Study on Electrochemical Migration of Sn-0.7Cu

In this study, the electrochemical migration behavior of Sn0.7Cu solder in deionized water was observed in situ by the method of water droplet test. The formation mechanism, morphology and composition of metallic deposits were studied by means of SEM, XRD and EDS. The results show that the preferential nucleation position happened where the Gibbs free energy is the least at the cathode interface. The reason for the morphology of the metal deposits is dendritic is that the competition between the ordered growth under equilibrium conditions and the disordered growth under non-equilibrium conditions. In addition, the dendrites mainly composed of Sn and Sn oxides, indicating that the electrochemical dissolution of Sn0.7Cu is mainly due to the dissolution of Sn in eutectic structure, while the intermetallic compound Cu6Sn5 nearly does not dissolve. The higher applied voltage, the faster the dendrites growth rate and shorter short-circuit time. When the spacing is 0.5 mm, the voltages of 1.5V, 3V, 5V and 8V are respectively applied, and the corresponding short-circuit failure time is 401s , 68s , 15 s and 11s respectively. The results show that when the voltage is less than 1.5V, the metal deposits can be observed for a long time. When the voltage exceeds 5V, the short-circuit time changes little, and the short-circuit failure time can be completed in nearly 10s.