JP3667926B2 - Gold / nickel / nickel three-layer plated copper alloy electronic component and method for manufacturing the same - Google Patents
Gold / nickel / nickel three-layer plated copper alloy electronic component and method for manufacturing the same Download PDFInfo
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- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
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Description
【０００１】
【発明の属する技術分野】
本発明は、大気雰囲気中で、鉛を含まないはんだを用いて、はんだ付けされる金／ニッケル／ニッケル３層めっき銅合金電子部品に関し、特には金線やアルミニウム線でのワイヤボンディング部の信頼性、および加熱後のはんだぬれ性に優れる金／ニッケル／ニッケル３層めっき銅合金電子部品に関するものである。なお、対象とする銅合金電子部品はリードフレームや自動車の電装部品、端子、コネクタ、ＪＢ（ジョイントボックス）などであるが、以下の説明では、発明を理解し易くするためリードフレームを例に説明する。
【０００２】
【従来の技術】
従来、リードフレームのはんだダイボンディングされる表面には、良好なはんだぬれ性を得るために銀めっき、金めっきなどの貴金属めっきが施されている。また、半導体装置のパッケージ後のアウターリード部へのはんだめっき工程を省略するために、リードフレーム製造時に前記ダイボンディング部だけでなく、リードフレーム全面に貴金属めっきを施す技術が考えられている。
【０００３】
例えば、特開昭54− 34760号公報にはリードフレームの表面にニッケルめっきを下地として部分的に金めっきを施す技術が示されているが、ここに開示の技術では、下地となるニッケルめっきについて厚みを 6〜10μｍと限定されているものの、その他の諸条件、例えば光沢めっきや無光沢めっき、あるいはめっき中の硫黄含有量などについて検討が行われておらず、このため金めっき厚みを薄くできないとともに、ワイヤボンディング性が劣ると言った問題が懸念される。
【０００４】
特開昭61−78150 号公報にはリードフレームの表面に金めっきを薄く施し、アウターリード部へのめっきを省略する技術が示されているが、金めっき前の下地めっきについては全く検討されていない。このため、鉄系を素材とした実施例で金めっきを施した例が示されているが、銅合金電子部品に適用することはできなかった。
【０００５】
特開平 4−152661号公報には特開昭54−34760 号公報と同様にリードフレームの表面にニッケルめっきを下地として金めっきを施す技術が示されているが、ここに開示の技術では、下地となるニッケルめっきについて厚みが 0.1〜 5μｍが好ましいと記載されているものの、その実施例１には銅合金リードフレームを対象に無光沢ニッケルめっきを0.5 μｍ施した例が示されているのみであり、このような厚み 0.5μｍの無光沢ニッケルめっきでは銅の拡散防止層としての機能が十分に得られず、また 0.5μｍ以上の厚さにめっきすると、詳細を段落番号〔０００８〕に説明するようにワイヤボンディング性が低下すると言った問題が懸念される。
【０００６】
最近、電気部品の高密度集積化によりリードフレームが受ける熱量は増加しており、耐酸化性、耐食性と耐熱信頼性に優れる金めっき銅合金リードフレームが望まれている。また、ワイヤボンディング技術の向上により、より短時間で生産性良く接合し得るワイヤボンディング装置が開発されているが、その性能を十分に発揮するために、ワイヤボンディング性の良い銅合金リードフレームが望まれている。しかしながら、上述したように、従来の技術ではワイヤボンディング性が良く、耐熱信頼性に優れる金めっき銅合金電子部品の要求に応え得るものは無かった。
【０００７】
【発明が解決しようとする課題】
そこで、本発明者は、上記要求に応えるべく研究を行った。しかしながら、従来の表面にニッケルめっきを下地として金めっきを施したリードフレームでは、下地が光沢ニッケルめっきの場合にはめっき皮膜に取り込まれた光沢剤成分が加熱により金の表面に拡散し、はんだ付け性を低下させると言った問題があり、金めっきの厚みを薄くできなかった。また金めっきが厚いと、コストが高くなるだけでなく、アルミニウム線で接合した場合に金−アルミニウム合金層の成長により、ワイヤ接合強度が極端に低下すると言った問題があった。
【０００８】
一方、下地が無光沢ニッケルめっきの場合にはニッケルめっきを厚くすると、表面の光沢がなくなり、表面が荒れると言った問題があった。表面が荒れるとワイヤボンディング性が低下するため、ニッケルめっきを厚くすることができない。また薄い無光沢ニッケルめっきでは素材の銅の拡散を防止する効果が不十分であり、信頼性に問題があった。
【０００９】
本発明は、上述した経緯を踏まえてなしたものであって、その目的は、ワイヤボンディング性と耐熱信頼性を向上させるニッケルめっきを厚く行うとともに、はんだ付け性と接合強度を向上させるべく金めっきを薄く行った、コストパーフォーマンスに優れる金めっき銅合金電子部品およびその製造方法を提供することである。
【００１０】
【課題を解決するための手段】
上記の目的を達成するために、本発明者は更なる研究を行った。その結果、上述した従来の下地ニッケルめっきを２層に分け、それぞれに特性を持たせ、その最上層に金めっきを施すと、従来の光沢ニッケルめっき下地を持つリードフレーム製品と同等以上である鏡面反射率30％以上の平滑な表面を持ちながら、金の特性を最大に生かした金めっき銅合金電子部品が得られることを見出し、本発明を完成したものである。
