How To Correctly Apply Thermal Paste
By Gabriel Torres e Daniel Barros e Cássio Lima on January 12, 2006


Introduction

With processors working at increasingly higher clock speeds, concern with thermal dissipation is necessary because the higher the clock used, the higher the heat produced. To give you an idea, a 486DX2-66 dissipated somewhere between three and six watts, while a Pentium 4 processor with 3.8 GHz dissipates 115 W! If you don’t utilize a thermal solution compatible with the specific model of processor that you use in your system, several problems can appear: random resets, freezes, reduction of processor lifespan, and even burning the CPU in extreme cases.

Several solutions were proposed to solve those problems, including the elaboration of a new motherboard standard (the BTX standard was created to maximize air circulation inside the PC) and the launching of cases with ventilation ducts and liquid cooling systems.

Those solutions are still expensive, and we are not always willing to pay for them. Individuals who work assembling and selling computers are aware of market problems and know how difficult it is to convince a client that the final cost of the computer increased due to a better cooling system. Usually, the client is not very interested in that; their only concern is the price.

A simple and inexpensive solution is the utilization of thermal paste (also known as thermal grease or thermal compound) that can help reduce the problem of processor overheating. The paste must be used with the right cooler for the specific model of processor installed.

In this tutorial, we’ll discuss the role of thermal paste in the process of thermal dissipation, how to correctly use it, and the most common mistakes made during thermal paste application.

We have a follow-up review to this tutorial, called “What is the Best Way to Apply Thermal Grease” that you should read as well.

What is the Purpose of Thermal Paste?

The device used to remove the processor’s heat is the cooler. Each processor requires a specific type of cooler. The use of an inefficient or wrongly dimensioned cooler can cause overheating problems.

However, the cooler alone doesn’t solve the overheating problem. There’s another “bad guy” in the story: heat transfer between the processor and the cooler.

From the microscopical point of view, the physical contact between the processor and the cooler isn’t perfect. Imperfections that exist both on the processor surface and the cooler surface prevent their being a 100% perfect contact between them.

As both surfaces aren’t perfectly even, minuscule gaps of air are formed when putting them together. Because air is a terrible heat conductor (its conductibility coefficient is 0.026 W/m°K), the heat will pass with more difficulty from the processor to the cooler, which can result in overheating.

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Figure 1: Air gaps formed by the junction of the processor and cooler

To solve the problem and improve the heat transfer between the processor and the cooler, we should apply thermal paste between them in order to fill in the tiny gaps of air. By doing so, the heat transfer between the processor and the cooler is easier since the thermal paste has a higher conductibility coefficient than the air.

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Figure 2: Gaps of air filled by thermal paste

Thermal paste can be found in electronics parts stores. Its use is indispensable and it’s a very inexpensive component.

On the following pages, we will discuss how to correctly apply thermal paste, as well as stating the most common mistakes made when applying it.

The Thermal Paste

The thermal paste is basically composed of silicone and zinc oxide, but there are more elaborate pastes that can even contain ceramic and silver – noble materials that promise more efficiency in heat transmission.

Its price can range between USD 2 and USD 32 (in pastes that have silver in their composition).

Thermal paste can be found in many kinds of packages and usually comes with the cooler. Figure 3 shows many kinds of packages.

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Figure 3: Many kinds of thermal pastes

There are also coolers which have some material applied from the factory. In addition, coolers that come with the processor (“in-a-box”), or even some coolers sold alone, are found on the market with thermal paste already applied.

In the case of coolers that come with the processor and coolers of recognized brands, the quality of the material applied is usually good, and both AMD and Intel recommend the use of those compounds.

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Figure 4: Cooler in-a-box for Pentium 4 with pre-applied thermal paste

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Figure 5: Cooler in-a-box for Athlon 64 with pre-applied thermal paste

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Figure 6: Cooler in-a-box for AMD socket 462 processors with pre-applied thermal paste

All of the above compounds are of good quality and have better efficiency than regular thermal pastes. If you bought a super thermal paste containing silver, you should remove the original compound and apply the new paste instead.

Unfortunately, the use of those compounds “from the factory” has some inconveniences. The first one is that they can be used only once. If you remove the cooler for some reason, you’ll have to clean the old compound and apply the original one again (which is hard to find) or apply thermal paste instead. Another very common problem is that the compound ends up sticking the heatsink to the processor, making cooler removal difficult.

In the case of Intel socket 478 and AMD sockets 754 or 939 processors, it’s very common to pull the cooler and take out the processor at the same time if it is stuck on the heatsink, something that ends up damaging the processor in most cases. The tip here is to use a hairdryer to heat the heatsink a little in order to melt the thermal compound and then remove the heatsink with lateral movements. But don’t use the hairdryer too much.

