High-toughness silicon nitride ceramic substrate and preparation method thereof

Abstract

The invention provides a high-toughness silicon nitride ceramic substrate and a preparation method thereof, and relates to the technical field of ceramic substrates, the preparation method comprises the following steps: mixing alpha-Si3N4 powder, a sintering aid and a flexibilizer CoSi2 to prepare a ceramic biscuit; and the oscillating pressure sintering process comprises the following steps: applying constant static pressure in a sintering heat preservation stage, and superposing periodically changing dynamic pressure on the basis of the static pressure. According to the preparation method, CoSi2 is introduced to form a residual compressive stress field and induce crack deflection for toughening, and compaction and long columnar crystal growth are promoted in combination with oscillation pressure sintering, so that synergistic improvement of high bending strength and excellent heat conductivity of the silicon nitride substrate is realized while process damage is avoided.

Description

Technical Field

[0001] This invention relates to the field of ceramic substrate technology, and more specifically, to a high-strength and high-toughness silicon nitride ceramic substrate and its preparation method. Background Technology

[0002] With the rapid development of fields such as intelligent vehicles, aerospace, and rail transportation, power electronic devices are evolving towards miniaturization, higher voltage, and higher power density. Under this trend, the electronic packaging substrate, as the core carrier, not only needs to provide mechanical support and electrical insulation but also plays a crucial role in efficient heat dissipation. Compared to resin substrates with poor heat resistance and metal substrates with complex insulation processes, ceramic substrates, with their excellent insulation, high thermal conductivity, and chemical stability, have become the preferred material for high-reliability power semiconductor packaging.

[0003] Among existing ceramic substrate systems, alumina (Al2O3) is the most widely used due to its mature technology and low cost, but its thermal conductivity is only 24~30 W / (m·K), which is insufficient to meet the heat dissipation requirements of high-power devices. Aluminum nitride (AlN), while having a high thermal conductivity of 170~200 W / (m·K), suffers from low fracture toughness, poor resistance to mechanical impact, and is prone to cracking during processing and use. Beryllium oxide (BeO) is limited due to the highly toxic nature of its raw materials. In contrast, silicon nitride (Si3N4) ceramic has a thermal expansion coefficient matching that of silicon chips and combines high fracture toughness with good thermal conductivity, making it a key material for solving the heat dissipation and reliability problems of high-power devices.

[0004] Despite the excellent overall performance of silicon nitride substrates, they still face challenges in practical applications. Statistics show that thermomechanical stress and fatigue failure are the main causes of power module failures, accounting for as much as 65%. This is due to the mismatch in the coefficients of thermal expansion (CTE) between the chip, solder, copper layer, and substrate, resulting in significant internal stress caused by differences in deformation between layers during temperature cycling. Currently, most commercially available silicon nitride substrates use the conventional gas pressure sintering (GPS) process, with bending strength typically ranging from 700 to 800 MPa. Facing increasingly demanding automotive application environments and extremely high safety requirements, the strength specifications of existing products are insufficient, making it difficult to completely avoid system failures caused by substrate fracture.

[0005] Crucially, with the widespread adoption of next-generation wide-bandgap semiconductors (such as SiC), chip junction temperatures will rise from 175°C to 200°C or even higher, exacerbating thermal expansion mismatch and thermal stress. Simultaneously, the fast-charging technology and complex operating conditions of new energy vehicles lead to faster temperature fluctuations, placing more stringent demands on the thermal fatigue resistance of materials. Existing silicon nitride substrates are prone to developing microcracks on their surface or edges under long-term high-frequency vibration and thermal shock, which can rapidly propagate and cause circuit breakage or poor soldering. Therefore, the toughness and durability of products manufactured using current techniques are insufficient to meet the ultra-high reliability requirements of future high-performance power modules.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a high-strength and high-toughness silicon nitride ceramic substrate and its preparation method. The preparation method introduces CoSi2 to form a residual compressive stress field and induces crack deflection. It also promotes densification and the growth of β-Si3N4 long columnar grains by oscillating pressure sintering process with specific amplitude and frequency. This method achieves a synergistic improvement in high bending strength and excellent thermal conductivity of silicon nitride ceramic substrate while avoiding process damage.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a method for preparing a high-strength and tough silicon nitride ceramic substrate, comprising: A ceramic green body was prepared by mixing α-Si3N4 powder, sintering aid and toughening agent CoSi2. The ceramic green body is sintered using an oscillating pressure sintering process, which includes: applying a constant static pressure during the sintering and holding stage, and superimposing a periodically changing dynamic pressure on the static pressure; wherein the amplitude of the dynamic pressure is ±1MPa to ±3MPa, and the oscillation frequency is 1Hz to 3Hz.

[0009] In an optional embodiment, taking the powder mixture formed by mixing α-Si3N4 powder, sintering aid, and toughening agent CoSi2 as 100%, the amount of toughening agent CoSi2 added is 0.5wt% to 4.5wt% of the total mass of the powder mixture; Preferably, the amount of toughening agent CoSi2 added is 1.0wt% to 3.0wt% of the total mass of the powder mixture.

[0010] In an optional embodiment, the toughening agent CoSi2 has an average particle size of 0.1 μm to 1.0 μm; In an optional embodiment, the sintering aid includes MgO and Y2O3; Preferably, the components in the powder mixture, by mass percentage, include: α-Si3N4 powder with a content of 0 wt% to 92.0 wt%; 0wt%~3.0wt% MgO; 0wt%~7.0wt% Y2O3; And the balance is CoSi2.

[0011] In an optional embodiment, the sintering temperature of the oscillating pressure sintering process is 1740℃~1760℃; and / or, The static pressure of the oscillating pressure sintering process is 25 MPa; and / or, The dynamic pressure variation curve of the oscillating pressure sintering process is a sinusoidal waveform; and / or, The oscillating pressure sintering process further includes a cooling and pressure relief step as follows: after sintering and holding at a certain temperature, the dynamic pressure is removed, the temperature is reduced at a rate of 7℃ / min to 9℃ / min, and the static pressure is maintained until the temperature drops to 1000℃ to unload the pressure; and / or, The method for preparing the ceramic green body includes: using the α-Si3N4 powder, the sintering aid and toughening agent CoSi2 as raw material powders, adding organic solvent, dispersant and binder, and ball milling and mixing to obtain a casting slurry; casting the casting slurry into shape, drying, cutting and stacking and hot pressing, and then placing it in a warm isostatic press for processing; preferably, the processing temperature of the warm isostatic press is 65℃~75℃; preferably, the holding time of the warm isostatic press is not less than 10min.

[0012] In an optional embodiment, the cast slurry comprises the following components by mass fraction, based on a total mass of 100%: 55%~60% of the raw material powder; 8%~12% anhydrous ethanol; 10%~14% polyvinyl butyral; 8%~12% dibutyl phthalate; 8%~12% triethyl phosphate.

[0013] In an optional embodiment, the ball milling mixture uses silicon nitride balls as the grinding medium; preferably, the silicon nitride balls are composed of a mixture of large balls, medium balls and small balls; wherein the diameter of the large balls is 5 mm, the diameter of the medium balls is 3 mm, and the diameter of the small balls is 1 mm; preferably, the mass ratio of the large balls, the medium balls and the small balls is 3:2:1. And / or, before preparing a ceramic green body by mixing α-Si3N4 powder, sintering aid and toughening agent CoSi2, the following pre-drying step is further included: placing the α-Si3N4 powder, the sintering aid and the toughening agent CoSi2 in an oven for heat preservation treatment; preferably, the temperature of the heat preservation treatment is 115℃~125℃; preferably, the heat preservation treatment time is 100min~140min.

[0014] In an optional embodiment, the casting slurry further includes a sieving process before casting. Preferably, the mesh size of the sieving process is 350 mesh to 450 mesh; and / or, Preferably, the process parameters for the casting process include: the height of the scraper at the feed inlet of the casting machine is 18μm~22μm; and / or, the casting speed is 2.5m / min~3.5m / min; and / or, the drying temperature is 55℃~65℃.

[0015] In a second aspect, the present invention provides a high-strength and high-toughness silicon nitride ceramic substrate, which is prepared by the preparation method of the high-strength and high-toughness silicon nitride ceramic substrate described in any of the foregoing embodiments; Preferably, the flexural strength of the high-strength and high-toughness silicon nitride ceramic substrate is not less than 850 MPa; Preferably, the thermal conductivity of the high-strength and high-toughness silicon nitride ceramic substrate is not less than 85 W / (m²). K); Preferably, the thermal conductivity of the high-strength and high-toughness silicon nitride ceramic substrate is not less than 90 W / (m²). K).

[0016] Thirdly, the present invention provides a power semiconductor module comprising a high-strength and tough silicon nitride ceramic substrate as described in the foregoing embodiments.

[0017] Fourthly, the present invention provides an electric vehicle including a power semiconductor module as described in the foregoing embodiments.

