JP2004179484A - Method for manufacturing semiconductor device with joined wire - Google Patents

Method for manufacturing semiconductor device with joined wire Download PDF

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Publication number
JP2004179484A
JP2004179484A JP2002345465A JP2002345465A JP2004179484A JP 2004179484 A JP2004179484 A JP 2004179484A JP 2002345465 A JP2002345465 A JP 2002345465A JP 2002345465 A JP2002345465 A JP 2002345465A JP 2004179484 A JP2004179484 A JP 2004179484A
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Prior art keywords
wire
bonding
housing
electrode pad
semiconductor device
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JP3918724B2 (en
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Yoichiro Baba
陽一郎 馬場
Takashi Ouchi
孝志 大内
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Toyota Motor Corp
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Toyota Motor Corp
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  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Wire Bonding (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device which has superior durability of a join part between an electrode pad and a wire and is applicable as a semiconductor device with a resin-made member. <P>SOLUTION: A semiconductor element 10 with an electrode pad 12 and a substrate 20 with a relay pad 22a are joined, and a wire 56 is joined with the electrode pad 21 and the relay pad 22a with an ultrasonic wave. This substrate 20 is soldered by reflowing to a heat radiation plate 30 and the join part 56a between the electrode pad 12 and the wire 56 is heat-treated to improve the joining durability. The obtained unit 102 is assembled in a resin-made housing 40, and a wire 58a is joined with a housing terminal 48 and the relay pad 22a to electrically connect the electrode pad 12 to the housing terminal 48. The join part 56a is heat-treated before the semiconductor element 10 is assembled in the housing 40, so the housing 40 is never damaged with the heat in the heat treatment. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】本発明は、半導体素子の表面に設けられた電極パッドとボンディングワイヤとの接合部の耐久性（ワイヤ接合耐久性）が改善された半導体装置を製造する方法に関する。また、本発明は、かかるワイヤ接合耐久性を向上させる方法に関する。
【０００２】
【従来の技術】半導体素子（チップ）の表面に設けられた導体部（電極パッド）と外部リード端子とを、金（Ａｕ）、アルミニウム（Ａｌ）等からなる極細線（ボンディングワイヤ）によって接続した後に、１５０℃以上の高温中で熱処理する技術が知られている（例えば、特許文献１を参照）。
しかし、樹脂製部材を備える半導体装置（例えば、樹脂製ハウジングを備えるパワーモジュール）に対してかかる技術を適用しようとすると、上記熱処理によって樹脂製部材が損傷（変形、変質等）する虞がある。また、上記公報に記載の技術は接合部の「初期接着強度」を向上させることを目的としており、接合部の耐久性（耐久強度等）に関するものではない。
【０００３】
【特許文献１】
特開平３−９１９３８号公報
【０００４】
【発明が解決しようとする課題】本発明は、樹脂製部材を備える半導体装置の製造にも好ましく適用することができ、電極パッドとボンディングワイヤとの接合部の耐久性（接合耐久性）に優れた半導体装置を製造することのできる半導体装置の製造方法を提供することを目的とする。関連する他の目的は、かかる製造方法により製造するのに適した半導体装置を提供することである。また、本発明の他の目的は、電極パッドとボンディングワイヤとの接合耐久性の向上方法を提供することである。
【０００５】
【課題を解決するための手段と作用と効果】本発明者は、半導体装置を所定の構造とし、樹脂製部材と半導体素子とを一体化する前に接合部を熱処理することにより上記課題を解決し得ることを見出した。また、所定の熱処理方法を採用することにより上記課題を解決し得ることを見出した。
【０００６】
本発明によると、ハウジングに半導体素子が組み付けられており、その半導体素子にアルミニウムまたはアルミニウム合金製のワイヤが接合されている半導体装置の製造方法が提供される
かかる製造方法の好ましい一例は、前記半導体素子を基板の表面に接合する工程と、前記半導体素子の非接合面に形成されている電極パッドに前記ワイヤを超音波接合する工程と、前記基板の裏面を金属板にリフロー半田付する工程と、前記金属板を前記ハウジングに組み付ける工程を包含する。このリフロー半田付工程では、前記電極パッドと前記ワイヤの接合部を前記ワイヤを構成する材料の結晶粒の成長を促進する温度域に加熱する条件で半田付する。この製造方法によると、リフロー半田付工程を実施することによって、ワイヤと電極パッドとの接合部が熱処理される。
【０００７】
かかる熱処理を施すことによって、ワイヤ構成材料（アルミニウムまたはアルミニウム合金）の結晶粒の成長が促進される。その結果、熱処理を施さない場合に比べてワイヤと電極パッドとの接合部の結晶粒が大きな半導体装置を得ることができる。ワイヤを構成する材料の結晶粒が大きくなるとクラックが進展しにくくなる。このことによって、電極パッドとワイヤとの接合耐久性（例えば、いわゆるパワーサイクル試験や冷熱サイクル試験等に対する耐久寿命）を向上させ得る。
本発明の製造方法によると、半導体素子とハウジングとが分離された状態で接合部に熱処理を施すことが可能である。したがって、このハウジングが樹脂製である場合にも、熱処理時の熱によってハウジングが損傷することがない。また、この製造方法では、リフロー半田付を行う際の雰囲気温度を利用してワイヤと電極パッドとの接合部に熱処理を施す。これにより半導体装置の生産効率および／またはエネルギー効率を向上させることができる。
【０００８】
本発明の方法は、前記ワイヤ（素子側ワイヤ）が基板の表面に設けられた中継パッドおよび前記電極パッドに接合されているとともに、ハウジング端子および中継パッドに接合されたハウジング側ワイヤを備えた構成の半導体装置の製造に好ましく適用される。本発明の好ましい態様では、樹脂製ハウジングに金属板を組み付けた後に、ハウジング端子および中継パッドにハウジング側ワイヤを接合する。これにより、素子側ワイヤ、ハウジング側ワイヤおよび両ワイヤが共通的に接合される中継パッドを介して、電極パッドとハウジング端子とが電気的に接続される。
かかる構成の半導体装置では、電極パッドからハウジング端子に至る導電経路が、素子側ワイヤとハウジング側ワイヤとに分割して形成されている。このことによって、半導体素子とハウジングとが分離された状態で電極パッドと素子側ワイヤとの接合部を熱処理し、次いで半導体素子とハウジングとを一体化し、その後にハウジング端子と中継パッドとを電気的に接合することができる。したがって本発明の方法で製造するのに適している。
【０００９】
また、上述したような半導体装置の他の好ましい製造方法は、前記半導体素子を基板の表面に接合する工程と、前記半導体素子の非接合面に形成されている電極パッドに前記ワイヤを超音波接合する工程と、前記電極パッドと前記ワイヤの接合部を熱処理する工程と、前記基板の裏面を金属板の表面にリフロー半田付する工程と、前記金属板を前記ハウジングに組み付ける工程を包含する。前記超音波接合工程は前記熱処理工程に先立って実行される。前記熱処理工程は前記組付工程よりも後に実行される。前記熱処理工程では、前記電極パッドと前記ワイヤの接合部を含んで前記ハウジングから離隔する範囲において前記金属板の裏面に発熱器を接触させる。その発熱器からの伝熱によって、前記接合部を、前記ワイヤを構成する材料の結晶粒の成長を促進する温度域に加熱する。
かかる製造方法によると、電極パッドとワイヤとの接合部に発熱器からの熱を効率よく伝えることができる。また、発熱器がハウジングに直接接触することがないので、熱によるハウジングの損傷を抑制し得る。
【００１０】
上述したような半導体装置の他の好ましい製造方法は、前記半導体素子を基板の表面に接合する工程と、前記半導体素子の非接合面に形成されている電極パッドに前記ワイヤを超音波接合する工程と、前記電極パッドと前記ワイヤの接合部を熱処理する工程と、前記基板の裏面を金属板にリフロー半田付する工程と、前記金属板を前記ハウジングに組み付ける工程を包含する。前記超音波接合工程は前記熱処理工程に先立って実行される。前記熱処理工程では、前記電極パッドと前記ワイヤの接合部に熱線を照射することによって、前記接合部を、前記ワイヤを構成する材料の結晶粒の成長を促進する温度域に加熱する。
かかる製造方法では、電極パッドとワイヤとの接合部に熱線を照射することによって該接合部を局部的に加熱する。したがって、前記組付工程よりも後に熱処理工程を実行する場合にも熱によるハウジングの損傷を抑制し得る。
【００１１】
前記熱処理は、ワイヤと電極パッドとの接合部が２００〜４５０℃（より好ましくは２５０〜４００℃）の温度域に加熱される条件で行うことが好ましい。かかる温度域は、アルミニウムまたはアルミニウム合金の結晶粒を効率よく成長させるために適しているとともに、半導体素子等の装置構成部品に損傷を与えにくいためである。
