JP3975728B2 - Conductive adhesive and circuit board such as semiconductor using the same - Google Patents
Conductive adhesive and circuit board such as semiconductor using the same Download PDFInfo
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- JP3975728B2 JP3975728B2 JP2001352788A JP2001352788A JP3975728B2 JP 3975728 B2 JP3975728 B2 JP 3975728B2 JP 2001352788 A JP2001352788 A JP 2001352788A JP 2001352788 A JP2001352788 A JP 2001352788A JP 3975728 B2 JP3975728 B2 JP 3975728B2
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- 0 CN(*N(C(C1C2C3C(C*=C)=C(*)C1C3)=O)C2=O)C(C(C(CC12)C(*)=C1*=C)C2C=*=O)=O Chemical compound CN(*N(C(C1C2C3C(C*=C)=C(*)C1C3)=O)C2=O)C(C(C(CC12)C(*)=C1*=C)C2C=*=O)=O 0.000 description 1
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Description
【０００１】
【発明の属する技術分野】
本発明は、導電性接着剤及びそれを用いた半導体等の回路基板に関し、さらに詳しくは、半導体等の回路基板で部品を接着、配線する場合に好適であって、特に２００〜３００℃程度で耐熱性があり、かつ導電性、接着性、熱伝導性にも優れた導電性接着剤及びそれを用いた半導体等の回路基板に関するものである。
【０００２】
【従来の技術】
導電性接着剤は、半導体素子やチップ部品（以下、半導体等ということがある）をリードフレームや各種基板に接着し、電気的もしくは熱的に導通させる材料であるが、従来、この種の接着方法としては、Ａｕ−Ｓｉの共晶ハンダや錫−鉛ハンダ等が主に使用されていた。
しかし、これらＡｕ−Ｓｉの共晶ハンダ、錫−鉛ハンダによる接合法には、Ａｕが高価であり、応力緩和性に欠け、耐熱特性に劣るだけでなく、作業温度が比較的高温を要している。
【０００３】
半導体素子やチップ部品は、小型化、高性能化が進み、素子自体の発熱量が増大している。また、上記の半導体等や、基板上の配線などは部品の製造工程や実装工程において、ハンダ炉やワイヤーボンディング工程を経て２００〜３００℃程度の高温に幾度となく曝されている。年々、環境問題が重視されつつあり、錫−鉛ハンダよりも鉛フリーハンダが多用され始め、これが加熱温度を更に上昇させる一因ともなっている。
こうした背景から、最近では、より安価で耐熱性のある導電性接着剤に置きかえられるようになってきた。
また、回路上の配線は銅箔板が多いが、ジャンパー用やスルーホール用、ビアホール用にも導電性接着剤が使用されている。
これまでに、ハンダ並みの熱伝導性をもち、良好な耐熱性をもつと期待される導電性接着剤として、導電性粉体、有機樹脂、溶剤及び触媒などを主成分とする接着剤組成物が知られている。接着剤成分である導電性粉体に、金、銀、銅、ニッケル又はカーボン等が選択され、有機樹脂としては、エポキシ樹脂、フェノール樹脂等の熱硬化性樹脂が一般に採用されている。
しかしながら、これらの導電性接着剤は、合金接合であるハンダに比べ、熱伝導性が劣り、また、ハンダ炉などで、加熱処理に晒された場合、接着剤中の熱硬化性樹脂が分解、低分子量化して、その接着力が極端に低下するという問題点が指摘されていた。
【０００４】
耐熱性に優れた樹脂を成分とする導電性接着剤が開発されており、例えば、特開平８−２４５９４２号公報には、半導体パッケージ製造用に、耐熱性樹脂とポリナジイミドを含有する耐熱性接着剤が提案されている。この耐熱性接着剤によって、優れた耐パッケージクラック性、かつ良好な成形性が達成される。しかしながら、かかる耐熱性接着剤によれば、導電性をどの程度まで改善しうるかには言及していない。
一方、本出願人は、先に特開平１１−１４０４１７号公報により、金属粉末、エポキシ樹脂、ビスアルケニル置換ナジイミド及び硬化剤を主成分とする導電性接着剤を提案しているが、これによって従来より耐熱性を向上できたが、熱伝導性の面では性能が未だ充分であるとは言えなかった。
こうした状況下、半導体等の回路基板における接着工程に適用でき、かつ耐熱性、導電性、熱伝導性に優れた接着剤が切望されていた。
【０００５】
【発明が解決しようとする課題】
本発明の課題は、前述した従来技術の問題点に鑑み、半導体等の回路基板で部品を接着、配線する場合に好適であって、特に２００〜３００℃程度で耐熱性をもち、かつ導電性、接着性、熱伝導性に優れた導電性接着剤及びそれを用いた半導体等の回路基板を提供することにある。
【０００６】
【課題を解決するための手段】
本発明者は、上記課題を解決するために鋭意研究を重ねた結果、銀粉末、エポキシ樹脂、ビスアルケニル置換ナジイミド及び硬化剤を必須成分とする導電性接着剤において、銀粉末を特定量配合し、その際、タップ密度が３．５ｇ／ｍｌ以上で８．０ｇ／ｍｌ以下の銀粉末、さらにタップ密度が０．１ｇ／ｍｌ以上で３．５ｇ／ｍｌ未満の銀粉末をそれぞれ特定量に調整すると、半導体等の回路基板上で接着、配線する場合に適用され、特に２００〜３００℃程度で耐熱性があり、かつ導電性、接着性、熱伝導性にも優れた導電性接着剤が得られることを見出し、本発明を完成するに至った。
【０００７】