[0018] This invention provides a high-strength and high-toughness silicon nitride ceramic substrate and its preparation method. Compared with the prior art, the preparation method introduces CoSi2 as a toughening agent into the α-Si3N4 and sintering aid system. By utilizing the difference between CoSi2 and the silicon nitride matrix in terms of thermal expansion coefficient and elastic modulus, a microscopic residual compressive stress field can be formed at the grain boundary during sintering and cooling, resulting in a crack pinning effect. At the same time, when the crack propagates to the two-phase interface, it will be deflected, increasing the crack propagation path and consuming more fracture energy, thereby significantly improving the fracture strength and toughness of silicon nitride ceramic.

[0019] By employing an oscillating pressure sintering process and strictly controlling the amplitude and frequency range of the dynamic pressure, periodic dynamic pressure superimposed on static pressure can more effectively promote particle rearrangement to fill pores in the early stages of sintering. In the later stages of sintering, continuous compression forces closed pores to shrink or disappear, significantly improving density. More importantly, during the high-temperature phase transformation stage, oscillating pressure with specific frequency and amplitude can accelerate the flow of viscous phase and particle mass transfer, promoting the anisotropic growth of β-Si3N4 long columnar grains and forming a high aspect ratio interlocked microstructure, further enhancing the mechanical properties of the material. Limiting the amplitude of the dynamic pressure to ±1MPa~±3MPa and the frequency to 1Hz~3Hz ensures sufficient sintering driving force while avoiding excessively high local pressure due to excessive amplitude, which could induce microcracks inside the ceramic, or excessively high frequency, which could exceed the material's response capacity and lead to a decrease in thermal properties. The synergistic effect of this specific combination of process parameters enables the prepared silicon nitride ceramic substrate to maintain extremely high bending strength while also possessing excellent thermal conductivity, thus effectively solving the problem of balancing strength and thermal conductivity in traditional sintering processes. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic flowchart of the preparation method of the high-strength and tough silicon nitride ceramic substrate in the embodiments of this application; Figure 2 This is a comparison of the XRD patterns of the silicon nitride ceramic substrate before and after sintering in the embodiments of this application; Figure 3 SEM comparison images of the microstructure of silicon nitride ceramics under different sintering processes are shown, where (a) is gas pressure sintering (GPS, corresponding to Example 2) and (b) is oscillating pressure sintering (OPS, corresponding to Example 2). Figure 4 A statistical comparison of β-Si3N4 grain size distribution under gas pressure sintering (GPS) and oscillating pressure sintering (OPS) processes; Figure 5 The image shown is a SEM image of the crack propagation path of the silicon nitride ceramic substrate in the embodiments of this application, illustrating the crack deflection and bridging phenomena. Detailed Implementation

[0022] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0023] refer to Figure 1 This application provides a method for preparing a high-strength and tough silicon nitride ceramic substrate, comprising: Step S1: Mix α-Si3N4 powder, sintering aid and toughening agent CoSi2 to prepare ceramic green body.

[0024] In terms of raw material selection, α-phase silicon nitride (α-Si3N4) was selected as the basic skeleton material, sintering aids for densification were selected, and cobalt disilicide (CoSi2) was specially introduced as a toughening agent.

[0025] In terms of processing, the three powders mentioned above are physically mixed. This process may involve mixing different materials with solvents (such as anhydrous ethanol), binders (such as PVB), dispersants, etc., and dispersing them evenly through methods such as ball milling to form a slurry.

[0026] Then, the well-mixed slurry can be processed into green bodies (i.e., unsintered semi-finished products) with a certain shape and strength.

[0027] The implementation methods typically include processes such as tape casting, drying, cutting, and hot pressing to ultimately obtain a ceramic green body with uniformly distributed components, wherein CoSi2 particles are uniformly dispersed in the silicon nitride matrix powder.

[0028] Introducing CoSi2 as a second phase lays the material foundation for the formation of toughening mechanisms (such as crack deflection and residual stress fields) during subsequent sintering. Compared to a single matrix, this hybrid system aims to improve the mechanical properties of the final product.

[0029] Step S2: The ceramic green body is sintered using an oscillating pressure sintering process. The oscillating pressure sintering process includes: applying a constant static pressure during the sintering and holding stage, and superimposing a periodically changing dynamic pressure on the basis of the static pressure; wherein the amplitude of the dynamic pressure is ±1MPa to ±3MPa (for example, it can be ±1MPa, ±2MPa, ±3MPa, etc.), and the oscillation frequency is 1Hz to 3Hz (for example, it can be 1Hz, 2Hz, 3Hz, etc.).

[0030] This step uses dynamic sintering technology, which is different from traditional static constant pressure sintering.

[0031] In its pressure application method, the baseline is to first apply a constant static pressure (e.g., 25 MPa) as the base pressure. On this static pressure, a dynamic pressure that fluctuates periodically over time (e.g., a sine wave) is then superimposed.

[0032] Parameter control can specifically be as follows: (1) Amplitude: The fluctuation range of dynamic pressure is strictly controlled between ±1MPa and ±3MPa. For example, if the static pressure is 25MPa and the amplitude is ±2MPa, the actual total pressure acting on the sample will cycle between 23MPa and 27MPa.

[0033] (2) Frequency: The rate of pressure change is controlled between 1 and 3 times per second (1Hz~3Hz).

[0034] Through a specific oscillating pressure field, the particles inside the ceramic rearrange themselves, the closed pores are effectively expelled or reduced, and the α-Si3N4 phase transforms into β-Si3N4 and forms long columnar grains.

[0035] Dynamic pressure at specific frequencies and amplitudes can more effectively promote particle rearrangement in the early stages of sintering and eliminate porosity in the later stages, significantly improving material density. Oscillating pressure at these frequencies (1Hz~3Hz) and amplitudes (±1MPa~±3MPa) can accelerate mass transfer at high temperatures, promoting anisotropic growth of β-Si3N4 grains along specific directions, forming a high aspect ratio grain structure, thus achieving self-toughening. Damage prevention: Limiting the amplitude to ±3MPa prevents excessive local pressure fluctuations from inducing microcracks within the ceramic; limiting the frequency to 3Hz ensures effective pressure transmission, avoiding lag in equipment or material response due to excessively high frequencies, thereby ensuring undamaged thermal properties.

[0036] Specifically, a sintering furnace equipped with a dynamic hydraulic system can be used. In the program settings, after the temperature is raised to the sintering temperature (e.g., 1750℃) and the heat preservation stage is entered, the hydraulic servo system is activated. While maintaining the main pressure (static pressure), the pressure head is driven to perform small reciprocating pressurization and depressurization movements according to the set sine waveform. The frequency is set to 1Hz~3Hz, and the pressure fluctuation amplitude is set to ±1MPa~±3MPa.

[0037] In some embodiments, taking the powder mixture formed by mixing α-Si3N4 powder, sintering aid and toughening agent CoSi2 as 100%, the amount of toughening agent CoSi2 added is 0.5wt% to 4.5wt% of the total mass of the powder mixture; for example, it can be 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, etc.

[0038] This embodiment clearly defines the scope of the term "total mass". Here, "100%" refers only to the total amount of inorganic powder raw materials that constitute the final ceramic matrix, and explicitly excludes the mass of organic solvents (such as anhydrous ethanol), binders (such as PVB), dispersants, plasticizers, and grinding media (silicon nitride balls) that may be added in subsequent processes.

[0039] In the total mass of the inorganic powder determined above, the mass percentage of cobalt disilicide is limited to between 0.5% and 4.5%. Assuming the total mass of the powder mixture is 1000g, the mass of CoSi2 powder weighed should be controlled between 5g and 45g, with the remaining 995g to 955g being silicon nitride powder and sintering aids.

[0040] In a preferred embodiment, the toughening agent CoSi2 is added at an amount of 1.0 wt% to 3.0 wt% of the total mass of the powder mixture. For example, it can be 1 wt%, 2 wt%, 3 wt%, etc.

[0041] In actual production, the weighing ratio of CoSi2 can be controlled between 1.0% and 3.0% (for example, the target is set at 2.0%).

[0042] The substrate prepared with this ratio exhibits the most complete development of long columnar grains in its microstructure and the lowest porosity. This represents the optimal balance between toughening effect and sintering densification. Experiments have confirmed that within this range (e.g., 2.0 wt%), the material's flexural strength can reach its peak value (e.g., >1000 MPa), while maintaining extremely high thermal conductivity (e.g., >90 W / (m²)). K)) achieves optimal mechanical and thermal properties.

[0043] In some embodiments, the toughening agent CoSi2 has an average particle size of 0.1 μm to 1.0 μm; for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.8 μm, 1.0 μm, etc.

[0044] In some embodiments, the sintering aids include MgO and Y2O3.

[0045] In this embodiment, a binary additive system composed of MgO and Y2O3 is explicitly selected.

[0046] In the raw material preparation stage, other unnecessary additives were excluded, and high-purity MgO and Y2O3 powders were specifically selected as auxiliary materials to construct a specific liquid-phase sintering environment.

