JP4969738B2 - Ceramic circuit board and semiconductor module using the same - Google Patents

Ceramic circuit board and semiconductor module using the same Download PDF

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JP4969738B2
JP4969738B2 JP2001197165A JP2001197165A JP4969738B2 JP 4969738 B2 JP4969738 B2 JP 4969738B2 JP 2001197165 A JP2001197165 A JP 2001197165A JP 2001197165 A JP2001197165 A JP 2001197165A JP 4969738 B2 JP4969738 B2 JP 4969738B2
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circuit board
metal plate
back metal
ceramic
semiconductor module
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JP2003017627A (en
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隆之 那波
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Toshiba Corp
Toshiba Materials Co Ltd
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Toshiba Corp
Toshiba Materials Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
    • H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
    • H01L23/3735—Laminates or multilayers, e.g. direct bond copper ceramic substrates
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    • C04B37/00—Joining burned ceramic articles with other burned ceramic articles or other articles by heating
    • C04B37/02—Joining burned ceramic articles with other burned ceramic articles or other articles by heating with metallic articles
    • C04B37/021—Joining burned ceramic articles with other burned ceramic articles or other articles by heating with metallic articles in a direct manner, e.g. direct copper bonding [DCB]
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  • Condensed Matter Physics & Semiconductors (AREA)
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  • Microelectronics & Electronic Packaging (AREA)
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Description

【０００１】
【発明の属する技術分野】
本発明はセラミックス回路基板を用いた半導体モジュールに係り、特に金属回路板等の接合部の半田層やセラミックス基板に熱応力や反りによるクラックが発生することを効果的に防止でき、長期間に亘って優れた耐久性と高い信頼性が得られるセラミックス回路基板を用いた半導体モジュールに関する。
【０００２】
【従来の技術】
従来からアルミナ（Ａｌ２Ｏ３）焼結体などのように絶縁性に優れたセラミックス基板の表面に、導電性を有する金属回路板をろう材や接着剤やメタライズ金属層で一体に接合したセラミックス回路基板がパワートランジスタモジュールなどの半導体モジュール用基板やスイッチング電源モジュール用基板として広く普及している。
【０００３】
しかしながら上記セラミックス回路基板においては、金属回路板とセラミックス基板との間に、ろう材や接着剤やメタライズ層のような介在物が存在するため、両者間の熱抵抗が大きくなり、金属回路上に設けられた半導体素子の発熱を系外に迅速に放熱させることが困難であるという問題点があった。
【０００４】
このような問題点を解消するため、上記ろう材や接着剤やメタライズ層を使用せずに、所定形状に打ち抜いた金属回路板をセラミックス基板上に接触配置させて加熱するだけで直接接合する方法が検討されている。すなわち、直接接合法は、セラミックスと金属とを、ろう材層や接着剤層やメタライズ層などの接合層を介在させずに直接的に接合する方法である。この直接接合法では金属中あるいは金属表面に存在する結合剤（銅の場合は酸素）と金属との共晶液相が生成されて両部材が直接的に接合される。
【０００５】
図４（Ａ），（Ｂ），（Ｃ）はそれぞれの従来のセラミックス回路基板の構成例を示す平面図，断面図および背面図である。セラミックス基板２の材質としては、アルミナ（Ａｌ２Ｏ３），ジルコニア（ＺｒＯ２），ムライト等の酸化物系セラミックス焼結体や窒化けい素（Ｓｉ３Ｎ４），窒化アルミニウム（ＡｌＮ）等の窒化物系焼結体が使用される。
【０００６】
すなわち、Ｓｉ３Ｎ４基板などのセラミックス基板２の表面側には、Ｃｕ回路板などの金属回路板４が一体に接合される一方、裏面側にはＣｕ板などの裏金属板５が接合され、金属回路板４の所定位置に半導体素子６が接合されてセラミックス回路基板１が構成されている。
【０００７】
また、上記従来のセラミックス回路基板１においては、発熱時の反りを防止するために、金属回路板４と裏銅板５との体積が１：１と等しくなるように調整されていた。
【０００８】
また、近年の半導体素子の高集積化，高出力化に伴って半導体素子からの発熱量も増大しており、この半導体素子６からの多量の発熱を効率的に拡散させるために、図４（Ｂ）に示すように、半導体モジュールでは、従来からセラミックス回路基板１の素子搭載面と反対側の裏銅板５に、銅（Ｃｕ）やＡｌ−ＳｉＣ系材料から成るヒートシンクベース７を半田付け法によって一体に接合している。
【０００９】
【発明が解決しようとする課題】
