A study of the microstructure, thermal properties and wetting kinetics of Sn-3Ag-xZn lead-free solders

Microstructure, thermal properties and wetting kinetics of Sn-3Ag-xZn solders (x = 0.4, 0.6, 0.8, 1, 2 and 4 wt%) were systematically investigated. The results indicate that a small amount of Zn (Zn wt% <= 1 wt%) has a rather moderate effect on the microstructure morphology of the Sn-3Ag-xZn solders. The microstructures are composed of a beta-Sn phase and the mixture of Ag3Sn and zeta-AgZn particles. However, the beta-Sn phase reduces its volume fraction in the entire microstructure and the intermetallic compounds population increases with the increasing of Zn content. The microstructure is dramatically changed with a further increase in the Zn content. The gamma-AgZn phase is formed in a Sn-3Ag-2Zn solder. The epsilon-AgZn phase is formed in a Sn-3Ag-4Zn solder. The melting temperature and the undercooling of the Sn-3Ag-xZn solder alloys decrease with the increase in Zn content, reach to a minimum value when the content of Zn is 1 wt%, and then increase with further increase in Zn content. The Sn-3Ag-1Zn demonstrates the minimum value of 228.13 degrees C in the melting temperature and 13.87 degrees C in undercooling. The wetting kinetics of the main spreading stage features the power law of R-n similar to t (n = 1), which is controlled by chemical reactions at the triple line.