【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銅等の金属箔から成る配線導体を埋入し、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、配線導体上の絶縁樹脂層に径が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金属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、このようなビルドアップ配線基板は、絶縁基板の熱膨張係数が１０×１０−６〜１５×１０−６／℃であり、銅等の金属箔から成る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加されると、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があった。
【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過マンガン酸カリウム水溶液等で粗化することが困難であり、加熱硬化後の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、熱履歴による応力によって配線基板に反りや変形が生じて、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あった。
【０００９】
さらに、コア基板および絶縁樹脂層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、コア基板と絶縁樹脂層との密着性は良好となるものの、絶縁樹脂層の表面を粗化することが困難で絶縁樹脂層と配線導体層との密着が弱いものとなり、配線基板に長期の熱履歴が印加されると、配線導体層が絶縁樹脂層から剥離して断線してしまう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加しても、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、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た下層およびエポキシ樹脂に無機絶縁フィラーを分散させた上層から成る絶縁層とめっきから成る配線導体層とを順次積層して成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、コア基板の配線導体を埋入した表面に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た下層およびエポキシ樹脂に無機絶縁フィラーを分散させた上層から成る絶縁層とめっきから成る配線導体層とを順次積層して成ることから、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加され、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たとしても、絶縁層を構成する下層のガラスクロスがクラックの伝播を防止し、絶縁層上のめっきからなる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く、接続信頼性に優れた配線基板とすることができる。
【００１３】
また、本発明の配線基板によれば、絶縁基板の加熱硬化後のアリル変性ポリフェニレンエーテル樹脂と絶縁層の下層のアリル変性ポリフェニレンエーテル樹脂とが強固に接合するので、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加され、絶縁基板と絶縁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、配線基板に反りや変形が生じたり、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もない。
【００１４】
さらに、絶縁層の上層がエポキシ樹脂に無機絶縁フィラーを分散させたものからなることから、エポキシ樹脂は過マンガン酸カリウム水溶液等で粗化することが容易であり絶縁層の表面を良好に粗化することができ、その結果、絶縁層と配線導体層および上下に位置する絶縁層同士の密着性が良好となり、配線基板に長期の熱履歴が印加された場合においても、配線導体層が絶縁層から剥離して断線したり、絶縁層間で剥離してしまうことはない。
【００１５】
【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は絶縁層、４ａは絶縁層４の上層、４ｂは絶縁層４の下層、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。
【００１６】
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アラミド不織布や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。
【００１７】
また、絶縁基板１の表面には金属箔から成る配線導体２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。
配線導体２は、銅や銀・アルミニウム・ニッケル等の金属箔から成り、その幅が２０〜２００μｍ、厚みが５〜５０μｍであり、後述する配線導体層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。なお、金属箔の材料としては、安価および低導電性の観点からは銅を用いることが好ましい。
【００１８】
また、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６ｂにより電気的に接続してもよい。このような貫通導体６ｂ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６ａ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６ｂを設ける場合、その直径が３０μｍ未満になると貫通導体６ｂ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６ｂ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。
【００１９】
さらに、コア基板３の表面、図１の例では上下面には、絶縁層４と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。絶縁層４は、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する。
【００２０】
本発明の配線基板においては、絶縁層４は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た下層４ｂとエポキシ樹脂に無機絶縁フィラーを分散させた上層４ａとから成り、そしてこのことが重要である。
【００２１】
本発明の配線基板によれば、配線基板がコア基板３の主面に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た下層４ｂおよびエポキシ樹脂に無機絶縁フィラーを分散させた上層４ａから成る絶縁層４とめっきから成る配線導体層５とを順次積層して成ることから、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加され、絶縁基板１と配線導体２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との境界に集中して配線導体２の側面と絶縁基板１との間に隙間が発生したとしても、絶縁層４を構成する下層４ｂのガラスクロスがクラックの伝播を防止し、絶縁層４上のめっきからなる配線導体層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く、接続信頼性に優れた配線基板とすることができる。
