JP2004063446A - Conductive paste - Google Patents

Conductive paste Download PDF

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JP2004063446A
JP2004063446A JP2003049073A JP2003049073A JP2004063446A JP 2004063446 A JP2004063446 A JP 2004063446A JP 2003049073 A JP2003049073 A JP 2003049073A JP 2003049073 A JP2003049073 A JP 2003049073A JP 2004063446 A JP2004063446 A JP 2004063446A
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silver
powder
weight
copper powder
conductive paste
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JP4235888B2 (en
Inventor
▲桑▼島　秀次
Hideji Kuwajima
Junichi Kikuchi
菊池　純一
Kuniaki Sato
佐東　国昭
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Showa Denko Materials Co Ltd
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Hitachi Chemical Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide the conductive paste increasing a blending ratio of conductive powder, improving the reliability in conductivity and migration resistance, being advantageous in price competition by reducing the silver plating, and being suitably used in forming a soldered electrode, conductive adhesive and the like. <P>SOLUTION: This conductive paste includes conductive powder including approximately spherical silver-coated copper powder of 50-94wt.% prepared by coating the surface of copper powder with silver and coating its surface with fatty acid of 0.02-0.5wt.% to the copper powder, flat silver-coated copper powder of 3-20wt.% prepared by coating the surface of copper powder with silver, and coating its surface with fatty acid of 0.02-1.2wt. %, the silver powder of 1-5wt. % having an average particle size of 7 μm and metal of low melting point, of 2-25wt.%, and a binder. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、配線板の回路形成、シールド層形成、電子部品の電極形成、はんだ付電極形成、導電性接着剤等に使用される導電ペーストに関する。
【０００２】
【従来の技術】
印刷配線板上に導電回路を形成する方法の１つに、金、銀、銅、カーボン等の導電性粉末を用い、それにバインダ、有樹溶剤及び必要に応じて添加剤などを加えてペースト状に混合して作製していた。特に高導電性が要求される分野では、金粉、銀粉、パラジウム粉又はこれらの合金粉が一般的に用いられていた。
【０００３】
【非特許文献１】
電子材料、１９９４年１０月号（第４２〜４６頁）
【０００４】
上記のうち銀粉を含有する導電ペーストは、導電性が良好なことから印刷配線板、電子部品等の配線層（導電層）又は電子部品の電気回路や電極の形成に使用されているが、これらは高温多湿の雰囲気下で電界が印加されると、電気回路や電極にマイグレーションと称する銀の電析が生じ電極間又は配線間が短絡するという欠点が生じる。このマイグレーションを防止するための方策はいくつか行われており、導体の表面に防湿塗料を塗布するか、導電ペーストに含窒素化合物などの腐食抑制剤を添加する等の方策が検討されているが十分な効果の得られるものではなかった。銀粉に替えて銀−パラジウム合金粉を使用すれば耐マイグレーション性は改善できるが、銀及びパラジウムが高価なため銀−パラジウム合金粉も高価になる欠点を有していた。
【０００５】
また、導通抵抗の良好な導体を得るには銀粉の配合量を増加しなければならず、銀粉が高価であることから導電ペーストも高価になるという欠点があった。銀被覆銅粉を使用すればマイグレーションを改善でき、これを用いれば安価な導電ペーストが得られることになる。しかし、銀で銅粉の表面を均一にかつ厚く被覆するとマイグレーションの改善効果が十分ではない。しかも得られる導電ペーストの塗膜に、直接はんだ付けを適用することができないという欠点があった。さらに銀粉を使用した導電ペーストにはんだ付けを行う場合、銀喰われが起こり、十分な接合が得られないという欠点もあった。
【０００６】
一方、銀粉以外に銅粉を使用する場合がある。しかし、銅粉を使用した導電ペーストは、加熱硬化後の銅の被酸化性が大きいため、空気中及びバインダ中に含まれる酸素と銅粉が反応し、その表面に酸化膜を形成し、導電性を著しく低下させる。そのため、各種還元剤を加えて、銅粉表面の酸化を防止し、導電性が安定した銅ペーストが開示されているが、導電性及び導電性の安定性は銀ペーストには及ばず、高温高湿試験などで導通抵抗値が増大するなどの欠点があった。
【０００７】
また、導電ペースト中の、銅粉の含有率を高くしなければ安定した導電性が得られない。しかし、銅粉の含有率を高くすると、この影響で接着性が悪くなったり、保存安定性が悪くなるなどの欠点があった。しかも、得られた銅ペーストの塗膜に、従来の銅ペーストでは、直接はんだ付けを適用することができないという欠点もあった。
【０００８】
従来、公知の導電ペーストは、接着剤として使用する場合、はんだペーストに比較して導電粉が高価であることから導電ペーストも高価であるという欠点を有していた。従って銅ペーストより導電性の信頼性が高く、かつ銀ペーストより耐マイグレーション性に優れ、はんだペースト及び乾燥硬化の作業性に優れた導電接着剤が望まれていた。
【０００９】
また、従来、公知の導電ペーストは、直接はんだ付けをすることができないため、導電ペーストの塗膜に活性化処理を施して無電解めっきするか又は塗膜を陰極としてめっき液中で電気銅めっきを施した後、めっきで得られた銅皮膜上にはんだ付けをしていた。しかし、塗膜と銅めっきとの層間の結合が確実でないと実用的ではない。従って、無電解めっき又は電気めっきを施す必要のないはんだ付け可能な導電ペーストが開発されれば、回路形成工程が大幅に短縮されるので、そのメリットは大きい。
【００１０】
はんだは金属とは接合し易いが、バインダとは接合しない。はんだ付けを行う場合、理想的には導電粉のみの塗膜を形成し、それにはんだ付けを行えばよいが、バインダを用いず導電粉のみでは塗膜を形成できないという問題点がある。
そのためバインダを使用し、導電ペーストにして用いている。しかし、信頼性及び塗膜形成の作業性を重視するためバインダの量についても制限があり、例えば、バインダの比率を高くすると、金属である導電粉をバインダが覆ってしまい、はんだと導電粉が接触する面積がなくなってしまうため、はんだが付かなくなり、導電性も低下するという欠点が生じる。
【００１１】
はんだが付くような導電ペーストにするためには、限りなく銅箔に近い組成にする必要がある。即ち、導電粉をあるスペースに入れた場合、導電粉の充填性が高く、導電粉同士の間にできた隙間の体積分だけバインダが占めるような組成にすることが理想である。
【００１２】
しかし、上記のように導電粉の比率を高くすると、導電ペーストの粘度が極端に高くなり、導電ペーストの作製が困難になり導電ペーストを塗布する作業性も悪くなると共に導電粉同士を結着させるバインダが少ないため塗膜の強度も低下する。また導電性接着剤として使用する場合には、接着性が低下するので、使用に適さない。さらに導電ペーストを用いてはんだ接合を行う場合には、はんだ付け性、導電性、作業性、強度さらにはコストのバランスがとれている導電ペーストが必要である。
【００１３】
はんだ代替材料として導電接着を目的として使用する場合、導電ペーストの印刷性、接着性及び導通の信頼性と共に、短時間で乾燥、硬化できる作業性も重要である。これまでチップ部品等のはんだ付けにアッセンブリメーカが使用していたリフロー炉を、はんだ代替接着剤の乾燥、硬化に使用できれば、設備の有効活用がはかれ、好ましい。一般の銀ペーストの場合、はんだリフロー炉のような高温、短時間の乾燥・硬化では膨れを生じやすい欠点がある。また銅ペーストも高温短時間の硬化では導電性が安定せず、また恒温恒湿試験又は気相冷熱試験等の信頼性試験で、導通をなくす所謂断線状態になる欠点を有する。
【００１４】
導電ペーストを用いる方法は、導電粉をバインダに分散させ、ペースト状にした導電ペーストを基板の表面に塗布又はスルーホールに充填して図１に示すような導電層を形成する方法である。なお図１において１は導電ペースト及び２は銅箔である。
また、印刷配線板に形成したスルーホールに導電層を形成する他の手段としては、スルーホール内壁に銅めっきを施して導電層を形成する方法がある。
【００１５】
一般的にスルーホール内に充填して用いる孔埋め導電ペーストを用いた場合の層間接続は、小さい孔でありながら高導電性を必要とするため、孔にできる限り導電ペーストを充填し、孔にすき間なく導電ペーストを埋め込む必要がある。そのため従来の孔埋め導電ペーストは導電粉の比率を高くする必要があるが、導電粉の比率を高くすると導電ペーストの粘度が高くなり孔への充填性が低下してしまう。これに対してバインダの比率を高くすると粘度が低くなり孔への充填性が向上するが導電性が低下してしまうという欠点が生じる。
【００１６】
その方策として、溶剤を含まない無溶剤型で、バインダとして液状エポキシ樹脂を主成分とした導電ペーストを用い、また孔の大きさにより溶剤を若干使用した導電ペーストを用いていた。
しかし、エポキシ樹脂はフェノール樹脂などと比較すると、熱による硬化収縮量が低いため、エポキシ樹脂を主成分とする導電ペーストの抵抗が低くなり難いという欠点があった。
抵抗を低くするためには、導電ペーストにおける導電粉の割合を高くするか、銀など高導電性の金属粉を使用すればその欠点を補うことは可能であるが、導電ペーストが高価になってしまう。
【００１７】
一方、フェノール樹脂を主成分とした導電ペーストもあるが、この導電ペーストはエポキシ樹脂を主成分とする導電ペーストより導電性は良好であるが、導電ペーストの粘度が高くなり孔への充填性に問題があった。
【００１８】
また、導電ペーストを用いてスルーホール内に導電層を形成する場合、溶剤を多量に含む導電ペーストを用いてスルーホール内を充填すると、溶剤の乾燥によりスルーホール内にボイドを生じることが避けられない。そのため図２に示すように、基材３の表面、導電ペーストを充填したスルーホール端部、銅箔ランド７上及び一部の銅箔回路８上に絶縁層５を形成し、さらに導電材料（ジャンパー導電ペースト）で絶縁層５上に導電材印刷回路（以下印刷回路とする）を形成するような多層回路板では、スルーホール内のボイドをなくし、スルーホール１０と銅箔ランド７、銅箔回路８及び印刷回路との接続の信頼性を高くしなければならないという欠点があった。なお図２において、４は導電層、６はジャンパー回路及び９はオーバーコート層である。
【００１９】
スルーホールの導通をスルーホール内壁に形成した銅めっきで行うようにして多層回路板を製作する場合、スルーホール内壁に銅めっきを施した後、スルーホールを埋めた導電ペースト上に蓋めっきを施せば、上記の欠点を解消することができるが、工程が増えコストも高くなるので好ましくない。
【００２０】
また、スルーホール内壁に銅めっきを施して導電層を形成し、空隙を樹脂で埋め込む方法もあるが、この方法においても工程数が多くなるためコストが高くなるという欠点がある。
【００２１】
また、スルーホール内にボイドレス又は略ボイドレスの導電材料を充填してスルーホールの導通を確保した後、基材表面に絶縁層及び印刷回路を形成する方法があるが、この方法ではスルーホール内に充填した導電材料と銅箔ランド部が銅箔の端部断面で接続されるため、接続の信頼性が低くなる欠点がある。これを回避するには、前記の蓋めっきを施せばよいが、これでは工程が増え、コストが高くなり好ましくない。
【００２２】
さらに、スルーホール内に、溶剤を１５重量％以上含む銀導電材料（銀ペースト）を充填する銀スルーホール配線板を使用し、この配線板の表面に絶縁層及び印刷回路を形成して多層回路板を作製する場合、溶剤の揮発に伴ってスルーホール内に生じる大きな空隙が信頼性を低下させる原因となる。即ち、洗浄工程などの際にボイド内にイオン性不純物が残存すると耐マイグレーション性が低下する。また銀スルーホール配線板では、銀ペーストが銅箔ランド上に厚く盛り上がる場合があり、部品実装の場合、この厚く盛り上がった銀ペーストの高さが障害になる場合がある。
【００２３】
一方、鉛を主成分とするはんだ材料もあるが、このようなはんだ材料は、融点が比較的低く、かつ作業性もよいため長期にわたって幅広く実用化されてきた。しかし、近年になって、毒性の高い鉛を含有するため、鉛含有廃棄物の処理で、人体又は環境の生態系に悪影響を及ぼし易いことから、鉛の使用規制が提案されている。現在、鉛の代替としてビスマスなどの比較的低融点の金属材料を使用する低融点金属ろう材が開発されているが、これらの融点は鉛はんだに比較して高いため、基板材料又は実装電子部品等の耐熱性を高くしなければならず、技術的な困難さ、コストアップを招く等の欠点があった。
【００２４】
一般的に使用されている孔埋め導電ペーストを用いた多層化積層工程は、孔に導電ペーストを充填し、予備乾燥させたビルドアップ層を積層し、本乾燥として加熱加圧を行う。そのため本乾燥後に導電ペーストが硬化していることが必要であり、また積層後加圧することによって加圧しない場合よりも導電性が向上している必要がある。
【００２５】
ところが、従来の孔埋め導電ペーストは、バインダの主成分がエポキシ樹脂でありその硬化剤としてイミダゾール類を一般的に用いているが、導電粉として凝集を解きほぐす解粒処理を行い表面に銅が露出している略球状銀被覆銅粉を用いた場合、導電ペーストの硬化性が低下することがあるという欠点があった。
【００２６】
解粒処理を行った銀被覆銅粉を使用するためには、銅とキレート結合を形成せず、エポキシ樹脂の硬化剤として働く物質を添加する必要がある。
また、略球状銀被覆銅粉は銀めっき加工工程で凝集し易く、タップ密度が低いため、高含有率で導電ペーストに配合すると粘度上昇を引き起こし好ましくない。
さらに、解粒処理を行った略球状銀被覆銅粉を使用するとレゾール型フェノール樹脂は銅とキレート結合を起こすため導電ペーストの保管中に粘度上昇を起こす欠点を有していた。
【００２７】
また、アルコキシ基含有レゾール型フェノール樹脂及びエポキシ樹脂をバインダとして用いて導電接着剤（導電ペースト）を作製した場合において、もし印刷配線板に接着した接着部品に不具合が生じて、接着部品を取り換える場合には、熱硬化性樹脂硬化物をゴム状態にできる高い温度に加熱しなければならないが、このようなときは、バインダとして熱可塑性樹脂を使用すれば上記の欠点を解消することができる。
【００２８】
【発明が解決しようとする課題】
請求項１記載の発明は、導電粉の高配合率化が可能で導電性の信頼性又は耐マイグレーション性に優れ、銀めっき量を低減することで価格競争力も高く、はんだ付電極形成用、導電接着剤用等に適した導電ペーストを提供するものである。請求項２記載の発明は、請求項１の発明に加えて、高充填性及び流動性に優れた導電ペーストを提供するものである。
請求項３記載の発明は、請求項１の発明に加えて、シェルフライフに優れ短時間での硬化が可能で、かつ遠赤外炉（以下ＩＲ炉とする）使用での短時間乾燥、硬化性に優れた配線板回路形成用、孔埋め用等に適した導電ペーストを提供するものである。
【００２９】
請求項４記載の発明は、請求項１の発明に加えて、低粘度、高充填量化でき、エポキシ当量が小さいことから耐熱性も良好な導電ペーストを提供するものである。
請求項５及び６記載の発明は、請求項１の発明に加えて、シェルフライフの安定した導電ペーストを提供するものである。
請求項７記載の発明は、請求項１の発明に加えて、印刷後における乾燥の際の滲みが少ない導電ペーストを提供するものである。
請求項８記載の発明は、請求項１の発明のうち、特に硬化性に優れた導電ペーストを提供するものである。
【００３０】
請求項９記載の発明は、請求項１の発明の発明に加えて、シェルフライフに優れ、接着部品の取り外し性が良好な導電接着剤に適した導電ペーストを提供するものである。
請求項１０記載の発明は、請求項９の発明に加えて、導電性が良好でシェルフライフの安定した導電ペーストを提供するものである。
請求項１１記載の発明は、請求項９の発明に加えて、印刷後における乾燥の際の滲みが少なく、接着性及び可撓性に優れた導電ペーストを提供するものである。
【００３１】
【課題を解決するための手段】
本発明は、銅粉の表面が銀で被覆され、さらにこの表面に銅粉に対して０．０２〜０．５重量％の脂肪酸が被覆された略球状銀被覆銅粉５０〜９４重量％、銅粉の表面が銀で被覆され、さらにこの表面に銅粉に対して０．０２〜１．２重量％の脂肪酸が被覆された偏平状銀被覆銅粉３〜２０重量％、平均粒径が７μｍ以下の銀粉１〜５重量％及び低融点金属を２〜２５重量％含む導電粉並びにバインダを含有してなる導電ペーストに関する。
