder foil formed by rolling a material containing It is connected using.
An electronic device having a first electronic component, a second electronic component, and a third electronic component, wherein the first electronic component and the second electronic component include metal particles and solder particles. By applying pressure to the solder material, the metal is in the form of particles, and the solder particles are connected using the first solder that fills the space between the metal particles, and the second electrons The component and the third electronic component are connected using a second solder having a melting point different from that of the first solder.
In the electronic device, the solder particles in the first solder are Sn.
An electronic device having a first electronic device, a second electronic device, and a third electronic device, wherein the first electronic device and the second electronic device are metal particles having a Sn plating layer The second electronic component and the third electronic component are connected to each other using a first solder, which is a solder foil formed by rolling a solder material including: a second melting point different from that of the first solder. It is connected using the solder.
An electronic device having a first electronic component, a second electronic component, and a third electronic component, wherein the first electronic component and the second electronic component are metal particles having a Sn plating layer When the pressure is applied to the metal, the metal is in a state of particles, and the Sn is connected by using a first solder that fills the space between the metal particles, and the second electronic component and the first The three electronic components are connected using a second solder having a melting point different from that of the first solder.
In the electronic device, metal particles in the first solder are Cu.
In the electronic device, the metal particles in the first solder are particles of any one of Al, Au, and Ag.
In the electronic device, the melting point of the second solder is lower than the melting point of the metal particles of the first solder.
In the electronic device, when Sn contained in the first solder is melted, the Cu particles react with the Sn, and the Cu particles are bonded by a compound containing Cu6Sn5.
In the electronic device, the metal particles have a diameter of 10 to 40 μm.
In the electronic device, the thickness of the first solder is 80 μm to 150 μm.
In the electronic device, the first solder further includes plastic particles.
In the electronic device, the first solder further includes other particles having a smaller coefficient of thermal expansion than the metal particles.
In the electronic device, the second solder is Sn-Ag-Cu-based lead-free solder.
An electronic device having a first electronic component and a second electronic component, wherein the first electronic component and the second electronic component are connected by a solder connection portion, and the solder connection portion is made of a metal It has an Sn portion filling between the particles and the metal particles.
In the electronic device, the metal particles are bonded by a compound formed of the metal and Sn.
A semiconductor device comprising a semiconductor chip, a tab on which the semiconductor chip is disposed, and a lead serving as a connection terminal to the outside, wherein the electrode of the semiconductor chip and the lead are connected by wire bonding, The semiconductor chip and the tab are connected using a solder foil in which metal particles and solder particles are mixed.
A semiconductor device comprising a semiconductor chip, a tab on which the semiconductor chip is disposed, and a lead serving as a connection terminal to the outside, wherein the electrode of the semiconductor chip and the lead are connected by wire bonding, The semiconductor chip and the tab have metal particles and solder particles. By applying pressure to the solder material, the metal is in a state of particles and the solder particles are filled between the metal particles. It is connected using the first solder.
A semiconductor device comprising a semiconductor chip, a tab on which the semiconductor chip is disposed, and a lead serving as a connection terminal to the outside, wherein the electrode of the semiconductor chip and the lead are connected by wire bonding, The semiconductor chip and the tab are connected to each other by a connection portion having a Sn portion filling between the metal particles and the metal particles.
In the semiconductor device, the metal particles are bound by a compound formed of the metal and Sn.
A module having a substrate, a passive component mounted on the substrate, and a semiconductor chip, wherein the electrode of the semiconductor chip and the electrode of the substrate are connected by a wire, and the surface of the semiconductor chip not connected by wire bonding and the substrate are The metal particles are connected to each other by a connecting portion having an Sn portion filling the space between the metal particles.
In the module, the passive component and the substrate are also connected by a connecting portion having a Sn portion filling between the metal particles and the metal particles.
In the module, the substrate has a through hole in a portion on which the semiconductor chip is mounted, and the inside of the through hole is also filled with solder filling between the metal particles. Is.
[0094]
【The invention's effect】
The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.
(1) It is possible to provide an electronic device by a completely new solder connection and a method for manufacturing the electronic device.
(2) It is possible to provide solder connection in a temperature hierarchy connection required in the method for manufacturing an electronic device, particularly high-temperature side solder connection.
