Mr. de Rooij, I must ask why you feel that any residue is not acceptable. In my experience, that stance is most often driven by fear (it's new), tradition (we've always cleaned), or by customers who fear. In many cases, low solids flux residues are primarily weak organic acids and are benign on an assembly surface. The layer of flux residue can provide a sort of protection, similar to conformal coating. If the no-clean flux is not designed for cleaning, you may have a difficult job removing the flux. That being said, we have worked with customers who, for one reason or another, clean a no-clean flux, usually for cosmetic reasons. I would not recommend a chlorinated solvent, nor a semi-aqueous material. You should look for a saponifier that runs in the 140-145F temp range with a good surfactant constituent. The saponifier attacks the weak organic acids while the surfactant breaks down the water tension, allowing the saponifier to get into low standoff areas. In any case, do not use tap water, which will give you nothing but grief. Use at least RO water, and DI water is preferred. Two saponifier packages that we have seen work very well with low solids flux residues are Kyzen Aquanox SSA and Envirosense Envirogold 816. The SSA runs at a 25-30% solution, the 816 runs in a 5-10% solution. Both are also very good at cleaning chlorides, which may remain from the board fabrication process. I know of several companies using these products successfully. Both formulations were originally designed for RMA flux residues, but work well for most fluxes we have examined. Hope this was of some help. Doug Pauls CSL [log in to unmask]