JP3565343B2

JP3565343B2 - Adhesive composition for circuit connection

Info

Publication number: JP3565343B2
Application number: JP2001301581A
Authority: JP
Inventors: 功塚越; 貢藤縄; 泰史後藤; 共久太田; 豊山口
Original assignee: Hitachi Chemical Co Ltd; Showa Denko Materials Co Ltd; Resonac Corp
Current assignee: Resonac Corp
Priority date: 2001-09-28
Filing date: 2001-09-28
Publication date: 2004-09-15
Anticipated expiration: 2019-09-15
Also published as: JP2002188070A

Description

【０００１】
【発明の属する技術分野】
本発明は、例えば液晶パネル等において２つの回路基板同士の電極間に形成し、両電極を接続するのに好適な回路接続用接着剤組成物に関する。
【０００２】
【従来の技術】
２つの回路基板同士を接着すると共に、これらの電極間に電気的導通を得る接着剤については、スチレン系やポリエステル系等の熱可塑性物質や、エポキシ系やシリコーン系等の熱硬化性物質が知られている。この場合、接着剤中に導電性粒子を配合し加圧により接着剤の厚み方向に電気的接続を得るもの（例えば特開昭５５−１０４００７号公報）と、導電性粒子を用いずに接続時の加圧により電極面の微細凹凸の接触により電気的接続を得るもの（例えば特開昭６０−２６２４３０号公報）とがある。
【０００３】
ところで、これらの接着剤による接続において、電気的接続不良であったり接続後に電子部品や回路が不良になると、回路間を剥がす等した後、接着剤を溶剤等で除去後に、再度良品を接着剤により接続することが行われている。この場合、微細回路や電極上の接着剤を汎用溶剤（例えばアセトン、メチルエチルケトン、トルエン、リグロイン、テトラハイドロフラン、アルコール等）を用いて、周辺の良好部に悪影響を与えず、迅速かつ容易に除去できることが重要である。接着剤が熱硬化性物質等の場合、溶剤として例えば塩化メチレンと酸等よりなるいわゆるエポキシ剥離剤を用いる場合が多い。
【０００４】
【発明が解決しようとする課題】
回路接続部の信頼性、即ち耐熱性、耐湿性等を考慮した場合、エポキシ系等の熱硬化性接着剤が有効である。しかしながら、この場合の補修方法は、エポキシ剥離剤等の強烈な溶剤を用いることが一般的である。この場合、再接続部の信頼性が低下する。一方、熱可塑性接着剤の場合には、耐熱性が不足しやはり接続部の信頼性が低下する。本発明は、接続部の信頼性が高くかつ汎用溶剤により容易に補修可能な回路接続用接着剤組成物を提供するものである。
【０００５】
【課題を解決するための手段】
本発明は、特定のアクリル樹脂とフェノキシ樹脂とエポキシ樹脂及び潜在性硬化剤を必須とする回路接続用接着剤組成物に関する。本発明は、下記成分を必須とする硬化後に汎用溶剤により除去可能な回路接続用接着剤組成物である。
（１）エポキシ基を有するモノマの量を他のモノマの量１００重量部に対して０．２〜７重量部共重合して得られるエポキシ基を有するアクリル樹脂
（２）分子量が１００００以上のフェノキシ樹脂
（３）エポキシ樹脂
（４）潜在性硬化剤
また、組成物中に占めるアクリル樹脂とフェノキシ樹脂の割合が５〜７０重量％であると好ましく、エポキシ基を有するアクリル樹脂のガラス転移温度（Ｔｇ）が、２０℃以下、重量平均分子量が１０万以上、組成物中に占めるアクリル樹脂の割合が２〜５０重量％であると好ましい。また、エポキシ樹脂がビスフェノールＦ型エポキシ樹脂であり、潜在性硬化剤がカプセル型であり活性温度５０〜２００℃であると好ましい回路接続用接着剤組成物である。
【０００６】
【発明の実施の形態】
本発明で用いるアクリル樹脂は、エポキシ基を有するモノマの量を他のモノマの量１００重量部に対して０．２〜７重量部共重合して得られるエポキシ基を有するアクリル樹脂が好適であり、例えばアクリル酸エステルとアクリロニトリルを主成分とし、０．２重量部以上のグリシジルアクリレート、グリシジルメタアクリレート等を１種以上含有した共重合体である。これらの官能基を有するアクリルモノマの量は、０．５〜７重量部が好ましく、０．７〜５重量部がより好ましい。この量が少ないと、回路面への吸着性が少ないので硬化後の汎用溶剤による除去性が不足し、過多であると接着剤の保存性が低下する。エポキシ基が存在すると組成物の相溶性が向上する。
【０００７】
上記の共重合体中のモノマ成分であるアクリル酸エステルとしては、メチルアクリレート、エチルアクリレート、ブチルアクリレート、オクチルアクリレート等があり、メチルメタアクリレート等のメタアクリル酸エステルを併用または代替することもできる。また、アクリロニトリルやスチレン等も適用できる。共重合体のＴｇは硬化前の組成物のタックに影響し、２０℃以下が好ましく、１０℃以下がより好ましい。組成物の適度のタックは、回路接続時の位置合わせ性が容易であり作業性が向上するので好ましい。本発明で用いるアクリル樹脂の分子量は１０万以上が好適であり、好ましくは３０万〜１２０万、さらに好ましくは４０万〜１００万である。分子量が小さいと接着剤系の凝集力が低下し高接着力が得にくい。大きすぎると他の成分との相溶性が低下しまた取り扱い難くなる。なお、本発明でいう分子量は、重量平均分子量（ＧＰＣ法によるスチレン換算値）である。組成物中に占めるアクリル樹脂の割合は２％以上、好ましくは３〜５０％、より好ましくは５〜４０％である。
【０００８】