There are also cheaper coolers that come with a graphite square or thermal tape similar to gum that are terrible heat conductors. In this case, you should remove those compounds and apply thermal paste instead.

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Figure 7: Cooler for Socket 7 with graphite compound you should remove

Many people believe that the more thermal paste, the better. A lot of paste turns out to be insulating, not to mention that paste in excess ends up dropping down and reaching motherboard contacts. Remember that most pastes don’t conduct electricity, but there are pastes that contain metal in their composition which turns them into conductors that may cause a short circuit and destroy your equipment.

We will show in detail how to apply thermal paste on several kinds of processors.

Removing The Original Thermal Paste

If the processor and/or cooler have thermal paste on them, you should remove it before applying a new thermal paste.

In Figure 8, there is a Sempron processor that was originally mounted with a cooler that already had thermal compound.

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Figure 8: Sempron processor with remains of thermal compound

In this case, first you must clean off the remains of the thermal compound. Use a cotton swab with isopropyl alcohol (isopropanol). This kind of alcohol is purer (doesn’t contain water) and can be found at electronics equipment stores or drugstores.

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Figure 9: Clean all the remains of thermal compound

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Figure 10: The processor is clean and ready to receive the thermal paste

You can also clean the rest of the thermal compound that remained on the heatsink. We used a utility knife to rub out the rest of the compound, being careful not to scratch the cooler base. To finish, use a piece of cloth with isopropyl alcohol (isopropanol) to remove the rest of the thermal compound.

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Figure 11: Cooler with rests of thermal compound

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Figure 12: With a utility knife, rub out the rests of the compound

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Figure 13: Final cleaning

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Figure 14: Cooler ready to be installed

With all the remains of the thermal compound removed, you can now apply the new thermal paste.

Socket 462 Processors

Socket 462 is used by Athlon, Athlon XP, Duron and Sempron socket 462 processors. How it is attached is similar to that of older processors (Pentium, Pentium III, Celeron and AMD K6). Therefore, the next instructions also pertain to those old processors.

Using a cotton swab, put a small amount of thermal paste on the processor. Don’t put too much paste because the excess can make the heat transfer worse instead of better.

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Figure 15: Apply a small amount of grease on the processor

Don’t worry about covering the entire area of the processor (the pink part) because the cooler pressure itself will make it uniform.

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Figure 16: Correct amount of thermal paste

Next, carefully install the cooler over the processor. Notice that socket 462 has one side bigger than the other; the side next to the processor installation lever is larger than the opposite side. Coolers for socket 462 will also have one side bigger than the other. Notice that one of the sides of the lock that joins the cooler to the socket is longer than the other. Therefore, the longer side should be facing the larger side of the socket (the side of the lever), while the shorter side should be facing the smaller side of the socket.

A common mistake when installing coolers on socket 462 processors is installing the cooler “inverted,” i.e., rotating it 180° in relation to its correct position.

In some PC cases, it may be necessary to remove the motherboard in order to install everything without having any problems.

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Figure 17: Put in position and fasten one side

Then, using a screwdriver, attach the cooler. Use the screwdriver as a lever to fasten the cooler clip to the socket. Don’t put excessive pressure on the cooler to avoid damaging the processor. Be careful not to let the screwdriver slip and hit the motherboard.

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Figure 18: Finishing the cooler installation

After installing the cooler, connect the fan power plug.

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Figure 19: Cooler correctly installed

Socket 754 and 939 Processors

Sockets 754 and 939 are used by Sempron socket 754, Athlon 64, Athlon 64 FX and Athlon 64 X2 processors.

First make sure both surfaces of the processor and the cooler are clean and free from impurities, as seen in Figure 20.

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Figure 20: Processor ready to receive the thermal paste

Using a small spatula (which can be made by cutting a piece of the hard transparent plastic from the processor box), apply some thermal paste on the center of the processor. Don’t worry about covering the whole processor area because the cooler pressure will make it uniform. See Figures 21 and 22.

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Figure 21: Applying the thermal paste

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Figure 22: Correct amount of thermal grease; the arrows indicate where you should fasten the cooler

Socket 754 and 939 Processors (Cont’d)

After applying the thermal paste, you should install the cooler. The process is relatively simple and doesn’t require the use of tools. Just attach the cooler and close its rotative lock, as we illustrate in the pictures below.

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Figure 23: Position and attach one side

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Figure 24: Fasten the other side and close the lock

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Figure 25: Pull the lock to the end

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Figure 26: Cooler locked

After installing the cooler over the processor, install the cooler power plug to the motherboard.

