Phase-Field Modelling of Lead-Free Solder Joint Void Growth Under Thermal-Electrical Coupled Stress

Micro-interconnection reliability analysis has been affected by a drastic solder joint size reduction and adoption of lead-free material. Furthermore, the current density in the solder joint has sharply increased. During actual operation, and under the action of thermal-electrical coupled stress, voids caused by atom migration appear in the solder joint and affect its reliability. In this study, a phase-field model considering the coupled stress is proposed to simulate the void evolution in solder joints and analyse the effect of coupled stress. Single- and double-void growths are simulated, as well as void migration. The results showed that the coupled influence of thermal and electrical stresses collectively contributed to the void growth. The effects of current density and temperature are positive. A higher external stress resulted in a higher growth rate. Double voids can grow independently or coalesce together, depending on the initial spacing of the centres of the two voids. The shorter the spacing, the less the time consumed on the procedure. However, it has a slight effect on the void growth dynamics. The void migration simulation revealed that a higher temperature gradient accelerates the migration velocity. In addition, there is an inverse relationship between the migration velocity and radius. This study provides a specific phase-field model to simulate void growth in lead-free solder joints under thermal-electrical coupled stress.