JP4654502B2

JP4654502B2 - Prepreg and method for manufacturing laminate using the same

Info

Publication number: JP4654502B2
Application number: JP2000318886A
Authority: JP
Inventors: 繁江草; 貴志山地; 守小松
Original assignee: Sumitomo Bakelite Co Ltd
Current assignee: Sumitomo Bakelite Co Ltd
Priority date: 2000-10-19
Filing date: 2000-10-19
Publication date: 2011-03-23
Anticipated expiration: 2020-10-19
Also published as: JP2002121303A

Description

【０００１】
【発明の属する技術分野】
本発明は、特に電気機器、電子機器、通信機器等に使用されるプリント回路基板用として好適なプリプレグ及びこのプリプレグを用いた積層板の製造方法に関するものである。
【０００２】
【従来の技術】
プリント回路基板用エポキシ樹脂積層板は一般的にエポキシ樹脂を繊維基材に塗布・乾燥させて得たプリプレグを１枚以上重ね、その上面に金属箔を重ね合わせて加熱加圧成形して得られている。また、多層プリント回路基板の製造方法は、両面または片面に回路加工及び黒化処理を施した内層回路基板にエポキシ樹脂を繊維基材に塗布・乾燥させたプリプレグを１枚以上重ね、その上面に金属箔を重ね合わせて、加熱加圧成形して得られる。一般的に加熱加圧成形はこれら組み合わせたプリント回路基板材料を金属鏡面板を使って交互に重ね、その最外部にクラフト紙等のクッション材を配し、加熱冷却が可能な高圧プレスを使って実施する。
【０００３】
プリプレグに使用される繊維基材はガラス織布を代表例とする織布である。織布は繊維のモノフィラメントを集束したヤーンを織ったものであり、そのまま直接硬化性樹脂ワニスを浸せきあるいは塗布等により含浸すると、モノフィラメント間の隙間に多くの空気を含んだプリプレグが得られる。更に加熱等により硬化性樹脂ワニスが繊維基材に浸透しても、幾らかの空気がモノフィラメント間の隙間に残存し、加熱加圧成形した後も空気が残存して製品として吸湿半田耐熱性の低下や長期絶縁信頼性の低下等不具合を多く発生するものとなる。
【０００４】
近年、基板成形後の板厚精度の高度化によるインピータンスコントロールが可能な樹脂の開発が行われている。基板の板厚精度は信号遅延と１倍の相関があり、一方、基板材料の低誘電率化については、誘電率はその平方根と信号遅延が相関するため、基板の板厚精度の高度化の方が有効な手段である基板の板厚精度向上のためには、成形中に発生する樹脂の金型外への流出（以下、フローアウトという）を減少させることが重要である。
例えば成形時の樹脂の最低溶融粘度を高くし、フローアウトを減少させることによってフローアウトのコントロールが行われてきた。具体的にはプリプレグに含浸する樹脂にフィラーや高分子量樹脂等を添加することにより樹脂の粘度を上げる手法であるが、樹脂の粘度を高くする手法ではガラス繊維基材への含浸性が低下することから、含浸時に繊維内ボイドの増加をまねき、基板成形時に成形不良が生じるおそれがある。
【０００５】
成形後の板厚精度にはプリプレグの厚みのバラツキ等のプリプレグ固有の問題があり、さらには成形時におけるプレス内での樹脂の流れ、成形圧力や温度のバラツキの影響がある。例えば成形時、樹脂の流れ方はプリプレグの中央や端において一様に流れるわけではなく、一般にプレスの鏡面板の中心部分よりも周辺部分の方が樹脂の流れが大きく、その結果周辺部分が中心部分よりも薄いことは良く知られている。成形時のこのようなバラツキによってもフローアウトの違いを生じ、プリプレグの厚みのバラツキとともに板厚精度を低下させる要因となっており、前述のようなフィラーや高分子量樹脂の添加による高粘度化だけでは効果が不十分である。
【０００６】
プリント回路基板用エポキシ樹脂積層板及び多層プリント回路基板の成形において、加熱加圧工程あるいはその前の重ね合わせ工程等において、プリプレグ切断部より発生した樹脂粉末や取り扱い時にプリプレグが折れ曲がる等により発生した樹脂粉末が金属鏡面板と金属箔の間に入り込み、そのまま成形すると、回路基板成形後回路パターン作製のためのエッチング工程において、この樹脂粉末がエッチングレジストと同じ作用をし、回路パターン不良の原因となっている。
このような問題を解決すべく、プリプレグの樹脂粉末の発生しやすい部分、あるいは樹脂粉末が付着している部分の樹脂粉末を再溶融してプリプレグからの樹脂粉末の発生、飛散を防止する等の対策が以前からなされている。しかしながら、このような方法では溶融方法によるエポキシ樹脂の性能変化の問題、あるいは設備投資や処理工数を必要とする。
以上のことから、樹脂粉末の発生が少なく、かつ基板の板厚精度の高度化と優れた成形性を併せ持つプリプレグが望まれている。
【０００７】
【発明が解決しようとする課題】
