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Silicon Nitride Ceramic Substrate: A Blue Ocean For Future High-Performance Power Module Designers

11/20/2023 10:59:09

With the significant improvement of the integration and power density of the third-generation semiconductor SiC power devices, the corresponding heat generated during operation has sharply increased. Therefore, the heat dissipation problem of electronic packaging systems has become a key factor affecting their performance and lifespan. To effectively solve the heat dissipation problem of devices, it is necessary to choose high thermal conductivity substrate materials.

Silicon nitride ceramic substrate

According to statistics, the failure rate of high-power devices caused by heat is as high as 55%. Moreover, in fields such as new energy vehicles and modern transportation tracks, complex application conditions such as bumps and vibrations need to be considered during the use of high-power devices, which puts higher demands on the mechanical properties and reliability of materials such as substrates. Silicon nitride performs best in terms of comprehensive performance, which is undoubtedly a very ideal substrate material with good heat dissipation performance.

Silicon nitride, the "full mark" material in the heat dissipation substrate

1. Full score for comprehensive performance
Compared to other materials, ceramic substrates have better performance, so choosing ceramic materials as substrates will have broader prospects. At present, the main ceramic materials that can be used as substrates include AlN, Al2O3, SiC, BeO, Si3N4, etc. Although BeO ceramic substrates have high thermal conductivity and low dielectric constant, their powders are toxic and harmful to health, and are currently rarely used. SiC has stable properties, but its dielectric loss is high and its breakdown voltage is low, making it unsuitable for high-voltage working environments. Al2O3 ceramic substrates have the longest and most mature application history, but due to their low theoretical and practical thermal conductivity, they cannot meet the heat dissipation requirements of large circuits and can only be used in small circuits. Compared to AlN ceramics, AlN ceramics have the characteristics of high thermal conductivity, good insulation, and low dielectric constant. However, AlN also has shortcomings that cannot be ignored, including easy hydrolysis of the material, insufficient strength and toughness, and fragility. Therefore, there is an urgent need for a more stable ceramic material to compensate for the limitations of AlN.

Material performance comparison

Material performance comparison

Compared with other materials, silicon nitride ceramics are recognized as the preferred material for high thermal conductivity ceramic substrates due to their high thermal conductivity (the thermal conductivity of their crystals can reach up to 320W · m-1 · K-1), low dielectric constant, non-toxicity, and matching thermal expansion coefficient with single crystal Si.
2. Demand trend "plus points"
With the increasing demand for performance, alumina (Al2O3) or aluminum nitride (AlN) ceramic materials are no longer outstanding in power templates, and more and more designers are considering using advanced substrate materials to replace them. For example, in the application of new energy vehicles (xEVs), when the chip temperature rises from 150 ° C to 200 ° C, its switching loss will be reduced by 10%. In addition, new packaging technologies such as welding and lead-free modules also place higher demands on materials.
Increasing the service life in harsh environments is also another driving factor for ceramic material iteration. For example, wind turbines have an expected service life of 15 years under all environmental conditions, during which they will not malfunction. Therefore, designers of wind turbines are also attempting to improve substrate technology. The third driving force for improving substrate products is the use of silicon carbide components (SiC). Compared with traditional modules, the first batch of modules using silicon carbide and optimized packaging technology reduced losses by 40% to 70%, but the latter requires the use of new packaging methods such as silicon nitride (Si3N4) substrates. The above trends will limit the future use of traditional aluminum oxide and aluminum nitride substrates, while silicon nitride based substrates will become the best choice for high-performance power module designers in the future.

Solving the Problem of Mass Production of High Performance Silicon Nitride Substrates

Although silicon nitride ceramic substrates are recognized as the best heat dissipation substrates with comprehensive performance, there are two thorny challenges that need to be solved in actual production, namely achieving "high thermal conductivity" and "sustained and stable mass production".
To achieve "high thermal conductivity", high-quality silicon nitride powder and scientific and advanced preparation technology are indispensable. In terms of raw materials, high-quality silicon nitride powder ensures the "excellent gene" of silicon nitride substrate at the source. The particle size, purity, and phase of the raw material powder are key factors affecting the mechanical properties and thermal conductivity of high thermal conductivity silicon nitride ceramics. Internal impurities and lattice defects can hinder the improvement of thermal conductivity of silicon nitride ceramics, so it is necessary to choose high-purity and high silicon nitride raw materials. In addition, the morphology of raw material powders is also very important. Powders with small initial particle size, large specific surface area, and "self formed" crystals have good sintering activity, making it easy to prepare high-density finished products.
For silicon nitride substrates, continuous and stable mass production is an industry challenge. It requires stable processes that can ensure that the substrate avoids warping, cracking, and other phenomena, as well as efficient continuous operations.

Market Prospects for Silicon Nitride Ceramic Substrates

With the rapid promotion of third-generation semiconductor chips based on SiC in new energy vehicles and 5G, the demand for silicon nitride ceramic substrates has also entered a rapid development stage. It is predicted that the global annual sales volume of electric vehicles will exceed 25 million in 2025. The proportion of SiC power devices is based on 37% of the estimated data from multiple investment institutions, and the existing Si3N4 ceramic substrate for electric vehicles is used as a standard chip (7.5 × Based on the usage of 2 standard pieces per vehicle for large vehicles such as buses, the global annual demand for high thermal conductivity silicon nitride substrates in 2025 is approximately 600000 square meters.
This is only a market forecast in the field of new energy vehicles. In addition, the demand for high-performance silicon nitride ceramic substrates in fields such as charging systems and LEDs is also rapidly increasing.

Conclusion

With the rapid development of electric vehicles and high-power electronic power devices, Si3N4 ceramic substrates will inevitably face huge market demand. China should further strengthen the collaborative cooperation among universities, research institutes, and enterprises in this field, focusing on breakthroughs in key technologies and equipment for the industrialization of high thermal conductivity Si3N4 substrates, fully opening up the Si3N4 substrate precision processing surface copper coating assessment application industry chain, and achieving the large-scale localization of high thermal conductivity Si3N4 substrates as soon as possible.


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