JP2004332035A - Electroless nickel-gold plating method - Google Patents
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- JP2004332035A JP2004332035A JP2003128287A JP2003128287A JP2004332035A JP 2004332035 A JP2004332035 A JP 2004332035A JP 2003128287 A JP2003128287 A JP 2003128287A JP 2003128287 A JP2003128287 A JP 2003128287A JP 2004332035 A JP2004332035 A JP 2004332035A
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【０００１】
【発明の属する技術分野】
本発明は、無電解ニッケル−金めっき方法に関する。
【０００２】
【従来の技術】
従来から、プリント配線板上に形成された例えば銀又は銅等からなる導体パターン上にのみ選択的にニッケル−金めっき皮膜を形成する方法として、電解めっき法と無電解めっき法が広く知られている。これらのうち、電解めっき法が、処理コスト及び浴安定性の観点で有利であることから、主として採用されている。
【０００３】
一方、近年においては、半導体デバイス等の配線基板への電子回路の実装を、より高集積化及び／又は極微細化する必要性が生じてきている。しかし、上記電解めっき法は、電源リードに対する設計上の制約があり、また、孤立パターン上へのめっき皮膜の形成が比較的困難であるため、上記要求に対応できない場合が生じている。従って、今後はこのような点で有利である無電解めっき法に対する必要性が高まるものと予想される。
【０００４】
この無電解めっき法によるニッケル−金めっきは、従来、概して以下のような工程で行われていた。まず、金属導体部を形成したプリント配線板を、脱脂液に浸漬し、続いて酸洗浄した後、無電解めっきの核となる例えばパラジウム系の触媒を吸着させる。その後、該配線板を無電解ニッケルめっき液、置換金めっき液、及び無電解金めっき液に順次浸漬して、所望のニッケル−金めっき皮膜で金属導体部を被覆したプリント配線板を得る。そして、各工程の合間には数分間の流水洗浄処理が行われるので、先の工程で用いた液が後の工程で用いる液に混入することはない。
【０００５】
一方、上述のような工程により無電解ニッケル−金めっき皮膜が形成されるより前に金属導体パターンが基板上に形成されるが、その形成方法は、主としてエッチング法或いは印刷法によるものである。このような方法を用いた場合、所望の導体パターン領域からはみ出した位置に、微量の金属導体部が形成される場合がある。しかし、従来の無電解めっき法では、このはみ出した金属導体部のみを選択的に除去することができないだけではなく、はみ出した該金属導体部上にめっきが析出してしまうこともあった（以下、この析出を「異常析出」という。）。
【０００６】
上記異常析出は、特に無電解金めっき工程の段階で起こり、最終的に得られる無電解ニッケル−金めっき製品の歩留まりを低下させる要因となっていた。このめっきの析出は、詳細なメカニズムについてはまだ解明されていないが、概ね以下のことが原因と考えられている。すなわち、導体パターン領域からはみ出した位置に形成された微量の金属導体部が、後の工程で浸漬される無電解ニッケルめっき液中の下記の金イオン由来の化学種の析出反応に対して活性な状態となる。そして、その後の無電解金めっき工程において、無電解金めっき液に長時間浸漬されることにより、該めっき液中の金イオン由来の化学種が活性な状態にある金属導体部の表面に金となって徐々に析出するものと考えられる。
【０００７】
このような所望の導体パターン領域以外の位置に析出した金めっきを除去する方法として、例えば特許文献１では、置換金めっき液に配線板を浸漬した後であって、無電解金めっき液に該配線板を浸漬する前に、シアン化合物を含有する溶液で処理することにより、所望の導体パターン領域以外の位置に析出した置換金めっきを選択的に除去する方法が提案されている。
【０００８】
更に、特許文献２には、無電解金めっき液自体に非イオン性界面活性剤及び／又は非イオン性ポリマーを添加することにより、導体パターン領域以外の位置への異常析出の防止を意図した無電解金めっき液自体の特性の改善方法について提案されている。
【０００９】
また、特許文献３では、シアン含有無電解金めっき液自体にニトロベンゼンスルホン酸ナトリウム及び／又はｐ−ニトロ安息香酸を添加することにより、導体パターン領域以外の位置への異常析出の防止を意図した無電解金めっき液自体の特性の改善方法について提案されている。
【００１０】
そして、特許文献４には、シアン含有無電解金めっき液自体にジメチルアミンを添加することにより、導体パターン領域以外の位置への異常析出の防止を意図した無電解金めっき液自体の特性の改善方法について提案されている。
【００１１】
【特許文献１】
特開平０９−２３５６７８号公報
【特許文献２】
特開平０６−２８００３９号公報
【特許文献３】
特開平０８−０６０３７７号公報
【特許文献４】
特開平０８−０６０３７８号公報
【００１２】
【発明が解決しようとする課題】
しかしながら、本発明者らは、上記特許文献１〜４に記載の従来の無電解ニッケル−金めっき方法について詳細に検討を行ったところ、いずれの方法も導体パターン領域からはみ出して形成された微量の金属導体部上に析出した金めっきを十分に除去できていないことを見出した。
【００１３】
すなわち、特許文献１にかかる方法は、所望の導体パターン領域に形成された金属導体部から、いわゆる「めっき広がり（金広がり）」により該領域以外の位置にはみ出して形成された金めっきを選択的に除去する方法であって、所望の導体パターンからはみ出した位置に形成された微量の金属導体部上に析出した金めっきを十分に除去できていないことを本発明者らは見出した。また、シアン化合物を用いる特許文献１に記載の方法は、シアン化合物を１〜１００ｇ／Ｌ含有する処理液を使用するため、かかる高濃度のシアン化合物溶液を用いると所望パターン上に析出された置換金めっき皮膜をも溶解してしまう点、及びシアン化合物の毒性が強い点でも問題があることを本発明者らは見出した。
【００１４】
更に、特許文献２〜４に記載の方法は、いずれも金属導体部上にのみ置換金めっき皮膜を形成するため、「めっき広がり」を抑制するという点では優れているものの、所望パターン領域からはみ出した位置に形成された金属導体部上への金めっき皮膜の形成までも抑制できるものではないことを、本発明者らは見出した。