フェノキシ樹脂について説明する。フェノキシ樹脂は、分子量が１００００以上の高分子量エポキシ樹脂であり、エポキシ樹脂と構造が似ていることから相溶性が良く、また接着性も良好な特徴を有する。分子量の大きいほどフィルム形成性が容易に得られ、また接続時の流動性に影響する溶融粘度を広範囲に設定できる。分子量１５０００以上が好ましい。これらの樹脂はヒドロキシル基やカルボキシル基等の極性基を含有すると、エポキシ樹脂との相溶性が向上し均一な外観や特性を有するフィルムの得られることや、硬化時の反応促進による短時間硬化を得る点からも好ましい。
【０００９】
本発明に用いるエポキシ樹脂は、例えばエピクロルヒドリンとビスフェノールＡやＦ、Ｄ等から誘導されるビスフェノール型エポキシ樹脂、エピクロルヒドリンとフェノールノボラックやクレゾールノボラックから誘導されるエポキシノボラック樹脂が代表的であり、その他グリシジルアミン、グリシジルエステル、脂環式、複素環式等の１分子内に２個以上のオキシラン基を有する各種のエポキシ化合物が適用できる。これらは単独又は２種以上混合して用いることが可能である。これらエポキシ樹脂は、不純物イオン（Ｎａ^＋、Ｃｌ⁻ 等）や、加水分解性塩素等を３００ｐｐｍ以下に低減した高純度品を用いることが、エレクトロンマイグレーション防止のために好ましい。
【００１０】
上記したエポキシ樹脂の中では、ビスフェノール型エポキシ樹脂が分子量の異なるグレードが広く入手可能で、接着性や反応性等を任意に設定できることから好ましい。中でもビスフェノールＦ型エポキシ樹脂は、粘度が特に低いことからフェノキシ樹脂との組み合わせで流動性を広範囲に設定できることや、液状であり粘着性も得やすいことから特に好ましい。また、１分子内に３個以上のオキシラン基を有するいわゆる多官能エポキシ樹脂も、組成物の架橋密度を向上し耐熱性が向上するので好ましく、溶剤による補修性を保つために組成物中に占める多官能エポキシ樹脂の割合を３０％以下として使用できる。
【００１１】
潜在性硬化剤としては、イミダゾール系、ヒドラジド系、三フッ素ホウ素−アミン錯体、アミンイミド、ポリアミンの塩、ジシアンジアミド等、及びこれらの変性物があり、これらは単独又は２種以上の混合体として使用できる。これらはアニオン又はカチオン重合型等のいわゆるイオン重合性の触媒型硬化剤であり、速硬化性を得やすくまたは化学当量的な考慮が少なくて良いことから好ましい。硬化剤としてはその他に、ポリアミン類、ポリメルカプタン、ポリフェノール、酸無水物等の適用や前記触媒型硬化剤との併用も可能である。
【００１２】
長期保存性と速硬化性という矛盾した特性の両立が要求される本発明の好ましい形態としては、これらの硬化剤を核としポリウレタン系、ポリエステル系等の高分子物質や、Ｎｉ、Ｃｕ等の金属薄膜及びケイ酸カルシウム等の無機物で被覆したマイクロカプセル型であることが好ましい。カプセル型硬化剤の使用に当たって注意すべき点は、カプセルの粒径を例えばフィルム状接着剤の厚みよりも小さくして保存時のカプセル破壊を防止することや、カプセルの被覆層の材質を組成物や溶剤等に対して耐性のあるものとすることである。本発明の硬化剤の活性温度は、５０〜２００℃が好ましく７０〜１５０℃がより好ましい。活性温度は、ＤＳＣ（元差走査熱量計）を用いて、エポキシ樹脂と硬化剤の配合物を試料として、室温から１０℃／分で昇温させた時の発熱ピーク温度を示す。
【００１３】
本発明に必要に応じて用いる粘着付与剤としては、ロジンやテルペン等の天然物系樹脂、脂肪族、脂環族、芳香族、クマロン・インデン、スチレン系等の重合系樹脂、及びフェノールやキシレン系等の縮合系樹脂等があり、これらの変性体や誘導体がある。これらは単独もしくは２種以上混合して用いることができる。これらは、接着剤系の凝集力を高める点から軟化点４０℃以上の固形物が好ましい。組成物中に占める前記フェノキシ樹脂とアクリル樹脂及び必要に応じて用いる粘着付与剤よりなる熱可塑成分の合計割合は、５〜７０％程度であり１０〜５０％が好ましく１５〜４０％がより好ましい。この量が少ないと溶剤による補修性が不足し、多いと接続部の信頼性が不足する。上記で得た接着剤組成物中には、通常の添加剤等として例えば、充填剤、軟化剤、促進剤、老化防止剤、着色剤、難燃化剤、チキソトロピック剤、カップリング剤及び、フェノール樹脂やメラミン樹脂、イソシアネート類等の硬化剤等を含有することもできる。これらの中では、導電粒子やシリカ等の充填剤及びシラン、チタン、クロム、ジルコニウム、アルミニウム、等の各系のカップリング剤が特に有用である。
【００１４】
導電粒子としては、Ａｕ、Ａｇ、Ｎｉ、Ｃｕ、はんだ等の金属粒子やカーボン等があり、これら及び非導電性のガラス、セラミック、プラスチック等に前記した導通層を被覆等により形成したものでも良い。プラスチックを核とした場合や熱溶融金属粒子の場合、加熱加圧により変形性を有するので接続時に電極との接触面積が増加し信頼性が向上するので好ましい。導電粒子は、０〜３０体積％の広範囲で用途により使い分ける。カップリング剤としては、アミン基やエポキシ基、及びイソシアネート基含有物が、接着性の向上の点から特に好ましい。
【００１５】
本発明の回路接続用接着剤組成物は一液型接着剤として、中でもフィルム状接着剤として特に有用である。この場合例えば、上記で得た接着剤組成物を溶剤あるいはエマルションの場合の分散液等として液状化して、離形紙等の剥離性基材上に形成し、あるいは不織布等の基材に前記配合液を含浸させて剥離性基材上に形成し、硬化剤の活性温度以下で乾燥し溶剤あるいは分散液等を除去すれば良い。この時、用いる溶剤は芳香族炭化水素系と含酸素系の混合溶剤が、材料の溶解性を向上させるため好ましい。ここに含酸素系溶剤のＳＰ値は８．１〜１０．７の範囲とすることが潜在性硬化剤の保護上好ましく、酢酸エステル類がより好ましい。また溶剤の沸点は１５０℃以下が適用できる。沸点が１５０℃を超すと乾燥に高温を要し潜在性硬化剤の活性温度に近いことから潜在性の低下を招き、低温では乾燥時の作業性が低下する。このため沸点が、６０〜１５０℃が好ましく、７０〜１３０℃がより好ましい。
