The Horizontal Sonocapillary Effect in Ultrasonic-Assisted Soldering

In this work, the horizontal sonocapillary effect in ultrasonic-assisted soldering was investigated via numerical simulations and experiments. The numerical simulation results indicated that acoustic pressures in the liquid solder exhibited distinct sinusoidal features with negative offsets, forming a negative average acoustic pressure. When the ultrasonic vibrations were transmitted to the lower substrate in the joint clearance, the average acoustic pressures decreased from the acoustic pressure center to the filling front, forming a negative acoustic pressure gradient in the horizontal direction. As a result, the solder was sucked into the joint clearance by a large negative acoustic pressure. This sonocapillary effect was verified with experiments. In the calculation model, a high ultrasonic amplitude, a small joint clearance width, and a high base material stiffness increased the acoustic pressure and its average difference on the horizontal direction in the solder, which further improved the driving force of the sonocapillary effect. However, the wetting angle had a small influence on the sonocapillary effect.