Calculating the diffusivity of Cu and Sn in Cu ₃Sn intermetallic by molecular dynamics simulations

In this paper, molecular dynamics (MD) simulations are performed to calculate the diffusivity of Cu and Sn atoms in the Cu ₃Sn intermetallic compound. Our MD results show that Cu atoms are the dominant diffusion species in Cu ₃Sn. The diffusion coefficient of Cu atoms in Cu ₃Sn is about 17 times higher at room temperature (300 K), and 7 times higher at the annealing temperature (423 K) than that of Sn. This large difference in diffusivity between Cu and Sn is believed to be the main cause of Kirkendall void formation within the Cu ₃Sn layer in lead-free solder joints.