JP4136695B2

JP4136695B2 - Flexible printed circuit board

Info

Publication number: JP4136695B2
Application number: JP2003032736A
Authority: JP
Inventors: 修二柏木; 祥悟稲田
Original assignee: Sumitomo Electric Printed Circuits Inc
Current assignee: Sumitomo Electric Printed Circuits Inc
Priority date: 2003-02-10
Filing date: 2003-02-10
Publication date: 2008-08-20
Anticipated expiration: 2023-02-10
Also published as: JP2004247352A

Description

【０００１】
【発明の属する技術分野】
本発明は、新規な構造を有する接続用のフレキシブルプリント基板に関するものである。
【０００２】
【従来の技術】
例えば折りたたみ式の携帯電話やＰＤＡ、ノート型パソコンなどにおいて、折りたたみのための関節部より上側の部分に配置した、液晶表示素子などを実装したメイン基板と、下側の部分に配置した、主制御回路などを実装したメイン基板とを、上記関節部を介しての折りたたみ可能な状態を維持しつつ電気的に接続するために、導体配線を備えた可とう配線部を有するフレキシブルプリント基板が使用されている。
【０００３】
また近時、とくに折りたたみ式の携帯電話やＰＤＡなどにおいては、そのさらなる小型化にともない、多層プリント基板のビルドアップ技術（例えば非特許文献１参照）を利用して、上記可とう配線部と、少なくとも一方のリジッドなメイン基板とを一体に形成した、いわゆるフレックス−リジッド基板が開発され、実用化されている。
【０００４】
【非特許文献１】
「極限の軽薄化を可能にしたビルドアップフレキシブル多層回路基板」（谷川聡、山崎博司、藤井弘文、日東技報第３９巻第１号、第４７〜５０頁、２００１年１月、日東電工株式会社発行）
【０００５】
【発明が解決しようとする課題】
しかしフレックス−リジッド基板は製造工程が複雑で生産性が低い上、メイン基板と可とう配線部のいずれか一方にでも不良が生じれば、製品の全体が不良となることから製造の歩留まりも悪く、携帯電話などのコストアップの原因となっている。
そこで、他の用途の場合と同様に携帯電話などの小型の機器類においても、可とう配線部を、メイン基板と独立したフレキシブルプリント基板として製造して、それをメイン基板と接続して使用することが検討されている。これにより、不良のないフレキシブルプリント基板とメイン基板とを組み合わせることができるため、製造の歩留まりを向上することが期待される。
【０００６】
フレキシブルプリント基板としては、例えば可とう配線部を、
・一枚のベースフィルムにて形成するとともに、その両面に導体配線を形成した、いわゆる両面板の構成としたものや、あるいは
・多層プリント基板の構成としたもの、
などが一般的に用いられる。
しかし、これら従来の構造を有する可とう配線部を備えたフレキシブルプリント基板はいずれも、フレックス−リジッド基板ほどでないものの、依然として製造工程が複雑で生産性が低いという問題がある。
【０００７】
これは、積層する層の数に応じた分だけ種々の形成工程が必要となる上、例えば両面板では一枚のベースフィルムの両面に形成した導体配線同士の接続に、また多層プリント基板では絶縁層を介して多重に積層された導体配線同士の接続に、それぞれスルーホール加工、ビアホール加工などの特殊な加工技術を必要とするためである。
また、上に述べた従来の構造を有する可とう配線部を備えたフレキシブルプリント基板はいずれも、屈曲時に、導体配線に加わる歪み応力が大きいため可とう配線部の耐屈曲性に限界がある。そして、可とう配線部を繰り返し屈曲させた際に導体配線が断線するに至る屈曲回数を現状よりもさらに延長して、その耐屈曲性を現在のレベル以上に改善するのが難しいという問題もある。
【０００８】
本発明の目的は、従来に比べて製造工程が簡単で生産性が高く、しかも製造の歩留まりにも優れる上、可とう配線部の屈曲時に、導体配線に加わる歪み応力を低減できるため、これまで以上に耐屈曲性にも優れた、新規なフレキシブルプリント基板を提供することにある。
【０００９】
【課題を解決するための手段および発明の効果】
請求項１記載の発明は、二つの回路部材間を接続するための導体配線を備えた可とう配線部を含むフレキシブルプリント基板であって、
(I) 折目線に沿って二つ折り可能に形成してあるとともに、この折目線を境とする一方の領域の、二つ折りした際に内側となる面に、可とう配線部の導体配線を一方の回路部材上の回路と接続するための端子を配列した端子部を設け、かつ他方の領域の、二つ折りした際に端子部と重なる位置に、二つ折りした状態で端子部を外部に露出させるための開口を形成してある第１接続部と、
(II) 上記第１接続部を折目線に沿って二つ折りした際に互いに重なるように、当該第１接続部の、折目線をはさんで対称位置から、折目線を軸として互いに略線対称の平面形状となるように突出形成してあるとともに、第１接続部を二つ折りした際にそれぞれ内側となる面にのみ導体配線を形成してあり、関節部の軸の周囲を一周するように巻き付けて使用される可とう配線部を構成する、前記巻き付けた際に、巻き付けの外側となる方が内側となる方よりも長めに形成された一対の可とう配線部材と、
