[PLUG] maybe plug-talk material, but ...

Keith Lofstrom keithl at kl-ic.com
Thu Oct 11 16:21:40 UTC 2007


On Wed, Oct 10, 2007 at 11:27:34PM -0700, Russell Senior wrote:
> 
> Over in Personal Telco land, we were doing some node maintenance
> today.  The node is an apartment building in which we had deployed 5
> devices that meshed together using WDS.  A while back we had noticed
> that something oily was dripping from several of them and we didn't
> (and don't) know what it was.  Today we were there and cracked one
> open and found this:
> 
>   <http://www.personaltelco.net/gallery/v/nodes/nodeloc/westovertowers/DSC03138.JPG.html>
> 
>   <http://www.personaltelco.net/gallery/v/nodes/nodeloc/westovertowers/DSC03137.JPG.html>
> 
> The goo was melted like that in three of the five devices and in the
> other two, remained in a crisply-cornered block above the radio card.
> 
> Two questions: 
> 
>   a) what is that stuff?  (we thought maybe the remnants of the
>      stay-puft marshmallow man, but that was just a guess);
> 
> and 
> 
>   b) what solvent would be appropriate for washing it off the circuit
>      board?

It is hard to tell from the pictures, but it looks like spray foam,
put in there to keep the PCMCIA card anchored.   It is probably a poor
thermal conductor, allowing stuff to heat up too much, melting it.
If you knew what the material was, you could google for the solvent,
otherwise you would risk hurting the electronic components.  You
might consider just heating it in a non-food oven to 250F or so,
inverted above an expendable catch pan, and letting the stuff melt off.

My guess is that a better material was specified in the design, and
the Chinese manufacturing shop substituted some cheap, low melting
point, low thermal conductivity crap.  Perhaps the same crap they
use in pet food and children's toys. 

Keith

-- 
Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs



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