Effect of Bi on the microstructure and tensile behavior of Sn‐3.7Ag solders

Abstract

PurposeThe purpose of this paper is to investigate a Pb‐free solder alternative, specifically the effect of Bi on the microstructure and tensile strength of Sn‐3.7Ag solders casted under different cooling rates.Design/methodology/approachSn‐3.7Ag solder paste was mechanically blended with different percentages of Bi particles (99.999 percent) to form composite solder pastes. The solder paste was cast under different cooling rates to form dog‐bone shape samples for tensile testing. The solder samples were subjected to tensile testing on an INSTRON 5543 tester with loading rate 10−3 s−1. Both the as‐cast and tensile‐tested samples were mounted, ground and polished for microstructure and fracture surface analysis. Scanning electron microscopy/Energy dispersive X‐ray spectroscopy was used to characterize the microstructure, morphology, and composition.FindingsThe tensile strength of Sn‐3.7Ag solder increased with increased Bi addition. However, elongation decreased with increased Bi addition. The tensile strength of Sn‐3.7Ag‐xBi (x=0, 1, 2, 3, 4 wt%) solders increased with increased cooling rates when Bi is lower than 3 wt%. The reason for improved strength of Sn‐3.7Ag‐xBi solders is the result of the combination of the solid solution strengthening and precipitation strengthening effects of Bi.Originality/valueTensile testing Bi reinforced Sn‐3.7Ag solder formed under different cooling rates is new in the paper. With the additions of Bi to Sn‐3.7Ag, the solder strength has been increased, which may be beneficial to the electronics industry and other researchers seeking a better replacement for Sn−Pb solder.