The Effect of Additives on the Electroless Deposition of Gold from a Thiosulfate-Ascorbic Acid Bath

Abstract

Conventional electroless gold plating utilises gold(I) cyanide as the gold source. However several factors, including safety and environmental issues, have driven efforts to develop alternative electroless baths. The performance of alternative thiosulfate baths, however, is still inferior to that of conventional gold electroless plating from cyanide. Possible methods of improving the performance have been investigated, including the addition of thallium and thiourea. It will be shown that although bath decomposition is a major problem when using ascorbic acid as the reducing agent, this can be largely overcome with the addition of thiosulfate. This has lead to the development of baths containing either thiourea or thallium which offer better plating rates and longer bath lifetime.