JP3879647B2 - Assembly of members with different linear expansion coefficients - Google Patents

Assembly of members with different linear expansion coefficients Download PDF

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JP3879647B2
JP3879647B2 JP2002289549A JP2002289549A JP3879647B2 JP 3879647 B2 JP3879647 B2 JP 3879647B2 JP 2002289549 A JP2002289549 A JP 2002289549A JP 2002289549 A JP2002289549 A JP 2002289549A JP 3879647 B2 JP3879647 B2 JP 3879647B2
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solder
resin
metal electrode
modulus
layer
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JP2004128176A (en
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正和 山添
崇 小島
雄二 八木
昭二 橋本
靖 山田
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Toyota Motor Corp
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Description

【０００１】
【発明の属する技術分野】
本発明は、線膨張係数が相違する２以上の部材を、半田層に代表される導電性接合材層で機械的電気的に接続した接合体であり、熱的変化に抗して、部材同士を安定的に接続し続けられる接合体に関する。
【０００２】
【従来の技術】
第１部材（例えばＣｕ，Ａｌ等の金属電極）と、第１部材より線膨張係数の小さい第２部材（例えば半導体素子）を、導電性接合材層（例えば半田層）で機械的電気的に接続することによって、接合体（例えば半導体装置）を構成することが広く行われている。金属電極と半導体素子を半田層によって直接に（ボンディングワイヤ等を介することなく）接続すると、半導体素子に対する電力供給路の電気抵抗を小さくすることができ、大電流を許容するパワー系の半導体装置が実現される。
【０００３】
【発明が解決しようとする課題】
上記の半導体装置に代表される接合体は、２つの部材の線膨張係数が異なるために、温度変化によって導電性接合材層にせん断応力がかかる。例えば上記の半導体装置では、金属電極は大きく熱膨張するのに対して半導体素子はほとんど熱膨張しないために、半田層に大きなせん断応力がかかる。
上記の接合体では、導電性接合材層の周辺領域において、特に大きなせん断応力がかかる。導電性接合材層の内側領域では、熱膨張に起因する第１部材と第２部材の相対的変位量が相対的に小さいのに対し、周辺領域にいくほど熱膨張に起因する相対的変位量が累積されて相対的に大きくなるからである。これにより、導電性接合材層の周辺領域にクラックが生じやすく、それが原因となって導電性接合材層全体が劣化するという問題がある。
【０００４】
上記の問題は、熱膨張に起因する第１部材と第２部材の相対的変位量が相対的に小さい内側領域にのみ導電性接合材層を設け、変位量が相対的に大きい周辺領域には導電性接合材層を設けないようにすることによって対処できるように思われる。導電性接合材層の面積を小さくしても、電力供給路の電気抵抗を十分に小さくできることが多い。
しかしながら導電性接合材層の面積を小さくすると、機械的接合強度が低下することが多い。また第１部材と第２部材の重複領域のうち、内側にのみ導電性接合材層を設け、周辺部には導電性接合材層を設けないようにすることが難しい。例えば、第１部材と第２部材の重複領域のうちの内側領域で伸びる半田箔を介在させた状態で第１部材と第２部材の積層体をリフロー炉に入れると、溶融した半田が周辺領域に流れ、大きなせん断応力を受ける周辺領域まで導電性接合材層がはみ出てしまう。
【０００５】
本発明は、上述した実情に鑑みてなされたものであり、第１部材や第２部材の機械的接合強度を維持しつつ導電性接合材層の劣化を防止することができる技術を提供する。
【０００６】
【課題を解決するための手段と作用と効果】
上記課題を解決するために創作された請求項１に記載の接合体は、第１部材と、第１部材よりも線膨張係数が小さい第２部材と、第１部材と第２部材の間にあって第１部材と第２部材を機械的電気的に接続している導電性接合材層とを有する接合体である。ここで、導電性接合材層の周辺領域には、その導電性接合材よりヤング率の小さい低ヤング率部材が埋め込まれており、導電性接合材層の内側領域には、前記した低ヤング率部材が埋め込まれていないことを特徴とする。
周辺領域にある低ヤング率部材が埋め込まれた導電性接合材層と、内側領域にある低ヤング率部材が埋め込まれていない導電性接合材層は、一体となって形成されていても良いし、分離して形成されていても良い。
熱膨張に起因して第１部材と第２部材が相対的に大きく変位する導電性接合材層の周辺領域には、ヤング率の小さい部材が埋め込まれているために、導電性接合材自体にかかるせん断応力を抑制できる。周辺領域にクラックが生じやすいという問題は解消する。導電性接合材層の内側領域には低ヤング率部材が埋め込まれていないために、必要とされる電気伝導度を確保できる。導電性接合材層は、周辺領域においても第１部材と第２部材を機械的に接続しており、機械的接続強度を確保することができる。また、導電性接合材層の広がる範囲を内側領域に限定する必要がなく、接続作業を容易に実施することができる。
