Tin is widely used as a coating material for copper metal in the electronics industry where tin whisker growth is a concern because it affects the reliability of electronic devices. Because whisker growth reduces joint reliability, it is important to monitor the growth of Cu₃Sn and Cu₆Sn₅, which is usually done by using an X-ray diffraction method to estimate the thickness of the tin layer. In this study, we use the sequential electrochemical reduction analysis (SERA) technique to measure the thickness of layers of pure tin, Cu₆Sn₅, and Cu₃Sn. We also discuss the depletion rate of tin layers at high-temperature aging and the growth of these intermetallics.