JP3861432B2 - Metal foil laminated film and flexible printed wiring board using the film - Google Patents

Description

で示されるいずれかの繰り返し単位からなり、二軸配向してなるポリベンゾアゾールフィルムの片面または両面に、接着剤層を介して金属箔が貼り合わされたものであるところに要旨を有する。ポリベンゾアゾールフィルムの厚さが３〜７５μｍ、かつ引張弾性率が縦方向および横方向のいずれもにおいて１０００ｋｇ／ｍｍ^２以上で、接着剤層の厚さが０．５〜５０μｍ、金属箔の厚さが３〜１００μｍであることが好ましい。ポリベンゾアゾールフィルムは、絶縁性、耐熱性、寸法安定性に優れると共に、高い熱伝導性を示すので、ポリベンゾアゾールフィルムに金属箔を積層することにより、前記課題を解決することができる。ポリベンゾアゾールフィルムの好ましい熱伝導率は、１〜５０Ｗ／ｍＫである。なお、本発明の「ポリベンゾアゾール」とは、ポリベンゾオキシアゾールまたはポリベンゾチアゾール、およびこれらのアルキルまたはハロゲン誘導体のことである。
【０００８】
ＦＰＣ用途としては金属箔として銅箔を用いることが電気伝導度の点から好ましい。また、ポリベンゾアゾールの中でも、ポリパラフェニレンベンズビスオキサゾールは、耐熱性等の各特性に優れているため好ましい。
【０００９】
なお本発明には、本発明の金属箔積層フィルムを基板とし、配線加工を施して得られるフレキシブルプリント配線板も含まれる。
【００１０】
【発明の実施の形態】
本発明の金属箔積層フィルムは、フィルム素材としてポリベンゾアゾールを用いたところに特徴を有する。ポリベンゾアゾールは、ベンゾオキシアゾールまたはベンゾチアゾールおよびこれらのアルキルまたはハロゲン誘導体のポリマーである。具体的には、下記構造式で示されるいずれかの繰り返し単位からなるポリマーである。なお、下記式中の芳香環部分には、アルキル基またはハロゲン原子が導入されていてもよく、下記繰り返し単位（ａ）〜（ｄ）のうち２種以上有する共重合体であってもよい。
【００１１】
【化３】

【００１２】
ポリベンゾアゾールの中でも、ポリパラフェニレンベンゾビスオキサゾールが耐熱性等の各特性が良好である。
【００１３】
ポリベンゾアゾールの合成方法は、特に限定されない。米国特許第４５３３６９３号等には、ポリベンゾアゾール等の合成方法として、ジオール等の第１モノマー成分の塩酸塩を出発原料として用い、これをポリリン酸中で加熱・減圧しながら塩酸を除去し、次いでテレフタル酸等の第２モノマー成分を添加して加熱・減圧することにより縮合合成する方法等が示されている。例えば、４，６−ジアミノレゾルシノール二塩酸塩とテレフタル酸からは、ポリシスパラフェニレンベンゾビスオキサゾールが、２，５−ジアミノレゾルシノール二塩酸塩とテレフタル酸からは、ポリトランスパラフェニレンベンゾビスオキサゾールが得られる。
【００１４】
ＦＰＣ用途という点でポリベンゾアゾールフィルムの機械的強度を考慮すれば、フィルム化した後のポリマーの極限粘度（メタンスルホン酸溶液中）が、５以上となるような重合体を用いることが好ましい。
【００１５】
フィルム化には、ポリベンゾアゾールのドープ（溶液）を不活性雰囲気下で押出す方法を採用するとよい。例えば、米国特許第４９７３４４２号には、リオトロピック液晶性ドープに、円筒状の逆転する回転ダイで剪断力を与えて押出すことにより、ポリマーを配向させて、押出し方向に対して＋θ度配向した層と−θ度配向した層を形成して多軸配向フィルムを得る方法が記載されている。ただしこの方法は、厚みの均一性が得られにくい問題がある。
【００１６】
一方、特表平６−５０３５２１号では、ポリベンゾアゾールを８〜２０重量％含有するポリリン酸ドープをＴダイから８０〜２００℃で押出し、不活性雰囲気化で冷却した後、このフィルム状ドープの両面を熱可塑性フィルムで挟み、これらのラミネート物をテンター等で横延伸した後に熱可塑性フィルムを取り除く方法が記載されている。フィルム状ドープは、Ｔダイから押出された時点で縦方向に配向するので、この方法によれば、厚みが均一な２軸配向フィルムが得られる。縦配向が弱ければ、横延伸の前または後にロール等による縦延伸工程を追加することもでき、またテンターで縦横同時に延伸してもよい。
【００１７】