【０００７】
周辺領域に埋め込む部材は、導電性接合材のヤング率の２０％以下のヤング率を持つ低ヤング率部材であることが好ましい。
周辺領域に埋め込む部材のヤング率が、導電性接合材のヤング率の２０％以下であると、導電性接合材層の周辺領域に存在する導電性接合材自体には、小さなせん断応力しかかからない。導電性接合材層の周辺領域からクラックが発生して劣化する現象を効果的に防止することができる。
【０００８】
低ヤング率部材が、導電性接合材層の幅の５０％以上の範囲に亘って埋め込まれていることが好ましい。即ち、第１部材と導電性接合材層と第２部材を断面視したときの導電性接合材層を、右端から２５％の右端部領域と、左端から２５％の左端部領域と、両者間に位置する５０％の中央領域に区分したときに、低ヤング率部材が埋め込まれている周辺領域は、右端部領域と左端部領域を超えて中央領域にまで進出し、低ヤング率部材が埋め込まれていない内側領域は、中央領域よりも小さいことが好ましい。
必要な電気伝導度を確保できる範囲で低ヤング率部材が埋め込まれていない内側領域の広がりを小さくすると、周辺領域の導電性接合材にかかるせん断応力を小さくできる。導電性接合材層の周辺領域からクラックが発生して劣化する現象を効果的に防止することができる。
【０００９】
第１部材が金属電極であり、第２部材が半導体素子であり、導電性接合材層が半田層であり、積層体によって半導体装置を構成するときに、本発明は良く機能する。
【００１０】
【発明の実施の形態】
上記各請求項に記載の発明は、下記の形態で好適に実施することができる。
（形態１）各請求項に記載の接合体において、第１部材が長方形状を有する場合は導電性接合材層も長方形状に形成する。この場合、低ヤング率部材は中央に開孔を有する長方形状（額縁状）の樹脂枠を採用する。
（形態２）各請求項に記載の接合体において、複数の第２部材に対して１つの第１部材を共通的に用いるようにしても良い。
【００１１】
【実施例】
（第１実施例） 図面を参照して、本発明に係る接合体の一実施例を説明する。図１は、接合体（この場合には半導体装置）１０の縦断面図である。半導体装置１０は、放熱板２０と第１半田層２２と絶縁基板２４と第２半田層２８と半導体素子３２と第３半田層３８と金属電極４０等から構成されている。放熱板２０は、例えばＣｕやＡｌ等で構成されている。絶縁基板２４は、例えばＳｉＣセラミックスやＡｌＮセラミックスやＡｌ２Ｏ３セラミックス等で構成されている。絶縁基板２４の上面には基板側電極２６が設けられている。半導体素子３２は、大電力の通電をオンオフするパワー素子系であり、ＭＯＳまたはＩＧＢＴ等である。半導体素子３２の下面にはコレクタ電極３０が形成されており、上面にはエミッタ電極３４が形成されている。金属電極４０は、例えばＣｕやＡｇやＺｎ等で構成されている。
第１半田層２２によって、放熱板２０と絶縁基板２４が接続されている。第２半田層２８によって、絶縁基板２４の基板側電極２６と半導体素子３２のコレクタ電極３０が、機械的にも電気的にも接続されている。第３半田層３８によって、半導体素子３２のエミッタ電極３４と金属電極４０が、機械的にも電気的にも接続されている。
【００１２】
第３半田層３８の周辺領域３８ｂには、樹脂３６が埋め込まれている。図３に示すように、樹脂３６の外形は長方形（第１部材である金属電極４０と、第２部材である半導体素子３２の平面形にほぼ等しい）であり、中央に長方形の開孔３６ａが形成されている。全体としては枠状である。図１に示すように、樹脂３６の中心開孔３６ａには、半田材が充填されている。第３半田層３８の内側領域３８ａは、半田材のみで構成されている（樹脂が埋め込まれていない）。以下では、第３半田層３８の内側領域３８ａを内側半田層３８ａと記載する場合がある。内側半田層３８ａのみで必要とされる通電量を確保できる大きさに設定されている。
樹脂３６の表面は半田層３８ｂで被覆されている。樹脂３６を被覆している半田層３８ｂは、通電のためというよりも、樹脂３６と金属電極４０、樹脂３６と半導体素子３２、樹脂３６と内側半田層３８ａを機械的に接続する役割を果たしている。
樹脂３６の開孔３６ａに第３半田層３８の内側半田層３８ａが形成される。本実施例では、開孔３６ａの横方向の長さは、樹脂３６の横方向の長さの半分に設定されている。また開孔３６ａの縦方向の長さは、樹脂３６の縦方向の長さの半分に設定されている。なお開孔３６ａの横方向や縦方向の長さは、樹脂３６の横方向や縦方向の長さの半分以下としても良い。
【００１３】
樹脂３６の厚みは５０〜５００μｍに設定されている。この厚さは、第３半田層３８の厚さによって変更される。樹脂３６の表面にはＮｉ膜（Ｃｕ膜等でも良い）がコーティングされている。ＮｉやＣｕは半田が付着し易い（樹脂には半田が付着し難い）。樹脂３６にＮｉ膜がコーティングされているために、第３半田層３８によって、金属電極４０と半導体素子３２と内側半田層３８ａに樹脂３６を機械的に強固に接続することができる。
本実施例では、樹脂３６のヤング率（弾性係数）が半田材のヤング率の２０％以下に設定されている。具体的には、ヤング率が約５ＧＰａであるジビニルベンゼン架橋共重合体を用いている。半田のヤング率は約３０ＧＰａであり、その比は約１７％である。ヤング率がもっと小さな樹脂を用いることもできる。埋め込み位置を限定することによって、半田材のヤング率の２０％以上のヤング率を有する樹脂を用いることもできる。
【００１４】
上記の半導体装置１０の半導体素子３２と金属電極４０は、第３半田層３８（樹脂３６）によって次のようにして接続される。
（準備工程）
半導体素子３２と金属電極４０を用意する。樹脂３６の開孔３６ａに樹脂３６の厚さより１０〜２０μｍ厚い半田板をすっぽり嵌め込む。半導体素子３２と金属電極４０の間に、半田板が嵌め込まれた樹脂３６をセットする。半田板が樹脂３６より厚く設定されているために、この状態では樹脂３６と金属電極４０の間に隙間がある。また樹脂３６と半導体素子３２の間にも隙間がある。
