【０００１】
【発明の属する技術分野】
本発明は、半導体素子等の電子部品を搭載するために用いられる配線基板およびその製造方法に関する。
【０００２】
【従来の技術】
一般に、現在の電子機器は、移動体通信機器に代表されるように小型・薄型・軽量・高性能・高機能・高品質・高信頼性が要求されてきており、このような電子機器に搭載される電子装置も小型・高密度化が要求されるようになってきている。そのため、電子装置を構成する配線基板にも小型・薄型・多端子化が求められてきており、それを実現するために信号導体等を含む配線導体層の幅を細くするとともにその間隔を狭くし、さらに配線導体層の多層化により高密度配線化が図られている。
【０００３】
このような高密度配線が可能な配線基板として、ビルドアップ法を採用して製作された配線基板が知られている。このビルドアップ配線基板は、例えば、次に述べる方法により製作される。
【０００４】
まず、ガラスクロスやアラミド不布織等の補強材に耐熱性や耐薬品性を有するアリル変性ポリフェニレンエーテル樹脂に代表される熱硬化性樹脂を含浸させた絶縁シートに配線導体をその表面が絶縁シートの表面と同一面となるように埋入し、しかる後これを加熱硬化して絶縁基板に配線導体が埋入して成るコア基板を得る。
【０００５】
次に、コア基板にエポキシ樹脂等の熱硬化性樹脂から成る樹脂フィルムを貼着し加熱硬化して、厚みが２０〜２００μｍの絶縁樹脂層を形成する。次に、配線導体の上に位置する絶縁樹脂層に径が５０〜２００μｍの貫通孔をレーザで穿設し、さらに絶縁樹脂層の表面および貫通孔の内面を過マンガン酸カリウム溶液等の粗化液で化学粗化し、次にセミアディティブ法を用いて絶縁樹脂層の表面および貫通孔の内面に銅めっきから成る導体膜を被着して配線導体層および貫通導体を形成する。そして、この上に絶縁樹脂層や貫通導体・配線導体層の形成を複数回繰り返すことによって、ビルドアップ配線基板が製作される。
【０００６】
【特許文献１】
特開２００２−２６１４５１号公報
【０００７】
【発明が解決しようとする課題】
しかしながら、上述の配線基板は、絶縁基板の熱膨張係数が１０×１０−６〜１５×１０−６／℃、配線導体の熱膨張係数が１５×１０−６〜２０×１０−６／℃であり絶縁基板の熱膨張係数と配線導体の熱膨張係数が異なることから、配線基板に電子部品を搭載した後に長期の熱履歴が繰り返し印可されると、絶縁基板と配線導体の熱膨張差により発生する熱応力が絶縁基板と配線導体との境界に集中して配線導体の側面と絶縁基板との間に隙間が発生し、その隙間を起点として絶縁樹脂層にクラックが生じるとともに配線導体層を切断して断線不良を発生させてしまうことがあるという問題点を有していた。
【０００８】
また、コア基板にアリル変性ポリフェニレンエーテル樹脂を用いた場合、アリル変性ポリフェニレンエーテル樹脂が化学的に安定で粗化することが困難であり、コア基板の表面にエポキシ樹脂を含む絶縁樹脂層を積層した場合、コア基板のアリル変性ポリフェニレンエーテル樹脂と絶縁樹脂層のエポキシ樹脂とが強固に結合することができず、その結果、コア基板とその上に積層された絶縁樹脂層との密着力が弱いものとなってしまい、例えば配線基板の表面に電子部品を実装する際に、配線基板に急激な温度変化が加わったりあるいは電子部品を実装した後に電子部品が作動する際に発生する熱や外部環境による熱等が長期間にわたり繰返し加わったりすると、絶縁樹脂層とコア基板との間で膨れや剥がれが発生してしまうことがあるという問題点も有していた。
【０００９】
他方、上述の配線基板の製造方法は、配線導体を絶縁基板に埋入することによって、および絶縁樹脂層を絶縁基板に被着することによって配線基板を製作することから、絶縁基板と配線導体および絶縁樹脂層との密着が弱く、配線基板に電子部品を搭載した後に長期の熱履歴が繰り返し印可されると、絶縁基板と配線導体および絶縁樹脂層との熱膨張差により発生する熱応力が絶縁基板と配線導体との境界および絶縁基板と絶縁樹脂層との境界に集中して、配線導体の側面と絶縁基板との間に隙間が発生し、その隙間を起点として絶縁樹脂層にクラックが生じるとともに配線導体層を切断して断線不良を発生させてしまう、あるいは絶縁樹脂層が絶縁基板から剥離してしまうことがあるという問題点を有していた。
【００１０】
本発明は、かかる従来技術の問題点に鑑み完成されたものであり、その目的は、電子部品を搭載した配線基板において、長期の熱履歴を繰り返し印可しても、熱応力に充分耐え、断線等が生じない接続信頼性の高い配線基板を提供することにある。
【００１１】
【課題を解決するための手段】
本発明の配線基板は、耐熱性繊維基材にアリル変性ポリフェニレンエーテル樹脂を含浸させた絶縁基板に金属箔から成る配線導体をその表面が前記絶縁基板の表面と同一面をなすように埋入して成るコア基板の前記配線導体を埋入した表面に、エポキシ樹脂を含む絶縁樹脂層と配線導体層とを交互に複数層積層して成る配線基板において、前記配線導体は、その幅方向の断面形状が前記絶縁基板側の底辺の長さが対向する底辺の長さより長い台形状であり、かつその側面と前記絶縁基板との間に前記エポキシ樹脂を介在させて埋入されていることを特徴とするものである。
【００１２】
本発明の配線基板によれば、配線導体は、その幅方向の断面形状が絶縁基板側の底辺の長さが対向する底辺の長さより長い台形状であり、かつその側面と絶縁基板との間にエポキシ樹脂を介在させて埋入されていることから、配線導体の側面と絶縁基板との間に介在させたエポキシ樹脂が接着材の機能を果たして絶縁基板と配線導体の側面とが強固に接着し、その結果、配線基板に電子部品を搭載した後に配線基板に長期の熱履歴が繰り返し印可され、絶縁基板と配線導体との熱膨張差により発生する熱応力が絶縁基板と配線導体との境界に集中したとしても、配線導体の側面と絶縁基板との間に隙間が発生することはなく、その隙間を起点として絶縁樹脂層にクラックが生じたり、このクラックが配線導体層を切断して断線不良を発生させてしまうということはない。
【００１３】
さらに、本発明の配線基板によれば、絶縁基板と絶縁樹脂層とが配線導体の側面と絶縁基板との間に介在させたエポキシ樹脂のアンカー効果により強固に接合し、その結果、配線基板に電子部品を搭載した後に長期の熱履歴が繰り返し印可され、絶縁基板と絶縁樹脂層の熱膨張差により発生する熱応力が両者の境界に集中したとしても、絶縁樹脂層が絶縁基板から剥離してしまうということもない。
【００１４】
また、本発明の配線基板の製造方法は、耐熱性繊維基材にアリル変性ポリフェニレンエーテル樹脂を含浸させた絶縁基板に、金属箔から成り、幅方向の断面形状が台形状の配線導体を、長さが短い底辺側の表面が前記絶縁基板の表面と同一面をなすように、かつ前記配線導体の側面と前記絶縁基板との間に隙間を形成するように埋入して成るコア基板を準備する工程と、このコア基板の前記配線導体を埋入した表面にエポキシ樹脂を含む絶縁樹脂層を被着するとともに前記隙間の内部に前記エポキシ樹脂を充填する工程と、前記絶縁樹脂層の表面に配線導体層を被着する工程とを具備することを特徴とするものである。
【００１５】