【００１２】
本発明の製造方法に用いるワイヤとしては、純度９９％以上（より好ましくは９９．９％以上、さらに好ましくは９９．９９％以上）のアルミニウムからなるものが特に好ましい。かかる組成のワイヤを用いた場合には、超音波接合後の加熱によりワイヤ接合耐久性を向上させるという本発明の効果が特に顕著に発揮される。
【００１３】
また、本発明によると、半導体素子表面に設けられた電極パッドと純度９９％以上（より好ましくは９９．９％以上、さらに好ましくは９９．９９％以上）のアルミニウムからなるワイヤとの超音波接合部の接合耐久性を向上させる方法が提供される。その方法では、該接合部を２００〜４５０℃の温度域に加熱する。接合部にかかる熱処理を施すことにより、ワイヤの加工硬化が緩和されて接合耐久性が向上する。かかる耐久性向上方法は、例えば、本発明のいずれかの半導体装置製造方法に対して好ましく適用することができる。
【００１４】
【発明の実施の形態】この発明はまた、下記の形態で実施することができる。
（形態１）
本発明の半導体装置に備えられる半導体素子が電力用半導体素子である。
電力用半導体素子は、その作動に伴う発熱量が大きいので、電極パッドとワイヤとの接合部に、素子とワイヤとの熱膨張率の違いに起因する大きな熱応力がかかりやすい。このため、電力用半導体素子の作動を繰り返すと、冷熱サイクルにより接合部にクラックが発生・進展しやすい傾向にある。したがって、本発明を適用することにより接合部の耐久性向上を図ることが特に有効である。
【００１５】
（形態２）
本発明によると、ハウジング端子を有するハウジングと、
そのハウジングに保持された金属板と、
その金属板に接合されているとともに表面に中継パッドが設けられた基板と、その基板に接合されているとともに非接合面に電極パッドが設けられた半導体素子と、
前記電極パッドと前記中継パッドに超音波接合された素子側ワイヤと、
前記ハウジング端子と前記中継パッドに接合されたハウジング側ワイヤとを備える半導体装置が提供される。
【００１６】
かかる構成の半導体装置は、電極パッドからハウジング端子に至る導電経路が、素子側ワイヤとハウジング側ワイヤとに分割して形成されている。このことは本発明の製造方法にとって都合がよい。例えば、半導体素子とハウジングとが分離された状態で電極パッドと素子側ワイヤとの接合部を熱処理し、次いで半導体素子とハウジングとを一体化し、その後にハウジング端子と中継パッドとを容易に電気的に接合することができる。半導体素子とハウジングとが分離された状態で熱処理を行うのに適しているということは、このハウジングが樹脂製である場合には特に有益である。なお、ハウジング側ワイヤに代えてワイヤ以外の形態を有する導電部材（例えば金属板等）を用い、この導電部材によって中継パッドとハウジング端子とが接続された構成の半導体装置であってもよい。
【００１７】
（形態３）
電極パッドにワイヤを超音波接合する工程では、そのワイヤの加工度が３０％以下（典型的には５〜３０％）、好ましくは２０％以下（典型的には５〜２０％）となるように超音波接合を行う。ここで「加工度」とは、接合前のワイヤの外形（典型的には直径）に対する接合後のワイヤの外形（典型的には幅）の変化率（潰れ量）をいう。例えば、直径４００μｍのワイヤを超音波接合し、これにより形成された接合部のワイヤ幅が４８０μｍであるとき、このワイヤの加工度は１２０％である。
電極パッドとワイヤとの接合部におけるワイヤの加工度が上記範囲にある場合には、接合後のワイヤを熱処理したときに結晶粒成長がよく促進される。したがって、上記範囲の加工度とすることにより効率よく熱処理を行うことができる。このことによって生産性が向上する。
【００１８】
本発明の製造方法を適用すると、電極パッドとワイヤとの接合部を熱処理することによりこの接合部の耐久性が向上する。したがって、熱処理を行わない場合に比べてワイヤの加工度を低くしても同等以上の（実用上十分な）耐久性を有する半導体装置を製造し得る。このようにワイヤの加工度を低くし得るということは、半導体素子へのボンディングダメージを軽減するという観点から好ましい。特に、比較的太いボンディングワイヤを電極パッドに接合する場合にはボンディングダメージが大きくなりがちなので、本実施形態の適用によりダメージを低減する実益が大きい。
【００１９】
本実施形態は、電極パッドに接合されるワイヤの直径が１５０μｍ以上（典型的には１５０〜１０００μｍ）である場合に好ましく適用され、ワイヤの直径が３００μｍ以上（典型的には３００〜１０００μｍ）である場合にさらに好ましく適用される。また、電力用半導体素子を備える半導体装置（パワーモジュール）の製造に好ましく適用される。
【００２０】
（形態４）
本発明は、一本のワイヤが一つの半導体素子表面の二点以上を含む箇所にステッチボンディングされている構成の半導体装置の製造に好ましく適用される。また、本発明のワイヤ接合耐久性向上方法は、このようにステッチボンディングされているワイヤに対して好ましく適用される。
かかる形態では、接合部（ステッチ）の間を結ぶワイヤの形状（ループ形状）が温度変化や外力等によって変形することがある。従来は、このようなループ形状の変化により接合部に応力が加わりやすかった。このため、ステッチボンディングされたワイヤでは接合耐久性が低下しやすかった。ステッチの間隔が比較的狭い場合にはこのような傾向が特に顕著であった。本発明によると、ワイヤの超音波接合部に熱処理を施すことによりワイヤの加工硬化が緩和される（熱処理前よりも柔らかくなる）。その結果、接合部のワイヤがループ形状の変化に追随して変形しやすくなるので、ループ形状が変化したときに接合部に加わる応力が低減される。このことによってワイヤの接合耐久性が向上する。
【００２１】
【実施例】以下、本発明の好適な実施例について詳細に説明する。
本発明を適用して製造される半導体装置に備えられる素子としては、各種の半導体素子（ＩＧＢＴ（Ｉｎｓｕｌａｔｅｄ Ｇａｔｅ Ｂｉｐｏｌａｒ Ｔｒａｎｓｉｓｔｏｒ）等のバイポーラトランジスタや、ＭＯＳ等の電界効果型トランジスタ等）を用いることができる。半導体装置がパワーモジュールである（典型的には、ＩＧＢＴ、パワーＭＯＳ等の電力用半導体素子（パワー素子）を備える）場合には、本発明を適用することによる効果（接合耐久性の向上等）が特によく発揮される。
【００２２】
本発明の製造方法で半導体素子の電極パッドに超音波接合されるワイヤは、アルミニウムまたはアルミニウム合金をその構成材料とする。ここで「アルミニウム合金」とは、アルミニウムを主体とする合金（例えばニッケル−アルミニウム合金）をいう。本発明においては、純度９９％以上（特に好ましくは９９．９９％以上）のアルミニウムからなるワイヤが特に好ましく用いられる。
【００２３】
このようなアルミニウム（Ａｌ）またはＡｌ合金からなるワイヤ（以下、「Ａｌ系ワイヤ」ということもある。）としては、比較的大きな平均結晶粒径を有するものが好ましく用いられる。例えば、冷間引抜後に熱処理加工（結晶粒を成長させるような熱処理加工）が施されたＡｌ系ワイヤ（特に好ましくは純度９９．９９％以上のＡｌ系ワイヤ）は、本発明の製造方法にとって好ましいＡｌ系ワイヤの典型例である。このようなＡｌ系ワイヤは、超音波接合後の熱処理によって結晶粒を効果的に成長させることができるためである。超音波接合に供される前の平均結晶粒径が１５μｍ以上（典型的には１５〜２００μｍ、好ましくは３０〜１５０μｍ）であるＡｌ系ワイヤが好ましく用いられる。
【００２４】
通常、このようなＡｌ系ワイヤを超音波接合に供すると、金属組織が振動されることにより結晶粒が細分化される。その結果、少なくとも接合界面付近の結晶粒径は小さくなる。例えば、接合界面付近の平均結晶粒径が５μｍ程度あるいはそれ以下になる。このように組織が細密化されることにより、ワイヤの硬度、内部応力、ヤング率等が上昇する（加工硬化現象）。このことによって、ワイヤの接合強度（一般にシェア強度で表される）は上昇する傾向にある。
この接合部に所定の温度域で熱処理を施すと、細分化された結晶粒が成長（再結晶および再成長）する。このときワイヤの加工硬化が緩和される。ワイヤの結晶粒径が大きくなると、、より結晶粒径が小さい場合に比べてクラックの発生および／または進展が抑制される。その結果、ワイヤ接合部の耐久寿命が改善される。特に限定するものではないが、熱処理後におけるＡｌ系ワイヤ（特にその接合界面付近）の平均結晶粒径は３０μｍ以上（典型的には３０〜２００μｍ）であることが好ましく、５０μｍ以上（典型的には５０〜１５０μｍ）であることがより好ましい。
【００２５】
ワイヤ接合部の熱処理に適した温度は、ワイヤの組成によっても異なる。純度９９．９９％以上のアルミニウムワイヤを用いる場合には、接合部を２００〜４５０℃（さらに好ましくは２５０〜４００℃）の温度域に加熱する熱処理を施すことが特に好ましい。この温度域では、アルミニウム結晶粒の成長がよく促進される。かかる温度域で熱処理を施すことにより、ワイヤの加工硬化（主として超音波接合に起因する）を効果的に緩和することができる。このことによって接合部の耐久性をよく向上させることができる。ここで、ワイヤの加工硬化が緩和されたことは、ワイヤの硬度低下、内部応力緩和、ヤング率低下等のうち少なくとも一つの事象として把握され得る。
なお、ワイヤ接合部の「初期接着強度」についてみると、上述した加工硬化の緩和、硬度低下、内部応力緩和およびヤング率低下は、いずれも初期接着強度を低下させる傾向にある。したがって、本発明の典型的な態様では、上記熱処理を施すことにより接合耐久性が向上する一方、熱処理前に比べて接合部の初期接着強度（シェア強度）はむしろ低下する。
【００２６】
本発明の製造方法に用いられる樹脂製ハウジングを構成する樹脂材料としては、ポリフェニレンサルファイド（ＰＰＳ）、ポリフェニレンエーテル（ＰＰＥ）、メラミン樹脂、ポリカーボネート（ＰＣ）、ポリエーテルスルホン（ＰＥＳ）、ポリスルホン（ＰＳＦ）、ポリエーテルイミド、ポリイミド、ポリアミド、ポリアミドイミド（ＰＡＩ）、アクリロニトリル−スチレン樹脂（ＡＳ樹脂）、ポリプロピレン（ＰＰ）、ポリエチレン（ＰＥ）、ポリメチルペンテン（ＰＭＰ）、ポリアリレート（ＰＡＲ）、ポリエーテルエーテルケトン（ＰＥＥＫ）、ポリエーテルケトン（ＰＥＫ）等の樹脂を選択することができる。これらのうち耐熱性が１５０℃以上の樹脂材料が好ましい。かかる樹脂材料の典型例としては、ＰＰＳ，ＰＥＥＫ，ＰＣ等が挙げられる。また、後述する第二実施例または第三実施例のように、半導体素子と樹脂製ハウジングとを一体化した後に接合部の熱処理を行う製造方法を採用する場合は、２００℃以上の耐熱性を有する樹脂材料を用いることが好ましい。本発明にとって特に好適な樹脂材料はＰＰＳである。
この樹脂製ハウジングは、上述したような樹脂材料に加えて繊維状または粉末状の充填材等を含有することができる。ガラスファイバー、アルミナ繊維等のセラミック系ファイバーが好ましく用いられる。
【００２７】
なお、本発明の製造方法は、あらかじめ超音波接合されたワイヤと電極パッドの接合部に、この接合部を覆うように熱硬化性樹脂（典型的にはポリイミド）を塗布して硬化させる工程を包含することができる。この場合には、硬化した樹脂によってワイヤと電極パッドの接合部を保護し、この接合部の耐久性をさらに向上させることができる。塗布された熱硬化性樹脂の硬化を促進するために、前記ワイヤを構成する材料の結晶粒の成長を促進する温度域に加熱してもよい。この場合には、熱硬化性樹脂を硬化させる際の加熱を利用してワイヤと電極パッドの接合部を熱処理することができるので好都合である。あるいは従来公知の他の耐久性向上方法を適用してもよい。
【００２８】
以下、本発明をパワーモジュールに適用した具体的実施例を説明するが、本発明をかかる実施例に示すものに限定することを意図したものではない。