また、本発明は、略球状銀被覆銅粉が、平均粒径が１〜１０μｍ及びタップ密度が相対値で５５〜７５％であり、かつその表面が平滑化されたものである前記の導電ペーストに関する。
また、本発明は、バインダの主成分が、アルコキシ基含有レゾール型フェノール樹脂及びエポキシ樹脂並びにこれらの硬化剤、添加剤及び溶剤である前記の導電ペーストに関する。
【００３２】
また、本発明は、エポキシ樹脂のエポキシ当量が、１３０〜３３０ｇ／ｅｑである前記の導電ペーストに関する。
また、本発明は、アルコキシ基含有レゾール型フェノール樹脂が、アルコキシ基の炭素数が１〜６である前記の導電ペーストに関する。
また、本発明は、アルコキシ基含有レゾール型フェノール樹脂が、アルコキシ化率が５〜９５％のものである前記の導電ペーストに関する。
また、本発明は、アルコキシ基含有レゾール型フェノール樹脂が、重量平均分子量が５００〜２００，０００である前記の導電ペーストに関する。
また、本発明は、アルコキシ基含有レゾール型フェノール樹脂とエポキシ樹脂の配合割合が、アルコキシ基含有レゾール型フェノール樹脂：エポキシ樹脂が重量比で５：９５〜６０：４０である前記の導電ペーストに関する。
【００３３】
また、本発明は、バインダの主成分が、熱可塑性樹脂並びにこれらの添加剤及び溶剤である前記の導電ペーストに関する。
また、本発明は、熱可塑性樹脂が、熱軟化温度が９０〜２４０℃の熱可塑性樹脂である前記の導電ペーストに関する。
さらに、本発明は、熱可塑性樹脂が、熱軟化温度が９０〜２４０℃のフェノキシ樹脂である前記の導電ペーストに関する。
【００３４】
【発明の実施の形態】
略球状銀被覆銅粉において、銅粉の表面への銀の被覆量は特に制限はないが、銅粉に対して２．５〜１２重量％の範囲であることが好ましく、２．５〜７．５重量％の範囲であることがさらに好ましい。銀の被覆量が１２重量％を超えると銀被覆工程での凝集割合が高くなり、タップ密度が低下する傾向があると共にコストアップとなり、一方、２．５重量％未満であると銅の露出割合が高くなり、導電性の信頼性が低くなり易くなる傾向がある。
【００３５】
本発明で用いられる略球状銀被覆銅粉の平均粒径は、印刷、吐出等の取扱い、価格の点で１〜１０μｍの範囲であることが好ましく、２〜７μｍの範囲出あることがさらに好ましい。
また、略球状銀被覆銅粉は、アスペクト比が１〜１．５の範囲であることが好ましく、１〜１．３の範囲であることがさらに好ましい。
【００３６】
一方、偏平状銀被覆銅粉においても、銅粉の表面への銀の被覆量は特に制限はなく、銅粉に対して３〜１２重量％の範囲であることが好ましく、３〜１０重量％の範囲であることがさらに好ましい。銀の被覆量が１２重量％を超えるとコストアップになる傾向があり、３重量％未満であると導電性の信頼性が低下する傾向がある。
【００３７】
本発明で用いられる偏平状銀被覆銅粉の平均粒径は、偏平状銀被覆銅粉を作製する際、表面の銀の被覆層が剥離又は損傷を防止する点で１０μｍ以下であることが好ましく、６．５〜９μｍの範囲がさらに好ましい。
また、偏平状銀被覆銅粉は、アスペクト比が２〜２０の範囲であることが好ましく、２〜１５の範囲であることがさらに好ましい。
【００３８】
なお、上記でいう平均粒径は、レーザー散乱型粒度分布測定装置により測定することができる。本発明においては、測定装置としてマスターサイザー（マルバン社製）を用いて測定した。
また、本発明におけるアスペクト比とは、銀被覆銅粉の粒子の長径と短径の比率（長径／短径）をいう。本発明においては、粘度の低い硬化性樹脂中に銀被覆銅粉の粒子をよく混合し、静置して粒子を沈降させると共にそのまま樹脂を硬化させ、得られた硬化物を垂直方向に切断し、その切断面に現れる粒子の形状を電子顕微鏡で拡大して観察し、少なくとも１００の粒子について一つ一つの粒子の長径／短径を求め、それらの平均値をもってアスペクト比とする。
【００３９】
ここで、短径とは、前記切断面に現れる粒子について、その粒子の外側に接する二つの平行線の組み合わせ粒子を挟むように選択し、それらの組み合わせのうち最短間隔になる二つの平行線の距離である。一方、長径とは、前記短径を決する平行線に直角方向の二つの平行線であって、粒子の外側に接する二つの平行線の組み合わせのうち、最長間隔になる二つの平行線の距離である。これらの四つの線で形成される長方形は、粒子がちょうどその中に納まる大きさとなる。
なお、本発明において行った具体的方法については後述する。
【００４０】
本発明において、銅粉の表面に銀を被覆する方法としては特に制限はないが、例えば置換めっき、電気めっき、無電解めっき等の方法があり、銅粉と銀の付着力が高いこと及びランニングコストが安価であることから、置換めっきで被覆することが好ましい。
【００４１】
本発明においては、銅粉の表面に銀を被覆した銀被覆銅粉の表面にさらに脂肪酸を被覆するものである。本発明で用いられる脂肪酸としては、ステアリン酸、ラウリン酸、カプリン酸、パルミチン酸などの飽和脂肪酸又はオレイン酸、リノール酸、リノレン酸、ソルビン酸などの不飽和脂肪酸等が挙げられる。
【００４２】
銀被覆銅粉の表面への脂肪酸の被覆量は、形状が略球状の場合は、銅粉に対して０．０２〜０．５重量％の範囲、好ましくは０．０２〜０．２重量％の範囲、さらに好ましくは０．０２〜０．１重量％の範囲とされ、０．５重量％を超えると銀被覆銅粉同士の凝集を解粒し易く、また銀被覆銅粉が樹脂溶液に濡れ易くなるが、反面脂肪酸が内部離型剤として働くため、接着力が低下する。一方、脂肪酸の被覆量が０．０２重量％未満であると銀被覆銅粉同士の凝集を解粒することが困難になる。
【００４３】
また、銀被覆銅粉の形状が偏平状の場合は、銅粉に対して０．０２〜１．２重量％の範囲、好ましくは０．０８〜１．０重量％の範囲、さらに好ましくは０．１５〜０．７重量％の範囲とされ、１．２重量％を超えると偏平状銀被覆銅粉が樹脂溶液に濡れ易くなるが、反面脂肪酸が内部離型剤として働くため、接着剤に使用した場合は、接着力が低下する。一方、０．０２重量％未満であると偏平状に加工することが困難である。
【００４４】
銀被覆銅粉の表面に脂肪酸を被覆すれば下記のような利点がある。即ち、銅粉に銀めっきを施した場合、その後の乾燥工程で銅粉に含まれる水分を乾燥させるが、このとき水分を直接乾燥させると水の蒸発潜熱が大きいため乾燥に多くの時間を要する。しかし、水分を予めアルコール、アセトン等の親水性の有機溶剤で置換し、この有機溶剤を乾燥すれば乾燥は容易になる。本発明はこれを利用したもので、前記、有機溶剤に脂肪酸を配合して乾燥を容易にすると共に、脂肪酸の被覆量を上記に示す範囲にすることにより、銀被覆銅粉の凝集を容易に解粒させ、接着力についても何ら問題はなく、タップ密度の高い略球状銀被覆銅粉を得ることができると共に樹脂溶液に濡れ易く、接着力についても何ら問題のない偏平状銀被覆銅粉を得ることができる。
【００４５】
略球状銀被覆銅粉のタップ密度は相対値で５５〜７５％の範囲であることが好ましく、５８〜７５％の範囲であることがさらに好ましい。タップ密度が５５％未満の場合、充填密度が低いため導電粉の配合割合を高くすると導電ペーストの粘度が高くなり、反面導電粉の配合割合を低くすると、十分な導電性及び信頼性が得られなくなる傾向がある。また銅粉を銀めっき処理すると銀被覆銅粉が得られるが、めっき処理しただけの銀被覆銅粉の表面は、銀の微結晶が析出しており、表面は平滑ではなく、粒子同士の流動性も低くなる傾向がある。また銀の微結晶間に粒界が存在するため、銀めっき層の導電性自体も低い場合がある。さらに、銀めっき処理を行った場合、銀めっき層とコア材の銅粉との密着性が十分でない場合もある。一方、タップ密度が上限の７５％を超える略球状銀被覆銅粉は、それ自体作製することが困難である。
【００４６】
また、偏平状銀被覆銅粉のタップ密度は相対値で２７〜５０％の範囲であることが好ましく、３０〜４５％の範囲であることがさらに好ましい。タップ密度が２７％未満の場合、略球状銀被覆銅粉と組み合わせて用いると、充填密度を低下させるため流動性が低下する傾向がある。一方、タップ密度が５０％を超えると形状が球状に近くなり略球状銀被覆銅粉同士の接触性を向上させる効果が小さくなる傾向がある。
【００４７】
なお、タップ密度の相対値とは、２５ｍｍのストロークでタッピングを１０００回行い、体積と質量から算出したタップ密度をその粒子の真密度又は理論密度で除した値である。
【００４８】
本発明において、導電粉としては上記の略球状銀被覆銅粉及び偏平状銀被覆銅粉の他に平均粒径が７μｍ以下の銀粉及び低融点金属が用いられる。
銀粉は、平均粒径が上記に示すように７μｍ以下、好ましくは６μｍ以下、さらに好ましくは０．１〜５μｍの範囲の銀粉を用いることが必要とされ、７μｍを超えると略球状銀被覆銅粉と混合した後の印刷又は吐出などの際の流動性が悪くなるおそれがある。また略球状銀被覆銅粉と混合した際に緻密な充填状態を得ることが困難になるなどの欠点が生じる。
【００４９】
低融点金属は、融点が１２０〜３００℃の金属を用いることが好ましく、１２０〜２８０℃の金属を用いることがさらに好ましい。このような金属としては、例えば、ビスマス、錫等が挙げられ、ペースト中に粉末の状態で混合してもよく、また略球状銀被覆銅粉の表面に付着する形態であってもよい。
【００５０】
低融点金属は粉末で添加する場合その粒径は小さいほど好ましく、印刷、吐出等の障害を防止する点で３００メッシュ以下が好ましく、４００メッシュ以下がより好ましく、５００メッシュ以下がさらに好ましい。また平均粒径が３μｍ以下、特に０．１〜２．５μｍの範囲であれば、略球状銀被覆銅粉の空隙を埋めることができ、少ない添加量で略球状銀被覆銅粉同士の接触確率を高められるのでさらに好ましい。
【００５１】
低融点金属の添加時機は特に制限はないが、銀めっき銅粉の解粒の際に添加し、均一混合と同時に粒子間の接合を進めれば、融点以下でも略球状銀被覆銅粉との接合が向上し、導電性を高くすることができる。特にＩＲ炉で乾燥、硬化させる場合、数分の短時間ではあるが２２０℃以上の高温を通過する。その際にバインダが硬化するだけでなく、低融点金属が略球状銀被覆銅粉との接合性を高めることができ、導電性及びその信頼性を向上できる。
【００５２】
略球状銀被覆銅粉、偏平状銀被覆銅粉及び平均粒径が７μｍ以下の銀粉の配合割合は、略球状銀被覆銅粉が５０〜９４重量％、偏平状銀被覆銅粉が３〜２０重量％、平均粒径が７μｍ以下の銀粉が１〜５重量％及び低融点金属が２〜２５重量％、好ましくは略球状銀被覆銅粉が６０〜９４重量％、偏平状銀被覆銅粉が３〜１５重量％、平均粒径が７μｍ以下の銀粉が１〜４重量％及び低融点金属が２〜２０重量％の範囲とされ、上記の範囲から外れると導電性が低下し、その信頼性が低下するという欠点がある。
【００５３】
本発明で用いられるバインダとしては、主成分がアルコキシ基含有レゾール型フェノール樹脂及びエポキシ樹脂並びにこれらの硬化剤、添加剤及び溶剤又は主成分が熱可塑性樹脂並びに添加剤及び溶剤が好ましいものとして挙げられる。
フェノール樹脂を使用した導電ペーストは、エポキシ樹脂を単独で使用した導電ペーストより高い導電性が得られる。これは硬化収縮量がエポキシ樹脂よりフェノール樹脂の方が大きいため、導電体の体積減少が大きく、導電粉同士の接触面積及び確率が高くなるためである。高導電性が要求される導電ペーストにはフェノール樹脂は不可欠であるが、導電ペーストの粘度が高くなり易く、導電粉の配合割合を高くすることが困難であるが、アルコキシ基含有レゾール型フェノール樹脂を使用することによりこれらの問題を回避することができる。
【００５４】
アルコキシ基含有レゾール型フェノール樹脂は、銅が露出した略球状銀被覆銅粉と混合しても、フェノール樹脂のメチロール基がアルコキシ基によってマスキングされているため、銅表面とメチロール基との反応が抑制できる。
一方、エポキシ樹脂は、その機械的性質、耐熱性及び接着性に優れるため、接着剤などの用途のバインダとして適する。しかし、硬化剤としてイミダゾール類を単独で使用する場合、硬化性を高くすると室温での暗反応が避けられず、シェルフライフが短くなることを避けられない。ところが、上記のアルコキシ基含有レゾール型フェノール樹脂とイミダゾールとを併用し、これらをエポキシ樹脂の硬化剤として使用すれば、シェルフライフが長く、かつ１６０℃前後での硬化性の優れた導電ペーストを得ることができる。
【００５５】
熱可塑性樹脂を使用して得られる導電接着剤（導電ペースト）は、印刷配線板上に接着した接着部品を交換する必要がある場合、アルコキシ基含有レゾール型フェノール樹脂及びエポキシ樹脂を使用して接着したものよりも接着部品を容易に交換することができるという効果を奏する。
【００５６】
溶剤は、粘性を調節して印刷、吐出等の作業性を制御するために使用可能であるが、その沸点が低いと作業中の粘度変化が大きく好ましくなく、一方、沸点が高すぎると乾燥性が悪くなり硬化、乾燥作業に支障をきたすため、大気圧での沸点が１５０〜２５０℃の溶剤を使用することが好ましく、１７０〜２４０℃の溶剤を使用することがさらに好ましい。上記の条件に該当する溶剤としては、例えばエチルカルビトール、ジプロピレングリコールメチルエーテル、ジプロピレングリコールエチルエーテル、ジプロピレングリコールイソプロピルメチルエーテル、ジプロピレングリコールイソプロピルエチルエーテル、トリプロピレングリコールメチルエーテル、プロピレングリコールエチルエーテルアセテート、エチレングリコールエチルエーテルアセテート、エチレングリコールブチルエーテル、ジエチレングリコールメチルエーテル、ジエチレングリコールエチルエーテル、３−メチル−３−メトキシブタノール、３−メチル−３−メトキシブチルエーテル、乳酸ブチル等が挙げられる。
【００５７】
本発明で用いられるエポキシ樹脂は常温で液状のものが好ましい。常温で結晶化するものは液状物と混合して結晶化を回避することができれば結晶性のエポキシ樹脂であっても使用できる。本発明における常温で液状のエポキシ樹脂とは、例えば常温で固形のものでも常温で液状のエポキシ樹脂と混合することで常温で安定して液状となるものも含む。なお本発明において常温とは温度が約２５℃を示すものを意味する。
また、エポキシ樹脂のエポキシ当量は１３０〜３３０ｇ／ｅｑの範囲のものを用いることが好ましく、１６０〜２５０ｅｑの範囲のものを用いることがさらに好ましい。
【００５８】
エポキシ樹脂は公知のものが用いられ、分子量中にエポキシ基を２個以上含有する化合物、例えばビスフェノールＡ、ビスフェノールＡＤ、ビスフェノールＦ、ノボラック、クレゾールノボラック類とエピクロールヒドリンとの反応により得られるポリグリシジルエーテル、ジヒドロキシナフタレンジグリシジルエーテル、ブタンジオールジグリシジルエーテル、ネオペンチルグリコールジグリシジルエーテル等の脂肪族エポキシ樹脂やジグリシジルヒダントイン等の複素環式エポキシ、ビニルシクロヘキセンジオキサイド、ジシクロペンタンジエンジオキサイド、アリサイクリックジエポキシアジペイトのような脂環式エポキシ樹脂が挙げられる。
【００５９】
必要に応じて可撓性付与剤が用いられる。可撓性付与剤は公知の物でよく、分子量中にエポキシ基を１個だけ有する化合物、例えばｎ−ブチルグリシジルエーテル、バーサティック酸グリシジルエステル、スチレンオキサイド、エチルヘキシルグリシジルエーテル、フェニルグリシジルエーテル、クレジルグリシジルエーテル、ブチルフェニルグリシジルエーテル等のような通常のエポキシ樹脂が挙げられる。
これらのエポキシ樹脂及び可撓性付与剤は、単独又は２種以上を混合して用いることができる。
【００６０】
アルコキシ基含有レゾール型フェノール樹脂とエポキシ樹脂とを併用し、なおかつ従来使用していた硬化剤を併用することで、上記のようにシェルフライフが長く、硬化性に優れ、かつ導電ペースト硬化物の耐溶剤性が良好になり好ましい。特に、融点、解離温度の異なる硬化剤を使用又は組み合わせて用いることにより、導電ペーストのセミキュア状態をコントロールできるので好ましい。その硬化剤としては、ポットライフの点でイミダゾール類が好ましいが、その他としては、例えばメンセンジアミン、イソフオロンジアミン、メタフェニレンジアミン、ジアミノジフェニルメタン、ジアミノジフェニルスルホン、メチレンジアニリン等のアミン類、無水フタル酸、無水トリメリット酸、無水ピロメリット酸、無水コハク酸、テトラヒドロ無水フタル酸等の酸無水物、ジシアンジアミド等の化合物系硬化剤を用いてもよく、必要に応じて、潜在性アミン硬化剤等の硬化剤と併用して用いてもよく、また３級アミン、トリフェニルホスフィン、テトラフェニルホスフェニルボレ−ト等といった化合物を添加してもよい。
これらの硬化剤の含有量は、導電ペースト硬化物のガラス転移点（Ｔｇ）の点でエポキシ樹脂１００重量部に対して０．１〜２０重量部の範囲であることが好ましく、１〜１０重量部の範囲であることがさらに好ましい。
【００６１】
導電ペーストのバインダとして使用した場合の粘度、導電性等の点からアルコキシ基含有レゾール型フェノール樹脂のアルコキシ基の炭素数は、１〜６であることが好ましく、２〜４であることがさらに好ましい。
また、レゾール型フェノール樹脂のアルコキシ化率、即ち全メチロール基のアルコキシ化されている割合は、導電ペーストの粘度、導電性及び信頼性の点から５〜９５％の範囲が好ましく、１０〜８５％の範囲がさらに好ましい。
【００６２】
さらに、アルコキシ基含有レゾール型フェノール樹脂中のアルコキシ基は、ベンゼン環１個当たりアルコキシ基が０．１〜２個の範囲が好ましく、０．３〜１．５個の範囲がより好ましく、０．５〜１．２個の範囲がさらに好ましい。
なお、アルコキシ化率又はアルコキシ基の数は、核磁気共鳴スペクトル分析法（以下ＮＭＲ法とする）で測定できる。
【００６３】
本発明におけるアルコキシ基含有レゾール型フェノール樹脂の重量平均分子量は、導電ペーストの粘度、シェルフライフ、導電ペーストの硬化性、導電性、接着性、靱性等の点から５００〜２００，０００の範囲が好ましく、５００〜１２０，０００の範囲がさらに好ましい。
なお、重量平均分子量はゲルパーミエーションクロマトグラフィー法で測定し、標準ポリスチレン換算する事により求めることができる。
【００６４】
アルコキシ基含有レゾール型フェノール樹脂とエポキシ樹脂の配合割合は、アルコキシ基含有レゾール型フェノール樹脂：エポキシ樹脂が重量比で５：９５〜６０：４０であることが好ましく、１０：９０〜４０：６０であることがさらに好ましい。アルコキシ基含有レゾール型フェノール樹脂の割合が上記の範囲を下回ると硬化剤としての働きが小さく、導電性も悪くなる傾向があり、上記の範囲を上回ると導電ペーストの導電性は高いものの接着性、靱性、粘度等のバランスが悪くなる傾向がある。
【００６５】