【００１６】
本発明で得た回路接続用接着剤組成物を用いアクリル樹脂含む層とフェノキシ樹脂を含む層とを分離して形成し、少なくとも前記層のいずれかにエポキシ樹脂および／または潜在性硬化剤を含有一体化してなる積層フィルムとすることも可能である。また両者のどちらか一方で他の一方の層をサンドイッチ状とし３層の積層フィルムとしても良い。アクリル樹脂及びフェノキシ樹脂はそれぞれ高分子量なので、エポキシ樹脂および／または潜在性硬化剤及びその他の配合材の含有によっても、分離して形成できる。そのためアクリル樹脂とフェノキシ樹脂の相溶性に問題のある場合や、エポキシ樹脂と硬化剤との反応が速く乾燥あるいは保存時の硬化反応を抑制する場合等に好適である。
【００１７】
本発明で得た回路接続用接着剤組成物を用いた回路や電極の接続について説明する。この方法は、回路接続用接着剤組成物を、基板上の相対峙する電極間に形成し、加熱加圧により両電極の接触と基板間の接着を得る電極の接続方法である。電極を形成する基板としては、半導体、ガラス、セラミック等の無機質、ポリイミド、ポリカーボネート等の有機物、ガラス／エポキシ等のこれら複合の各組み合わせが適用できる。
【００１８】
【作用】
本発明によれば、アクリル樹脂とフェノキシ樹脂とエポキシ樹脂及び潜在性硬化剤を必須とする接着剤組成物を用いることにより、接続部の信頼性が高くかつ汎用溶剤により容易に補修可能である。この理由は、アクリル樹脂とフェノキシ樹脂とエポキシ樹脂がいずれも金属や酸化金属で構成される回路類と接着性が良好なこと、硬化物の耐熱性に優れること等により、接続部の信頼性が良好である。一方、エポキシ樹脂硬化物を海としたとき高分子量であり架橋密度の低いアクリル樹脂とフェノキシ樹脂は島状に存在するか、あるいはアクリル樹脂とフェノキシ樹脂のヒドロキシル基やカルボキシル基の作用でこれらが金属や酸化金属で構成される回路類表面に吸着形成され表面に高濃度に傾斜的に存在するものと考えられる。そのため硬化系内のアクリル樹脂とフェノキシ樹脂の島状もしくは傾斜部等の高濃度部は、汎用溶剤により容易に膨潤又は溶解し、又はこの部分がきっかけとなり硬化物を膨潤又は溶解し補修可能となる。また、海島状の場合にはフィルム状とした時、やや不透明性であり、ガラス回路上の透明電極の認識が容易である特徴も有する。この厚み方向に傾斜的に存在する作用効果を、更に簡単に得る方法がアクリル樹脂を含む層とフェノキシ樹脂を含む層とに分離して形成し、少なくとも前記層のいずれかにエポキシ樹脂および／または潜在性硬化剤を含有一体化してなる積層フィルムである。この場合、汎用溶剤により容易に膨潤又は溶解する層が回路表面に高濃度に接続時から存在するので、補修が更に容易となる。この時アクリル樹脂を含む層とフェノキシ樹脂を含む層との２層の場合、溶剤の種類を回路表面ごとに使い分けることもできる。
【００１９】
本発明においては、組成物中に占める前記フェノキシ樹脂とアクリル樹脂及び必要に応じて用いる粘着付与剤よりなる熱可塑成分の合計割合を調節することにより、溶剤による補修性と接続部の信頼性との両立が可能である。この時、フェノキシ樹脂とアクリル樹脂は、それぞれ分子量が１万以上及び１０万以上と高分子量であり必要に応じて用いる粘着付与剤の量は少量なことから、接続部の信頼性を高度に維持することが可能である。
【００２０】
【実施例】
以下、本発明を実施例に基づいて詳細に説明する。
【００２１】
実施例１、２、比較例１及び参考例１〜８
（１）アクリル樹脂
ブチルアクリレート（ＢＡ）、エチルアクリレート（ＥＡ）、アクリロニトリル（ＡＮ）、メチルメタアクリレート（ＭＭＡ）を主モノマ成分とし、アクリル酸（ＡＡ）、メタアクリル酸（ＭＡＡ）、グリシジルメタアクリレート（ＧＭＡ）、ヒドロキシルエチルメタアクリレート（ＨＥＭＡ）を官能基成分として、表１に示す重量比からなるモノマをパール重合により重合し、記号Ａ〜Ｋのアクリル系共重合体を得た。この共重合体をトルエンに溶解し固形分１０重量％の溶液とした。ここに共重合体のＴｇは、特公昭４５−２２２２１号公報に示される方法により主モノマ成分の重量比から算出した。
【００２２】
【表１】

【００２３】
（２）組成物の作製
ＰＫＨＡ（フェノキシ樹脂、分子量２５０００、ヒドロキシル基６％、ユニオンカーバイト株式会社製商品名）と、エピコートＹＬ−９８３Ｕ（ビスフェノールＦ型高純度液状エポキシ樹脂、加水分解性塩素イオン１１０ｐｐｍ、油化シェルエポキシ株式会社製商品名、９８３Ｕと略）とを、５０ｇ／５０ｇで秤量し、トルエン／酢酸ブチル＝５０／５０（重量比）の混合溶剤に溶解して固形分４０重量％の溶液とした。この溶液と前記アクリル樹脂溶液とを、表２に示す組み合わせの固形分比になるように混合した。また潜在性硬化剤は、ノバキュア３７４２（イミダゾール変性体を核としその表面をポリウレタンで被覆してなる平均粒径２μｍのマイクロカプセル型硬化剤、活性温度１２４℃、旭化成工業株式会社製商品名、３７４２と略）を、固形分比で３０重量％となるように混合した。上記混合液の固形分１００重量部に対し、０．５重量部のエポキシ系シランカップリング剤と、２体積部の導電粒子（平均粒径５μｍのスチレン−ジビニルベンゼン共重合樹脂球の表面に金属薄層を有する、プラと略）を添加撹拌し、ポリテトラフルオロエチレンフィルム（セパレータ）上にロールコータを用いて塗布後、１００℃１０分の乾燥により、接着剤層の厚みが２０μｍのフィルム状を得た。
【００２４】
（３）評価
このフィルム状物を用いて、ライン幅４０μｍ、ピッチ８０μｍ、厚み２０μｍの銅回路上に錫の薄層を有するフレキシブル回路板（ＦＰＣ）と、全面に酸化インジウム（ＩＴＯ）の薄層を有する厚み１．１ｍｍのガラス板とを、１７０℃−３０ｋｇ／ｍｍ^２ −２０秒により、幅２ｍｍで接続した。この際、あらかじめＦＰＣ上にフィルム状物を貼り付け後７０℃−５ｋｇ／ｍｍ^２ −５秒の仮接続を行い、次いでセパレータを剥離してＩＴＯとの接続を行った。結果を表２に示す。