＜第一実施例＞
本実施例は、本発明を適用して図１に示す構造の半導体装置（パワーモジュール）を製造する例である。
図１に示すように、半導体装置１００は、ＰＰＳ樹脂製のハウジング４０に、複数（図１には二つを示している）のパワーユニット１０２を組み付けて構成されている。各ユニット１０２は、電力用半導体素子（ＩＧＢＴ）１０と、セラミックス（ここでは窒化アルミニウム）を主体とする絶縁基板２０と、銅−モリブデン合金製の放熱板３０と、素子１０と基板２０との間に架け渡された素子側ワイヤ５６とを備える。
【００２９】
基板２０の表面（図１で上側の面：素子１０が接合される側の面）には、導電性接合材層（ここでは半田を導電性接合材とする半田層）５２によって、半導体素子１０の一面が接合されている。一方、基板２０の裏面（図１で下側の面：素子１０が接合される側とは反対側の面）は、半田層５４によって放熱板３０に接合されている。基板２０の両面にはＡｌ箔２２，２４が設けられている。基板２０の表面に設けられたＡｌ箔２２のうち、素子１０よりも外方に位置する一部は中継パッド２２ａを構成している。
なお、導電性接合材層５２を構成する導電性接合材としては、半田を用いることが特に好ましいが、半田以外の低融点金属類を用いてもよい。また、有機高分子等からなるマトリックス樹脂中に導電性充填材が分散された導電性樹脂材料を用いてもよい。このマトリックス樹脂としてはエポキシ樹脂、ポリイミド樹脂、フェノール樹脂、シリコーン樹脂等を用いることができる。導電性充填材としては、銅、銀、金、白金、ニッケル、カーボン等からなる導電性繊維、導電性微粒子等を用いることができる。
【００３０】
半導体素子１０の他面（非接合面）には、厚さ約４μｍのＡｌ膜から構成された複数（図１には二つを示している）の電極パッド１２が設けられている。素子側ワイヤ５６は、複数の電極パッド１２および中継パッド２２ａに超音波接合されている。本実施例では、素子側ワイヤ５６が一つの電極パッド１２に接合された箇所と他の電極パッド１２に接合された箇所との間隔（ステッチ間隔）は約３ｍｍである。この素子側ワイヤ５６を介して電極パッド１２と中継パッド２２ａとが電気的に接続されている。なお、本実施例で用いた素子側ワイヤ５６は微量のＮｉを含むＡｌ（Ａｌ純度約９９．９９％）からなる。その直径は約４００μｍである。
【００３１】
ハウジング４０は、外壁４２とその外壁に囲まれた底面４４とを有する。底面４４には複数の開口部４６が形成されている。各ユニット１０２を構成する放熱板３０をハウジング４０の下側から各開口部４６に嵌合させることにより、ハウジング４０にユニット１０２が組み付けられている。放熱板３０に接合された基板２０および素子１０は外壁４２の内側に位置している。開口部４６の周囲の底面４４には、Ａｌ膜によって構成されたハウジング端子４８が設けられている。このハウジング端子４８および中継パッド２２ａに、導電性金属（ここでは素子側ワイヤ５６と同様の構成材料）からなるハウジング側ワイヤ５８ａが超音波接合されている。中継パッド２２ａには、電極パッド１２に接合された素子側ワイヤ５６と、ハウジング端子４８に接合されたハウジング側ワイヤ５８ａとが共通的に接合されている。このことによって電極パッド１２とハウジング端子４８が電気的に接続されている。他のハウジング側ワイヤ５８ｂは、中継パッド２２ａ以外の部分のＡｌ箔２２とハウジング端子４８とに接合されて、これらを電気的に接続している。この場合には二つの素子１０が直列に接続される。なお、これらのハウジング側ワイヤ５８ａ，５８ｂの直径はいずれも約４００μｍである。
【００３２】
以下、図面を用いてこの半導体素子１００の製造例を説明する。
まず、図２に示すように、基板２０の所定箇所に半導体素子１０を半田付する。この半田付は、一般的な半導体素子実装方法等により実施することができる。
【００３３】
次いで、図３に示すように、複数（ここでは二つ）の電極パッド１２および中継パッド２２ａに素子側ワイヤ５６を超音波接合（ウェッジボンディング）する。この超音波接合は、例えば、ウェッジツールにより素子側ワイヤ５６を被接合物（ここでは電極パッド１２または中継パッド２２ａ）に押し付け、６０ＫＨｚ〜１００ＫＨｚの超音波振動を加えることによって実施することができる。本実施例では、ワイヤの加工度が約２０％となるように超音波接合を行った。
【００３４】
超音波接合前の素子側ワイヤ５６を走査型イオン顕微鏡（ＳＩＭ：Ｓｃａｎｎｉｎｇ Ｉｏｎ Ｍｉｃｒｏｓｃｏｐｅ） により観察したところ、その構成材料の結晶粒径は主として３０〜１００μｍの範囲にあった。また、超音波接合後においても、電極パッド１２と素子側ワイヤ５６との接合部５６ａから離れた箇所では、ワイヤ構成材料の結晶粒径は主として同範囲にあった。一方、接合部５６ａ（特に接合界面付近）における結晶粒径は主として５μｍ以下であり、超音波接合前に比べて明らかに結晶粒径が小さく（結晶粒が細かく）なっていた。
【００３５】
次に、図４に示すように、基板２０の裏面を放熱板３０にリフロー半田付により接合する。すなわち、基板２０と放熱板３０との間に半田箔を挟み、この状態でリフロー炉内に投入し、所定の温度プロファイルで半田箔を溶融させる。その後に冷却して、基板２０の裏面と放熱板３０とを接合する半田層５４を形成する。本実施例では、２００℃以上の温度域に２５〜３０分、そのうち３００℃以上の温度域に１５〜２０分保持されるような温度プロファイルでリフロー半田付を行った。このときの最高到達温度は３１０〜３４０℃であった。このリフロー半田付工程により、素子側ワイヤ５６と電極パッド１２の接合部５６ａおよび素子側ワイヤ５６と中継パッド２２ａの接合部に熱処理を施した。リフロー半田付工程後、上記と同様にして接合部５６ａをＳＩＭにて観察したところ、該リフロー半田付工程前には５μｍ以下であった接合界面付近の結晶粒径が５０〜１００μｍと顕著に大きくなっていた。
【００３６】
このようにして作製されたユニット１０２を、図５に示すように、ハウジング４０の開口部４６に組み付ける。その後、図１に示すように、ハウジング端子４８および中継パッド２２ａにハウジング側ワイヤ５８ａを、またハウジング端子４８およびＡｌ箔２２にハウジング側ワイヤ５８ｂを超音波接合する。この超音波接合は、例えば、上述した素子側ワイヤ５６の接合条件と同様の条件により行うことができる。以上のようにして半導体装置１００を作製した。
【００３７】
本実施例の製造方法では、電極パッド１２と素子側ワイヤ５６との接合部５６ａを有するユニット１０２をハウジング４０に組み付ける前に（ハウジング４０と分離された状態で）、その接合部５６ａに熱処理を施す。したがってハウジング４０が熱処理時の熱によって損傷を受けることが回避される。また、基板２０を放熱板３０にリフロー半田付する際の加熱を利用して上記熱処理を行うので、生産効率およびエネルギー効率が良い。
【００３８】
＜第二実施例＞
本実施例は、本発明を適用して図６に示す構造の半導体装置（パワーモジュール）を製造する例である。以下、第一実施例に係る部材と同様の機能を果たす部材については同じ符号を付し、その説明を省略する。
この半導体装置１１０は、図６に示すように、ＰＰＳ樹脂製のハウジング４０に、複数（図１には二つを示している）のパワーユニット１１２を組み付けて構成されている。ワイヤ５７は、第一実施例で用いた素子側ワイヤ５６（図１参照）と同様の材料により構成されている。その性状（直径および結晶粒径等）も第一実施例で用いた素子側ワイヤ５６と同様である。本実施例では、複数（図６には二つを示している）の電極パッド１２およびハウジング端子４８にワイヤ５７が接合されている。このワイヤ５７によって電極パッド１２とハウジング端子４８とが電気的に接続されている。すなわち、本実施例で製造する半導体装置１１０には、図１に示すような中継パッド２２ａは設けられていない。その他の部分の構成は第一実施例と概ね同様である。
【００３９】
以下、この半導体装置１１０の製造例につき説明する。
まず、図７に示すように、基板２０の所定箇所に半導体素子１０を半田付する。この半田付は、一般的な半導体素子実装方法等により実施することができる。次いで、図８に示すように、リフロー半田付によって基板２０の裏面を放熱板３０に接合する。このリフロー半田付工程は、例えば第一実施例と同様の温度プロファイルにより行うことができる。あるいは、第一実施例とは異なる温度プロファイルでリフロー半田付工程を行ってもよい。例えば、３００℃に到達しない温度プロファイル、２００℃に到達しない温度プロファイル等を採用することも可能である。さらに、リフロー半田付以外の方法（例えば、導電性接合材として上述したような導電性樹脂材料を用いる方法）によって基板２０と放熱板３０とを接合してもよい。
【００４０】
このようにして作製したユニット１１２を、図９に示すように、ハウジング４０の開口部４６に組み付ける。そして、図６に示すように、複数（ここでは二つ）の電極パッド１２およびハウジング端子４８にワイヤ５７を超音波接合する。また、基板２０の表面に設けられたＡｌ箔２２およびハウジング端子４８にハウジング側ワイヤ５８ｂを超音波接合する。これらの超音波接合は、例えば、第一実施例で述べた素子側ワイヤの接合条件と同様の条件により行うことができる。また、接合部におけるワイヤの加工度は５〜３０％（例えば２０％）とすることができる。
【００４１】
そして、図１０に示すような熱処理装置を用いて、ワイヤ５７と電極パッド１２との接合部５７ａに熱処理を施す。この熱処理装置６０は、発熱器６２と、この発熱器６２を放熱板３０の所定箇所に安定的に接触させる熱処理治具６４とを備える。
発熱器６２は、発熱体６２ａおよびこれを埋設する保持体６２ｂを備える。発熱体６２ａは、高抵抗の金属線（ここではニクロム線）等から構成されており、通電により発熱する性質を有する。保持体６２ｂは、熱伝導性がよくかつ柔軟な材料から構成されることが好ましい。本実施例では、保持材６２ｂの構成材料としてニトリルもしくはシリコンゴムを用いた。
【００４２】
熱処理治具６４は、基台６４ａおよび押さえ板６４ｂと、これらを締め付けるボルト６４ｃとを備える。基台６４ａの上に発熱器６２を配置し、その上に半導体装置１１０を載せる。ハウジング４０の上に押さえ板６４ｂを載せてボルト６４ｃを締めると、発熱器６２が放熱板３０に押し付けられる。このとき発熱器６２は、図１０に示すように、放熱板３０のうちハウジング４０から離隔しているとともに、電極パッド１２とワイヤ５７との接合部５７ａを放熱板３０に投影した箇所（図１０で接合部５７ａの真下に位置する箇所）を含む範囲に接触させる。本実施例では、放熱板３０の中央部に素子１０が搭載されているとともに放熱板３０の外周がハウジング４０に保持されているので、図１０に示すように、放熱板３０の中央部に発熱器６２を接触させている。
この状態で発熱体６２ａに通電して発熱させ、その熱によって接合部５７ａを約２００〜４５０℃の範囲（例えば約２５０℃）に加熱する。加熱時間は特に限定されないが、通常は約１〜３０分間（例えば約５分間）の範囲とすることが適当である。この熱処理によって接合部５７ａの耐久性を向上させる。
【００４３】
本実施例では、発熱器６２が上述した範囲に配置されていることにより、この発熱器６２からの熱を接合部５７ａに効率よく伝えることができる。また、発熱器６２がハウジング４０に直接接触することはないので、熱によるハウジング４０の損傷を抑制し得る。かかる構成の熱処理装置６０を用いるとともに、保持体６２ｂとして柔軟性に優れた材質を選択することにより、発熱器６２と放熱板３０とをよく密着させることができる。このことによって熱処理効率をさらに向上させ得る。
【００４４】
＜第三実施例＞