熱可塑性樹脂は、熱軟化温度が９０〜２４０℃、好ましくは１３０〜２００℃の熱可塑性樹脂を用いることが望ましく、例えばフェノキシ樹脂、熱可塑性ポリエステル樹脂、ポリスチレン樹脂等が挙げられ、これらのうち熱軟化温度が９０〜２４０℃のフェノキシ樹脂を用いれば、機械的強度、耐熱性、接着性に優れるので好ましい。熱可塑性樹脂は、銅が露出した略球状銀被覆銅粉と混合しても、銅表面と官能基との反応が抑制できる。また熱可塑性樹脂を用いれば、シェルフライフが長く、かつ１００〜１６０℃前後で乾燥するだけでよい導電ペーストを得ることができる。
【００６６】
本発明に用いられるバインダには、上記の材料以外に必要に応じてシラン系、チタネート系、アルミネート系等のカップリング剤、チキソ剤、消泡剤、粉末表面処理剤、沈降防止剤等を添加して均一に混合して得られる。必要に応じて添加されるカップリング剤、チキソ剤、消泡剤、粉末表面処理剤、沈降防止剤等の含有量は、導電ペーストに対して０．０１〜１重量％の範囲であることが好ましく、０．０３〜０．５重量％の範囲であることがさらに好ましい。
【００６７】
本発明の導電ペーストは、上記のバインダ、導電粉及び必要に応じて添加されるカップリング剤、チキソ剤、消泡剤、粉末表面処理剤、沈降防止剤、溶剤等と共に、らいかい機、ニーダー、三本ロール等で均一に混合、分散して得ることができる。
【００６８】
【実施例】
以下、本発明を実施例により説明する。
実施例１
アルコキシ基含有レゾール型フェノール樹脂（当社試作品、アルコキシ基の炭素数が４、アルコキシ化率６５％、重量平均分子量１，２００）３８重量部、エポキシ当量が１７０ｇ／ｅｑのビスフェノールＦ型エポキシ樹脂（三井石油化学工業（株）製、商品名エポミックＲ１１０）５７重量部及び２−フェニル−４−メチル−イミダゾール（四国化成（株）製、商品名キュアゾール２Ｐ４ＭＺ）５重量部を均一に混合してバインダとした。
なお、アルコキシ基含有レゾール型フェノール樹脂とビスフェノールＦ型エポキシ樹脂の割合は、重量比でフェノール樹脂：エポキシ樹脂が４０：６０であった。
【００６９】
次に、アトマイズ法で作製した平均粒径が５．１μｍの球状銅粉（日本アトマイズ加工（株）製、商品名ＳＦＲ−Ｃｕ）を希塩酸及び純水で洗浄した後、水１リットルあたりＡｇＣＮ８０ｇ及びＮａＣＮ７５ｇを含むめっき溶液で球状銅粉に対して銀の被覆量が３重量％になるように置換めっきを行い、水洗、乾燥して銀めっき銅粉（銀被覆銅粉）を得た。なお上記の乾燥の際に水分をエタノールで３回置換した。特に３回目のエタノールには、使用した銅粉１ｋｇあたり０．５ｇ（銅粉に対して被覆量が０．０５重量％に相当）のステアリン酸を溶解し、このステアリン酸を溶解したエタノールで上記銀めっき銅粉に含む水分を置換した後乾燥してステアリン酸処理した銀めっき銅粉を得た。
【００７０】
この後、２リットルのボールミル容器内に上記で得たステアリン酸処理した銀めっき銅粉２５０ｇ及び直径が３ｍｍのジルコニアボール２ｋｇを投入し、３時間回転させて、アスペクト比が平均１．１及び平均粒径が５．１μｍの解粒並びに表面平滑化処理した略球状銀被覆銅粉を得た。
なお、略球状銀被覆銅粉のタップ密度は相対値で６７％であった。
【００７１】
一方、上記と同様の球状銅粉を使用し、上記と同様の工程を経て作製した球状銅粉に対して銀の被覆量（以下単に銀の被覆量とする）が１２重量％、球状銅粉に対してステアリン酸の被覆量（以下単にステアリン酸の被覆量とする）が０．２重量％のステアリン酸処理した銀めっき銅粉を得た。
【００７２】
この後、２リットルのボールミル容器内に上記で得たステアリン酸処理した銀めっき銅粉２５０ｇ及び直径が５ｍｍのジルコニアボール２ｋｇを投入し、２時間振動させてアスペクト比が平均６．０及び平均粒径が７．３μｍの偏平状銀被覆銅粉を得た。
なお、偏平状銀被覆銅粉のタップ密度は相対値で３８％であった。
【００７３】
上記で得たバインダ５０ｇに、上記で得た略球状銀被覆銅粉４２３ｇ、上記で得た偏平状銀被覆銅粉１３．５ｇ、平均粒径が２．２μｍの鱗片状銀粉（徳力化学研究所製、商品名ＴＣＧ−１）４．５ｇ、平均粒径が３．２μｍのビスマス粉（高純度化学研究所製）９ｇ及び溶剤としてエチルカルビトール１５ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
【００７４】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、鱗片状銀粉、及びビスマス粉）の割合は略球状銀被覆銅粉９４重量％に対し、偏平状銀被覆銅粉３重量％、鱗片状銀粉１重量％及びビスマス粉２重量％であった。
また、バインダと導電粉の割合は、重量比でバインダ：導電粉が１０：９０であった。
【００７５】
次に、上記で得た導電ペーストを用いて、図３に示すポリイミドフィルム１１上にテストパターン１２を印刷し、乾燥機に入れた後１７０℃まで１３分間で昇温し、その温度で１時間の加熱処理を行い配線板を得た。
得られた配線板について、導電ペーストの硬化性をＪＩＳの塗膜用鉛筆引かき試験（Ｋ５４０１−６９）で評価した結果、評価は６Ｈだった。また導体のシート抵抗は１０７ｍΩ／□であった。
【００７６】
さらに、厚さが１．２ｍｍのガラスコンポジット基板表面の銅箔をエッチアウトした基板上にテストパターンを印刷し、ＩＲ炉で２４０℃まで１０分間で昇温し、次いで２４０℃で０．５分間加熱処理し、硬化させテスト基板を得た。このテスト基板のシート抵抗は７９ｍΩ／□であり、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ２．７％及び８．７％であった。上記の恒温恒湿試験は、８５℃８５％相対湿度中に保管し、気相冷熱試験は−６５℃３０分間〜１２５℃３０分間を１サイクルとして行った（以下同じ）。
【００７７】
なお、本実施例におけるアスペクト比の具体的測定法を以下に示す。低粘度のエポキシ樹脂（ビューラー社製）の主剤（Ｎｏ．１０−８１３０）８ｇと硬化剤（Ｎｏ．１０−８１３２）２ｇを混合し、ここへ導電粉２ｇを混合してよく分散させ、そのまま３０℃で真空脱泡した後、１０時間３０℃の条件で静置して粒子を沈降させ硬化させた。その後、得られた硬化物を垂直方向に切断し、切断面を電子顕微鏡で１０００倍に拡大して切断面に現れた１５０個の粒子について長径／短径を求め、それらの平均値をもって、アスペクト比とした。
【００７８】
実施例２
いずれも実施例１で用いたアルコキシ基含有レゾール型フェノール樹脂１９重量部、ビスフェノールＦ型エポキシ樹脂７６重量部及び２−フェニル−４−メチル−イミダゾール５重量部を均一に混合してバインダとした。
なお、アルコキシ基含有レゾール型フェノール樹脂とビスフェノールＦ型エポキシ樹脂の割合は、重量比でフェノール樹脂：エポキシ樹脂が２０：８０であった。
【００７９】
上記で得たバインダ５０ｇに、実施例１で得た略球状銀被覆銅粉３６０ｇ、実施例１と同様の工程を経て銀の被覆量が５重量％及びステアリン酸の被覆量が０．５重量％のステアリン酸処理した銀めっき銅粉を作製し、さらに実施例１と同様の工程を経て得たアスペクト比が平均３及び平均粒径が６．８μｍの偏平状銀被覆銅粉３６ｇ、実施例１で用いた鱗片状銀粉９ｇ、実施例１で用いたビスマス粉４５ｇ並びに溶剤としてエチルカルビトール１０ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
【００８０】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、鱗片状銀粉及びビスマス粉）の割合は、略球状銀被覆銅粉８０重量％に対し、偏平状銀被覆銅粉８重量％、鱗片状銀粉２重量％及びビスマス粉１０重量％であった。
また、偏平状銀被覆銅粉のタップ密度は相対値で４１％であった。
さらに、バインダと導電粉の割合は、重量比でバインダ：導電粉が１０：９０であった。
【００８１】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は６Ｈ及び導体のシート抵抗は９８ｍΩ／□であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は７５ｍΩ／□であり、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ２．４％及び７．７％であった。
【００８２】
実施例３
アルコキシ基含有レゾール型フェノール樹脂（当社試作品、アルコキシ基の炭素数が４、アルコキシ化率６５％、重量平均分子量２０，０００）４．７５重量部、実施例１で用いたビスフェノールＦ型エポキシ樹脂９０．２５重量部及び実施例１で用いた２−フェニル−４−メチル−イミダゾール５重量部を均一に混合してバインダとした。
なお、アルコキシ基含有レゾール型フェノール樹脂とビスフェノールＦ型エポキシ樹脂の割合は、重量比でフェノール樹脂：Ｆ型エポキシ樹脂が５：９５であった。
【００８３】
上記で得たバインダ５０ｇに、実施例１と同様の工程を経て銀の被覆量が５重量％及びステアリン酸の被覆量が０．１重量％のステアリン酸処理した銀めっき銅粉を作製し、さらに実施例１と同様の工程を経て得たアスペクト比が１．１及び平均粒径が５．５μｍの解粒、表面平滑化処理した略球状銀被覆銅粉３１５ｇ、実施例２で得た偏平状銀被覆銅粉６７．５ｇ、一次粒径が１μｍ以下の凝集性を有する銀粉（ディーエムシースクエアジャパン（株）製、商品名ＳＦＫ−ＥＤ）２２．５ｇ、錫粉（高純度化学研究所製）４５ｇ並びに溶剤としてエチルカルビトール１５ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
【００８４】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、銀粉及び錫粉）の割合は、略球状銀被覆銅粉７０重量％に対し、偏平状銀被覆銅粉１５重量％、銀粉５重量％及び錫粉１０重量％であった。
また、略球状銀被覆銅粉のタップ密度は、相対値で６３％であった。
さらに、バインダと導電粉の割合は、重量比でバインダ：導電粉が１０：９０であった。
【００８５】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は６Ｈ及び導体のシート抵抗は８９ｍΩ／□であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は７０ｍΩ／□であり、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ２．５％及び７．３％であった。
【００８６】
実施例４
実施例３で用いたアルコキシ基含有レゾール型フェノール樹脂４．７５重量部、実施例１で用いたビスフェノールＦ型エポキシ樹脂９０．２５重量部及び実施例１で用いた２−フェニル−４−メチル−イミダゾール５重量部を均一に混合してバインダとした。
なお、アルコキシ基含有レゾール型フェノール樹脂とビスフェノールＦ型エポキシ樹脂の割合は、重量比でフェノール樹脂：エポキシ樹脂が５：９５であった。
【００８７】
上記で得たバインダ５０ｇに、実施例１と同様の工程を経て銀の被覆量が１２重量％及びステアリン酸の被覆量が０．１５重量％のステアリン酸処理した銀めっき銅粉を作製し、さらに実施例１と同様の工程を経て得たアスペクト比が平均１．１及び平均粒径が１．１μｍの解粒、表面平滑化処理した略球状銀被覆銅粉２７０ｇ、実施例１と同様の工程を経て作製した銀の被覆量が３重量％及びステアリン酸の被覆量が０．５重量％のステアリン酸処理した銀めっき銅粉を作製し、さらに実施例１と同様の工程を経て得たアスペクト比が平均２．２及び平均粒径が６．２μｍの偏平状銀被覆銅粉９０ｇ、実施例３で用いた一次粒径が１μｍ以下の凝集性を有する銀粉２２．５ｇ、実施例３で用いた錫粉６７．５ｇ並びに溶剤としてエチルカルビトール１０ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
【００８８】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、銀粉及び錫粉）の割合は、略球状銀被覆銅粉６０重量％に対し、偏平状銀被覆銅粉２０重量％、銀粉５重量％及び錫粉１５重量％であった。
また、略球状銀被覆銅粉のタップ密度は相対値で６０％及び偏平状銀被覆銅粉のタップ密度は相対値で４３％であった。
さらに、バインダと導電粉の割合は、重量比でバインダ：導電粉が１０：９０であった。
【００８９】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は６Ｈ及び導体のシート抵抗は７８ｍΩ／□であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は６３ｍΩ／□であり、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ１．９％及び８．３％であった。
【００９０】
比較例１
いずれも実施例１で用いたアルコキシ基含有レゾール型フェノール樹脂３８重量部、ビスフェノールＦ型エポキシ樹脂５７重量部及び２−フェニル−４−メチル−イミダゾール５重量部を均一に混合してバインダとした。
なお、アルコキシ基含有レゾール型フェノール樹脂とビスフェノールＦ型エポキシ樹脂の割合は、重量比でフェノール樹脂：エポキシ樹脂が４０：６０であった。
【００９１】
上記で得たバインダ５０ｇに、実施例１と同様の工程を経て銀の被覆量が２重量％及びステアリン酸の付着量が０．００５重量％のステアリン酸処理した銀めっき銅粉を作製し、さらに実施例１と同様の工程を経て得たアスペクト比が平均１．１及び平均粒径が５．５μｍの解粒、表面平滑化処理した略球状銀被覆銅粉４２３ｇ、実施例１と同様の工程を経て銀の被覆量が２重量％及びステアリン酸の被覆量が０．０５重量％のステアリン酸処理した銀めっき銅粉を作製し、さらに実施例１と同様の工程を経て得たアスペクト比が平均１．５及び平均粒径が５．８μｍの偏平状銀被覆銅粉１３．５ｇ、実施例１で用いた鱗片状銀粉４．５ｇ、実施例１で用いたビスマス粉９ｇ並びに溶剤としてエチルカルビトール２２ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
【００９２】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、鱗片状銀粉及びビスマス粉）の割合は、略球状銀被覆銅粉９４重量％に対し、偏平状銀被覆銅粉３重量％、鱗片状銀粉１重量％及びビスマス粉２重量％であった。
また、略球状銀被覆銅粉のタップ密度は相対値で６２％及び偏平状銀被覆銅粉のタップ密度は相対値で４５％であった。
さらに、バインダと導電粉の割合は、重量比でバインダ：導電粉が１０：９０であった。
【００９３】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は６Ｈ及び導体のシート抵抗は１９７ｍΩ／□と高い値であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は１３９ｍΩ／□であり、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ１１４％及び１２１％と大きかった。
【００９４】
比較例２
いずれも実施例１で用いたアルコキシ基含有レゾール型フェノール樹脂４．７５重量部、ビスフェノールＦ型エポキシ樹脂９０．２５重量部及び２−フェニル−４−メチル−イミダゾール５重量部を均一に混合してバインダとした。
なお、アルコキシ基含有レゾール型フェノール樹脂とビスフェノールＦ型エポキシ樹脂の割合は、重量比でフェノール樹脂：Ｆ型エポキシ樹脂が５：９５であった。
【００９５】
上記で得たバインダ５０ｇに、実施例１と同様の工程を経て銀の被覆量が２重量％及びステアリン酸の被覆量が０．６重量％のステアリン酸処理した銀めっき銅粉を作製し、さらに実施例１と同様の工程を経て得たアスペクト比が平均１．１及び平均粒径が５．３μｍの解粒、表面平滑化処理した略球状銀被覆銅粉４３６．５ｇ、実施例１と同様の工程を経て銀の被覆量が２重量％及びステアリン酸の被覆量が２重量％のステアリン酸処理した銀めっき銅粉を作製し、さらに実施例１と同様の工程を経て得たアスペクト比が平均２．４及び平均粒径が６．３μｍの偏平状銀被覆銅粉４．５ｇ、実施例１で用いた鱗片状銀粉４．５ｇ、実施例１で用いたビスマス粉４．５ｇ並びに溶剤としてエチルカルビトール４５ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
【００９６】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、鱗片状銀粉及びビスマス粉）の割合は、略球状銀被覆銅粉９７重量％に対し、偏平状銀被覆銅粉１重量％、鱗片状銀粉１重量％及びビスマス粉１重量％であった。
また、略球状銀被覆銅粉のタップ密度は相対値で４８％及び偏平状銀被覆銅粉のタップ密度は相対値で４３％であった。
さらに、バインダと導電粉の割合は、重量比でバインダ：導電粉が１０：９０であった。
【００９７】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は２Ｈと柔らかく、導体のシート抵抗は２６６ｍΩ／□と高い値であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は２１８ｍΩ／□であり、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行ったところ、回路抵抗の変化率はそれぞれ１４７％及び１５２％と大きかった。
【００９８】
比較例３
実施例１で用いたビスフェノールＦ型エポキシ樹脂９５重量部及び２−エチル−４−メチル−イミダゾール（四国化成（株）製、商品名キュアゾール２Ｅ４ＭＺ）５重量部を均一に混合してバインダとした。
【００９９】
上記で得たバインダ５０ｇに、実施例１と同様の工程を経て銀の被覆量が１２重量％及びステアリン酸の付着量が０．１５重量％のステアリン酸処理した銀めっき銅粉を作製し、さらに実施例１と同様の工程を経て得たアスペクト比が平均１．１及び平均粒径が５．５μｍの解粒、平滑化処理した略球状銀被覆銅粉１８０ｇ、実施例１と同様の工程を経て銀の被覆量が１２重量％及びステアリン酸の被覆量が０．２重量％のステアリン酸処理した銀めっき銅粉を作製し、さらに実施例１と同様の工程を経て得たアスペクト比が平均６及び平均粒径が７．３μｍの偏平状銀被覆銅粉１３５ｇ、実施例３で用いた一次粒径が１μｍ以下の凝集性を有する銀粉２２．５ｇ、実施例３で用いた錫粉１１２．５ｇ並びに溶剤としてエチルカルビトール２６ｇを加えて撹拌らいかい機及び三本ロールで均一に混合分散して導電ペーストを得た。この導電ペーストのシェルフライフは冷蔵保管で２日であり、実施例４で得た導電ペーストの冷蔵保管６０日以上に比較して大幅に悪かった。