【００１１】
すなわち、本発明は、上層に厚みが0.001 〜0.2 μｍの金および金合金層を持ち、中間層に厚みが0.1 〜0.5 μｍで硫黄含有量が0.02質量％以下のニッケル層を持ち、下層に硫黄含有量が0.02質量％を越える0.5 〜5 μｍのニッケル層を持つとともに、その表面の鏡面反射率が30％以上であることを特徴とするワイヤボンディング信頼性、はんだぬれ性に優れる金／ニッケル／ニッケル３層めっき銅合金電子部品とするものである。以下、本発明の構成並びに作用効果を詳細に説明する。
【００１２】
従来の下地ニッケルめっきは金めっきへの素材の拡散を防止するものでしかなかった。しかし、ワイヤボンディング技術の発達と電子部品の高集積化・小型化・ハイブリット化により、金めっきに要求される特性が多くなり、さらに、コストダウンの観点より金めっきを薄くする必要性が生じた。しかし、金めっきを薄くすると、下地ニッケルめっきの表面特性が金の特性を大きく左右するということが分かった。
そこで、本発明者は下地ニッケルめっきがはんだぬれ性、ワイヤボンディング性、耐熱信頼性などに及ぼす影響を鋭意検討した。その結果、下記に説明するようにニッケルめっき皮膜中の硫黄含有量が特性に影響を及ぼしていることを見出した。
【００１３】
すなわち、金線およびアルミニウム線によるワイヤボンディング性は被接合表面の平滑さの影響を受ける。ワイヤボンディング装置の荷重と超音波の関係でも異なるが、超音波の効果を有効に得るには被接合表面は平滑な方が望ましい。ニッケルめっきでは光沢剤などを添加することにより鏡面反射率50％以上の平滑な表面を得ることができる。しかし、調査した結果、光沢度の高い、平滑なニッケルめっき皮膜中には光沢剤や均一電着剤、応力緩和剤などの成分が取り込まれており、そこには0.02質量％を越える硫黄やカーボン、リンなどの不純物を含むことが分かった。
これらの不純物は電子部品組み立て工程において受ける熱によって表面層に拡散し、ワイヤボンディング性やはんだぬれ性、接触抵抗、接合信頼性を低下させることを見出した。また、ワイヤボンディングとは金やアルミニウム、銅などの合金線を用い、超音波を使ってチップとリードを接合するものであるが、接合信頼性はリードフレーム表面が平滑なほど良好であること、また表面が平滑な方が、はんだ接合時のはんだが拡がり易いことを見い出した。
また、最表面に金めっき層を施し、ワイヤボンディング性やはんだぬれ性を向上させる場合にも、金めっき層を 0.2μｍを越えて厚くしなければ、上記下地ニッケルめっき層の不純物の悪影響を受けることが分かった。
【００１４】
上述の検討、研究により、本発明者は下地ニッケルめっき層の不純物を制御することにより、ワイヤボンディング性やはんだぬれ性などの問題を解決できることを突き止めたが、添加剤を含まない無光沢ニッケルめっきを厚く施すと、鏡面反射率は30％より低くなり、表面が荒れるとともにワイヤボンディング性が低下すると言った新たな問題が発生し、また無光沢ニッケルめっきは光沢ニッケルめっきに比べピンホールができ易く、銅素材の拡散防止効果や加工後の信頼性が劣っていた。なお、ピンホールは、本発明で下地ニッケルめっき層を２層にしたことにより低減した。ピンホールが低減する理由は次のような理由による。すなわち、無光沢ニッケルめっきのニッケルの組織は素材から表面に向け縦方向に成長しており、最初に未めっき部が発生した場合、表面まで穴が貫通してピンホールとなる。光沢ニッケルめっきでは光沢剤が縦方向の結晶成長を抑制するため無光沢ニッケルめっきより素材に沿って層状のめっきが成長する。光沢ニッケルめっきであっても無光沢ニッケルめっきと同様にめっき初期のめっき核生成時にピンホールの起点ができる。ニッケルめっきを２層にした場合、めっき初期の核生成が２度行われることになり、下層めっき時にあったピンホールが中間層めっき時のめっき核生成により消されるためピンホールが低減できる。
【００１５】
そこで、本発明者は、ニッケルめっき厚みと光沢度の関係を鋭意検討した結果、添加剤を含まない無光沢ニッケルめっきでもめっき厚みが 0.5μｍ以下であれば、鏡面反射率を低下させない範囲があることを見い出した。
さらに、無光沢ニッケルめっき厚みと硫黄やカーボン、リンなどの不純物の拡散抑制効果の関係を検討した結果、通常の電子部品組み立て工程では、無光沢ニッケルめっきが 0.1μｍ以上であれば光沢ニッケルめっき皮膜中の不純物の影響を低減できることを見い出したのである。
【００１６】
また、ニッケルめっきの上にパラジウムめっきを施し、その上に金めっきを施すという３層めっきも考えたが、コストが高くなり実用化には問題点があった。
これらの知見により、それぞれの特徴を最大限に生かすべく検討を重ねた結果、本発明に係る金／ニッケル／ニッケルの３層めっき銅合金電子部品を得たものである。
【００１７】
上層の金層厚みを 0.001〜 0.2μｍとしたのは、金層厚みが 0.001μｍより小さいとニッケルの酸化を防止する効果が弱く、電子部品に組み立てた後のはんだぬれが低下するとともに、金線によるワイヤボンディング性が低下するためであり、金層厚みが 0.2μｍ以下としたのは 0.2μｍを越えてめっきするとコストが高くなるだけでなく、アルミニウム線で接合した部分に金−アルミニウム合金層が厚く成長し、耐熱試験において接合部の剥離が起こるためである。
【００１８】
金層は純金層が望ましいが、金層が薄ければ接合後はワイヤまたははんだ中に金が拡散し、接合信頼性には影響を及ぼさないので、Au−Co、Au−P 、Au−Niなど合金層でも良い。薄い金層を作る方法としては電気めっき法や蒸着めっきなどが行われるが、最近多くの無電解金めっき浴が実用化され、使用されている。非シアンの置換金めっきやパルスめっきを用いて金層を施しても良い。金−アルミニウム合金層の成長抑制のためには金層は0.01μｍより薄い方が望ましい。
【００１９】
中間層の不純物（特に硫黄）の少ないニッケルめっきの厚みを 0.1〜 0.5μｍとしたのは、 0.1μｍより薄いと下層ニッケルめっき中の不純物の拡散による特性低下を抑制できないためであり、 0.5μｍ以下としたのは 0.5μｍを越えると表面が荒れるためである。