[0047] MgO and Y2O3 can react with silicon dioxide on the surface of silicon nitride at high temperatures to form a liquid phase (viscous phase). This specific liquid phase system helps promote the phase transformation from α-Si3N4 to β-Si3N4 and accelerates grain growth.

[0048] Furthermore, the components in the powder mixture, by mass percentage, include: α-Si3N4 powder with a content of 0 wt% to 92.0 wt%; for example, it can be 0 wt%, 10 wt%, 20 wt%, 50 wt%, 70 wt%, 90 wt%, 92 wt%, etc.

[0049] 0wt%~3.0wt% MgO; for example, it can be 0wt%, 1wt%, 2wt%, 3wt%, etc.

[0050] Y2O3 of 0wt% to 7.0wt%; for example, it can be 0wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, etc.

[0051] And the balance is CoSi2.

[0052] The aforementioned mass fraction ensures that the final product possesses the inherent superior properties of silicon nitride ceramics (high hardness, good thermal compatibility). Insufficient liquid phase will fail to completely fill the voids between materials, leading to porosity; while an appropriate additive ratio can promote mass transfer. This range ensures sufficient liquid phase to fill the interparticle gaps and promote densification, without compromising thermal conductivity due to excessive grain boundary phase (grain boundary phases typically have low thermal conductivity).

[0053] After determining the mass of the matrix (α-Si3N4 powder) and additives (MgO, Y2O3), any remaining portion not reaching 100% was supplemented by toughening agent. This proportioning logic ensures that the toughening agent content is always within a reasonable range that matches the matrix and additives, thereby synergizing with the oscillating pressure sintering process and achieving the technical effect of "high strength and toughness" through crack deflection and residual stress field mechanisms.

[0054] In some embodiments, the sintering temperature of the oscillating pressure sintering process is 1740℃~1760℃. For example, it can be 1740℃, 1750℃, 1760℃, etc.

[0055] In this embodiment, the temperature inside the sintering furnace is heated and maintained within the range of 1740°C to 1760°C. This is the target temperature range for the high-temperature sintering stage.

[0056] Specifically, a heating program can be used to raise the furnace temperature to this range at a certain heating rate (e.g., 10℃ / min), and sintering can be carried out at this temperature. Results and advantages: Results: Within this temperature range, silicon nitride undergoes an α-to-β phase transformation, and the viscosity of the liquid phase formed by the sintering aid is suitable.

[0057] This temperature range (centered around 1750℃) is the optimal window for ensuring densification and grain development of silicon nitride. Too low a temperature will lead to incomplete densification or incomplete phase transformation, while too high a temperature may cause material decomposition or abnormally coarse grains.

[0058] For example, the target temperature can be set to 1750℃ through the temperature control system of the sintering furnace (such as a PID controller), with a tolerance range of ±10℃.

[0059] In some embodiments, the static pressure of the oscillating pressure sintering process is 25 MPa.

[0060] In this embodiment, a constant basic mechanical pressure value is applied during the sintering process.

[0061] A continuous uniaxial pressure is applied to the mold or sample through a hydraulic system, stabilizing it at 25 MPa, thereby providing the basic driving force for sintering.

[0062] A static pressure of 25 MPa promotes interparticle contact and initial densification. It serves as a baseline for dynamic oscillation pressure, ensuring that after superimposing dynamic pressure (e.g., ±25 MPa), the total pressure remains positive (i.e., always under pressure, preventing voids) and maintaining the stability of the sintering process.

[0063] In some embodiments, the dynamic pressure variation curve of the oscillating pressure sintering process is a sine wave.

[0064] This is the dynamic pressure superimposed on the static pressure, and its change over time follows a sinusoidal function relationship. Specifically, the pressurization device (such as a hydraulic servo system) can be controlled to make its output pressure P(t) follow the formula: ; in, A represents static pressure (e.g., 25 MPa), A represents amplitude, f represents frequency, and t represents time.

[0065] By controlling the parameters described above, the pressure increases and decreases smoothly and periodically. Compared to square or triangular waves, the pressure change of a sinusoidal waveform is the smoothest, without abrupt inflection points. This helps to avoid impact damage to the ceramic green body caused by sudden and drastic pressure changes, while continuously and uniformly promoting liquid phase flow and particle rearrangement.

[0066] In some embodiments, the oscillating pressure sintering process further includes a cooling and depressurization step as follows: after the sintering and holding period is completed, the dynamic pressure is removed, and the temperature is reduced at a rate of 7°C / min to 9°C / min (for example, it can be 7°C / min, 8°C / min, 9°C / min, etc.), and the static pressure is maintained until the temperature drops to 1000°C to unload the pressure.

[0067] After sintering, the specific timing of temperature drop and pressure removal can also be controlled in a coordinated manner.

[0068] Specifically, after the sintering holding time is completed, the oscillation is stopped first, and the periodically changing pressure is no longer applied. While keeping the static pressure (25 MPa) constant, the furnace temperature is controlled to decrease at a rate of 7℃ / min to 9℃ / min. Unloading pressure: The static pressure is removed only when the temperature drops to 1000℃, followed by natural cooling or continued cooling, so that the ceramic substrate is always constrained by pressure during the cooling process in the high-temperature section.

[0069] This is a crucial step in preventing microcrack formation. Due to the different coefficients of thermal expansion of CoSi2 and Si3N4, internal stress will be generated during cooling. Maintaining high pressure during the high-temperature stage (from 1750℃ to 1000℃) can suppress the initiation and propagation of cracks caused by thermal expansion mismatch, ensuring the structural integrity of the finished product. Controlling the cooling rate (7℃ / min~9℃ / min) is to avoid thermal shock.

[0070] In some embodiments, the method for preparing the ceramic green body includes: using the α-Si3N4 powder, the sintering aid and the toughening agent CoSi2 as raw material powders, adding organic solvent, dispersant and binder for ball milling and mixing to obtain a casting slurry; casting the casting slurry into shape, drying, cutting and stacking hot pressing, and then placing it in a warm isostatic press for processing.

[0071] Furthermore, the processing temperature of the isostatic press is 65°C to 75°C (for example, it can be 65, 70, 75, etc.).

[0072] Furthermore, the holding time of the isostatic press is not less than 10 minutes.

[0073] This step provides a complete process from powder to green body to be sintered, especially by introducing warm isostatic pressing.

[0074] Specifically, α-Si3N4, additives, CoSi2, organic solvents (anhydrous ethanol), dispersants (triethyl phosphate), and binders (PVB) can be mixed and ball-milled to obtain a uniform cast slurry. Forming and Lamination: The slurry is cast and dried to form a film strip, which is then cut, stacked, and subjected to preliminary hot pressing. Warm Isostatic Pressing: The stacked samples are placed in a warm isostatic press, and isotropic pressure is applied in a liquid medium at 6℃~75℃ for at least 10 minutes to obtain a green preform with higher density and tighter interlayer bonding.

[0075] Ensure uniform dispersion of the toughening agent CoSi2 to prevent agglomeration. Warm isostatic pressing: Utilize temperature (65℃~75℃) to soften the binder, and combine with isostatic pressing to eliminate minute voids and density inconsistencies between the cast film layers. This provides a high-quality preform for subsequent oscillatory pressure sintering, a prerequisite for obtaining a high-density and high-strength substrate.

[0076] In some embodiments, the cast slurry comprises the following components by mass fraction, based on a total mass of 100%: The raw material powder comprises 55% to 60%; for example, it can be 55%, 56%, 57%, 58%, 59%, 60%, etc.

[0077] Anhydrous ethanol of 8% to 12%; for example, it can be 8%, 9%, 10%, 11%, 12%, etc.

[0078] 10%~14% polyvinyl butyral; for example, it can be 10%, 11%, 12%, 13%, 14%, etc.

[0079] Dibutyl phthalate (DBP) of 8% to 12%; for example, it can be 8%, 9%, 10%, 11%, 12%, etc.

[0080] 8%~12% triethyl phosphate. For example, it can be 8%, 9%, 10%, 11%, 12%, etc.

[0081] In some embodiments, the ball milling mixture uses silicon nitride balls as the grinding medium; preferably, the silicon nitride balls are composed of a mixture of large balls, medium balls, and small balls; wherein the diameter of the large balls is 5 mm, the diameter of the medium balls is 3 mm, and the diameter of the small balls is 1 mm. Furthermore, the mass ratio of the large ball, the medium ball, and the small ball is 3:2:1.

[0082] In the ball milling process for preparing ceramic slurry, it is clearly specified that the material of the grinding balls must be consistent with the matrix material, that is, silicon nitride ceramic balls should be used, rather than alumina balls, zirconia balls or steel balls.

[0083] When filling the grinding jar, only silicon nitride balls are selected as the grinding medium to ensure that the wear debris introduced during the grinding process has the same composition as the matrix.

[0084] During ball milling, the grinding balls inevitably experience slight wear. Using silicon nitride balls avoids introducing other impurity elements (such as iron, zirconium, and aluminum), thus ensuring the purity of the powder. Impurities typically form low-melting-point phases or grain boundary defects, reducing high-temperature performance; homogeneous grinding eliminates this potential problem.

