Cyanide-free silver bath composition and uses thereof

Abstract

Cyanide-free silver bath composition comprising: - silver methanesulfonate; - a chelating agent selected from hydantoin, one of its methyl and / or hydroxymethyl derivatives or a mixture thereof, preferably selected from hydantoin, 5,5-dimethylhydantoin, 1-methylhydantoin and mixtures thereof; - a brightening agent selected from polyethyleneimine and bipyridine, advantageously being polyethyleneimine; - a pH regulator selected from potassium or sodium hydroxide, advantageously potassium hydroxide, and - Water; wherein the pH of the composition is between 8.5 and 13.5, advantageously between 11.0 and 13.0 and its electrolytic conductivity is greater than or equal to 10 mS / cm, advantageously greater than or equal to 50 mS / cm, characterized in that the composition does not comprise any brightening agents other than that selected from polyethyleneimine and bipyridine.

Claims

[1] Cyanide-free silver bath composition comprising: - silver methanesulfonate; - a chelating agent selected from hydantoin, one of its methyl and / or hydroxymethyl derivatives or a mixture thereof, preferably selected from hydantoin, 5,5-dimethylhydantoin, 1-methylhydantoin and mixtures thereof; - a brightening agent selected from polyethyleneimine and bipyridine, advantageously being polyethyleneimine; - a pH regulator selected from potassium or sodium hydroxide, advantageously potassium hydroxide, and - Water; wherein the pH of the composition is between 8.5 and 13.5, advantageously between 11.0 and 13.0 and its electrolytic conductivity is greater than or equal to 10 mS / cm, advantageously greater than or equal to 50 mS / cm, characterized bythat the composition does not comprise any brightening agents other than that selected from polyethyleneimine and bipyridine. [2] Composition according to claim 1, characterized by that the content of silver ions is between 10 and 80 g / l. [3] Composition according to one of claims 1 or 2, characterized by that it does not contain any other chelating and / or complexing agents. [4] A process for preparing the composition according to any one of claims 1 to 3, comprising the following successive steps: a) adding the pH regulator, advantageously potassium hydroxide, in demineralized water at room temperature to obtain a pH between 8.5 and 13.5 and an electrolytic conductivity greater than or equal to 10 mS / cm; b) adding the chelating agent at room temperature while maintaining the pH between 8.5 and 13.5 and the electrolytic conductivity at a value greater than or equal to 10 mS / cm; c) adding silver methanesulfonate at room temperature while maintaining the pH between 8.5 and 13.5 and the electrolytic conductivity at a value greater than or equal to 10 mS / cm; d) adding the brightening agent, advantageously polyethyleneimine, while maintaining the pH between 8.5 and 13.5 and the electrolytic conductivity at a value greater than or equal to 10 mS / cm. [5] Use of the composition according to any one of claims 1 to 3 for the electrolytic deposition of silver on a metal substrate. [6] Use according to claim 5, characterized by that the metal substrate is a substrate made of copper or a copper alloy, an aluminum alloy or nickel. [7] Use according to one of claims 5 or 6, characterized by that the metal substrate is an electrical component, advantageously a conductor, a metal contact, a connector or a housing. [8] A process for the electrolytic deposition of silver on a metal substrate, comprising the following successive steps: A) Surface preparation of the metal substrate; B) pre-silvering the metal substrate obtained in step A), advantageously by using a pre-silvering bath whose composition comprises silver methanesulfonate, a chelating agent selected from hydantoin, one of its methyl and / or hydroxymethyl derivatives or a mixture thereof, in particular selected from hydantoin, 5,5-dimethylhydantoin, 1-methylhydantoin and their mixture, a pH regulator selected from potassium or sodium hydroxide, in particular potassium hydroxide, and water, the pH of the composition being between 8.5 and 13.5, preferably between 11.0 and 13.0, and its electrolytic conductivity being greater than or equal to 10 mS / cm, preferably greater than or equal to 50 mS / cm; C) silver plating the metal substrate obtained in step B) by using the composition according to any one of claims 1 to 3; D) Recovering the metal substrate coated with a silver layer. [9] Method according to claim 8, characterized by that step A) comprises degreasing and / or surface activation and / or pickling and optionally the addition of a metallic underlayer. [10] Method according to one of claims 8 or 9, characterized by that it is continuous or discontinuous.