本実施例は、第二実施例の製造方法において、電極パッド１２とワイヤ５７との接合部５７ａを熱処理する際の操作方法が異なる例である。以下、第二実施例に係る部材と同様の機能を果たす部材については同じ符号を付し、その説明を省略する。
【００４５】
第二実施例と同様にして作製されたユニット１１２をハウジング４０の開口部４６に組み付け、ワイヤ５７およびハウジング側ワイヤ５６ｂをそれぞれ所定の箇所に超音波接合する。
その後、図１１に示すように、電極パッド１２とワイヤ５７との接合部５７ａに熱線照射器７０を用いて熱線Ｈを照射する。これにより接合部５７ａを約２００〜４５０℃の範囲（例えば約２５０℃）に加熱する。照射時間（加熱時間）は特に限定されないが、通常は約０．５〜３０秒間（例えば約２秒間）の範囲とすることが適当である。熱線照射器７０としては、一般的なキセノンランプ、レーザ（例えばＹＡＧレーザ、ＣＯ２レーザ等）等を用いることができる。本実施例では熱線照射器７０としてキセノンランプを用いた。また、特に限定するものではないが、通常は接合部から約５〜１００ｍｍ（ここでは約２０ｍｍ）程度の距離から熱線Ｈを照射することが適当である。このようにして接合部５７ａに熱処理を施し、接合部５７ａの耐久性を向上させた。
【００４６】
本実施例の製造方法では、熱線照射器７０を用いた局部加熱によって接合部５７ａに熱処理を施す。したがって、ハウジング４０が熱により損傷を受けることが抑制される。また、必要箇所のみを直接加熱するので生産効率およびエネルギー効率がよい。
【００４７】
＜実験例１＞
ワイヤ構成材料の結晶粒成長に及ぼす熱処理条件の影響について検討した。
第一実施例で用いた素子側ワイヤと同じＡｌ系ワイヤ（Ａｌ純度約９９．９９％）を、第一実施例と同様の条件で電極パッドに超音波接合した。ここで、接合部におけるワイヤの加工度は約６０％とした。接合直後にその接合部をＳＩＭにより観察したところ、ワイヤ構成材料の平均結晶粒径は５μｍ以下であった。
このようにして半導体素子の電極パッドにワイヤを接合したもの（素子−ワイヤ接合物）を５つ作製し、それぞれ１００℃、２００℃、２５０℃、３００℃、４００℃および５００℃の各温度に５分間保持する熱処理を施した。その後、再び電極パッドとワイヤとの接合部を観察して、同部分の平均結晶粒径を求めた。その結果を図１２に示す。
【００４８】
図１２から判るように、熱処理温度が１００℃では結晶粒の成長はほとんどみられない。一方、２００℃以上では熱処理による結晶粒の成長がみられ、２００℃から３００℃までの温度域では熱処理温度の上昇とともに結晶粒の成長を促進する効果が大きくなる。その結晶粒成長促進効果は、熱処理温度３００℃以上ではほぼ飽和する。このことは、２００℃以上の温度域で５分間の熱処理を施すことにより接合耐久性を向上させ得ること、３００℃以上の温度域で熱処理することによりさらに良好な結果が得られることを示している。
【００４９】
＜実験例２＞
ワイヤ構成材料の結晶粒成長に及ぼすワイヤ加工度の影響について検討した。第一実施例で用いた素子側ワイヤと同じＡｌ系ワイヤ（Ａｌ純度約９９．９９％）を電極パッドに超音波接合した。ここで、超音波接合条件を調整することにより、加工度の異なる複数の素子−ワイヤ接合物を作製した。これらの接合物を３００℃に１０分間保持した。このようにして熱処理を施した後、その接合部をＳＩＭにより観察して平均結晶粒径を求めた。その結果を図１３に示す。
図１３から判るように、ワイヤの加工度を５〜３０％以上（特に５〜２０％）とすると、この加工度がより高い場合（例えば４０％以上の場合）に比べて結晶粒の成長がよく促進される。
【００５０】
＜実験例３＞
熱処理の有無が接合部の耐久性に及ぼす影響につき検討した。
第二実施例により製造した半導体装置（サンプル１）と、熱処理を行わない点を除いてはサンプル１と同様にして製造した半導体装置（サンプル２）との接合耐久性を以下のようにして比較した。
すなわち、これらの半導体装置にそれぞれ電源を接続して２秒通電／１０秒遮断のサイクルを行った。このとき、接合部のΔＴｊ（１サイクル中の素子の温度変化の幅を示す）が約１００℃となるように条件を調整した。このパワーサイクル試験によって、サイクル数（パワーサイクル数）と接合部のシェア強度（剪断試験による強度）との関係を求めた。その結果を図１４に示す。
【００５１】
図１４から判るように、パワーサイクル試験開始時のシェア強度は、熱処理を施したサンプル１よりも熱処理を施さないサンプル２のほうがむしろ大きい。これは、超音波接合によって起こるＡｌの加工硬化が、サンプル１では熱処理によって緩和されている（したがって熱処理前よりもワイヤが柔らかくなっている）ためと考えられる。この関係はサイクル数１０００前後で逆転し、以後は熱処理を施したサンプル１のほうが高いシェア強度を示すようになる。シェア強度がゼロになる（接合部が破断した状態に相当する）までのサイクルは、サンプル２よりもサンプル１のほうが５０％程度多かった。すなわち、熱処理を施すことによって接合部の耐久寿命を５０％程度延ばすことができた。
【００５２】
なお、本明細書により開示される技術には以下のものが含まれる。
素子表面に設けられた電極パッドにアルミニウムまたはアルミニウム合金を構成材料とするワイヤを加工度５〜３０％（好ましくは５〜２０％）で超音波接合する工程と、その接合部を２００〜４５０℃（より好ましくは２５０〜４００℃）の温度域で熱処理する工程とを包含する半導体装置製造方法。
この製造方法は、ワイヤの直径が１５０μｍ以上（典型的には１５０〜１０００μｍ）である場合に好ましく適用され、３００μｍ以上（典型的には３００〜１０００μｍ）である場合に特に好ましく適用される。また、半導体装置を構成する半導体素子が電力用半導体素子である場合に好ましく適用される。
【００５３】
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。
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】第一実施例により製造された半導体装置を示す模式的断面図である。
【図２】第一実施例による半導体装置製造過程を示す模式的断面図である。
【図３】第一実施例による半導体装置製造過程を示す模式的断面図である。
【図４】第一実施例による半導体装置製造過程を示す模式的断面図である。
【図５】第一実施例による半導体装置製造過程を示す模式的断面図である。
【図６】第二実施例により製造された半導体装置を示す模式的断面図である。
【図７】第二実施例による半導体装置製造過程を示す模式的断面図である。
【図８】第二実施例による半導体装置製造過程を示す模式的断面図である。
【図９】第二実施例による半導体装置製造過程を示す模式的断面図である。
【図１０】第二実施例による半導体装置製造過程を示す模式的断面図である。
【図１１】第三実施例による半導体装置製造過程を示す模式的断面図である。
【図１２】熱処理温度と結晶粒の大きさとの関係を示す特性図である。
【図１３】ワイヤ加工度と結晶粒の大きさとの関係を示す特性図である。
【図１４】熱処理の有無と接合部の耐久性との関係を示す特性図である。
【符号の説明】
１０ ：半導体素子
１２ ：電極パッド
２０ ：絶縁基板（基板）
２２ａ：中継パッド
３０ ：放熱板（金属板）
４０ ：ハウジング
４６ ：開口部
４８ ：ハウジング端子
５２ ：半田層（導電性接合材層）
５４ ：半田層
５６ ：素子側ワイヤ（ワイヤ）
５７ ：ワイヤ
５８ａ，５８ｂ：ハウジング側ワイヤ
６２ ：発熱器
６２ａ：発熱体
６２ｂ：保持体
７０ ：熱線照射器
１００，１１０：半導体装置
１０２，１１２：パワーユニット[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device having improved durability (wire bonding durability) of a bonding portion between an electrode pad provided on the surface of a semiconductor element and a bonding wire. The present invention also relates to a method for improving the wire bonding durability.
[0002]
2. Description of the Related Art A conductor (electrode pad) provided on the surface of a semiconductor element (chip) and an external lead terminal are connected by a fine wire (bonding wire) made of gold (Au), aluminum (Al) or the like. Later, a technique of heat treatment at a high temperature of 150 ° C. or higher is known (see, for example, Patent Document 1).
However, if such a technique is applied to a semiconductor device including a resin member (for example, a power module including a resin housing), the resin member may be damaged (deformed, altered, or the like) by the heat treatment. The technique described in the above publication is intended to improve the “initial adhesive strength” of the joint, and is not related to the durability (durability, etc.) of the joint.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 3-91938
[0004]
The present invention can be preferably applied to the manufacture of a semiconductor device having a resin member, and is excellent in durability (bonding durability) of the joint between the electrode pad and the bonding wire. Another object of the present invention is to provide a method of manufacturing a semiconductor device that can manufacture the semiconductor device. Another related object is to provide a semiconductor device suitable for manufacturing by such a manufacturing method. Another object of the present invention is to provide a method for improving the bonding durability between an electrode pad and a bonding wire.