[0085] The silicon nitride balls are composed of a mixture of large, medium, and small balls, instead of using a single-size grinding ball, to construct a multi-level grinding system. In this embodiment, three specific diameter specifications are clearly defined: 5mm (large), 3mm (medium), and 1mm (small).

[0086] By screening or sourcing, prepare silicon nitride balls of the three specific diameters mentioned above to create grinding environments with different impact forces and filling rates. Large balls (5mm): Provide greater impact force, primarily responsible for breaking up larger agglomerates or hard particles. Small balls (1mm): Provide more contact points and grinding surface area, mainly refining powder particles through grinding and shearing actions. Medium balls (3mm): Serve as a transition, combining impact and grinding functions.

[0087] The mass ratio of large, medium, and small grinding balls is 3:2:1, which quantitatively controls the proportion of grinding balls of different sizes. Specifically, the balls can be weighed according to this 3:2:1 mass ratio. For example, if the total ball weight is 600g, weigh out 300g of large balls, 200g of medium balls, and 100g of small balls, mix them, and then place them in the grinding jar to obtain the optimal bulk density and porosity.

[0088] This specific gradation (which allows for more thorough ball milling) enables smaller balls to fill the gaps between larger balls, maximizing the effective contact area between the grinding media and the powder, significantly improving ball milling efficiency and slurry uniformity, and ensuring that the toughening agent CoSi2 is highly dispersed in the matrix.

[0089] In some embodiments, before preparing a ceramic green body by mixing α-Si3N4 powder, sintering aid, and toughening agent CoSi2, the following pre-drying step is further included: placing the α-Si3N4 powder, the sintering aid, and the toughening agent CoSi2 in an oven for heat preservation treatment; preferably, the temperature of the heat preservation treatment is 115℃~125℃ (for example, it can be 115℃, 120℃, 125℃, etc.); preferably, the heat preservation treatment time is 100min~140min (for example, it can be 100min, 110min, 120min, 130min, 140min, etc.).

[0090] Before weighing and mixing, the α-Si3N4 powder, sintering aids (MgO, Y2O3), and toughening agent CoSi2 are dehumidified. The process involves placing the raw powders into clean trays or crucibles and then placing them in a forced-air drying oven to remove adsorbed physical water (moisture) from the powder surface.

[0091] Ceramic powders (especially nano-sized powders) have a large specific surface area and are highly susceptible to moisture absorption. The absorbed moisture increases the powder weight, leading to a lower actual amount of effective component (e.g., only 2.0 wt% CoSi2), deviating from the designed formulation. Pre-drying ensures accurate stoichiometry of the ingredients. It also prevents defects: moisture introduced into organic solvent systems (such as ethanol and PVB) can cause agglomeration, phase separation, or bubbles in the cast film; pre-drying eliminates these process defects at the source.

[0092] Furthermore, by setting a specific drying process window, the oven temperature can be set between 115°C and 125°C (preferably 120°C), and maintained at this temperature for 100 to 140 minutes (preferably 120 minutes) to completely evaporate the moisture without changing the properties of the powder.

[0093] Temperature (>100℃), higher than the boiling point of water, ensures that moisture can evaporate quickly and completely. Time (>100min) ensures that heat can fully penetrate to the center of the powder accumulation layer, ensuring that the entire batch of powder dries evenly and without residual moisture.

[0094] In some embodiments, the casting slurry further includes a sieving process before casting; Furthermore, the mesh size of the sieving process is 350 to 450 mesh. For example, it can be 350 mesh, 380 mesh, 400 mesh, 420 mesh, 450 mesh, etc.

[0095] In this step, the cast slurry is filtered using a sieve with a specific mesh density. "Mesh count" refers to the number of openings per square inch of the sieve; the higher the number, the smaller the pore size. A mesh count of 350 to 450 mesh corresponds to an pore size of approximately 30 to 40 μm.

[0096] Specifically, the slurry after ball milling can be pumped or poured into a filter device equipped with a 350-450 mesh screen. Gravity or air pressure forces the slurry through the screen, intercepting and removing any residue trapped on the screen. Results and advantages: Results: A pure slurry free of large particles is obtained.

[0097] Sieving effectively removes micro-dust, unground hard agglomerates, or broken grinding ball debris mixed in with the environment; and ensures complete removal of impurities and large particles. If large particles are present in the cast film, they will form huge stress concentration points or pores after sintering, directly leading to a significant decrease in the bending strength of the substrate. This step is fundamental to ensuring high strength.

[0098] Furthermore, the process parameters for the casting process include: the height of the scraper at the feed inlet of the casting machine is 18μm~22μm (e.g., it can be 18μm, 19μm, 20μm, 21μm, 22μm, etc.); and / or, the casting speed is 2.5m / min~3.5m / min (e.g., it can be 2.5m / min, 2.8m / min, 3.0m / min, 3.2m / min, 3.5m / min, etc.); and / or, the drying temperature is 55℃~65℃ (e.g., it can be 55℃, 58℃, 60℃, 62℃, 65℃, etc.).

[0099] This section involves the physical process of converting liquid slurry into solid flexible membrane strips (preforms), and the quality of the membrane strips is controlled synergistically through three core parameters.

[0100] (1) The height of the scraper at the feed inlet of the casting machine is 18μm~22μm, so as to accurately set the vertical gap distance between the scraper edge and the casting carrier tape (usually PET film) at the bottom. This parameter directly determines the thickness of the wet film (undried slurry layer).

[0101] Specifically, a micrometer or the automatic adjustment system of the casting machine can be used to lock the doctor blade height within the range of 18μm~22μm (preferably 20μm), so that the slurry is "scraped" into an extremely thin and uniform liquid film by the doctor blade as it moves with the carrier belt.

[0102] Precise control of the thickness of each green body layer; this height, combined with a specific casting speed, can generate suitable shear force, causing the ceramic particles in the slurry to arrange in an orderly manner, which helps to improve the packing density of the green body.

[0103] The above embodiments also include controlling the forward movement rate of the casting machine carrier tape (baseband).

[0104] Specifically, the speed of the drive motor can be adjusted so that the carrier belt passes under the scraper at a speed of 2.5m / min to 3.5m / min and enters the drying zone (e.g., 3m / min), thereby determining the efficiency of slurry coating and the residence time in the drying zone.

[0105] This speed range is moderate, preventing streaks or thickness fluctuations caused by insufficient slurry leveling due to excessive speed, while also preventing low production efficiency due to excessively slow speed. It is matched with the drying temperature to ensure the film belt reaches the ideal dryness state upon exiting the drying tunnel, avoiding both over-drying and re-dampening.

[0106] Set the ambient temperature within the drying tunnel of the casting machine to evaporate the organic solvents (mainly anhydrous ethanol) in the slurry. Specifically, the heating system can be activated to stabilize the tunnel temperature between 55℃ and 65℃ (e.g., 60℃), thereby allowing the organic solvents to evaporate smoothly, the PVB binder to solidify, and the liquid slurry to transform into a solid ceramic film with a certain strength and toughness.

[0107] This temperature range is mild and moderate. If the temperature is too high (e.g., >80℃), the solvent surface will evaporate too quickly, forming a "skin" that blocks the internal solvent channels, causing the membrane to bubble or crack. If the temperature is too low, drying will be incomplete, the membrane will become sticky, and it will be impossible to peel off from the carrier. Uniform microstructure: A stable solvent evaporation process helps to prevent particle migration or sedimentation, ensuring a uniform distribution of components within the green body.

[0108] This application also provides a high-strength and high-toughness silicon nitride ceramic substrate, which is prepared by the preparation method of the high-strength and high-toughness silicon nitride ceramic substrate described in any of the foregoing embodiments; Furthermore, the high-strength and high-toughness silicon nitride ceramic substrate has a bending strength of not less than 850 MPa; preferably, the bending strength of the high-strength and high-toughness silicon nitride ceramic substrate is not less than 900 MPa. Even further, the bending strength of the high-strength and high-toughness silicon nitride ceramic substrate is not less than 1000 MPa.

[0109] Furthermore, the thermal conductivity of the high-strength and high-toughness silicon nitride ceramic substrate is not less than 85 W / (m²). K); Furthermore, the thermal conductivity of the high-strength and high-toughness silicon nitride ceramic substrate is not less than 90 W / (m²). K).

[0110] This product is a ceramic substrate with high mechanical strength and high thermal conductivity used in electronic packaging. From a material composition perspective, this substrate is essentially a multiphase ceramic material. The components included can be as described in the foregoing embodiments, and the microstructure of this product consists of the following parts: Matrix phase: β-Si3N4 grains formed by the transformation of α-Si3N4 raw material at high temperature constitute the framework of ceramic.

[0111] Grain boundary phase (viscous phase): A glassy or partially crystalline phase formed by the reaction of sintering aids (MgO and Y2O3) with silicon dioxide on the surface of silicon nitride at high temperature. It is distributed between grains and plays a role in bonding and densification.

[0112] Toughening phase: Cobalt disilicide (CoSi2) particles dispersed in the matrix. This is a key structural feature that distinguishes this product from traditional silicon nitride substrates.

