JP3847220B2

JP3847220B2 - Wiring board

Info

Publication number: JP3847220B2
Application number: JP2002177391A
Authority: JP
Inventors: 高志山崎
Original assignee: Kyocera Corp
Current assignee: Kyocera Corp
Priority date: 2002-06-18
Filing date: 2002-06-18
Publication date: 2006-11-22
Anticipated expiration: 2022-06-18
Also published as: JP2004022893A

Description

【０００１】
【発明の属する技術分野】
本発明は、半導体素子や圧電振動子等の電子部品を搭載するための配線基板に関するものである。
【０００２】
【従来の技術】
従来、半導体素子や圧電振動子等の電子部品を搭載するための配線基板は、一般に、略四角板状のセラミックス材料から成り、上面に電子部品搭載部を有する絶縁基体と、該絶縁基体の電子部品搭載部より絶縁基体内部を介して側面に導出されている複数個の配線層と、前記絶縁基体の上面で、前記電子部品搭載部を取り囲むように形成されている枠状の金属層と、前記絶縁基体の下面外周部に形成されている複数個の接続パッドと、前記絶縁基体の側面に形成され、各配線層と各接続パッドとを電気的に接続する複数個のキャスタレーション導体とにより構成されており、絶縁基体の電子部品搭載部に電子部品を搭載するとともに、電子部品の信号用、接地用等の各電極を各配線層にボンディングワイヤ等の導電性接続部材を介して電気的に接続し、しかる後、絶縁基体上面の枠状金属層に電子部品を覆うようにして鉄−ニッケル−コバルト合金や鉄−ニッケル合金等から成る金属製の蓋体をロウ材等を介して接合し電子部品を封止することによって電子装置となる。
【０００３】
かかる電子装置は、絶縁基体下面の外周部に形成した接続パッドを外部電気回路基板の配線導体に錫−鉛半田等の半田を介して接続することによって外部電気回路基板に実装され、同時に電子部品の各電極は配線層とキャスタレーション導体と接続パッドとを介して外部電気回路に電気的に接続されることとなる。
【０００４】
なお、前記キャスタレーション導体のうち、少なくとも電子部品の接地用の電極が接続されるもの（通常、全接続パッド中約２０〜５０％）は、一部が絶縁基体上面に形成されている枠状の金属層まで導出されており、枠状金属層を接地できるようになっている。
【０００５】
また前記各キャスタレーション導体は絶縁基体の側面に垂直方向に形成されており、枠状金属層と接続されるキャスタレーション導体は絶縁基体の側面で下面部から上面部にかけて形成されている。
【０００６】
更に前記複数個の接続パッドは一般に四角形状をなし、その一辺を絶縁基体の下面外周辺として絶縁基体の下面外周辺の略全体にわたって均一間隔に配列配置されている。
【０００７】
【発明が解決しようとする課題】
しかしながら、近時、各種電子装置は環境、人体に対する悪影響を防止するため従来使用されている錫−鉛半田に代わり、錫−銀−ビスマス系、錫−銀−銅−ビスマス系等の鉛を含有しない、いわゆる鉛フリー半田を用いて外部電気回路基板に接続されるようになってきており、かかる鉛フリー半田は、従来の錫−鉛半田に比べて溶融時に流れやすいため電子装置を外部電気回路基板に実装するとき、半田がキャスタレーション導体を伝って絶縁基体上面の枠状金属層や枠状金属に取着されている金属製蓋体にまで這い上がり、その結果、絶縁基体の接続パッドと、外部電気回路の配線導体との間に介在する半田の量が極めて少量となり、電子装置を外部回路基板に強固に実装することができないという欠点を有していた。
【０００８】
また、外部電気回路基板の配線導体に電子装置の接続パッドを錫−銀−ビスマス系等の鉛フリー半田を介して接続し外部電気回路基板に電子装置を実装させた後、電子装置と外部電気回路基板に熱が作用し電子装置の絶縁基体と外部電気回路基板との間に両者の熱膨張係数の相違に起因する熱応力が発生した場合、絶縁基体と外部電気回路基板との熱膨張係数の相違に起因して発生する熱応力は絶縁基体の中心部から放射状の方向に向かって作用すること、前記熱応力は絶縁基体の中心部からの距離が長いほど大きくなること、錫−銀−ビスマス系等の鉛フリー半田は従来の錫−鉛半田に比べて硬く、変形し難いこと、絶縁基体の下面外周の各辺に設けた四角形状の接続パッドは絶縁基体の外周辺を一辺として形成されており、前記熱応力が作用する方向とは一致せず、熱応力が作用する方向での接続パッドと鉛フリー半田との接合距離が短いこと等から、特に絶縁基体の各辺に設けた接続パッドのうち最外部の各辺に設けた接続パッドのうち最外部に位置する接続パッドに接合する鉛フリー半田に亀裂等の機械的破壊が発生し、電子装置の外部電気回路基板に対する接続の信頼性が低いという欠点も有していた。
【０００９】
本発明は、上記欠点に鑑み案出されたものであり、その目的は、接続パッドを外部電気回路基板の配線導体に鉛フリー半田を介して強固に接合し、それにより外部電気回路基板に強固にかつ高信頼性で実装することが可能な配線基板を提供することにある。
【００１０】
【課題を解決するための手段】
本発明の配線基板は、上面に電子部品搭載部および該搭載部を取り囲む枠状の金属層を有し、下面の外周部に接続パッドを有する絶縁基体と、前記絶縁基体の側面に形成され、前記接続パッドと枠状の金属層とを接続するキャスタレーション導体とを具備する配線基板であって、前記キャスタレーション導体は接続パッドから導出する第１領域と、枠状の金属層から導出する第２領域とから成り、前記第１領域と第２領域は絶縁基体側面の幅方向に位置がずれているとともに前記絶縁基体内部に形成された内部配線層を介して接続されており、かつ前記接続パッドは前記絶縁基体の下面中心部に向かって形成されていることを特徴とするものである。
【００１１】