本発明の配線基板の製造方法によれば、耐熱性繊維基材にアリル変性ポリフェニレンエーテル樹脂を含浸させた絶縁基板に、金属箔から成り、幅方向の断面形状が台形状の配線導体を、長さが短い底辺側の表面が絶縁基板の表面と同一面をなすように、かつ配線導体の側面と絶縁基板との間に隙間を形成するように埋入して成るコア基板を準備し、このコア基板の配線導体を埋入した表面にエポキシ樹脂を含む絶縁樹脂層を被着するとともに隙間の内部にエポキシ樹脂を充填することから、エポキシ樹脂が接着材の役割をはたし、配線導体と絶縁基板とが強固に接着した配線基板を提供することができる。また、絶縁基板と絶縁樹脂層とが配線導体の側面と絶縁基板との間に介在させたエポキシ樹脂のアンカー効果により強固に接合することから、絶縁基板と絶縁樹脂層との接合が強固な配線基板を提供することができる。
【００１６】
【発明の実施の形態】
次に、本発明の配線基板を添付の図面に基づいて詳細に説明する。
図１は、本発明の配線基板の実施の形態の一例を示す断面図であり、図２は、図１の要部拡大断面図である。これらの図において、１は絶縁基板、２は配線導体、３は絶縁基板１と配線導体２とから成るコア基板、４は絶縁樹脂層、５は配線導体層で、主にこれらで本発明の配線基板が構成されている。
【００１７】
コア基板３を構成する絶縁基板１は、例えば耐熱性繊維基材であるガラス繊維を縦横に織り込んだガラスクロスにアリル変性ポリフェニレンエーテル樹脂を含浸させて成る厚みが０．１５〜１．５ｍｍの略四角形状の基板であり、配線導体２および絶縁層４の支持体としての機能を有するとともに配線基板に強度を付与する機能を有する。絶縁基板１は、その厚みが０．１５ｍｍ未満であると配線基板の剛性が低下し、反りが発生し易くなる傾向があり、１．５ｍｍを超えると配線基板が不要に厚いものとなり配線基板を軽量化することが困難となる傾向がある。従って、絶縁基板１の厚みは０．１５〜１．５ｍｍの範囲が好ましい。
【００１８】
また、絶縁基板１の表面には銅箔から成る配線導体２がその表面が絶縁基板１の表面と同一面をなすように埋入されている。
【００１９】
このような銅箔から成る配線導体２は、その幅が２０〜２００μｍ、厚みが５〜５０μｍであり、配線導体層５とともに搭載する半導体素子等の電子部品（図示せず）の各電極を外部電気回路基板（図示せず）に電気的に接続する導電路の一部としての機能する。配線導体２は、その幅が２０μｍ未満となると配線導体２の変形や断線が発生しやすくなる傾向があり、２００μｍを超えると高密度配線が形成できなくなる傾向がある。また、配線導体２の厚みが５μｍ未満になると配線導体２の強度が低下し変形や断線が発生しやすくなる傾向があり、５０μｍを超えると絶縁基板１への埋入が困難となる傾向がある。従って、配線導体２は、その幅を２０〜２００μｍ、厚みを５〜５０μｍの範囲とすることが好ましい。
【００２０】
なお、上下に位置する配線導体２同士を、絶縁基板１に形成した貫通導体１ｂにより電気的に接続してもよい。このような貫通導体１ｂは、その直径が３０〜１００μｍであり、例えば、絶縁基板１に設けた貫通孔１ａの内部に銅や銀・錫合金等の金属粉末とトリアジン系熱硬化性樹脂等とから成る導体を埋め込むことにより形成される。貫通導体１ｂを設ける場合、その直径が３０μｍ未満になると貫通導体１ｂの形成が困難となる傾向があり、１００μｍを超えると高密度配線が形成できなくなる傾向がある。従って、貫通導体１ｂを設ける場合、その直径は３０〜１００μｍの範囲とすることが好ましい。
【００２１】
また、コア基板３の主面、図１の例では上下面には、エポキシ樹脂を含有する絶縁樹脂層４と銅めっきから成る配線導体層５とが交互に積層されている。絶縁樹脂層４は、銅めっきから成る配線導体層５の支持体としての機能を有し、その厚みが１０〜８０μｍであり、エポキシ樹脂と平均粒径が０．０１〜２μｍで含有量が１０〜５０重量％のシリカやアルミナ・窒化アルミニウム等の無機絶縁フィラーとから成る。
【００２２】
無機絶縁フィラーは、絶縁樹脂層４の熱膨張係数を調整し配線導体層５の熱膨脹係数と整合させるとともに、絶縁樹脂層４の表面に適度な凹凸を形成し、配線導体層５と絶縁樹脂層４との密着性を良好となす機能を有する。なお、無機絶縁フィラーは、その平均粒径が０．０１μｍ未満であると、無機絶縁フィラー同士が凝集して均一な厚みの絶縁樹脂層４を形成することが困難となる傾向があり、２μｍを超えると絶縁樹脂層４の表面の凹凸が大きなものとなり過ぎて配線導体層５と絶縁樹脂層４との密着性を低下させてしまう傾向がある。従って、無機絶縁フィラーの平均粒径は、０．０１〜２μｍの範囲が好ましい。
【００２３】
また、無機絶縁フィラーの含有量が１０重量％未満であると、絶縁樹脂層４の熱膨張係数を調整する作用が小さくなる傾向があり、５０重量％を超えると絶縁樹脂層４の樹脂量が減少し絶縁樹脂層４を成形することが困難となる傾向がある。従って、無機絶縁フィラーの含有量は、１０〜５０重量％の範囲が好ましい。
【００２４】
また、絶縁樹脂層４には、レーザ加工によりビア孔６が形成されており、このビア孔６の内部に銅めっきから成る配線導体層５の一部を被着させることにより絶縁樹脂層４を挟んで上下に位置する配線導体２と配線導体層５、および配線導体層５同士が電気的に接続されている。なお、配線導体層５は、その幅が２０〜２００μｍであり、その厚みが１〜２μｍの無電解銅めっき層と厚みが１０〜３０μｍの電解銅めっき層とから成り、配線基板に搭載される半導体素子等の電子部品の各電極を外部電気回路基板に電気的に接続する導電路としての機能を有する。
【００２５】
配線導体層５は、その幅が２０μｍ未満となると配線導体層５の変形や断線が発生しやすくなる傾向があり、２００μｍを超えると高密度配線が形成できなくなる傾向がある。また、配線導体層５の厚みが１１μｍ未満になると配線導体層５の強度が低下し変形や断線が発生しやすくなる傾向があり、３２μｍを超えると配線導体層５の形成に長時間を要してしまう傾向がある。従って、配線導体層５は、その幅を２０〜２００μｍ、厚みを１１〜３２μｍの範囲とすることが好ましい。
【００２６】
そして、本発明の配線基板においては、配線導体２は、その幅方向の断面形状が絶縁基板１側の底辺の長さが対向する底辺の長さより長い台形状であり、かつ絶縁基板１に配線導体２の側面２ａと絶縁基板１との間にエポキシ樹脂を介在させて埋入されており、またこのことが重要である。
【００２７】
本発明の配線基板によれば、配線導体２は、その幅方向の断面形状が絶縁基板１側の底辺の長さが対向する底辺の長さより長い台形状であり、かつ絶縁基板１に配線導体２の側面２ａと絶縁基板１との間にエポキシ樹脂を介在させて埋入されていることから、配線導体２の側面２ａと絶縁基板１との間に介在させたエポキシ樹脂が接着材の機能を果たして絶縁基板１と配線導体２とが強固に接着し、その結果、配線基板に電子部品を搭載した後に配線基板に長期の熱履歴が繰り返し印可され、絶縁基板１と配線導体２との熱膨張差により発生する熱応力が絶縁基板１と配線導体２との境界に集中したとしても、配線導体２の側面２ａと絶縁基板１との間に隙間が発生することはなく、その隙間を起点として絶縁樹脂層４にクラックが生じたり、このクラックが配線導体層５を切断して断線不良を発生させてしまうということはない。
