Solder Ball Attach With Water Soluble Air Reflowable Tacky Fluxes

Selected physical properties of four water-soluble tacky fluxes were measured, including viscosity, acid number, pH, weight loss during heating, and rheological properties. The capability of the fluxes to perform ball attach in air and N2 using an in-house test board with Cu-organic solderability preservative surface finish was studied in a Malcom reflow simulator using highly oxidized SAC305 solder spheres. Flux performance was rated from the observations of fluxing action in a reflow simulator and the ability to realign deliberately misplaced solder balls and eliminate the occurrence of crescent defects. Two of the four fluxes exhibited good ability to realign misplaced solder balls and one flux exhibited outstanding ease of cleaning. Contrary to common perception, the best performing flux did not have the highest acid number.