JP3768920B2

JP3768920B2 - Circuit board manufacturing method and power conversion module using the circuit board

Info

Publication number: JP3768920B2
Application number: JP2002152763A
Authority: JP
Inventors: 浩一平野; 嘉久山下; 誠一中谷
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2001-06-07
Filing date: 2002-05-27
Publication date: 2006-04-19
Anticipated expiration: 2022-05-27
Also published as: JP2003060346A

Description

【０００１】
【発明の属する技術分野】
本発明は、電気電子機器に使用される回路基板およびその製造方法に関するものであり、特に比較的大電流を使用するパワーエレクトロニクス分野に好適な回路基板の製造方法に関するものである。
【０００２】
【従来の技術】
近年、電子機器の高性能化、小型化の要求に伴い、半導体等の高密度、高機能化が要請されている。これにより半導体等を実装するための回路基板もまた小型高密度なものが望まれている。その結果、回路基板の放熱を考慮した設計が重要となってきている。回路基板の放熱性を改良する技術として、一般的なガラス−エポキシ樹脂によるプリント基板に対し、絶縁基材自体の熱伝導率を高め、局所的な温度上昇を押さえる基板が求められている。ガラス−エポキシ樹脂よりも高い熱伝導率を持つ基板としては、銅やアルミニウムなどの金属板を使用し、この金属板の片面に電気絶縁層を介して回路パターンを形成する金属ベース基板が知られている。しかし、金属ベース基板は比較的厚い金属板を使用するために重量が大きくなり、小型軽量化が困難である。また、基板の熱伝導を高めるためには絶縁層の厚みを薄くしなければならず、絶縁耐圧の低下や浮遊容量が大きくなるなどの課題がある。また、セラミック基板やガラス−セラミック基板はガラス−エポキシ基板よりも熱伝導率は高いが、導電体として金属粉末やその焼成体を使用しているため比較的配線抵抗が高くなり、大電流を使用する場合の損失や、そこで発生するジュール熱が大きくなるという課題がある。
【０００３】
これらの課題を解決して、一般的なガラス−エポキシ基板に近いプロセスで作製でき、高い熱伝導性を持つ回路基板としては、例えば特開平１０−１７３０９７号公報に開示されている。その熱伝導基板の製造方法を図７に示す。これによると、無機質フィラーと熱硬化性樹脂とを少なくとも含む混合物スラリーを造膜してシート状の熱伝導混合物７１を作製し、それを乾燥させた後、図７（ａ）に示すように金属箔７２と重ね合わせ、次いで図７（ｂ）に示すように加熱加圧してシート状の熱伝導混合物７１を硬化させ電気絶縁層７３とする。その後、図７（ｃ）に示すように貫通穴７４の加工を行い、その後銅メッキ法により層間接続を行い、回路パターン７５を形成して図７（ｄ）に示すような熱伝導基板を作製している。
【０００４】
【発明が解決しようとする課題】
このような方法によって回路基板を製造する場合には、貫通穴加工法としてドリル加工を行うことが一般的である。しかしながら、熱伝導率を高めるために熱伝導混合物中の無機質フィラーの比率を高くすると、絶縁体中の堅い無機質フィラーによりドリルの磨耗が著しくなり、またチッピングなどが発生しやすくなるため、穴品質の劣化が高頻度で発生するようになる。これを防ぐためにドリル交換を頻繁に行うと、通常のプリント配線板に比べてその生産性は大幅に低下し、穴加工コストが増大するという課題を有していた。
【０００５】
また、熱硬化性樹脂が未硬化状態である熱伝導混合物に穴加工し、その後金属箔を接着させて加熱加圧して硬化させると、加熱により熱伝導混合物が軟化して穴形状を保つことができず、貫通穴を形成することが困難であり、その後のメッキ加工ができなくなるという課題を有していた。
【０００６】
そこで、本発明は前記従来の課題を解決するためになされたものであり、貫通穴加工の生産性を向上させ、低コストで穴加工を行える高放熱性を有する回路基板の製造方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
前記目的を達成するため、本発明の回路基板の製造方法は、（１）無機質フィラー７０〜９５質量％と、未硬化の熱硬化性樹脂、熱可塑性樹脂および潜在性硬化剤を少なくとも含む樹脂組成物５〜３０質量％と、からなる熱伝導樹脂組成物を作製する工程と、（２）前記熱伝導樹脂組成物中の前記熱硬化性樹脂が硬化を開始する温度よりも低い温度で加熱加圧して前記熱伝導樹脂組成物を非可逆的に固形化して回路基板前駆体を作製する工程と、（３）前記回路基板前駆体の任意の位置に貫通穴を形成する工程と、（４）前記回路基板前駆体中の前記熱硬化性樹脂を硬化させる工程とを含んでいることを特徴とする。
【０００８】
また、本発明の回路基板の製造方法は、前記回路基板前駆体を作製する工程（２）が、金属箔と前記熱伝導樹脂組成物とを接触させ、前記熱伝導樹脂組成物中の前記熱硬化性樹脂が硬化を開始する温度よりも低い温度で加熱加圧して前記金属箔と前記熱伝導樹脂組成物とを接着させるとともに前記熱伝導樹脂組成物を非可逆的に固形化して回路基板前駆体を作製する工程からなり、さらに別工程として、前記金属箔を加工して回路パターンを形成する工程を含むことができる。
【０００９】
また、本発明の回路基板の製造方法は、前記回路基板前駆体を作製する工程（２）が、２枚の金属箔で前記熱伝導樹脂組成物を挟みこみ、前記熱伝導樹脂組成物中の前記熱硬化性樹脂が硬化を開始する温度よりも低い温度で加熱加圧して前記金属箔と前記熱伝導樹脂組成物とを接着させるとともに前記熱伝導樹脂組成物を非可逆的に固形化して回路基板前駆体を作製する工程からなり、さらに別工程として、前記貫通穴に銅メッキによるスルーホールを形成して前記金属箔を電気的に接続させる工程と、前記金属箔を加工して回路パターンを形成する工程とを含むことができる。
【００１０】
これらの回路基板の製造方法によれば、熱伝導樹脂組成物中の熱硬化性樹脂が未硬化状態のまま前記熱伝導樹脂組成物を固形化して金属箔と接着させることができるため、回路基板を所望の平板形状に加工することができる。また、固形化した後での加工が容易なため、簡便な方法で貫通穴の形成ができる。更に、その後に熱硬化性樹脂を硬化させた場合でも、通常のプリント配線板の形成時のような加圧が必要でないため、貫通穴の変形や埋まりがなく、また硬化収縮による寸法変化を小さくすることができる。
【００１１】
また、本発明の回路基板の製造方法は、前記熱伝導樹脂組成物を作製する工程（１）の後で、前記熱伝導樹脂組成物を補強材と一体化する工程を追加することが好ましい。これにより回路基板の強度が向上する。また、補強材が含まれるために金属箔との接着時に絶縁層の厚みが保持され、熱伝導樹脂組成物の過剰な流出を防ぐことができる。
【００１２】
また、本発明の回路基板の製造方法は、前記補強材がセラミック繊維もしくはガラス繊維からなることが好ましい。これらは強度が高く、また比較的熱伝導性に優れているからである。
【００１３】
また、本発明の回路基板の製造方法は、前記回路基板前駆体を作製する工程（２）における加熱加圧が真空中で行われることが好ましい。これにより、基板のボイドが低減でき、また金属箔の劣化を防止することができる。
【００１４】
また、本発明の回路基板の製造方法は、前記回路基板前駆体中の前記熱硬化性樹脂を硬化させる工程（４）における硬化が加熱加圧して行われることが好ましい。これにより金属箔と絶縁基体との接着性が向上する。
【００１５】
また、本発明の回路基板の製造方法は、前記熱伝導樹脂組成物の粘度が１００〜１０００００Ｐａ・ｓの範囲であり、前記熱伝導樹脂組成物を非可逆的に固形化させたときの粘度が８×１０⁴〜３×１０⁶Ｐａ・ｓであることが好ましい。この粘度範囲にある場合には、基板状に形状加工することが容易であり、また固形化させた場合にも貫通穴の加工が容易に行える。
【００１６】
また、本発明の回路基板の製造方法は、前記回路基板前駆体の任意の位置に貫通穴を形成する工程（３）における貫通穴の加工の方法が、パンチングマシンによる打ち抜き加工、金型による打ち抜き加工およびドリル加工からなる群から選択された１つの方法であることが好ましい。
【００１７】
また、本発明の回路基板の製造方法は、前記回路基板前駆体の任意の位置に貫通穴を形成する工程（３）における貫通穴の加工を行う際に、同時に基板の少なくとも一部分に外形加工を行って所望の形状に加工することが好ましい。
【００１８】
また、本発明の回路基板の製造方法は、前記金属箔の少なくとも片面が粗化された厚さ１２〜２００μｍの銅箔であることが好ましい。
【００１９】
また、本発明の回路基板の製造方法は、前記熱伝導樹脂組成物を非可逆的に固形化させるときの温度が、７０〜１４０℃であることが好ましい。
【００２０】
また、本発明の回路基板の製造方法は、前記無機質フィラーがＡｌ₂Ｏ₃、ＳｉＯ₂、ＭｇＯ、ＢｅＯ、Ｓｉ₃Ｎ₄、ＳｉＣ、ＡｌＮ、ＢＮからなる群から選択された少なくとも１種類を含んでいることが好ましい。
【００２３】
また、本発明の電力変換モジュールは、前記製造方法で製造した回路基板に、少なくとも半導体および受動部品を実装してなることを特徴とする。なお、ここでいう電力変換モジュールとは、単体もしくは補助的な回路と接続することにより、電圧や電力を変換させる機能を有するモジュールのことを指し、例えばＤＣ−ＤＣコンバータやインバータなどを指す。
【００２４】
【発明の実施の形態】
本発明の実施の形態にかかる回路基板の製造方法においては、無機質フィラーと、未硬化の熱硬化性樹脂、熱可塑性樹脂および潜在性硬化剤を少なくとも含む樹脂組成物とからなる熱伝導樹脂組成物を基本要素とする。前記の熱伝導樹脂組成物は形状の自由度が高いため、シート状や層状に加工することが容易であり、また補強材に塗布あるいは含浸させることも容易である。また、熱伝導樹脂組成物はその中に含まれる樹脂が未硬化であるため、配線パターンであるリードフレームや放熱板と加熱加圧により接着させることが可能であり、高い絶縁性、気密性、接着性を得ることができる。更に、無機質フィラーを高い比率で混合させることが可能であるため、高い熱伝導性を実現でき、また基板の熱膨張係数を低下させることができる。更に、熱可塑性樹脂を含むことにより、この熱可塑性樹脂が、未硬化の熱硬化性樹脂をそれが硬化を開始する温度より低い温度で吸収して増粘して固体化できるため、形状を維持して貫通穴の加工を行うことが可能であり、生産性に優れ高精度の貫通穴の加工が可能になる。このように、上記熱伝導樹脂組成物を用いることにより、高い電気的絶縁性と熱伝導性や信頼性を両立することが可能になり、簡便な方法で放熱性に優れた回路基板を得ることができる。
【００２５】
本発明の実施の形態１にかかる回路基板の製造方法は、金属箔と前記熱伝導樹脂組成物を接触させ、前記熱伝導樹脂組成物中の前記熱硬化性樹脂が硬化を開始する温度よりも低い温度で加熱加圧して前記金属箔と前記熱伝導樹脂組成物を接着させるとともに前記熱伝導樹脂組成物を非可逆的に固形化して回路基板前駆体を作製する工程と、前記回路基板前駆体の任意の位置に貫通穴を形成する工程と、前記回路基板前駆体中の前記熱硬化性樹脂を硬化させる工程と、前記金属箔を加工して回路パターンを形成する工程とをこの順で含んだものである。
【００２６】
本発明の実施の形態２にかかる回路基板の製造方法は、２枚の金属箔で前記熱伝導樹脂組成物を挟みこみ、前記熱伝導樹脂組成物中の前記熱硬化性樹脂が硬化を開始する温度よりも低い温度で加熱加圧して前記金属箔と前記熱伝導樹脂組成物を接着させるとともに前記熱伝導樹脂組成物を非可逆的に固形化して回路基板前駆体を作製する工程と、前記回路基板前駆体の任意の位置に貫通穴を形成する工程と、前記回路基板前駆体中の前記熱硬化性樹脂を硬化させる工程と、前記貫通穴に銅メッキによるスルーホールを形成して前記金属箔を電気的に接続させる工程と、前記金属箔を加工して回路パターンを形成する工程とをこの順で含んだものである。
【００２７】
本発明の実施の形態３にかかる回路基板の製造方法は、前記熱伝導樹脂組成物を補強材に塗布もしくは含浸して一体化する工程と、２枚の金属箔で前記熱伝導樹脂組成物を挟みこみ、前記熱伝導樹脂組成物中の前記熱硬化性樹脂が硬化を開始する温度よりも低い温度で加熱加圧して前記金属箔と前記熱伝導樹脂組成物を接着させるとともに前記熱伝導樹脂組成物を非可逆的に固形化して回路基板前駆体を作製する工程と、前記回路基板前駆体の任意の位置に貫通穴を形成する工程と、前記回路基板前駆体中の前記熱硬化性樹脂を硬化させる工程と、前記貫通穴に銅メッキによるスルーホールを形成して前記金属箔を電気的に接続させる工程と、前記金属箔を加工して回路パターンを形成する工程とをこの順で含んだものである。
【００２８】
また、本発明の実施の形態４にかかる電力変換モジュールの製造方法は、上記の各実施の形態で製造された回路基板上に、少なくとも半導体および受動部品を実装して電気回路を構成し、電力変換機能を持たせたものである。
【００２９】
以下、本発明の回路基板の製造方法およびその実装体である電力変換モジュールの製造方法を図面を用いて説明する。
【００３０】
（実施の形態１）
図１に、本発明の実施の形態における回路基板を示す。図１において、１１は上記熱伝導樹脂組成物を硬化させた絶縁基板であり、１２は回路パターンであり、１３は貫通穴である。貫通穴１３は本回路基板の任意の位置に形成されている。
【００３１】
図２は、本発明の実施の形態１における回路基板の製造方法を示す工程別断面図である。図２（ａ）に示すように、熱伝導樹脂組成物２１と金属箔２２を重ね合わせる。２３は熱伝導樹脂組成物２１の接着を防止するための離型性フィルムである。その後、熱伝導樹脂組成物２１中の熱硬化性樹脂が硬化を開始する温度よりも低い温度で加熱加圧することで、図２（ｂ）に示すように、金属箔２２と熱伝導樹脂組成物２１を接着させるとともに基板状に成形し、かつ熱伝導樹脂組成物２１を非可逆的に固形化して回路基板前駆体２４を形成する。その後、図２（ｃ）に示すように、穴あけ加工を施して貫通穴２５を設けた後、図２（ｄ）に示すように、加熱して熱伝導樹脂組成物２１を硬化させて絶縁基板２６を形成し、更に離型性フィルム２３を除去する。その後、図２（ｅ）に示すように、金属箔２２を加工して回路パターン２７を形成して回路基板を得る。
【００３２】
熱伝導樹脂組成物２１は、無機質フィラーと、未硬化の液状の熱硬化性樹脂、熱可塑性樹脂粉末および潜在性硬化剤を少なくとも含む樹脂組成物とからなる。無機質フィラーとしては、熱伝導率および絶縁性に優れた材料を適宜選択すればよいが、特に、Ａｌ₂Ｏ₃、ＳｉＯ₂、ＭｇＯ、ＢｅＯ、Ｓｉ₃Ｎ₄、ＳｉＣ、ＡｌＮ、ＢＮからなる群のうちの少なくとも１種類の粉末を主成分として含むことが好ましい。これらの粉末は熱伝導性に優れており、高い熱放散性を持つ基板を作製することが可能になるからである。特に、Ａｌ₂Ｏ₃やＳｉＯ₂を用いた場合、前記樹脂組成物との混合が容易になる。また、ＡｌＮを用いた場合、絶縁基板２６の熱放散性が特に高くなる。更に、無機質フィラーの粒径が０．１〜１００μｍの範囲にあることが好ましい。この範囲から外れた粒径の場合、フィラーの充填性や基板の放熱性が低下する。
【００３３】
熱伝導樹脂組成物２１およびその硬化物である絶縁基板２６の無機質フィラーの比率は、７０〜９５質量％であることが必要であり、８５〜９５質量％であることがより好ましい。無機質フィラーの配合比率がこの範囲より小さい場合、基板の放熱性が不良になる。また、この範囲より多い場合には、熱伝導樹脂組成物２１の流動性および接着性が低下し、金属箔２２および回路パターン２７と接着させることが困難になる。
【００３４】
熱伝導樹脂組成物２１は液状の熱硬化性樹脂を少なくとも含むものであり、熱硬化性樹脂としては、エポキシ樹脂が耐熱性や機械的強度、電気絶縁性に優れる点で好ましい。また、液状であるために熱伝導樹脂組成物の粘度が低減され、溶剤を含まない場合でも熱伝導樹脂組成物の加工性が良好になり、絶縁基板として加工することが容易になるという利点がある。更に、溶剤を含まないために絶縁基板のボイド発生を低減することができ、絶縁基板の絶縁性を向上させることができる点で好ましい。液状のエポキシ樹脂としては、室温で液状を示すものであればよく、例えばビスフェノールＡ型エポキシ樹脂、ビスフェノールＦ型エポキシ樹脂、ビスフェノールＡＤ型エポキシ樹脂、フェノールノボラック型エポキシ樹脂などが使用できる。また、この他にも室温で固体状であるエポキシ樹脂を添加してもよく、その場合でも上記と同様なエポキシ樹脂が使用できる。また、一部を臭素化したエポキシ樹脂を添加してもよく、この場合熱伝導樹脂組成物およびその硬化物である絶縁基板の難燃性が向上する点で好ましい。
【００３５】
また、熱伝導樹脂組成物２１は熱可塑性樹脂を少なくとも含むものであり、この熱可塑性樹脂は前記熱伝導樹脂組成物中の液状の熱硬化性樹脂を吸収して膨潤する作用を有する。前記熱可塑性樹脂としては、特にその種類は限定されず上記の作用を発揮する粉末状のものが好ましく、例えばポリ塩化ビニル、ポリメタクリル酸メチル、ポリエチレン、ポリスチレン、ポリ酢酸ビニルなどの粉末が使用できる。また、上記熱可塑性樹脂粉末の粒径は１〜１００μｍにあることが好ましい。この場合、無機質フィラーと液状エポキシ樹脂との混合が容易になるからである。
【００３６】
また、熱伝導樹脂組成物２１は潜在性硬化剤を少なくとも含むものである。潜在性硬化剤としては特に限定されず熱硬化性樹脂に使用可能であればよく、例えばアミンアダクト系硬化剤やジシアンジアミド系硬化剤が使用できる。
【００３７】
また、上記の液状熱硬化性樹脂、熱可塑性樹脂粉末および潜在性硬化剤を少なくとも含む樹脂組成物に、更にカップリング剤、分散剤、着色剤から選ばれた少なくとも１種が添加されていることが好ましい。カップリング剤は無機質フィラーおよび金属箔と樹脂組成物との接着性を向上させることができ、例えばエポキシシラン系カップリング剤やアミノシラン系カップリング剤、チタネート系カップリング剤などが使用できる。分散剤は熱伝導樹脂組成物の分散性を向上させて均質化させる点で好ましく、例えばリン酸エステルが使用できる。着色剤は熱伝導樹脂組成物に着色することでその熱輻射性を向上させることが可能な点で好ましく、例えばカーボンが使用できる。
【００３８】
熱伝導樹脂組成物２１の製造方法としては、各原料を秤量して混合すればよい。混合の方法としては、例えばボールミル、プラネタリーミキサー、攪拌機を使用できる。また、熱伝導樹脂組成物２１の性状としては粘土状もしくはペースト状であることが好ましく、このときの熱伝導樹脂組成物２１の粘度は１００〜１０００００Ｐａ・ｓであることが好ましく、１０００〜８００００Ｐａ・ｓであることがより好ましい。この範囲であれば熱伝導樹脂組成物の取り扱いが容易になり、またその後の加熱加圧により絶縁基板状に加工することが容易になるからである。なお、この粘度は図２（ｂ）で用いた加熱温度よりも低い温度での粘度を示しており、室温から上記加熱温度の範囲におけるある一定温度での粘度が上記範囲に該当すればよい。
【００３９】
また、熱伝導樹脂組成物２１をシート状に加工することが好ましい。これにより、熱伝導樹脂組成物の取り扱いが容易になり、また図２（ｂ）で示すように絶縁基板状に加工することが容易になり、かつ熱伝導樹脂組成物中のボイドの含有量を減少させることができる。シート状に加工する方法としては特に限定されず、熱伝導樹脂組成物の粘度や性状に応じて適宜選択すればよいが、例えば、押出し成形機による押出し方法、ロールコーターやカーテンコーターによる塗膜方法、印刷による方法、ドクターブレード法等が使用できる。
【００４０】
金属箔２２としては、導電性に優れ回路パターンを形成できるものであればよく、例えば銅、ニッケル、アルミニウムおよびこれらのいずれかの金属を主成分とする合金が使用できるが、特に銅および銅を主成分とする合金が好ましい。銅は電気伝導性に優れ、安価で回路パターン形成が容易に行えるからである。また、金属箔２２の熱伝導樹脂組成物と接する片方の面は粗化されていることが好ましい。金属箔２２と熱伝導樹脂組成物２１との接着強度が向上するからである。また、金属箔の厚さとしては、１２〜２００μｍの範囲にあることが好ましく、特には３５〜１００μｍの範囲にあることがより好ましい。金属箔が好ましい範囲より薄すぎると単位幅あたりの許容電流値が低下するため、大電流に対応するためには回路面積が増大し、小型化に不利である。また、金属箔が好ましい範囲より厚すぎると、高精度で回路パターンを形成するのが困難になる。
【００４１】
離型性フィルム２３は本発明の回路基板の製造に必須な要素ではないが、簡便に離型性を得られる点で好ましく、例えばポリエチレンテレフタレート（ＰＥＴ）やポリフェニレンサルファイド（ＰＰＳ）のフィルムが使用できる。また、それらのフィルム表面にシリカなどによる離型処理が施されたものが好ましい。
【００４２】
図２（ｂ）に示した回路基板前駆体２４を形成する工程においては、熱伝導樹脂組成物２１を加熱加圧して金属箔２２と熱伝導樹脂組成物２１を接着させるとともに基板状に成形し、同時に熱伝導樹脂組成物２１中の熱可塑性樹脂粉末に液状のエポキシ樹脂を吸収させて膨潤させることによって粘度上昇を起こさせて非可逆的に固形化している。このときの加熱温度は熱硬化性エポキシ樹脂が硬化を開始する温度よりも低い温度でなければならず、同時に熱可塑性樹脂粉末のガラス転移点温度もしくは軟化点より高く、溶融開始温度よりも低い温度であることが好ましい。具体的には７０〜１４０℃であることが好ましく、８０〜１３０℃であることがより好ましい。加圧圧力は特に限定されず、金属箔と熱伝導樹脂組成物との接着や基板状に成形することが可能であれば良いが、通常２〜２０ＭＰａ、好ましくは２〜５ＭＰａである。上記の加熱加圧には、例えば熱板付プレス装置が使用できる。更に、上記の加熱加圧が真空中で行われることが好ましい。金属箔の酸化を防止し、熱伝導樹脂組成物中のボイドを除去する効果が得られるからである。この場合の真空とは大気圧以下の減圧状態を示す。
【００４３】
上記の加熱加圧により、前記熱伝導樹脂組成物を非可逆的に固形化させたときの粘度は、８×１０⁴〜３×１０⁶Ｐａ・ｓであることが好ましく、１×１０⁵〜１×１０⁶Ｐａ・ｓであることがより好ましい。この好ましい範囲にあれば、通常の取り扱いにおいても基板形状の状態を保持することができ、かつ図２（ｃ）に示したような貫通穴の加工が容易に行えるからである。この好ましい範囲よりも粘度が低い場合は、基板形状を保持したまま貫通穴の加工を行うことが困難になる。また、この好ましい範囲よりも粘度が高い場合は、貫通穴の加工が困難になる。上記の好ましい粘度に調整するためには、熱伝導樹脂組成物２１中の液状エポキシ樹脂と熱可塑性樹脂粉末との配合比率を調整すればよい。配合比率は熱可塑性樹脂粉末の種類により異なるが、通常液状エポキシ樹脂１００質量部に対して熱可塑性樹脂粉末が１０〜１００質量部程度である。
【００４４】
図２（ｃ）に示した貫通穴２５の加工方法は特に限定されず、絶縁基板２６の厚みや所望の穴径に応じて適宜選択すればよいが、例えばパンチングマシンによる打ち抜き加工法や金型による打ち抜き加工法、ドリルによる加工法が使用でき、これらは簡便で高い位置精度で穴加工できる点で好ましい。特に、パンチングマシンによる打ち抜き加工法がより好ましい。パンチング加工はドリル加工に比べて加工具と基板材料との接触が少なく、加工具の磨耗が低減されてその耐久性が大きく向上し、工業上大きく優位であるからである。
【００４５】
また、これと同時に前記回路基板前駆体２４の少なくとも一部に外形加工を行い、基板を分割もしくは部分的に分割することが好ましい。この方法によると、熱硬化性樹脂の硬化後に外形加工を行うのに比べて外形加工が容易になり、また１枚の基板に複数の回路パターンを形成する場合においても、その分割が容易になるからである。外形加工の方法としては上記の貫通穴の加工と同時に行えるものが好ましく、上記の貫通穴加工方法の好ましい例と同様に、例えばパンチングマシンによる打ち抜き切断、金型による切断、ドリルによる加工が使用できる。
【００４６】
