JP2004183091A - Plating solution containing, tin-silver-copper electrolytic plating method, plating film containing tin-silver-copper and soldering method using this plating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plating film with a low-melting point containing tin-silver-copper, containing a plating solution tin-silver-copper for obtaining this showing a high liquid stability, an electrolytic plating method and a soldering method using the plating film. <P>SOLUTION: The plating solution containing tin-silver-copper showing a high liquid stability contains sulfonates, tin ion, copper ion and silver ion in a water-based medium. Here, the concentrations of silver ion, tin ion and copper ion are 0.01-0.1 mol/l, 0.21-2 mol/l and 0.002-0.02 mol/l, respectively. The plating film with a low-melting point comprises 2.6-3.4 wt.% silver, 0.4-0.7 wt.% copper and the balance substantially being tin. The electrolytic plating method for obtaining the above plating film uses the above plating solution, and the soldering method uses the above plating film. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００５０】
【表２】

【００５１】
【表３】

【００５２】
〔実施例１ａ〕
表１に示すめっき液ａを使用し、本発明の電解めっき方法でめっきしてめっき被膜を作った。めっき液ａを５００ｍＬビーカーに入れ、アノードとして純Ｓｎの直方体インゴットを２個用意し、整流器＋側より２本配線を出しそれぞれインゴットにクリップでしっかり固定した。一方、整流器−側より１本配線を出し被めっき物（０．３ｄｍ^２ の４２アロイテストピース（Ｎｉ４２重量％、Ｆｅ５８重量％）に同様に固定した。
電流密度を５．８Ａ／ｄｍ^２ 、電流波形を直流波形とし、１８℃で２１６秒間の電解めっきを行った。その結果、膜厚が８μｍの良好な半光沢のめっき被膜が４２アロイテストピース上に得られた。めっき被膜した４２アロイテストピースを水道水にて充分水洗し、次に純水にて仕上げ水洗をした。その後乾燥させた。
【００５３】
得られためっき被膜について、被膜中の金属含有率、外観、接合強度、はんだ濡れ性、融点について以下に示す（１）〜（７）の方法により測定及び試験した。結果を表４の実施例１ａに示す。表４に示すように、実施例１ａで得られためっき被膜の組成は銀２．８１重量％、銅０．５１重量％、残部は錫であった。はんだ濡れ性も良好で融点も錫、銀、銅の共晶点に近い２１７℃であり、低い温度ではんだ付けを行うことが可能となった。また、接合強度試験の結果も２３．３Ｎと良好であった。
【００５４】
（１）被膜中の金属含有率をＩＰＣ発光分光分析法（高周波プラズマ誘導結合プラズマ発光分光分析法）により測定する。
めっき後の被膜を溶解し、ＩＰＣ発光分光分析法で定量した。
（２）仕上がり外観
各めっき浴から得られた電着被膜について、被膜表面の状態を目視観察した。色ムラが見られず均一な白色外観であった場合に合格とした。
【００５５】
（３）被膜の接合強度の測定
めっき被膜の接合強度を見るために、表１に示すめっき液ａを使用し、実施例１ａの電解めっき方法によりめっき被膜したテストピースを以下に示すリフロー方式による本発明のはんだ付け方法を用いて、基板とはんだ付けした。
本発明のはんだ付け方法は、ガラスエポキシ製の銅被覆テスト基板（１２ｍｍ×１２ｍｍ、厚さ３ｍｍ）にステンレスマスク（マスクの厚さ０．８ｍｍ）をセットし、基板のランド上にはんだペースト（ペースト中の合金の組成：銀３．０重量％、銅０．５重量％、残部錫）をスキージングし、厚さ約０．８ｍｍのはんだペースト膜を形成した。マスクをはずし、はんだペースト上に実施例１ａにてめっき被膜したテストピースをマウントした。これを加熱炉に入れ、図１のはんだ付け温度の概略図に示すように、１８０℃にて９０秒加熱し、４０秒かけて２４０℃まで昇温し、２４０℃で１０秒保持した。その後、冷却した。なお、昇温及び降温に際して、２２０℃以上の範囲が３０秒となるようにした。冷却後、はんだ付けされた基板とテストピースを取り出した。基板とテストピースの接合強度をＪＩＳ Ｃ ００５４、ＥＩＡＪＥＴ−７４０３に記載の方法により測定した。
【００５６】
（４）はんだ濡れ性をＪＩＳ Ｃ ００５３、ＥＩＡＪＥＴ−７４０１に記載の方法により測定した。
（５）融点は、ＤＳＣ（示差走査熱分析法）により測定した。
（６）接合部の元素分析は、ＥＰＭＡ（電子プローブＸ線マイクロアナライザー）によるマッピングで確認した。
（７）めっき被膜の膜厚
蛍光Ｘ線を利用した膜厚計によって測定した。検量線として３．５重量％銀、残部錫の合金を用いた。
【００５７】
【表４】

【００５８】
〔実施例１ｂ〕
実施例１ａにおける０．３ｄｍ^２ の４２アロイテストピースを０．３ｄｍ^２ の銅製のテストピースに代えた以外は実施例１ａと同様にめっきを行った。
結果を表４の実施例１ｂに示す。被膜中のＣｕ含有量、Ａｇ含有量は未測定であるが、実施例１ａと略同じ組成であると考えられる。
ガラスエポキシ製の銅被覆テスト基板との接合強度が非常に良くなった以外は いずれの試験結果も実施例１ａと略等しく、合格であった。
【００５９】
〔実施例２〕
実施例１ａにおける直流波形の電流密度を５．０Ａ／ｄｍ^２ とした以外は実施例１ａと同様にめっきを行ったところ、電流密度を変えてめっきした場合も電子顕微鏡で見た表面形状は実施例１ａと略同じで、粒子の大きさが均一でばらつきがなく滑らかな表面形状のめっきとなっていた。
〔実施例３〕
実施例１ａにおける直流波形の電流密度を１０．０Ａ／ｄｍ^２ とした以外は実施例１ａと同様にめっきを行ったところ、電子顕微鏡で見た表面形状は実施例１ａと略同じで、粒子の大きさが均一でばらつきがなく滑らかな表面形状のめっきとなっていた。
〔実施例４〕
実施例１ａにおける直流波形の電流密度を１５．０Ａ／ｄｍ^２ とした以外は実施例１ａと同様にめっきを行ったところ、電子顕微鏡で見た表面形状は実施例１ａと略同じで、粒子の大きさが均一でばらつきがなく滑らかな表面形状のめっきとなっていた。
実施例１〜４の結果から、本発明のめっき液を使用した本発明の電解めっき方法は、広い範囲の電流密度に対応でき、例え、電流密度の多少のばらつきがあっても、ばらつきのないめっきができることがわかる。
【００６０】
〔実施例５〕
次に光沢めっきを得る場合について実験した。光沢めっきを得るために、めっき液に光沢剤を添加し、電流波形としてパルス電流波形（周期０．１秒：０．０５秒オン、０．０５秒オフ）を用いてめっきを行った。
実施例１ａで使用しためっき液ａに、光沢剤１（ディップソール社製光沢剤Ｓ−２）５ｍＬ／Ｌ、及び光沢剤２（ディップソール社製光沢剤Ｓ−３）２０ｍＬ／Ｌを添加してめっき液ｄを調整した。このめっき液ｄを用い、電流密度を１１．６Ａ／ｄｍ^２ 、電流波形をパルス電流波形とした以外は実施例１ａと同様にめっきを行ったところ、めっき時間２１６秒にて、外観の良好な光沢のめっき被膜（８μｍ）が得られた。
得られためっき被膜について、実施例１ａと同じ方法で、組成、融点を測定し、外観、はんだ濡れ性について試験した。更に、上述の方法で、テスト基板とのはんだ付けを行い、接合強度を測定した。結果を表４の実施例５に示す。
めっき被膜の組成は、銀３．０重量％、銅０．５０重量％、残部は錫で、融点は２１８℃であった。はんだ濡れ性、接合強度共によかった。
【００６１】
〔実施例６ａ〕
さらに、実施例１ａで使用しためっき液を、電流密度を５．８Ａ／ｄｍ^２ 、電流波形を直流波形とし、２５℃一定のもとで、めっき時間２１６秒にて４２アロイのテストピースにめっきすると約８μｍのめっき被膜が得られた。このめっき被膜の組成は、銅０．５０重量％、銀３．０重量％、残部が錫であった。得られためっき被膜について、外観、融点、はんだ濡れ性について実施例１ａと同じ方法で測定あるいは試験した。また、実施例１ａと同じ方法ではんだ付けを行い、接合強度を測定した。接合強度は２１．５Ｎだった。更に、ウィスカー試験（猫の髭状の錫が伸びてきてめっきをする際ショートするのを避けるため、髭の伸びを見る）として、２５℃、湿度４０％の条件で、８０日間、３２０日間放置した後、４０倍の光学顕微鏡で表面を観察した。結果を表４の実施例６ａに示す。８０日間、３２０日間の放置によってもウィスカーは出なかった。外観、及びはんだ濡れ性は合格で、融点も２１７℃で低かった。
〔実施例６ｂ〕
実施例６ａにおけるテストピース（４２アロイ）を銅製のテストピースに代えた以外は実施例６ａと同様にめっきを行った。結果を表４の実施例６ｂに示す。
接合強度が２７．８で、はんだ濡れ性が若干悪くなった以外は実施例６ａと略同じで外観、めっき被膜融点も２１７℃で低く、良好であった。また、実施例６ａと同じ条件でウィスカー試験を行ったが、８０日間、３２０日間放置してもウィスカーは出なかった。被膜組成も実施例６ａと略同じと考えられる。
【００６２】
【表５】

【００６３】
〔比較例１〕
錫イオンとして０．２ｍｏｌ／Ｌ、第２銅イオンとして０．００２５ｍｏｌ／Ｌ、銀イオンとして０．０１ｍｏｌ／Ｌを含有する従来のめっき液ｂ（表２に示す）を用いて、実施例１ａと同様の方法でめっきを行った。
得られためっき被膜について実施例１ａと同じ方法で、組成を測定し、外観について試験した。結果を表５の比較例１に示す。めっき被膜表面は、黒色がかった外観不良で不合格であった。
【００６４】
〔比較例２〕
錫イオンとして０．１９６８ｍｏｌ／Ｌ、第２銅イオンとして０．００２６ｍｏｌ／Ｌ、銀イオンとして０．０００６６ｍｏｌ／Ｌを含有する従来のめっき液ｃ（表３に示す）を用いて、実施例１ａと同様の方法でめっきを行った。
得られためっき被膜について実施例１ａと同じ方法で、組成を測定し、外観について試験した。結果を表５の比較例２に示す。
めっき被膜表面は、黒色がかった外観不良で不合格であった。
〔比較例３〕
比較例１における電流密度を３Ａ／ｄｍ^２ に換えた以外は比較例１と同様にめっきを行ったところ、８μｍの被膜を作成するためのめっき時間が２３４秒と長くなった。
得られためっき被膜について実施例１ａと同じ方法で、組成、融点を測定し、外観、はんだ濡れ性について試験した。更に、はんだ付けを行い、接合強度を測定した。結果を表５の比較例３に示す。
めっき被膜の組成は、銀１．９６重量％、銅０．５０重量％、残部は錫であった。被膜の外観は合格だったが、接合強度が実施例１ａに較べて弱く、また、融点も２２７℃で高かった。