ポリベンゾアゾールフィルムの厚みは、３〜３００μｍとすることが好ましい。フィルムが厚過ぎると、可撓性が低下して、フレキシブルなプリント配線板を得ることが難しい。しかし、フィルムが薄過ぎると、腰が弱くなり、機械的強度が低下すると共に、電気絶縁性も低下するため好ましくない。フィルム厚を１５０μｍ以下とするのがより好ましく、７５μｍ以下がさらに好ましい。最も好ましい厚さの上限値は４０μｍである。また下限値は、５μｍ以上とするのが好ましく、７μｍ以上がより好ましい。
【００１８】
ポリベンゾアゾールフィルムは、引張弾性率が縦方向および横方向のいずれもにおいて１０００ｋｇ／ｍｍ² 以上であることが機械的強度の点から好ましい。。１０００ｋｇ／ｍｍ² より小さいと、特に薄肉のフィルムにしたときの強度が不足することがある。
【００１９】
熱伝導率は大きいことが好ましく、本発明で用いられるポリベンゾアゾールは１〜５０Ｗ／ｍＫの範囲のものとすることが好ましい。熱伝導率をこの範囲にするには、フィルムのヤング率が４００ｋｇ／ｍｍ² 以上、より好ましくは１５００ｋｇ／ｍｍ² 以上になるように配向させることが望まれる。一般的なプラスチックは０．１〜０．５Ｗ／ｍＫ程度であり、放熱性に乏しいが、本発明では熱伝導率のよいポリベンゾアゾールをフィルム基材として用いているので、金属箔と積層した後でも優れた熱放散性を示し、小型電気機器や高密度実装用のＦＰＣとして最適である。
【００２０】
ポリベンゾアゾールフィルムには、公知のフィルム用添加剤、例えば、紫外線吸収剤・安定剤、熱安定剤、滑剤、顔料、延伸助剤等を加えることができる。またフィルムと金属箔との接着性を上げるために、フィルムに対して、アンカーコート剤のコーティングや、ケミカルエッチング処理、コロナ処理、プラズマ処理を施してもよい。
【００２１】
金属箔とポリベンゾアゾールフィルムを積層するための接着剤は、フィルムの可撓性を損なうことのないように、柔軟で、かつ耐熱性を有するものであれば、熱硬化性でも熱可塑性でもよく、特に接着剤の種類は限定されない。具体例としては、ポリイミド系、ポリアミド系、ポリアミドイミド系、エポキシ樹脂系、ポリエステル系、アクリル樹脂系、ポリベンゾイミダゾール系、マレイミド系、ウレタン樹脂系、フェノール樹脂系、フェノキシ樹脂系、メラミン樹脂系等が挙げられる。なお接着剤層には、電気絶縁性を損なわない範囲で、カーボンブラックや金属微粉末を添加することにより、接着剤層の熱伝導率を高め、放熱性を向上させることができる。
【００２２】
接着剤層の厚さは０．１〜５０μｍの範囲が好ましい。薄過ぎると、金属箔とポリベンゾアゾールフィルムの接着力が不充分になることがあり、厚過ぎると、積層フィルムの可撓性が失われるためである。接着剤層の厚さは、３〜３０μｍの範囲にすることがより好ましく、５〜２０μｍの範囲であればさらに好ましい。
【００２３】
積層される金属箔の種類としては、ＦＰＣに一般的に用いられている銅箔に限定されることなく、各種金属の箔を用いることができる。例えば、Ｂｅ、Ｍｇ、Ａｌ、Ｓｉ、Ｃａ、Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ｇａ、Ｇｅ、Ａｓ、Ｓｅ、Ｓｒ、Ｙ、Ｚｒ、Ｎｂ、Ｍｏ、Ｔｃ、Ｒｕ、Ｒｈ、Ｐｄ、Ａｇ、Ｃｄ、Ｉｎ、Ｓｎ、Ｓｂ、Ｔｅ、Ｂａ、ランタノイド系金属、Ｈｆ、Ｔａ、Ｗ、Ｒｅ、Ｏｓ、Ｉｒ、Ｐｔ、Ａｕ、Ｔｌ、Ｐｂ、Ｂｉ等の常温で固体の金属やこれらの合金が挙げられる。合金としては、Ｆｅ−Ｃｏ系合金、Ｆｅ−Ｎｉ系合金、Ｆｅ−Ｓｉ系合金、Ｆｅ−Ｃ系合金、Ｃｕ−Ｚｎ系合金、Ｃｕ−Ｓｎ系合金、Ｎｉ−Ｃｒ系合金等の２元合金や、Ｆｅ−Ｎｉ−Ｃｒ系合金等の３元合金等、あるいは４元系以上の合金も利用可能である。また、酸化錫、酸化インジウム、酸化バナジウム、酸化ルテニウム等の導電性を有する金属酸化物を用いてもよい。
【００２４】
金属箔の製法は特に限定されず、電解箔、圧延箔、無電解メッキ箔等や、真空蒸着、スパッタリング等のＰＶＤ法や、ＣＶＤ法で製造した箔を用いることができる。金属箔の厚みは、通常３〜１００μｍである。５０μｍ以下が好ましく、３０μｍ以下がより好ましい。また、５〜２０μｍの厚みの金属箔は、高い屈曲性と微細な細線加工が要求される用途に適している。
【００２５】