（リフロー工程）
その状態でリフロー炉にいれて半田板を加熱溶融させる。その後に半田材を固化させる。半田板を樹脂３６より厚くしておいたので、半田板と樹脂３６の開口３６ａとの間に隙間があったとしてもその隙間は溶けた半田材によって埋められる。また溶けた半田材は、樹脂３６と金属電極４０の間の隙間や、樹脂３６と半導体素子３２の間の隙間に流れ込む。このリフロー工程により、周辺領域に樹脂３６が埋め込まれた半田層（第３半田層３８）ができる。
【００１５】
上記構成を有する半導体装置１０の作用と効果を説明する。
金属電極４０は線膨張係数が大きいために、半導体装置１０が昇温すると金属電極４０は大きく膨張する。これに対し、半導体素子３２は線膨張係数が小さいために、半導体装置１０が昇温してもほとんど膨張しない。図２に、半導体装置１０が昇温したときの金属電極４０と第３半田層３８と半導体素子３２の状態を極端に誇張して示す。図２に、金属電極４０が伸びたために第３半田層３８が歪んでいる様子が良く示されている。金属電極４０の中央部４０ａでは熱膨張しても半導体素子３２に対して大きく変位しないために、第３半田層３８の内側半田層３８ａはほとんど歪まない。一方、金属電極４０の周辺部４０ｂでは熱膨張が累積するために半導体素子３２に対して大きく変位する。この結果、第３半田層３８の周辺領域３８ｂは歪む。ただし、本実施例の半導体装置１０では、第３半田層３８の周辺領域３８ｂにヤング率の小さい樹脂３６が埋め込まれているために、金属電極４０の熱膨張に追従して樹脂３６が大きく歪む。樹脂３６を被覆している薄い半田層には、純粋な引張り応力と圧縮応力がかかることがあっても強いせん断応力はかからない。
−４０℃から＋１０５℃の冷熱サイクル試験を半導体装置１０に実施したところ、３０００サイクル繰り返しても第３半田層３８にクラックは生じなかった。
【００１６】
（第２実施例）図４に、本実施例の半導体装置２００の断面図が示されている。図４では、第１実施例と同様の部分には同じ符号を付している。
絶縁基板２４の上面には、２つの基板側電極２６，２６が設けられている。右側の基板側電極２６の上面には、第２半田層５０によって半導体素子５４のコレクタ電極５２が機械的にも電気的にも接続されている。半導体素子５４の上面のエミッタ電極５６には第３半田層５８によって金属電極９０が機械的にも電気的にも接続されている。第３半田層５８の周辺領域には、第１実施例と同様に樹脂６０が埋めこまれている。左側の基板側電極２６の上面には、第２半田層７０によって半導体素子７４のコレクタ電極７２が機械的にも電気的にも接続されている。半導体素子７４の上面のエミッタ電極７６には、第３半田層７８によって金属電極９０が機械的にも電気的にも接続されている。第３半田層７８の周辺領域には、第１実施例と同様に樹脂８０が埋めこまれている。
左右の半導体素子５４，７４に接続される金属電極９０は共通の一枚のプレートである。
【００１７】
上記の半導体装置２００が昇温すると共通の金属電極９０が伸びる。金属電極９０はしなやかであり、半導体素子５４，７４に接していない部分（宙に浮いている中央部９０ａ）ではしなやかに湾曲する。このために、金属電極９０の膨張に起因する金属電極９０と半導体素子５４、または、金属電極９０と半導体素子７４の相対変位を考慮する場合には、金属電極９０が二つの半導体素子５４，７４に共通に利用されていることを考慮する必要がなく、金属電極９０と半導体素子５４、または、金属電極９０と半導体素子７４の相対変位を独立に考慮すればよい（宙に浮いている中央部９０ａで金属電極９０がしなやかに湾曲するために、左右の領域９０ｂが独立しているものとできる）。
このため金属電極９０が熱膨張したときには、第３半田層５８，７８のそれぞれの周辺領域で、金属電極９０が半導体素子５４，７４に対して大きく相対的に変位する。大きく変位する部分には、ヤング率が低くて変形しやすい樹脂６０，８０が設けられているために、強いせん断応力が半田材にかかることはない。
−４０℃から＋１０５℃の冷熱サイクル試験を半導体装置２００に実施したところ、第３半田層５８，７８の耐性が従来より向上する結果が得られた。
なお共通金属電極９０が厚く、宙に浮いた部分で変形して膨張の影響を吸収できない場合には、左右の第３半田層５８，７８が共通金属電極９０によって力学的に連続しているものとみなすことができる。この場合は、図５に示すように、力学的には連続しているものとみなした第３半田層５８，７８の周辺領域に樹脂枠６０，８０を埋め込んでもよい。この場合、樹脂枠６０，８０の一つ一つは、平面視したときにコ字状を呈している。第３半田層５８，７８の周辺領域のうち、内側で向かい合う辺に沿った周辺領域には、樹脂が埋め込まれないで半田材が充填される。
このときにも、金属電極９０と半導体素子５４，７４の相対変位は、共通金属電極９０によって力学的に一体化されている第３半田層５８、７８の周辺領域で大きい。この相対変位量が大きい領域に樹脂枠６０，８０が埋め込まれているために、第３半田層５８，７８の周辺領域でクラックが発生して劣化することを防止できる。
【００１８】
（第３実施例）図６は、本実施例に係る半導体装置１００の断面図である。半導体装置１００において、放熱板１２０、第１半田層１２２、絶縁基板１２４、第２半田層１５０，１７０、半導体素子１５４，１７４、金属板１９０は第２実施例と同様である。金属板１９０は、しなやかであり、半導体素子１５４，１７４に接していない部分（宙に浮いている中央部１９０ａ）ではしなやかに湾曲する。宙に浮いている中央部１９０ａで金属電極１９０がしなやかに湾曲するために、左右の領域１９０ｂが独立しているものとみなせる。半導体装置１００は、第３半田層１５８，１７８の構成が第２実施例と異なる。次に、半導体素子１５４，１７４と金属電極１９０の接続方法を説明しながら、本実施例の第３半田層１５８，１７８の構成を説明する。
【００１９】
（準備工程）
