The thermal resistance Rth
Let’s start with the most important aspect, the thermal resistance Rth. The most important property of Rth is that it correlates nicely linearly with the layer thickness, while the thermal conductivity describes a completely different curve and remains anything but linear. But the experienced reader already knows all this, of course. We are interested in layer thicknesses of 200 µm and less on the CPU; on the GPU it is usually even 100 µm and significantly less, depending on the bending.
First, we compare the four pastes from Cooler Master with each other. We can see that the CryoFuze 5 Violet is by far the worst performer across the entire BLT range. The CryoFuze 7 and the MasterGel Maker, on the other hand, are very close together at the top. The MasterGel Pro V2 is solidly in the middle of the field, also here in these measurement curves:
Now once again the comparison to the six best pastes measured so far:
I have now compared the relevant layer thicknesses from 50 to 400 µm as a bar chart for Rth. And why don’t I compare down to 25 µm? The explanation is simple, because the TF9 and the TFX have a problem with the minimum layer thickness! Both pastes can hardly be compressed any further below 50 µm with normal contact pressures and 35 µm is actually the limit. I will write more about this later, including the causes.
Minimum possible layer thickness
This is exactly why I wanted to know how far you can go with a little pressure and how much a paste can still be compressed. I use the usual 60 Psi (41 N) on the measuring surface of 1 cm², which is completely sufficient and more than what a GPU cooler, for example, achieves.
Interface Resistance
What also seems interesting is the contact resistance, in our case the interface resistance. Here you can see how well the surface of the material “clings” to the contact surfaces (IHS, heatsink). These values are also easy to compare and meaningful, as they are always the same calibrated reference blocks. Coarser degrees of grinding or a less favorable microstructure can also be a negative factor, which then influences the effective thermal resistance and thus also the conductivity, as can too low temperatures and too high a viscosity.
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