本発明は、プリプレグに関して樹脂粉末発生の低減および成形後の基板の板厚精度および成形性の両立という問題を解決すべく、プリプレグの製造方法を鋭意検討を進めた結果、本発明を完成するに至った。本発明は、プリプレグのモノフィラメント間の隙間に残存するボイドを低減させ、プリプレグの構成を変えることにより、樹脂粉末の発生が少なく、かつ良好な成形性を維持しつつ、成形後の基板の板厚精度を向上することができる。
【０００８】
【課題を解決するための手段】
本発明は、（１）Ｎ，Ｎ−ジメチルホルムアミドをガラス繊維基材に含浸する工程、続いて、（２）熱硬化性樹脂ワニスをガラス繊維基材に含浸し、１４０〜１７０℃乾燥硬化する工程、次いで（３）この片側もしくは両側に熱硬化性樹脂ワニスを塗布し乾燥する工程を有することを特徴とするプリプレグの製造方法に関するものである。
工程（１）において、有機溶剤をガラス繊維基材に含浸する時間は３０〜４２０秒が好ましい。
工程（２）において、熱硬化性樹脂の付着量がガラス繊維基材１００重量部に対し４０〜１００重量部であることが好ましい。
工程（３）において、熱硬化性樹脂の付着量が、工程（２）における熱硬化性樹脂の付着量１００重量部に対して、５〜２５０重量部であることが好ましい。
さらに、本発明は、このようにして得られたプリプレグの１枚又は２枚以上を加熱成形することを特徴とする積層板の製造方法に関するものである。
【０００９】
【発明の実施の形態】
本発明において、有機溶剤をガラス繊維基材に含浸する工程（１）は、ガラスクロス内の空隙を溶剤に置き換えるために実施されるものである。有機溶剤は特に限定されないが、蒸気圧の高い溶剤は、次の工程（２）である熱硬化性樹脂の含浸までに蒸発し、モノフィラメント間の隙間が発生し、いわゆるストランドボイドの原因となり、有機溶剤をガラス繊維基材に含浸する意味が小さくなるので、蒸気圧が温度２０〜５０℃の範囲において、２５０ｍｍＨｇ以下であることが好ましい。生産において安定した製品を得るために、蒸気圧が低いＮ，Ｎ−ジメチルホルムアミド等を使用することがより好ましい。
溶剤の含浸は、溶剤が基材の繊維間に十分に浸透するために、３０〜４２０秒間、溶剤槽に浸漬するかもしくは溶剤を塗布することにより基材が濡れた状態にする。３０秒未満では基材細部への含浸が不十分となり、ボイドの発生原因となる。また、４２０秒を越えても含浸向上のそれ以上の効果はみられず、生産性低下となる。より好ましくは、基材細部への含浸と効率を考慮して１５０〜３００秒である。含浸を効率的に行い含浸時間を短縮するため、超音波、高圧シャワー等を使用してもよい。また、ガラス繊維基材を開繊処理することも有効な手段である。溶剤の付着量は、基材のモノフィラメント間を完全に満たす量であればよく、次の工程において前記溶剤が熱硬化性樹脂ワニスに持ち込まれることによるワニス粘度の低下（これは樹脂含浸量のばらつきを生じ、プリプレグ及び積層板の品質のバラツキにつながる）を防止するために、工程（１）の後に、絞りロール等で余剰の溶剤を除去することが好ましい。
【００１０】
熱硬化性樹脂ワニスをガラス繊維基材に含浸し乾燥硬化する工程（２）において、熱硬化性樹脂は、エポキシ樹脂、熱硬化性ポリイミド樹脂、シアネート樹脂等の１種または２種以上から選ばれるものであり、必要に応じて硬化剤、硬化触媒、充填剤、界面活性剤、シランカップリング剤等の添加剤を加えることができる。通常、この熱硬化性樹脂は溶剤に溶解したワニスの形で使用するが、用いられる溶剤は樹脂に対して良好な溶解性を示すことが望ましい。また、悪影響を及ぼさない範囲で貧溶媒を使用してもかまわない。また樹脂が粉砕等により微粉化が可能な場合、粉体で塗布することも可能である。
この工程で付着させる樹脂量は空隙を発生させない樹脂量が必要であり、ガラス繊維基材１００重量部に対し、４０〜１００重量部であることが好ましい。４０重量部より少ないと、ガラス繊維基材のモノフィラメント間の間隙を十分に埋めるだけの樹脂絶対量が不足し、１００重量部より大きいと樹脂量が多すぎて成形が容易でなく得られた積層板の種々の特性が低下するようになる。
【００１１】
工程（２）の乾燥条件は工程（１）で使用する溶剤及び工程（２）で使用する樹脂を溶解する溶剤の沸点によって決められるが、本発明において使用される溶剤においては１００〜２００℃が適当である。１００℃未満では溶剤の蒸発に多くの時間を要するか、溶剤の残存が生じることがあり、２００℃を越える温度では溶剤の突沸により空隙が生じるおそれがある。沸点よりある温度以上低い温度で乾燥すると多くの溶剤が残存し、プリプレグ及び積層板の信頼性を大きく低下させることになり、ある温度以上高い温度で乾燥すると溶剤が突沸し空隙が生じるようになる。例えば、Ｎ，Ｎ−ジメチルホルムアミドを使用した場合、その沸点は１５３℃であることから、乾燥温度は１４０〜１７０℃が最適である。また、熱風による乾燥を行った場合、その風速によって突沸が生じなければ生産性向上のため、温度をより高くすることができる。
【００１２】
本発明は、樹脂粉末の発生を低減し、厚み精度に優れかつ成形性に優れるプリプレグ及び積層板を得ることを目的とするが、このために、上記で得られた熱硬化性樹脂含浸基材の樹脂層（以下、ａ層という）とこれに次ぐ工程（３）でこのａ層の外側に形成される樹脂層（以下、ｂ層という）との樹脂量及び硬化度を検討して、各層にそれぞれ異なる機能を発揮させるように設計した。すなわち、ａ層は成形時にフローアウトが生じないように、かつ樹脂粉末が発生しないように硬化を進めることで、板厚精度を良好にする機能を有し、ｂ層は銅箔等との接着や内層回路間への埋め込みを行う機能を有する。ａ層の厚み精度は塗布時の厚み精度、即ち数％以内の精度に制御可能であり、樹脂硬化度は二次含浸時後の乾燥条件（乾燥温度、乾燥時間）によって制御可能である。樹脂硬化がＣステージ化もしくはそれに近い状態にすることによって、プレス等による成形の際にもフローアウトせず、成形後の厚み精度が良好に維持される。また、プリプレグの切断等においてａ層からの樹脂粉末の発生が防止される。
