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Subject: Re: Thermal effects of potting compound?
Date: Sat, 19 Oct 2002 09:19:35 +1000
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
"James Meyer" wrote in message
> 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
> >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
> >then be even better off with a 10cm thick layer? Or will 1mm be better?
> 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
> air is so very, very high; it makes differences in the thermal resistance
> 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.
So if I bury a 10W resistor in the middle of a 1m cube of epoxy, it will run
cooler than in free air? What if I use styrofoam? I shouldn't worry about
the thermal resistance of the coating?
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