【００２２】
また、絶縁基板１の加熱硬化後のアリル変性ポリフェニレンエーテル樹脂と絶縁層４の下層４ｂを構成するアリル変性ポリフェニレンエーテル樹脂とが強固に接合するので、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加され、絶縁基板１と絶縁層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、配線基板に反りや変形が生じたり、絶縁層４とコア基板３との間で膨れや剥がれが発生してしまうこともない。
【００２３】
さらに、絶縁層４の上層４ａがエポキシ樹脂に無機絶縁フィラーを分散させたものからなることから、エポキシ樹脂は過マンガン酸カリウム水溶液等で粗化することが容易であり絶縁層４の表面を良好に粗化することができ、その結果、絶縁層４と配線導体層５および上下に位置する絶縁層４同士の密着性が良好となり、配線基板に長期の熱履歴が印加された場合においても、配線導体層５が絶縁層４から剥離して断線したり、絶縁層４間で剥離してしまうことはない。
【００２４】
なお、絶縁層４の下層４ｂは、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り、絶縁層に強度を付与する機能を有する。このようなガラスクロスは、その織り方により平織、綾織、朱子織の種類があり、アリル変性ポリフェニレンエーテル樹脂との密着性を向上するために、シランカップリング処理がなされている。また、これらのガラスクロスは、通常Ｅガラスが使用されているが、ＤガラスやＳガラス・高誘電率ガラスなどを用いても良い。
【００２５】
また、絶縁層４の上層４ａは、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り、粗化されて配線導体層５のと密着性を向上する機能を有する。このような無機絶縁フィラーは、絶縁層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、絶縁層４の表面に適度な凹凸を形成し、配線導体層５と絶縁層４との密着性を良好となす機能を有する。
【００２６】
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。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％を超えると絶縁層４の樹脂量が減少し絶縁層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。
【００２７】
また、絶縁層４の厚みは、１０〜６０μｍが好ましい。絶縁層４の厚みが１０μｍより薄いと絶縁性が低下する傾向にあり、６０μｍより厚いとレーザで後述するビア孔７を穿孔するのが難しくなる傾向にある。従って、絶縁層４の厚みは、１０〜６０μｍ程度が好ましい。
【００２８】
さらに、絶縁層４の下層４ｂの厚みは、絶縁層４の厚みの１／４〜３／４であることが好ましい。下層４ｂの厚みが、絶縁層４の厚みの１／４より薄いと配線基板の剛性が低下する傾向にあり、３／４より厚いと上層４ａが薄くなるので絶縁層４の粗化面が小さなものとなり、絶縁層４に配線導体層５が強固に密着できなくなる傾向にある。従って、絶縁層４の下層４ｂの厚みは、絶縁層４の厚みの１／４〜３／４であることが好ましい。絶縁層４の下層４ｂの厚みを絶縁層４の厚みの１／４〜３／４とすることにより、コア基板３の厚みを薄くしても配線基板の剛性を防止することができ、配線基板に実装される電子部品の作動による発熱に起因する応力が発生しても、この応力によって配線基板に反りや変形が生じず、電子部品が配線基板から剥がれてしまうことはない。
【００２９】
また、絶縁層４には、レーザ加工によりビア孔７が形成されており、このビア孔７の内部にめっきから成る配線導体層５の一部を充填させることにより絶縁層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の無電解めっき層と厚みが１０〜３０μｍの電解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。
【００３０】
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。
なお、めっきには銅やニッケル・クロム・銀等の金属が用いられ、安価および低導電性の観点からは銅を用いることが好ましい。
【００３１】
さらに、絶縁層４の一方の最外層表面に形成された配線導体層５の一部は、電子部品の各電極に半田バンプ９ａを介して接合される電子部品接続用の実装用電極５ａを形成し、絶縁層４の他方の最外層表面に形成された配線導体層５の一部は、外部電気回路基板（図示せず）の各電極に導体バンプ９ｂを介して接続される外部接続用の実装用電極５ｂを形成している。
【００３２】
なお、実装用電極５ａ・５ｂの表面には、その酸化腐蝕を防止するとともに半田バンプ９ａ・９ｂとの接続を良好とするために、半田との濡れ性が良好で耐腐蝕性に優れたニッケル−金等のめっき層が被着されている。
【００３３】
また、最外層の絶縁層４および実装用電極５ａ・５ｂには、必要に応じて実装用電極５ａ・５ｂの中央部を露出させる開口を有する耐半田樹脂層１０が被着されている。耐半田樹脂層１０は、その厚みが１０〜５０μｍであり、例えばアクリル変性エポキシ樹脂等の感光性樹脂と光開始剤等とから成る混合物に３０〜７０重量％のシリカやタルク等の無機粉末フィラーを含有させた絶縁材料から成り、隣接する実装用電極５ａ・５ｂ同士が半田バンプ（図示せず）により電気的に短絡することを防止するとともに、実装用電極５ａ・５ｂと絶縁層４との接合強度を向上させる機能を有する。
【００３４】
このような耐半田樹脂層１０は、感光性樹脂と光開始剤と無機粉末フィラーとから成る未硬化樹脂フィルムを最外層の絶縁層４表面に被着させる、あるいは、熱硬化性樹脂と無機粉末フィラーとから成る未硬化樹脂ワニスを最外層の絶縁層４表面に塗布するとともに乾燥し、しかる後、露光・現像により開口部を形成し、これをＵＶ硬化および熱硬化させることにより形成される。
【００３５】
かくして、本発明の配線基板によれば、コア基板３の配線導体２が埋入された表面に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た下層４ｂおよびエポキシ樹脂に無機絶縁フィラーを分散させた上層４ａから成る絶縁層４と、めっきから成る配線導体層５とを順次積層して成ることから、配線導体２の側面からクラックが発生しても下層４ｂのガラスクロスがクラックの伝播を防止し、絶縁層４上のめっきからなる配線導体層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。
【００３６】
また、本発明の配線基板によれば、絶縁基板１の加熱硬化後のアリル変性ポリフェニレンエーテル樹脂と絶縁層４の下層４ｂのアリル変性ポリフェニレンエーテル樹脂とが強固に接合し、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加され、絶縁基板１と絶縁層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、配線基板に反りや変形が生じず、絶縁層４が絶縁基板１から剥離してしまうということもない。
【００３７】
次に、本発明の配線基板の製造方法について述べる。