また、中間層のニッケルめっき層の硫黄含有量を0.02質量％以下としたのは、硫黄含有量が0.02質量％を越えてると、段落番号〔００１３〕に説明したように、電子部品組み立て工程において受ける熱によって表面層に拡散し、組み立て後に表面より不純物が確認され、はんだ拡がりなどが低下するためである。
【００２０】
下層のニッケルめっきの厚みを 0.5〜 5μｍとしたのは、 0.5μｍより薄いと銅素材からの銅拡散を抑制することができないためであり、 5μｍ以下としたのはニッケルめっきを厚く施すと生産性が低下するだけでなく、曲げ加工性が悪くなるためである。
下層のニッケルめっきは光沢剤を含むニッケルめっきやスルファミン酸ニッケルめっきやニッケル合金めっきでも加工性の低下が顕著でなく、光沢を向上させるものであれば良い。
また、下層のニッケルめっき層の硫黄含有量を0.02質量％を越える量としたのは、銅合金電子部品の鏡面反射率を30％以上とし、ワイヤボンディング性の低下を防ぐためで、銅合金電子部品の鏡面反射率を30％以上とするにはニッケルめっき皮膜中の硫黄含有量は0.02質量％を越える量が必要となるためで、硫黄含有量が0.02質量％以下ではこのような作用効果が期待できないためである。さらに下層のニッケルめっき皮膜中の硫黄含有量が0.02質量％を越える量であれば、中間層のニッケルめっき層との腐食電流の差により、下層ニッケルめっき層が中間層ニッケルめっき層の犠牲陽極となり、腐食が生じた場合でも中間層ニッケルめっき層は守られる。
【００２１】
なお、金層の上に、通常のめっき封孔処理や溶剤洗浄で除去できるか、または加熱により分解する防錆剤、酸化防止剤を施しても良い。金層は金線接合部や加熱後のはんだ付け部のみに限定して施してもよいが、全面に施すことが望ましい。前記封孔処理、酸化防止剤としてはペトロラクタムやアルケニルコハクサンエステルなどの有機皮膜でも良いが、加熱により分解し、気化性の高いジシクロヘキシルアンモニウム塩やエチレンジアミン四酢酸ナトリウム塩などが望ましい。ニッケルめっき条件により結晶配向性が変化する。酸化防止のためには原子密度が小さく、酸化速度の遅い(111) 面の結晶配向指数が(200) 面の結晶配向指数より高いことが望ましい。また、めっき層間の密着性を確保するため、めっきはめっき槽が多槽に分かれた１ラインで行うことが望ましい。これにより下層ニッケルめっきを乾燥させることなく中間層ニッケルめっきを施すことができ、めっき層間の密着性を高めることができる。
【００２２】
本発明の金／ニッケル／ニッケル３層めっき銅合金電子部品に、１つ以上の半導体チップを鉛レスはんだまたはペーストで接合し、金線とアルミニウム線の１種以上でワイヤボンディングを行い、パッケージング後にリードと基盤を融点 240℃以下のはんだで接合し、金／ニッケル／ニッケル３層めっき銅合金電子部品を用いたＩＣを製造することができる。
【００２３】
銅合金素材は、電子部品に強度と熱放散性を持たせるので強度が高く、導電率が高い程望ましいが、熱放散性が重要なものでは導電率が80％IACS以上のFeやP を含む銅合金素材がよく、強度が重要なものでは引張強さが588MPa以上のSnやNiを含む銅合金素材が望ましい。
本発明の金／ニッケル／ニッケル３層めっき銅合金電子部品は、金線とアルミニウム線の両方でワイヤボンディング性が良く、さらにボンディング部の接合信頼性も高い。またはんだぬれ性が良好であり、外装はんだめっきを省略できるなど優れた特性を持ち、金めっきに代えてパラジウムを用いためっきより安価な銅合金電子部品を提供できる。
なお、本発明の金／ニッケル／ニッケル３層めっき銅合金電子部品においては、上層の金層および／または中間層のニッケル層にコバルト、ルテニウム、ロジウム、白金、パラジウム、リン、クロム、ボロンのうち少なくとも１種を含有してもよく、これらの元素を含有させることにより、金層の被膜硬度を高くしたり、金層中のニッケルの拡散を抑制する効果がある。また中間層のニッケルの酸化を抑制したり、ニッケルの上層への拡散および下層ニッケルからの硫黄の拡散を抑制する効果がある。
金層の硬さは金の磨耗性や挿抜性やワイヤボンディング性に影響を与える。
酸化を防止する方法としては酸化しにくい金属（ルテニウム、ロジウム、白金、パラジウム）や優先的に酸化して昇華する成分（リン、ボロン）を添加する方法が行える。
加熱時間が長い製造条件では硫黄の拡散防止やニッケルの拡散を抑制するために、ニッケルまたは金に対して拡散係数の低い金属（コバルト、クロム）を添加することが有効である。またコバルトやリンはめっき製造条件により不可避的にめっき被膜中に取り込まれる場合がある。
【００２４】
【発明の実施の形態】
以下、本発明の実施形態について実施例をもとに説明する。
【００２５】
【実施例】
Fe：0.1 質量％、 P：0.03質量％、Sn： 2質量％とZn： 2質量％を含む銅合金素材に、表１に示す硫黄含有量と厚さの下層ニッケルめっきおよび中間層ニッケルめっきを施し、さらにその中間層ニッケルめっきの上に表１に示す厚さの金メッキを施し、金／ニッケル／ニッケル３層めっき銅合金リードフレームを製造した。そして、得られた金／ニッケル／ニッケル３層めっき銅合金リードフレームの鏡面反射率を測定した。その測定結果を表１に併せて示す。またさらに、得られた金／ニッケル／ニッケル３層めっき銅合金リードフレームを対象に、はんだぬれ性、金線ワイヤボンディング性、アルミニウム(Al)線ワイヤボンディング性および繰り返し曲げ回数の調査評価を行った。その結果を表２に示す。なお表２の評価の欄の○は合格、×は不合格を意味する。
【００２６】
【表１】
【表２】
鏡面反射率の測定方法について：JIS Z 8741に準じ、45度で光束を入射し、鏡面反射において反射光束の入射光束に対する比を測定した。
【００２９】
繰り返し曲げ回数評価について：３層めっきを施した幅 0.9mmのリードに荷重600gを掛け、 0.25Rで90°曲げを繰り返し、破断するまでの繰り返し曲げ回数を測定した。 3回以上を合格とした。
【００３０】
