Puget Systems print logo

https://www.pugetsystems.com

Read this article at https://www.pugetsystems.com/guides/1292
Matt Bach (Senior Puget Labs Technician)

Graphite Pads vs. Thermal Paste: Which Is Better?

Written on December 3, 2018 by Matt Bach
Share:

Graphite pads: theoretically way better than paste

About a month ago, we mentioned on a Twitter post that we were looking into using graphite pads instead of thermal paste on our CPUs.

For those unfamiliar with these concepts, thermal paste is the traditional material to use between a CPU (processor) and a CPU heatsink to ensure that they are making good contact. Since no man-made surface is perfectly smooth and flat, thermal paste is used to fill any minuscule gaps between the two surfaces in order to ensure that all of the heat from the CPU is efficiently transferred to the heatsink.

The issue with thermal paste is that no one agrees on the proper application technique (even after we have done testing showing that it largely doesn't matter) and if you need to do a lot of CPU swaps like we do in Puget Labs, it can get messy, annoying, and somewhat expensive.

Graphite pads, on the other hand, come in sheets that can be cut down to the exact size you need. Rather than applying from a tube, you simply set it on top of the CPU and throw on the heatsink. There have been numerous posts and forum threads about this (just search Google for "graphite pad vs thermal paste"), but what got us interested in them was reports that not only do they cool as well or better than thermal paste, but that a single pad can be used over and over again.

No more cleaning and reapplying thermal paste over and over when doing CPU benchmark testing? Customers not needing to apply thermal paste if doing a CPU swap or upgrade in the field? Sounds amazing!

The unfortunate reality of graphite pads vs thermal paste

We did plenty of thermal testing, and rather than getting into details let's just say that the graphite pad was just as good as high-quality thermal paste. For most of the Intel X-series refresh testing we did in Puget Labs, it was terrific since we didn't have to deal with messy thermal paste multiple times a day.

However, issues started cropping up after we had done about a dozen CPU swaps. At first, we just had a few random reboots which we blamed on either overnight Windows updates or simple pre-launch bugs. However, it got worse and worse to the point that we were no longer able to finish even our Adobe Photoshop CC benchmark. We looked at the CPU core temperatures and while they seemed a bit high, they were nowhere near problem levels - only 83C at max. We even tried bumping up the CPU voltage which was something we used to have do on previous gen CPUs like the i7 7820X. That helped, but didn't resolve the issue.

What fixed the problem? Switching back to thermal paste.


Our best guess as to what happened is that since a graphite pad doesn't "bounce back" after being compressed, we were no longer getting the full space-filling effect needed to ensure proper contact between the CPU and heatsink. We were obviously getting decent contact since the CPU core temperatures were still just fine, but it must not have been enough.

As we did more and more CPU swaps, different areas of the graphite pad were being compressed. Since one CPU may have a surface bump in one place, but another CPU doesn't, this resulted in a pad that did not fit the contours of the CPU surface. Either the last CPU we tested had a very uneven surface, or this issue simply compounded over time.

Are graphite pads a failure?

The issue with graphite pads is that they are not really reusable. If you think of them as a one-time use item, they should work just fine and are arguably easier and certainly cleaner than thermal paste. But the more times you reuse the pad, the more likely you are to run into problems.

The issue for us is that there is no real way to know how many uses you can safely get out of a graphite pad. If the CPUs are very similar in surface contour, you might get 20 or more uses in a row before problems start cropping up. On the other hand, if you have two CPUs that are very different, you might get stability issues right after that first CPU swap. This unknown quality removes one of the primary benefits of graphite pads.

This hasn't completely soiled the idea of graphite pads to us since we could simply replace the pad on every CPU swap. However, in many ways it is easier to have a big tube of thermal paste rather than a stack of graphite pads since with the pads you need to make sure they stay relatively clean and free from dust. On the other hand, it would be much easier to simply send along a graphite pad rather than a tube of thermal paste to a customer in the field who wants/needs to do a CPU reseat, replacement, or upgrade. So, at the moment, we are still somewhat on the fence about which is better.

Graphite pads are not quite the homerun we had hoped they would be, but that doesn't mean they don't have their place. The question we need to decide is simply whether they are a good idea for our workstations or if the tried and true method of using thermal paste is what we should stick with.

