Abstract: Two electroplated Cu substrates were prepared at current densities of 1.7 mA ·cm^-2 and 50 mA ·cm^-2. Then by reflow soldering the electroplated Cu substrates and Sn granular, the Sn/Cu joints were obtained and aged at 150℃ for different times (10, 20 d). The surface morphology of the electroplated Cu substrates and interface morphology of the Sn/Cu joints were observed and the evolution mechanism of Kirkendall voids during aging was also analyzed. The results show that after the aging treatment, the voids were formed at Cu₃Sn/Cu interface of the two Sn/Cu joints and the density of voids increased gradually with the expansion of aging time and was relatively high at a relatively high current density. Before aging treatment, the voids appeared at the interface of the joint with the electroplated Cu substrate prepared at a relatively high current density; after aging treatment, the voids aggregated gradually and then changed into cavities. The inner surface of cavities became the channels for the rapid diffusion of Cu. The microstructure of the surface electroplate layer was influenced by the current density, which in turn influenced the interfacial microstructure in the following aging process.