【００１５】
そこで、本発明は上記事情に鑑みてなされたものであり、めっきを施されるべき導体パターン領域からはみ出した位置に微量の導体部が形成されていても、該微量の導体部上にはめっき皮膜を形成せず、前記導体パターン領域内に形成された導体部上にのみ選択的にめっき皮膜を形成する無電解ニッケル−金めっき方法を提供することを目的とする。
【００１６】
【課題を解決するための手段】
本発明者らは、上記目的を達成すべく鋭意研究を重ねた結果、無機硫黄化合物が金属導体部の縁端部上への金めっきの析出のみを選択的に抑制する作用を有することを見出し、本発明を完成するに至った。
【００１７】
すなわち、本発明の無電解ニッケル−金めっき方法は、基体に形成された導体部上に無電解ニッケルめっき皮膜を形成する無電解ニッケルめっき工程と、該無電解ニッケルめっき皮膜上に置換金めっき皮膜を形成する置換金めっき工程と、更に前記置換金めっき皮膜上に無電解金めっき皮膜を形成する無電解金めっき工程と、を含む無電解ニッケル−金めっき方法であって、前記無電解ニッケルめっき工程と前記置換金めっき工程との間に、無機硫黄化合物を含有する水溶液を用いて、前記無電解ニッケルめっき工程により得られた被めっき物を処理する硫黄処理工程を含むことを特徴とする。
【００１８】
上記硫黄処理工程を設けることにより本発明の目的が達成される理由については、明確には解明されていないが、本発明者らは以下のように考えている。
【００１９】
すなわち、本発明の無電解ニッケル−金めっき方法は、微量の金属導体部上にいわゆる触媒毒として作用する無機硫化物由来の硫黄を金めっきより先の段階で吸着させることにより、該微量の金属導体部上への金めっきの形成を阻害する。一方、所望導体パターン領域内の金属導体部上には相対的に少量の硫黄しか吸着させないため、該所望導体パターン領域の金属導体部上への金めっき皮膜の形成にほとんど影響を与えないものと考えられる。
【００２０】
また、上記導体部の材料は、電気の良導体である金属導体であることが好ましく、その中でも特に導電率の高い銀又は銅であることが更に好ましい。
【００２１】
そして、基体は、絶縁性の高いセラミックス基体であることが好ましい。
【００２２】
また、上記無機硫黄化合物は、硫化カリウム、硫化ナトリウム九水和物及び硫化アンモニウムからなる群より選ばれる少なくとも１種の化合物であることが好ましい。これらの無機硫黄化合物は、比較的迅速且つ容易に金属導体部を硫黄で被毒させる傾向にあるので、工程の短縮化等に繋がる。この中でも、比較的有害性又は腐食性の強くない硫化カリウムが、取り扱いの観点から特に好ましい。
【００２３】
更に、前記水溶液中の前記無機硫黄化合物の濃度が硫化物イオン（Ｓ２−）濃度として０．１〜５０ｍｇ／Ｌであると好ましい。
【００２４】
また、置換金めっき工程又は無電解金めっき工程において、シアン化合物を含有しない金めっき液を用いることが好ましい。
【００２５】
【発明の実施の形態】
以下、本発明の好適な実施形態について詳細に説明する。
【００２６】
本発明の無電解ニッケル−金めっき方法は、基体に形成された導体部上に無電解ニッケルめっき皮膜を形成する無電解ニッケルめっき工程と、該無電解ニッケルめっき皮膜上に置換金めっき皮膜を形成する置換金めっき工程と、更に前記置換金めっき皮膜上に無電解金めっき皮膜を形成する無電解金めっき工程と、を含む無電解ニッケル−金めっき方法であって、前記無電解ニッケルめっき工程と前記置換金めっき工程との間に、無機硫黄化合物を含有する水溶液を用いて、前記無電解ニッケルめっき工程により得られた被めっき物を処理する硫黄処理工程を含むことを特徴する。
【００２７】
（前処理）
本発明の無電解ニッケル−金めっき方法では、従来のめっき方法と同様に、前処理として脱脂、酸洗浄及び触媒付与を行うことができる。従って、概して以下のような前処理を行った後に各めっき工程を行ってもよい。すなわち、セラミックス製又は樹脂製等の基板上に銀又は銅等の材料を用いた導体パターンを印刷法又はエッチング法等により形成して得られた配線板を、まず脱脂液浸漬して、表面の油脂汚れ等を除去する。続いて該配線板を水洗後、導体パターンの表面を均一化するために、通常は、硫酸過酸化水素水溶液等のエッチング液で該表面をマイルドエッチングする。更に水洗後、希硫酸水溶液等を用いて該配線板の表面を洗浄する。次に水洗後、例えば置換タイプのパラジウム触媒液等で該配線板の導体パターン上にのみ触媒を形成させる。
【００２８】
（無電解ニッケルめっき工程）
無電解ニッケルめっき工程は、上述の前処理終了後に水洗された配線板を無電解ニッケルめっき液に浸漬することにより行われる。
【００２９】
無電解ニッケルめっき液は、従来用いられていたものであれば特に限定されない。従って、例えば、該無電解ニッケルめっき液は、塩化ニッケル若しくは硫酸ニッケル等のニッケルイオン源及び次亜りん酸塩若しくはアミンホウ素化合物等の還元剤に加えて、クエン酸、マロン酸若しくは酒石酸等の有機酸或いはその塩等の錯化剤、又はその他のｐＨ調整剤等の通常用いる各種添加剤を適量含むことができる。
【００３０】
配線板浸漬時の無電解ニッケルめっき液の温度及び該めっき液への配線板の浸漬時間は、所望の膜厚のニッケルめっき皮膜を得ることができるように、適宜設定することができる。すなわち、ニッケルめっき皮膜を比較的厚くしたい場合は、該めっき液の温度を高めに設定し、及び／又は、配線板の浸漬時間を長くすればよい。逆に、ニッケルめっき皮膜を比較的薄くしたい場合は、該めっき液の温度を低めに設定し、及び／又は、配線板の浸漬時間を短くすればよい。但し、ニッケルめっき皮膜の膜厚はその下側にある導体部が露出しない程度の膜厚である必要がある。
【００３１】
この工程において、配線板の導体パターン上にある触媒及び還元剤の作用により、該触媒上でニッケルイオンが還元されてニッケルめっき皮膜が形成される。
【００３２】
上記無電解ニッケルめっき工程が終了したら、配線板は水洗される。
【００３３】
（硫黄処理工程）
本発明の無電解ニッケル−金めっき方法は、上記水洗後に、本発明の大きな特徴である硫黄処理工程を行う。
【００３４】
本明細書において硫黄処理工程とは、無機硫黄化合物を含有する水溶液（以下、「無機硫黄化合物水溶液」という。）を用いて配線板を処理する工程をいう。具体的な処理工程としては、例えば、配線板を無機硫黄化合物水溶液に浸漬して処理する工程、或いは無機硫黄化合物水溶液を配線板に吹き付けて処理する工程などを挙げることができる。
【００３５】