しかしながら、上記従来のセラミックス回路基板を使用した半導体モジュールにおいては、セラミックス基板の寸法および厚さ，金属回路板のパターン形状や厚さによっては、セラミックス回路基板およびヒートシンクベースの反り量や反り方向が相反することが多いため、ヒートシンクベースに回路基板を半田付けした後に作用する繰り返しの熱履歴によって半田接合部にクラックが発生し、セラミックス回路基板の耐久性および動作信頼性が短期間で低下してしまうという問題点があった。
【００１０】
また、現在までのセラミックス基板の材質や金属回路板等の接合方法の改良により、セラミックス基板と金属回路板との接合に関して、回路基板としての繰り返しの熱サイクル特性（ＴＣＴ特性）の向上はある程度までは達成されている。しかしながら、裏金属板とヒートシンクベースとの接合構造までを含めた回路基板の熱サイクル特性の改善効果は未だに十分な域には達していないといった問題点があった。
【００１１】
本発明は上記問題点を解決するためになされたものであり、特に金属回路板等の接合部の半田層やセラミックス基板に熱応力や反りによるクラックが発生することを効果的に防止でき、長期間に亘って優れた耐久性と高い信頼性が得られるセラミックス回路基板およびそれを用いた半導体モジュールを提供することを目的とする。
【００１２】
【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発明に係る半導体モジュールは、セラミックス基板の表面側に金属回路板を接合する一方、裏面側に裏金属板を接合したセラミックス回路基板の裏金属板に半田層を介してヒートシンクベースを配設した半導体モジュールにおいて、上記裏金属板に、上記金属回路板の厚さの１０〜９０％の深さを有する熱応力緩和部を設けるとともに、上記金属回路板の体積に対する裏金属板の体積の比が０．４〜０．６の範囲であり、かつ前記裏金属板の厚さが０．１５〜０．５ｍｍの範囲であり、上記金属回路板および裏金属板は、銅またはアルミニウムから成る一方、上記セラミックス基板が、窒化けい素，窒化アルミニウムまたはアルミナのいずれかから成り、上記熱応力緩和部が裏金属板に形成された段差、複数の溝、凹陥部のいずれかであり、上記裏金属板の熱応力緩和部に充填される半田の割合が１０〜９０容量％の範囲内としたことを特徴とする。
【００１３】
また、上記セラミックス回路基板において、前記熱応力緩和部が、裏金属板の外周縁に形成された段差であることが好ましい。さらに、前記熱応力緩和部が、裏金属板に形成された複数の溝であることも好ましい。また、前記熱応力緩和部を、裏金属板に形成された凹陥部で形成することもできる。
【００１４】
本発明においては、裏金属板に所定深さの段差，溝，凹陥部で形成した熱応力緩和部を設けているため、ヒートシンクベースと裏金属板との間の一部分に厚い半田層が形成されることになり、繰り返して熱サイクルが作用した場合においても熱応力が大幅に緩和され、半田クラックが発生しにくく、高い信頼性を有する回路基板が得られる。
【００１５】
すなわち、半田層は、熱伝導率が小さいため、可及的に薄く形成することが望ましいが、過度に薄いと繰り返しの熱履歴によって半田層での熱応力が大きくなり、半田クラックが生じ易くなる。しかるに、上記のような熱応力緩和部を設けることにより、ヒートシンクベースと裏金属板とを半田接合した際に、熱応力緩和部に対応する半田層の部分に軟質で厚い半田部が形成される。この半田部によって半田層内に生じる熱応力が大幅に緩和低減されて半田クラックが発生しにくい回路基板が得られるのである。また、熱が作用したときに発生するヒートシンクベースの反りも、上記熱応力緩和部において吸収され、ヒートシンクベースの反りが回路基板に与える影響も少なくなる。
【００１６】
特に半田クラックは、応力集中部となる裏金属板とヒートシンクベースとの接合部の外周部に発生し易いため、熱応力緩和部は外周方向に開放される形状であることが好ましい。その点で、特に熱応力緩和部を裏金属板の外周縁に段差として形成することが好ましい。
【００１７】
また、上記段差，溝，凹陥部から成る熱応力緩和部の深さは、裏金属板表面より、金属回路板の厚さの１０〜９０％の範囲の深さを有することが好ましい。上記深さが１０％未満の場合には熱応力の緩和効果が少ない。一方、９０％を超えるように深くなると、裏金属板の強度が低下してしまうのでセラミックス基板と裏金属板の接合部に生じた応力により裏金属板が変形してしまう可能性がある。そのため、熱応力緩和部の深さは金属回路板の厚さの１０〜９０％とされるが３０〜７０％の範囲がより好ましい。
【００１８】
なお、上記段差，溝，凹陥部からなる熱応力緩和部の形成方法としては、予めプレス加工等により段差等を形成した裏金属板をセラミックス基板の裏面に接合する方法、または金属回路板素材および裏金属板素材をセラミックス基板に接合し、金属回路板素材をエッチング処理して回路形成した後に、裏金属板素材のみをソフトエッチング処理して段差等を形成する方法などが採用できる。
【００１９】
また本発明のセラミックス回路基板においては、金属回路板の体積に対する裏金属板の体積の比を０．６以下とし、相対的に裏金属板量を低減しているため、熱が回路基板に作用したときに裏金属板側が重点的に凹となるように所定量の反りが発生する。このような方向に反りが生じたとしても、裏金属板側に熱応力緩和部があることから、反りにより生じた変形を裏金属板のみで緩和できるのである。
【００２０】
なお、金属回路板または裏金属板が複数の金属板片から成る場合において、金属回路板または裏金属板の体積は、それぞれの金属板片の体積を合計した値として計算したものである。
【００２１】
上記金属回路板の体積に対する裏金属板の体積の比が０．６を超えると、反りの方向が金属回路板側に凹となり易くなり裏金属板に熱応力緩和部を設ける効果が得られなくなる。また、裏金属板の体積があまり小さ過ぎても反り量が増大するので、上記体積比は０．６以下と規定されるが０．４〜０．６の範囲がより好ましい。
【００２２】
また、本発明に係るセラミックス回路基板において、裏金属板のセラミックス基板に対する接合面積をＸ、金属回路板（表金属板）のセラミックス基板に対する接合面積をＹとしたとき、Ｘ＜Ｙとすることも可能である。一般に、金属回路板と裏金属板の材質が同じであった場合、接合面積が大きい方が金属板が伸びるので反り量が大きくなり、接合面積の大きい側が凸状に反りが生じる。しかしながら、本発明に係るセラミックス回路基板では、金属回路板と裏金属板の体積比［（裏金属板の体積比／金属回路板の体積比）］を０．６以下にしているため、熱応力が生じたときに裏金属板側が凹状に反るように反り方向を制御しているため、上記Ｘ＜Ｙのような形状をとることも可能である。
【００２３】
このようなＸ＜Ｙの形状を満たすことにより、金属回路板上に接続された半導体素子等の発熱素子から生じた熱を金属回路板およびセラミックス基板を介して、裏金属板、さらにはヒートシンクベースへ直線的に熱を逃すことができる。そのため、セラミックス基板と表裏金属板との接合部、さらには裏金属板とヒートシンクベースの接合部の熱サイクル特性を向上でき信頼性の高い半導体モジュールが得られる。
【００２４】
さらに本発明に係るセラミックス回路基板において、裏金属板の厚さを０．１５〜０．５ｍｍの範囲とすることにより、セラミックス回路基板の構成材の熱膨張差による変形などの影響を低減することができる。
【００２５】