本発明の配線基板によれば、絶縁基体上面に形成されている枠状金属層と絶縁基体下面に形成されている接続パッドとを電気的に接続するキャスタレーション導体を、接続パッドから導出する第１領域と、金属層から導出する第２領域とにより構成するとともに、前記第１領域と第２領域を絶縁基体側面の幅方向に位置をずらせたことから接続パッドと外部電気回路の配線導体とを鉛フリー半田を用いて接合したとしても、鉛フリー半田がキャスタレーション導体を伝って枠状金属層や金属製蓋体にまで這い上がることはなく、その結果、接続パッドと外部電気回路基板の配線導体との間に十分な量の半田を介在させることができ、配線基板（電子装置）を外部電気回路基板に極めて強固に接合することができる。
【００１２】
また本発明の配線基板によれば、絶縁基体の下面外周部に設けた接続パッドをその各々が絶縁基体の下面中心部に向かうよう形成したことから、外部電気回路基板の配線導体に電子装置の接続パッドを錫−銀−ビスマス系等の鉛フリー半田を介して接続し外部電気回路基板に電子装置を実装させた後、電子装置と外部電気回路基板に熱が作用し電子装置の絶縁基体と外部電気回路基板との間に両者の熱膨張係数の相違に起因する熱応力が発生したとしても、その熱応力の作用方向は接続パッドの形成方向に合致することとなって熱応力の作用方向における接続パッドと鉛フリー半田との接合距離が長いものとなり、これによって接続パッドに接合する鉛フリー半田に熱応力の作用により機械的破壊を生じるのが有効に防止され、電子装置の外部電気回路基板に対する接続の信頼性を極めて高いものとなすことができる。
【００１３】
【発明の実施の形態】
次に、本発明を添付図面に基づき詳細に説明する。
図１（ａ）乃至（ｃ）は、本発明の配線基板を半導体素子を収容する半導体素子収納用パッケージに適用した場合の一実施例を示し、１は絶縁基体、２は配線層、３は枠状金属層、４は接続パッド、５はキャスタレーション導体である。この絶縁基体１、配線層２、枠状金属層３、接続パッド４及びキャスタレーション導体５により半導体素子６を搭載するための配線基板７が形成される。
【００１４】
前記絶縁基体１は、酸化アルミニウム質焼結体、窒化アルミニウム質焼結体、ムライト質焼結体、ガラスセラミック焼結体等の電気絶縁材料から成り、その上面に半導体素子６を搭載する搭載部を有し、該搭載部に半導体素子６がガラス、樹脂、ロウ材等の接着材を介して接着固定される。
【００１５】
前記絶縁基体１は、例えば、酸化アルミニウム質焼結体から成る場合には、酸化アルミニウム、酸化珪素、酸化カルシウム、酸化マグネシウム等の原料粉末に適当な有機バインダー、溶剤を添加混合して泥漿状のセラミックスラリーとなし、次に前記セラミックスラリーを従来周知のドクターブレード法やカレンダーロール法等のシート成形技術によりシート状となして所定形状のセラミックグリーンシート（セラミック生シート）を得る、最後に前記セラミックグリーンシートを複数枚積層するとともに還元雰囲気中、約１６００℃の温度で焼成することによって製作される。
【００１６】
また前記絶縁基体１はその上面の半導体素子６が搭載される搭載部周囲から絶縁基体１の内部を介し側面にかけて複数個の配線層２が形成されており、該配線層２は半導体素子６の信号用、接地用の各電極を接続パッド４に接続するための導電路として作用し、搭載部側の一端には半導体素子６の信号用、接地用等の電極がボンディングワイヤ８を介して電気的に接続される。
【００１７】
前記配線層２はタングステン、モリブデン、マンガン、銅、銀、金、パラジウム等の金属粉末から成り、タングステン等の金属粉末に適当な有機バインダーや溶剤を添加混合して得た金属ペーストを絶縁基体１となるセラミックグリーンシートに予め従来周知のスクリーン印刷法により所定パターンに印刷塗布しておくことによって絶縁基体１の上面から絶縁基体１の内部を介し側面にかけて被着形成される。
【００１８】
また前記絶縁基体１はその上面で、半導体素子６が搭載される搭載部を取り囲むようにして枠状の金属層３が被着されており、該枠状の金属層３は後述する金属製蓋体９を絶縁基体１に取着させる際の下地金属層として作用し、タングステン、モリブデン、マンガン、銅、銀、金、パラジウム等の金属粉末により形成されている。
【００１９】
前記枠状金属層３には金属製蓋体９がロウ材を介してロウ付け取着され、これによって絶縁基体１の半導体素子搭載部に搭載されている半導体素子６は大気から気密に封止されることとなる。
【００２０】
なお、前記枠状金属層３は前述の配線層２と同様の方法によって絶縁基体１の上面で、半導体素子搭載部を取り囲むように形成される。
【００２１】
更に前記絶縁基体１の下面外周部には複数個の接続パッド４が形成されており、該接続パッド４は外部電気回路基板の配線導体に鉛フリー半田を介して接続され、半導体素子６の信号用、接地用の各電極を外部電気回路に電気的に接続する作用をなす。
【００２２】
前記接続パッド４は、タングステン、モリブデン、マンガン、銅、銀、金、パラジウム等の金属粉末より成り、前述の配線層２と同様の方法によって絶縁基体１の下面外周部に所定形状に形成される。
【００２３】
また更に前記絶縁基体１はその側面に複数個のキャスタレーション導体５（絶縁基体１の側面に断面半円状の凹部を設け、該凹部内に形成されている導体）が被着されており、該キャスタレーション導体５は配線層２と接続パッド４とを電気的に接続する作用をなす。
【００２４】
前記キャスタレーション導体５はタングステン、モリブデン、マンガン、銅、銀、金、パラジウム等の金属粉末より成り、絶縁基体１となるセラミックグリーンシートの側面に打ち抜き加工法により半円形の凹部を形成するとともに該凹部内にタングステン等の金属粉末に適当な有機バインダーや溶剤を添加混合して得た金属ペーストを予め従来周知のスクリーン印刷法により所定パターンに印刷塗布しておくことによって絶縁基体１の側面に所定形状に形成される。
【００２５】
前記キャスタレーション導体５はまた半導体素子６の接地用の電極と導通する配線層２に接続されるものについては一部が絶縁基体１上面の枠状金属層３にまで導出されており、枠状金属層３を接地するようになっている。
【００２６】
