Dynamic Behavior of Solder Filling during Ultrasonic Soldering

In this work, the dynamic behavior of solder filling in a nonwetting joint capillary under ultrasonic agitation was visually observed by using a high-speed camera. The filling process, sputtering of solder, and cavitation phenomena were recorded and discussed. Filling variation was correlated with ultrasonic power, base material type, and clearance width. Notably, the filling rate of liquid metal varied along the joint clearance and was dependent on the surface vibration strength of the substrate. The sputtering and cavitation of liquid metal became pronounced when the surface vibration of the base material exceeded a critical value. High ultrasonic power, high base material stiffness, and narrow clearance increased filling rate. The evidence in this research showed cavitation is not necessary for initiation of the ultrasonic capillary effect.