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February 2009

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 26 Feb 2009 11:05:39 -0600
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Your choice may be dependent on the cost of the assembly. If you want it
to be reworkable should it fail during periodic testing, then a
reworkable CC may be the way to go. Potted assemblies are not very
reworkable. So the cost of the assembly may be a consideration if you
have to throw it away when it doesn't work.
Secondly, if you do choose an RTV compound and encapsulate it, make sure
you use an electronic-grade RTV. Many RTVs used for potting electronics
are not meant to be used for that purpose, and corrosive reactions are
common when this happens. 
Conformal coating is a barrier, but usually is not an impervious
hermetic seal. Moisture can and will condense onto areas not perfectly
sealed inside the coating, and moisture condensation inside of the
sealed box can be absorbed inside of the CC.
I have performed a combination of potting over high-reliability
components and CC only over specific components that will probably
require rework within a 3-10 year lifetime.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: Thursday, February 26, 2009 10:53 AM
To: [log in to unmask]
Subject: [TN] Conformal coating or encapsulating

Hi all,

I'm working on a design that will have some lithium batteries on a
circuit board.  The board will be in a marine application where it must
be waterproof, sit idle for 5-7 years and must work during an emergency
situation.  No maintenance is expected or desired.  Should I conformally
coat the batteries/board and install in a gasketed (NEMA?) box or should
I encapsulate the board in RTV or epoxy?

Thanks in advance,

Phil Nutting
Design for Manufacturing Engineer
Kaiser Systems, Inc.
126 Sohier Road
Beverly, MA 01915
voice: 978-922-9300 x1310
fax: 978-922-8374
e-mail: [log in to unmask]
www.kaisersystems.com

Note: All the information contained in this e-mail and its attachments
is proprietary to Kaiser Systems, Inc. and it may not be reproduced
without the prior written permission of sender.  If you have received
this email in error, please immediately return it to sender and delete
the copy you received.

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