すなわち、本発明の第１の発明によれば、銀粉末（Ａ）、エポキシ樹脂（Ｂ）、下記の一般式（１）で示されるビスアルケニル置換ナジイミド（Ｃ）及び硬化剤（Ｄ）を必須成分とする導電性接着剤において、銀粉末（Ａ）は、全量に対して８０〜９５重量％含有させ、その際、タップ密度が３．５ｇ／ｍｌ以上で８．０ｇ／ｍｌ以下の銀粉末（ａ）を全量に対して４０〜９５重量％、さらにタップ密度が０．１ｇ／ｍｌ以上で３．５ｇ／ｍｌ未満の銀粉末（ｂ）を５０重量％以下とすることを特徴とする導電性接着剤が提供される。
【化２】
【０００８】
また、本発明の第２の発明によれば、第１の発明において、銀粉末（Ａ）が、球状の銀粉末と、フレーク状の銀粉末とからなることを特徴とする導電性接着剤が提供される。
【０００９】
また、本発明の第３の発明によれば、第１の発明において、エポキシ樹脂（Ｂ）は、全量に対して１〜１５重量％含有させることを特徴とする導電性接着剤が提供される。
【００１０】
また、本発明の第４の発明によれば、第１の発明において、ビスアルケニル置換ナジイミド（Ｃ）は、全量に対して０．１〜５重量％含有させることを特徴とする導電性接着剤が提供される。
【００１１】
また、本発明の第５の発明によれば、第１の発明において、さらに、希釈剤（Ｅ）を全量に対して１〜２０重量％含有させることを特徴とする導電性接着剤が提供される。
【００１２】
さらに、本発明の第６の発明によれば、第１の発明において、ビスアルケニル置換ナジイミド（Ｃ）は、エポキシ樹脂（Ｂ）に対して、重量比で０．０１〜５倍含有させることを特徴とする導電性接着剤が提供される。
【００１３】
一方、本発明の第７の発明によれば、第１〜６の発明のいずれかの導電性接着剤を用いてなる半導体等の回路基板。
【００１４】
【発明実態の形態】
以下、本発明の実施の形態について詳細に説明する。
【００１５】
１．導電性接着剤
本発明に係る導電性接着剤は、銀粉末と、エポキシ樹脂、ビスアルケニル置換ナジイミド及び硬化剤が配合された導電性接着剤において、導電性付与に充分な量の銀粉末を含有させ、その際、該銀粉末を、タップ密度が３．５ｇ／ｍｌ以上で８．０ｇ／ｍｌ以下の銀粉末と、タップ密度が０．１ｇ／ｍｌ以上で３．５ｇ／ｍｌ未満の銀粉末とを組合せ、それぞれ特定量を配合したことを特徴としている。
【００１６】
Ａ．銀粉末
本発明において重要な銀粉末は、全量に対して８０〜９５重量％となるように配合して導電性接着剤の導電性成分とする。該銀粉末は、タップ密度の大きさによって特性が異なることが究明され、タップ密度３．５ｇ／ｍｌ以上で８．０ｇ／ｍｌ以下の銀粉末（ａ）、タップ密度が０．１ｇ／ｍｌ以上で３．５ｇ／ｍｌ未満の銀粉末（ｂ）に分けると、銀粉末（ａ）を全量に対して４０〜９５重量％、銀粉末（ｂ）を５０重量％以下の量で配合することが必要である。
【００１７】
ここで、タップ密度とは、金属粉末など粉体の嵩密度であり、ＪＩＳ Ｚ２５００に準拠し、シリンダー容量：２０ｍｍ、タップストローク：２０ｍｍ、ストローク回数：５０回の条件で測定した数値である。
タップ密度が３．５ｇ／ｍｌ以上で８．０ｇ／ｍｌ以下の銀粉末（ａ）は分散性に優れているため、樹脂接着剤中に高充填することが可能である。一方、タップ密度が０．１ｇ／ｍｌ以上で３．５ｇ／ｍｌ未満の銀粉末（ｂ）は分散性が劣るので、樹脂接着剤中に高充填できないが、タップ密度が大きい銀粉末（ａ）と併用することにより、ハンダ並みの熱伝導性、優れた導電性を得ることができる。このような観点から、分散性を悪化させず、ハンダ並みの高い熱伝導性、導電性が得られるよう、それぞれの配合量を決定することが重要である。
なお、タップ密度が８．０ｇ／ｍｌ以上の銀粉末は、現在のところ入手しにくいが、上記の範囲内で添加しても差し支えない。
【００１８】
銀粉末は、形状によって、球状銀粉末とフレーク状銀粉末とに大別できるが、これら両者を一定の割合で混合すれば、印刷性と導電性を共に満足させることが可能となる。球状銀粉末とフレーク状銀粉末との混合物を配合した導電性接着剤であれば、印刷性に優れるだけでなく、接着膜の電気抵抗（体積抵抗値）を例えば１００μΩ・ｃｍ以下に低下できる場合がある。
【００１９】
銀粉末の平均粒径は、特に制限されないが、例えば、半導体等の回路基板用接着剤であれば、平均粒径は３０μｍ以下、好ましくは２０μｍ以下、特に５μｍ以下が望ましい。
また、銀粉末の配合割合は、８０〜９５重量％の範囲内に設定されるが、８０重量％未満であるとハンダに比べ熱伝導性が劣り、９５重量％を超えると接着強度が著しく低下し、接着剤としての役割を果たさなくなる。
銀粉末は、通常、鉛を含まない純粋な銀を用いるが、スズ、ビスマス、インジウム、パラジウムなどとの合金を採用してもよい。この場合、第二成分は５重量％以下であることが望ましい。
【００２０】
Ｂ．エポキシ樹脂
アルケニル置換ナジイミドと併用されるエポキシ樹脂は、公知のエポキシ樹脂全てが使用でき、特に制限はない。公知のエポキシ樹脂の例を挙げると、主に電子材料の成形や接着に使用されているビスフェノールＡジグリシジルエーテルをはじめ、ビスフェノールＦジグリシジルエーテル、ノボラックグリシジルエーテル、テトラグリシジルジアミノジフェニルメタン等が挙げられる。接着剤の用途を考えると液状が望ましく、また、対象が主に電子材料であることから、塩素イオンをはじめとするイオン性不純物などが８００ｐｐｍ以下であることが望ましい。また、これらのエポキシ樹脂は単独でも複数種を混合して用いても差し支えない。
なお、エポキシ樹脂には、本発明の目的を損なわない範囲内で、フェノール樹脂、不飽和ポリエステル樹脂など公知の熱硬化性樹脂を配合してもよい。
【００２１】
Ｃ．ビスアルケニル置換ナジイミド
