Phil: A white residue is a sign of a contaminated surface. Although, I do not know if the presence of lead carbonate will cause dewetting, I can explain a possible source of the lead carbonate. A chlorinated hot air leveling flux may leave an HCl residue which,if not thoroughly cleaned off the board, will attack the lead (Pb) in the solder producing lead chloride: Pb + 2HCl --> PbCl2 + 2H+ The lead chloride 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+ This 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. If you have any questions, please give me a call. Harry \\'''''// (o o) @----oOO---------(_)----------------@ | Harry O'Halloran | | DSC Communications Corporation | | 1000 Coit Road | | Plano, TX 75075-5813 | | Phone: (214) 519-7123 | | [log in to unmask] | @--------------------------oOO------@ | __ | __ | | | | | ooO Ooo ______________________________ Reply Separator _________________________________ Subject: Dewetting & Pumice Scrub Author: [log in to unmask] at SMTPLINK Date: 9/18/96 10:02 AM Technetters In the mid 1970's Paul Davis of Tin Research wrote an article on dewetting as result of pumice scrub. Does anyone have a reference to where this was published. Also does anyone have any input as to dewetting as result of pumice scrub in relation to a sequence of: (1) pumice scrub, (2)apply solder mask, (3) hot air level, (4)solderability test and dewet.. Another question on dewetting. Has anybody seen dewetting as a result of a white residue on the lands and board which was analyzed as lead carbonate? And another:where does the lead carbonate come ? Phil Hinton Hinton PWB Engineering [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************