Formation of particle of bismuth–indium alloys and particle diameter by ultrasonic cavitation

The miniaturization of electronic equipment requires fine bonding. Therefore, it is necessary to miniaturize the solder particles used for bonding different materials. Ultrasonic cavitation is a technique that uses ultrasonic irradiation to synthesize such microparticles. In this study, we investigated the effects of ultrasonic irradiation conditions on synthetic microparticles produced by this technique. Spherical particles were obtained by irradiating Bi-45 wt% In melted in a solvent with ultrasonic waves for 15 s, and the resultant metal composition was found to be equivalent to the raw material composition. We found a clear correlation between the ultrasonic irradiation time and particle size. When irradiated for 60 min, the average particle diameter was 3.3 μm. In addition, the particle division rate decreased as the irradiation time increased, which is probably due to attenuation of the vibration wave as the boundary surface increased with the refinement of the particle.