ビスアルケニル置換ナジイミドは、一般式（１）で示される耐熱性成分であって、特開昭５９−８０６６２号公報、特開昭６０−１７８８６２号公報、及び特開昭６３−１７０３５８号公報に記載されているビスアルケニル置換ナジイミドを用いることができる。例えば、Ｎ，Ｎ’−ヘキサメチレン−ビス（アリルビシクロ［２．２．１］へプト−５−エン−２，３−ジカルボキシイミド）、Ｎ，Ｎ’−ｐ−キシリレン−ビス（アリルビシクロ［２．２．１］ヘプト−５−エン−２，３−ジカルボキシイミド）、Ｎ，Ｎ’−ｍ−キシリレン−ビス（アリルビシクロ［２．２．１］ヘプト−５−エン−２，３−ジカルボキシイミド）、ビス｛４−（アリルビシクロ［２．２．１］ヘプト−５−エン−２，３−ジカルボキシイミド）フェニル｝メタン等がある。このようなビスアルケニル置換ナジイミドは単独でも、複数種を混合して用いてもよい。
【００２２】
ビスアルケニル置換ナジイミドは、エポキシ樹脂と、硬化時に反応するわけではないが、それぞれが分かれて偏在せず、３次元網目構造をとり、互いに絡み合って硬化する。そのため、非常に均一で、２００〜３００℃程度では変質せず、耐熱性、熱伝導性が良好で、優れた接着性を発揮する。また、導電性接着剤の組成物としてみた場合、エポキシ樹脂と、ビスアルケニル置換ナジイミドは、希釈剤との相溶性が良いため、保存安定性に優れており、かつ比較的低温でも短時間で硬化反応が進行する等の特徴を備えている。
【００２３】
本発明において、ビスアルケニル置換ナジイミドの配合割合は、ビスアルケニル置換ナジイミドの効果が発揮される範囲内において任意であるが、接着性、導電性、熱伝導性、耐熱性をさらに向上させるには、ビスアルケニル置換ナジイミドを、全量に対して０．１〜５重量％配合することが望ましい。０．１重量％未満では耐熱性が低下することがあり、また、５重量％を超えると硬化温度が上昇したり硬化時間が長くなるなどの弊害が生ずることがある。
ビスアルケニル置換ナジイミドは、エポキシ樹脂に対して、重量比で０．０１〜５倍含有させることが望ましい。重量比で０．０１倍未満ではビスアルケニル置換ナジイミドの耐熱性効果が得られにくく、一方、５倍を超えると導電性接着剤の曳糸性が大きく、接着作業に困難をきたすだけでなく、硬化温度が上昇し、硬化時間も長くなり、接着力を低下させる場合がある。
【００２４】
Ｄ．硬化剤
また、硬化剤としては、６０〜３００℃に加熱すると、エポキシ樹脂と速やかに反応し、かつ室温で長期間の貯蔵安定性を満足できるものであれば特に制限はない。
一般的には、イミダゾール類の２−エチル−４−メチルイミダゾール、２−フェニル−４，５−ジヒドロキシメチルイミダゾール、２−フェニル−４−メチル−５−ヒドロキシメチルイミダゾールや、フェノールノボラック化合物、ジシアンジアミド、アジピン酸ジヒドラジド、酸無水物系のテトラヒドロメチル無水フタル酸、ヘキサヒドロ無水フタル酸、ルイス酸錯体のＢＦ３塩等が考えられる。これらは単独でも、複数種を混合して用いてもよい。この他に本発明では硬化促進作用が認められるもの、例えばアミン塩、プロックイソシアネート等も使用できる。
【００２５】
Ｅ．希釈剤
エポキシ樹脂及びビスアルケニル置換ナジイミドは、通常、希釈剤に溶解させて使用する。接着剤が硬化する際、希釈剤成分の少なくとも一部が揮発・蒸発し、又は分解して飛散してしまう有機化合物が使用できる。
一般的には、エポキシ樹脂及び硬化剤と反応しない、２，２，４−トリメチル−３−ヒドロキシジペンタンイソブチレート、２，２，４−トリメチルペンタン−１，３−イソブチレート、イソブチルブチレート、ジエチレングリコールモノブチルエーテル、エチレングリコールモノブチルエーテル等、又は加熱時にエポキシ樹脂及び硬化剤と反応し得る、フェニルグリシジルエーテル、エチルヘキシルグリシジルエーテルや、３−アミノプロピルトリエトキシシラン、３−グリシドキシプロピルメチルジメトキシシラン等が挙げられる。これらは単独でも、複数種を混合して使用してもよい。
【００２６】
希釈剤は、１〜２０重量％配合することが望ましい。１重量％未満であると導電性接着剤の粘度が高くなって、印刷性、塗布性を悪化させる場合があり、逆に、２０重量％を超えて配合すると粘度が低すぎて、印刷時および塗布時にダレや接着力の低下などを引き起こすことがある。
【００２７】
２．半導体等の回路基板
本発明の導電性接着剤は、半導体素子及びチップ抵抗、チップＬＥＤ等のチップ部材をリードフレーム、プリント配線基板（ＰＷＢ）、フレキシブルプリント基板（ＦＰＣ）等の回路基板に接着する際や、回路基板上で配線する際に使用される。回路上の配線は、銅箔板が主流であるが、ジャンパー用やスルーホール用、ビアホール用などにも使用できる。
【００２８】
この接着剤は、通常、回路基板に直接、塗布して用いるが、予めシート状に成形しておき、必要量を切断して用いてもよい。
上記の半導体素子やチップ部品、基板上の配線など部品の製造工程や実装工程において、導電性接着剤には、ハンダ炉やワイヤーボンディング工程を経て２００〜３００℃程度の加熱処理が幾度となく加えられるが、本発明の導電性接着剤であれば、導電性、接着性のいずれも低下させることはない。
【００２９】
【実施例】
以下に、実施例に基づき本発明を具体的に説明するが、本発明は、これら実施例によって何ら限定されるものではない。
なお、実験例１〜５及び、比較例１〜４の各試料は混錬後、下記に示す評価を行った。
【００３０】
（１）体積抵抗値の測定
アルミナ基板上に幅０．６ｍｍ、長さ６ｍｍの長方形状に試料（導電性接着剤）を印刷し、２００℃のオーブン中に６０分間放置し、硬化した後、室温まで冷却し、導電性接着剤上の両端で抵抗値を測定した。続いて、印刷し硬化した熱導電性接着剤の膜厚を測定し、抵抗値と膜厚から体積抵抗値を求めた。
【００３１】
（２）接着強度の測定
銀メッキを施した２．５ｃｍ角の銅基板上に試料（導電性接着剤）を滴下し、１．５ｍｍ角のシリコンチップを載せ、２００℃のオーブン中に６０分間放置して硬化させた。室温まで冷却した後、この銅基板に対し、水平方向からシリコンチップに力を加え、該シリコンチップが剥がれたときの力を接着強度として測定した。
【００３２】
（３）熱間強度の測定