従来のプリプレグは、本発明のプリプレグが有するａ層に相当する層が無く、樹脂すべてが同程度の硬化度であり、かつ含浸や回路への埋め込みを板厚精度より優先させる結果、加熱時には樹脂が低粘度化するものであった。このため、成形時にフローアウトが生じ、板厚精度が低下する要因となっていた。このため、板厚精度をよくする目的で充填材や高分子成分の添加により樹脂分を高粘度化することが行われていたが、高粘度化により、繊維内ボイドの残存等を生じ成形性の悪化を導いた。
【００１３】
次に、工程（３）においては、前記熱硬化性樹脂含浸基材の片側もしくは両側に熱硬化性樹脂ワニスを塗布し乾燥する。即ち、ａ層の外側にｂ層を形成する。ｂ層は主に回路間への埋め込みや他の層との接着を目的とする。ａ層は樹脂の硬化が進んでいるため、流動性が小さく、接着性も小さいからである。
ｂ層は、ａ層と異なり、プレスやロールによる成形時に樹脂が一部フローアウトするため、基板の板厚精度に大きな影響を及ぼす。ここで板厚精度が良好に保つａ層と板厚精度の悪いｂ層との割合が重要となる。ａ層の割合が多ければ板厚精度は良くなるが、回路の埋め込みや接着性が悪くなる。逆にｂ層の割合が多ければ成形後の板厚精度が悪くなる。また、ｂ層はプリプレグ切断等において樹脂粉末の発生にも大きな影響を及ぼす。ここで樹脂粉末の発生が極めて少ないａ層の樹脂量と樹脂粉末の発生し易いｂ層の樹脂量との割合が重要となる。ａ層の樹脂量の割合が多ければ、樹脂粉末の発生は少なくなるが、回路間の埋め込みや接着性が悪くなる。逆にｂ層の樹脂量の割合が多ければ、樹脂粉末の発生が多くなる。ｂ層は、プレスやロールにより回路間への埋め込みが必要であるため、樹脂の硬化がＢステージ状態でなければならない。
しかしながら、本発明のプリプレグはａ層があるため、フローアウトが起こる樹脂分はｂ層しかなく、流動する樹脂の絶対量が従来のプリプレグよりも少なく、樹脂粉末の発生も少ない。そのため、ｂ層が低粘度の樹脂であってもプリプレグ全体のフローアウトは従来のものよりも小さくなる。更に流動する樹脂の絶対量が少ないことにより、成形時の圧力や温度のバラツキが樹脂の流動性に与える影響も小さくなることから、本発明によるプリプレグは板厚精度と成形性の両方に優れ、かつ樹脂粉末の発生も低減される。
【００１４】
本発明者による検討の結果、ｂ層／ａ層の樹脂の割合は、０．０５〜２．５の範囲内であれば、板厚精度と回路への埋め込みが良くなることを見出した。ｂ層／ａ層の割合が２．５よりも多ければ成形後の板厚精度が従来と同じ程度で、樹脂粉末の発生量も従来と変わらず、改善の効果が不十分である。０．０５よりも少なければ、樹脂の流れが不十分で、成形時プリプレグ相互及び銅箔との接着が不十分となりやすく、多層成形の場合回路間に完全に埋め込まれず、ボイドの残存や吸湿半田試験でのミズリングやフクレの発生が認められるようになる。
ｂ層で使用できる熱硬化性樹脂としては、ａ層と同様にエポキシ樹脂、熱硬化性ポリイミド、シアネート樹脂等の熱硬化性樹脂であり、２種以上を混合して使用することもできる。樹脂粉末の発生を更に少なくするためには、ｂ層の樹脂はエポキシ当量で９００〜４０００程度の末端２官能直鎖状エポキシ樹脂のような高分子の樹脂を含んでいるものが好ましい。必要に応じて硬化剤、硬化触媒、充填剤、界面活性剤、シランカップリング剤等の添加剤を加えることができる。また、ａ層と同じ組成の樹脂であっても、異なる組成の樹脂であってもよい。通常、溶剤に溶解したワニスの形で使用するが、用いられる溶剤は樹脂に対して良好な溶解性を示すことが望ましい。また、悪影響を及ぼさない範囲で貧溶媒を使用することもできる。また樹脂が粉砕等により微粉化が可能な場合、粉体としてａ層に塗布することも可能である。
【００１５】
本発明で得られるプリプレグは適当な長さに切断し、金属箔や内層回路板と重ね合わせて加熱加圧成形することにより、回路基板あるいは多層回路基板を得ることができる。また、プリプレグを長尺のまま巻き取り、銅箔、アルミニウム箔やニッケル箔等の金属箔や内層回路板に連続的にラミネートを行うことにより回路基板あるいは多層回路基板とすることができる。
【００１６】
【実施例】
以下、本発明を実施例及び比較例により説明する。
【００１７】
実施例１
＜エポキシ樹脂ワニスの調製＞
エポキシ当量約４５０のビスフェノールＡ型エポキシ樹脂７０重量部とエポキシ当量約１９０のフェノールノボラック型エポキシ樹脂３０重量をメチルエチルケトン５０重量部に溶解した。この溶液に、ジシアンジアミド３重量部と２−フェニル−４−メチルイミダゾール０．１５重量部をジメチルホルムアミド２０重量部に溶解した溶液を加え、攪拌混合した。この様にしてエポキシ樹脂ワニスを調製した。
【００１８】
＜プリプレグの作成＞