【００２５】
【表２】

【００２６】
表２において、補修性は上記接続部のＦＰＣをＩＴＯから剥離し、ＩＴＯ上に残存する一定面積（２０×２ｍｍ）の接着剤をアセトンを浸漬した綿棒で拭き取るのに要した時間である。また、信頼性は８５℃、８５％ＲＨ−５００ｈ後の接続抵抗値であり、ＦＰＣの隣接回路の抵抗２００点のｘ＋３σ（平均＋標準偏差σの３倍）で示した。表２から、実施例１、２はいずれも良好な補修性と信頼性の両立を得た。一方、比較例１は、アクリル樹脂が官能基成分を有しないため補修性と信頼性に劣った。Ｔｇが２０℃以下であるとタックが出てきて、ＦＰＣにフィルム状物を貼りつけるのに容易であり、分子量が１０万以上であるので高接着力が得られ、補修性、信頼性ともに良好であった。
【００２７】
参考例９〜１２及び比較例２、３
参考例６と同様であるが、表２に示すようにアクリル樹脂とフェノキシ樹脂との配合比を変え、エポキシ樹脂の一部にＥＰＰＮ５０１Ｈ（トリフェニルグリシジルエーテル型エポキシ樹脂、日本化薬株式会社製商品名、ＥＰＰＮと略）を用い、また粘着付与剤としてヒタノール２０８４（アルキルフェノール、軟化点７０℃、日立化成工業株式会社製商品名、２０８４と略）を用いた。更に導電粒子として平均粒径３μｍのニッケルを用いた。結果を表２に示すが、各実施例とも良好な補修性と信頼性の両立を得た。なお従来より、耐アセトン性の不十分な硬化体は耐水・耐湿性に劣るといわれていたが、上記各実施例のように本発明では耐水・耐湿性に優れることが分かった。一方、比較例２はアクリル樹脂を有しないので補修性が困難であり、比較例３はフェノキシ樹脂を有しないので信頼性に劣った。
【００２８】
参考例１３〜１６
参考例９〜１２と同様であるが、導電粒子を使用しなかった。また、セパレータを用いずにＦＰＣ上に直接塗布後、１００℃１０分の乾燥により、接着剤層の厚みが２０μｍでラインと直角方向に幅が２ｍｍのフィルム付きＦＰＣを得た。本参考例の場合、セパレータ及び仮接続工程が不要であり、コスト的に有利である。結果を表２に示すが、この場合も良好な補修性と信頼性の両立を得た。本参考例では、接続時の加熱加圧により回路面の微細凹凸の直接接触により高信頼性を得た。また導電粒子を使用しなかったので、溶剤補修時に導電粒子の流れ出しよる近接回路へのリークの心配がなく接続作業が極めて簡単であった。
【００２９】
実施例３〜５および参考例１７〜１９
参考例１５と同様配合であるが、アクリル樹脂Ｇに変えアクリル樹脂Ｉ及びＪ（表１）を用いた（参考例１７及び実施例３）。更にこの配合中に、１体積部の以下に示す導電粒子を添加した。導電粒子は、実施例１、２のもの（参考例１８及び実施例４）と、参考例９〜１２のもの（参考例１９及び実施例５）を用いた。これら配合物をセパレータ上にロールコータを用いて塗布後、１００℃、１０分の乾燥により溶剤を除去し、接着剤層の厚みが２０μｍのフィルム状物を得た。参考例１７、１８、１９のＡＡとＨＥＭＡ含有に比べ、エポキシ基であるＧＭＡ含有の実施例３、４、５は組成物の相溶性が良好だったが、いずれもフィルム化が可能であった。一方、ガラス板上に半導体チップ（３×１０ｍｍ、高さ０．５ｍｍ、主面の４辺周囲にバンプと呼ばれる５０μｍ角、高さ２０μｍの突起した金電極が形成）のバンプ配置と対応した接続端子を有するＩＴＯ回路を形成した配線板を用意した。半導体チップのバンプ面と、配線板の回路との間に前記フィルムを裁置した。この時各フィルムは、室温で粘着性を有しておりバンプ面に簡単に仮接続できた。この後セパレータを剥離し、ガラス回路とバンプの位置合わせを行い、次いで１７０℃−３０ｇ／バンプ−２０秒の加熱加圧で接続した。上記接続品は、接続部への気泡混入がなかった。接続品の導通チェックを行ったところいずれも良好な接続であり、バンプ間のショートも無かった。更にＰＣＴ（プレッシャークッカーテスト）−１２１℃−１００ｈ後も、各例とも良好だった。接続部断面を走査型電子顕微鏡で観察したところ、参考例１７及び実施例３の粒子なし系では一部のバンプが変形して平坦性を得て接続端子と良く接触していた。同様に参考例１８及び実施例４はプラスチック粒子が加圧方向に潰されるように、参考例１９及び実施例５は一部のバンプにニッケルが突き刺さるように、それぞれ導電粒子を介して接続端子と良く接触していた。これらのことから、粒子なし系やプラスチック粒子ではバンプ高さのバラツキに対応可能であり、参考例１９、実施例５は電極面の汚染層を突き破る効果をそれぞれ得ていることが分かる。各実施例、参考例の接続品を、接着剤硬化物のＴｇ１３０℃より高い１５０℃に加熱し硬化物の凝集力を低下させて半導体チップを配線板から剥離後、アセトン中に浸漬し５分後に洗浄したところ、接着剤の除去が可能であった。また別途各実施例の接続品を、メチルエチルケトン／テトラハイドロフラン／トルエン＝３５／３５／３０（重量比）及びメチルエチルケトン／ジメチルホルムアミド／リグロイン＝５０／３０／２０（重量比）よりなる混合溶剤中に浸漬し３０分後に観察したところ、両浸漬品とも半導体チップは配線板から剥離し残存した接着剤は膨潤していた。半導体チップと配線板をメタノール含浸布で洗浄したところ接着剤の除去が容易であった。
【００３０】
【発明の効果】
以上詳述したように本発明によれば、接続信頼性が高くかつ汎用の溶剤により容易に補修可能な回路接続用接着剤組成物を提供することが可能になった。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a circuit connection adhesive composition formed between electrodes of two circuit boards in a liquid crystal panel or the like, and suitable for connecting both electrodes.
