Phase field simulation of Kirkendall voids at the interface of microscale Sn/Cu system lead-free interconnects

During the soldering process, Kirkendall voids may form at the Cu/Cu₃Sn interface and in Cu₃Sn compound layer. Excessive formation and growth of Kirkendall voids may increase the potential for brittle interfacial fracture, and the existence of voids will reduce the thermal conductivity. Thus, characterization of formation and growth of Kirkendall voids is very important to the evaluation of performance and reliability of solder interconnects. In this paper, a phase field crystal model of a substitutional binary is developed and applied to simulate the formation and growth of Kirkendall voids in the Cu/Cu₃Sn interface in the atomic scale. The simulation results show that the formation and growth of Kirkendall voids includes four stages: incubation, nucleation, growth and healing stages. With increasing the grain boundary angle, more Kirkendall voids may form and the average diameter of Kirkendall voids decreases due to the competitive growth between different Kirkendall voids.