半導体素子１５４，１７４と金属電極１９０を用意する。また四角形の半田材を２つ用意するとともに球形の半田材を複数用意する。この球形の半田材の内部には、上記した各実施例で用いた樹脂（ジビニルベンゼン架橋共重合体）が埋め込まれている。ただし、四角形の半田材の内部には樹脂が埋め込まれていない。
半導体素子１５４と金属電極１９０との間に四角形の半田材をセットするとともに、その四角形の半田材の周辺に球形の半田材を複数セットする。このとき、四角形の半田材と球形の半田材は接触するように配置し、球形の半田材同士も接触するように配置する。同様に、半導体素子１７４と金属電極１９０との間に四角形の半田材をセットするとともに、その四角形の半田材の周辺に球形の半田材を複数セットする。
（リフロー工程）
この状態でリフロー炉にいれて半田材を加熱溶融させる。その後に半田材を固化させる。これにより、球形の半田材と四角形の半田材は、金属電極１９０や半導体素子１５４，１７４と接合する。また球形の半田材は、隣合う球形の半田材や四角形の半田材と接合する。このリフロー工程を実施することによって第３半田層１５８，１７８が形成される。即ち、内側領域は半田材のみで形成されており、周辺領域は樹脂が埋め込まれた半田材１６０，１８０で形成されている第３半田層１５８，１７８が形成される。第３半田層１５８，１７８によって、金属電極１９０と半導体素子１５４，１７４が機械的にも電気的に接続される。
金属電極１９０と半導体素子１５４，１７４が接続された状態では、リフローによって溶融した球形半田材の球形が維持されていない場合もある。図６では、金属電極１９０と半導体素子１５４，１７４を球形半田材によって接続したことを説明するために、周辺領域１６０，１８０を複数の円で図示している。
【００２０】
金属電極１９０と半導体素子１５４，１７４の熱膨張による相対的変位が大きいために、第３半田層１５８，１７８の周辺領域１６０，１８０は大きく歪む。但し、周辺領域１６０，１８０には低ヤング率樹脂が埋め込まれているために、金属電極１９０の熱膨張に追従して樹脂が大きく歪む。樹脂を被覆している半田層には、純粋な引張り応力と圧縮応力がかかることがあっても強いせん断応力はかからない。このため、第３半田層１５８，１７８の周辺領域１６０，１８０にクラックが生じることを防止できる。−４０℃から＋１０５℃の冷熱サイクル試験を半導体装置１００に実施したところ、第３半田層１５８，１７８の耐性が従来より向上する結果が得られた。
【００２１】
以上、本発明の具体例を詳細に説明したが、これらは例示にすぎず、特許請求の範囲を限定するものではない。特許請求の範囲に記載の技術には、以上に例示した具体例を様々に変形、変更したものが含まれる。
上記実施例では、半導体装置を例にしている。しかしながら本発明の技術は、半導体装置に限定されるものではない。本発明の技術は、線膨張係数の異なる２つの部材を接合して構成される接合体一般に適用可能である。また、例えば上記の第１半田層２２や第２半田層２８の周辺領域に樹脂を埋め込むことによって、第１半田層２２や第２半田層２８の耐性を向上させることもできる。
【００２２】
また機械的接合強度が低くてもよい場合には、第１実施例の樹脂枠を半田層で覆う必要はない。即ち、樹脂枠を金属電極や半導体素子に直接接続しても良い。この場合、樹脂枠はスペーサとして機能する。この様子を図７に示している。図７では、第１実施例と同じ構成の部分は同一の符号を付している。この半導体装置２５０は、金属電極４０の周辺領域４０ｂと半導体素子３２の間にスペーサ２４０が配置されている。スペーサ２４０は、第１実施例の樹脂３６と同じ樹脂で構成されており、その形状は額縁状である。スペーサ２４０は、その上面が金属電極４０に固定されている。その下面は、半導体素子３２の素子側電極３４に固定されている。またスペーサ２４０の内側側面にはＮｉ膜がコーティングされている。そして、スペーサ２４０の内側側面が第３半田層３８に固定されている。スペーサ２４０を用いて第３半田層３８の範囲を内側領域に限定することによって、熱変化に強い接合体が実現されている。
【００２３】
また、本明細書または図面に説明した技術要素は、単独であるいは各種の組み合わせによって技術的有用性を発揮するものであり、出願時請求項記載の組み合わせに限定されるものではない。また、本明細書または図面に例示した技術は複数目的を同時に達成するものであり、そのうちの一つの目的を達成すること自体で技術的有用性を持つものである。
【図面の簡単な説明】
【図１】 第１実施例の半導体装置の断面図を示す。
【図２】 金属電極が熱膨張した様子を示す。
【図３】 樹脂の平面図を示す。
【図４】 第２実施例の半導体装置の断面図を示す。
【図５】 第２実施例の半導体装置の変形例を示す。
【図６】 第３実施例の半導体装置の断面図を示す。
【図７】 本発明の変形例である半導体装置の断面図を示す。
【符号の説明】
１０・・半導体装置
２０・・放熱板
２２・・第１半田層
２４・・絶縁基板
２６・・基板側電極
２８・・第２半田層
３０・・コレクタ電極
３２・・半導体素子
３４・・エミッタ電極
３６・・樹脂
３８・・第３半田層
３８ａ・・第３半田層の内側領域
３８ｂ・・第３半田層の周辺領域
４０・・金属電極
４０ａ・・金属電極の内側領域
４０ｂ・・金属電極の周辺領域[0001]
BACKGROUND OF THE INVENTION
The present invention is a joined body in which two or more members having different linear expansion coefficients are mechanically and electrically connected by a conductive bonding material layer typified by a solder layer. It is related with the conjugate | zygote which can continue connecting stably.