【００６５】
〔比較例４〕
比較例２における電流密度を３Ａ／ｄｍ^２ に換えた以外は比較例２と同様にめっきを行ったところ、８μｍの被膜を作成するためのめっき時間が２８９秒と長くなった。
得られためっき被膜について実施例１ａと同じ方法で、組成、融点を測定し、外観、はんだ濡れ性について試験した。更に、はんだ付けを行い、接合強度を測定した。結果を表５の比較例４に示す。
めっき被膜の組成は、銀０．３２重量％、銅０．８重量％、残部は錫であり、融点は２３０℃と高かった。また、外観は良好であったが、接合強度が２２．１Ｎで実施例１ａに較べて弱かった。
【００６６】
〔比較例５ａ〕
他の鉛フリーめっき液として、錫及び銀を含有するめっき液を用いて、実施例６ａと同様な方法で、４２アロイテストピースに錫−銀合金（錫９６．６重量％、銀３．４重量％）のめっき被膜を形成し、得られためっき被膜について、外観、はんだ濡れ性について実施例１ａと同じ方法で測定あるいは試験した。
更に、実施例１ａと同じ方法ではんだ付けを行い、接合強度を測定し、さらに実施例６ａと同じ条件（２５℃、湿度４０％）でウィスカー試験を行った。８０日間、３２０日間放置しても、ウィスカーは見られなかった。結果を表５の比較例５ａに示す。外観、及びはんだ濡れ性は合格だったが、接合強度は２０．５Ｎで弱く、融点が２２１℃で高かった。
【００６７】
〔比較例６ａ〕
他の鉛フリーめっき液として、錫及び銅を含有するめっき液を用いて実施例６ａと同様な方法で、４２アロイテストピースに錫−銅合金（錫９８．５重量％、銅１．５重量％）のめっき被膜を形成し、得られためっき被膜について、外観、はんだ濡れ性について実施例１ａと同じ方法で測定あるいは試験した。更に、実施例１ａと同じ方法ではんだ付けを行い、接合強度を測定し、さらに実施例６ａと同じ条件でウィスカー試験を行った。結果を表５に示す。８０日間、３２０日間の放置でもウィスカーは見られなかった。また、外観は良好だが、接合強度が１９．３と弱く、融点も２２７℃と高かった。
【００６８】
〔比較例７ａ〕
他の鉛フリーめっき液として、錫及びビスマスを含有するめっき液を用いて実施例６ａと同様な方法で、４２アロイテストピースに錫−ビスマス合金（錫９７．０重量％、ビスマス３．０重量％）のめっき被膜を形成し、得られためっき被膜について、外観、はんだ濡れ性について実施例１ａと同じ方法で測定あるいは試験した。更に、実施例１ａと同じ方法ではんだ付けを行い、接合強度を測定し、さらに実施例６ａと同じ条件でウィスカー試験を行った。結果を表５に示す。８０日間、３２０日間の放置でもウィスカーは見られなかった。また、外観は良好だが、接合強度が１９．９と弱く、融点も２２６℃と高かった。
【００６９】
〔実施例７〕
実施例７として、図２（ａ）に示すように、上記実施例６ｂではんだ付けされた、ガラスエポキシ製の銅被覆テスト基板１０上のはんだペースト１１と、めっき被膜された銅製のテストピース１２との境界部（はんだペースト１１とめっき被膜との溶融はんだ部、以下溶融はんだ部ともいう）１３のＡｇ分布状態について、ＥＰＭＡ（電子プローブＸ線マイクロアナライザー）によるマッピング（地図化）で確認した。
このはんだペースト１１には、共晶点に近い組成を有する錫−銀−銅合金（錫９６．５重量％、銀３．０重量％、銅０．５％）が使用されており、実施例の錫−銀−銅含有めっき被膜との溶融はんだ部１３では、Ａｇの分布状態を図示した図２（ｂ）に示すように、銀が均一に散在し、はんだ中に多く存在するＳｎとの間でＡｇ_３ Ｓｎのネットワーク（網状構造）１４ができていると思われる。なお、図２の１５は空気を示す。
【００７０】
〔比較例５ｂ〕
他の鉛フリーめっき液として、錫及び銀を含有する比較例５ａと同じめっき液を用いて、実施例６ｂと同様な方法で、銅製のテストピースに錫−銀合金（錫９６．６重量％、銀３．４重量％）のめっき被膜を形成した。得られためっき被膜について、外観、はんだ濡れ性について実施例１ｂと同じ方法で測定あるいは試験した。さらに実施例６ａと同じ条件でウィスカー試験を行った。結果を表５の比較例５ｂに示す。８０日間、３２０日間の放置でもウィスカーは見られなかった。外観、はんだ濡れ性、接合強度も問題無かったが、融点が２２１℃で少し高かった。
更に、実施例１ｂと同じ方法ではんだ付けを行い、接合強度を測定し、そのめっき被膜を実施例７と同様な方法で、はんだ付けしためっき被膜とはんだペーストとの溶融はんだ部１３のＡｇ分布状態について、ＥＰＭＡによるマッピングで確認した。結果を図２（ｃ）に示す。
【００７１】
〔比較例６ｂ〕
他の鉛フリーめっき液として、錫及び銅を含有する比較例６ａと同じめっき液を用いて実施例６ｂと同様な方法で、錫−銅合金（錫９８．５重量％、銅１．５重量％）のめっき被膜を形成し、比較例５ｂと同様、試験した。さらに実施例６ａと同じ条件でウィスカー試験を行った。結果を表５の比較例６ｂに示す。８０日間の放置でウィスカーは見られなかったが３２０日間の放置で針状の結晶が観察された。外観、はんだ濡れ性、接合強度は問題無かったが、融点が２２７℃で少し高かった。
そのめっき被膜について、実施例７と同様な方法で、はんだ付けしためっき被膜とはんだペーストとの溶融はんだ部１３のＡｇ分布状態について、ＥＰＭＡによるマッピングで確認した。結果を図２（ｄ）に示す。
【００７２】
〔比較例７ｂ〕
他の鉛フリーめっき液として、錫及びビスマスを含有する比較例７ａと同じめっき液を用いて実施例６ｂと同様な方法で、錫−ビスマス合金（錫９７．２重量％、ビスマス２．８重量％）のめっき被膜を形成し、比較例５ｂと同様、試験した。結果を表５の比較例７ｂに示す。はんだ濡れ性、外観は良好であったが、融点が２２６℃と高く、また、ウィスカー試験の結果は３２０日の放置で表面に針状の結晶が観察された。
そのめっき被膜について実施例７と同様な方法で、はんだ付けした溶融はんだ部１３のＡｇ分布状態について、ＥＰＭＡによるマッピングで確認した。結果を図２（ｅ）に示す。
図２に示すように、Ｓｎ−Ａｇめっき被膜、Ｓｎ−Ｃｕめっき被膜、又はＳｎ−Ｂｉめっき被膜とはんだとの溶融はんだ部１３については、いずれも溶融はんだ部１３で銀が斑状になっており、Ｓｎ−Ａｇ−Ｃｕめっき被膜の場合に見られるようなＡｇ_３ Ｓｎのネットワークの存在は推察できなかった。一般にＡｇ_３ Ｓｎのネットワークは基板とめっき被膜の接合性を強くすると言われることから、本発明の錫−銀−銅含有めっき被膜についても基板と強い接合性を示すと考えられる。
【００７３】
次にはんだ濡れ性について比較した。
表４に示すように、Ｎｉ４２重量％、Ｆｅ５８重量％（４２アロイ）のテストピースへの本発明の錫−銀−銅含有めっき被膜のはんだ濡れ性は、めっき直後の被膜についても、更に、スチーム飽和蒸気で４時間経過という過酷な条件の経過後も略良好であった。
【００７４】
表５の比較例５ａ、５ｂに示す従来のＳｎ−Ａｇめっき被膜、比較例６ａ、６ｂに示す従来のＳｎ−Ｃｕめっき被膜、比較例７ａ、７ｂに示す従来のＳｎ−Ｂｉめっき被膜は４２アロイにめっきした場合にはいずれも接合強度が弱く、また、４２アロイ、あるいは銅板のいずれにめっきした場合も本実施例に比較して融点が高かった。
また、本発明のいずれのめっき被膜も前記ウィスカー試験でウィスカーが見られることは無かったが、従来のＳｎ−Ｂｉ、Ｓｎ−Ｃｕめっき液を用いて銅、更に真鍮のテストピースにめっきした従来のＳｎ−Ｂｉ、Ｓｎ−Ｃｕめっき被膜は、２５℃、湿度４０％の同じ条件で３２０日放置すると、針状結晶が生成していた。
さらに、本発明の錫−銀−銅含有めっき被膜をリードフレームと実施例１ａに記載の方法によりはんだ付けした基板の実装性について比較した結果においても、本発明の錫−銀−銅含有めっき被膜は基板に完全溶融してはんだ付けされていたが、従来の製品であるＳｎ−Ａｇ、Ｓｎ−Ｂｉ、Ｓｎ−Ｃｕめっき被膜は、基板である４２アロイと未溶融ではんだ付けされていた。
【００７５】
上記結果から、本発明のめっき液を使用しためっき被膜は外観、接合強度、はんだ濡れ性のいずれも他の鉛フリー種に比較して優れていることが判った。特に、近年、鉛フリーのはんだ材料（はんだペースト）の基礎はんだとして使用されている共融点に近い組成を有する錫−銀−銅合金を使用したはんだに、本発明の錫−銀−銅含有めっき被膜が非常に適していることがわかる。
上記結果に示すように、本実施例のめっき液ａを使用して４２アロイあるいは銅板にめっきしためっき被膜は、４２アロイあるいは銅板のいずれにめっきした場合にも、外観も良好、接合強度も良好、はんだ濡れ性も略良好であった。
また、本実施例のめっき液ａに光沢剤を添加し、電流波形としてパルス電流波形を用いてめっきした場合も光沢があり外観良好ではんだ濡れ性も良好、接合強度も良好なめっき被膜が得られた。
また、本発明のめっき液は、４ｄｍ^２ 以上の高い電流密度でも、安定しためっきが可能であり、高速めっきにも適用できることが判った。
更に、両者共、融点が錫、銀、銅の共晶点に近い２１７℃、２１８℃であり、図１のはんだ付け温度の概略図に示すように、低い温度ではんだ付けを行うことが可能となった。
【００７６】
次に、めっき液ａ〜ｃについてめっき液の経時安定性を見るために、建浴直後及び１ケ月後の外観及び吸光度について比較した。吸光度の測定方法は純水をリファレンス側とし、波長６６０ｎｍの光を石英セルに照射して測定点をセットした後に、８００〜４００ｎｍまでの光を連続照射して測定することにより行った。６６０ｎｍの波長での結果を表６に示す。
【００７７】
【表６】

【００７８】
表６に示すように、めっき液ａは建浴直後及び１ケ月後についても外観は透明で変わらず、１ケ月後の吸光度も０．０２９と高くなっていない事から不純物の析出は少ないと考えられた。一方、従来のめっき液ｂについては建浴直後の外観も不良、液も濁りが多かった。同じく従来のめっき液ｃについては１ケ月後の外観が不良で両者とも、安定性が悪かった。
上記結果より、本実施例のめっき液は保存性が良いことがわかる。
【００７９】
【発明の効果】
本発明の錫−銀−銅含有めっき被膜、めっき被膜を有する積層体及び該積層体を有する電子部品は、融点が低く実装時の加熱温度を低くすることが可能であり、はんだ材と接合したときに強度の強い合金を形成することができる。
本発明の錫−銀−銅含有めっき液及び電解めっき方法は、錫−銀−銅合金の共晶点に近い融点を有するめっき被膜を形成できる。
本発明のはんだ付け方法は、錫−銀−銅合金の共晶点に近いはんだ材料が設けられた基板と、はんだ材料と類似の組成を有するめっき被膜で被覆された電子部品とを加熱接合するので、非常に接合性が良いと同時に、低い温度ではんだ付けをすることができ、電子部品の熱による損傷を防ぐことができると共に、消費エネルギーの低減ができる。
本発明の電子回路は、接合強度が高いため、信頼性が高い。
【図面の簡単な説明】
【図１】部品耐熱性評価用のはんだ付け温度の説明図である。
【図２】めっき種類別の溶融はんだ部のＡｇ分布状態の比較図である。
【符号の説明】
１０：銅被覆テスト基板、１１：はんだペースト、１２：銅製のテストピース、１３：境界部、１４：Ａｇ_３ Ｓｎのネットワーク（網状構造）、１５：空気[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a tin-silver-copper-containing plating solution used for lead-free solder plating, an electrolytic plating method using the same, a plating film, and a soldering method.
