What is thermal grease?

Thermally conductive silicone grease is commonly known as thermal grease or thermally conductive paste. Thermally conductive silicone grease is made of silicone as the main raw material and added with heat-resistant and thermally excellent materials to make a thermally conductive silicone grease-like compound for power amplifiers The heat conduction and heat dissipation of electronic components such as, transistors, electronic tubes, CPUs, etc., so as to ensure the stability of the electrical performance of electronic instruments and meters.

Thermally conductive silicone grease is a kind of material used to fill the gap between the CPU and the heat sink. This material is also called a thermal interface material. Its function is to conduct the heat emitted by the CPU to the heat sink, keep the CPU temperature at a stable working level, prevent the CPU from being damaged due to poor heat dissipation, and extend its service life.

In thermal management applications, even two planes with very smooth surfaces will have gaps when they are in contact with each other. The air in these gaps is a poor conductor of heat and will hinder the conduction of heat to the heat sink. Thermally conductive silicone grease is a material that can fill these gaps and make the heat conduction more smoothly and quickly.

Since thermal grease is a chemical substance, it also has related performance parameters that reflect its own working characteristics. As long as we understand the meaning of these parameters, we can judge the performance of a thermal grease thermal grease.

Thermal conductivity

The thermal conductivity of thermal grease is basically the same as that of the radiator. Its unit is W/mK, that is, when the temperature difference of a cylinder with a cross-sectional area of 1 square meter along the axis of 1 meter is 1 Kelvin (1K = 1°C) Thermal conduction power. The larger the value, the faster the heat transfer rate of the material and the better the thermal conductivity. At present, the thermal conductivity of Nuofeng Electronic Thermal Grease can reach 5.2W/m.K.

Thermal resistance coefficient

The thermal resistance coefficient represents the hindering effect of an object on heat conduction. The concept of thermal resistance is very similar to resistance, and the unit is similar to it (℃/W), that is, the temperature difference between the two ends of the heat conduction path when the object's continuous heat transfer power is 1W. Obviously, the lower the thermal resistance, the better, because under the same ambient temperature and thermal power, the lower the thermal resistance, the lower the temperature of the heating object. The size of the thermal resistance has a great relationship with the material used in the thermal grease.

At present, the thermal resistance coefficient of mainstream thermal grease is less than 0.1℃/w, and the excellent ones can reach 0.005℃/W.

Operating temperature

Due to the characteristics of silicone grease itself, its operating temperature range is very wide. Working temperature is an important parameter to ensure that the thermal grease is in a solid or liquid state. If the temperature is too high, the fluid volume of the thermal grease will expand, the distance between molecules will be extended, the interaction will be weakened, and the viscosity will decrease; the temperature will decrease, the volume of the fluid will shrink, and the distance between molecules Shorten, strengthen interaction, and increase viscosity, both of which are not conducive to heat dissipation.

The working temperature of thermal grease is generally -40℃~200℃. We don’t have to worry about the working temperature of thermal grease. After all, it is difficult to get the CPU/GPU temperature beyond this range by conventional means.

Viscosity

Viscosity is a measure of fluid viscosity. It refers to the resistance of the fluid against the flow. It is expressed by the ratio of the shear stress to the fluid and the shear rate. There are many ways to measure the viscosity. For example, the unit of dynamic viscosity is Pa ·second.

For thermal conductive silicone grease, the viscosity is about 2500 Pa·s, and it has good flatness, and can be easily flattened around the surface of the chip under a certain pressure, and a certain viscosity is guaranteed, so that it will not be squeezed. The excess silicone grease will flow.

Dielectric constant

The dielectric constant is used to measure the performance of an insulator to store electrical energy. It refers to the ratio of the capacitance between two metal plates when the insulating material is used as the medium to the same two plates when the air is the medium or vacuum. The dielectric constant represents the degree of polarization of the dielectric, that is, the ability to bind charges. The greater the dielectric constant, the stronger the binding ability to charges.

Ordinary thermal conductive silicone grease is made of materials with better insulation, but some special silicone greases (such as silver-containing silicone grease, etc.) may have certain electrical conductivity. The dielectric constant of air is about 1, and the dielectric constant of common thermal grease is about 5.

Oil separation

The degree of oil separation is a guide to the amount of silicone oil that is deposited after the thermal silicone grease is kept at 200°C for 24 hours, and is an index for evaluating the heat resistance and stability of the product. Apply the silicone grease to white paper and observe, you will see the oil leakage phenomenon. If the oil separation degree is high, the oil separation phenomenon is obvious; or open a container with silicone grease that has been stored for a long time. Obvious oil separation is seen on the surface of the silicone grease or around the container.

There are many types of silicone grease on the market, and different parameters and physical properties determine different uses. Thermally conductive silicone grease is a kind of high thermal conductivity insulating organic silicon material, which almost never cures, and can maintain the state of grease when used for a long time at a temperature of -40°C to 200°C. Thermal conductive silicone grease has excellent electrical insulation, excellent thermal conductivity, low oil separation (towards zero), high and low temperature resistance, water resistance, ozone resistance, and weathering resistance. Thermal conductive silicone grease can be widely applied to various electronic products, between the heating element (power tube, thyristor, electric heating pile, etc.) and heat dissipation facilities (heat sink, heat sink, shell, etc.) in electrical equipment The contact surface acts as a heat transfer medium and has the properties of moisture proof, dust proof, corrosion proof, and shock proof. Thermally conductive silicone grease is suitable for surface coating or overall potting of various microwave devices such as microwave communications, microwave transmission equipment, microwave dedicated power supplies, and stabilized power supplies. This type of silicon material provides excellent heat-generating electronic components. Thermal effect.