Cleaning before Conformal Coating

2017/2/20 6:52:37

Hi, I am running a circuit board that needs a part to be put on it after cleaning and before conformal coating. the only problem is that after cleaning and hand assembly of the part, there is a thin whitish residue in the ckt board that one can see when seen at an angle under light. brushing with xylene will clean it. After conformal coating, the ckt boards that were left uncleaned of this white residue show good conformal coat coverage, but the ckt boards scrubbed clean with xylene shoe dewetting on the coat. I am using Humiseal UR coat. does anyone have an idea of what this whitish layer is??