[0002]
[Prior art]
Conventionally, components that require soldering, such as components that make up electronic devices such as chip components, crystal oscillators, bumps, connector pins, lead frames, various hoop materials, package lead pins, printed circuit boards, etc. And tin plating or tin-lead alloy plating. Pure tin plating has problems such as deterioration of solderability and formation of whiskers in the film. In recent years, the use of lead has been refrained from the viewpoint of environmental protection, and lead-free plating has been desired.
[0003]
As plating not containing lead, for example, tin-silver alloy, tin-bismuth alloy, tin-copper alloy, etc. are being studied, but tin-silver alloy is easily decomposed in a plating bath, and tin-bismuth alloy is used for plating film. There is a disadvantage that cracks are easily generated.
On the other hand, the tin-copper alloy hardly causes cracks and has excellent bonding strength, but has a problem of a high melting point. As the tin-copper alloy plating, a plating bath containing a specific organic compound component, and further, a tin-silver-copper alloy plating bath are disclosed (for example, see Patent Document 1).
[0004]
It is also desired that lead-free solder material on the substrate side to be bonded to the plating film is used. For example, a tin-silver-copper alloy having a composition close to the eutectic point has been used as a solder material. (For example, see Patent Documents 2 and 3). If a plating film similar to the composition of the solder material on the substrate side is used, it is expected that the energy cost at the time of joining can be reduced and that the joining property is excellent. Several results have been disclosed regarding the production of a silver-copper-containing plating solution and a plating film using the same (for example, see Non-Patent Documents 1 and 2). However, due to the instability of the plating solution, a plating film having a composition similar to that of the tin-silver-copper alloy has not yet been obtained, and has good bonding properties with a solder material using the tin-silver-copper alloy. There has been a demand for a plating film having a good quality.
[Patent Document 1]
JP 2001-164396 A (Nos. 3, 4, 7, 8, 25 to 27)
[Patent Document 2]
JP-A-5-50286
[Patent Document 3]
U.S. Pat. No. 5,527,628
[Non-patent document 1]
"Effect of T3HPP on Electrodeposition and Bath Stability of Sn-0.7Cu-0.3Ag Ternary Alloy from Methanesulfonic Acid Bath", Proc. Of the 103rd Lecture Meeting, Surface Technology Association, March 5, 2001 Days, p. 54
[Non-patent document 2]
"Sn-Ag-Cu Alloy Plating for Lead-Free Solder", Proc. Of the 103rd Lecture Meeting, Surface Technology Association, March 5, 2001, p. 58
[0005]
[Problems to be solved by the invention]
However, in the plating bath compositions specifically disclosed in Patent Literature 1 and Non-Patent Literatures 1 and 2, each metal concentration is low or the balance is poor, and productivity is low for use in industrial plating. Had a problem. Further, the tin-silver-copper alloy plating bath is more excellent than the tin-copper alloy plating bath in terms of solder wettability, liquid stability, and strength, but contains three kinds of metal ions and a complex of metal ions. In addition, it is difficult to prepare a solution, especially on an industrial scale, the amount of plating chemicals handled becomes large, and since it is used over a long period of time, solids may occur during plating and the liquid quality may change, As a result, there are problems such as unstable plating quality.
[0006]
Furthermore, the conventionally known lead-free plating film has a melting point of about 20 degrees higher than that of the tin-lead plating film, so that the melting point is reduced in order to reduce the energy cost at the time of joining and the amount of heating to other parts. Therefore, a lead-free plating film having a low density has been desired.
Further, a tin-silver-copper alloy having a composition close to the eutectic point has been used as a solder material, but a tin-silver-copper-containing plating film having a composition similar to the tin-silver-copper alloy has been used. Has not yet been obtained due to the difficulty in producing a plating solution as described above, and a plating film having good bonding properties with a solder material using a tin-silver-copper alloy has been desired.
It is an object of the present invention to provide a tin-silver-copper-containing plating solution having a low solid deposition and a good storage stability over a long period of time. Electroplating method that can perform plating even if density is increased, tin-silver-copper-containing plating film with low melting point, hard to crack, and excellent bonding strength, and heating during mounting using this plating film An object of the present invention is to provide a soldering method capable of lowering the temperature.
[0007]
[Means for Solving the Problems]
The tin-silver-copper-containing plating solution according to the first invention is a plating solution containing sulfonic acids, tin ions, copper ions, and silver ions in a medium mainly composed of water, wherein the concentration of the silver ions is 0%. 0.01 to 0.1 mol / L.
In the tin-silver-copper-containing plating solution, it is very difficult to control the concentration of silver ions, and the concentration of silver ions is maintained at 0.01 to 0.1 mol / L. By controlling the copper ion concentration, an ideal plating solution could be obtained.
The tin-silver-copper-containing plating solution according to the second invention is the tin-silver-copper-containing plating solution according to the first invention, wherein the tin ion concentration is 0.21 to 2 mol / L, The concentration is 0.002 to 0.02 mol / L.
The tin-silver-copper-containing plating solution according to the third invention is the tin-silver-copper-containing plating solution according to the first and second inventions, wherein the molar ratio of the concentration of the silver ion to the concentration of the copper ion is , In the range of 4.5 to 5.58.
Here, by setting each metal ion concentration in the above range, a tin-silver-copper alloy having a low melting point can be plated with high productivity, and more preferably, the tin ion concentration is 0.3 to 1 mol / L, and the silver ion concentration is Is set to 0.02 to 0.05 mol / L and the copper ion concentration is set to 0.003 to 0.01 mol / L, more preferably, the silver ion concentration with respect to the copper ion concentration is set to 4.5 to 5.58 (mol). As a result of intensive studies conducted by the present inventors through many experiments, the tin-silver-copper alloy having a lower melting point can be plated with high productivity by setting the ratio in the above range.
[0008]
A tin-silver-copper-containing plating solution according to a fourth invention is the tin-silver-copper-containing plating solution according to the first to third inventions, wherein the concentration of the sulfonic acid is 0.5 to 5 mol / L. .
If the concentration of sulfonic acids is less than 0.5 mol / L, tin, silver and copper compounds, which are hardly soluble in water, may not be dissolved in water. If the concentration is more than 5 mol / L, the concentration of metal ions temporarily increases. In some cases, a uniform plating solution cannot be obtained.
The tin-silver-copper-containing plating solution according to a fifth aspect of the present invention further includes a mercaptan compound in the tin-silver-copper-containing plating solution according to the first to fourth aspects.
Furthermore, since it contains a mercaptan compound, tin ions, copper ions, and silver ions become stable as complex compounds.
The tin-silver-copper-containing plating solution according to a sixth aspect of the present invention further includes an aromatic amino compound in the tin-silver-copper-containing plating solution according to the first to fifth aspects.
Further, since it contains an aromatic amino compound, a complex compound of tin ions, silver ions and copper ions is further stabilized.
The tin-silver-copper-containing plating solution according to a seventh aspect of the present invention further includes a nonionic surfactant in the tin-silver-copper-containing plating solution according to the first to sixth aspects.
Furthermore, since it contains a nonionic surfactant, the appearance, denseness, smoothness, adhesion and throwing power of the plating film are improved.
[0009]
An electrolytic plating method according to an eighth aspect of the present invention is the electroplating method using the tin-silver-copper-containing plating solution according to the first to seventh aspects, wherein a current at the time of plating is applied to the metal base material to be plated. Density is 0.01 to 50 A / dm ² , Preferably 4 to 50 A / dm ² It is. Current density of 0.01 to 50 A / dm ² Therefore, it can be applied to various plating apparatuses, and further, from a thin plating layer to a thick plating layer, and 4 to 50 A / dm. ² (More preferably 20 to 50 A / dm ² ) Can be applied to high-speed plating, and a stable plating layer can be formed.