無機硫黄化合物としては、水溶液中で硫化物イオン（以下、「Ｓ２−」という。）を生成するものが好ましい。従って、例えば、硫化カリウム、硫化ナトリウム九水和物若しくは硫化アンモニウム等の硫化物塩などを用いることができ、これらのうち二以上を混合して用いることもできる。これらの中で、比較的有害性及び腐食性の低い硫化カリウムを用いることが更に好ましい。
【００３６】
また、無機硫黄化合物水溶液中の無機硫黄化合物の濃度は、Ｓ２−濃度に換算して０．１〜５０ｍｇ／Ｌの範囲であることが好ましい。Ｓ２−濃度が０．１ｍｇ／Ｌ未満では、導体パターン領域外に無電解金めっきが異常析出することを抑制する効果がほとんど得られない傾向にある。また、Ｓ２−濃度が５０ｍｇ／Ｌを越えると、水溶液中でのＳ２−の安定性が悪いため、短時間で液の濁りや成分の沈降が起こり使用に適さない傾向にある。
【００３７】
硫黄処理工程における無機硫黄化合物水溶液の温度は特に制限されないが、取り扱いの容易さ等の観点から５〜３５℃であることが好ましい。
【００３８】
また、硫黄処理工程の所要時間は１〜１０分であることが好ましい。硫黄処理時間が１分未満であると、硫黄処理により得られるべき効果を十分に得ることができない傾向にある。また、硫黄処理時間が１０分を超えると、得られるべき効果の大きさに変化が現れない傾向にあるので、それ以上の処理は単なる時間の浪費になってしまい、作業効率が低下する。
【００３９】
本発明の無電解ニッケル−金めっき方法は、置換金めっき工程の前にこの硫黄処理工程を行うことにより、それ以降に行われる置換金めっき工程及び無電解金めっき工程において、配線板上の導体パターン領域からはみ出した位置に形成された微量の導体部上への金めっき皮膜の形成を阻害することができる。この要因の一つとしては、導体パターン領域からはみ出した位置に形成された微量の導体部上に、無機硫黄化合物由来の硫黄又は硫黄化合物が吸着し、該硫黄又は硫黄化合物が、金の該微量の導体部上への吸着を阻害する触媒毒として作用することが考えられる。
【００４０】
一方、該硫黄又は硫黄化合物は、所望の導体パターン領域内にある金属導体部上には相対的に少量しか吸着しないため、該所望の導体パターン領域の金属導体部上への金めっき皮膜の形成をほとんど阻害しないものと考えられる。
【００４１】
なお、上記硫黄又は硫黄化合物の吸着量に差異が生ずる要因の一つとしては、銅体表面へのそれら物質の吸着がいわゆる構造敏感性を有することが考えられる。すなわち導体パターンの縁端部は、導体パターンのその他の部分と比較して、不規則な表面構造（例えば、ステップ、原子欠陥等）を有する傾向にあり、かかる不規則な表面構造上に硫黄又は硫黄化合物が優先的に吸着すると推測される。
【００４２】
（置換金めっき工程）
置換金めっき工程は、上述の硫黄処理を施された配線板を水洗した後、置換金めっき液に浸漬することにより行われる。
【００４３】
置換金めっき液は、ニッケルと該液中の金イオンとの置換反応により、ニッケルめっき皮膜上に金めっき皮膜を形成するために従来用いられていたものであれば特に限定されない。従って、例えば、該置換金めっき液は、シアン化金ナトリウム若しくはシアン化金カリウム等のシアン系金イオン源（シアン化金塩）或いは亜硫酸金塩、チオ硫酸金塩若しくは塩化金塩等の非シアン系金イオン源、亜硫酸塩若しくはカルボン酸塩等の錯化剤、又はその他の置換金めっき液に通常用いる各種添加剤を適量含むことができる。
【００４４】
この置換金めっき液中には、シアン化合物を含有しないことが好ましい。シアン化合物は概して毒性が強いため、その取り扱いが困難である傾向にあり、また、シアン化合物の濃度が高すぎる場合には、それらの金めっき液を浸漬した際に、下地の導体部或いは無電解ニッケル皮膜が溶解する傾向にある。
【００４５】
配線板浸漬時の置換金めっき液の温度は、所望の膜厚の置換金めっき皮膜を得ることができるように適宜設定することができるが、８０〜９０℃程度であることが好ましい。置換金めっき液の温度が８０℃より低いと、金の析出速度が遅くなりすぎる傾向にあり、９０℃より高いと、置換金めっき液が速やかに揮発してしまう、又は該めっき液中の成分が熱分解してしまうため、該液中の金イオンの安定性が著しく低下する傾向にある。
【００４６】
また、置換金めっき液のｐＨは、該めっき液の液安定性又は置換金めっき皮膜の膜厚確保の観点から、シアン系金イオン源を含有する場合は５〜７、非シアン系金イオン源を含有する場合は６〜９であることが好ましい。
【００４７】
そして該めっき液への配線板の浸漬時間は、所望の膜厚の置換金めっき皮膜を得ることができるように、適宜設定することができる。すなわち、置換金めっき皮膜を比較的厚くしたい場合は、配線板の該めっき液への浸漬時間を長くすればよい。逆に、置換金めっき皮膜を比較的薄くしたい場合は、配線板の該めっき液への浸漬時間を短くすればよい。但し、置換金めっき工程を行う際は、ある程度の膜厚（３０〜１００ｎｍ程度）の金めっき皮膜が形成された後は、それ以上の時間浸漬しても該皮膜の膜厚はほとんど変化しない傾向にあるため、これを考慮して製造コスト削減の観点から浸漬時間を設定することが好ましい。
【００４８】
この工程により、配線板は、導体パターン領域上にのみ比較的薄い置換金めっき皮膜を形成され、導体パターン領域からはみ出した位置に形成された導体部上には置換金めっきが析出しない。
【００４９】
更に、導体パターン領域上に形成された置換金めっき皮膜が導体パターン領域外にまではみ出る「めっき広がり」もほとんど認められない。これは、上述の硫黄処理により導体パターン上のニッケルめっき皮膜の縁端部に比較的多くの硫黄が吸着し、その部分上には金めっき皮膜が形成されないので、本来ならその部分に形成された金めっき皮膜から生ずる「めっき広がり」が抑制されるためと考えられる。
【００５０】
（無電解金めっき工程）
無電解金めっき工程は、上述の置換金めっき皮膜を施された配線板を水洗した後、無電解金めっき液に浸漬することにより行われる。
【００５１】
ここで、本明細書における無電解金めっきとは、還元剤の作用により金イオンを金に還元して配線板上にめっき皮膜を析出させることであり、上述した置換金めっきを除外する概念である。
【００５２】
無電解金めっき液は、従来用いられていたものであれば特に限定されない。従って、例えば、該無電解金めっき液は、シアン化金カリウム、亜硫酸金ナトリウム、塩化金酸ナトリウム等の水溶性金イオン源、シアン化物イオン、亜硫酸イオン、チオ硫酸イオン、「塩化物イオン」（Ｃｌ−）等の水溶性イオン源を供給する錯化剤、水素化ホウ素ナトリウム、ジメチルアミンボラン、ヒドラジン、チオ尿素、アスコルビン酸ナトリウム等の還元剤、又はその他のｐＨ調整剤等の通常用いる各種添加剤を適量含むことができる。
【００５３】
この無電解金めっき液には、上述した置換金めっき液と同様の理由により、シアン化合物を含有しないことが好ましい。