[0002]
[Prior art]
Adhesives that bond two circuit boards together and provide electrical continuity between these electrodes include thermoplastic materials such as styrene and polyester, and thermosetting materials such as epoxy and silicone. Have been. In this case, a method in which conductive particles are mixed in an adhesive to obtain an electrical connection in the thickness direction of the adhesive by applying pressure (for example, Japanese Patent Application Laid-Open No. 55-104007) and a method in which connection is performed without using conductive particles. (See, for example, Japanese Patent Application Laid-Open No. Sho 60-262430).
[0003]
By the way, in the connection with these adhesives, if the electrical connection is poor or the electronic components or the circuit become defective after the connection, peel off the circuit, remove the adhesive with a solvent, etc. Connection is performed by In this case, the adhesive on the fine circuit or the electrode is quickly and easily removed using a general-purpose solvent (for example, acetone, methyl ethyl ketone, toluene, ligroin, tetrahydrofuran, alcohol, etc.) without adversely affecting the surrounding good parts. What you can do is important. When the adhesive is a thermosetting substance or the like, a so-called epoxy release agent composed of, for example, methylene chloride and an acid is often used as a solvent.
[0004]
[Problems to be solved by the invention]
In consideration of the reliability of the circuit connecting portion, that is, heat resistance, moisture resistance, and the like, a thermosetting adhesive such as an epoxy-based adhesive is effective. However, the repair method in this case generally uses a strong solvent such as an epoxy stripper. In this case, the reliability of the reconnection unit decreases. On the other hand, in the case of a thermoplastic adhesive, the heat resistance is insufficient, and the reliability of the connection part is also lowered. An object of the present invention is to provide an adhesive composition for circuit connection, which has high reliability of a connection portion and can be easily repaired with a general-purpose solvent.
[0005]
[Means for Solving the Problems]
The present invention relates to an adhesive composition for circuit connection, which essentially requires a specific acrylic resin, a phenoxy resin, an epoxy resin, and a latent curing agent. The present invention is an adhesive composition for circuit connection which can be removed with a general-purpose solvent after curing, which essentially comprises the following components.
(1) Acrylic resin having an epoxy group obtained by copolymerizing an amount of a monomer having an epoxy group with 0.2 to 7 parts by weight based on 100 parts by weight of another monomer. (2) Phenoxy having a molecular weight of 10,000 or more. Resin (3) Epoxy resin (4) Latent curing agent The ratio of the acrylic resin and the phenoxy resin in the composition is preferably 5 to 70% by weight, and the glass transition temperature (Tg) of the acrylic resin having an epoxy group is preferred. ) Is preferably 20 ° C. or less, the weight average molecular weight is 100,000 or more, and the proportion of the acrylic resin in the composition is 2 to 50% by weight. Further, the epoxy resin is a bisphenol F type epoxy resin, the latent curing agent is a capsule type, and an active temperature of 50 to 200 ° C. is a preferable adhesive composition for circuit connection.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
The acrylic resin used in the present invention is preferably an acrylic resin having an epoxy group obtained by copolymerizing the amount of the monomer having an epoxy group with 0.2 to 7 parts by weight based on 100 parts by weight of the other monomer . For example, a copolymer mainly containing an acrylate and acrylonitrile and containing at least 0.2 part by weight of glycidyl acrylate, glycidyl methacrylate, or the like. The amount of the acrylic monomer having these functional groups is preferably 0.5 to 7 parts by weight, more preferably 0.7 to 5 parts by weight. If the amount is small, the adsorbability to the circuit surface is small, so that the removability with a general-purpose solvent after curing is insufficient. Compatibility of the composition with an epoxy group is present you upper direction.
[0007]
Examples of the acrylate which is a monomer component in the above-mentioned copolymer include methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate and the like, and methacrylate such as methyl methacrylate can be used in combination or substituted. In addition, acrylonitrile, styrene and the like can be applied. The Tg of the copolymer affects the tack of the composition before curing, and is preferably 20 ° C or lower, more preferably 10 ° C or lower. An appropriate tackiness of the composition is preferred because the alignment at the time of circuit connection is easy and the workability is improved. The molecular weight of the acrylic resin used in the present invention is preferably 100,000 or more, preferably 300,000 to 1,200,000, and more preferably 400,000 to 1,000,000. If the molecular weight is small, the cohesive strength of the adhesive system is reduced, and it is difficult to obtain high adhesive strength. If it is too large, the compatibility with other components is reduced and handling becomes difficult. The molecular weight referred to in the present invention is a weight average molecular weight (converted into styrene by GPC method). The proportion of the acrylic resin in the composition is 2% or more, preferably 3 to 50%, more preferably 5 to 40%.
[0008]
The phenoxy resin will be described. The phenoxy resin is a high-molecular-weight epoxy resin having a molecular weight of 10,000 or more, and has a feature that the structure is similar to the epoxy resin, so that it has good compatibility and good adhesiveness. The larger the molecular weight, the easier the film-forming properties can be obtained, and the melt viscosity that affects the fluidity during connection can be set in a wide range. The molecular weight is preferably 15,000 or more. When these resins contain a polar group such as a hydroxyl group or a carboxyl group, compatibility with the epoxy resin is improved, and a film having a uniform appearance and characteristics can be obtained. It is also preferable from the viewpoint of obtaining.
