FLux fumes will contain evolved hydrocarbon solvents, their thermal breakdown products and that of any flux (usually high molecular weight organic acids), together with bits of the uppers and downers the manufacturer puts in for rheology control and so on. Speak to them or ask for their MSDS for a qualtiative guide. However I think it doesn't matter what the fumes are precisely as whatever they are they will contain lots of Cs and Hs which will cause low apparent O2 ppm readings with any sensor measuring weight increase due to oxidation. This is because the resulting CO2 and H2O will be taken out of the system and and not recorded. Mike Fenner ################################################################ 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 ################################################################