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From: James Meyer
Subject: Re: Thermal effects of potting compound?
X-Newsreader: Forte Agent 1.91/32.564
Date: Fri, 18 Oct 2002 22:33:18 GMT
NNTP-Posting-Date: Fri, 18 Oct 2002 18:33:18 EDT
On Sat, 19 Oct 2002 01:04:21 +1000, "davidjudy"
>> FWIW I use Robnor PX314ZG, which has a Thermal Conductivity of 0.38W/mK
>If my sums are right a thermal conductivity of 0.4 watt/metre per degree K
>translates into a thermal resistance of 125'C/W for a 1 sq cm, 5mm thick
>section. I can't understand how adding 125'C/W to the junction-to-air
>thermal resistance of a heat generating device can make it cooler. Would I
>then be even better off with a 10cm thick layer? Or will 1mm be better? Or
Thermal resistance works like this:
Source (die or such) ---> package ---> other stuff ---> air --->
theoretically infinite heat sink (the rest of the whole known universe).
The thermal resistance from the source to the final infinite heat sink
is the sum of all the intermediate resistances. Since the thermal resistance of
air is so very, very high; it makes differences in the thermal resistance of any
coatings (other stuff) negligible in comparison.
Quit worrying about the thermal resistance of your coating. Use a
coating (or not) depending on other things like moisture protection.
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