[0002]
[Prior art]
A first member (for example, a metal electrode such as Cu or Al) and a second member (for example, a semiconductor element) having a smaller linear expansion coefficient than the first member are mechanically and electrically connected by a conductive bonding material layer (for example, a solder layer). It is widely performed to form a joined body (for example, a semiconductor device) by connecting. When the metal electrode and the semiconductor element are directly connected by a solder layer (without a bonding wire or the like), the electric resistance of the power supply path to the semiconductor element can be reduced, and a power semiconductor device that allows a large current is provided. Realized.
[0003]
[Problems to be solved by the invention]
In the joined body typified by the above semiconductor device, since the linear expansion coefficients of the two members are different, shear stress is applied to the conductive joining material layer due to temperature change. For example, in the above semiconductor device, the metal electrode expands greatly, while the semiconductor element hardly expands. Therefore, a large shear stress is applied to the solder layer.
In the above joined body, particularly large shear stress is applied in the peripheral region of the conductive joining material layer. In the inner region of the conductive bonding material layer, the relative displacement between the first member and the second member due to thermal expansion is relatively small, whereas the relative displacement due to thermal expansion toward the peripheral region. This is because is accumulated and becomes relatively large. Accordingly, there is a problem that cracks are likely to occur in the peripheral region of the conductive bonding material layer, which causes the entire conductive bonding material layer to deteriorate.
[0004]
The above problem is that the conductive bonding material layer is provided only in the inner region where the relative displacement amount of the first member and the second member due to thermal expansion is relatively small, and in the peripheral region where the displacement amount is relatively large. It seems that this can be dealt with by not providing the conductive bonding material layer. In many cases, even if the area of the conductive bonding material layer is reduced, the electric resistance of the power supply path can be sufficiently reduced.
However, when the area of the conductive bonding material layer is reduced, the mechanical bonding strength often decreases. Further, it is difficult to provide the conductive bonding material layer only on the inner side of the overlapping region of the first member and the second member and not to provide the conductive bonding material layer in the peripheral portion. For example, when the laminated body of the first member and the second member is put in a reflow furnace with a solder foil extending in the inner region of the overlapping region of the first member and the second member interposed, the molten solder is placed in the peripheral region. Thus, the conductive bonding material layer protrudes to the peripheral region that receives a large shear stress.
[0005]
This invention is made | formed in view of the situation mentioned above, and provides the technique which can prevent deterioration of a conductive joining material layer, maintaining the mechanical joining strength of a 1st member or a 2nd member.
[0006]
[Means, actions and effects for solving problems]
The joined body according to claim 1, which has been created to solve the above problem, is between the first member, the second member having a smaller linear expansion coefficient than the first member, and the first member and the second member. A joined body having a conductive joining material layer that mechanically and electrically connects the first member and the second member. Here, a low Young's modulus member having a Young's modulus smaller than that of the conductive bonding material is embedded in the peripheral region of the conductive bonding material layer, and the low Young's modulus described above is embedded in the inner region of the conductive bonding material layer. The member is not embedded.
The conductive bonding material layer embedded with the low Young's modulus member in the peripheral region and the conductive bonding material layer without the low Young's modulus member embedded in the inner region may be integrally formed. , May be formed separately.
A member having a small Young's modulus is embedded in the peripheral region of the conductive bonding material layer where the first member and the second member are relatively largely displaced due to thermal expansion. Such shear stress can be suppressed. The problem that cracks are likely to occur in the peripheral area is solved. Since the low Young's modulus member is not embedded in the inner region of the conductive bonding material layer, the required electrical conductivity can be ensured. The conductive bonding material layer mechanically connects the first member and the second member also in the peripheral region, and can ensure mechanical connection strength. Moreover, it is not necessary to limit the range in which the conductive bonding material layer extends to the inner region, and the connection work can be easily performed.
[0007]
The member embedded in the peripheral region is preferably a low Young's modulus member having a Young's modulus of 20% or less of the Young's modulus of the conductive bonding material.
When the Young's modulus of the member embedded in the peripheral region is 20% or less of the Young's modulus of the conductive bonding material, the conductive bonding material itself existing in the peripheral region of the conductive bonding material layer is subjected to only a small shear stress. It is possible to effectively prevent a phenomenon in which cracks are generated from the peripheral region of the conductive bonding material layer and deteriorate.
[0008]
It is preferable that the low Young's modulus member is embedded over a range of 50% or more of the width of the conductive bonding material layer. That is, when the first member, the conductive bonding material layer, and the second member are viewed in cross-section, the conductive bonding material layer is divided into a right end region of 25% from the right end and a left end region of 25% from the left end. When the area is divided into 50% of the central region, the peripheral region where the low Young's modulus member is embedded extends beyond the right end region and the left end region to the central region, and the low Young modulus member is embedded. Preferably, the inner region that is not smaller is smaller than the central region.
If the spread of the inner region where the low Young's modulus member is not embedded is reduced within a range in which the necessary electrical conductivity can be ensured, the shear stress applied to the conductive bonding material in the peripheral region can be reduced. It is possible to effectively prevent a phenomenon in which cracks are generated from the peripheral region of the conductive bonding material layer and deteriorate.
[0009]
The present invention functions well when the first member is a metal electrode, the second member is a semiconductor element, the conductive bonding material layer is a solder layer, and a semiconductor device is constituted by a laminate.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The invention described in the above claims can be suitably implemented in the following forms.
(Mode 1) In the joined body according to each claim, when the first member has a rectangular shape, the conductive bonding material layer is also formed in a rectangular shape. In this case, the low Young's modulus member employs a rectangular (frame-shaped) resin frame having an opening in the center.
(Mode 2) In the joined body described in each claim, one first member may be commonly used for a plurality of second members.
