System News: Thermal paste is love

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System News: Thermal paste is love

Mark Williams contemplates proposing to his CPU with a giant synthetic diamond ring.

Thermal Interface Material (TIM) – aka thermal paste: every PC uses it. It’s the goop that mates CPU and heatsink, removing unwanted airgaps between the two surfaces allowing heat to transfer efficiently from one surface to the other.

There’s many different types you can find, with even the likes of peanut butter and toothpaste being tried. 

Ultimately, you’ll want a TIM that has the highest thermal conductivity possible, as your heatsink can only dissipate heat that has passed through the TIM to it.

So, what’s a good TIM? Many decent manufacturers state a thermal conductivity rating for their premium thermal compounds. This is generally given as a measurement of W/mK; watts per square metre of surface area, for a temperature gradient of one kelvin for every metre thickness. It sounds complicated but just think of it as the rate at which heat travels through the TIM. Higher numbers are more desirable.

Cheap bulk thermal grease might have a rating of just 1W/mK. The stuff that comes pre-attached to OEM heatsinks and thermal pads would be around 2 to 3W/mK. Regular third-party TIM will get you anywhere from 4 up to 12W/mK; the venerable Arctic Silver 5 paste is rated at 8.7W/mK for example.

Then there’s the exotic stuff. Colloquially known as liquid metals, these TIMs are solely composed of metals and alloys like Indium or Gallium (as opposed to the regular stuff that’s more polymer-based, with flakes of metal such as silver thrown in), which are naturally liquid at room temperatures, making them easy to use and apply as a TIM. These offer thermal ratings as high as 86W/mK! However, they do have a drawback: they’re quite corrosive when used with certain types of metals, like aluminium, for example. So do your research before going out and getting some liquid metal TIM.

Speaking of metal, solid metal has some of the best thermal conductivity around. Aluminium found in cheaper heatsinks is rated at 205W/mK and copper from higher end ones rated at 401W/mK. Something like silver is only fractionally better at 429W/mK, with gold being worse at 310W/mK.

However, the best stuff is diamond, rated around 1000W/mK naturally, with purified synthetic diamonds capable of up to 2500W/mK! That’ll make you look at your mother's wedding ring in a different light the next time you see it!

So, what got me thinking about TIM’s this month? Intel. These days integrated heat spreaders (IHS) are common, and are only there to protect the brittle CPU die underneath, which can crack easily if mounting the heatsink directly to it incorrectly (hello Athlon XP days!).

Obviously, the chip maker must thermally connect the CPU die to the underside of the IHS to transfer the heat, and as I’ve just described, metals are far better at conductivity than your regular $10 TIM. So, it beggars belief that Intel, on its new top of the line i9 series CPUs that cost a cool $1,300 and up, would use - effectively - regular TIM paste underneath the IHS.

AMD, on the other hand, is using metal solder to connect its CPU dies to the IHS, providing far superior conductivity.

How much of a difference does all this make? Well, a de-lidded i9-7900X who’s IHS has been reapplied using liquid metal dropped load temperatures by around 25 °C. That’s impressive for just a compound switch, and allowed the overclockers to push on from mid 4GHz up to 5GHz.

So, Intel, why?


SHOP TALK 
Do you use 3rd party thermal paste for your PC builds, if so, what is it?

John, TI Computers:

“At TI we only use the finest parts. I handpick from a verity of options available on the market. The thermal paste is one of them, as it plays an essential part in heat transfer between the IHS and the cooler base. A great cooler cannot perform at its fullest without them for sure. Certainly, as a responsible dealer shop, we cannot and do not open up the IHS to replace TIM under them due to warranty concerns. However, we do generally remove the existing paste and replace with a very thin layer of evenly spread quality paste such as Noctua NT-H1 when building high-performance TI systems.” 

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