Ammonia-free electroless nickel-plating bath and method for nickel-plating dielectrics

摘要

An ammonia-free, electroless nickel-plating bath is proposed which has a high tolerance to the presence of palladium(II) ions. The bath consists of an aqueous solution which contains approximately from 0.025 to 0.2 mol/l of nickel ions, approximately from 0.1 to 0.5 mol/ l of hypophosphite ions, a non-amine, ammonia-free chelating agent (chelatant) for nickel ions in excess of the stoichiometric amount required for complexing the nickel ions, and a soluble amine in an amount which results in complexing of palladium(II) ions without significantly reducing the nickel deposition rate. In addition, an improved method for electroless nickel-plating of a dielectric (insulator, non-conductor) is proposed, which employs the bath according to the invention. Preferred non-amine, ammonia-free chelating agents are carboxylic acids and their salts, which can form a nickel complex having a Kf above approximately 102. Said amines are able to form a palladium/amine complex with a Kf which is numerically greater than the Kf of the non-amine, ammonia-free chelatant/nickel complex. Examples for amines are ethylenediamine, triethanolamine, monoethanolamine and diethylenetriamine.