Most of the steps in building your own desktop PC are fairly self-explanatory: thanks to the modular nature of PC parts, it’s actually hard to mess up. But there’s one exception, and it can get messy.
When it comes to applying thermal paste, less is more: a small, pea-sized drop is all you need. Don’t spread it around, either—the heatsink will spread it out evenly as you screw it in.Thermal paste (also known as thermal grease, thermal interface material, or thermal gel) is the semi-fluid compound you apply to the metal housing of the CPU to allow efficient heat transfer to the cooler mounted directly above it. And if you’ve never used it before, it can be tough to know exactly how much you need—and the internet is full of bad advice on the subject.
Before we get started: thermal paste is applied to the top of the CPU, not the bottom. It should applied to the smooth metal plate (where the manufacturer and model information is printed), not to to the hundreds of squares or pins on the underside. Thermal paste does not go on the motherboard’s CPU socket directly. This point might seem obvious to the experienced system builder, but it’s a mistake often made by first-timers…that can unfortunately ruin an expensive CPU (and motherboard).
Also note that if you’re using the cooler that was included with your CPU purchase, it might already have thermal paste applied from the factory. Check the copper-colored heat transfer plate beneath the fan and heatsink assembly: if it has even patches of grey material on it, the paste is already in place, and you don’t need to apply any yourself. If you’re swapping out for a new CPU, you will need to clean off any old, excess paste with isopropyl alcohol and apply fresh material.
Worried about what kind of thermal paste to use? Don’t—it doesn’t make that big a difference in your temperatures. If your cooler came with a tube of thermal paste, it’s probably good enough.
The correct amount of applied paste is, bluntly, “not much.” Both Intel and AMD recommend squeezing a “pea-sized” glob of paste out of the tube (which is either included with the purchase of a CPU-and-cooler combo or sold separately) and onto the direct center of the CPU before placing the cooler on top and affixing it with the mounting hardware. To be perfectly clear, we’re talking about a single drop of material, no more than a centimeter (half an inch) wide at any point. (You may need a little more if you have a rather large CPU, like some of Intel’s six- or eight-core processors.)
Don’t worry if it’s not perfectly even, and don’t try to spread it out across the entire surface of the metal plate. You’re not making a peanut butter sandwich here. The cooler mounts directly onto the CPU itself, so the paste will spread out laterally as it’s compressed, making an ideal surface for heat transfer more or less on its own. Some users have more elaborate methods of covering the CPU, but it really isn’t necessary.
If you’re worried about getting it wrong, well, don’t. But if you’re still worried, remember this: too little thermal paste is better than too much. Because the cooler plate and the CPU are so close, too much paste can expand out beyond the chip and the plate, filling into the space of the CPU socket itself and transferring undesirable heat to the CPU’s electrical contacts or the surrounding PCB. That’s bad. If you apply too little paste and your CPU runs too hot resulting in computer crashes, you can always clean it off and reapply, but cleaning paste out of the socket itself is much more problematic.
Once you have the paste applied as above, simply set the cooler on top and screw it into place on the motherboard with its included mounting hardware.
Image credit: Intel