まず、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た絶縁基板１に銅箔から成る配線導体２を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して成るコア基板３を準備する。
【００３８】
このようなコア基板３は、次に述べる方法により製作される。耐熱性樹脂から成る転写用シート基材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と、ガラスクロス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とを用意する。
【００３９】
転写用シート基材は、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。
【００４０】
転写用シート基材は、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、転写用シート基材の厚みは２０〜５０μｍが好ましい。
【００４１】
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。
【００４２】
このような転写用シートは、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の一方の主面全体に接着材を介して厚みが１２μｍ程度の銅箔を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、塩化第二鉄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、最後に、感光性レジストを剥離除去してパターン状の配線導体２を形成することにより製作される。
【００４３】
他方、絶縁基板１と成る前駆体シートは、ガラスクロスやアラミド繊維等の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。
【００４４】
次に、前駆体シートの表面に転写用シートを積層するとともにそれらを加熱加圧して配線導体２を前駆体シートに熱圧着した後、前駆体シートから転写用シート基材を剥離して、前駆体シートにその表面が前駆体シートの表面と同一面をなすように配線導体２を転写埋入してする。
【００４５】
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１２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。
【００４６】
さらに、それらを加熱加圧して前駆体シートのアリル変性ポリフェニレンエーテル樹脂を熱硬化して、絶縁基板１にその表面が絶縁基板１の表面と同一面をなすように配線導体２を埋入したコア基板３を得る。なお、加熱処理にあたっては、前駆体シート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。
【００４７】
次に、コア基板３にプラズマを、出力が０．５〜３ｋｗ、酸素／四弗化炭素＝１／１のガス比率の条件で、３００〜５００秒間照射することによって、絶縁基板１の主面に算術平均粗さＲａが０．５〜３μｍの凹凸を形成する。この凹凸により絶縁基板１と絶縁層４との接着力を向上させることができる。
【００４８】
次に、プラズマを照射したコア基板３を約２５℃の温度の蟻酸・銅イオン溶液に数分間浸漬することにより、配線導体２の表面を算術平均粗さが０．１〜２μｍの凹凸を有するように粗化する。
【００４９】
次に、コア基板３の配線導体２が埋入された表面に、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たフィルムを貼着し、その上にエポキシ樹脂に無機絶縁フィラーを分散させたフィルムを貼着した後に、１５０〜１８０℃で数時間熱硬化することによりコア基板３の主面に絶縁層４を形成する。なお、絶縁層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コア基板３の粗化面に樹脂が良好に充填される。そして、コア基板３の表面と絶縁層４とが強固に接着される。
【００５０】
次に、絶縁層４の上面に銅めっきから成る配線導体層５を被着・形成する。さらに必要に応じてその上に次層の絶縁層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。
【００５１】
なお、絶縁層４の上面に銅めっきから成る配線導体層５を被着・形成するには、まず、絶縁層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貫通孔の内面に厚みが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。
【００５２】
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、本発明においてはコア基板３の配線導体２を埋入した表面に、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た下層４ｂおよびエポキシ樹脂に無機絶縁フィラーを分散させた上層から成る絶縁層４を積層することが重要であり、２層目以降の絶縁層には、例えばエポキシ樹脂に無機絶縁フィラーを分散させた絶縁層を積層してもよい。
【００５３】
【発明の効果】
本発明の配線基板によれば、コア基板の配線導体を埋入した表面に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た下層およびエポキシ樹脂に無機絶縁フィラーを分散させた上層から成る絶縁層とめっきから成る配線導体層とを順次積層して成ることから、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加され、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たとしても、絶縁層を構成する下層のガラスクロスがクラックの伝播を防止し、絶縁層上のめっきからなる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く、接続信頼性に優れた配線基板とすることができる。
【００５４】
また、本発明の配線基板によれば、絶縁基板のアリル変性ポリフェニレンエーテル樹脂と絶縁層の下層のアリル変性ポリフェニレンエーテル樹脂とが強固に接合するので、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加され、絶縁基板と絶縁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、配線基板に反りや変形が生じたり、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もない。
【００５５】
さらに、絶縁層の上層がエポキシ樹脂に無機絶縁フィラーを分散させたものからなることから、エポキシ樹脂は過マンガン酸カリウム水溶液等で粗化することが容易であり絶縁層の表面を良好に粗化することができ、その結果、絶縁層と配線導体層および上下に位置する絶縁層同士の密着性が良好となり、配線基板に長期の熱履歴が印加された場合においても、配線導体層が絶縁層から剥離して断線したり、絶縁層間で剥離してしまうことはない。
【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。
【符号の説明】
１・・・・・・・・・・絶縁基板
２・・・・・・・・・・配線導体
３・・・・・・・・・・コア基板
４・・・・・・・・・・絶縁層
４ａ・・・・・・・・・絶縁層の上層
４ｂ・・・・・・・・・絶縁層の下層
５・・・・・・・・・・配線導体層[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.