図２（ｄ）に示した絶縁基板２６は加熱による熱硬化性エポキシ樹脂の硬化により形成される。加熱温度はエポキシ樹脂および潜在性硬化剤の反応に応じて適宜選択すればよいが、１４０〜２４０℃であることが好ましく、１５０〜２００℃であることがより好ましい。この好ましい範囲よりも低い場合、硬化が不十分になる恐れや硬化に時間がかかる恐れがあり、好ましい範囲より高い場合、樹脂が熱分解を開始する恐れがある。また、この加熱時に同時に加圧することが好ましい。これにより、熱硬化時の基板のそりが抑制され平坦度の高い基板が作製でき、また金属箔と絶縁基板との接着性が向上する。加圧圧力は適宜決定すればよいが、通常３ＭＰａ以下、好ましくは０．００１〜１ＭＰａである。この範囲より高い場合、貫通穴が変形する恐れがある。また、加熱硬化時に金属箔の酸化防止のために真空もしくは非酸化性雰囲気中で加熱を行うことが好ましい。なお、図２（ｄ）においては、離型性フィルム２３をこの時点で剥離しているが、剥離は離型性フィルムが不用になった時点で剥離してもよく、例えば図２（ｃ）に示した貫通穴加工時に除去してもよい。
【００４７】
図２（ｅ）に示した回路パターン２７の形成方法としては特に限定されず、従来公知の方法が使用でき、例えば化学的エッチングによる方法が使用できる。
【００４８】
（実施の形態２）
図３に、本発明の別の実施の形態における回路基板を示す。図３において、３１は熱伝導樹脂組成物を硬化させた絶縁基板であり、３２は回路パターンであり、３３は絶縁基板３１中に設けられた貫通穴にめっきを施して両面の回路パターンを電気的に接続させるスルーホールである。
【００４９】
図４は、本発明の実施の形態２における回路基板の製造方法を示す工程別断面図である。図４（ａ）に示すように、複数の熱伝導樹脂組成物４１を金属箔４２で挟み込み、熱伝導樹脂組成物４１中の熱硬化性樹脂が硬化を開始する温度よりも低い温度で加熱加圧することで、図４（ｂ）に示すように、金属箔４２と熱伝導樹脂組成物４１を接着させるとともに、複数の熱伝導樹脂組成物４１を一体化して基板状に成形し、かつ一体化した熱伝導樹脂組成物４１を非可逆的に固形化して回路基板前駆体４３を形成する。その後、図４（ｃ）に示すように、回路基板前駆体４３に穴あけ加工を施して貫通穴４４を形成してから加熱して、図４（ｄ）に示すように、貫通穴４４の形状を保持したまま熱伝導樹脂組成物４１を硬化させて絶縁基板４５にする。その後、図４（ｅ）に示すように、めっきを施して両面の金属箔４２を電気的に接続させるスルーホール４６を形成し、更に図４（ｆ）に示すように、金属箔４２を加工して回路パターン４７を形成して回路基板を得る。
【００５０】
本実施の形態２で使用した熱伝導樹脂組成物４１、金属箔４２は実施の形態１で使用したものと同様のものが使用できる。また、回路基板前駆体４３の形成方法、貫通穴４４の形成方法、絶縁基板４５の製造方法、回路パターン４７の形成方法として、実施の形態１で説明した各方法が使用できる。
【００５１】
図４（ｅ）に示したスルーホール４６の形成方法としては、全面銅めっきによる接続方法が好ましい。抵抗値が低く許容電流値が大きいからである。この場合にも金属箔４２は銅箔であることが好ましい。金属箔とめっき間の熱膨張係数がマッチして信頼性が向上するからである。
【００５２】
（実施の形態３）
図５は、本発明の別の実施の形態における回路基板の製造方法を示す工程別断面図である。図５（ａ）で示した５１は、補強材に熱伝導樹脂組成物を塗布あるいは含浸させて一体化したシート状熱伝導樹脂組成物である。図５（ｂ）に示すように、シート状熱伝導樹脂組成物５１を金属箔５２で挟み込み、シート状熱伝導樹脂組成物５１中の熱硬化性樹脂が硬化を開始する温度よりも低い温度で加熱加圧することで、金属箔５２とシート状熱伝導樹脂組成物５１を接着させるとともに基板状に成形し、かつシート状熱伝導樹脂組成物５１を非可逆的に固形化して回路基板前駆体５３を形成する。その後、図５（ｃ）に示すように、回路基板前駆体５３に穴あけ加工を施して貫通穴５４を形成してから加熱して、図５（ｄ）に示すように、貫通穴５４の形状を保持したままシート状熱伝導樹脂組成物５１を硬化させて絶縁基板５５にする。その後、図５（ｅ）に示すように、めっきを施して両面の金属箔５２を電気的に接続させるスルーホール５６を形成し、更に図５（ｆ）に示すように金属箔５２を加工して回路パターン５７を形成して回路基板を得る。
【００５３】
本実施の形態３で使用したシート状熱伝導樹脂組成物５１中の熱伝導樹脂組成物、金属箔５２は実施の形態１で使用したものと同様のものが使用できる。また、回路基板前駆体５３の形成方法、貫通穴５４の形成方法、絶縁基板５５の製造方法、回路パターン５７の形成方法として、実施の形態１で説明した各方法が使用できる。更に、スルーホール５６の形成方法としては、実施の形態２で説明したものと同様な方法が使用できる。
【００５４】
本実施の形態で使用した補強材としては、例えばセラミック繊維、ガラス繊維、樹脂繊維を使用した布などが使用できるが、特にセラミック繊維もしくはガラス繊維が好ましい。セラミックやガラスは耐熱性に優れているので高信頼性であり、また樹脂に比べてその熱伝導率が高いため基板の熱伝導性が良好になる。セラミックとしては、例えばアルミナやシリカ、窒化珪素が使用できる。また、前記の繊維を使用した場合、補強材が不織布であることが好ましい。不織布は織布に比べて補強材の密度が低くポーラスであるので、熱伝導樹脂組成物を塗布もしくは含浸させる際に無機質フィラーを取り込みやすく、前記熱伝導樹脂組成物の組成比を変化させずに塗布もしくは含浸することが容易になるからである。更に、前記の繊維の直径は１０μｍ以下であることが好ましい。これより大きすぎると、基板成形時の圧縮性が減少し、無機質フィラー同士の熱伝導が妨げられやすくなり、その結果基板の熱抵抗が高くなる恐れがある。
【００５５】
上記の補強材と熱伝導樹脂組成物とを一体化してシート状熱伝導樹脂組成物５１を製造する方法としては特に限定されず、例えば熱伝導樹脂組成物を補強材に塗布する方法、熱伝導樹脂組成物を補強材に含浸させる方法、シート状に加工した熱伝導樹脂組成物を補強材に張り合わせる方法が使用できる。
【００５６】
なお、本実施の形態３ではシート状熱伝導樹脂組成物５１を使用して両面配線がスルーホール接続された基板について説明したが、上記実施の形態１と同様な方法を用いることにより、補強材と一体化した熱伝導樹脂組成物を絶縁基板とした片面配線回路基板を製造することができる。
【００５７】
（実施の形態４）
図６は、本発明の別の実施の形態における電力変換モジュールを示す断面図である。図６において、６１は上記各実施の形態で説明した方法で作製した回路基板であり、その上に各種の半導体素子６２および受動部品６３が実装されて電力変換回路を形成しており、更に外部取り出し電極などの機構部品６４が接続されている。
【００５８】
各部品の実装方法としては、従来公知の技術を使用すればよく、例えばリフロー半田付け、フロー半田付け、ワイヤボンディング、フリップチップ接続が使用できる。半田付けを行う場合、回路基板６１上に半田レジスト膜が形成されていてもよく、半田の不要な流出を防ぐことができる点で好ましい。また、回路パターン表面に金属コートを施して回路パターンである金属箔の酸化や腐食を防止することが好ましく、金属コートとしてはたとえば半田又はすずが使用できる。
【００５９】
【実施例】
次に、具体的実施例に基づいて、本発明の回路基板およびその実装体の製造方法を更に詳しく説明する。
【００６０】
（実施例１）
熱伝導樹脂組成物を作製するために、無機質フィラーと樹脂組成物を混合した。それらの材料および配合比を以下に示す。
【００６１】
（１）無機質フィラー：Ａｌ₂Ｏ₃（“ＡＳ−４０”、昭和電工社製、平均粒径１２μｍ）８７質量％
（２）液状の熱硬化性樹脂：ビスフェノールＡ型エポキシ樹脂（“エピコート８２８”、油化シェルエポキシ社製）７質量％
（３）熱可塑性樹脂粉末：ポリメタクリル酸メチル（関東化学社製）３.５質量％
（４）潜在性硬化剤：アミン系硬化剤（“アミキュアＰＮ−２３”、味の素社製）１．５質量％
（５）その他の添加物：カーボンブラック（東洋カーボン社製）０．５質量％、カップリング剤（“プレンアクトＫＲ−４６Ｂ”、味の素社製）０．５質量％これらの材料を秤量し、プラネタリーミキサーで混合して熱伝導樹脂組成物を作製した。その後、この熱伝導樹脂組成物をロールコーターで厚さ約０．８ｍｍのシート状に加工した。この熱伝導樹脂組成物の粘度を動的粘弾性測定装置（ＵＢＭ社製）で昇温させながら測定したところ、図８に示すような粘度特性を示した。図８から明らかなように、温度が約８０℃を超えると熱伝導樹脂組成物の非可逆的な固形化が開始され、温度が約１００℃に達すると非可逆的な固形化が完了する。その後に昇温を続けると温度が約１４０℃まではほぼ一定の粘度を維持するが、さらに昇温すると熱伝導樹脂組成物の硬化が開始され、温度が約１７０℃以上になると完全に硬化する。
【００６２】
厚さ７０μｍのＰＰＳ離型性フィルム上に上記のシート状熱伝導樹脂組成物を配置し、更にその上に厚さ３５μｍの片面粗化銅箔（古河電工社製）を、その粗化面が熱伝導樹脂組成物に接するようにして図２（ａ）に示したように配置した。これらを減圧した状態において１００℃の熱プレス機で加熱しながら３ＭＰａの圧力で１０分間加圧して、銅箔と熱伝導樹脂組成物を接着させるとともに、図２（ｂ）に示すような基板形状に成形し、同時に熱伝導樹脂組成物を非可逆的に固形化して厚さ約０．８ｍｍの回路基板前駆体を形成した。次いで、上記の回路基板前駆体にドリル加工により図２（ｃ）に示すような直径０．６ｍｍの貫通穴を設けた。その後、上記の回路基板前駆体を窒素雰囲気中で１７０℃で１時間加熱して熱伝導樹脂組成物中のエポキシ樹脂を硬化させ、離型性フィルムを除去して図２（ｄ）に示すような銅箔付き絶縁基板を作製した。更に、金属箔上に光硬化性のドライフィルムレジスト（ニチゴーモートン社製）をラミネートし、回路パターンを露光、現像してから、塩化鉄水溶液中でエッチングして回路パターンを形成し、その後ドライフィルムレジスト膜を除去して図２（ｅ）に示すような片面配線回路基板を完成させた。
【００６３】
比較例１として、本実施例１と同じシート状熱伝導樹脂組成物、銅箔および離型性フィルムを用いて、図２（ａ）に示すように重ね合わせ、減圧した状態で１７０℃の熱プレス機で加熱しながら３ＭＰａの圧力で１．５時間加圧して熱伝導樹脂組成物中のエポキシ樹脂を硬化させ、片面銅張基板を作製した。その後、ドリル加工により直径０．６ｍｍの貫通穴を設け、回路基板を作製した。
【００６４】
上記の実施例１と比較例１において、ドリル加工時における超硬合金製のドリル刃（ユニオン・ツール社製）の耐久性を比較した。実施例１の場合、１０００回の穴開け加工した後でもドリル刃の磨耗は少なく、その後の穴開け加工が可能でありチッピングも発生しなかった。また、貫通穴の壁面のバリは発生しなかった。しかし、比較例１の場合にはドリル刃の磨耗が激しく、１００回の穴開けで銅箔にバリが生じ、その後の穴開け加工が不可能になった。このことから本実施例１の回路基板の製造方法は貫通穴の加工性に優れていることがわかる。
【００６５】
（実施例２）
熱伝導樹脂組成物を作製するために、無機質フィラーと樹脂組成物を混合した。それらの材料および配合比を以下に示す。
【００６６】
（１）無機質フィラー：Ａｌ₂Ｏ₃（“ＡＳ−４０”、昭和電工社製、平均粒径１２μｍ）８８質量％
（２）液状の熱硬化性樹脂：ビスフェノールＦ型エポキシ樹脂（“エピコート８０７”、油化シェルエポキシ社製）５質量％
（３）臭素化されたエポキシ樹脂（“エピコート５０５０”、油化シェルエポキシ社製）２質量％
（４）熱可塑性樹脂粉末：ポリメタクリル酸メチル（関東化学社製）３質量％
（５）潜在性硬化剤：アミン系硬化剤（“アミキュアＰＮ−２３”、味の素社製）１質量％、ジシアンジアミド（大日本インク社製）０．４質量％
（６）その他の添加物：カーボンブラック（東洋カーボン社製）０．４質量％、カップリング剤（“プレンアクトＫＲ−４６Ｂ”、味の素社製）０．２質量％
これらの材料を秤量し、攪拌混練機で混合して熱伝導樹脂組成物を作製した。その後、この熱伝導樹脂組成物を押出し成形機で厚さ約１．０ｍｍのシート状に加工した。この熱伝導樹脂組成物の粘度を測定したところ、５０℃で約９０００Ｐａ・ｓ、１１０℃で約８０００００Ｐａ・ｓであった。
【００６７】
厚さ７０μｍの片面粗化銅箔（古河サーキットフォイル社製）を、その粗化面が熱伝導樹脂組成物に接するようにして図４（ａ）に示したように挟み込んだ。ただし、本実施例２の熱伝導樹脂組成物はシート状であり図面とは異なる。これらを減圧した状態で９０℃の熱プレス機で加熱しながら３ＭＰａの圧力で１５分間加圧して、銅箔と熱伝導樹脂組成物を接着させるとともに図４（ｂ）に示すような基板形状に成形し、同時に熱伝導樹脂組成物を非可逆的に固形化して厚さ約１．０ｍｍの回路基板前駆体を形成した。次いで、上記の回路基板前駆体にパンチングマシン（ＵＨＴ社製）による加工により図４（ｃ）に示すような直径０．５ｍｍの貫通穴を設けた。その後、上記の回路基板前駆体に０．０１ＭＰａの加重を加えながら１７０℃で２時間加熱して熱伝導樹脂組成物中のエポキシ樹脂を硬化させて図４（ｄ）に示すような銅箔付き絶縁基板を作製した。その後、全面に厚さ約３０μｍの銅めっきを施して図４（ｅ）に示すような銅めっきスルーホールを形成した。更に、実施例１と同様な方法で回路パターンを形成して図４（ｆ）に示すような両面配線回路基板を完成させた。
【００６８】
なお、本実施例２と同じシート状熱伝導樹脂組成物、銅箔および離型性フィルムを用いて、図４（ａ）に示すように重ね合わせ、減圧した状態で１７０℃の熱プレス機で加熱しながら３ＭＰａの圧力で１．５時間加圧して熱伝導樹脂組成物中のエポキシ樹脂を硬化させ、厚さ約１．０ｍｍの両面銅張基板を作製した。その後、上記のパンチング加工により直径０．５ｍｍの貫通穴を設けようとしたが、パンチングマシンのピンが前記基板を貫通せず、貫通穴が作製できなかった。このことから本実施例２の回路基板の製造方法は貫通穴の加工性が優れていることがわかる。
【００６９】
比較例２として、ほぼ同じ厚さの絶縁層、配線層を持ち、銅めっきスルーホールを形成したガラス−エポキシプリント両面配線板（ＡＮＳＩグレードＦＲ−４相当）を作製した。
【００７０】
実施例２と比較例２の基板に同様のスルーホールチェーンパターン（５００穴連結）を形成して、その抵抗値を測定しながら、２０℃と２６０℃の油中に各１０秒ずつディップを繰り返すホットオイル試験を行った。その結果、比較例２の基板においては３５０サイクルで抵抗の増大が現れて断線したが、実施例２の基板においては３０００サイクルでも抵抗値の増大はみられず接続性は良好であった。このことから本実施例２による回路基板が高信頼性であることが分かる。
【００７１】
（実施例３）
上記実施例１と同様の材料を混合して熱伝導樹脂組成物を作製した。
【００７２】
補強材としてガラス不織布（厚み約０．２ｍｍ、繊維径９μｍ）を用意し、上記の熱伝導樹脂組成物をガラス不織布の両面からロールで塗布して、図５（ａ）に示すような厚さ０．８ｍｍの補強材入り熱伝導樹脂組成物を作製した。
【００７３】
厚さ３５μｍの片面粗化銅箔（古河電工社製）を、その粗化面が熱伝導樹脂組成物に接するようにして図５（ｂ）に示したように挟み込んだ。これらを減圧した状態で１００℃の熱プレス機で加熱しながら３ＭＰａの圧力で１０分間加圧して、銅箔と熱伝導樹脂組成物を接着させるとともに図５（ｃ）に示すような基板形状に成形し、同時に熱伝導樹脂組成物を非可逆的に固形化して厚さ約０．８ｍｍの回路基板前駆体を形成した。次いで、上記の回路基板前駆体に金型により図４（ｃ）に示すような直径０．８ｍｍの貫通穴を設け、同時に上記回路基板前駆体の回路形成部分とその外周部分との間に、数個所のつなぎ部分を残して幅１ｍｍのスリットを設けた。その後、上記の回路基板前駆体を窒素雰囲気中で１７０℃で２時間加熱して熱伝導樹脂組成物中のエポキシ樹脂を硬化させて、図５（ｄ）に示すような両面銅箔付き絶縁基板を作製した。その後、全面に厚さ約３０μｍの銅めっきを施して図５（ｅ）に示すような銅めっきスルーホールを形成した。更に、実施例１と同様な方法で回路パターンを形成して図５（ｆ）に示すような両面配線回路基板を完成させた。その後、つなぎ部分を割ることで所望の外形寸法を持つ回路基板を容易に得ることができた。
【００７４】
実施例１と本実施例３の基板を同サイズに加工し、銅箔を除去してからその抗折強度を測定したところ、実施例１の基板の抗折強度が２１０ＭＰａであったのに対し、実施例３の基板では２８０ＭＰａであった。この結果から、実施例１の基板においても基板として実用的な強度があるが、更に補強材を入れることにより基板の強度が向上していることがわかる。
【００７５】
また、実施例１、３および比較例２の基板の熱抵抗を測定した。熱抵抗は基板に発熱素子が搭載された場合の、出力電力に対する温度上昇を表したものであり、この値が小さいほど温度上昇が小さくなり部品の動作許容範囲が大きくなる。熱抵抗測定は、熱抵抗測定機（キャッツ電子設計社製）を用いた。すなわち、各基板の同一パターン上にＦＥＴ（ＴＯ−２２０パッケージ）を取り付け、理想定温熱溜としてのフィン付きヒートシンクに回路基板のＦＥＴ実装面の反対面を接着し、その状態で半導体に一定の電力を与えたときの半導体のＰＮ接合部の電圧変化から半導体温度の変化を見積もり、温度差を電力で割った値を求めた。その結果、実施例１の基板の熱抵抗が１．０２℃／Ｗであったのに対し、実施例３では１．１１℃／Ｗであり、比較例２では８．４℃／Ｗであった。この結果から、補強材が内蔵されていても基板の熱抵抗に大きな差はなく、比較例２のような一般的なプリント配線板に比べて本実施例の基板の熱抵抗が非常に小さく、熱的に有利であることが分かる。
【００７６】
（実施例４）
上記実施例２および比較例２で作製した回路基板に、メタルマスクを用いてスクリーン印刷法で半田ペースト（千住金属社製）を印刷し、その上に半導体素子（三菱電機社製）およびコンデンサ、トランス、チョーク、抵抗などの各種受動部品（松下電子部品社製）および外部取り出し端子などの機構部品を搭載してからリフロー炉（松下電工社製）で半田付けを行い、電力変換モジュールとしてＤＣ−ＤＣコンバータを作製した。
【００７７】
このＤＣ−ＤＣコンバータに３０Ｗの負荷を与え、負荷開始から１０分後のパワー半導体の温度をサーモビュアー（ニコン社製）で測定したところ、実施例２の回路基板を用いた場合では４８℃であったが、比較例２の回路基板を用いた場合では６３℃であった。この結果から、実施例２の基板を用いた電力変換モジュールは部品の温度上昇が小さく、動作および信頼性の面で有利であることがわかる。
【００７８】
【発明の効果】
以上説明したように、本発明の回路基板の製造方法によれば、樹脂組成物に無機質フィラーを高濃度に混合して熱伝導性を高めた絶縁基板の貫通穴の加工が容易に行え、実用上困難であった貫通穴を有した高熱伝導絶縁基板の製造を簡便に行うことが可能になる。またこれにより、貫通穴にめっきを施したスルーホールを有する両面配線基板の製造を簡便に行うことが可能になる。更に、補強材を含むことにより、より強度の高い高熱伝導な回路基板を製造することが可能になる。
【００７９】
また、本発明によれば、熱伝導性に優れ十分な強度を保持し、大電流に対応することが可能な回路基板を提供することが可能になる。また、本発明の回路基板の実装体である電力変換モジュールによれば、熱放散性に優れ部品の温度上昇が抑制されることにより、大電流が使用可能になり、高密度な部品実装が可能になり、機器を小型高密度化することが可能になる。
【図面の簡単な説明】
【図１】本発明の実施の形態１における回路基板を示す断面図である。
【図２】本発明の実施の形態１における回路基板の製造方法を示す工程別断面図である。
【図３】本発明の実施の形態２における回路基板を示す断面図である。
【図４】本発明の実施の形態２における回路基板の製造方法を示す工程別断面図である。
【図５】本発明の実施の形態３における回路基板の製造方法を示す工程別断面図である。
【図６】本発明の実施の形態４における電力変換モジュールを示す断面図である。
【図７】従来例の回路基板の製造方法を示す工程別断面図である。
【図８】本発明の実施例１における熱伝導樹脂組成物の粘度を示す図である。
【符号の説明】
１１、２６、３１、４５、５５絶縁基板
１２、２７、３２、４７、５７、７５回路パターン
１３、２５、４４、５４、７４貫通穴
２１、４１熱伝導樹脂組成物
２２、４２、５２、７２金属箔
２３離型性フィルム
２４、４３、５３回路基板前駆体
３３、４６、５６スルーホール
５１シート状熱伝導樹脂組成物
６１回路基板
６２半導体素子
６３受動部品
６４機構部品
７１熱伝導混合物
７３電気絶縁層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a circuit board used for electrical and electronic equipment and a method for manufacturing the circuit board, and more particularly to a method for manufacturing a circuit board suitable for the field of power electronics using a relatively large current.
[0002]
[Prior art]
In recent years, with the demand for higher performance and miniaturization of electronic devices, there has been a demand for higher density and higher functionality of semiconductors and the like. Accordingly, a circuit board for mounting a semiconductor or the like is also desired to be small and dense. As a result, the design considering the heat dissipation of the circuit board has become important. As a technique for improving the heat dissipation of a circuit board, there is a demand for a board that increases the thermal conductivity of the insulating base material itself and suppresses a local temperature rise with respect to a general glass-epoxy resin printed board. As a substrate having a higher thermal conductivity than glass-epoxy resin, a metal base substrate using a metal plate such as copper or aluminum and forming a circuit pattern on one side of the metal plate via an electric insulating layer is known. ing. However, since the metal base substrate uses a relatively thick metal plate, its weight increases, and it is difficult to reduce the size and weight. In addition, in order to increase the heat conduction of the substrate, it is necessary to reduce the thickness of the insulating layer, and there are problems such as a decrease in withstand voltage and an increase in stray capacitance. In addition, ceramic substrate and glass-ceramic substrate have higher thermal conductivity than glass-epoxy substrate, but use metal powder or its fired body as the conductor, so the wiring resistance is relatively high and large current is used. In this case, there is a problem that the loss and the Joule heat generated there increase.
