Hi Phil:
     
     I have two references that talk about the solderability and pumice 
     scrub interactions:
     
     "Thwaites, C.J. and Mackay, C.A., "Some Effects of Abrasive Cleaning 
     on the Solderability of Printed Circuits", Metal Finishing Journal, 
     Sept. 1968, pp. 291-294 (Tin Research Institute Publication 386).
     
     "Spiliotis, N.J., "Tin Lead Plating Practices That Assure Proper 
     Wetting Upon Reflow", Insulation/Circuits, June 1978, pp. 64-71."
     

I imagine that Paul Davis used the Thwaites/Mackay efforts for at least part of 
a publication - I can't find any record of a paper by him on pumice scrubbing 
but then my library has a few holes in it.  As for your dewetting and white 
residue question - NO, I have run into that situation several times but it was 
never a lead species related issue. Tin preferentially oxidizes on a tin/lead 
surface which makes the formation of a lead species a process specific cause. Do
the pwbs see some type of chemistry and/or environmental exposure that would 
promote a lead carbonate? I think Bill Hampshire (formerly of the Tin Research 
Institute) published a paper that talked about the formation of lead species - 
you may want to get ahold of him (I know I have the paper but I just can't find 
it!). 


Dave Hillman
Rockwell Collins
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______________________________ Reply Separator _________________________________
Subject: Dewetting & Pumice Scrub
Author:  [log in to unmask] at ccmgw1
Date:    9/18/96 10:41 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] 
     
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