Phil, When you say that the white residue, which appears either as isolated spots or globally, appears after final cleaning, it indicates to me that the residue is either abietic acid, if you are using a high-solids rosin flux/paste, or an interactive product between the weak organic acids and water, if you are using a low solids flux. If you are using a water soluble flux, the white residue could be residual paste/flux, especially if you are using tap water as a cleaning media. Some questions to answer: 1. What flux technology are you using? A formulation reference would be helpful. 2. What cleaning solutions are you using? Tap water? DI? Saponifier? (Gasp)- CFC? 3. Are you doing fine pitch work? Surface Mount? Through hole? We often do residue analysis for customers who ask "What is this stuff?" Please give me a call and we can discuss it. I can synopsize for TechNet people later. Doug Pauls Contamination Studies Laboratories [log in to unmask] (317) 457-8095