Study on properties of low-Ag content Sn-Ag-Zn lead-free solders

Sn-Ag solder has been regarded as the most promising solder which can in place of Sn-Pb solder in the future, but there are reliability and cost problems limit its use. Therefore low-Ag content Sn-Ag-Cu solder, SAC105 was researched, it also has some problems. On the other hand, Sn-Ag-Zn solder has some advantages comparing with Sn-Ag-Cu solder, but the low-Ag Content Sn-Ag-Zn solder isn´t reported yet. In this paper, melt and tensile properties of Sn-xAg-1Zn (x=1, 2, 3) solders is researched, it was found the properties of Sn- 2Ag-1Zn solder much better than Sn-1Ag-1Zn solder. So we further researched the melt and tensile properties, solder joint strength on C194 substrate and microstructure of Sn-2Ag-xZn (x=1, 2, 3, 4) solders, otherwise, these solders with 0.1 wt% Cr doping were also researched. The results show that when the Zn contains more than 3 wt%, the liquidus would be decreased while the pasty range would be enlarged. Doping of Cr will increase the liquidus slightly, has little effect in general. In the tensile test, Sn-2Ag-2Zn solder has the best strength but the worst plasticity. Increasing Zn content will improve the plasticity while decrease the tensile strength. Doping of Cr will enhance tensile strength of the all solders and improve plasticity while the Zn content higher than 2 wt%. In solder joint strength test, the as-soldered samples have similar strength. After a few days aging, the solders with high Zn content and doped with Cr have better strength. After 16 days aging, except Sn-2Ag-3Zn-0.1Cr solder, the strength of most solder joints is decreasing.