[0009]
The epoxy resin used in the present invention is, for example, a bisphenol-type epoxy resin derived from epichlorohydrin and bisphenol A or F, D, etc., and an epoxy novolak resin derived from epichlorohydrin and phenol novolak or cresol novolac, and other glycidylamines. And various epoxy compounds having two or more oxirane groups in one molecule such as glycidyl ester, alicyclic and heterocyclic. These can be used alone or in combination of two or more. It is preferable to use a high-purity epoxy resin in which impurity ions (Na ⁺ , Cl ^−, etc.), hydrolyzable chlorine, and the like are reduced to 300 ppm or less for preventing electron migration.
[0010]
Among the epoxy resins described above, bisphenol-type epoxy resins are preferred because grades having different molecular weights are widely available and adhesiveness and reactivity can be arbitrarily set. Among them, bisphenol F type epoxy resin is particularly preferable because its viscosity is particularly low, so that the fluidity can be set in a wide range in combination with a phenoxy resin, and because it is liquid and easily adhesive. Further, a so-called polyfunctional epoxy resin having three or more oxirane groups in one molecule is also preferable because the crosslink density of the composition is improved and the heat resistance is improved. The ratio of the polyfunctional epoxy resin can be used as 30% or less.
[0011]
Latent curing agents include imidazoles, hydrazides, boron trifluoride-amine complexes, amine imides, polyamine salts, dicyandiamide, and the like, and modified products thereof, which can be used alone or as a mixture of two or more. . These are so-called ion-polymerizable catalyst-type curing agents such as anion- or cationic-polymerization types, and are preferable because they can easily obtain fast curing properties or require little consideration of chemical equivalents. In addition, as the curing agent, polyamines, polymercaptans, polyphenols, acid anhydrides, and the like can be applied, or the curing agent can be used in combination with the catalyst-type curing agent.
[0012]
As a preferred embodiment of the present invention, which requires compatibility between the contradictory properties of long-term storage and fast-curing properties, a polymer such as a polyurethane-based or polyester-based material and a metal such as Ni or Cu with these curing agents as nuclei. It is preferably a microcapsule type coated with a thin film and an inorganic substance such as calcium silicate. When using a capsule-type curing agent, it should be noted that the particle size of the capsule is made smaller than, for example, the thickness of the film adhesive to prevent capsule breakage during storage, and the material of the capsule coating layer is made of a composition. That is, it is necessary to have resistance to the solvent and the like. The activation temperature of the curing agent of the present invention is preferably from 50 to 200C, more preferably from 70 to 150C. The activation temperature indicates an exothermic peak temperature when the temperature is raised from room temperature at a rate of 10 ° C./minute using a mixture of an epoxy resin and a curing agent as a sample by using a DSC (source difference scanning calorimeter).
[0013]
Examples of the tackifier used as necessary in the present invention include natural resins such as rosin and terpene, aliphatic, alicyclic, aromatic, coumarone-indene, and polymer resins such as styrene, and phenol and xylene. And modified resins and derivatives thereof. These can be used alone or in combination of two or more. These are preferably solids having a softening point of 40 ° C. or higher from the viewpoint of increasing the cohesive strength of the adhesive system. The total ratio of the thermoplastic component composed of the phenoxy resin, the acrylic resin, and the tackifier used as needed in the composition is about 5 to 70%, preferably 10 to 50%, more preferably 15 to 40%. . When the amount is small, the repairability by the solvent is insufficient, and when the amount is large, the reliability of the connection portion is insufficient. In the adhesive composition obtained above, for example, fillers, softeners, accelerators, antioxidants, coloring agents, flame retardants, thixotropic agents, coupling agents and the like as ordinary additives, A curing agent such as a phenol resin, a melamine resin, and an isocyanate may be contained. Among them, fillers such as conductive particles and silica and coupling agents of various systems such as silane, titanium, chromium, zirconium, and aluminum are particularly useful.
[0014]
Examples of the conductive particles include metal particles such as Au, Ag, Ni, Cu, and solder, carbon, and the like, and those obtained by forming the above-described conductive layer on a non-conductive glass, ceramic, plastic, or the like by coating or the like. . In the case of using plastic as a nucleus or hot-melt metal particles, they are deformable by heating and pressing, so that the contact area with the electrode at the time of connection increases and reliability is improved, which is preferable. The conductive particles are properly used in a wide range of 0 to 30% by volume depending on the application. As the coupling agent, an amine group, an epoxy group, and an isocyanate group-containing material are particularly preferable from the viewpoint of improving adhesiveness.
[0015]
The adhesive composition for circuit connection of the present invention is particularly useful as a one-part adhesive, especially as a film adhesive. In this case, for example, the adhesive composition obtained above is liquefied as a solvent or a dispersion in the case of an emulsion, and formed on a peelable substrate such as release paper, or mixed with a substrate such as a nonwoven fabric. The solution may be impregnated and formed on a peelable substrate, and dried at a temperature lower than the activation temperature of the curing agent to remove a solvent or a dispersion. At this time, a mixed solvent of an aromatic hydrocarbon type and an oxygen-containing type is preferably used as the solvent for improving the solubility of the material. Here, the SP value of the oxygen-containing solvent is preferably in the range of 8.1 to 10.7 from the viewpoint of protection of the latent curing agent, and acetates are more preferable. Further, the boiling point of the solvent may be 150 ° C. or less. When the boiling point exceeds 150 ° C., a high temperature is required for drying and the activation temperature is close to the activation temperature of the latent curing agent, thereby lowering the potential. At a low temperature, the workability during drying decreases. Therefore, the boiling point is preferably from 60 to 150C, more preferably from 70 to 130C.
[0016]
A layer containing an acrylic resin and a layer containing a phenoxy resin are separately formed using the adhesive composition for circuit connection obtained in the present invention, and at least one of the layers contains an epoxy resin and / or a latent curing agent. It is also possible to form an integrated laminated film. Alternatively, one of the two layers may be formed into a sandwich film with the other one layer being a sandwich film to form a three-layer laminated film. Since the acrylic resin and the phenoxy resin each have a high molecular weight, they can be formed separately even by containing an epoxy resin and / or a latent curing agent and other compounding materials. Therefore, it is suitable when there is a problem with the compatibility between the acrylic resin and the phenoxy resin, or when the reaction between the epoxy resin and the curing agent is fast and the curing reaction during drying or storage is suppressed.