金属箔とポリベンゾアゾールフィルムの積層方法は、フィルムおよび／または金属箔に接着剤を塗布し、両者を積層する方法を採用することができる。接着剤の塗布方法は、例えば、ロールコート法、リバースコート法、ロールブラッシュ法、スプレーコート法、エアーナイフコート法、グラビアコート法、含浸（ディッピング）法、カーテンコート法等を用いればよく、シート状接着剤でドライラミネートをする方法や、溶融押出ラミネート、共押出しラミネート等の方法でフィルムか金属箔の上に直接接着剤層を形成する方法等も利用することができる。本発明の金属箔積層フィルムは、ポリベンゾアゾールフィルムの少なくとも片面に接着剤層を介して金属箔を貼り合わせたものである。フィルムに金属箔を貼り合わせた上に、さらにフィルムおよび金属箔を貼り合わせ、多層構造にすることもできる。ＦＰＣとして回路加工が施される場合は、フィルムの片面に金属箔が貼り合わされた１層タイプか、フィルムの両面に金属箔が貼り合わされた２層タイプが主に使用される。
【００２６】
本発明の金属箔積層フィルムの金属箔をエッチング加工して回路パターンを形成すれば、フレキシブルプリント配線板を得ることができる。上記２層タイプの金属箔積層フィルムを用いて、両面の金属箔の間をメッキ加工や導電ペーストを用いて導通確保すれば、両面スルホール回路とすることもでき、ビルドアップ法でさらに多層化することもできる。また、ポリベンゾアゾールフィルムを型抜（パンチ）してから金属箔と貼り合わせるいわゆるプレパンチ法を適用することにより、ＴＡＢ（テープオートメイテッドボンディング）法のテープ基材として利用することも可能である。
【００２７】
【実施例】
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はもとより下記実施例によって制限を受けるものではなく、前・後記の趣旨に適合し得る範囲で適当に変更を加えて実施することも可能であり、それらはいずれも本発明の技術的範囲に包含される。
【００２８】
実施例１
［ポリパラフェニレンベンズビスオキサゾールの合成］
槽型反応器中に、窒素気流下において、１１６％（純Ｈ₃ ＰＯ₄ を１００％として）のポリリン酸４３．８６重量部に五酸化二リン１４．４９重量部を加え、さらに、４，６−ジアミノレゾルシノール二塩酸塩９．１０重量部と平均粒径２μｍになるように微粉化したテレフタル酸７．１０重量部を加え、８０℃に加熱して撹拌混合した。次いで１５０℃で１０時間混合した後、２００℃に熱した２軸押出機内で重合した。シス−ポリパラフェニレンベンズビスオキサゾールのポリマードープが得られた。このポリマードープは、黄色であり、メタンスルホン酸溶液で測定した極限粘度は、３８ｄｌ／ｇであった。
【００２９】
［フィルムの作製］
上記ポリマードープを、１５０℃でＴダイから押出し、押出された高粘度のフィルム状ドープを不活性雰囲気下で金属ロールにキャストして冷却した。次いで、未延伸ポリプロピレンフィルムをフィルム状ドープの両面にラミネートし、この両面ラミネートシートごとテンターで１５０℃で横方向に延伸した。ラミネートしたポリプロピレンフィルムを剥離して取り除き、フィルム状ドープを２４時間水洗した後、２８０℃で熱固定した。厚さ５０μｍの２軸配向したポリパラフェニレンベンズビスオキサゾールフィルムが得られた。このフィルムの引張弾性率は、縦方向で２３００ｋｇ／ｍｍ² 、横方向で２８００ｋｇ／ｍｍ² であった。またフィルムの熱伝導率は、縦方向が２０Ｗ／ｍＫ、横方向が３０Ｗ／ｍＫであった。なお、熱伝導率は、ジャーナル・オブ・アプライド・フィジクス３６巻［Ｊ．Ａｐｐｌ．Ｐｈｙｓ．Ｖｏｌ．３６（１９７７）］の５６３４頁に記載されている定常熱流束法を用いて測定した。
【００３０】
［金属箔積層フィルムの作製］
固形分換算で、フェノール樹脂３０重量部と、アクリルニトリル−ブタジエン共重合体２０重量部、ビスフェノールＡ型エポキシ樹脂３０重量部、ブチラール樹脂２０重量部、シリカ１２重量部およびメチルエチルケトン４００重量部を混合溶解して接着剤Ａを調製した。上記ポリパラフェニレンベンズビスオキサゾールフィルムの両面に、接着剤Ａを乾燥後の膜厚が２０μｍになるように塗布し、１３０℃の熱風乾燥ゾーンで約１０分、乾燥した。続いて、両面の接着剤層上に厚さ１８μｍの電解銅箔をロールから繰り出して、温度：１７０℃、速度：０．３ｍ／分、圧力：３．５ｋｇｆ／ｃｍ² の条件でラミネートして、管に巻き取り、１２５℃のオーブン中で１２時間アフターキュアして、２層タイプ（両面）の金属箔積層フィルムを得た。
【００３１】
［ＦＰＣ加工］
