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July 2001

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Subject:
From:
"Brooks,Bill" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 16 Jul 2001 09:11:17 -0700
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Bill,
I don't claim to be an expert in the field of over molding or potting
electronics... but the first guy I would talk with in researching the
molding of plastics in any form would be Bill Sandford at Hi-Rel Corp in
Riverside Calif. He has done some work for me in the past and I recommend
him highly. A very knowledgeable guy.
Also, the potting of transformers and chokes would be cleaner if they were
molded similar to the way axial leaded capacitors are over molded. I was
involved with a leaded chip capacitor application where we used pelletized
thermoplastic resin and injection over molded the capacitors into a DIP
pattern for the '2 pin dip' style caps that have been replaced with surface
mounted caps today, (lead-less). I know that Pico over molds their
transformers for current sense applications.. A similar process should work
for you. Figure to spend 10K on Tooling, and have a high volume application
so you can amortize the cost of the tooling over the life of the product...
If you have a low volume product, you may be stuck with the messy potting
compounds for cost reasons...

Hope that helps a little... ;)
Bill Brooks
PCB Design Engineer
DATRON WORLD COMMUNICATIONS INC.
3030 Enterprise Court
Vista, CA 92083
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510
mailto:[log in to unmask]
IPC Designers Council, San Diego Chapter
http://www.ipc.org/SanDiego/
http://home.fda.net/bbrooks/pca/pca.htm



-----Original Message-----
From: Kasprzak, Bill (sys) USX [mailto:[log in to unmask]]
Sent: Monday, July 16, 2001 8:51 AM
To: [log in to unmask]
Subject: [TN] Recommendations for developing a mold


Hello all,

I am involved with a project that requires that I encapsulate a pc board in
mold so that when completed, it will be a ring with an ID of 1.37" and an OD
of 1.64". The ring will be .13" thick and .35" tall. There will be six, 28
AWG wires exiting the finished potted assembly. The potting compound will be
Emerson & Cumings 2651-40 with Catalyst 11.

        I have a basic 3 piece mold that works OK, but the pieces only
reflect what the final product should look like. It takes a little work to
get the mold apart even though mold release is used. The cure for the
potting is 8 - 16 hours at 180 deg F

What I'm looking for is any tricks and hints that should be incorporated
into the mold design that would facilitate easy processing. What I mean is
to make it easier to pour the material, easy to assemble into the mold, easy
to take apart, etc. etc. Right now the whole process just seems to be crude
and messy. Maybe, that's just the nature of the beast.

Any and all responses appreciated. Thanks.

Bill Kasprzak
Moog Inc., Electronic Assembly Engineering

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