ガラスクロス（厚さ０．１０ｍｍ）をＮ，Ｎ−ジメチルホルムアミドに２００秒間浸漬し、絞りロールで余剰の溶剤を除去した。続いて、このガラスクロスを上記のように調製したエポキシ樹脂ワニスに樹脂固形分がガラスクロス１００重量部に対して６５重量部になるように含浸し、１７０℃の乾燥炉中で３分間乾燥し、ａ層が形成されたエポキシ樹脂含浸カラスクロスを作成した。次にこのエポキシ樹脂含浸ガラスクロスに、前記エポキシ樹脂ワニスを樹脂固形分がガラスクロス１００重量部に対して４５重量部になるよう塗布を行い、１７０℃の乾燥炉中で１．５分間乾燥し、ｂ層を作成した。ａ層とｂ層の樹脂の割合は、ｂ層／ａ層で約０．７である。このようにしてａ層とｂ層からなるプリプレグを作成した。
【００１９】
参考例１
ガラスクロス（厚さ０．１０ｍｍ）をメチルエチルケトンに２００秒浸漬し、絞りロールで余剰の溶剤を除去した。続いて、上記のように調製したエポキシ樹脂ワニスを樹脂固形分がガラスクロス１００重量部に対して６５重量部になるように含浸し、１１０℃の乾燥炉中で３０分間乾燥し、ａ層が形成されたエポキシ樹脂含浸ガラスクロスを作成した。以下、実施例１と同様にしてａ層とｂ層からなるプリプレグを作成した。
【００２０】
比較例１
実施例１と同様にしてエポキシ樹脂ワニスを調整した後、ガラスクロス（厚さ０．１０ｍｍ）に１回のみ含浸を行って、樹脂固形分がガラスクロス１００重量部に対して１１０量部になるようにした。次いで１７０℃１．５分間乾燥させ、プリプレグを作成した。
【００２１】
比較例２
ガラスクロスにＮ，Ｎ−ジメチルホルムアミドを含浸する工程を省略したことを除いて、実施例１の方法を実施し、ａ層とｂ層からなるプリプレグを作成した。
【００２２】
比較例３
ガラスクロスにメチルエチルケトンを含浸する工程を省略したことを除いて、参考例１の方法を実施し、ａ層とｂ層からなるプリプレグを作成した。
【００２３】
以上のようにして得られたプリプレグを用いて、以下に示す方法にて両面銅張積層板及び４層回路基板を作成し、その特性を評価した。
＜プリプレグの樹脂粉末発生量評価＞
プリプレグをカッターで１００ｍｍ×１００ｍｍにカットし、１０枚重ね合わせ、一定の高さから数回落下させて、樹脂粉末の発生量を測定した。
＜積層板の成形＞
前記プリプレグ１枚の上下に厚さ１８μｍの銅箔を重ねた。次いで圧力４０ｋｇｆ／ｃｍ² 、温度１７０℃で６０分間加熱加圧成形を行い、絶縁層厚さ０．１ｍｍの両面銅張積層板を得た。
＜積層板の評価＞
板厚精度と成形性は、サイズ５００ｍｍ×５００ｍｍの両面銅張積層板をエッチングにより銅箔を除去したものについて測定した。
板厚精度は碁盤目状に測定点を３６点設定し、厚みを測定した。この平均値と範囲を求め、板厚精度とした。
成形性は、サイズ５００ｍｍ×５００ｍｍの基板について空隙ボイドの有無、その他異常は見られないか目視および光学顕微鏡により確認を行った。
１８μｍ銅箔ピール強度は、ＪＩＳＣ６４８１に準じて行った。
半田耐熱性の測定は、片面のみをエッチングし、５０ｍｍ×５０ｍｍのサイズに切断後、１２１℃、２．０気圧のプレッシャークッカー条件で１時間および２時間の吸湿処理を行った。続いて、２６０℃半田槽に１２０秒浸漬した後、フクレ、ミーズリングの評価を目視および光学顕微鏡により確認を行った。
【００２４】
＜４層回路基板の作成＞
内層板として厚さ０．８ｍｍの両面銅張積層板の銅箔（厚さ３５μｍ）の表面に酸化処理（黒化処理）を施し、その上下に前記プリプレグを各１枚重ね、更にその上下に１８μｍの銅箔を重ね、圧力４０ｋｇｆ／ｃｍ² 、温度１７０℃で１２０分間加熱加圧成形して４層回路基板を作成した。
＜４層回路基板の評価＞
板厚精度は、サイズ５００ｍｍ×５００ｍｍの基板について碁盤目状に測定点を３６点設定し、厚みを測定た。この平均値と範囲を求め、板厚精度とした。
成形性は、サイズ５００ｍｍ×５００ｍｍの基板について空隙ボイドの有無、その他異常は見られないか目視および光学顕微鏡により確認を行った。
内層ピール強度は、この基板の内層黒化処理銅箔とプリプレグの界面におけるピール強度をＪＩＳＣ６４８１に準じて測定した。
半田耐熱性の測定は、片面のみをエッチングし、５０ｍｍ×５０ｍｍのサイズに切断後、１２１℃、２．０気圧のプレッシャークッカー条件で１時間および２時間の吸湿処理を行った。続いて、２６０℃半田槽に２分浸漬した後、フクレ、ミーズリングの評価を目視および光学顕微鏡により確認を行った。
【００２５】

【００２６】
実施例１により得られたプリプレグは樹脂粉末の発生が少なく、板厚精度に優れ、かつ成形性良好である。比較例１は従来方法で作成されたプリプレグの例であり、樹脂粉末の発生が実施例の場合よりも多く、板厚精度が悪い。比較例２及び３は、初めに有機溶剤を含浸する工程がないため、成形性が悪く、積層板にはボイドが発生しており半田耐熱性も低下している。
【００２７】
【発明の効果】
以上の結果からも明らかなように、本発明の方法により得られたプリプレグは、切断等において樹脂粉末の発生が少なく、かつ良好な成形性を維持しつつ、成形後の基板の板厚精度を向上することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a prepreg suitable for a printed circuit board particularly used for electrical equipment, electronic equipment, communication equipment, and the like, and a method of manufacturing a laminate using the prepreg.
