I have been posed a hypothetical question. If flux dissolves a metallic oxide into solution, can this oxide reappear as contamination at a later point? The actual case is a nickel "stain" on a ceramic substrate. One theory as to where the stain is coming from is that it is left behind after flux residue removal. Furthermore, the theory is that the flux can spray this contaminant around due to the boiling process as it activates. If this is so, I really don't see why this isn't a major problem in all areas of soldering. I also can't see why it would only happen in this particular application. It would make my case easier however, if I had a more complete understanding of the chemical process through which flux removes the oxidation, and where the oxidation "goes". Thanks for any help. ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################