In a message dated 08/05/2007 00:42:07 GMT Daylight Time,
mcqueen_34@... writes:
Potting compound actually helps the heat issue by
creating more mass that the transistor must heat and
providing more surface area to radiate the heat it
does produce.
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Sorry to ruin your fantasy, but, in the majority of cases, if not all, that
doesn't make any sense whatsoever.
Potting compounds generally have relatively poor thermal conductivity and
the heat is much more likely to build up in the vicinity of potted devices
rather than be carried away to the surface.
Having more mass to heat, without that mass being able to conduct the heat
elsewhere, just leads to localised temperature rise and potential destruction.
In other words, your potting compound is likely to be a good insulator that
keeps the heat in rather than a good conductor that lets it out.
Heat what can't reach the surface can't radiate so the enhanced surface area
in that case means sweet FA.
It isn't so much mass that's important as being able to conduct the heat
away quickly and then disperse it over an increased surface area which can
radiate it more effectively.
That's why heatsinks are made of metal and exposed to free or forced air
supplies and why efforts are made to ensure the thermal resistance between
device and heatsink is minimised.
Fluid cooling is, of course, another option but I don't think potting
compound cooling is ever gonna catch on:-)
regards
Nigel
GM8PZR