[0002]
[Prior art]
Epoxy resin laminates for printed circuit boards are generally obtained by stacking one or more prepregs obtained by applying and drying an epoxy resin to a fiber base material, and overlaying a metal foil on the upper surface to obtain a hot press molding. ing. In addition, the method for producing a multilayer printed circuit board is such that one or more prepregs obtained by applying and drying an epoxy resin on a fiber base material are laminated on an inner layer circuit board that has been subjected to circuit processing and blackening treatment on both sides or one side, and the upper surface thereof is laminated. It is obtained by overlapping metal foils and heating and pressing. In general, heat and pressure molding uses these high-pressure presses that can heat and cool the printed circuit board materials that are combined with each other by using metal mirror plates, and by placing cushion materials such as kraft paper on the outermost part. carry out.
[0003]
The fiber base material used for the prepreg is a woven fabric represented by a glass woven fabric. The woven fabric is a woven yarn in which monofilaments of fibers are bundled. When the curable resin varnish is directly immersed or impregnated by coating or the like, a prepreg containing a large amount of air in the gap between the monofilaments is obtained. Furthermore, even if the curable resin varnish penetrates into the fiber substrate due to heating or the like, some air remains in the gaps between the monofilaments, and air remains after heating and pressing to produce moisture-absorbing solder heat resistant products. Many problems such as a decrease and a decrease in long-term insulation reliability occur.
[0004]
In recent years, resins capable of impedance control have been developed by increasing the thickness accuracy after substrate molding. The thickness accuracy of the substrate has a one-time correlation with the signal delay. On the other hand, the reduction in the dielectric constant of the substrate material has a correlation with the square root of the dielectric constant and the signal delay. In order to improve the thickness accuracy of the substrate, which is a more effective means, it is important to reduce the outflow (hereinafter referred to as flow out) of the resin generated during molding to the outside of the mold.
For example, the flow-out has been controlled by increasing the minimum melt viscosity of the resin during molding and decreasing the flow-out. Specifically, it is a technique to increase the viscosity of the resin by adding a filler or a high molecular weight resin to the resin to be impregnated into the prepreg, but the technique of increasing the viscosity of the resin decreases the impregnation property to the glass fiber substrate. For this reason, voids in the fiber are increased at the time of impregnation, and molding defects may occur at the time of substrate molding.
[0005]
The plate thickness accuracy after molding has problems inherent to the prepreg, such as variations in the thickness of the prepreg, and is further affected by variations in resin flow, molding pressure, and temperature in the press during molding. For example, during molding, the resin flow does not flow uniformly at the center or end of the prepreg, and generally the resin flow is greater in the peripheral part than in the central part of the press specular plate, and as a result, the peripheral part is centered. It is well known that it is thinner than the part. This variation in molding also causes a difference in flow-out, which is a factor that reduces the thickness accuracy of the prepreg as well as the thickness of the prepreg, and only increases the viscosity by adding fillers and high molecular weight resins as described above. Then the effect is insufficient.
[0006]
In the formation of epoxy resin laminates for printed circuit boards and multilayer printed circuit boards, the resin powder generated from the prepreg cutting part or the prepreg bent during handling in the heating and pressurizing step or the previous overlapping step, etc. If the powder enters between the metal mirror plate and the metal foil and is molded as it is, this resin powder acts in the same way as the etching resist in the etching process for circuit pattern preparation after circuit board molding, causing circuit pattern defects. ing.
In order to solve such problems, it is possible to prevent the generation and scattering of resin powder from the prepreg by remelting the resin powder of the prepreg where the resin powder is likely to be generated or where the resin powder is adhered. Measures have been taken for some time. However, such a method requires the problem of the performance change of the epoxy resin due to the melting method, or equipment investment and processing man-hours.
In view of the above, there is a demand for a prepreg that generates less resin powder and that has both high precision of the thickness of the substrate and excellent moldability.
[0007]
[Problems to be solved by the invention]
In order to solve the problems of reduction of resin powder generation and compatibility of plate thickness accuracy and moldability of the molded substrate with respect to the prepreg, the present invention has completed the present invention as a result of intensive studies on a method for producing the prepreg. It came. The present invention reduces the voids remaining in the gaps between the monofilaments of the prepreg, and changes the prepreg configuration to reduce the generation of resin powder and maintain good moldability while maintaining the thickness of the substrate after molding. Accuracy can be improved.
[0008]
[Means for Solving the Problems]
The present invention comprises (1) a step of impregnating a glass fiber substrate with N, N-dimethylformamide , followed by (2) impregnating the glass fiber substrate with a thermosetting resin varnish, followed by drying and curing at 140 to 170 ° C. The present invention relates to a method for producing a prepreg characterized by comprising a step, and then (3) a step of applying and drying a thermosetting resin varnish on one side or both sides.
In step (1), the time for impregnating the organic solvent to the glass fiber substrate is arbitrarily favored is from 30 to 420 seconds.
In step (2), it is preferred adhered amount of the thermosetting resin is 40 to 100 parts by weight per 100 parts by weight of material glass fiber base.
