My company manufactures memory modules and I'm finding solder specs on the gold fingers following the reflow process. We are using a no-clean solder paste. The spec sheet warns against crossing the 140 degree C mark during the soak stage, preventing any violent outgassing, possibly spraying solder balls onto the gold fingers. I've adjusted our profile to ensure that 140 is not crossed. I've also adjusted (down) the ramp rate at which the soak stage is reached, but I am still finding this problem.. Any ideas will be tried out. Thanks.
Try looking for paste contamination somewhere. Dirty stencil, printer table or fixtures. Placement table/fixtures. Reflow belt/conveyer. Reuseable finger covers, if used. Try covering the fingers with Kapton tape during different stages of the process to narrow down where it occurs. Is it only in one area or spread around? Dry/old paste can "spit" with a proper profile if a crust or shell dries around the paste before reflow. Good luck John Thorup