銀メッキを施した２．５ｃｍの角の銅基板上に試料（導電性接着剤）を滴下し、１．５ｍｍ角のシリコンチップを載せ、２００℃のオーブン中に６０分間放置して硬化させた。室温まで冷却した後、２５０℃に加熱されたホットプレート上に、この銅基板を２分間放置し、その後、加熱したまま銅基板に対し、水平方向からシリコンチップに力を加え、このシリコンチップが剥がれたときの力を熱間強度として測定した。
【００３３】
（４）熱伝導性の測定
リードフレーム上に試料（導電性接着剤）を滴下し、半導体チップをマウントし、２００℃のオーブン中で６０分間放置して硬化させた。硬化後、リードフレーム及び半導体チップの電極部にマイクロプローブをあて、最初５ｍＡの電流を３ｍｓ流し、電圧を測定した。この時の電圧をＶ１とする。続けて、３００ｍＡの電流を５０ｍｓ流して半導体のチップを発熱させ、その後、再び５ｍＡの電流を３ｍｓ流し、電圧を測定した。この時の電圧をＶ２とし、Ｖ１−Ｖ２の値が３０ｍＶ以下であれば熱伝導性が良（〇）とし、それ以外は不可（×）とした。
【００３４】
（５）印刷性の評価
試料（導電性接着剤）を用いて、４００メッシュのスクリーンにて幅１００μｍ、長さ２０ｍｍの直線を１０本印刷し、印刷面に欠け、かすれ、ダレ等があるものは不可（×）、それらが観察されない場合は良（〇）とした。
【００３５】
（６）総合評価
上記の５項目において、体積抵抗値は１００μΩ・ｃｍ以下、接着強度は３０Ｎ以上、熱間強度は８Ｎ以上、熱伝導性、印刷性については、良（〇）の条件を全て満たしたもののみ良（〇）とし、１つでも以上の条件に満たないものがある場合は、不可（×）とした。
【００３６】
（実施例１〜５）
表１に記載した金属粉末成分、樹脂成分、硬化剤成分、及び希釈剤成分を原料として、接着剤組成物を調製し、３本ロール型混錬機を使用して混練し、本発明の導電性接着剤を得た。
この接着剤を用いて、アルミナ基板に印刷し、上記の条件で体積抵抗率を測定した。また銅基板に滴下し、硬化させてから、接着強度、熱間強度を測定した。リードフレーム上に本発明の導電性接着剤を滴下し、半導体チップをマウントし、硬化後、熱伝導率を測定した。さらに、本発明の導電性接着剤をスクリーンにより基板へ印刷し、印刷性を評価した。この結果は表１に併記した。
【００３７】
表１中、各成分の濃度は重量％で示している。球状銀粉Ａはタップ密度が４．５ｇ／ｍｌの銀粉末（平均粒径１．９μｍ）、球状銀粉Ｂはタップ密度が２．０ｇ／ｍｌの銀粉末（平均粒径０．７μｍ）、フレーク状銀粉Ｃはタップ密度が４．８ｇ／ｍｌの銀粉末（平均粒径２．３μｍ）、フレーク状銀粉Ｄはタップ密度が２．８ｇ／ｍｌの銀粉末（平均粒径１．８μｍ）である。
また、エポキシ樹脂Ａは、ビスフェノールＡジグリシジルエーテルであり、エポキシ樹脂Ｂは、ノボラックグリシジルエーテルである。
ビスアルケニル置換ナジイミドとしては、Ｎ，Ｎ’−ヘキサメチレン−ビス（アリルビシクロ［２．２．１］ヘプト−５−エン−２，３−ジカルボキシイミド）を用いた。
さらに硬化剤として、ジシアンジアミド、アジピン酸ジヒドラジド、２−フェニル−４，５−ジヒドロキシメチルイミダゾールの混合物を用いた。希釈剤Ａはフェニルグリシジルエーテル、希釈剤Ｂはジエチレングリコールモノブチルエーテルである。
【００３８】
（比較例１〜４）
上記の実施例と同様にして、表１に記載した成分の組成を変えて配合し、３本ロール型混錬機を使用して混練し、比較例の導電性接着剤を得た。
この接着剤を用いて、上記の条件で体積抵抗率、接着強度、熱間強度、熱伝導率を測定し、さらに、印刷性を評価した。結果は表１に併記した。
【００３９】
【表１】
表１から明らかなように、実施例１〜５の導電性接着剤は、導電性、接着性、耐熱性、熱伝導性、印刷性のいずれも優れていることが分かる。なお実施例４は、やや接着強度が弱いが、実用上問題のないレベルである。
これに対し、比較例１は、銀粉末混合物が９５重量％を超えているため、接着強度、熱間強度が弱く、印刷性も不可であった。比較例２は、銀粉末混合物が８０重量％未満であるため、体積抵抗値が高く、熱伝導性も不可となった。比較例３は、樹脂成分がエポキシ樹脂のみの場合で、熱間強度が低く不可となっている。さらに、比較例４は、樹脂成分がエポキシ樹脂組成物のみ、かつ銀粉末がタップ密度３．５ｇ／ｍｌ未満の銀粉のみを使用したので、体積抵抗値が高く、耐熱性にも劣り、また熱伝導性も不可となった。
【００４１】
【発明の効果】
この発明によれば、銀粉末、エポキシ樹脂、ビスアルケニル置換ナジイミド及び硬化剤を必須成分とし、該銀粉末の総量を特定量とし、その際、タップ密度が異なる二種類の銀粉末を、それぞれ特定量ずつ組合せて調製したため、２００〜３００℃程度で耐熱性があり、接着性、作業性、導電性、熱伝導性等を改善することができる。
従って、半導体等の回路基板に適用した場合にも、導電性を損なうことなく、優れた接着性能を発揮しうる導電性接着剤が提供でき、その工業的価値は極めて大きい。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conductive adhesive and a circuit board such as a semiconductor using the conductive adhesive. More specifically, the present invention is suitable for bonding and wiring components on a circuit board such as a semiconductor, particularly at about 200 to 300 ° C. The present invention relates to a conductive adhesive having heat resistance and excellent conductivity, adhesion, and thermal conductivity, and a circuit board such as a semiconductor using the conductive adhesive.
