John said:
Before installing a heatsink. I would like to fill in some gaps
around the heat pipes that are sandwiched between an aluminum and
copper plate (that sits on the CPU).
Don't like the idea of using an epoxy mix. I'm uncomfortable with
using them, and I would rather be able to very neatly apply the
compound. After mixing epoxy, you're sort of stuck using a spoon
or some other flat clumsy tool for the application.
Looking at this...
http://www.amazon.com/Arctic-Silver-Alumina-Polysynthetic-Compound/dp/B004Z9XG0I/ref=pd_cp_pc_2
Does it dry?
That says it "Will not run, separate, migrate, or bleed".
Hopefully that means it won't ooze out of the holes.
Thanks.
Thermal compounds use a viscous substrate material which
resists "pump-out". Normally, when a heatsink heats up, the
materials in the area expand at different rates, and
"stuff moves around". This translates to a pumping action
(as there is normal force pushing down on the whole thing).
If the substrate compound is fluid-like (such as zinc oxide in
silicon oil), the oil can leave fairly rapidly, in a few days.
The Arctic Silver product I have, is pretty thick. It also
tends to "set" in a few days. There are some materials, which
are a bit "drier" and they're almost the consistency of cookie
dough, and tend to break off in dough like pieces. Users who
have worked with that stuff, hate it, because it's so hard
to apply. There's no way to spread it on stuff. So when these
companies go too far with the "thick" idea, the product
goes down hill because of it.
*******
Yes, you can use thermal paste between heatpipes and spreader
plate. They may not meet all that well in the first place
though (not much surface area comes into direct contact), because
of the difficulty of milling exact curves and mating the stuff
nicely. When they make stuff like the old copper-core aluminum
heatsinks, where the items are heated before assembly, and basically
"crush" one another when they cool off, that's an example of
a more intimate mating (a true compression fit, with tons of
force). Heatpipes on the other hand, you can put thermal paste
around them, but any areas where the thermal paste is 1/16" thick,
it's virtually useless. The heatpipe is more conductive than
solid copper (due to the phase change action that makes pipes
so good in the first place). As soon as the pipe is separated
from the base metal by even a tiny distance, the thermal
resistance of paste is so high by comparison, it's like there
is no thermal path there at all. If the paste is really thin,
and boron nitride particles are pressed between two metal surfaces,
that conducts pretty well.
So it's really better if the metals are precisely formed
and large areas make metal to metal contact. The paste
can help, if there is a small air gap, but gross errors
in milling, bending or shaping, the paste would just
be wasted filling gaps like that. So if you sloshed
the stuff in the gap, only areas of metal separated
from their mate by 0.001", are going to get some
benefit conduction-wise. Any areas where the metals
are far apart, the paste really can't bridge them in
a useful way.
The same would happen with thermal epoxy. The math hasn't
changed. If there was some way to "crush" the components
together (more metal to metal touches), that would help,
but of course if you bust the seal on the pipe, that
ruins it. If the working fluid gets out, the pipe almost
becomes an insulator - it's performance would be terrible
without the phase change action that transfers the heat.
That's why multi-pipe coolers are preferred. If you have
four pipes, and one springs a leak, all is not lost.
Paul
