I have a white residue problem that is becoming all to common. The white residue appears between and behind soldered leads on the polyimide substrate. It does not appear on or inside of soldered-through holes. On some boards I can find it between all the leads. On others I see it only between a few leads. I have analyzed this residue many times with FTIR. Everytime, I get proteinaceous matter (protein). I see no evidence of rosin-based or water-soluble flux, but at times I see cellulose fibers mixed in with the proteinaceous matter. What is this stuff? We have considered: 1. skin residue (dandruff) 2. debris from camel hair brushes 3. fungus There appears to be far too much residue to consider 1. and 2. The problem appears after the final cleaning/rinsing step. Any ideas would be greatly appreciated. Thank you. --Phil