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To prepare for this answer, I started reading some other topics here:Here is something I never quite understood; look at the temperature drop for a typical power, area, thickness and thermal conductivity
View attachment 360503
P = 100W
A = 3 cm^2
k = 20 W/(m.K)
Dx = 1/20 mm
How then can thermal pastes differ by say 2 to 3°C degrees?
- https://www.techpowerup.com/forums/...opper-ihs-upgrades-for-intel-amd-cpus.292436/
- https://www.techpowerup.com/forums/...delids-the-amd-ryzen-5-2600-processor.243627/
Why?
- The deltaX is supposed to be usually thicker then 0,05mm & that thin is ideal. But we should tend to be within 0,1~0,2mm, which is optimal from a thickness perspective, as it would give us the sweet spot of not going too thick with paste (as it is far lower conductive material - will explain later) & not too shallow to have "air gaps".
- 1/k is not calculated this way, but like this:
If you do calculate if only for this, you will get only conductance of the paste itself. Which is not good at all & you can't get any info from that!
- Also, as you do not need 1/alphas, as you do not have transfer to fluids in case of transfer of heat between CPU & Cooler. Actually, you do - but you do not need to know how to do that on side of the cooler base! Why? As most of temperature is conducted by vacuum tubes, not on the top of the cooler based (Cu heat exchanger).
- So, you get a formula such as this:
In order to compare the 4W/mK, 6W/mK & 11W/mK pastes on the same calculation with 0,1mm thickness of paste you get deltaT with 4,8K, 3,9K & 3K.
If you do the same comparison of 4W/mK, 6W/mK & 11W/mK pastes on calculation with achievable 0,2mm thickness of paste you get deltaT with 7,6K, 5,7K & 4K.
So that is where you get your difference in temp., especially if you put more paste.
Why?
Well he Ni plated Cu based CPU IHS lid has conduciveness of ~315W/mK, while Cooler usually has Cu based ~380W/mK. So the paste with 4~11W/mK acts more like a resistance, then a transmitter of temperature. But it is, how it is - maybe we will find better suiting materials in the future?!
Also, do note that Ag (silver) has the far most temperature conduciveness of ~415W/mK. But probably it is too costly to make CPU IHS or CPU Coolers from Ag...
Hope this fairly engineering explanations gives you more hint about the issues with changes in temperatures between pastes.