In the step (3), the amount of the thermosetting resin attached is preferably 5 to 250 parts by weight with respect to 100 parts by weight of the thermosetting resin attached in the step (2).
Furthermore, this invention relates to the manufacturing method of the laminated board characterized by heat-molding 1 sheet or 2 sheets or more of the prepreg obtained in this way.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the step (1) of impregnating the glass fiber base material with the organic solvent is carried out to replace the voids in the glass cloth with the solvent. The organic solvent is not particularly limited, but the solvent having a high vapor pressure evaporates until the impregnation of the thermosetting resin, which is the next step (2), and a gap between monofilaments is generated, causing a so-called strand void. Since the meaning of impregnating the glass fiber substrate with the solvent becomes small, the vapor pressure is preferably 250 mmHg or less in the temperature range of 20 to 50 ° C. In order to obtain a stable product in production, it is more preferable to use N, N-dimethylformamide or the like having a low vapor pressure.
In the impregnation with the solvent, in order for the solvent to sufficiently permeate between the fibers of the base material, the base material is wetted by immersing in the solvent tank or applying the solvent for 30 to 420 seconds. If it is less than 30 seconds, the base material is not sufficiently impregnated and causes voids. Moreover, even if it exceeds 420 seconds, the further effect of impregnation improvement is not seen, but it becomes productivity fall. More preferably, it is 150 to 300 seconds in consideration of the impregnation into the substrate details and the efficiency. In order to efficiently impregnate and shorten the impregnation time, ultrasonic waves, high pressure showers, and the like may be used. It is also an effective means to open the glass fiber substrate. The adhesion amount of the solvent may be an amount that completely fills the space between the monofilaments of the base material, and the varnish viscosity is reduced by bringing the solvent into the thermosetting resin varnish in the next step. In order to prevent the prepreg and the laminate from being dispersed in quality, it is preferable to remove excess solvent with a squeeze roll or the like after the step (1).
[0010]
In the step (2) of impregnating a glass fiber base material with a thermosetting resin varnish and drying and curing, the thermosetting resin is selected from one or more of epoxy resin, thermosetting polyimide resin, cyanate resin and the like. It is a thing and additives, such as a hardening | curing agent, a hardening catalyst, a filler, surfactant, and a silane coupling agent, can be added as needed. Normally, this thermosetting resin is used in the form of a varnish dissolved in a solvent, but it is desirable that the solvent used exhibits good solubility in the resin. Moreover, you may use a poor solvent in the range which does not exert a bad influence. When the resin can be pulverized by pulverization or the like, it can be applied in powder form.
The amount of resin deposited in this step needs to be a resin amount that does not generate voids, and is preferably 40 to 100 parts by weight with respect to 100 parts by weight of the glass fiber substrate. If the amount is less than 40 parts by weight, the absolute amount of resin sufficient to sufficiently fill the gap between the monofilaments of the glass fiber substrate is insufficient. If the amount is more than 100 parts by weight, the amount of resin is too large and molding is not easy. Various properties of the plate are degraded.
[0011]
The drying conditions in step (2) are determined by the boiling point of the solvent used in step (1) and the solvent used to dissolve the resin used in step (2). In the solvent used in the present invention, 100 to 200 ° C. is used. Is appropriate. If the temperature is lower than 100 ° C., it may take much time for the solvent to evaporate, or the solvent may remain. If the temperature exceeds 200 ° C., voids may occur due to bumping of the solvent. When dried at a temperature lower than the boiling point, a large amount of solvent remains, and the reliability of the prepreg and the laminate is greatly reduced. When dried at a temperature higher than a certain temperature, the solvent bumps and a void is generated. . For example, when N, N-dimethylformamide is used, the boiling point is 153 ° C., and therefore the optimum drying temperature is 140 to 170 ° C. In addition, when drying with hot air is performed, if bumping does not occur due to the wind speed, the temperature can be increased to improve productivity.
[0012]
The object of the present invention is to obtain a prepreg and a laminate having reduced thickness of resin powder, excellent thickness accuracy and excellent moldability. For this purpose, the thermosetting resin-impregnated substrate obtained above is used. Each resin layer (hereinafter referred to as “a layer”) and the resin layer (hereinafter referred to as “b layer”) formed on the outer side of this a layer in the next step (3) were studied, and each layer was examined. Designed to show different functions. That is, the a layer has a function of improving the plate thickness accuracy by proceeding with curing so that no flow-out occurs during molding and no resin powder is generated, and the b layer is bonded to a copper foil or the like. And a function of embedding between inner layer circuits. The thickness accuracy of the a layer can be controlled to a thickness accuracy at the time of application, that is, an accuracy within several percent, and the resin curing degree can be controlled by the drying conditions (drying temperature, drying time) after the secondary impregnation. By setting the resin curing to a C-stage or a state close thereto, it does not flow out during molding by a press or the like, and the thickness accuracy after molding is maintained well. Moreover, generation | occurrence | production of the resin powder from a layer in the cutting | disconnection of a prepreg etc. is prevented.
The conventional prepreg does not have a layer corresponding to the a layer of the prepreg of the present invention, all the resins have the same degree of curing, and give priority to impregnation and circuit embedding over the plate thickness accuracy. The viscosity decreased. For this reason, a flow-out occurs during molding, which has been a factor in reducing the plate thickness accuracy. For this reason, the resin content has been made highly viscous by adding fillers and polymer components for the purpose of improving plate thickness accuracy. Led to worsening.
[0013]
Next, in step (3), a thermosetting resin varnish is applied to one side or both sides of the thermosetting resin-impregnated base material and dried. That is, the b layer is formed outside the a layer. The b layer is mainly intended for embedding between circuits and adhesion with other layers. This is because the a-layer is hardened by resin and has low fluidity and low adhesion.
