Hi. This is an appropriate group.
A good newbie starter is GC Electronics P/N 10-8109 Zinc Oxide and
Silicone-based Heat Sink Compound. It's got a silicone and zinc oxide
base, it's a highly visible white, and it's relatively inexpensive.
This will allow you to do a visual inspection as you develop skill in
applying the right amount of compound between the IC and the heat sink.
Make sure both the surface of the IC and the heat sink are absolutely
clean, and that the heat sink is free of burrs, warping, or other
visible imperfections. I like to do an alcohol wipe with a lint-free
cloth before application of heat sink compound to remove any dust or
grit.
Apply a very small dab of the white zinc oxide/silicone heat sink
compound to your very clean finger (or ideally, with a fresh finger cot
over your index finger) . Rub the compound over the mating surface of
the IC, such that you can barely see through the heat sink compound to
the surface. Then evenly place the heat sink on the IC, and evenly
press down with the clip or fastener.
Now that you've done the work, undo it. Carefully remove the clip or
fastener so that the surface of the heat sink doesn't slide around on
the IC. Then pull it straight off. Look at your work. You should see
a kind of fine fish-scaling of the heat sink compound across the entire
surface of the heat sink like lacework, with a tiny amount of the
compound extruded out past the edges of the IC. If you don't see the
fish-scaling, you (probably) put too much compound on the IC. It's
always way too thick the first time. Start over and do it again, first
wiping the IC and the heat sink clean with alcohol and the lint-free
cloth (it's sometimes better to just scoop off most of it with a paper
towel first, then use the alcohol and the lint-free cloth).
Once you do this successfully a couple of times, you'll be able to do
it well consistently in the future. It's like riding a bike -- you
don't forget. Practice with each type of IC and transistor package.
If you use a TO-3 or other heat sink that requires multiple screws, you
should tighten evenly a little at a time on each side, ideally using a
torque indicator to get the screws tightened down evenly. Just
remember that way too much heat sink compound is actually worse than
none. And by the way, make sure to clean off the heat sink compund
carefully -- it's not good for you.
It also might be a good idea, once you're in practice, to use another
type of heat sink compound if your application is high reliability or
you're dealing with a lot of heat. Plain zinc oxide-based heat sink
compounds tend to dry out and lose their effectiveness over time
(years). Others tend to extrude out over time with thousands of
thermal expansion-contraction cycles. Once you're in practice, and if
you need the reliability, there are a number of translucent
silicone-based compounds that have good thermal conductivity if applied
properly, will not dry out over time, and are viscous enough to stay
put. You might want to look at
http://www.aavidthermalloy.com/
for a variety of good products, and some good technical papers and app
notes.
And of course, there's always the elusive search for the perfect heat
sink compound. The last time I was walking along that path, I started
seeing Monster Cables and other audiophile excesses lurking in the
bushes, so I turned back to avoid brain cramp. But I've heard there
are a number of very expensive silver-loaded heat sink compounds that
have somewhat better thermal conductivity than silicone-based, and
measurably better thermal conductivity than plain-Jane zinc
oxide-silicone. For applications right on the bleeding edge (where the
extra 0.2 degree C/W makes all the difference), you just might need
something this good. But usually, you just put in a bigger fan or go
to water cooling instead.
You might get a more specific answer if you describe what you're doing,
and some more about your project requirements.
Chris