Preparation method of Si3N4-C composite reinforced aluminum nitride ceramic substrate

Abstract

This invention discloses a method for preparing a Si3N4-C composite-enhanced aluminum nitride ceramic substrate, belonging to the field of ceramic substrate material technology. The method involves first dispersing carbon material in a dispersion medium, then adding silicon nitride nanoparticles for mixing. This allows the silicon nitride nanoparticles to uniformly adhere to and coat the surface of the carbon material, forming a core-shell structured composite powder with carbon material as the core and silicon nitride as the shell. The core-shell structured composite powder is then mixed with aluminum nitride powder to obtain a composite slurry, which is then formed, degreased, and sintered to obtain the ceramic substrate. The mass percentage of carbon material in the core-shell structured composite powder is 1–8 wt%, and the mass ratio of silicon nitride to carbon material is 1:1–5:1. This invention solves the problems of uneven carbon material dispersion and weak interfacial bonding through the core-shell structure design. The silicon nitride shell not only isolates the carbon material to prevent agglomeration but also acts as an interfacial transition layer to strengthen the bond between the carbon material and the AlN matrix, while simultaneously exerting a synergistic strengthening and toughening effect. The resulting substrate possesses both high thermal conductivity and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of ceramic substrate materials technology, specifically to a method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate. Background Technology

[0002] Aluminum nitride (AlN) ceramics are widely used as packaging substrates and heat dissipation substrates for high-power electronic devices due to their high thermal conductivity, good electrical insulation, and thermal expansion coefficient that matches that of silicon. However, the inherent brittleness, low fracture toughness, and bending strength of aluminum nitride ceramics make it difficult to meet the increasingly demanding application requirements, limiting their application in scenarios requiring higher reliability.

[0003] To improve the mechanical properties of aluminum nitride ceramics, existing technologies have included introducing silicon nitride (Si3N4) as a second phase into the aluminum nitride matrix. Silicon nitride possesses high strength and toughness, and its mechanical properties can be improved to some extent through particle dispersion or whisker toughening. Additionally, there are reports of introducing carbon materials (such as graphite and carbon black) as additive phases into the ceramic matrix to improve its electrical conductivity or tribological properties. However, excessive addition of silicon nitride significantly reduces the overall thermal conductivity of the composite ceramic, failing to simultaneously meet the requirements of high strength and high thermal conductivity. While small amounts of carbon materials can improve the thermal conductivity and strength of the composite ceramic, the poor wettability of carbon materials with the AlN matrix leads to agglomeration, and they are easily oxidized during high-temperature sintering, resulting in weak interfacial bonding and limited reinforcing effect. Furthermore, existing technologies that simply mechanically mix carbon materials with silicon nitride and aluminum nitride powders struggle to achieve uniform dispersion of carbon materials in the matrix, and the weak interfacial bonding between carbon materials and the ceramic matrix easily creates stress concentration points and thermally resistive interfaces, making it difficult to simultaneously achieve optimal mechanical and thermal conductivity properties in the composite material. Existing technologies do not involve structural design of carbon material surfaces to optimize interfacial bonding, nor do they address the key issues of carbon material dispersion and interfacial control.

[0004] Therefore, developing a preparation method that can simultaneously improve the mechanical and thermal properties of aluminum nitride ceramic substrates, and achieve uniform carbon material dispersion and good interfacial bonding, has significant application value. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing Si3N4-C composite-enhanced aluminum nitride ceramic substrates. This method achieves uniform dispersion and strong interfacial bonding of carbon materials in the aluminum nitride matrix by constructing a silicon nitride core-shell structure on the surface of carbon materials, thereby simultaneously improving the bending strength, fracture toughness and thermal conductivity of the ceramic substrate.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate, comprising the following steps: Carbon material is dispersed in a dispersion medium, and silicon nitride nanoparticles are added for the first mixing, so that the silicon nitride nanoparticles are uniformly attached to and coated on the surface of the carbon material, forming a core-shell structured composite powder with carbon material as the core and silicon nitride as the shell. The core-shell structured composite powder is mixed with aluminum nitride powder to obtain a composite slurry; The composite slurry is molded, degreased, and sintered to obtain the ceramic substrate; The carbon material is graphene or carbon nanotubes, and the mass percentage of carbon material in the core-shell composite powder is 1-8 wt%, while the mass ratio of silicon nitride to carbon material is 1:1-5:1.

