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.



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     ______________________________ 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.

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