【００２８】
さらに、本発明の配線基板によれば、絶縁基板１と絶縁樹脂層４とが配線導体２の側面２ａと絶縁基板１との間に介在させたエポキシ樹脂のアンカー効果により強固に接合し、その結果、配線基板に電子部品を搭載した後に長期の熱履歴が繰り返し印可され、絶縁基板１と絶縁樹脂層４の熱膨張差により発生する熱応力が両者の境界に集中したとしても、絶縁樹脂層４が絶縁基板１から剥離してしまうということもない。
【００２９】
なお、配線導体２の幅方向の断面の、長さが長い底辺と側面２ａとのなす角度は４５〜６０度が好ましい。長さが長い底辺と側面２ａとのなす角度が４５度未満であると、配線導体２が変形し絶縁基板１に良好に埋入させることが困難となる傾向にあり、６０度を超えると配線導体２の側面２ａと絶縁基板１との間の隙間が狭くなり絶縁樹脂層４のエポキシ樹脂を良好に充填することが困難となる傾向にある。従って、配線導体２の幅方向の断面の、長さが長い底辺と側面２ａとのなす角度は４５〜６０度が好ましい。
【００３０】
また、配線導体２の側面２ａと絶縁基板１とで形成された隙間の、配線導体２の幅方向の断面形状は、図２に示すように楔形形状であり、開口の幅は１〜５μｍであることが好ましい。開口の幅が１μｍ未満であると、配線導体２の側面２ａと絶縁基板１との間にエポキシ樹脂を充填することが困難となる傾向にあり、５μｍを超えると、このような大きな間隔を形成するのが困難となる傾向がある。従って、間隔の開口の幅は１〜５μｍであることが好ましい。
【００３１】
さらに、配線導体２の側面２ａは、その算術平均粗さＲａが０．１μｍ未満の場合、配線導体２の側面２ａと絶縁基板１との間に介在させたエポキシ樹脂との接合が弱いものとなる傾向にあり、他方、２μｍを超える場合、そのような粗面を形成するのに長時間を要し、形成することが困難となる傾向にある。従って、配線導体２の側面２ａは、その算術平均粗さＲａを０．１〜２μｍの範囲とすることが好ましい。
【００３２】
かくして、本発明の配線基板によれば、配線導体２は、その幅方向の断面形状が絶縁基板１側の底辺の長さが対向する底辺の長さより長い台形状であり、かつ絶縁基板１に配線導体２の側面２ａと絶縁基板１との間にエポキシ樹脂を介在させて埋入されていることから、配線導体２の側面と絶縁基板１との間に介在させたエポキシ樹脂が接着材の機能を果たし、配線導体２と絶縁基板１とが強固に接着した配線基板とすることができる。
【００３３】
なお、本発明は上述の実施の形態の一例に限定されるものではなく、本発明の要旨を逸脱しない範囲であれば種々の変更は可能であり、本実施例では、絶縁基板を１層から成るものとした例を示したが、絶縁基板を２層以上から成るものとし、内部に配線導体や、上下に位置するこれらの配線導体同士を電気的に接続する貫通導体を複数形成してもよい。
【００３４】
次に、本発明の配線基板の製造方法を、図３に基づいて詳細に説明する。
図３（ａ）〜（ｄ）は、本発明の配線基板の製造方法を説明するための各工程毎の要部断面図であり、１１は転写用シート基材、１２は転写用シート、１３は前駆体シートである。なお、図３において、図１および図２と同じ部材・箇所には同じ符合を付した．
まず、図３（ａ）に示すように、耐熱性樹脂から成る転写用シート基材１１に銅箔から成る配線導体２を被着して成る転写用シート１２と、耐熱性繊維に未硬化のアリル変性ポリフェニレンエーテル樹脂を含浸させて成る絶縁基板１と成る前駆体シート１３とを用意する。
【００３５】
転写用シート基材１１は、ポリエチレンテレフタレート（ＰＥＴ）樹脂やポリカーボネート（ＰＣ）等の耐熱性樹脂が用いられ、銅箔をエッチングして配線導体２を形成する際の支持体、および配線導体２を転写する際の支持体としての機能を有する。
【００３６】
転写用シート基材１１は、その厚みが２０〜５０μｍであることが好ましく、厚みが２０μｍ未満であると剛性が低下し銅箔をエッチングする際に配線導体２が変形し易くなる傾向にあり、５０μｍを超えると柔軟性が低下し絶縁基板１から剥離し難くなる傾向にある。従って、転写用シート基材１１の厚みは２０〜５０μｍが好ましい。
【００３７】
また、配線導体２は、その厚みは５〜５０μｍが好ましく、さらには１０〜２０μｍが好ましい。配線導体２の厚みが５μｍ未満になると配線導体２の強度が低下し変形や断線が発生しやすくなる傾向があり、５０μｍを超えると前駆体シートへの埋入が困難となる傾向がある。従って、配線導体２ａの厚みは５〜５０μｍが好ましい。
【００３８】
このような転写用シート１２は、例えば厚みが２５μｍ程度のポリエチレンテレフタレート等の耐熱性樹脂から成る転写シート基材１１の一方の主面全体に、厚みが１２〜３０μｍ程度の銅箔を接着材を介して剥離可能に接着した後、銅箔上にフィルム状感光性レジストを被着するとともにこのレジストを露光・現像して配線導体２のパターンに対応するパターンのエッチングマスクを形成し、しかる後、４０〜６０℃で数分間、塩化第二鉄／塩酸水溶液中に浸漬して銅箔の非パターン部をエッチング除去し、さらに転写シート基材１１側の底辺の長さがエッチングマスク側の底辺の長さよりも短くなるまで、具体的にはエッチングマスク側の底辺と側面２ａとのなす角度が４５〜６０度となるまで側面２ａをエッチングして、幅方向の断面形状が台形状の配線導体２を形成することにより製作される。
【００３９】
他方、絶縁基板１と成る前駆体シート１３は、ガラスクロスやアラミド繊維等の耐熱性繊維にアリル変性ポリフェニレンエーテル樹脂を含浸させて半硬化させたものから成り、その表面は配線導体２を埋入可能な程度の可塑性を備えている。さらに、絶縁基板１と成る前駆体シート１３にレーザで貫通孔１ａを穿孔し、この貫通孔１ａに金属粉末からなる導電性材料を充填して貫通導体１ｂを形成する。
【００４０】
次に、図３（ｂ）に示すように、貫通導体１ｂと配線導体２とが接合するように前駆体シート１３の表面に転写用シート１２を積層するとともにそれらを加熱加圧して配線導体２を前駆体シート１３に熱圧着して、配線導体２の長さの短い側の底辺と前駆体シート１３の表面とが同一面となるように埋入する。なおこのとき、配線導体２の断面形状が前駆体シート１３側の底辺の長さが対向する底辺の長さ、すなわち転写用シート１２側の底辺の長さより長い台形状となっていることから、配線導体２を前駆体シート１３に埋入させる際に、配線導体２の側面２ａと前駆体シート１３との間に、配線導体２の幅方向の断面形状が楔形形状の隙間７が形成される。
【００４１】
このような熱圧着は、熱プレス機を用いて温度が１００〜１５０℃、圧力が０．５〜５ＭＰａの条件で数分間加圧することにより行なわれる。なお、熱圧着は加熱に先行して加圧のみを行なう方が良い。加熱を先に行なうと熱によって転写用シート１１が伸び、配線導体２を所望の位置に正確に埋入することが困難となってしまう危険性がある。従って、熱圧着は加熱に先行して加圧を行なうことが好ましい。
【００４２】
