Enhanced wettability in ultrasonic-assisted soldering to glass substrates

Abstract Ultrasonic-assisted soldering (UAS) creates an enhanced metal-to-glass bond that is linked to the increased wettability of the solder line. Precision experiments are performed using an automated UAS system, with precise control over a large number of experimental parameters, to investigate the wetting properties of solder to glass. Results show that wettability is increased with (i) increasing ultrasonic power and (ii) decreasing solder tip height above substrate, both of which are linked to the acoustic radiation pressure delivered by the vibrating solder tip to the liquid solder melt. Surface tension forces dominate the mechanics and a capillary shape equation is derived that includes the effect of acoustic radiation pressure. Numerical solutions to the capillary shape equation compare well with experimental observations, suggesting the solder bead geometry can be predicted a priori from the model.