Effect of twin grain boundary on the diffusion of Cu in bulk β-Sn

SG Hao and HL Li, COMPUTATIONAL MATERIALS SCIENCE, 226, 112200 (2023).

DOI: 10.1016/j.commatsci.2023.112200

For Cu is the dominant diffusing species in the Cu/Sn diffusion couple, the diffusion behaviors of Cu in the beta-Sn grain and at the twin grain boundary (TGB) have been studied in this paper by combining the first- principles calculation and molecular dynamics simulation, which has a significant impact on solder joint reliability. The results show that the energy barrier for Cu bulk diffusion in beta-Sn depends on the diffusion path, ranging from 0.01 eV to 0.33 eV. Among the three possible diffusion paths at the (101) TGB, the primary diffusion path is along the 010 direction of the TGB plane. However, this diffusion path along the TGB still presents a relatively high energy barrier of 0.26 eV compared to the energy barrier for bulk diffusion. Furthermore, due to the segregation of Cu atoms at the beta-Sn TGB and the inhibition effect of multiple energy barriers for diffusion crossing the TGB, long-range diffusion of Cu across the TGB between the two beta-Sn bulk grains is difficult. As a result, the (101) TGB actually inhibits the diffusion of Cu in beta-Sn. It can be concluded that increasing the number of TGBs inside a Cu/Sn solder joint can effectively suppress the interdiffusion between Cu and Sn, which will prevent the growth of Cu-Sn intermetallic compounds and improve the reliability of the solder joint.

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