さらに、それらを加熱加圧して前駆体シート１３のアリル変性ポリフェニレンエーテル樹脂を熱硬化し、コア基板３を製作する。なお、加熱処理にあたっては、前駆体シート１３をフッ素系樹脂などから成る離型性シートで上下から挟みこみ、１〜５ＭＰａの圧力で１５０〜２４０℃の温度で熱処理することにより、前駆体シートの熱硬化性樹脂を熱硬化させる。
【００４３】
次に、コア基板３を約２５℃の温度の蟻酸／銅イオン水溶液に数分間浸漬することにより、配線導体２の露出部を算術平均粗さが０．１〜２μｍの凹凸を有するように粗化する。その後、コア基板３の主面にエポキシ樹脂から成り絶縁樹脂層４と成るフィルムを貼着するとともに１５０〜１８０℃で数時間熱硬化することにより、図３（ｃ）に断面図で示すように、コア基板３の主面に絶縁樹脂層４を被着するとともに隙間７内に絶縁樹脂層４のエポキシ樹脂を充填する。なお、絶縁樹脂層４用のフィルムは、熱硬化の際に一旦、溶融軟化するのでその際に絶縁樹脂層４のエポキシ樹脂が隙間７の内部に良好に充填される。そして、隙間７内に充填されたエポキシ樹脂により絶縁基板１の表面に埋入された配線導体２と絶縁基板１とが強固に接着される。
【００４４】
このように本発明の配線基板の製造方法によれば、耐熱性繊維基材にアリル変性ポリフェニレンエーテル樹脂を含浸させた絶縁基板１に、金属箔から成り、幅方向の断面形状が台形状の配線導体２を、長さが短い底辺側の表面が絶縁基板１の表面と同一面をなすように、かつ配線導体２の側面２ａと絶縁基板１との間に隙間７を形成するように埋入して成るコア基板３を準備し、このコア基板３の配線導体２を埋入した表面にエポキシ樹脂を含む絶縁樹脂層４を被着するとともに隙間７の内部にエポキシ樹脂を充填することから、エポキシ樹脂が接着材の役割をはたし、配線導体２と絶縁基板１とが強固に接着した配線基板を提供することができる。また、絶縁基板１と絶縁樹脂層４とが配線導体２の側面２ａと絶縁基板１との間に介在させたエポキシ樹脂のアンカー効果により強固に接合することから、絶縁基板１と絶縁樹脂層４との接合が強固な配線基板を提供することができる。
【００４５】
なお、絶縁樹脂層４は、その厚みが１０〜８０μｍであり、エポキシ樹脂と平均粒径が０．０１〜２μｍで含有量が１０〜５０重量％のシリカやアルミナ・窒化アルミニウム等の無機絶縁フィラーとから成る。
【００４６】
次に、図３（ｄ）に断面図で示すように、絶縁樹脂層３の上面に銅めっきから成る配線導体層５を被着させる。さらに必要に応じてその上に次層の絶縁樹脂層４および配線導体層５を積層することによって配線基板が完成する。
【００４７】
なお、絶縁樹脂層４の上面に銅めっきから成る配線導体層５を被着させるには、まず、絶縁樹脂層４の表面を過マンガン酸塩類水溶液等の粗化液に浸漬して粗化した後、無電解めっき用パラジウム触媒の水溶液中に浸漬し表面にパラジウム触媒を付着させ、さらに、硫酸銅・ホルマリン・ＥＤＴＡナトリウム塩・安定剤等から成る無電解銅めっき液に約３０分間浸漬して厚みが１〜２μｍ程度の無電解銅めっき層を析出させる。次に、無電解銅めっき層の上面に耐めっき樹脂層を被着し露光・現像により銅めっきの配線導体層５のパターン形状に、電解銅めっき層を被着させるための開口部を複数形成し、さらに、硫酸・硫酸銅５水和物・塩素・光沢剤等から成る電解銅めっき液に数Ａ／ｄｍ２の電流を印加しながら数時間浸漬することにより開口部およびビア孔６の内面に厚みが１０〜３０μｍ程度の電解銅めっき層を被着させる。しかる後、耐めっき樹脂層を水酸化ナトリウムで剥離し、さらに、耐めっき樹脂層を剥離したことにより露出する無電解銅めっき層を硫酸と過酸化水素水の混合物等の硫酸系水溶液によりエッチング除去することにより形成される。
【００４８】
かくして、本発明の配線基板の製造方法によれば、配線導体２と絶縁基板１との密着が強固であるとともに、絶縁基板１と絶縁樹脂層４との接合が強固な配線基板を提供することができる。
【００４９】
なお、本発明は、上述の実施の形態の一例に限定されるものではなく、本発明の要旨を逸脱しない範囲であれば種々の変更は可能である。
【００５０】
【発明の効果】
本発明の配線基板によれば、配線導体は、その幅方向の断面形状が絶縁基板側の底辺の長さが対向する底辺の長さより長い台形状であり、かつその側面と絶縁基板との間にエポキシ樹脂を介在させて埋入されていることから、配線導体の側面と絶縁基板との間に介在させたエポキシ樹脂が接着材の機能を果たして絶縁基板と配線導体の側面とが強固に接着し、その結果、配線基板に電子部品を搭載した後に配線基板に長期の熱履歴が繰り返し印可され、絶縁基板と配線導体との熱膨張差により発生する熱応力が絶縁基板と配線導体との境界に集中したとしても、配線導体の側面と絶縁基板との間に隙間が発生することはなく、その隙間を起点として絶縁樹脂層にクラックが生じたり、このクラックが配線導体層を切断して断線不良を発生させてしまうということはない。
【００５１】
また、本発明の配線基板によれば、絶縁基板と絶縁樹脂層とが配線導体の側面と絶縁基板との間に介在させたエポキシ樹脂のアンカー効果により強固に接合し、その結果、配線基板に電子部品を搭載した後に長期の熱履歴が繰り返し印可され、絶縁基板と絶縁樹脂層の熱膨張差により発生する熱応力が両者の境界に集中したとしても、絶縁樹脂層が絶縁基板から剥離してしまうということもない。
【００５２】
さらに、本発明の配線基板の製造方法によれば、耐熱性繊維基材にアリル変性ポリフェニレンエーテル樹脂を含浸させた絶縁基板に、金属箔から成り、幅方向の断面形状が台形状の配線導体を、長さが短い底辺側の表面が絶縁基板の表面と同一面をなすように、かつ配線導体の側面と絶縁基板との間に隙間を形成するように埋入して成るコア基板を準備し、このコア基板の配線導体を埋入した表面にエポキシ樹脂を含む絶縁樹脂層を被着するとともに隙間の内部にエポキシ樹脂を充填することから、エポキシ樹脂が接着材の役割をはたし、配線導体と絶縁基板とが強固に接着した配線基板を提供することができる。また、絶縁基板と絶縁樹脂層とが配線導体の側面と絶縁基板との間に介在させたエポキシ樹脂のアンカー効果により強固に接合することから、絶縁基板と絶縁樹脂層との接合が強固な配線基板を提供することができる。
【図面の簡単な説明】
【図１】本発明の配線基板の実施の形態の一例を示す断面図である。
【図２】図１の要部拡大断面図である。
【図３】（ａ）〜（ｄ）は、本発明の配線基板の製造方法を説明するための各工程毎の要部断面図である。
【符号の説明】
１・・・・・・・・・・絶縁基板
２・・・・・・・・・・配線導体
２ａ・・・・・・・・・配線導体の側面
３・・・・・・・・・・コア基板
４・・・・・・・・・・絶縁樹脂層
５・・・・・・・・・・配線導体層
７・・・・・・・・・・隙間[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wiring board used for mounting an electronic component such as a semiconductor element, and a method for manufacturing the same.