[0007] This invention, by pre-constructing a composite powder with a carbon core and a silicon nitride shell, and then introducing it into an aluminum nitride matrix, offers the following advantages: First, the silicon nitride shell effectively isolates the carbon material, preventing its agglomeration during subsequent slurry preparation and ensuring uniform dispersion of the carbon material. Second, the silicon nitride shell serves as an interfacial transition layer between the carbon material and the AlN matrix, preventing harmful interfacial reactions between the carbon material and AlN at high temperatures, and achieving strong interfacial bonding through the good chemical compatibility of Si3N4 and AlN, effectively transferring loads. Third, the core-shell structure within the matrix simultaneously exerts the pull-out and bridging toughening effects of the carbon material, as well as the crack deflection and pinning effects of silicon nitride, resulting in a significant synergistic strengthening and toughening effect. By controlling the carbon material content and the ratio of silicon nitride to carbon, the bending strength and fracture toughness of the substrate can be significantly improved while maintaining high thermal conductivity.

[0008] Preferably, the core-shell composite powder is formed by dispersing carbon material in a precursor solution containing a silicon source, forming a SiO2 gel layer on the surface of the carbon material through sol-gel treatment, and then nitriding at 800–1200°C under an ammonia atmosphere to convert SiO2 into a Si3N4 shell with a shell thickness of 10–200 nm. In the core-shell composite powder, the silicon nitride shell and the carbon material core are bonded by Si-C chemical bonds. By combining the sol-gel method with carbothermal nitriding, a dense and uniform Si3N4 shell with controllable thickness can be grown in situ on the surface of the carbon material, and Si-C chemical bonds are formed between the shell and the carbon core, which significantly enhances the bonding strength of the core-shell interface, facilitates efficient load transfer from the matrix to the reinforcement, and further optimizes the reinforcement effect.

[0009] Preferably, the first mixing employs an ultrasonic-assisted chemical coating method, with an ultrasonic power of 200–600 W and a processing time of 1–6 h, to uniformly adhere Si3N4 nanoparticles to the surface of the carbon material, achieving an adhesion coverage rate of 60%–95%. The ultrasonic-assisted process effectively overcomes the van der Waals forces between the carbon material and the silicon nitride nanoparticles, achieving high coverage and uniform coating without damaging the carbon material structure. The process is simple and highly controllable.

[0010] Preferably, a sintering aid is added to the second mixture. The sintering aid includes at least two combinations selected from Y₂O₃, MgO, Li₂O, and CaO, with a total addition amount of 2–6 wt% of the total mass of AlN and Si₃N₄. When the sintering aid includes both Y₂O₃ and MgO, their mass ratio is 2:1 to 4:1. Using a multi-component composite sintering aid system can form a low-temperature liquid phase, promoting the densification process. Simultaneously, through optimization of the liquid phase composition, a high thermal conductivity phase is formed at the grain boundaries, balancing densification and the maintenance of thermal conductivity.

[0011] Preferably, the sintering is performed using hot pressing or spark plasma sintering, employing a two-step sintering process: the first step involves holding at 1500–1650℃ and 20–50 MPa for 10–30 min; the second step involves holding at 1700–1850℃ and atmospheric pressure for 1–3 h. In the first step of the two-step sintering process, the low-temperature pressurization quickly eliminates most of the porosity, achieving preliminary densification and inhibiting abnormal grain growth; the second step, holding at atmospheric pressure and high temperature, further eliminates residual porosity through liquid phase rearrangement, perfecting the grain boundary structure, thereby obtaining a nearly completely dense microstructure with fine grains, which is beneficial for the simultaneous improvement of thermal conductivity and mechanical properties.

