Morphology of intermetallic compounds formed between lead-free Sn-Zn based solders and Cu substrates

摘要

The morphologies of intermetallic compounds formed between Sn-Zn based solders and Cu substrates were investigated in this study. The investigated solders were Sn-9Zn, Sn-8.55Zn-0.45Al, and Sn-8.55Zn-0.45Al-0.5Ag. The experimental results indicated that the Sn-9Zn solder formed Cu5Zn8 and CuZn5 compounds on the Cu substrate, while the Al-containing solders formed the Al4.2Cu3.2Zn0.7 compound. The addition of Ag to the Sn-8.55Zn-0.45Al solder resulted in the formation of the AgZn3 compound at the interface between the Al4.2Cu3.2Zn0.7 compound and the solder. Furthermore, it was found that the cooling rate of the specimen after soldering had an effect on the quantity of AgZn3 compound formed at the interface. The AgZn3 compound formed with an air-cooling condition exhibited a rougher surface and larger size than with a water-quenched condition. It was believed that the formation of the AgZn3 compound at the interface occurs through heterogenous nucleation during solidification.