２層タイプの金属箔積層フィルムにドリル加工を施し、最小径０．２ｍｍの貫通孔を形成し、スルホール導通加工を行った。スルホール導通加工は、コンディショニング、触媒付与、触媒活性化、無電解銅メッキ、パネル電気銅メッキ、の順で行った。最終的なスルホール部分の導体厚みは３５μｍとした。次いで、２５μｍ厚のドライフィルムレジストを用いて、最小幅５０μｍ、最小線間隔５０μｍの導体パターンを形成し、カバーフィルムとして感光性ポリイミドフィルムを用いてマスクして、両面ＦＰＣを得た。
【００３２】
［評価］
ＦＰＣの加工工程中における寸法変動を、ドライフィルムレジストパターンと得られた導体回路パターンとで比較したところ、０．００１２％であった。また得られたＦＰＣに消費電力１．０［Ｗ］の素子を実装し、２５℃の室内で動作させて素子の温度上昇を記録したところ、１０分後の素子温度上昇は＋１２℃であった。
【００３３】
比較例１
ポリパラフェニレンベンズベンゾアゾールフィルムに代えて、厚さ５０μｍのポリイミドフィルム（商品名「カプトン」；デュポン社製）を用いた以外は実施例１と同様にして両面ＦＰＣを作製した。このＦＰＣの寸法変動率は、０．２５％であった。また実施例１と同様にして素子の温度上昇を測定したところ、素子の温度は、動作１０分後に＋３５℃も上昇した。
【００３４】
実施例２
実施例１で得られたシス−ポリパラフェニレンベンズビスオキサゾールのポリマードープを、ステンレス鋼製のプレートに塗布してポリリン酸を除去した後、この第１層の上に、さらに、ポリマードープを、その塗布方向が第１層と直交するように塗布して、ポリリン酸を除去した。この工程を繰り返し、厚さ２００μｍのポリパラフェニレンベンズビスオキサゾールの厚手フィルムを作製した。
【００３５】
２，２−ビス（４−シアナトフェニル）プロパン７５重量部を１６０℃で４時間予備反応させて、プレポリマーを合成した。このプレポリマーに、飽和ポリエステル樹脂（商品名「バイロン」；東洋紡績社製）２５重量部、ビスフェノールＡ型エポキシ樹脂５重量部、オクチル酸亜鉛０．０１重量部、メチルエチルケトン１００重量部を混合溶解して、接着剤Ｂを調製した。上記ポリパラフェニレンベンズビスオキサゾールフィルムと接着剤Ｂを用いて、実施例１と同様にして両面ＦＰＣを製造した。
【００３６】
このＦＰＣの寸法変動率は０．０１％であった。また実施例１と同様にして素子の温度上昇を測定したところ、動作１０分後に＋８℃であった。
【００３７】
実施例３
実施例１で得られたポリパラフェニレンベンズビスオキサゾールフィルムの両面に熱可塑性ポリイミドをそれぞれ厚さ２０μｍになるように塗布し、片面に厚さ１８μｍの電解銅箔を、もう片面には離型シートを貼着し、温度：３００℃、圧力：１０ｋｇｆ／ｃｍ² でプレスして、１層タイプ（片面）の金属箔積層フィルムを作製した。この積層フィルムの銅箔上に、２５μｍ厚のドライフィルムレジストを用いて、最小幅５０μｍ、最小線間隔５０μｍ、最小径２００μｍのランドを有する一辺が２５０ｍｍの正方形状の片面ＦＰＣを作製した。ランド部には、炭酸ガスレーザー加工で直径０．１ｍｍのビア孔を形成し、銀系導電ペーストを埋め込んだ。８枚の片面ＦＰＣを位置合わせしてプレス成形し、８層基板を作製したところ、ランド部の位置ずれは、最大で１５μｍであった。
【００３８】
比較例２
厚さ５０μｍのポリイミドフィルム（商品名「カプトン」；デュポン社製）を用いて、実施例３と同様にして８層基板を作製したところ、ランド部の位置ずれが７０μｍとなった。
【００３９】
【発明の効果】
本発明の金属箔積層フィルムは、ポリベンゾトリアゾールフィルムに金属箔が積層されたものであり、ＦＰＣ用途に有用である。本発明の積層フィルムから得られるフレキシブルプリント配線板は、加工精度、位置精度が良好であり、しかも高い放熱性を有するので、特に、消費電力の高い、すなわち発熱量の大きな素子を高密度に搭載した電子回路設計用として最適である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a metal foil laminated film obtained by laminating a metal foil on a polybenzoazole film excellent in heat resistance, thermal conductivity, and insulation, and a flexible printed wiring board using the film. The “film” in the present invention represents a film and a sheet.