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Figure 27: Connect the fan wire.

That’s it! The thermal paste is correctly applied and your cooler is installed.

Socket 478 Processors

Socket 478 is used by the older Pentium 4 and Celeron socket 478 models. The process of applying thermal paste to those processors is similar to the process for socket 754 and 939 processors.

First make sure the processor surface is completely clean and free from dirt as well as remains of thermal paste from past applications. See Figure 28.

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Figure 28: Checking if the processor surface is clean

Using a small spatula (which can be made by cutting a piece of the hard transparent plastic from the processor box), apply some thermal paste on the center of the processor. Don’t worry about covering the whole processor area because the cooler pressure will make it uniform. See Figures 29 and 30.

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Figure 29: Applying the thermal paste

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Figure 30: Thermal grease correctly applied; the arrows show the loops for installing the CPU cooler

The next step is to install the cooler over the processor.

Socket 478 Processors (Cont.)

To install the cooler, just place it over the processor and press it so that the thermal paste will spread correctly.

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Figure 31: Installing the cooler

Next, move the cooler lever back and forth. This will move the four cooler hooks in such a way as to make them connect to the four supports on the motherboard. See Figures 32 and 33.

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Figure 32: Moving the cooler lever

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Figure 33: Move the cooler lever to the end

Then, install the fan power plug to the motherboard. That’s it! The thermal paste will be applied and the cooler installed.

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Figure 34: Installing the fan plug

Socket 775 Processors

Socket LGA775 is used by Pentium 4, Pentium D and Celeron D processors. The way of attaching it is very different from other types of processors. In socket LGA775, the pins are on the motherboard and not on the processor. That’s why the motherboard officially supports only 20 installation and removal operations. After that, there’s no guarantee that the board will work properly. So, don’t unnecessarily remove your socket LGA775 processor from the motherboard!

First make sure both surfaces of the processor and the cooler are clean and free from impurities and that the processor is well-installed.

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Figure 35: Processor ready to receive the thermal paste

Using a small spatula (which can be made by cutting a piece of the hard transparent plastic from the processor box), apply some thermal paste on the center of the processor. Don’t worry about covering the whole processor area because the cooler pressure will make it uniform.

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Figure 36: Applying the thermal paste

Next, install the processor cooler, as we’ll show in the next page.

Socket 775 Processors (Cont.)

The cooler must be aligned to the four holes located on the motherboard.

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Figure 37: Installing the cooler

After putting the cooler over the processor, you should “close” all the cooler locks by using a screwdriver. Observe Figure 38 to know the correct position. The arrow must face the outer side and the notch of the white part must touch the black support.

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Figure 38: Lock in the correct position

You should press the locks two-by-two, diagonally.

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Figure 39: Locking the cooler on one side

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Figure 40: Locking the cooler on the other side

It’s very important to check if the cooler really is well-installed and if all the locks are in the correct position.

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Figure 41: Cooler correctly installed

Most Common Mistakes

Every day in our labs we see many different mistakes regarding cooler installation and use of thermal paste.

The most common mistake is using too much thermal paste. Excess thermal paste interferes with and spoils the correct heat dissipation. Additionally, there is the possibility of paste spilling over to the outside and placing the system in danger.

Processors that have exposed components, such as the Athlon XP, can be subject to short circuits if the thermal paste closes the contact of these exposed components.

In the processor in Figure 42, besides the excess thermal paste, someone stuck a warranty sticker directly on top of the processor rubber pads that support the cooler. The thickness of that seal increases the pressure on top of the processor, and this pressure can break it.

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Figure 42: Duron with too much thermal paste and sticker covering the rubber pads

Another very common mistake is the placement of warranty seals on the contact part between the heatsink and the processor. Don’t accept a processor with seals covering it. If you have a processor with a seal on its top, remove it right away.

The processor in Figure 43 is a poor 200 MHz Pentium MMX. In addition to the sticker covering practically the entire contact area between the processor and the heatsink, it was also using the cooler in Figure 7, which uses graphite as the heat conductor.

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Figure 43: Sticker covering practically all of the processor

Other problems that we frequently see are broken processors – mainly Athlon XP and Sempron socket 462 processors – due to mistakes during cooler installation (putting the cooler in the wrong position or using too much strength when attaching the cooler), and people who substitute the thermal paste with toothpaste, liquid silicone, olive oil, glue, etc. Believe us, it happens!

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Figure 44: Socket 462 cooler installed in the wrong position

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Figure 45: Processor damaged due to bad cooler mounting

Originally at http://www.hardwaresecrets.com/article/How-To-Correctly-Apply-Thermal-Paste/274


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