はんだぬれ性評価について：３層めっき銅合金リードフレームを大気中 350℃のプレート上で 3分加熱後、メニスコグラフ法で60Sn−40Pbはんだを用いて 230℃ではんだぬれ時間を測定した。 3秒以下を合格とした。
【００３１】
金線ワイヤボンディング性評価について：１mil(25μｍ）の金線（99.99 ％）を用いて、大気中、 240℃で超音波印加法によるワイヤボンディング（ボンディング時間：10ms、荷重：50g 、ＵＶ出力：0.1w）を行った。 150℃で50時間加熱後に接合された金線を真ん中で切断し、金線が３層めっきと接合されているセカンドボンド部の接合状態を調査した（ツィザー強度）。
【００３２】
アルミニウム線ワイヤボンディング性評価：５mil(125 μｍ）のアルミニウム線（99.99 ％, annealed）を用いて、大気中、25℃で超音波（パルス60kHz)印加法によるワイヤボンディング（ボンディング時間：100ms 、荷重：250g、ＵＶ出力：5.5w）を行った。 150℃で50時間加熱後に接合されたアルミニウム線を真ん中で切断し、アルミニウム線が３層めっきと接合されているセカンドボンド部の接合状態を調査した。
ワイヤ破断率（％）＝（ワイヤ破断本数）／（全試験本数）×100
なお、はんだぬれ性評価と繰り返し曲げ回数評価はそれぞれ 5本づつ、また金線ワイヤボンディング性評価とAl線ワイヤボンディング性評価はそれぞれ20本づつを行った。
【００３３】
上述した測定結果および試験結果は表１および表２に示す通りのもので、これら表１および表２より明らかなように、本発明例１〜５のものは、表面の鏡面反射率が30％以上であって、下地ニッケルめっき層の硫黄含有量が0.02質量％を越えて高いにもかかわらず、その上の中間層のニッケルめっきにより下地ニッケルめっき層下地からの硫黄等の不純物の拡散が制御され、はんだぬれ性が優れており、組み立て時の加熱を受けても良好なはんだ拡がりを示した。またワイヤボンディング性が良好であり、 150℃で50時間加熱を受けても良好な接合強度を示した。
【００３４】
上記の本発明例に対し、比較例１は金層が無い例で、金層が無いため、加熱により表面のニッケルが酸化し、はんだぬれ性、ワイヤボンディング性が低下していた。
比較例２は中間の無光沢ニッケルめっき層が無い例で、中間の無光沢ニッケルめっき層が無いため、加熱により下地ニッケルめっき皮膜中の硫黄が表面まで拡散し、はんだぬれ性、ワイヤボンディング性が低下していた。
比較例３は下層の光沢ニッケルめっきが無い例で、下層の光沢ニッケルめっきが無いため、加熱により銅素材が表面へ拡散し、はんだぬれ性、ワイヤボンディング性が低下していた。
比較例４は中間の無光沢ニッケルめっき層を厚くした例で、中間の無光沢ニッケルめっき層が厚いため、鏡面反射率が低く、表面が荒れており、ワイヤボンディング性が低下した。
比較例５は中間の無光沢ニッケルめっき層中の硫黄含有量が多い例で、中間の無光沢ニッケルめっき層中の硫黄含有量が多いため、加熱により硫黄が表面まで拡散し、はんだ拡がり、ワイヤボンディング性が低下していた。
比較例６は下層の光沢ニッケルめっきを厚くした例で、下層の光沢ニッケルめっきが厚いため、繰り返し曲げ回数が低下していた。
比較例７は下層の光沢ニッケルめっき中の硫黄含有量が少ない例で、下層の光沢ニッケルめっき中の硫黄含有量が少ないため、鏡面反射率が低く、表面が荒れており、ワイヤボンディング性が低下し、樹脂バリも除去しにくかった。
比較例８は金層が厚い例で、金層が厚いため、コストが高くなるだけでなく、硫黄などとの合金層の成長により加熱後にアルミニウム線接合部で剥離が発生した。
【００３５】
【発明の効果】
以上説明したように、本発明に係る金／ニッケル／ニッケル３層めっき銅合金電子部品であれば、金線とアルミニウム線の両方でワイヤボンディング性が良好であり、また加熱後のボンディング部の接合信頼性も高く、さらにはんだぬれ性が良好であることから、この銅合金電子部品を用いて信頼性の高い高品質の製品ができる。またさらに、金めっきが薄く特性が優れており、他の貴金属（パラジウムなど）めっき銅合金電子部品に比較してコストパーフォーマンスに優れる 。
【００３６】
また、本発明に係る金／ニッケル／ニッケル３層めっき銅合金電子部品によれば、めっき層間の接合強度を高めることができるとともに、上記効果を有する金／ニッケル／ニッケル３層めっき銅合金電子部品を経済的に製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gold / nickel / nickel three-layer plated copper alloy electronic component to be soldered using a lead-free solder in an air atmosphere, and in particular, the reliability of a wire bonding portion with a gold wire or an aluminum wire. The present invention relates to a gold / nickel / nickel three-layer plated copper alloy electronic component having excellent heat resistance and solder wettability after heating. The target copper alloy electronic parts are lead frames, automobile electrical parts, terminals, connectors, JBs (joint boxes), etc., but in the following description, the lead frame will be described as an example for easy understanding of the invention. To do.