[0005]
[Means for Solving the Problems, Actions and Effects] The present inventor has solved the above-mentioned problems by making the semiconductor device a predetermined structure and heat-treating the joint before the resin member and the semiconductor element are integrated. I found that I could do it. Moreover, it discovered that the said subject could be solved by employ | adopting a predetermined heat processing method.
[0006]
According to the present invention, there is provided a method of manufacturing a semiconductor device in which a semiconductor element is assembled to a housing and an aluminum or aluminum alloy wire is bonded to the semiconductor element.
A preferable example of such a manufacturing method includes a step of bonding the semiconductor element to the surface of the substrate, a step of ultrasonically bonding the wire to an electrode pad formed on a non-bonding surface of the semiconductor element, and a back surface of the substrate. Including reflow soldering to a metal plate and assembling the metal plate to the housing. In this reflow soldering step, soldering is performed under the condition that the joint between the electrode pad and the wire is heated to a temperature range that promotes the growth of crystal grains of the material constituting the wire. According to this manufacturing method, the bonding portion between the wire and the electrode pad is heat-treated by performing the reflow soldering process.
[0007]
By performing such heat treatment, the growth of crystal grains of the wire constituent material (aluminum or aluminum alloy) is promoted. As a result, it is possible to obtain a semiconductor device in which the crystal grains at the bonding portion between the wire and the electrode pad are larger than when heat treatment is not performed. When the crystal grains of the material constituting the wire are increased, cracks are difficult to progress. This can improve the durability of bonding between the electrode pad and the wire (for example, the durability life against a so-called power cycle test or a thermal cycle test).
According to the manufacturing method of the present invention, it is possible to heat-treat the joint portion in a state where the semiconductor element and the housing are separated. Therefore, even when the housing is made of resin, the housing is not damaged by heat during heat treatment. Further, in this manufacturing method, heat treatment is performed on the bonding portion between the wire and the electrode pad using the atmospheric temperature when performing reflow soldering. Thereby, the production efficiency and / or energy efficiency of the semiconductor device can be improved.
[0008]
In the method of the present invention, the wire (element-side wire) is bonded to the relay pad provided on the surface of the substrate and the electrode pad, and includes a housing-side wire bonded to the housing terminal and the relay pad. It is preferably applied to the manufacture of semiconductor devices. In a preferred aspect of the present invention, after the metal plate is assembled to the resin housing, the housing side wire is joined to the housing terminal and the relay pad. Thereby, the electrode pad and the housing terminal are electrically connected through the element side wire, the housing side wire, and the relay pad to which both wires are commonly joined.
In the semiconductor device having such a configuration, the conductive path from the electrode pad to the housing terminal is divided into an element side wire and a housing side wire. This heat-treats the joint between the electrode pad and the element-side wire in a state where the semiconductor element and the housing are separated, then integrates the semiconductor element and the housing, and then electrically connects the housing terminal and the relay pad. Can be joined. Therefore, it is suitable for manufacturing by the method of the present invention.
[0009]
Further, another preferable manufacturing method of the semiconductor device as described above includes a step of bonding the semiconductor element to a surface of a substrate, and ultrasonic bonding of the wire to an electrode pad formed on a non-bonding surface of the semiconductor element. A step of heat-treating a bonding portion between the electrode pad and the wire, a step of reflow soldering the back surface of the substrate to the surface of the metal plate, and a step of assembling the metal plate to the housing. The ultrasonic bonding process is performed prior to the heat treatment process. The heat treatment step is performed after the assembly step. In the heat treatment step, a heater is brought into contact with the back surface of the metal plate in a range including the joint between the electrode pad and the wire and being separated from the housing. The joint is heated to a temperature range that promotes the growth of crystal grains of the material constituting the wire by heat transfer from the heat generator.
According to this manufacturing method, the heat from the heater can be efficiently transmitted to the joint between the electrode pad and the wire. Further, since the heat generator does not directly contact the housing, damage to the housing due to heat can be suppressed.
[0010]
Another preferable manufacturing method of the semiconductor device as described above includes a step of bonding the semiconductor element to a surface of a substrate and a step of ultrasonically bonding the wire to an electrode pad formed on a non-bonding surface of the semiconductor element. And a step of heat-treating the joint between the electrode pad and the wire, a step of reflow soldering the back surface of the substrate to a metal plate, and a step of assembling the metal plate to the housing. The ultrasonic bonding process is performed prior to the heat treatment process. In the heat treatment step, the bonding portion is heated to a temperature range that promotes the growth of crystal grains of the material constituting the wire by irradiating the bonding portion between the electrode pad and the wire with heat rays.
In such a manufacturing method, the joint is locally heated by irradiating the joint between the electrode pad and the wire with heat rays. Therefore, even when the heat treatment step is executed after the assembly step, damage to the housing due to heat can be suppressed.
[0011]
The heat treatment is preferably performed under the condition that the bonding portion between the wire and the electrode pad is heated to a temperature range of 200 to 450 ° C. (more preferably 250 to 400 ° C.). This is because such a temperature range is suitable for efficiently growing aluminum or aluminum alloy crystal grains, and is difficult to damage device components such as semiconductor elements.
[0012]
As the wire used in the production method of the present invention, a wire made of aluminum having a purity of 99% or higher (more preferably 99.9% or higher, more preferably 99.99% or higher) is particularly preferable. When a wire having such a composition is used, the effect of the present invention that the wire bonding durability is improved by heating after ultrasonic bonding is particularly remarkable.
[0013]
Further, according to the present invention, ultrasonic bonding between an electrode pad provided on the surface of a semiconductor element and a wire made of aluminum having a purity of 99% or more (more preferably 99.9% or more, more preferably 99.99% or more). A method for improving the joining durability of a part is provided. In this method, the joint is heated to a temperature range of 200 to 450 ° C. By applying the heat treatment to the joint, the work hardening of the wire is relaxed and the joining durability is improved. Such a durability improving method can be preferably applied to, for example, any one of the semiconductor device manufacturing methods of the present invention.
[0014]
DETAILED DESCRIPTION OF THE INVENTION The present invention can also be carried out in the following forms.
(Form 1)
The semiconductor element provided in the semiconductor device of the present invention is a power semiconductor element.
Since the power semiconductor element generates a large amount of heat due to its operation, a large thermal stress is likely to be applied to the joint between the electrode pad and the wire due to the difference in coefficient of thermal expansion between the element and the wire. For this reason, when the operation of the power semiconductor element is repeated, cracks tend to be generated and propagated in the joint portion due to the thermal cycle. Therefore, it is particularly effective to improve the durability of the joint by applying the present invention.
[0015]
(Form 2)
According to the present invention, a housing having a housing terminal;
A metal plate held in the housing;
A substrate bonded to the metal plate and provided with a relay pad on the surface; a semiconductor element bonded to the substrate and provided with an electrode pad on a non-bonded surface;
An element side wire ultrasonically bonded to the electrode pad and the relay pad;
A semiconductor device is provided that includes the housing terminal and a housing-side wire joined to the relay pad.
[0016]
In the semiconductor device having such a configuration, the conductive path from the electrode pad to the housing terminal is divided into an element side wire and a housing side wire. This is convenient for the production method of the present invention. For example, in a state where the semiconductor element and the housing are separated, the joint between the electrode pad and the element side wire is heat-treated, then the semiconductor element and the housing are integrated, and then the housing terminal and the relay pad are easily electrically connected. Can be joined. The fact that it is suitable for performing the heat treatment in a state where the semiconductor element and the housing are separated is particularly beneficial when the housing is made of resin. A semiconductor device having a configuration in which a conductive member (for example, a metal plate) having a form other than the wire is used instead of the housing-side wire and the relay pad and the housing terminal are connected by the conductive member may be used.
[0017]
(Form 3)
In the step of ultrasonically bonding the wire to the electrode pad, the processing degree of the wire is 30% or less (typically 5 to 30%), preferably 20% or less (typically 5 to 20%). Ultrasonic bonding is performed. Here, the “working degree” refers to a rate of change (crush amount) of the outer shape (typically width) of the wire after bonding with respect to the outer shape (typically diameter) of the wire before bonding. For example, when a wire having a diameter of 400 μm is ultrasonically bonded and the wire width of the bonded portion formed thereby is 480 μm, the processing degree of the wire is 120%.
When the degree of processing of the wire at the joint between the electrode pad and the wire is in the above range, crystal grain growth is well promoted when the joined wire is heat-treated. Therefore, heat treatment can be efficiently performed by setting the processing degree within the above range. This improves productivity.
[0018]
When the manufacturing method of the present invention is applied, the durability of the joint is improved by heat-treating the joint between the electrode pad and the wire. Accordingly, a semiconductor device having the same or higher (practical enough) durability can be manufactured even if the degree of processing of the wire is reduced as compared with the case where heat treatment is not performed. Thus, it is preferable from the viewpoint of reducing bonding damage to the semiconductor element that the degree of processing of the wire can be reduced. In particular, when a relatively thick bonding wire is bonded to the electrode pad, the bonding damage tends to be large. Therefore, the benefit of reducing the damage by applying this embodiment is great.
[0019]
This embodiment is preferably applied when the diameter of the wire bonded to the electrode pad is 150 μm or more (typically 150 to 1000 μm), and the wire diameter is 300 μm or more (typically 300 to 1000 μm). In some cases, it is more preferably applied. Moreover, it is preferably applied to the manufacture of a semiconductor device (power module) including a power semiconductor element.
[0020]
(Form 4)
The present invention is preferably applied to the manufacture of a semiconductor device having a structure in which one wire is stitch-bonded to a portion including two or more points on the surface of one semiconductor element. In addition, the wire bonding durability improving method of the present invention is preferably applied to the wire thus stitch-bonded.
In such a form, the shape (loop shape) of the wire connecting between the joint portions (stitches) may be deformed by a temperature change, an external force, or the like. Conventionally, stress is easily applied to the joint due to such a change in the loop shape. For this reason, the bonding durability of the wire subjected to the stitch bonding is likely to be lowered. This tendency was particularly remarkable when the interval between stitches was relatively narrow. According to the present invention, the work hardening of the wire is eased by applying a heat treatment to the ultrasonic bonding portion of the wire (softer than before the heat treatment). As a result, the wire at the joint is easily deformed following the change in the loop shape, so that the stress applied to the joint is reduced when the loop shape is changed. This improves the bonding durability of the wire.
[0021]
The preferred embodiments of the present invention will be described in detail below.
