Thermal paste is a seemingly simple component that plays a critical role in CPU cooling. This thermally conductive compound fills microscopic gaps between your CPU and cooler, enabling efficient heat transfer. Proper application ensures optimal cooling performance, while mistakes can lead to elevated temperatures and reduced lifespan. Let's master this essential skill.
Why Thermal Paste Matters
Despite appearing smooth to the naked eye, both CPU heat spreaders and cooler bases have microscopic imperfections and irregularities. When metal contacts metal directly, these imperfections create tiny air gaps. Since air is a poor thermal conductor, these gaps significantly impede heat transfer from your CPU to the cooler.
Thermal paste fills these gaps with a material that conducts heat far better than air. Quality thermal compounds can reduce CPU temperatures by 10-20°C compared to metal-on-metal contact, making them essential for any CPU installation.
The difference between budget and premium thermal paste is typically only 2-5°C. Proper application technique matters far more than the specific compound you choose.
Types of Thermal Compounds
Standard Thermal Paste
Most thermal pastes use silicone-based compounds with thermally conductive fillers like zinc oxide, aluminium oxide, or ceramic particles. These are non-conductive, affordable, and perfectly adequate for most users. Popular options include Noctua NT-H1, Arctic MX-4, and Thermal Grizzly Kryonaut.
Liquid Metal
Liquid metal compounds use gallium-based alloys that offer dramatically better thermal conductivity than traditional paste. However, they're electrically conductive, can damage aluminium heatsinks, and require careful application. Only experienced builders should consider liquid metal, and only for specific high-performance scenarios.
Pre-Applied Thermal Paste
Many coolers come with thermal paste pre-applied to the contact surface. This paste is typically adequate, and you should use it unless you have a specific reason to replace it with your own compound.
Liquid metal is electrically conductive. Any contact with motherboard components will cause short circuits and permanent damage. It also chemically reacts with aluminium, destroying aluminium heatsinks over time.
Application Methods
The internet has endless debates about the "correct" application method. The truth is that several methods work well, and the differences between them are minimal with modern paste formulations.
The Pea Method (Recommended)
Apply a small pea-sized dot (about 4mm diameter) to the centre of the CPU. The mounting pressure of your cooler will spread the paste evenly across the heat spreader. This method works reliably for most CPUs and paste types.
The X Method
Draw a small X pattern across the CPU surface, with lines about 1-2mm wide. This provides slightly better initial coverage for larger CPUs but uses more paste.
The Spread Method
Spread a thin, even layer across the entire CPU surface using a plastic spreader or card. This ensures complete coverage but risks introducing air bubbles and tends to use excessive paste.
The Line Method
Apply a thin line down the centre of rectangular CPUs. This works particularly well for AMD Threadripper and Intel Xeon processors with large, elongated heat spreaders.
For most desktop CPUs (AMD Ryzen, Intel Core), the pea method with a 4mm dot is reliable and foolproof. Larger CPUs benefit from the X or line methods.
Step-by-Step Application
Step 1: Prepare Your Workspace
Work in a clean area with good lighting. Have isopropyl alcohol (90%+ concentration) and lint-free cloths or coffee filters ready for cleanup. Avoid paper towels, which can leave fibres behind.
Step 2: Clean Surfaces (If Replacing Paste)
If removing old thermal paste, apply isopropyl alcohol to a lint-free cloth and gently wipe both the CPU and cooler surfaces. Remove all old paste residue and wait for the alcohol to evaporate completely.
Step 3: Apply Thermal Paste
Squeeze a pea-sized amount onto the centre of the CPU. Don't spread it manually unless using the spread method. The paste should be about the size of a small pea or BB pellet.
Step 4: Mount the Cooler
Place the cooler directly onto the CPU and press down evenly. Secure the mounting mechanism using a cross pattern (opposite corners) to ensure even pressure. Don't remove and reposition the cooler once contact is made—this can introduce air bubbles.
Step 5: Verify Your Work
Boot your system and check temperatures at idle and under load. Idle temperatures should be 35-50°C depending on your cooling solution and ambient temperature. If temperatures are unusually high, you may need to remount the cooler.
If you need to remove and remount your cooler, always clean off the old paste and apply fresh compound. Reusing spread paste introduces air pockets and degrades thermal performance.
Common Mistakes to Avoid
Too Much Paste: Excessive paste doesn't improve cooling and can actually insulate heat. If paste squeezes out the sides when mounting, you've used too much.
Too Little Paste: Insufficient paste leaves gaps in coverage, creating hot spots. If your temperatures are unusually high, insufficient paste coverage might be the cause.
Uneven Pressure: Tightening mounting screws unevenly causes poor contact on one side. Always use a cross pattern and tighten gradually.
Touching the Paste: Oils from your fingers contaminate thermal paste and reduce effectiveness. Apply directly from the tube or syringe.
When to Replace Thermal Paste
Quality thermal paste maintains effectiveness for 3-5 years under normal use. Consider replacing it if you notice gradually increasing temperatures over time, if you're removing your cooler for any reason, or when upgrading cooling solutions.
There's no need for annual replacement unless you're chasing the lowest possible temperatures. Modern pastes are remarkably stable and don't "dry out" as quickly as older formulations.