Conformal coating should be used when reliability is a concern due the 
presence of liquid water (condensation), conductive and or corrosive 
pollution including contaminants from handling, and where dielectric 
strength needs to be increased for UL trace spacings requirements. 
 Silicones are not vapor barriers, however.
 ----------
From: TechNet-request
To: technet
Subject: Fwd: conformal coating
Date: Thursday, September 19, 1996 3:49PM

On Thu, 19 Sep 1996 13:01:25 -0400
[log in to unmask] wrote:

>From:  [log in to unmask] (Mark Sattel)
>Resent-from:   [log in to unmask]
>To:    [log in to unmask]
>Date: 96-09-19 12:40:03 EDT
>
>Sirs:
>
>I am presently investigating the need for conformal coatings on our
>printed circuit assemblies.  Do you have any literature that discusses
>the relative merits and disadvantages?  To date, our company has
>conformal coated 100% of our PCAs.  But the cost of masking, spraying,
>and unmasking are staggering.  My first instinct was to eliminate the
>coating except in high heat, high humidity environments.  Our operating
>environments vary from freezing cold to hot and humid.  Any information
>that you can supply will be greatly appreciated.

I am also very interested in this subject and people's experiences.

There's a study being conducted by the circuit card assembly and materials
task force of the EMPF (http://www.empf.org) to develope guidelines for the
use/non-use of conformal coatings.  The study is underway now.  I haven't
heard of any interim results.  Check with them for further details.
_________________________________________________________
Gregg Klawson                        tel: +1.508.880.1822
GTE Government Systems Corp          fax: +1.508.880.4316
Taunton, Massachusetts USA         email:  [log in to unmask]

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