[0012] Preferably, the carbon material is a carboxyl-modified multi-walled carbon nanotube with a carboxyl content of 2–8 at%, a diameter of 10–30 nm, and a length of 1–20 μm. Carboxylation modification can introduce oxygen-containing functional groups onto the surface of carbon nanotubes, significantly improving their wettability and dispersibility in the dispersion medium. It also provides more active sites for subsequent attachment or in-situ growth of silicon nitride, which is beneficial for improving the integrity and uniformity of the shell.

[0013] Preferably, the degreasing treatment is carried out in an H2 / N2 mixed atmosphere, with H2 accounting for 5% to 20% of the volume, a degreasing temperature of 400 to 700°C, a heating rate of 0.5 to 2°C / min, and a holding time of 2 to 8 hours. The carbon material retention rate after degreasing is not less than 80%. Using a hydrogen-containing mixed atmosphere can effectively suppress the oxidation and burn-off of carbon materials during the degreasing process, ensure the content of the structural reinforcing phase, and thus ensure the mechanical strengthening effect of the final substrate.

[0014] Preferably, the aluminum nitride powder has a particle size D50 of 1–5 μm and an oxygen content ≤0.8 wt%; the silicon nitride powder is α-Si3N4 with a particle size D50 of 0.2–1.5 μm and an α-phase content ≥85%. The low oxygen content of the aluminum nitride powder helps to suppress the influence of AlN lattice oxygen defects on phonon scattering, ensuring high thermal conductivity of the substrate; the use of silicon nitride powder with high α-phase content and small particle size helps to promote phase transformation and densification during sintering, while obtaining a more uniform and fine microstructure.

[0015] Preferably, the molding process employs one of the following: casting, dry pressing, or cold isostatic pressing. This allows for flexible selection based on the thickness, size, and shape requirements of the target substrate, providing strong process adaptability.

[0016] Preferably, the obtained Si3N4-C composite reinforced aluminum nitride ceramic substrate has a relative density ≥98%, thermal conductivity ≥130 W / (m·K), flexural strength ≥500 MPa, and fracture toughness ≥6.0 MPa·m. 1 / 2 The dielectric constant is ≤9.2@1MHz, the dielectric loss is ≤0.002@1MHz, and compared with the control sample prepared by simple mixing of the same components, the flexural strength is increased by ≥20% and the fracture toughness is increased by ≥30%. The preparation method provided by this invention can endow AlN ceramics with significantly improved mechanical properties while maintaining their excellent thermal conductivity and dielectric properties.

[0017] Compared with existing technologies, the preparation method of this Si3N4-C composite-enhanced aluminum nitride ceramic substrate has the following advantages: 1. Core-shell structure design for optimized interface bonding: A silicon nitride shell is coated on the surface of carbon material through a core-shell structure design to form a core-shell composite powder. Silicon nitride is used as an intermediate transition layer to improve the physicochemical compatibility between carbon material and aluminum nitride matrix. At the same time, it effectively prevents the oxidation of carbon material during high-temperature sintering. Furthermore, the carbon core and silicon nitride shell are bonded by Si-C chemical bonds, resulting in high interface bonding strength and effectively avoiding carbon material agglomeration and interface debonding problems.

[0018] 2. Combining high thermal conductivity and high strength and toughness: The aluminum nitride matrix and carbon material core provide a continuous high thermal conductivity pathway, significantly improving the thermal conductivity of the composite ceramic. Simultaneously, the core-shell structure of the carbon material plays a toughening role, and the Si3N4 shell has good compatibility with the AlN matrix, effectively enhancing the strength and toughness of the composite ceramic. Through synergistic effects, the bottleneck of the incompatibility between strength and thermal conductivity of a single reinforcing phase is overcome, achieving a synergistic improvement in performance.