As an element provided in a semiconductor device manufactured by applying the present invention, various semiconductor elements (bipolar transistors such as IGBT (Insulated Gate Bipolar Transistor) and field effect transistors such as MOS) can be used. . When the semiconductor device is a power module (typically provided with a power semiconductor element (power element) such as IGBT, power MOS, etc.), the effects of applying the present invention (improvement of junction durability, etc.) Is particularly well demonstrated.
[0022]
The wire ultrasonically bonded to the electrode pad of the semiconductor element by the manufacturing method of the present invention is made of aluminum or aluminum alloy. Here, the “aluminum alloy” refers to an alloy mainly composed of aluminum (for example, nickel-aluminum alloy). In the present invention, a wire made of aluminum having a purity of 99% or more (particularly preferably 99.99% or more) is particularly preferably used.
[0023]
As such a wire made of aluminum (Al) or an Al alloy (hereinafter sometimes referred to as “Al-based wire”), a wire having a relatively large average crystal grain size is preferably used. For example, an Al-based wire (particularly preferably an Al-based wire having a purity of 99.99% or more) that has been subjected to a heat treatment after the cold drawing (a heat treatment that grows crystal grains) is preferable for the production method of the present invention. This is a typical example of an Al-based wire. This is because such an Al-based wire can effectively grow crystal grains by heat treatment after ultrasonic bonding. An Al-based wire having an average crystal grain size of 15 μm or more (typically 15 to 200 μm, preferably 30 to 150 μm) before being subjected to ultrasonic bonding is preferably used.
[0024]
Usually, when such an Al-based wire is subjected to ultrasonic bonding, crystal grains are subdivided by vibration of the metal structure. As a result, at least the crystal grain size near the bonding interface becomes small. For example, the average crystal grain size near the bonding interface is about 5 μm or less. As the structure becomes finer in this way, the hardness, internal stress, Young's modulus, etc. of the wire increase (work hardening phenomenon). As a result, the bonding strength of the wire (generally expressed by the shear strength) tends to increase.
When this joint is heat-treated in a predetermined temperature range, the subdivided crystal grains grow (recrystallization and regrowth). At this time, the work hardening of the wire is eased. As the crystal grain size of the wire increases, the generation and / or progress of cracks is suppressed as compared to the case where the crystal grain size is smaller. As a result, the durable life of the wire joint is improved. Although not particularly limited, the average crystal grain size of the Al-based wire (particularly in the vicinity of the bonding interface) after the heat treatment is preferably 30 μm or more (typically 30 to 200 μm), preferably 50 μm or more (typically Is more preferably 50 to 150 μm.
[0025]
The temperature suitable for the heat treatment of the wire joint varies depending on the composition of the wire. In the case of using an aluminum wire with a purity of 99.99% or more, it is particularly preferable to perform a heat treatment for heating the joint to a temperature range of 200 to 450 ° C. (more preferably 250 to 400 ° C.). In this temperature range, the growth of aluminum crystal grains is well promoted. By performing heat treatment in such a temperature range, work hardening of the wire (mainly due to ultrasonic bonding) can be effectively mitigated. This can improve the durability of the joint well. Here, the fact that the work hardening of the wire has been alleviated can be grasped as at least one of events such as a decrease in the hardness of the wire, relaxation of internal stress, and a decrease in Young's modulus.
Regarding the “initial bond strength” of the wire joint, all of the above-described relaxation of work hardening, decrease in hardness, relaxation of internal stress, and decrease in Young's modulus tend to decrease the initial bond strength. Therefore, in the typical embodiment of the present invention, the bonding durability is improved by performing the heat treatment, but the initial bond strength (shear strength) of the bonded portion is rather lowered as compared with that before the heat treatment.
[0026]
Examples of the resin material constituting the resin housing used in the production method of the present invention include polyphenylene sulfide (PPS), polyphenylene ether (PPE), melamine resin, polycarbonate (PC), polyethersulfone (PES), and polysulfone (PSF). , Polyetherimide, polyimide, polyamide, polyamideimide (PAI), acrylonitrile-styrene resin (AS resin), polypropylene (PP), polyethylene (PE), polymethylpentene (PMP), polyarylate (PAR), polyetherether Resins such as ketone (PEEK) and polyether ketone (PEK) can be selected. Of these, a resin material having a heat resistance of 150 ° C. or higher is preferable. Typical examples of such a resin material include PPS, PEEK, PC, and the like. In addition, when adopting a manufacturing method in which a semiconductor element and a resin housing are integrated and heat-treated at a joint portion as in a second embodiment or a third embodiment described later, heat resistance of 200 ° C. or higher is required. It is preferable to use the resin material which has. A particularly preferred resin material for the present invention is PPS.
This resin housing can contain a fibrous or powdery filler in addition to the resin material as described above. Ceramic fibers such as glass fibers and alumina fibers are preferably used.
[0027]
Note that the manufacturing method of the present invention includes a step of applying a thermosetting resin (typically polyimide) to a bonding portion between a wire and an electrode pad that have been ultrasonically bonded in advance so as to cover the bonding portion, and then curing the step. Can be included. In this case, the cured resin can protect the joint between the wire and the electrode pad, and the durability of the joint can be further improved. In order to accelerate the curing of the applied thermosetting resin, the wire may be heated to a temperature range that promotes the growth of crystal grains of the material constituting the wire. In this case, since the heat | fever at the time of hardening a thermosetting resin can be utilized, the junction part of a wire and an electrode pad can be heat-processed conveniently. Alternatively, other conventionally known methods for improving durability may be applied.
[0028]
Hereinafter, although the specific Example which applied this invention to the power module is described, it is not intending to limit this invention to what is shown to this Example.
<First Example>
The present embodiment is an example of manufacturing the semiconductor device (power module) having the structure shown in FIG. 1 by applying the present invention.
As shown in FIG. 1, the semiconductor device 100 is configured by assembling a plurality of (two shown in FIG. 1) power units 102 into a PPS resin housing 40. Each unit 102 includes a power semiconductor element (IGBT) 10, an insulating substrate 20 mainly made of ceramics (here, aluminum nitride), a heat sink 30 made of copper-molybdenum alloy, and between the element 10 and the substrate 20. And an element-side wire 56 that is stretched over the wire.
[0029]
On the surface of the substrate 20 (the upper surface in FIG. 1: the surface to which the element 10 is bonded) is provided with a conductive bonding material layer (here, a solder layer using solder as a conductive bonding material) 52, thereby providing the semiconductor element 10. Are joined together. On the other hand, the back surface of the substrate 20 (the lower surface in FIG. 1: the surface opposite to the surface to which the element 10 is bonded) is bonded to the heat sink 30 by the solder layer 54. Al foils 22 and 24 are provided on both surfaces of the substrate 20. A part of the Al foil 22 provided on the surface of the substrate 20 located outside the element 10 constitutes a relay pad 22a.
Note that as the conductive bonding material constituting the conductive bonding material layer 52, it is particularly preferable to use solder, but low melting point metals other than solder may be used. Alternatively, a conductive resin material in which a conductive filler is dispersed in a matrix resin made of an organic polymer or the like may be used. As this matrix resin, an epoxy resin, a polyimide resin, a phenol resin, a silicone resin, or the like can be used. As the conductive filler, conductive fibers made of copper, silver, gold, platinum, nickel, carbon, conductive fine particles, or the like can be used.
[0030]
On the other surface (non-bonding surface) of the semiconductor element 10, there are provided a plurality (two are shown in FIG. 1) of electrode pads 12 made of an Al film having a thickness of about 4 μm. The element-side wire 56 is ultrasonically bonded to the plurality of electrode pads 12 and the relay pad 22a. In this embodiment, the interval (stitch interval) between the portion where the element-side wire 56 is bonded to one electrode pad 12 and the portion bonded to the other electrode pad 12 is about 3 mm. The electrode pad 12 and the relay pad 22a are electrically connected via the element-side wire 56. The element-side wire 56 used in this example is made of Al containing a trace amount of Ni (Al purity of about 99.99%). Its diameter is about 400 μm.
[0031]
The housing 40 has an outer wall 42 and a bottom surface 44 surrounded by the outer wall. A plurality of openings 46 are formed in the bottom surface 44. The unit 102 is assembled to the housing 40 by fitting the heat sink 30 constituting each unit 102 into each opening 46 from the lower side of the housing 40. The substrate 20 and the element 10 bonded to the heat sink 30 are located inside the outer wall 42. A housing terminal 48 made of an Al film is provided on the bottom surface 44 around the opening 46. A housing side wire 58a made of a conductive metal (here, the same constituent material as the element side wire 56) is ultrasonically bonded to the housing terminal 48 and the relay pad 22a. An element side wire 56 joined to the electrode pad 12 and a housing side wire 58a joined to the housing terminal 48 are commonly joined to the relay pad 22a. As a result, the electrode pad 12 and the housing terminal 48 are electrically connected. The other housing-side wire 58b is joined to the Al foil 22 and the housing terminal 48 at portions other than the relay pad 22a to electrically connect them. In this case, the two elements 10 are connected in series. The diameters of these housing-side wires 58a and 58b are both about 400 μm.
[0032]
Hereinafter, an example of manufacturing the semiconductor element 100 will be described with reference to the drawings.
First, as shown in FIG. 2, the semiconductor element 10 is soldered to a predetermined portion of the substrate 20. This soldering can be performed by a general semiconductor element mounting method or the like.
[0033]
Next, as shown in FIG. 3, the element-side wire 56 is ultrasonically bonded (wedge bonding) to a plurality (here, two) of electrode pads 12 and relay pads 22a. This ultrasonic bonding can be performed, for example, by pressing the element-side wire 56 against an object to be bonded (here, the electrode pad 12 or the relay pad 22a) with a wedge tool and applying ultrasonic vibration of 60 KHz to 100 KHz. In this example, ultrasonic bonding was performed so that the degree of processing of the wire was about 20%.
[0034]
When the element-side wire 56 before ultrasonic bonding was observed with a scanning ion microscope (SIM), the crystal grain size of the constituent material was mainly in the range of 30 to 100 μm. In addition, even after ultrasonic bonding, the crystal grain size of the wire constituent material was mainly in the same range at a position away from the bonding portion 56 a between the electrode pad 12 and the element-side wire 56. On the other hand, the crystal grain size at the joint 56a (especially in the vicinity of the joint interface) is mainly 5 μm or less, and the crystal grain size is clearly smaller (fine crystal grains) than before ultrasonic bonding.