【０１００】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、銀粉及び錫粉）の割合は、略球状銀被覆銅粉４０重量％に対し、偏平状銀被覆銅粉３０重量％、銀粉５重量％及び錫粉２５重量％であった。
また、略球状銀被覆銅粉のタップ密度は相対値で５９％及び偏平状銀被覆銅粉のタップ密度は相対値で３８％であった。
さらに、バインダと導電粉の割合は、重量比でバインダ：導電粉が１０：９０であった。
【０１０１】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は３Ｈと柔らかく、導体のシート抵抗は３７２ｍΩ／□と高い値であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は９７ｍΩ／□であり、恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ３５．１％及び４２．１％と大きかった。
【０１０２】
実施例５
フェノキシ樹脂〔フェノキシ　スペシャリティーズ（Ｐｈｅｎｏｘｙ　Ｓｐｅｃｉａｌｔｉｅｓ）社製、商品名ＰＫＨＪ、熱軟化温度１７０℃〕５０重量部及びチタネート系カップリング剤（味の素（株）製、商品名ＫＲ−ＴＴＳ２）０．４重量部に、溶剤としてジエチレングリコールモノエチルエーテル（日本乳化剤（株）製、商品名ＥｔＤＧ）７５重量部を加えて均一に混合、溶解して熱可塑性樹脂溶液を作製し、これをバインダとした。
【０１０３】
上記で得たバインダ１２５ｇに、実施例１で得た略球状銀被覆銅粉４２３ｇ、実施例１で用いた偏平状銀被覆銅粉１３．５ｇ、実施例１で用いた鱗片状銀粉９ｇ、実施例１で用いたビスマス粉４．５ｇ及び溶剤としてエチルカルビトール１７ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
【０１０４】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、鱗片状銀粉及びビスマス粉）の割合は、略球状銀被覆銅粉９４重量％に対し、偏平状銀被覆銅粉３重量％、鱗片状銀粉２重量％及びビスマス粉１重量％であった。
また、バインダと導電粉の割合は、重量比でバインダ：導電粉が１０：９０であった。
【０１０５】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は５Ｈ及び導体のシート抵抗は１３８ｍΩ／□であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は９５ｍΩ／□であり、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ３．４％及び１５％であった。
さらに、上記で得た導電ペーストを用いてチップ抵抗を銅箔上に接着し、その後チップ抵抗を取り外す為に加熱したところ、温度１８０℃で容易に取り外すことができた。
【０１０６】
実施例６
実施例５で得たバインダ１２５ｇに、実施例１で得た略球状銀被覆銅粉４０５ｇ、実施例１で用いた偏平状銀被覆銅粉２２．５ｇ、実施例１で用いた鱗片状銀粉１３．５ｇ、実施例１で用いたビスマス粉９ｇ及び溶剤としてエチルカルビトール１３ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
【０１０７】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、鱗片状銀粉及びビスマス粉）の割合は、略球状銀被覆銅粉９０重量％に対し、偏平状銀被覆銅粉５重量％、鱗片状銀粉３重量％及びビスマス粉２重量％であった。
また、バインダと導電粉の割合は、重量比でバインダ：導電粉が１０：９０であった。
【０１０８】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は４Ｈ及び導体のシート抵抗は１４１ｍΩ／□であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は１０８ｍΩ／□であり、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ２．０％及び９．８％であった。
【０１０９】
実施例７
いずれも実施例５で用いたフェノキシ樹脂３０重量部及びチタネート系カップリング剤０．５重量部に、溶剤としてジエチレングリコールモノエチルエーテル８５重量部を加えて均一に混合、溶解して熱可塑性樹脂溶液を作製し、これをバインダとした。
【０１１０】
上記で得たバインダ１１５ｇに、実施例３で得た略球状銀被覆銅粉２３５ｇ、実施例１で用いた偏平状銀被覆銅粉９４ｇ、実施例３で用いた一次粒径が１μｍの凝集性を有する銀粉２３．５ｇ、実施例１で用いたビスマス粉１１７．５ｇ及び溶剤としてエチルカルビトール１５ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
【０１１１】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、鱗片状銀粉及びビスマス粉）の割合は、略球状銀被覆銅粉５０重量％に対し、偏平状銀被覆銅粉２０重量％、鱗片状銀粉５重量％及びビスマス粉２５重量％であった。
また、バインダと導電粉の割合は、重量比でバインダ：導電粉が６：９４であった。
【０１１２】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は４Ｈ及び導体のシート抵抗は１１２ｍΩ／□であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は７９ｍΩ／□であり、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ３．１％及び１２．１％であった。
【０１１３】
実施例８
いずれも実施例５で用いたフェノキシ樹脂７０重量部及びチタネート系カップリング剤０．５重量部に、溶剤としてジエチレングリコールモノエチルエーテル７７重量部を加えて均一に混合、溶解して熱可塑性樹脂溶液を作製し、これをバインダとした。
【０１１４】
上記で得たバインダ１４７ｇに、実施例４で得た略球状銀被覆銅粉３７６ｇ、実施例４で用いた偏平状銀被覆銅粉２３．５ｇ、実施例３で用いた一次粒径が１μｍ以下の凝集性を有する銀粉２３．５ｇ、実施例４で用いた錫粉４７ｇ及び溶剤としてエチルカルビトール２０ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
【０１１５】
なお、導電粉（略球状銀被覆銅粉、偏平状銀被覆銅粉、銀粉及び錫粉）の割合は、略球状銀被覆銅粉８０重量％に対し、偏平状銀被覆銅粉５重量％、銀粉５重量％及び錫粉１０重量％であった。
また、バインダと導電粉の割合は、重量比でバインダ：導電粉が１４：８６であった。
【０１１６】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は４Ｈ及び導体のシート抵抗は１４５ｍΩ／□であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は１１８ｍΩ／□であり、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ５．３％及び２１．３％であった。
【０１１７】
比較例４
実施例５で得たバインダ１２５ｇに、比較例１で得た略球状銀被覆銅粉４５０ｇ及び溶剤としてエチルカルビトール１０ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
なお、バインダと導電粉の割合は、重量比でバインダ：導電粉が１０：９０であった。
【０１１８】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は５Ｈであったが、導体のシート抵抗は２７０ｍΩ／□と高い値であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は２９１ｍΩ／□と高く、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ５９．５％及び８６．１％と大きかった。
【０１１９】
比較例５
実施例８で得たバインダ１４７ｇに、比較例２で得た略球状銀被覆銅粉４３０ｇ及び溶剤としてエチルカルビトール３６ｇを加えて撹拌らいかい機及び三本ロールで均一に混合、分散して導電ペーストを得た。
なお、バインダと導電粉の割合は、重量比でバインダ：導電粉が１４：８６であった。
【０１２０】
次に、実施例１と同様の工程を経て配線板を作製し特性を評価した結果、塗膜用鉛筆引かき試験は２Ｈと柔らかく、導体のシート抵抗は３２５ｍΩ／□と高い値であった。
また、実施例１と同様の工程を経てテスト基板を作製したところ、テスト基板のシート抵抗は３５４ｍΩ／□と高く、該テスト基板を恒温恒湿試験で４，０００時間及び気相冷熱試験で３，０００サイクルの信頼性試験を行った結果、回路抵抗の変化率はそれぞれ１０２％及び１３３％と大きかった。
【０１２１】
【発明の効果】
請求項１記載の導電ペーストは、導電粉の高配合率化が可能で導電性の信頼性又は耐マイグレーションに優れ、はんだ付電極形成用、導電接着剤用に適する。請求項２記載の導電ペーストは、請求項１記載の導電ペーストに加えて、高充填性及び導電ペーストの流動性に優れる。
請求項３記載の導電ペーストは、請求項１記載の導電ペーストに加えて、シェルフライフに優れ、かつＩＲ炉使用での短時間乾燥、硬化性に優れる。
請求項４記載の導電ペーストは、請求項１記載の導電ペーストに加えて、低粘度、高充填量化でき、また耐熱性が良好である。
請求項５及び６記載の導電ペーストは、請求項１記載の導電ペーストに加えて、シェルフライフの安定性に優れる。
請求項７記載の導電ペーストは、請求項１記載の導電ペーストに加えて、印刷後の乾燥、硬化の際の滲みが少ない。
請求項８記載の導電ペーストは、請求項１記載の導電ペーストのうち、硬化性に優れる。
請求項９記載の導電ペーストは、請求項１記載の導電ペーストに加えて、シェルフライフに優れ、接着部品の取り外し性が良好な導電接着剤に適する。
請求項１０記載の導電ペーストは、請求項９記載の導電ペーストに加えて、導電性が良好でシェルフライフが安定である。
請求項１１記載の導電ペーストは、請求項９の導電ペーストに加えて、印刷後における乾燥の際の滲みが少なく、接着性及び可撓性に優れる。
【図面の簡単な説明】
【図１】スルーホールを導電ペーストで接続した状態を示す断面図である。
【図２】従来のスルーホール配線板の断面図である。
【図３】ポリイミドフィルム上にテストパターンを形成した状態を示す平面図である。
【符号の説明】
１　導電ペースト
２　銅箔
３　基材
４　導電層
５　絶縁層
６　ジャンパー回路
７　銅箔ランド
８　銅箔回路
９　オーバーコート層
１０　スルーホール
１１　ポリイミドフィルム
１２　テストパターン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conductive paste used for circuit formation of a wiring board, shield layer formation, electrode formation of an electronic component, soldered electrode formation, conductive adhesive, and the like.
[0002]
[Prior art]
One method of forming a conductive circuit on a printed wiring board is to use a conductive powder such as gold, silver, copper, carbon, etc., and add a binder, a resinous solvent, and additives as necessary to a paste. It was prepared by mixing with. In particular, gold powder, silver powder, palladium powder, or an alloy powder thereof has been generally used in a field where high conductivity is required.
[0003]
[Non-Patent Document 1]
Electronic Materials, October 1994 Issue (pp. 42-46)
[0004]
Among the above, the conductive paste containing silver powder is used for forming printed circuit boards, wiring layers (conductive layers) of electronic components, etc. or electric circuits and electrodes of electronic components because of its good conductivity. When an electric field is applied in an atmosphere of high temperature and humidity, there is a disadvantage that silver electrodeposition called migration occurs in an electric circuit or an electrode, causing a short circuit between electrodes or wirings. Several measures have been taken to prevent this migration, and measures such as applying a moisture-proof paint to the surface of the conductor or adding a corrosion inhibitor such as a nitrogen-containing compound to the conductive paste have been studied. A sufficient effect was not obtained. If silver-palladium alloy powder is used instead of silver powder, the migration resistance can be improved. However, silver and palladium are expensive, so that silver-palladium alloy powder is also expensive.
[0005]
Moreover, in order to obtain a conductor with good conduction resistance, the blending amount of silver powder must be increased, and since silver powder is expensive, the conductive paste is also expensive. If silver-coated copper powder is used, migration can be improved, and if this is used, an inexpensive conductive paste can be obtained. However, if the surface of the copper powder is uniformly and thickly coated with silver, the effect of improving migration is not sufficient. Moreover, there is a drawback that direct soldering cannot be applied to the coating film of the obtained conductive paste. Furthermore, when soldering is performed on a conductive paste using silver powder, silver erosion occurs and there is a disadvantage that sufficient bonding cannot be obtained.
[0006]
On the other hand, copper powder may be used in addition to silver powder. However, since the conductive paste using copper powder has high oxidizability of copper after heat curing, the oxygen contained in the air and the binder reacts with the copper powder to form an oxide film on the surface, and the conductive paste Remarkably decreases the performance. Therefore, various reducing agents are added to prevent oxidation of the copper powder surface, and a copper paste with stable conductivity is disclosed. However, the conductivity and conductivity stability do not reach that of silver paste, and the high temperature and high stability. There have been drawbacks such as an increase in conduction resistance in a humidity test.