[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 made of metal foil such as copper is applied to 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. The conductor is embedded and then cured by heating to obtain a core substrate in which the wiring conductor is 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 on the wiring conductor by a laser, and the surface of the insulating resin layer and the inner surface of the through hole are chemically formed with a roughening solution such as a potassium permanganate solution. Then, a conductor film made of metal plating is applied to the surface of the insulating resin layer and the inner surface of the through hole by using a semi-additive method to form a wiring conductor 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 such a build-up 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 made of a metal foil such as copper is 15 ×. Since the thermal expansion coefficient of the insulating substrate and the thermal expansion coefficient of the wiring conductor are different from 10 −6 to 20 × 10 −6 / ° C., if a long-term thermal history is repeatedly applied after mounting the electronic component on the wiring substrate. The thermal stress generated by the thermal expansion difference between the insulating substrate and the wiring conductor 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. There is a problem that cracks occur in the resin layer and the wiring conductor layer is cut to cause disconnection failure.
[0008]
Further, 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 with an aqueous potassium permanganate solution or the like, and the surface of the core substrate after heat curing is hardened. When an insulating resin layer containing an epoxy resin is laminated on the core substrate, 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 core substrate and the For example, when mounting an electronic component on the surface of a wiring board, the temperature of the wiring board may be suddenly changed, or after mounting the electronic component, the electronic component may be weakened. If heat generated during operation or heat from the external environment is repeatedly applied for a long period of time, wiring due to stress due to thermal history Warpage or deformation occurs in the plate, blistering and peeling between the insulating resin layer and the core substrate was also a problem that sometimes occurs.
[0009]
Furthermore, when an allyl-modified polyphenylene ether resin is used for the core substrate and the insulating resin layer, the adhesion between the core substrate and the insulating resin layer becomes good, but it is difficult to roughen the surface of the insulating resin layer, and There is a problem that the adhesion between the layer and the wiring conductor layer becomes weak, and when a long-term heat history is applied to the wiring substrate, the wiring conductor layer is separated from the insulating resin layer and disconnected.
[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, which can withstand thermal stress sufficiently even when a long-term heat history is repeatedly applied, and that a disconnection occurs. 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 conductor comprising a lower layer of glass cloth impregnated with an allyl-modified polyphenylene ether resin and an upper layer of an epoxy resin in which an inorganic insulating filler is dispersed, and a wiring conductor comprising plating, on the surface of the core substrate having the wiring conductor embedded therein. And layers are sequentially laminated.
[0012]
According to the wiring board of the present invention, an insulating layer consisting of a lower layer in which a glass cloth is impregnated with an allyl-modified polyphenylene ether resin on the surface of a core substrate in which wiring conductors are embedded, and an upper layer in which an inorganic insulating filler is dispersed in an epoxy resin. Since the wiring conductor layer made of plating is sequentially laminated, a long-term heat history is repeatedly applied after mounting the electronic component on the wiring board, and the thermal stress generated due to the difference in thermal expansion between the insulating substrate and the wiring conductor is insulated. Even if a gap occurs between the side surface of the wiring conductor and the insulating substrate at the boundary between the substrate and the wiring conductor, the lower glass cloth constituting the insulating layer prevents the propagation of cracks, It is possible to provide a wiring board having excellent connection reliability without causing a disconnection failure by cutting the wiring conductor layer made of plating.
[0013]
Further, according to the wiring board of the present invention, since the allyl-modified polyphenylene ether resin after heat curing of the insulating substrate and the allyl-modified polyphenylene ether resin of the lower layer of the insulating layer are firmly joined, the electronic component is mounted on the wiring board. Even if a long-term thermal history is repeatedly applied later and the thermal stress generated due to the difference in thermal expansion between the insulating substrate and the insulating layer concentrates on the boundary between them, the wiring substrate may be warped or deformed, or the insulating resin layer and the core substrate may be deformed. There is no swelling or peeling between them.