[0002]
[Prior art]
There is known a printed wiring board formed by attaching a copper foil to a paper-phenol base material or a glass-epoxy base material, printing a wiring portion, and etching the other portion. These wiring boards are called rigid printed wiring boards because of their hard base material. However, in recent years, as electronic devices have become smaller, lighter, and more dense, they have been replaced by rigid printed wiring boards. Wiring boards have come to be used frequently. A flexible printed wiring board (hereinafter abbreviated as FPC) is a laminate of a flexible insulating film and copper foil, which is subjected to wiring processing, is thin and lightweight, and has the freedom of three-dimensional wiring. However, since the movable part can be incorporated in the circuit, the demand is increasing year by year.
[0003]
As an insulating film material for FPC, inorganic / organic composites such as glass epoxy sheets are also used. Generally, polymers having relatively high heat resistance such as polyimide, polyester, and aromatic polyamide are used. Is used as a film. However, polyester has a limited use because it is not heat resistant enough to withstand the soldering temperature. In addition, aromatic polyamides, particularly para-oriented wholly aromatic polyamides, have the advantages of high crystallinity, high melting point, excellent heat resistance, and a rigid molecular structure, resulting in high mechanical strength. However, there is a demerit that dimensional stability is poor because the expansion due to moisture absorption is large and the thermal contraction rate is large. Attempts have been made to introduce substitution of chlorine atoms into the aromatic ring for the purpose of improving moisture absorption characteristics, but the thermal dimensionality has further deteriorated, and there has been a problem that the metal foil corrodes due to chlorine atoms when used at high temperatures. .
[0004]
For this reason, polyimide having excellent heat resistance is most frequently used for FPC, but the problem of dimensional change due to heat shrinkage and moisture absorption remains in polyimide. Furthermore, the current film thickness is mainly 25 μm, but if you try to make it thinner, the cost will be high, or the elasticity of polyimide will be low and the film will be weak and practical. The problem of disappearing.
[0005]
On the other hand, the trend of downsizing, weight reduction, and densification of electronic devices has caused problems associated with heat generation in the circuit. Recently, semiconductor devices that operate at high speed have come to be used even in small electronic devices. However, this high-speed operation semiconductor device generates a large amount of heat and is coupled with the high-density mounting state. Whether to increase the dispersibility is a big problem. However, many polymer materials including polyimide have low thermal conductivity and cannot be expected in terms of heat dissipation. Attempts have been made to increase the thermal conductivity by using metal foil with good heat conductivity as part of the base material to form a metal base substrate, or by blending metal fine powder or carbon black into a polymer material. These thermal conductivity improving means increase electrical conductivity and decrease insulation, which is not preferable for FPC.
[0006]
[Problems to be solved by the invention]
Therefore, in the present invention, a material having excellent dimensional stability and heat dissipation as well as insulation and heat resistance is found, and it is an object to provide an FPC excellent in dimensional stability that can dissipate heat generated in a high-density circuit. As listed.
[0007]
[Means for Solving the Problems]
The metal foil laminated film of the present invention has the following structural formula:

The present invention is summarized in that a metal foil is bonded to one side or both sides of a polybenzoazole film made of any one of the repeating units shown in FIG. The thickness of the polybenzoazole film is 3 to 75 μm, the tensile modulus is 1000 kg / mm ² or more in both the longitudinal direction and the transverse direction, the thickness of the adhesive layer is 0.5 to 50 μm, the thickness of the metal foil Is preferably 3 to 100 μm. Since the polybenzoazole film is excellent in insulation, heat resistance, and dimensional stability and exhibits high thermal conductivity, the above-described problems can be solved by laminating a metal foil on the polybenzoazole film. The preferable thermal conductivity of the polybenzoazole film is 1 to 50 W / mK. The “polybenzoazole” of the present invention refers to polybenzooxyazole or polybenzothiazole, and alkyl or halogen derivatives thereof.
[0008]
For FPC applications, copper foil is preferably used as the metal foil from the viewpoint of electrical conductivity. Among polybenzoazoles, polyparaphenylene benzbisoxazole is preferable because it has excellent properties such as heat resistance.
[0009]
The present invention also includes a flexible printed wiring board obtained by using the metal foil laminated film of the present invention as a substrate and performing wiring processing.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The metal foil laminated film of the present invention is characterized by using polybenzoazole as a film material. Polybenzoazole is a polymer of benzooxyazole or benzothiazole and their alkyl or halogen derivatives. Specifically, it is a polymer composed of any repeating unit represented by the following structural formula. In addition, an alkyl group or a halogen atom may be introduced into the aromatic ring moiety in the following formula, and a copolymer having two or more of the following repeating units (a) to (d) may be used.
[0011]
[Chemical 3]

[0012]
Among the polybenzoazoles, polyparaphenylene benzobisoxazole has good properties such as heat resistance.
[0013]
The method for synthesizing polybenzoazole is not particularly limited. In US Pat. No. 4,533,693 and the like, as a synthesis method of polybenzoazole, etc., the hydrochloride of the first monomer component such as diol is used as a starting material, and hydrochloric acid is removed while heating and reducing the pressure in polyphosphoric acid, Next, a method of condensing and synthesizing by adding a second monomer component such as terephthalic acid and heating and depressurizing is shown. For example, polycisparaphenylenebenzobisoxazole is obtained from 4,6-diaminoresorcinol dihydrochloride and terephthalic acid, and polytransparaphenylenebenzobisoxazole is obtained from 2,5-diaminoresorcinol dihydrochloride and terephthalic acid. .