さらに本発明のセラミックス回路基板を構成する金属回路板および裏金属板としては、特に限定されるものではないが、銅，アルミニウム，タングステン，モリブデンおよびそれらの合金の少なくとも１種から構成するとよい。特に熱伝導性，原料コストおよび導電性の観点から、銅，アルミニウムが好ましい。
【００２６】
また、セラミックス基板の種類についても、特に限定されるものではないが、窒化けい素（Ｓｉ３Ｎ４），窒化アルミニウム（ＡｌＮ），アルミナ（Ａｌ２Ｏ３），ジルコニア（ＺｒＯ２）およびＡｌ−Ｚｒセラミックスのいずれかで構成するとよい。特に特開２０００−３４１７２に開示しているように、高強度で６０Ｗ／ｍ・Ｋ以上の熱伝導率を有する窒化けい素焼結体で形成した基板が好ましい。
【００２７】
さらに金属回路板は、直接接合法，活性金属接合法およびアルミニウム系ろう材接合法のいずれかによってセラミックス基板に接合することが好ましい。なお、上記Ａｌ−Ｚｒセラミックスとは、Ａｌ２Ｏ３およびＺｒＯ２の合計量に対し、Ａｌ２Ｏ３を２０〜８０質量％含有したセラミックス焼結体のことである。また、各種セラミックスは必要に応じて焼結助剤等を含有してよいことは言うまでもない。
【００２８】
ここで、直接接合法を用いる場合で、金属回路板が銅回路板である場合、銅直接接合法（ＤＢＣ法）における結合剤は酸素であるので、この銅回路板はＣｕ−Ｏ共晶化合物によりセラミックス基板に接合されることになる。さらに金属回路板がアルミニウム回路板である場合、アルミニウム直接接合法（ＤＢＡ法）における結合剤はけい素が好ましいので、このアルミニウム回路板はＡｌ−Ｓｉ共晶化合物によりセラミックス基板に接合される。
【００２９】
また活性金属法は、Ｔｉ，Ｚｒ，Ｈｆなどの活性金属を含有するろう材を介して金属回路板をセラミックス基板に一体に接合する方法であり、Ａｌろう材接合法は、Ａｌを含有するろう材を介して金属回路板をセラミックス基板に一体に接合する方法である。
【００３０】
本発明に係る半導体モジュールは、上記のように調製したセラミックス回路基板の裏金属板に半田層を介してヒートシンクベースを配設して構成される。
【００３１】
上記構成に係るセラミックス回路基板およびそれを用いた半導体モジュールによれば、裏金属板に所定深さを有する段差，溝，凹陥部からなる熱応力緩和部を形成しているため、ヒートシンクベースと裏金属板との間の一部分に厚い半田層が形成されることになり、繰り返して熱サイクルが作用した場合においても熱応力が大幅に緩和され、半田クラックが発生しにくく、高い信頼性を有する回路基板が得られる。上記一部分に厚い半田層を形成することにより、裏金属板／（裏金属板＋半田）／半田層／ヒートシンクベース、の傾斜組成構造が実質的に形成されることになり熱応力の緩和効果が得られるものと考えられる。また、必ずしも熱応力緩和部に半田をすべて充填する必要はなく、応力緩和部の体積に対し１０容量％以上、好ましくは１０〜９０容量％で半田が充填されていれば本発明の効果は十分得られる。
【００３２】
なお、本発明の裏金属板とヒートシンクベースの接合には、一般的に使用されている半田のみならず、ＢＡｇ−８等のろう材や高分子を主成分とした接着剤などを使用しても問題はない。また、本発明のヒートシンクベースは、いわゆるヒートシンク（放熱板）のみを示すものではなく、実装ボードなどのセラミックス回路基板が接合または実装されるものは全て含むものとする。
【００３３】
また金属回路板の体積に対する裏金属板の体積の比を０．６以下とし、相対的に裏金属板量を低減しているため、熱が回路基板に作用したときに裏金属板側が重点的に凹となるように所定量の反りが発生する。この反り方向であれば、裏金属板の熱応力緩和部で反りにより生じた応力を緩和できるので、反りにより起きる不具合を解消できる。
【００３４】
【発明の実施の形態】
次に本発明の実施形態について以下に示す実施例を参照して具体的に説明する。
【００３５】
実施例１〜１０および比較例１〜６
表１に示すように、セラミックス基板として縦５５ｍｍ×横３７ｍｍのＳｉ３Ｎ４基板，ＡｌＮ基板およびＡｌ２Ｏ３基板を多数用意した。各セラミックス基板の厚さは表１に示す通りである。一方、表１に示す厚さを有するＣｕまたはＡｌ製の表金属板（金属回路板）および裏金属板を多数用意した。
【００３６】
なお、各実施例用の裏金属板にはソフトエッチング加工により、それぞれ熱応力緩和部としての段差，溝，または凹陥部を形成した。すなわち、実施例１，４〜１０用の裏金属板の外周部には、図１に示すように、深さが０．１２ｍｍであり幅が２ｍｍの段差３を形成した。また実施例２用の裏金属板には、図２に示すように幅が０．１ｍｍの半円断面を有する溝３ａを形成した。さらに、実施例３用の裏金属板は、図３に示すように５ｍｍ角で深さが０．１２ｍｍの凹陥部３ｂを形成した。一方、各比較例用の裏金属板は、図４に示すように熱応力緩和部を形成しないものを採用した。
【００３７】
また、表金属板（金属回路板）の体積に対する裏金属板の体積の比は表１に示す値となるように、表金属板の回路パターンを調整した。
【００３８】
こうして調製した表金属板および裏金属板を表１に示す活性金属法、ＤＢＣ法またはＤＢＡ法を使用して各セラミックス基板に接合した。上記活性金属法では、６５％Ａｇ−３０％Ｃｕ−５％Ｔｉ（質量％）から成るろう材ペーストを使用し、表裏金属板とセラミックス基板との積層体を真空中で温度８５０℃で５〜１５分間保持して一体に接合した。
【００３９】
一方、ＤＢＣ法では積層体を窒素ガス雰囲気中で温度１０７５℃で５〜１５分間加熱して一体に接合した。またＤＢＡ法では温度６５０℃で５〜１５分間加熱して一体に接合した。
【００４０】
各接合体の金属回路板の接合面積は、各実施例および比較例とともに、裏金属板の接合面積よりも小さくなるように金属回路板のサイズを調整した。
【００４１】
そして上記のように調整した各接合体の表側の金属回路板の所定位置に、低温半田を用いて半導体素子（Ｓｉチップ）を半田接合して各実施例および比較例に係るセラミックス回路基板を製造した。しかる後に、表２に示す材料から成るヒートシンクベースを裏金属板側に高温半田を介して一体に接合することにより、図１〜図３に示すような各実施例および比較例に係る評価用半導体モジュールを作製した。なお、裏金属板の熱応力緩和部に充填される半田の割合は１０〜９０容量％の範囲内とした。
【００４２】
図１は裏金属板５ａの外周縁に熱応力緩和部３としての段差を形成したセラミックス回路基板１ａの構成を示す図であり、セラミックス基板２の表面側に金属回路板４が接合される一方、裏面側に上記裏金属板５ａが接合されている。また金属回路板４の所定位置に半導体素子６が接合される一方、裏金属板５ａにヒートシンクベース７が一体に接合されて半導体モジュールが形成される。
【００４３】
図２は裏金属板５ｂの縦方向に熱応力緩和部３ａとしての溝を形成したセラミックス回路基板１ｂの構成を示す図であり、セラミックス基板２の表面側に金属回路板４が接合される一方、裏面側に上記裏金属板５ｂが接合されている。また金属回路板４の所定位置に半導体素子６が接合される一方、裏金属板５ｂにヒートシンクベース７が一体に接合されて半導体モジュールが形成される。
【００４４】
図３は裏金属板５ｃの表面部に熱応力緩和部３ｂとしての凹陥部を形成したセラミックス回路基板１ｃの構成を示す図であり、セラミックス基板２の表面側に金属回路板４が接合される一方、裏面側に上記裏金属板５ｃが接合されている。また金属回路板４の所定位置に半導体素子６が接合される一方、裏金属板５ｃにヒートシンクベース７が一体に接合されて半導体モジュールが形成される。