[0014]
Furthermore, since the upper layer of the insulating layer is made of epoxy resin with inorganic insulating filler dispersed, it is easy to roughen the epoxy resin with an aqueous solution of potassium permanganate, etc. As a result, the adhesiveness between the insulating layer and the wiring conductor layer and between the insulating layers located above and below is improved, and even when a long-term heat history is applied to the wiring board, the wiring conductor layer remains in the insulating layer. There is no disconnection due to peeling, or peeling between insulating layers.
[0015]
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 layer, 4a is an upper layer of the insulating layer 4, and 4b is a lower layer of the insulating layer 4. Reference numerals 5 and 5 denote wiring conductor layers, which mainly constitute the wiring board of the present invention.
[0016]
The insulating substrate 1 constituting the core substrate 3 has, for example, a glass cloth in which an aramid nonwoven fabric or a glass fiber which is a heat-resistant fiber base material is woven vertically and horizontally, is impregnated with an allyl-modified polyphenylene ether resin, and has a thickness of 0.15 to 1. It is a substantially square substrate of 5 mm, 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.
[0017]
The surface of the wiring conductor 2 made of metal foil is embedded in the surface of the insulating substrate 1 so as to be flush with the surface of the insulating substrate 1.
The wiring conductor 2 is made of a metal foil such as copper, silver, aluminum, nickel, or the like, has a width of 20 to 200 μm, and a thickness of 5 to 50 μm. (Not shown) function as a part of a conductive path for electrically connecting each electrode to an external 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. As a material of the metal foil, it is preferable to use copper from the viewpoint of low cost and low conductivity.
[0018]
Further, the wiring conductors 2 positioned above and below may be electrically connected to each other by the through conductor 6b formed on the insulating substrate 1. Such a through conductor 6b 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 6a provided in the insulating substrate 1. Formed by embedding a conductor consisting of When the through conductor 6b is provided, if the diameter is less than 30 μm, it tends to be difficult to form the through conductor 6b, and if it exceeds 100 μm, there is a tendency that high-density wiring cannot be formed. Therefore, when the through conductor 6b is provided, the diameter thereof is preferably in the range of 30 to 100 μm.
[0019]
Further, insulating layers 4 and wiring conductor layers 5 made of plating are alternately laminated on the surface of the core substrate 3, that is, the upper and lower surfaces in the example of FIG. The insulating layer 4 has a function as a support for the wiring conductor layer 5 made of plating.
[0020]
In the wiring board of the present invention, the insulating layer 4 comprises a lower layer 4b in which glass cloth is impregnated with an allyl-modified polyphenylene ether resin and an upper layer 4a in which an inorganic insulating filler is dispersed in epoxy resin, and this is important. .
[0021]
According to the wiring board of the present invention, the wiring board has an insulating layer composed of a lower layer 4b in which glass cloth is impregnated with an allyl-modified polyphenylene ether resin on a main surface of a core substrate 3 and an upper layer 4a in which an inorganic insulating filler is dispersed in epoxy resin. 4 and the wiring conductor layer 5 made of plating are sequentially laminated, so that a long-term thermal history is repeatedly applied after the electronic component is mounted on the wiring board, and is generated due to a difference in thermal expansion between the insulating substrate 1 and the wiring conductor 2. Even if thermal stress is concentrated on the boundary between the insulating substrate 1 and the wiring conductor 2 and a gap is generated between the side surface of the wiring conductor 2 and the insulating substrate 1, the glass cloth of the lower layer 4b constituting the insulating layer 4 is not To prevent the propagation of cracks and prevent the wiring conductor layer 5 made of plating on the insulating layer 4 from being cut to cause a disconnection defect, and to provide a wiring board having excellent connection reliability. It can be.
[0022]
Further, since the allyl-modified polyphenylene ether resin after the heat curing of the insulating substrate 1 and the allyl-modified polyphenylene ether resin constituting the lower layer 4b of the insulating layer 4 are firmly joined, a long-term heat after mounting the electronic component on the wiring board is obtained. Even if the history is repeatedly applied and the thermal stress generated due to the difference in thermal expansion between the insulating substrate 1 and the insulating layer 4 concentrates on the boundary between them, the wiring substrate may be warped or deformed, or the insulating layer 4 and the core substrate 3 No swelling or peeling occurs between them.
[0023]
Further, since the upper layer 4a of the insulating layer 4 is made of an epoxy resin in which an inorganic insulating filler is dispersed, the epoxy resin can be easily roughened with a potassium permanganate aqueous solution or the like, and the surface of the insulating layer 4 can be improved. As a result, the adhesion between the insulating layer 4 and the wiring conductor layer 5 and between the upper and lower insulating layers 4 is improved, and even when a long-term heat history is applied to the wiring board, There is no possibility that the wiring conductor layer 5 is separated from the insulating layer 4 and disconnected, or separated between the insulating layers 4.