(III) 両可とう配線部材の各々先端部に形成してあるとともに、第１接続部を二つ折りした際にそれぞれ内側となる面に、可とう配線部材の導体配線を他方の回路部材の表裏両面に形成した回路とそれぞれ接続するための端子を配列した端子部を設けてある第２および第３接続部とを、
１枚のベースフィルムにて一体に形成したことを特徴とするフレキシブルプリント基板である。
【００１０】
請求項１の構成では、導体配線や端子となる金属の薄膜をいずれも、上記各部を構成する１枚のベースフィルムの片面、すなわち第１接続部を折目線に沿って二つ折りした際に内側となる面にのみ形成するだけで、フレキシブルプリント基板を製造することができる。つまり、いわゆる片面板の製造工程によって、上記各部を備えたフレキシブルプリント基板を製造できる。
このため請求項１の構成によれば、従来に比べて製造工程が簡単で生産性が高く、しかも製造の歩留まりにも優れたフレキシブルプリント基板を提供することができる。
【００１１】
また請求項1の構成では、一対の可とう配線部材を単に重ね合わせるだけで可とう配線部を形成してあり、両可とう配線部材は互いに自由動が可能な状態を維持しているため、それぞれの可とう配線部材が片面板の構造であることと相まって、屈曲時に導体配線に加わる歪み応力を低減することができる。
したがって請求項1の構成によれば、現状よりも可とう配線部の耐屈曲性をさらに向上したフレキシブルプリント基板を提供することもできる。
【００１２】
【発明の実施の形態】
図１は、本発明のフレキシブルプリント基板の、実施の形態の一例を示す平面図である。
図に見るようにこの例のフレキシブルプリント基板ＦＰは、
(i) 折目線ＢＬに沿って二つ折り可能に形成してある略矩形状の第１接続部１と、
(ii) 当該第１接続部１の、折目線ＢＬをはさんで対称位置からそれぞれ上下方向に突出形成してある一対の可とう配線部材４１、４２と、
(iii) 両可とう配線部材４１、４２の各々先端部に形成してある、それぞれ略矩形状の第２および第３接続部２、３とを、
１枚のベースフィルムにて一体に形成したものである。
【００１３】
このうち第１接続部１の、折目線ＢＬを境として図において上側の領域１１の、二つ折りした際に内側となる面（図に示した側の面）には、複数の端子を直線状に配列した２列の端子列Ｔ１ａ、Ｔ１ｂからなる端子部Ｔ１を設けてある。
また折目線ＢＬを境として下側の領域１２の、二つ折りした際に端子部Ｔ１と重なる位置には、二つ折りにした状態で当該端子部Ｔ１を外部に露出させる〔図２(a)参照〕ための開口１２ａを形成してある。
【００１４】
そしてこの例では端子部Ｔ１の、上記２列の端子列Ｔ１ａ、Ｔ１ｂ上に、図２(c)および図３に示すように開口１２ａを通過しうるサイズのコネクタＣ１を実装して、このコネクタＣ１と、回路部材としての一方のメイン基板Ｍ１上に実装したコネクタＣ２とを図２(c)中に白抜きの矢印で示すように互いに接続することで、端子部Ｔ１を構成する各端子を、メイン基板Ｍ１上の、個々の回路と電気的に接続可能としてある。
【００１５】
コネクタＣ１の、端子部Ｔ１への実装には、ハンダ付けや、あるいは異方導電膜をはさんでの圧着などの、従来公知の種々の方法を採用することができる。
また第２接続部２、および第３接続部３の、ともに二つ折りした際に内側となる面（図１に示した側の面）には、それぞれ複数の端子を平行に配列して端子部Ｔ２、Ｔ３を形成してある。
そしてこの例では、図２(b)に示すように、回路部材としての他方のメイン基板Ｍ２の表裏両面に形成した回路（図示せず）と、上記二つの接続部２、３のそれぞれ内側面に設けた端子部Ｔ２、Ｔ３との間に、接着性または粘着性を有する異方導電膜ＯＣ、ＯＣを挿入した状態で、図中に黒矢印で示すように二つの接続部２、３によってメイン基板Ｍ２を表裏両面からはさんで圧着することで、
・異方導電膜ＯＣ、ＯＣの接着性または粘着性によって、二つの接続部２、３を、メイン基板Ｍ２の表裏両面に機械的に接着、固定するとともに、
・当該異方導電膜ＯＣ、ＯＣの、膜の厚み方向の導電抵抗が低く、かつ面方向の導電抵抗が高い異方導電特性によって、端子部Ｔ２、Ｔ３を形成する個々の端子を、隣接する端子と電気的に絶縁した状態で、異方導電膜ＯＣ、ＯＣをはさんで対応するメイン基板Ｍ２の表裏両面の、個々の回路と電気的に接続可能としてある。
【００１６】
上側の可とう配線部材４１は、図１に示すように、第１接続部１のうち上側の領域１１の上辺から、折目線ＢＬと直交させて上方に延設した、一定幅を有する直線部４１ａと、第２接続部２の下辺から、上記直線部４１ａと平行に下方に延設した、同じ一定幅を有する直線部４１ｂとを、両直線部４１ａ、４１ｂの幅よりも大きく、幅方向に互いにずらして配置するとともに、両直線部４１ａ、４１ｂ間を略Ｓ字状の曲線部４１ｃでつないだ平面形状に形成してある。
【００１７】
また下側の可とう配線部材４２は、上記上側の可とう配線部材４１と、前述したように第１接続部１の、折目線ＢＬをはさんで対称位置から、折目線ＢＬを軸として略線対称の平面形状となるように突出形成してある。
すなわち可とう配線部材４２は、第１接続部１のうち下側の領域１２の下辺から、折目線ＢＬと直交させて下方に延設した、直線部４１ａ、４１ｂと同じ一定幅を有する直線部４２ａと、第３接続部３の上辺から、上記直線部４２ａと平行に上方に延設した、同じ一定幅を有する直線部４２ｂとを、直線部４１ａ、４１ｂと同方向に、同寸法ずらして配置するとともに、両直線部４２ａ、４２ｂ間を略Ｓ字状の曲線部４２ｃでつないだ平面形状に形成してある。
