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Why does a CPU Need Thermal Grease?

By R. Kayne
Updated May 17, 2024
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Thermal grease, also called a thermal compound, aids a heat sink in cooling a central processing unit (CPU). A CPU is the integrated circuit responsible for running a computer. The CPU is made up of millions of tiny electronic ‘switches’ jammed together into a core. Each time a switch operates, a small amount of heat is generated. With millions of these switches activating thousands of times each second, heat builds quickly. For intensive programs like computer gaming, a CPU works very hard and can potentially get very hot. Overclocking also increases thermal production.

A heat sink is a device that clamps on to the CPU, designed to draw heat away from the chip to protect it. The bottom surface of the heat sink is designed to be extremely smooth to maximize surface-to-surface contact with the CPU. But imperfections and pits in the CPU wafer allow tiny gaps that reduce the effectiveness of the heat sink. This is where thermal grease comes in. This is a thin layer of one of a variety of compounds that thermally binds the CPU and heat sink together. It fills any pits, gaps or imperfections that would allow air pockets between the chip and the heat sink.

Because thermal grease must conduct heat to be effective, it is made from specific materials that do this rather well. Some types are better at conducting, or transferring heat, than others. Expensive thermal grease contains particles of silver for maximum effectiveness, while inexpensive compounds are silicon-based. Ceramic grease is a mid-grade compound; one notable brand outperforms silver-based compounds according to many independent tests.

With a properly installed heat sink using this material to maximize contact, heat is pulled off the chip and drawn upwards into the fins of the sink where it is dissipated by a fan. A CPU should never be operated without thermal grease and a heat sink. Temperatures can quickly rise to melt the core, making it inoperable.

CPUs sold with a heat sink and fan in a retail box include thermal grease, often in the form of a thin thermal pad. In most cases the warranty of the CPU depends on using the supplied thermal pad, heat sink and fan. If buying an original equipment manufacturer (OEM) CPU and supplying your own heat sink and fan, don’t forget to purchase thermal grease and apply it carefully per accompanying instructions.

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Discussion Comments

By anon939284 — On Mar 12, 2014

Thermal grease is easy to assemble and is more convenient for the production line when compared to thermal conductive pads. However, it can't be reworked, which is the advantage of thermal conductive pads instead. It has great effect for heat conduction.

By anon172806 — On May 05, 2011

I'm just about to spend $120 on a CPU cooler tomorrow, because the four core temps in my Core i7 950 CPU are now running at between 94 and 100 deg C - enough to boil water.

But, there is some thermal paste there. I even have the tube of Arctic Silver 5. I'll ask the tech to make sure he uses some tomorrow.

Bottom line is, you need to use this stuff!

By anon154472 — On Feb 21, 2011

You only need a small amount less than pea sized blob in the center. Once the Heatsink is mounted it will spread the grease. Too much and you risk it getting onto other components and possibly causing a short-out. Compound shouldn't dry up and glue - so don't worry about that. bear in mind this stuff is designed to function in very hot temperatures.

By anon86175 — On May 24, 2010

you should apply it only onto the top of your CPU (don't put it on both, CPU and heatsink). Excessive grease is not quite the best choice.

By anon54797 — On Dec 02, 2009

i have a question i accidentally wiped some of the grease off, not knowing it should be there. there is still grease on it will it be enough? what should i do? - O.A.

By anon33539 — On Jun 08, 2009

Thank you for this very informative article.

During cleaning and removing dust from fan and heat sink I removed the fan and heat sink not knowing there should be a thermal compound in there, I replaced everything and have been experiencing thermal event shut downs ever since. I bet just a dab I'll do me.


By anon22495 — On Dec 04, 2008

Question: I need to reinstall my Celeron 25. GHz CPU (478 pins), which is connected to the heat sink with a thermal pad (as described in your article). Should I replace the thermal pad with the thermal grease, and if so, should I apply the grease to both the heat sink and the CPU top. Should the CPU adhere to the heat sink, and if so, will it harden like a glue? What else should I worry about, other than ESD? Thank you for your assistance. Anonymous Newbie

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