[0002]
[Prior art]
Conventionally, noble metal plating such as silver plating and gold plating is applied to the surface of the lead frame on which the solder die is bonded in order to obtain good solder wettability. Further, in order to omit the solder plating step on the outer lead portion after packaging of the semiconductor device, a technique of performing noble metal plating not only on the die bonding portion but also on the entire lead frame at the time of manufacturing the lead frame is considered.
[0003]
For example, Japanese Patent Application Laid-Open No. Sho 54-34760 discloses a technique for performing gold plating partially on the surface of a lead frame using nickel plating as a base. Although the thickness is limited to 6 to 10 μm, other conditions such as bright plating and matte plating, or the sulfur content during plating have not been studied, so the gold plating thickness cannot be reduced. At the same time, there is a concern that the wire bonding property is inferior.
[0004]
Japanese Patent Application Laid-Open No. 61-78150 discloses a technique in which the surface of the lead frame is thinly plated with gold and the plating on the outer lead is omitted. However, the underlying plating before gold plating has not been studied at all. Absent. For this reason, although the example which gave gold plating in the Example which used the iron system as a raw material is shown, it was not applicable to a copper alloy electronic component.
[0005]
Japanese Patent Laid-Open No. 4-152661 discloses a technique for performing gold plating on the surface of a lead frame with nickel plating as a base, as in Japanese Patent Laid-Open No. 54-34760. Although it is described that a thickness of 0.1 to 5 μm is preferable for the nickel plating to become, Example 1 only shows an example in which a matte nickel plating is applied to a copper alloy lead frame by 0.5 μm. Such a matte nickel plating with a thickness of 0.5 μm does not provide a sufficient function as a copper diffusion preventing layer, and when plated to a thickness of 0.5 μm or more, the details will be described in paragraph [0008]. In addition, there is a concern that the wire bonding property is deteriorated.
[0006]
Recently, the amount of heat received by a lead frame due to high-density integration of electrical components has increased, and a gold-plated copper alloy lead frame that is excellent in oxidation resistance, corrosion resistance, and heat resistance is desired. In addition, wire bonding equipment that can bond with high productivity in a shorter time has been developed by improving wire bonding technology, but in order to fully demonstrate its performance, a copper alloy lead frame with good wire bonding is desired. It is rare. However, as described above, none of the conventional techniques can meet the demands for gold-plated copper alloy electronic components having good wire bonding properties and excellent heat resistance reliability.
[0007]
[Problems to be solved by the invention]
Therefore, the present inventor has conducted research to meet the above requirements. However, in the case of a lead frame with a gold plating on a conventional surface, the brightener component incorporated in the plating film diffuses to the gold surface by heating when the base is a bright nickel plating, and soldering The thickness of the gold plating could not be reduced. Further, when the gold plating is thick, not only the cost is increased, but also there is a problem that the wire bonding strength is extremely lowered due to the growth of the gold-aluminum alloy layer when bonded by an aluminum wire.
[0008]
On the other hand, when the base is matte nickel plating, there is a problem that if the nickel plating is thickened, the surface becomes dull and the surface becomes rough. If the surface is rough, the wire bonding property deteriorates, so that the nickel plating cannot be made thick. In addition, thin matte nickel plating has an insufficient effect of preventing the diffusion of copper as a material, and has a problem in reliability.
[0009]
The present invention has been made in light of the above-described circumstances, and its purpose is to perform thick nickel plating to improve wire bonding property and heat-resistant reliability, and to perform gold plating to improve solderability and bonding strength. It is to provide a gold-plated copper alloy electronic component excellent in cost performance and a manufacturing method thereof.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present inventor conducted further research. As a result, when the above-mentioned conventional base nickel plating is divided into two layers, each of which has characteristics, and gold plating is applied to the uppermost layer, the mirror surface is equivalent to or better than that of a lead frame product having a conventional bright nickel plating base The present invention has been completed by finding that a gold-plated copper alloy electronic component that maximizes the characteristics of gold while having a smooth surface with a reflectance of 30% or more can be obtained.
[0011]
That is, the present invention has a gold and gold alloy layer having a thickness of 0.001 to 0.2 μm in the upper layer, a nickel layer having a thickness of 0.1 to 0.5 μm and a sulfur content of 0.02% by mass or less in the intermediate layer, and a sulfur layer in the lower layer. Gold / nickel / excellent in wire bonding reliability and solder wettability, characterized by having a nickel layer with a content of 0.5-5 μm exceeding 0.02% by mass and having a specular reflectance of 30% or more on its surface This is a nickel three-layer plated copper alloy electronic component. Hereinafter, the configuration and operational effects of the present invention will be described in detail.
[0012]
Conventional nickel base plating only prevents diffusion of the material into the gold plating. However, with the development of wire bonding technology and the high integration, miniaturization, and hybridization of electronic components, the characteristics required for gold plating have increased, and it has become necessary to make gold plating thinner from the viewpoint of cost reduction. . However, it was found that when the gold plating is thinned, the surface characteristics of the underlying nickel plating greatly affect the characteristics of the gold.
Therefore, the present inventor diligently studied the influence of the base nickel plating on solder wettability, wire bonding property, heat resistance reliability, and the like. As a result, as described below, it was found that the sulfur content in the nickel plating film affects the characteristics.