なお、前記配線層２、枠状の金属層３、接続パッド４及びキャスタレーション導体５は、その露出する表面に、ニッケル、金等の耐蝕性やボンディングワイヤ８のボンディング性、半田の濡れ性等が良好な金属から成るめっき層を被着させておくと配線層２や枠状の金属層３等の酸化腐食を有効に防止することができるとともに枠状金属層３への金属製蓋体９の取着、接続パッド４の外部電気回路基板への接続が確実、強固となる。従って、前記配線層２、枠状金属層３、接続パッド４及びキャスタレーション導体５は、その露出する表面に、ニッケル、金等の耐蝕性やボンディング性、半田の濡れ性等が良好な金属をめっき法により被着させておくことが好ましく、特に、例えば、厚さ１〜１０μｍのニッケルめっき層、０．０５〜３μｍの厚さの金めっき層を順次被着させておくことが好ましい。
【００２７】
この場合、金めっき層の厚みは、被着する部位や金めっき層の結晶配向等に応じて異なる厚みとしてもよく、例えば、金めっき層のＸ線回折における結晶配向を極力（１１１）面に揃えるようにするとともに、ボンディングワイヤ８が接続される領域も含め、全域で約０．３〜１μｍとするようにしてもよく、半田付け用の領域のみ約０．３μｍ以下の薄いものとし、錫−金の脆い金属間化合物の生成を抑えて半田付けの信頼性をより一層高めるようにしてもよい。
【００２８】
かくして本発明の配線基板７によれば、絶縁基体１上面の搭載部に半導体素子６を搭載するとともに半導体素子６の信号用、接地用の各電極を配線層２にボンディングワイヤ８を介して接続し、しかる後、絶縁基体１上面の枠状金属層３に鉄−ニッケル−コバルト合金や鉄−ニッケル合金等からなる金属製蓋体９をロウ材等を介して接合させ、金属製蓋体９で半導体素子６を気密に封止することによって製品としての電子装置（半導体装置）が完成する。
【００２９】
なお、この半導体装置は絶縁基体１下面外周部の接続パッド４を外部電気回路基板の配線導体に鉛フリー半田を介して接合することによって外部電気回路基板上に実装され、同時に半導体素子６の信号用、接地用の各電極が外部電気回路基板の配線導体に電気的に接続される。
【００３０】
本発明の配線基板７においてはキャスタレーション導体５のうち枠状金属層３と接続パッド４とを接続しているキャスタレーション導体５ａを図２に示すように接続パッド４から導出する第１領域５ｂと、枠状の金属層３から導出する第２領域５ｃとに分け、第１領域５ｂと第２領域５ｃとを絶縁基体１側面の幅方向に位置をずらせておくとともに絶縁基体１内部で内部配線層１０を介して電気的に接続しておくことが重要である。
【００３１】
前記枠状金属層３と接続パッド４とを接続しているキャスタレーション導体５ａを接続パッド４から導出する第１領域５ｂと、枠状金属層３から導出する第２領域５ｃとに分け、各々を絶縁基体１側面の幅方向に位置をずらせておくと接続パッド４と外部電気回路の配線導体とを鉛フリー半田を用いて接合したとしても、鉛フリー半田がキャスタレーション導体５ａを伝って枠状金属層３や金属製蓋体９にまで這い上がることはなく、その結果、接続パッド４と外部電気回路基板の配線導体との間に十分な量の半田を介在させることができ、配線基板（電子装置）を外部電気回路基板に極めて強固に接合することができる。
【００３２】
なお、前記枠状金属層３と接続パッド４とを接続しているキャスタレーション導体５ａの第１領域５ｂと第２領域５ｃとの分割位置は、使用する半田の種類や、絶縁基体１の厚さ、配線層２の設計上の都合等に応じて適宜決めるようにすればよく、例えば、キャスタレーション導体５ａが直径０．３ｍｍ〜０．７ｍｍの半円状で、半田として錫−銀系半田を用いる場合であれば、第１領域５ｂの長さを０．３ｍｍ〜１ｍｍの範囲とすればよい。
【００３３】
また、本発明の配線基板７においては、図１（ｃ）に示すように前記絶縁基体１の下面外周部に設けた接続パッド４を絶縁基体１の下面中心部に向かって形成しておくことが重要である。
【００３４】
前記接続パッド４を絶縁基体１の下面中心部に向かうよう形成しておくと、外部電気回路基板の配線導体に電子装置（半導体装置）の接続パッド４を錫−銀−ビスマス系等の鉛フリー半田を介して接続し外部電気回路基板に電子装置を実装させた後、電子装置と外部電気回路基板に熱が作用し電子装置の絶縁基体１と外部電気回路基板との間に両者の熱膨張係数の相違に起因する熱応力が発生したとしても、その熱応力の作用方向は接続パッド４の形成方向に合致することとなって熱応力の作用方向における接続パッド４と鉛フリー半田との接合距離が長いものとなり、これによって接続パッド４に接合する鉛フリー半田に熱応力の作用により機械的破壊を生じるのが有効に防止され、電子装置の外部電気回路基板に対する接続の信頼性を極めて高いものとなすことができる。
【００３５】
また、前記接続パッド４は、図３に示すように、その角部を円弧状に面取りしておくと、角部に熱応力が集中して鉛フリー半田や半田と接続パッド４との接合界面にクラック等の破壊が生じることを効果的に防止することができ、配線基板７の外部電気回路基板に対する接続信頼性をより一層良好とすることができる。したがって、前記接続パッド４は、その角部を円弧状に面取りしておくことが好ましい。
【００３６】
更に前記キャスタレーション導体５ａの接続パッド４から導出する第１領域５ｂは、図４に示すように、その内側に突出する突出部１１を形成しておけば接続パッド４を外部電気回路基板の配線導体に半田を介して接合するとき、前記突出部１１が半田の中に食い込むようにして接合されて接合強度がより一層強固となる。従って、前記キャスタレーション導体５ａの接続パッド４から導出する第１領域５ｂは、図４に示すように、その内側に突出する突出部１１を形成しておくことが好ましい。
【００３７】
なお、本発明は上述の実施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、例えば、上述の実施例では本発明の配線基板を半導体素子を収容する半導体素子収納用パッケージに適用したが、混成集積回路基板等の他の用途に適用してもよい。
【００３８】
また、図１では、絶縁基体１下面の２辺に接続パッド４が形成されている例を示したが、絶縁基体１下面の４辺全周等に接続パッド４が形成されている配線基板であってもよい。
【００３９】
【発明の効果】
