Thermal paste makes a lot of difference in the computer’s central processing unit (CPU). It is important to know the uses of thermal paste and how they work. For this reason, we have decided to write this guide on thermal paste and its benefits.
What Is Thermal Paste?
Thermal paste (also known as thermal grease or thermal compound) is a substance applied between the processor and the heat sink. You can buy small tubes of thermal paste at electronics stores, sometimes accompanied by a small shovel-like tool called an applicator.
When you buy a graphics card, for example, the thermal solution is already integrated. You don’t usually have to worry about installing a cooler onto a GPU unless you are interested in aftermarket solutions like custom liquid cooling. With a CPU cooler, you have the option to choose the one you want, but that means you’ll usually need to install it yourself.
When you’re building a PC, you’ll need a tube of thermal paste for your PC to run smoothly. Some CPU heat sinks come with thermal paste pre-applied to them so you can install it and go. Some hardware enthusiasts, however, will swear by and manually apply their favorite brand of thermal paste.
The role of thermal paste is to help transfer heat away from the CPU and into the heat sink. The heat sink then expels the heat away from the hardware. This keeps the CPU cool, especially when it’s hard at work processing tasks.
You may also find the term “stock thermal paste.” This kind is thermal paste applied by the manufacturer, such as on a pre-built machine. However, some manufacturers skimp out on the thermal paste and use a compound that’s not very effective at conducting heat.
As such, enthusiasts will often replace this stock thermal paste with their preferred brand of “aftermarket” paste—the stuff you buy off the shelves.
Terms You Need to Know
In order to properly explain how thermal paste functions, it’s worth defining some of the terms we will be using.
- Central Processing Unit (CPU) – The information processing center of a PC. It executes all operational instructions and sends instructions to the other hardware in the computer. If the computer is a body, then the CPU is the brain, and it is absolutely critical to the functioning of any PC. Modern CPUs execute a high volume of operations per second, and this generates heat.
- In order for a CPU to operate at peak efficiency, it needs to be properly cooled, usually with a cooling apparatus designed just for this purpose. This is where thermal paste becomes important. If you’d like to learn more about how a CPU is made, you can read more about the manufacturing process.
- Integrated Heat Spreader (IHS) – The metal “lid” of the CPU. This serves as a heat sink designed to distribute heat from the processor itself to a CPU cooler, as well as provide protection to the processor inside. This is the part of the CPU that is still exposed after being installed in a motherboard and is the surface to which you apply thermal paste.
- CPU Cooler – The device that keeps your CPU running at optimal temperatures. CPU coolers usually use air or liquid to relocate the heat created by the operation of the CPU.
- Base-Plate – The metal base of an air cooler that attaches to the IHS of the CPU. This design allows the transfer of heat through convection to the fins of the heat sink, where it can then be redistributed with a fan.
- Waterblock – The apparatus that attaches to the IHS when using an All-in-One (AIO) liquid cooler or a custom cooling loop. It transfers heat from the IHS to the heat transfer fluid, which then relocates that heat to be redistributed by fans at a radiator.
- Thermal Paste – A silvery-gray substance that you apply to a processor before installing a cooling solution. It allows for an efficient transfer of heat from the IHS of the processor to the base plate or water block of the CPU cooler that is designed to dissipate that heat.
How Does Thermal Paste Work?
CPUs can get very hot, so it’s essential to draw heat from them as quickly as possible. Unfortunately, the air is a terrible conductor of heat, so there needs to be as little air as possible between the CPU and the heat sink for optimum transfer.
If you’ve prodded around inside a computer, you’ll know that the heat sink presses tightly against the CPU. This seal may seem good enough to stop air from getting in; unfortunately, even a tight squeeze isn’t enough to keep air out.
The surface of the CPU and the heat sink’s contact plate is covered in tiny grooves and gaps. If not properly sealed up, these gaps allow air between the processor and the heat sink, reducing the heat transfer efficiency between the two.
This is where thermal paste comes in. Not only is thermal paste a good conductor of heat, but it can get into those small gaps and grooves on the surfaces of the hardware. This creates an air-tight seal and increases the rate of heat transfer.
Over time, the thermal paste will get old and dry. The dryness reduces its effectiveness and causes the CPU to get toasty. This occurrence is why people suggest re-applying the thermal paste to prevent a computer from overheating.
What is a thermal paste made of?
