JP3697181B2 - Electroless gold plating solution - Google Patents

Description

〔ここで、Ｘは電子供与性置換基を示し、Ｙは電子吸引性置換基を示す。ｍは１≦ｍ≦４の整数であり、ｎは１≦ｎ≦４の整数であり、ｍ＋ｎは２≦ｍ＋ｎ≦６である。ｍが２以上のとき、複数存在するＸは同一であっても異なっていてもよい。また、ｎが２以上のとき、複数存在するＹは同一であっても異なっていてもよい。Ｒは水素原子または芳香族環を示す。〕
上記金塩としては、下記のものが挙げられる。
シアン化第一金カリウム、シアン化第二金カリウム、塩化第一金カリウム、塩化第一金ナトリウム、塩化第二金カリウム、塩化第二金ナトリウム、亜硫酸金カリウム、亜硫酸金ナトリウム、チオ硫酸金カリウム、チオ硫酸金ナトリウム、及びこれらの混合物などである。これらの中では、特にシアン化第一金カリウムおよび亜硫酸金ナトリウムが好ましい。
これらの金塩のメッキ液中での濃度は、一般的には０．１ｇ／Ｌから１００ｇ／Ｌの範囲、好ましくは０．５ｇ／Ｌから２０ｇ／Ｌの範囲である。
【００１５】
上記還元剤としては下記のものが挙げられる。
アスコルビン酸、エリソルビン酸、グリオキシル酸、ギ酸、ギ酸塩、チオ尿素、１−アリル−２−チオ尿素、１−アリル−３−（２−ヒドロキシエチル）−２−チオ尿素、１，３−ジエチル−２−チオ尿素、トリメチルチオ尿素、１，３−ジメチルチオ尿素、１−アセチルチオ尿素、Ｎ−アリルチオ尿素、エチレンチオ尿素、Ｎ−メチルチオ尿素、チオセミカルバジド、チオグリコール酸、チオグリコール酸ナトリウム、ホルムアミンジスルフィン酸、ヒドラジン、Ｐ−ヒドラジンベンゼンスルホン酸、イソニコチン酸ヒドラジド、硫酸ヒドラジン、ジメチルアミノボラン、水素化ホウ素ナトリウム、水素化ホウ素カリウム、ジエチルアミノボラン、トリエチルアミノボラン、ホルマリン、アルコール類、次亜燐酸ナトリウムおよびこれらの混合物などである。これらの中では、特にチオ尿素およびチオ尿素誘導体が好ましい。
これらの還元剤のメッキ液中での濃度は、０．０１ｇ／Ｌから５０ｇ／Ｌの範囲、好ましくは０．３ｇ／Ｌから２５ｇ／Ｌの範囲である。
【００１６】
上記緩衝剤としては下記のものが挙げられる。
アジピン酸、安息香酸、クエン酸、リンゴ酸、コハク酸、酢酸、乳酸、マロン酸、フタル酸、蓚酸、酒石酸、グリシン、グルタミン酸、グルタル酸、イミノ２酢酸、デヒドロ酢酸、マレイン酸等のカルボン酸及びその塩、エチレンジアミン、ヒドロキシルアミン、エタノールアミン、ジエタノールアミン、トリエタノールアミンなどのアミン化合物、ホウ酸、ホウ酸塩、燐酸、リン酸塩、チオ硫酸塩、亜硫酸塩、硝酸塩、塩化物塩、チオシアン酸塩などの無機化合物およびこれらの混合物などである。上記の塩化合物としては、カリウム塩化合物およびアンモニウム塩化合物が好ましい。これらの緩衝剤の中では、特にカルボン酸及びその塩、ホウ酸及びその塩が好ましい。
緩衝剤のメッキ液中での濃度は、５ｇ／Ｌから５００ｇ／Ｌの範囲、好ましくは１０ｇ／Ｌから２５０ｇ／Ｌの範囲である。
【００１７】
上記再生剤としては、下記一般式〔Ｉ〕で示される芳香族化合物が望ましい。
【００１８】
【化３】

〔ここで、Ｘは電子供与性置換基を示し、Ｙは電子吸引性置換基を示す。ｍは１≦ｍ≦４、特に好ましくは１≦ｍ≦２の整数であり、ｎは１≦ｎ≦４、特に好ましくは１≦ｎ≦２の整数であり、ｍ＋ｎは２≦ｍ＋ｎ≦６、特に好ましくは２≦ｍ＋ｎ≦４である。ｍが２以上のとき、複数存在するＸは同一であっても異なっていてもよい。また、ｎが２以上のとき、複数存在するＹは同一であっても異なっていてもよい。Ｒは水素原子または芳香族環を示す。〕
この一般式〔Ｉ〕で示される芳香族化合物において、電子供与性置換基Ｘの好ましい具体例としては、水酸基、アミノ基、アルキル基およびアルコキシ基を例示することができる。本発明では特に水酸基が好ましい。電子吸引性置換基Ｙの好ましい具体例としては、ハロゲン（特にＣｌ）、スルホン酸基、スルホン酸塩（特にナトリウム塩、カリウム塩）、ニトロ基、カルボニル基およびカルボキシル基を例示することができる。本発明では特にスルホン酸基またはスルホン酸塩が好ましい。芳香族環中の電子供与性置換基Ｘおよび電子吸引性置換基Ｙに置換されていない残りの炭素原子には水素原子（Ｒ）が結合しているか、当該炭素原子が隣接するときは当該隣接するこの２つの炭素原子はこれらの２炭素原子を共有して縮合環を構成する別の芳香族環（Ｒ）を形成していてもよい。
