Solder wetting kinetics in narrow V-grooves

Experiments are performed to observe capillary flow in grooves cut into copper surfaces. Flow kinetics of two liquids, 1-heptanol and eutectic SnPb solder, are modeled with modified Washburn kinetics and compared to flow data. It is shown that both liquids flow parabolically in narrow V-grooves, and the data scale as predicted by the modified Washburn model. The early portions of the flow kinetics are characterized by curvature in the length vs time relationship which is not accounted for in the modified Washburn model. This effect is interpreted in terms of a dynamic contact angle. It is concluded that under conditions of rapid flow, solder spreading can be understood as a simple fluid flow process. Slower kinetics, e.g. solder droplet spreading on flat surfaces, may be affected by subsidiary chemical processes such as reaction.