[0002]
[Prior art]
A conductive adhesive is a material that adheres a semiconductor element or chip component (hereinafter sometimes referred to as a semiconductor or the like) to a lead frame or various substrates and electrically or thermally conducts it. As a method, Au—Si eutectic solder, tin-lead solder, etc. were mainly used.
However, these Au-Si eutectic solder and tin-lead solder joining methods require not only high cost of Au, lack of stress relaxation, inferior heat resistance, but also a relatively high working temperature. ing.
[0003]
Semiconductor elements and chip parts have been reduced in size and performance, and the amount of heat generated by the elements themselves has increased. In addition, the semiconductor and the like, wiring on the substrate, and the like are exposed to high temperatures of about 200 to 300 ° C. several times through a solder furnace and a wire bonding process in a component manufacturing process and a mounting process. Environmental problems are becoming more important year by year, and lead-free solders are used more frequently than tin-lead solders, which contributes to further increasing the heating temperature.
Against this background, recently, cheaper and more heat-resistant conductive adhesives have been replaced.
Further, the wiring on the circuit is often a copper foil plate, but a conductive adhesive is also used for jumpers, through holes, and via holes.
Up to now, an adhesive composition mainly composed of conductive powder, organic resin, solvent and catalyst as a conductive adhesive expected to have good heat resistance with thermal conductivity similar to solder It has been known. Gold, silver, copper, nickel, carbon, or the like is selected as the conductive powder that is an adhesive component, and thermosetting resins such as epoxy resins and phenol resins are generally employed as organic resins.
However, these conductive adhesives are inferior in thermal conductivity compared to solder that is alloy bonded, and when exposed to heat treatment in a solder furnace or the like, the thermosetting resin in the adhesive decomposes, It has been pointed out that the molecular weight is lowered and the adhesive strength is extremely lowered.
[0004]
A conductive adhesive having a resin having excellent heat resistance as a component has been developed. For example, Japanese Patent Application Laid-Open No. 8-245492 discloses a heat resistant adhesive containing a heat resistant resin and polynadiimide for manufacturing a semiconductor package. Has been proposed. With this heat-resistant adhesive, excellent package crack resistance and good moldability are achieved. However, it does not mention how much the conductivity can be improved by such a heat-resistant adhesive.
On the other hand, the present applicant has previously proposed a conductive adhesive mainly composed of a metal powder, an epoxy resin, a bisalkenyl-substituted nadiimide and a curing agent according to Japanese Patent Application Laid-Open No. 11-140417. Although the heat resistance could be further improved, the performance was still not sufficient in terms of thermal conductivity.
Under such circumstances, an adhesive that can be applied to an adhesion process on a circuit board such as a semiconductor and has excellent heat resistance, conductivity, and thermal conductivity has been desired.
[0005]
[Problems to be solved by the invention]
The object of the present invention is suitable in the case of bonding and wiring parts with a circuit board such as a semiconductor in view of the above-mentioned problems of the prior art, and has heat resistance particularly at about 200 to 300 ° C. and is conductive. Another object of the present invention is to provide a conductive adhesive excellent in adhesiveness and thermal conductivity and a circuit board such as a semiconductor using the conductive adhesive.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventor has formulated a specific amount of silver powder in a conductive adhesive containing silver powder, epoxy resin, bisalkenyl-substituted nadiimide and a curing agent as essential components. In this case, the silver powder having a tap density of 3.5 g / ml or more and 8.0 g / ml or less, and the tap density of 0.1 g / ml or more and less than 3.5 g / ml are adjusted to specific amounts, respectively. Then, it is applied when bonding and wiring on a circuit board such as a semiconductor, and in particular, a conductive adhesive having heat resistance at about 200 to 300 ° C. and excellent in conductivity, adhesion and thermal conductivity is obtained. As a result, the present invention has been completed.
[0007]
That is, according to the first invention of the present invention, the silver powder (A), the epoxy resin (B), the bisalkenyl-substituted nadiimide (C) represented by the following general formula (1) and the curing agent (D) are essential. In the conductive adhesive as a component, the silver powder (A) is contained in an amount of 80 to 95% by weight based on the total amount, and at this time, the silver powder having a tap density of 3.5 g / ml or more and 8.0 g / ml or less. Conductivity characterized in that (a) is 40 to 95% by weight with respect to the total amount, and silver powder (b) having a tap density of 0.1 g / ml or more and less than 3.5 g / ml is 50% by weight or less. Adhesive is provided.
[Chemical formula 2]
[0008]
According to the second invention of the present invention, there is provided a conductive adhesive according to the first invention, wherein the silver powder (A) comprises a spherical silver powder and a flaky silver powder. Provided.
[0009]
According to a third aspect of the present invention, there is provided the conductive adhesive according to the first aspect, wherein the epoxy resin (B) is contained in an amount of 1 to 15% by weight based on the total amount. .
[0010]
According to a fourth aspect of the present invention, in the first aspect, the bisalkenyl-substituted nadiimide (C) is contained in an amount of 0.1 to 5% by weight based on the total amount. Is provided.