The thermal paste consists of a base matrix and contains a thermally-conductive filler. Typical matrix materials are epoxies, silicones, urethanes, and acrylates. Fillers include carbon micro-particles, aluminum oxide, boron nitride, zinc oxide, and aluminum nitride. The filler content can be up to 70–80% by mass and raises the thermal conductivity of the base matrix from 0.17–0.3 W/m·K up to about 4 W/m·K, depending on the formulation. Metal fillers tend to have higher thermal conductivities.
Each formulation is designed for a particular use case; regardless, the final result must be easy to apply, fill gaps effectively, conduct heat well, and remain stable for thousands of hours without drying out or flaking.
M.G. Chemicals’ Type 860 is a good example of a silicon-based silicone heat transfer compound. It uses zinc oxide as the filler to achieve a thermal conductivity of 0.66 W/m·K. The product is electrically-insulating and non-corrosive with an operating temperature range of -40 to 200 °C.
If higher performance is required, silver-based compounds can have a thermal conductivity of 3 to 8 W/m·K or more. These consist of micronized silver particles suspended in a silicone medium. However, the metal-based thermal paste can be electrically conductive and capacitive and can cause malfunctions or damage if it flows onto electrical circuitry.
The thermal formulations with the highest performance (and highest cost) consist almost entirely of liquid metal, usually a variation of the alloy Galinstan™ — a mixture of gallium, indium, and tin. Metal pastes can attain thermal conductivities greater than 13 W/m·K but are difficult to apply evenly and have the greatest risk of causing a malfunction due to spillage. In addition, gallium is highly corrosive to aluminum, so it cannot be used with aluminum heat sinks.
Important Preparations for Thermal Paste Application
Most processors require some sort of thermal solution to properly operate at peak efficiency, but the process of installing a CPU cooler in a PC is unique.
Every CPU cooler needs thermal paste, but many have it pre-applied, which simplifies the installation process. To find out if you have a pre-applied paste, check the bottom of the base plate or water block of your CPU cooler that attaches to the CPU. If the silver paste is already there, you don’t need to add any more during the installation process.
A few things to keep in mind before starting:
- Make sure that the CPU is clean, and that there isn’t any old thermal paste on it. If there is, carefully remove the old paste from the lid of the CPU with isopropyl alcohol and a microfiber cloth or paper towel that doesn’t shed, and let it dry before continuing.
- Before you start applying the thermal paste, make sure the rest of your CPU cooler is ready to install. Consult the instructions, ensure that every step has been completed up to attaching the CPU cooler, and make sure you have any necessary tools close at hand.
Tips for applying thermal paste
As a conductor of heat, thermal paste is better than air, but not as good as metal, so it is important to use the minimum amount needed to fill the air gaps. If an excessive amount is used the thermal paste will act like an insulator since its thermal performance is inferior to that of the metals it is connecting.
The conductive paste performance depends heavily on surface preparation. Improperly prepared contact surfaces can degrade the paste’s stability, conductivity, and lubrication characteristics. Before applying the paste, the two surfaces should be cleaned with a non-oil-based cleaner such as isopropyl alcohol; the paste should be spread in a thin layer.
The application pattern is usually determined empirically to provide good coverage of both surfaces to be thermally connected while minimizing excess use. Popular choices include dots, circles, and “X” patterns.
Situations to Avoid:
Make sure to use the correct amount of thermal paste, which is roughly the size of a pea or a grain of rice. An insufficient amount might not cover the surface area needed in order to be effective. Too much reduces the efficacy of the paste, due to the metal surfaces being too far apart, and also risks spilling out onto the motherboard during installation.
It might be tempting to spread the thermal paste onto the CPU yourself. We recommend letting the pressure from the base plate or water block being installed do it for you. The incorrect manual application can cause air bubbles to form in the past, which can negatively impact thermal conductivity.
Reusing paste can also cause air bubbles to form. If a problem occurs during the installation process and you have to remove the CPU cooler, you should completely clean off all paste as mentioned above, then try again with a fresh application. If you absolutely need to reuse an application — while waiting for replacement paste, for example — you can, but keep in mind this is a short-term solution, and that we recommend a proper reapplication before long-term use of your CPU cooler.
In conclusion, thermal paste is of utmost importance. Do not hesitate to get one for yourself. Also, Knowing how to properly apply thermal paste can help to make sure you’re getting the best performance from your CPU.