Process and theoretical research on electroplating Cu–Sn alloys of low Sn

Abstract

Imitation gold electroplating of a citric acid system was studied using citric acid as the main complexing agent, copper sulphate and sodium stannate as the main salts and NaOH as the buffering agent in the electroplating solution. The effects of different electroplating solutions on the microtopography, composition, phase structure and colour of the electroplated layer were evaluated by SEM, EDS, XRD and photo analysis. Different electroplating solutions were analysed and compared by electrochemical analysis, UV–Vis, FTIR and NMR spectroscopy to analyse the mechanism of the electrochemical reaction. The results showed that at pH 9.5, copper and tin ions exist in the form of Cu2Cit2H-24− and Sn(OH)62−, respectively, in the solution. The cathode had only a single deposition peak at\u2009−\u20091.3 V vs. Hg|HgO. Therefore, the above two complex ions can be reduced and codeposited at the same voltage to form Cu, [Cu, Sn], Cu6Sn5, Cu10Sn3 and Cu4O3 phases. A gold-coloured, dense, low-Sn binary Cu–Sn alloy coating containing 13.72% Sn was finally obtained. These results provide a theoretical basis for the electrodeposition of Cu–Sn alloys.