Silicon Nitride Substrates
A silicon nitride substrate is a substrate material primarily composed of si3n4, which has been used in many applications. Based on high fracture stress, hardness and resistance, which applied in cutting tools and low friction bearing. Silicon nitride si3n4 have two kinds of ceramic forms. They are sintered, bonded and amorphous. In electronic application, Si₃N₄as a high performance material, providing electrical insulation, surface protection film, and protective passivation layers. Which are conductive to increasing power density and high demand of heat generating in the power module. In addition, silicon nitride substrates can undertake large thermal stress from electronic control module.
Key Properties of Si₃N₄ Ceramic Substrate
Silicon nitride substrate shows outstanding electrical and chemical properties, including high electrical resistance (approximately 10¹⁴ Ω·cm), high dielectric strength (~10⁷ V/cm), and excellent resistance to chemical corrosion. Moreover, The unique silicon nitride properties variants, combining compositional modification and adaptable fabrication techniques. Which enable precise microstructural engineering and allow the development of ceramics with optimized and diverse characteristics of performance. These characteristics make Si₃N₄ a promising material for advanced microelectronic and semiconductor applications.
Mechanical Properties
Different silicon nitride applications forms exhibit unique fabrication methods, compositions, microstructural features, and performance characteristics. silicon nitride properties are fundamentally controlled by the atomic structure and chemical bonding of the Si₃N₄ unit, regarding as the foundation for the mechanical properties, thermal, and si3n4 dielectric constant.
Silicon nitride ceramics have a strong relationship between microstructure and mechanical properties. Fine-grained elongated grain structure are generally associated with high strength, while coarser grains can improved fracture toughness by promoting crack deflection and increasing fracture resistance. To be specific, appropriate grain boundary engineering includes the formation of relatively weak interfaces, enables energy consuming transgranular fracture behavior and enhances damage resistance. Owing to their combination of high strength, fracture toughness, thermal shock resistance, and temperature stability, silicon nitride material have become promising candidates for advanced structural application, such as gas turbine components, engine valve, and wear resistant parts.
The mechanical performance of silicon nitride ceramics is strongly influenced by sintering process and microstructural characteristics. Studies on microwave assisted sintering and gas pressure sintering have demonstrated that thermal treatment can modify grain morphology and grain boundary phases, thereby affecting fracture resistance. In particular, increasing the grain size of Si₃N₄ during densification promotes crack deflection along grain boundaries, resulting in enhanced fracture toughness. However, excessive grain growth may reduce the effectiveness of crack deflection and limit further improvement in toughness. Therefore, optimizing grain size and microstructural evolution is essential for achieving a balance between reliable mechanical and damage resistance in silicon nitride ceramics.
Electrical Insulation Properties
Silicon nitride possesses excellent electrical insulation properties, with a resistivity higher than 10¹⁴ Ω·cm at room temperature and above 10⁶ Ω·cm at 1200 °C. The electrical conductivity of Si₃N₄ based SiAlON ceramics slightly increases with increasing substitution level (z), reaching 2 × 10⁻⁹ and 2 × 10⁻⁷ (Ω·cm)⁻¹ for z = 1.5 and 3.2 at 700 °C, respectively. The conduction mechanism of change from impurity related electronic conductivity at lower temperatures to ionic conductivity above 900–1000 °C, with activation energies of approximately 1 ev below 800 °C and 1.8–2 ev near 1000 °C.
Thermal Cycling Reliability
Silicon nitride (Si₃N₄) ceramics exhibit excellent thermal cycling reliability due to their low coefficient of thermal expansion and superior mechanical properties. The thermal expansion coefficient of Si₃N₄ is typically around 3.1–3.6 × 10⁻⁶ K⁻¹, which helps reduce thermal mismatch stress between the ceramic substrate, metal layers, and semiconductor components during repeated heating and cooling cycle. In addition, the high strength and fracture toughness of Si₃N₄ enable the substrate to withstand thermal stresses generated in high power electronic module, which could prevent crack and device failure.
Silicon Nitride Substrate and Aluminium Nitride Substrate
For power application, the electric breakdown is essential, since the modular packaging need to undertake high thermal stress. As power electron devices and circuits become more compact while operating at higher power density, the demand of thinner ceramic PCB become mainstream. However,the dielectric breakdown voltage decreases with thinner ceramic PCB. On the contrary, the ability of heat transfer increase. Hence, the breakdown strength is mainly decided by the ceramic substrate thickness. Although aluminium nitride substrate with excellent thermal conductivity. Maintaining a minimum thickness of approximately 640 μm is often necessary, as further thinning may cause difficulties during grinding and polishing process. In terms of silicon nitride material shows outstanding mechanical properties and thermal conductivity. Compared with aluminium nitride substrate, the silicon substrate thickness range from 250 to 640 μm. The breakdown strength performance better than aln substrate. It is noticed that a dielectric breakdown voltage of approximately 1.5 kV even at an ultra thin thickness of only 15 μm. Which imply silicon nitride substrate is better choice for EVs, aerospace, inverter generator, and renewable energy.
Applications of Si₃N₄ Ceramic Substrate
The outstanding reliability of silicon nitride material has been proven through their successful application in demanding aerospace systems, including hybrid bearings used in the main engine pumps of the Space Shuttle and various components in aircraft auxiliary power units.
Inverter Generator
Currently, the main market of si3n4 is diesel and spark engines. The characterizes of low density, mechanical strength and toughness to withstand impact and mechanical damageIn diesel truck engines, silicon nitride material including injector links, check balls, brake pads, and fuel pump rollers have demonstrated reliable long term performance, with thousands of parts being manufactured monthly for continuous industrial applications. These applications are not high temperature when operating. Due lost of wear and weight, it has remarkable strength. Silicon nitride ceramics are also utilized in advanced high pressure common-rail injection pump systems to minimize wear and enhance service durability.
Electronic Vehicles
For electronic vehicles, achieving long term reliability and safety remains a critical challenge. Thermal cycling resistance is the key factor. Si3n4 substrate can satisfy the thermal shock from running vehicles. In addition, the thermal conductivity is 80W/m·K and the function far exceed clamped copper foils ceramic substrates.
Manufacturing process
The manufacturing process of Si₃N₄ ceramic substrates mainly includes powder preparation, forming, debinding, and high temperature sintering. High-purity silicon nitride powder is mixed with sintering additives and processed into a uniform powder before shaping through pressing methods. After binder removal, the formed bodies undergo sintering, where the α-Si₃N₄ phase transforms into β-Si₃N₄, forming an interlocking grain structure that improves strength and fracture toughness. Additional densification processes such as hot isostatic pressing (HIP) can further reduce porosity and enhance mechanical reliability.