Tags: Thermal Paste, Graphite Pad
Lance Lund

cost man! what do they cost? using a TON of thermal paste on threadripper is probably more expensive

Posted on 2018-12-12 20:38:23

Honestly, the cost is pretty negligible either way (at least for us buying in bulk). We use 30g tubes of Arctic Cooling MX-2 which is about $15 and lasts for at least 50 applications. So maybe 25 cents every time we apply it? Graphite pads are $10 each if you buy the pre-cut stuff that is "designed" to use on CPUs. Or, if you buy it in big sheets and cut it down, it gets closer to $1 per piece.

So if the graphite pad lasts 4 CPUs, it about breaks even with the thermal paste in terms of cost. If cost is a factor for you, thermal paste is 100% the way to go. We were just hoping that we could pay a bit more and save on the mess and fuss of paste.

Posted on 2018-12-12 20:49:51
E pluribus unum

sure but a "lab" has experience in putting thermal paste, you don't need graphite pads. But a novice that reads this will think that thermal paste is better for his application where it's not because the likelyhood of him changing processor 4 times even in a decade are really slim, and they don't have to deal with possible spills and cleanup. And I think the distinction is not made really well.

Posted on 2019-01-30 21:38:38
fidalgoman

I have noticed that on my son's gaming machines that the thermal tape/paste used on the graphics cards sometimes deteriorates and kills the chip. Long term, what might be the effect of thermal cycling and the different coefficients of expansion between the Cooler face, the CPU die and the thermal pad? Though slight, there still is movement.

Posted on 2019-01-05 23:56:33
E pluribus unum

but you said "after about a dozen swaps"... thermal paste has 1 use and you can't reposition it even once... be fair. No one would expect to reuse it 10 times

Posted on 2019-01-30 20:56:31

Graphite pads are a lot more expensive than a single application of thermal paste, so we had been hoping that they would be reusable to make up for that - and to make it easier for folks to do CPU swaps. We change CPUs a lot in Puget Labs, but have gone back to thermal paste because of the issue described above.

Posted on 2019-01-30 21:34:19
Hannibal

The Main poin is that the graphite pad does not try up, like thermal paste does, so if you keep the cpu longer than e years, it may be usefull to use graphite pad, because it is after 6 year just as good as after 1 day. The thermal paste is best when it is new and in few years it is better to change it, if you want to get best result.
Is there difference in thermal between thermal paste and graphic pad? Is not, to normal user who newer change his cpu, the pad is much better in the long run...

Posted on 2019-02-04 16:50:18
Damien

What about if you have an older laptop with a potentially problematic heatsink? I have a 2011 Dell XPS with an Intel i7-2860QM and the first core averages out at 70c, while the 3rd and 4th core average out at 50c, that's a 20c difference. In this case should I try a thermal pad? I have tried re-pasting... (This also shouldn't be an IHS issue as mobile chips don't have a heat spreader).

Posted on 2019-02-17 18:08:10
Jerome Poulin, PhD

Hi Guys, I'm Engineering Leader for a LED Lighting designer & manufacturing group. We have done lots of R&D of TIM (Thermal Interface Material). We stopped paste completely because its messy and performance is inconsistent, even misapplied, its sometimes worse than no-paste at all. I feel similar results apply to CPU cooling regarding TIM. When area is large and even (over an inch square), carbon is really a excellent performer, we never tried really re-using them. However, we play with 3 different thicknesses 5 mil, 10 mil and 20 mil. Thinner is thermally better but thicker is better for gap filling and accomodating uneven pressure or level between heat sink mounting mechanics and the CPU. In case you don't know, use 10 mil. Cost don't really change a lot with thickness.

However, when its getting real real hot or heat concentrated on a smaller surface, there is a superior material to carbon and that is Phase Change Material (PCM). Its sort of a wax-like polymer film that turns "fluid" with heat above 50 celsius. However it won't flow out so don't worry. This ultimately "wets" perfectly the interface. I recommend you try LairdTech TPCM5810, you can get this stuff on digikey, buy by the sheet and cut it down with scissors as you need it. Not reusable at all, if you have the reseat heat sink,. scrape it down and put a new one. Hope this helps you all.

Posted on 2019-02-22 22:16:29