本発明の配線基板によれば、絶縁基体上面に形成されている枠状金属層と絶縁基体下面に形成されている接続パッドとを電気的に接続するキャスタレーション導体を、接続パッドから導出する第１領域と、金属層から導出する第２領域とにより構成するとともに、前記第１領域と第２領域を絶縁基体側面の幅方向に位置をずらせたことから接続パッドと外部電気回路の配線導体とを鉛フリー半田を用いて接合したとしても、鉛フリー半田がキャスタレーション導体を伝って枠状金属層や金属製蓋体にまで這い上がることはなく、その結果、接続パッドと外部電気回路基板の配線導体との間に十分な量の半田を介在させることができ、配線基板（電子装置）を外部電気回路基板に極めて強固に接合することができる。
【００４０】
また本発明の配線基板によれば、絶縁基体の下面外周部に設けた接続パッドを絶縁基体の下面中心部に向かうよう形成したことから、外部電気回路基板の配線導体に電子装置の接続パッドを錫−銀−ビスマス系等の鉛フリー半田を介して接続し外部電気回路基板に電子装置を実装させた後、電子装置と外部電気回路基板に熱が作用し電子装置の絶縁基体と外部電気回路基板との間に両者の熱膨張係数の相違に起因する熱応力が発生したとしても、その熱応力の作用方向は接続パッドの形成方向に合致することとなって熱応力の作用方向における接続パッドと鉛フリー半田との接合距離が長いものとなり、これによって接続パッドに接合する鉛フリー半田に熱応力の作用により機械的破壊を生じるのが有効に防止され、電子装置の外部電気回路基板に対する接続の信頼性を極めて高いものとなすことができる。
【図面の簡単な説明】
【図１】（ａ）（ｂ）（ｃ）は本発明の配線基板の一実施例を示す側面図、平面図、底面図である。
【図２】本発明の配線基板の要部拡大斜視図である。
【図３】本発明の配線基板の他の実施例の要部拡大底面図である。
【図４】本発明の配線基板の他の実施例の要部拡大底面図である。
【符号の説明】
１・・・・・絶縁基体
２・・・・・配線層
３・・・・・枠状の金属層
４・・・・・接続パッド
５・・・・・キャスタレーション導体
５ａ・・・・接続パッドと枠状金属層とを接続しているキャスタレーション導体５ｂ・・・・第１領域
５ｃ・・・・第２領域
６・・・・・半導体素子
７・・・・・配線基板
８・・・・・ボンディングワイヤ
９・・・・・蓋体
１０・・・・内部配線層
１１・・・・突出部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wiring board for mounting electronic components such as semiconductor elements and piezoelectric vibrators.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, wiring boards for mounting electronic components such as semiconductor elements and piezoelectric vibrators are generally made of a substantially square plate-like ceramic material and have an electronic component mounting portion on the upper surface, and the electronic of the insulating substrate. A plurality of wiring layers led out from the component mounting portion to the side surface through the inside of the insulating base, and a frame-shaped metal layer formed on the upper surface of the insulating base so as to surround the electronic component mounting portion; A plurality of connection pads formed on the outer peripheral portion of the lower surface of the insulating base, and a plurality of castellation conductors formed on the side surface of the insulating base and electrically connecting each wiring layer and each connection pad. The electronic component is mounted on the electronic component mounting portion of the insulating base, and each electrode for signal and grounding of the electronic component is electrically connected to each wiring layer via a conductive connecting member such as a bonding wire. After that, a metal lid made of iron-nickel-cobalt alloy or iron-nickel alloy is joined to the frame-like metal layer on the upper surface of the insulating base with a brazing material or the like so as to cover the electronic component. By sealing the electronic component, an electronic device is obtained.
