Competitive failure mechanism and load tolerance of solder joint under thermo-mechano-electrical coupling

Abstract

A strong coupling thermo-mechano-electro-diffusional phase field model is presented and used to investigating the failure mechanism of a Cu/Sn/Cu solder joint during service and assembly. The inter-diffusion behaviour between Cu and Sn is characterised by the diffusion coefficients and effective charge numbers of Cu in Cu, Cu3Sn, Cu6Sn5, and Sn, and those of Sn in Sn, Cu3Sn, Cu6Sn5, and Cu. The simulation results reveal that electromigration (EM)-induced void propagation occurs at the interface between the solder and intermetallic compounds (IMCs), and leading to thermal, mechanical, and electrical concentration effects at the void tip, and eventually to electrical failure. The presence of a strain gradient can retard the EM-induced void propagation, which can be obtained by parameterizing the coupling coefficient. The rapid increase in the energy release rate (ERR) at the void tip induced by the void propagation may cause void initiation failure. Furthermore, electrical failure and void initiation failure compete with each other. The mixed-mode critical fracture toughness and the deviation rate of voltage are introduced in the corresponding failure criteria for determining the safety of assembly.