Electrochemical plating of Cu-Sn alloy in non-cyanide solution to substitute for Ni undercoating layer

This study aims to investigate the electrochemical co-deposition of a Cu-Sn alloy to substitute for the Ni undercoating layer between the outmost coating layer and substrate. The electrodeposition was performed in a sulfuric acid bath containing a mixture of additives such as complex agent (EDTP), auxiliary complex agent (TEA), chelating agent, and pit prevent agent. The effect of each additive on co-deposition was studied by cyclic voltammetry using a rotating disk electrode, which showed that each additive helps to shift the reduction onset potential of Cu closer to that of Sn, thus resulting in uniform Cu-Sn coating. Electroplating of the Sn-rich Cu-Sn alloy was performed for various current densities and plating times, and the results showed that a bright-white-colored, thick, uniform, and compact layer of the above alloy can be deposited under optimized conditions (1 A dm−2 and 30 min). Based on the results of SEM, EDS mapping, XPS, and XRD, we found that Cu and Sn were uniformly distributed throughout the deposited layer with almost equal contents when a relatively low current density (less than 3 A dm−2) was employed.