Growth kinetics of intermetallic compounds formation between liquid Sn-9Zn-0.1S solders and Cu substrates interface

The microstructure and growth kinetics of intermetallic compounds formed during the soldering reactions between Sn-9Zn-0.1S solders and Cu substrates at various temperatures ranging from 230 to 260℃ were investigated using scanning electron microscope and optical microscope. The results indicate that a thick planar layer of γ-Cu₅Zn₈ next to Cu substrate and a thin particulate layer of CuZn adjacent to solder can be formed at the Sn-9Zn-0.1S/Cu interface, and the constituent of the interfacial intermetallics do not change with the increase of soldering temperature and the prolonged reaction time, while the thickness of γ-Cu₅Zn₈ layer increases with the soldering temperature and reaction time. The relationship between the thickness of γ-Cu₅Zn₈ layer and the square root of reaction time fits linear, which shows that the growth of the intermetallic layer is diffusion-controlled. Kinetics analysis indicated that the activation energy of the intermetallic growth was 22.09 kJ/mol.