Abstract
Self-organization assembly（SOA）method is a way to form conductive paths using thermoset resin containing solder fillers applied between an electric component and a print circuit board（PCB）. A lot of phenomena such as movement, melting, coalescence and wetting of solder fillers, and reduction of surface oxide film, have to be controlled to realize the SOA method. The authors revealed the effect of viscosity of resin and reduction of oxide film on coalescence behavior of solder fillers. Since the viscosity of resin decreased at elevated temperature, solder fillers sank in the resin to the PCB before melting. Coalescence behavior depended on wettability of solder fillers in the resin. When the wettability was poor, the solder fillers were not coalesced sufficiently and many fillers left between electrodes. When the wettability was fine, the solder particles sunk on the PCB were fused together and subsequently separated and wetted on each electrode.