[0007]
In addition, stable conductivity cannot be obtained unless the content of the copper powder in the conductive paste is increased. However, when the content of the copper powder is increased, there are drawbacks such as poor adhesion and poor storage stability due to this effect. In addition, the conventional copper paste cannot be directly applied to the obtained copper paste coating.
[0008]
Conventionally, when a known conductive paste is used as an adhesive, the conductive powder is more expensive than the solder paste, and thus the conductive paste is also expensive. Accordingly, there has been a demand for a conductive adhesive having higher conductivity reliability than copper paste, better migration resistance than silver paste, and excellent solder paste and dry-curing workability.
[0009]
In addition, conventionally known conductive pastes cannot be soldered directly, so the conductive paste coating film is subjected to activation treatment and electroless plated, or the coating film is used as a cathode for electro copper plating in a plating solution. Then, soldering was performed on the copper film obtained by plating. However, it is not practical unless the bonding between the coating film and the copper plating is reliable. Therefore, if a solderable conductive paste that does not require electroless plating or electroplating is developed, the circuit forming process is greatly shortened, and the merit is great.
[0010]
Solder is easy to join with metal, but not with binder. When soldering, ideally, a coating film made of only conductive powder may be formed and soldered thereto. However, there is a problem that a coating film cannot be formed using only conductive powder without using a binder.
Therefore, a binder is used and used as a conductive paste. However, there is a limit on the amount of the binder because importance is placed on the reliability and workability of the coating film formation.For example, when the binder ratio is increased, the conductive powder which is a metal covers the binder, and the solder and the conductive powder are separated. Since the contact area is lost, there is a disadvantage that the solder is not attached and the conductivity is lowered.
[0011]
In order to obtain a conductive paste to which solder is attached, it is necessary to make the composition as close as possible to the copper foil. That is, when the conductive powder is put in a certain space, it is ideal that the conductive powder has a high filling property, and the binder occupies the volume of the gap formed between the conductive powders.
[0012]
However, when the ratio of the conductive powder is increased as described above, the viscosity of the conductive paste becomes extremely high, it becomes difficult to produce the conductive paste, the workability of applying the conductive paste is deteriorated, and the conductive powder is bound. Since there is little binder, the intensity | strength of a coating film also falls. Moreover, when using as a conductive adhesive, since adhesiveness falls, it is not suitable for use. Further, when solder bonding is performed using a conductive paste, a conductive paste that balances solderability, conductivity, workability, strength, and cost is required.
[0013]
When using as a solder substitute material for the purpose of conductive adhesion, the workability that can be dried and cured in a short time is also important as well as the printability, adhesiveness and conduction reliability of the conductive paste. If the reflow furnace that has been used by assembly manufacturers for soldering chip parts, etc., can be used for drying and curing of solder substitute adhesives, the equipment can be used effectively, which is preferable. In the case of a general silver paste, there is a drawback that it tends to swell when dried and cured at a high temperature for a short time like a solder reflow furnace. Further, copper paste also has a drawback that the conductivity is not stable when cured at a high temperature for a short time, and in a reliability test such as a constant temperature and humidity test or a vapor phase cooling test, it becomes a so-called disconnection state that eliminates conduction.
[0014]
The method using a conductive paste is a method in which conductive powder is dispersed in a binder and the paste-like conductive paste is applied to the surface of the substrate or filled in through holes to form a conductive layer as shown in FIG. In FIG. 1, 1 is a conductive paste and 2 is a copper foil.
Further, as another means for forming a conductive layer in a through hole formed in a printed wiring board, there is a method of forming a conductive layer by performing copper plating on the inner wall of the through hole.
[0015]
In general, when using a hole-filling conductive paste that fills a through-hole, the interlayer connection requires a high conductivity even though it is a small hole. Therefore, the hole is filled with a conductive paste as much as possible. It is necessary to embed the conductive paste without any gaps. Therefore, the conventional hole-filling conductive paste needs to increase the ratio of the conductive powder. However, if the ratio of the conductive powder is increased, the viscosity of the conductive paste increases and the filling property into the holes decreases. On the other hand, when the ratio of the binder is increased, the viscosity is lowered and the filling property into the holes is improved, but the conductivity is lowered.
[0016]
As a countermeasure, a solvent-free type containing no solvent, a conductive paste mainly composed of a liquid epoxy resin as a binder, and a conductive paste slightly using a solvent depending on the size of the holes were used.
However, the epoxy resin has a disadvantage that the resistance of the conductive paste mainly composed of the epoxy resin is difficult to decrease because the amount of cure shrinkage due to heat is lower than that of the phenol resin.
In order to reduce the resistance, it is possible to compensate for the disadvantage by increasing the proportion of the conductive powder in the conductive paste or using a highly conductive metal powder such as silver, but the conductive paste becomes expensive. End up.
[0017]
On the other hand, there is also a conductive paste mainly composed of phenol resin, but this conductive paste has better conductivity than a conductive paste mainly composed of epoxy resin, but the viscosity of the conductive paste is increased and the filling property to the holes is improved. There was a problem.
[0018]
In addition, when a conductive layer is formed in a through hole using a conductive paste, if the through hole is filled with a conductive paste containing a large amount of solvent, voids in the through hole due to drying of the solvent can be avoided. Absent. Therefore, as shown in FIG. 2, the insulating layer 5 is formed on the surface of the base material 3, the end portion of the through hole filled with the conductive paste, the copper foil land 7 and a part of the copper foil circuit 8, and further the conductive material ( In a multilayer circuit board in which a conductive material printed circuit (hereinafter referred to as a printed circuit) is formed on the insulating layer 5 with a jumper conductive paste), voids in the through hole are eliminated, the through hole 10, the copper foil land 7, and the copper foil. There was a drawback that the reliability of connection with the circuit 8 and the printed circuit had to be increased. In FIG. 2, 4 is a conductive layer, 6 is a jumper circuit, and 9 is an overcoat layer.
[0019]
When manufacturing a multilayer circuit board in which the conduction of the through hole is performed by copper plating formed on the inner wall of the through hole, after the copper plating is applied to the inner wall of the through hole, the cover plating is applied to the conductive paste filling the through hole. In this case, the above disadvantages can be solved, but this is not preferable because the number of steps increases and the cost increases.
[0020]
In addition, there is a method in which the inner wall of the through hole is plated with copper to form a conductive layer, and the gap is filled with a resin. However, this method also has a disadvantage that the number of steps increases and the cost increases.
[0021]
In addition, there is a method of forming an insulating layer and a printed circuit on the surface of a substrate after filling the through hole with a conductive material of a voidless or substantially voidless to ensure conduction of the through hole. Since the filled conductive material and the copper foil land portion are connected at the end cross section of the copper foil, there is a drawback that the connection reliability is lowered. In order to avoid this, the above-described lid plating may be performed. However, this increases the number of processes and increases the cost, which is not preferable.
[0022]
Furthermore, a silver through-hole wiring board in which a silver conductive material (silver paste) containing 15% by weight or more of a solvent is filled in the through hole is used, and an insulating layer and a printed circuit are formed on the surface of the wiring board to form a multilayer circuit. When a plate is produced, a large gap generated in the through hole as the solvent volatilizes causes a decrease in reliability. That is, migration resistance decreases if ionic impurities remain in the void during a cleaning process or the like. Moreover, in the silver through-hole wiring board, the silver paste sometimes swells thickly on the copper foil land, and in the case of component mounting, the height of this thick swelled silver paste may become an obstacle.
[0023]
On the other hand, there is a solder material mainly composed of lead. However, such a solder material has been widely put into practical use for a long time because it has a relatively low melting point and good workability. However, in recent years, because lead contains highly toxic lead, the use of lead has been proposed because the treatment of lead-containing waste tends to adversely affect the human body or the environmental ecosystem. Currently, low melting point metal brazing materials that use relatively low melting point metal materials such as bismuth have been developed as an alternative to lead, but these melting points are higher than lead solder, so board materials or mounted electronic components The heat resistance such as the above had to be increased, resulting in technical difficulties and increased costs.
[0024]
In a multi-layer lamination process using a hole-filling conductive paste, which is generally used, a hole is filled with a conductive paste, a pre-dried build-up layer is stacked, and heat-pressing is performed as main drying. Therefore, the conductive paste needs to be cured after the main drying, and the conductivity needs to be improved as compared with the case where no pressure is applied by pressurization after lamination.
[0025]
However, in the conventional hole-filling conductive paste, the main component of the binder is an epoxy resin, and imidazoles are generally used as its curing agent, but copper is exposed on the surface by conducting a pulverization treatment to break up the aggregation as a conductive powder. When the substantially spherical silver-coated copper powder is used, there is a drawback that the curability of the conductive paste may be lowered.
[0026]
In order to use the silver-coated copper powder that has been subjected to the pulverization treatment, it is necessary to add a substance that does not form a chelate bond with copper and acts as a curing agent for the epoxy resin.
Moreover, since the substantially spherical silver-coated copper powder easily aggregates in the silver plating process and has a low tap density, it is not preferable to add it to a conductive paste at a high content rate, resulting in an increase in viscosity.
Furthermore, when a substantially spherical silver-coated copper powder that has undergone pulverization treatment is used, the resol type phenolic resin has a drawback of causing a viscosity increase during storage of the conductive paste because it causes chelate bonding with copper.
[0027]
Also, when a conductive adhesive (conductive paste) is produced using an alkoxy group-containing resol-type phenolic resin and epoxy resin as a binder, if the adhesive part that adheres to the printed wiring board is defective, the adhesive part is replaced. In this case, it is necessary to heat the thermosetting resin cured product to a high temperature at which the rubber can be made into a rubber state. In such a case, the use of a thermoplastic resin as a binder can eliminate the above-mentioned drawbacks.
[0028]
[Problems to be solved by the invention]
The invention according to claim 1 is capable of increasing the blending ratio of conductive powder, is excellent in electrical reliability or migration resistance, and has high price competitiveness by reducing the amount of silver plating. The present invention provides a conductive paste suitable for an adhesive or the like. The invention according to claim 2 provides a conductive paste excellent in high filling property and fluidity in addition to the invention of claim 1.
In addition to the invention of claim 1, the invention of claim 3 is excellent in shelf life and can be cured in a short time, and can be dried and cured in a short time using a far-infrared furnace (hereinafter referred to as an IR furnace). It is an object of the present invention to provide a conductive paste suitable for forming a wiring board circuit and filling a hole with excellent properties.
[0029]
In addition to the invention of claim 1, the invention described in claim 4 provides a conductive paste that can have a low viscosity, a high filling amount, and that has a low epoxy equivalent, and also has good heat resistance.
In addition to the invention of claim 1, the inventions of claims 5 and 6 provide a conductive paste having a stable shelf life.
In addition to the invention of claim 1, the invention of claim 7 provides a conductive paste with less bleeding at the time of drying after printing.
The invention according to claim 8 provides a conductive paste having excellent curability in the invention of claim 1.
[0030]
In addition to the invention of the first aspect, the ninth aspect of the present invention provides a conductive paste suitable for a conductive adhesive having an excellent shelf life and good detachability of adhesive parts.
In addition to the invention of claim 9, the invention of claim 10 provides a conductive paste having good conductivity and stable shelf life.
In addition to the invention of claim 9, the invention of claim 11 provides a conductive paste that has less bleeding during drying after printing and is excellent in adhesion and flexibility.
[0031]
[Means for Solving the Problems]
In the present invention, the surface of the copper powder is coated with silver, and the surface of the copper powder is coated with 0.02 to 0.5% by weight of fatty acid with respect to the copper powder. The surface of the copper powder is coated with silver, and the surface is coated with 0.02 to 1.2% by weight of fatty acid with respect to the copper powder. The present invention relates to a conductive paste containing 1 to 5% by weight of silver powder of 7 μm or less and 2 to 25% by weight of a low melting point metal and a binder.
Further, the present invention provides the conductive paste, wherein the substantially spherical silver-coated copper powder has an average particle diameter of 1 to 10 μm, a tap density of 55 to 75% in relative value, and a smooth surface. About.
Moreover, this invention relates to the said electrically conductive paste whose main component of a binder is an alkoxy group containing resol type phenol resin and epoxy resin, and these hardening | curing agents, an additive, and a solvent.
[0032]
Moreover, this invention relates to the said electrically conductive paste whose epoxy equivalent of an epoxy resin is 130-330 g / eq.
Moreover, this invention relates to the said electrically conductive paste whose alkoxy group containing resol type phenol resin is C1-C6 of an alkoxy group.
The present invention also relates to the above conductive paste, wherein the alkoxy group-containing resol type phenol resin has an alkoxylation rate of 5 to 95%.
Moreover, this invention relates to the said electrically conductive paste whose alkoxy group containing resol type phenol resin is a weight average molecular weight 500-200,000.
The present invention also relates to the above conductive paste, wherein the mixing ratio of the alkoxy group-containing resol type phenol resin and the epoxy resin is 5:95 to 60:40 by weight ratio of the alkoxy group containing resol type phenol resin: epoxy resin.
[0033]
Moreover, this invention relates to the said electrically conductive paste whose main component of a binder is a thermoplastic resin, these additives, and a solvent.
Moreover, this invention relates to the said electrically conductive paste whose thermoplastic resin is a thermoplastic resin whose heat softening temperature is 90-240 degreeC.
Furthermore, this invention relates to the said electrically conductive paste whose thermoplastic resin is a phenoxy resin whose heat softening temperature is 90-240 degreeC.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
In the substantially spherical silver-coated copper powder, the coating amount of silver on the surface of the copper powder is not particularly limited, but is preferably in the range of 2.5 to 12% by weight with respect to the copper powder, and 2.5 to 7 More preferably, it is in the range of 5% by weight. If the silver coating amount exceeds 12% by weight, the agglomeration ratio in the silver coating process increases, and the tap density tends to decrease and the cost increases. On the other hand, if it is less than 2.5% by weight, the copper exposure ratio Tends to be high, and the reliability of conductivity tends to be low.
[0035]
The average particle diameter of the substantially spherical silver-coated copper powder used in the present invention is preferably in the range of 1 to 10 μm, more preferably in the range of 2 to 7 μm in terms of handling such as printing and discharging, and cost. .
The substantially spherical silver-coated copper powder preferably has an aspect ratio in the range of 1 to 1.5, and more preferably in the range of 1 to 1.3.
[0036]
On the other hand, in the flat silver-coated copper powder, the coating amount of silver on the surface of the copper powder is not particularly limited, and is preferably in the range of 3 to 12% by weight with respect to the copper powder. More preferably, it is the range. If the silver coating amount exceeds 12% by weight, the cost tends to increase, and if it is less than 3% by weight, the conductivity reliability tends to decrease.
[0037]
The average particle diameter of the flat silver-coated copper powder used in the present invention is preferably 10 μm or less in that the silver coating layer on the surface prevents peeling or damage when producing the flat silver-coated copper powder. A range of 6.5 to 9 μm is more preferable.
Further, the flat silver-coated copper powder preferably has an aspect ratio in the range of 2 to 20, and more preferably in the range of 2 to 15.
[0038]
In addition, the average particle diameter mentioned above can be measured with a laser scattering type particle size distribution measuring apparatus. In this invention, it measured using the master sizer (made by Malvern company) as a measuring apparatus.
In addition, the aspect ratio in the present invention refers to the ratio of the major axis to the minor axis (major axis / minor axis) of the silver-coated copper powder particles. In the present invention, the silver-coated copper powder particles are mixed well in a curable resin having a low viscosity, and the particles are allowed to settle, and the resin is cured as it is, and the resulting cured product is cut in the vertical direction. Then, the shape of the particles appearing on the cut surface is magnified and observed with an electron microscope, the major axis / minor axis of each particle is determined for at least 100 particles, and the average value thereof is taken as the aspect ratio.
[0039]
Here, the minor axis is selected so as to sandwich a combination particle of two parallel lines in contact with the outside of the particle appearing on the cut surface, and the two parallel lines that are the shortest interval among the combinations are selected. Distance. On the other hand, the major axis is a distance between two parallel lines that are perpendicular to the parallel line that determines the minor axis and that is the longest interval among the two parallel lines that are in contact with the outside of the particle. is there. The rectangle formed by these four lines is the size that the particles just fit within.
A specific method performed in the present invention will be described later.
[0040]
In the present invention, there is no particular limitation on the method for coating the surface of the copper powder with silver. For example, there are methods such as displacement plating, electroplating, electroless plating, and the like. Since the cost is low, coating with displacement plating is preferable.
[0041]
In the present invention, the surface of the silver-coated copper powder in which the surface of the copper powder is coated with silver is further coated with a fatty acid. Examples of the fatty acid used in the present invention include saturated fatty acids such as stearic acid, lauric acid, capric acid, and palmitic acid, and unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, and sorbic acid.
