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Subject: Re: TWL: Conformal coating PC boards
From: Arild Jensen (elnav@XXX.XXX)
Date: Wed Mar 27 2002 - 00:58:10 EST
At 10:03 AM 3/25/2002 -0800, Jeff Patton wrote:
>I don't remember clearly as it's been many years, but I seem to remember
>that when we applied conformal coating in medical electronics assembly, we
>masked some of the components before coating.
>
>Does anyone know more about this? Seems to be an item of general interest.
REPLY
In one of my past careers I was the production manager for an electronics
firm and we used conformal coatings.
Not all coatings are the same. Some are applied by dipping, others are
best sprayed on; and some you dip the whole assembly into.
When you have edge connectors or plug in chip sets it is very important
to protect the contact surfaces from getting any conformal coating onto
them.
Which now leaves the question of how do you protect them after assembly.
Very thin liquid types will wick into tiny cracks and the finger
contacts. Avoid these if you have plug in connectors or sockets.
Be aware that most of the urethane coatings render the boards unrepairable
in the event of a component failure.
Such boards now become throwaways
Urethane coatings are the ones most often found in places like Radio Shack
and elecrtonic supply stores.
We also used a thick coating made by Dow corning ( sorrry can't recall the
name - RTV ??? ) which was a rubbery semi translucent stuff.
You could actually remove it with iosol and then recoat the board after
replacing components.
For mil spec applications we used a special solution containing a
fungicide - sometimes called tropicalization.
I'm not sure this is something I would attempt to do myself.
Conformal coatin an electronic device after it has been built requires a
lot of dis-assembly.
I would be more inclined to spray liberally with Corrosion Block and
repeat the treatment once a year.
regards
Arild
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