【００１８】
また両可とう配線部材４１、４２の、ともに二つ折りした際に内側となる面（図１に示した側の面）には、それぞれ二つのメイン基板Ｍ１、Ｍ２間を電気的に接続するための導体配線５１、５２を形成してある。
このうち導体配線５１は、銅箔等の金属薄膜にて、可とう配線部材４１上に形成した本配線部５１ａを、第１接続部１のうち上側の領域１１に形成した接続配線部５１ｂによって、端子部Ｔ１のうち端子列Ｔ１ａと接続するとともに、第２接続部２に形成した接続配線部５１ｃによって端子部Ｔ２と接続した平面形状に一体に形成してある。
【００１９】
また導体配線５２は、同様に銅箔等の金属薄膜にて、可とう配線部材４２上に形成した本配線部５２ａを、第１接続部のうち下側の領域１２に形成した、開口１２ａを回避して二つに分岐し、さらに折目線ＢＬの部分では二つ折りを容易にするために四つに分岐して上側の領域１１に達する接続配線部５２ｂによって、端子部Ｔ１のうち端子列Ｔ１ｂと接続するとともに、第３接続部３に形成した接続配線部５２ｃによって端子部Ｔ３と接続した平面形状に一体に形成してある。
【００２０】
なお図では、両導体配線５１、５２をいずれも一枚の平板状に略記してあるが、実際には、導体配線５１は、端子列Ｔ１ａの個々の端子と、端子部Ｔ２の個々の端子とを、例えば１対１で電気的に接続するための、複数の微細配線の集合体である。同様に導体配線５２は、端子列Ｔ１ｂの個々の端子と、端子部Ｔ３の個々の端子とを、例えば１対１で電気的に接続するための、複数の微細配線の集合体である。
【００２１】
それぞれの可とう配線部材４１、４２において導体配線５１、５２を形成する微細配線の数は、両可とう配線部材４１、４２がともに片面板の構成であるため、前述した従来の、両面板の構成を有するものや、あるいは多層プリント基板の構成を有するものに比べて少ない。
しかし、２枚の可とう配線部材４１、４２を重ねて可とう配線部４を形成するため、スルーホール部などを設けるスペースが不要で配線密度を向上できることと相まって、当該可とう配線部４上に形成しうる微細配線の総数は、同寸法の、両面板の構成を有するものと同等またはそれ以上とすることができる。
【００２２】
可とう配線部４は、２枚の可とう配線部材４１、４２を、第１接続部１を折目線ＢＬで二つ折りして互いに重ね合わせることによって、図２(a)に示すように、一定幅を有する直線部４ａ（直線部４１ａ、４２ａの重なった部分）と、同じ一定幅を有する直線部４ｂ（直線部４１ｂ、４２ｂの重なった部分）とを、略Ｓ字状の曲線部４ｃ（曲線部４１ｃ、４２ｃの重なった部分）でつないだ平面形状に形成される。
【００２３】
かかる平面形状を有する可とう配線部４によれば、例えば図３に示すように両直線部４ａ、４ｂを、曲線部４ｃをはさむことによって幅方向にずらして互いに支障しない状態としながら、折りたたみ式の携帯電話などの、関節部の軸ＡＸ（同図中に一点鎖線で示す）の周囲を一周するように巻き付けることができる。
このため、関節部の上下に配置した二つのメイン基板を、上記軸ＡＸを中心とした回動による、関節部を介しての折りたたみが可能な状態を維持しつつ、導体配線５１、５２によって電気的に接続することができる。
【００２４】
なお、一対の可とう配線部材４１、４２は、巻き付けの外側となる可とう配線部材（この場合は可とう配線部材４１）を、内側となる可とう配線部材（この場合は可とう配線部材４２）より少し長めに形成する必要がある。これにより、巻き付けの内外の円周差を吸収して、両者を重ねた状態で、よりスムースに軸ＡＸに巻き付けることが可能となる。また、可とう配線部４の耐屈曲性をさらに向上することも可能となる。
【００２５】
上記各部からなるこの例のフレキシブルプリント基板ＦＰにおいては、以上で説明したように第１接続部１、一対の可とう配線部材４１、４２、第２接続部２、および第３接続部３の、いずれも折目線ＢＬに沿って二つ折りした際に内側となる同じ側の面にのみ、端子部Ｔ１〜Ｔ３、および導体配線５１、５２を形成してある。
【００２６】
したがってかかるフレキシブルプリント基板ＦＰは、いわゆる片面板の製造工程によって製造することができるため、従来に比べて製造工程が簡単で生産性が高く、しかも製造の歩留まりにも優れたものとなる。
また、この例のフレキシブルプリント基板ＦＰは、一対の可とう配線部材４１、４２を、それぞれ折目線ＢＬと直交させて上下方向に延設することによって、その全体を、図１に見るようにほぼ一直線状に形成してある。
【００２７】
このため一枚の定尺のベースフィルム上に、フレキシブルプリント基板ＦＰとなる領域を複数、配置して、各領域内にそれぞれ端子部Ｔ１〜Ｔ３、導体配線５１、５２を形成したのち、第１接続部１、可とう配線部材４１、４２、第２および第３接続部２、３に対応する平面形状に抜き加工して複数のフレキシブルプリント基板ＦＰを製造する際の、上記領域の間隔をできるだけ詰めて配置することができる。
【００２８】
したがって、一枚の定尺のベースフィルムから製造できるフレキシブルプリント基板ＦＰの個数を増やして、その生産性をさらに向上することも可能となる。また、可とう配線部４となる二つの可とう配線部材４１、４２は、第１接続部１を折目線ＢＬに沿って二つ折りした際に単に重ね合わせてあるだけであり、重ね合わせた後も互いに自由動が可能な状態を維持している。このため、それぞれの可とう配線部材４１、４２が前記のように片面板の構造であることと相まって、屈曲時に導体配線５１、５２に加わる歪み応力を低減することができる。
