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Date: | 23 Oct 96 07:50:30 -0500 |
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If you get dewetting from plastic components, then they are dirty, or
you are using the wrong coating.
This can pose a reliability issue. An extreme example is a fin pitch J
lead. If the coating dewets the body, are the leads covered adjacent
to the body. Will the dewetting prohibit coverage of the solder joint
under the component body?
I have tested and qualified coatings. This was found on some, but not
all coatings, and usually upon one specific part or supplier. I
disqualified all coatings that exhibited this problem from the matrix,
and implemented a coating that does not dewet from them.
It is acceptable to leave plastic bodies uncoated using masking or a
Nordson, since plastic is generally inert relative to tin/lead, but
don't allow dewetted coating. It can result in catastrophic failure.
Aric Parr
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______________________________ Reply Separator _________________________________
Subject: FWD: pwb-cca : conformal coating
Author: [log in to unmask] at internet
Date: 10/23/96 7:01 AM
Technet,
I'm forwarding this from a colleague.
Cindy Kemp
Lockheed Martin
Orlando, FL
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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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