【００１９】
ここでいう、電子吸引性置換基とは、それが結合している芳香族環から電子を置換基の方に引っ張る傾向のある置換基のことであり、一方、電子供与性置換基とは、それが結合している芳香族環に、置換基の電子を押し出す傾向のある置換基のことであって、例えば有機化学の成書（例えば、Organic Chemistry 著書 Brewster & McEwen 出版社 Prentice Hall）の芳香族化合物の章に解説されているものである。
【００２０】
上記一般式〔Ｉ〕で示される芳香族化合物のうちで、本発明の再生剤として特に好ましい化合物の具体例としては、ハイドロキノンスルホン酸およびその塩を挙げることができる。
【００２１】
特開平３−１０４８７７号公報に記載されている還元促進剤も、本発明の再生剤も芳香族化合物ではあるが、還元促進剤は好ましい置換基として何れも電子供与性のものを挙げているのに対し、再生剤は電子供与性置換基と電子吸引性置換基の両方を必要としている。芳香環上の電子密度は、再生剤に於ては、還元促進剤よりも低くなっており、これが、再生剤が還元促進剤よりも熱的に安定である原因と考えられる。
【００２２】
このように、下記一般式〔Ｉ〕で示される芳香族化合物からなる再生剤は、電子吸引基と電子供与基を同一分子内に有することにより、自身は熱的に安定で、かつ酸化体となった還元剤を元に戻す機能を有するものである。本発明による無電解金メッキ液は、このような再生剤を含むことによって上記目的を達成することができる。
再生剤のメッキ液中での濃度は０．１ｇ／Ｌから１００ｇ／Ｌの範囲、好ましくは０．２ｇ／Ｌから４０ｇ／Ｌの範囲である。
【００２３】
本発明の金メッキ液は、上記必須成分のほかに、必要に応じて各種の任意成分（例えば錯化剤、沈殿防止剤、界面活性剤、光沢剤、ｐＨ調整剤、結晶調整剤、色素など）を含有させることも可能である。
【００２４】
上記の必須成分、及び任意成分から成る金メッキ液は、常法に従って調製、及び使用することが出来る。例えば、イオン交換樹脂で処理した脱イオン水に、所定の上記必須成分、及び任意成分を同時にあるいは別々に添加、溶解させることにより調製される。
【００２５】
金メッキ液の使用条件も常法を用いることが出来る。温度は３０℃から９０℃の範囲で、用途や目的に応じてｐＨを酸性、中性、アルカリ性に調整して使用することができる。本発明の金メッキ液の主要な補充成分は金塩だけとなり、他の還元剤、再生剤等の補充は大巾に削減されることになる。メッキされる基材に付着して金メッキ液が槽外に持出される量が多い場合は、当然ではあるが必要な金メッキ液全成分を補充することが必要である。
【００２６】
【実施例】
以下の実施例は、本発明による無電解メッキ液の好ましい具体例に関するものである。従って、本発明は下記実施例に具体的に開示された範囲内のもののみに限定されないことは言うまでもない。
実施例および比較例にて実施された無電解還元金メッキは、以下のようなプロセスで行われた。
【００２７】
銅回路基板の表面を脱脂、エッチングした後、Ｎｉメッキが施され、次いで無電解置換金メッキが施され、その上に無電解還元金メッキを施した。
【００２８】
無電解置換金メッキは、０．１μｍ以下の薄い金メッキを析出させるもので、ここで析出した金が次の工程の還元金メッキ反応の触媒となり、還元金メッキ層が形成されるものである。
【００２９】

（分析条件）
以下の実施例の分析は下記の装置を用いて行った。
【００３０】
メッキ液中の金属分析 ＩＣＰＳ−１０００ 島津製作所製
メッキ膜厚測定 ＳＦＴ−８００ セイコーインスツルメンツ製
メッキ液中の有機化合物分析 ＣＡＰＩ−３２００ 大塚電子製
金メッキの結晶形状測定 走査型電子顕微鏡 Ｓ−８００ 日立製作所製
金メッキの結晶配向測定 Ｘ線回析 ＪＤＸ−８０３０ 日本電子製
＜実施例１＞
下記の組成の無電解金メッキ液を調合した。
Ｎａ_３Ａｕ（ＳＯ_３）_２ ２．５ｇ／Ｌ 金塩
Ｎａ_２ＳＯ_３ ３０ｇ／Ｌ 緩衝剤
Ｎａ_２Ｓ_２Ｏ_３・５Ｈ_２Ｏ ２０ｇ／Ｌ 緩衝剤
４ホウ酸ナトリウム ２０ｇ／Ｌ 緩衝剤
リンゴ酸 １５ｇ／Ｌ 緩衝剤