[0035]
Next, as shown in FIG. 4, the back surface of the substrate 20 is joined to the heat sink 30 by reflow soldering. That is, a solder foil is sandwiched between the substrate 20 and the heat radiating plate 30 and put in a reflow furnace in this state to melt the solder foil with a predetermined temperature profile. Thereafter, cooling is performed to form a solder layer 54 that joins the back surface of the substrate 20 and the heat sink 30. In this example, reflow soldering was performed with a temperature profile such that the temperature was maintained in a temperature range of 200 ° C. or higher for 25 to 30 minutes, of which the temperature range of 300 ° C. or higher was maintained for 15 to 20 minutes. The highest temperature reached at this time was 310 to 340 ° C. By this reflow soldering process, heat treatment was applied to the bonding portion 56a between the element side wire 56 and the electrode pad 12 and the bonding portion between the element side wire 56 and the relay pad 22a. After the reflow soldering process, the joint portion 56a was observed by SIM in the same manner as described above. As a result, the crystal grain size in the vicinity of the joint interface, which was 5 μm or less before the reflow soldering process, was remarkably large as 50 to 100 μm. It was.
[0036]
The unit 102 thus fabricated is assembled to the opening 46 of the housing 40 as shown in FIG. Thereafter, as shown in FIG. 1, the housing side wire 58 a is ultrasonically bonded to the housing terminal 48 and the relay pad 22 a, and the housing side wire 58 b is ultrasonically bonded to the housing terminal 48 and the Al foil 22. This ultrasonic bonding can be performed, for example, under the same conditions as the bonding conditions for the element-side wire 56 described above. The semiconductor device 100 was produced as described above.
[0037]
In the manufacturing method of the present embodiment, before the unit 102 having the joint portion 56a between the electrode pad 12 and the element side wire 56 is assembled to the housing 40 (in a state separated from the housing 40), the joint portion 56a is subjected to heat treatment. Apply. Therefore, the housing 40 is prevented from being damaged by the heat during the heat treatment. Moreover, since the said heat processing is performed using the heating at the time of reflow soldering the board | substrate 20 to the heat sink 30, production efficiency and energy efficiency are good.
[0038]
<Second Example>
This embodiment is an example in which the present invention is applied to manufacture a semiconductor device (power module) having the structure shown in FIG. Hereinafter, members having the same functions as those according to the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
As shown in FIG. 6, the semiconductor device 110 is configured by assembling a plurality of (two shown in FIG. 1) power units 112 to a PPS resin housing 40. The wire 57 is made of the same material as the element-side wire 56 (see FIG. 1) used in the first embodiment. Its properties (diameter, crystal grain size, etc.) are the same as those of the element-side wire 56 used in the first embodiment. In this embodiment, a wire 57 is joined to a plurality (two are shown in FIG. 6) of electrode pads 12 and housing terminals 48. The electrode pad 12 and the housing terminal 48 are electrically connected by the wire 57. That is, the relay pad 22a as shown in FIG. 1 is not provided in the semiconductor device 110 manufactured in this embodiment. The configuration of the other parts is substantially the same as in the first embodiment.
[0039]
Hereinafter, a manufacturing example of the semiconductor device 110 will be described.
First, as shown in FIG. 7, the semiconductor element 10 is soldered to a predetermined portion of the substrate 20. This soldering can be performed by a general semiconductor element mounting method or the like. Next, as shown in FIG. 8, the back surface of the substrate 20 is joined to the heat sink 30 by reflow soldering. This reflow soldering process can be performed by, for example, the same temperature profile as in the first embodiment. Alternatively, the reflow soldering process may be performed with a temperature profile different from that of the first embodiment. For example, a temperature profile that does not reach 300 ° C., a temperature profile that does not reach 200 ° C., or the like can be employed. Furthermore, you may join the board | substrate 20 and the heat sink 30 by methods other than reflow soldering (for example, the method of using the conductive resin material as mentioned above as a conductive bonding material).
[0040]
The unit 112 thus fabricated is assembled to the opening 46 of the housing 40 as shown in FIG. Then, as shown in FIG. 6, a wire 57 is ultrasonically bonded to a plurality (here, two) of electrode pads 12 and the housing terminal 48. Further, the housing-side wire 58 b is ultrasonically bonded to the Al foil 22 and the housing terminal 48 provided on the surface of the substrate 20. These ultrasonic bondings can be performed, for example, under the same conditions as the element-side wire bonding conditions described in the first embodiment. Moreover, the processing degree of the wire in a junction part can be 5 to 30% (for example, 20%).
[0041]
Then, heat treatment is performed on the bonding portion 57a between the wire 57 and the electrode pad 12 using a heat treatment apparatus as shown in FIG. The heat treatment apparatus 60 includes a heat generator 62 and a heat treatment jig 64 that stably contacts the heat generator 62 with a predetermined portion of the heat sink 30.
The heater 62 includes a heating element 62a and a holding body 62b in which the heating element 62a is embedded. The heating element 62a is made of a high-resistance metal wire (here, nichrome wire) and has a property of generating heat when energized. The holding body 62b is preferably made of a flexible material having good thermal conductivity. In this example, nitrile or silicon rubber was used as the constituent material of the holding material 62b.
[0042]
The heat treatment jig 64 includes a base 64a and a pressing plate 64b, and a bolt 64c for fastening them. The heat generator 62 is disposed on the base 64a, and the semiconductor device 110 is mounted thereon. When the pressing plate 64 b is placed on the housing 40 and the bolt 64 c is tightened, the heat generator 62 is pressed against the heat radiating plate 30. At this time, as shown in FIG. 10, the heat generator 62 is separated from the housing 40 in the heat radiating plate 30, and a portion where the joint portion 57 a between the electrode pad 12 and the wire 57 is projected onto the heat radiating plate 30 (FIG. 10). And a range including a portion located immediately below the joint portion 57a). In the present embodiment, since the element 10 is mounted at the center of the heat sink 30 and the outer periphery of the heat sink 30 is held by the housing 40, heat is generated at the center of the heat sink 30 as shown in FIG. The vessel 62 is in contact.
In this state, the heating element 62a is energized to generate heat, and the heat is used to heat the joining portion 57a to a range of about 200 to 450 ° C. (for example, about 250 ° C.). Although the heating time is not particularly limited, it is usually suitable to be in the range of about 1 to 30 minutes (for example, about 5 minutes). This heat treatment improves the durability of the joint portion 57a.
[0043]
In the present embodiment, since the heat generator 62 is arranged in the above-described range, the heat from the heat generator 62 can be efficiently transmitted to the joint portion 57a. Moreover, since the heat generator 62 does not contact the housing 40 directly, damage to the housing 40 due to heat can be suppressed. By using the heat treatment apparatus 60 having such a configuration and selecting a material having excellent flexibility as the holding body 62b, the heat generator 62 and the heat radiating plate 30 can be brought into close contact with each other. This can further improve the heat treatment efficiency.
[0044]
<Third embodiment>
This embodiment is an example in which, in the manufacturing method of the second embodiment, the operation method when heat-treating the joint portion 57a between the electrode pad 12 and the wire 57 is different. Hereinafter, members having the same functions as those of the member according to the second embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0045]
The unit 112 manufactured in the same manner as in the second embodiment is assembled to the opening 46 of the housing 40, and the wire 57 and the housing-side wire 56b are ultrasonically bonded to predetermined positions.
After that, as shown in FIG. 11, the heat ray H is irradiated to the joint portion 57 a between the electrode pad 12 and the wire 57 using the heat ray irradiator 70. As a result, the joining portion 57a is heated to a range of about 200 to 450 ° C. (for example, about 250 ° C.). The irradiation time (heating time) is not particularly limited, but it is usually appropriate to be in the range of about 0.5 to 30 seconds (for example, about 2 seconds). As the heat ray irradiator 70, a general xenon lamp, laser (for example, YAG laser, CO2) 2 A laser or the like). In this embodiment, a xenon lamp is used as the heat ray irradiator 70. Moreover, although it does not specifically limit, it is appropriate to irradiate the heat ray H from the distance of about 5-100 mm (here about 20 mm) from a joining part normally. In this way, the bonding portion 57a was heat treated to improve the durability of the bonding portion 57a.
[0046]
In the manufacturing method of the present embodiment, heat treatment is performed on the bonding portion 57 a by local heating using the heat ray irradiator 70. Therefore, the housing 40 is suppressed from being damaged by heat. Moreover, since only a required part is heated directly, production efficiency and energy efficiency are good.
[0047]
<Experimental example 1>
The effects of heat treatment conditions on the grain growth of wire constituent materials were investigated.
The same Al wire (Al purity of about 99.99%) as the element side wire used in the first example was ultrasonically bonded to the electrode pad under the same conditions as in the first example. Here, the degree of processing of the wire at the joint was about 60%. Immediately after bonding, the bonded portion was observed by SIM. As a result, the average crystal grain size of the wire constituting material was 5 μm or less.
In this way, five devices (device-wire bonded products) in which wires are bonded to the electrode pads of the semiconductor device were produced, and the temperatures were 100 ° C., 200 ° C., 250 ° C., 300 ° C., 400 ° C., and 500 ° C., respectively. A heat treatment was applied for 5 minutes. Thereafter, the joint between the electrode pad and the wire was again observed, and the average crystal grain size of the same portion was determined. The result is shown in FIG.
[0048]
As can be seen from FIG. 12, the growth of crystal grains is hardly observed when the heat treatment temperature is 100 ° C. On the other hand, growth of crystal grains is observed at a temperature of 200 ° C. or higher, and in the temperature range from 200 ° C. to 300 ° C., the effect of promoting the growth of crystal grains increases with an increase in the heat treatment temperature. The crystal grain growth promoting effect is almost saturated at a heat treatment temperature of 300 ° C. or higher. This indicates that the bonding durability can be improved by performing a heat treatment for 5 minutes in a temperature range of 200 ° C. or higher, and that a better result can be obtained by performing the heat treatment in a temperature range of 300 ° C. or higher. Yes.
[0049]
<Experimental example 2>
The influence of the degree of wire processing on the grain growth of wire constituent materials was investigated. The same Al wire (Al purity of about 99.99%) as the element side wire used in the first example was ultrasonically bonded to the electrode pad. Here, by adjusting the ultrasonic bonding conditions, a plurality of element-wire assemblies having different degrees of processing were produced. These joints were held at 300 ° C. for 10 minutes. After heat treatment was performed in this manner, the joint was observed by SIM to determine the average crystal grain size. The result is shown in FIG.
As can be seen from FIG. 13, when the processing degree of the wire is 5 to 30% or more (especially 5 to 20%), the growth of crystal grains is higher than when the processing degree is higher (for example, 40% or more). Well promoted.
[0050]
<Experimental example 3>
The effect of heat treatment on the durability of the joint was investigated.
