Corsair XTM70 Extreme Performance Thermal Grease Review – Just missed the top spot but really good and unfortunately also very expensive

1 - Introduction and technical data 2 - Test methods and equipment 3 - Thermal resistance 4 - Thermal conductivity and real-world simulations 5 - Material analysis 6 - Summary and conclusion

Microscopy and material analysis

It is very interesting to observe how a paste can be spread and when it actually tears on and off the glass substrate, because it also allows conclusions to be drawn about the mixture. You can see that the Corsair XTM70 Extreme Performance still adheres well, but cannot be peeled off endlessly thin without tearing off. The heels are not quite as high due to the slightly lower viscosity compared to the Thermalright TF8, but the paste hardly pulls any disgusting threads and has something sandy about it if you increase the size.

This is probably due to its composition, as the Corsair XTM70 Extreme Performance is also a fairly “dry” mixture of many thermally conductive fillers and slightly less silicone (polysiloxanes). The final consistency is therefore mainly achieved by the fillers. You could also use a firmer matrix and fewer fillers to thicken the paste, but then you would have a lower performance again.

The risk of outgassing or bleeding of the silicone base is probably also of secondary importance here. At this point, I also have fewer concerns about the long-term durability at high temperatures. We will have to see how well everything performs after 6 to 9 months, but I am quite hopeful. You can see the matrix with the embedded particles very clearly under extreme magnification.

Very different degrees of grinding were used here, which is reflected in the particle sizes. This ranges from the nano range to a few particles of up to 7 µm, which also explains why the paste cannot be squeezed endlessly thin and why no less than 8 µm was possible even under pressure. However, the matrix of the Corsair XTM70 Extreme Performance was not quite as stubborn as that of the TF8, but rather soft.

Now let’s take a closer look at what’s actually inside and what’s not. The paste contains a lot of fillers, mainly very fine aluminum oxide. The proportion of zinc oxide is significantly lower, but still sufficient. The ZnO is primarily used as a gap filler between the somewhat larger (and harder) Al2O3 grains. The paste therefore benefits from its viscosity and you have to take these circumstances into account when applying it. But it is quite feasible. It is somewhat similar to the Thermalright TF8 in this respect, as the particles are similarly weighted.

Test equipment for material tests, accuracy and test preparation

My Keyence VHX 7000 and EA-300 are responsible for material testing and measuring the pastes and pads, enabling both exact measurements and fairly precise mass determinations of the chemical elements. But how does it actually work? The laser-induced breakdown spectroscopy (LIBS) I used for this article is a type of atomic emission spectroscopy in which a pulsed laser is directed at a sample in order to vaporize a small part of it and thus generate a plasma.

The emitted radiation from this plasma is then analyzed to determine the elemental composition of the sample. LIBS has many advantages over other analytical techniques. Since only a tiny amount of the sample is needed for analysis, the damage to the sample is minimal. The real damage is caused in today’s article by my rather coarse cutting and separating tools. This still quite new laser technique generally requires no special preparation of the samples for material analysis. Even solids, liquids and gases can be analyzed directly.

LIBS can detect multiple elements simultaneously in a sample and can be used for a variety of samples, including biological, metallic, mineral and other materials. And you get true real-time analysis, which saves a tremendous amount of time. As LIBS generally requires no consumables or hazardous reagents, it is also a relatively safe technique that does not require a vacuum as with SEM EDX. As with any analytical technique, there are of course certain limitations and challenges with LIBS, but in many of my applications, especially where speed, versatility and minimally invasive sampling are an advantage, it offers significant benefits.

I would first like to point out that the results of the percentages in the overviews and tables have been intentionally rounded to full percentages (wt%, i.e. weight percent), as it happens often enough that production variations can occur even within the presumably same material. Analyses in the parts-per-thousand range are nice, but not very useful today when it comes to reliable evaluation and not trace elements. However, every day in the laboratory starts with the same procedure, because when I start, I work through a checklist that I have drawn up. This takes up to 30 minutes each time, although I have to wait for the laser to warm up and the room to reach the right temperature anyway.

• Mechanical calibration of the X/Y table and the camera alignment (e.g. for stitching)
• White balance of the camera for all lighting fixtures used
• Check alignment of LIBS optics and standard lens, calibrate alignment of laser to own optics (x300)
• Test standard samples of the materials to be measured and correct the curve if necessary (see image above)