厚付け無電解金めっきについて

Abstract

A new type of electroless gold plating bath has been developed using tetracyanoaurate (III). The trivalent gold bath showd excellent stability even in the absence of KCN because the tetracyanoaurate (III) was reduced to monovalence by BH4- liberating the cyanide ions. The deposition rate of gold was increased by a factor of 8 to 9 with the addition of trace amounts of PbCl2 or TlCl. This enhancement of electroless gold deposition can be explained by a model for the catalytic action of adsorbed heavy metal atoms proposed by McIntyre. The adsorbed foreign atoms seemed to influence the crystallographic orientation of the gold deposits. In the initial stage of the deposition of gold on the base metal, displacement and autocatalytic reactions may occur in parallel, but the displacement reaction diminished and the deposition rate decreased significantly when the substrate was completely covered with gold film. The autocatalytic deposition of gold is enhanced by the forced convection of the plating solution, so that the rate of deposition of gold was increased markably by stirring the solution. The stirring also enhanced the incorporation of oxygen into the solution, and this improved the stability of the electroless gold plating bath. In contrast, it was confirmed that excessive agitation of air inhibited the deposition of gold. The stability of the electroless gold plating bath was markedly reduced by introducing a trace amount of nickel ion. It is, therefore, essential in the heavy deposition of electroless gold for nickel substrates to be pretreated by displacement gold plating.