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 silver or silver alloy layers with a 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 the inventive electrolyte composition by the method according to the invention are dull and ductile.
1. A cyanide-free electrolyte composition for the deposition of a silver or silver alloy layer on a substrate comprising:
silver as silver methane sulfonate;
a sulfonic acid and/or a derivative of a sulfonic acid;
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 composition has a lifetime of more than one year and wherein the composition has a pH between 8 and 14.
2. The cyanide-free electrolyte composition of claim 1 , wherein the silver concentration is between 10 and 50 g/l.
3. The cyanide-free electrolyte composition of claim 1 , wherein the silver concentration is between 20 and 40 g/l.
4. The cyanide-free electrolyte composition of claim 1 , wherein the concentration of the sulfonic acid and/or the derivative of a sulfonic acid is between 50 g/l and 500 g/l.
5. The cyanide-free electrolyte composition of claim 1 , wherein the concentration of the sulfonic acid and/or the derivative of a sulfonic acid is between 100 g/l and 300 g/l.
6. The cyanide-free electrolyte composition of claim 1 , wherein the sulfonic acid and/or the derivative of a sulfonic acid comprises potassium methane sulfonate.
7. The cyanide-free electrolyte composition of claim 6 , wherein the hydantoin comprises 5,5-dimethylhydantoin.
8. The cyanide-free electrolyte composition of claim 1 , wherein the potassium bromide concentration is between 100 and 200 mg/L.
9. The cyanide-free electrolyte composition of claim 1 , wherein the hydantoin comprises 5,5-dimethylhydantoin.
10. The cyanide-free electrolyte composition of claim 1 , further comprising an inorganic silver salt selected from the group consisting of silver oxide, silver nitrate, and silver sulfate.
11. The cyanide-free electrolyte composition of claim 1 , further comprising a wetting agent.
12. The cyanide-free electrolyte composition of claim 11 , wherein the wetting agent comprises a naphthalene sulfonic acid formaldehyde polycondensate and/or a sulfopropylated polyalkoxylated naphthol.
13. The cyanide-free electrolyte composition of claim 1 , further comprising sodium thiosulfate.
14. The cyanide-free electrolyte composition of claim 13 , wherein the sodium thiosulfate has a concentration between 100 and 200 mg/L.
15. The cyanide-free electrolyte composition of claim 1 , wherein the pH is between 9 and 12.5.
16. The cyanide-free electrolyte composition of claim 1 , wherein the composition has a stability of ≧100 Ah/L.
17. The cyanide-free electrolyte composition of claim 1 , wherein:
the silver concentration is between 10 and 50 g/l,
the concentration of the sulfonic acid and/or the derivative of a sulfonic acid is between 50 g/l and 500 g/l, and
the composition further comprises a wetting agent.
18. The cyanide-free electrolyte composition of claim 1 , wherein:
the silver concentration is between 10 and 50 g/l,
the sulfonic acid and/or the derivative of a sulfonic acid comprises potassium methane sulfonate,
the potassium methane sulfonate concentration is between 50 g/l and 500 g/l,
the hydantoin comprises 5,5-dimethylhydantoin, and
the composition further comprises a wetting agent.
19. The cyanide-free electrolyte composition of claim 1 wherein a current density between 0.1 and 2.0 A/dm 2 is applied to thereby deposit the silver or silver alloy layer.