Numerical simulation of the atomic migration and diffusion during current stressing in the Cu/Sn-58Bi/Cu solder joints

In this work, we tried to use the finite element analysis (FEA) method to simulate the atom migration during current stressing at different temperatures. Based on the FEA tool of ABAQUS, the heat transfer subroutine of UMATHT was secondary developed, establishing the corresponding relationship between heat transfer and classical diffusion theory. The Bi migration content with current stressing time was given. Results showed that the Bi content at the anode interface increased upon the stressing time. Moreover, the Bi migration rate underwent a sharp increase at the initial stage as the EM effect occurred, and then dropped and tended to be stable. When the stressing time was up to 48h, the Bi content at the anode interface could reach 97%, which definitely proved that most Bi atoms had migrated and aggregated at the anode interface to form a continuous Bi layer. Furthermore, the experimental test was conducted with the same EM condition. EDX analysis results indicated that the Bi content at the anode after current stressing for 48h was in accordance with the simulation results, which validated the simulation method.