【００４５】
そして上記のように調製した各実施例および比較例に係る評価用半導体モジュールの耐久性および信頼性を評価するために下記のような熱衝撃試験（ヒートサイクル試験：ＴＣＴ）を実施し、裏金属板とヒートシンクベースとの間の半田層におけるクラック発生状況を調査した。ヒートサイクル試験は、各モジュールを−４０℃で３０分間保持し、次に室温（ＲＴ）まで昇温して１０分間保持し、さらに１２５℃まで昇温して３０分間保持し、引き続き室温まで冷却して１０分間保持するまでを１サイクルとする昇温−降温サイクルを１００サイクル繰り返して実施した。そして１００サイクル終了後に、裏金属板とヒートシンクベースとの間の半田層におけるクラックの発生の有無を超音波探傷法により調査し、クラックが発生したモジュールの割合を調査した。
【００４６】
各モジュールに使用したセラミックス回路基板の仕様を表１に示すとともに、各モジュールの評価結果を下記表２に示す。
【００４７】
【表１】

Figure 0004969738
【００４８】
【表２】
Figure 0004969738
【００４９】
上記表１〜２に示す結果から明らかなように、裏金属板に段差，溝，凹陥部のいずれかの熱応力緩和部を設けるとともに、表裏の金属板の体積比を所定の範囲に規定した回路基板を有する各実施例の半導体モジュールでは、ＴＣＴ試験後におけるクラックの発生は皆無であり、優れた耐久性および信頼性を有することが判明した。
【００５０】
一方、熱応力緩和部を設けず、かつ表裏の金属板の体積比が過大な各比較例に係るモジュールでは、いずれも半田クラックが発生し、モジュールとしての特性が低下することが再確認できた。
【００５１】
なお、各実施例および比較例のモジュールを構成するセラミックス回路基板においては、いずれもセラミックス基板自体にはクラックが発生しないことが確認されている。
【００５２】
実施例１１〜１６
前記実施例２に係る半導体モジュールにおいて、セラミックス基板の表裏面に設ける金属回路板の接合面積と裏金属板の接合面積との大小関係を変えるとともに、裏金属板の厚さを表３に示すように種々変えた点以外は実施例２と同様に処理して実施例１１〜１６に係る半導体モジュールを製造した。
【００５３】
次に各モジュールに対して前記した昇温−降温条件による熱衝撃試験（ＴＣＴ）を１０００サイクル実施した後におけるセラミックス基板の反り方向を調査するとともに、半田層におけるクラックの発生率を測定して下記表３に示す結果を得た。また反りの方向によって凹面が形成される側で表示した。
【００５４】
【表３】
Figure 0004969738
【００５５】
上記表３に示す結果から明らかなように、表金属板（金属回路板）の接合面積Ｙが裏金属板の接合面積Ｘより小さい条件を満足する場合には、回路基板の反り方向が裏金属板側になり、そりの反りによって発生した応力が、裏金属板に形成した溝により効果的に緩和されているため、半田クラックの発生率が低下することが判明した。
【００５６】
一方、裏金属板が０．１５ｍｍより薄い実施例１５の場合および表裏金属板の接合面積の大小がＸ＞Ｙを満たさない実施例１６の場合では、熱応力緩和部としての溝を設ける効果が少ないことが確認できた。
【００５７】
特に、Ｘ＜Ｙである実施例１６ではＴＣＴ試験による表金属板の熱収縮が大きいため反り方向が逆になってしまうことが確認された。また、このような形態では表金属板に半導体素子を搭載したときに、素子の熱が直線的にヒートシンクベースに伝わらないので、同様の不具合が生じてしまうといえる。
【００５８】
【発明の効果】
以上説明の通り、本発明に係るセラミックス回路基板およびそれを用いた半導体モジュールによれば、裏金属板に所定深さを有する段差，溝，凹陥部からなる熱応力緩和部を形成しているため、ヒートシンクベースと裏金属板との間の一部分に厚い半田層が形成されることになり、繰り返して熱サイクルが作用した場合においても熱応力が大幅に緩和され、半田クラックが発生しにくく、高い信頼性を有する回路基板が得られる。
【００５９】
また金属回路板の体積に対する裏金属板の体積の比を０．６以下とし、相対的に裏金属板量を低減しているため、熱が回路基板に作用したときに裏金属板側が重点的に凹となるように所定量の反りが発生する。この反りの方向および反り量は、ヒートシンクベースの反りの方向および反り量と一致することになるため、反りに起因する曲げ応力による基板の割れは解消される。
【図面の簡単な説明】
【図１】（Ａ），（Ｂ）はそれぞれ本発明の一実施例に係るセラミックス回路基板の断面図および背面図。
【図２】（Ａ），（Ｂ）はそれぞれ本発明の他の実施例に係るセラミックス回路基板の断面図および背面図。
【図３】（Ａ），（Ｂ）はそれぞれ本発明の他の実施例に係るセラミックス回路基板の断面図および背面図。
【図４】（Ａ），（Ｂ），（Ｃ）はそれぞれ従来のセラミックス回路基板の構成を示す平面図、断面図および背面図。
【符号の説明】
１，１ａ，１ｂ，１ｃ セラミックス回路基板
２ セラミックス基板
３，３ａ，３ｂ 熱応力緩和部（段差，溝，凹陥部）
４ 金属回路板
５，５ａ，５ｂ，５ｃ 裏金属板
６ 半導体素子
７ ヒートシンクベース[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor module using a ceramic circuit board, it can effectively prevent the particular cracks due to thermal stress and warp in the solder layer and the ceramic substrate of the bonded portion of the metal circuit plate or the like, a long period of time over and a semiconductor module using the excellent durability and high reliability can be obtained a ceramic circuit board.
[0002]
[Prior art]
Conventionally, ceramics in which a conductive metal circuit board is integrally joined with a brazing material, an adhesive, or a metallized metal layer on the surface of a ceramic substrate having excellent insulating properties such as an alumina (Al 2 O 3 ) sintered body Circuit boards are widely used as semiconductor module substrates such as power transistor modules and switching power supply module substrates.
