Two comments,

a)  Dewetting of coating is generally caused by the surface not being clean 
enough/residue.  We use a variety of UR type coatings on plastic devices and 
don't have a wetting issue.  You may want to investigate the cause /correct the 
process.

b)  For hardware already coated, I would suggest that dewetted areas that don't 
reduce the electrical spacing between non-common conductors to less than the 
design limit (ie. electrical spacing required as a function typically of voltage
differntial) should not be reworked.   See ANSI/J-STD-001B section 10.1.2.2 for 
some additional insites.

Jim Maguire
Senior Principal Engineer
Boeing Defense & Space Group
PO Box 3999 M/S 3W-97
Seattle, WA  98124-2499
Phone 206-657-9063
FAX    206-657-8903
Email:  [log in to unmask]
______________________________ Reply Separator _________________________________
Subject: FWD: pwb-cca : conformal coating
Author:  [log in to unmask] at esdigate
Date:    10/23/96 4:37 AM


Technet,
     
I'm forwarding this from a colleague.
     
Cindy Kemp
Lockheed Martin
Orlando, FL
*******************************************************************************
     
From: [log in to unmask]
Date: Tue, 22 Oct 96 16:35:22 EDT
Message-Id: <[log in to unmask]> 
To: [log in to unmask]
Subject: pwb-cca : conformal coating 
Sender: [log in to unmask]
Precedence: bulk
     
hi group;
     
We are finding that in designs using conformal coating (UR) over plastic parts 
that the cc is dewetting on the parts.
     
Question - is this seen as a problem ?
     
I am proposing that a note should be added to our designs as follows:
     
 CONFORMAL COAT DEWETTING ON PLASTIC ENCAPSULATED MICROCIRCUIT 
 COMPONENT BODY IS ACCEPTABLE.
     
If there is a better way please let me here from you.
     
What is the real would doing ?
     
     
   thanx; Skip Greb
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