[0024]
The lower layer 4b of the insulating layer 4 is formed by impregnating glass cloth, which is a heat-resistant fiber base material, with glass fibers vertically and horizontally, with an allyl-modified polyphenylene ether resin, and has a function of imparting strength to the insulating layer. Such glass cloths are classified into plain weave, twill weave, and satin weave depending on the weaving method, and silane coupling treatment is performed to improve the adhesiveness with the allyl-modified polyphenylene ether resin. Although E glass is usually used for these glass cloths, D glass, S glass, high dielectric constant glass, or the like may be used.
[0025]
The upper layer 4a of the insulating layer 4 is made of 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, and is roughened. Thus, it has a function of improving the adhesion to the wiring conductor layer 5. Such an inorganic insulating filler adjusts the coefficient of thermal expansion of the insulating layer 4 so as to match the coefficient of thermal expansion of the wiring conductor layer 5, and forms appropriate irregularities on the surface of the insulating layer 4. 4 has a function of improving the adhesiveness to 4.
[0026]
If the average particle size of the inorganic insulating filler is less than 0.01 μm, it tends to be difficult to form an insulating layer 4 having a uniform thickness due to aggregation of the inorganic insulating fillers, and more than 2 μm. In addition, the unevenness of the surface of the insulating layer 4 becomes too large, and the adhesion between the wiring conductor layer 5 and the insulating 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. 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 layer 4 tends to be small, and when it exceeds 50% by weight, the resin amount of the insulating layer 4 decreases. It tends to be difficult to form the insulating layer 4. Therefore, the content of the inorganic insulating filler is preferably in the range of 10 to 50% by weight.
[0027]
The thickness of the insulating layer 4 is preferably 10 to 60 μm. If the thickness of the insulating layer 4 is smaller than 10 μm, the insulating property tends to decrease, and if it is larger than 60 μm, it becomes difficult to form a via hole 7 described later with a laser. Therefore, the thickness of the insulating layer 4 is preferably about 10 to 60 μm.
[0028]
Furthermore, the thickness of the lower layer 4b of the insulating layer 4 is preferably １ ／ to ／ of the thickness of the insulating layer 4. If the thickness of the lower layer 4b is smaller than 1/4 of the thickness of the insulating layer 4, the rigidity of the wiring board tends to decrease. If the thickness of the lower layer 4b is larger than 3/4, the upper layer 4a becomes thin, so that the roughened surface of the insulating layer 4 is small. And the wiring conductor layer 5 tends to be unable to firmly adhere to the insulating layer 4. Therefore, the thickness of the lower layer 4 b of the insulating layer 4 is preferably １ ／ to ／ of the thickness of the insulating layer 4. By setting the thickness of the lower layer 4b of the insulating layer 4 to 〜 to ／ of the thickness of the insulating layer 4, the rigidity of the wiring board can be prevented even if the thickness of the core substrate 3 is reduced. Even if stress is generated due to heat generated by the operation of the electronic component mounted on the wiring board, the stress does not cause the wiring board to warp or deform, and the electronic component does not peel off from the wiring board.
[0029]
Further, via holes 7 are formed in the insulating layer 4 by laser processing. By filling a part of the wiring conductor layer 5 made of plating into the via holes 7, the via holes 7 are vertically arranged with the insulating layer 4 interposed therebetween. The located wiring conductor 2 and the wiring conductor layer 5, 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, an electroless plating layer and a thickness of 10 to 30 μm. It has a function as a conductive path for electrically connecting each electrode of the electronic component to an external electric circuit board.
[0030]
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.
Note that copper or a metal such as nickel, chromium, or silver is used for plating, and copper is preferably used from the viewpoint of low cost and low conductivity.
[0031]
Further, a part of the wiring conductor layer 5 formed on one outermost layer surface of the insulating layer 4 forms a mounting electrode 5a for connecting an electronic component, which is joined to each electrode of the electronic component via a solder bump 9a. A part of the wiring conductor layer 5 formed on the surface of the other outermost layer of the insulating layer 4 is connected to each electrode of an external electric circuit board (not shown) via a conductor bump 9b for external connection. The mounting electrode 5b is formed.
[0032]
The surface of the mounting electrodes 5a and 5b is formed of nickel having good wettability with solder and excellent corrosion resistance in order to prevent the oxidative corrosion and to make the connection with the solder bumps 9a and 9b good. A plating layer of gold or the like is applied;
[0033]
Further, the outermost insulating layer 4 and the mounting electrodes 5a and 5b are covered with a solder-resistant resin layer 10 having an opening for exposing a central portion of the mounting electrodes 5a and 5b as necessary. The solder-resistant resin layer 10 has a thickness of 10 to 50 μm. For example, 30 to 70% by weight of an inorganic powder filler such as silica or talc is added to a mixture of a photosensitive resin such as an acrylic-modified epoxy resin and a photoinitiator. To prevent the adjacent mounting electrodes 5a and 5b from being electrically short-circuited by solder bumps (not shown), and to prevent the mounting electrodes 5a and 5b from being electrically connected to the insulating layer 4. It has the function of improving the bonding strength.
