I agree, in a highly chlorinated flux there may be a percentage of HCl available which,if not thoroughly cleaned off the board, will attack the lead (Pb) in the solder producing lead chloride: Pb + 2HCl --> PbCl2 + 2H+ The surface will adsorb water and carbon dioxide from the atmosphere and form lead carbonate, releasing hydrochloric acid, which will attack additional lead in the solder producing lead chloride: PbCl2 + H2O + CO2 --> PbCl2 + H2CO3 --> PbCO3 + 2HCl Pb + 2HCl --> PbCl2 + 2H+ The chain reaction can continue until all lead on the surface is consumed. Lead carbonate is a white material and may be the white residue you are observing. \\'''''// (o o) @----oOO---------(_)----------------@ | Harry O'Halloran | | DSC Communications Corporation | | 1000 Coit Road | | Plano, TX 75075-5813 | | Phone: (214) 519-3916 | | [log in to unmask] | @--------------------------oOO-----@ | __ | __ | | | | | ooO Ooo ______________________________ Reply Separator _________________________________ Subject: Re: White residue/lead oxide Author: [log in to unmask] at SMTPLINK Date: 5/7/96 12:41 PM DON'T KNOW IF THIS WILL HELP. BUT, MANY YEARS AGO WHITE RESIDUE WAS OBSERVED ON COMPONENTS THAT HAD BEEN FLUXED WITH A HIGHLY CHLORINATED FLUX.. IT WAS DETERMINED TO BE SOLUBLE "ONLY" IN A DILUTED SOLUTION OF THE ORIGINAL FLUX.. SORRY, THAT'S ALL I CAN OFFER. ______________________________ Reply Separator _________________________________ Subject: White residue/lead oxide Author: [log in to unmask] at smtp Date: 5/7/96 10:16 AM We have a white residue problem at another division that has been analyzed using FTIR and SEM EDAX that has shown it to be lead oxide. The white residue is located on pads/solder fillets. The following process is used: a. Yokota flow solder (preheat 220F topside, 495F solder pot (less than 3 seconds), conveyor speed 3.5 ft/min) b. Kester 197 foam fluxer (rma) c. Cleaner is Bioact EC7R in a Ney spray under immersion or ECD batch diswasher. Temperature of EC7R 90-95F, Rinse waters 130F. The white residue is observed after cleaning and is insoluble in alcohol water/EC7R. Any input on things to look for would be greatly appreciated. We are running tests at other divisions with different flux chemistries/board design/process parameters. [log in to unmask]