An electroplating method according to a ninth aspect is the electroplating method according to the eighth aspect, wherein the current waveform during plating is a pulse current waveform. Therefore, bright plating can be obtained.
An electroplating method according to a tenth aspect is the electroplating method according to the eighth aspect, wherein the current waveform at the time of plating is a DC waveform.
Since the current waveform is a flat DC waveform without pulsation, semi-glossy plating can be obtained. By setting the DC voltage to be 1.9 V or less, and more preferably in the range of 0.2 to 1.2 V, beautiful semi-glossy plating can be obtained with high productivity.
[0010]
The tin-silver-copper-containing plating film according to the eleventh invention has a silver content of 2.6 to 3.4% by weight, a copper content of 0.4 to 0.7% by weight, The balance is substantially tin.
Since the contents of silver and copper are within the above ranges, a plating film having a low eutectic point of tin, silver and copper alloy is obtained, and the heating temperature during mounting can be lowered.
The tin-silver-copper-containing plating film according to the twelfth invention has a thickness of 3 to 20 μm in the tin-silver-copper-containing plating film according to the eleventh invention. Therefore, it is possible to perform soldering without unevenness and high bonding strength. If the thickness of the plating film is less than 3 μm, it is too thin, so that it is difficult to solder, and the bonding strength is weak. If the thickness is more than 20 μm, unevenness occurs and it is useless.
The tin-silver-copper-containing plating film according to the thirteenth invention is a plating film obtained by performing electrolytic plating using the tin-silver-copper-containing plating solution according to the first to seventh inventions, Is 2.6 to 3.4% by weight, the copper content is 0.4 to 0.7% by weight, and the balance is substantially tin.
The plating film thus obtained has a low melting point, and the heating temperature during mounting can be lowered.
The tin-silver-copper-containing plating film according to the fourteenth invention is a plating film obtained by the electrolytic plating method according to the eighth to tenth inventions, and has a silver content of 2.6 to 3.0. 4% by weight, the content of copper is 0.4 to 0.7% by weight, and the balance is substantially tin.
[0011]
The laminate according to a fifteenth aspect of the present invention provides the tin-silver-copper-containing plating film according to the eleventh to fourteenth aspects, wherein the tin-silver-copper-containing plating film is formed of any one of copper, nickel, iron, and an alloy containing one or more of these. On a metal substrate. Further, an electronic component according to a sixteenth invention has the laminate according to the fifteenth invention.
Here, the laminate refers to a plurality of metal layers plated on a metal substrate (there are plate-like and linear ones), and specifically, a lowermost base plating (for example, a nickel plating layer) , An intermediate corrosion-resistant plating layer (for example, a gold, silver, palladium plating layer), and a surface plating layer (a tin-silver-copper-containing plating film layer according to the eleventh to fourteenth aspects). In the case where the tin-silver-copper-containing plating film layer according to the eleventh to fourteenth inventions is directly plated on a metal substrate, the tin-silver-copper-containing plating film layer This includes the case where a base plating layer is formed below.
The laminate has a silver content of 2.6 to 3.4% by weight on a metal substrate made of one of copper, nickel, iron, and an alloy containing one or more of these, Has a plating film whose content is 0.4 to 0.7% by weight, and the balance is substantially tin, so that the laminate and the electronic component having the laminate are not uneven and have a high bonding strength. Can be attached, and desired conductivity can be secured.
[0012]
An electronic circuit according to a seventeenth aspect is the electronic circuit according to the sixteenth aspect, wherein the content of silver is 2 to 4% by weight, the content of copper is 0.3 to 0.8% by weight, An electronic circuit board provided with a solder material containing an alloy whose balance is substantially tin is heated and joined.
Accordingly, the composition of the plating film of the laminate of electronic components and the composition of the solder material provided on the electronic circuit board are similar, and the bonding property is extremely improved.
[0013]
The soldering method according to an eighteenth aspect of the present invention is the soldering method according to the sixteenth aspect, wherein the content of silver is 2 to 4% by weight, and the content of copper is 0.3 to 0.8% by weight. The substrate is heated and joined in contact with a substrate provided with a solder material containing an alloy whose balance is substantially tin.
Since the heat-bonding is performed in a state in which the plating film of the electronic component and the substrate having the similar composition of the solder material are brought into contact with each other, a soldering method with very good bondability can be provided.
In a soldering method according to a nineteenth aspect, in the soldering method according to the eighteenth aspect, a maximum temperature of the electronic component and the substrate at the time of heating and joining is in the range of 220 to 260 ° C. Therefore, energy can be saved and the cost can be reduced.
If the maximum temperature at the time of overheating is lower than 220 ° C., the plating film and the solder material are not easily melted and soldering is difficult. If the maximum temperature is higher than 260 ° C., the electronic components may be damaged.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
(Plating solution)
A tin-silver-copper-containing plating solution according to an embodiment of the present invention (hereinafter, also simply referred to as a plating solution) is a medium containing water as a main component, and tin, silver and copper as essential components as sulfonic acids and metal components. Contains.
The metal component is present as metal ions in the plating solution, and a plating solution can be obtained by mixing a plating mother liquor mainly composed of water and sulfonic acids with a metal compound. Contains complexing agent.
[0015]
Specific examples of the tin compound include tin salts of organic sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, 2-propanolsulfonic acid, and p-phenolsulfonic acid, tin sulfate, tin oxide, tin nitrate, tin chloride, and bromide. Tin, tin iodide, tin phosphate, tin pyrophosphate, tin acetate, tin formate, tin citrate, tin gluconate, tin tartrate, tin lactate, tin succinate, tin sulfamate, tin borofluoride, tin fluorosilicate, etc. Of stannous compounds. These tin compounds can be used alone or in combination of two or more.
[0016]
As the copper compound, copper salts of the above sulfonic acids, copper sulfate, copper oxide, copper nitrate, copper chloride, copper bromide, copper iodide, copper phosphate, copper pyrophosphate, copper acetate, copper formate, copper citrate, Examples include copper gluconate, copper tartrate, copper lactate, copper succinate, copper sulfamate, copper borofluoride, and copper silicofluoride. These copper compounds can be used alone or in combination of two or more.
[0017]
Examples of the silver compound include silver, silver sulfate, silver oxide, silver chloride, silver nitrate, silver bromide, silver iodide, silver phosphate, silver pyrophosphate, silver acetate, silver formate, silver citrate, and silver gluconate of the above sulfonic acid. Silver, silver tartrate, silver lactate, silver succinate, silver sulfamate, silver borofluoride, silver silicofluoride, and the like. These silver compounds can be used alone or in combination of two or more.
Among these, silver oxide is preferably used because of its solubility and ease of industrial use.
[0018]
Sulfonic acids can be used as long as they can dissolve the above-mentioned metal components, and examples thereof include aliphatic sulfonic acids such as methanesulfonic acid and ethanesulfonic acid, benzenesulfonic acid, and toluenesulfonic acid. Can be Among these, aliphatic sulfonic acids are preferred in terms of solubility of metal salts and ease of wastewater treatment, and methanesulfonic acid is particularly preferred.
The content of these sulfonic acids in the plating solution is preferably 0.5 to 5 mol / L, more preferably 1 to 3 mol / L.
[0019]
In the plating solution, the metal component is an example of a strong acid ion. For example, a sulfonic acid ion is dissolved as a counter anion in a medium mainly composed of water in the form of a metal ion and a complex of the metal ion. ²⁺ And / or Sn ⁴⁺ , Copper ion is Cu ⁺ And / or Cu ²⁺ And silver ion is Ag ⁺ Exist as. The amount of each metal in the plating solution is Sn ²⁺ 0.21 to 2 mol / L, preferably 0.25 to 1 mol / L, 0.01 to 0.1 mol / L as silver, preferably 0.02 to 0.05 mol / L, and 0.002 to 0 as copper. 0.02 mol / L, preferably 0.003 to 0.01 mol / L. Here, Sn ions are involved in plating as Sn ions. ²⁺ Therefore, Sn ²⁺ Regulate the amount of
Further, the silver ion concentration (molar ratio) with respect to the copper ion concentration is preferably in the range of 4.5 to 5.58, and in this range, a tin-silver-copper plating film having a low melting point should be prepared. Becomes easier.
It should be noted that, depending on the plating apparatus, the solution around the anode and the plating solution on the cathode side may be separated by a diaphragm or the like. In that case, it is preferable to adjust within the above range at least on the cathode side where plating is performed.
[0020]
Further, if the composition of the tin-silver-copper ternary plating solution is regulated by the compounding amount of tin, silver, and copper, the composition of the plating film formed using the plating solution is also regulated. The composition of tin, silver and copper is determined so that the melting point of the plating film to be produced is as low as possible. Further, a trace amount of a metal element may be contained as long as the effect of lowering the melting point of the plating film is not impaired. Examples of the trace metal include nickel, cobalt, gold, bismuth, lead, palladium, antimony, zinc, iron, germanium, and indium, and the content is preferably smaller than the content of copper.
[0021]
Further, a sulfonic acid salt soluble in the plating mother liquor, an organic acid and a salt thereof, and an inorganic acid and a salt thereof can be blended with a sulfonic acid as long as the performance of the plating solution is not impaired. Examples of the inorganic acid include sulfuric acid, phosphoric acid, condensed phosphoric acid, nitric acid, hydrofluoric acid, and borofluoric acid. Examples of the organic acid include sulfamic acid, carboxylic acid, and phosphonic acid. The salts of the above-mentioned acids may be any soluble salts, for example, alkali metal salts such as Na salt and K salt, alkaline earth metal salts such as Ca salt, alkylamine salts such as diethylamine salt, ammonium salts and the like. Can be used.
[0022]
The plating solution preferably contains a specific organic complexing agent as an additive.
Preferred organic complexing agents are mercaptan compounds, thiourea compounds and aromatic amino compounds.
Any mercaptan compound (also called a thiol compound) can be used as long as it has an SH group in the molecule. Note that a compound having a disulfide bond may be used and reduced in a plating bath to generate a thiol compound. As the thiourea compound, any compound having a thiourea skeleton can be used. As the aromatic amino compound, any compound having an amino group directly on an aromatic ring can be used. It is preferable that these organic complexing agents have a certain degree of solubility in the plating mother liquor from the viewpoint of preparing a stable plating solution. The solubility is preferably 3 g / L or more, more preferably 5 g / L or more, and particularly preferably 10 g / L. That is all. If the complexing agent molecule is too large, the complexing ability tends to decrease. Therefore, the molecular weight is preferably 2000 or less, more preferably 1000 or less, and particularly preferably 80 to 500.
