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August 2001

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From:
"<Peter George Duncan>" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 21 Aug 2001 08:57:32 +0800
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[This e-mail is confidential and may also be privileged. If you are not the
intended recipient, please delete it and notify us immediately; you should
not copy or use it for any purpose, nor disclose its contents to any other
person. Thank you.]
Phil,

We don't have quite the same application as you, but we're having to
extract heat from the top of vulnerable chips using thermallly conductive
material between the chips and an overhead heat-dissipation plate. We have
been using a product called T-ply by Thermagon and it comes in various
thicknesses. Thermagon claim that it's been used in satellites, so it
stands up to quite a challenging set of temperatures, pressures and
vibration levels. It does have some silicon associated with it, but it
doesn't ooze, doesn't change phase, isn't electrically conductive and can
be compressed to up to 50% of its native thickness. It is quite expensive
though, but pretty effective thermally at 5.3W/mK.

They can be found at www.thermagon.com

Regards

Pete Duncan




                    Phil Nutting
                    <PNutting@KAISERSY        To:     [log in to unmask]
                    STEMS.COM>                cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
                    Sent by: TechNet          Subject:     [TN] Thermal Compound considerations
                    <[log in to unmask]>


                    08/20/01 09:42 PM
                    Please respond to
                    "TechNet E-Mail
                    Forum."






Here is this morning's question(s).

I posted a note last week about using the old style thermal grease.  I
agree with your comments about using some of the new Berquist or Power
Devices insulator pads, some of which we currently use.  Today I am
looking for some of your thoughts on an alternate style material (grease
"replacement").

There are several products on the market which are phase change (at
60 $B!k (BC/140 $B!k (BF) thixotropic, non-silicon products which prevent run out
(oozing out from under the device) at operating temperature.

Now assuming we use this material on TO-220 packages and mount the
device with the standard mounting hole in the tab the device tends to
not sit completely flat on the heat sink  (This is a problem not
associated with the thermal compound but the mechanical design of the
device).  On concern brought to my attention is water trapped under the
device.  And our intent is to solder these devices to the PWB (through
hole) and de-flux (OA flux) the boards after assembly in a batch DI wash
with no saponifiers.  Do any of you see this as an issue?  We presently
use the old style thermal grease in this manner mostly with TO-220
devices and heat sinks which are the same size as the body.  If our DI
wash is running at 120 $B!k (BF and the wash chamber is set for 135 $B!k (BF are there
any significant issues with approaching the phase change point that will
degrade the thermal compound's operational characteristics?

We may end up using one of the pad style items, but I wanted to tap into
your collective wisdom to help with the end decision.  This manual
application tends to be messy, time consuming and different by each
assembler.

Thanks in advance.

Phil Nutting

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