[0034]
Such a solder-resistant resin layer 10 is formed by applying an uncured resin film composed of a photosensitive resin, a photoinitiator, and an inorganic powder filler on the surface of the outermost insulating layer 4 or by using a thermosetting resin and an inorganic powder filler. An uncured resin varnish comprising a filler is applied to the surface of the outermost insulating layer 4 and dried, and thereafter, an opening is formed by exposure and development, and this is formed by UV curing and heat curing.
[0035]
Thus, according to the wiring board of the present invention, the inorganic insulating filler is dispersed in the lower layer 4b in which the glass cloth is impregnated with the allyl-modified polyphenylene ether resin on the surface of the core substrate 3 in which the wiring conductor 2 is embedded and the epoxy resin. Since the insulating layer 4 composed of the upper layer 4a and the wiring conductor layer 5 composed of plating are sequentially laminated, even if a crack occurs from the side surface of the wiring conductor 2, the glass cloth of the lower layer 4b prevents the propagation of the crack. Also, there is no possibility that the wiring conductor layer 5 made of plating on the insulating layer 4 is cut to cause a disconnection failure.
[0036]
Further, according to the wiring board of the present invention, the allyl-modified polyphenylene ether resin of the insulating substrate 1 after heat curing and the allyl-modified polyphenylene ether resin of the lower layer 4b of the insulating layer 4 are firmly joined, and as a result, Even if a long-term thermal history is repeatedly applied after mounting the electronic component, even if the thermal stress generated due to the difference in thermal expansion between the insulating substrate 1 and the insulating layer 4 concentrates on the boundary between them, the wiring substrate does not warp or deform. In addition, the insulating layer 4 does not peel off from the insulating substrate 1.
[0037]
Next, a method for manufacturing a wiring board according to the present invention will be described.
First, a core substrate 3 having a wiring conductor 2 made of copper foil embedded in an insulating substrate 1 in which glass cloth is impregnated with an allyl-modified polyphenylene ether resin so that the surface thereof is flush with the surface of the insulating substrate 1 is provided. prepare.
[0038]
Such a core substrate 3 is manufactured by a method described below. A transfer sheet in which a wiring conductor 2 made of copper foil is applied to a transfer sheet base made of a heat-resistant resin, and an insulating substrate 1 in which a glass cloth is impregnated with an uncured allyl-modified polyphenylene ether resin. And a precursor sheet.
[0039]
The transfer sheet base material is made of a heat-resistant resin such as polyethylene terephthalate (PET) resin or polycarbonate (PC), and is used to transfer the support and the wiring conductor 2 when the copper foil is etched to form the wiring conductor 2. It has a function as a support when performing.
[0040]
The transfer sheet base material preferably has a thickness of 20 to 50 μm. 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, 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 is preferably 20 to 50 μm.
[0041]
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.
[0042]
Such a transfer sheet is capable of peeling a copper foil having a thickness of about 12 μm through an adhesive over the entire one main surface of a transfer sheet base made of a heat-resistant resin such as polyethylene terephthalate having a thickness of about 25 μm. After bonding, a film-shaped 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. Thereafter, a ferric chloride solution The non-patterned portion of the copper foil is removed by etching by dipping in the inside, and finally, the photosensitive resist is peeled off to form the patterned wiring conductor 2.
[0043]
On the other hand, the precursor sheet to be the insulating substrate 1 is made of a heat-resistant fiber base material such as glass cloth or aramid fiber impregnated with an allyl-modified polyphenylene ether resin and semi-cured. It has enough plasticity to enter.
[0044]
Next, the transfer sheet is laminated on the surface of the precursor sheet, and the wiring conductors 2 are heated and pressurized to thermally press-bond the wiring conductors 2 to the precursor sheet. The wiring conductors 2 are transferred and embedded in the body sheet so that the surface thereof is flush with the surface of the precursor sheet.
[0045]
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 transfer sheet 12 is stretched by the heat, and there is a risk that it is 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.
[0046]
Further, they are heated and pressurized to thermally cure the allyl-modified polyphenylene ether resin of the precursor sheet, and the core in which the wiring conductor 2 is embedded in the insulating substrate 1 so that the surface thereof is flush with the surface of the insulating substrate 1. A substrate 3 is obtained. In the heat treatment, the precursor sheet is sandwiched from above and below by a release sheet made of a fluororesin or the like, and heat-treated at a pressure of 1 to 5 MPa at a temperature of 150 to 240 ° C. The curable resin is cured by heat.