【００２９】
したがってフレキシブルプリント基板ＦＰの、可とう配線部４の耐屈曲性を、現状よりさらに向上することもできる。
フレキシブルプリント基板ＦＰのもとになるベースフィルムとしては、柔軟な樹脂のフィルムを使用する。とくに寸法安定性、耐熱性、耐久性、柔軟性等を考慮してポリイミドフィルムが好ましい。
また、端子部Ｔ１〜Ｔ３や導体配線５１、５２は、前記のように銅箔等の金属薄膜にて形成する。形成方法としては、サブトラクティブ法やアディティブ法などの、従来公知の種々の方法を採用することができる。
【００３０】
また例えばフレキシブルプリント基板ＦＰの、折目線ＢＬをはさんで図１において上側の領域（領域１１、可とう配線部材４１、および第２接続部２）の表面には、図示していないが、端子部Ｔ１、Ｔ２を露出させつつ導体配線５１を被覆するべく、樹脂フィルムなどからなるカバーレイを積層するのが好ましい。これにより、フレキシブルプリント基板ＦＰを二つ折りした際に導体配線５１、５２が接触して短絡等を生じるのを防止することができる。また、二つ折りして重ねた可とう配線部材４１、４２間の滑りを良くして、可とう配線部４の耐屈曲性をさらに向上することもできる。
【００３１】
なおカバーレイは、フレキシブルプリント基板ＦＰの、折目線ＢＬをはさんで図１において下側の領域（領域１２、可とう配線部材４２、および第３接続部３）の表面に、端子部Ｔ３を露出させつつ導体配線５２を被覆するべく積層してもよい。また、上記両方の領域にそれぞれカバーレイを積層してもよい。
また、とくに前記のように端子部Ｔ１上にコネクタＣ１を実装する第１接続部１には、補強のために、樹脂フィルムなどからなる補強板を積層するのが好ましい。補強板は、第１接続部１を折目線ＢＬに沿って二つ折りした状態の平面形状と同等程度の大きさと形状に形成したものを、第１接続部１のうち端子部Ｔ１を形成した上側の領域１１の裏面に積層すればよい。
【００３２】
上記カバーレイや補強板のもとになる樹脂フィルムとしては、それぞれ前記と同じ理由で、ポリイミドフィルムが好ましい。
またサブトラクティブ法などにおいて、端子部Ｔ１〜Ｔ３や導体配線５１、５２のもとになる銅箔等の金属箔をベースフィルムの表面に積層、接着したり、あるいはカバーレイや補強板となる樹脂フィルムを積層、接着したりするためには接着剤を用いる。かかる接着剤としては、各層の前記特性を損なわないために、硬化性樹脂系の接着剤が好ましく、とくにエポキシ樹脂系の接着剤が好ましい。
【００３３】
【実施例】
実施例１
ベースフィルムとしての、厚み２５μｍのポリイミドフィルムの片面に、厚み１０μｍのエポキシ樹脂系の接着剤層を介して、厚み１８μｍの銅箔を積層した片面板を用いて、サブトラクティブ法によって銅箔をパターン形成して、上記ベースフィルムの片面に、図１に示す平面形状を有する端子部Ｔ１〜Ｔ３、導体配線５１、５２を形成した。
【００３４】
次に上記ベースフィルムの、折目線ＢＬより上側に対応する領域に、端子部Ｔ１、Ｔ２を露出させるための通孔を有する厚み２５μｍのポリイミドフィルムを、厚み２０μｍのエポキシ樹脂系の接着剤層を介して積層、接着して導体配線５１を被覆するカバーレイを形成したのち打ち抜き加工して、図１に示す平面形状を有するフレキシブルプリント基板ＦＰを製造した。
なお一対の可とう配線部材４１、４２は、巻き付けの外側となる可とう配線部材４１の長さを、内側となる可とう配線部材４２の長さより僅かに長めに形成した。
【００３５】
比較例１
ベースフィルムとしての、厚み２５μｍのポリイミドフィルムの両面に、それぞれ厚み１０μｍのエポキシ樹脂系の接着剤層を介して、厚み１８μｍの銅箔を積層した両面板を用いて、サブトラクティブ法によって銅箔をパターン形成して、上記ベースフィルムの一方の面には導体配線５１と同じ寸法、形状の導体配線を、また他方の面には導体配線５２と同じ寸法、形状の導体配線を、それぞれの形成位置がベースフィルムの表裏で一致するように位置合わせしながら形成した。
【００３６】
次に上記ベースフィルムの両面に、それぞれ厚み２５μｍのポリイミドフィルムを、厚み３０μｍのエポキシ樹脂系の接着剤層を介して積層、接着して導体配線５１、５２を被覆するカバーレイを形成したのち、図１の、折目線ＢＬより上側と同形状に打ち抜き加工して、両面板の構造を有する比較例１のフレキシブルプリント基板を製造した。
耐屈曲性試験
上記実施例１で製造したフレキシブルプリント基板ＦＰは、折目線ＢＬに沿って二つ折りし、次いで可とう配線部４を、図３および図４(a)に示すように軸ＡＸの周囲を一周するように巻き付けた状態で、第１接続部１を試験機の一方のクランプで保持するとともに、互いに重ね合わされた第２および第３接続部２、３を他方のクランプで保持した。
【００３７】
また比較例１で製造したフレキシブルプリント基板は、同様に可とう配線部を、軸ＡＸの周囲を一周するように巻き付けた状態で、一方の接続部を試験機の一方のクランプで保持するとともに、他方の接続部を他方のクランプで保持した。そして一方のクランプを固定した状態で、他方のクランプを、軸ＡＸを中心として、図４(a)に示す「開」状態と、図４(b)に示す「閉」状態との間で１８０°の回転角度で連続的に往復回転させることによって、フレキシブルプリント基板ＦＰの可とう配線部４を繰り返し屈曲させて、導体配線が断線するに至った屈曲回数を計数した。
【００３８】
結果を表１に示す。
【００３９】
【表１】