【００５４】
配線板浸漬時の無電解金めっき液の温度は、所望の膜厚の無電解金めっき皮膜を得ることができるように適宜設定することができるが、６０〜８０℃程度であることが好ましい。無電解金めっき液の温度が６０℃より低いと、金の析出速度が遅くなりすぎる傾向にあり、８０℃より高いと、該めっき液の液安定性が著しく低下する傾向にある。
【００５５】
また、無電解金めっき液のｐＨは、該めっき液の液安定性等の観点から、シアン系金イオン源を含有する場合は１３以上、非シアン系金イオン源を含有する場合は６〜９であることが好ましい。
【００５６】
本発明においては、無電解金めっき工程が厚膜の金めっきを形成するために、従来の無電解金めっき工程と同様に比較的長時間に亘る処理が必要となるにも関わらず、配線板の導体パターン領域上にのみ無電解金めっき皮膜が形成され、該導体パターン領域からはみ出した位置に形成された金属導体部上へは無電解金めっき皮膜は形成されない。また、置換金めっき工程と同様に、導体パターン領域上に形成された無電解金めっき皮膜が導体パターン領域外にまではみ出る「めっき広がり」もほとんど認められない。
【００５７】
【実施例】
以下、実施例により本発明を更に詳細に説明するが、本発明はこれらの実施例に限定されるものではない。
【００５８】
（実施例１）
本実施例のめっき試験用配線板として、１０ｃｍ×１０ｃｍ×１ｍｍのセラミックス基板上に印刷法により銀ペーストで配線を形成したものを使用した。
【００５９】
最初に、基板の表面の油脂や汚れ等を除去するために、酸性脱脂液ＣＬＣ−５０００（日立化成工業株式会社製、製品名）を５０℃に調整して、その液中に４分間該配線板を浸漬した。更に余分な界面活性剤を除去するために、５０℃の純水で１分間湯洗した後、水洗処理を２分間行った。次に表面の形状を均一化するために、硝酸水溶液（１００ｍＬ／Ｌ）に配線板を浸漬し、室温で３０秒間浸漬処理するソフトエッチング処理を行った後、水洗処理を１分間行った。続いて、表面の酸化膜を除去するために硫酸（１００ｍＬ／Ｌ）に浸漬し、室温で１分間浸漬処理を行い、その後、水洗処理を１分間行った。次に置換パラジウム触媒液ＳＡ−１００（日立化成工業株式会社製、製品名）に浸漬し、室温で５分間浸漬処理を行った後、水洗処理を５分間行い、めっき処理前の配線板を得た。
【００６０】
次に、該配線板を８５℃の無電解Ｎｉ−Ｐめっき液ＮＩＰ−１００（日立化成工業株式会社製、製品名）に浸漬した状態で２５分間維持し、ニッケル−リンの合金めっき皮膜を５μｍ程度形成した。
【００６１】
そして、水洗処理を１分間行った後、該配線板を、硫化カリウム濃度が１．７ｍｇ／Ｌ（Ｓ２−濃度として０．５ｍｇ／Ｌ）である硫化カリウム水溶液に浸漬し、１０℃で２分間硫黄処理を行い、更に水洗処理を１分間行った。
【００６２】
次に該配線板を置換金めっき液ＨＧＳ−１００（日立化成工業株式会社製、製品名）に浸漬し、８５℃で１０分間浸漬処理して、０．０５〜０．１μｍ程度の膜厚の金めっき膜を形成した。
【００６３】
更に該配線板の水洗処理を１分間行った後、最後に無電解金めっきＨＧＳ−５４００（日立化成工業株式会社製、製品名）に浸漬し、６５℃で４０分間浸漬処理して、０．４〜０．６μｍ程度の膜厚の金めっき膜を形成して、所望の配線板を得た。
【００６４】
（実施例２〜１０）
実施例２〜１０においては、上記実施例１の無電解ニッケル−金めっき方法のうち、硫化カリウム濃度（Ｓ２−濃度）、硫黄処理温度及び硫黄処理時間を種々変化させて、実施例１と同様の方法により無電解ニッケル−金めっきを行い、該めっきを施した配線板を得た。実施例１〜１０のそれらの条件についての具体的な数値は表１に示す。
【００６５】
【表１】
（実施例１１〜２０）
実施例１１〜２０においては、無機硫黄化合物として実施例１の硫化カリウムに代えて硫化ナトリウム九水和物を用いた。そして、その水溶液中の濃度、硫黄処理温度及び硫黄処理時間を種々変化させて、実施例１と同様の工程により無電解ニッケル−金めっきを行い、該めっきを施した配線板を得た。実施例１１〜２０のそれらの条件についての具体的な数値は表２に示す。
【００６７】
【表２】
（実施例２１〜２８）
実施例２１〜２８においては、無機硫黄化合物として硫化カリウムを用い、その水溶液中の濃度、硫黄処理温度及び硫黄処理時間を種々変化させて、実施例１と同様の方法により無電解ニッケル−金めっきを行い、該めっきを施した配線板を得た。実施例２１〜２８のそれらの条件についての具体的な数値は表３に示す。なお、これらの実施例のうち実施例２１〜２３は、硫化カリウムの水溶液中の濃度を好ましい範囲から外れた数値に調整したものであり、実施例２４〜２８は、硫黄処理時間を好ましい範囲から外れた数値に調整したものである。
【００６９】
【表３】
（比較例１）
比較例１においては、無電解ニッケルめっき工程の後、硫黄処理工程を行わずに置換金めっき工程及び無電解金めっき工程を行うことにより、無電解ニッケル−金めっきを施した配線板を得た。
【００７１】
［金めっき異常析出評価］
上記実施例１〜２８並びに比較例１の方法で得られた無電解ニッケル−金めっきされた配線板について、導体パターン領域外に金めっき皮膜が形成されているか否かを、実体顕微鏡（１００倍）での視認により調べた。その結果を表１〜３の最下欄に示す。なお、各表中にある評価記号の意味（判定基準）は表４に示すとおりである。
【００７２】
【表４】
これらの表から明らかなとおり、無機硫黄化合物水溶液を用いた硫黄処理工程を介して無電解ニッケル−金めっきされた配線板は、いずれも導体部間のショートが認められなかったのに対し、該硫黄処理工程を行わずに無電解ニッケル−金めっきされた配線板は、部分的に金めっきを経由した導体部間のショートが認められた。そして、硫黄処理工程を行って無電解ニッケル−金めっきされた配線板のうち、無機硫黄化合物の水溶液中濃度が硫黄濃度として０．１〜５０ｍｇ／Ｌの範囲内にあって、且つ硫黄処理時間が１〜１０分間の範囲内にあるものは、導体部間のショートが認められないことはもちろんのこと、所望の導体パターン領域外への金の異常析出も一切認められなかった。
【００７４】
【発明の効果】
以上説明したように、本発明の無電解ニッケル−金めっきの製造方法によれば、めっきすべき導体パターン領域からはみ出した位置に微量の導体部が形成されていても、該微量の導体部上にはめっき皮膜を形成せず、前記導体パターン領域内に形成された導体部上にのみ選択的にめっき皮膜を形成することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electroless nickel-gold plating method.