[0011]
According to a fifth aspect of the present invention, there is provided the conductive adhesive according to the first aspect, further comprising 1 to 20% by weight of the diluent (E) based on the total amount. The
[0012]
Furthermore, according to the sixth invention of the present invention, in the first invention, the bisalkenyl-substituted nadiimide (C) is contained 0.01 to 5 times by weight with respect to the epoxy resin (B). A featured conductive adhesive is provided.
[0013]
On the other hand, according to the seventh aspect of the present invention, there is provided a circuit board such as a semiconductor using the conductive adhesive according to any one of the first to sixth aspects.
[0014]
[Mode of Invention]
Hereinafter, embodiments of the present invention will be described in detail.
[0015]
1. Conductive adhesive The conductive adhesive according to the present invention contains a silver powder and a sufficient amount of silver powder for imparting conductivity in a conductive adhesive containing an epoxy resin, a bisalkenyl-substituted nadiimide and a curing agent. In this case, the silver powder is divided into a silver powder having a tap density of 3.5 g / ml to 8.0 g / ml, and a silver powder having a tap density of 0.1 g / ml to less than 3.5 g / ml. And is characterized by blending specific amounts.
[0016]
A. Silver powder The silver powder important in the present invention is blended so as to be 80 to 95% by weight based on the total amount to be a conductive component of the conductive adhesive. It has been determined that the silver powder has different characteristics depending on the tap density. The silver powder (a) having a tap density of 3.5 g / ml to 8.0 g / ml and a tap density of 0.1 g / ml or more. When the silver powder (b) is less than 3.5 g / ml, the silver powder (a) may be blended in an amount of 40 to 95% by weight and the silver powder (b) in an amount of 50% by weight or less. is necessary.
[0017]
Here, the tap density is a bulk density of a powder such as metal powder, and is a numerical value measured under the conditions of cylinder capacity: 20 mm, tap stroke: 20 mm, and stroke number: 50 in accordance with JIS Z2500.
Since the silver powder (a) having a tap density of 3.5 g / ml or more and 8.0 g / ml or less is excellent in dispersibility, it can be highly filled in the resin adhesive. On the other hand, the silver powder (b) having a tap density of 0.1 g / ml or more and less than 3.5 g / ml has poor dispersibility, so that it cannot be highly filled in the resin adhesive, but has a high tap density. By using together, thermal conductivity similar to solder and excellent conductivity can be obtained. From such a viewpoint, it is important to determine the amount of each compound so that dispersibility is not deteriorated and high thermal conductivity and conductivity similar to solder can be obtained.
Silver powder having a tap density of 8.0 g / ml or more is currently difficult to obtain, but may be added within the above range.
[0018]
Silver powders can be roughly classified into spherical silver powders and flaky silver powders depending on their shapes, but if both are mixed at a certain ratio, both printability and conductivity can be satisfied. A conductive adhesive containing a mixture of spherical silver powder and flaky silver powder not only has excellent printability but also can reduce the electrical resistance (volume resistance value) of the adhesive film to, for example, 100 μΩ · cm or less. There is.
[0019]
The average particle size of the silver powder is not particularly limited. For example, in the case of an adhesive for a circuit board such as a semiconductor, the average particle size is 30 μm or less, preferably 20 μm or less, particularly 5 μm or less.
The blending ratio of the silver powder is set in the range of 80 to 95% by weight, but if it is less than 80% by weight, the thermal conductivity is inferior to that of solder. And no longer serves as an adhesive.
As the silver powder, pure silver not containing lead is usually used, but an alloy with tin, bismuth, indium, palladium or the like may be used. In this case, the second component is desirably 5% by weight or less.
[0020]
B. As the epoxy resin used in combination with the epoxy resin alkenyl-substituted nadiimide, all known epoxy resins can be used, and there is no particular limitation. Examples of known epoxy resins include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, novolac glycidyl ether, tetraglycidyl diaminodiphenylmethane, etc., which are mainly used for molding and bonding electronic materials. Considering the use of the adhesive, liquid is desirable, and since the target is mainly electronic materials, it is desirable that ionic impurities such as chlorine ions are 800 ppm or less. These epoxy resins may be used alone or in combination of a plurality of types.
In addition, you may mix | blend well-known thermosetting resins, such as a phenol resin and an unsaturated polyester resin, in the epoxy resin in the range which does not impair the objective of this invention.
[0021]
C. Bisalkenyl-substituted nadiimide Bisalkenyl-substituted nadiimide is a heat-resistant component represented by the general formula (1), and is disclosed in JP-A-59-80662, JP-A-60-178862, and JP-A-63- Bisalkenyl-substituted nadiimides described in Japanese Patent No. 170358 can be used. For example, N, N′-hexamethylene-bis (allylbicyclo [2.2.1] hept-5-ene-2,3-dicarboximide), N, N′-p-xylylene-bis (allylbicyclo) [2.2.1] hept-5-ene-2,3-dicarboximide), N, N′-m-xylylene-bis (allylbicyclo [2.2.1] hept-5-ene-2, 3-dicarboximide), bis {4- (allylbicyclo [2.2.1] hept-5-ene-2,3-dicarboximido) phenyl} methane and the like. Such bisalkenyl-substituted nadiimides may be used singly or as a mixture of plural kinds.
[0022]
The bisalkenyl-substituted nadiimide does not react with the epoxy resin at the time of curing, but each bisalkenyl-substituted nadiimide is not unevenly distributed and takes a three-dimensional network structure and is entangled with each other and cured. Therefore, it is very uniform, does not change at about 200 to 300 ° C., has good heat resistance and thermal conductivity, and exhibits excellent adhesiveness. In addition, when viewed as a conductive adhesive composition, epoxy resin and bisalkenyl-substituted nadiimide have good compatibility with diluents, so they have excellent storage stability and cure in a short time even at relatively low temperatures. It has features such as reaction progress.
