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What is thermal conductive silicone sheet?

2024-07-08 23:16:39

Thermal conductive silicone sheet is a kind of thermal conductive medium material synthesized by special process with silicone as base material and various auxiliary materials such as metal oxides. In the industry, it is also called thermal conductive silicone pad, thermal conductive silicone sheet, soft thermal conductive pad, thermal conductive silicone gasket, etc. It is specially produced for the design scheme of transferring heat through gaps. It can fill the gaps and complete the heat transfer between the heating part and the heat dissipation part. At the same time, it also plays the role of insulation, shock absorption, sealing, etc. It can meet the design requirements of miniaturization and ultra-thinness of equipment. It is highly processable and usable, and has a wide range of thickness applications. It is an excellent thermal conductive filling material.

The production process of thermal conductive silicone sheet mainly includes the following steps: raw material preparation → plasticization, mixing → molding and vulcanization → trimming and cutting → inspection, etc.

Process flow:

1. Raw material preparation

The thermal conductivity of ordinary organic silicone is usually only about 0.2W/m·K. However, mixing thermal conductive fillers in ordinary silicone can improve its thermal conductivity. Commonly used thermal conductive fillers are metal oxides (such as Al2O3, MgO, BeO, etc.) and metal nitrides (such as SiN, AlN, BN, etc.). The thermal conductivity of the filler is not only related to the material itself, but also closely related to the particle size distribution, morphology, interface contact, and degree of bonding within the molecule of the thermal conductive filler. Generally speaking, fibrous or foil-shaped thermal conductive fillers have better thermal conductivity.

2. Plastication and mixing

Plastication and mixing are a process in silicone processing, which refers to the use of mechanical or chemical methods to reduce the molecular weight and viscosity of raw rubber to improve its plasticity and obtain appropriate fluidity to meet the needs of further processing by mixing and molding. The raw materials for making thermal conductive silicone sheets are generally destroyed by mechanical high-speed stirring. After color matching and mixing, the milky white silicone is transformed into flakes of various colors.

3. Molding vulcanization

If you want to make a soft, elastic and tensile thermal conductive silicone sheet, you need to use organic silicone that has undergone secondary vulcanization. Vulcanization can actually be called curing. After the liquid thermal conductive silicone is heated and formed in the first stage, its cross-linking density is not enough. It needs to be further vulcanized to increase the tensile strength, resilience, hardness, swelling degree, density, and thermal stability of the thermal conductive silicone sheet. It is much better than the primary vulcanization. If the secondary vulcanization is not performed, the performance of the thermal conductive silicone sheet produced may be affected to a certain extent, and a product with better performance may not be obtained. The product parameters after the primary vulcanization are not exactly the same as those after the secondary vulcanization, which is also related to the actual operation process and steps.

4. Trimming and cutting

The thermal conductive silicone sheet after high temperature treatment needs to be placed for a period of time, and it needs to be naturally cooled before cutting into different sizes and specifications, and other rapid cooling methods cannot be used. Otherwise, it will directly affect the product performance of the thermal conductive silicone pad.

5. Finished product inspection

The main items that need to be inspected for finished products include: thermal conductivity, temperature resistance range, volume resistivity, voltage resistance, flame retardancy, tensile strength, hardness, thickness, etc.

Advantages of thermal conductive silicone sheet

1.The material is relatively soft, has good compression performance, good thermal conductivity and insulation performance, a relatively large adjustable range of thickness, suitable for filling cavities, and has natural stickiness on both sides, strong operability and maintainability;

2.The main purpose of selecting thermally conductive silicone sheets is to reduce the contact thermal resistance between the heat source surface and the contact surface of the heat dissipation device. Thermally conductive silicone sheets can fill the gaps on the contact surface very well;

3. Since air is a poor conductor of heat, it will seriously hinder the transfer of heat between the contact surfaces. Installing thermally conductive silicone sheets between the heat source and the heat sink can squeeze the air out of the contact surface;

4.With the addition of thermally conductive silicone sheets, the contact surface between the heat source and the heat sink can be better and fully contacted, and face-to-face contact can be achieved. The temperature reaction can achieve the smallest possible temperature difference;

5. The thermal conductivity coefficient of the thermally conductive silicone sheet is adjustable, and the thermal stability is also better;

6. The thermally conductive silicone sheet can bridge the process tolerance of the structure and reduce the process tolerance requirements of the heat sink and the heat dissipation structure;

7. The thermally conductive silicone sheet has insulation properties (this feature requires the addition of appropriate materials during production);

8. The thermally conductive silicone sheet has the effect of shock absorption and sound absorption;

9. The thermally conductive silicone sheet is convenient for installation, testing, and reusability.

Application fields of thermal conductive silicone sheets

◆LED industry use

●Thermal conductive silicone sheet is used between aluminum substrate and heat sink

●Thermal conductive silicone sheet is used between aluminum substrate and shell

Power supply industry

Used for heat conduction between MOS tube, transformer (or capacitor/PFC inductor) and heat sink or shell

◆Communication industry

●Thermal conduction and heat dissipation between product motherboard IC and heat sink or shell

●Thermal conduction and heat dissipation between set-top box DC-DC IC and shell

◆Application in automotive electronics industry

Automotive electronics industry applications (such as xenon lamp ballast, audio, car series products, etc.) can all use thermal conductive silicone sheet

◆PDP/LED TV application

Thermal conduction between power amplifier IC, image decoder IC and heat sink (shell)

◆Household appliance industry

Microwave oven/air conditioner (between fan motor power IC and shell)/induction cooker (between thermistor and heat sink)

Selection of thermal conductive silicone sheet

◆Selection of thermal conductivity coefficient

The selection of thermal conductivity mainly depends on the power consumption of the heat source and the heat dissipation capacity of the heat sink or heat dissipation structure. Generally, the chip temperature specification parameters are relatively low, or they are sensitive to temperature, or the heat flux density is relatively large (generally greater than 0.6w/cm3 requires heat dissipation treatment, and generally when the surface is less than 0.04w/cm2, only natural convection treatment is required). These chips or heat sources need to be heat-dissipated, and try to choose thermally conductive silicone sheets with higher thermal conductivity.

The consumer electronics industry generally does not allow the chip junction temperature to be higher than 85 degrees, and it is also recommended to control the chip surface to be less than 75 degrees during high-temperature testing. The components of the entire board are basically commercial-grade components, so the internal temperature of the system is recommended not to exceed 50 degrees at room temperature. The first appearance surface, or the surface that the end customer can contact, is recommended to be lower than 45 degrees at room temperature. Choosing a thermally conductive silicone sheet with a higher thermal conductivity can meet the design requirements and retain some design margins.

Note: Heat flux density: defined as the amount of heat that passes through a cross section per unit area (1 square meter) per unit time (1 second). Junction temperature is usually higher than the case temperature and the device surface temperature. The junction temperature can measure the time required for heat dissipation from the semiconductor wafer to the package device case and the thermal resistance.

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