【００４０】
表より、本発明の構成を有する実施例１のフレキシブルプリント配線板は、従来の、両面板の構成を有する比較例１のものに比べて、導体配線が破断するに至る屈曲回数をほぼ２倍に増加させて、耐屈曲性を著しく改善できることが確認された。
【図面の簡単な説明】
【図１】本発明のフレキシブルプリント基板の、実施の形態の一例を示す平面図である。
【図２】同図(a)は、上記例のフレキシブルプリント基板を第１接続部の折目線に沿って二つ折りした状態を示す平面図、同図(b)は、上記状態のフレキシブルプリント基板の、第２接続部と第３接続部の間に他方のメイン基板をはさんで圧着した状態を示す断面図、同図(c)は、上記状態のフレキシブルプリント基板の、二つ折りした第１接続部にコネクタを実装して、一方のメイン基板に実装したコネクタと接続する直前の状態を示す断面図である。
【図３】上記例のフレキシブルプリント基板を二つ折りして、第２接続部と第３接続部の間に他方のメイン基板をはさんで圧着し、かつ第１接続部にコネクタを実装するとともに、折りたたみ式の携帯電話などの、関節部の軸の周囲を一周するように巻き付けた状態を示す平面図である。
【図４】本発明の実施例、比較例で製造したフレキシブルプリント基板の耐屈曲性を評価すべく、当該フレキシブルプリント基板を、軸の周囲を一周するように巻き付けて繰り返し屈曲させている途中の状態を示す図であって、同図(a)は「開」状態を示す図、同図(b)は「閉」状態を示す図である。
【符号の説明】
ＦＰフレキシブルプリント基板
ＢＬ折目線
１第１接続部
１１、１２領域
１２ａ開口
２第２接続部
３第３接続部
４可とう配線部
４１、４２可とう配線部材
５１、５２導体配線
Ｔ１〜Ｔ３端子部
Ｍ１、Ｍ２メイン基板（回路部材）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flexible printed circuit board for connection having a novel structure.
[0002]
[Prior art]
For example, in a foldable mobile phone, PDA, notebook computer, etc., a main board with a liquid crystal display element, etc., placed on the upper part of the joint for folding, and a main control, placed on the lower part. A flexible printed circuit board having a flexible wiring part provided with a conductor wiring is used to electrically connect a main board mounted with a circuit or the like while maintaining a foldable state through the joint part. ing.
[0003]
Recently, particularly in folding mobile phones and PDAs, with the further miniaturization, using the multilayer printed circuit board build-up technology (see, for example, Non-Patent Document 1), the flexible wiring section, A so-called flex-rigid substrate in which at least one rigid main substrate is integrally formed has been developed and put into practical use.
[0004]
[Non-Patent Document 1]
“Build-up flexible multi-layer circuit board that enables extreme lightening” (Satoshi Tanikawa, Hiroshi Yamazaki, Hirofumi Fujii, Nitto Giho, Vol. 39, No. 1, pp. 47-50, January 2001, Nitto Denko Corporation Company issue)
[0005]
[Problems to be solved by the invention]
However, the flex-rigid board has a complicated manufacturing process and low productivity, and if a defect occurs in either the main board or the flexible wiring section, the entire product becomes defective, resulting in poor manufacturing yield. This is a cause of cost increase of mobile phones.
Therefore, as in other applications, even in small devices such as mobile phones, the flexible wiring part is manufactured as a flexible printed board independent of the main board and used by connecting it to the main board. It is being considered. As a result, a flexible printed circuit board free from defects and the main circuit board can be combined, and it is expected to improve the manufacturing yield.
[0006]
As a flexible printed circuit board, for example, a flexible wiring part,
・ A double-sided board with a single base film and conductor wiring on both sides, or a multilayer printed circuit board,
Are generally used.
However, all of the flexible printed boards having the flexible wiring portion having the conventional structure are not as flexible as the flex-rigid board, but still have a problem that the manufacturing process is complicated and the productivity is low.
[0007]
This requires various formation processes according to the number of layers to be laminated. For example, in the case of a double-sided board, it is used to connect conductor wirings formed on both sides of a single base film. This is because a special processing technique such as through-hole processing or via-hole processing is required to connect conductor wirings stacked in multiple layers through layers.
In addition, any flexible printed circuit board having a flexible wiring portion having the conventional structure described above has a limit on the bending resistance of the flexible wiring portion because a large strain stress is applied to the conductor wiring at the time of bending. Further, there is a problem that it is difficult to further improve the bending resistance beyond the current level by further extending the number of times that the conductor wiring is disconnected when the flexible wiring portion is repeatedly bent. .
[0008]
The purpose of the present invention is that the manufacturing process is simpler and more productive than the conventional one, and the manufacturing yield is excellent, and the strain stress applied to the conductor wiring can be reduced when the flexible wiring portion is bent. It is an object of the present invention to provide a novel flexible printed circuit board that is excellent in bending resistance.
[0009]
[Means for Solving the Problems and Effects of the Invention]
The invention according to claim 1 is a flexible printed circuit board including a flexible wiring portion provided with a conductor wiring for connecting between two circuit members,
(I) It is formed so that it can be folded in two along the crease line, and one side of the conductor wiring of the flexible wiring section is placed on the inner surface when folded in half in one area with this crease line as a boundary. A terminal part in which terminals for connecting to a circuit on the circuit member of the above are arranged is provided, and the terminal part is exposed to the outside in a state where it is folded in the other region at a position overlapping with the terminal part when folded in half. A first connecting portion having an opening for forming the first connecting portion;
(II) From the symmetrical position of the first connection part across the crease line, and substantially symmetric with respect to the crease line so as to overlap each other when the first connection part is folded in two along the crease line The conductor wiring is formed only on the inner surface when the first connection part is folded in two so as to make a round around the axis of the joint part. A flexible wiring member that is used by being wound, a pair of flexible wiring members that are formed longer than the inner side when the winding is wound,
(III) The conductor wiring of the flexible wiring member is formed on the inner surface when the first connecting portion is folded in two, and is formed on the front and back sides of the other circuit member. A second and a third connecting portion provided with terminal portions in which terminals for connecting to circuits formed on both sides are arranged;
A flexible printed circuit board formed integrally with a single base film.
[0010]
In the configuration of claim 1, both the metal thin film serving as the conductor wiring and the terminal are inside when one side of the base film constituting each of the above portions, that is, the first connection portion is folded in two along the crease line. A flexible printed circuit board can be manufactured only by forming it on the surface. That is, a flexible printed circuit board having the above-described parts can be manufactured by a so-called single-sided plate manufacturing process.
Therefore, according to the configuration of the first aspect, it is possible to provide a flexible printed circuit board that has a simpler manufacturing process and higher productivity than the conventional one, and that is excellent in manufacturing yield.
[0011]
Further, in the configuration of claim 1, a flexible wiring part is formed simply by superposing a pair of flexible wiring members, and both flexible wiring members maintain a state in which they can freely move. Coupled with the fact that each flexible wiring member has a single-sided plate structure, strain stress applied to the conductor wiring during bending can be reduced.
Therefore, according to the configuration of claim 1, it is also possible to provide a flexible printed board in which the bending resistance of the flexible wiring portion is further improved as compared with the current situation.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a plan view showing an example of an embodiment of a flexible printed board according to the present invention.
As shown in the figure, the flexible printed circuit board FP of this example is
(i) a substantially rectangular first connecting portion 1 formed so as to be foldable along the fold line BL;
(ii) a pair of