[0003]
A circuit board that can solve these problems and can be manufactured by a process similar to a general glass-epoxy substrate and has high thermal conductivity is disclosed in, for example, Japanese Patent Laid-Open No. 10-173097. The manufacturing method of the heat conductive substrate is shown in FIG. According to this, a sheet slurry containing at least an inorganic filler and a thermosetting resin is formed to produce a sheet-like heat conduction mixture 71, which is dried, and then a metal as shown in FIG. The sheet 72 is superposed on the foil 72, and then heated and pressed to cure the sheet-like heat conduction mixture 71 as shown in FIG. Thereafter, the through hole 74 is processed as shown in FIG. 7 (c), and then interlayer connection is performed by a copper plating method to form a circuit pattern 75 to produce a heat conductive substrate as shown in FIG. 7 (d). is doing.
[0004]
[Problems to be solved by the invention]
When a circuit board is manufactured by such a method, drilling is generally performed as a through hole processing method. However, if the ratio of the inorganic filler in the heat transfer mixture is increased to increase the heat conductivity, the hard inorganic filler in the insulator will cause significant wear on the drill and chipping may occur more easily. Deterioration occurs frequently. If drill exchange is frequently performed to prevent this, the productivity is greatly reduced as compared with a normal printed wiring board, and the hole machining cost is increased.
[0005]
Also, if the thermosetting resin is drilled into a thermally conductive mixture in an uncured state, and then the metal foil is bonded and heated and pressurized and cured, the heat conductive mixture softens by heating and maintains the hole shape. In other words, it is difficult to form a through hole and subsequent plating cannot be performed.
[0006]
Accordingly, the present invention has been made to solve the above-described conventional problems, and provides a method for manufacturing a circuit board having high heat dissipation that can improve the productivity of through-hole processing and perform hole processing at low cost. For the purpose.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing a circuit board according to the present invention comprises (1) a resin composition comprising 70 to 95% by mass of an inorganic filler, and at least an uncured thermosetting resin, a thermoplastic resin, and a latent curing agent. (2) heating at a temperature lower than the temperature at which the thermosetting resin in the heat conductive resin composition starts to cure. Forming a circuit board precursor by irreversibly solidifying the thermally conductive resin composition by pressing, (3) forming a through hole at an arbitrary position of the circuit board precursor, and (4) And a step of curing the thermosetting resin in the circuit board precursor.
[0008]
Further, in the method for producing a circuit board according to the present invention, in the step (2) of producing the circuit board precursor, the metal foil and the heat conductive resin composition are brought into contact with each other, and the heat in the heat conductive resin composition is obtained. A circuit board precursor is prepared by heating and pressurizing at a temperature lower than the temperature at which the curable resin starts to cure to adhere the metal foil and the thermally conductive resin composition and irreversibly solidify the thermally conductive resin composition. The method includes a step of manufacturing a body, and can further include a step of processing the metal foil to form a circuit pattern as another step.
[0009]
Further, in the method for producing a circuit board according to the present invention, in the step (2) of producing the circuit board precursor, the thermally conductive resin composition is sandwiched between two metal foils. The thermosetting resin is heated and pressed at a temperature lower than the temperature at which curing begins to adhere the metal foil and the heat conductive resin composition, and the heat conductive resin composition is solidified irreversibly to form a circuit. A process for producing a substrate precursor, and as a further process, forming a through hole by copper plating in the through hole to electrically connect the metal foil; and processing the metal foil to form a circuit pattern Forming.
[0010]
According to these circuit board manufacturing methods, the thermosetting resin in the heat conductive resin composition can be solidified and bonded to the metal foil while the thermosetting resin is in an uncured state. Can be processed into a desired flat plate shape. Moreover, since the processing after solidification is easy, the through hole can be formed by a simple method. Furthermore, even when the thermosetting resin is subsequently cured, there is no need to apply pressure as in the formation of a normal printed wiring board, so there is no deformation or filling of the through hole, and dimensional change due to curing shrinkage is reduced. can do.
[0011]
Moreover, it is preferable that the manufacturing method of the circuit board of this invention adds the process of integrating the said heat conductive resin composition with a reinforcing material after the process (1) which produces the said heat conductive resin composition. This improves the strength of the circuit board. In addition, since the reinforcing material is included, the thickness of the insulating layer is maintained at the time of adhesion to the metal foil, and an excessive outflow of the heat conductive resin composition can be prevented.
[0012]
In the method for manufacturing a circuit board according to the present invention, the reinforcing material is preferably made of ceramic fiber or glass fiber. This is because they are high in strength and relatively excellent in thermal conductivity.
[0013]
In the method for producing a circuit board according to the present invention, it is preferable that the heating and pressurizing in the step (2) of producing the circuit board precursor is performed in a vacuum. Thereby, the void of a board | substrate can be reduced and deterioration of metal foil can be prevented.
[0014]
In the method for producing a circuit board of the present invention, it is preferable that the curing in the step (4) of curing the thermosetting resin in the circuit board precursor is performed by heating and pressing. This improves the adhesion between the metal foil and the insulating substrate.
[0015]
In the method for producing a circuit board according to the present invention, the viscosity of the heat conductive resin composition is in a range of 100 to 100,000 Pa · s, and the viscosity when the heat conductive resin composition is solidified irreversibly. 8 × 10 ^Four ~ 3x10 ⁶ Pa · s is preferred. When it is in this viscosity range, it is easy to shape the substrate, and even when solidified, the through hole can be easily processed.
[0016]
In the method for manufacturing a circuit board according to the present invention, the through hole processing method in the step (3) of forming a through hole at an arbitrary position of the circuit board precursor is performed by punching with a punching machine or punching with a die. Preferably, the method is one selected from the group consisting of machining and drilling.
[0017]
In the method for manufacturing a circuit board according to the present invention, when the through hole is formed in the step (3) of forming the through hole at an arbitrary position of the circuit board precursor, at least a part of the board is processed at the same time. It is preferable to carry out and process into a desired shape.
[0018]
Moreover, it is preferable that the manufacturing method of the circuit board of this invention is 12-200 micrometers thick copper foil by which the at least single side | surface of the said metal foil was roughened.
[0019]
Moreover, it is preferable that the temperature when the manufacturing method of the circuit board of this invention solidifies the said heat conductive resin composition irreversibly is 70-140 degreeC.
[0020]
In the method for manufacturing a circuit board according to the present invention, the inorganic filler is Al. ₂ O _Three , SiO ₂ , MgO, BeO, Si _Three N _Four Preferably, at least one selected from the group consisting of SiC, AlN, and BN is included.
[0023]
The power conversion module of the present invention is characterized in that at least a semiconductor and a passive component are mounted on a circuit board manufactured by the manufacturing method. Here, the power conversion module refers to a module having a function of converting voltage and power by being connected to a single or auxiliary circuit, for example, a DC-DC converter or an inverter.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
In the method for manufacturing a circuit board according to the embodiment of the present invention, a thermally conductive resin composition comprising an inorganic filler and a resin composition containing at least an uncured thermosetting resin, a thermoplastic resin, and a latent curing agent. Is the basic element. Since the heat conductive resin composition has a high degree of freedom in shape, it can be easily processed into a sheet or a layer, and can be easily applied or impregnated into a reinforcing material. In addition, since the resin contained in the heat conductive resin composition is uncured, it can be bonded to a lead frame or a heat radiating plate as a wiring pattern by heating and pressing, and has high insulation, air tightness, Adhesiveness can be obtained. Furthermore, since it is possible to mix the inorganic filler at a high ratio, high thermal conductivity can be realized, and the thermal expansion coefficient of the substrate can be reduced. In addition, the inclusion of a thermoplastic resin allows the thermoplastic resin to absorb uncured thermosetting resin at a temperature lower than the temperature at which it begins to cure and thicken to solidify, thus maintaining its shape. Thus, it is possible to process through holes, and it is possible to process through holes with high productivity and high accuracy. As described above, by using the above heat conductive resin composition, it is possible to achieve both high electrical insulation and heat conductivity and reliability, and to obtain a circuit board excellent in heat dissipation by a simple method. Can do.
[0025]