ハイドロキノンスルホン酸カリウム ４ｇ／Ｌ 再生剤
チオ尿素 １ｇ／Ｌ 還元剤
メッキ液を加温（６５℃）したまま、５ｃｍ角の基板を用いて連続的に金メッキを行った。メッキにて消費される金塩は０．１ターン（初期濃度の１０％量の金が消費された時）ごとに補充し、その他の成分は一切補充せずに１ターンのメッキを終了した。メッキ速度は０．８ミクロン／時で安定しており、メッキ液中に金の微粒子が析出することもなかった。１ターン終了後のメッキ液中の還元剤、再生剤の分析を行ったところ、チオ尿素は１００％が残存しており、ハイドロキノンスルホン酸カリウムは７５％が残存していた。
【００３１】
＜比較例１＞
電子吸引性の置換基のないハイドロキノンを実施例１の再生剤の代わりに使用し、メッキスピードを実施例１と同じに調整した下記の組成のメッキ液を調合し、実施例１と同様に１ターンのメッキテストを行った。
Ｎａ_３Ａｕ（ＳＯ_３）_２ ２．５ｇ／Ｌ 金塩
Ｎａ_２ＳＯ_３ ３０ｇ／Ｌ 緩衝剤
Ｎａ_２Ｓ_２Ｏ_３・５Ｈ_２Ｏ ２０ｇ／Ｌ 緩衝剤
４ホウ酸ナトリウム ２０ｇ／Ｌ 緩衝剤
リンゴ酸 １５ｇ／Ｌ 緩衝剤
ハイドロキノン １ｇ／Ｌ 還元促進剤
チオ尿素 １ｇ／Ｌ 還元剤
１ターンに到達する前に、メッキ液には金の微細な析出物が分散しているのが認められた。また、１ターンを終えたメッキ液の還元剤、還元促進剤を分析したところ、チオ尿素は９５％が残存していたが、ハイドロキノンの残存量は初期濃度の１９％に過ぎなかった。
【００３２】
＜実施例２＞
下記の組成の金メッキ液を調合し、室温にて４５日保存後、評価を行った。
Ｎａ_３Ａｕ（ＳＯ_３）_２ ２．５ｇ／Ｌ
Ｎａ_２ＳＯ_３ ５０ｇ／Ｌ
Ｎａ_２Ｓ_２Ｏ_３・５Ｈ_２Ｏ ２０ｇ／Ｌ
ホウ酸アンモニウム ２０ｇ／Ｌ
クエン酸２アンモニウム ２０ｇ／Ｌ
ハイドロキノンスルホン酸カリウム ３ｇ／Ｌ
Ｎ−メチルチオ尿素 ５ｇ／Ｌ
保存後の金メッキ液には析出物は認められず、還元剤、再生剤濃度を分析したところ、Ｎ−メチルチオ尿素、ハイドロキノンスルホン酸カリウムともに初期濃度の１００％、９８％が残存していた。
次に、このメッキ液を６５℃に昇温し、メッキ実験を行ったところ、調合直後のメッキ液と同じ速度でメッキが可能であり、金の色調、結晶形状も調合直後のものと同じであった。
【００３３】
＜比較例２＞
電子吸引性置換基のない芳香環を有するハイドロキノンを再生剤の代わりに添加し、他の成分は実施例２と同じ組成である下記のメッキ液を調合し、実施例２と同じ条件にて４５日間の保存テストを行った。
Ｎａ_３Ａｕ（ＳＯ_３）_２ ２．５ｇ／Ｌ
Ｎａ_２ＳＯ_３ ５０ｇ／Ｌ
Ｎａ_２Ｓ_２Ｏ_３・５Ｈ_２Ｏ ２０ｇ／Ｌ
ホウ酸アンモニウム ２０ｇ／Ｌ
クエン酸２アンモニウム ２０ｇ／Ｌ
ハイドロキノン １．５ｇ／Ｌ
Ｎ−メチルチオ尿素 ５ｇ／Ｌ
４５日後のメッキ液には容器の底面を前面被うほどの析出物が認められ、メッキテストを行える状態でなくなっていた。還元剤、添加剤を分析すると、Ｎ−メチルチオ尿素の残量は９０％だったが、ハイドロキノンの残存量は５０％であった。
【００３４】
＜実施例３＞
下記の組成のメッキ液を調合し、６５℃のオーブンに１週間保管後、評価を行った。
Ｎａ_３Ａｕ（ＳＯ_３）_２ ２．５ｇ／Ｌ
Ｎａ_２ＳＯ_３ ５０ｇ／Ｌ
Ｎａ_２Ｓ_２Ｏ_３・５Ｈ_２Ｏ ２０ｇ／Ｌ
ホウ酸アンモニウム ２０ｇ／Ｌ
ハイドロキノンスルホン酸カリウム ４ｇ／Ｌ
チオ尿素 １ｇ／Ｌ
クエン酸２アンモニウム ２０ｇ／Ｌ
１週間保管後も、メッキ液には金粒子の析出は見られず、メッキ速度も０．７ミクロン／時で、調合直後の値と同じであった。続いて実施例１と同様な条件で、金塩以外の成分は一切補充せずに１ターンのメッキを行った。メッキ終了後のチオ尿素、ハイドロキノンスルホン酸カリウムの残量は初期濃度の各々１００％、７２％であった。
【００３５】
＜比較例３＞
電子吸引性の置換基のないハイドロキノンを実施例３の再生剤の代わりに使用し、メッキ速度は実施例３と同じに調整した下記の組成のメッキ液を調合し、実施例３と同様にオーブンテストを行った。
【００３６】
Ｎａ_３Ａｕ（ＳＯ_３）_２ ２．５ｇ／Ｌ
Ｎａ_２ＳＯ_３ ５０ｇ／Ｌ
Ｎａ_２Ｓ_２Ｏ_３・５Ｈ_２Ｏ ２０ｇ／Ｌ
ホウ酸アンモニウム ２０ｇ／Ｌ
ハイドロキノン １ｇ／Ｌ