Comparison of bonding durability between the semiconductor device manufactured according to the second embodiment (sample 1) and the semiconductor device manufactured as in sample 1 except that no heat treatment is performed (sample 2) is as follows. did.
That is, a power supply was connected to each of these semiconductor devices, and a cycle of energization for 2 seconds / 10 interruptions for 10 seconds was performed. At this time, the conditions were adjusted so that ΔTj (indicating the temperature change width of the element during one cycle) of the junction was about 100 ° C. By this power cycle test, the relationship between the number of cycles (number of power cycles) and the shear strength of joints (strength by shear test) was determined. The result is shown in FIG.
[0051]
As can be seen from FIG. 14, the shear strength at the start of the power cycle test is larger in the sample 2 not subjected to the heat treatment than in the sample 1 subjected to the heat treatment. This is presumably because the work hardening of Al caused by ultrasonic bonding is relaxed by heat treatment in sample 1 (therefore, the wire is softer than before heat treatment). This relationship is reversed around the number of cycles of 1000, and after that, the heat-treated sample 1 shows a higher shear strength. The cycle until the shear strength became zero (corresponding to a state where the joint was broken) was about 50% more in Sample 1 than in Sample 2. In other words, it was possible to extend the durable life of the joint by about 50% by applying heat treatment.
[0052]
In addition, the following are included in the technique disclosed by this specification.
The step of ultrasonically bonding a wire made of aluminum or an aluminum alloy to the electrode pad provided on the surface of the element at a processing degree of 5 to 30% (preferably 5 to 20%), and the bonded portion at 200 to 450 ° C. (More preferably 250 to 400 ° C.) a heat treatment process in a temperature range.
This manufacturing method is preferably applied when the diameter of the wire is 150 μm or more (typically 150 to 1000 μm), and particularly preferably when the diameter is 300 μm or more (typically 300 to 1000 μm). Further, it is preferably applied when the semiconductor element constituting the semiconductor device is a power semiconductor element.
[0053]
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 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 schematic cross-sectional view showing a semiconductor device manufactured according to a first embodiment.
FIG. 2 is a schematic cross-sectional view showing a semiconductor device manufacturing process according to the first embodiment.
FIG. 3 is a schematic cross-sectional view showing a semiconductor device manufacturing process according to the first embodiment.
FIG. 4 is a schematic cross-sectional view showing a semiconductor device manufacturing process according to the first embodiment.
FIG. 5 is a schematic cross-sectional view showing a semiconductor device manufacturing process according to the first embodiment.
FIG. 6 is a schematic cross-sectional view showing a semiconductor device manufactured according to a second embodiment.
FIG. 7 is a schematic cross-sectional view showing a semiconductor device manufacturing process according to the second embodiment.
FIG. 8 is a schematic cross-sectional view showing a semiconductor device manufacturing process according to the second embodiment.
FIG. 9 is a schematic cross-sectional view showing a semiconductor device manufacturing process according to the second embodiment.
FIG. 10 is a schematic cross-sectional view showing a semiconductor device manufacturing process according to the second embodiment.
FIG. 11 is a schematic cross-sectional view showing a semiconductor device manufacturing process according to the third embodiment;
FIG. 12 is a characteristic diagram showing the relationship between the heat treatment temperature and the size of crystal grains.
FIG. 13 is a characteristic diagram showing the relationship between the degree of wire processing and the size of crystal grains.
FIG. 14 is a characteristic diagram showing the relationship between the presence or absence of heat treatment and the durability of the joint.
[Explanation of symbols]
10: Semiconductor element
12: Electrode pad
20: Insulating substrate (substrate)
22a: Relay pad
30: radiator plate (metal plate)
40: housing
46: opening
48: Housing terminal
52: Solder layer (conductive bonding material layer)
54: Solder layer
56: Element side wire (wire)
57: Wire
58a, 58b: Housing side wire
62: Heating device
62a: heating element
62b: holder
70: Heat ray irradiator
100, 110: Semiconductor device
102, 112: Power unit

Claims (7)

ハウジングに半導体素子が組み付けられており、その半導体素子にアルミニウムまたはアルミニウム合金製のワイヤが接合されている半導体装置の製造方法であり、
前記半導体素子を基板の表面に接合する工程と、
前記半導体素子の非接合面に形成されている電極パッドに前記ワイヤを超音波接合する工程と、
前記基板の裏面を金属板にリフロー半田付する工程と、
前記金属板を前記ハウジングに組み付ける工程を含み、
前記超音波接合工程は前記リフロー半田付工程に先立って実行され、
前記リフロー半田付工程では、前記電極パッドと前記ワイヤの接合部を前記ワイヤを構成する材料の結晶粒の成長を促進する温度域に加熱する条件で半田付することを特徴とする半導体装置の製造方法。A semiconductor device is assembled in a housing, and a semiconductor device manufacturing method in which a wire made of aluminum or an aluminum alloy is joined to the semiconductor element,
Bonding the semiconductor element to a surface of a substrate;
A step of ultrasonically bonding the wire to an electrode pad formed on a non-bonding surface of the semiconductor element;
Reflow soldering the back surface of the substrate to a metal plate;
Assembling the metal plate to the housing,
The ultrasonic bonding step is performed prior to the reflow soldering step,
In the reflow soldering step, the bonding between the electrode pad and the wire is soldered under a condition of heating to a temperature range that promotes the growth of crystal grains of the material constituting the wire. Method. 前記基板の表面に中継パッドが形成されており、前記ハウジングにハウジング端子が形成されており、
前記超音波接合工程では前記ワイヤを前記電極パッドと前記中継パッドに接合し、
前記組み付け工程で前記金属板を前記ハウジングに組み付けたあとに、ハウジング側ワイヤを前記中継パッドと前記ハウジング端子に接合することを特徴とする請求項１に記載の製造方法。A relay pad is formed on the surface of the substrate, a housing terminal is formed on the housing,
In the ultrasonic bonding step, the wire is bonded to the electrode pad and the relay pad,
The manufacturing method according to claim 1, wherein after the metal plate is assembled to the housing in the assembling step, a housing-side wire is joined to the relay pad and the housing terminal. 樹脂製のハウジングに半導体素子が組み付けられており、その半導体素子にアルミニウムまたはアルミニウム合金製のワイヤが接合されている半導体装置の製造方法であり、
前記半導体素子を基板の表面に接合する工程と、
前記半導体素子の非接合面に形成されている電極パッドに前記ワイヤを超音波接合する工程と、
前記電極パッドと前記ワイヤの接合部を熱処理する工程と、
前記基板の裏面を金属板の表面にリフロー半田付する工程と、
前記金属板を前記ハウジングに組み付ける工程を含み、
前記超音波接合工程は前記熱処理工程に先立って実行され、前記熱処理工程は前記組付工程よりも後に実行され、前記熱処理工程では、前記電極パッドと前記ワイヤの接合部を含んで前記ハウジングから離隔する範囲において前記金属板の裏面に発熱器を接触させ、その発熱器からの伝熱によって前記接合部を前記ワイヤを構成する材料の結晶粒の成長を促進する温度域に加熱することを特徴とする半導体装置の製造方法。A semiconductor device is assembled in a resin housing, and a semiconductor device manufacturing method in which an aluminum or aluminum alloy wire is joined to the semiconductor element,
Bonding the semiconductor element to a surface of a substrate;
A step of ultrasonically bonding the wire to an electrode pad formed on a non-bonding surface of the semiconductor element;
Heat treating the joint between the electrode pad and the wire;
Reflow soldering the back surface of the substrate to the surface of the metal plate;
Assembling the metal plate to the housing,
The ultrasonic bonding step is performed prior to the heat treatment step, and the heat treatment step is performed after the assembly step. In the heat treatment step, the electrode pad and the wire are joined and separated from the housing. A heating device is brought into contact with the back surface of the metal plate within a range to be heated, and the junction is heated to a temperature range that promotes the growth of crystal grains of the material constituting the wire by heat transfer from the heating device. A method for manufacturing a semiconductor device. 樹脂製のハウジングに半導体素子が組み付けられており、その半導体素子にアルミニウムまたはアルミニウム合金製のワイヤが接合されている半導体装置の製造方法であり、
前記半導体素子を基板の表面に接合する工程と、
前記半導体素子の非接合面に形成されている電極パッドに前記ワイヤを超音波接合する工程と、
前記電極パッドと前記ワイヤの接合部を熱処理する工程と、
前記基板の裏面を金属板にリフロー半田付する工程と、
前記金属板を前記ハウジングに組み付ける工程を含み、
前記超音波接合工程は前記熱処理工程に先立って実行され、前記熱処理工程では、前記電極パッドと前記ワイヤの接合部に熱線を照射することによって、前記接合部を前記ワイヤを構成する材料の結晶粒の成長を促進する温度域に加熱することを特徴とする半導体装置の製造方法。A semiconductor device is assembled in a resin housing, and a semiconductor device manufacturing method in which an aluminum or aluminum alloy wire is joined to the semiconductor element,
Bonding the semiconductor element to a surface of a substrate;
A step of ultrasonically bonding the wire to an electrode pad formed on a non-bonding surface of the semiconductor element;
Heat treating the joint between the electrode pad and the wire;
Reflow soldering the back surface of the substrate to a metal plate;
Assembling the metal plate to the housing,
The ultrasonic bonding step is performed prior to the heat treatment step, and in the heat treatment step, the bonding portion between the electrode pad and the wire is irradiated with heat rays, thereby crystal grains of the material constituting the wire. A method for manufacturing a semiconductor device, comprising heating to a temperature range that promotes growth of the semiconductor device. 前記接合部を２００〜４５０℃の温度域に加熱することによって前記ワイヤを構成する材料の結晶粒の成長を促進することを特徴とする請求項１から４のいずれか一項に記載の製造方法。The manufacturing method according to claim 1, wherein the bonding portion is heated to a temperature range of 200 to 450 ° C. to promote the growth of crystal grains of the material constituting the wire. . 前記ワイヤは純度９９％以上のアルミニウムからなる請求項１から５のいずれか一項に記載の製造方法。The manufacturing method according to any one of claims 1 to 5, wherein the wire is made of aluminum having a purity of 99% or more. 半導体素子表面に設けられた電極パッドと純度９９％以上のアルミニウムからなるワイヤとの超音波接合部の接合耐久性を向上させる方法であって、
該接合部を２００〜４５０℃の温度域に加熱することを特徴とするワイヤ接合耐久性向上方法。A method for improving the bonding durability of an ultrasonic bonding portion between an electrode pad provided on a semiconductor element surface and a wire made of aluminum having a purity of 99% or more,
A method for improving the durability of wire bonding, wherein the bonding portion is heated to a temperature range of 200 to 450 ° C.
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