Evaluation of solder/substrate thermal conductance and wetting angle of Sn–0.7 wt%Cu–(0–0.1 wt%Ni) solder alloys

• The lowest wetting angles against copper were found for the Sn–0.7 wt%Cu–500 ppm Ni.
• The wetting behavior is in the same level with some other Pb-free solders.
• A decrease in the initial wetting angle means increase in hi values.

Wettability is defined as the tendency of a liquid metal to spread on a solid surface. The solder/substrate thermal conductance represented by a heat transfer coefficient, hi, states the heat ability to flow across the solder/substrate interface during solidification, being affected by the wettability. This letter aims to investigate the wetting behavior of Sn–0.7 wt%Cu–(Ni) lead-free solders by measuring the contact angles (θ) on a copper substrate as a function of the alloy Ni content. Furthermore, time-dependent hi profiles are determined from thermal readings during directional solidification (DS) of Sn–0.7 wt%Cu–(xNi) alloys. It is shown that a smaller initial contact angle (θi=32.7) characterizes the Sn–0.7 wt%Cu–0.05 wt%Ni associated with the highest hi value of 11,500t−0.03 W/m2 K (t: time).