[0014]
In consideration of the mechanical strength of the polybenzoazole film in terms of FPC use, it is preferable to use a polymer having an intrinsic viscosity (in a methanesulfonic acid solution) of 5 or more after the film is formed.
[0015]
For film formation, a method of extruding a polybenzoazole dope (solution) in an inert atmosphere may be employed. For example, U.S. Pat. No. 4,973,442 discloses a layer in which a polymer is oriented by extruding a lyotropic liquid crystalline dope by applying a shearing force with a cylindrical rotating rotating die and oriented at + θ degrees with respect to the extrusion direction. And a method of obtaining a multiaxially oriented film by forming a layer oriented at −θ degrees. However, this method has a problem that it is difficult to obtain thickness uniformity.
[0016]
On the other hand, in JP-A-6-503521, a polyphosphoric acid dope containing 8 to 20% by weight of polybenzoazole is extruded from a T die at 80 to 200 ° C., cooled in an inert atmosphere, A method is described in which both surfaces are sandwiched between thermoplastic films and the laminate is laterally stretched with a tenter or the like and then the thermoplastic film is removed. Since the film dope is oriented in the longitudinal direction when it is extruded from the T-die, according to this method, a biaxially oriented film having a uniform thickness can be obtained. If the longitudinal orientation is weak, a longitudinal stretching step using a roll or the like may be added before or after the lateral stretching, or the stretching may be performed simultaneously in the longitudinal and lateral directions with a tenter.
[0017]
The thickness of the polybenzoazole film is preferably 3 to 300 μm. When the film is too thick, the flexibility is lowered and it is difficult to obtain a flexible printed wiring board. However, if the film is too thin, the waist becomes weak, the mechanical strength is lowered, and the electrical insulation is also lowered, which is not preferable. The film thickness is more preferably 150 μm or less, and further preferably 75 μm or less. The upper limit of the most preferable thickness is 40 μm. The lower limit is preferably 5 μm or more, more preferably 7 μm or more.
[0018]
The polybenzoazole film preferably has a tensile elastic modulus of 1000 kg / mm ² or more in both the longitudinal and transverse directions from the viewpoint of mechanical strength. . If it is less than 1000 kg / mm ² , the strength may be insufficient particularly when a thin film is formed.
[0019]
The thermal conductivity is preferably large, and the polybenzoazole used in the present invention is preferably in the range of 1 to 50 W / mK. In order to make the thermal conductivity within this range, it is desired to orient the film so that the Young's modulus of the film is 400 kg / mm ² or more, more preferably 1500 kg / mm ² or more. A general plastic is about 0.1 to 0.5 W / mK and is poor in heat dissipation, but in the present invention, polybenzoazole having a good thermal conductivity is used as a film base material, and thus laminated with a metal foil. It exhibits excellent heat dissipation even later, and is optimal as an FPC for small electrical equipment and high-density mounting.
[0020]
A known additive for film, for example, an ultraviolet absorber / stabilizer, a heat stabilizer, a lubricant, a pigment, a stretching aid and the like can be added to the polybenzoazole film. In order to improve the adhesion between the film and the metal foil, the film may be subjected to an anchor coating agent coating, chemical etching treatment, corona treatment, or plasma treatment.
[0021]
The adhesive for laminating the metal foil and the polybenzoazole film may be either thermosetting or thermoplastic so long as it is soft and heat resistant so as not to impair the flexibility of the film. In particular, the type of adhesive is not limited. Specific examples include polyimide, polyamide, polyamideimide, epoxy resin, polyester, acrylic resin, polybenzimidazole, maleimide, urethane resin, phenol resin, phenoxy resin, melamine resin, etc. Is mentioned. In addition, by adding carbon black or metal fine powder to the adhesive layer as long as the electrical insulation is not impaired, the thermal conductivity of the adhesive layer can be increased and the heat dissipation can be improved.
[0022]
The thickness of the adhesive layer is preferably in the range of 0.1 to 50 μm. If it is too thin, the adhesive force between the metal foil and the polybenzoazole film may be insufficient, and if it is too thick, the flexibility of the laminated film is lost. The thickness of the adhesive layer is more preferably in the range of 3 to 30 μm, and even more preferably in the range of 5 to 20 μm.
[0023]
The type of metal foil to be laminated is not limited to the copper foil generally used for FPC, and various metal foils can be used. For example, Be, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Room temperature such as Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Ba, lanthanoid metal, Hf, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb, Bi And solid metals and their alloys. As alloys, binary alloys such as Fe-Co alloys, Fe-Ni alloys, Fe-Si alloys, Fe-C alloys, Cu-Zn alloys, Cu-Sn alloys, Ni-Cr alloys, etc. Alternatively, ternary alloys such as Fe-Ni-Cr alloys, etc., or alloys of quaternary or more can also be used. Alternatively, conductive metal oxides such as tin oxide, indium oxide, vanadium oxide, and ruthenium oxide may be used.
