Application of Thermal Conductive Silicone Rubber in Electronic and Electrical Industry

With the development of industrial production and science and technology, people constantly put forward new requirements for materials. In the field of electronics and electrical appliances, due to the rapid development of integrated technology and assembly technology, electronic components and logic circuits are developing in the direction of light, thin and small, and the heat generation is also increasing. Therefore, insulating materials with high thermal conductivity are needed to effectively remove the heat generated by electronic equipment, which is related to the service life and quality reliability of products.

The traditional method to solve the heat dissipation of electronic equipment is to pad a layer of insulating medium between the heating body and the radiator as the heat conducting material, such as mica, polytetrafluoroethylene and beryllium oxide ceramics. This method has a certain effect, but it has the disadvantages of poor heat conductivity, low mechanical properties and high price [1]. At present, some of the heat dissipation of electronic equipment is solved through various types of radiators, but most of them must be solved through thermal conductive materials. Thermal conductive silicone rubber materials are the most important thermal conductive materials. This paper mainly introduces the types of thermal conductive silicone rubber materials, and puts forward some application solutions for thermal conductive products.

1. Thermal conduction mechanism of silicone rubber

Thermal conductive silicone rubber material is a typical polymer composite material. Its thermal conductivity is mainly determined by the type of thermal conductive filler and the distribution of thermal conductive filler in the silicone rubber matrix. Metal fillers (such as Al, Ag, etc.) have high thermal conductivity, but most of them are conductive; The thermal conductivity of inorganic non-metallic materials (such as AlN, SiC, etc.) is also high, but the price is quite expensive; At present, metal oxides (such as Al2O3, ZnO, etc.) are mainly used as thermal conductive fillers. Table 1 shows the thermal conductivity of some thermal conductive fillers. The heat conduction mechanisms of various filler materials are different. Metal materials conduct heat mainly by the movement of electrons. The thermal conductivity of metals decreases with the increase of temperature. The thermal diffusion rate of nonmetals mainly depends on the vibration of adjacent atoms and the binding groups. In materials with strong covalent bonds, heat conduction in ordered crystal lattice is more efficient [2]. Therefore, when non-metallic materials are used as thermal conductive fillers, how to improve the thermal conductivity "stacking degree" in the system is the main means to improve the thermal conductivity.

2. Types and Applications of Thermal Conductive Silicone Rubber Materials

2.1 Thermal conductive silicone paste and thermal conductive gasket

Thermal conductive silicone paste is a mechanical mixed paste of silicone oil and thermal conductive filler, which has the characteristics of being shaped at any time, high thermal conductivity, non curing, and non corrosive to interface materials. In electronic equipment, there are many contact surfaces and assembly surfaces between various electronic components. There are gaps between them, which leads to poor heat flow. To solve this problem, thermal conductive silicon paste is usually filled between the contact surfaces. The flow of thermal conductive silicon paste is used to remove the air between the interfaces, reducing or even eliminating the thermal resistance. The thermal conductive gasket is a sheet thermal conductive insulating silicone rubber material processed by a special production process. It has the characteristics of natural viscosity, high thermal conductivity, high compression resistance, high cushioning, etc. It is mainly used as the gap filling material between the heating device and the radiator and the casing. Because of its soft material and elastic variable under the effect of low pressure force, it can make a close contact with the device surface or even a rough surface, It can reduce the thermal impedance of air and solve the problems of silicone oil seepage and dust on the surface of thermal conductive silicone paste after high temperature.

2.2 Thermal conductive and flame retardant silicone rubber materials

In recent years, silicone rubber material has been widely used in the electronic and electrical industry, but because it is a polymer material, flammable, smoke, sometimes it is the direct fuse of fire; Therefore, flame retardant silicone rubber has gradually become the main force of silicone rubber materials in the electronic and electrical industry. The company has developed SKF323 silicone sealant for heat conduction and flame retardancy with flame retardancy of UL94V-0 and thermal conductivity of more than 1.0W/m · K (both tested and certified by the authority) by using heat-conducting filler with surface treatment and self-made flame retardant, which is now widely used in automotive modules, circuit modules, PCB boards and other electronic and electrical products with high requirements for both heat conduction and flame retardancy.

2.3 Thermal conductive encapsulating silicone rubber material

Potting can be divided into local potting and overall potting. Local potting is only used for potting high-power devices, so that they are connected with the radiator through the thermal conductive potting silicone rubber material, so that the generated heat can be quickly transferred to the radiator. Overall encapsulation is to encapsulate all the components on the printed circuit board, so that the heat generated can be rapidly diffused and directly distributed to the external environment [3]. This kind of product is generally two-component. When using, the two components are mixed and bubbled, poured on the circuit board, and vulcanized into elastomer. This kind of product not only has the function of heat dissipation and insulation, but also has the function of shock absorption and three proofing. Now it is widely used in the encapsulation and bonding of LED lights, and the insulation and sealing of other circuits and household appliances.

2.4 High thermal conductivity silicone rubber adhesive

High thermal conductivity adhesives are mostly used in insulation applications, because in the development of the electronic and electrical industry, the field of electronic and electrical materials is in urgent need of thermal conductivity insulating materials, especially in high-power heat dissipation applications, such as the bonding of semiconductors and radiators, the protection of tube cores, the sealing of tube shells, the thermal insulation of electronic rectifiers and thermistors, the thermal insulation assembly of multilayer boards in micro packaging, and other thermal conductivity insulating adhesives with different process properties.

2.5 Heat conductive and high temperature resistant silicone rubber

Heat conductive and high temperature resistant silicone rubber is mainly used for bonding and sealing of low-voltage and high current transformers; Thermal insulation of radar magnetic field coil; Assembly of various high-temperature power tubes, radiators and printed boards; Micro packaging technology, electrical appliances, military appliances and other high-temperature heat sinks.

3. Summary

The research of thermal conductive silicone rubber materials is relatively mature abroad. For example, Dow Corning, GE Toshiba, etc. have developed a variety of thermal conductive silicone rubber products, while domestic research is still in the development stage. If the overall performance and process performance can be unified, thermal conductive silicone rubber will certainly have a good development prospect. In a word, thermal conductive silicone rubber not only has good thermal conductivity, but also has many properties that other materials do not have, such as weather resistance, adhesion, etc., so its development prospect is considerable and its application will be more and more extensive.