The experimental study of the reaction diffusion under direct electric current in Cu—Sn system at temperature of 275°C is performed. The current density is of 7.3$\cdot$10$^{7}$ А/m$^{2}$. In these experiments, anode and cathode have no joint contact through the solder layer. With this design of sample, the diffusion of copper atoms from the cathode to the anode is impossible. In these experimental conditions, the growth of the Cu$_{3}$Sn + Cu$_{6}$Sn$_{5}$ phase on the anode is faster than on the cathode. The growth kinetics of phase on the electrodes corresponds to a linear time law $\Delta x \propto t$. The voids’ growth on the cathode is not observed. When the anode is joined to cathode by the solder layer, the formation and growth of voids on the cathode are observed. Using model of reaction diffusion process at electromigration, the analysis of the obtained experimental results is carried out. Based on the obtained results, it is possible to conclude that the joint layer of tin between copper electrodes can significantly influence on the growth kinetics of intermetallic compounds and lead to emergence of voids on the cathode.