Steve,

Terry Munson at Foresite has been able to clean many badly contaminated assembled boards with a steam process that does not damage the components.  

With his C3 instrument he can extract/analyze residues with a steam extraction process that can be applied to a single part as small as the smallest QFN package or 020X smt resistor.  The extracted liquid is then put thru a liquid chromatograph and other insttumentation to determine the cause of the contamination.

I've visited his facility in Kokomo; its quite impressive. 

Bob

On Jun 22, 2012, at 9:08 AM, "Steve Gregory" <[log in to unmask]> wrote:

> Morning All,
> 
> 
> 
> Boy, I'm looking for it to cool off here this weekend, the last couple of
> days have been brutal! Heat indexes up around 100 F.!
> 
> 
> 
> Anyways, ran into a peculiar white residue issue with a few boards we just
> got through building. We've never had this problem before (that I've seen)
> with the solder paste we use here. Here's a photo of the residue on some
> 20-mil pitch TSSOP leads:
> 
> 
> 
> http://stevezeva.homestead.com/White_residue.jpg
> 
> 
> 
> The flux in the solder paste is a water soluble RELO, and we normally have
> no problem cleaning the residues. We use 130 F. DI water in a inline
> cleaner. Once the residue was noticed, we tried running them through the
> cleaner again, no luck. We tried a trick I remembered from a while back to
> remove white residues which was to take some of the same flux and apply it,
> then heat the board for a bit and run it through the cleaner again, no luck.
> 
> 
> 
> It seems the only way to remove it is to mechanically brush it away. Like I
> said, we've never had this problem before with this solder paste.
> 
> 
> 
> The two assemblies that we are seeing this problem with do have a different
> finish than we normally have on the boards we build. Most all of our boards
> are gold finished. But one of the boards that we saw the white residue with
> was finished with Immersion Tin (.ugh!), the other was HASL'ed with Sn/Pb.
> Do you think that had anything to do with it? With one assembly the white
> residues weren't on all the boards, only some of them, which is strange. We
> hand solder all our through-hole here, and some of the boards may have sat
> around for a few days longer than others waiting on their through-hole
> before they were cleaned which may explain why some had white residues, and
> others didn't.
> 
> 
> 
> We only built 34 of these boards and they have already been brushed and
> cleaned, so I can't get anything analyzed now. But I'm wondering if any of
> you have an idea of what might have been going on here to cause these
> residues?
> 
> 
> 
> Thanks!
> 
> 
> 
> Steve
> 
> 
> 
> 
> 
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