flexible wiring members

41, 42 that are formed so as to protrude vertically from the symmetrical position across the crease line BL of the first connection portion 1,
(iii) the substantially rectangular second and third connecting

portions

2 and 3 respectively formed at the distal ends of the

flexible wiring members

41 and 42;
A single base film is integrally formed.
[0013]
Of these, a plurality of terminals are linearly formed on the surface (the surface on the side shown in the drawing) of the first connection portion 1 on the inner side when folded in two in the upper region 11 in the drawing with the crease line BL as a boundary. A terminal portion T1 including two terminal rows T1a and T1b arranged in a row is provided.
Further, the terminal region T1 is exposed to the outside in a folded state at the position of the lower region 12 that overlaps the terminal portion T1 when folded in half, with the crease line BL as a boundary [see FIG. 2 (a). ] Is formed.
[0014]
In this example, a connector C1 having a size that can pass through the opening 12a as shown in FIGS. 2 (c) and 3 is mounted on the two terminal rows T1a and T1b of the terminal portion T1. C1 and a connector C2 mounted on one main board M1 as a circuit member are connected to each other as indicated by a white arrow in FIG. The circuit can be electrically connected to each circuit on the main board M1.
[0015]
For mounting the connector C1 on the terminal portion T1, various conventionally known methods such as soldering or crimping with an anisotropic conductive film sandwiched can be employed.
In addition, a plurality of terminals are arranged in parallel on the inner surface (the surface on the side shown in FIG. 1) of the second connection part 2 and the third connection part 3 when both are folded in half. T2 and T3 are formed.
In this example, as shown in FIG. 2B, a circuit (not shown) formed on both the front and back surfaces of the other main board M2 as a circuit member, and inner surfaces of the two

connection portions

2 and 3 are used. With the anisotropic conductive films OC and OC having adhesiveness or tackiness inserted between the terminal portions T2 and T3 provided on the two

terminals

2 and 3 as shown by the black arrows in the figure. By crimping the main board M2 between both sides,
-By mechanically adhering and fixing the two

connection portions

2 and 3 to the front and back surfaces of the main substrate M2 by the adhesion or stickiness of the anisotropic conductive films OC and OC,
-The anisotropic conductive characteristics of the anisotropic conductive films OC, OC are low in the thickness direction of the film and have high anisotropic conductivity characteristics in the surface direction, so that the individual terminals forming the terminal portions T2, T3 are adjacent to each other. In a state of being electrically insulated from the terminals, the circuit can be electrically connected to individual circuits on both the front and back surfaces of the corresponding main substrate M2 across the anisotropic conductive films OC and OC.
[0016]
As shown in FIG. 1, the upper flexible wiring member 41 is a straight portion having a certain width and extending upward from the upper side of the upper region 11 in the first connection portion 1 so as to be orthogonal to the crease line BL. 41a and a straight portion 41b having the same constant width and extending downward from the lower side of the second connection portion 2 in parallel with the straight portion 41a are larger than the widths of both the

straight portions

41a and 41b and in the width direction. The two

linear portions

41a and 41b are formed in a planar shape connected by a substantially S-shaped curved portion 41c.
[0017]
The lower flexible wiring member 42 is substantially the same as the upper flexible wiring member 41 and the first connecting portion 1 as described above from the symmetrical position across the crease line BL, with the crease line BL as an axis. The protrusion is formed so as to have a line symmetrical plane shape.
That is, the flexible wiring member 42 is a straight portion having the same constant width as the

straight portions

41a and 41b, extending downward from the lower side of the lower region 12 in the first connection portion 1 so as to be orthogonal to the crease line BL. 42a and a straight portion 42b having the same constant width and extending upward from the upper side of the third connection portion 3 in parallel with the straight portion 42a are shifted in the same direction as the

straight portions

41a and 41b by the same dimension. In addition to the arrangement, the two

straight portions

42a and 42b are formed in a planar shape connected by a substantially S-shaped curved portion 42c.
[0018]
Also, the two main boards M1 and M2 are electrically connected to the inner surface (the surface on the side shown in FIG. 1) of the both

flexible wiring members

41 and 42 when folded in two.

Conductor wirings

51 and 52 are formed.
Among these, the conductor wiring 51 is formed by connecting a main wiring part 51 a formed on the flexible wiring member 41 with a metal thin film such as a copper foil by a connection wiring part 51 b formed in the upper region 11 of the first connection part 1. The terminal portion T1 is integrally formed in a planar shape connected to the terminal row T1a and connected to the terminal portion T2 by the connection wiring portion 51c formed in the second connection portion 2.
[0019]
Similarly, the conductor wiring 52 is formed by forming a main wiring portion 52a formed on the flexible wiring member 42 with a metal thin film such as a copper foil in the lower region 12 of the first connection portion, and opening 12a. The terminal line T1b of the terminal part T1 is branched by the connection wiring part 52b that branches into two parts and further divides into four parts at the crease line BL to reach the upper region 11 in order to make the folding easier. And is integrally formed in a planar shape connected to the terminal portion T3 by the connection wiring portion 52c formed in the third connection portion 3.
[0020]
In the drawing, both conductor wirings 51 and 52 are abbreviated as a single flat plate. However, in actuality, the conductor wiring 51 includes individual terminals of the terminal row T1a and individual terminals of the terminal portion T2. Is an aggregate of a plurality of fine wirings for electrically connecting, for example, one to one. Similarly, the conductor wiring 52 is an aggregate of a plurality of fine wirings for electrically connecting individual terminals of the terminal row T1b and individual terminals of the terminal portion T3, for example, one to one.
[0021]
The number of fine wirings forming the conductor wirings 51 and 52 in each

