Development of a flux-less soldering method by ultrasonic modulated laser

Solder wetting behavior on pad was studied under continuous and ultrasonic modulated laser with an 8 Pa low vacuum condition. Based on these results, a novel ultrasonic modulated laser flux-less soldering method was put forward and its mechanism was also investigated in detail. Ultrasonic oscillation of temperature field, which resulted in an ultrasonic vibration of the surface of the solder droplet, was generated at the surface of the solder droplet induced by the heating of the ultrasonic modulated laser. The ultrasonic cavitation phenomenon was appeared at the solder wetting interface when the surface ultrasonic vibration was transmitted to the inside of the solder droplet, which force the molten solder to wet on the pad.