Thermal Paste vs Thermal Pad – Why don’t we use these??
If you’ve ever built a PC, or watch tech YouTubers enough, you’ll know of thermal paste. It’s the grey goopy stuff you spurt onto your CPU before you plonk a big cooler on top. Sometimes the cooler has some pre-applied, sometimes you need to add some yourself, but either way it’s kinda messy. If you take the cooler off you have to wipe it all away and apply new, fresh paste. It can leak everywhere – and don’t get me started on how you can find thermal paste fingerprints everywhere around my house – so what’s the deal?
Why can’t we use something like this, a thermal PAD instead? I mean it’s not one-time-use, it’s (mostly) solid so there is nothing to leak, and you shouldn’t need to replace it after every insertion and removal, so why aren’t we all using these?! This must be another conspiracy by big fan to keep you buying more and more thermal paste right? I mean a consumable item you have to replace every time you take the cooler off, making you buy more and more tubes of it… Actually, yeah, it makes sense. Here’s why.
This is ARCTIC’s APT2560, a high performance thermal pad with almost identical thermal conductivity to their latest and greatest paste, ARCTIC MX-5. They sent over all the various sizes from 0.5mm to 1.5mm, although I’ll be using the thinnest 0.5mm version here. Let’s take a look at the thermals, with ambient correction, between this 0.5mm pad and their MX-5 paste. Oh my… that’s a pretty massive difference! You are looking at 87°c peak with the thermal pad, and just 64°c for the paste on this Ryzen 5900X using ARCTIC’s Liquid Freezer II 360 A-RGB cooler running in Cinebench R23 multi threaded for 30 minutes. To say that’s a sizable advantage to the paste would be the understatement of the century.
And the difference doesn’t stop there, look at the core ratios, the orange pad line is noticeably lower meaning the CPU was actively running slower than when properly cooled. While rendering the Gooseberry scene in Blender it’s the same painful temperature differential, but more importantly… That gap at the end, where the blue line ends but the orange one carries on, that’s not just me moving the data around, that’s where the run ended. There’s almost a 30 second difference there, where the pad ran around 200MHz lower clock speeds throughout the run thanks to the temps. That’s a massive difference – and of course that’s without trying to overclock the CPU with Precision Boost Overdrive, something the paste is more than capable of doing but the pad? Yeah, no chance.
So, why is the pad that much worse? I mean, if it has the same thermal conductivity of 6W/mK as the paste, it should perform just as well right? Sure, if you were able to use as much paste as there is pad. The reason every PC build guide says “use a grain of rice sized drop” isn’t to help you conserve your precious supply of thermal paste, it’s because using too much paste actively hurts performance and this type of pad is basically like adding a full 4g tube of paste all at once.
To understand why you really can have too much thermal paste, you need to know what it’s actually there for. The thing is, you totally can just mount your CPU cooler direct to your chip, no thermal interface material (TIM) required. But if you do, you’ll quickly find out that it sucks and your CPU is overheating. There are a number of factors there, but the main one is that neither your CPU nor cooling plate are perfectly flat. They’ll be slightly bowed either concave or convex, one corner might be slightly lower than another, and the metals themselves have tiny bumps and dents that will cause air to be trapped between the CPU and the cooling plate, and that’s bad.
See, air is an insulator, a really good one actually, as it’s thermal conductivity at room temperature is 0.026W/mK, so those little pockets of air are refusing almost all that heat energy forcing it to the relatively small places where the two pieces of metal actually touch. That reduces the effective surface area drastically, to the point where it’s no longer effectively cooling your CPU.
So, by adding the thermal paste what you are doing is replacing that air with a material that is over 200 times more thermally conductive meaning it can evenly transfer that heat over the whole chip die and into your cooling plate rather than at tiny little points. So more paste is better right? Well, here’s the thing. Aluminium’s thermal conductivity is somewhere around 240 W/mK, and copper? That’s somewhere around 400 W/mK, so the ideal solution actually is to have no paste and a perfect mount as that is by far the most thermally efficient, but failing that, having just enough paste to remove all the air but otherwise not impede any direct contact is about as good as you’re gonna get.
You can use a more thermally conductive material, liquid metal thermal pastes are up into 70W/mK, but that’s still not as good as aluminium or copper and so again you want to use as little as you can get away with.
When using a thermal pad like this, you block any direct contact that could have been made completely, replacing a say 20-50W/mK connection with exclusive transfer through the pad at just 6W/mK, hence the performance difference.
So, if not for CPUs, what are these pads for? Well, you’ve probably seen them poking out of motherboard VRMs, or on graphics cards. These are great for components that don’t need too much heat sinked away, or as a good solution to cooling complex shapes and heights with a single block. Sure thermal paste might technically be more efficient but for the sorts of applications where you’ll find these the outright efficiency doesn’t matter as much as just cooling the parts evenly, plus these are more durable as paste can dry out and become less efficient. Sure, pads do age too, but much slower by comparison.
So, if you need to repaste your GPU, need to replace your motherboard’s VRM heatsinks, or maybe want to cool your blisteringly fast Gen 4 NVME SSD, take a look at these pads from ARCTIC, they’ve even got a more budget friendly option too. But, for your CPU and GPU, stick to the thermal paste.