flexible wiring member

41 and 42 is such that both the

flexible wiring members

41 and 42 have a single-sided plate structure. There are few compared with what has a structure, or what has the structure of a multilayer printed circuit board.
However, since the flexible wiring portion 4 is formed by overlapping the two

flexible wiring members

41 and 42, a space for providing a through hole portion or the like is not necessary, and the wiring density can be improved. The total number of fine wirings that can be formed in the same manner can be equal to or more than that of a double-sided board having the same size.
[0022]
As shown in FIG. 2 (a), the flexible wiring portion 4 is formed by folding the two

flexible wiring members

41 and 42 by folding the first connection portion 1 along the crease line BL and overlapping each other. A straight portion 4a having a width (a portion where the

straight portions

41a and 42a overlap) and a straight portion 4b having the same constant width (a portion where the

straight portions

41b and 42b overlap) are formed into a substantially S-shaped curved portion 4c ( It is formed in a planar shape that is connected by a portion where the

curved portions

41c and 42c overlap.
[0023]
According to the flexible wiring portion 4 having such a planar shape, for example, as shown in FIG. 3, the

linear portions

4a and 4b are shifted in the width direction by sandwiching the curved portion 4c so as not to interfere with each other. Can be wound around the axis AX (shown by a one-dot chain line in the figure) of the joint portion of the mobile phone or the like.
For this reason, the two main boards arranged above and below the joint part are electrically connected by the conductor wirings 51 and 52 while maintaining a state in which the two main boards can be folded through the joint part by turning around the axis AX. Can be connected.
[0024]
The pair of variable Tou wiring member 41, the winding can with the outer become soluble Tou wiring members (the variable Tou wiring member 41 in this case), soluble Tou wiring member comprising an inner (in this case allowed Tou wiring It is necessary to form it slightly longer than the member 42). As a result, it is possible to absorb the difference in circumference between the inside and outside of the winding and to wrap the shaft AX more smoothly in a state where both are overlapped. In addition, the bending resistance of the flexible wiring portion 4 can be further improved.
[0025]
In the flexible printed circuit board FP in this embodiment including upper Symbol each section, the first connecting portion 1 as described above, a pair of variable Tou wiring member 41, the second connecting portion 2, and the third connecting portion 3 In either case, the terminal portions T1 to T3 and the conductor wirings 51 and 52 are formed only on the same side surface which is the inner side when folded in two along the crease line BL.
[0026]
Therefore, since the flexible printed circuit board FP can be manufactured by a manufacturing process of a so-called single-sided board, the manufacturing process is simpler and the productivity is higher than the conventional one, and the manufacturing yield is also excellent.
In addition, the flexible printed circuit board FP of this example has a pair of

flexible wiring members

41, 42 extending vertically in a direction perpendicular to the crease line BL, as shown in FIG. It is formed in a straight line.
[0027]
For this reason, a plurality of regions to be the flexible printed circuit board FP are arranged on a single standard base film, and the terminal portions T1 to T3 and the conductor wirings 51 and 52 are formed in the respective regions. The space between the regions as much as possible when manufacturing a plurality of flexible printed circuit boards FP by punching into a planar shape corresponding to the connecting portion 1, the

flexible wiring members

41, 42, the second and third connecting

portions

2, 3 is possible. Can be packed and placed.
[0028]
Therefore, the number of flexible printed circuit boards FP that can be manufactured from one standard base film can be increased to further improve the productivity. Further, the two

flexible wiring members

41 and 42 to be the flexible wiring part 4 are simply overlapped when the first connection part 1 is folded in two along the crease line BL. Are still in a state where they can move freely. For this reason, coupled with the

flexible wiring members

41 and 42 having a single-sided plate structure as described above, the strain stress applied to the conductor wirings 51 and 52 during bending can be reduced.
[0029]
Therefore, the bending resistance of the flexible wiring portion 4 of the flexible printed circuit board FP can be further improved from the current level.
A flexible resin film is used as the base film for the flexible printed circuit board FP. In particular, a polyimide film is preferable in consideration of dimensional stability, heat resistance, durability, flexibility, and the like.
Further, the terminal portions T1 to T3 and the conductor wirings 51 and 52 are formed of a metal thin film such as a copper foil as described above. As a forming method, various conventionally known methods such as a subtractive method and an additive method can be employed.
[0030]
Further, for example, on the surface of the upper region (region 11, flexible wiring member 41, and second connection portion 2) in FIG. 1 across the crease line BL of the flexible printed circuit board FP, although not shown, a terminal In order to cover the conductor wiring 51 while exposing the portions T1 and T2, a cover lay made of a resin film or the like is preferably laminated. Thereby, when the flexible printed circuit board FP is folded in half, it is possible to prevent the conductor wirings 51 and 52 from coming into contact and causing a short circuit or the like. In addition, it is possible to improve the bending resistance of the flexible wiring portion 4 by improving the sliding between the

flexible wiring members

41 and 42 folded in two.
[0031]
The coverlay has a terminal portion T3 on the surface of the lower region (region 12, flexible wiring member 42, and third connection portion 3) of FIG. 1 across the crease line BL of the flexible printed circuit board FP. You may laminate | stack so that the conductor wiring 52 may be coat | covered, exposing. Moreover, you may laminate | stack a coverlay in both said area | regions, respectively.
In particular, it is preferable to laminate a reinforcing plate made of a resin film or the like for reinforcement on the first connection portion 1 for mounting the connector C1 on the terminal portion T1 as described above. The reinforcing plate formed in the same size and shape as the planar shape in which the first connection portion 1 is folded in two along the crease line BL is the upper side of the first connection portion 1 on which the terminal portion T1 is formed. What is necessary is just to laminate | stack on the back surface of the area | region 11 of this.
[0032]
As the resin film used as the base of the said coverlay or a reinforcement board, a polyimide film is preferable for the same reason as the above, respectively.
Also, in the subtractive method, etc., a metal foil such as a copper foil that forms the terminal portions T1 to T3 and the conductor wirings 51 and 52 is laminated and bonded to the surface of the base film, or a resin that becomes a coverlay or a reinforcing plate An adhesive is used for laminating and bonding the films. As such an adhesive, a curable resin-based adhesive is preferable, and an epoxy resin-based adhesive is particularly preferable in order not to impair the properties of each layer.
[0033]
【Example】
Example 1
A copper foil is patterned by a subtractive method using a single-sided plate in which a copper foil with a thickness of 18 μm is laminated on one side of a polyimide film with a thickness of 25 μm as a base film via an epoxy resin adhesive layer with a thickness of 10 μm. The terminal portions T1 to T3 and the conductor wirings 51 and 52 having the planar shape shown in FIG. 1 were formed on one side of the base film.
[0034]
Next, a polyimide film having a thickness of 25 μm having a through hole for exposing the terminal portions T1 and T2 in a region corresponding to the upper side of the crease line BL of the base film, and an epoxy resin adhesive layer having a thickness of 20 μm. Then, a cover lay for covering and covering the conductor wiring 51 was formed by stacking and bonding, and punching was performed to manufacture a flexible printed circuit board FP having a planar shape shown in FIG.
The pair of

