Introduction

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.

What is thermal paste and what does it do?

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.



This is an exaggerated view of what these microscopic imperfections would look like. All the white area would represent the air pockets, and this is what the TIM would fill in. It wouldn't be such a gap like this, but this just an example to give you a rough idea of what it would look like.

If you could have a perfectly flat heatsink base, and CPU, you would not need thermal paste. But it is impossible to do so, and that’s why we need thermal paste.

Types of thermal paste

There are essentially three types of thermal pastes:

• Metal based
• Ceramic based
• Silicon based

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, more on this later.



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.



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.



There are also thermal epoxies, these are basically the same thing as regular grease, but are actually used to permanently attach the heatsink. They are not recommended for most cases, but in some they are of course. One main example for a use of an epoxy is, attaching heatsinks to video memory. Most of the time you use thermal pads that don’t perform very well, so an alternative is thermal epoxy. But the disadvantage is, that most of the time you will not get the heatsinks off once they are put on.

What can be tried to get epoxied heatsinks off is to put the video card in the freezer before trying to remove the heatsink. The low temperature will make the epoxy brittle, so it goes off easier.

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.