[0019] 3. Uniform dispersion of carbon materials: Silicon nitride nanoparticles are pre-attached to the surface of carbon materials by ultrasonic-assisted chemical coating to form a core-shell structure. After this process, the surface properties of the carbon materials are transformed into a ceramic-friendly surface similar to silicon nitride, making it easy to disperse uniformly when mixed with aluminum nitride powder in the future, thus avoiding the agglomeration problem when directly mixed.

[0020] 4. Excellent process controllability: By adjusting the mass ratio of carbon materials to silicon nitride, shell thickness, type and content of sintering aids, and sintering process parameters, the microstructure and properties of the composite ceramic substrate can be flexibly adjusted to meet the needs of different application scenarios. The ultrasonic-assisted chemical coating method and sol-gel nitriding method used in this invention have easily controllable process parameters, making them suitable for large-scale industrial production.

[0021] 5. Two-step sintering process optimization: A two-step process is adopted, which combines hot pressing sintering or spark plasma sintering. The first step is to apply pressure at a lower temperature to achieve rapid densification. The second step is to hold at a higher temperature and normal pressure to regulate the grain boundary phase and carbon material structure. This ensures high density and avoids performance degradation caused by over-sintering. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the preparation method of the Si3N4-C composite enhanced aluminum nitride ceramic substrate of the present invention; Figure 2 This is a schematic diagram summarizing the test results of various embodiments and comparative examples of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Please see Figure 1-2 The present invention provides the following technical solutions: Example 1

[0025] This embodiment provides a method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate, the specific steps of which are as follows: (1) Preparation of core-shell composite powder: Carboxyl-modified multi-walled carbon nanotubes (MWCNTs) with a carboxyl content of 5 at% and a diameter of 15–25 nm and a length of 5–15 μm were selected as the carbon material. 0.5 g of carboxyl-modified MWCNTs were added to 200 mL of anhydrous ethanol and ultrasonically dispersed for 2 h at 400 W to obtain a uniform carbon material dispersion. Subsequently, 1.5 g of α-Si3N4 nanoparticles (D50 0.5 μm, α-phase content 90%) were added to the dispersion, and the mixture was further treated with ultrasonic power at 400 W for 4 h to ensure uniform adhesion and coating of Si3N4 nanoparticles onto the surface of the carbon nanotubes, achieving an adhesion coverage rate of 82%. After filtration, washing, and drying, a core-shell composite powder with a carbon nanotube core and a silicon nitride shell was obtained, with a silicon nitride to carbon material mass ratio of 3:1.

[0026] (2) Preparation of composite slurry: The core-shell composite powder obtained in step (1) and aluminum nitride powder (D50 of 2.5 μm and oxygen content of 0.6 wt%) were weighed and mixed at a ratio of 6 wt% of the composite powder to the total mass of the mixed powder. The mass percentage of carbon material in the core-shell composite powder was 1.5 wt%. Sintering aids Y2O3 and MgO were added at a mass ratio of 3:1, with a total addition amount of 4 wt% of the total mass of AlN and Si3N4. The above powder was added to anhydrous ethanol and ball-milled at 200 rpm for 12 h in a planetary ball mill to obtain a uniform composite slurry.

[0027] (3) Molding: The composite slurry obtained in step (2) is dried by rotary evaporation at 60°C, then passed through a 100-mesh sieve and pressed into shape under a pressure of 15MPa using a dry pressing method to obtain a ceramic substrate blank.

[0028] (4) Defatting: The green blank obtained in step (3) was placed in a tube furnace for degreasing. The degreasing atmosphere was a H2 / N2 mixed atmosphere, in which the volume percentage of H2 was 10%. The temperature was increased to 550℃ at a heating rate of 1℃ / min and held for 4 hours. The carbon material retention rate after degreasing was found to be 89%.

[0029] (5) Sintering: The degreased green blank was placed in a hot-press sintering furnace for sintering using a two-step sintering process: the first step was to hold at 1600℃ and 30MPa for 20 minutes; the second step was to raise the temperature to 1800℃ and hold at atmospheric pressure for 2 hours. The entire sintering process was carried out under a nitrogen atmosphere. After sintering, the blank was cooled to room temperature with the furnace, and then cut, ground, and polished to obtain a Si3N4-C composite reinforced aluminum nitride ceramic substrate.