[0023]
In the present invention, the blending ratio of the bisalkenyl-substituted nadiimide is arbitrary within the range in which the effect of the bisalkenyl-substituted nadiimide is exhibited, but in order to further improve the adhesiveness, conductivity, thermal conductivity, and heat resistance, The bisalkenyl-substituted nadiimide is desirably blended in an amount of 0.1 to 5% by weight based on the total amount. If it is less than 0.1% by weight, the heat resistance may be lowered, and if it exceeds 5% by weight, adverse effects such as an increase in curing temperature and a longer curing time may occur.
The bisalkenyl-substituted nadiimide is desirably contained 0.01 to 5 times by weight with respect to the epoxy resin. If the weight ratio is less than 0.01 times, it is difficult to obtain the heat resistance effect of the bisalkenyl-substituted nadiimide. On the other hand, if it exceeds 5 times, the conductive adhesive has a large spinnability, which not only makes the bonding work difficult, The curing temperature rises, the curing time becomes longer, and the adhesive strength may be reduced.
[0024]
D. The curing agent or the curing agent is not particularly limited as long as it reacts quickly with the epoxy resin when heated to 60 to 300 ° C. and can satisfy long-term storage stability at room temperature.
In general, imidazoles such as 2-ethyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, phenol novolac compounds, dicyandiamide, Adipic acid dihydrazide, acid anhydride-based tetrahydromethylphthalic anhydride, hexahydrophthalic anhydride, BF 3 salt of Lewis acid complex, and the like are conceivable. These may be used alone or as a mixture of two or more. In addition to this, in the present invention, those which are recognized to have a curing accelerating action, such as amine salts and block isocyanates, can also be used.
[0025]
E. The diluent epoxy resin and bisalkenyl-substituted nadiimide are usually used after being dissolved in a diluent. When the adhesive is cured, an organic compound in which at least a part of the diluent component volatilizes and evaporates, or decomposes and scatters can be used.
Generally, 2,2,4-trimethyl-3-hydroxydipentane isobutyrate, 2,2,4-trimethylpentane-1,3-isobutyrate, isobutyl butyrate, which does not react with epoxy resin and curing agent, Diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, etc., or phenyl glycidyl ether, ethylhexyl glycidyl ether, 3-aminopropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, etc. that can react with epoxy resin and curing agent when heated Is mentioned. These may be used alone or in combination of two or more.
[0026]
The diluent is desirably blended in an amount of 1 to 20% by weight. If it is less than 1% by weight, the viscosity of the conductive adhesive may increase, and printability and applicability may be deteriorated. Conversely, if it exceeds 20% by weight, the viscosity will be too low, and during printing and When applied, it may cause sagging or a decrease in adhesive strength.
[0027]
2. Circuit boards such as semiconductors The conductive adhesive of the present invention adheres semiconductor elements, chip resistors, and chip members such as chip LEDs to circuit boards such as lead frames, printed wiring boards (PWB), and flexible printed boards (FPC). It is used when wiring on a circuit board. Copper wiring is the mainstream for wiring on the circuit, but it can also be used for jumpers, through holes, and via holes.
[0028]
This adhesive is usually used by directly applying to the circuit board, but it may be formed into a sheet in advance and used after cutting the required amount.
In the manufacturing process and mounting process of components such as the above semiconductor elements, chip components, and wiring on the substrate, the conductive adhesive is repeatedly subjected to heat treatment at about 200 to 300 ° C. through a solder furnace and a wire bonding process. However, with the conductive adhesive of the present invention, neither conductivity nor adhesiveness is reduced.
[0029]
【Example】
EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.
In addition, each sample of Experimental Examples 1 to 5 and Comparative Examples 1 to 4 was subjected to evaluation shown below after kneading.
[0030]
(1) Measurement of volume resistance value After printing a sample (conductive adhesive) in a rectangular shape having a width of 0.6 mm and a length of 6 mm on an alumina substrate, leaving it in an oven at 200 ° C. for 60 minutes and curing, After cooling to room temperature, the resistance value was measured at both ends on the conductive adhesive. Then, the film thickness of the heat conductive adhesive which printed and hardened was measured, and the volume resistance value was calculated | required from the resistance value and the film thickness.
[0031]
(2) Measurement of adhesive strength A sample (conductive adhesive) was dropped on a 2.5 cm square copper substrate subjected to silver plating, a 1.5 mm square silicon chip was placed, and placed in an oven at 200 ° C. for 60 minutes. Allowed to cure. After cooling to room temperature, a force was applied to the silicon substrate from the horizontal direction on the copper substrate, and the force when the silicon chip was peeled was measured as the adhesive strength.
[0032]
(3) Measurement of hot strength A sample (conductive adhesive) is dropped on a 2.5 cm square copper substrate subjected to silver plating, a 1.5 mm square silicon chip is placed, and placed in an oven at 200 ° C. It was left to cure for 60 minutes. After cooling to room temperature, this copper substrate is left on a hot plate heated to 250 ° C. for 2 minutes. After that, the silicon substrate is heated and applied with force to the silicon chip from the horizontal direction. The force at the time of peeling was measured as the hot strength.
[0033]
(4) Measurement of thermal conductivity A sample (conductive adhesive) was dropped on a lead frame, a semiconductor chip was mounted, and allowed to cure in an oven at 200 ° C. for 60 minutes. After curing, a microprobe was applied to the lead frame and the electrode part of the semiconductor chip, and a current of 5 mA was first applied for 3 ms to measure the voltage. The voltage at this time is V1. Subsequently, a current of 300 mA was supplied for 50 ms to heat the semiconductor chip, and then a current of 5 mA was supplied again for 3 ms to measure the voltage. The voltage at this time was V2, and if the value of V1-V2 was 30 mV or less, the thermal conductivity was good (◯), and the others were not possible (×).
[0034]
(5) Printable evaluation sample (conductive adhesive) is used to print 10 straight lines with a width of 100 μm and a length of 20 mm on a 400 mesh screen, and the printed surface has chipping, blurring, sagging, etc. Is not possible (×), and when they are not observed, it is judged as good (◯).
[0035]
(6) Comprehensive evaluation In the above five items, the volume resistance value is 100 μΩ · cm or less, the adhesive strength is 30 N or more, the hot strength is 8 N or more, and the thermal conductivity and printability are all good (◯) conditions. Only the satisfied ones were judged as good (◯), and when there was one that did not meet the above conditions, it was judged as impossible (×).