[0017]
The connection of circuits and electrodes using the adhesive composition for circuit connection obtained in the present invention will be described. In this method, an adhesive composition for circuit connection is formed between opposing electrodes on a substrate, and the electrodes are connected by heating and pressing to obtain contact between the two electrodes and adhesion between the substrates. As the substrate on which the electrodes are formed, inorganic materials such as semiconductors, glass and ceramics, organic materials such as polyimide and polycarbonate, and combinations of these composite materials such as glass / epoxy can be applied.
[0018]
[Action]
ADVANTAGE OF THE INVENTION According to this invention, the reliability of a connection part is high and it can be easily repaired by a general-purpose solvent by using the adhesive composition which essentially requires an acrylic resin, a phenoxy resin, an epoxy resin, and a latent curing agent. This is because the acrylic resin, phenoxy resin, and epoxy resin all have good adhesion to circuits composed of metal or metal oxide, and the cured product has excellent heat resistance. Good. On the other hand, acrylic resin and phenoxy resin having high molecular weight and low cross-linking density when the cured epoxy resin is the sea exist in the form of islands, or these are formed by the action of hydroxyl groups or carboxyl groups of acrylic resin and phenoxy resin. It is conceivable that this is adsorbed and formed on the surface of circuits composed of metal or metal oxide and exists at a high concentration and gradient on the surface. Therefore, high concentration parts such as islands or inclined parts of the acrylic resin and the phenoxy resin in the curing system easily swell or dissolve with a general-purpose solvent, or this part triggers the swelling or dissolution of the cured product to be repairable. . In the case of a sea-island shape, when it is formed into a film shape, it is slightly opaque, and it has a feature that it is easy to recognize a transparent electrode on a glass circuit. A method for more easily obtaining the function and effect present inclining in the thickness direction is to separately form a layer containing an acrylic resin and a layer containing a phenoxy resin, and form an epoxy resin and / or at least one of the layers. It is a laminated film containing a latent curing agent and integrated. In this case, since a layer easily swelled or dissolved by the general-purpose solvent exists on the circuit surface at a high concentration from the time of connection, repair is further facilitated. At this time, in the case of two layers, that is, a layer containing an acrylic resin and a layer containing a phenoxy resin, the type of solvent can be properly used for each circuit surface.
[0019]
In the present invention, by adjusting the total ratio of the thermoplastic component consisting of the phenoxy resin and the acrylic resin and optionally a tackifier used in the composition, the repairability by the solvent and the reliability of the connection portion. It is possible to achieve both. At this time, the phenoxy resin and the acrylic resin have a high molecular weight of 10,000 or more and 100,000 or more, respectively, and the amount of the tackifier used as needed is small, so that the reliability of the connection part is maintained at a high level. It is possible to do.
[0020]
【Example】
Hereinafter, the present invention will be described in detail based on examples.
[0021]
Examples 1 and 2, Comparative Example 1 and Reference Examples 1 to 8
(1) Acrylic resin butyl acrylate (BA), ethyl acrylate (EA), acrylonitrile (AN), methyl methacrylate (MMA) as main monomer components, acrylic acid (AA), methacrylic acid (MAA), glycidyl methacrylate (GMA) and hydroxyl ethyl methacrylate (HEMA) were used as functional group components, and monomers having the weight ratios shown in Table 1 were polymerized by pearl polymerization to obtain acrylic copolymers A to K. This copolymer was dissolved in toluene to form a solution having a solid content of 10% by weight. Here, the Tg of the copolymer was calculated from the weight ratio of the main monomer components by the method disclosed in Japanese Patent Publication No. 45-22221.
[0022]
[Table 1]

[0023]
(2) Preparation of composition PKHA (phenoxy resin, molecular weight 25,000, hydroxyl group 6%, trade name, manufactured by Union Carbide Co., Ltd.) and Epicoat YL-983U (bisphenol F type high-purity liquid epoxy resin, hydrolyzable chloride ion) 110 ppm, trade name, 983 U manufactured by Yuka Shell Epoxy Co., Ltd.) was weighed at 50 g / 50 g, dissolved in a mixed solvent of toluene / butyl acetate = 50/50 (weight ratio), and solid content was 40% by weight. Solution. This solution and the acrylic resin solution were mixed so as to have a solid content ratio of the combination shown in Table 2. The latent curing agent is Novacure 3742 (a microcapsule-type curing agent having an average particle diameter of 2 μm obtained by coating a surface of a modified imidazole nucleus with polyurethane, an activation temperature of 124 ° C., a trade name of Asahi Chemical Industry Co., Ltd., 3742 ) Was mixed so as to have a solid content ratio of 30% by weight. With respect to 100 parts by weight of the solid content of the above mixture, 0.5 parts by weight of the epoxy silane coupling agent and 2 parts by volume of conductive particles (metal on the surface of a styrene-divinylbenzene copolymer resin sphere having an average particle diameter of 5 μm) Add a thin layer, abbreviated as plastic), stir, apply on a polytetrafluoroethylene film (separator) using a roll coater, and dry at 100 ° C for 10 minutes to form a film with an adhesive layer thickness of 20 µm. Got.
[0024]
(3) Evaluation Using this film-like material, a flexible circuit board (FPC) having a thin layer of tin on a copper circuit having a line width of 40 μm, a pitch of 80 μm, and a thickness of 20 μm, and a thin layer of indium oxide (ITO) on the entire surface And a glass plate having a thickness of 1.1 mm and having a width of 2 mm at 170 ° C.-30 kg / mm ² -20 seconds. At this time, after a film-like material was pasted on the FPC in advance, temporary connection was performed at 70 ° C.-5 kg / mm ² -5 seconds, and then the separator was peeled off to connect with ITO. Table 2 shows the results.
[0025]
[Table 2]

[0026]
In Table 2, the repairability is the time required to peel off the FPC of the connection portion from the ITO and wipe off the adhesive having a fixed area (20 × 2 mm) remaining on the ITO with a cotton swab dipped in acetone. The reliability is a connection resistance value after 85 ° C. and 85% RH-500 h, and is represented by x + 3σ (mean + three times the standard deviation σ) of 200 resistances of the adjacent circuit of the FPC. From Table 2, Examples 1 and 2 both achieved good repairability and reliability. On the other hand, Comparative Example 1 was poor in repairability and reliability because the acrylic resin had no functional group component. When the Tg is 20 ° C. or less, a tack comes out and it is easy to attach a film-like material to the FPC. Since the molecular weight is 100,000 or more, high adhesive strength is obtained, and both repairability and reliability are good. Met.