(3) It is possible to provide a completely new solder and a manufacturing method thereof.
[Brief description of the drawings]
1 is a diagram of the production process of composite metal made from composite balls.
FIG. 2 is a cross-sectional model view before and after rolling in a state where elastic plastic balls are dispersed.
FIG. 3 is a cross-sectional model showing an example of a die bonding process.
[Fig.4] Cross-sectional model of die-bonded joint with Cu, Sn-mixed solder foil
FIG. 5 is a cross-sectional model of connecting LSI and cap to the substrate.
FIG. 6 is a cross-sectional model of a power module
7 is a cross-sectional model of a module mounted on a printed circuit board.
[Fig.8] RF module mounting cross-section model diagram
FIG. 9 is a flowchart showing an RF module mounting process.
FIG. 10 is a plane and cross-sectional model view of a high-power resin package.
FIG. 11 is a flowchart showing a process of a high-power resin package.
FIG. 12 is a cross-sectional model view of a plastic package.
FIG. 13 is a plan view and a cross-sectional view of a model blended with metal fibers.
FIG. 14 is a plan view of a model using cross metal fibers.
FIG. 15 is a sectional view of a model using wire mesh fibers.
FIG. 16 is a plan view and a cross-sectional view in which elongated metal fibers are randomly placed and flattened.
FIG. 17 is a cross section of a model using strip metal and non-metal fibers.
[Explanation of symbols]
1. Carbon jig 2. Cu ball
3.Sn ball 4.Sn
5. Roll 6. Plastic ball
7. Resistance heating tool 8. Si chip
9.Vacuum suction hole 10.Nitrogen
11.Solder foil 12.Silicone gel
13.Al2O3 substrate 14.W (sintered) -Cu plating electrode
15. Preheater heater 16. Nitrogen
17.Cu, Sn mixed foil 18.Bump
19.Soft resin 20.Lead
21. Solder ball bumps 22. Printed circuit board
23.Al fin 24.Junction with fin
25. Joint with lead 26. Lead
27. Solder foil 28. Board terminals
29. Module board 30. Terminal
31.Cu 32.Organic substrate
33.Cu through-hole conductor 34.Ag-Pd conductor
35.Wire bond 36.AlN relay board
37.Connection terminal 38.Cr-Cu-Au
39. Die bond 40. Solder foil
41.Pressure body 42.Ni-Au plating metallization
43. Relay board 44. Cr-Ni-Au metallization
45. Chemical Ni plating 46. Electric Ni plating
47.Solder 48.Cu disk
49.Cu base 50.Al2O3 insulation substrate
51.Cu lead 52.Chip component
53.Cu pad 54.TQFP-LSI
55.Sn-Ag-Cu solder 56.Lead
57. Dam cutting part
58.Resin 59.Through hole
60.W-Ni-Au thick film electrode 61.W-Ni (or Ag-Pd, Ag) thick film conductor
62.Au plating electrode 63.Caulking part
64. Thermal diffusion plate (header) 65. Lead frame
66. Tab 67. Conductive paste
68.Solder 69.Fiber
70.Cu mesh (cross section) 71.Cu mesh (longitudinal section)
72.Solder (sea) 73.Striped fiber
74. Strip fiber

Claims (14)

Cu 、 Ag 、 Au または Al の第１の粒子(体積比率５０％〜７４％)と、Sn または In の第２の粒子とを分散混入したはんだ材料を、前記第２の粒子の融点より低い温度で、および真空中、還元性雰囲気中もしくは不活性雰囲気中で加圧して前記はんだ材料に塑性流動を起こさせて複合材料の塊に成形し、前記複合材料の塊をロール圧延して形成したはんだ箔であって、
前記第２の粒子の融点以上の温度で、溶融した前記第２の粒子の金属が前記第１の粒子の金属の表面部と化合物を形成することを特徴とするはんだ箔。 A solder material in which first particles of Cu , Ag , Au, or Al (volume ratio of 50% to 74%) and second particles of Sn or In are dispersed is mixed at a temperature lower than the melting point of the second particles. And in a vacuum, a reducing atmosphere or an inert atmosphere to cause plastic flow in the solder material to form a mass of the composite material, and the solder formed by rolling the mass of the composite material Foil,