[0042]
The coating amount of fatty acid on the surface of the silver-coated copper powder is 0.02 to 0.5% by weight, preferably 0.02 to 0.2% by weight, based on the copper powder, when the shape is substantially spherical. More preferably, it is in the range of 0.02 to 0.1% by weight, and when it exceeds 0.5% by weight, the aggregation of the silver-coated copper powder is easy to break up, and the silver-coated copper powder is added to the resin solution. Although it becomes easy to get wet, since the fatty acid acts as an internal mold release agent, the adhesive strength is reduced. On the other hand, when the coating amount of the fatty acid is less than 0.02% by weight, it becomes difficult to break up the aggregation of the silver-coated copper powder.
[0043]
Further, when the shape of the silver-coated copper powder is flat, it is in the range of 0.02 to 1.2% by weight, preferably in the range of 0.08 to 1.0% by weight, more preferably 0, relative to the copper powder. .15 to 0.7% by weight, and if it exceeds 1.2% by weight, the flat silver-coated copper powder is easily wetted by the resin solution. However, since the fatty acid acts as an internal mold release agent, When used, the adhesive strength is reduced. On the other hand, if it is less than 0.02% by weight, it is difficult to process into a flat shape.
[0044]
If the surface of the silver-coated copper powder is coated with a fatty acid, the following advantages are obtained. In other words, when silver plating is applied to the copper powder, the moisture contained in the copper powder is dried in the subsequent drying process. However, if the moisture is directly dried at this time, the latent heat of vaporization of the water is large, which requires a lot of time for drying. . However, if the moisture is previously replaced with a hydrophilic organic solvent such as alcohol or acetone, and the organic solvent is dried, drying becomes easy. The present invention utilizes this, and the fatty acid is blended in the organic solvent to facilitate drying, and the coating amount of the fatty acid is within the range shown above, so that the aggregation of the silver-coated copper powder is facilitated. There is no problem regarding the adhesive strength by pulverization, and it is possible to obtain a substantially spherical silver-coated copper powder having a high tap density, and it is easy to get wet with the resin solution, and a flat silver-coated copper powder having no problem with the adhesive force. Can be obtained.
[0045]
The tap density of the substantially spherical silver-coated copper powder is preferably in the range of 55 to 75% in relative value, and more preferably in the range of 58 to 75%. If the tap density is less than 55%, the packing density is low, so increasing the blending ratio of the conductive powder increases the viscosity of the conductive paste, while reducing the blending ratio of the conductive powder results in sufficient conductivity and reliability. There is a tendency to disappear. Silver-coated copper powder can be obtained by silver-plating the copper powder, but the surface of the silver-coated copper powder that has just been plated is precipitated with silver crystallites, the surface is not smooth, and the flow of particles Tend to be low. Further, since grain boundaries exist between silver microcrystals, the conductivity of the silver plating layer itself may be low. Furthermore, when a silver plating process is performed, the adhesiveness of a silver plating layer and the copper powder of a core material may not be enough. On the other hand, it is difficult to produce a substantially spherical silver-coated copper powder having a tap density exceeding 75% of the upper limit.
[0046]
The tap density of the flat silver-coated copper powder is preferably in the range of 27 to 50% in relative value, and more preferably in the range of 30 to 45%. When the tap density is less than 27%, when used in combination with the substantially spherical silver-coated copper powder, the fluidity tends to decrease because the packing density is decreased. On the other hand, when the tap density exceeds 50%, the shape becomes nearly spherical and the effect of improving the contact property between the substantially spherical silver-coated copper powders tends to be small.
[0047]
The relative value of the tap density is a value obtained by performing tapping 1000 times with a stroke of 25 mm and dividing the tap density calculated from the volume and mass by the true density or theoretical density of the particles.
[0048]
In the present invention, as the conductive powder, in addition to the substantially spherical silver-coated copper powder and the flat silver-coated copper powder, silver powder having a mean particle size of 7 μm or less and a low melting point metal are used.
As for silver powder, as shown above, it is necessary to use silver powder having an average particle size of 7 μm or less, preferably 6 μm or less, more preferably 0.1 to 5 μm. There is a possibility that the fluidity at the time of printing or discharging after mixing with the ink will deteriorate. Moreover, when mixed with the substantially spherical silver-coated copper powder, there is a drawback that it becomes difficult to obtain a dense filling state.
[0049]
As the low melting point metal, a metal having a melting point of 120 to 300 ° C. is preferably used, and a metal having a temperature of 120 to 280 ° C. is more preferably used. Examples of such a metal include bismuth and tin. The metal may be mixed in a powder state in the paste, or may be attached to the surface of the substantially spherical silver-coated copper powder.
[0050]
When the low melting point metal is added as a powder, the particle size is preferably as small as possible, and is preferably 300 mesh or less, more preferably 400 mesh or less, and even more preferably 500 mesh or less in terms of preventing problems such as printing and ejection. If the average particle size is 3 μm or less, particularly 0.1 to 2.5 μm, the gap between the substantially spherical silver-coated copper powders can be filled, and the contact probability between the substantially spherical silver-coated copper powders with a small addition amount. Is more preferable.
[0051]
The timing of adding the low melting point metal is not particularly limited, but it is added at the time of pulverization of the silver-plated copper powder. Bonding is improved and conductivity can be increased. In particular, when drying and curing in an IR furnace, it passes a high temperature of 220 ° C. or higher for a short time of several minutes. At that time, not only the binder is cured, but also the low melting point metal can enhance the bonding property with the substantially spherical silver-coated copper powder, and the conductivity and its reliability can be improved.
[0052]
The blending ratio of the substantially spherical silver-coated copper powder, the flat silver-coated copper powder and the silver powder having an average particle size of 7 μm or less is 50 to 94% by weight of the substantially spherical silver-coated copper powder, and 3 to 20 of the flat silver-coated copper powder. 1% to 5% by weight of silver powder having an average particle diameter of 7 μm or less, 2 to 25% by weight of low melting point metal, preferably 60 to 94% by weight of substantially spherical silver-coated copper powder, and flat silver-coated copper powder 3 to 15% by weight, silver powder having an average particle diameter of 7 μm or less is in the range of 1 to 4% by weight, and the low melting point metal is in the range of 2 to 20% by weight. Has the disadvantage of lowering.
[0053]
As the binder used in the present invention, it is preferable that the main component is an alkoxy group-containing resol-type phenol resin and epoxy resin, and these curing agents, additives and solvents, or the main component is a thermoplastic resin and additives and solvents. .
A conductive paste using a phenolic resin has higher conductivity than a conductive paste using an epoxy resin alone. This is because the amount of curing shrinkage is larger in the phenol resin than in the epoxy resin, so that the volume of the conductor is greatly reduced, and the contact area and probability between the conductive powders are increased. Phenol resin is indispensable for conductive pastes that require high conductivity, but the viscosity of the conductive paste tends to be high, and it is difficult to increase the blending ratio of conductive powder. These problems can be avoided by using.
[0054]
Alkoxy group-containing resol-type phenolic resin suppresses reaction between copper surface and methylol group even when mixed with copper powder exposed substantially spherical silver-coated copper powder because methylol group of phenol resin is masked by alkoxy group it can.
On the other hand, an epoxy resin is suitable as a binder for uses such as an adhesive because of its excellent mechanical properties, heat resistance and adhesiveness. However, when an imidazole is used alone as a curing agent, if the curability is increased, a dark reaction at room temperature cannot be avoided, and the shelf life cannot be avoided. However, when the above alkoxy group-containing resol type phenol resin and imidazole are used in combination, and these are used as a curing agent for the epoxy resin, a conductive paste having a long shelf life and excellent curability at around 160 ° C. is obtained. be able to.
[0055]
Conductive adhesive (conductive paste) obtained using a thermoplastic resin is bonded using an alkoxy group-containing resol-type phenolic resin and an epoxy resin when it is necessary to replace the adhesive parts bonded on the printed wiring board. As a result, it is possible to replace the adhesive part more easily than the above.
[0056]
Solvents can be used to control the workability of printing, discharging, etc. by adjusting the viscosity, but if the boiling point is low, the viscosity change during work is not large, and on the other hand, if the boiling point is too high, the drying property is low. In view of this problem, it is preferable to use a solvent having a boiling point of 150 to 250 ° C, more preferably 170 to 240 ° C. Examples of the solvent corresponding to the above conditions include ethyl carbitol, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol isopropyl methyl ether, dipropylene glycol isopropyl ethyl ether, tripropylene glycol methyl ether, propylene glycol ethyl. Examples include ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, 3-methyl-3-methoxybutanol, 3-methyl-3-methoxybutyl ether, and butyl lactate.
[0057]
The epoxy resin used in the present invention is preferably liquid at room temperature. A crystalline epoxy resin that can be crystallized at room temperature can be used even if it can be mixed with a liquid material to avoid crystallization. The epoxy resin that is liquid at normal temperature in the present invention includes, for example, those that are solid at normal temperature and that are stably liquid at normal temperature by mixing with an epoxy resin that is liquid at normal temperature. In the present invention, the normal temperature means a temperature of about 25 ° C.
The epoxy equivalent of the epoxy resin is preferably in the range of 130 to 330 g / eq, more preferably in the range of 160 to 250 eq.
[0058]
Known epoxy resins are used, and compounds obtained by reaction of compounds containing two or more epoxy groups in the molecular weight, such as bisphenol A, bisphenol AD, bisphenol F, novolac, cresol novolacs, and epichlorohydrin. Aliphatic epoxy resins such as glycidyl ether, dihydroxynaphthalene diglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, heterocyclic epoxy such as diglycidyl hydantoin, vinylcyclohexene dioxide, dicyclopentane diene dioxide, Examples include alicyclic epoxy resins such as alicyclic diepoxy adipate.
[0059]
A flexibility imparting agent is used as necessary. The flexibility imparting agent may be a known one, and is a compound having only one epoxy group in the molecular weight, such as n-butyl glycidyl ether, versatic acid glycidyl ester, styrene oxide, ethylhexyl glycidyl ether, phenyl glycidyl ether, cresyl Examples include ordinary epoxy resins such as glycidyl ether and butylphenyl glycidyl ether.
These epoxy resins and flexibility-imparting agents can be used alone or in admixture of two or more.
[0060]
By using an alkoxy group-containing resol-type phenolic resin and an epoxy resin together with a curing agent that has been used in the past, the shelf life is long, the curability is excellent, and the resistance of the cured conductive paste is as described above. Solvent property is good and preferable. In particular, it is preferable to use a curing agent having a different melting point and dissociation temperature because the semi-cured state of the conductive paste can be controlled. As the curing agent, imidazoles are preferable in terms of pot life, but other examples include amines such as mensendiamine, isophoronediamine, metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, and methylenedianiline, anhydrous Compound curing agents such as phthalic acid, trimellitic anhydride, pyromellitic anhydride, succinic anhydride, tetrahydrophthalic anhydride, and compound curing agents such as dicyandiamide may be used. These compounds may be used in combination with a curing agent such as tertiary amine, triphenylphosphine, tetraphenylphosphenyl borate and the like.
The content of these curing agents is preferably in the range of 0.1 to 20 parts by weight with respect to 100 parts by weight of the epoxy resin in terms of the glass transition point (Tg) of the cured conductive paste. More preferably, it is in the range of parts.
[0061]
The number of carbon atoms of the alkoxy group of the alkoxy group-containing resol type phenol resin is preferably 1 to 6 and more preferably 2 to 4 in terms of viscosity, conductivity and the like when used as a binder of the conductive paste. .
Further, the alkoxylation rate of the resol type phenolic resin, that is, the ratio of alkoxylation of all methylol groups is preferably in the range of 5 to 95% from the viewpoint of the viscosity, conductivity and reliability of the conductive paste, and is preferably 10 to 85%. The range of is more preferable.
[0062]
Further, the alkoxy group in the alkoxy group-containing resol type phenol resin preferably has a range of 0.1 to 2 alkoxy groups per benzene ring, more preferably a range of 0.3 to 1.5. The range of 5 to 1.2 is more preferable.
The alkoxylation rate or the number of alkoxy groups can be measured by nuclear magnetic resonance spectrum analysis (hereinafter referred to as NMR method).
[0063]
The weight average molecular weight of the alkoxy group-containing resol type phenol resin in the present invention is preferably in the range of 500 to 200,000 from the viewpoints of the viscosity of the conductive paste, shelf life, curability of the conductive paste, conductivity, adhesiveness, toughness and the like. A range of 500 to 120,000 is more preferable.
In addition, a weight average molecular weight can be calculated | required by measuring by gel permeation chromatography method and converting into standard polystyrene.
[0064]
The blending ratio of the alkoxy group-containing resol type phenol resin and the epoxy resin is preferably 5: 95-60: 40 by weight ratio of the alkoxy group-containing resol type phenol resin: epoxy resin, and 10: 90-40: 60. More preferably it is. If the proportion of the alkoxy group-containing resol type phenol resin is below the above range, the action as a curing agent is small and the conductivity tends to be poor, and if it exceeds the above range, the conductivity of the conductive paste is high, but the adhesion, There is a tendency that the balance of toughness, viscosity and the like is deteriorated.
[0065]
As the thermoplastic resin, it is desirable to use a thermoplastic resin having a heat softening temperature of 90 to 240 ° C., preferably 130 to 200 ° C., and examples thereof include phenoxy resin, thermoplastic polyester resin, polystyrene resin and the like. It is preferable to use a phenoxy resin having a softening temperature of 90 to 240 ° C. because it is excellent in mechanical strength, heat resistance, and adhesiveness. Even when the thermoplastic resin is mixed with the substantially spherical silver-coated copper powder from which copper is exposed, the reaction between the copper surface and the functional group can be suppressed. If a thermoplastic resin is used, a conductive paste that has a long shelf life and only needs to be dried at around 100 to 160 ° C. can be obtained.
[0066]
In addition to the above materials, the binder used in the present invention includes coupling agents such as silane, titanate, and aluminate, thixotropic agents, antifoaming agents, powder surface treatment agents, anti-settling agents, and the like as necessary. It is obtained by adding and mixing uniformly. The content of coupling agents, thixotropic agents, antifoaming agents, powder surface treatment agents, anti-settling agents and the like added as necessary may be in the range of 0.01 to 1% by weight with respect to the conductive paste. The range is preferably 0.03 to 0.5% by weight.
[0067]
The conductive paste of the present invention includes a binder, a conductive powder, and a coupling agent, a thixotropic agent, an antifoaming agent, a powder surface treatment agent, an anti-settling agent, a solvent, and the like that are added as necessary. It can be obtained by uniformly mixing and dispersing with three rolls.
[0068]
【Example】
Hereinafter, the present invention will be described with reference to examples.
Example 1
Alkoxy group-containing resol-type phenolic resin (our prototype, bisphenol F-type epoxy resin having an alkoxy group of 4 carbon atoms, alkoxylation ratio of 65%, weight average molecular weight of 1,200) and 38 parts by weight of epoxy equivalent of 170 g / eq ( Binder was prepared by uniformly mixing 57 parts by weight of Mitsui Petrochemical Co., Ltd., trade name Epomic R110) and 5 parts by weight of 2-phenyl-4-methyl-imidazole (trade name Curesol 2P4MZ, manufactured by Shikoku Kasei Co., Ltd.). It was.
In addition, the ratio of the alkoxy group-containing resol type phenol resin and bisphenol F type epoxy resin was 40:60 phenol resin: epoxy resin in weight ratio.
[0069]
Next, after washing spherical copper powder having an average particle diameter of 5.1 μm produced by the atomizing method (trade name SFR-Cu, manufactured by Nippon Atomizing Co., Ltd.) with dilute hydrochloric acid and pure water, 80 g of AgCN per liter of water and Substitution plating was performed with a plating solution containing 75 g of NaCN so that the coating amount of silver was 3% by weight with respect to the spherical copper powder, followed by washing with water and drying to obtain a silver-plated copper powder (silver-coated copper powder). In the above drying, water was replaced with ethanol three times. In particular, in the third ethanol, 0.5 g of stearic acid per 1 kg of copper powder used (the coating amount is equivalent to 0.05% by weight with respect to the copper powder) is dissolved. After replacing the water contained in the silver-plated copper powder, it was dried and stearic acid-treated silver-plated copper powder was obtained.
[0070]
Thereafter, 250 g of the stearic acid-treated silver-plated copper powder obtained above and 2 kg of zirconia balls having a diameter of 3 mm were put into a 2 liter ball mill container and rotated for 3 hours. The aspect ratio was 1.1 and average. A substantially spherical silver-coated copper powder having a particle size of 5.1 μm and a surface smoothing treatment was obtained.
The tap density of the substantially spherical silver-coated copper powder was 67% as a relative value.