[0003]
Such an electronic device is mounted on an external electric circuit board by connecting a connection pad formed on the outer peripheral portion of the lower surface of the insulating base to a wiring conductor of the external electric circuit board via solder such as tin-lead solder, and at the same time an electronic component These electrodes are electrically connected to an external electric circuit through the wiring layer, the castellation conductor and the connection pad.
[0004]
Among the castellation conductors, at least a grounding electrode of an electronic component is connected (usually about 20 to 50% of all connection pads), a part of which is formed on the upper surface of the insulating base. The metal layer is led out so that the frame-like metal layer can be grounded.
[0005]
Each of the castellation conductors is formed in a direction perpendicular to the side surface of the insulating base, and the castellation conductor connected to the frame-like metal layer is formed from the bottom surface to the top surface on the side surface of the insulating base.
[0006]
Further, the plurality of connection pads generally have a quadrangular shape, and one side of the connection pads is arranged around the entire outer periphery of the lower surface of the insulating base at a uniform interval.
[0007]
[Problems to be solved by the invention]
However, recently, various electronic devices contain lead such as tin-silver-bismuth, tin-silver-copper-bismuth, etc. instead of tin-lead solder which is conventionally used to prevent adverse effects on the environment and human body. The so-called lead-free solder is used to connect to an external electric circuit board, and such a lead-free solder is easier to flow at the time of melting than a conventional tin-lead solder. When mounting on the board, the solder crawls up to the frame-like metal layer on the upper surface of the insulating base and the metal lid attached to the frame-like metal through the castellation conductor. The amount of solder interposed between the wiring conductors of the external electric circuit is extremely small and the electronic device cannot be firmly mounted on the external circuit board.
[0008]
In addition, after connecting the connection pad of the electronic device to the wiring conductor of the external electric circuit board via lead-free solder such as tin-silver-bismuth system and mounting the electronic device on the external electric circuit board, the electronic device and the external electric circuit are mounted. If thermal stress is generated between the insulating base of the electronic device and the external electric circuit board due to heat acting on the circuit board, the thermal expansion coefficient between the insulating base and the external electric circuit board The thermal stress generated due to the difference in the above acts from the central part of the insulating substrate in the radial direction, the thermal stress increases as the distance from the central part of the insulating substrate increases, tin-silver- Lead-free solder such as bismuth is harder and harder to deform than conventional tin-lead solder, and the rectangular connection pads provided on each side of the outer periphery of the lower surface of the insulating base form the outer periphery of the insulating base as one side. The thermal stress is The connection distance between the connection pad and the lead-free solder in the direction in which the thermal stress acts is short, etc. The lead-free solder bonded to the outermost connection pads among the connection pads provided on the side is subject to mechanical damage such as cracks, and the reliability of the connection of the electronic device to the external electric circuit board is low. Was.
[0009]
The present invention has been devised in view of the above disadvantages, and its purpose is to firmly connect the connection pad to the wiring conductor of the external electric circuit board via lead-free solder, thereby firmly connecting to the external electric circuit board. Another object of the present invention is to provide a wiring board that can be mounted with high reliability.
[0010]
[Means for Solving the Problems]
The wiring board of the present invention has an electronic component mounting portion on the upper surface and a frame-shaped metal layer surrounding the mounting portion, an insulating base having a connection pad on the outer periphery of the lower surface, and formed on the side surface of the insulating base, A wiring board including a castellation conductor for connecting the connection pad and a frame-shaped metal layer, wherein the castellation conductor is a first region derived from the connection pad and a first region derived from the frame-shaped metal layer. The first region and the second region are displaced in the width direction of the side surface of the insulating base and are connected via an internal wiring layer formed inside the insulating base, and the connection The pad is formed toward the center of the lower surface of the insulating base.