[0002]
[Prior art]
In general, modern electronic devices are required to be small, thin, lightweight, high-performance, high-performance, high-quality, and high-reliable, as represented by mobile communication devices. Electronic devices to be used are also required to be smaller and higher in density. For this reason, there is a demand for smaller, thinner, and more multi-terminal wiring boards for electronic devices. To achieve this, the width of wiring conductor layers including signal conductors and the like must be reduced and the spacing between them must be reduced. Further, high-density wiring has been achieved by increasing the number of wiring conductor layers.
[0003]
As a wiring board capable of such high-density wiring, a wiring board manufactured by employing a build-up method is known. This build-up wiring board is manufactured, for example, by the method described below.
[0004]
First, a wiring conductor is placed on an insulating sheet in which a reinforcing material such as glass cloth or aramid non-woven fabric is impregnated with a thermosetting resin represented by an allyl-modified polyphenylene ether resin having heat resistance and chemical resistance. And then heat-cured to obtain a core substrate in which the wiring conductors are embedded in the insulating substrate.
[0005]
Next, a resin film made of a thermosetting resin such as an epoxy resin is adhered to the core substrate and cured by heating to form an insulating resin layer having a thickness of 20 to 200 μm. Next, a through hole having a diameter of 50 to 200 μm is formed in the insulating resin layer located above the wiring conductor by a laser, and the surface of the insulating resin layer and the inner surface of the through hole are roughened with a potassium permanganate solution or the like. The surface of the insulating resin layer and the inner surface of the through hole are coated with a conductive film made of copper plating using a semi-additive method to form a wiring conductive layer and a through conductor. Then, a build-up wiring board is manufactured by repeating the formation of the insulating resin layer and the through conductor / wiring conductor layer a plurality of times thereon.
[0006]
[Patent Document 1]
JP 2002-261451 A
[Problems to be solved by the invention]
However, in the above-mentioned wiring board, the thermal expansion coefficient of the insulating substrate is 10 × 10 −6 to 15 × 10 −6 / ° C., and the thermal expansion coefficient of the wiring conductor is 15 × 10 −6 to 20 × 10 −6 / ° C. Because the thermal expansion coefficient of the insulating substrate and the thermal expansion coefficient of the wiring conductor are different, if a long-term thermal history is repeatedly applied after mounting electronic components on the wiring substrate, it is caused by the difference in thermal expansion between the insulating substrate and the wiring conductor. Thermal stress concentrates on the boundary between the insulating substrate and the wiring conductor, and a gap is generated between the side surface of the wiring conductor and the insulating substrate, and the gap causes the insulating resin layer to crack and cut the wiring conductor layer As a result, there is a problem that a disconnection failure may occur.
[0008]
When an allyl-modified polyphenylene ether resin is used for the core substrate, the allyl-modified polyphenylene ether resin is chemically stable and difficult to roughen, and an insulating resin layer containing an epoxy resin is laminated on the surface of the core substrate. In the case where the allyl-modified polyphenylene ether resin of the core substrate and the epoxy resin of the insulating resin layer cannot be firmly bonded, as a result, the adhesion between the core substrate and the insulating resin layer laminated thereon is weak. For example, when mounting an electronic component on the surface of a wiring board, a sudden temperature change is applied to the wiring board or heat generated when the electronic component operates after mounting the electronic component or due to an external environment. If heat or the like is repeatedly applied for a long period of time, swelling or peeling may occur between the insulating resin layer and the core substrate. Also had problems.
[0009]
On the other hand, the above-described method of manufacturing a wiring board involves embedding a wiring conductor in an insulating substrate, and manufacturing a wiring board by attaching an insulating resin layer to the insulating substrate. If the long-term thermal history is repeatedly applied after mounting electronic components on the wiring board due to weak adhesion with the insulating resin layer, the thermal stress generated due to the difference in thermal expansion between the insulating substrate and the wiring conductor and the insulating resin layer is insulated. Concentration occurs at the boundary between the substrate and the wiring conductor and at the boundary between the insulating substrate and the insulating resin layer, and a gap occurs between the side surface of the wiring conductor and the insulating substrate, and cracks occur in the insulating resin layer starting from the gap. At the same time, there is a problem that the wiring conductor layer may be cut to cause a disconnection failure, or the insulating resin layer may be separated from the insulating substrate.
[0010]
The present invention has been completed in view of the problems of the related art, and an object of the present invention is to provide a wiring board on which electronic components are mounted, to withstand thermal stress sufficiently even when a long-term heat history is repeatedly applied, and to achieve disconnection. It is an object of the present invention to provide a wiring board with high connection reliability that does not cause any problem.
[0011]
[Means for Solving the Problems]
The wiring board of the present invention, a wiring conductor made of metal foil is embedded in an insulating substrate in which an allyl-modified polyphenylene ether resin is impregnated in a heat-resistant fiber base material so that the surface thereof is flush with the surface of the insulating substrate. A wiring board having a plurality of insulating resin layers containing epoxy resin and wiring conductor layers alternately laminated on the surface of the core substrate having the wiring conductor embedded therein, wherein the wiring conductor has a cross section in the width direction. The shape is a trapezoid in which the length of the base on the side of the insulating substrate is longer than the length of the opposite base, and is embedded between the side surface and the insulating substrate with the epoxy resin interposed therebetween. It is assumed that.
[0012]
According to the wiring board of the present invention, the wiring conductor has a trapezoidal cross-sectional shape in the width direction in which the length of the base on the insulating substrate side is longer than the length of the opposing base, and between the side surface and the insulating substrate. The epoxy resin interposed between the side of the wiring conductor and the insulating substrate serves as an adhesive, and the insulating substrate and the side of the wiring conductor are firmly bonded. As a result, a long-term heat history is repeatedly applied to the wiring board after the electronic components are mounted on the wiring board, and the thermal stress generated due to a difference in thermal expansion between the insulating substrate and the wiring conductor is generated at the boundary between the insulating substrate and the wiring conductor. Even if the wiring conductor layer is concentrated, there is no gap between the side surface of the wiring conductor and the insulating substrate, and cracks occur in the insulating resin layer starting from the gap, and the crack cuts the wiring conductor layer to break the wire. Cause defects It does not that put away.
[0013]
Furthermore, according to the wiring board of the present invention, the insulating substrate and the insulating resin layer are firmly joined by the anchor effect of the epoxy resin interposed between the side surface of the wiring conductor and the insulating substrate, and as a result, Even after long-term thermal history is repeatedly applied after mounting electronic components, even if the thermal stress generated due to the difference in thermal expansion between the insulating substrate and the insulating resin layer concentrates on the boundary between them, the insulating resin layer peels off from the insulating substrate. It doesn't even happen.
[0014]
Further, the method for producing a wiring board of the present invention is characterized in that a wiring conductor made of metal foil and having a trapezoidal cross-section in the width direction is formed on a heat-resistant fiber substrate impregnated with an allyl-modified polyphenylene ether resin. A core substrate is prepared by embedding such that the surface on the bottom side is shorter than the surface of the insulating substrate and forms a gap between the side surface of the wiring conductor and the insulating substrate. And applying an epoxy resin-containing insulating resin layer to the surface of the core substrate in which the wiring conductors are embedded, and filling the inside of the gap with the epoxy resin. And a step of applying a wiring conductor layer.
