Sorry but I disagree with your comments. I have found lead oxide on 
     solder joints due to improper cleaning parameters in the cleaning 
     process verified by several different techniques. As with everything, 
     never rule out what seems unlikely. We do agree on one point - Rosin 
     flux is the culprit for a majority of the white residue problems the 
     industry sees but as other TechNet commenters will undoubtedly show is 
     that a multitude of possibilities can exist for the source of a white 
     residue. With the increased use of low residue and no clean fluxes it 
     will be interesting to see what "residues" will crop up. FTIR is a 
     very powerful tool - yes, the evaluation of the test results can be 
     difficult to interpret but if carefully prepared "suspect" samples are 
     used the test results can be very revealing.
     
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]
     


______________________________ Reply Separator _________________________________
Subject: Re: White residue between soldered leads
Author:  [log in to unmask] at ccmgw1
Date:    5/7/96 7:56 PM


     
There have been several posts recently asking about white residue on PC boards. 
It has been variously identified in the posts as lead oxide and here as 
"proteinaceous material."  From past experience I doubt that it is either. White
residue is often the result of delayed cleaning of printed circuit boards after 
soldering using a rosin based flux.  There was a workshop on this problem 
several years ago at China Lake.  The outcome of the workshop was that the exact
nature of the white residue remained an unknown but that it showed structural 
similarities to the abietic and pimaric acid components of rosin based flux. 
These similarities can be seen using FTIR.  Typically, lead could be detected 
chemically or by x-ray fluorescence.  The condition is agravated by prolonged 
exposure to heat and by delayed cleaning.
     
A few words on FTIR.  While it is a wonderful technique for identifying pure 
materials and if coupled other techniques such as gas chromatography can be used
effectively to identify the constituents of a solution.  It is virtually 
impossible to identify the components of a complex solid solution using FTIR. 
What you can do is show that certain bands are similar to those obtained from 
certain molecular groups such -OH or -COOH.  Unfortunately, there is enough 
overlap of bands that if you have any preconceived notion of what should be in a
sample, you will probably think you see it. 
_______________________________________________________________________________ 
Subject: White residue between soldered leads
From:    [log in to unmask] at Internet 
Date:    5/7/96  2:31 PM
     
     I have a white residue problem that is becoming all to common. The 
     white residue appears between and behind soldered leads on the 
     polyimide substrate.  It does not appear on or inside of 
     soldered-through holes.  On some boards I can find it between all the 
     leads.  On others I see it only between a few leads.
     I have analyzed this residue many times with FTIR.  Everytime, I get 
     proteinaceous matter (protein).  I see no evidence of rosin-based or 
     water-soluble flux, but at times I see cellulose fibers mixed in with 
     the proteinaceous matter.
     
     What is this stuff?
     
     We have considered:
     
     1. skin residue (dandruff)
     2. debris from camel hair brushes
     3. fungus
     
     There appears to be far too much residue to consider 1. and 2. 
     The problem appears after the final cleaning/rinsing step.
     Any ideas would be greatly appreciated.
     
     Thank you.
     
     --Phil