A brief introduction to several thermal materials

Speaking of the cooling system, many people think of the fan and heat sink. In fact, they ignore a media that does not understand, but plays an important role in the media. So we talk about thermal materials. I hope you discuss, to express their own power dissipation of various types of devices and views.

Why do you need thermal media?

Some people may think that the bottom of the CPU surface or heat sink is very smooth, they do not need between the thermal medium. This view is wrong! As the machining can not make an idealized flat surface, so there is a lot of gully or gap between the CPU and the radiator, which are air. We know that the thermal resistance of the air is high, so you must use other substances to reduce the thermal resistance, or the performance of the radiator will be greatly reduced, or even unable to play a role. So the heat conduction medium came into being, and its role is to fill the processor and the radiator between the large and small gaps, increase the heat source and the heat sink contact area. Therefore, the heat conduction is only a role in the thermal medium, increasing the effective contact area of ??the CPU and the radiator is its most important role.

What are the thermal media?

1,Thermal grease

Thermal grease is currently the most widely used as a thermal medium, it is a silicone oil as raw materials, and add thickeners and other fillers, after heating decompression, grinding and other processes formed after an ester, the material There is a certain degree of viscosity, no obvious grainy. Thermal grease operating temperature is generally in -50 ℃ ~ 220 ℃, it has a good thermal conductivity, high temperature, anti-aging and Waterproof properties.

In the heat dissipation process, after heating to a certain state, the thermal grease will show a semi-liquid state, and fully fill the gap between the CPU and the heat sink, making the connection between the two more closely, and then strengthen the heat conduction. Usually, the thermal grease is insoluble in water, is not easy to be oxidized, but also has a certain degree of lubrication and electrical insulation.

2,Thermal silica gel

And thermal grease, thermal silica gel is also added by the silicone oil chemical raw materials, and after chemical processing. But unlike the thermal grease, there is some kind of sticky material in the chemical raw material it adds, so the thermal silica gel of the finished product has a certain adhesive force.

The biggest feature of thermal silica gel is hard after solidification, the thermal conductivity slightly lower than the thermal grease. At present, there are two kinds of thermal silica on the market: one after solidification for the white solid, the other after solidification for the black with a glossy solid. General manufacturers are accustomed to using the first silicone as a heat sink and heat between the object of the adhesive, its advantage is very strong sticky, but it has just become its shortcomings. When we need to repair, often in the effort to separate the adhesive device and the radiator separation, you will find the contact surface of the large number of solid white silica gel, these silica is very difficult to clean.

In contrast, the second silicone advantage is more obvious: one of its cooling efficiency is higher than the first, and second it solidified after the formation of black solid brittle, the residue is easy to remove. In any case, thermal conductivity of thermal conductivity of silica gel is not strong, and easy to device and heat sink "stick dead", so unless the special circumstances recommended users.

3,Thermal silicone film

Soft silicone thermal insulation pad has a good thermal conductivity and high-grade pressure insulation, thermal conductivity 2.6W / mK, anti-voltage breakdown value of more than 4000 volts, is to replace the thermal grease of alternative products, the material itself has a certain Of the flexibility, a good fit between the power device and the heat of aluminum or the machine between the shell, so as to achieve the best thermal and cooling purposes, in line with the current requirements of the electronics industry for thermal conductivity material is to replace the thermal grease grease two The best product of the cooling system. Such products can be arbitrarily cut, to help meet the automated production and product maintenance.

Silicone thermal insulation pad of the process thickness ranging from 0.5mm ~ 14mm, every 0.5mm a plus, that is, 0.5mm 1mm 1.5mm 2mm ~ 5mm specifically for the use of the gap to pass the heat of the design program to fill the gap to complete the heat and heat Parts of the heat transfer, but also play a role such as shock insulation seal, to meet the miniaturization of social equipment, ultra-thin design requirements, is a great process and the use of new materials.

Flame retardant performance in line with U.L 94V-0 requirements, and in line with the EU SGS environmental certification

4,Synthetic graphite sheet

This thermal medium is relatively rare, generally applied to some of the smaller heat on the object. It uses graphite composite materials, after a certain chemical treatment, excellent thermal conductivity, suitable for electronic chips, CPU and other products of the cooling system. In the early Intel boxed P4 processor, the material attached to the bottom of the radiator is a graphite thermal pad called M751, the advantage of this thermal medium is no sticky, not in the demolition of the radiator The CPU from the base of the "uprooted."

Several of the above-mentioned common thermal medium, aluminum foil thermal pad, phase change thermal pads (plus protective film) are also thermal media, but these products are rare in the market.

Thermal conductivity materials also have performance parameters

As the thermal grease is a chemical substance, so it also reflects the performance characteristics of their own related parameters. We just understand the meaning of these parameters, you can determine the performance of a thermal conductivity material.

1,Thermal conductivity

Thermal conductivity of the thermal grease and heat sink is basically the same, its unit is W / mK, that is, the cross-sectional area of ??1 square meters of the cylinder along the axial 1 meter distance of the temperature difference of 1 Kelvin (1K = 1 ℃) Heat conduction power. The larger the value, the faster the heat transfer rate of the material, the better the thermal conductivity. At present, the thermal conductivity of the mainstream thermal grease is greater than 1.134W / mK.

2,Working temperature

The operating temperature is an important parameter to ensure that the thermally conductive material is in solid or liquid state. The temperature is too high and the thermal conductivity material is due to the liquid; the temperature is too low and it will become solid due to the increase in viscosity. Heat dissipation. Thermal grease operating temperature is generally in -50 ℃ ~ 220 ℃. For the thermal grease operating temperature, we do not have to worry, after all, through conventional means it is difficult to CPU temperature beyond this range.

3,Thermal resistance coefficient

The thermal resistance coefficient represents the effect of the object on heat conduction. The concept of thermal resistance is very similar to the resistance, the unit is also similar (℃ / W), that is, the object continued heat transfer power of 1W, the thermal path at both ends of the temperature difference. Thermal resistance is clearly the lower the better, because the same ambient temperature and thermal conductivity, the lower the thermal resistance, the lower the temperature of the heated object. The size of the thermal resistance and thermal grease used in the material has a great relationship.

4,Dielectric constant

For some CPU without metal cover protection, the dielectric constant is a very important parameter, which is related to the existence of a short circuit inside the computer. Common thermal grease used in the insulation are better materials, but some special grease (such as silver-containing silicone grease, etc.) may have a certain conductivity. Many CPUs are now fitted with metal caps for heat conduction and protection of the core, so there is no need to worry about the short circuit caused by the thermal grease spill. At present, the dielectric heat of the thermal grease used in the mainstream heat sink is greater than 5.1.

5,Viscosity

Viscosity is to guide the thermal grease viscosity. In general, the thermal grease viscosity of 68 or so.

6,Insulation