[0071]
On the other hand, a spherical copper powder similar to the above is used, and the spherical copper powder produced through the same process as described above has a silver coating amount (hereinafter simply referred to as silver coating amount) of 12% by weight. In contrast, stearic acid-treated silver-plated copper powder having a stearic acid coating amount (hereinafter simply referred to as a stearic acid coating amount) of 0.2% by weight was obtained.
[0072]
Thereafter, 250 g of the stearic acid-treated silver-plated copper powder obtained above and 2 kg of zirconia balls having a diameter of 5 mm were placed in a 2 liter ball mill container and shaken for 2 hours to have an average aspect ratio of 6.0 and average grains. A flat silver-coated copper powder having a diameter of 7.3 μm was obtained.
The tap density of the flat silver-coated copper powder was 38% as a relative value.
[0073]
50 g of the binder obtained above, 423 g of the substantially spherical silver-coated copper powder obtained above, 13.5 g of the flat silver-coated copper powder obtained above, and scaly silver powder having an average particle size of 2.2 μm (Tokuriku Chemical Laboratory) Manufactured, trade name TCG-1) 4.5 g, bismuth powder having an average particle size of 3.2 μm (manufactured by High Purity Chemical Laboratories) 9 g and ethyl carbitol 15 g as a solvent, stirring with a stirrer and three rolls A conductive paste was obtained by uniformly mixing and dispersing.
[0074]
The ratio of the conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, scaly silver powder, and bismuth powder) is approximately 3% by weight of the flat silver-coated copper powder with respect to 94% by weight of the substantially spherical silver-coated copper powder. %, Scaly silver powder 1% by weight and bismuth powder 2% by weight.
The ratio of binder to conductive powder was 10:90 in terms of weight ratio of binder: conductive powder.
[0075]
Next, using the conductive paste obtained above, a test pattern 12 was printed on the polyimide film 11 shown in FIG. 3, and after putting in a dryer, the temperature was raised to 170 ° C. in 13 minutes, and that temperature was 1 hour. Then, the wiring board was obtained.
About the obtained wiring board, as a result of evaluating the curability of an electrically conductive paste by the pencil scratch test for coating films (K5401-69) of JIS, evaluation was 6H. The sheet resistance of the conductor was 107 mΩ / □.
[0076]
Further, a test pattern is printed on the substrate obtained by etching out the copper foil on the surface of the glass composite substrate having a thickness of 1.2 mm, heated to 240 ° C. for 10 minutes in an IR furnace, and then heated to 240 ° C. for 0.5 minutes. The test substrate was obtained by heat treatment and curing. The sheet resistance of this test substrate is 79 mΩ / □, and the test substrate was subjected to a reliability test of 4,000 hours in a constant temperature and humidity test and 3,000 cycles in a gas phase cooling / heating test. Were 2.7% and 8.7%, respectively. The above constant temperature and humidity test was stored in 85 ° C. and 85% relative humidity, and the gas phase cooling and heating test was performed in a cycle of −65 ° C. for 30 minutes to 125 ° C. for 30 minutes (the same applies hereinafter).
[0077]
In addition, the specific measuring method of the aspect ratio in a present Example is shown below. 8 g of a main agent (No. 10-8130) of a low-viscosity epoxy resin (manufactured by Buehler) and 2 g of a curing agent (No. 10-8132) are mixed, and then 2 g of conductive powder is mixed and dispersed well. After vacuum degassing at 0 ° C., the particles were allowed to stand for 10 hours at 30 ° C. to settle and harden the particles. Thereafter, the obtained cured product was cut in the vertical direction, the cut surface was magnified 1000 times with an electron microscope, and the major axis / minor axis were obtained for 150 particles appearing on the cut surface. Ratio.
[0078]
Example 2
In any case, 19 parts by weight of the alkoxyl-containing resol type phenol resin used in Example 1, 76 parts by weight of bisphenol F type epoxy resin and 5 parts by weight of 2-phenyl-4-methyl-imidazole were uniformly mixed to obtain a binder.
In addition, the ratio of the alkoxy group-containing resol type phenol resin and the bisphenol F type epoxy resin was 20:80 of phenol resin: epoxy resin by weight ratio.
[0079]
50 g of the binder obtained above, 360 g of the substantially spherical silver-coated copper powder obtained in Example 1, through the same steps as in Example 1, the silver coating amount is 5 wt% and the stearic acid coating amount is 0.5 wt. % Of silver-plated copper powder treated with stearic acid and 36 g of flat silver-coated copper powder having an average aspect ratio of 3 and an average particle diameter of 6.8 μm obtained through the same steps as in Example 1, A conductive paste was obtained by adding 9 g of flaky silver powder used in No. 1 and 45 g of bismuth powder used in Example 1 and 10 g of ethyl carbitol as a solvent and uniformly mixing and dispersing with a stirrer and three rolls.
[0080]
The ratio of the conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, scaly silver powder and bismuth powder) is approximately 8% by weight of the flat silver-coated copper powder with respect to 80% by weight of the substantially spherical silver-coated copper powder. %, Scaly silver powder 2% by weight and bismuth powder 10% by weight.
The tap density of the flat silver-coated copper powder was 41% as a relative value.
Furthermore, the ratio of binder to conductive powder was 10:90 in terms of weight ratio of binder: conductive powder.
[0081]
Next, as a result of producing a wiring board through the same steps as in Example 1 and evaluating the characteristics, the pencil scratch test for the coating film was 6H and the sheet resistance of the conductor was 98 mΩ / □.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was 75 mΩ / □, and the test substrate was 4,000 hours in the constant temperature and humidity test and 3 in the gas phase cooling test. As a result of performing a reliability test for 1,000 cycles, the rate of change in circuit resistance was 2.4% and 7.7%, respectively.
[0082]
Example 3
4.75 parts by weight of an alkoxy group-containing resol-type phenol resin (our prototype, alkoxy group having 4 carbon atoms, alkoxylation ratio of 65%, weight average molecular weight of 20,000), bisphenol F-type epoxy resin used in Example 1 90.25 parts by weight and 5 parts by weight of 2-phenyl-4-methyl-imidazole used in Example 1 were uniformly mixed to obtain a binder.
In addition, the ratio of the alkoxy group-containing resol type phenol resin and the bisphenol F type epoxy resin was 5:95 phenol resin: F type epoxy resin in weight ratio.
[0083]
A silver-plated copper powder treated with stearic acid having a silver coating amount of 5% by weight and a stearic acid coating amount of 0.1% by weight through the same steps as in Example 1 was prepared in 50 g of the binder obtained above. Further, 315 g of a substantially spherical silver-coated copper powder subjected to pulverization and surface smoothing with an aspect ratio of 1.1 and an average particle size of 5.5 μm obtained through the same steps as in Example 1, and the flatness obtained in Example 2 67.5 g of silver-coated copper powder, 22.5 g of agglomerated silver powder having a primary particle size of 1 μm or less (trade name SFK-ED, manufactured by DMC Square Japan Co., Ltd.), tin powder (manufactured by High Purity Chemical Research Laboratory) ) 45 g and 15 g of ethyl carbitol as a solvent were added and mixed and dispersed uniformly with a stirrer and a three roll to obtain a conductive paste.
[0084]
In addition, the ratio of the conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, silver powder and tin powder) is 15% by weight of flat silver-coated copper powder with respect to 70% by weight of the substantially spherical silver-coated copper powder. The amount was 5% by weight of silver powder and 10% by weight of tin powder.
Moreover, the tap density of the substantially spherical silver-coated copper powder was 63% as a relative value.
Furthermore, the ratio of binder to conductive powder was 10:90 in terms of weight ratio of binder: conductive powder.
[0085]
Next, as a result of producing a wiring board through the same steps as in Example 1 and evaluating the characteristics, the pencil scratch test for the coating film was 6H and the sheet resistance of the conductor was 89 mΩ / □.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was 70 mΩ / □, and the test substrate was 4,000 hours in the constant temperature and humidity test and 3 in the vapor phase cooling test. As a result of a reliability test of 1,000 cycles, the rate of change in circuit resistance was 2.5% and 7.3%, respectively.
[0086]
Example 4
4.75 parts by weight of the alkoxy group-containing resol type phenol resin used in Example 3, 90.25 parts by weight of the bisphenol F type epoxy resin used in Example 1, and 2-phenyl-4-methyl- used in Example 1 A binder was prepared by uniformly mixing 5 parts by weight of imidazole.
In addition, the ratio of the alkoxy group-containing resol type phenol resin and the bisphenol F type epoxy resin was 5:95 in a weight ratio of phenol resin: epoxy resin.
[0087]
A silver-plated copper powder treated with stearic acid having a silver coating amount of 12% by weight and a stearic acid coating amount of 0.15% by weight through the same steps as in Example 1 was prepared in 50 g of the binder obtained above. Furthermore, 270 g of substantially spherical silver-coated copper powder subjected to pulverization and surface smoothing with an average aspect ratio of 1.1 and an average particle diameter of 1.1 μm obtained through the same steps as in Example 1, and the same as in Example 1 A silver-plated copper powder treated with stearic acid having a silver coating amount of 3% by weight and a stearic acid coating amount of 0.5% by weight produced through the steps was prepared, and further obtained through the same steps as in Example 1. 90 g of flat silver-coated copper powder with an average aspect ratio of 2.2 and an average particle size of 6.2 μm, 22.5 g of agglomerated silver powder with a primary particle size of 1 μm or less used in Example 3, and in Example 3 67.5 g of tin powder used and ethylcarby as solvent Over uniformly mixed Le 10g with stirring kneader and three-roll was added to give a dispersed conductive paste.
[0088]
In addition, the ratio of the conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, silver powder and tin powder) is approximately 20% by weight of flat silver-coated copper powder with respect to 60% by weight of the substantially spherical silver-coated copper powder. Silver powder 5% by weight and tin powder 15% by weight.
Moreover, the tap density of the substantially spherical silver-coated copper powder was 60% as a relative value, and the tap density of the flat silver-coated copper powder was 43% as a relative value.
Furthermore, the ratio of binder to conductive powder was 10:90 in terms of weight ratio of binder: conductive powder.
[0089]
Next, as a result of producing a wiring board through the same steps as in Example 1 and evaluating the characteristics, the pencil scratch test for the coating film was 6H and the sheet resistance of the conductor was 78 mΩ / □.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was 63 mΩ / □, and the test substrate was 4,000 hours in the constant temperature and humidity test and 3 in the gas phase cooling test. As a result of performing a reliability test for 1,000 cycles, the rate of change in circuit resistance was 1.9% and 8.3%, respectively.
[0090]
Comparative Example 1
In any case, 38 parts by weight of the alkoxyl group-containing resol type phenol resin, 57 parts by weight of bisphenol F type epoxy resin and 5 parts by weight of 2-phenyl-4-methyl-imidazole used in Example 1 were uniformly mixed to obtain a binder.
In addition, the ratio of the alkoxy group-containing resol type phenol resin and bisphenol F type epoxy resin was 40:60 phenol resin: epoxy resin in weight ratio.
[0091]
A silver-plated copper powder treated with stearic acid having a silver coating amount of 2% by weight and a stearic acid adhesion amount of 0.005% by weight through the same steps as in Example 1 was prepared in 50 g of the binder obtained above. Further, 423 g of substantially spherical silver-coated copper powder subjected to pulverization and surface smoothing with an average aspect ratio of 1.1 and an average particle size of 5.5 μm obtained through the same steps as in Example 1, and the same as in Example 1 A silver-plated copper powder treated with stearic acid with a silver coating amount of 2% by weight and a stearic acid coating amount of 0.05% by weight through the steps was produced, and the aspect ratio obtained through the same steps as in Example 1 13.5 g of flat silver-coated copper powder having an average of 1.5 and an average particle diameter of 5.8 μm, 4.5 g of flaky silver powder used in Example 1, 9 g of bismuth powder used in Example 1, and ethyl as a solvent Stirring machine with 22g of carbitol And it mixed and disperse | distributed uniformly with 3 rolls, and obtained the electrically conductive paste.
[0092]
The ratio of the conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, scaly silver powder and bismuth powder) is 94% by weight of the substantially spherical silver-coated copper powder and 3 weights of the flat silver-coated copper powder. %, Scaly silver powder 1% by weight and bismuth powder 2% by weight.
Moreover, the tap density of the substantially spherical silver-coated copper powder was 62% as a relative value, and the tap density of the flat silver-coated copper powder was 45% as a relative value.
Furthermore, the ratio of binder to conductive powder was 10:90 in terms of weight ratio of binder: conductive powder.
[0093]
Next, as a result of producing a wiring board through the same steps as in Example 1 and evaluating the characteristics, the pencil scratch test for the coating film had a high value of 6H and the sheet resistance of the conductor was 197 mΩ / □.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was 139 mΩ / □, and the test substrate was 4,000 hours in the constant temperature and humidity test and 3 in the vapor phase cooling test. As a result of a reliability test of 1,000 cycles, the rate of change in circuit resistance was as large as 114% and 121%, respectively.
[0094]
Comparative Example 2
In any case, 4.75 parts by weight of the alkoxy group-containing resol type phenol resin used in Example 1, 90.25 parts by weight of bisphenol F type epoxy resin and 5 parts by weight of 2-phenyl-4-methyl-imidazole were mixed uniformly. A binder was used.
In addition, the ratio of the alkoxy group-containing resol type phenol resin and the bisphenol F type epoxy resin was 5:95 phenol resin: F type epoxy resin in weight ratio.
[0095]
A silver-plated copper powder treated with stearic acid having a silver coating amount of 2% by weight and a stearic acid coating amount of 0.6% by weight through the same steps as in Example 1 was prepared in 50 g of the binder obtained above. Furthermore, 436.5 g of substantially spherical silver-coated copper powder having an aspect ratio of 1.1 average and an average particle diameter of 5.3 μm obtained through the same steps as in Example 1 and a surface smoothing treatment were obtained. Through the same process, stearic acid-treated silver-plated copper powder having a silver coating amount of 2% by weight and a stearic acid coating amount of 2% by weight was prepared, and the aspect ratio obtained through the same process as in Example 1 4.5 g of flat silver-coated copper powder having an average of 2.4 and an average particle size of 6.3 μm, 4.5 g of flaky silver powder used in Example 1, 4.5 g of bismuth powder used in Example 1, and a solvent Add 45g of ethyl carbitol as a stirrer and A conductive paste was obtained by uniformly mixing and dispersing with three rolls.
[0096]
In addition, the ratio of conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, scaly silver powder and bismuth powder) is 1 weight of flat silver-coated copper powder with respect to 97 weight% of substantially spherical silver-coated copper powder. %, Scaly silver powder 1% by weight and bismuth powder 1% by weight.
Moreover, the tap density of the substantially spherical silver-coated copper powder was 48% as a relative value, and the tap density of the flat silver-coated copper powder was 43% as a relative value.
Furthermore, the ratio of binder to conductive powder was 10:90 in terms of weight ratio of binder: conductive powder.
[0097]
Next, as a result of producing a wiring board through the same process as in Example 1 and evaluating the characteristics, the pencil scratch test for coating film was as soft as 2H, and the sheet resistance of the conductor was as high as 266 mΩ / □.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was 218 mΩ / □, and the test substrate was 4,000 hours in the constant temperature and humidity test and 3 in the gas phase cooling test. When a reliability test of 1,000 cycles was performed, the rate of change in circuit resistance was as large as 147% and 152%, respectively.
[0098]
Comparative Example 3
95 parts by weight of the bisphenol F type epoxy resin used in Example 1 and 5 parts by weight of 2-ethyl-4-methyl-imidazole (manufactured by Shikoku Kasei Co., Ltd., trade name: Curazole 2E4MZ) were uniformly mixed to obtain a binder.
[0099]
A silver-plated copper powder treated with stearic acid having a silver coating amount of 12% by weight and a stearic acid adhesion amount of 0.15% by weight through the same steps as in Example 1 was prepared in 50 g of the binder obtained above. Furthermore, 180 g of substantially spherical silver-coated copper powder subjected to pulverization and smoothing with an average aspect ratio of 1.1 and an average particle size of 5.5 μm obtained through the same steps as in Example 1, and the same steps as in Example 1 A silver-plated copper powder treated with stearic acid with a silver coating amount of 12% by weight and a stearic acid coating amount of 0.2% by weight was prepared, and the aspect ratio obtained through the same steps as in Example 1 was 135 g of flat silver-coated copper powder having an average of 6 and an average particle diameter of 7.3 μm, 22.5 g of agglomerated silver powder having a primary particle diameter of 1 μm or less used in Example 3, and tin powder 112 used in Example 3 .5 g and ethyl carbitol 26 as solvent To obtain a conductive paste was uniformly mixed and dispersed with a stirring kneader and three-roll in addition. The shelf life of this conductive paste was 2 days in refrigerated storage, and was significantly worse than that in the refrigerated storage of 60 days or more of the conductive paste obtained in Example 4.
