Effect of Zn addition on interfacial reactions between Sn-Bi solder and Cu substrate

Abstract

A comparative study of the formation, growth, and morphology of the interfacial intermetallic compounds (IMCs) of the eutectic Sn-Bi and Sn-Bi-Zn solder joints was conducted, and the shear strengths of the two solder joints were evaluated. The cross-sectional microstructures of the joints were investigated and the fracture surfaces of the joints were examined after the shear tests. The results of the microstructural analysis of the joints indicated that the addition of Zn suppressed the growth of the interfacial IMCs significantly after both reflow and thermal aging. Although the shear-test results indicated that the addition of Zn decreased the shear strength of the Sn-Bi solder joint, the fracture surface examination after the shear tests revealed the cause of the degradation of the shear strength and a possible solution to prevent this degradation is suggested in the paper.