[0003]
However, in the ceramic circuit board, since there are inclusions such as a brazing material, an adhesive, and a metallized layer between the metal circuit board and the ceramic board, the thermal resistance between them increases, and the metal circuit board There is a problem in that it is difficult to quickly dissipate heat generated from the provided semiconductor element outside the system.
[0004]
In order to solve such problems, a method of directly joining a metal circuit board punched into a predetermined shape on a ceramic substrate without heating using the brazing material, adhesive, or metallized layer, and heating it. Is being considered. That is, the direct bonding method is a method in which ceramics and metal are directly bonded without interposing a bonding layer such as a brazing material layer, an adhesive layer, or a metallized layer. In this direct joining method, a eutectic liquid phase of a binder (oxygen in the case of copper) present in the metal or on the metal surface and the metal is generated, and both members are joined directly.
[0005]
4 (A), 4 (B), and 4 (C) are a plan view, a cross-sectional view, and a rear view showing a configuration example of each conventional ceramic circuit board. Examples of the material of the ceramic substrate 2 include oxide ceramic sintered bodies such as alumina (Al 2 O 3 ), zirconia (ZrO 2 ), mullite, silicon nitride (Si 3 N 4 ), and aluminum nitride (AlN). A nitride-based sintered body is used.
[0006]
That is, a metal circuit board 4 such as a Cu circuit board is integrally bonded to the front surface side of the ceramic substrate 2 such as a Si 3 N 4 substrate, and a back metal plate 5 such as a Cu plate is bonded to the back surface side. The ceramic circuit board 1 is configured by bonding the semiconductor element 6 to a predetermined position of the metal circuit board 4.
[0007]
In the conventional ceramic circuit board 1, the volume of the metal circuit board 4 and the back copper board 5 is adjusted to be equal to 1: 1 in order to prevent warpage during heat generation.
[0008]
In addition, the amount of heat generated from the semiconductor element is increasing with the recent increase in integration and output of the semiconductor element. In order to efficiently diffuse a large amount of heat generated from the semiconductor element 6, FIG. As shown in B), in a semiconductor module, a heat sink base 7 made of copper (Cu) or an Al—SiC material is conventionally soldered to a back copper plate 5 on the side opposite to the element mounting surface of the ceramic circuit board 1 by a soldering method. They are joined together.
[0009]
[Problems to be solved by the invention]
However, in a semiconductor module using the above-described conventional ceramic circuit board, depending on the dimensions and thickness of the ceramic board and the pattern shape and thickness of the metal circuit board, the warping amount and the warping direction of the ceramic circuit board and the heat sink base may conflict with each other. In many cases, cracks occur in the solder joints due to repeated thermal history that acts after soldering the circuit board to the heat sink base, and the durability and operational reliability of the ceramic circuit board are reduced in a short period of time. There was a problem.
[0010]
In addition, due to improvements in the bonding method of ceramic substrate materials and metal circuit boards to date, repeated thermal cycle characteristics (TCT characteristics) as a circuit board have been improved to some extent with respect to bonding between ceramic substrates and metal circuit boards. Has been achieved. However, there is a problem that the effect of improving the thermal cycle characteristics of the circuit board including the bonding structure between the back metal plate and the heat sink base has not yet reached a sufficient range.
[0011]
The present invention has been made to solve the above-mentioned problems, and in particular, can effectively prevent the occurrence of cracks due to thermal stress and warpage in the solder layer and ceramic substrate of the joint portion such as a metal circuit board. It is an object of the present invention to provide a ceramic circuit board and a semiconductor module using the ceramic circuit board that can provide excellent durability and high reliability over a period of time.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a semiconductor module according to the present invention has a metal circuit board bonded to the front side of a ceramic substrate, while a back metal plate is bonded to the back side of the ceramic circuit board via a solder layer. In the semiconductor module provided with the heat sink base, the back metal plate is provided with a thermal stress relaxation portion having a depth of 10 to 90% of the thickness of the metal circuit plate, and the back of the metal circuit plate with respect to the volume. The volume ratio of the metal plate is in the range of 0.4 to 0.6, and the thickness of the back metal plate is in the range of 0.15 to 0.5 mm. The metal circuit plate and the back metal plate are while made of copper or aluminum, the ceramic substrate, silicon nitride consists of either aluminum nitride or alumina, a step in which the thermal stress alleviating portion is formed on the back metal plate, a plurality of grooves Is either recess, the proportion of the solder filled in the thermal stress absorbing portions of the backing metal plate characterized by being in the range of 10 to 90 volume%.
[0013]
In the ceramic circuit board, the thermal stress relaxation portion is preferably a step formed on the outer peripheral edge of the back metal plate. Furthermore, it is preferable that the thermal stress relaxation part is a plurality of grooves formed in the back metal plate. Further, the thermal stress relaxation portion can be formed by a recessed portion formed in the back metal plate.
[0014]
In the present invention, the back metal plate is provided with a thermal stress relaxation portion formed by steps, grooves, and recesses of a predetermined depth, so that a thick solder layer is formed in a portion between the heat sink base and the back metal plate. Therefore, even when the thermal cycle is repeatedly applied, the thermal stress is greatly relieved, solder cracks are hardly generated, and a highly reliable circuit board can be obtained.
[0015]
That is, since the thermal conductivity of the solder layer is small, it is desirable to make it as thin as possible. However, if it is too thin, thermal stress in the solder layer increases due to repeated thermal history, and solder cracks are likely to occur. . However, by providing the thermal stress relaxation part as described above, when the heat sink base and the back metal plate are soldered together, a soft and thick solder part is formed in the part of the solder layer corresponding to the thermal stress relaxation part. . The thermal stress generated in the solder layer is greatly relaxed and reduced by the solder portion, and a circuit board in which solder cracks are hardly generated can be obtained. Further, the heat sink base warp generated when heat acts is absorbed by the thermal stress relaxation portion, and the influence of the heat sink base warp on the circuit board is reduced.
[0016]
In particular, since solder cracks are likely to occur at the outer peripheral portion of the joint portion between the back metal plate and the heat sink base, which is a stress concentration portion, it is preferable that the thermal stress relaxation portion is open in the outer peripheral direction. In that respect, it is particularly preferable to form the thermal stress relaxation portion as a step on the outer peripheral edge of the back metal plate.