[0030] The performance test results of the ceramic substrate obtained in this embodiment are as follows: relative density 99.1%, thermal conductivity 148 W / (m·K), flexural strength 545 MPa, and fracture toughness 6.6 MPa·m. 1 / 2 Dielectric constant 8.7@1MHz, dielectric loss 0.0015@1MHz. Example 2

[0031] This embodiment provides a method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate, the specific steps of which are as follows: (1) Preparation of core-shell composite powder: Graphene was selected as the carbon material. 0.3 g of graphene was added to 200 mL of deionized water and ultrasonically dispersed for 1.5 h at 500 W to obtain a graphene dispersion. Then, 0.9 g of α-Si3N4 nanoparticles (D50 0.8 μm, α-phase content 88%) were added to the dispersion, and the mixture was further treated with ultrasonic power at 500 W for 3 h to ensure uniform adhesion of Si3N4 nanoparticles to the graphene surface, achieving an adhesion coverage of 75%. After filtration, washing, and drying, a core-shell composite powder with graphene as the core and silicon nitride as the shell was obtained, with a silicon nitride to carbon material mass ratio of 3:1.

[0032] (2) Preparation of composite slurry: The core-shell composite powder obtained in step (1) was mixed with aluminum nitride powder (D50 of 3 μm and oxygen content of 0.5 wt%) in a certain proportion, and the mass percentage of carbon material in the core-shell composite powder was 1.0 wt%. Sintering aids Li2O and Y2O3 were added at the same time, with a mass ratio of 1:2, and the total addition amount was 3 wt% of the total mass of AlN and Si3N4. The above powder was added to anhydrous ethanol and ball-milled for 10 h to obtain a uniform composite slurry.

[0033] (3) Molding: After drying and granulation, the composite slurry obtained in step (2) is formed under a pressure of 200 MPa by cold isostatic pressing to obtain a ceramic substrate blank.

[0034] (4) Defatting: The green blank obtained in step (3) was degreased in a mixed H2 / N2 atmosphere with H2 accounting for 15% of the volume. The temperature was increased to 600℃ at a rate of 0.8℃ / min and held for 6 hours. The carbon material retention rate after degreasing was found to be 91%.

[0035] (5) Sintering: The degreased green body was sintered using spark plasma sintering (SPS) in two steps: first, the body was held at 1550℃ and 40MPa for 15 minutes; second, the temperature was raised to 1750℃ and held at atmospheric pressure for 2.5 hours. After sintering, the green body was cooled and then processed to obtain the ceramic substrate.

[0036] The performance test results of the ceramic substrate obtained in this embodiment are as follows: relative density 98.8%, thermal conductivity 139 W / (m·K), flexural strength 528 MPa, and fracture toughness 6.3 MPa·m. 1 / 2 Dielectric constant 9.0@1MHz, dielectric loss 0.0018@1MHz. Example 3

[0037] This embodiment provides a method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate, the specific steps of which are as follows: (1) Preparation of core-shell composite powder: A sol-gel combined nitriding method was employed. Carboxyl-modified multi-walled carbon nanotubes (MWCNTs) with a carboxyl content of 6 at% and a diameter of 10–20 nm and a length of 8–18 μm were selected as the carbon material. 0.8 g of carboxyl-modified MCCNTs were dispersed in 200 mL of a mixture of anhydrous ethanol and deionized water (volume ratio 1:1) and ultrasonically dispersed for 1 h. Tetraethyl orthosilicate (TEOS) was then added as a silicon source, and the pH was adjusted to 9–10 with ammonia. The mixture was stirred in a 60 °C water bath for 6 h, allowing TEOS to hydrolyze and condense on the surface of the carbon nanotubes to form a SiO2 sol. After aging and drying, carbon nanotubes with a SiO2 gel layer were obtained. The powder was then placed in a tube furnace and nitrided at 1000 °C for 4 h under an ammonia atmosphere to convert SiO2 into a Si3N4 shell with a thickness of approximately 80 nm. In the obtained core-shell composite powder, the silicon nitride shell and the carbon nanotube core are bonded by Si-C chemical bonds, and the mass ratio of silicon nitride to carbon material is 4:1.