チオ尿素 １ｇ／Ｌ
クエン酸２アンモニウム ２０ｇ／Ｌ
オーブンから取り出されたメッキ液には沈殿が発生しており、メッキテストを行うことは出来なかった。また、上澄み液を分析したところ、チオ尿素の残量は９０％だったが、ハイドロキノンの残量は９％に過ぎなかった。
【００３７】
＜実施例４＞
下記の組成のメッキ液を調合し、６５℃のオーブンに１週間保存後、評価を行った。
Ｎａ_３Ａｕ（ＳＯ_３）_２ ２．５ｇ／Ｌ
Ｎａ_２ＳＯ_３ ４０ｇ／Ｌ
Ｎａ_２Ｓ_２Ｏ_３・５Ｈ_２Ｏ ２０ｇ／Ｌ
ホウ酸カリウム ３０ｇ／Ｌ
コハク酸 ２０ｇ／Ｌ
２，５−ジヒドロキシアセトフェノン １．３ｇ／Ｌ
エチレンチオ尿素 １．５ｇ／Ｌ
１週間保管後も、メッキ液には金の析出は観測されず、メッキ速度もｐＨ９．０、６５℃の条件で１．２μｍ／時で調合直後と同じであった。
【００３８】
【発明の効果】
本発明によれば、還元剤の分解が有効に防止されかつ還元剤と還元促進剤との反応生成物がメッキ液中に蓄積することもない。よって、本発明によれば、保存性に優れ、還元剤と金塩とが混合された状態で保存しても、金の析出が起こらず、メッキ反応に使用された分の金塩を補充するだけで継続的に使用することが可能な還元型金メッキ液を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gold plating solution used for electronic parts. In particular, the invention relates to a reduced electroless gold plating solution.
[0002]
With the advancement of electronics technology, electronic components are becoming smaller and higher in density, and the importance of gold plating for ensuring the reliability of connection terminals is also increasing. In particular, great expectations are placed on electroless gold plating as a plating technique for electrodes isolated on an electric circuit on a fine circuit board.
[0003]
[Prior art]
There are two methods of electroless gold plating: displacement gold plating and reduction gold plating. The displacement gold plating method uses a potential difference based on a difference in ionization tendency between gold and a base metal of a substrate. In this method, the plating reaction stops when gold coats the base metal surface. For this reason, the problem that the precipitation film thickness was low and there were many pinholes in a film was seen.
[0004]
The reduction plating method uses electrons generated by the oxidation reaction of the reducing agent. Even after the gold is covered with the base metal surface, the oxidation reaction of the reducing agent proceeds and a thick gold film can be formed. It becomes.