[0002]
[Prior art]
Conventionally, as a method for selectively forming a nickel-gold plating film only on a conductor pattern made of, for example, silver or copper formed on a printed wiring board, electrolytic plating and electroless plating are widely known. I have. Among these, the electrolytic plating method is mainly employed because it is advantageous in terms of processing cost and bath stability.
[0003]
On the other hand, in recent years, there has been a need to mount electronic circuits on wiring boards such as semiconductor devices with higher integration and / or ultrafineness. However, the above-mentioned electrolytic plating method has limitations in designing power supply leads, and it is relatively difficult to form a plating film on an isolated pattern. Therefore, it is expected that the need for an electroless plating method that is advantageous in this respect will increase in the future.
[0004]
Conventionally, nickel-gold plating by this electroless plating method has been generally performed in the following steps. First, the printed wiring board on which the metal conductor is formed is immersed in a degreasing solution and then washed with an acid, and then, for example, a palladium-based catalyst serving as a core of electroless plating is adsorbed. Thereafter, the wiring board is sequentially immersed in an electroless nickel plating solution, a replacement gold plating solution, and an electroless gold plating solution to obtain a printed wiring board having a metal conductor portion covered with a desired nickel-gold plating film. Since the running water washing process is performed for several minutes between each step, the liquid used in the previous step does not mix with the liquid used in the subsequent step.
[0005]
On the other hand, the metal conductor pattern is formed on the substrate before the electroless nickel-gold plating film is formed by the above-described steps, and the formation method is mainly by an etching method or a printing method. When such a method is used, a small amount of metal conductor may be formed at a position protruding from a desired conductor pattern region. However, in the conventional electroless plating method, not only the protruding metal conductor portion cannot be selectively removed, but also plating may be deposited on the protruding metal conductor portion (hereinafter, referred to as “metal plating”). This precipitation is referred to as “abnormal precipitation”).
[0006]
The abnormal deposition occurs particularly at the stage of the electroless gold plating step, and is a factor that lowers the yield of the finally obtained electroless nickel-gold plated product. Although the detailed mechanism of this plating deposition has not been elucidated yet, it is generally considered that the following is the cause. That is, a trace amount of the metal conductor formed at a position protruding from the conductor pattern region is active against the deposition reaction of the following gold ion-derived chemical species in the electroless nickel plating solution immersed in a later step. State. Then, in the subsequent electroless gold plating step, by being immersed in the electroless gold plating solution for a long time, the gold species on the surface of the metal conductor portion in which the chemical species derived from gold ions in the plating solution are in an active state. It is considered that the precipitate gradually precipitates.
[0007]
As a method for removing the gold plating deposited at a position other than the desired conductor pattern region, for example, in Patent Document 1, after the wiring board is immersed in a replacement gold plating solution, the gold plating is applied to the electroless gold plating solution. A method has been proposed in which, before immersing a wiring board, treatment with a solution containing a cyanide compound to selectively remove the replacement gold plating deposited at a position other than a desired conductor pattern region.
[0008]
Further, Patent Literature 2 discloses a non-electrolytic gold plating solution itself which contains a non-ionic surfactant and / or a non-ionic polymer to prevent abnormal deposition at a position other than the conductor pattern region. A method for improving the characteristics of the electrolytic gold plating solution itself has been proposed.
[0009]
Further, in Patent Document 3, by adding sodium nitrobenzenesulfonate and / or p-nitrobenzoic acid to the cyanide-containing electroless gold plating solution itself, it is intended to prevent abnormal deposition at positions other than the conductor pattern region. A method for improving the characteristics of the electrolytic gold plating solution itself has been proposed.
[0010]
Patent Document 4 discloses that by adding dimethylamine to a cyan-containing electroless gold plating solution itself, the characteristics of the electroless gold plating solution itself intended to prevent abnormal deposition at positions other than the conductor pattern region are improved. A method has been proposed.
[0011]
[Patent Document 1]
JP 09-235678 A
[Patent Document 2]
JP 06-280039 A
[Patent Document 3]
JP-A-08-060377
[Patent Document 4]
JP-A-08-060378
[0012]
[Problems to be solved by the invention]
However, the present inventors have conducted a detailed study on the conventional electroless nickel-gold plating methods described in Patent Documents 1 to 4 above, and found that any of the methods has a trace amount formed by protruding from the conductor pattern region. It was found that the gold plating deposited on the metal conductor was not sufficiently removed.
[0013]
That is, the method according to Patent Document 1 selectively removes gold plating formed by protruding from a metal conductor portion formed in a desired conductor pattern region to a position other than the region by so-called “plating spread (gold spread)”. The present inventors have found that it is not possible to sufficiently remove gold plating deposited on a small amount of a metal conductor portion formed at a position protruding from a desired conductor pattern. Further, the method described in Patent Document 1 using a cyanide compound uses a processing solution containing the cyanide compound in an amount of 1 to 100 g / L. The present inventors have found that there is also a problem in that the gold plating film is also dissolved and that the toxicity of the cyanide compound is strong.
[0014]
Further, the methods described in Patent Documents 2 to 4 are all excellent in suppressing the “plating spread” because the replacement gold plating film is formed only on the metal conductor portion, but they protrude from the desired pattern region. The present inventors have found that it is not possible to suppress the formation of a gold plating film on a metal conductor portion formed at a different position.
[0015]
Accordingly, the present invention has been made in view of the above circumstances, and even if a small amount of conductor is formed at a position protruding from a conductor pattern region to be plated, plating is performed on the minute amount of conductor. An object of the present invention is to provide an electroless nickel-gold plating method for selectively forming a plating film only on a conductor portion formed in the conductor pattern region without forming a film.
[0016]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that an inorganic sulfur compound has an action of selectively suppressing deposition of gold plating only on an edge of a metal conductor portion. Thus, the present invention has been completed.
[0017]
That is, the electroless nickel-gold plating method of the present invention comprises an electroless nickel plating step of forming an electroless nickel plating film on a conductor portion formed on a substrate, and a substitution gold plating film on the electroless nickel plating film. Forming an electroless nickel-gold plating film, and further forming an electroless gold plating film on the replacement gold plating film, wherein the electroless nickel plating method comprises: A sulfur treatment step is provided between the step and the displacement gold plating step, in which an object to be plated obtained in the electroless nickel plating step is treated using an aqueous solution containing an inorganic sulfur compound.
[0018]
The reason why the object of the present invention is achieved by providing the above sulfur treatment step has not been clearly elucidated, but the present inventors think as follows.
[0019]
That is, the electroless nickel-gold plating method of the present invention is characterized in that sulfur from inorganic sulfide acting as a so-called catalyst poison is adsorbed on a small amount of metal conductor at a stage prior to gold plating, whereby the trace amount of metal is removed. Inhibits the formation of gold plating on conductors. On the other hand, since only a relatively small amount of sulfur is adsorbed on the metal conductor portion in the desired conductor pattern region, it hardly affects the formation of the gold plating film on the metal conductor portion in the desired conductor pattern region. Conceivable.