[0017]
Moreover, it is preferable that the depth of the thermal stress relaxation part composed of the step, the groove, and the recessed part is in the range of 10 to 90% of the thickness of the metal circuit board from the surface of the back metal board. When the depth is less than 10%, the thermal stress relaxation effect is small. On the other hand, if the depth is greater than 90%, the strength of the back metal plate is lowered, and therefore the back metal plate may be deformed by the stress generated at the joint between the ceramic substrate and the back metal plate. Therefore, the depth of the thermal stress relaxation portion is 10 to 90% of the thickness of the metal circuit board, but more preferably in the range of 30 to 70%.
[0018]
In addition, as a method for forming the thermal stress relaxation portion including the step, groove, and recessed portion, a method of joining a back metal plate, on which a step or the like has been formed in advance by pressing or the like, to the back surface of the ceramic substrate, A method may be employed in which a back metal plate material is bonded to a ceramic substrate, a metal circuit board material is etched to form a circuit, and then only the back metal plate material is soft etched to form a step or the like.
[0019]
In the ceramic circuit board of the present invention, the ratio of the volume of the back metal plate to the volume of the metal circuit plate is set to 0.6 or less, and the amount of the back metal plate is relatively reduced, so that heat acts on the circuit board. When this occurs, a predetermined amount of warpage occurs so that the back metal plate side is concavely focused. Even if the warp occurs in such a direction, the deformation caused by the warp can be alleviated only by the back metal plate because there is a thermal stress relaxation portion on the back metal plate side.
[0020]
When the metal circuit plate or the back metal plate is composed of a plurality of metal plate pieces, the volume of the metal circuit plate or the back metal plate is calculated as a total value of the volumes of the respective metal plate pieces.
[0021]
If the ratio of the volume of the back metal plate to the volume of the metal circuit plate exceeds 0.6, the direction of warpage tends to be concave on the metal circuit plate side, and the effect of providing a thermal stress relaxation portion on the back metal plate cannot be obtained. . Further, since the amount of warpage increases even if the volume of the back metal plate is too small, the volume ratio is defined as 0.6 or less, but the range of 0.4 to 0.6 is more preferable.
[0022]
Further, in the ceramic circuit board according to the present invention, X <Y, where X is the bonding area of the back metal plate to the ceramic substrate and Y is the bonding area of the metal circuit board (front metal plate) to the ceramic substrate. Is possible. In general, when the metal circuit board and the back metal plate are made of the same material, the larger the bonding area, the longer the metal plate, the larger the amount of warpage, and the larger the bonding area, the higher the warpage. However, in the ceramic circuit board according to the present invention, the volume ratio [(volume ratio of the back metal plate / volume ratio of the metal circuit board)] of the metal circuit plate and the back metal plate is set to 0.6 or less. Since the warping direction is controlled so that the back metal plate side warps in a concave shape when the occurrence of sag occurs, it is possible to take a shape such as X <Y.
[0023]
By satisfying such a shape of X <Y, heat generated from a heating element such as a semiconductor element connected on the metal circuit board is transferred through the metal circuit board and the ceramic substrate to the back metal plate, and further to the heat sink base. Heat can be released linearly. Therefore, the thermal cycle characteristics of the joint between the ceramic substrate and the front and back metal plates, and the joint between the back metal plate and the heat sink base can be improved, and a highly reliable semiconductor module can be obtained.
[0024]
Furthermore, in the ceramic circuit board according to the present invention, by setting the thickness of the back metal plate in the range of 0.15 to 0.5 mm, the influence of deformation due to the difference in thermal expansion of the constituent material of the ceramic circuit board is reduced. Can do.
[0025]
Further, the metal circuit board and the back metal board constituting the ceramic circuit board of the present invention are not particularly limited, but may be composed of at least one of copper, aluminum, tungsten, molybdenum and alloys thereof. In particular, copper and aluminum are preferable from the viewpoints of thermal conductivity, raw material cost, and conductivity.
[0026]
Also, the type of the ceramic substrate is not particularly limited, but silicon nitride (Si 3 N 4 ), aluminum nitride (AlN), alumina (Al 2 O 3 ), zirconia (ZrO 2 ) and Al— It may be composed of any of Zr ceramics. In particular, as disclosed in JP 2000-34172, a substrate formed of a silicon nitride sintered body having high strength and a thermal conductivity of 60 W / m · K or more is preferable.
[0027]
Further, the metal circuit board is preferably bonded to the ceramic substrate by any one of a direct bonding method, an active metal bonding method and an aluminum brazing material bonding method. Note that the above Al-Zr ceramic, the total amount of Al 2 O 3 and ZrO 2, is that the ceramic sintered body and the Al 2 O 3 containing 20 to 80 wt%. It goes without saying that various ceramics may contain a sintering aid or the like as necessary.
[0028]
Here, when the direct bonding method is used and the metal circuit board is a copper circuit board, since the binder in the copper direct bonding method (DBC method) is oxygen, the copper circuit board is made of a Cu-O eutectic compound. Is bonded to the ceramic substrate. Further, when the metal circuit board is an aluminum circuit board, silicon is preferably used as the binder in the aluminum direct bonding method (DBA method), so that the aluminum circuit board is bonded to the ceramic substrate with an Al-Si eutectic compound.
[0029]
The active metal method is a method in which a metal circuit board is integrally bonded to a ceramic substrate through a brazing material containing an active metal such as Ti, Zr, or Hf, and the Al brazing material bonding method is a method that contains Al. In this method, the metal circuit board is integrally bonded to the ceramic substrate through the material.
[0030]
The semiconductor module according to the present invention is configured by disposing a heat sink base on a back metal plate of a ceramic circuit board prepared as described above via a solder layer .
[0031]
According to the ceramic circuit board and the semiconductor module using the ceramic circuit board according to the above configuration, the back metal plate is formed with the thermal stress relaxation portion including a step, a groove, and a recessed portion having a predetermined depth. A thick solder layer is formed in a part between the metal plate, and even when a thermal cycle is repeatedly applied, thermal stress is greatly relieved, solder cracks hardly occur, and a highly reliable circuit A substrate is obtained. By forming a thick solder layer on the part, a gradient composition structure of back metal plate / (back metal plate + solder) / solder layer / heat sink base is substantially formed, and the effect of reducing thermal stress is achieved. It is considered to be obtained. Further, it is not always necessary to fill the thermal stress relaxation part with solder, and the effect of the present invention is sufficient if the solder is filled with 10% by volume or more, preferably 10 to 90% by volume with respect to the volume of the stress relaxation part. can get.
