Mechanical and corrosion resistances of a Sn–0.7 wt.%Cu lead-free solder alloy

• β-Sn cell and dendrite forms of Sn–0.7 wt.%Cu alloy are characterized.
• Cu6Sn5 interphase and cell/dendritic spacing are determined.
• Solidification thermal parameters (mainly cooling rate) are stressed.
• Relations of mechanical strength and corrosion to the microstructure are derived.

Sn–Cu alloys are interesting lead-free solder alternatives, with particular interest in the eutectic/near-eutectic compositions. However, little is known about the corrosion responses of these solders while subjected to corrosive environments. The present study examines the Sn–0.7 wt.%Cu solder alloy and the experimental results include a range of cooling rates and growth rates during solidification, metallography with comprehensive characterization of the distinct dendritic and cellular regions and the resulting corrosion and tensile mechanical parameters (potential, corrosion rate, polarization resistance, tensile strength). A β-Sn phase having a dendritic morphology is shown to characterize regions that are associated with higher cooling rates during solidification, while for lower cooling rates (<0.9 K/s) the prevalence of eutectic cells is observed. It was found that lower corrosion resistance and higher mechanical strength are associated with a microstructure formed by an arrangement of very fine dendritic branches and Cu6Sn5 fibrous intermetallic compound (IMC).