[0038] (2) Preparation of composite slurry: The core-shell composite powder obtained in step (1) was mixed with aluminum nitride powder (D50 of 2 μm and oxygen content of 0.7 wt%) in a certain proportion, and the mass percentage of carbon material in the core-shell composite powder was 2.0 wt%. Sintering aids Y2O3, MgO and CaO were added at the same time in a mass ratio of 5:2:1, and the total amount added was 5 wt% of the total mass of AlN and Si3N4. The above powder was added to a mixed solvent of toluene and ethanol and ball-milled for 16 h to obtain a uniform composite slurry.

[0039] (3) Molding: After adding the composite slurry obtained in step (2) to the binder and plasticizer, a cast film with a thickness of 0.8 mm is obtained by casting molding. After lamination and isostatic pressing, a ceramic substrate blank is obtained.

[0040] (4) Defatting: The green blank obtained in step (3) was degreased in a mixed atmosphere of H2 / N2 with H2 accounting for 8% of the volume. The temperature was increased in stages: first, the temperature was increased to 350℃ at 1.5℃ / min and held for 2 hours, and then increased to 650℃ at 0.5℃ / min and held for 5 hours. The carbon material retention rate after degreasing was found to be 86%.

[0041] (5) Sintering: The degreased green blank was placed in a hot pressing sintering furnace, and the two-step sintering process was as follows: the first step was to hold at 1620℃ and 35MPa for 25 minutes; the second step was to raise the temperature to 1820℃ and hold at normal pressure for 1.5 hours. After sintering, the ceramic substrate was obtained by cutting, grinding and polishing.

[0042] The performance test results of the ceramic substrate obtained in this embodiment are as follows: relative density 99.3%, thermal conductivity 152 W / (m·K), flexural strength 568 MPa, and fracture toughness 7.1 MPa·m. 1 / 2 Dielectric constant 8.5@1MHz, dielectric loss 0.0013@1MHz. Example 4

[0043] The difference between this embodiment and Embodiment 1 is that: in step (1), the mass ratio of silicon nitride to carbon material is 1:1, that is, 0.5g of α-Si3N4 nanoparticles are added, and the adhesion coverage rate is 65%. In step (2), the mass percentage of carbon material in the core-shell composite powder is 3.0wt%. The sintering aids are Y2O3 and Li2O, with a mass ratio of 3:1 and a total addition amount of 6wt%. The remaining steps and parameters are the same as in Embodiment 1.

[0044] The performance test results of the ceramic substrate obtained in this embodiment are as follows: relative density 98.3%, thermal conductivity 135 W / (m·K), flexural strength 520 MPa, and fracture toughness 6.8 MPa·m. 1 / 2 Dielectric constant 9.1@1MHz, dielectric loss 0.0019@1MHz. Example 5

[0045] The difference between this embodiment and Embodiment 1 is that in step (1), the mass ratio of silicon nitride to carbon material is 5:1, that is, 2.5g of α-Si3N4 nanoparticles are added, and the adhesion coverage rate is 92%. In step (5), the first sintering temperature is 1650℃, the pressure is 20MPa, and the holding time is 10min; the second sintering temperature is 1850℃, and the holding time is 1h under normal pressure. The remaining steps and parameters are the same as in Embodiment 1.

[0046] The performance test results of the ceramic substrate obtained in this embodiment are as follows: relative density 99.0%, thermal conductivity 132 W / (m·K), flexural strength 560 MPa, and fracture toughness 6.5 MPa·m. 1 / 2 Dielectric constant 8.8@1MHz, dielectric loss 0.0016@1MHz. Example 6

[0047] The difference between this embodiment and Embodiment 1 is that in step (4) degreasing, the volume percentage of H2 is 5%, the degreasing temperature is 700℃, the heating rate is 2℃ / min, and the holding time is 2h. The carbon material retention rate after degreasing was found to be 81%. The remaining steps and parameters are the same as in Embodiment 1.

