Effects of Ag on Properties of Sn-9Zn Lead-Free Solder

The influences of different Ag contents on the properties of Sn-9Zn lead-free solder were investigated. The results indicate that Ag plays an important role not only in the solderability and the structure of the solder, but also in the mechanical property of the soldered joint. In particular, adding 0.3% (mass fraction) Ag can improve the oxidation resistance of the solder, so the solderability of the solder is significantly improved. Sn-9Zn-0.3Ag shows finer and more uniform microstructure than Sn-9Zn. Results also indicate that when the content of Ag is 0.3%, the best mechanical property of the soldered joint can be obtained, and the fracture micrographs show that plenty of small and uniform dimples are found on the soldered joints fractures. Some Cu-Zn and Ag-Zn intermetallic compounds appear at the bottom of dimples when the content of Ag is up to 1%, and the mechanical property of the soldered joint is reduced.