Molecular dynamics simulation and experimental study of tin growth in SAC lead-free microsolder joints under thermo-mechanical-electrical coupling

Abstract

Sn-Ag-Cu system lead-free solders are considered to be promising solder series. The growth of Sn whiskers on the solder surface is an important factor that threatens the reliability of electronic products. In this study, the IMC evolution and whiskers growth of Sn-0.3Ag-0.7Cu (SAC0307) microsolder joints under thermal-mechanical-electrical coupling were investigated by the combination of molecular dynamics simulation and experimental methods. The simulation and experimental results revealed that the electric field intensity had the greatest influence on the atomic diffusion. When the electric field intensity was 0.004 V/Å, the diffusion speed of copper atom to solder reached the maximum, and the intermetallic compounds Cu6Sn5 and Cu3Sn were formed at the interface, which provided the long-term driving force for the growth of tin whiskers at the weak oxide film on the surface. Tin whiskers were inclined to grow at the anode, while holes and cracks were tend to produce at the cathode. When the external pressure stress was 0.03 nN, most of tin atoms were precipitated. When the temperature was 393 K, the whiskers slowly grew to 3.3 µm in length at the growth rate of 0.0182 Å/s. The results can provide the basis for the growth mechanism of tin whisker in real service situations.