Wetting and spreading of molten SnPb solder on a Cu–10%Nb micro-composite

The wetting and spreading behaviors of molten SnPb solder on a Cu–10%Nb micro-composite and pure Cu are investigated by sessile drop experiments at 250 °C for various times up to 500 s. Very limited extent of spreading of molten solder on the Cu–10%Nb micro-composite is observed, as compared with the spreading on pure copper. Whereas the wetting angle becomes essentially zero for pure Cu after 100 s reflow, it remains as high as about 30° for the Cu–10%Nb alloy, even after a prolonged reflow. Insoluble Nb particles in the copper matrix appear non-wetting with molten SnPb solder and are responsible for both limited spreading and high wetting angle for the Cu–10%Nb micro-composite. The observed quasi-static wetting angle of molten SnPb solder for the Cu–10%Nb is discussed in terms of a surface tension balance at the contact line, utilizing the rule of mixture for surface tension in a wetting system which contains non-wetting particles.