[0048] The performance test results of the ceramic substrate obtained in this embodiment are as follows: relative density 98.7%, thermal conductivity 142 W / (m·K), flexural strength 530 MPa, and fracture toughness 6.4 MPa·m. 1 / 2 . Example 7

[0049] The difference between this embodiment and Embodiment 1 is that step (5) uses spark plasma sintering. The first step is to hold the temperature at 1500℃ and 50MPa for 30 minutes; the second step is to hold the temperature at 1700℃ and normal pressure for 3 hours. The remaining steps and parameters are the same as in Embodiment 1.

[0050] The performance test results of the ceramic substrate obtained in this embodiment are as follows: relative density 98.5%, thermal conductivity 136 W / (m·K), flexural strength 510 MPa, and fracture toughness 6.1 MPa·m. 1 / 2 .

[0051] Comparative Example 1 This comparative example uses a traditional mechanical mixing method to prepare composite ceramic substrates. 0.5g of carboxylated multi-walled carbon nanotubes without core-shell structure treatment, 1.5g of α-Si3N4 powder, and aluminum nitride powder were directly ball-milled and mixed in the same proportions as in Example 1, along with the same sintering aids. The remaining molding, debinding, and sintering processes were the same as in Example 1.

[0052] The performance test results of the ceramic substrate obtained in this comparative example are as follows: relative density 96.5%, thermal conductivity 118 W / (m·K), flexural strength 412 MPa, and fracture toughness 4.8 MPa·m. 1 / 2 Compared to Example 1, the flexural strength decreased by 24.4%, and the fracture toughness decreased by 27.3%.

[0053] Comparative Example 2 This comparative example only adds carbon nanotubes without introducing a silicon nitride shell. 0.5g of carboxylated multi-walled carbon nanotubes were directly ball-milled and mixed with aluminum nitride powder and sintering aid. The carbon nanotube content, amount of sintering aid added, molding, degreasing, and sintering processes were all the same as in Example 1.

[0054] The performance test results of the ceramic substrate obtained in this comparative example are as follows: relative density 95.8%, thermal conductivity 108 W / (m·K), flexural strength 385 MPa, and fracture toughness 4.2 MPa·m. 1 / 2 Compared with Example 1, the flexural strength decreased by 29.4% and the fracture toughness decreased by 36.4%.

[0055] Comparative Example 3 This comparative example only adds silicon nitride powder without introducing carbon materials. 1.5g of α-Si3N4 powder was directly ball-milled and mixed with aluminum nitride powder and sintering aid. The molding, debinding, and sintering processes were the same as in Example 1.

[0056] The performance test results of the ceramic substrate obtained in this comparative example are as follows: relative density 97.8%, thermal conductivity 112 W / (m·K), flexural strength 468 MPa, and fracture toughness 5.2 MPa·m. 1 / 2 Compared with Example 1, the flexural strength decreased by 14.1% and the fracture toughness decreased by 21.2%.

[0057] The test results of each embodiment and comparative example are summarized as follows: Figure 2 .

[0058] Depend on Figure 2 Data comparison shows that the Si3N4-C composite reinforced aluminum nitride ceramic substrates prepared in each embodiment of the present invention all have a relative density of over 98%, a thermal conductivity of ≥130 W / (m·K), a flexural strength of ≥500 MPa, and a fracture toughness of ≥6.0 MPa·m. 1 / 2 Compared to the control sample prepared by the simple mixing method in Comparative Example 1, the flexural strength of Example 1 increased by 32.3% and the fracture toughness increased by 37.5%, far exceeding the target of ≥20% increase in flexural strength and ≥30% increase in fracture toughness set by this invention. Comparative Example 2, which only added carbon nanotubes without a silicon nitride shell for protection, had the worst performance; Comparative Example 3, which only added silicon nitride without carbon materials, showed improved mechanical properties but a significant decrease in thermal conductivity. This indicates that this invention, by constructing a core-shell structured composite powder, fully utilizes the synergistic reinforcing and toughening effects of carbon materials and silicon nitride, while ensuring excellent thermal conductivity and dielectric properties.

