Immersion tin (I-Sn) coatings on copper were prepared in a stannous methanesulfonate bath with thiourea being the potential altering agent. The electrochemical displacement process was studied by the galvanic couple current method (GCCM) on an electrochemical workstation. The morphology of the I-Sn coatings were observed by field-emission-gun scanning electron microscopy (FEG-SEM). The I-Sn process can be divided into three stages: (i) rapid increase in galvanic current, (ii) sudden decrease in galvanic current after a peak current, and (iii) low or residual galvanic current stages. It is demonstrated that the galvanic current method is a useful and efficient tool to identify the optimum ending time of the immersion plating process. This optimum immersion time results in a smooth and conformal deposit with a fine grain size.