[0011]
According to the wiring board of the present invention, the castellation conductor that electrically connects the frame-shaped metal layer formed on the upper surface of the insulating base and the connection pad formed on the lower surface of the insulating base is led out from the connection pad. 1 region and a second region derived from the metal layer, and since the first region and the second region are shifted in the width direction of the side surface of the insulating base, the connection pad and the wiring conductor of the external electric circuit Even if they are joined using lead-free solder, lead-free solder does not crawl up to the frame-like metal layer or metal lid through the castellation conductor. A sufficient amount of solder can be interposed between the wiring conductors and the wiring board (electronic device) can be bonded to the external electric circuit board very firmly.
[0012]
Further, according to the wiring board of the present invention, since the connection pads provided on the outer peripheral portion of the lower surface of the insulating base are formed so as to face the center of the lower surface of the insulating base, the wiring conductor of the external electric circuit board is connected to the wiring conductor of the electronic device. After connecting the connection pads via lead-free solder such as tin-silver-bismuth system and mounting the electronic device on the external electric circuit board, heat acts on the electronic device and the external electric circuit board, and the insulating substrate of the electronic device Even if a thermal stress is generated between the external electrical circuit board and the thermal expansion coefficient between the two, the direction of action of the thermal stress coincides with the direction in which the connection pad is formed. As a result, the bonding distance between the connection pad and lead-free solder in the lead is increased, which effectively prevents mechanical damage to the lead-free solder bonded to the connection pad due to the action of thermal stress. It can be made extremely high reliability of the connection to the electrical circuit board.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in detail with reference to the accompanying drawings.
FIGS. 1A to 1C show an embodiment in which the wiring board of the present invention is applied to a package for housing a semiconductor element for housing a semiconductor element, wherein 1 is an insulating substrate, 2 is a wiring layer, 3 is A frame-shaped metal layer, 4 is a connection pad, and 5 is a castellation conductor. The insulating substrate 1, the wiring layer 2, the frame-shaped metal layer 3, the connection pad 4 and the castellation conductor 5 form a wiring substrate 7 for mounting the semiconductor element 6.
[0014]
The insulating substrate 1 is made of an electrically insulating material such as an aluminum oxide sintered body, an aluminum nitride sintered body, a mullite sintered body, or a glass ceramic sintered body, and a mounting portion on which a semiconductor element 6 is mounted. The semiconductor element 6 is bonded and fixed to the mounting portion via an adhesive such as glass, resin, or brazing material.
[0015]
When the insulating substrate 1 is made of, for example, an aluminum oxide sintered body, a suitable organic binder and solvent are added to and mixed with raw material powders such as aluminum oxide, silicon oxide, calcium oxide, and magnesium oxide to form a mud-like shape. Next, the ceramic slurry is formed into a sheet shape by a sheet forming technique such as a conventionally known doctor blade method or calendar roll method to obtain a ceramic green sheet (ceramic raw sheet) having a predetermined shape. It is manufactured by laminating a plurality of green sheets and firing them at a temperature of about 1600 ° C. in a reducing atmosphere.
[0016]
The insulating base 1 is formed with a plurality of wiring layers 2 from the periphery of the mounting portion on which the semiconductor element 6 on the upper surface is mounted to the side surface through the inside of the insulating base 1. The signal and ground electrodes act as conductive paths for connecting to the connection pads 4, and the signal and ground electrodes of the semiconductor element 6 are electrically connected via bonding wires 8 at one end on the mounting portion side. Connected.
[0017]
The wiring layer 2 is made of a metal powder such as tungsten, molybdenum, manganese, copper, silver, gold, palladium, etc., and a metal paste obtained by adding and mixing an appropriate organic binder or solvent to the metal powder such as tungsten is used as the insulating substrate 1. The ceramic green sheet to be formed is preliminarily printed and applied in a predetermined pattern by a well-known screen printing method so that the ceramic green sheet is deposited from the upper surface of the insulating substrate 1 to the side surface through the inside of the insulating substrate 1.
[0018]
The insulating base 1 is covered with a frame-shaped metal layer 3 so as to surround the mounting portion on which the semiconductor element 6 is mounted on the upper surface of the insulating substrate 1, and the frame-shaped metal layer 3 is a metal lid described later. It acts as a base metal layer when the body 9 is attached to the insulating substrate 1, and is formed of metal powder such as tungsten, molybdenum, manganese, copper, silver, gold, palladium.
[0019]
A metal lid 9 is brazed and attached to the frame-shaped metal layer 3 via a brazing material, whereby the semiconductor element 6 mounted on the semiconductor element mounting portion of the insulating base 1 is hermetically sealed from the atmosphere. Will be.
[0020]
The frame-shaped metal layer 3 is formed on the upper surface of the insulating substrate 1 so as to surround the semiconductor element mounting portion by the same method as the wiring layer 2 described above.
[0021]
Further, a plurality of connection pads 4 are formed on the outer peripheral portion of the lower surface of the insulating base 1, and the connection pads 4 are connected to the wiring conductor of the external electric circuit board via lead-free solder, and the signal of the semiconductor element 6 Each electrode for grounding and grounding is electrically connected to an external electric circuit.
[0022]
The connection pad 4 is made of a metal powder such as tungsten, molybdenum, manganese, copper, silver, gold, or palladium, and is formed in a predetermined shape on the outer periphery of the lower surface of the insulating substrate 1 by the same method as that for the wiring layer 2 described above. .
