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Date: | Wed, 08 May 96 10:23:48 EDT |
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Gee Harry,
That sounds all too familiar to some work done at a board shop in S.
FL using high temp/RH and a CO2 rich atmosphere to accelerate this
condition by a Chicago chemist his english office mate and their token
yank apprentice.
Bob Hall
Bellcore
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Subject: Re[2]: White residue/lead oxide
Author: [log in to unmask] at SMTP
Date: 5/7/96 6:48 PM
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 |
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ooO Ooo
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_________________________________ 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.
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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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