The manufacturing method of the circuit board concerning Embodiment 1 of this invention makes metal foil and the said heat conductive resin composition contact, and is higher than the temperature which the said thermosetting resin in the said heat conductive resin composition starts hardening. A step of heating and pressurizing at a low temperature to bond the metal foil and the heat conductive resin composition and irreversibly solidifying the heat conductive resin composition to produce a circuit board precursor; and the circuit board precursor. Including a step of forming a through hole at an arbitrary position, a step of curing the thermosetting resin in the circuit board precursor, and a step of processing the metal foil to form a circuit pattern in this order. It is a thing.
[0026]
In the method for manufacturing a circuit board according to the second embodiment of the present invention, the thermally conductive resin composition is sandwiched between two metal foils, and the thermosetting resin in the thermally conductive resin composition starts to be cured. Heating and pressurizing at a temperature lower than the temperature to bond the metal foil and the heat conductive resin composition, and irreversibly solidifying the heat conductive resin composition to produce a circuit board precursor; and the circuit A step of forming a through hole at an arbitrary position of the substrate precursor, a step of curing the thermosetting resin in the circuit board precursor, and forming a through hole by copper plating in the through hole to form the metal foil And a step of processing the metal foil to form a circuit pattern in this order.
[0027]
A method for manufacturing a circuit board according to a third embodiment of the present invention includes a step of applying or impregnating the heat conductive resin composition to a reinforcing material and integrating the heat conductive resin composition with two metal foils. The heat conductive resin composition is sandwiched between the metal foil and the heat conductive resin composition by heating and pressing at a temperature lower than the temperature at which the thermosetting resin in the heat conductive resin composition starts to cure. Forming a circuit board precursor by irreversibly solidifying an object, forming a through hole at an arbitrary position of the circuit board precursor, and the thermosetting resin in the circuit board precursor A step of curing, a step of forming a through hole by copper plating in the through hole to electrically connect the metal foil, and a step of processing the metal foil to form a circuit pattern in this order. Is.
[0028]
In addition, the method for manufacturing a power conversion module according to the fourth embodiment of the present invention configures an electric circuit by mounting at least a semiconductor and passive components on the circuit board manufactured in each of the above-described embodiments. It has a conversion function.
[0029]
Hereinafter, the manufacturing method of the circuit board of this invention and the manufacturing method of the power conversion module which is the mounting body are demonstrated using drawing.
[0030]
(Embodiment 1)
FIG. 1 shows a circuit board according to an embodiment of the present invention. In FIG. 1, 11 is an insulating substrate obtained by curing the heat conductive resin composition, 12 is a circuit pattern, and 13 is a through hole. The through hole 13 is formed at an arbitrary position on the circuit board.
[0031]
FIG. 2 is a cross-sectional view for each process showing the method for manufacturing a circuit board in the first embodiment of the present invention. As shown in FIG. 2A, the heat conductive resin composition 21 and the metal foil 22 are overlapped. Reference numeral 23 denotes a releasable film for preventing adhesion of the heat conductive resin composition 21. Thereafter, the metal foil 22 and the heat conductive resin composition are heated and pressed at a temperature lower than the temperature at which the thermosetting resin in the heat conductive resin composition 21 starts to cure, as shown in FIG. The circuit board precursor 24 is formed by adhering 21 and forming into a substrate and solidifying the heat conductive resin composition 21 irreversibly. Thereafter, as shown in FIG. 2 (c), after drilling is performed to provide a through hole 25, as shown in FIG. 2 (d), the heat conductive resin composition 21 is cured by heating to form an insulating substrate. 26 is formed, and the releasable film 23 is further removed. Thereafter, as shown in FIG. 2E, the metal foil 22 is processed to form a circuit pattern 27 to obtain a circuit board.
[0032]
The heat conductive resin composition 21 includes an inorganic filler and a resin composition containing at least an uncured liquid thermosetting resin, a thermoplastic resin powder, and a latent curing agent. As the inorganic filler, a material excellent in thermal conductivity and insulation may be selected as appropriate. ₂ O _Three , SiO ₂ , MgO, BeO, Si _Three N _Four It is preferable that at least one kind of powder of the group consisting of SiC, AlN, and BN is included as a main component. This is because these powders are excellent in thermal conductivity, and it becomes possible to produce a substrate having high heat dissipation. In particular, Al ₂ O _Three And SiO ₂ When is used, mixing with the resin composition becomes easy. In addition, when AlN is used, the heat dissipation property of the insulating substrate 26 is particularly high. Furthermore, the particle size of the inorganic filler is preferably in the range of 0.1 to 100 μm. When the particle diameter is out of this range, the filler filling property and the heat dissipation property of the substrate are lowered.
[0033]
The ratio of the inorganic filler of the heat conductive resin composition 21 and the insulating substrate 26 that is a cured product thereof needs to be 70 to 95% by mass, and more preferably 85 to 95% by mass. When the blending ratio of the inorganic filler is smaller than this range, the heat dissipation of the substrate becomes poor. Moreover, when more than this range, the fluidity | liquidity and adhesiveness of the heat conductive resin composition 21 will fall, and it will become difficult to make it adhere with the metal foil 22 and the circuit pattern 27. FIG.
[0034]
The thermally conductive resin composition 21 contains at least a liquid thermosetting resin, and as the thermosetting resin, an epoxy resin is preferable in that it has excellent heat resistance, mechanical strength, and electrical insulation. In addition, since it is liquid, the viscosity of the heat conductive resin composition is reduced, and even when no solvent is contained, the workability of the heat conductive resin composition is improved and it is easy to process as an insulating substrate. is there. Furthermore, since it does not contain a solvent, it is preferable in that the generation of voids in the insulating substrate can be reduced and the insulating properties of the insulating substrate can be improved. Any liquid epoxy resin may be used as long as it is liquid at room temperature. For example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, phenol novolac type epoxy resin, and the like can be used. In addition to this, an epoxy resin that is solid at room temperature may be added, and even in this case, an epoxy resin similar to the above can be used. Moreover, you may add the epoxy resin which brominated partially, In this case, it is preferable at the point which the flame retardance of the heat conductive resin composition and the insulated substrate which is the hardened | cured material improves.
[0035]
The heat conductive resin composition 21 contains at least a thermoplastic resin, and this thermoplastic resin has a function of absorbing and swelling the liquid thermosetting resin in the heat conductive resin composition. The type of the thermoplastic resin is not particularly limited and is preferably a powder that exhibits the above action. For example, powders such as polyvinyl chloride, polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate can be used. . Moreover, it is preferable that the particle size of the said thermoplastic resin powder exists in 1-100 micrometers. In this case, the inorganic filler and the liquid epoxy resin can be easily mixed.
[0036]
Moreover, the heat conductive resin composition 21 contains a latent hardening | curing agent at least. The latent curing agent is not particularly limited as long as it can be used for a thermosetting resin. For example, an amine adduct curing agent or a dicyandiamide curing agent can be used.
[0037]
In addition, at least one selected from a coupling agent, a dispersant, and a colorant is added to the resin composition containing at least the liquid thermosetting resin, the thermoplastic resin powder, and the latent curing agent. Is preferred. The coupling agent can improve the adhesion between the inorganic filler and metal foil and the resin composition. For example, an epoxysilane coupling agent, an aminosilane coupling agent, a titanate coupling agent, and the like can be used. The dispersant is preferable in terms of improving the dispersibility of the heat conductive resin composition and homogenizing it. For example, a phosphate ester can be used. The colorant is preferable in that the heat radiation property can be improved by coloring the heat conductive resin composition. For example, carbon can be used.
[0038]
What is necessary is just to weigh and mix each raw material as a manufacturing method of the heat conductive resin composition 21. FIG. As a mixing method, for example, a ball mill, a planetary mixer, or a stirrer can be used. Moreover, as a property of the heat conductive resin composition 21, it is preferable that it is a clay form or a paste-like, and it is preferable that the viscosity of the heat conductive resin composition 21 at this time is 100-100000 Pa.s, 1000-80000 Pa.s. More preferably, it is s. This is because the heat conductive resin composition can be easily handled within this range, and can be easily processed into an insulating substrate by subsequent heating and pressing. In addition, this viscosity has shown the viscosity in the temperature lower than the heating temperature used in FIG.2 (b), and the viscosity in the fixed temperature in the range of room temperature to the said heating temperature should just correspond to the said range.
[0039]
Moreover, it is preferable to process the heat conductive resin composition 21 into a sheet form. This facilitates the handling of the heat conductive resin composition, facilitates processing into an insulating substrate as shown in FIG. 2 (b), and reduces the void content in the heat conductive resin composition. Can be reduced. The method for processing into a sheet is not particularly limited, and may be appropriately selected according to the viscosity and properties of the heat conductive resin composition. For example, an extrusion method using an extruder, a coating method using a roll coater or a curtain coater. A printing method, a doctor blade method, or the like can be used.
