Silicon nitride has high bending strength, fracture toughness, good creep resistance, hardness, and wear resistance. It is considered the best-performing material in the family of structural ceramics. As a strategic emerging industry with rapid growth in technological innovation, the demand for ceramic components in the field of new energy vehicles is increasing, and silicon nitride plays multiple important roles.
First of all, silicon nitride bearings are key components known as the “chip” of the mechanical industry. They are mainly used to support rotating machinery and reduce the coefficient of friction to ensure precise rotation performance. The density of silicon nitride is about 42% of that of bearing steel, with a high elastic modulus of 320 GPa, a tensile strength of 1600 MPa, and a compressive strength of up to 3600 MPa. In addition, its mechanical properties remain almost unchanged below 900°C, making it an ideal material for rolling elements of rolling bearings. At present, bearings using silicon nitride balls as rolling elements have become the most popular, high-performance, and widely used advanced ceramic bearings in the world. In the field of new energy vehicles, the adoption of silicon nitride bearings is mainly due to the following reasons:
1. Motor bearings require materials with low density and high wear resistance to adapt to higher speeds.
2. The alternating current generated by the motor causes changes in the surrounding electromagnetic field, requiring good insulation properties to reduce corrosion caused by bearing discharge.
3. The bearing ball needs to have a smooth surface and minimal wear. Ceramic balls are very suitable for high-speed rotation conditions due to their low density, high hardness, and excellent wear resistance. They are particularly irreplaceable in high-temperature, strong magnetic and high-vacuum environments. In the field of new energy vehicles, ceramic bearings have gradually replaced steel ball bearings.
Secondly, silicon nitride ceramic substrates are ceramic plates made by sintering silicon nitride powder with a small amount of oxides and rare earth materials. These substrates exhibit excellent comprehensive performance and reliability, including high thermal conductivity, high mechanical strength, low thermal expansion coefficient, oxidation resistance, heat corrosion resistance, low dielectric loss, and low friction coefficient. Silicon nitride ceramics have extremely high theoretical thermal conductivity (about 400 W/(m·K)) and low thermal expansion coefficient (about 3.0×10-6°C), making them compatible with materials such as Si, SiC, and GaAs. Therefore, the high strength and high thermal conductivity of silicon nitride substrates meet the high temperature, high power, high heat dissipation, and high reliability requirements of automotive electronic power device module packaging. Some people believe that silicon nitride ceramic substrates are upgraded products compared with alumina ceramic substrates and aluminum nitride ceramic substrates. At present, silicon nitride substrates are mainly used for the packaging of Si IGBTs and SiC MOSFETs, and the specific applications are as follows:
1. For automotive-grade IGBTs, the heat dissipation efficiency is much higher than that of industrial-grade. The internal temperature of the inverter is extremely high, and strong vibration conditions need to be considered. The performance requirements of automotive-grade IGBTs far exceed those of industrial-grade. Silicon nitride substrates are very suitable for automotive-grade IGBT packaging, can adapt to high temperature and high-pressure working environments, effectively dissipate the high heat generated in the power supply system, protect the normal operation of the chip, and extend the service life of electronic equipment.
2. For silicon carbide MOSFET, the use of silicon carbide MOSFET devices in the core motor drive of new energy vehicles can increase the driving range by 5% to 10% compared with traditional Si IGBT. The Silicon carbide MOSFET chip area is small and has high heat dissipation requirements. Silicon nitride ceramic substrates have excellent heat dissipation capabilities and high reliability and are almost a must for the main application of silicon carbide MOSFET in the field of new energy vehicles. For example, Tthe esla Model 3 widely uses silicon nitride ceramic substrates to solve the heat dissipation problem of SiC MOSFET devices.
In summary, the two main application directions of silicon nitride ceramics in the field of new energy vehicles are silicon nitride bearings and high thermal conductivity silicon nitride substrates. Silicon nitride bearings exhibit excellent mechanical properties and wear resistance, making them suitable for high-speed rotation and harsh working conditions, and have been widely used in the motor system of new energy vehicles. Silicon nitride ceramic substrates have high thermal conductivity and mechanical strength, meet the requirements of high temperature, high power, high heat dissipation, and high reliability of automotive electronic power device modules, and are widely used in the packaging of Si IGBT and SiC MOSFET. These applications contribute to the development of new energy vehicles and improve their performance and reliability.
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