[0100]
The ratio of the conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, silver powder and tin powder) is 30% by weight of the flat silver-coated copper powder with respect to 40% by weight of the substantially spherical silver-coated copper powder. They were 5% by weight of silver powder and 25% by weight of tin powder.
In addition, the tap density of the substantially spherical silver-coated copper powder was 59% as a relative value, and the tap density of the flat silver-coated copper powder was 38% as a relative value.
Furthermore, the ratio of binder to conductive powder was 10:90 in terms of weight ratio of binder: conductive powder.
[0101]
Next, as a result of producing a wiring board through the same process as in Example 1 and evaluating the characteristics, the pencil scratch test for the coating film was as soft as 3H, and the sheet resistance of the conductor was as high as 372 mΩ / □.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was 97 mΩ / □, and it was 4,000 hours in the constant temperature and humidity test and 3,000 cycles in the gas phase cooling / heating test. As a result of the reliability test, the rate of change in circuit resistance was 35.1% and 42.1%, respectively.
[0102]
Example 5
50 parts by weight of a phenoxy resin (Phenoxy Specialties, trade name PKHJ, heat softening temperature 170 ° C.) and a titanate coupling agent (Ajinomoto Co., trade name KR-TTS2) 0.4 parts by weight In addition, 75 parts by weight of diethylene glycol monoethyl ether (trade name EtDG, manufactured by Nippon Emulsifier Co., Ltd.) was added as a solvent, and mixed and dissolved uniformly to prepare a thermoplastic resin solution, which was used as a binder.
[0103]
125 g of the binder obtained above, 423 g of substantially spherical silver-coated copper powder obtained in Example 1, 13.5 g of flat silver-coated copper powder used in Example 1, 9 g of flaky silver powder used in Example 1, A conductive paste was obtained by adding 4.5 g of bismuth powder used in Example 1 and 17 g of ethyl carbitol as a solvent, and uniformly mixing and dispersing with a stirrer and three rolls.
[0104]
The ratio of the conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, scaly silver powder and bismuth powder) is 94% by weight of the substantially spherical silver-coated copper powder and 3 weights of the flat silver-coated copper powder. %, Scaly silver powder 2% by weight and bismuth powder 1% by weight.
The ratio of binder to conductive powder was 10:90 in terms of weight ratio of binder: conductive powder.
[0105]
Next, as a result of producing a wiring board through the same steps as in Example 1 and evaluating the characteristics, the pencil scratch test for coating film was 5H and the sheet resistance of the conductor was 138 mΩ / □.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was 95 mΩ / □, and the test substrate was 4,000 hours in the constant temperature and humidity test and 3 in the gas phase cooling test. As a result of a reliability test of 1,000 cycles, the rate of change in circuit resistance was 3.4% and 15%, respectively.
Furthermore, when the chip resistor was bonded onto the copper foil using the conductive paste obtained above and then heated to remove the chip resistor, it could be easily removed at a temperature of 180 ° C.
[0106]
Example 6
125 g of the binder obtained in Example 5, 405 g of the substantially spherical silver-coated copper powder obtained in Example 1, 22.5 g of the flat silver-coated copper powder used in Example 1, and the flaky silver powder 13 used in Example 1 0.5 g, 9 g of bismuth powder used in Example 1 and 13 g of ethyl carbitol as a solvent were added, and mixed and dispersed uniformly with a stirrer and three rolls to obtain a conductive paste.
[0107]
The ratio of the conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, scaly silver powder and bismuth powder) is about 5% by weight of the flat silver-coated copper powder with respect to 90% by weight of the substantially spherical silver-coated copper powder. %, Scaly silver powder 3% by weight and bismuth powder 2% by weight.
The ratio of binder to conductive powder was 10:90 in terms of weight ratio of binder: conductive powder.
[0108]
Next, as a result of producing a wiring board through the same steps as in Example 1 and evaluating the characteristics, the pencil scratch test for coating film was 4H and the sheet resistance of the conductor was 141 mΩ / □.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was 108 mΩ / □, and the test substrate was 4,000 hours in the constant temperature and humidity test and 3 in the gas phase cooling test. As a result of a reliability test of 1,000 cycles, the change rates of the circuit resistance were 2.0% and 9.8%, respectively.
[0109]
Example 7
In either case, 85 parts by weight of diethylene glycol monoethyl ether as a solvent was added to 30 parts by weight of the phenoxy resin and 0.5 parts by weight of the titanate coupling agent used in Example 5, and the mixture was uniformly mixed and dissolved to obtain a thermoplastic resin solution. This was produced and used as a binder.
[0110]
115 g of the binder obtained above, 235 g of the substantially spherical silver-coated copper powder obtained in Example 3, 94 g of the flat silver-coated copper powder used in Example 1, and agglomeration with a primary particle size of 1 μm used in Example 3 27.5 g of silver powder having 112.5 g of bismuth powder used in Example 1 and 15 g of ethyl carbitol as a solvent were added, and the mixture was uniformly mixed and dispersed with a stirrer and three rolls to obtain a conductive paste.
[0111]
In addition, the ratio of conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, scaly silver powder and bismuth powder) is about 20% by weight of flat silver-coated copper powder with respect to 50% by weight of the substantially spherical silver-coated copper powder. %, Flaky silver powder 5% by weight and bismuth powder 25% by weight.
Moreover, the ratio of the binder and the conductive powder was 6:94 in terms of weight ratio of binder: conductive powder.
[0112]
Next, as a result of producing a wiring board through the same steps as in Example 1 and evaluating the characteristics, the pencil scratch test for coating film was 4H and the sheet resistance of the conductor was 112 mΩ / □.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was 79 mΩ / □, and the test substrate was tested for 4,000 hours in a constant temperature and humidity test and 3 in a gas phase cooling test. As a result of performing a reliability test of 1,000 cycles, the rate of change in circuit resistance was 3.1% and 12.1%, respectively.
[0113]
Example 8
In both cases, 77 parts by weight of diethylene glycol monoethyl ether as a solvent was added to 70 parts by weight of the phenoxy resin and 0.5 parts by weight of the titanate coupling agent used in Example 5, and mixed and dissolved to obtain a thermoplastic resin solution. This was produced and used as a binder.
[0114]
147 g of the binder obtained above, 376 g of the substantially spherical silver-coated copper powder obtained in Example 4, 23.5 g of the flat silver-coated copper powder used in Example 4, and the primary particle size used in Example 3 is 1 μm or less. 23.5 g of cohesive silver powder, 47 g of tin powder used in Example 4 and 20 g of ethyl carbitol as a solvent were added, and mixed and dispersed uniformly with a stirrer and three rolls to obtain a conductive paste. .
[0115]
In addition, the ratio of the conductive powder (substantially spherical silver-coated copper powder, flat silver-coated copper powder, silver powder and tin powder) is approximately 5% by weight of the flat silver-coated copper powder with respect to 80% by weight of the substantially spherical silver-coated copper powder. The amount was 5% by weight of silver powder and 10% by weight of tin powder.
Moreover, the ratio of the binder and the conductive powder was 14:86 in terms of weight ratio of binder: conductive powder.
[0116]
Next, as a result of producing a wiring board through the same steps as in Example 1 and evaluating the characteristics, the pencil scratch test for coating film was 4H and the sheet resistance of the conductor was 145 mΩ / □.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was 118 mΩ / □, and the test substrate was 4,000 hours in the constant temperature and humidity test and 3 in the vapor phase cooling test. As a result of a reliability test of 1,000 cycles, the rate of change in circuit resistance was 5.3% and 21.3%, respectively.
[0117]
Comparative Example 4
To the binder 125 g obtained in Example 5, 450 g of the substantially spherical silver-coated copper powder obtained in Comparative Example 1 and 10 g of ethyl carbitol as a solvent were added and mixed and dispersed uniformly with a stirrer and three rolls to conduct electricity. A paste was obtained.
In addition, the ratio of binder and conductive powder was 10:90 in terms of weight ratio of binder: conductive powder.
[0118]
Next, as a result of producing a wiring board through the same process as in Example 1 and evaluating the characteristics, the pencil scratch test for the coating film was 5H, but the sheet resistance of the conductor was a high value of 270 mΩ / □. It was.
Further, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was as high as 291 mΩ / □, and the test substrate was 4,000 hours in the constant temperature and humidity test and 3 in the vapor phase heat test. As a result of performing a reliability test of 1,000,000 cycles, the rate of change in circuit resistance was as large as 59.5% and 86.1%, respectively.
[0119]
Comparative Example 5
To the binder 147 g obtained in Example 8, 430 g of the substantially spherical silver-coated copper powder obtained in Comparative Example 2 and 36 g of ethyl carbitol as a solvent were added, and mixed and dispersed uniformly with a stirrer and three rolls to conduct electricity. A paste was obtained.
In addition, the ratio of binder and conductive powder was 14:86 in terms of weight ratio of binder: conductive powder.
[0120]
Next, as a result of producing a wiring board through the same process as in Example 1 and evaluating the characteristics, the pencil scratch test for coating film was as soft as 2H, and the sheet resistance of the conductor was as high as 325 mΩ / □.
In addition, when a test substrate was manufactured through the same steps as in Example 1, the sheet resistance of the test substrate was as high as 354 mΩ / □, and the test substrate was 4,000 hours in the constant temperature and humidity test and 3 in the gas phase cooling test. As a result of a reliability test of 1,000 cycles, the rate of change in circuit resistance was as large as 102% and 133%, respectively.
[0121]
【The invention's effect】
The conductive paste according to claim 1 is capable of increasing the blending ratio of the conductive powder, has excellent conductivity reliability or migration resistance, and is suitable for forming a soldered electrode and a conductive adhesive. In addition to the conductive paste according to claim 1, the conductive paste according to claim 2 is excellent in high filling property and fluidity of the conductive paste.
In addition to the conductive paste according to claim 1, the conductive paste according to claim 3 is excellent in shelf life and excellent in drying and curability for a short time when using an IR furnace.
In addition to the conductive paste according to claim 1, the conductive paste according to claim 4 can have a low viscosity and a high filling amount, and has good heat resistance.
In addition to the electrically conductive paste of Claim 1, the electrically conductive paste of Claim 5 and 6 is excellent in shelf life stability.
In addition to the conductive paste according to claim 1, the conductive paste according to claim 7 has less bleeding at the time of drying and curing after printing.
The conductive paste according to claim 8 is excellent in curability among the conductive paste according to claim 1.
In addition to the conductive paste of claim 1, the conductive paste of claim 9 is suitable for a conductive adhesive that has excellent shelf life and good detachability of adhesive parts.
The conductive paste according to claim 10 has good conductivity and stable shelf life in addition to the conductive paste according to claim 9.
In addition to the conductive paste according to claim 9, the conductive paste according to claim 11 has less bleeding at the time of drying after printing, and is excellent in adhesiveness and flexibility.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a state in which through holes are connected by a conductive paste.
FIG. 2 is a cross-sectional view of a conventional through-hole wiring board.
FIG. 3 is a plan view showing a state in which a test pattern is formed on a polyimide film.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Conductive paste 2 Copper foil 3 Base material 4 Conductive layer 5 Insulating layer 6 Jumper circuit 7 Copper foil land 8 Copper foil circuit 9 Overcoat layer 10 Through hole 11 Polyimide film 12 Test pattern

Claims (11)

銅粉の表面が銀で被覆され、さらにこの表面に銅粉に対して０．０２〜０．５重量％の脂肪酸が被覆された略球状銀被覆銅粉５０〜９４重量％、銅粉の表面が銀で被覆され、さらにこの表面に銅粉に対して０．０２〜１．２重量％の脂肪酸が被覆された偏平状銀被覆銅粉３〜２０重量％、平均粒径が７μｍ以下の銀粉１〜５重量％及び低融点金属を２〜２５重量％含む導電粉並びにバインダを含有してなる導電ペースト。The surface of the copper powder is coated with silver, and the surface of the copper powder is coated with 50 to 94% by weight of a substantially spherical silver-coated copper powder coated with 0.02 to 0.5% by weight of fatty acid with respect to the copper powder. Is coated with silver and the surface is coated with 0.02 to 1.2% by weight of fatty acid with respect to the copper powder. The flat silver coated copper powder is 3 to 20% by weight and the average particle size is 7 μm or less. A conductive paste comprising conductive powder containing 1 to 5% by weight and 2 to 25% by weight of a low melting point metal, and a binder. 略球状銀被覆銅粉が、平均粒径が１〜１０μｍ及びタップ密度が相対値で５５〜７５％であり、かつその表面が平滑化されたものである請求項１記載の導電ペースト。2. The conductive paste according to claim 1, wherein the substantially spherical silver-coated copper powder has an average particle diameter of 1 to 10 [mu] m, a tap density of 55 to 75% in relative value, and a smooth surface. バインダの主成分が、アルコキシ基含有レゾール型フェノール樹脂及びエポキシ樹脂並びにこれらの硬化剤、添加剤及び溶剤である請求項１又は２記載の導電ペースト。The conductive paste according to claim 1 or 2, wherein the main component of the binder is an alkoxy group-containing resol-type phenol resin and epoxy resin, and curing agents, additives, and solvents thereof. エポキシ樹脂のエポキシ当量が、１３０〜３３０ｇ／ｅｑである請求項１〜３のいずれかに記載の導電ペースト。The electrically conductive paste according to any one of claims 1 to 3, wherein an epoxy equivalent of the epoxy resin is 130 to 330 g / eq. アルコキシ基含有レゾール型フェノール樹脂が、アルコキシ基の炭素数が１〜６である請求項１〜４のいずれかに記載の導電ペースト。The electrically conductive paste according to any one of claims 1 to 4, wherein the alkoxy group-containing resol type phenol resin has 1 to 6 carbon atoms in the alkoxy group. アルコキシ基含有レゾール型フェノール樹脂が、アルコキシ化率５〜９５％のものである請求項１〜５のいずれかに記載の導電ペースト。The electrically conductive paste according to any one of claims 1 to 5, wherein the alkoxy group-containing resol type phenol resin has an alkoxylation rate of 5 to 95%. アルコキシ基含有レゾール型フェノール樹脂が、重量平均分子量が５００〜２００，０００である請求項１〜６のいずれかに記載の導電ペースト。The electrically conductive paste according to any one of claims 1 to 6, wherein the alkoxy group-containing resol type phenol resin has a weight average molecular weight of 500 to 200,000. アルコキシ基含有レゾール型フェノール樹脂とエポキシ樹脂の配合割合が、アルコキシ基含有レゾール型フェノール樹脂：エポキシ樹脂が重量比で５：９５〜６０：４０である請求項１〜７のいずれかに記載の導電ペースト。The conductive ratio according to any one of claims 1 to 7, wherein a mixing ratio of the alkoxy group-containing resol type phenol resin and the epoxy resin is 5:95 to 60:40 by weight ratio of the alkoxy group containing resol type phenol resin: epoxy resin. paste. バインダの主成分が、熱可塑性樹脂並びにこれらの添加剤及び溶剤である請求項１又は２記載の導電ペースト。The conductive paste according to claim 1 or 2, wherein a main component of the binder is a thermoplastic resin, and an additive and a solvent thereof. 熱可塑性樹脂が、熱軟化温度が９０〜２４０℃の熱可塑性樹脂である請求項１、２又は９記載の導電ペースト。The conductive paste according to claim 1, 2 or 9, wherein the thermoplastic resin is a thermoplastic resin having a thermal softening temperature of 90 to 240C. 熱可塑性樹脂が、熱軟化温度が９０〜２４０℃のフェノキシ樹脂である請求項１、２又は９記載の導電ペースト。The conductive paste according to claim 1, 2, or 9, wherein the thermoplastic resin is a phenoxy resin having a heat softening temperature of 90 to 240 ° C.
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JP2013149527A (en) * 2012-01-20 2013-08-01 Toyo Aluminium Kk Flake-like conductive filler
JP2014203652A (en) * 2013-04-04 2014-10-27 イー・アイ・デュポン・ドウ・ヌムール・アンド・カンパニーＥ．Ｉ．Ｄｕ Ｐｏｎｔ Ｄｅ Ｎｅｍｏｕｒｓ Ａｎｄ Ｃｏｍｐａｎｙ Polymer type conductive paste and method of producing electrode by using the same
JP2015079656A (en) * 2013-10-17 2015-04-23 東洋紡株式会社 Conductive paste and print circuit using the same
JP2015162392A (en) * 2014-02-27 2015-09-07 京セラケミカル株式会社 Conductive paste, electric/electronic component, and method of manufacturing the same
JP2016004659A (en) * 2014-06-16 2016-01-12 株式会社村田製作所 Conductive resin paste and ceramic electronic part
US10453613B2 (en) 2014-06-16 2019-10-22 Murata Manufacturing Co., Ltd. Conductive resin paste and ceramic electronic component
CN104143376A (en) * 2014-06-30 2014-11-12 永利电子铜陵有限公司 Conductive silver paste containing nickel powder of PCB and preparation method thereof

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