[0013]
That is, the wire bonding property by the gold wire and the aluminum wire is affected by the smoothness of the surface to be joined. Although the relationship between the load of the wire bonding apparatus and the ultrasonic wave differs, it is desirable that the surface to be bonded be smooth in order to effectively obtain the ultrasonic effect. In nickel plating, a smooth surface having a specular reflectance of 50% or more can be obtained by adding a brightener or the like. However, as a result of investigation, components such as brighteners, uniform electrodeposition agents, and stress relaxation agents are incorporated into the smooth and smooth nickel plating film with high glossiness, and there are more than 0.02% by mass of sulfur and carbon. It was found to contain impurities such as phosphorus.
It has been found that these impurities diffuse into the surface layer due to heat received in the electronic component assembling process, thereby reducing wire bonding property, solder wettability, contact resistance, and bonding reliability. In addition, wire bonding uses alloy wires such as gold, aluminum, copper, etc., and joins the chip and the lead using ultrasonic waves, but the bonding reliability is better as the lead frame surface is smoother, Also, it was found that the smoother the surface, the easier the solder spreads during solder joining.
In addition, even when a gold plating layer is applied to the outermost surface to improve wire bonding and solder wettability, if the gold plating layer is not thickened to a thickness exceeding 0.2 μm, it will be adversely affected by the impurities of the underlying nickel plating layer. I understood that.
[0014]
Based on the above studies and researches, the present inventor has found that problems such as wire bonding and solder wettability can be solved by controlling impurities in the underlying nickel plating layer, but the matte nickel plating does not contain any additives. Applying a thick layer causes the specular reflectivity to be lower than 30%, resulting in new problems that the surface becomes rough and the wire bondability deteriorates. Also, matte nickel plating makes pinholes easier than bright nickel plating. The diffusion prevention effect of copper material and the reliability after processing were inferior. In addition, the pinhole was reduced by making the base nickel plating layer into two layers by this invention. The reason why pinholes are reduced is as follows. That is, the nickel structure of the matte nickel plating grows in the vertical direction from the material to the surface, and when an unplated portion is first generated, the hole penetrates to the surface and becomes a pinhole. In bright nickel plating, the brightening agent suppresses crystal growth in the vertical direction, so that layered plating grows along the material than matte nickel plating. Even in the case of bright nickel plating, a pinhole can be generated when plating nuclei are generated at the initial stage of plating as in the case of non-glossy nickel plating. When nickel plating is made into two layers, nucleation at the initial stage of plating is performed twice, and pinholes that were present at the time of lower layer plating are eliminated by nucleation of plating at the time of intermediate layer plating, so that pinholes can be reduced.
[0015]
Therefore, as a result of intensive studies on the relationship between the nickel plating thickness and the glossiness, the present inventor has a range in which the specular reflectance is not lowered if the plating thickness is 0.5 μm or less even when the matte nickel plating does not contain an additive. I found out.
Furthermore, as a result of examining the relationship between the thickness of the matte nickel plating and the effect of suppressing the diffusion of impurities such as sulfur, carbon, and phosphorus, the glossy nickel plating film can be obtained if the matte nickel plating is 0.1 μm or more in the normal electronic component assembly process. It was found that the influence of impurities inside can be reduced.
[0016]
Further, although three-layer plating in which palladium plating is performed on nickel plating and then gold plating is also considered, the cost is increased and there is a problem in practical use.
Based on these findings, as a result of repeated studies to make the best use of each feature, a gold / nickel / nickel three-layer plated copper alloy electronic component according to the present invention was obtained.
[0017]
The gold layer thickness of the upper layer is set to 0.001 to 0.2 μm. If the gold layer thickness is smaller than 0.001 μm, the effect of preventing nickel oxidation is weak, and the solder wettability after assembling to electronic parts is reduced. This is because the wire bondability is reduced by the above, and the thickness of the gold layer is set to 0.2 μm or less. Not only does the cost increase when plating exceeds 0.2 μm, but a gold-aluminum alloy layer is formed on the part joined by the aluminum wire. This is because it grows thick and peeling of the joint occurs in the heat resistance test.
[0018]
The gold layer is preferably a pure gold layer, but if the gold layer is thin, gold diffuses into the wire or solder after bonding and does not affect the bonding reliability. Therefore, Au-Co, Au-P, Au-Ni An alloy layer may be used. As a method for forming a thin gold layer, electroplating or vapor deposition is performed. Recently, many electroless gold plating baths have been put into practical use and used. The gold layer may be applied using non-cyan substitution gold plating or pulse plating. In order to suppress the growth of the gold-aluminum alloy layer, the gold layer is preferably thinner than 0.01 μm.
[0019]
The reason why the thickness of the nickel plating with few impurities (especially sulfur) in the intermediate layer is 0.1 to 0.5 μm is that if it is thinner than 0.1 μm, the characteristic deterioration due to the diffusion of impurities in the lower nickel plating cannot be suppressed. The reason is that the surface becomes rough when the thickness exceeds 0.5 μm.
Moreover, the sulfur content of the nickel plating layer of the intermediate layer is set to 0.02% by mass or less when the sulfur content exceeds 0.02% by mass in the electronic component assembling process as described in paragraph [0013]. This is because the heat is diffused into the surface layer, impurities are confirmed from the surface after assembly, and solder spread is reduced.
[0020]
The reason why the thickness of the lower nickel plating is set to 0.5-5 μm is that if it is thinner than 0.5 μm, copper diffusion from the copper material cannot be suppressed. This is because not only is lowering, but bending workability is deteriorated.
The lower layer nickel plating may be a nickel plating containing a brightener, nickel sulfamate plating, or nickel alloy plating as long as the workability is not significantly lowered and the gloss is improved.
