Thermal Paste - Compound what does it do how do i apply

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Whenever you install a heatsink on a CPU or a video card, you always have to apply thermal paste. It is very crucial to the performance of the heatsink. You could get a very high-end heatsink, and without thermal paste, it will fail to work in the way it was designed too.

Thermal paste is a very high heat conductive paste that is used between two objects (usually a heatsink and a CPU/GPU) to get better heat conduction. It fills in all those microscopic imperfections on the heatsink and CPU/GPU that can trap air in them and cause a loss in the heatsink’s performance. Air is a very poor conductor of heat. Thermal Interface Materials (TIM) can be up to a 100 times greater conductor of heat than air.

However, thermal paste is not near as good of a conductor as copper. Thus, too much thermal paste will hinder a heatsink’s ability to cool properly.

Types of Thermal Paste

There are essentially three types of thermal pastes:

1. Metal Based    2 .Ceramic Based    3 . Silicon Based


1.    2.   3.

1. Metal-based TIM’s are the most popular as they have the best performance out of the three. These pastes have lots of little metal particles in the grease that have a high thermal conductivity. One disadvantage of this type of paste is that it is also electrically conductive as well, which can cause a problem

2. Ceramic-based TIM’s are also a popular solution that doesn’t perform quite as well as metal-based pastes, but the difference is minimal       (1-3C). These consist of some form of thermally conductive material with lots of little ceramic particles. The advantage of ceramic-based pastes is that they do not conduct electricity.

3. Silicon-based TIM’s are usually what thermal pads that come on stock heatsinks are made of. These work well, but nowhere near to what other pastes will. Usually they come with cooling kits.

Choosing the right thermal paste

When choosing a paste for your heatsink, you have two main types that are usually considered; metal-based or ceramic-based. In most cases people use the metal-based, simply because it performs better as stated before. But nowadays, especially with GPUs, there are a lot of transistors/electrical components that are very close to the die.

So when applying thermal paste, if you are not very experienced with applying it, there is a chance that when you place the heatsink, some of the paste can be squeezed out onto theses transistors/electrical components and cause a short. This is very bad of course and is a nightmare for anyone.

This is where a ceramic-based compound has the advantage. With RAM module heatsinks, ceramic-based is almost a given to use. GPUs and chipsets are also examples that you might want to use a ceramic paste on, unless you are comfortable with using metal-based. But do not use a metal-based paste on RAM. Metal-based is usually used on CPUs that have an Integrated Heat Spreader (IHS). All modern CPUs have an IHS, but some people will actually remove it to get better performance.

For brands of thermal paste, the best around is Arctic Silver. They make very high quality thermal materials that are the most used by end-users. You can't go wrong with Arctic Silver. Other makes will work great, but maybe not as good. For the few extra pounds that are needed for Arctic Silver, it's usually worth it.

Cleaning your chip first

If you’re installing a new heatsink before you even had a heatsink on you CPU, then there is no need to do this. But in the case of putting a new one on, or changing a video card cooler, then you must clean your chip first.

For this, most used is Isopropyl Alcohol, Acetone, or a solution called ArctiClean. For using the cleaners, use non-linty cloth or Cotton buds. Cotton buds are great where they're small and easy to get where you want, plus you can also see exactly what you are doing.

Personal tip

If you dont have anything in hand to clean the block with you can use anything that is citrus based i personally have used Cif Lemon spray and it does exactly the same job. Just remeber you need citrus base to break up the grease.

Note: Never use any oil-based cleaners, as oil will ruin your coolers performance because it adds an oil layer through which heat travels slowly.

When you have your cleaner, dip your cloth/cotton bud in, then gently rube the surface of the chip until all the old paste is gone. You will probably have to do this more than once to get it nice and clean. It is usually a good idea to use a credit card to scrape most of the old TIM off, and then use the cleaners.

The exact same process is used to clean the CPU/GPU. Just be careful if you're cleaning the CPU out of it’s socket. If you push to hard on it, you might bend a pin.

Note: Make sure you do not touch the surface of the chip with your bare finger, as your skin has natural oils on it as well.

To remove thermal pads, use a credit card or some other plastic object (do not use a metal object as it could scratch the cooler's base). Then follow the same procedure as stated above. You want to make sure all of the old paste or thermal pad is gone, otherwise it can affect performance of the cooler.

Applying Thermal Paste

Applying thermal paste is a simple task, but you must take your time as with all things. Remember what the thermal paste does. It gives better conduction between the heatsink and CPU/GPU because it fills in all those little imperfections on the heatsink that cause poor conduction due to having air in them. You only need as much thermal paste as it takes to fill in these little holes/divots.
Some people will lap thier heatasink to get a smoother finish. This will increase performance even more. The more area that the heatsink has touching the CPU/GPU, the better it will perform. When you lap your heatsink, and you do a good job of it, you will require even less thermal pastes, as these imperfections have got even smaller.

Once your CPU is nice and clean and you have your TIM, now it’s time to apply it.

On the CPU,  thermal compound should only be applied to the top of the core. The core is the raised rectangle in the center of the CPU and is highlighted in red in the photos below of AMD and Intel CPUs.




On an Intel P4 or Athlon64 type CPU with a large metal heat spreader, put a small amount of compound onto the center of the heat spreader

P4  About the size of an uncooked grain of short-grain white rice.

Athlon64 About the size of one and a half uncooked grains of short-grain white rice.

Spread the thermal compound over the CPU core as shown in the photo below.  A razor blade or the clean edge of a credit card can be used as the application tool. You may use whatever tool you choose as long as it is CLEAN and allows you to control the application area and thickness. The flatter the mating surfaces, the thinner the layer that is required. Stock  processors and/or heatsinks with normal surface irregularities will require a layer 0.003" to 0.005 thick as shown below to  fill the resultant gaps. (Equal to the thickness of about 1 sheet of standard weight paper.) Properly lapped heatsinks with mirror finishes  will only require a translucent haze.

RECHECK to make sure no foreign contaminants are present on either the bottom of the heatsink or the top of the CPU core. Mount the heatsink on the CPU per the heatsink's instructions. Be sure to lower the heatsink straight down onto the CPU. Once the heatsink is properly mounted, grasp the heatsink and very gently twist it slightly clockwise and counterclockwise one time each if possible. (Just one or two degrees or so.)

Please note some heatsinks can not be twisted once mounted.

Testings have shown that this method minimizes the possibility of air bubbles and voids in the thermal interface between the heat spreader and the heatsink. Since the vast majority of the heat from the core travels directly through the heat spreader, it is more important to have a good interface directly above the actual CPU core than it is to have the heat spreader covered with compound from corner to corner.

The photo below shows how the pressure from the heatsink base spreads the compound and also shows a P4 with the heat spreader removed to show the location of the actual CPU core that is the source of the heat.

While the Cpu core on the Athlon 64 is slightly larger than the P4 core is still much smaller than the metal CPU Cap that covers it.

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