The solder foil , wherein the molten metal of the second particles forms a compound with the metal surface portion of the first particles at a temperature equal to or higher than the melting point of the second particles . 請求項１に記載のはんだ箔であって、前記第１の粒子の粒径は１０〜４０μｍであることを特徴とするはんだ箔。 The solder foil according to claim 1, wherein the first particles have a particle size of 10 to 40 μm . 請求項１または２に記載のはんだ箔であって、前記第１の粒子の粒径は３〜１０μｍであることを特徴とするはんだ箔。 3. The solder foil according to claim 1, wherein the particle diameter of the first particles is 3 to 10 μm . 4. 請求項１から３のいずれか１項に記載のはんだ箔であって、前記第１の粒子の表面に Ni めっきもしくは Ni/Au めっき層を有することを特徴とするはんだ箔。 4. The solder foil according to claim 1, wherein the surface of the first particle has a Ni plating layer or a Ni / Au plating layer . 5. 請求項１から４のいずれか１項に記載のはんだ箔であって、前記箔の少なくとも前記第１の粒子が露出している部分を前記第２の粒子の材料でめっきすることを特徴とするはんだ箔。 5. The solder foil according to claim 1, wherein at least a portion of the foil where the first particles are exposed is plated with a material of the second particles. Solder foil. 請求項１から５のいずれか１項に記載のはんだ箔であって、前記はんだ箔の厚さが８０μｍから１５０μｍであることを特徴とするはんだ箔。 6. The solder foil according to claim 1, wherein the solder foil has a thickness of 80 μm to 150 μm . 請求項１から６のいずれか１項に記載のはんだ箔であって、前記はんだ箔の厚さが１５０μｍから２５０μｍであることを特徴とするはんだ箔。 The solder foil according to any one of claims 1 to 6, wherein the solder foil has a thickness of 150 to 250 µm . 請求項１から７のいずれか１項に記載のはんだ箔であって、プラスチック粒子を有することを特徴とするはんだ箔。 The solder foil according to any one of claims 1 to 7, comprising plastic particles . 請求項１から７のいずれか１項に記載のはんだ箔であって、前記第１の粒子よりも熱膨張係数が小さい材料の第３の粒子を有することを特徴とするはんだ箔。 The solder foil according to any one of claims 1 to 7, wherein the solder foil has third particles made of a material having a smaller thermal expansion coefficient than the first particles . 請求項９に記載のはんだ箔であって、前記第１の粒子よりも熱膨張係数が小さい材料の第３の粒子はインバー系、シリカ、アルミナ、 AlN 、 SiC の粒子であることを特徴とするはんだ箔。 10. The solder foil according to claim 9, wherein the third particles made of a material having a smaller thermal expansion coefficient than the first particles are Invar, silica, alumina, AlN , and SiC particles. Solder foil. 請求項１に記載のはんだ箔であって、圧延率が１５％から２０％であることを特徴とするはんだ箔。 The solder foil according to claim 1, wherein the rolling rate is 15% to 20% . 前記 Cu 、 Ag 、 Au または Al の第１の粒子に代えて、 Cu 、 Ag 、 Au または Al の金属繊維を混入したはんだ材料から形成したことを特徴とする請求項１に記載のはんだ箔。 The Cu, Ag, instead of the first particles of Au or Al, Cu, Ag, solder foil according to claim 1, characterized in that formed from the solder material obtained by mixing metal fibers of Au or Al. 前記 Cu 、 Ag 、 Au または Al の第１の粒子に代えて、 Zn − Al 系合金、または Au − Sn 系合金の粒子を混入したはんだ材料から形成したことを特徴とする請求項１に記載のはんだ箔。 2. The soldering material according to claim 1, wherein the first particles of Cu , Ag , Au, or Al are formed of a solder material mixed with particles of a Zn — Al alloy or Au — Sn alloy. Solder foil. 前記第１の粒子に Sn 層をめっき形成した粒子を混入したはんだ材料から形成したことを特徴とする請求項１に記載のはんだ箔。 2. The solder foil according to claim 1, wherein the solder foil is formed from a solder material in which particles obtained by plating an Sn layer on the first particles are mixed .
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