[0023]
Specific examples of the mercaptan compound include, for example, butanethiol, aliphatic thiol compounds such as pentanethiol, thiophenol, toluenethiol, aromatic thiol compounds such as o-aminothiophenol, mercaptoacetic acid, mercaptosuccinic acid, mercaptolactic acid and the like. And a mercapto group-containing amino acid such as cysteine and a mercapto group-containing amino acid derivative such as acetylcysteine. Among these, from the viewpoints of solubility in water, performance as a complexing agent, and low odor, mercapto group-containing carboxylic acids or mercapto group-containing amino acids and derivatives thereof are preferable, and acetylcysteine is particularly preferable.
[0024]
Specific examples of the thiourea compound include thiourea, dimethylthiourea, trimethylthiourea, N, N'-diisopropylthiourea, acetylthiourea, allylthiourea, 1,3-diphenylthiourea, and thiosemicarbazide. .
Specific examples of the aromatic amino compound include aniline compounds such as aniline, methylaniline, and methoxyaniline, and compounds having two aniline rings in a molecule such as 2,2'-dithiodianiline. Particularly, 2,2'-dithiodianiline is preferable.
The compounding amount of the organic complexing agent in the plating solution is preferably 1 to 100 g / L, more preferably 1 to 30 g / L, and further preferably 2 to 20 g / L. These organic complexing agents may be used in combination. Preferably, a mercaptan compound and an aromatic amino compound are used in combination, and particularly, acetylcysteine and 2,2'-dithiodianiline are used in combination.
[0025]
A surfactant may be added to the plating solution in addition to the above components.
Surfactants are used to improve the appearance, denseness, smoothness, adhesion, throwing power and the like of the plating film. As the surfactant, a nonionic surfactant is preferable, and specifically, for example, C1 to C20 alkanol, phenol, naphthol, bisphenols, C1 to C25 alkylphenol, arylalkylphenol, C1 to C25 alkylnaphthol, C1 to C25 alkoxylation Phosphoric acid (salt), sorbitan ester, styrenated phenol, polyalkylene glycol, C1-C30 aliphatic amine, C1-C22 aliphatic amide, and at least one selected from ethylene oxide (EO) and propylene oxide (PO) An alkylene oxide-based compound obtained by addition-condensation of alkylene oxide by 2 to 300 mol is exemplified.
[0026]
Among them, alkylene oxide compounds are preferable, and specifically, for example, polyoxyethylene α-naphthol ether, polyoxyethylene β-naphthol ether, ethylene oxide propylene oxide block copolymer, polyoxyethylene alkyl ether, polyoxyethylene phenyl ether, Examples thereof include polyoxyethylene alkylamino ether, polyoxyethylene fatty acid ester, polyoxyethylene polyhydric alcohol ether, polyethylene glycol, and polypropylene glycol.
When the surfactant is used, the amount is preferably 0.1 to 50 g / L, more preferably 2 to 10 g / L.
[0027]
An aldehyde compound can be added to the plating solution as a brightening agent for the plating film surface.
As the aldehyde compound, specifically, for example, 1-naphthaldehyde, 2-naphthaldehyde, o-chlorobenzaldehyde, m-chlorobenzaldehyde, p-chlorobenzaldehyde, 2,4-dichlorobenzaldehyde, acetaldehyde, propionaldehyde, salicylaldehyde, Examples thereof include 2-thiophenaldehyde, 3-thiophenaldehyde, o-anisaldehyde, m-anisaldehyde, p-anisaldehyde, salicylaldehyde allyl ether, and 2-oxy-3-methoxybenzaldehyde.
When the aldehyde compound is used, the compounding amount is preferably 0.001 to 10 g / L, and more preferably 0.05 to 0.5 g / L.
In addition to the above components, various additives such as known antioxidants, pH adjusters, and buffering agents can be added to the plating solution according to the purpose.
[0028]
(Method of manufacturing plating solution)
Next, a method for producing a tin-silver-copper-containing plating solution according to one embodiment of the present invention will be described. In producing a plating solution, it is necessary to dissolve each of the above components in a mixture of water and sulfonic acids, but it has been found that the plating solution is stabilized by specifying the order of dissolution. Since the plating solution has a high metal concentration, unevenness tends to occur particularly when a large amount of plating solution is adjusted on an industrial scale. In the production of a conventional binary plating solution, each metal component and additive are added with water. There is no particular restriction on the order of dissolution in water, but in a ternary system of tin-silver-copper, the order of dissolution in water is important.
[0029]
In particular, it is preferable that a predetermined amount of a copper compound and a silver compound are dissolved in a bath containing sulfonic acids as a main component, and then a predetermined amount of a tin compound is dissolved.
Further, it is preferable that the silver compound is dissolved and then the copper compound is dissolved. Since silver compounds, especially silver oxide, are more insoluble than copper compounds, first dissolve the silver compound in the paddy water containing sulfonic acids as the main component, and then dissolve the copper compound to dissolve both well in the paddy water. Can be.
[0030]
In addition, a predetermined amount of a copper compound and a silver compound are separately dissolved in a bath containing sulfonic acid as a main component, and these are mixed to form a mixed solution. Further, a predetermined amount of a tin compound is further dissolved in the mixed solution to produce a mixture. You can also. According to this method, since the copper compound and the silver compound are separately dissolved in the bedding water containing sulfonic acid as a main component, both can be well dissolved in the bedding water.
[0031]
In the tin-copper-silver-containing plating solution, the metal components tin, silver, and copper need to be dissolved as ions in the plating solution, but the solubility of each component in water is not so high. It is necessary to mix the metal components in the presence of the sulfonic acid.
Therefore, it is preferable to first prepare a bath with at least 50% by weight of the sulfonic acids contained in the plating solution as the final product and at least 30% by weight of water in the plating solution, and to mix the metal component with the bath. .
[0032]
At the time of preparing the spreading water, if the amount of the sulfonic acids is less than 50% by weight of the sulfonic acids contained in the plating solution, the metal compound may not be dissolved. On the other hand, if the amount of water is less than 30% by weight of water in the plating solution, the concentration of the metal compound becomes temporarily too high, so that a uniform plating solution cannot be obtained.
The amount of water used for laying water is preferably 30 to 90% by weight of water in the plating solution, and more preferably 30 to 80% by weight. The sulfonic acids are preferably from 50 to 100% by weight, more preferably from 70 to 100% by weight, even more preferably from 80 to 97% by weight of the sulfonic acids contained in the plating solution.
[0033]
Further, it is preferable to add a complexing agent after dissolving the copper compound and the silver compound in the bath water and before dissolving the tin compound. Here, the complexing agent converts metal ions into complex ions, and by converting them into complex ions, it is possible to stabilize copper and silver ions in the form of ions in an aqueous sulfonic acid solution. Specific examples of the complexing agent include the above-described mercaptan compounds, thiourea compounds, and aromatic amino compounds.
[0034]
(Electroplating method)
In the electrolytic plating method according to one embodiment of the present invention, except that the above-described tin-silver-copper-containing plating solution is used, a conventional method can be adopted, for example, a high-speed plating method, a rack method, Any electrolytic plating method such as a barrel method can be adopted without limitation.
As the anode used in the electrolytic plating method according to the present embodiment, a soluble anode or a combination of a soluble anode and an insoluble anode, preferably a combination of a soluble anode and an insoluble anode.
The soluble anode used in the present invention is a soluble anode containing 90% or more of tin, and contains nickel, gold, bismuth, lead, palladium, antimony, zinc, iron, indium, and other metals in the properties of the plating solution. May be contained alone or in combination of two or more as long as they are not impaired. By using this dissolvable anode, the metal constituting the dissolvable anode can be converted to a corresponding metal ion, particularly Sn ²⁺ The ions can be supplied to the plating solution.
[0035]
An object to be plated (object to be plated) is used for the cathode. The object to be plated is not particularly limited as long as it is conductive, but is particularly preferably made of a metal substrate made of copper, nickel, iron, and an alloy containing one or more of these. A lead or terminal for connecting an electronic component is preferable.
Examples of electronic components include semiconductor chips, pressed components, crystal oscillators, bumps, connectors, connector pins, lead frames, various hoop materials, package lead pins, pin grid arrays, ball grid arrays, printed circuit boards, switches, and resistors. , A variable resistor, a capacitor, a filter, an inductor, a thermistor, a crystal oscillator, and the like.
[0036]
The cathode side current density of electrolytic plating is 0.01 to 100 A / dm by these plating methods. ² It can be.
The electrolytic plating method according to the present embodiment is particularly 0.01 to 50 A / dm. ² Is appropriately selected in the range of, but in the case of the high-speed plating method, it is usually 3 to 50 A / dm. ² , Especially 5 to 40 A / dm ² In the case of the rack method, usually 0.5 to 5 A / dm ² , Especially 1-4 A / dm ² In the case of the barrel method, it is usually 0.01 to 1 A / dm. ² , Especially 0.05 to 0.5 A / dm ² It is. The plating temperature can be 10 to 50 ° C., particularly 15 to 40 ° C., and stirring can be performed without stirring, or a method such as cathode rocking, stirring with a stirrer, or liquid flow with a pump can be used.
The plating solution is a high-speed plating method, particularly 5 to 40 A / dm. ² It is industrially useful in that a plating film having excellent appearance can be formed even when plating is performed at a current density of.
[0037]
In addition, the appearance of plating is bright, semi-glossy, and dull. To obtain bright plating, a brightener is usually added to a plating solution. When bright plating is obtained, it is preferable to use a pulse current waveform as the current waveform. The frequency when the pulse current waveform is used is not particularly limited, but is usually 20 to 100 Hz, and preferably 40 to 70 Hz.
When semi-glossy plating is to be obtained, usually a DC waveform is preferably used. When a DC waveform is used, the voltage is preferably 1.9 V or less, more preferably 0.2 to 1.2 V.
[0038]
(Management of plating solution)
When performing the electrolytic plating, the tin ion concentration, the silver ion concentration, and the copper ion concentration in the plating solution can be easily managed in an appropriate range. In this case, in order to be able to stably obtain the desired good plating film composition ratio and film physical properties, the respective ion concentrations of tin, copper, and silver in the plating bath are determined by volume analysis, optical analysis, The plating bath is analyzed by using one or two or more analytical methods selected from an electric analysis, a thermal analysis, an X-ray analysis, a colorimetric analysis, a gravimetric analysis and the like so that a concentration of an intended numerical value is obtained. It is preferable to supply in the plating bath.