[0047]
Next, the core substrate 3 is irradiated with plasma for 300 to 500 seconds under the conditions of a gas output of 0.5 to 3 kw and a gas ratio of oxygen / carbon tetrafluoride = 1/1, so that the main surface of the insulating substrate 1 is exposed. An unevenness having an arithmetic average roughness Ra of 0.5 to 3 μm is formed. Due to the unevenness, the adhesive strength between the insulating substrate 1 and the insulating layer 4 can be improved.
[0048]
Next, the core substrate 3 irradiated with plasma is immersed in a formic acid / copper ion solution at a temperature of about 25 ° C. for several minutes, so that the surface of the wiring conductor 2 has irregularities with an arithmetic average roughness of 0.1 to 2 μm. Roughening.
[0049]
Next, a film in which an allyl-modified polyphenylene ether resin is impregnated on a glass cloth is adhered to the surface of the core substrate 3 in which the wiring conductor 2 is embedded, and a film in which an inorganic insulating filler is dispersed in an epoxy resin is adhered thereon. Then, the insulating layer 4 is formed on the main surface of the core substrate 3 by thermosetting at 150 to 180 ° C. for several hours. The film for the insulating layer 4 once melts and softens during thermosetting, so that the resin is satisfactorily filled in the roughened surface of the core substrate 3 at that time. Then, the surface of the core substrate 3 and the insulating layer 4 are firmly bonded.
[0050]
Next, a wiring conductor layer 5 made of copper plating is attached and formed on the upper surface of the insulating layer 4. Further, if necessary, the next insulating layer 4 and the wiring conductor layer 5 are laminated thereon to complete the wiring board.
[0051]
In order to apply and form the wiring conductor layer 5 made of copper plating on the upper surface of the insulating layer 4, first, the surface of the insulating layer 4 was roughened by immersion in a roughening solution such as an aqueous solution of permanganates. 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, by dipping 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 to the inner surface of the opening and the through-hole, An electrolytic copper plating layer having a thickness of about 10 to 30 μm is applied. 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.
[0052]
It should be noted that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. It is important to laminate an insulating layer 4 composed of a lower layer 4b in which an allyl-modified polyphenylene ether resin is impregnated in a glass cloth and an upper layer in which an inorganic insulating filler is dispersed in an epoxy resin, on the surface in which 2 is embedded. For example, an insulating layer in which an inorganic insulating filler is dispersed in an epoxy resin may be stacked on the insulating layers after the first one.
[0053]
【The invention's effect】
According to the wiring board of the present invention, an insulating layer consisting of a lower layer in which a glass cloth is impregnated with an allyl-modified polyphenylene ether resin on the surface of a core substrate in which wiring conductors are embedded, and an upper layer in which an inorganic insulating filler is dispersed in an epoxy resin. Since the wiring conductor layer made of plating is sequentially laminated, a long-term heat history is repeatedly applied after mounting the electronic component on the wiring board, and the thermal stress generated due to the difference in thermal expansion between the insulating substrate and the wiring conductor is insulated. Even if a gap occurs between the side surface of the wiring conductor and the insulating substrate at the boundary between the substrate and the wiring conductor, the lower glass cloth constituting the insulating layer prevents the propagation of cracks, It is possible to provide a wiring board having excellent connection reliability without causing a disconnection failure by cutting the wiring conductor layer made of plating.
[0054]
Further, according to the wiring board of the present invention, since the allyl-modified polyphenylene ether resin of the insulating substrate and the allyl-modified polyphenylene ether resin of the lower layer of the insulating layer are firmly joined, a long-term heat after mounting the electronic component on the wiring board is obtained. Even if the history is repeatedly applied and the thermal stress generated due to the difference in thermal expansion between the insulating substrate and the insulating layer concentrates on the boundary between them, the wiring board may be warped or deformed or the insulating resin layer and the core substrate may be deformed. No swelling or peeling occurs.
[0055]
Furthermore, since the upper layer of the insulating layer is made of epoxy resin with inorganic insulating filler dispersed, it is easy to roughen the epoxy resin with an aqueous solution of potassium permanganate, etc. As a result, the adhesiveness between the insulating layer and the wiring conductor layer and between the insulating layers located above and below is improved, and even when a long-term heat history is applied to the wiring board, the wiring conductor layer remains in the insulating layer. There is no disconnection due to peeling, or peeling between insulating layers.
[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.
[Explanation of symbols]
1 ... Insulating substrate 2 ... Wiring conductor 3 ... Core substrate 4 ... Insulating layer 4a ... Upper layer 4b of insulating layer ... Lower layer 5 of insulating layer ... Wiring conductor layer