[0023]
Furthermore, the insulating base 1 is coated with a plurality of castoration conductors 5 (conductors provided with a semicircular recess in the side face of the insulating base 1 and formed in the recess) on the side surface, The castellation conductor 5 serves to electrically connect the wiring layer 2 and the connection pad 4.
[0024]
The castellation conductor 5 is made of a metal powder such as tungsten, molybdenum, manganese, copper, silver, gold, palladium, etc., and a semicircular recess is formed on the side surface of the ceramic green sheet serving as the insulating substrate 1 by a punching method. A metal paste obtained by adding and mixing a suitable organic binder or solvent to a metal powder such as tungsten in the recess is preliminarily printed in a predetermined pattern by a well-known screen printing method, and then predetermined on the side surface of the insulating substrate 1. It is formed into a shape.
[0025]
A part of the castellation conductor 5 connected to the wiring layer 2 electrically connected to the grounding electrode of the semiconductor element 6 is led out to the frame-like metal layer 3 on the upper surface of the insulating base 1. The metal layer 3 is grounded.
[0026]
The wiring layer 2, the frame-shaped metal layer 3, the connection pad 4, and the castoration conductor 5 have corrosion resistance such as nickel and gold, bonding property of the bonding wire 8, solder wettability, etc. on the exposed surface. If a plating layer made of a good metal is applied, the oxidative corrosion of the wiring layer 2 and the frame-shaped metal layer 3 can be effectively prevented and the metal lid 9 on the frame-shaped metal layer 3 can be prevented. And the connection of the connection pad 4 to the external electric circuit board is ensured and strong. Therefore, the wiring layer 2, the frame-shaped metal layer 3, the connection pad 4, and the castellation conductor 5 are made of a metal having good corrosion resistance such as nickel and gold, bonding properties, solder wettability, etc. on the exposed surface. It is preferable to deposit by a plating method. In particular, it is preferable to sequentially deposit, for example, a nickel plating layer having a thickness of 1 to 10 μm and a gold plating layer having a thickness of 0.05 to 3 μm.
[0027]
In this case, the thickness of the gold plating layer may be different depending on the part to be deposited, the crystal orientation of the gold plating layer, etc. For example, the crystal orientation in the X-ray diffraction of the gold plating layer is as much as possible to the (111) plane. In addition, the entire region including the region to which the bonding wire 8 is connected may be about 0.3 to 1 μm, and only the region for soldering should be as thin as about 0.3 μm or less. -Generation | occurrence | production of the gold brittle intermetallic compound may be suppressed, and you may make it improve the reliability of soldering further.
[0028]
Thus, according to the wiring substrate 7 of the present invention, the semiconductor element 6 is mounted on the mounting portion on the upper surface of the insulating base 1 and the signal and ground electrodes of the semiconductor element 6 are connected to the wiring layer 2 via the bonding wires 8. Thereafter, a metal lid body 9 made of iron-nickel-cobalt alloy, iron-nickel alloy, or the like is joined to the frame-like metal layer 3 on the upper surface of the insulating base 1 via a brazing material or the like. Thus, the semiconductor device 6 is hermetically sealed to complete an electronic device (semiconductor device) as a product.
[0029]
The semiconductor device is mounted on the external electric circuit board by joining the connection pads 4 on the outer periphery of the lower surface of the insulating base 1 to the wiring conductor of the external electric circuit board via lead-free solder, and simultaneously the signal of the semiconductor element 6 The electrodes for grounding and grounding are electrically connected to the wiring conductor of the external electric circuit board.
[0030]
In the wiring board 7 of the present invention, the caster conductor 5a connecting the frame-like metal layer 3 and the connection pad 4 out of the caster conductor 5 is led out from the connection pad 4 as shown in FIG. And the second region 5c derived from the frame-shaped metal layer 3, and the first region 5b and the second region 5c are displaced in the width direction of the side surface of the insulating base 1 and are internally formed inside the insulating base 1. It is important to be electrically connected via the wiring layer 10.
[0031]
The castellation conductor 5a connecting the frame-shaped metal layer 3 and the connection pad 4 is divided into a first region 5b derived from the connection pad 4 and a second region 5c derived from the frame-shaped metal layer 3, Is shifted in the width direction of the side surface of the insulating base 1, even if the connection pad 4 and the wiring conductor of the external electric circuit are joined using lead-free solder, the lead-free solder is transmitted through the castellation conductor 5a. As a result, a sufficient amount of solder can be interposed between the connection pad 4 and the wiring conductor of the external electric circuit board. The (electronic device) can be bonded to the external electric circuit board very firmly.
[0032]
The dividing position of the first region 5b and the second region 5c of the castellation conductor 5a that connects the frame-shaped metal layer 3 and the connection pad 4 depends on the type of solder used and the thickness of the insulating substrate 1. The wiring layer 2 may be appropriately determined according to the design convenience of the wiring layer 2. For example, the castellation conductor 5 a has a semicircular shape with a diameter of 0.3 mm to 0.7 mm, and tin-silver solder as the solder. In the case of using the first region 5b, the length of the first region 5b may be in the range of 0.3 mm to 1 mm.
[0033]
Further, in the wiring board 7 of the present invention, as shown in FIG. 1 (c), the connection pads 4 provided on the outer periphery of the lower surface of the insulating substrate 1 are formed toward the center of the lower surface of the insulating substrate 1. is important.
