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.