flexible wiring members

41 and 42 are formed so that the length of the flexible wiring member 41 on the outer side of the winding is slightly longer than the length of the flexible wiring member 42 on the inner side.
[0035]
Comparative Example 1
Using a double-sided board in which a copper foil with a thickness of 18 μm is laminated on both sides of a polyimide film with a thickness of 25 μm as a base film via an epoxy resin adhesive layer with a thickness of 10 μm, a copper foil is formed by a subtractive method. A pattern is formed, and a conductor wire having the same size and shape as the conductor wire 51 is formed on one surface of the base film, and a conductor wire having the same size and shape as the conductor wire 52 is formed on the other surface. Were formed while aligning so that the front and back of the base film coincided with each other.
[0036]
Next, a polyimide film having a thickness of 25 μm is laminated on both surfaces of the base film via an epoxy resin adhesive layer having a thickness of 30 μm and bonded to form a coverlay that covers the conductor wirings 51 and 52. The flexible printed circuit board of Comparative Example 1 having a double-sided plate structure was manufactured by punching into the same shape as the upper side of the crease line BL in FIG.
Flexibility test The flexible printed circuit board FP manufactured in Example 1 was folded in two along the crease line BL, and then the flexible wiring portion 4 was placed on the axis AX as shown in FIGS. 3 and 4A. The first connection portion 1 was held by one clamp of the testing machine while being wound around the periphery, and the second and

third connection portions

2 and 3 overlapped with each other were held by the other clamp.
[0037]
In addition, the flexible printed circuit board manufactured in Comparative Example 1 similarly holds the flexible wiring portion around the axis AX and holds one connection portion with one clamp of the testing machine, The other connection was held with the other clamp. Then, with one clamp fixed, the other clamp is rotated about the axis AX between the “open” state shown in FIG. 4 (a) and the “closed” state shown in FIG. 4 (b). The flexible wiring portion 4 of the flexible printed circuit board FP was repeatedly bent by continuously reciprocating at a rotation angle of °, and the number of bendings until the conductor wiring was disconnected was counted.
[0038]
The results are shown in Table 1.
[0039]
[Table 1]

[0040]
According to the table, the flexible printed wiring board of Example 1 having the configuration of the present invention has almost twice the number of bendings until the conductor wiring breaks, compared to the conventional Comparative Example 1 having the configuration of the double-sided board. It was confirmed that the bending resistance can be remarkably improved by increasing the resistance.
[Brief description of the drawings]
FIG. 1 is a plan view showing an example of an embodiment of a flexible printed board of the present invention.
FIG. 2A is a plan view showing a state in which the flexible printed board of the above example is folded in two along the fold line of the first connecting portion, and FIG. 2B is a flexible printed board in the above state. Sectional drawing which shows the state which crimped | bonded the other main board | substrate between the 2nd connection part and the 3rd connection part, The same figure (c) is the 1st folded in half of the flexible printed circuit board of the said state. It is sectional drawing which shows the state just before connecting with the connector mounted in one main board | substrate after mounting a connector in a connection part.
FIG. 3 shows a flexible printed circuit board of the above example folded in half, and the other main board is sandwiched between the second connection portion and the third connection portion, and a connector is mounted on the first connection portion. It is a top view which shows the state wound around the axis | shaft of a joint part, such as a folding-type mobile phone.
FIG. 4 is a diagram showing the flexible printed circuit board manufactured in Examples and Comparative Examples of the present invention, in which the flexible printed circuit board is wound around the axis and repeatedly bent in order to evaluate the bending resistance. FIG. 2A is a diagram showing an “open” state, and FIG. 2B is a diagram showing a “closed” state.
[Explanation of symbols]
FP flexible printed circuit board BL crease line 1

1st connection part

11,12 area | region 12a opening 2 2nd connection part 3 3rd connection part 4

flexible wiring part

41,42

flexible wiring member

51,52 conductor wiring T1-T3 terminal part M1, M2 Main board (circuit member)

Claims

A flexible printed circuit board including a flexible wiring portion having a conductor wiring for connecting two circuit members,
(I) It is formed so that it can be folded in two along the crease line, and one side of the conductor wiring of the flexible wiring section is placed on the inner surface when folded in half in one area with this crease line as a boundary. A terminal part in which terminals for connecting to a circuit on the circuit member of the above are arranged is provided, and the terminal part is exposed to the outside in a state where it is folded in the other region at a position overlapping with the terminal part when folded in half. A first connecting portion having an opening for forming the first connecting portion;
(II) From the symmetrical position of the first connection part across the crease line, and substantially symmetric with respect to the crease line so as to overlap each other when the first connection part is folded in two along the crease line The conductor wiring is formed only on the inner surface when the first connection part is folded in two so as to make a round around the axis of the joint part. A flexible wiring member that is used by being wound, a pair of flexible wiring members that are formed longer than the inner side when the winding is wound,
(III) The conductor wiring of the flexible wiring member is formed on the inner surface when the first connecting portion is folded in two, and is formed on the front and back sides of the other circuit member. A second and a third connecting portion provided with terminal portions in which terminals for connecting to circuits formed on both sides are arranged;
A flexible printed circuit board formed integrally with a single base film.