[0039]
Tin ions, copper ions, and silver ions, which are the main metal ions in these plating baths, are previously formulated at appropriate concentrations so as to give the desired plating film alloy composition ratio and film physical properties. As it becomes more and more, the metal ion concentration in the plating bath fluctuates. Along with this, it is possible to maintain the concentration set in advance by dissolving the consumed metal ions from the anode and / or replenishing the metal bath with a concentrated solution of the metal salt from outside the plating bath.
[0040]
The volume analysis includes a redox titration method, a chelate titration method, a precipitation titration method, and the like. Optical analysis includes colorimetric analysis, atomic absorption analysis, high frequency plasma inductively coupled plasma emission spectroscopy, and the like. In the electrical analysis, there are polarography, coulometry, potentiometry, and the like. In the thermal analysis, there are a differential thermal analysis, a differential scanning calorimetry, and the like. The X-ray analysis includes an X-ray diffraction measurement method, a fluorescent X-ray analysis method, and the like.
[0041]
Before replenishing the plating solution with tin ions, silver ions, and copper ions, which are main metal ions, the concentration of the metal ions in the plating bath is measured by one or more analysis methods selected from the above-described analysis methods. Analyze and measure the plating bath in combination, calculate the excess or deficiency, elute the metal ions from the anode and / or select from outside a concentrated solution of metal salt, powder, paste, or solid One or two or more can be replenished.
[0042]
In addition, the above-mentioned anode may be used in combination with the above-mentioned anode and one or two or more kinds of external supply selected from a concentrated solution, powder, paste and solid of a metal salt. It is preferable to use them together in order to prevent impurities from being introduced. In this case, the concentrated solution, powder, paste, or solid of the metal salt may be replenished with the metal supplying each metal ion alone or as a mixture. In addition, replenishment with a metal salt powder, paste, or solid requires sufficient stirring, and replenishment with a concentrated solution is particularly preferable.
[0043]
(Plating film)
The tin-silver-copper-containing plating solution according to the embodiment has a specific mixing ratio of tin, silver, and copper and is substantially free of lead. A tin-silver-copper-containing plating film formed by electrolytic plating using this plating solution has a solder joint strength comparable to that of a conventional tin-lead alloy film. Therefore, the plating solution of the present invention can form a plating film having excellent solderability when an electronic component is to be plated.
[0044]
The tin-silver-copper-containing plating film (hereinafter, simply referred to as a plating film) according to one embodiment of the present invention thus obtained has a silver content of 2.6 to 3.4% by weight, and is preferably It is 2.7 to 3.3% by weight, and more preferably 2.8 to 3.2% by weight. The content of copper is 0.4 to 0.7% by weight, preferably 0.4 to 0.6% by weight, and more preferably 0.45 to 0.55% by weight. When the content of silver and copper is in the above range, a plating film having a low melting point is obtained.
Incidentally, the plating film, silver, metal components other than copper is substantially tin, but even if a small amount of metal element is contained within a range that does not impair the effect of lowering the melting point of the plating film, which is a feature of the present invention. good. Examples of the trace metal include nickel, cobalt, gold, bismuth, lead, palladium, antimony, zinc, iron, and indium. The content is preferably smaller than the copper content, and is preferably 0.1% by weight. It is more preferred that:
The thickness of the plating film is not particularly limited, but is preferably 3 to 20 μm, more preferably 4 to 18 μm, and particularly preferably 5 to 15 μm. Within the above preferred range, soldering with high bonding strength can be performed. Such a thin film cannot be obtained by a method such as rolling of a tin-silver-copper alloy, and is a novel film substantially obtained for the first time by the electrolytic plating method of the present invention.
[0045]
(Soldering method)
Next, a soldering method using a plating film according to one embodiment of the present invention will be described.
The plating film is plated on the above-mentioned plating object such as a lead or a terminal for connection of an electronic component, and the terminal or the like (laminated body) of the plated electronic component is a substrate of an electronic component, an electronic device, or the like. And soldered. On the substrate side, a solder material containing a solder alloy is provided. As the solder alloy, for example, a tin-silver-copper alloy is used, and is usually mounted on a substrate as a solder paste dispersed as metal particles in a highly viscous liquid soldering activator called flux (fatty). You.
The plating film has good bondability with a solder paste using a tin-silver-copper alloy, and has a high bonding strength (soldering strength) due to its similar composition, and a low melting point, The amount of heat required for attachment can be reduced. In particular, a solder paste (solder material) using an alloy having a silver content of 2 to 4% by weight, a copper content of 0.3 to 0.8% by weight, and the balance being substantially tin This is suitable for bonding a substrate provided with a member to a member provided with a plating film. The maximum temperature at the time of soldering is 220 to 260 ° C, preferably 230 to 255 ° C. If the maximum soldering temperature is higher than the above, parts other than metal, such as electronic components and electronic equipment, tend to be damaged. On the other hand, if it is lower than the above range, the soldering tends to be insufficient.
[0046]
In particular, a solder paste using an alloy having a silver content of 2 to 4% by weight, a copper content of 0.3 to 0.8% by weight and a balance substantially of tin was provided. An electronic circuit board and a plating film having a silver content of 2.6 to 3.4% by weight, a copper content of 0.4 to 0.7% by weight and a balance substantially of tin When an electronic circuit is manufactured by heating and joining the coated electronic components, since there is no unevenness in soldering and the strength is strong, an electronic circuit having high strength and high stability can be obtained.
Here, as a soldering method, a free method or a reflow method is preferable.
The free method is a method in which a component on which a plating film is formed in advance is fixed on a printed wiring board and the component is brought into contact with molten solder and soldered. The reflow method is a method in which a solder paste is applied to the printed wiring board. Is printed, and the component on which the plating film is formed is fixed, heated and melted, and soldered.
[0047]
【Example】
Hereinafter, the present invention will be described more specifically with reference to the drawings, but the present invention is not limited to the following examples unless it exceeds the gist.
FIG. 1 is an explanatory diagram of a soldering temperature for evaluating the heat resistance of components, and FIG. 2 is a comparison diagram of an Ag distribution state of a molten solder portion for each plating type.
The tin-silver-copper-containing plating solution of the present invention was used to examine the effects of the tin-silver-copper-containing plating solution, the electrolytic plating method, the plating film, and the soldering method according to the present invention. The metal content in the plating film, the finished appearance, and the melting point of the plating film plated by the method were experimentally measured. Further, this plated film was soldered by the soldering method of the present invention, and the bonding strength and solder wettability of the plated film were tested and measured.
[0048]
A tin-silver-copper-containing plating solution according to one example of the present invention was prepared as follows.
The entire volume of a 54% by weight aqueous solution of methanesulfonic acid was placed in one-third of the water required for adjusting the plating solution in a stirring vessel, and used as a sprinkling water.
Next, while stirring, add the required volume of silver oxide and confirm that it was completely transparent without black sedimentation. After adding acetylcysteine as an example of a mercaptan compound as an agent and confirming dissolution, 2,2′-dithiodianiline as an example of an aromatic amino compound as another complexing agent was added.
When it became a pale blue gel-like liquid, stannous methanesulfonate was immediately added. The liquid became yellow and transparent. Next, 2/3 of required water was added to the plating solution, and finally, 3 g / L of α-naphthol polyethoxylate (10 mol of EO), which is an example of a surfactant, was added, and the adjustment of the plating solution was completed. A plating solution a in which the concentration of methanesulfonic acid in the plating solution is 2.64 mol / L, the concentration of tin ions is 0.337 mol / L, the concentration of copper ions is 0.005 mol / L, and the concentration of silver ions is 0.0237 mol / L. Was adjusted. Table 1 shows the concentration of the final plating solution containing other components of the plating solution a, and Tables 2 and 3 show the compositions of the conventional plating solutions b and c as comparative examples.
[0049]
[Table 1]

[0050]
[Table 2]

[0051]
[Table 3]

[0052]
[Example 1a]
Using the plating solution a shown in Table 1, plating was performed by the electrolytic plating method of the present invention to form a plating film. The plating solution a was placed in a 500 mL beaker, and two pure Sn rectangular parallelepiped ingots were prepared as anodes, and two wires were drawn out from the rectifier + side and each was firmly fixed to the ingot with a clip. On the other hand, one wiring is taken out from the rectifier side and the plating object (0.3 dm ² Was fixed in the same manner on a 42 alloy test piece (Ni 42% by weight, Fe 58% by weight).
Current density of 5.8 A / dm ² The current was changed to a DC waveform, and electrolytic plating was performed at 18 ° C. for 216 seconds. As a result, a favorable semi-glossy plating film having a thickness of 8 μm was obtained on the 42 alloy test piece. The plated 42 alloy test piece was sufficiently washed with tap water and then finished and washed with pure water. Thereafter, it was dried.
[0053]
About the obtained plating film, the metal content in the film, appearance, bonding strength, solder wettability, and melting point were measured and tested by the following methods (1) to (7). The results are shown in Example 1a of Table 4. As shown in Table 4, the composition of the plating film obtained in Example 1a was 2.81% by weight of silver, 0.51% by weight of copper, and the balance was tin. The solder wettability was good, and the melting point was 217 ° C., which is close to the eutectic point of tin, silver, and copper, making it possible to perform soldering at a low temperature. Also, the result of the joint strength test was as good as 23.3N.
[0054]
(1) The metal content in the coating is measured by IPC emission spectroscopy (high frequency plasma inductively coupled plasma emission spectroscopy).
The coating after plating was dissolved and quantified by IPC emission spectroscopy.
(2) Finished appearance
The state of the surface of the electrodeposited film obtained from each plating bath was visually observed. A sample was judged to be acceptable if it had a uniform white appearance without any color unevenness.
[0055]
(3) Measurement of bonding strength of coating
In order to check the bonding strength of the plating film, using the plating solution a shown in Table 1, a test piece plated by the electrolytic plating method of Example 1a was subjected to the reflow soldering method of the present invention shown below. , Soldered to the board.
According to the soldering method of the present invention, a stainless steel mask (mask thickness 0.8 mm) is set on a glass epoxy copper-coated test substrate (12 mm × 12 mm, thickness 3 mm), and a solder paste (paste) is placed on a land of the substrate. The composition of the alloy in the middle was 3.0% by weight of silver, 0.5% by weight of copper, and the balance of tin) to form a solder paste film having a thickness of about 0.8 mm. The mask was removed, and the test piece plated with the solder paste in Example 1a was mounted. This was placed in a heating furnace, heated at 180 ° C. for 90 seconds, raised to 240 ° C. over 40 seconds, and held at 240 ° C. for 10 seconds, as shown in the schematic diagram of the soldering temperature in FIG. Then, it cooled. When the temperature was raised and lowered, the range of 220 ° C. or more was set to 30 seconds. After cooling, the soldered substrate and test piece were removed. The bonding strength between the substrate and the test piece was measured by the method described in JIS C0054, EIAJET-7403.