[0011]
【Example】
(First Example) An example of a joined body according to the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a joined body (in this case, a semiconductor device) 10. The semiconductor device 10 includes a heat sink 20, a first solder layer 22, an insulating substrate 24, a second solder layer 28, a semiconductor element 32, a third solder layer 38, a metal electrode 40, and the like. The heat sink 20 is made of, for example, Cu or Al. The insulating substrate 24 is made of, for example, SiC ceramics, AlN ceramics, Al 2 O 3 ceramics, or the like. A substrate-side electrode 26 is provided on the upper surface of the insulating substrate 24. The semiconductor element 32 is a power element system that turns on and off the energization of a large power, and is a MOS or IGBT. A collector electrode 30 is formed on the lower surface of the semiconductor element 32, and an emitter electrode 34 is formed on the upper surface. The metal electrode 40 is made of, for example, Cu, Ag, Zn, or the like.
The heat sink 20 and the insulating substrate 24 are connected by the first solder layer 22. By the second solder layer 28, the substrate-side electrode 26 of the insulating substrate 24 and the collector electrode 30 of the semiconductor element 32 are mechanically and electrically connected. The third solder layer 38 connects the emitter electrode 34 of the semiconductor element 32 and the metal electrode 40 both mechanically and electrically.
[0012]
Resin 36 is embedded in the peripheral region 38 b of the third solder layer 38. As shown in FIG. 3, the outer shape of the resin 36 is rectangular (substantially equal to the planar shape of the metal electrode 40 as the first member and the semiconductor element 32 as the second member), and a rectangular opening 36a is formed at the center. Is formed. The overall shape is a frame. As shown in FIG. 1, the center hole 36a of the resin 36 is filled with a solder material. The inner region 38a of the third solder layer 38 is composed only of a solder material (no resin is embedded). Hereinafter, the inner region 38a of the third solder layer 38 may be referred to as an inner solder layer 38a. It is set to a size that can secure the energization amount required only by the inner solder layer 38a.
The surface of the resin 36 is covered with a solder layer 38b. The solder layer 38b covering the resin 36 serves to mechanically connect the resin 36 and the metal electrode 40, the resin 36 and the semiconductor element 32, and the resin 36 and the inner solder layer 38a rather than for energization. .
An inner solder layer 38 a of the third solder layer 38 is formed in the opening 36 a of the resin 36. In this embodiment, the lateral length of the opening 36 a is set to half of the lateral length of the resin 36. Further, the length of the opening 36 a in the vertical direction is set to half the length of the resin 36 in the vertical direction. The length of the opening 36a in the horizontal direction or the vertical direction may be half or less than the length of the resin 36 in the horizontal direction or the vertical direction.
[0013]
The thickness of the resin 36 is set to 50 to 500 μm. This thickness is changed depending on the thickness of the third solder layer 38. The surface of the resin 36 is coated with a Ni film (or a Cu film or the like). Ni and Cu are likely to adhere to solder (solder is less likely to adhere to resin). Since the Ni film is coated on the resin 36, the resin 36 can be mechanically and firmly connected to the metal electrode 40, the semiconductor element 32, and the inner solder layer 38 a by the third solder layer 38.
In this embodiment, the Young's modulus (elastic coefficient) of the resin 36 is set to 20% or less of the Young's modulus of the solder material. Specifically, a divinylbenzene crosslinked copolymer having a Young's modulus of about 5 GPa is used. The Young's modulus of the solder is about 30 GPa, and the ratio is about 17%. A resin having a smaller Young's modulus can also be used. By limiting the embedding position, a resin having a Young's modulus of 20% or more of the Young's modulus of the solder material can be used.
[0014]
The semiconductor element 32 and the metal electrode 40 of the semiconductor device 10 are connected by the third solder layer 38 (resin 36) as follows.
(Preparation process)
A semiconductor element 32 and a metal electrode 40 are prepared. A solder plate 10 to 20 μm thicker than the thickness of the resin 36 is completely fitted into the opening 36 a of the resin 36. A resin 36 into which a solder plate is fitted is set between the semiconductor element 32 and the metal electrode 40. Since the solder plate is set thicker than the resin 36, there is a gap between the resin 36 and the metal electrode 40 in this state. There is also a gap between the resin 36 and the semiconductor element 32.
(Reflow process)
In that state, the solder plate is heated and melted in a reflow furnace. Thereafter, the solder material is solidified. Since the solder plate is thicker than the resin 36, even if there is a gap between the solder plate and the opening 36 a of the resin 36, the gap is filled with the molten solder material. Also, the melted solder material flows into the gap between the resin 36 and the metal electrode 40 and the gap between the resin 36 and the semiconductor element 32. By this reflow process, a solder layer (third solder layer 38) in which the resin 36 is embedded in the peripheral region is formed.
[0015]
The operation and effect of the semiconductor device 10 having the above configuration will be described.
Since the metal electrode 40 has a large coefficient of linear expansion, the metal electrode 40 expands greatly when the temperature of the semiconductor device 10 rises. On the other hand, since the semiconductor element 32 has a small coefficient of linear expansion, it hardly expands even when the temperature of the semiconductor device 10 rises. FIG. 2 shows the state of the metal electrode 40, the third solder layer 38, and the semiconductor element 32 when the temperature of the semiconductor device 10 is increased. FIG. 2 clearly shows that the third solder layer 38 is distorted because the metal electrode 40 is extended. In the central portion 40a of the metal electrode 40, the inner solder layer 38a of the third solder layer 38 is hardly distorted because it is not greatly displaced with respect to the semiconductor element 32 even when thermally expanded. On the other hand, the peripheral portion 40b of the metal electrode 40 is largely displaced with respect to the semiconductor element 32 due to the accumulation of thermal expansion. As a result, the peripheral region 38b of the third solder layer 38 is distorted. However, in the semiconductor device 10 of the present embodiment, since the resin 36 having a low Young's modulus is embedded in the peripheral region 38b of the third solder layer 38, the resin 36 is greatly distorted following the thermal expansion of the metal electrode 40. . Even if pure tensile stress and compressive stress are applied to the thin solder layer covering the resin 36, a strong shear stress is not applied.