[0005]
The electroless gold plating technology was first developed using cyan gold salt, and then non-cyan gold salt. For example, JP-A-57-54264 discloses a gold plating solution using potassium cyanoaurate as a gold salt and hydroxylamine as a reducing agent. However, the plating solution containing a cyanide compound, however, has a safety problem at the time of work and waste liquid treatment. Japanese Laid-Open Patent Publication No. 3-215677 discloses a gold plating solution in which a gold sulfite compound is used as a gold salt and a hydrazine compound is used as a reducing agent instead of cyan gold, and corresponds to an improvement in safety.
[0006]
[Problems to be solved by the invention]
However, these reduced electroless gold plating solutions have a problem in that the storage stability and stability of the solution are not sufficient. That is, the above two methods for reducing electroless gold plating both require a large amount of reducing agent, and the reducing agent used in these methods is easily reactive. The reaction of the agent started, and gold fine particles were precipitated in the plating solution, and the life of the gold plating solution was several hours. In order to cope with this poor storage stability, Japanese Patent Application Laid-Open No. 6-101055 presents a technique for minimizing the contact between the gold salt and the reducing agent, storing them in separate containers, and mixing them immediately before use. ing.
[0007]
In order to solve such a problem, JP-A-3-104877 introduces an additive of the concept of a reduction accelerator. A reduction accelerator restores the reducing agent that has undergone an oxidation reaction and is a substance that itself becomes a stable oxidant. By adding the reduction accelerator to the gold plating solution, consumption of the reducing agent is greatly reduced. It will be.
[0008]
In this respect, a reduction-type gold plating solution using a reduction accelerator is remarkable in terms of plating technology, but there is still a problem with respect to the storage stability of the gold plating solution. That is, according to the above method, although the consumption of the reducing agent is reduced, the reduction accelerator is thermally unstable and easily decomposed, which in turn tends to reduce the stability of the plating solution.
[0009]
Even if the reducing agent decomposes during storage of the gold plating solution, it returns to its original state due to the action of the reduction accelerator, but there is no defense against the decomposition of the reduction accelerator, and as a result, the storage stability of the plating solution is satisfied. The power level has not been reached.
[0010]
[Means for Solving the Problems]
In order to improve the stability of the reduced gold plating solution, it has the function of returning the reducing agent after oxidation reaction, but it is thermally stable and does not decompose even if dissolved in the gold plating solution. As a result, it is necessary to introduce a “regeneration agent” that improves the storage stability of the gold plating solution. If a regenerant is introduced, the storage stability of the reduced gold plating solution will increase dramatically, and even if the plating solution is used for a long period of time, supplemental components other than gold salt can be suppressed, making it an ideal electroless plating solution. Become.
[0011]
The present inventors tackled this problem and arrived at the present invention that realizes this problem by introducing a new material called a regenerant instead of the conventional reduction accelerator.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The first object of the present invention is to have a function of returning the reacted reducing agent, but it is thermally stable and does not decompose even in a temperature range (50 to 80 ° C.) where the gold plating solution is used. To find the material “regenerant”.
The second object is to provide a reduced gold plating solution that has excellent storage stability by introducing a regenerant and that does not cause gold deposition for a long time even when the reducing agent and gold salt are mixed. .
A third object is to provide a gold plating solution capable of plating on isolated and complex electrodes on a fine circuit board, and to meet the demands of the electronics industry.
This object is achieved by a gold plating solution containing a gold salt, a buffering agent, a reducing agent, and a regenerative agent.
[0013]
Therefore, the electroless gold plating solution according to the present invention is characterized by comprising a regenerating agent comprising a gold salt, a buffering agent, a reducing agent and an aromatic compound represented by the following general formula [I].
[0014]
[Chemical formula 2]

[Wherein X represents an electron-donating substituent, and Y represents an electron-withdrawing substituent. m is an integer of 1 ≦ m ≦ 4, n is an integer of 1 ≦ n ≦ 4, and m + n is 2 ≦ m + n ≦ 6. When m is 2 or more, a plurality of Xs may be the same or different. When n is 2 or more, a plurality of Y may be the same or different. R represents a hydrogen atom or an aromatic ring. ]
The following are mentioned as said gold salt.
Potassium cyanide, potassium chloride cyanide, potassium chloride chloride, sodium chloride chloride, potassium chloride chloride, sodium chloride chloride, sodium chloride chloride, potassium gold sulfite, sodium gold sulfite, gold potassium thiosulfate , Sodium gold thiosulfate, and mixtures thereof. Among these, potassium potassium cyanide and sodium gold sulfite are particularly preferable.
The concentration of these gold salts in the plating solution is generally in the range of 0.1 g / L to 100 g / L, preferably in the range of 0.5 g / L to 20 g / L.
[0015]
Examples of the reducing agent include the following.