[0034]
When the connection pad 4 is formed so as to face the center of the lower surface of the insulating substrate 1, the connection pad 4 of the electronic device (semiconductor device) is connected to the wiring conductor of the external electric circuit board by a lead-free material such as a tin-silver-bismuth system. After the electronic device is mounted on the external electric circuit board by connecting via the solder, heat is applied to the electronic device and the external electric circuit board, and the thermal expansion of both between the insulating base 1 of the electronic device and the external electric circuit board is performed. Even if the thermal stress due to the difference in coefficient is generated, the direction of action of the thermal stress coincides with the direction in which the connection pad 4 is formed, and the connection pad 4 and the lead-free solder are joined in the direction of action of the thermal stress. As a result, the distance between the lead pad and the lead-free solder joined to the connection pad 4 is effectively prevented from being mechanically damaged by the action of thermal stress, and the reliability of the connection of the electronic device to the external electric circuit board is extremely high. It can be made as high Te.
[0035]
In addition, as shown in FIG. 3, when the corner of the connection pad 4 is chamfered in an arc shape, thermal stress concentrates on the corner and lead-free solder or a bonding interface between the solder and the connection pad 4 is formed. It is possible to effectively prevent cracks and the like from being broken, and to further improve the connection reliability of the wiring board 7 to the external electric circuit board. Therefore, it is preferable that the connection pad 4 has its corners chamfered in an arc shape.
[0036]
Further, as shown in FIG. 4, the first region 5b led out from the connection pad 4 of the castellation conductor 5a is provided with a protruding portion 11 protruding inside thereof, so that the connection pad 4 is wired to the external electric circuit board. When joining to a conductor via solder, the said protrusion part 11 is joined so that it may bite into solder, and joining strength will become still stronger. Therefore, it is preferable that the first region 5b led out from the connection pad 4 of the castellation conductor 5a is formed with a protruding portion 11 protruding inward as shown in FIG.
[0037]
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiments, the wiring board of the present invention is a semiconductor. Although the present invention is applied to a package for housing a semiconductor element that houses elements, it may be applied to other uses such as a hybrid integrated circuit board.
[0038]
FIG. 1 shows an example in which the connection pads 4 are formed on the two sides of the lower surface of the insulating base 1. However, in the wiring board in which the connection pads 4 are formed all around the four sides of the lower surface of the insulating base 1. There may be.
[0039]
【The invention's effect】
According to the wiring board of the present invention, the castellation conductor that electrically connects the frame-shaped metal layer formed on the upper surface of the insulating base and the connection pad formed on the lower surface of the insulating base is led out from the connection pad. 1 region and a second region derived from the metal layer, and since the first region and the second region are shifted in the width direction of the side surface of the insulating base, the connection pad and the wiring conductor of the external electric circuit Even if they are joined using lead-free solder, lead-free solder does not crawl up to the frame-like metal layer or metal lid through the castellation conductor. A sufficient amount of solder can be interposed between the wiring conductors and the wiring board (electronic device) can be bonded to the external electric circuit board very firmly.
[0040]
Further, according to the wiring board of the present invention, since the connection pad provided on the outer periphery of the lower surface of the insulating base is formed so as to face the center of the lower surface of the insulating base, the connection pad of the electronic device is connected to the wiring conductor of the external electric circuit board. After the electronic device is mounted on the external electric circuit board by connecting via a lead-free solder such as tin-silver-bismuth system, heat is applied to the electronic device and the external electric circuit board, and the insulating base of the electronic device and the external electric circuit Even if thermal stress due to the difference in thermal expansion coefficient between the two occurs with the substrate, the direction of action of the thermal stress matches the direction of formation of the connection pad, and the connection pad in the direction of action of thermal stress The lead-free solder has a long joint distance, which effectively prevents mechanical damage from being caused by thermal stress in the lead-free solder that is joined to the connection pad. It can be made extremely high reliability connections to the plate.
[Brief description of the drawings]
1A, 1B and 1C are a side view, a plan view and a bottom view showing an embodiment of a wiring board according to the present invention.
FIG. 2 is an enlarged perspective view of a main part of a wiring board according to the present invention.
FIG. 3 is an enlarged bottom view of an essential part of another embodiment of the wiring board of the present invention.
FIG. 4 is an enlarged bottom view of an essential part of another embodiment of the wiring board of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Insulation base | substrate 2 ... Wiring layer 3 ... Frame-shaped metal layer 4 ... Connection pad 5 ... Castoration conductor 5a ... Connection Castoration conductor 5b connecting the pad and the frame-like metal layer .... first region 5c .... second region 6 ... semiconductor element 7 ... wiring substrate 8 .... ... Bonding wire 9 ... Lid 10 ... Internal wiring layer 11 ... Projection

Claims

An insulating base having an electronic component mounting portion on the upper surface and a frame-shaped metal layer surrounding the mounting portion, and having a connection pad on the outer peripheral portion of the lower surface; formed on the side surface of the insulating base; A wiring board comprising a castellation conductor for connecting to a metal layer, wherein the castellation conductor comprises a first region derived from a connection pad and a second region derived from a frame-shaped metal layer, The first region and the second region are displaced in the width direction of the side surface of the insulating base and are connected via an internal wiring layer formed inside the insulating base, and the connection pad is a lower surface of the insulating base. A wiring board characterized by being formed toward the center of the wiring board.