Important note
You will soon be redeemed, but the following still applies this time: The chart graphics in these first tests are still static graphics, but I will also use interactive graphics later, analogous to the former fan bank. But that still has to be programmed first.
The thermal resistors Rth
Let’s start with the most important aspect, the thermal resistance Rth. Since I can’t set the Apex against the reference because it is the reference itself, I use a second paste as a substitute, which I also used for calibration, DOWSIL 340. This is a popular constant in the industry, but it is not suitable for CPUs or GPUs. However, it is very stable over the long term and has no surprises. 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.
We are interested in layer thicknesses of 200 µm and less on the CPU, while on the GPU it is usually 100 µm and less, depending on the bending. Everything else is really for the gallery. Some manufacturers also specify the pure, idealized bulk value here, but this is completely unrealistic. The Thermalright TF8 was the best paste so far, even if you need medium-high skills to apply it. However, the Corsair XTM70 Extreme Performance is hardly any worse, but is easier to apply. Even without an applicator. That’s why it’s more of a draw for me, especially since the Corsair XTM70 Extreme Performance has the advantage below 50 µm. Even if only very slightly.
I now have the relevant layer thicknesses from 200 to 50 µm as a bar chart for Rth comparing the pastes:
Control curve of Rth in the TIMA analysis
In the data interface, you can check the determined values again and deselect the deviating values (here everything from 25 µm downwards) for the determination.
Minimum possible layer thickness
But at least I wanted to know how far you can go with proper pressure. I could have pressed the whole thing with 300 N, but then nothing would change. But what minimum layer thicknesses can still be achieved? Around 8 µm is really good, but is only finally achieved after a few minutes. The paste therefore needs a certain amount of time for a “burn-in”, in this case displacement. This paste started at 11.
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 paste “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 be just as much a negative factor, which then influences the effective thermal resistance and thus also the conductivity, as too low temperatures and too high a viscosity. Anything below 20 is acceptable and below 10 is the top class.
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