Unlike the a layer, the b layer has a large influence on the thickness accuracy of the substrate because part of the resin flows out during molding with a press or roll. Here, the ratio of the a layer that maintains good plate thickness accuracy and the b layer that has poor plate thickness accuracy is important. If the ratio of the a layer is large, the plate thickness accuracy is improved, but circuit embedding and adhesiveness are deteriorated. On the other hand, if the ratio of the b layer is large, the plate thickness accuracy after molding becomes poor. Further, the b layer has a great influence on the generation of resin powder in prepreg cutting or the like. Here, the ratio between the amount of resin in the a layer where the generation of the resin powder is extremely small and the amount of resin in the b layer where the resin powder is easily generated is important. If the proportion of the resin amount in the a layer is large, the generation of resin powder is reduced, but the embedding and adhesion between circuits are deteriorated. Conversely, if the proportion of the resin amount in the b layer is large, the generation of resin powder increases. Since the b layer needs to be embedded between circuits by a press or a roll, the resin must be cured in a B-stage state.
However, since the prepreg of the present invention has the a layer, the resin component in which the flow-out occurs is only the b layer, the absolute amount of the flowing resin is smaller than that of the conventional prepreg, and the generation of the resin powder is small. Therefore, even if the b layer is a low-viscosity resin, the flow-out of the entire prepreg is smaller than the conventional one. Furthermore, since the absolute amount of resin that flows is small, the influence of variations in pressure and temperature during molding on the fluidity of the resin is reduced, so the prepreg according to the present invention is excellent in both plate thickness accuracy and moldability, In addition, the generation of resin powder is reduced.
[0014]
As a result of the study by the present inventors, it has been found that if the ratio of the resin of the b layer / a layer is in the range of 0.05 to 2.5, the thickness accuracy and the embedding in the circuit are improved. If the ratio of b layer / a layer is more than 2.5, the plate thickness accuracy after molding is about the same as the conventional one, the amount of resin powder generated is the same as the conventional one, and the improvement effect is insufficient. If it is less than 0.05, the resin flow is insufficient, and the prepreg and copper foil are not sufficiently bonded to each other at the time of molding. In the case of multilayer molding, it is not completely embedded between the circuits, and voids remain or moisture-absorbing solder. Occurrence of mistling and blistering in the test.
The thermosetting resin that can be used in the b layer is a thermosetting resin such as an epoxy resin, a thermosetting polyimide, or a cyanate resin as in the a layer, and two or more types can be used in combination. In order to further reduce the generation of the resin powder, the resin of the b layer preferably contains a high molecular resin such as a terminal bifunctional linear epoxy resin having an epoxy equivalent of about 900 to 4000. If necessary, additives such as a curing agent, a curing catalyst, a filler, a surfactant, and a silane coupling agent can be added. Moreover, even if it is resin of the same composition as a layer, resin of a different composition may be sufficient. Usually, it is used in the form of a varnish dissolved in a solvent, but it is desirable that the solvent used exhibits good solubility in the resin. Moreover, a poor solvent can also be used in the range which does not have a bad influence. When the resin can be pulverized by pulverization or the like, it can be applied to the a layer as a powder.
[0015]
The prepreg obtained by the present invention can be cut into a suitable length, and superimposed on a metal foil or an inner layer circuit board and heated and pressed to obtain a circuit board or a multilayer circuit board. Moreover, a prepreg is wound up with a long length, and is continuously laminated on a metal foil such as a copper foil, an aluminum foil or a nickel foil, or an inner layer circuit board, whereby a circuit board or a multilayer circuit board can be obtained.
[0016]
【Example】
Hereinafter, the present invention will be described with reference to examples and comparative examples.
[0017]
Example 1
<Preparation of epoxy resin varnish>
70 parts by weight of a bisphenol A type epoxy resin having an epoxy equivalent of about 450 and 30 parts by weight of a phenol novolac type epoxy resin having an epoxy equivalent of about 190 were dissolved in 50 parts by weight of methyl ethyl ketone. To this solution, a solution prepared by dissolving 3 parts by weight of dicyandiamide and 0.15 parts by weight of 2-phenyl-4-methylimidazole in 20 parts by weight of dimethylformamide was added and mixed with stirring. In this way, an epoxy resin varnish was prepared.
[0018]
<Create prepreg>
Glass cloth (thickness: 0.10 mm) was immersed in N, N-dimethylformamide for 200 seconds, and excess solvent was removed with a squeeze roll. Subsequently, the glass cloth was impregnated with the epoxy resin varnish prepared as described above so that the resin solid content was 65 parts by weight with respect to 100 parts by weight of the glass cloth, and dried in a drying furnace at 170 ° C. for 3 minutes. An epoxy resin-impregnated crow cloth in which a layer was formed was prepared. Next, the epoxy resin varnish was applied to the epoxy resin impregnated glass cloth so that the resin solid content was 45 parts by weight with respect to 100 parts by weight of the glass cloth, and dried in a drying furnace at 170 ° C. for 1.5 minutes. , B layer was created. The ratio of the resin of a layer and b layer is about 0.7 in b layer / a layer. Thus, the prepreg which consists of a layer and b layer was created.
[0019]
Reference example 1
A glass cloth (thickness: 0.10 mm) was immersed in methyl ethyl ketone for 200 seconds, and excess solvent was removed with a drawing roll. Subsequently, the epoxy resin varnish prepared as described above was impregnated so that the resin solid content was 65 parts by weight with respect to 100 parts by weight of the glass cloth, and dried in a drying furnace at 110 ° C. for 30 minutes. The formed epoxy resin impregnated glass cloth was produced. Thereafter, a prepreg composed of a layer and b layer was prepared in the same manner as in Example 1.
