SELECTION OF THERMALLY CONDUCTIVE MATERIALS

When it comes to heat dissipation system, many people think of fans and heat sinks.

In fact, they ignore an insignificant but important medium - thermal conductive media.

Computer CPU is a typical power device that needs good heat dissipation, so let's talk about thermal conductive materials.

Why do we need thermal conductive media?

Some people may think that the CPU surface or the bottom of the heatsink are very smooth and do not need thermal conductivity between them. This view is wrong! Since machining is impossible to make an idealized flat surface, there are many grooves or gaps between the CPU and the heatsink, which are filled with air. We know that air has a high thermal resistance value, so other substances must be used to reduce the thermal resistance, otherwise the performance of the heat sink will be reduced or even unable to function. So the thermal conductivity medium came into existence, its role is to fill the processor and the heat sink between the small and large gaps, increasing the contact area between the heat source and the heat sink. Therefore, heat conduction is only a role of the thermal conductivity media, increase the effective contact area of the CPU and heat sink is its most important role.        

What are the common thermal conductive media?

1. Thermally conductive silicone grease        

Thermally conductive silicone grease is the most widely used thermal conductive medium. It is an ester-like substance formed by taking silicone oil as raw material and adding filler such as thickener, after heating and decompression, grinding and other processes, which has a certain viscosity and no obvious granularity. The working temperature of thermally conductive silicone grease is generally from -50℃ to 180℃, and it has good thermal conductivity, high temperature resistance, aging resistance and waterproof characteristics.        

In the process of device heat dissipation, after being heated to a certain state, the thermal conductive silicone grease becomes semi-fluid and fills the gap between CPU and heat sink, making the joint between them tighter and enhancing heat conduction. Normally, thermal grease is insoluble in water, not easy to be oxidized, and also has certain lubricity and electrical insulation.

2. Thermal conductive silicone pad

It belongs to the sheet material, its hardness is relatively moderate, compared to the thermal conductive silicone grease hardness is harder, softer than the thermal radiation patch. And silicone thermal pad use range is relatively wide, can be used for electrical equipment in the heating body (power tube, silicon controlled, electric heat stack, etc.) and heat dissipation facilities (heat sink, heat dissipation strip, shell, etc.) between the contact surface, play the role of heat transfer medium and moisture, dust, corrosion, shock resistance and other properties. Suitable for microwave communication, microwave transmission equipment, microwave special power supply, voltage stabilization power supply, etc. surface coating or overall potting of various microwave devices, such silicon materials for heat-generating electronic components, providing excellent thermal conductivity. Such as: transistors, CPU assembly, thermistors, temperature sensors, automotive electronic parts, automotive refrigerators, power supply modules, printer heads, etc.

3 Graphite sheet

Synthetic graphite sheet is a polyimide film that undergoes certain chemical treatment to retain 99.999% of the carbon, which provides excellent thermal conductivity and is suitable for heat dissipation systems for electronic chips, CPUs and other products. The advantage of this thermal conductivity medium is that it is not sticky and will not "uproot" the CPU from its base when the graphite sheet is removed. Graphite sheet both thermal and electrical conductivity, thermal conductivity up to 1900w / mk.

In addition to the above common thermal conductive media, aluminum foil thermal conductive gaskets, phase change thermal conductive gaskets (plus protective film) also belong to the thermal conductive media, but these products are rarely seen on the market.