In addition, the reason why the sulfur content of the lower nickel plating layer exceeds 0.02 mass% is to make the specular reflectivity of the copper alloy electronic parts 30% or more and to prevent deterioration of wire bonding properties. In order to make the specular reflectivity of parts 30% or more, the amount of sulfur in the nickel plating film must exceed 0.02% by mass, and this effect is achieved when the sulfur content is 0.02% by mass or less. This is because it cannot be expected. Furthermore, if the sulfur content in the lower nickel plating film exceeds 0.02 mass%, the lower nickel plating layer becomes the sacrificial anode of the intermediate nickel plating layer due to the difference in corrosion current from the intermediate nickel plating layer. Even when corrosion occurs, the intermediate nickel plating layer is protected.
[0021]
It should be noted that a rust preventive or antioxidant that can be removed by ordinary plating sealing treatment or solvent washing or decomposed by heating may be applied on the gold layer. The gold layer may be applied only to the gold wire bonding part or the soldered part after heating, but it is desirable to apply it to the entire surface. As the sealing treatment and antioxidant, an organic film such as petrolactam or alkenyl succinic ester may be used, but dicyclohexylammonium salt or ethylenediaminetetraacetic acid sodium salt, which decomposes by heating and has high vaporization property, is desirable. The crystal orientation changes depending on the nickel plating conditions. In order to prevent oxidation, it is desirable that the crystal orientation index of the (111) plane with a low atomic density and a low oxidation rate is higher than the crystal orientation index of the (200) plane. Moreover, in order to ensure the adhesiveness between plating layers, it is desirable to perform plating in one line in which plating tanks are divided into multiple tanks. Thereby, intermediate | middle layer nickel plating can be given, without drying lower layer nickel plating, and the adhesiveness between plating layers can be improved.
[0022]
One or more semiconductor chips are joined to the gold / nickel / nickel three-layer plated copper alloy electronic component of the present invention with lead-free solder or paste, and wire bonding is performed with one or more of gold wire and aluminum wire, and packaging Later, the lead and the substrate can be joined with a solder having a melting point of 240 ° C. or lower to produce an IC using a gold / nickel / nickel three-layer plated copper alloy electronic component.
[0023]
Copper alloy materials have higher strength and higher electrical conductivity because they give strength and heat dissipation to electronic components. However, if heat dissipation is important, it contains Fe or P with an electrical conductivity of 80% IACS or higher. If the copper alloy material is good and strength is important, a copper alloy material containing Sn or Ni with a tensile strength of 588 MPa or more is desirable.
The gold / nickel / nickel three-layer plated copper alloy electronic component of the present invention has good wire bonding properties for both gold wires and aluminum wires, and also has high bonding reliability at the bonding portion. In addition, it has excellent solder wettability, has excellent characteristics such as the ability to omit external solder plating, and can provide a copper alloy electronic component that is cheaper than plating using palladium instead of gold plating.
In the gold / nickel / nickel three-layer plated copper alloy electronic component of the present invention, cobalt, ruthenium, rhodium, platinum, palladium, phosphorus, chromium, and boron are used for the upper gold layer and / or the intermediate nickel layer. At least one kind may be contained, and inclusion of these elements has an effect of increasing the coating hardness of the gold layer and suppressing the diffusion of nickel in the gold layer. In addition, there is an effect of suppressing oxidation of nickel in the intermediate layer and suppressing diffusion of nickel into the upper layer and diffusion of sulfur from the lower layer nickel.
The hardness of the gold layer affects the wear and insertability of the gold and the wire bonding properties.
As a method for preventing oxidation, a method of adding a metal that is difficult to oxidize (ruthenium, rhodium, platinum, palladium) or a component that preferentially oxidizes and sublimates (phosphorus, boron) can be added.
In manufacturing conditions with a long heating time, it is effective to add a metal (cobalt or chromium) having a low diffusion coefficient with respect to nickel or gold in order to prevent sulfur diffusion or suppress nickel diffusion. Cobalt and phosphorus may be inevitably taken into the plating film depending on the plating production conditions.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described based on examples.
[0025]
【Example】
Copper alloy material containing Fe: 0.1% by mass, P: 0.03% by mass, Sn: 2% by mass and Zn: 2% by mass is subjected to lower layer nickel plating and intermediate layer nickel plating with the sulfur content and thickness shown in Table 1. Further, gold plating having a thickness shown in Table 1 was applied on the intermediate layer nickel plating to produce a gold / nickel / nickel three-layer plated copper alloy lead frame. Then, the specular reflectance of the obtained gold / nickel / nickel three-layer plated copper alloy lead frame was measured. The measurement results are also shown in Table 1. Furthermore, investigation and evaluation of solder wettability, gold wire wire bondability, aluminum (Al) wire wire bondability, and number of repeated bendings were performed on the obtained gold / nickel / nickel three-layer plated copper alloy lead frame. . The results are shown in Table 2. In the evaluation column of Table 2, ○ means pass and × means fail.
[0026]
[Table 1]
[Table 2]
Specular reflectance measurement method: According to JIS Z 8741, a light flux was incident at 45 degrees, and the ratio of the reflected light flux to the incident light flux was measured in specular reflection.
[0029]
Evaluation of the number of repeated bendings: A load of 600 g was applied to a 0.9 mm wide lead subjected to three-layer plating, bending was repeated 90 ° at 0.25R, and the number of repeated bendings until breaking was measured. Three or more times passed.
[0030]
Solder wettability evaluation: A three-layer plated copper alloy lead frame was heated on a plate at 350 ° C. for 3 minutes in the atmosphere, and then measured for solder wetting time at 230 ° C. using 60Sn-40Pb solder by the meniscograph method. 3 seconds or less were accepted.
[0031]
Gold wire bonding evaluation: 1mil (25μm) gold wire (99.99%), wire bonding by the ultrasonic wave application method at 240 ℃ in the air (bonding time: 10ms, load: 50g, UV output: 0.1) w) went. The gold wire bonded after heating at 150 ° C. for 50 hours was cut in the middle, and the bonding state of the second bond portion where the gold wire was bonded to the three-layer plating was investigated (Tweezer strength).
