Breaking up of liquid SnPb film on the gold-coated copper wetting channel

The Au/Cu film was prepared by vacuum evaporation plating method and patterned by the standard lithography process. The eutectic SnPb solder ball was reflowed on the designed film pattern with H2 protection. The liquid solder would flow along the Au/Cu zones and the final wetting shape reflected the original structure of the pattern. The liquid film was extended ahead of the main liquid front and forced to spread fast along the wetting channel due to the strong Au-Sn affinity. The quantity of liquid solder was far different from the pad center to the Au/Cu line end. The liquid film would break up when the liquid solder was enough to consume the underneath Cu film.