rms wrote:
you'd
actually be dumping heat back into the substrate

Interesting theory, but I'm not sure I buy it, especially in the
case of a water-cooled system like mine.

Ah, yes, I should have been a little more specific In most air-cooled
systems, the horozontal gradient is relatively low on the bottom of the HSF,
with a steep gradient right near the edge (where there is significant air
circulation and whirlpooling). This is primarily due to the dead area of air
circulation above the HSF base. The main temperature gradient is vertical in
these cases. I saw some thermal imaging camera pics of this somewhere
(LostCircuits I thought) but I don't have any links on me at the moment.
Waterblocks and (some) non-standard HSF designs get around this.

For a well-designed waterblock, you can effectively treat the inside surface
as being at water temperature. This means that the horozontal gradient is
very steep (as is the vertical gradient as you've only got a few mm of
copper between the heat source and the inner surface), and hence the shim
would actually help cooling as long as it didn't reduce the pressure, etc
between the block and the die. I still don't think it would be particularily
great, as the thermal resistance of the substrate is relatively high, but it
would probably drop your substrate temps (ie: socket temps) and make you
feel a bit better It'd be interesting to see what it would do for die
temps (though repeated installation and removal of the shim would be
necessary to get some idea of the standard error of the measurements created
from WB installation variations).

[...]
Also, in the ideal situation, with a more or less perfect heatsink
that instantly removes all heat without spreading it out over the
heatsink surface, it should be clear that more surface area equals
more heat removal. So the better the heatsink, the more a cpu copper
shim should help. That's my argument anyway.

Agreed

[...]

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Michael Brown
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