Intermetallic compounds formed at the interface between Cu substrate and an Sn–9Zn–0.5Ag lead-free solder

The intermetallic compounds (IMCs) formed at the interface between Cu substrate and an Sn–9Zn–0.5Ag lead-free solder alloy have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction (ED). The XRD patterns show that the main IMCs formed at the interface of Sn–9Zn–0.5Ag/Cu are γ-Cu5Zn8 and η′-Cu6Sn5. The Ag3Sn IMC with orthorhombic structure was also observed at the Sn–9Zn–0.5Ag/Cu interface by TEM and ED analyses. The interfacial adhesion strength between the Cu substrate and Sn–9Zn–0.5Ag lead-free solder alloy is higher than that of the Sn–9Zn alloy due to the formation of Ag3Sn IMC at the interface.