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 β-Sn phase and the mixture of Ag₃Sn and ζ-AgZn particles. However, the β-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 γ-AgZn phase is formed in a Sn–3Ag–2Zn solder. The ε-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 °C in the melting temperature and 13.87 °C in undercooling. The wetting kinetics of the main spreading stage features the power law of Rⁿ ~ t (n = 1), which is controlled by chemical reactions at the triple line.