[0027]
Reference Examples 9 to 12 and Comparative Examples 2 and 3
Same as Reference Example 6, except that the mixing ratio of the acrylic resin and the phenoxy resin was changed as shown in Table 2 and EPPN501H (a triphenylglycidyl ether type epoxy resin, a product of Nippon Kayaku Co., Ltd.) was used as a part of the epoxy resin. Name and EPPN), and as a tackifier, hitanol 2084 (alkylphenol, softening point 70 ° C., trade name, manufactured by Hitachi Chemical Co., Ltd., 2084) was used. Further, nickel having an average particle size of 3 μm was used as conductive particles. The results are shown in Table 2. In each example, both good repairability and good reliability were obtained. It has been heretofore known that a cured product having insufficient acetone resistance is inferior in water resistance and moisture resistance. However, it has been found that the present invention is excellent in water resistance and moisture resistance as in the above-described embodiments. On the other hand, Comparative Example 2 did not have an acrylic resin and thus was difficult to repair, and Comparative Example 3 did not have a phenoxy resin and thus was inferior in reliability.
[0028]
Reference Examples 13 to 16
Same as Reference Examples 9 to 12, but no conductive particles were used. In addition, after applying directly on the FPC without using a separator, drying was performed at 100 ° C. for 10 minutes to obtain an FPC with a film having a thickness of the adhesive layer of 20 μm and a width of 2 mm in a direction perpendicular to the line. In the case of this reference example, the separator and the temporary connection step are unnecessary, which is advantageous in cost. The results are shown in Table 2. In this case as well, both good repairability and good reliability were obtained. In this reference example, high reliability was obtained by direct contact of fine irregularities on the circuit surface by heating and pressing at the time of connection. In addition, since no conductive particles were used, there was no need to worry about leakage to a nearby circuit due to the flow of the conductive particles during solvent repair, and the connection operation was extremely simple.
[0029]
Examples 3 to 5 and Reference Examples 17 to 19
The composition was the same as that of Reference Example 15, except that Acrylic Resins I and J (Table 1) were used instead of Acrylic Resin G (Reference Example 17 and Example 3). Further, 1 part by volume of the following conductive particles was added during the compounding. As the conductive particles, those of Examples 1 and 2 (Reference Examples 18 and 4) and those of Reference Examples 9 to 12 (Reference Examples 19 and 5) were used. After applying these compositions on a separator using a roll coater, the solvent was removed by drying at 100 ° C. for 10 minutes to obtain a film having an adhesive layer thickness of 20 μm. In Examples 3, 4, and 5 containing GMA, which is an epoxy group, the compositions were more compatible than those of AA and HEMA of Reference Examples 17, 18, and 19, but all of them could be formed into films. . On the other hand, a connection corresponding to the bump arrangement of a semiconductor chip (3 × 10 mm, height 0.5 mm, protruded gold electrodes of 50 μm square and 20 μm height called bumps formed around four sides of the main surface) on a glass plate A wiring board on which an ITO circuit having terminals was formed was prepared. The film was placed between the bump surface of the semiconductor chip and the circuit of the wiring board. At this time, each film had an adhesive property at room temperature and could be temporarily temporarily connected to the bump surface. Thereafter, the separator was peeled off, the glass circuit and the bump were aligned, and then connected by heating and pressing at 170 ° C.-30 g / bump-20 seconds. In the above-mentioned connection product, there was no air bubble in the connection portion. When the continuity of the connected products was checked, all the connections were good and there was no short between the bumps. Further, after PCT (pressure cooker test) -121 ° C. for 100 hours, the results were good in each case. When the cross section of the connection portion was observed with a scanning electron microscope, it was found that in the particle-free systems of Reference Example 17 and Example 3, some bumps were deformed to obtain flatness and to make good contact with the connection terminal. Similarly, in Reference Examples 18 and 4, the plastic particles are crushed in the pressing direction, and in Reference Examples 19 and 5, nickel is pierced into some of the bumps, and the connection terminals are connected to each other through conductive particles. He was in good contact. From these facts, it can be seen that the particle-free system and the plastic particles can cope with the variation of the bump height, and that Reference Example 19 and Example 5 respectively have the effect of breaking through the contamination layer on the electrode surface. The connection product of each Example and Reference Example was heated to 150 ° C. higher than the Tg of the adhesive cured product of 130 ° C. to reduce the cohesive force of the cured product, peel the semiconductor chip from the wiring board, and dipped in acetone for 5 minutes. After washing, the adhesive could be removed. Separately, the connection product of each example was placed in a mixed solvent consisting of methyl ethyl ketone / tetrahydrofuran / toluene = 35/35/30 (weight ratio) and methyl ethyl ketone / dimethylformamide / ligroin = 50/30/20 (weight ratio). Observation 30 minutes after immersion, in both immersed products, the semiconductor chip was separated from the wiring board and the remaining adhesive was swollen. When the semiconductor chip and the wiring board were washed with a cloth impregnated with methanol, the adhesive was easily removed.
[0030]
【The invention's effect】
As described above in detail, according to the present invention, it has become possible to provide an adhesive composition for circuit connection which has high connection reliability and can be easily repaired with a general-purpose solvent.

Claims

The adhesive composition for circuit connection which can be removed with a general-purpose solvent after curing, which essentially comprises the following components (1) The amount of the monomer having an epoxy group is 0.2 to 7 parts by weight based on 100 parts by weight of the other monomers. Acrylic resin having an epoxy group obtained by copolymerization (2) Phenoxy resin having a molecular weight of 10,000 or more (3) Epoxy resin (4) Latent curing agent

The adhesive composition for circuit connection according to claim 1, wherein the proportion of the acrylic resin and the phenoxy resin in the composition is 5 to 70% by weight.

The glass transition temperature (Tg) of the acrylic resin having an epoxy group is 20 ° C. or less, the weight average molecular weight is 100,000 or more, and the proportion of the acrylic resin in the composition is 2 to 50% by weight. 3. The adhesive composition for circuit connection according to 2.

The adhesive composition for circuit connection according to any one of claims 1 to 3, wherein the epoxy resin is a bisphenol F type epoxy resin, the latent curing agent is a capsule type, and has an activation temperature of 50 to 200 ° C.