Nucleation of Tin and Tin–Silver Alloy on Copper and Nickel in Acid Plating Baths

The rate of nucleation and number density of nuclei of tin and tin–silver deposits on copper and nickel substrates in acid sulfate and acid methanesulfonate baths were measured by application of a nucleation model to chronoamperometric data. Based on the dependence of nucleation rate on overpotential, the critical Gibbs free energy of nucleation and the critical nucleation size were calculated. A mechanism of alloy nucleation in the presence of thiourea is proposed.