[0024]
The method for producing the metal foil is not particularly limited, and electrolytic foil, rolled foil, electroless plating foil, etc., PVD methods such as vacuum deposition and sputtering, and foils produced by the CVD method can be used. The thickness of the metal foil is usually 3 to 100 μm. 50 micrometers or less are preferable and 30 micrometers or less are more preferable. A metal foil having a thickness of 5 to 20 μm is suitable for applications requiring high flexibility and fine fine wire processing.
[0025]
As a method for laminating the metal foil and the polybenzoazole film, a method of applying an adhesive to the film and / or the metal foil and laminating them can be adopted. The adhesive coating method may be, for example, a roll coating method, a reverse coating method, a roll brush method, a spray coating method, an air knife coating method, a gravure coating method, an impregnation (dipping) method, a curtain coating method, etc. It is also possible to use a method of dry laminating with a shaped adhesive, a method of directly forming an adhesive layer on a film or metal foil by a method such as melt extrusion laminating or coextrusion laminating. The metal foil laminated film of the present invention is obtained by bonding a metal foil to at least one surface of a polybenzoazole film via an adhesive layer. A film and a metal foil can be further bonded together after a metal foil is bonded to a film to form a multilayer structure. When circuit processing is performed as FPC, a one-layer type in which a metal foil is bonded to one side of a film or a two-layer type in which a metal foil is bonded to both sides of a film is mainly used.
[0026]
If the metal foil of the metal foil laminated film of the present invention is etched to form a circuit pattern, a flexible printed wiring board can be obtained. By using the above-mentioned two-layer type metal foil laminated film and ensuring conduction between the metal foils on both sides by using plating or conductive paste, a double-sided through-hole circuit can be formed, and further multilayered by the build-up method. You can also. Further, by applying a so-called pre-punch method in which a polybenzoazole film is die-cut (punched) and then bonded to a metal foil, it can be used as a tape substrate for a TAB (tape automated bonding) method.
[0027]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to carry out and they are all included in the technical scope of the present invention.
[0028]
Example 1
[Synthesis of polyparaphenylenebenzbisoxazole]
In a tank reactor, 14.49 parts by weight of diphosphorus pentoxide was added to 43.86 parts by weight of polyphosphoric acid 116% (based on 100% pure H ₃ PO ₄ ) under a nitrogen stream. 6.10 parts by weight of 6-diaminoresorcinol dihydrochloride and 7.10 parts by weight of terephthalic acid micronized to an average particle size of 2 μm were added, and the mixture was heated to 80 ° C. and mixed with stirring. Next, after mixing at 150 ° C. for 10 hours, polymerization was carried out in a twin-screw extruder heated to 200 ° C. A polymer dope of cis-polyparaphenylenebenzbisoxazole was obtained. This polymer dope was yellow, and the intrinsic viscosity measured with a methanesulfonic acid solution was 38 dl / g.
[0029]
[Production of film]
The polymer dope was extruded from a T-die at 150 ° C., and the extruded high-viscosity film-like dope was cast into a metal roll under an inert atmosphere and cooled. Next, an unstretched polypropylene film was laminated on both sides of the film dope, and the double-sided laminate sheet was stretched in the transverse direction at 150 ° C. with a tenter. The laminated polypropylene film was removed by peeling, and the film-like dope was washed with water for 24 hours and then heat-set at 280 ° C. A bipara-oriented polyparaphenylene benzbisoxazole film having a thickness of 50 μm was obtained. Tensile modulus of the film in the longitudinal direction 2300 kg / mm ^2, in the horizontal direction was 2800 kg / mm ^2. The thermal conductivity of the film was 20 W / mK in the vertical direction and 30 W / mK in the horizontal direction. The thermal conductivity was measured in Journal of Applied Physics, Volume 36 [J. Appl. Phys. Vol. 36 (1977)], page 5634, and measured using the steady heat flux method.
[0030]
[Production of metal foil laminated film]
30 parts by weight of phenol resin, 20 parts by weight of acrylonitrile-butadiene copolymer, 30 parts by weight of bisphenol A type epoxy resin, 20 parts by weight of butyral resin, 12 parts by weight of silica, and 400 parts by weight of methyl ethyl ketone are mixed and dissolved. Thus, an adhesive A was prepared. Adhesive A was applied to both sides of the polyparaphenylenebenzbisoxazole film so that the film thickness after drying was 20 μm, and dried in a hot air drying zone at 130 ° C. for about 10 minutes. Subsequently, an electrolytic copper foil having a thickness of 18 μm is drawn out from the roll on the adhesive layers on both sides, and laminated under the conditions of temperature: 170 ° C., speed: 0.3 m / min, pressure: 3.5 kgf / cm ^2. The film was wound on a tube and aftercured in an oven at 125 ° C. for 12 hours to obtain a two-layered (double-sided) metal foil laminated film.