[0040]
The metal foil 22 may be any metal foil as long as it is excellent in conductivity and can form a circuit pattern. For example, copper, nickel, aluminum, and alloys containing any one of these metals as main components can be used. An alloy having a main component is preferred. This is because copper is excellent in electrical conductivity, inexpensive and can easily form a circuit pattern. Moreover, it is preferable that the one surface which contact | connects the heat conductive resin composition of the metal foil 22 is roughened. This is because the adhesive strength between the metal foil 22 and the heat conductive resin composition 21 is improved. The thickness of the metal foil is preferably in the range of 12 to 200 μm, and more preferably in the range of 35 to 100 μm. If the metal foil is too thin than the preferred range, the allowable current value per unit width decreases, so that the circuit area increases in order to cope with a large current, which is disadvantageous for miniaturization. If the metal foil is too thick than the preferred range, it becomes difficult to form a circuit pattern with high accuracy.
[0041]
The releasable film 23 is not an essential element for the production of the circuit board of the present invention, but is preferable in terms of easily obtaining releasability. For example, a film of polyethylene terephthalate (PET) or polyphenylene sulfide (PPS) can be used. . In addition, it is preferable that those film surfaces are subjected to a release treatment with silica or the like.
[0042]
In the step of forming the circuit board precursor 24 shown in FIG. 2 (b), the heat conductive resin composition 21 is heated and pressurized to bond the metal foil 22 and the heat conductive resin composition 21 and to form a substrate. At the same time, the thermoplastic resin powder in the heat conductive resin composition 21 absorbs a liquid epoxy resin and swells it, thereby causing an increase in viscosity and solidifying irreversibly. The heating temperature at this time must be lower than the temperature at which the thermosetting epoxy resin begins to cure, and at the same time, higher than the glass transition temperature or softening point of the thermoplastic resin powder and lower than the melting start temperature. It is preferable that Specifically, the temperature is preferably 70 to 140 ° C, and more preferably 80 to 130 ° C. The pressurizing pressure is not particularly limited as long as it can be bonded to the metal foil and the heat conductive resin composition or can be molded into a substrate, but is usually 2 to 20 MPa, preferably 2 to 5 MPa. For the heating and pressurization, for example, a press device with a hot plate can be used. Furthermore, it is preferable that the heating and pressing be performed in a vacuum. This is because the effect of preventing oxidation of the metal foil and removing voids in the heat conductive resin composition can be obtained. The vacuum in this case indicates a reduced pressure state below atmospheric pressure.
[0043]
The viscosity when the heat conductive resin composition is solidified irreversibly by the heating and pressing is 8 × 10. ^Four ~ 3x10 ⁶ It is preferably Pa · s, 1 × 10 ^Five ~ 1x10 ⁶ More preferably, it is Pa · s. If it is within this preferred range, the substrate shape can be maintained even during normal handling, and the through hole as shown in FIG. 2C can be easily processed. When the viscosity is lower than this preferable range, it becomes difficult to process the through hole while maintaining the substrate shape. Moreover, when the viscosity is higher than this preferable range, it is difficult to process the through hole. In order to adjust to the above-mentioned preferable viscosity, the blending ratio of the liquid epoxy resin and the thermoplastic resin powder in the heat conductive resin composition 21 may be adjusted. The blending ratio varies depending on the type of the thermoplastic resin powder, but the thermoplastic resin powder is usually about 10 to 100 parts by mass with respect to 100 parts by mass of the liquid epoxy resin.
[0044]
The processing method of the through hole 25 shown in FIG. 2C is not particularly limited, and may be appropriately selected according to the thickness of the insulating substrate 26 and a desired hole diameter. For example, a punching method using a punching machine or a die Can be used, and these are preferred because they are simple and can be drilled with high positional accuracy. In particular, a punching method using a punching machine is more preferable. This is because punching has less contact between the processing tool and the substrate material than drilling, wear of the processing tool is reduced, its durability is greatly improved, and it has a significant industrial advantage.
[0045]
At the same time, it is preferable that at least a part of the circuit board precursor 24 is subjected to outline processing to divide or partially divide the board. According to this method, the outer shape processing becomes easier as compared with the case where the outer shape processing is performed after the thermosetting resin is cured, and the division is facilitated even when a plurality of circuit patterns are formed on one substrate. Because. As the outer shape processing method, a method that can be performed simultaneously with the processing of the above-described through-hole is preferable. Like the preferable example of the above-described through-hole processing method, for example, punch cutting with a punching machine, cutting with a mold, processing with a drill can be used. .
[0046]
The insulating substrate 26 shown in FIG. 2 (d) is formed by curing a thermosetting epoxy resin by heating. The heating temperature may be appropriately selected according to the reaction between the epoxy resin and the latent curing agent, but is preferably 140 to 240 ° C, and more preferably 150 to 200 ° C. If it is lower than this preferred range, the curing may be insufficient or the curing may take time, and if it is higher than the preferred range, the resin may start thermal decomposition. Moreover, it is preferable to pressurize simultaneously at the time of this heating. Thereby, the board | substrate of the board | substrate at the time of thermosetting is suppressed, a board | substrate with high flatness can be produced, and the adhesiveness of metal foil and an insulated substrate improves. The pressurizing pressure may be appropriately determined, but is usually 3 MPa or less, preferably 0.001 to 1 MPa. If it is higher than this range, the through hole may be deformed. Moreover, it is preferable to heat in a vacuum or non-oxidizing atmosphere in order to prevent oxidation of the metal foil during heat curing. In FIG. 2D, the releasable film 23 is peeled off at this point. However, the peeling may be peeled off when the releasable film becomes unnecessary. For example, FIG. You may remove at the time of the through-hole processing shown in.
[0047]
The method for forming the circuit pattern 27 shown in FIG. 2E is not particularly limited, and a conventionally known method can be used. For example, a method by chemical etching can be used.
[0048]
(Embodiment 2)
FIG. 3 shows a circuit board according to another embodiment of the present invention. In FIG. 3, 31 is an insulating substrate obtained by curing a heat conductive resin composition, 32 is a circuit pattern, 33 is a plated through hole provided in the insulating substrate 31, and the circuit patterns on both sides are electrically connected. Through-holes to be connected.
[0049]
FIG. 4 is a cross-sectional view for each process showing the method for manufacturing a circuit board in the second embodiment of the present invention. As shown in FIG. 4A, a plurality of heat conductive resin compositions 41 are sandwiched between metal foils 42 and heated at a temperature lower than the temperature at which the thermosetting resin in the heat conductive resin composition 41 starts to cure. As shown in FIG. 4B, the metal foil 42 and the heat conductive resin composition 41 are bonded to each other, and the plurality of heat conductive resin compositions 41 are integrated into a substrate shape and integrated. The heat conductive resin composition 41 is solidified irreversibly to form the circuit board precursor 43. Thereafter, as shown in FIG. 4C, the circuit board precursor 43 is drilled to form the through hole 44 and then heated, and as shown in FIG. 4D, the shape of the through hole 44 is formed. The thermally conductive resin composition 41 is cured while holding the insulating substrate 45. Thereafter, as shown in FIG. 4 (e), plating is performed to form a through hole 46 that electrically connects the metal foils 42 on both sides, and the metal foil 42 is further processed as shown in FIG. 4 (f). Then, a circuit pattern 47 is formed to obtain a circuit board.
[0050]
The heat conductive resin composition 41 and metal foil 42 used in the second embodiment can be the same as those used in the first embodiment. Further, as the method for forming the circuit board precursor 43, the method for forming the through hole 44, the method for manufacturing the insulating substrate 45, and the method for forming the circuit pattern 47, each method described in the first embodiment can be used.
[0051]
As a method for forming the through hole 46 shown in FIG. 4 (e), a connection method using copper plating over the entire surface is preferable. This is because the resistance value is low and the allowable current value is large. Also in this case, the metal foil 42 is preferably a copper foil. This is because the thermal expansion coefficient between the metal foil and the plating matches to improve the reliability.
[0052]
(Embodiment 3)
FIG. 5 is a sectional view by process showing a method of manufacturing a circuit board according to another embodiment of the present invention. Reference numeral 51 shown in FIG. 5A denotes a sheet-like heat conductive resin composition integrated by applying or impregnating a heat conductive resin composition to a reinforcing material. As shown in FIG.5 (b), the sheet-like heat conductive resin composition 51 is inserted | pinched with the metal foil 52, and the temperature lower than the temperature at which the thermosetting resin in the sheet-like heat conductive resin composition 51 starts hardening. By heating and pressurizing, the metal foil 52 and the sheet-like heat conductive resin composition 51 are bonded and formed into a substrate, and the sheet-like heat conductive resin composition 51 is irreversibly solidified to form a circuit board precursor 53. Form. Thereafter, as shown in FIG. 5 (c), the circuit board precursor 53 is drilled to form a through hole 54 and then heated to form the shape of the through hole 54 as shown in FIG. 5 (d). The sheet-like heat conductive resin composition 51 is cured to make the insulating substrate 55 while holding the film. Thereafter, as shown in FIG. 5 (e), plating is performed to form a through hole 56 that electrically connects the metal foils 52 on both sides, and the metal foil 52 is further processed as shown in FIG. 5 (f). The circuit pattern 57 is formed to obtain a circuit board.
