Wetting behaviour and interfacial microstructure of Sn–Ag–Zn solder alloys on nickel coated aluminium substrates

Abstract

Wetting behaviours of two lead free solders (Sn–2·625Ag–2·25Zn and Sn–1·75Ag–4·5Zn) on nickel coated aluminium substrates were investigated. Sn–2·625Ag–2·25Zn exhibited better wettability compared to Sn–1·75Ag–4·5Zn solder. Contact angles of the solders increased with increasing roughness of the substrate. The Young–Dupre equation was used to evaluate the work of adhesion of solder on the substrate. Sn–2·625Ag–2·25Zn solder exhibited higher work of adhesion than Sn–1·75Ag–4·5Zn. A thin continuous layer of Ni₃Sn was detected at the interface between Sn–2·625Ag–2·25Zn solder and nickel coated Al substrate. Sn–1·75Ag–4·5Zn solder exhibited scallop intermetallic compounds (IMCs) growing into the solder field as well as a thin continuous IMC in some cases. Ni₃Sn and Ni₃Sn₄ IMCs were observed at the interface of Sn–1·75Ag–4·5Zn solder and nickel coated Al.