[0113] Due to the use of an oscillating pressure sintering process, the periodic dynamic pressure effectively eliminates closed pores. Therefore, the product has extremely low internal porosity and a highly dense microstructure. Unique grain morphology: The oscillating pressure promotes mass transfer and phase transformation at high temperatures, resulting in long, columnar, interlocking β-Si3N4 grains in the matrix. This structure is similar to microscopic "reinforced concrete," significantly improving fracture toughness. Due to the introduction of CoSi2, its coefficient of thermal expansion (CTE) and elastic modulus differ from those of the matrix Si3N4. During the cooling process after sintering, a residual compressive stress field forms at the two-phase interface.

[0114] This further defines the product's two core performance indicators: flexural strength and thermal conductivity.

[0115] Traditional gas pressure sintering of silicon nitride substrates typically operates at 700-800 MPa, while this product reaches over 850 MPa, and in the preferred embodiment, it reaches 1000 MPa.

[0116] The principle is that the residual compressive stress field generated by the dispersed CoSi2 particles can "pin" the crack tip and prevent it from propagating; at the same time, when the crack encounters CoSi2 particles, the path will be deflected, increasing the fracture surface area and consuming more fracture energy; the long columnar β-Si3N4 grains induced by the OPS process will have a pull-out effect during fracture, further dissipating energy.

[0117] The extremely high strength enables the substrate to withstand more severe mechanical vibration, impact, and thermomechanical stress caused by temperature cycling, significantly reducing the risk of physical failure under extreme conditions (such as driving of new energy vehicles and emergency braking) and improving the reliability of the power module.

[0118] Furthermore, the thermal conductivity is not less than 85 W / (m²). K) (Preferred 90W / (m) It should be noted that heat is primarily transferred in ceramics through lattice vibrations (phonons). Pores are strong phonon scattering centers, significantly reducing thermal conductivity. This product eliminates micropores through the OPS process, ensuring unobstructed phonon transport channels. Reasonable sintering aid ratios and process control reduce the thickness of the amorphous grain boundary phase, thereby lowering grain boundary thermal resistance.

[0119] High thermal conductivity can rapidly dissipate the large amount of heat generated by power semiconductor chips (such as SiC and IGBT), reducing the chip's junction temperature. This is crucial for wide-bandgap semiconductor devices operating at temperatures exceeding 200°C, effectively preventing damage from overheating and extending their lifespan.

[0120] In summary, the aforementioned silicon nitride ceramic substrate, through specific composition (introduction of CoSi2) and specific structure (densification and grain lengthening by OPS process), simultaneously solves the contradiction of "difficulty in achieving both high strength and high thermal conductivity" in traditional materials, and achieves a synergistic improvement in mechanical and thermal properties.

[0121] In this embodiment, a power semiconductor module is also provided, including a high-strength and tough silicon nitride ceramic substrate as described in the foregoing embodiments.

[0122] This embodiment provides a power semiconductor module integrating specific high-performance insulating and heat dissipation components, which uses the aforementioned high-strength and tough silicon nitride ceramic substrate as the chip carrier and heat dissipation platform. This means that during the module packaging process, power chips such as IGBTs or SiC are connected to the metallization layer of this specific substrate through soldering or sintering silver processes. The high bending strength (≥1000MPa) and high thermal conductivity (≥85W / (m²)) brought by the dense microstructure formed by the substrate through oscillating pressure sintering and the CoSi2 toughening phase are utilized. K) effectively alleviates the thermomechanical stress caused by the mismatch in thermal expansion coefficients between the chip and the substrate. This design enables the module to prevent substrate cracking or delamination when subjected to frequent temperature cycles and high-power operation shocks, thereby significantly improving the reliability and heat dissipation efficiency of the power module in high-temperature and high-pressure environments.

[0123] In this application embodiment, an electric vehicle is also provided, including the power semiconductor module as described in the foregoing embodiments.

[0124] This embodiment provides an electric vehicle equipped with the aforementioned high-performance power semiconductor module. This means that the power module, which includes a high-strength and tough silicon nitride ceramic substrate, is assembled and applied to the core power system of the electric vehicle, such as the motor controller (inverter), on-board charger (OBC), or DC-DC converter. By applying this module, which has excellent resistance to mechanical vibration and thermal shock, the electric vehicle can better adapt to the bumps and vibrations under complex road conditions and the severe heat generation challenges under fast charging or aggressive driving modes. As a result, the risk of failure in the vehicle's power system due to thermal fatigue or mechanical fracture of core components is significantly reduced, and the overall vehicle safety and long-term durability are significantly enhanced.

[0125] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0126] Example 1 This embodiment provides a ceramic substrate.

[0127] Experimental methods: S1. Before weighing, place the raw materials α-Si3N4, MgO, Y2O3, and CoSi2 in an oven at 120℃ for 120 minutes to ensure moisture removal. The average particle size (D) of the selected CoSi2 powder is specified. 50 The particle size is 0.5 μm. Weigh out powder formulation B (91 wt% α-Si3N4, 2.0 wt% MgO, 5.0 wt% Y2O3, 2 wt% CoSi2).

[0128] S2. Weigh the raw materials according to the mass ratio of anhydrous ethanol to silicon nitride balls = 1:2:3 and place them in a polyurethane ball mill jar. In order to make the ball milling more thorough, the silicon nitride ball gradation ratio is large balls (Φ5): medium balls (Φ3): small balls (Φ1) = 3:2:1. Use a planetary ball mill at a speed of 400 r / min for 24 hours.

[0129] S3. After the slurry is milled, it is sieved to remove the silicon nitride balls and then dried in an oven at 70°C for 8 hours. The dried slurry is then crushed in a mortar and sieved through a 120-mesh sieve to obtain powder.

[0130] S4. Weigh 58% ceramic powder, then add 10% anhydrous ethanol, DBP, triethyl phosphate, and 12wt% PVB, and place them in a polyurethane ball mill jar. Use a planetary ball mill at a speed of 400 r / min for 48 h to obtain a uniform cast slurry.

[0131] S5. Pass the resulting slurry through a 400-mesh sieve to ensure complete removal of impurities and large particles.

[0132] S6. Adjust the height of the scraper at the feed port of the casting machine to 20um, slowly pour the cast ceramic slurry into the feed port, and the casting speed is 3m / min. Under the action of the scraper, a ceramic film is formed, which is then cut to obtain the cast sheet.

[0133] S7. Place the cut cast sheet into an oscillating pressure furnace for sintering. The heating rate is 10℃ / min. The external pressure is slowly increased to 25MPa and kept constant. When the temperature inside the furnace rises to 1750℃, based on the constant external pressure of 25MPa, the program is set to provide a dynamic pressure of -2~2MPa (±2MPa) to the powder, so that the total dynamic oscillation pressure after coupling is 23~27MPa. The oscillation frequency is set to 2Hz. The dynamic pressure change curve is based on a sine wave. The oscillation pressure program is maintained until the target program is finished. Then the external oscillation pressure is removed, the cooling rate is set to 8℃ / min, and the constant pressure of 25MPa is maintained until the furnace temperature drops to 1000℃ and unloaded.

[0134] S8. The mechanical properties and thermal conductivity of the sintered silicon nitride substrate were tested. In this embodiment, the silicon nitride substrate with 2.0 wt% CoSi2 added and sintered by oscillation pressure had a thermal conductivity of 95.1 W / (m²). K), with a bending strength of over 1000 MPa.

[0135] Example 2 This embodiment provides a ceramic substrate.

[0136] The experimental method was basically the same as in Example 1, except that the toughening agent content was 0.5wt%CoSi2.

[0137] Example 3 This embodiment provides a ceramic substrate.

[0138] The experimental method was basically the same as in Example 1, except that the toughening agent content was 4wt%CoSi2.

[0139] Example 4 This embodiment provides a ceramic substrate.

[0140] The experimental method was basically the same as in Example 1, except that the toughening agent content was 1wt%CoSi2.

[0141] Example 5 This embodiment provides a ceramic substrate.

[0142] The experimental method was basically the same as in Example 1, except that the toughening agent content was 3wt%CoSi2.

[0143] Example 6 This embodiment provides a ceramic substrate.

[0144] The experimental method is basically the same as in Example 2, except that the amplitude (dynamic pressure) is ±1MPa.

[0145] Example 7 This embodiment provides a ceramic substrate.

[0146] The experimental method is basically the same as in Example 2, except that the amplitude (dynamic pressure) is ±3MPa.

[0147] Example 8 This embodiment provides a ceramic substrate.

[0148] The experimental method is basically the same as in Example 2, except that the frequency is 2Hz.

[0149] Example 9 This embodiment provides a ceramic substrate.

[0150] The experimental method is basically the same as in Example 2, except that the frequency is 1Hz.

[0151] Example 10 This embodiment provides a ceramic substrate.

[0152] The experimental method is basically the same as in Example 2, except that the frequency is 3Hz.