[0036]
(Examples 1-5)
Using the metal powder component, resin component, curing agent component, and diluent component described in Table 1 as raw materials, an adhesive composition was prepared, kneaded using a three-roll kneader, and the conductive material of the present invention. Adhesive was obtained.
Using this adhesive, printing was performed on an alumina substrate, and the volume resistivity was measured under the above conditions. Moreover, after dripping on the copper substrate and making it harden | cure, the adhesive strength and the hot strength were measured. The conductive adhesive of the present invention was dropped on the lead frame, the semiconductor chip was mounted, and after curing, the thermal conductivity was measured. Furthermore, the conductive adhesive of the present invention was printed on a substrate with a screen, and the printability was evaluated. The results are also shown in Table 1.
[0037]
In Table 1, the concentration of each component is shown in wt%. Spherical silver powder A is silver powder (average particle size 1.9 μm) with a tap density of 4.5 g / ml, and spherical silver powder B is silver powder (average particle size 0.7 μm) with a tap density of 2.0 g / ml, flaky Silver powder C is a silver powder (average particle size 2.3 μm) with a tap density of 4.8 g / ml, and flaky silver powder D is a silver powder (average particle size 1.8 μm) with a tap density of 2.8 g / ml.
Epoxy resin A is bisphenol A diglycidyl ether, and epoxy resin B is novolak glycidyl ether.
As the bisalkenyl-substituted nadiimide, N, N′-hexamethylene-bis (allylbicyclo [2.2.1] hept-5-ene-2,3-dicarboximide) was used.
Furthermore, a mixture of dicyandiamide, adipic acid dihydrazide, and 2-phenyl-4,5-dihydroxymethylimidazole was used as a curing agent. Diluent A is phenyl glycidyl ether and Diluent B is diethylene glycol monobutyl ether.
[0038]
(Comparative Examples 1-4)
In the same manner as in the above examples, the composition of the components described in Table 1 was changed and blended, and kneaded using a three-roll kneader to obtain a conductive adhesive of a comparative example.
Using this adhesive, volume resistivity, adhesive strength, hot strength, and thermal conductivity were measured under the above conditions, and printability was further evaluated. The results are shown in Table 1.
[0039]
[Table 1]
As is clear from Table 1, the conductive adhesives of Examples 1 to 5 are all excellent in conductivity, adhesiveness, heat resistance, thermal conductivity, and printability. In Example 4, although the adhesive strength is slightly weak, there is no practical problem.
On the other hand, in Comparative Example 1, since the silver powder mixture exceeded 95% by weight, the adhesive strength and the hot strength were weak, and the printability was not possible. In Comparative Example 2, since the silver powder mixture was less than 80% by weight, the volume resistance value was high and the thermal conductivity was not possible. In Comparative Example 3, the resin component is only an epoxy resin, and the hot strength is low and cannot be used. Furthermore, since Comparative Example 4 used only the epoxy resin composition as the resin component and only silver powder having a tap density of less than 3.5 g / ml, the volume resistance value was high, the heat resistance was inferior, and the heat Conductivity is also impossible.
[0041]
【The invention's effect】
According to the present invention, silver powder, epoxy resin, bisalkenyl-substituted nadiimide and curing agent are essential components, and the total amount of the silver powder is a specific amount, and at that time, two kinds of silver powders having different tap densities are specified respectively. Since it was prepared by combining each amount, it has heat resistance at about 200 to 300 ° C., and can improve adhesiveness, workability, conductivity, thermal conductivity and the like.
Therefore, even when applied to a circuit board such as a semiconductor, a conductive adhesive capable of exhibiting excellent adhesion performance without impairing conductivity can be provided, and its industrial value is extremely large.
Claims (7)
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| Application Number | Priority Date | Filing Date | Title |
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| JP2001352788A JP3975728B2 (en) | 2001-11-19 | 2001-11-19 | Conductive adhesive and circuit board such as semiconductor using the same |
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| JP2001352788A JP3975728B2 (en) | 2001-11-19 | 2001-11-19 | Conductive adhesive and circuit board such as semiconductor using the same |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP4962156B2 (en) * | 2007-06-19 | 2012-06-27 | 住友金属鉱山株式会社 | Conductive adhesive |
| JP2009185112A (en) * | 2008-02-04 | 2009-08-20 | Denso Corp | Conductive adhesive and semiconductor device having the same |
| JP5281529B2 (en) * | 2009-09-28 | 2013-09-04 | 京都エレックス株式会社 | Heat curable conductive paste composition, electrode and wiring pattern forming method using the conductive paste composition |
| JP5297344B2 (en) * | 2009-11-04 | 2013-09-25 | 京都エレックス株式会社 | Heat curable conductive paste composition |
| JP5915541B2 (en) * | 2010-12-20 | 2016-05-11 | セメダイン株式会社 | Conductive adhesive |
| JP5146567B2 (en) * | 2011-05-30 | 2013-02-20 | 東洋インキＳｃホールディングス株式会社 | Conductive ink, laminate with conductive pattern and method for producing the same |
| JP5764824B2 (en) * | 2012-03-26 | 2015-08-19 | 住友金属鉱山株式会社 | Conductive adhesive composition and electronic device using the same |
| JP6048166B2 (en) * | 2012-04-04 | 2016-12-21 | 住友金属鉱山株式会社 | Conductive adhesive composition and electronic device using the same |
| WO2014103569A1 (en) | 2012-12-25 | 2014-07-03 | 住友金属鉱山株式会社 | Conductive adhesive composition and electronic element using same |
| JPWO2019111778A1 (en) * | 2017-12-04 | 2019-12-12 | 住友ベークライト株式会社 | Paste adhesive composition and semiconductor device |
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| JPH10251606A (en) * | 1997-03-10 | 1998-09-22 | Asahi Chem Ind Co Ltd | Conductive adhesive |
| JP3484957B2 (en) * | 1997-11-10 | 2004-01-06 | 住友金属鉱山株式会社 | Conductive adhesive |
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