Special features of the Thermal Grizzly KryoSheet
The difference between a graphene thermal pad like the KryoSheet and a simple graphite thermal pad lies in the material used and its specific properties. Graphene is a single layer of carbon atoms arranged in a two-dimensional honeycomb pattern. It is known for its exceptional thermal conductivity. In this particular case, however, the KryoSheet goes one step further.
While both materials are carbon-based and have similar properties in terms of thermal conductivity, graphene is thinner at the molecular level and can offer higher performance. Graphite, on the other hand, is less expensive and still very effective, making it a more common choice for many industrial applications. Nevertheless, Thermal Grizzly opted for graphene. And rightly so. The only thing that doesn’t work so easily this time is the technical data, because there are no such generalized data.
The disadvantage of “normal” graphite or graphene pads usually lies in their structure, which has an exorbitantly high thermal conductivity in the horizontal plane, but almost completely fails vertically. As a result, the waste heat is distributed perfectly on the heatspreader or the die, but the thermal resistance upwards to the heatsink is unfortunately significantly greater. In order to find a solution to this problem, SHT arranged many very thin graphite plates overlapping each other and then cut them off at an angle. This can already be seen here in the longitudinal strips, which unfortunately also represent the weak point of the sheets, because they can quickly tear or break off right there.
I have now analyzed the structure under the microscope in more detail (and more clearly) and created a height profile. We can now also clearly see why a certain contact pressure is required to ensure that this jagged surface fits snugly against the interface. Because without pressure, this surface made up of individual plates cut at an angle is more of a riot:
Material analysis
Of course, I can’t and don’t want to reveal the manufacturing secret of this sheet or at least comment on it, but a few general explanations as to why there is silicon in addition to the carbon material seem appropriate in order to better understand the sheet. Similar to the GT-TIM GT-90SPRO, the KryoSheet (FrostSheet) utilizes synergistic effects where the two materials together offer better properties than either material on its own. Graphene can improve thermal conductivity, while silicon provides mechanical stability. Graphene is a very flexible material that can be easily molded into different shapes and structures. In combination with the mechanical flexibility of silicon, sheets can then be produced that adapt well to uneven surfaces and provide better thermal contact.
The dilemma with contact pressure and the discrepancy between theory and PC practice
Although the cryosheet is in a different league to normal pastes or pads, it can unfortunately only really be used effectively between 100 and 175 µm. And if you take into account the forces that actually act on the PC hardware, 175 µm is already the limit, because no GPU or CPU cooler can generate sufficient contact pressure. What we see in the curve diagram is my measurement, which I took with various forces acting on this square centimeter. Because from around 150 N, the pad no longer becomes thinner and at 300 N it’s gone.
You can convert this for yourself, because you simply have to divide the area of the GPU or CPU in mm² by these 100 mm² of the test specimen to get the multiplier or divisor (depending on the desired calculation). A graphics card with a chip area of just under 400 mm² would therefore result in a ratio of 1:4. A maximum force of around 40 N (slightly less than 60 PSI) is assumed for a GeForce RTX 4080, although in practice 30 N is more likely to be the rule. But never mind, let’s stick with 40 N. To be able to classify this correctly with the table, we are at the 10 N mark on the X-axis with the assumed ratio of 4. Please remember this for the next few pages.
This reduces the pad from the original 180 µm to around 175 µm; no further. However, this also increases the interface resistance, which we then have to take into account in daily use. And so the theoretical >90 W/(m-K) thermal conductivity quickly becomes just 3 to 4 W/(m-K). But I’ll come to that in the next few pages. The important question for us is whether such a long-term stable sheet works at least similarly to good pastes, whose durability is clearly surpassed in long-term use. And that is precisely why I am now measuring both in theory and with the subsequent derivation for practice. Please turn the page!
- 1 - Introduction and background information
- 2 - Test methods and equipment
- 3 - The "secrets" of the KryoSheet and material analysis
- 4 - Thermal resistance in theory and practice
- 5 - Thermal condiuctivity in theory and practice
- 6 - Tests with a GeForce RTX 4080 and Core i9-13900K
- 7 - Summary and conclusion
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