Thermal paste: what is it, types, how is it used ...

thermal paste

La thermal paste is a substance widely used in the world of electronics. Generally as an interface to improve heat dissipation between high-performance processing chips and heatsinks. But it is not the only place where it is used, it can also be used for high power transistors, to peltier effect plates, etc.

In this article you will know what exactly is this substance, its function, how it is applied properly, the types that exist in the market and the best brands you can buy.

What is thermal paste?

thermal paste

It can be called in several ways: thermal paste, thermal silicone, thermal grease, etc. All these terms are synonymous, and there is no difference between them. Refers to a substance that has good thermal conductivity properties to help better dissipate heat when there is an interface between two surfaces. For example, when a heatsink is used on a chip, to fill in the "gaps" that could be between one surface and another and thus make conduction more efficient.

Thermal paste has different elements in its composition:

  • Polymerizable liquid matrix: it is the base of the paste, which makes it a fluid substance. Generally, these types of gels or pastes are usually based on silicones (hence their name), epoxy resins, acrylates, urethanes, etc., and they can even be arranged in adhesives or pads instead of in paste form.
  • Particles: these fillers usually represent between 70 and 80% of the composition of thermal paste. In this case, they can be very varied, such as copper, aluminum, silver, zinc oxide, boron nitride, etc.

Due to all this composition, this thermal paste can be toxic if swallowed. Therefore, precautions must be taken when using it, wash your hands if handled without gloves and avoid leaving it within the reach of children. In addition, it is also irritating to the skin, eyes, and mucous membranes, so you should use protection elements when handling it. Some video tutorials show how they apply it even by hand, but this should not be done.

If you are in front of a new electronic component, and you are not sure if you can use thermal paste on its surface or which one to use, I recommend you always read the manufacturers datasheets. In this documentation you will find information about it, in addition to the dissipation needs, power, maximum and minimum temperatures supported, values ​​such as junction-case, junction-air, etc.

Properties

CPU

Thermal paste not only has properties of thermal conductivity, but also others, and it is necessary to pay special attention to them, since they could condition the use according to which electronic elements. This substance is mainly characterized by:

  • Thermal conductivity: It is the most important factor in a thermal paste, since it is a substance whose purpose is to dissipate heat. Therefore, they must have a good ability to conduct heat. Units such as the watt per meter-Kelvin are used to measure this factor. Depending on the type of pasta or the brand, this conductivity can vary greatly. For example, those of copper, silver, diamond or aluminum have very good properties in this regard, others such as zinc oxide, aluminum nitride, etc., not so much.
  • Electric conductivity: It is related to one of the problems that thermal paste can cause if it conducts electricity well. Generally, pasta manufacturers tend to show the electrical resistance that their product presents. The higher (ohms per centimeter), the better insulator it will be, so it can be much better. If the paste has low resistance and conducts well then it could lead to short circuit problems if it comes into contact with some tracks or pins.
  • Thermic dilatation coefficient: is the other unit to pay attention to. In this case, you have to look for a paste whose coefficient is the lowest possible, that is, so that it expands as little as possible with the heat. Otherwise, it could cause tension problems between components.

Types of thermal grease

heating pad

There are several types of thermal paste on the market, and it is important to distinguish between all the available solutions to know which one to choose in each case, since they all have their advantages and disadvantages:

  • Heating pad: It is an adhesive or pad that acts as a heat conductive interface and its purpose is exactly the same as thermal paste, but it can be used more easily, and does not involve controlling quantities, making sure it expands homogeneously, etc., since it simply sticks on the surface of the component to be dissipated or on the heatsink. They are sold separately, although they also usually come pre-installed in some refrigeration systems to facilitate assembly. These are generally made of silicone or paraffin wax mixed with solid conductive particles. At room temperature they appear more solid, but when they are working, they become more fluid.
  • Thermal paste: is the viscous liquid substance that is sold in cans with application brush, tubes or syringes for easy application. Within this paste you can find the following types:
    • Of metal: they use metallic particles (zinc, copper, aluminum, silver, gold ...) for the filling, and they usually have a greyish color. They are very popular, and they are not too expensive. They behave quite well in terms of thermal conductivity, being able to lower the temperature up to 6ºC in some cases. However, they have a problem, and it is their electrical conductivity. With metal particles, it could short-circuit between contacts if there are leaks.
    • Ceramics: the filler particles are ceramic (zinc oxide, silicon dioxide, aluminum oxide, ...), giving light gray or white colors. The strong point of these thermal silicones is that they are very cheap and have a low electrical conductivity, so they are safer in case of leaks. However, their thermal conductivity is worse, so they will only help to lower the temperature 1 to 3ºC compared to an interface that does not use it.
    • Carbon: they are more expensive and newer, but they offer better results. They are generally intended for systems that need higher heat dissipation, such as overclocked chips, high-performance or high-power equipment, etc. They are based on particles like diamond dust, graphene oxide, etc. In this case, the properties are almost perfect, since on the one hand they have very good thermal conductivity like those of metal, and on the other they have very low electrical conductivity like those of ceramics.
    • Liquid metal: They are not that common, but are often used by some manufacturers or enthusiasts for heatsink blocks of processing units etc. Although they have good dissipation properties, even somewhat better than those based on metal, this other type is usually expensive and can react with aluminum heatsinks, since they use metals such as indium or gallium.
    • Hybrids: There are also some hybrid thermal pastes, that is, they mix different filler components as a base to improve the properties.

What product to buy?

If you want to buy a thermal paste product, here are some of the best brands and options that you find in the market:


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