From: John Larkin
Subject: Re: Thermal resistance--does this sound right?
Date: Fri, 06 Sep 2002 11:02:56 -0700
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On Fri, 06 Sep 2002 02:51:56 -0000, firstname.lastname@example.org
(Bob Wilson) wrote:
>In article , John@0.com says...
>>On Thu, 05 Sep 2002 20:55:11 -0700, "Christopher R. Carlen"
>>>Spehro Pefhany wrote:
>>>> The renowned Christopher R. Carlen wrote:
>>>>>I found a figure of k = 0.004 W C^-1 m^-1 for heatsink grease.
>>>> That number is several orders of magnitude too low.
>>>> Best regards,
>>>> Spehro Pefhany
>>>Troublingly, I have discovered that a tube of the stuff is in my drawer,
>>>and it has the figure printed on it. It says:
>>>0.00178 Cal/(s cm C)
>>>So that is about 0.745 W C^-1 m^-1.
>>>Uhm, I see that when I read the table showing 0.004, I didn't notice
>>>that it too was in cm! Oops. Why can't people use only SI units?
>>>Oh that's much better!
>>Plus, a 1 mil gap seems a lot for the grease. If the mating surfaces
>>are really flat - this is worth some machining - the gap should be
>Not MUCH less! The particulates that give the grease its conductivity limit
>the amount to which it can be squeezed out to.
I just squished some Dow 340 thermal grease in my dial calipers. It's
hard to tell, as the minimum indication is 1 mil, but I'd guess I'm
seeing 0.1 mils, without really squeezing very hard. Where's that
damned micrometer anyhow?
We recently did a high-voltage (2 KV, 2 ns, 500 KHz) pulse generator.
We clamp-mounted the critical semis on flat-machined, gold-plated,
water-cooled copper blocks. Electronic can be fun when cost doesn't