Study on melt properties, microstructure, tensile properties of low Ag content Sn–Ag–Zn Lead-free solders

Sn–Ag solders have been regarded as the most promising solders to replace Sn–Pb solders in the future, but the reliability and cost issues limit its use. Therefore a low-Ag content Sn–Ag–Cu solder, SAC105 was researched, which still has some problems. Sn–Ag–Zn solders are obviously superior in many aspects in comparison to Sn–Ag–Cu solders, but the low-Ag Sn–Ag–Zn solders were rarely studied. In this paper, properties of Sn–xAg–yZn (x=1, 1.5, 2, 3; y=1, 1.5, 2, 2.5, 3, 4) solders, including melt properties, microstructure, and tensile properties were investigated. It was found that reduction of Ag content in Sn–Ag–Zn solders leads to the same problems as in Sn–Ag–Cu solders in melt properties and tensile properties. Although Sn–xAg–1Zn solders have higher strength, the elongation is lower. Results show that melt properties and tensile properties can be improved by the optimization of Zn content, but excessive Zn additon could lead to worse properties as well. Sn–2Ag–2.5Zn and Sn–1.5Ag–2Zn solders were found to have optimized properties. In addition, relations between melt properties and microstructure, as well as microstructure and tensile properties, were discussed.