Acidic zinc and zinc nickel alloy plating bath composition and electroplating method
The present invention relates to an acidic zinc or zinc-nickel alloy plating bath composition comprising a source for zinc ions, optionally a source for nickel ions, a source for chloride ions and at least one dithiocarbamyl alkyl sulfonic acid or salt thereof. Said plating bath composition and the corresponding plating method result in zinc or zinc-nickel alloy layers having an improved throwing power and thickness distribution, particularly when plating substrates having a complex shape and/or in rack-and-barrel plating.
1. An acidic zinc-nickel alloy plating bath composition comprising a source for zinc ions, a source for nickel ions, a source for chloride ions and having a pH value in the range of 2 to 6.5,
characterized in that the composition further comprises at least one dithiocarbamyl alkyl sulfonic acid or salt thereof represented by formula (I)
(R 1 R 2 )N—C(S)SR 3 —SO 3 R 4 (I)
wherein
R 1 and R 2 are independently selected from the group consisting of hydrogen, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, and tert-butyl,
R 3 is selected from the group consisting of methylene, ethylene, propylene, butylene, pentylene and hexylene and
R 4 is selected from the group consisting of hydrogen and a cation,
and the composition is free of polyalkyleneglycols and other alloying metals than zinc and nickel ions,
wherein the concentration of the at least one dithiocarbamyl alkyl sulfonic acid or salt thereof ranges from 0.5 to 100 mg/l; and
wherein the concentration of zinc ions ranges from 5 to 100 g/l, and
wherein the concentration of chloride ions ranges from 70 to 200 g/l.
2. The acidic zinc-nickel alloy plating bath composition according to claim 1 wherein the concentration of the at least one dithiocarbamyl alkyl sulfonic acid or salt thereof ranges from 1 to 50 mg/l.
3. The acidic zinc-nickel alloy plating bath composition according to claim 1 wherein said acidic zinc-nickel alloy plating bath composition further comprises at least one aromatic carboxylic acid, salt, ester or amide thereof.
4. The acidic zinc-nickel alloy plating bath composition according to claim 3 wherein the at least one aromatic carboxylic acid, salt, ester or amide thereof is selected from the group consisting of benzoic acid, phthalic acid, 1,3,5-benzene tricarboxylic acid, 1-naphtalene carboxylic acid, 1,3-naphtalene dicarboxylic acid, naphthalene tricarboxylic acid, regioisomeric derivatives thereof, sodium, potassium and ammonium salts and methyl, ethyl and propyl esters of the aforementioned.
5. The acidic zinc-nickel alloy plating bath composition according to claim 4 wherein the concentration of the at least one aromatic carboxylic acid, salt, ester or amide thereof ranges from 0.1 to 20 g/l.
6. The acidic zinc-nickel alloy plating bath composition according to claim 1 wherein the concentration of zinc ions ranges from 10 to 100 g/l.
7. The acidic zinc-nickel alloy plating bath composition according to claim 1 wherein the concentration of chloride ions ranges from 100 to 200 g/l.
8. The acidic zinc-nickel alloy plating bath composition according to claim 1 wherein the concentration of nickel ions ranges from 5 to 100 g/l.
9. The acidic zinc-nickel alloy plating bath composition according to claim 1 further comprising a complexing agent for nickel ions selected from the group consisting of aliphatic amines, poly-(alkylenimines), non-aromatic poly-carboxylic acids, non-aromatic hydroxyl carboxylic acids and mixtures of the aforementioned.
10. The acidic zinc-nickel alloy plating bath composition according to claim 9 wherein the concentration of the complexing agent for nickel ions ranges from 0.1 to 150 g/l.
11. The acidic zinc-nickel alloy plating bath composition according to claim 1 wherein the concentration of the at least one dithiocarbamyl alkyl sulfonic acid or salt thereof ranges from 0.5 to 50 mg/l.
12. A method for zinc-nickel alloy electroplating comprising, in this order, the steps of:
(i) providing a substrate having a metallic surface as a cathode,
(ii) contacting said substrate with the acidic zinc-nickel alloy plating bath composition according to claim 1 , and
(iii) applying an electrical current between said substrate and at least one anode and thereby depositing a zinc-nickel alloy layer with an improved thickness uniformity onto said substrate.