[0031]
[FPC processing]
The two-layer type metal foil laminated film was subjected to drilling to form a through hole having a minimum diameter of 0.2 mm, and through-hole conduction processing was performed. The through-hole conductive processing was performed in the order of conditioning, catalyst application, catalyst activation, electroless copper plating, and panel copper electroplating. The final through hole conductor thickness was 35 μm. Next, a conductive pattern having a minimum width of 50 μm and a minimum line interval of 50 μm was formed using a dry film resist having a thickness of 25 μm, and masked using a photosensitive polyimide film as a cover film to obtain a double-sided FPC.
[0032]
[Evaluation]
When the dimensional variation during the processing step of the FPC was compared between the dry film resist pattern and the obtained conductor circuit pattern, it was 0.0012%. In addition, an element with power consumption of 1.0 [W] was mounted on the obtained FPC, and the temperature rise of the element was recorded by operating in a room at 25 ° C. .
[0033]
Comparative Example 1
A double-sided FPC was produced in the same manner as in Example 1 except that a polyimide film (trade name “Kapton”; manufactured by DuPont) having a thickness of 50 μm was used instead of the polyparaphenylenebenzbenzoazole film. The dimensional variation rate of this FPC was 0.25%. Further, when the temperature rise of the device was measured in the same manner as in Example 1, the temperature of the device rose by + 35 ° C. after 10 minutes of operation.
[0034]
Example 2
After applying the polymer dope of cis-polyparaphenylenebenzbisoxazole obtained in Example 1 to a stainless steel plate to remove polyphosphoric acid, a polymer dope was further formed on the first layer. The polyphosphoric acid was removed by coating so that the coating direction was orthogonal to the first layer. This process was repeated to produce a thick film of polyparaphenylenebenzbisoxazole having a thickness of 200 μm.
[0035]
A prepolymer was synthesized by prereacting 75 parts by weight of 2,2-bis (4-cyanatophenyl) propane at 160 ° C. for 4 hours. In this prepolymer, 25 parts by weight of a saturated polyester resin (trade name “Byron” manufactured by Toyobo Co., Ltd.), 5 parts by weight of a bisphenol A type epoxy resin, 0.01 parts by weight of zinc octylate, and 100 parts by weight of methyl ethyl ketone are mixed and dissolved. Thus, an adhesive B was prepared. A double-sided FPC was produced in the same manner as in Example 1 using the polyparaphenylene benzbisoxazole film and the adhesive B.
[0036]
The dimensional variation rate of this FPC was 0.01%. Further, when the temperature rise of the device was measured in the same manner as in Example 1, it was + 8 ° C. after 10 minutes of operation.
[0037]
Example 3
A thermoplastic polyimide was applied to both sides of the polyparaphenylene benzbisoxazole film obtained in Example 1 so as to have a thickness of 20 μm, an electrolytic copper foil having a thickness of 18 μm on one side, and a release sheet on the other side. Was pasted and pressed at a temperature of 300 ° C. and a pressure of 10 kgf / cm ² to prepare a single layer type (single side) metal foil laminated film. A square single-sided FPC having a minimum width of 50 μm, a minimum line spacing of 50 μm, and a minimum diameter of 200 μm and a side of 250 mm was prepared on a copper foil of the laminated film using a dry film resist having a thickness of 25 μm. A via hole having a diameter of 0.1 mm was formed in the land portion by carbon dioxide laser processing, and a silver-based conductive paste was embedded. When eight single-sided FPCs were aligned and press-molded to produce an eight-layer substrate, the land portion had a maximum positional deviation of 15 μm.
[0038]
Comparative Example 2
Using a polyimide film (trade name “Kapton”; manufactured by DuPont) having a thickness of 50 μm, an 8-layer substrate was produced in the same manner as in Example 3. As a result, the land portion was displaced by 70 μm.
[0039]
【The invention's effect】
The metal foil laminated film of the present invention is obtained by laminating a metal foil on a polybenzotriazole film and is useful for FPC applications. The flexible printed wiring board obtained from the laminated film of the present invention has good processing accuracy and positional accuracy, and also has high heat dissipation, so in particular, high power consumption, that is, a large amount of heat generation elements are mounted at high density. It is ideal for designing electronic circuits.

Claims (4)

The following structural formula

A metal foil is bonded to one or both sides of a polybenzoazole film made of any one of the repeating units and biaxially oriented via an adhesive layer, and the thickness of the polybenzoazole film 3 to 75 μm, the tensile modulus is 1000 kg / mm ² or more in both the longitudinal direction and the transverse direction, the thickness of the adhesive layer is 0.5 to 50 μm, and the thickness of the metal foil is 3 to 100 μm. A metal foil laminated film characterized by that. The metal foil laminated film according to claim 1 , wherein the polybenzoazole film has a thermal conductivity of 1 to 50 W / mK. The metal foil laminated film according to claim 1 or 2 , wherein the metal foil is a copper foil. The flexible printed wiring board characterized by using a metal foil laminated film according as the substrate in any one of claims 1-3.