Phase-Field Study of IMC Growth in Sn–Cu/Cu Solder Joints Including Elastoplastic Effects

Lead-free solders are being researched over the last decade in order to replace the lead-tin solder which was used as a connecting material in electronic devices. During the solid-state annealing processing step and during service in electronic devices, solder joints experience stresses that lead to elastoplastic deformation. These stresses influence the kinetics and morphology of the brittle intermetallic compounds that are formed, in turn affecting there liability of the joint. In this article, we aim to study the problem of the growth of intermetallic phases in solder joints undergoing mechanical deformation, using a phase-field model for multi-phase systems that can treat diffusion, elastic and plastic deformation. A suitable model is formulated and applied to Sn–Cu/Cu lead-free solder joints. The growth of the intermetallic layers during solid-state annealing is simulated for different strain states.The stiffness tensors required as input are calculated by ab initio methods to corroborate the values available in literature. We find that the growth rate of the Cu3Sn intermetallic layer increases with applied tensile strain but decreases with applied compressive strain, as also observed in experiments. We thereby establish the importance of strain in the growth of intermetallic layers and the need for more targeted experiments on the role of strain in the reliability of the solder joint.