[0020]
The material of the conductor is preferably a metal conductor that is a good conductor of electricity, and more preferably silver or copper, which has particularly high conductivity.
[0021]
The base is preferably a ceramic base having high insulating properties.
[0022]
The inorganic sulfur compound is preferably at least one compound selected from the group consisting of potassium sulfide, sodium sulfide nonahydrate and ammonium sulfide. These inorganic sulfur compounds tend to poison the metal conductor portion with sulfur relatively quickly and easily, leading to shortening of the process and the like. Among them, potassium sulfide, which is not relatively harmful or corrosive, is particularly preferable from the viewpoint of handling.
[0023]
Further, the concentration of the inorganic sulfur compound in the aqueous solution is determined by the sulfide ion (S 2- ) The concentration is preferably 0.1 to 50 mg / L.
[0024]
In the displacement gold plating step or the electroless gold plating step, it is preferable to use a gold plating solution containing no cyanide compound.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail.
[0026]
The electroless nickel-gold plating method of the present invention comprises an electroless nickel plating step of forming an electroless nickel plating film on a conductor portion formed on a base, and forming a displacement gold plating film on the electroless nickel plating film. And electroless nickel-gold plating method, further comprising an electroless gold plating step of forming an electroless gold plating film on the replacement gold plating film, wherein the electroless nickel plating step The method is characterized by including a sulfur treatment step of treating an object to be plated obtained by the electroless nickel plating step using an aqueous solution containing an inorganic sulfur compound, between the displacement gold plating step.
[0027]
(Preprocessing)
In the electroless nickel-gold plating method of the present invention, as in the conventional plating method, degreasing, acid washing, and catalyst application can be performed as pretreatments. Therefore, each plating step may be generally performed after performing the following pretreatment. That is, a wiring board obtained by forming a conductor pattern using a material such as silver or copper on a substrate made of ceramics or resin by a printing method, an etching method, or the like, is first immersed in a degreasing solution, Removes oil and dirt. Subsequently, after washing the wiring board with water, the surface is usually mildly etched with an etching solution such as an aqueous solution of sulfuric acid and hydrogen peroxide in order to make the surface of the conductor pattern uniform. After washing with water, the surface of the wiring board is washed with a dilute sulfuric acid aqueous solution or the like. Next, after washing with water, a catalyst is formed only on the conductor pattern of the wiring board using, for example, a substitution-type palladium catalyst solution.
[0028]
(Electroless nickel plating process)
The electroless nickel plating step is performed by immersing the wiring board, which has been washed with water after the above-described pretreatment, in an electroless nickel plating solution.
[0029]
The electroless nickel plating solution is not particularly limited as long as it has been conventionally used. Therefore, for example, the electroless nickel plating solution may contain an organic source such as citric acid, malonic acid or tartaric acid in addition to a nickel ion source such as nickel chloride or nickel sulfate and a reducing agent such as hypophosphite or an amine boron compound. A proper amount of various commonly used additives such as a complexing agent such as an acid or a salt thereof, and other pH adjusting agents can be contained.
[0030]
The temperature of the electroless nickel plating solution at the time of immersion of the wiring board and the immersion time of the wiring board in the plating solution can be appropriately set so that a nickel plating film having a desired film thickness can be obtained. That is, when it is desired to make the nickel plating film relatively thick, the temperature of the plating solution may be set higher and / or the immersion time of the wiring board may be increased. Conversely, when it is desired to make the nickel plating film relatively thin, the temperature of the plating solution may be set lower and / or the immersion time of the wiring board may be shortened. However, it is necessary that the thickness of the nickel plating film is such that the underlying conductor portion is not exposed.
[0031]
In this step, nickel ions are reduced on the catalyst by the action of the catalyst and the reducing agent on the conductor pattern of the wiring board to form a nickel plating film.
[0032]
After the completion of the electroless nickel plating step, the wiring board is washed with water.
[0033]
(Sulfur treatment process)
The electroless nickel-gold plating method of the present invention performs a sulfur treatment step, which is a major feature of the present invention, after the above-mentioned water washing.
[0034]
In this specification, the sulfur treatment step refers to a step of treating a wiring board using an aqueous solution containing an inorganic sulfur compound (hereinafter, referred to as an “inorganic sulfur compound aqueous solution”). Specific processing steps include, for example, a step of immersing the wiring board in an aqueous solution of an inorganic sulfur compound to perform the processing, or a step of spraying an aqueous solution of the inorganic sulfur compound onto the wiring board to perform the processing.
[0035]
As the inorganic sulfur compound, a sulfide ion (hereinafter referred to as “S 2- " ) Are preferred. Accordingly, for example, sulfide salts such as potassium sulfide, sodium sulfide nonahydrate, and ammonium sulfide can be used, and two or more of these can be used in combination. Among these, it is more preferable to use potassium sulfide having relatively low toxicity and corrosiveness.
[0036]
The concentration of the inorganic sulfur compound in the aqueous solution of the inorganic sulfur compound is S 2- The concentration is preferably in the range of 0.1 to 50 mg / L in terms of concentration. S 2- If the concentration is less than 0.1 mg / L, the effect of suppressing abnormal deposition of electroless gold plating outside the conductor pattern region tends to be hardly obtained. Also, S 2- If the concentration exceeds 50 mg / L, S 2- Is poor in stability, so that turbidity of the liquid and sedimentation of components occur in a short time, which tends to be unsuitable for use.
[0037]
The temperature of the aqueous solution of the inorganic sulfur compound in the sulfur treatment step is not particularly limited, but is preferably 5 to 35 ° C from the viewpoint of easy handling.
[0038]
Further, the time required for the sulfur treatment step is preferably 1 to 10 minutes. If the sulfur treatment time is less than 1 minute, the effect to be obtained by the sulfur treatment tends not to be sufficiently obtained. On the other hand, if the sulfur treatment time exceeds 10 minutes, there is a tendency that no change occurs in the magnitude of the effect to be obtained. Therefore, any further treatment wastes time and reduces the working efficiency.
[0039]
The electroless nickel-gold plating method of the present invention performs the sulfur treatment step before the displacement gold plating step, so that in the subsequent displacement gold plating step and the electroless gold plating step, It is possible to inhibit the formation of the gold plating film on the minute amount of the conductor portion formed at the position protruding from the pattern region. One of the causes is that sulfur or a sulfur compound derived from an inorganic sulfur compound is adsorbed on a trace of a conductor portion formed at a position protruding from the conductor pattern region, and the sulfur or the sulfur compound is reduced to the trace amount of gold. It is conceivable that this acts as a catalyst poison that inhibits the adsorption of the compound on the conductor.