When the semiconductor device 10 was subjected to a thermal cycle test of −40 ° C. to + 105 ° C., no cracks were generated in the third solder layer 38 even after repeating 3000 cycles.
[0016]
(Second Embodiment) FIG. 4 is a sectional view of a semiconductor device 200 according to this embodiment. In FIG. 4, the same parts as those in the first embodiment are denoted by the same reference numerals.
Two substrate-side electrodes 26 and 26 are provided on the upper surface of the insulating substrate 24. The collector electrode 52 of the semiconductor element 54 is mechanically and electrically connected to the upper surface of the right substrate side electrode 26 by the second solder layer 50. A metal electrode 90 is mechanically and electrically connected to the emitter electrode 56 on the upper surface of the semiconductor element 54 by a third solder layer 58. The resin 60 is embedded in the peripheral region of the third solder layer 58 as in the first embodiment. The collector electrode 72 of the semiconductor element 74 is mechanically and electrically connected to the upper surface of the left substrate-side electrode 26 by the second solder layer 70. A metal electrode 90 is mechanically and electrically connected to the emitter electrode 76 on the upper surface of the semiconductor element 74 by a third solder layer 78. Resin 80 is buried in the peripheral region of the third solder layer 78 as in the first embodiment.
The metal electrode 90 connected to the left and right semiconductor elements 54 and 74 is a common plate.
[0017]
When the temperature of the semiconductor device 200 increases, the common metal electrode 90 extends. The metal electrode 90 is supple and bends flexibly at a portion not in contact with the semiconductor elements 54 and 74 (a central portion 90a floating in the air). Therefore, when the relative displacement between the metal electrode 90 and the semiconductor element 54 or the metal electrode 90 and the semiconductor element 74 due to the expansion of the metal electrode 90 is taken into consideration, the metal electrode 90 has two semiconductor elements 54 and 74. The relative displacement between the metal electrode 90 and the semiconductor element 54 or between the metal electrode 90 and the semiconductor element 74 may be considered independently (the central part floating in the air). Since the metal electrode 90 bends smoothly at 90a, the left and right regions 90b can be independent.
Therefore, when the metal electrode 90 is thermally expanded, the metal electrode 90 is largely displaced relative to the semiconductor elements 54 and 74 in the peripheral regions of the third solder layers 58 and 78. Since the resin 60 and 80 that have a low Young's modulus and are easily deformed are provided in the portion that is greatly displaced, strong shear stress is not applied to the solder material.
When a thermal cycle test of −40 ° C. to + 105 ° C. was performed on the semiconductor device 200, the result that the resistance of the third solder layers 58 and 78 was improved as compared with the conventional one was obtained.
In the case where the common metal electrode 90 is thick and cannot be absorbed by the deformation caused by the floating part in the air, the left and right third solder layers 58 and 78 are mechanically continuous by the common metal electrode 90. Can be considered. In this case, as shown in FIG. 5, resin frames 60 and 80 may be embedded in the peripheral area of the third solder layers 58 and 78 that are considered to be mechanically continuous. In this case, each of the resin frames 60 and 80 has a U-shape when viewed in plan. Of the peripheral regions of the third solder layers 58 and 78, the peripheral region along the side facing inside is filled with the solder material without being embedded in the resin.
Also at this time, the relative displacement between the metal electrode 90 and the semiconductor elements 54 and 74 is large in the peripheral region of the third solder layers 58 and 78 that are mechanically integrated by the common metal electrode 90. Since the resin frames 60 and 80 are embedded in the region where the relative displacement amount is large, it is possible to prevent the peripheral regions of the third solder layers 58 and 78 from being cracked and deteriorated.
[0018]
(Third Embodiment) FIG. 6 is a sectional view of a semiconductor device 100 according to this embodiment. In the semiconductor device 100, the heat sink 120, the first solder layer 122, the insulating substrate 124, the second solder layers 150 and 170, the semiconductor elements 154 and 174, and the metal plate 190 are the same as in the second embodiment. The metal plate 190 is supple and bends flexibly at the portions not in contact with the semiconductor elements 154 and 174 (the central portion 190a floating in the air). Since the metal electrode 190 is bent flexibly at the central portion 190a floating in the air, the left and right regions 190b can be regarded as independent. The semiconductor device 100 differs from the second embodiment in the configuration of the third solder layers 158 and 178. Next, the configuration of the third solder layers 158 and 178 of this embodiment will be described while explaining a method of connecting the semiconductor elements 154 and 174 and the metal electrode 190.
[0019]
(Preparation process)
Semiconductor elements 154 and 174 and a metal electrode 190 are prepared. Two rectangular solder materials are prepared and a plurality of spherical solder materials are prepared. The resin (divinylbenzene cross-linked copolymer) used in each of the above embodiments is embedded in the spherical solder material. However, resin is not embedded in the rectangular solder material.
A square solder material is set between the semiconductor element 154 and the metal electrode 190, and a plurality of spherical solder materials are set around the square solder material. At this time, the rectangular solder material and the spherical solder material are arranged so as to contact each other, and the spherical solder materials are arranged so as to contact each other. Similarly, a square solder material is set between the semiconductor element 174 and the metal electrode 190, and a plurality of spherical solder materials are set around the square solder material.