Ascorbic acid, erythorbic acid, glyoxylic acid, formic acid, formate, thiourea, 1-allyl-2-thiourea, 1-allyl-3- (2-hydroxyethyl) -2-thiourea, 1,3-diethyl- 2-thiourea, trimethylthiourea, 1,3-dimethylthiourea, 1-acetylthiourea, N-allylthiourea, ethylenethiourea, N-methylthiourea, thiosemicarbazide, thioglycolic acid, sodium thioglycolate, formamine disulfinic acid , Hydrazine, P-hydrazinebenzenesulfonic acid, isonicotinic acid hydrazide, hydrazine sulfate, dimethylaminoborane, sodium borohydride, potassium borohydride, diethylaminoborane, triethylaminoborane, formalin, alcohols, sodium hypophosphite and these of Compounds, and the like. Of these, thiourea and thiourea derivatives are particularly preferable.
The concentration of these reducing agents in the plating solution is in the range of 0.01 g / L to 50 g / L, preferably in the range of 0.3 g / L to 25 g / L.
[0016]
Examples of the buffer include the following.
Carboxylic acids such as adipic acid, benzoic acid, citric acid, malic acid, succinic acid, acetic acid, lactic acid, malonic acid, phthalic acid, succinic acid, tartaric acid, glycine, glutamic acid, glutaric acid, iminodiacetic acid, dehydroacetic acid, maleic acid and the like Its salts, amine compounds such as ethylenediamine, hydroxylamine, ethanolamine, diethanolamine, triethanolamine, boric acid, borate, phosphoric acid, phosphate, thiosulfate, sulfite, nitrate, chloride salt, thiocyanate Inorganic compounds such as and mixtures thereof. As said salt compound, a potassium salt compound and an ammonium salt compound are preferable. Among these buffers, carboxylic acid and its salt, boric acid and its salt are particularly preferable.
The concentration of the buffering agent in the plating solution is in the range of 5 g / L to 500 g / L, preferably in the range of 10 g / L to 250 g / L.
[0017]
As the regenerant, an aromatic compound represented by the following general formula [I] is desirable.
[0018]
[Chemical 3]

[Wherein X represents an electron-donating substituent, and Y represents an electron-withdrawing substituent. m is an integer of 1 ≦ m ≦ 4, particularly preferably 1 ≦ m ≦ 2, n is an integer of 1 ≦ n ≦ 4, particularly preferably 1 ≦ n ≦ 2, and m + n is 2 ≦ m + n ≦ 6. Particularly preferably, 2 ≦ m + n ≦ 4. When m is 2 or more, a plurality of Xs may be the same or different. When n is 2 or more, a plurality of Y may be the same or different. R represents a hydrogen atom or an aromatic ring. ]
In the aromatic compound represented by the general formula [I], preferred specific examples of the electron-donating substituent X include a hydroxyl group, an amino group, an alkyl group, and an alkoxy group. In the present invention, a hydroxyl group is particularly preferable. Preferable specific examples of the electron withdrawing substituent Y include halogen (particularly Cl), sulfonic acid group, sulfonate (particularly sodium salt, potassium salt), nitro group, carbonyl group and carboxyl group. In the present invention, a sulfonic acid group or a sulfonate is particularly preferable. The remaining carbon atoms not substituted by the electron-donating substituent X and the electron-withdrawing substituent Y in the aromatic ring are bonded to hydrogen atoms (R) or adjacent to each other when the carbon atoms are adjacent to each other. These two carbon atoms may form another aromatic ring (R) constituting the condensed ring by sharing these two carbon atoms.
[0019]
As used herein, an electron-withdrawing substituent is a substituent that tends to pull electrons toward the substituent from the aromatic ring to which it is bonded, while an electron-donating substituent is: A substituent that tends to push the electron of the substituent into the aromatic ring to which it is attached, for example, the fragrance of an organic chemistry book (eg, Organic Chemistry book Brewster & McEwen publisher Prentice Hall) It is described in the chapter on group compounds.
[0020]
Of the aromatic compounds represented by the general formula [I], hydroquinonesulfonic acid and salts thereof may be mentioned as specific examples of particularly preferred compounds as the regenerant of the present invention.
[0021]
Although the reduction accelerator described in JP-A-3-104877 and the regenerative agent of the present invention are both aromatic compounds, the reduction accelerators are preferably electron-donating compounds as preferred substituents. In contrast, the regenerant requires both an electron donating substituent and an electron withdrawing substituent. The electron density on the aromatic ring is lower in the regenerative agent than in the reduction accelerator, and this is considered to be the reason why the regenerative agent is more thermally stable than the reduction accelerator.
[0022]
Thus, the regenerant composed of an aromatic compound represented by the following general formula [I] has an electron-withdrawing group and an electron-donating group in the same molecule, so that it is thermally stable and has an oxidant. It has a function of returning the reduced reducing agent. The electroless gold plating solution according to the present invention can achieve the above object by including such a regenerant.
