Electrodeposition of Cu-Sn alloys from a methanesulfonic acid electrolyte containing benzyl alcohol

Deposition of Cu-Sn alloys from a methanesulfonic acid electrolyte containing small amounts of benzyl alcohol was investigated. Polarisation experiments (cylic and linear sweep voltammetry) were carried out using a rotating disc electrode to identify the reduction and dissolution processes that take place in the system and to determine the effect of the solution constituents on them. Potentiostatic deposition was performed onto a rotating cylinder electrode and the resulting deposits were charactised using SEM and XRD. The results showed that co-deposition of copper and tin is possible even at potentials less cathodic than tin discharge potential. The latter was attributed to the underpotential deposition of Sn2+ on a copper substrate. Smooth and compact deposits were obtained at various deposition potentials and Cu2+ concentrations, with Sn contents between 1.6 - 62.4 wt.%. Several stable phases, such as pure copper, α-CuSn, ϵ-Cu3Sn and η′-Cu6Sn5 phase, were detected at different operating conditions. Finally, it was found that BA increases the amount of tin in the deposit when Cu2+ concentrations in the solution is kept low, especially at high overpotentials. This additive also inhibits the formation of dendrites and reduces surface roughness.