[0015]
According to the method for manufacturing a wiring board of the present invention, a wiring conductor made of metal foil and having a trapezoidal cross-section in the width direction is formed on a heat-resistant fiber substrate impregnated with an allyl-modified polyphenylene ether resin. The core substrate is prepared by embedding the short side of the bottom side so as to be flush with the surface of the insulating substrate and forming a gap between the side surface of the wiring conductor and the insulating substrate. Since the insulating resin layer containing epoxy resin is applied to the surface of the core board where the wiring conductor is embedded and the inside of the gap is filled with epoxy resin, the epoxy resin serves as an adhesive, It is possible to provide a wiring board to which an insulating substrate is firmly bonded. Also, since the insulating substrate and the insulating resin layer are firmly joined by the anchor effect of the epoxy resin interposed between the side surface of the wiring conductor and the insulating substrate, the wiring between the insulating substrate and the insulating resin layer is firmly bonded. A substrate can be provided.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the wiring board of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a sectional view showing an example of an embodiment of a wiring board of the present invention, and FIG. 2 is an enlarged sectional view of a main part of FIG. In these figures, 1 is an insulating substrate, 2 is a wiring conductor, 3 is a core substrate composed of the insulating substrate 1 and the wiring conductor 2, 4 is an insulating resin layer, and 5 is a wiring conductor layer. A wiring board is configured.
[0017]
The insulating substrate 1 constituting the core substrate 3 is, for example, a glass cloth in which glass fibers as a heat-resistant fiber base material are woven vertically and horizontally is impregnated with an allyl-modified polyphenylene ether resin and has a thickness of about 0.15 to 1.5 mm. It is a rectangular substrate, which has a function as a support for the wiring conductor 2 and the insulating layer 4 and a function to give strength to the wiring board. If the thickness of the insulating substrate 1 is less than 0.15 mm, the rigidity of the wiring substrate is reduced, and warpage tends to occur. If the thickness exceeds 1.5 mm, the wiring substrate becomes unnecessarily thick, and It tends to be difficult to reduce the weight. Therefore, the thickness of the insulating substrate 1 is preferably in the range of 0.15 to 1.5 mm.
[0018]
A wiring conductor 2 made of copper foil is embedded in the surface of the insulating substrate 1 so that the surface thereof is flush with the surface of the insulating substrate 1.
[0019]
The wiring conductor 2 made of such a copper foil has a width of 20 to 200 μm and a thickness of 5 to 50 μm, and connects each electrode of an electronic component (not shown) such as a semiconductor element mounted together with the wiring conductor layer 5 to the outside. It functions as a part of a conductive path electrically connected to an electric circuit board (not shown). When the width of the wiring conductor 2 is less than 20 μm, deformation and disconnection of the wiring conductor 2 tend to occur, and when the width exceeds 200 μm, high-density wiring tends not to be formed. Further, when the thickness of the wiring conductor 2 is less than 5 μm, the strength of the wiring conductor 2 tends to decrease and deformation or disconnection tends to occur, and when it exceeds 50 μm, it tends to be difficult to embed in the insulating substrate 1. . Therefore, the wiring conductor 2 preferably has a width of 20 to 200 μm and a thickness of 5 to 50 μm.
[0020]
The upper and lower wiring conductors 2 may be electrically connected to each other by the through conductor 1b formed on the insulating substrate 1. Such a through conductor 1 b has a diameter of 30 to 100 μm. For example, a metal powder such as copper, silver, or tin alloy and a triazine-based thermosetting resin are provided inside a through hole 1 a provided in the insulating substrate 1. Formed by embedding a conductor consisting of When the through conductor 1b is provided, if the diameter is less than 30 μm, it tends to be difficult to form the through conductor 1b, and if it exceeds 100 μm, there is a tendency that high-density wiring cannot be formed. Therefore, when the through conductor 1b is provided, the diameter thereof is preferably in the range of 30 to 100 μm.
[0021]
Also, an insulating resin layer 4 containing an epoxy resin and a wiring conductor layer 5 made of copper plating are alternately laminated on the main surface of the core substrate 3, that is, the upper and lower surfaces in the example of FIG. The insulating resin layer 4 functions as a support for the wiring conductor layer 5 made of copper plating, has a thickness of 10 to 80 μm, has an average particle size of 0.01 to 2 μm with the epoxy resin, and has a content of 10 to 10 μm. -50% by weight of an inorganic insulating filler such as silica or alumina / aluminum nitride.
[0022]
The inorganic insulating filler adjusts the coefficient of thermal expansion of the insulating resin layer 4 to match the coefficient of thermal expansion of the wiring conductor layer 5, and forms moderate irregularities on the surface of the insulating resin layer 4. 4 has a function of improving the adhesiveness to 4. If the average particle size of the inorganic insulating filler is less than 0.01 μm, it tends to be difficult to form the insulating resin layer 4 having a uniform thickness by agglomeration of the inorganic insulating fillers. If it exceeds, the irregularities on the surface of the insulating resin layer 4 become too large, and the adhesion between the wiring conductor layer 5 and the insulating resin layer 4 tends to be reduced. Therefore, the average particle size of the inorganic insulating filler is preferably in the range of 0.01 to 2 μm.
[0023]
When the content of the inorganic insulating filler is less than 10% by weight, the effect of adjusting the thermal expansion coefficient of the insulating resin layer 4 tends to be small. When the content exceeds 50% by weight, the resin amount of the insulating resin layer 4 is reduced. Therefore, it tends to be difficult to form the insulating resin layer 4. Therefore, the content of the inorganic insulating filler is preferably in the range of 10 to 50% by weight.
[0024]
Further, via holes 6 are formed in the insulating resin layer 4 by laser processing. The insulating resin layer 4 is formed by applying a part of the wiring conductor layer 5 made of copper plating to the inside of the via hole 6. The wiring conductors 2 and the wiring conductor layers 5, which are located vertically above and below, and the wiring conductor layers 5 are electrically connected to each other. The wiring conductor layer 5 has a width of 20 to 200 μm, a thickness of 1 to 2 μm, and an electroless copper plating layer of 10 to 30 μm in thickness, and is mounted on a wiring board. It has a function as a conductive path for electrically connecting each electrode of an electronic component such as a semiconductor element to an external electric circuit board.
[0025]
If the width of the wiring conductor layer 5 is less than 20 μm, the wiring conductor layer 5 tends to be easily deformed or disconnected, and if it exceeds 200 μm, high-density wiring tends not to be formed. If the thickness of the wiring conductor layer 5 is less than 11 μm, the strength of the wiring conductor layer 5 tends to decrease, and deformation or disconnection tends to occur. If the thickness exceeds 32 μm, it takes a long time to form the wiring conductor layer 5. Tend to be. Accordingly, the wiring conductor layer 5 preferably has a width in the range of 20 to 200 μm and a thickness in the range of 11 to 32 μm.
[0026]
In the wiring board according to the present invention, the wiring conductor 2 has a trapezoidal shape in cross section in the width direction whose base on the side of the insulating substrate 1 is longer than the length of the opposite base. It is embedded between the side surface 2a of the conductor 2 and the insulating substrate 1 with an epoxy resin interposed therebetween, and this is important.
[0027]
According to the wiring board of the present invention, the wiring conductor 2 has a trapezoidal cross-sectional shape in the width direction in which the length of the base on the side of the insulating substrate 1 is longer than the length of the opposing base. Since the epoxy resin is embedded between the side surface 2a of the wiring conductor 2 and the insulating substrate 1, the epoxy resin interposed between the side surface 2a of the wiring conductor 2 and the insulating substrate 1 functions as an adhesive. As a result, the insulating substrate 1 and the wiring conductor 2 are firmly adhered to each other. As a result, a long-term heat history is repeatedly applied to the wiring substrate after the electronic components are mounted on the wiring substrate, and the heat between the insulating substrate 1 and the wiring conductor 2 is increased. Even if the thermal stress generated due to the difference in expansion is concentrated on the boundary between the insulating substrate 1 and the wiring conductor 2, no gap is generated between the side surface 2a of the wiring conductor 2 and the insulating substrate 1, and the gap is used as a starting point. Cracks in the insulating resin layer 4 It is not that the crack will have to generate a disconnection failure by cutting the wiring conductor layer 5.