The concentration of the regenerant in the plating solution is in the range of 0.1 g / L to 100 g / L, preferably in the range of 0.2 g / L to 40 g / L.
[0023]
In addition to the above essential components, the gold plating solution of the present invention includes various optional components as required (for example, complexing agents, precipitation inhibitors, surfactants, brighteners, pH adjusters, crystal adjusters, dyes, etc.) It is also possible to contain.
[0024]
The gold plating solution comprising the above essential components and optional components can be prepared and used according to a conventional method. For example, it is prepared by adding or dissolving the predetermined essential components and optional components simultaneously or separately in deionized water treated with an ion exchange resin.
[0025]
Conventional methods can be used for the use conditions of the gold plating solution. The temperature is in the range of 30 ° C. to 90 ° C., and the pH can be adjusted to acidic, neutral or alkaline depending on the application or purpose. The main replenishment component of the gold plating solution of the present invention is only gold salt, and replenishment of other reducing agents, regenerants, etc. is greatly reduced. If the amount of the gold plating solution that adheres to the substrate to be plated and is taken out of the bath is large, it is necessary to replenish all necessary components of the gold plating solution.
[0026]
【Example】
The following examples relate to preferred embodiments of the electroless plating solution according to the present invention. Therefore, it is needless to say that the present invention is not limited to those within the scope specifically disclosed in the following examples.
The electroless reduction gold plating carried out in the examples and comparative examples was performed by the following process.
[0027]
After degreasing and etching the surface of the copper circuit board, Ni plating was performed, followed by electroless displacement gold plating, and then electroless reduction gold plating was performed thereon.
[0028]
The electroless displacement gold plating deposits a thin gold plating of 0.1 μm or less, and the deposited gold serves as a catalyst for the reduction gold plating reaction in the next step, thereby forming a reduction gold plating layer.
[0029]

(Analysis conditions)
The following examples were analyzed using the following apparatus.
[0030]
Metal Analysis in Plating Solution ICPS-1000 Shimadzu Plating Film Thickness Measurement SFT-800 Organic Compound Analysis in Seiko Instruments Plating Solution CAPI-3200 Otsuka Electronics Gold Plating Crystal Shape Measurement Scanning Electron Microscope S-800 Hitachi Measurement of crystal orientation of gold plating X-ray diffraction JDX-8030 JEOL <Example 1>
An electroless gold plating solution having the following composition was prepared.
Na ₃ Au (SO ₃ ) ₂ 2.5 g / L Gold salt Na ₂ SO ₃ 30 g / L Buffer Na ₂ S ₂ O ₃ .5H ₂ O 20 g / L Buffer 4 Sodium borate 20 g / L Buffer Malic acid 15 g / L potassium hydroquinonesulfonate buffer 4 g / L regenerant thiourea 1 g / L Gold plating was continuously performed using a 5 cm square substrate while the reducing agent plating solution was heated (65 ° C.). Gold salt consumed for plating was replenished every 0.1 turn (when 10% of the initial concentration of gold was consumed), and one turn of plating was completed without supplementing any other components. The plating rate was stable at 0.8 micron / hour, and gold fine particles did not precipitate in the plating solution. Analysis of the reducing agent and regenerant in the plating solution after the end of one turn revealed that 100% of thiourea remained and 75% of potassium hydroquinonesulfonate remained.
[0031]
<Comparative Example 1>
A hydroquinone having no electron-withdrawing substituent was used instead of the regenerant of Example 1, and a plating solution having the following composition with the same plating speed as that of Example 1 was prepared. A turn plating test was performed.
Na ₃ Au (SO ₃ ) ₂ 2.5 g / L Gold salt Na ₂ SO ₃ 30 g / L Buffer Na ₂ S ₂ O ₃ .5H ₂ O 20 g / L Buffer 4 Sodium borate 20 g / L Buffer Malic acid 15 g / L buffer hydroquinone 1 g / L reduction accelerator thiourea 1 g / L Before reaching one turn of reducing agent, it was observed that fine deposits of gold were dispersed in the plating solution. Further, when the reducing agent and reduction accelerator of the plating solution after one turn were analyzed, 95% of thiourea remained, but the remaining amount of hydroquinone was only 19% of the initial concentration.
[0032]
<Example 2>
A gold plating solution having the following composition was prepared, and evaluated after storage at room temperature for 45 days.
Na ₃ Au (SO ₃ ) ₂ 2.5 g / L
Na ₂ SO ₃ 50 g / L
_{Na 2 S 2 O 3 · 5H} 2 O 20g / L
Ammonium borate 20g / L
20g / L diammonium citrate
Potassium hydroquinone sulfonate 3g / L
N-methylthiourea 5g / L
No deposits were observed in the gold plating solution after storage, and the concentration of the reducing agent and the regenerant was analyzed. As a result, 100% and 98% of the initial concentration remained for both N-methylthiourea and potassium hydroquinonesulfonate.