[0032]
Aluminum wire wire bondability evaluation: Wire bonding (bonding time: 100 ms, load: 5 mil (125 μm) aluminum wire (99.99%, annealed) using an ultrasonic wave (pulse 60 kHz) at 25 ° C in the atmosphere. 250 g, UV output: 5.5 w). The aluminum wire bonded after heating at 150 ° C. for 50 hours was cut in the middle, and the bonding state of the second bond portion where the aluminum wire was bonded to the three-layer plating was investigated.
Wire breakage rate (%) = (Number of wire breaks) / (Total number of tests) x 100
The solder wettability evaluation and the repeated bending frequency evaluation were performed 5 times each, and the gold wire wire bondability evaluation and the Al wire wire bondability evaluation were performed 20 times each.
[0033]
The measurement results and test results described above are as shown in Tables 1 and 2, and as is clear from Tables 1 and 2, Examples 1 to 5 of the present invention have a specular reflectance of 30% on the surface. Even though the sulfur content of the underlying nickel plating layer is higher than 0.02% by mass, the diffusion of impurities such as sulfur from the underlying nickel plating layer substrate is controlled by the nickel plating of the intermediate layer above it. It was excellent in solder wettability and showed good solder spread even when heated during assembly. The wire bondability was also good, and it showed good bonding strength even when heated at 150 ° C for 50 hours.
[0034]
In contrast to the above inventive example, Comparative Example 1 is an example without a gold layer, and since there is no gold layer, nickel on the surface was oxidized by heating, and solder wettability and wire bonding property were deteriorated.
Comparative Example 2 is an example in which there is no intermediate matte nickel plating layer. Since there is no intermediate matte nickel plating layer, sulfur in the base nickel plating film diffuses to the surface by heating, and solder wettability and wire bonding properties are improved. It was falling.
Comparative Example 3 is an example in which there is no bright nickel plating in the lower layer, and since there is no bright nickel plating in the lower layer, the copper material diffuses to the surface by heating, and the solder wettability and the wire bonding property are reduced.
Comparative Example 4 was an example in which the intermediate matte nickel plating layer was thickened. Since the intermediate matte nickel plating layer was thick, the specular reflectance was low, the surface was rough, and the wire bonding property was lowered.
Comparative Example 5 is an example in which the sulfur content in the intermediate matte nickel plating layer is large. Since the sulfur content in the intermediate matte nickel plating layer is large, sulfur diffuses to the surface by heating, the solder spreads, the wire Bondability was degraded.
Comparative Example 6 is an example in which the lower bright nickel plating was thickened, and the lower bright nickel plating was thick, so the number of repeated bendings was reduced.
Comparative Example 7 is an example in which the sulfur content in the lower bright nickel plating is low, and since the sulfur content in the lower bright nickel plating is low, the specular reflectance is low, the surface is rough, and the wire bonding property is reduced. However, it was difficult to remove resin burrs.
Comparative Example 8 is an example in which the gold layer is thick. Since the gold layer is thick, not only the cost is increased, but peeling is generated at the aluminum wire joint after heating due to the growth of the alloy layer with sulfur or the like.
[0035]
【The invention's effect】
As described above, the gold / nickel / nickel three-layer plated copper alloy electronic component according to the present invention has good wire bondability with both a gold wire and an aluminum wire, and bonding of a bonded portion after heating. High reliability and good solder wettability make it possible to produce highly reliable and high quality products using this copper alloy electronic component. Furthermore, the gold plating is thin and has excellent characteristics, and is superior in cost performance as compared with other noble metal (such as palladium) plated copper alloy electronic parts.
[0036]
In addition, according to the gold / nickel / nickel three-layer plated copper alloy electronic component according to the present invention, it is possible to increase the bonding strength between the plating layers, and to have the above effects, the gold / nickel / nickel three-layer plated copper alloy electronic component. Can be manufactured economically.
Claims (3)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6069897A JP3667926B2 (en) | 1997-03-14 | 1997-03-14 | Gold / nickel / nickel three-layer plated copper alloy electronic component and method for manufacturing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6069897A JP3667926B2 (en) | 1997-03-14 | 1997-03-14 | Gold / nickel / nickel three-layer plated copper alloy electronic component and method for manufacturing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH10251860A JPH10251860A (en) | 1998-09-22 |
| JP3667926B2 true JP3667926B2 (en) | 2005-07-06 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP6069897A Expired - Lifetime JP3667926B2 (en) | 1997-03-14 | 1997-03-14 | Gold / nickel / nickel three-layer plated copper alloy electronic component and method for manufacturing the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3667926B2 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6872470B2 (en) * | 2000-02-24 | 2005-03-29 | Ibiden Co., Ltd. | Nickel-gold plating exhibiting high resistance to corrosion |
| JP4598238B2 (en) * | 2000-06-01 | 2010-12-15 | 常木鍍金工業株式会社 | Contact member and manufacturing method thereof |
| JP2002256444A (en) * | 2001-03-05 | 2002-09-11 | Okuno Chem Ind Co Ltd | Wiring board |
| JP4667637B2 (en) * | 2001-05-02 | 2011-04-13 | 古河電気工業株式会社 | Bonding method of electronic parts |
| US7615255B2 (en) * | 2005-09-07 | 2009-11-10 | Rohm And Haas Electronic Materials Llc | Metal duplex method |
| JP2008101260A (en) * | 2006-10-20 | 2008-05-01 | Osaka Prefecture Univ | Electroconductive fine particle and production method therefor |
| DE102011085471B4 (en) * | 2011-10-28 | 2021-09-16 | Robert Bosch Gmbh | Arrangement for direct contacting of contact means and associated connection unit for a pressure measuring cell |
| JP7232053B2 (en) * | 2018-02-08 | 2023-03-02 | 株式会社ダイセル | Method for manufacturing glossy plating film |
-
1997
- 1997-03-14 JP JP6069897A patent/JP3667926B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH10251860A (en) | 1998-09-22 |
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