[0032]
For joining the back metal plate and the heat sink base of the present invention, not only a commonly used solder but also a brazing material such as BAg-8 or an adhesive mainly composed of a polymer is used. There is no problem. In addition, the heat sink base of the present invention does not indicate only a so-called heat sink (heat radiating plate), but includes all those to which a ceramic circuit board such as a mounting board is bonded or mounted.
[0033]
In addition, the ratio of the volume of the back metal plate to the volume of the metal circuit plate is set to 0.6 or less, and the amount of the back metal plate is relatively reduced. Therefore, when the heat acts on the circuit board, the back metal plate side is important. A predetermined amount of warpage occurs so as to be concave. With this warping direction, the stress caused by the warp in the thermal stress relaxation portion of the back metal plate can be relaxed, so that the problem caused by the warp can be eliminated.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the following examples.
[0035]
Examples 1-10 and Comparative Examples 1-6
As shown in Table 1, a large number of 55 mm × 37 mm Si 3 N 4 substrates, AlN substrates, and Al 2 O 3 substrates were prepared as ceramic substrates. The thickness of each ceramic substrate is as shown in Table 1. On the other hand, a number of front metal plates (metal circuit plates) and back metal plates made of Cu or Al having the thicknesses shown in Table 1 were prepared.
[0036]
The back metal plate for each example was formed with a step, a groove, or a recessed portion as a thermal stress relaxation portion by soft etching. That is, as shown in FIG. 1, a step 3 having a depth of 0.12 mm and a width of 2 mm was formed on the outer peripheral portion of the back metal plate for Examples 1 and 4 to 10. Further, a groove 3a having a semicircular cross section with a width of 0.1 mm was formed on the back metal plate for Example 2 as shown in FIG. Furthermore, as shown in FIG. 3, the back metal plate for Example 3 was formed with a recessed portion 3b having a 5 mm square and a depth of 0.12 mm. On the other hand, as the back metal plate for each comparative example, as shown in FIG.
[0037]
Further, the circuit pattern of the front metal plate was adjusted so that the ratio of the volume of the back metal plate to the volume of the front metal plate (metal circuit plate) became the value shown in Table 1.
[0038]
The front metal plate and the back metal plate thus prepared were bonded to each ceramic substrate using the active metal method, DBC method or DBA method shown in Table 1. In the active metal method, a brazing paste made of 65% Ag-30% Cu-5% Ti (mass%) is used, and the laminate of the front and back metal plates and the ceramic substrate is vacuumed at a temperature of 850 ° C. It was held for 15 minutes and joined together.
[0039]
On the other hand, in the DBC method, the laminated body was heated and bonded at a temperature of 1075 ° C. for 5 to 15 minutes in a nitrogen gas atmosphere. In the DBA method, heating was performed at a temperature of 650 ° C. for 5 to 15 minutes, and bonding was performed integrally.
[0040]
The size of the metal circuit board was adjusted so that the joining area of the metal circuit board of each joined body was smaller than the joining area of the back metal board together with each of the examples and comparative examples.
[0041]
Then, a ceramic circuit board according to each of the examples and comparative examples is manufactured by soldering a semiconductor element (Si chip) using a low-temperature solder to a predetermined position of the metal circuit board on the front side of each joined body adjusted as described above. did. Thereafter, a heat sink base made of the material shown in Table 2 is integrally joined to the back metal plate side via a high-temperature solder so that the semiconductors for evaluation according to the examples and comparative examples as shown in FIGS. A module was produced. In addition, the ratio of the solder with which the thermal stress relaxation part of a back metal plate is filled was made into the range of 10-90 volume%.
[0042]
FIG. 1 is a diagram showing a configuration of a ceramic circuit board 1a in which a step as a thermal stress relaxation part 3 is formed on the outer peripheral edge of a back metal plate 5a, and the metal circuit board 4 is joined to the surface side of the ceramic substrate 2. The back metal plate 5a is joined to the back side. In addition, the semiconductor element 6 is bonded to a predetermined position of the metal circuit board 4, while the heat sink base 7 is integrally bonded to the back metal plate 5a to form a semiconductor module.
[0043]
FIG. 2 is a diagram showing a configuration of the ceramic circuit board 1b in which grooves as the thermal stress relaxation portions 3a are formed in the longitudinal direction of the back metal plate 5b, and the metal circuit board 4 is joined to the surface side of the ceramic substrate 2. The back metal plate 5b is joined to the back side. Further, the semiconductor element 6 is joined to a predetermined position of the metal circuit board 4, while the heat sink base 7 is joined integrally to the back metal board 5b to form a semiconductor module.
[0044]
FIG. 3 is a diagram showing a configuration of a ceramic circuit board 1c in which a recessed portion as a thermal stress relaxation part 3b is formed on the surface portion of the back metal plate 5c, and the metal circuit plate 4 is bonded to the surface side of the ceramic substrate 2. On the other hand, the back metal plate 5c is joined to the back side. Further, the semiconductor element 6 is joined to a predetermined position of the metal circuit board 4, while the heat sink base 7 is joined integrally to the back metal board 5c to form a semiconductor module.
[0045]
Then, in order to evaluate the durability and reliability of the semiconductor modules for evaluation according to the examples and comparative examples prepared as described above, the following thermal shock test (heat cycle test: TCT) was performed, and the back metal The occurrence of cracks in the solder layer between the board and the heat sink base was investigated. In the heat cycle test, each module is held at −40 ° C. for 30 minutes, then heated to room temperature (RT) and held for 10 minutes, further heated to 125 ° C. and held for 30 minutes, and then cooled to room temperature. Then, the temperature increase / decrease cycle with one cycle until holding for 10 minutes was repeated 100 times. After the end of 100 cycles, the presence or absence of cracks in the solder layer between the back metal plate and the heat sink base was examined by ultrasonic flaw detection, and the proportion of modules in which cracks occurred was investigated.
[0046]
The specifications of the ceramic circuit board used for each module are shown in Table 1, and the evaluation results of each module are shown in Table 2 below.
[0047]
[Table 1]
Figure 0004969738
[0048]
[Table 2]
Figure 0004969738
[0049]
As is clear from the results shown in Tables 1 and 2, the back metal plate is provided with a thermal stress relaxation portion of any one of a step, a groove, and a recessed portion, and the volume ratio of the front and back metal plates is defined within a predetermined range. In the semiconductor module of each example having a circuit board, it was found that cracks did not occur after the TCT test and had excellent durability and reliability.
[0050]
On the other hand, it was reconfirmed that the module according to each comparative example in which the thermal stress relaxation part was not provided and the volume ratio of the front and back metal plates was excessively caused a solder crack and the characteristics as the module were deteriorated. .
