We recently had to replace some BGA's. The replacement ones did not work, and when removed there was residue. Unfortuneatly I didn't get a chance to see the residue. It was described as "fuzzy and grungy". The pads had been cleaned with solder wick and then alcohol. We are now going to try "flux-off". We need a quick easy way to clean the site after the BGA is removed.
What flux are you using to put them back on? you should be able to adequately clean the site after removal with alcohol or water depending upon the type of flux. "White grungy" usually comes from a liquid flux such as Alpha 857 being squirted on the pads and then it gets burnt during the reflow process (I have found that convection heat and this flux are not a good match as far as residues)and does not clean with anything I have found except for brushing and such. We use tacky paste fluxes which seem to eliminate this problem.