[0028]
Further, according to the wiring board of the present invention, the insulating substrate 1 and the insulating resin layer 4 are firmly joined by the anchor effect of the epoxy resin interposed between the side surface 2a of the wiring conductor 2 and the insulating substrate 1, As a result, a long-term thermal history is repeatedly applied after the electronic component is mounted on the wiring board, and even if the thermal stress generated due to the difference in thermal expansion between the insulating substrate 1 and the insulating resin layer 4 is concentrated on the boundary between them, 4 does not peel off from the insulating substrate 1.
[0029]
The angle formed by the long base and the side surface 2a of the cross section in the width direction of the wiring conductor 2 is preferably 45 to 60 degrees. If the angle between the long base and the side surface 2a is less than 45 degrees, the wiring conductor 2 tends to be deformed and it is difficult to satisfactorily embed it in the insulating substrate 1. There is a tendency that the gap between the side surface 2a of the conductor 2 and the insulating substrate 1 becomes narrow, and it becomes difficult to fill the insulating resin layer 4 with the epoxy resin satisfactorily. Therefore, the angle formed by the long base and the side surface 2a of the cross section in the width direction of the wiring conductor 2 is preferably 45 to 60 degrees.
[0030]
The cross-sectional shape of the gap formed between the side surface 2a of the wiring conductor 2 and the insulating substrate 1 in the width direction of the wiring conductor 2 is a wedge shape as shown in FIG. 2, and the width of the opening is 1 to 5 μm. Preferably, there is. If the width of the opening is less than 1 μm, it tends to be difficult to fill the space between the side surface 2 a of the wiring conductor 2 and the insulating substrate 1. If the width exceeds 5 μm, such a large gap is formed. Tend to be difficult to do. Therefore, it is preferable that the width of the opening of the interval is 1 to 5 μm.
[0031]
Further, when the arithmetic mean roughness Ra is less than 0.1 μm, the side surface 2a of the wiring conductor 2 has a weak joint with the epoxy resin interposed between the side surface 2a of the wiring conductor 2 and the insulating substrate 1. On the other hand, if it exceeds 2 μm, it takes a long time to form such a rough surface, and it tends to be difficult to form. Therefore, it is preferable that the arithmetic mean roughness Ra of the side surface 2a of the wiring conductor 2 be in the range of 0.1 to 2 μm.
[0032]
Thus, according to the wiring board of the present invention, the wiring conductor 2 has a trapezoidal shape in which the cross-sectional shape in the width direction is longer than the length of the opposite base on the side of the insulating substrate 1. Since the epoxy resin is interposed between the side surface 2a of the wiring conductor 2 and the insulating substrate 1, the epoxy resin interposed between the side surface of the wiring conductor 2 and the insulating substrate 1 is used as an adhesive. It is possible to provide a wiring board which fulfills the function and in which the wiring conductor 2 and the insulating substrate 1 are firmly bonded.
[0033]
Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. Although an example in which the wiring substrate is formed is shown, the insulating substrate may be formed of two or more layers, and a plurality of wiring conductors or through conductors that electrically connect these wiring conductors located above and below may be formed inside. Good.
[0034]
Next, a method for manufacturing a wiring board according to the present invention will be described in detail with reference to FIG.
3 (a) to 3 (d) are cross-sectional views of a main part of each step for explaining the method of manufacturing a wiring board according to the present invention, in which 11 is a transfer sheet substrate, 12 is a transfer sheet, and 13 is a transfer sheet substrate. Is a precursor sheet. In FIG. 3, the same members and portions as those in FIGS. 1 and 2 are denoted by the same reference numerals.
First, as shown in FIG. 3A, a transfer sheet 12 in which a wiring conductor 2 made of copper foil is applied to a transfer sheet base material 11 made of a heat-resistant resin, and an uncured heat-resistant fiber. A precursor sheet 13 serving as an insulating substrate 1 impregnated with an allyl-modified polyphenylene ether resin is prepared.
[0035]
The transfer sheet base material 11 is made of a heat-resistant resin such as polyethylene terephthalate (PET) resin or polycarbonate (PC), and is used as a support when the copper foil is etched to form the wiring conductor 2 and the wiring conductor 2. It has a function as a support when transferring.
[0036]
The transfer sheet substrate 11 preferably has a thickness of 20 to 50 μm, and if the thickness is less than 20 μm, the rigidity is reduced and the wiring conductor 2 tends to be easily deformed when etching the copper foil, If it exceeds 50 μm, the flexibility tends to decrease, and it tends to be difficult to peel off from the insulating substrate 1. Therefore, the thickness of the transfer sheet substrate 11 is preferably 20 to 50 μm.
[0037]
The thickness of the wiring conductor 2 is preferably 5 to 50 μm, more preferably 10 to 20 μm. If the thickness of the wiring conductor 2 is less than 5 μm, the strength of the wiring conductor 2 tends to decrease and deformation or disconnection tends to occur, and if it exceeds 50 μm, it tends to be difficult to embed the precursor sheet. Therefore, the thickness of the wiring conductor 2a is preferably 5 to 50 μm.
[0038]
Such a transfer sheet 12 is formed by applying a copper foil having a thickness of about 12 to 30 μm to an entirety of one main surface of a transfer sheet substrate 11 made of a heat-resistant resin such as polyethylene terephthalate having a thickness of about 25 μm. Then, a film-like photosensitive resist is applied on the copper foil, and the resist is exposed and developed to form an etching mask having a pattern corresponding to the pattern of the wiring conductor 2. The non-patterned portion of the copper foil is removed by etching by dipping in an aqueous ferric chloride / hydrochloric acid solution at 40 to 60 ° C. for several minutes. The side surface 2a is etched until it becomes shorter than the length, specifically until the angle between the bottom side on the etching mask side and the side surface 2a becomes 45 to 60 degrees, and the cross-sectional shape in the width direction is obtained. It is manufactured by forming the wiring conductor 2 having a trapezoidal shape.
[0039]
On the other hand, the precursor sheet 13 serving as the insulating substrate 1 is made of a heat-resistant fiber such as glass cloth or aramid fiber impregnated with an allyl-modified polyphenylene ether resin and semi-cured, and has a surface on which the wiring conductor 2 is embedded. It has as much plasticity as possible. Further, a through-hole 1a is pierced by a laser in the precursor sheet 13 serving as the insulating substrate 1, and the through-hole 1a is filled with a conductive material made of a metal powder to form a through conductor 1b.
[0040]
Next, as shown in FIG. 3 (b), the transfer sheet 12 is laminated on the surface of the precursor sheet 13 so that the through conductor 1b and the wiring conductor 2 are joined, and they are heated and pressed to form the wiring conductor 2. Is thermocompressed to the precursor sheet 13 and embedded so that the bottom side of the shorter side of the wiring conductor 2 and the surface of the precursor sheet 13 are flush with each other. At this time, since the cross-sectional shape of the wiring conductor 2 is a trapezoidal shape in which the length of the base on the precursor sheet 13 side is opposite to the length of the base opposite thereto, that is, the length of the base on the transfer sheet 12 side. When the wiring conductor 2 is embedded in the precursor sheet 13, a gap 7 having a wedge-shaped cross section in the width direction of the wiring conductor 2 is formed between the side surface 2 a of the wiring conductor 2 and the precursor sheet 13. .
[0041]
Such thermocompression bonding is performed by using a hot press machine at a temperature of 100 to 150 ° C. and a pressure of 0.5 to 5 MPa for several minutes. In the thermocompression bonding, it is better to perform only pressurization prior to heating. If the heating is performed first, the heat causes the transfer sheet 11 to expand, and there is a risk that it becomes difficult to accurately embed the wiring conductor 2 at a desired position. Therefore, in thermocompression bonding, it is preferable to apply pressure prior to heating.