[0040]
On the other hand, since the sulfur or the sulfur compound is relatively little adsorbed on the metal conductor portion in the desired conductor pattern region, formation of a gold plating film on the metal conductor portion in the desired conductor pattern region Is considered to be hardly inhibited.
[0041]
In addition, as one of the factors which cause the difference in the amount of adsorption of the sulfur or the sulfur compound, it is considered that the adsorption of these substances on the surface of the copper body has a so-called structural sensitivity. That is, the edges of the conductor pattern tend to have an irregular surface structure (e.g., steps, atomic defects, etc.) as compared to other portions of the conductor pattern, and sulfur or It is assumed that sulfur compounds are preferentially adsorbed.
[0042]
(Displacement gold plating process)
The replacement gold plating step is performed by rinsing the wiring board subjected to the sulfur treatment described above with water and then immersing the board in a replacement gold plating solution.
[0043]
The replacement gold plating solution is not particularly limited as long as it has been conventionally used to form a gold plating film on a nickel plating film by a substitution reaction between nickel and gold ions in the solution. Therefore, for example, the substituted gold plating solution may be a cyanide-based gold ion source (gold cyanide) such as sodium gold cyanide or potassium gold cyanide, or a non-cyanide such as gold sulfite, gold thiosulfate, or gold chloride. An appropriate amount of a complexing agent such as a systemic gold ion source, a sulfite or a carboxylate, or other additives commonly used in other substituted gold plating solutions can be included.
[0044]
It is preferable that the substituted gold plating solution does not contain a cyanide compound. Cyanide compounds are generally highly toxic and tend to be difficult to handle.If the concentration of the cyanide compound is too high, when the gold plating solution is immersed, the underlying conductor or electroless The nickel coating tends to dissolve.
[0045]
The temperature of the replacement gold plating solution during immersion in the wiring board can be appropriately set so as to obtain a replacement gold plating film having a desired film thickness, but is preferably about 80 to 90 ° C. If the temperature of the replacement gold plating solution is lower than 80 ° C., the deposition rate of gold tends to be too slow. If the temperature is higher than 90 ° C., the replacement gold plating solution will volatilize quickly, or the components in the plating solution Is thermally decomposed, and the stability of gold ions in the liquid tends to be significantly reduced.
[0046]
The pH of the displacement gold plating solution is 5 to 7 when a cyan gold ion source is contained from the viewpoint of the stability of the plating solution or the thickness of the substitution gold plating film, and the non-cyan gold ion source. When it contains, it is preferable that it is 6-9.
[0047]
The immersion time of the wiring board in the plating solution can be appropriately set so that a substituted gold plating film having a desired film thickness can be obtained. That is, when the replacement gold plating film is desired to be relatively thick, the immersion time of the wiring board in the plating solution may be lengthened. Conversely, when the replacement gold plating film is to be made relatively thin, the immersion time of the wiring board in the plating solution may be shortened. However, when performing the displacement gold plating step, after a gold plating film having a certain thickness (about 30 to 100 nm) is formed, the film thickness of the film hardly changes even if it is immersed for a longer time. In view of this, it is preferable to set the immersion time from the viewpoint of manufacturing cost reduction.
[0048]
By this step, the wiring board has a relatively thin substitutional gold plating film formed only on the conductor pattern region, and no substitutional gold plating is deposited on the conductor portion formed at a position protruding from the conductor pattern region.
[0049]
Further, there is almost no "plating spread" in which the replacement gold plating film formed on the conductor pattern region protrudes outside the conductor pattern region. This is because a relatively large amount of sulfur is adsorbed on the edge of the nickel plating film on the conductor pattern by the above-described sulfur treatment, and a gold plating film is not formed on that portion, so it was originally formed on that portion. It is considered that "plating spread" generated from the gold plating film is suppressed.
[0050]
(Electroless gold plating process)
The electroless gold plating step is performed by rinsing a wiring board provided with the above-described substitutional gold plating film with water and then immersing it in an electroless gold plating solution.
[0051]
Here, electroless gold plating in the present specification is to reduce gold ions to gold by the action of a reducing agent to deposit a plating film on a wiring board, and is a concept excluding the above-described substitutional gold plating. is there.
[0052]
The electroless gold plating solution is not particularly limited as long as it has been conventionally used. Therefore, for example, the electroless gold plating solution includes a water-soluble gold ion source such as potassium gold cyanide, sodium gold sulfite, sodium chloroaurate, cyanide ion, sulfite ion, thiosulfate ion, “chloride ion” ( Cl − ), A reducing agent such as sodium borohydride, dimethylamine borane, hydrazine, thiourea, sodium ascorbate, or other commonly used additives such as a pH adjuster. Suitable amounts can be included.
[0053]
It is preferable that the electroless gold plating solution does not contain a cyanide compound for the same reason as the replacement gold plating solution described above.
[0054]
The temperature of the electroless gold plating solution during immersion of the wiring board can be appropriately set so as to obtain an electroless gold plating film having a desired film thickness, but is preferably about 60 to 80 ° C. If the temperature of the electroless gold plating solution is lower than 60 ° C., the deposition rate of gold tends to be too slow, and if it is higher than 80 ° C., the stability of the plating solution tends to be significantly reduced.
[0055]
From the viewpoint of the stability of the electroless gold plating solution, the pH of the electroless gold plating solution is 13 or more when a cyan-based gold ion source is contained, and 6 to 9 when a non-cyanide-based gold ion source is contained. It is preferable that
[0056]
In the present invention, although the electroless gold plating step forms a thick film of gold plating, a process for a relatively long time is required similarly to the conventional electroless gold plating step. The electroless gold plating film is formed only on the conductor pattern region of No. 1, and the electroless gold plating film is not formed on the metal conductor portion formed at a position protruding from the conductor pattern region. Also, as in the displacement gold plating step, almost no “plating spread” in which the electroless gold plating film formed on the conductor pattern region protrudes outside the conductor pattern region is recognized.
[0057]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
[0058]
(Example 1)
As the wiring board for plating test of this example, a wiring board formed of silver paste by a printing method on a ceramic substrate of 10 cm × 10 cm × 1 mm was used.
[0059]
First, in order to remove grease and dirt on the surface of the substrate, an acidic degreasing liquid CLC-5000 (product name, manufactured by Hitachi Chemical Co., Ltd.) was adjusted to 50 ° C., and the wiring was placed in the liquid for 4 minutes. The plate was dipped. Further, in order to remove excess surfactant, the substrate was washed with pure water at 50 ° C. for 1 minute and then washed with water for 2 minutes. Next, in order to make the surface shape uniform, the wiring board was immersed in an aqueous nitric acid solution (100 mL / L), subjected to soft etching treatment of immersion treatment at room temperature for 30 seconds, and then subjected to water washing treatment for 1 minute. Subsequently, in order to remove an oxide film on the surface, the substrate was immersed in sulfuric acid (100 mL / L), immersed at room temperature for 1 minute, and then washed with water for 1 minute. Next, the substrate was immersed in a substituted palladium catalyst solution SA-100 (manufactured by Hitachi Chemical Co., Ltd., product name), immersed at room temperature for 5 minutes, and then washed with water for 5 minutes to obtain a wiring board before plating. Was.