[0056]
(4) Solder wettability was measured by the method described in JIS C 0053, EIAJET-7401.
(5) The melting point was measured by DSC (differential scanning calorimetry).
(6) Elemental analysis of the junction was confirmed by mapping with EPMA (Electron Probe X-ray Microanalyzer).
(7) Thickness of plating film
It was measured by a film thickness meter using fluorescent X-rays. As a calibration curve, an alloy of 3.5% by weight of silver and the balance of tin was used.
[0057]
[Table 4]

[0058]
[Example 1b]
0.3 dm in Example 1a ² 0.3 dm 42 alloy test piece ² The plating was performed in the same manner as in Example 1a except that the test piece was made of copper.
The results are shown in Example 1b of Table 4. Although the Cu content and the Ag content in the coating have not been measured, it is considered that they have substantially the same composition as in Example 1a.
All the test results were almost the same as those of Example 1a except that the bonding strength with the glass epoxy copper-coated test substrate was very good, and the test passed.
[0059]
[Example 2]
The current density of the DC waveform in Example 1a was 5.0 A / dm. ² The plating was performed in the same manner as in Example 1a, except that the surface shape was substantially the same as that in Example 1a when observed with an electron microscope even when the plating was performed with changing the current density. The plating was smooth and had a smooth surface.
[Example 3]
The current density of the DC waveform in Example 1a was 10.0 A / dm. ² The plating was performed in the same manner as in Example 1a, except that the surface shape was observed by an electron microscope, and the surface shape was substantially the same as in Example 1a. I was
[Example 4]
The current density of the DC waveform in Example 1a was 15.0 A / dm. ² The plating was performed in the same manner as in Example 1a, except that the surface shape was observed by an electron microscope, and the surface shape was substantially the same as in Example 1a. I was
From the results of Examples 1 to 4, the electrolytic plating method of the present invention using the plating solution of the present invention can cope with a wide range of current density, and even if there is some variation in current density, there is no variation. It can be seen that plating is possible.
[0060]
[Example 5]
Next, an experiment was performed to obtain bright plating. In order to obtain bright plating, a brightener was added to the plating solution, and plating was performed using a pulse current waveform (period: 0.1 seconds: 0.05 seconds on, 0.05 seconds off) as the current waveform.
To the plating solution a used in Example 1a, 5 mL / L of brightener 1 (brightener S-2 manufactured by Dipsol) and 20 mL / L of brightener 2 (brightener S-3 manufactured by Dipsol) were added. Thus, a plating solution d was prepared. Using this plating solution d, the current density was 11.6 A / dm. ² The plating was performed in the same manner as in Example 1a except that the current waveform was changed to a pulse current waveform. As a result, a glossy plating film (8 μm) having a good appearance was obtained in a plating time of 216 seconds.
The composition and melting point of the obtained plating film were measured in the same manner as in Example 1a, and the appearance and the solder wettability were tested. Further, soldering with the test substrate was performed by the above-described method, and the bonding strength was measured. The results are shown in Example 5 of Table 4.
The composition of the plating film was 3.0% by weight of silver, 0.50% by weight of copper, and the balance was tin, and the melting point was 218 ° C. Both solder wettability and bonding strength were good.
[0061]
[Example 6a]
Further, the plating solution used in Example 1a was supplied with a current density of 5.8 A / dm. ² When a 42-alloy test piece was plated with a current waveform of a direct current waveform and a constant plating temperature of 25 ° C. for a plating time of 216 seconds, a plating film of about 8 μm was obtained. The composition of the plating film was 0.50% by weight of copper, 3.0% by weight of silver, and the balance being tin. The appearance, melting point, and solder wettability of the obtained plating film were measured or tested in the same manner as in Example 1a. Soldering was performed in the same manner as in Example 1a, and the bonding strength was measured. The bonding strength was 21.5N. Further, as a whisker test (see the growth of the beard in order to avoid short-circuiting when plating the cat's whisker-like tin to extend it), leave it at 25 ° C and 40% humidity for 80 days and 320 days. After that, the surface was observed with a 40 × optical microscope. The results are shown in Example 6a of Table 4. No whiskers appeared after leaving for 80 days or 320 days. The appearance and solder wettability were acceptable, and the melting point was low at 217 ° C.
[Example 6b]
Plating was performed in the same manner as in Example 6a, except that the test piece (42 alloy) in Example 6a was replaced with a copper test piece. The results are shown in Example 6b of Table 4.
The appearance was almost the same as that of Example 6a except that the bonding strength was 27.8 and the solder wettability was slightly deteriorated. A whisker test was performed under the same conditions as in Example 6a, but no whisker appeared after leaving the apparatus for 80 days or 320 days. The coating composition is also considered to be substantially the same as in Example 6a.
[0062]
[Table 5]

[0063]
[Comparative Example 1]
Using a conventional plating solution b (shown in Table 2) containing 0.2 mol / L as tin ions, 0.0025 mol / L as cupric ions, and 0.01 mol / L as silver ions, Examples 1a and Plating was performed in the same manner.
The composition of the obtained plating film was measured in the same manner as in Example 1a, and the appearance was examined. The results are shown in Comparative Example 1 in Table 5. The plating film surface was unacceptable due to poor appearance with blackish appearance.
[0064]
[Comparative Example 2]
Using a conventional plating solution c (shown in Table 3) containing 0.1968 mol / L as tin ions, 0.0026 mol / L as cupric ions, and 0.00066 mol / L as silver ions, Examples 1a and Plating was performed in the same manner.
The composition of the obtained plating film was measured in the same manner as in Example 1a, and the appearance was examined. The results are shown in Comparative Example 2 in Table 5.
The plating film surface was unacceptable due to poor appearance with blackish appearance.
[Comparative Example 3]
The current density in Comparative Example 1 was 3 A / dm. ² The plating was performed in the same manner as in Comparative Example 1 except that the plating time was changed. As a result, the plating time for forming an 8 μm coating film was increased to 234 seconds.
The composition and melting point of the obtained plating film were measured in the same manner as in Example 1a, and the appearance and the solder wettability were tested. Furthermore, soldering was performed and the bonding strength was measured. The results are shown in Comparative Example 3 in Table 5.
The composition of the plating film was 1.96% by weight of silver, 0.50% by weight of copper, and the balance was tin. The appearance of the coating was acceptable, but the bonding strength was weaker than in Example 1a, and the melting point was high at 227 ° C.
[0065]
[Comparative Example 4]
The current density in Comparative Example 2 was 3 A / dm. ² The plating was performed in the same manner as in Comparative Example 2 except that the plating time was changed to a longer plating time of 289 seconds for forming an 8 μm film.
The composition and melting point of the obtained plating film were measured in the same manner as in Example 1a, and the appearance and the solder wettability were tested. Furthermore, soldering was performed and the bonding strength was measured. The results are shown in Comparative Example 4 in Table 5.
The composition of the plating film was 0.32% by weight of silver, 0.8% by weight of copper, and the balance was tin, and the melting point was as high as 230 ° C. The appearance was good, but the bonding strength was 22.1 N, which was lower than that of Example 1a.
[0066]
[Comparative Example 5a]
Using a plating solution containing tin and silver as another lead-free plating solution, a tin-silver alloy (96.6% by weight of tin, 3.4% of silver) was applied to a 42 alloy test piece in the same manner as in Example 6a. (% By weight), and the resulting plated film was measured or tested for appearance and solder wettability in the same manner as in Example 1a.
Further, soldering was performed in the same manner as in Example 1a, the bonding strength was measured, and a whisker test was performed under the same conditions (25 ° C., 40% humidity) as in Example 6a. No whiskers were seen after leaving for 80 days or 320 days. The results are shown in Comparative Example 5a of Table 5. Although the appearance and the solder wettability were acceptable, the bonding strength was weak at 20.5 N and the melting point was high at 221 ° C.
[0067]
[Comparative Example 6a]
In the same manner as in Example 6a, using a plating solution containing tin and copper as another lead-free plating solution, a tin-copper alloy (98.5% by weight of tin, 1.5% by weight of copper) was added to a 42 alloy test piece. %), And the appearance and solder wettability of the resulting plating film were measured or tested in the same manner as in Example 1a. Further, soldering was performed in the same manner as in Example 1a, the bonding strength was measured, and a whisker test was performed under the same conditions as in Example 6a. Table 5 shows the results. No whiskers were seen even after leaving for 80 days or 320 days. Although the appearance was good, the bonding strength was weak at 19.3 and the melting point was as high as 227 ° C.
[0068]
[Comparative Example 7a]
In the same manner as in Example 6a, using a plating solution containing tin and bismuth as another lead-free plating solution, a tin-bismuth alloy (97.0% by weight of tin, 3.0% by weight of bismuth) was added to a 42 alloy test piece. %), And the appearance and solder wettability of the resulting plating film were measured or tested in the same manner as in Example 1a. Further, soldering was performed in the same manner as in Example 1a, the bonding strength was measured, and a whisker test was performed under the same conditions as in Example 6a. Table 5 shows the results. No whiskers were seen even after leaving for 80 days or 320 days. Although the appearance was good, the bonding strength was weak at 19.9 and the melting point was high at 226 ° C.
[0069]
[Example 7]
As a seventh embodiment, as shown in FIG. 2A, a solder paste 11 on a glass-epoxy copper-coated test substrate 10 soldered in the above-mentioned embodiment 6b, and a plated copper-made test piece 12 (The molten solder portion between the solder paste 11 and the plating film, hereinafter also referred to as the molten solder portion) 13 was confirmed by mapping (mapping) using EPMA (Electron Probe X-ray Microanalyzer).
For the solder paste 11, a tin-silver-copper alloy (tin 96.5% by weight, silver 3.0% by weight, copper 0.5%) having a composition close to the eutectic point is used. In the molten solder portion 13 with the tin-silver-copper-containing plating film of FIG. 2, as shown in FIG. Ag between ₃ It seems that the Sn network (network structure) 14 has been formed. In addition, 15 of FIG. 2 shows air.