[0153] Example 11 This embodiment provides a ceramic substrate. The experimental method is basically the same as in Example 2, except that the content of the toughening agent CoSi2 is 4.5 wt%.

[0154] Example 12 This embodiment provides a ceramic substrate. The experimental method is basically the same as in Example 2, except that the content of the toughening agent CoSi2 is 0.5wt%.

[0155] Comparative Example 1 This comparative example provides a ceramic substrate.

[0156] The experimental method was basically the same as in Example 1, except that the sintering method was gas pressure sintering and the toughening agent content was 0wt%CoSi2.

[0157] Comparative Example 2 This comparative example provides a ceramic substrate.

[0158] The experimental method was basically the same as in Example 1, except that the sintering method was gas pressure sintering and the toughening agent content was 2wt%CoSi2.

[0159] Comparative Example 3 This comparative example provides a ceramic substrate.

[0160] The experimental method was basically the same as in Example 1, except that the sintering method was gas pressure sintering and the toughening agent content was 4wt%CoSi2.

[0161] Comparative Example 4 This comparative example provides a ceramic substrate.

[0162] The experimental method is basically the same as that in Example 2, except that the sintering method is gas pressure sintering with an amplitude (dynamic pressure) of ±5MPa.

[0163] Comparative Example 5 This comparative example provides a ceramic substrate.

[0164] The experimental method is basically the same as that in Example 2, except that the sintering method is gas pressure sintering, and the amplitude (dynamic pressure) is ±7MPa.

[0165] Comparative Example 6 This comparative example provides a ceramic substrate.

[0166] The experimental method is basically the same as in Example 2, except that the frequency is 5Hz.

[0167] Comparative Example 7 This comparative example provides a ceramic substrate. The experimental method is basically the same as in Example 2, except that the content of the toughening agent CoSi2 is 5.5 wt%.

[0168] Comparative Example 8 This comparative example provides a ceramic substrate. The experimental method is basically the same as in Example 2, except that the average particle size of the toughening agent CoSi2 powder used is 40 μm (micrometer level).

[0169] Comparative Example 9 This comparative example provides a ceramic substrate. The experimental method is basically the same as in Example 2, except that the average particle size of the toughening agent CoSi2 powder used is 50 nm (nanometer level).

[0170] Comparative Example 10 This comparative example provides a ceramic substrate. The experimental method is basically the same as that in Example 1, except that: in step S1, the toughening agent CoSi2 is not added (i.e., the CoSi2 content is 0wt%, and the α-Si3N4 content is adjusted to 93wt%), and the sintering process adopts the same oscillating pressure sintering (OPS) as in Example 1.

[0171] Test Experiment 1. Testing method: (1) The bending strength of the samples was tested using the three-point bending method. First, the sintered silicon nitride ceramic substrate was cut, ground, and polished to make a standard strip specimen with dimensions of 3mm×3mm×36mm. The specimen was placed on a universal testing machine with a span of 30mm and a loading rate of 0.5mm / min until the specimen broke. The maximum breaking load was recorded, and the bending strength was calculated according to the formula. Five specimens were tested for each group of samples, and the average value was taken.

[0172] (2) Thermal conductivity testing: The thermal conductivity of the samples was tested using the laser flare method (LFA). The sintered substrate was processed into circular samples with a diameter of 12.7 mm and a thickness of 1 mm, and a graphite layer was uniformly sprayed on both sides of the samples to improve heat absorption and emissivity. The thermal diffusivity of the samples was measured at room temperature (25 °C) using a laser thermal conductivity meter, and the final thermal conductivity value was calculated by combining the density measured by the Archimedes displacement method and the theoretical specific heat capacity.

[0173] (3) Volume resistivity test: The sample was tested at room temperature (293K) using a high resistivity meter. The sintered substrate was processed into a circular sample with a diameter of 50mm and a thickness of 1mm. Silver electrodes were coated on the upper and lower surfaces. A test voltage of 1000V was applied, and the volume resistivity value was read and recorded.

[0174] 2. Test Results: (1) Investigation on the effects of sintering process and toughening agent content on material properties: To verify the superiority of the oscillating pressure sintering process (OPS) proposed in this invention over the traditional gas pressure sintering process (GPS), and the key role of the toughening agent CoSi2 in silicon nitride substrates, comparative experiments were designed for Examples 1-5 and Comparative Examples 1-3.

[0175] The experimental design employed the method of controlling variables: 1) Process Comparison: Comparative Examples 1-3 were set up using the traditional gas pressure sintering process, corresponding to the formulations of Example 1 (0wt% CoSi2), Example 2 (2.0wt% CoSi2), and Example 3 (4.0wt% CoSi2), respectively. By comparing the product performance under the same formulation but different sintering methods (e.g., Example 1 vs. Comparative Example 1, Example 2 vs. Comparative Example 2), the aim was to verify the unique advantages of oscillating pressure sintering in promoting densification and grain growth.

[0176] 2) Optimal Content: Building upon the established advantages of the OPS process, Examples 1-5 further investigated the effect of CoSi2 addition (0wt%~4.0wt%) on material properties. By setting gradient contents (0%, 1%, 2%, 3%, 4%), the aim was to explore the structure-property relationship between toughening agent content and flexural strength and thermal conductivity, and to confirm the rationality of the preferred content range (1.0wt%~3.0wt%) defined in this application.

[0177] The specific test results are shown in Table 1 below: Table 1. Performance Test Results

[0178] (2) Investigation on the influence of dynamic pressure amplitude in oscillating pressure sintering process: After determining the preferred toughening agent content (2.0 wt%) and fundamental frequency (2 Hz), in order to further explore the influence boundary of the core parameter "dynamic pressure amplitude" in the oscillating pressure sintering process on the material structure and properties, comparative experiments were designed in Examples 2, 6, and 7, as well as Comparative Examples 4 and 5.

[0179] In this group of experiments, the baseline static pressure (25 MPa) was kept constant, and only the amplitude of the superimposed dynamic sinusoidal pressure was adjusted: 1) Valid range verification: Examples 6 (±1MPa), 2 (±2MPa) and 7 (±3MPa) represent the low, medium and high amplitude levels within the protection range of this application, respectively, and are intended to verify whether a high-performance substrate can be stably obtained within this range.

[0180] 2) Boundary failure verification: Comparative Example 4 (±5MPa) and Comparative Example 5 (±7MPa) were subjected to excessive amplitudes exceeding the protection range. This setting was intended to reveal whether severe pressure fluctuations, when the oscillation amplitude is too large, can damage the internal microstructure of the ceramic (such as inducing microcracks), thereby leading to a decline in mechanical and thermal properties.

[0181] The specific test results are shown in Table 2 below: Table 2, Performance Test Results

[0182] (3) Investigation on the influence of oscillation frequency in oscillating pressure sintering process: The oscillation frequency is another key kinetic parameter that determines the particle rearrangement efficiency and mass transfer rate during sintering. To determine the optimal frequency window, comparative experiments were conducted in Examples 2, 9, 10, and Comparative Example 6.

[0183] The experiment fixed the toughening agent content (2.0 wt%) and the optimal amplitude (±2 MPa), only changing the oscillation frequency of the dynamic pressure: 1) Optimal frequency verification: Examples 9 (1Hz), 2 (2Hz), and 10 (3Hz) cover the low-to-mid-frequency range defined in this application. The purpose is to verify whether the oscillation pressure can effectively match the formation rate of the sintering neck and the grain boundary migration rate within this frequency range, thereby promoting the benign growth of β-Si3N4 long columnar crystals.

[0184] 2) High-frequency failure verification: Comparative Example 6 (5Hz) was set with a relatively high oscillation frequency. This setting was intended to examine whether exceeding the high-temperature rheological response limit of the material would lead to an obstruction of the densification process or an increase in lattice defects, thereby affecting the final thermal conductivity and strength of the material.

[0185] The specific test results are shown in Table 3 below: Table 3. Performance Test Results

[0186] (4) Investigation on the effect of toughening agent content on the insulation performance of the substrate: Since CoSi2 is an intermetallic compound with good metallic conductivity, its content must be strictly controlled when introduced as a second phase into silicon nitride ceramics. This is to ensure that the prepared silicon nitride ceramic substrate, while achieving toughening, still possesses the insulation properties required for power module use (volume resistivity typically required to reach 10 Ω·cm). 14 (Ω·m or above).

[0187] To verify the insulation reliability of the technical solution in this application and to determine the safety boundary of the CoSi2 addition amount, samples with different CoSi2 contents (covering the range of 0wt% to 5.5wt%) were selected for volume resistivity testing (test temperature 293K). The test results are shown in Table 4 below: Table 4. Volume resistivity test results

[0188] 3. Analysis: Based on the test results in Tables 1 to 3 above, the performance of the silicon nitride ceramic substrates prepared in the embodiments and comparative examples of the present invention is analyzed in detail as follows: (1) Analysis of the influence of sintering process and toughening agent content on material properties: Referring to the data comparison of the examples and comparative examples in Table 1, the advantages of oscillating pressure sintering (OPS) process and the influence of CoSi2 addition amount were mainly explored.

