The Effect of Bi and Zn Additives on Sn-Ag-Cu Lead-Free Solder Alloys for Ag Reduction

Abstract

This study aimed to investigate the effects of the addition of Bi and Zn on the mechanical properties of Sn-Ag-Cu lead-free alloy frequently used as a soldering material in the semiconductor packaging process. To reduce the Ag content of the commercial alloy SAC305 (Sn-3Ag-0.5Cu) by 1 wt.%, Bi and Zn were admixed in different ratios and the changes in mechanical and electrical properties were analyzed. Compared to the SAC305 alloy, electrical conductivity and elongation at break decreased while tensile strength increased following the addition of the two elements. In particular, upon the addition of 1 wt.% Bi, the tensile strength increased to a maximum of 43.7 MPa, whereas the tensile strength was 31.9 MPa in the alloy with 1 wt.% Zn. Differential thermal analysis and scanning electron microscopy revealed that the changes in physical properties can be ascribed to a reduction in the activation energy required for formation intermetallic compound when Bi was added, and the refinement of the structure due to a decrease in undercooling degree when Zn was added. When Bi and Zn were added at the same time, each characteristic for the change in the microstructure was applied in a complex manner, but the effect on the change of the physical properties worked independently.