[0053]
The heat conductive resin composition and the metal foil 52 in the sheet-like heat conductive resin composition 51 used in the third embodiment can be the same as those used in the first embodiment. Further, as the method for forming the circuit board precursor 53, the method for forming the through hole 54, the method for manufacturing the insulating substrate 55, and the method for forming the circuit pattern 57, each method described in the first embodiment can be used. Further, as a method for forming the through hole 56, a method similar to that described in the second embodiment can be used.
[0054]
As the reinforcing material used in the present embodiment, for example, a fabric using ceramic fiber, glass fiber, resin fiber, or the like can be used, and ceramic fiber or glass fiber is particularly preferable. Ceramics and glass have high heat resistance because they are excellent in heat resistance, and their thermal conductivity is higher than that of resin, so that the thermal conductivity of the substrate is improved. As the ceramic, for example, alumina, silica, or silicon nitride can be used. Moreover, when the said fiber is used, it is preferable that a reinforcing material is a nonwoven fabric. Since the density of the reinforcing material is low and the nonwoven fabric is porous compared to the woven fabric, it is easy to incorporate an inorganic filler when applying or impregnating the heat conductive resin composition, and without changing the composition ratio of the heat conductive resin composition. It is because it becomes easy to apply or impregnate. Furthermore, the diameter of the fiber is preferably 10 μm or less. If it is too large, the compressibility at the time of molding the substrate is reduced, and heat conduction between the inorganic fillers tends to be hindered, and as a result, the thermal resistance of the substrate may be increased.
[0055]
The method for producing the sheet-like heat conductive resin composition 51 by integrating the reinforcing material and the heat conductive resin composition is not particularly limited. For example, a method of applying the heat conductive resin composition to the reinforcing material, heat conduction A method of impregnating the reinforcing material with the resin composition or a method of attaching the heat conductive resin composition processed into a sheet to the reinforcing material can be used.
[0056]
In addition, in this Embodiment 3, although the board | substrate with which the double-sided wiring was through-hole connected using the sheet-like heat conductive resin composition 51 was demonstrated, by using the method similar to the said Embodiment 1, a reinforcing material is used. A single-sided wiring circuit board using a thermally conductive resin composition integrated with the insulating substrate can be manufactured.
[0057]
(Embodiment 4)
FIG. 6 is a cross-sectional view showing a power conversion module according to another embodiment of the present invention. In FIG. 6, reference numeral 61 denotes a circuit board manufactured by the method described in each of the above embodiments, on which various semiconductor elements 62 and passive components 63 are mounted to form a power conversion circuit. A mechanical component 64 such as an extraction electrode is connected.
[0058]
As a method for mounting each component, a conventionally known technique may be used. For example, reflow soldering, flow soldering, wire bonding, or flip chip connection can be used. In the case of performing soldering, a solder resist film may be formed on the circuit board 61, which is preferable in that unnecessary outflow of solder can be prevented. Moreover, it is preferable to apply a metal coat on the surface of the circuit pattern to prevent oxidation and corrosion of the metal foil as the circuit pattern. As the metal coat, for example, solder or tin can be used.
[0059]
【Example】
Next, based on a specific Example, the manufacturing method of the circuit board of this invention and its mounting body is demonstrated in more detail.
[0060]
(Example 1)
In order to produce a heat conductive resin composition, an inorganic filler and a resin composition were mixed. The materials and blending ratios are shown below.
[0061]
(1) Inorganic filler: Al ₂ O _Three ("AS-40", manufactured by Showa Denko KK, average particle size 12 μm) 87% by mass
(2) Liquid thermosetting resin: 7% by mass of bisphenol A type epoxy resin (“Epicoat 828”, manufactured by Yuka Shell Epoxy Co., Ltd.)
(3) Thermoplastic resin powder: Polymethyl methacrylate (manufactured by Kanto Chemical Co., Inc.) 3.5% by mass
(4) Latent curing agent: amine-based curing agent (“Amicure PN-23”, manufactured by Ajinomoto Co., Inc.) 1.5 mass%
(5) Other additives: carbon black (manufactured by Toyo Carbon Co., Ltd.) 0.5% by mass, coupling agent (“Plenact KR-46B”, Ajinomoto Co., Inc.) 0.5% by mass. A heat conductive resin composition was prepared by mixing with a Lee mixer. Thereafter, this heat conductive resin composition was processed into a sheet having a thickness of about 0.8 mm by a roll coater. When the viscosity of this heat conductive resin composition was measured while raising the temperature with a dynamic viscoelasticity measuring apparatus (manufactured by UBM), viscosity characteristics as shown in FIG. 8 were shown. As is apparent from FIG. 8, when the temperature exceeds about 80 ° C., irreversible solidification of the heat conductive resin composition starts, and when the temperature reaches about 100 ° C., irreversible solidification is completed. After that, when the temperature is continued to rise, the viscosity is maintained at a substantially constant level until the temperature reaches about 140 ° C. However, when the temperature is further raised, the heat conductive resin composition starts to be cured, and when the temperature reaches about 170 ° C. or higher, it is completely cured. .
[0062]
The above sheet-like heat conductive resin composition is placed on a PPS release film having a thickness of 70 μm, and further a single-side roughened copper foil (manufactured by Furukawa Electric Co., Ltd.) having a thickness of 35 μm is provided on the roughened surface. It arrange | positioned as shown to Fig.2 (a) so that a heat conductive resin composition might be touched. In a state in which these are decompressed, while being heated with a hot press at 100 ° C., pressurization is performed at a pressure of 3 MPa for 10 minutes to adhere the copper foil and the heat conductive resin composition, and the substrate shape as shown in FIG. At the same time, the heat conductive resin composition was solidified irreversibly to form a circuit board precursor having a thickness of about 0.8 mm. Next, a through hole having a diameter of 0.6 mm as shown in FIG. 2C was provided in the circuit board precursor by drilling. Thereafter, the circuit board precursor is heated in a nitrogen atmosphere at 170 ° C. for 1 hour to cure the epoxy resin in the thermally conductive resin composition, and the release film is removed, as shown in FIG. An insulating substrate with a copper foil was produced. Furthermore, a photo-curable dry film resist (manufactured by Nichigo Morton) is laminated on the metal foil, the circuit pattern is exposed and developed, and then etched in an aqueous iron chloride solution to form a circuit pattern. The resist film was removed to complete a single-sided wiring circuit board as shown in FIG.
[0063]
As Comparative Example 1, using the same sheet-like heat conductive resin composition, copper foil and releasable film as in Example 1, as shown in FIG. The epoxy resin in the heat conductive resin composition was cured by applying pressure at 3 MPa for 1.5 hours while being heated with a press, and a single-sided copper-clad substrate was produced. Thereafter, a through hole having a diameter of 0.6 mm was provided by drilling to produce a circuit board.
[0064]
In Example 1 and Comparative Example 1 described above, the durability of a cemented carbide drill blade (manufactured by Union Tool Co., Ltd.) during drilling was compared. In the case of Example 1, wear of the drill blade was small even after 1000 times of drilling, and subsequent drilling was possible and no chipping occurred. Moreover, the burr | flash of the wall surface of a through-hole did not generate | occur | produce. However, in the case of the comparative example 1, the wear of the drill blade was severe, and burrs were generated in the copper foil after 100 times of drilling, and subsequent drilling was impossible. From this, it can be seen that the circuit board manufacturing method of Example 1 is excellent in the processability of the through hole.
[0065]
(Example 2)
In order to produce a heat conductive resin composition, an inorganic filler and a resin composition were mixed. The materials and blending ratios are shown below.
[0066]
(1) Inorganic filler: Al ₂ O _Three (“AS-40”, manufactured by Showa Denko KK, average particle size 12 μm) 88% by mass
(2) Liquid thermosetting resin: 5% by mass of bisphenol F type epoxy resin (“Epicoat 807”, manufactured by Yuka Shell Epoxy Co., Ltd.)
(3) Brominated epoxy resin (“Epicoat 5050”, manufactured by Yuka Shell Epoxy Co., Ltd.) 2% by mass
(4) Thermoplastic resin powder: 3% by mass of polymethyl methacrylate (manufactured by Kanto Chemical Co., Inc.)
(5) Latent curing agent: amine curing agent (“Amicure PN-23”, manufactured by Ajinomoto Co., Inc.) 1% by mass, dicyandiamide (produced by Dainippon Ink Co., Ltd.) 0.4% by mass
(6) Other additives: Carbon black (manufactured by Toyo Carbon Co., Ltd.) 0.4 mass%, coupling agent (“Plenact KR-46B”, manufactured by Ajinomoto Co.) 0.2 mass%
These materials were weighed and mixed with a stirring kneader to prepare a heat conductive resin composition. Thereafter, this heat conductive resin composition was processed into a sheet having a thickness of about 1.0 mm by an extrusion molding machine. When the viscosity of this heat conductive resin composition was measured, it was about 9000 Pa · s at 50 ° C. and about 800,000 Pa · s at 110 ° C.
[0067]
