Spreading of Sn-Ag-Ti and Sn-Ag-Ti(-Al) solder droplets on the surface of porous graphite through ultrasonic vibration

Highlights: • The spreading process of active solder on graphite under ultrasonic action was captured by using high-speed camera. • The spreading distance and rate of Sn5Ag8Ti solder were significantly less than that of Sn5Ag2Ti1Al solder. • The spreading rate was determined by solder composition and thickness of the oxide film on the solder surface. • The wettability of active solder on graphite was promoted under the ultrasonic effect. The spreading process of an active solder droplet on porous graphite surface was captured by using high-speed camera. The spreading characteristics of the Sn5Ag8Ti and Sn5Ag2Ti1Al active solder under ultrasonic vibrations were analysed. The results showed that applying ultrasonic waves during the soldering process enable the active solder to spread on the graphite surface at a relatively low temperature under atmospheric condition. Initially, the solder spread slowly on the graphite surface in the direction opposite to that of the ultrasonic wave transmission because of the rapid attenuation of ultrasonic amplitude on the surface of the graphite. Then graphite pores were rapidly filled with solder under the action of ultrasonic vibration, which prevented the ultrasonic attenuation. Subsequently, the solder spread out rapidly along the direction of transmission. In addition, the spreading distance and rate of Sn5Ag8Ti were significantly less than that of Sn5Ag2Ti1Al solder, which was determined by the composition and thickness of the oxide film on the surface of the active solder.