Thermal Cycling-Electric Current Coupling Damage Mechanisms of SnAgCu/Cu Solder Joints Under Different Temperature Ranges

In this study, in situ investigation of the coupling damage mechanisms of SnAgCu/Cu solder joints under thermal cycling and current was carried out to compare the thermal fatigue under the same temperature range, and to analyze the influence of temperature. It was found that the current increased the temperature of the solder joint, making it obviously higher than the ambient temperature. On the other hand, there was little difference between the thermal-electrical coupling damage and thermal fatigue before a significant increase in solder temperature; the interfacial plastic deformation was only slightly more serious, and the electromigration was not significant. With an increasing number of thermal cycles, the damage, resistance, and temperature of the solder joint increased, and the plastic deformation resistance of the solder decreased, leading to further damage and temperature increase, exhibiting an accelerating damage process. After the temperature reached a certain degree, the solder softened significantly, and its deformation behavior was similar to that of high-viscosity fluids, resulting in surface unevenness with significant height differences. As the temperature of the solder joint increased, the electromigration of Cu in the solder gradually increased, and the migration rate was dominated by the solder grain orientation. With higher peak temperature of the ambient thermal cycle, the thermal cycling-electric current coupling damage rate increased substantially.