One-side roughened copper foil (manufactured by Furukawa Circuit Foil Co., Ltd.) having a thickness of 70 μm was sandwiched as shown in FIG. 4 (a) so that the roughened surface was in contact with the heat conductive resin composition. However, the heat conductive resin composition of this Example 2 is a sheet form, and is different from drawing. While these are decompressed and heated with a 90 ° C. hot press, pressurize at a pressure of 3 MPa for 15 minutes to bond the copper foil and the heat conductive resin composition and form a substrate shape as shown in FIG. At the same time, the heat conductive resin composition was solidified irreversibly to form a circuit board precursor having a thickness of about 1.0 mm. Next, a through-hole having a diameter of 0.5 mm as shown in FIG. 4C was provided in the circuit board precursor by processing with a punching machine (manufactured by UHT). Thereafter, the circuit board precursor is heated at 170 ° C. for 2 hours while applying a load of 0.01 MPa to cure the epoxy resin in the heat conductive resin composition, and with a copper foil as shown in FIG. An insulating substrate was produced. Thereafter, copper plating with a thickness of about 30 μm was applied to the entire surface to form a copper plating through hole as shown in FIG. Further, a circuit pattern was formed by the same method as in Example 1 to complete a double-sided wiring circuit board as shown in FIG.
[0068]
In addition, using the same sheet-like heat conductive resin composition, copper foil and releasable film as in Example 2, they were superimposed and decompressed with a hot press at 170 ° C. as shown in FIG. 4 (a). The epoxy resin in the heat conductive resin composition was cured by heating at a pressure of 3 MPa for 1.5 hours while being heated, and a double-sided copper-clad substrate having a thickness of about 1.0 mm was produced. Thereafter, an attempt was made to provide a through hole with a diameter of 0.5 mm by the above punching process, but the pin of the punching machine did not penetrate the substrate, and the through hole could not be produced. From this, it can be seen that the circuit board manufacturing method of Example 2 is excellent in workability of the through hole.
[0069]
As Comparative Example 2, a glass-epoxy printed double-sided wiring board (corresponding to ANSI grade FR-4) having an insulating layer and a wiring layer having substantially the same thickness and having a copper plated through hole was produced.
[0070]
A similar through-hole chain pattern (500 hole connection) is formed on the substrates of Example 2 and Comparative Example 2, and the dip is repeated for 10 seconds each in oil at 20 ° C. and 260 ° C. while measuring the resistance value. A hot oil test was conducted. As a result, the substrate of Comparative Example 2 showed an increase in resistance at 350 cycles and was disconnected, but the substrate of Example 2 had good connectivity with no increase in resistance even at 3000 cycles. From this, it can be seen that the circuit board according to Example 2 is highly reliable.
[0071]
Example 3
The same material as in Example 1 was mixed to prepare a heat conductive resin composition.
[0072]
A glass nonwoven fabric (thickness: about 0.2 mm, fiber diameter: 9 μm) is prepared as a reinforcing material, and the above heat conductive resin composition is applied by rolls from both sides of the glass nonwoven fabric, and the thickness as shown in FIG. A heat conductive resin composition containing a 0.8 mm reinforcing material was prepared.
[0073]
A single-side roughened copper foil (manufactured by Furukawa Electric Co., Ltd.) having a thickness of 35 μm was sandwiched as shown in FIG. 5B so that the roughened surface was in contact with the heat conductive resin composition. While being heated with a hot press at 100 ° C. under reduced pressure, pressurization is performed at a pressure of 3 MPa for 10 minutes to bond the copper foil and the heat conductive resin composition and form a substrate shape as shown in FIG. At the same time, the thermally conductive resin composition was solidified irreversibly to form a circuit board precursor having a thickness of about 0.8 mm. Next, a through hole with a diameter of 0.8 mm as shown in FIG. 4C is provided in the circuit board precursor by a mold, and at the same time, between the circuit forming portion of the circuit board precursor and the outer peripheral portion thereof, A slit having a width of 1 mm was provided, leaving several connecting portions. Thereafter, the circuit board precursor is heated in a nitrogen atmosphere at 170 ° C. for 2 hours to cure the epoxy resin in the heat conductive resin composition, and an insulating board with double-sided copper foil as shown in FIG. Was made. Thereafter, copper plating with a thickness of about 30 μm was applied to the entire surface to form a copper plating through hole as shown in FIG. Further, a circuit pattern was formed by the same method as in Example 1 to complete a double-sided wiring circuit board as shown in FIG. Thereafter, the circuit board having a desired external dimension could be easily obtained by breaking the connecting portion.
[0074]
The substrate of Example 1 and Example 3 were processed to the same size, and the bending strength was measured after removing the copper foil. The bending strength of the substrate of Example 1 was 210 MPa. In the substrate of Example 3, it was 280 MPa. This result shows that the substrate of Example 1 also has practical strength as a substrate, but the strength of the substrate is improved by adding a reinforcing material.
[0075]
Further, the thermal resistance of the substrates of Examples 1 and 3 and Comparative Example 2 was measured. The thermal resistance represents a temperature rise with respect to the output power when a heating element is mounted on the substrate. The smaller this value, the smaller the temperature rise and the larger the allowable operation range of the component. A thermal resistance measuring machine (manufactured by Cats Electronics Design Co., Ltd.) was used for the thermal resistance measurement. That is, an FET (TO-220 package) is mounted on the same pattern of each substrate, and the surface opposite to the FET mounting surface of the circuit substrate is bonded to a finned heat sink as an ideal constant temperature heat reservoir, and in this state, a constant power is supplied to the semiconductor. The change in the semiconductor temperature was estimated from the change in the voltage at the PN junction of the semiconductor when given, and the value obtained by dividing the temperature difference by the power was obtained. As a result, the thermal resistance of the substrate of Example 1 was 1.02 ° C./W, whereas in Example 3, it was 1.11 ° C./W, and in Comparative Example 2, it was 8.4 ° C./W. It was. From this result, even if the reinforcing material is built in, there is no great difference in the thermal resistance of the substrate, the thermal resistance of the substrate of this example is very small compared to the general printed wiring board as in Comparative Example 2, It can be seen that it is thermally advantageous.
[0076]
(Example 4)
A solder paste (manufactured by Senju Metal Co., Ltd.) is printed on the circuit boards produced in Example 2 and Comparative Example 2 by a screen printing method using a metal mask, and a semiconductor element (manufactured by Mitsubishi Electric Co., Ltd.) and a capacitor, Various passive parts such as transformers, chokes and resistors (made by Matsushita Electronics Parts Co., Ltd.) and mechanical parts such as external lead terminals are mounted and then soldered in a reflow furnace (made by Matsushita Electric Works Co., Ltd.). A DC converter was produced.
[0077]
When a load of 30 W was applied to this DC-DC converter and the temperature of the power semiconductor 10 minutes after the start of the load was measured with a thermoviewer (Nikon Corp.), it was 48 ° C. when the circuit board of Example 2 was used. However, the temperature was 63 ° C. when the circuit board of Comparative Example 2 was used. From this result, it can be seen that the power conversion module using the substrate of Example 2 has a small increase in the temperature of the components and is advantageous in terms of operation and reliability.
[0078]
【The invention's effect】
As described above, according to the method for manufacturing a circuit board of the present invention, it is possible to easily process the through hole of the insulating substrate in which the inorganic conductivity is mixed with the resin composition at a high concentration to increase the thermal conductivity. It becomes possible to easily manufacture a highly heat-conductive insulating substrate having a through hole, which has been difficult. This also makes it possible to easily manufacture a double-sided wiring board having a through hole with a plated through hole. Further, by including a reinforcing material, it is possible to manufacture a circuit board having higher strength and high thermal conductivity.
[0079]
In addition, according to the present invention, it is possible to provide a circuit board that is excellent in thermal conductivity, maintains sufficient strength, and can cope with a large current. In addition, according to the power conversion module which is a mounting body of the circuit board of the present invention, it is excellent in heat dissipation and the temperature rise of the component is suppressed, so that a large current can be used and high-density component mounting is possible. Thus, it becomes possible to reduce the size and density of the device.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a circuit board according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view for each process showing the method for manufacturing a circuit board in the first embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a circuit board in a second embodiment of the present invention.
FIG. 4 is a cross-sectional view showing a method for manufacturing a circuit board according to the second embodiment of the present invention.
FIG. 5 is a cross-sectional view showing a method for manufacturing a circuit board according to Embodiment 3 of the present invention.
FIG. 6 is a cross-sectional view showing a power conversion module according to Embodiment 4 of the present invention.
FIG. 7 is a cross-sectional view for each process showing a circuit board manufacturing method of a conventional example.
FIG. 8 is a diagram showing the viscosity of a heat conductive resin composition in Example 1 of the present invention.
[Explanation of symbols]
11, 26, 31, 45, 55 Insulating substrate
12, 27, 32, 47, 57, 75 Circuit pattern
13, 25, 44, 54, 74 Through hole
21, 41 Thermal conductive resin composition
22, 42, 52, 72 Metal foil
23 Releasable film
24, 43, 53 Circuit board precursor
33, 46, 56 Through hole
51 Sheet-like heat conductive resin composition
61 Circuit board
62 Semiconductor device
63 Passive components
64 Mechanical parts
71 Heat conduction mixture
73 Electrical insulation layer