[0189] Process Advantages (OPS vs GPS): Compared to samples with the same formulation, the samples sintered by oscillating pressure (OPS) showed significantly better performance than those sintered by gas pressure (GPS). For example, without the addition of toughening agents, Comparative Example 10 (OPS, 859 MPa) had significantly higher strength than Comparative Example 1 (GPS, 712 MPa); and at the same 2.0 wt% content, Example 1 (OPS, 1036 MPa) also significantly outperformed Comparative Example 2 (GPS, 824 MPa). This clearly demonstrates that the dynamic pressure applied by the OPS process provides additional driving force, effectively eliminating closed pores and promoting densification.

[0190] Content Optimization and Lower Limit Verification: In Examples 1, 3-5, 11-12, and Comparative Example 10, the gradient changes in CoSi2 content were systematically investigated. Experiments showed that even with only 0.5 wt% CoSi2 addition (Example 12), the flexural strength of the material reached 905 MPa, a significant improvement compared to the control group without addition (Comparative Example 10, 859 MPa). This fully demonstrates that 0.5 wt%, as the lower limit of the scope of protection of this application, is sufficient to trigger an effective crack deflection toughening mechanism. With further increases in content, the flexural strength showed an upward trend, reaching a peak of 1036 MPa at 2.0 wt% (Example 1). Although the strength slightly decreased as the content increased to 4.0 wt% (Example 3), it remained at a high level overall. This indicates that the 0.5 wt% to 4.5 wt% range defined in this application is an effective range that has been rigorously verified experimentally.

[0191] (2) Analysis of the influence of dynamic pressure amplitude on the stability of material structure: Referring to the data of the examples and comparative examples 4-5 in Table 2, the "double-edged sword" effect of amplitude parameter is revealed.

[0192] Effective range: Within the range of ±1 MPa to ±3 MPa (Examples 6, 2, and 7), the samples maintained extremely high strength (>990 MPa). The performance was optimal at ±2 MPa, indicating that moderate pressure fluctuations are most conducive to promoting mass transport.

[0193] Overload damage: When the amplitude increased to ±5MPa (Comparative Example 4) or even ±7MPa (Comparative Example 5), the flexural strength dropped sharply to 789MPa and 656MPa, respectively. Analysis suggests that excessive pressure fluctuations produced a fatigue-like destructive effect during the ceramic hardening stage, inducing microcrack initiations within the material and ultimately compromising its integrity. Therefore, strictly limiting the amplitude to within ±3MPa is crucial for ensuring yield.

[0194] (3) Analysis of the influence of oscillation frequency on sintering kinetics: Referring to the data in Table 3, the matching relationship between frequency and liquid phase viscous flow was explored.

[0195] Frequency matching: The material properties are stable in the low-frequency range of 1Hz to 3Hz (Examples 9, 2, 10). This is because this frequency range matches the viscous flow response time of the grain boundary liquid phase at high temperatures, allowing pressure waves to be effectively transmitted to the particle contact points.

[0196] High-frequency failure: When the frequency was increased to 5Hz (Comparative Example 6), the performance showed a significant degradation (the flexural strength dropped to 874MPa). This is because the frequency was too high, exceeding the rheological response limit of the liquid phase, resulting in lag or uneven pressure transmission, and failing to effectively promote combustion. This confirms the scientific validity of the 1~3Hz low-frequency oscillation selected in this application.

[0197] (4) As shown in Table 4, when the CoSi2 content is within the range specified in this application (0wt% to 4.5wt%), the volume resistivity decreases slightly with the increase of toughening agent content, but remains at 10 Ω·cm. 15 The order of magnitude is Ω·m. Compared to the control group (Comparative Example 10, 4.73 × 10⁻⁶), the result is on the order of Ω·m. 15 Ω·m) and the optimal enhancement group (Example 1, 3.78 × 10 15 (Ω·m), the resistivity did not undergo an order-of-magnitude jump and is still far higher than the insulation requirements of electronic packaging substrates (>10 Ω·m). 14 (Ω·m). This is because within this content range, CoSi2 particles are isolated and dispersed in the silicon nitride matrix, failing to form a continuous conductive path; at this time, current transmission is mainly limited by the potential barrier of the insulating matrix, and even if there is a tunneling effect at the micro level, the macroscopic resistivity is still extremely high.

[0198] However, as shown in Comparative Example 7, when the CoSi2 content was further increased to 5.5 wt%, the volume resistivity showed a significant decrease (although it still possessed some insulation properties, it decreased by an order of magnitude compared to the low-content sample). This indicates that when the conductive phase content exceeds a certain threshold (percolation threshold), isolated CoSi2 particles begin to overlap or their spacing shortens to a point sufficient to form a local conductive network, thereby impairing the insulation properties of the material.

[0199] Therefore, this application strictly limits the amount of CoSi2 added to between 0.5wt% and 4.5wt%, not only to obtain excellent mechanical properties, but also to achieve the best balance between "high strength and toughness" and "high insulation" to ensure the safety of the product in the field of power semiconductor applications.

[0200] (5) Analysis of the influence of oscillating pressure sintering on microstructure and grain growth: To investigate the microscopic mechanism by which oscillating pressure sintering (OPS) improves material properties, XRD phase analysis and SEM micromorphology observation were performed on samples before and after sintering.

[0201] like Figure 2 As shown, comparing the XRD patterns before and after sintering, it can be seen that after sintering at 1750℃, the α-Si3N4 phase in the raw material has been completely transformed into the β-Si3N4 phase, and no other impurity phases have appeared, indicating that the sintering reaction has been carried out very thoroughly.

[0202] Further comparison of the microstructure under different sintering processes. Figure 3 SEM cross-sectional images of gas pressure sintering (GPS, Comparative Example 2) and oscillating pressure sintering (OPS, Example 2) are shown. Figure 3 As shown in (a), the sample prepared using the traditional GPS process has limited grain development and fewer long columnar grains; while... Figure 3 As shown in (b), the sample prepared using the OPS process of this application exhibits a very prominent long rod-like structure in its internal β-Si3N4 grains, and the grains are intertwined and tightly interlocked, forming a skeleton structure similar to "self-toughening".

[0203] To quantify this difference, a statistical analysis was performed on the β-Si3N4 grain size under the two processes, and the results are as follows: Figure 4 As shown in the figure. Statistical data shows that the diameter of silicon nitride grains prepared by the GPS process is mainly distributed in the range of 0.2μm to 0.7μm, and the length is distributed in the range of 0.7μm to 2.5μm; while the grain diameter prepared by the OPS process increases to 0.4μm to 1.2μm, and the length increases significantly to 2.2μm to 5.0μm.

[0204] Mechanistic analysis suggests that the growth of β-Si3N4 grains is controlled by a diffusion mechanism. Compared to the constant pressure in the GPS process, the oscillating pressure introduced by the OPS process alters the sintering driving force, significantly increasing the mass transport rate at grain boundaries. This dynamic pressure field accelerates the dissolution of α-Si3N4 and the diffusion of Si and N atoms, thereby promoting rapid anisotropic growth of β-phase grains along their long axis, ultimately forming coarse columnar crystals with a higher aspect ratio. The pull-out of these high aspect ratio grains requires more energy, thus significantly improving the material's fracture toughness and flexural strength.

[0205] (6) Analysis of the toughening mechanism of toughening agent CoSi2: In this application, the flexural strength of the material increased significantly from 859 MPa (Example 1) to 1036 MPa (Example 2) after adding an appropriate amount of CoSi2. The strengthening mechanism can be attributed to the synergistic effect of "residual stress field enhancement" and "physical resistance".

[0206] First, from a thermodynamic perspective, the coefficient of thermal expansion of CoSi2 is approximately 10.14 × 10⁻⁶. -6The coefficient of thermal expansion of the matrix β-Si3N4 (approximately 3.2 × 10⁻⁶ K) is similar to that of the matrix β-Si3N4. -6 There are significant differences between the two phases ( / K). During the cooling process after high-temperature sintering, due to the different shrinkage rates of the two phases, the dispersed CoSi2 particles are physically constrained by the matrix, thereby inducing a microscopic residual compressive stress field at the interface between the two phases.

[0207] The existence of this residual stress field is confirmed by both macroscopic mechanical properties and microscopic crack propagation behavior: Macroscopic performance confirms this: As shown in Table 1, based on grain size optimization (OPS process), the flexural strength of the substrate was improved by nearly 20% simply by introducing 2.0 wt% CoSi2. This nonlinear strength gain indirectly confirms the existence of an internal stress mechanism (i.e., residual compressive stress field) that can effectively counteract the applied tensile stress.

[0208] Microscopic crack behavior confirms this: such as Figure 5 As shown in the SEM image of the indentation crack propagation, the crack does not directly pass through the CoSi2 particles during its propagation path. Instead, it undergoes significant deflection and bridging upon encountering the particles (or the stress field region surrounding them). This is a typical characteristic of the interaction between the crack tip and the residual compressive stress field: the compressive stress field exerts a "pinning" effect on the crack tip, forcing the crack to change direction and seek a propagation path with higher energy consumption, thereby significantly improving the fracture toughness of the material.

