Investigation of wetting behavior of Sn-3Ag-0.5Cu solder paste to BGA solder ball

Wetting behavior of Sn-3Ag-0.5Cu (mass%) solder paste to BGA solder ball was investigated through the measurement of wetting force loaded onto the solder ball in reflow soldering process. The effect of the oxide film thickness on the solder ball, desorption of the solder ball from solder paste and timing of dipping for solder paste were investigated on wetting properties. Wetting properties were degraded by increasing the thickness of oxide film. Two steps in wetting behavior, which consists of wetting of flux and wetting of molten solder, were observed when the oxide film thickness is over approximately 6 nm. The increase of desorption time at temperature over the activated temperature of flux causes degradation in wetting properties. In the dipping temperature changing test, the effect of the oxide film thickness on wetting properties is negligible in the case of a few nm thick oxide film.