Influence of 0.05 wt% Pr addition on interfacial microstructure and mechanical properties of Sn–0.3Ag–0.7Cu/Cu solder joint during thermal shocking

Abstract

In this study, the influence of 0.05 wt% rare earth (RE) Pr element addition on the thermal shocking reliability of low-silver Sn–0.3Ag–0.7Cu (SAC0307) solder joint was investigated. The results indicated that during thermal shocking test (− 196 to 150 °C), the interfacial layers of both plain SAC0307/Cu and SAC0307–0.05Pr/Cu joints gradually thickened with the emergence of Cu3Sn intermetallic compounds (IMCs) layer. However, the addition of RE Pr element slowed down the diffusion of Sn and Cu atoms, resulting in thinner interfacial layers and reducing time exponent n of Cu–Sn IMCs from 0.677 to 0.570. After 400 thermal shocks, the shear strengths of SAC0307/Cu and SAC0307–0.05Pr/Cu joints declined by more than 40%, reaching 26.1 and 31.5 MPa, respectively. The decrement in shear strengths was mainly due to the thickening of the brittle interfacial layers and the accumulated thermal stress concentration caused by extreme temperature change (ΔT = 346 °C) during thermal shocking. The ductility of SAC0307/Cu joint deteriorated with thermal shocks and the fracture location gradually transformed from the solder matrix to the solder/Cu–Sn IMCs interface. The addition of RE Pr element reduced the ductility loss due to its inhibitory effect on the interfacial layer growth, and thus the fracture mode of SAC0307–0.05Pr/Cu joint was still ductile fracture.