[0051]
In addition, in the ceramic circuit board which comprises the module of each Example and a comparative example, it has been confirmed that a crack does not generate | occur | produce in any ceramic board itself.
[0052]
Examples 11-16
In the semiconductor module according to Example 2, the magnitude relationship between the bonding area of the metal circuit plate provided on the front and back surfaces of the ceramic substrate and the bonding area of the back metal plate is changed, and the thickness of the back metal plate is shown in Table 3. The semiconductor module which concerns on Example 11-16 was manufactured by processing like Example 2 except the point which changed variously.
[0053]
Next, the thermal shock test (TCT) under the temperature increase / decrease conditions described above was performed on each module for 1000 cycles, and the warp direction of the ceramic substrate was investigated, and the crack generation rate in the solder layer was measured to determine the following: The results shown in Table 3 were obtained. Moreover, it displayed on the side in which a concave surface is formed according to the direction of curvature.
[0054]
[Table 3]
Figure 0004969738
[0055]
As is clear from the results shown in Table 3 above, when the joining area Y of the front metal plate (metal circuit board) satisfies the condition smaller than the joining area X of the back metal plate, the warping direction of the circuit board is the back metal. It has been found that the stress generated by warpage of the warp on the plate side is effectively relieved by the grooves formed in the back metal plate, so that the rate of occurrence of solder cracks is reduced.
[0056]
On the other hand, in the case of Example 15 where the back metal plate is thinner than 0.15 mm and in the case of Example 16 where the joining area of the front and back metal plates does not satisfy X> Y, there is an effect of providing a groove as a thermal stress relaxation part. It was confirmed that there were few.
[0057]
In particular, in Example 16 where X <Y, it was confirmed that the warping direction was reversed because the thermal contraction of the surface metal plate by the TCT test was large. Moreover, in such a form, when a semiconductor element is mounted on the front metal plate, the heat of the element is not transmitted linearly to the heat sink base, so that it can be said that the same problem occurs.
[0058]
【Effect of the invention】
As described above, according to the ceramic circuit board and the semiconductor module using the ceramic circuit board according to the present invention, the thermal stress relaxation portion including the step, the groove, and the recessed portion having a predetermined depth is formed on the back metal plate. , A thick solder layer will be formed between the heat sink base and the back metal plate, and thermal stress is greatly relieved even when repeated thermal cycles are applied, solder cracks are less likely to occur, and high A reliable circuit board can be obtained.
[0059]
In addition, the ratio of the volume of the back metal plate to the volume of the metal circuit plate is set to 0.6 or less, and the amount of the back metal plate is relatively reduced. Therefore, when the heat acts on the circuit board, the back metal plate side is important. A predetermined amount of warpage occurs so as to be concave. Since the direction and the amount of warpage of the warp coincide with the direction and the amount of warp of the heat sink base, the crack of the substrate due to the bending stress caused by the warp is eliminated.
[Brief description of the drawings]
FIGS. 1A and 1B are a sectional view and a rear view of a ceramic circuit board according to an embodiment of the present invention, respectively.
2A and 2B are a sectional view and a rear view of a ceramic circuit board according to another embodiment of the present invention, respectively.
FIGS. 3A and 3B are a sectional view and a rear view of a ceramic circuit board according to another embodiment of the present invention, respectively.
4A, 4B, and 4C are a plan view, a cross-sectional view, and a rear view showing the configuration of a conventional ceramic circuit board, respectively.
[Explanation of symbols]
1, 1a, 1b, 1c Ceramic circuit board 2 Ceramic board 3, 3a, 3b Thermal stress relaxation part (step, groove, concave part)
4 Metal circuit boards 5, 5a, 5b, 5c Back metal plate 6 Semiconductor element 7 Heat sink base

Claims (4)

セラミックス基板の表面側に金属回路板を接合する一方、裏面側に裏金属板を接合したセラミックス回路基板の裏金属板に半田層を介してヒートシンクベースを配設した半導体モジュールにおいて、上記裏金属板に、上記金属回路板の厚さの１０〜９０％の深さを有する熱応力緩和部を設けるとともに、上記金属回路板の体積に対する裏金属板の体積の比が０．４〜０．６の範囲であり、かつ前記裏金属板の厚さが０．１５〜０．５ｍｍの範囲であり、上記金属回路板および裏金属板は、銅またはアルミニウムから成る一方、上記セラミックス基板が、窒化けい素，窒化アルミニウムまたはアルミナのいずれかから成り、上記熱応力緩和部が裏金属板に形成された段差、複数の溝、凹陥部のいずれかであり、上記裏金属板の熱応力緩和部に充填される半田の割合が１０〜９０容量％の範囲内としたことを特徴とする半導体モジュール。In a semiconductor module in which a metal circuit board is bonded to the front surface side of a ceramic substrate, and a heat sink base is disposed on the back metal plate of the ceramic circuit board having a back metal plate bonded to the back surface side through a solder layer, the back metal plate In addition, a thermal stress relaxation part having a depth of 10 to 90% of the thickness of the metal circuit board is provided, and the ratio of the volume of the back metal plate to the volume of the metal circuit plate is 0.4 to 0.6. The thickness of the back metal plate is in the range of 0.15 to 0.5 mm, and the metal circuit plate and the back metal plate are made of copper or aluminum, while the ceramic substrate is made of silicon nitride. consists either of aluminum nitride or alumina, a step in which the thermal stress alleviating portion is formed on the back metal plate, a plurality of grooves, is either recess, charging the thermal stress absorbing portions of the backing metal plate Semiconductor module proportion of solder characterized by being in the range of 10 to 90 volume percent being. 前記金属回路板のセラミックス基板に対する接合面積が前記裏金属板のセラミックス基板に対する接合面積より小さいことを特徴とする請求項１記載の半導体モジュール。  2. The semiconductor module according to claim 1, wherein a bonding area of the metal circuit board to the ceramic substrate is smaller than a bonding area of the back metal plate to the ceramic substrate. セラミックス回路基板が、裏金属板側が凹になるように反っていることを特徴とする請求項１記載の半導体モジュール。  2. The semiconductor module according to claim 1, wherein the ceramic circuit board is warped so that the back metal plate side is concave. 前記金属回路板は、直接接合法，活性金属接合法およびアルミニウム系ろう材接合法のいずれかによって前記セラミックス基板に接合されていることを特徴とする請求項１記載の半導体モジュール。  2. The semiconductor module according to claim 1, wherein the metal circuit board is bonded to the ceramic substrate by any one of a direct bonding method, an active metal bonding method and an aluminum brazing material bonding method.
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