[0209] In summary, the introduction of CoSi2 successfully constructed a composite toughening system of "stress field toughening + particle dispersion toughening", which is the key internal factor for achieving ultra-high strength in this application.

[0210] (7) Analysis of the particle size effect of toughening agent CoSi2: This test further investigated the effect of CoSi2 on the properties of silicon nitride ceramics at three scales: micrometer, submicrometer, and nanometer.

[0211] Three different CoSi2 powders with different particle sizes were selected for preparation in the experiment (other process parameters were kept the same as in Example 2), and the test results are shown in Table 5 below: Table 5. Effect of different CoSi2 particle sizes on mechanical properties

[0212] Mechanism analysis: Based on the data in Table 5 and the microstructure analysis, it can be seen that the particle size of CoSi2 directly determines its dispersion state in the matrix and the quality of interfacial bonding, thus determining the final toughening effect. The optimal effect of submicron (0.5 μm) particle size: As shown in Example 2, when the particle size is controlled at around 0.5 μm, the CoSi2 particles match the grain size of the silicon nitride matrix, achieving highly uniform dispersion and forming a strong interfacial bond with the matrix. This state is most conducive to inducing crack deflection and pinning effects, thereby obtaining the highest flexural strength (1036 MPa).

[0213] Micrometer-scale (40 μm) defect effects: As shown in Comparative Example 8, when the particles are too large, the huge CoSi2 particles not only fail to effectively prevent the formation of microcracks, but also become stress concentration points (flaws) inside the material. In addition, the interfacial bonding between large particles and the matrix is ​​weak, and cracks tend to propagate directly around or through the interface, resulting in a significant reduction in strength (down to 824 MPa).

[0214] Nanoscale (50 nm) agglomeration effect: As shown in Comparative Example 9, although nanoparticles theoretically have better toughening potential, in actual preparation, 50 nm CoSi2 particles are prone to agglomeration. After sintering, the agglomerates not only fail to exert a nano-toughening effect, but also form low-density defect regions, significantly reducing the material's density and mechanical properties (785 MPa). Furthermore, the high specific surface area of ​​the nanoparticles may introduce more impurities, affecting insulation.

[0215] In summary, this application explicitly prefers the direct introduction of submicron (0.1~1.0μm) CoSi2 powder, as this scale is a key window for balancing dispersibility, interfacial bonding, and toughening efficiency.

[0216] In summary, this application successfully prepared a silicon nitride ceramic substrate with both high strength and high thermal conductivity by employing an "oscillating pressure sintering (OPS) process" combined with a "submicron-sized CoSi2 toughening agent." Experimental data and microscopic mechanism analysis show that: First, the OPS process with specific parameters (amplitude ±1~3MPa, frequency 1~3Hz) alters the sintering driving force, significantly promoting the anisotropic growth and interlocking of β-Si3N4 grains, laying the foundation for a high-strength framework; Second, the introduction of an appropriate amount (0.5wt%~4.5wt%) of CoSi2 particles with a matching particle size (~0.5μm) utilizes the mismatch in their thermal expansion coefficients with the matrix to construct a microscopic residual compressive stress field, inducing crack deflection and pinning, achieving significant synergistic toughening; Simultaneously, strict control of composition and particle size effectively avoids the degradation of insulation performance (volume resistivity maintained at 10 Ω·cm). 14 The technology addresses the challenges of achieving optimal mechanical properties (above Ω·m) and microscopic defects. Ultimately, this solution effectively solves the technical problem of traditional silicon nitride materials struggling to balance thermal and electrical properties while pursuing ultimate mechanical performance, resulting in a power electronic packaging substrate with a bending strength exceeding 1000 MPa and excellent thermal conductivity.

[0217] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-strength and high-toughness silicon nitride ceramic substrate, characterized in that, include: A ceramic green body was prepared by mixing α-Si3N4 powder, sintering aid and toughening agent CoSi2. The ceramic green body is sintered using an oscillating pressure sintering process, which includes: applying a constant static pressure during the sintering and holding stage, and superimposing a periodically changing dynamic pressure on the static pressure; wherein the amplitude of the dynamic pressure is ±1MPa to ±3MPa, and the oscillation frequency is 1Hz to 3Hz.

2. The method for preparing a high-strength and tough silicon nitride ceramic substrate as described in claim 1, characterized in that, Based on the powder mixture formed by mixing α-Si3N4 powder, sintering aid and toughening agent CoSi2 as 100%, the amount of toughening agent CoSi2 added is 0.5wt% to 4.5wt% of the total mass of the powder mixture.

3. The method for preparing a high-strength and tough silicon nitride ceramic substrate as described in claim 2, characterized in that, The toughening agent CoSi2 is added at an amount of 1.0 wt% to 3.0 wt% of the total mass of the powder mixture; and / or, The toughening agent CoSi2 has an average particle size of 0.1 μm to 1.0 μm; and / or, The sintering aids include MgO and Y2O3.

4. The method for preparing a high-strength and tough silicon nitride ceramic substrate as described in claim 3, characterized in that... The components in the powder mixture, by mass percentage, include: α-Si3N4 powder, 88.0wt%~92.0wt%; 1.0wt%~3.0wt% MgO; 3.0wt%~7.0wt% Y2O3; And the balance is CoSi2.

5. The method for preparing a high-strength and tough silicon nitride ceramic substrate as described in claim 1, characterized in that, The sintering temperature of the oscillating pressure sintering process is 1740℃~1760℃; and / or, The static pressure of the oscillating pressure sintering process is 25 MPa; and / or, The dynamic pressure variation curve of the oscillating pressure sintering process is a sinusoidal waveform; and / or, The oscillating pressure sintering process also includes a cooling and depressurization step as follows: after the sintering and heat preservation is completed, the dynamic pressure is removed, the temperature is reduced at a rate of 7℃ / min to 9℃ / min, and the static pressure is maintained until the temperature drops to 1000℃ and the pressure is unloaded. And / or, The method for preparing the ceramic blank includes: using the α-Si3N4 powder, the sintering aid and toughening agent CoSi2 as raw material powders, adding organic solvent, dispersant and binder for ball milling and mixing to obtain a casting slurry; casting the casting slurry into shape, drying, cutting and stacking hot pressing, and then placing it in a warm isostatic press for processing.

6. The method for preparing a high-strength and tough silicon nitride ceramic substrate as described in claim 5, characterized in that, The temperature of the isostatic press is 65℃~75℃; and / or, The holding time of the isostatic press is not less than 10 minutes; and / or, The cast slurry, based on a total mass of 100%, comprises the following components by mass fraction: 55%~60% of the raw material powder; 8%~12% anhydrous ethanol; 10%~14% polyvinyl butyral; 8%~12% dibutyl phthalate; 8%~12% triethyl phosphate.

7. The method for preparing a high-strength and tough silicon nitride ceramic substrate as described in claim 5, characterized in that, The ball milling mixture uses silicon nitride balls as the grinding medium; and / or... Before preparing a ceramic green body by mixing α-Si3N4 powder, sintering aid and toughening agent CoSi2, the following pre-drying step is also included: placing the α-Si3N4 powder, the sintering aid and toughening agent CoSi2 in an oven for heat preservation treatment; And / or, The casting slurry also undergoes sieving before casting.

8. The method for preparing a high-strength and tough silicon nitride ceramic substrate as described in claim 7, characterized in that, The silicon nitride spheres are composed of a mixture of large, medium, and small spheres; wherein the diameter of the large spheres is 5 mm, the diameter of the medium spheres is 3 mm, and the diameter of the small spheres is 1 mm; the mass ratio of the large, medium, and small spheres is 3:2:1; and / or, The temperature for the heat preservation treatment is 115℃~125℃; and / or, The heat preservation treatment time is 100 min to 140 min; and / or, The sieving process uses a mesh size of 350-450 mesh; and / or, The process parameters for tape casting include: the height of the scraper at the feed inlet of the tape casting machine is 18μm~22μm; and / or, the tape casting speed is 2.5m / min~3.5m / min; and / or, the drying temperature is 55℃~65℃.

9. A high-strength and high-toughness silicon nitride ceramic substrate, characterized in that, It is prepared by the method for preparing high-strength and tough silicon nitride ceramic substrate according to any one of claims 1-8.

10. The high-strength and high-toughness silicon nitride ceramic substrate as described in claim 9, characterized in that, The high-strength and tough silicon nitride ceramic substrate has a bending strength of not less than 850 MPa; and / or, The thermal conductivity of the high-strength and tough silicon nitride ceramic substrate is not less than 85 W / (m). K); and / or, The thermal conductivity of the high-strength and tough silicon nitride ceramic substrate is not less than 90 W / (m). K).

11. A power semiconductor module, characterized in that, Including the high-strength and tough silicon nitride ceramic substrate as described in claim 9 or 10.

12. An electric vehicle, characterized in that, Includes the power semiconductor module as described in claim 11.

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