Investigation of Ni-Microalloyed Sn-0.5Cu Lead-Free Solders

In this study the effects of small amounts of nickel addition (0-2000 ppm) on the microstructure, on Cu6Sn5 intermetallic compound formation and the mechanical properties of a Sn-0.5Cu lead-free solder were investigated. It is known that even ppm level additions of Ni have significant effects on the microstructure of Sn-Cu solder alloys. Ni suppresses the growth of β-Sn dendrites in favour of eutectic formation. As the nickel content increases, the microstructure undergoes a morphology evolution from hypoeutectic through fully eutectic to hypereutectic. Furthermore, the presence of Ni in the Cu6Sn5 intermetallic compound phase stabilises its high-temperature allotrope η-Cu6Sn5.