Quote:
Originally posted by #Rotor
This perceived gain is as a result of the diminished length of the thermal compound barrier( or layer), between the two surfaces.This length-reduction as result of added pressure, is however finite, once the two surfaces are touching (remember, they are not going to deform each other) the compound will not be able to get squeezed any more, right. That is where the optimal seat is achieved, more downforce from this point on, will not help, as there is nothing more to give way.
a graph.... I hope it makes sence.
(graph removed, see previous page in thread)
note that anything from about 25N and more, gains are virtually flat-lining.
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You seem to be ignoring the other line in the graph - In dry conditions (no thermal interface material) the thermal resistance is still reduced with pressure. The surfaces are obviously touching, so SOMETHING is changing with pressure.
The fact is that there is no such thing as a smooth surface. As you measure on a smaller and smaller scale, no matter how much you've lapped and smoothed, there will be imperfections. These peaks and valleys on both the mating surfaces will be deformed by the contact pressure, squeezing the air (or TIM) out and increasing the contact area.
There are a couple different limits to this decrease in thermal resistance - the most likely we will see is the difference will quickly become smaller than any of our abilities to measure it. Also, with high enough pressure all voids will be removed down to a molecular scale, there will still be a thermal resistance because of the two different materials. If it was 2 pieces of copper instead, this type of pressure would be enough to cold weld them together. However, before the pressure gets that high, it's likely that one of the materials will fail as it goes beyond it's maximum compressive strength.