Cyanide-free electrolyte composition, and method for the deposition of silver or silver alloy layers on substrates
View Patent ↗The invention relates to a cyanide-free electrolyte composition for depositing a silver or silver alloy layer on a substrate as well as a method for depositing such layers with the help of said cyanide-free electrolyte composition. The electrolyte composition according to the invention comprises at least one silver ion source, a sulfonic acid and/or a sulfonic acid derivative, a wetting agent and a hydantoin. The silver or silver alloy layers deposited from such an electrolyte composition by means of the method according to the invention are dull and ductile.
1. A method for electrolytic deposition of a silver or a silver alloy layer on a substrate comprising, contacting the substrate with an electrolyte composition in the presence of an applied current having a current density between 0.1 and 2.0 A/dm 2 to thereby deposit the silver or silver alloy layer wherein said layer has a uniform dull appearance;
wherein the electrolyte composition is cyanide-free and comprises:
Ag in a concentration between 10 and 50 g/L as silver methane sulfonate (Ag-MSA);
potassium methane sulfonate in a concentration of 50 to 500 g/L;
a wetting agent;
potassium bromide in a concentration between 50 and 200 mg/L; and
a hydantoin of the formula
where R1 and R2 are independently H, an alkyl group having 1 to 5 carbon atoms or a substituted or unsubstituted aryl group;
wherein the electrolyte composition has a pH between 8 and 14 and a bath stability of greater than or equal to 100 Ah/L; and
wherein the electrolyte composition has a bath life of more than a year.
2. The method of claim 1 wherein the electrolyte composition consists essentially of the Ag as Ag-MSA, the potassium methane sulfonate, the wetting agent, the potassium bromide, and the hydantoin.
3. The method of claim 2 wherein the hydantoin is 5,5-dimethylhydantoin.
4. The method of claim 2 wherein:
the Ag has a concentration between 20 and 40 g/L;
the potassium methane sulfonate has a concentration between 100 and 300 g/L; and
the potassium bromide has a concentration between 100 and 200 mg/L.
5. The method of claim 1 wherein the hydantoin is 5,5-dimethylhydantoin.
6. The method of claim 1 wherein the electrolyte composition further comprises an inorganic silver salt selected from the group consisting of silver oxide, silver nitrate, and silver sulfate.
7. The method of claim 1 wherein the pH is between 9 and 12.5.
8. The method of claim 1 wherein the pH is between 9.5 and 12.
9. The method of claim 1 wherein the potassium methane sulfonate has a concentration between 100 and 300 g/L.
10. The method of claim 1 wherein the electrolyte composition comprises:
30 g/l Ag as silver methane sulfonate (Ag-MSA)
150 g/l potassium methane sulfonate
120 g/l 5,5-dimethylhydantoin
20 g/l wetting agent
150 mg/L potassium bromide.
11. The method of claim 1 wherein the electrolyte composition further comprises sodium thiosulfate.
12. The method of claim 11 wherein the electrolyte composition comprises:
35 g/l Ag as silver methane sulfonate (Ag-MSA)
150 g/l potassium methane sulfonate
120 g/l 5,5-dimethylhydantoin
20 g/l wetting agent
75 mg/L sodium thiosulfate
75 mg/L potassium bromide.
13. The method of claim 11 wherein the electrolyte composition consists essentially of:
35 g/l Ag as silver methane sulfonate (Ag-MSA)
150 g/l potassium methane sulfonate
120 g/l 5,5-dimethylhydantoin
20 g/l wetting agent
75 mg/L sodium thiosulfate
75 mg/L potassium bromide.
14. The method of claim 11 wherein the sodium thiosulfate has a concentration between 100 and 200 mg/L.
15. The method of claim 14 wherein the electrolyte composition comprises:
35 g/l Ag as silver methane sulfonate (Ag-MSA)
150 g/l potassium methane sulfonate
120 g/l 5,5-dimethylhydantoin
20 g/l wetting agent
150 mg/L sodium thiosulfate.
16. The method of claim 14 wherein the electrolyte composition consists essentially of:
30 g/l Ag as silver methane sulfonate (Ag-MSA)
150 g/l potassium methane sulfonate
120 g/l 5,5-dimethylhydantoin
20 g/l wetting agent
150 mg/L potassium bromide.
17. The method of claim 14 wherein the electrolyte composition consists essentially of:
35 g/l Ag as silver methane sulfonate (Ag-MSA)
150 g/l potassium methane sulfonate
120 g/l 5,5-dimethylhydantoin
20 g/l wetting agent
150 mg/L sodium thiosulfate.
18. The method of claim 11 wherein the total concentration of potassium bromide and sodium thiosulfate is between 50 and 500 mg/L.
19. The method of claim 1 wherein the electrolyte composition comprises the potassium bromide in a concentration between 100 and 200 mg/L.
20. The method of claim 1 wherein the wetting agent comprises naphthalene sulfonic acid formaldehyde polycondensate.