[0070]
[Comparative Example 5b]
As another lead-free plating solution, the same plating solution as in Comparative Example 5a containing tin and silver was used, and in the same manner as in Example 6b, a tin-silver alloy (tin 96.6% by weight) was applied to a copper test piece. , 3.4% by weight of silver). The appearance and solder wettability of the obtained plating film were measured or tested in the same manner as in Example 1b. Further, a whisker test was performed under the same conditions as in Example 6a. The results are shown in Comparative Example 5b of Table 5. No whiskers were seen even after leaving for 80 days or 320 days. Although there were no problems in appearance, solder wettability, and bonding strength, the melting point was slightly higher at 221 ° C.
Further, soldering was performed in the same manner as in Example 1b, the bonding strength was measured, and the Ag distribution of the molten solder portion 13 of the plated film and the solder paste was measured for the plated film in the same manner as in Example 7. The state was confirmed by EPMA mapping. The results are shown in FIG.
[0071]
[Comparative Example 6b]
As another lead-free plating solution, a tin-copper alloy (98.5% by weight of tin, 1.5% by weight of copper) was prepared in the same manner as in Example 6b, using the same plating solution as in Comparative Example 6a containing tin and copper. %) And a test was conducted as in Comparative Example 5b. Further, a whisker test was performed under the same conditions as in Example 6a. The results are shown in Comparative Example 6b of Table 5. Whiskers were not observed after 80 days, but needle-like crystals were observed after 320 days. Although there was no problem in appearance, solder wettability, and bonding strength, the melting point was slightly higher at 227 ° C.
With respect to the plating film, in the same manner as in Example 7, the Ag distribution state of the molten solder portion 13 between the soldered plating film and the solder paste was confirmed by EPMA mapping. The results are shown in FIG.
[0072]
[Comparative Example 7b]
As another lead-free plating solution, a tin-bismuth alloy (97.2% by weight of tin, 2.8% by weight of bismuth) was prepared in the same manner as in Example 6b using the same plating solution as in Comparative Example 7a containing tin and bismuth. %) And a test was conducted as in Comparative Example 5b. The results are shown in Comparative Example 7b of Table 5. Although the solder wettability and appearance were good, the melting point was as high as 226 ° C., and as a result of the whisker test, needle-like crystals were observed on the surface after standing for 320 days.
In the same manner as in Example 7, the Ag distribution state of the molten solder portion 13 to which the plated coating was applied was confirmed by mapping using EPMA. The results are shown in FIG.
As shown in FIG. 2, with respect to the molten solder portion 13 of the Sn-Ag plating film, the Sn-Cu plating film, or the Sn-Bi plating film and the solder, the silver was patchy in the molten solder portion 13. , Ag as seen in the case of Sn-Ag-Cu plating film ₃ The existence of the Sn network could not be inferred. Generally Ag ₃ Since the Sn network is said to enhance the bondability between the substrate and the plating film, it is considered that the tin-silver-copper-containing plating film of the present invention also exhibits strong bondability with the substrate.
[0073]
Next, the solder wettability was compared.
As shown in Table 4, the solder wettability of the tin-silver-copper-containing plating film of the present invention on a test piece of 42% by weight of Ni and 58% by weight of Fe (42 alloy) was evaluated for the film immediately after plating. It was almost good even after the rigorous conditions of 4 hours with saturated steam.
[0074]
The conventional Sn-Ag plating films shown in Comparative Examples 5a and 5b in Table 5, the conventional Sn-Cu plating films shown in Comparative Examples 6a and 6b, and the conventional Sn-Bi plating films shown in Comparative Examples 7a and 7b are 42 alloys. In each case, the bonding strength was low, and the melting point was higher than that of the present example in the case of plating either a 42 alloy or a copper plate.
In addition, whiskers were not observed in the whisker test in any of the plating films of the present invention, but the conventional Sn-Bi, conventional Sn-Bi or Sn-Cu plating solution was used to plate copper, and further to the conventional brass test piece. When the Sn—Bi and Sn—Cu plating films were left under the same conditions at 25 ° C. and a humidity of 40% for 320 days, needle crystals were formed.
Furthermore, the results of comparing the mountability of the tin-silver-copper-containing plating film of the present invention with the lead frame and the substrate soldered by the method described in Example 1a also show the tin-silver-copper-containing plating film of the present invention. Was completely melted and soldered to the substrate, but the Sn-Ag, Sn-Bi, and Sn-Cu plating films of the conventional product were soldered unmelted to the 42 alloy of the substrate.
[0075]
From the above results, it was found that the plating film using the plating solution of the present invention was superior in appearance, bonding strength and solder wettability as compared with other lead-free types. In particular, the tin-silver-copper-containing plating of the present invention is applied to a solder using a tin-silver-copper alloy having a composition close to the eutectic point, which is used as a base solder of a lead-free solder material (solder paste) in recent years. It turns out that the coating is very suitable.
As shown in the above results, the plating film plated on the 42 alloy or copper plate using the plating solution a of the present example has a good appearance and good bonding strength when plated on either the 42 alloy or the copper plate. The solder wettability was also substantially good.
Also, when a brightener is added to the plating solution a of the present embodiment and plating is performed using a pulse current waveform as a current waveform, a plated film having gloss, good appearance, good solder wettability, and good bonding strength is obtained. Was done.
In addition, the plating solution of the present invention is 4 dm. ² It has been found that stable plating is possible even at the above-mentioned high current density, and it is also applicable to high-speed plating.
Furthermore, both have a melting point of 217 ° C. and 218 ° C. close to the eutectic point of tin, silver and copper, so that soldering can be performed at a low temperature as shown in the schematic diagram of the soldering temperature in FIG. It became.
[0076]
Next, in order to check the aging stability of the plating solutions a to c, the appearance and the absorbance immediately after the bathing and one month later were compared. The absorbance was measured by irradiating light having a wavelength of 660 nm to a quartz cell to set a measurement point, and then continuously irradiating light from 800 to 400 nm to measure the absorbance. Table 6 shows the results at a wavelength of 660 nm.
[0077]
[Table 6]

[0078]
As shown in Table 6, the plating solution a was transparent and did not change its appearance immediately after the bathing and one month after, and the absorbance after one month was not as high as 0.029. Was done. On the other hand, as for the conventional plating solution b, the appearance immediately after the bathing was poor and the solution was turbid. Similarly, the appearance of the conventional plating solution c after one month was poor, and both were poor in stability.
From the above results, it can be seen that the plating solution of this example has good storage stability.
[0079]
【The invention's effect】
The tin-silver-copper-containing plating film of the present invention, the laminate having the plating film, and the electronic component having the laminate can have a low melting point and a low heating temperature at the time of mounting, and are bonded to the solder material. Sometimes a strong alloy can be formed.
The tin-silver-copper-containing plating solution and the electrolytic plating method of the present invention can form a plating film having a melting point close to the eutectic point of a tin-silver-copper alloy.
The soldering method of the present invention heat-bonds a substrate provided with a solder material close to the eutectic point of a tin-silver-copper alloy and an electronic component covered with a plating film having a composition similar to the solder material. Therefore, it is possible to perform soldering at a low temperature at the same time as having very good bonding properties, to prevent damage to electronic components due to heat, and to reduce energy consumption.
The electronic circuit of the present invention has high reliability because of high bonding strength.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a soldering temperature for evaluating heat resistance of components.
FIG. 2 is a comparison diagram of an Ag distribution state of a molten solder portion for each plating type.
[Explanation of symbols]
10: Copper-coated test board, 11: Solder paste, 12: Copper test piece, 13: Boundary, 14: Ag ₃ Sn network (network structure), 15: air

Claims (19)

A plating solution containing a sulfonic acid, tin ions, copper ions, and silver ions in a medium mainly composed of water, wherein tin-silver-copper-containing silver ions having a concentration of 0.01 to 0.1 mol / L is contained. Plating solution. 2. The tin-silver-copper-containing plating solution according to claim 1, wherein the concentration of the tin ions is 0.21 to 2 mol / L, and the concentration of the copper ions is 0.002 to 0.02 mol / L. Copper-containing plating solution. The tin-silver-copper-containing plating solution according to any one of claims 1 and 2, wherein a molar ratio of the concentration of the silver ion to the concentration of the copper ion is in a range of 4.5 to 5.58. Tin-silver-copper-containing plating solution. The tin-silver-copper-containing plating solution according to any one of claims 1 to 3, wherein the concentration of the sulfonic acids is 0.5 to 5 mol / L. The tin-silver-copper-containing plating solution according to any one of claims 1 to 4, further comprising a mercaptan compound. The tin-silver-copper-containing plating solution according to any one of claims 1 to 5, further comprising an aromatic amino compound. The tin-silver-copper-containing plating solution according to any one of claims 1 to 6, further comprising a nonionic surfactant. The plating method using the tin-silver-copper-containing plating solution according to any one of claims 1 to 7, wherein a current density at the time of plating is 0.01 to 50 A with respect to a metal base material to be plated. / dm ² a is electrolytic plating method. 9. The electrolytic plating method according to claim 8, wherein the current waveform during plating is a pulse current waveform. 9. The electrolytic plating method according to claim 8, wherein a current waveform during plating is a DC waveform. A tin-silver-copper-containing plating film having a silver content of 2.6 to 3.4% by weight, a copper content of 0.4 to 0.7% by weight, and the balance substantially tin. . The tin-silver-copper-containing plating film according to claim 11, wherein the coating thickness is 3 to 20 μm. A plating film obtained by performing electroplating using the tin-silver-copper-containing plating solution according to any one of claims 1 to 7, wherein the silver content is 2.6 to 3.4 weight. %, The content of copper is 0.4 to 0.7% by weight, and the balance is substantially tin. The tin-silver-copper-containing plating film. It is a tin-silver-copper-containing plating film obtained by the electrolytic plating method according to any one of claims 8 to 10, wherein the silver content is 2.6 to 3.4% by weight, and A tin-silver-copper-containing plating film having a content of 0.4 to 0.7% by weight and a balance of substantially tin. The tin-silver-copper-containing plating film according to any one of claims 11 to 14, on a metal substrate made of any one of copper, nickel, iron, and an alloy containing one or more of these. Laminate. An electronic component comprising the laminate according to claim 15. 17. The electronic component according to claim 16, comprising an alloy having a silver content of 2 to 4% by weight, a copper content of 0.3 to 0.8% by weight, and the balance being substantially tin. An electronic circuit in which an electronic circuit board provided with a solder material is heated and joined. 17. The electronic component according to claim 16, comprising an alloy having a silver content of 2 to 4% by weight, a copper content of 0.3 to 0.8% by weight, and the balance being substantially tin. A soldering method characterized by heating and joining in a state in which a substrate provided with a solder material is in contact with the substrate. 19. The soldering method according to claim 18, wherein a maximum temperature of the electronic component and the substrate at the time of heating and joining is in a range of 220 to 260C.

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