Claims

(1) A heat conductive resin composition comprising 70 to 95% by mass of an inorganic filler and 5 to 30% by mass of a resin composition containing at least an uncured thermosetting resin, a thermoplastic resin and a latent curing agent is prepared. And (2) heating and pressurizing at a temperature lower than the temperature at which the thermosetting resin in the thermal conductive resin composition starts to cure, and solidifying the thermal conductive resin composition irreversibly. A step of producing a substrate precursor, (3) a step of forming a through hole at an arbitrary position of the circuit substrate precursor, and (4) a step of curing the thermosetting resin in the circuit substrate precursor; A method for manufacturing a circuit board, comprising:

The step (2) of producing the circuit board precursor brings the metal foil and the heat conductive resin composition into contact with each other, and the temperature is lower than the temperature at which the thermosetting resin in the heat conductive resin composition starts to cure. It consists of a step of heating and pressurizing at a temperature to adhere the metal foil and the heat conductive resin composition and irreversibly solidifying the heat conductive resin composition to produce a circuit board precursor, and as a further step The method for manufacturing a circuit board according to claim 1, further comprising a step of processing the metal foil to form a circuit pattern.

From the temperature at which the step (2) of producing the circuit board precursor sandwiches the heat conductive resin composition between two metal foils, and the thermosetting resin in the heat conductive resin composition starts to cure. And heat and pressure at a low temperature to bond the metal foil and the heat conductive resin composition, and irreversibly solidify the heat conductive resin composition to produce a circuit board precursor. The process includes a step of forming a through hole by copper plating in the through hole to electrically connect the metal foil, and a step of processing the metal foil to form a circuit pattern. The manufacturing method of the circuit board of description.

The manufacturing method of the circuit board of Claim 1 which added the process of integrating the said heat conductive resin composition with a reinforcing material after the process (1) which produces the said heat conductive resin composition.

The method for manufacturing a circuit board according to claim 4, wherein the reinforcing material is made of ceramic fiber or glass fiber.

The method for manufacturing a circuit board according to claim 1, wherein the heating and pressing in the step (2) of producing the circuit board precursor is performed in a vacuum.

The method for manufacturing a circuit board according to claim 1, wherein the curing in the step (4) of curing the thermosetting resin in the circuit board precursor is performed by heating and pressing.

The viscosity of the heat conductive resin composition is in the range of 100 to 100,000 Pa · s, and the viscosity when the heat conductive resin composition is solidified irreversibly is 8 × 10 ^{4 to} 3 × 10 ⁶ Pa · s. The method of manufacturing a circuit board according to claim 1.

The through hole processing method in the step (3) of forming a through hole at an arbitrary position of the circuit board precursor is selected from the group consisting of punching with a punching machine, punching with a die, and drilling 1 The method of manufacturing a circuit board according to claim 1, which is one of the two methods.

2. The processing according to claim 1, wherein when processing the through hole in the step (3) of forming the through hole at an arbitrary position of the circuit board precursor, at least a part of the substrate is simultaneously processed into a desired shape. The manufacturing method of the circuit board of description.

The method for manufacturing a circuit board according to claim 2, wherein the metal foil is a copper foil having a thickness of 12 to 200 μm, at least one surface of which is roughened.

The method for producing a circuit board according to claim 1, wherein a temperature at which the heat conductive resin composition is solidified irreversibly is 70 to 140 ° C. 2.

_2. The circuit board according to claim 1, wherein the inorganic filler includes at least one selected from the group consisting of Al ₂ O ₃ , SiO ₂ , MgO, BeO, Si ₃ N ₄ , SiC, AlN, and BN. Production method.

A power conversion module comprising at least a semiconductor and passive components mounted on a circuit board manufactured by the method according to claim 1.