I have my doubts re your analysis of the residue.  Lead oxide wouldn't 
     be white but would vary from yellow-red to brown color (depending on 
     what chemical form the oxide took).  We've had a variety of "white 
     residues" and they have generally been one of four types:
        a.  Polymerized flux residue (due to either inadequate cleaning leaving  
            flux which reacts with water cleaner and/or excessive heat in 
            soldering) (this one is ~90% of the time)
        b.  "Etching" or chemical attack of solder (typically related to use of  
            hot/high resistivity DI water (7-12 Megohms); surface affect only no 
            structural impact (5-10%)
        c.  Bromide salts (reaction between flux and bromide in fire retardant 
            used in Gl/Ep) (1-3%)
        d.  Discolored solder mask (typically etching/chemical attach of 
            undercured mask) (1-3%)
     
     What we do to differentiate is a) look at location; (c) and (d) are 
     typically on laminate, not on joints themselves).  We have found that using 
     the "like disolves like" idea; a mildly acivated flux (e.g. Kester 197) on 
     the residue followed by mild heating (100-150F) to increase activity of 
     acid in activator then "normal" cleaning can remove most of the residue.  
     
     Note that we had a LOT of trouble with white residue on initially using 
     semi-aqueous cleaning.  We found reducing preheat helped, reducing conveyor 
     speed/dwell time helped a lot, reducing solids content in flux helped some; 
     going to a more thermally stable (e.g. tall oil) type flux (e.g. Alpha 615 
     or Kester 186) eliminated the problem.  We also found some cleaners more 
     effective than others in removing the residues (e.g. Kyzen FCR).  
     
     If you have any questions, call.
     
     Jim Maguire
     Senior Principal Engineer
     Boeing Defense & Space Group
     PO Box 3999 M/S 3W-97
     Seattle, WA  98124-2499
     Phone 206-657-9063
     FAX    206-657-8903
     Email:  [log in to unmask]
     
     ______________________________ Reply Separator 
     _________________________________
     Subject: White residue/lead oxide
Author:  [log in to unmask] at esdigate
Date:    5/7/96 10:04 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.
     
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