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Subject:
From:
Brian Ellis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 25 May 2000 17:52:26 +0200
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Roger

First of all make sure that your boards are as clean as poss before
coating - you don't mention what soldering/cleaning process you use.
Then I recommend any coating OTHER than silicone, which is the world's
worst for moisture penetration. Choose between good acrylic or 2 part
flexible epoxy or polyurethane products. Personally, if coating, I
prefer not to have soldermask, if possible, but my friends say I'm being
controversial. Do it all in one fell swoop with the coating (cheaper and
less risk of compatibility problems).

If you e-mail me privately with more details, I may be able to be a lot
more specific.

Brian

"Roger M. Stoops" wrote:
>
> Hey y'all:
>
> We have seen some problems on SMD boards using 0805 package Rs and Cs.
> These boards have soldermask and are silicone-coated twice.  They are used
> in machine control products (machines such as bulldozers, motor graders,
> drag scrapers), and so moisture presents a constant problem, as well as
> temperature extremes (-20C to +70C).
>
> We are having product failures after the product has been installed and
> functioned normally for a few months.  A typical example would be a 4.75K
> resistor on a failed unit would measure about 200 ohms after product
> failure.  We take the part off; R between pads is in the meg-ohms (what we
> expect).  Replace the part, problem goes away.
>
> Does anyone know of a service that would help us find out what the probable
> problem is, and maybe the cause and solution?  We think it might be
> contamination left over from assembly process (vendor doesn't think so)
> that moisture may affect after time in field.
>
> Immense thanks.
>
> Roger Stoops
> Spectra Precision Inc.
>
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--
Brian Ellis
Protonique SA
PO Box 78
CH-1032 Romanel-sur-Lausanne, Switzerland
Voice: +41 21-648 23 34 Fax: +41 21-648 24 11
E-mail: [log in to unmask]
URL: Technical and consultancy divisions:
       http://www.protonique.com
     Web services division:
       http://www.protonique.com/webserv

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