The Effects of the Bath Composition on the Electroless Palladium Nickel Alloy Ratio

Several amines used as complexing agents for electroless palladium-nickel plating baths do not ensure bath stability and only a fixed ratio of a 9: 1 (palladium: nickel) alloy is obtained in such baths. We studied bath composition, focusing on complexing agent selection and conditions for improving bath stability and changing the alloy ratio. Bath stability is greatly improved by the addition of carboxylic acid as a secondary complexing agent beside the addition of amines. The alloy ratio can be changed from 9: 1 to 7: 3 (Pd/Ni ratio) by changing the carboxylic acid concentration. The bath construction sequence greatly influences bath stability. Palladium and nickel ions are preliminarily complexed with ethylene diamine and carboxylic acid, then each solution is mixed to construct the bath, yielding a stable electroless palladium-nickel plating bath.