[0059] Contents not described in detail in this specification are prior art known to those skilled in the art. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate, characterized in that, Includes the following steps: Carbon material is dispersed in a dispersion medium, and silicon nitride nanoparticles are added for the first mixing, so that the silicon nitride nanoparticles are uniformly attached to and coated on the surface of the carbon material, forming a core-shell structured composite powder with carbon material as the core and silicon nitride as the shell. The core-shell structured composite powder is mixed with aluminum nitride powder to obtain a composite slurry; The composite slurry is molded, degreased, and sintered to obtain the ceramic substrate; The carbon material is graphene or carbon nanotubes, and the mass percentage of carbon material in the core-shell composite powder is 1-8 wt%, while the mass ratio of silicon nitride to carbon material is 1:1-5:

1.

2. The method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate according to claim 1, characterized in that: The core-shell composite powder is formed by dispersing carbon material in a precursor solution containing a silicon source, forming a SiO2 gel layer on the surface of the carbon material through sol-gel treatment, and then nitriding at 800-1200℃ under an ammonia atmosphere to convert SiO2 into a Si3N4 shell with a shell thickness of 10-200 nm; in the core-shell composite powder, the silicon nitride shell and the carbon material core are bonded by Si-C chemical bonds.

3. The method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate according to claim 1, characterized in that: The first mixture is prepared by ultrasonic-assisted chemical coating, with an ultrasonic power of 200-600W and a treatment time of 1-6h, so that Si3N4 nanoparticles are uniformly attached to the surface of carbon materials with an attachment coverage rate of 60%-95%.

4. The method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate according to claim 1, characterized in that: The second mixture includes a sintering aid, which includes at least two combinations of Y2O3, MgO, Li2O and CaO, with a total addition amount of 2 to 6 wt% of the total mass of AlN and Si3N4.

5. The method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate according to claim 1, characterized in that: The sintering process employs hot pressing or spark plasma sintering, and involves a two-step sintering process: the first step involves holding the temperature at 1500–1650℃ and 20–50 MPa for 10–30 min; the second step involves holding the temperature at 1700–1850℃ and at normal pressure for 1–3 h.

6. The method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate according to claim 1, characterized in that: The carbon material is a multi-walled carbon nanotube that has undergone carboxylation modification, with a carboxyl content of 2-8 at%, a diameter of 10-30 nm, and a length of 1-20 μm.

7. The method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate according to claim 1, characterized in that: The degreasing treatment is carried out in an H2 / N2 mixed atmosphere, with H2 accounting for 5% to 20% of the volume. The degreasing temperature is 400 to 700°C, the heating rate is 0.5 to 2°C / min, the holding time is 2 to 8 hours, and the carbon material retention rate after degreasing is not less than 80%.

8. The method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate according to claim 1, characterized in that: The aluminum nitride powder has a particle size D50 of 1–5 μm and an oxygen content ≤0.8 wt%; the silicon nitride powder is α-Si3N4 with a particle size D50 of 0.2–1.5 μm and an α phase content ≥85%.

9. The method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate according to claim 1, characterized in that: The molding process employs one of the following: casting, dry pressing, or cold isostatic pressing.

10. The method for preparing a Si3N4-C composite reinforced aluminum nitride ceramic substrate according to claim 1, characterized in that: The obtained Si3N4-C composite reinforced aluminum nitride ceramic substrate has a relative density ≥98%, thermal conductivity ≥130 W / (m·K), flexural strength ≥500 MPa, and fracture toughness ≥6.0 MPa·m. 1 / 2 Dielectric constant ≤ 9.2@1MHz, dielectric loss ≤ 0.002@1MHz.

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