[0042]
Further, they are heated and pressurized to thermally cure the allyl-modified polyphenylene ether resin of the precursor sheet 13 to produce the core substrate 3. In the heat treatment, the precursor sheet 13 is sandwiched from above and below with a release sheet made of a fluorine-based resin or the like, and heat-treated at a pressure of 1 to 5 MPa at a temperature of 150 to 240 ° C. The thermosetting resin is thermoset.
[0043]
Next, the exposed portions of the wiring conductors 2 are immersed in an aqueous solution of formic acid / copper ion at a temperature of about 25 ° C. for several minutes so that the exposed portions of the wiring conductors 2 have irregularities with an arithmetic average roughness of 0.1 to 2 μm. Become Thereafter, a film made of an epoxy resin and serving as an insulating resin layer 4 is attached to the main surface of the core substrate 3 and thermally cured at 150 to 180 ° C. for several hours, as shown in a sectional view of FIG. Then, the insulating resin layer 4 is attached to the main surface of the core substrate 3 and the epoxy resin of the insulating resin layer 4 is filled in the gap 7. Note that the film for the insulating resin layer 4 once melts and softens during thermosetting, so that the epoxy resin of the insulating resin layer 4 is favorably filled into the gap 7 at that time. Then, the wiring conductor 2 embedded in the surface of the insulating substrate 1 and the insulating substrate 1 are firmly bonded by the epoxy resin filled in the gap 7.
[0044]
As described above, according to the method for manufacturing a wiring board of the present invention, the insulating substrate 1 in which the heat-resistant fiber base material is impregnated with the allyl-modified polyphenylene ether resin is made of a metal foil and has a trapezoidal cross-sectional shape in the width direction. The conductor 2 is embedded such that the surface on the bottom side having a shorter length is flush with the surface of the insulating substrate 1 and that a gap 7 is formed between the side surface 2 a of the wiring conductor 2 and the insulating substrate 1. A core substrate 3 is prepared, and an insulating resin layer 4 containing epoxy resin is applied to the surface of the core substrate 3 in which the wiring conductor 2 is embedded, and the inside of the gap 7 is filled with epoxy resin. The epoxy resin serves as an adhesive, and a wiring board in which the wiring conductor 2 and the insulating substrate 1 are firmly bonded can be provided. Further, since the insulating substrate 1 and the insulating resin layer 4 are firmly joined by the anchor effect of the epoxy resin interposed between the side surface 2a of the wiring conductor 2 and the insulating substrate 1, the insulating substrate 1 and the insulating resin layer 4 To provide a wiring board having a strong bond.
[0045]
The insulating resin layer 4 has a thickness of 10 to 80 μm, an epoxy resin and an inorganic insulating filler such as silica or alumina / aluminum nitride having an average particle diameter of 0.01 to 2 μm and a content of 10 to 50% by weight. Consisting of
[0046]
Next, as shown in the sectional view of FIG. 3D, a wiring conductor layer 5 made of copper plating is applied to the upper surface of the insulating resin layer 3. Further, if necessary, the next insulating resin layer 4 and the wiring conductor layer 5 are laminated thereon to complete the wiring board.
[0047]
In order to apply the wiring conductor layer 5 made of copper plating on the upper surface of the insulating resin layer 4, first, the surface of the insulating resin layer 4 was roughened by immersing it in a roughening solution such as an aqueous solution of permanganate. Then, immersed in an aqueous solution of a palladium catalyst for electroless plating to adhere the palladium catalyst to the surface, and further immersed in an electroless copper plating solution composed of copper sulfate, formalin, sodium EDTA, a stabilizer, etc. for about 30 minutes. An electroless copper plating layer having a thickness of about 1 to 2 μm is deposited. Next, a plating-resistant resin layer is deposited on the upper surface of the electroless copper plating layer, and a plurality of openings for depositing the electrolytic copper plating layer are formed in the pattern shape of the copper-plated wiring conductor layer 5 by exposure and development. Further, the inner surface of the opening and the via hole 6 is immersed in an electrolytic copper plating solution comprising sulfuric acid / copper sulfate pentahydrate / chlorine / brightener for several hours while applying a current of several A / dm 2. Is applied with an electrolytic copper plating layer having a thickness of about 10 to 30 μm. Thereafter, the plating-resistant resin layer is peeled off with sodium hydroxide, and the electroless copper plating layer exposed by peeling the plating-resistant resin layer is removed by etching with a sulfuric acid-based aqueous solution such as a mixture of sulfuric acid and hydrogen peroxide solution. It is formed by doing.
[0048]
Thus, according to the method for manufacturing a wiring board of the present invention, it is possible to provide a wiring board in which the adhesion between the wiring conductor 2 and the insulating substrate 1 is strong and the bonding between the insulating substrate 1 and the insulating resin layer 4 is strong. Can be.
[0049]
Note that the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present invention.
[0050]
【The invention's effect】
According to the wiring board of the present invention, the wiring conductor has a trapezoidal cross-sectional shape in the width direction in which the length of the base on the insulating substrate side is longer than the length of the opposing base, and between the side surface and the insulating substrate. The epoxy resin interposed between the side of the wiring conductor and the insulating substrate serves as an adhesive, and the insulating substrate and the side of the wiring conductor are firmly bonded. As a result, a long-term heat history is repeatedly applied to the wiring board after the electronic components are mounted on the wiring board, and the thermal stress generated due to a difference in thermal expansion between the insulating substrate and the wiring conductor is generated at the boundary between the insulating substrate and the wiring conductor. Even if the wiring conductor layer is concentrated, there is no gap between the side surface of the wiring conductor and the insulating substrate, and cracks occur in the insulating resin layer starting from the gap, and the crack cuts the wiring conductor layer to break the wire. Cause defects It does not that put away.
[0051]
Further, according to the wiring board of the present invention, the insulating substrate and the insulating resin layer are firmly joined to each other by the anchor effect of the epoxy resin interposed between the side surface of the wiring conductor and the insulating substrate. Even after long-term thermal history is repeatedly applied after mounting electronic components, even if the thermal stress generated due to the difference in thermal expansion between the insulating substrate and the insulating resin layer concentrates on the boundary between them, the insulating resin layer peels off from the insulating substrate. It doesn't even happen.
[0052]
Furthermore, according to the method for manufacturing a wiring board of the present invention, a wiring conductor made of metal foil and having a trapezoidal cross section in the width direction is formed on an insulating substrate in which a heat-resistant fiber base material is impregnated with an allyl-modified polyphenylene ether resin. Prepare a core substrate which is embedded so that the surface on the bottom side having a shorter length is flush with the surface of the insulating substrate and forms a gap between the side surface of the wiring conductor and the insulating substrate. The epoxy resin acts as an adhesive because the insulating resin layer containing epoxy resin is applied to the surface of the core substrate with the wiring conductor embedded and the gap is filled with epoxy resin. It is possible to provide a wiring board in which a conductor and an insulating substrate are firmly bonded. In addition, since the insulating substrate and the insulating resin layer are firmly joined by the anchor effect of the epoxy resin interposed between the side surface of the wiring conductor and the insulating substrate, the bonding between the insulating substrate and the insulating resin layer is strong. A substrate can be provided.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of an embodiment of a wiring board of the present invention.
FIG. 2 is an enlarged sectional view of a main part of FIG.
FIGS. 3A to 3D are main-portion cross-sectional views of each process for describing the method of manufacturing a wiring board according to the present invention;
[Explanation of symbols]
1 Insulating substrate 2 Wiring conductor 2a Side surface 3 of wiring conductor・ Core substrate 4 ・ ・ ・ ・ ・ ・ ・ ・ ・ Insulating resin layer 5 ・ ・ ・ ・ ・ ・ ・ ・ ・ Wiring conductor layer 7 ・ ・ ・ ・ ・ ・ ・ ・ ・ Gap