[0060]
Next, the wiring board was immersed in an electroless Ni-P plating solution NIP-100 (product name, manufactured by Hitachi Chemical Co., Ltd.) at 85 ° C. for 25 minutes, and the nickel-phosphorus alloy plating film was 5 μm thick. Degree formed.
[0061]
Then, after performing a water-washing treatment for one minute, the wiring board was washed with a potassium sulfide concentration of 1.7 mg / L (S 2- It was immersed in an aqueous solution of potassium sulfide having a concentration of 0.5 mg / L), subjected to sulfur treatment at 10 ° C. for 2 minutes, and further washed with water for 1 minute.
[0062]
Next, the wiring board is immersed in a replacement gold plating solution HGS-100 (manufactured by Hitachi Chemical Co., Ltd., product name) and immersed at 85 ° C. for 10 minutes to form a film having a thickness of about 0.05 to 0.1 μm. A gold plating film was formed.
[0063]
Further, after performing the water washing treatment of the wiring board for 1 minute, it was finally immersed in electroless gold plating HGS-5400 (product name, manufactured by Hitachi Chemical Co., Ltd.), and immersed at 65 ° C. for 40 minutes. A desired wiring board was obtained by forming a gold plating film having a thickness of about 4 to 0.6 μm.
[0064]
(Examples 2 to 10)
In Examples 2 to 10, the concentration of potassium sulfide (S 2- Concentration), the sulfur treatment temperature and the sulfur treatment time were variously changed, and electroless nickel-gold plating was performed in the same manner as in Example 1 to obtain a plated wiring board. Table 1 shows specific numerical values of those conditions in Examples 1 to 10.
[0065]
[Table 1]
(Examples 11 to 20)
In Examples 11 to 20, sodium sulfide nonahydrate was used as the inorganic sulfur compound instead of the potassium sulfide of Example 1. Then, the concentration in the aqueous solution, the sulfur treatment temperature, and the sulfur treatment time were variously changed, and electroless nickel-gold plating was performed in the same process as in Example 1 to obtain a plated wiring board. Table 2 shows specific numerical values of those conditions in Examples 11 to 20.
[0067]
[Table 2]
(Examples 21 to 28)
In Examples 21 to 28, electroless nickel-gold plating was performed in the same manner as in Example 1, except that potassium sulfide was used as the inorganic sulfur compound and the concentration in the aqueous solution, the sulfur treatment temperature and the sulfur treatment time were variously changed. To obtain a plated wiring board. Table 3 shows specific numerical values of those conditions in Examples 21 to 28. In Examples 21 to 23, the concentration of potassium sulfide in the aqueous solution was adjusted to a value outside the preferred range. In Examples 24 to 28, the sulfur treatment time was adjusted from the preferred range. The values have been adjusted to outliers.
[0069]
[Table 3]
(Comparative Example 1)
In Comparative Example 1, after the electroless nickel plating step, the replacement gold plating step and the electroless gold plating step were performed without performing the sulfur treatment step, thereby obtaining a wiring board subjected to electroless nickel-gold plating. .
[0071]
[Evaluation of abnormal deposition of gold plating]
For the electroless nickel-gold plated wiring boards obtained by the methods of Examples 1 to 28 and Comparative Example 1, it was determined whether or not a gold plating film was formed outside the conductive pattern region by a stereoscopic microscope (100 times magnification). ). The results are shown in the lowermost columns of Tables 1 to 3. The meanings (criteria) of the evaluation symbols in each table are as shown in Table 4.
[0072]
[Table 4]
As is clear from these tables, the electroless nickel-gold plated wiring boards through the sulfur treatment step using the inorganic sulfur compound aqueous solution did not show any short circuit between the conductor parts, whereas In the wiring board plated with electroless nickel-gold without performing the sulfur treatment step, a short circuit between the conductor portions via the gold plating was partially observed. The concentration of the inorganic sulfur compound in the aqueous solution is in the range of 0.1 to 50 mg / L as the sulfur concentration in the electroless nickel-gold plated wiring board after performing the sulfur treatment step, and the sulfur treatment time In the range of 1 to 10 minutes, not only a short circuit between the conductor portions was not observed, but also no abnormal deposition of gold outside the desired conductor pattern region was observed at all.
[0074]
【The invention's effect】
As described above, according to the method for producing electroless nickel-gold plating of the present invention, even if a small amount of conductor is formed at a position protruding from the conductor pattern region to be plated, the small amount of conductor A plating film can be selectively formed only on the conductor portion formed in the conductor pattern region without forming a plating film on the conductor pattern region.
Claims (7)
前記無電解ニッケルめっき工程と前記置換金めっき工程との間に、無機硫黄化合物を含有する水溶液を用いて、前記無電解ニッケルめっき工程により得られた被めっき物を処理する硫黄処理工程を含むことを特徴とする無電解ニッケル−金めっき方法。An electroless nickel plating step of forming an electroless nickel plating film on a conductor portion formed on a base, a substitution gold plating step of forming a substitution gold plating film on the electroless nickel plating film, and the substitution gold plating film An electroless nickel-gold plating method, further comprising: an electroless gold plating step of forming an electroless gold plating film thereon.
Between the electroless nickel plating step and the displacement gold plating step, using an aqueous solution containing an inorganic sulfur compound, including a sulfur treatment step of treating an object to be plated obtained by the electroless nickel plating step An electroless nickel-gold plating method.
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| JP2003128287A JP4059133B2 (en) | 2003-05-06 | 2003-05-06 | Electroless nickel-gold plating method |
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| JP2003128287A JP4059133B2 (en) | 2003-05-06 | 2003-05-06 | Electroless nickel-gold plating method |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20140186521A1 (en) * | 2008-10-02 | 2014-07-03 | E I Du Pont De Nemours And Company | Nickel-gold plateable thick film silver paste, and plating process for low temperature co fired ceramic devices and ltcc devices made therefrom |
| CN106325629A (en) * | 2015-07-06 | 2017-01-11 | 湖州胜僖电子科技有限公司 | ITO wiring design method capable of optimizing separation of chemical plated gold |
-
2003
- 2003-05-06 JP JP2003128287A patent/JP4059133B2/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20140186521A1 (en) * | 2008-10-02 | 2014-07-03 | E I Du Pont De Nemours And Company | Nickel-gold plateable thick film silver paste, and plating process for low temperature co fired ceramic devices and ltcc devices made therefrom |
| CN106325629A (en) * | 2015-07-06 | 2017-01-11 | 湖州胜僖电子科技有限公司 | ITO wiring design method capable of optimizing separation of chemical plated gold |
| CN106325629B (en) * | 2015-07-06 | 2024-01-02 | 湖州胜僖电子科技有限公司 | ITO wiring design method for optimizing electroless gold plating precipitation |
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