(Reflow process)
In this state, the solder material is heated and melted in a reflow furnace. Thereafter, the solder material is solidified. Thereby, the spherical solder material and the square solder material are joined to the metal electrode 190 and the semiconductor elements 154 and 174. In addition, the spherical solder material is joined to the adjacent spherical solder material or square solder material. By performing this reflow process, third solder layers 158 and 178 are formed. That is, the inner region is formed of only a solder material, and the peripheral region is formed with third solder layers 158 and 178 formed of solder materials 160 and 180 embedded with resin. The metal electrodes 190 and the semiconductor elements 154 and 174 are mechanically and electrically connected by the third solder layers 158 and 178.
In a state where the metal electrode 190 and the semiconductor elements 154 and 174 are connected, the spherical shape of the spherical solder material melted by reflow may not be maintained. In FIG. 6, in order to explain that the metal electrode 190 and the semiconductor elements 154 and 174 are connected by a spherical solder material, the peripheral regions 160 and 180 are illustrated by a plurality of circles.
[0020]
Since the relative displacement due to thermal expansion between the metal electrode 190 and the semiconductor elements 154 and 174 is large, the peripheral areas 160 and 180 of the third solder layers 158 and 178 are greatly distorted. However, since the low Young's modulus resin is embedded in the peripheral regions 160 and 180, the resin is greatly distorted following the thermal expansion of the metal electrode 190. Even if a pure tensile stress and a compressive stress are applied to the solder layer covering the resin, a strong shear stress is not applied. For this reason, it is possible to prevent cracks from occurring in the peripheral areas 160 and 180 of the third solder layers 158 and 178. When a thermal cycle test of −40 ° C. to + 105 ° C. was performed on the semiconductor device 100, the result that the durability of the third solder layers 158 and 178 was improved as compared with the prior art was obtained.
[0021]
Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
In the above embodiment, a semiconductor device is taken as an example. However, the technology of the present invention is not limited to semiconductor devices. The technology of the present invention can be applied to general joined bodies formed by joining two members having different linear expansion coefficients. In addition, for example, the resistance of the first solder layer 22 and the second solder layer 28 can be improved by embedding a resin in the peripheral region of the first solder layer 22 and the second solder layer 28.
[0022]
If the mechanical bonding strength may be low, it is not necessary to cover the resin frame of the first embodiment with a solder layer. That is, the resin frame may be directly connected to the metal electrode or the semiconductor element. In this case, the resin frame functions as a spacer. This is shown in FIG. In FIG. 7, the same components as those in the first embodiment are denoted by the same reference numerals. In the semiconductor device 250, a spacer 240 is disposed between the peripheral region 40 b of the metal electrode 40 and the semiconductor element 32. The spacer 240 is made of the same resin as the resin 36 of the first embodiment, and its shape is a frame shape. The upper surface of the spacer 240 is fixed to the metal electrode 40. The lower surface is fixed to the element side electrode 34 of the semiconductor element 32. The inner side surface of the spacer 240 is coated with a Ni film. The inner side surface of the spacer 240 is fixed to the third solder layer 38. By using the spacer 240 to limit the range of the third solder layer 38 to the inner region, a bonded body resistant to thermal changes is realized.
[0023]
In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.
[Brief description of the drawings]
FIG. 1 is a sectional view of a semiconductor device according to a first embodiment.
FIG. 2 shows a state where a metal electrode is thermally expanded.
FIG. 3 shows a plan view of the resin.
FIG. 4 is a sectional view of a semiconductor device according to a second embodiment.
FIG. 5 shows a modification of the semiconductor device of the second embodiment.
FIG. 6 is a sectional view of a semiconductor device according to a third embodiment.
FIG. 7 is a cross-sectional view of a semiconductor device which is a modified example of the present invention.
[Explanation of symbols]
10..Semiconductor device 20..Heat radiator 22..First solder layer 24..Insulating substrate 26..Substrate side electrode 28..Second solder layer 30..Collector electrode 32..Semiconductor element 34..Emitter electrode 36..Resin 38..Third solder layer 38a..Third solder layer inner region 38b..Third solder layer peripheral region 40..Metal electrode 40a..Metal electrode inner region 40b. Surrounding area

Claims (4)

第１部材と、第１部材よりも線膨張係数が小さい第２部材と、第１部材と第２部材の間にあって第１部材と第２部材を機械的電気的に接続している導電性接合材層とを有する接合体であり、
前記導電性接合材層の周辺領域には、その導電性接合材よりヤング率の小さい低ヤング率部材が埋め込まれており、
前記導電性接合材層の内側領域には、前記低ヤング率部材が埋め込まれていないことを特徴とする接合体。A first member, a second member having a smaller linear expansion coefficient than the first member, and a conductive joint between the first member and the second member and mechanically and electrically connecting the first member and the second member A joined body having a material layer,
In the peripheral region of the conductive bonding material layer, a low Young's modulus member having a smaller Young's modulus than that of the conductive bonding material is embedded,
The joined body, wherein the low Young's modulus member is not embedded in an inner region of the conductive joining material layer. 前記低ヤング率部材のヤング率が、導電性接合材のそれの２０％以下であることを特徴とする請求項１に記載の接合体。  The bonded body according to claim 1, wherein a Young's modulus of the low Young's modulus member is 20% or less of that of the conductive bonding material. 前記低ヤング率部材が、導電性接合材層の幅の５０％以上の範囲に亘って埋め込まれていることを特徴とする請求項１又は２に記載の接合体。  The joined body according to claim 1 or 2, wherein the low Young's modulus member is embedded over a range of 50% or more of the width of the conductive joining material layer. 前記第１部材が金属電極であり、前記第２部材が半導体素子であり、前記導電性接合材層が半田層であることを特徴とする請求項１から３のいずれかに記載の接合体。  4. The joined body according to claim 1, wherein the first member is a metal electrode, the second member is a semiconductor element, and the conductive joining material layer is a solder layer. 5.
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