[0020]
Comparative Example 1
After adjusting the epoxy resin varnish in the same manner as in Example 1, the glass cloth (thickness: 0.10 mm) was impregnated only once, and the resin solid content was 110 parts by weight with respect to 100 parts by weight of the glass cloth. I did it. Subsequently, it was dried at 170 ° C. for 1.5 minutes to prepare a prepreg.
[0021]
Comparative Example 2
Except that the step of impregnating glass cloth with N, N-dimethylformamide was omitted, the method of Example 1 was performed to prepare a prepreg composed of a layer and b layer.
[0022]
Comparative Example 3
Except that the step of impregnating the glass cloth with methyl ethyl ketone was omitted, the method of Reference Example 1 was carried out to prepare a prepreg composed of a layer and b layer.
[0023]
Using the prepreg obtained as described above, a double-sided copper-clad laminate and a four-layer circuit board were prepared by the following method, and the characteristics were evaluated.
<Evaluation of amount of resin powder generated from prepreg>
The prepreg was cut into 100 mm × 100 mm with a cutter, 10 sheets were stacked, dropped several times from a certain height, and the amount of resin powder generated was measured.
<Formation of laminated plate>
Copper foil having a thickness of 18 μm was stacked on the top and bottom of one prepreg. Next, heat-pressure molding was performed at a pressure of 40 kgf / cm ² and a temperature of 170 ° C. for 60 minutes to obtain a double-sided copper-clad laminate having an insulating layer thickness of 0.1 mm.
<Evaluation of laminated board>
The plate thickness accuracy and formability were measured on a double-sided copper clad laminate having a size of 500 mm × 500 mm, from which the copper foil was removed by etching.
For the plate thickness accuracy, 36 measurement points were set in a grid pattern, and the thickness was measured. The average value and range were obtained and used as the plate thickness accuracy.
The moldability was confirmed visually and by an optical microscope with respect to a substrate having a size of 500 mm × 500 mm, whether or not there were voids and other abnormalities.
The 18 μm copper foil peel strength was measured in accordance with JIS C 6481.
The solder heat resistance was measured by etching only one surface and cutting it to a size of 50 mm × 50 mm, and then performing moisture absorption treatment for 1 hour and 2 hours under pressure cooker conditions of 121 ° C. and 2.0 atmospheres. Subsequently, after immersion in a solder bath at 260 ° C. for 120 seconds, the evaluation of swelling and mesuring was confirmed visually and with an optical microscope.
[0024]
<Creation of 4-layer circuit board>
Oxidation treatment (blackening treatment) is applied to the surface of a copper foil (thickness 35 μm) of a double-sided copper clad laminate having a thickness of 0.8 mm as an inner layer plate. A copper foil of 18 μm was stacked, and heat-pressed for 120 minutes at a pressure of 40 kgf / cm ² and a temperature of 170 ° C. to prepare a four-layer circuit board.
<Evaluation of 4-layer circuit board>
The plate thickness accuracy was determined by setting 36 measurement points in a grid pattern on a substrate of size 500 mm × 500 mm, and measuring the thickness. The average value and range were obtained and used as the plate thickness accuracy.
The moldability was confirmed visually and by an optical microscope with respect to a substrate having a size of 500 mm × 500 mm to confirm whether or not there were any voids and other abnormalities.
For the inner layer peel strength, the peel strength at the interface between the inner layer blackened copper foil and the prepreg of this substrate was measured according to JIS C 6481.
The solder heat resistance was measured by etching only one surface and cutting it to a size of 50 mm × 50 mm, and then performing moisture absorption treatment for 1 hour and 2 hours under pressure cooker conditions of 121 ° C. and 2.0 atmospheres. Subsequently, after being immersed in a 260 ° C. solder bath for 2 minutes, the evaluation of swelling and mesuring was confirmed visually and with an optical microscope.
[0025]

[0026]
More resulting prepreg in Example 1 less generation of resin powder is excellent in accuracy of plate thickness, and a moldability good. Comparative Example 1 is an example of a prepreg produced by a conventional method, and the generation of resin powder is more than in the example, and the plate thickness accuracy is poor. In Comparative Examples 2 and 3, since there is no step of impregnating with an organic solvent at first, the moldability is poor, voids are generated in the laminate, and solder heat resistance is also lowered.
[0027]
【The invention's effect】
As is clear from the above results, the prepreg obtained by the method of the present invention has less generation of resin powder during cutting and the like, and maintains a good moldability while maintaining the plate thickness accuracy of the molded substrate. Can be improved.

Claims

(1) A step of impregnating a glass fiber substrate with N, N-dimethylformamide, (2) a step of impregnating a glass fiber substrate with a thermosetting resin and drying and curing at 140 to 170 ° C., then ( 3) A method for producing a prepreg comprising a step of applying and drying a thermosetting resin on one side or both sides.

The method for producing a prepreg according to claim 1, wherein the impregnation time is 30 to 420 seconds in the step (1).

The method for producing a prepreg according to claim 1 or 2, wherein, in the step (2), the adhesion amount of the thermosetting resin is 40 to 100 parts by weight with respect to 100 parts by weight of the glass fiber substrate.

The adhesion amount of the thermosetting resin in the step (3) is 5 to 250 parts by weight with respect to 100 parts by weight of the adhesion amount of the thermosetting resin in the step (2). Prepreg manufacturing method.

The method for producing a prepreg according to any one of claims 1 to 4, wherein the glass fiber substrate is subjected to a fiber opening treatment.

A method for producing a laminated board, wherein one or more of the prepregs according to any one of claims 1 to 5 are thermoformed.