[sdiy] Heat Paste/Compound

[Terry Michaels]

Message text written by INTERNET:djblue at graffiti.net
>and... what would people recommend... I'm
pasting a tempco to a tranny-pair...

thanks.
-ben.<

Hi Ben:

IMHO, any type of heat sink compound will do the job.  The tempco resistor
compensates the expo transistor scale factor, and the compensation will be
less than perfect if the tempco and the expo transistors are at different
temperatures, however the heat dissipated in these devices is very small,
probably in the microwatt range, so the temperature differential will be
very small with the use of almost any type of heat sink compound.   It
should take only a small amount of thermal conductance to equalize the
temperatures.  

You could make a good case for using a dab of epoxy between the devices to
create a permanent mechanical bond between them.  After all, silicone
grease could dry out and fall away after a long time, so you might
eventually lose some thermal conductance.  

This is quite a different situation than putting a power transistor on a
heat sink and running a hundred or so watts into it, in that case you want
the best possible heat transfer to minimize the temperature rise in the
power transistor.

ARP used to put their VCO's and other circuits in blocks of epoxy
supposedly for better heat transfer, but that was way overkill.  I'm sure
they did it only to prevent people like us from reverse engineering their
circuitry.

Terry Michaels