Electroless Deposition of Ni-Sn Layers Having High Sn Content（＞ 30 at.%）on Fe Substrates（3）: Examination of bath additives to prevent the formation of cracks and pinholes on the Ni-Sn layers

This study investigated plating bath additive effects on the improvement of electroless Ni-Sn plating film resistance against aqueous sodium hypochlorite solutions. Surfaces of conventional electroless Ni-Sn coatings show numerous cracks and pinholes. Through these gaps, a sodium hypochlorite aqueous solution can corrode the substrate, thereby decreasing the chemical resistance of the plated coating. A plating solution bath to which a combination of thiourea and hydroquinone had been added reduced the internal stress of the plating film, suppressed the rate of crack formation on the film surface, and reduced pinhole formation. Findings also revealed that the resultant film had higher resistance than conventional Ni-Sn films.