Thermal Conductance 101 with Dr. Fylladitakis

Simplified, thermal conductance is the ability of a material or arrangement to conduct heat. Thermal conductance is inversely related to the absolute thermal resistance, meaning that a lower absolute thermal resistance will improve thermal conductance. In our particular case study, that arrangement is the CPU/Cooler setup. When studying arrangements, the absolute thermal resistance of the entire arrangement is the sum of the thermal resistance that each individual part has. Anything that lowers the absolute thermal resistance of the CPU/Cooler arrangement will result to better thermal conductance, i.e. lower operating temperatures. Vice versa, if the absolute thermal resistance of the arrangement increases, the thermal conductance will be lowered.

The figure above displays a simplified CPU/Cooler arrangement. At the bottom layer we have our CPU die(s), the middle layer is the CPU’s copper lid and, finally, the top layer is the CPU cooler. With such a setup, we have three individual thermal resistances: R1) the CPU’s die (heat conduction from the CPU die to the CPU lid), R2) the CPU’s lid (heat conduction from the CPU’s lid to the cooler), and R3) the cooler’s absolute thermal resistance. These three resistances sum up to make the total absolute thermal resistance of the CPU/Cooler arrangement. Simplified and assuming one-dimensional conduction, each absolute thermal resistance depends on three things: a) the length of the material in parallel to the heat flow (i.e. its thickness), b) the thermal conductivity of the material, and c) the cross-sectional contact area.

The cooler’s absolute thermal resistance obviously depends on the cooler itself (size, materials, design, air flow, etc.). However, no matter how good a cooler is, the absolute thermal resistance of the entire arrangement can still be poor if any other thermal resistance is too high. For example, it is known amongst enthusiasts that some of Intel’s previous processor generations had poor thermal performance that was unjustified given their very low power requirements. That was because the CPU’s lid was making poor contact with the CPU’s die(s), greatly decreasing the thermal flow between the die and the lid. Hardcore enthusiasts were “delidding” their processors in order to fix this issue.

Introduction AMD Threadripper Processors & Cooler Compatibility
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  • FireSnake - Wednesday, March 14, 2018 - link

    Awesome review, thank you!
  • iter - Wednesday, March 14, 2018 - link

    Hmm, the cooler should cover the chip it is cooling... who would have thought that to be the case?

    "AMD’s Threadripper processors certainly do not require liquid coolers to function properly at stock"

    Moot point, as nigh end noctua coolers easily beat AIO water coolers and can only be marginally bested by significant custom loop systems.

    Finally, it might have been a good idea for amd to invest in a third socket for dual die chips. Sure they saved some money on underusing SP3 for TR, but that might have backfired more than the savings - the socket is huge, complex and expessive, takes up too much space, limits mobo designs and a lot of users report serious problems with the installation. On top of rendering existing coolers rather inefficient, something that would not have been a problem with a dual die socket.
  • ravyne - Wednesday, March 14, 2018 - link

    I wager we might see AMD introduce a new socket with Threadripper being a success. It's been reported that TR was essentially a passion-project for the engineers and so they didn't have the full resources at their disposal, even if they had the blessing of execs. There's the Epyc embedded 3000 series just coming out, which is a 1-or-2-die package supporting full PCIe lane potential and quad-channel memory in the two-die configuration, but it's designed to be soldered. Perhaps we'll see a socketed version, which would make ITX form factors possible and uATX more comfortable, and possibly reduce motherboard socket costs. I think they've committed to supporting the current TR socket for 3 generations of CPUs, but supporting two different sockets shouldn't be overly difficult given the multi-die/interposer construction and being able to leverage similarities/economies-of-scale with Epic 7000. Plus, if mainstream core counts continue to increase we're gonna need more PCIe and DRAM channels anyway, so maybe this just becomes the new mainstream socket.
  • eek2121 - Wednesday, March 21, 2018 - link

    We won't see a new socket for a while. Threadripper was a HUGE success and AMD wants to keep the Gravy Train rolling. I bought an Enermax 360 for mine and even when overclocked to 4.1 the machine runs silent and cool.
  • Martin Malice - Thursday, April 19, 2018 - link

    I have Enermax 360, I'm having troubles with cooling. Idk why but my Threadripper can't fall below 45 degrees Celsius when I'm working. When I start rendering something the temp goes up to 68 and clock speed starts dropping down. I don't know what's the problem, I've re-applied the thermal paste recently but the problem went away just for a short time and then it slowly reappeared.
  • Alexvrb - Wednesday, March 14, 2018 - link

    Not sure how you could have "serious problems" with the install. I for one like the overbuilt socket. I mean, unless you're one of the strange people aiming for an ITX TR build.

    I don't have any plans to own a TR system for personal use... I don't need more than 8 cores, quad channel RAM, or a crapload of PCIe lanes. But if you do it's a decent platform, and relatively affordable.
  • eek2121 - Wednesday, March 21, 2018 - link

    I would love to see them make a mobile variant.
  • LostWander - Thursday, March 15, 2018 - link

    No need for the hate. It's an obvious conclusion but it's nice to have some of the "why" laid out so well for those of us with only introductory engineering knowledge.
  • iter - Thursday, March 15, 2018 - link

    I wasn't aware that it takes engineering knowledge, introductory or otherwise, to possess common sense. "Contact" IMO is a pretty intuitive and self-explanatory concept...

    Yet it seems certain overly sensitive individuals have put emphasis on developing nonsensical sensibilities and neglected developing precious common sense... To the point of misidentifying sarcasm as "hate"... It is not hate, it is simply not being a dumb robot person whose worldview is so narrow that literally techniques slip outside of his norms for "appropriate"...

    I for one don't find it all that positive that people need such things explained in the first place, it is rather alarming to say the least.
  • LostWander - Thursday, March 15, 2018 - link

    Lots of assumptions there friend. Really sad honestly there were a lot of better (and more accurate) interpretations of my comment available.

    I'm so sorry for anyone in your life. Get help for their sake.

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