Next, when this plating solution was heated to 65 ° C. and a plating experiment was conducted, it was possible to plate at the same speed as the plating solution immediately after compounding, and the gold color tone and crystal shape were the same as those just after compounding. there were.
[0033]
<Comparative example 2>
Hydroquinone having an aromatic ring having no electron-withdrawing substituent is added in place of the regenerant, and the following plating solution having the same composition as in Example 2 is prepared as the other components. A daily storage test was conducted.
Na ₃ Au (SO ₃ ) ₂ 2.5 g / L
Na ₂ SO ₃ 50 g / L
_{Na 2 S 2 O 3 · 5H} 2 O 20g / L
Ammonium borate 20g / L
20g / L diammonium citrate
Hydroquinone 1.5g / L
N-methylthiourea 5g / L
In the plating solution after 45 days, precipitates were found so as to cover the bottom surface of the container on the front surface, and the plating test was not possible. When the reducing agent and additive were analyzed, the remaining amount of N-methylthiourea was 90%, but the remaining amount of hydroquinone was 50%.
[0034]
<Example 3>
A plating solution having the following composition was prepared and stored in an oven at 65 ° C. for 1 week for evaluation.
Na ₃ Au (SO ₃ ) ₂ 2.5 g / L
Na ₂ SO ₃ 50 g / L
_{Na 2 S 2 O 3 · 5H} 2 O 20g / L
Ammonium borate 20g / L
Potassium hydroquinone sulfonate 4g / L
Thiourea 1g / L
20g / L diammonium citrate
After storage for 1 week, no gold particles were observed in the plating solution, and the plating rate was 0.7 micron / hour, which was the same as that immediately after the preparation. Subsequently, plating was performed for one turn under the same conditions as in Example 1 without supplementing any components other than gold salt. The remaining amounts of thiourea and potassium hydroquinonesulfonate after plating were 100% and 72% of the initial concentrations, respectively.
[0035]
<Comparative Example 3>
A hydroquinone having no electron-withdrawing substituent was used in place of the regenerant of Example 3, and a plating solution having the following composition adjusted to the same plating rate as in Example 3 was prepared. Tested.
[0036]
Na ₃ Au (SO ₃ ) ₂ 2.5 g / L
Na ₂ SO ₃ 50 g / L
_{Na 2 S 2 O 3 · 5H} 2 O 20g / L
Ammonium borate 20g / L
Hydroquinone 1g / L
Thiourea 1g / L
20g / L diammonium citrate
Precipitation occurred in the plating solution taken out from the oven, and the plating test could not be performed. When the supernatant was analyzed, the remaining amount of thiourea was 90%, but the remaining amount of hydroquinone was only 9%.
[0037]
<Example 4>
A plating solution having the following composition was prepared and stored in an oven at 65 ° C. for 1 week for evaluation.
Na ₃ Au (SO ₃ ) ₂ 2.5 g / L
Na ₂ SO ₃ 40 g / L
_{Na 2 S 2 O 3 · 5H} 2 O 20g / L
Potassium borate 30g / L
Succinic acid 20g / L
2,5-Dihydroxyacetophenone 1.3 g / L
Ethylenethiourea 1.5g / L
Even after storage for 1 week, no gold deposition was observed in the plating solution, and the plating rate was 1.2 μm / hour under the conditions of pH 9.0 and 65 ° C., which was the same as immediately after the preparation.
[0038]
【The invention's effect】
According to the present invention, the decomposition of the reducing agent is effectively prevented, and the reaction product of the reducing agent and the reduction accelerator does not accumulate in the plating solution. Therefore, according to the present invention, the preservability is excellent, even if the reducing agent and the gold salt are mixed and stored, the gold salt does not precipitate, and the gold salt used for the plating reaction is replenished. It is possible to obtain a reduced-type gold plating solution that can be used continuously only.

Claims (2)

An electroless gold plating solution comprising a gold salt, a buffering agent, a reducing agent, and a regenerant composed of an aromatic compound represented by the following general formula [I].

[Wherein X is an electron-donating substituent and represents a hydroxyl group , and Y is an electron-withdrawing substituent and is selected from sulfonic acid, sulfonate, and carbonyl group . m is 2, n is 1 or 2, m + n is Ru 3 ≦ m + n ≦ 4 der. Also, when n is 2 or more, Y existing in plural numbers may be the same or different. R represents a hydrogen atom or an aromatic ring. ] The electroless gold plating solution according to claim 1 , wherein the reducing agent is a thiourea organic compound and a derivative thereof.