High thermal conductivity silicon nitride ceramic substrate and method of making same

Abstract

The application discloses a high-thermal-conductivity silicon nitride ceramic substrate and a preparation method thereof, and relates to the technical field of silicon nitride ceramics. The application uses glass fibers to replace part of silicon nitride ceramic raw materials, and is compounded with multi-walled carbon nanotubes and silicon nitride seeds. The glass fibers can be used as flux, and the non-silicon dioxide components in the glass fibers can be used as functional additives to further enhance the performance of the ceramic substrate. The multi-walled carbon nanotubes can be used as nucleation sites, and through the reduction performance of carbon, the silicon dioxide in the matrix is reduced, and a silicon carbide transition layer is generated. Then, the mixed material is subjected to shock wave activation treatment, so that the multi-walled carbon nanotubes are converted into crystal forms. Meanwhile, the shock wave forms a high-pressure stress field around the carbon nanotubes, and a large amount of dislocation lines and dislocation line groups are generated in the large-particle silicon nitride powder, so that the mechanical properties are enhanced.

Description

Technical Field

[0001] This invention relates to the field of silicon nitride ceramics technology, specifically to a high thermal conductivity silicon nitride ceramic substrate and its preparation method. Background Technology

[0002] In recent years, semiconductor devices have developed rapidly towards higher power, higher frequency, and greater integration, occupying an increasingly important position in industries such as LED lighting, new energy development, and electric vehicles. Common modular high-power units are composed of several semiconductor devices, such as insulated-gate bipolar transistor (IGBT) modules. These modules mainly consist of three parts: a semiconductor chip at the top, a metallized substrate in the middle, and a heat sink at the bottom. The metallized substrate is the most critical component, and rigid metallized substrates are typically copper-clad laminates. Most of the losses generated by semiconductor devices during operation are converted into heat, making heat a key factor in semiconductor device failure. Statistics show that the thermal failure rate of semiconductor devices is as high as 55%. Therefore, the thermal properties of the non-conductive substrate determine the heat dissipation performance of the semiconductor device; simultaneously, power modules composed of semiconductor devices also require good mechanical properties, as they may be used in environments subject to mechanical vibration and impact.

[0003] High power and the complex mechanical properties of operating environments place extremely stringent demands on the service reliability of packaging materials. Silicon nitride ceramics are the semiconductor insulating substrate material that combines the best heat dissipation performance, reliability, and electrical performance. Silicon nitride ceramic substrates are destined to be the future development trend of ceramic substrates for semiconductor devices and will provide a solid material foundation for the development of third-generation semiconductors. However, silicon nitride ceramics perform poorly under bending stress, which may make them unsuitable for some applications requiring excellent flexural strength, such as in mechanical structures that need to withstand bending stress. During the sintering process, silicon nitride ceramics may develop micropores or cracks on the surface or inside. These defects not only affect the appearance quality of the product but, more importantly, significantly reduce the mechanical properties of the material, thereby affecting the reliability and lifespan of the final product. Therefore, it is particularly necessary to prepare a silicon nitride ceramic with both high thermal conductivity and high mechanical properties. Summary of the Invention

[0004] The purpose of this invention is to provide a high thermal conductivity silicon nitride ceramic substrate and its preparation method, so as to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a silicon nitride ceramic substrate with high thermal conductivity, comprising the following steps: (1) Multi-walled carbon nanotubes and glass fibers were subjected to ultrasonic-assisted ball milling, and then silicon nitride ceramic raw materials and silicon nitride seed crystals were added to obtain composite ceramic raw materials; (2) Argon gas with a flow rate of 5L / min is used to treat the composite ceramic raw material, and then it is mixed with sintering aid and anhydrous ethanol by ball milling. It is dried at 80℃ for 2~4h, placed in a mold and pressed into shape. The loading pressure is 30MPa and the holding time is 2min. Then it is subjected to cold isostatic pressing to eliminate the pressure gradient inside the blank. The pressure is 300MPa. Finally, it is sintered to obtain a high thermal conductivity silicon nitride ceramic substrate.

[0006] Furthermore, in step (1), the mass ratio of the multi-walled carbon nanotubes, glass fibers, silicon nitride ceramic raw materials, and silicon nitride seed crystals is 1~3:5~10:70~80:0.5~2.

[0007] Furthermore, the glass fiber in step (1) is low-sodium glass fiber.

[0008] Furthermore, the silicon nitride seed crystals in step (1) are β-Si3N4 with a particle size of 2~5μm.

[0009] Furthermore, the process parameters for the ultrasonic-assisted ball milling process in step (1) are: ultrasonic frequency of 30~40kHz, milling medium of silicon nitride balls, ball-to-material ratio of 10~20:1, rotation speed of 300~500rpm, and time of 1~3h.

[0010] Furthermore, the process parameters of the shock wave in step (2) are: pressure of 15.7~30.6GPa and pulse frequency of 20~50Hz.

[0011] Furthermore, in step (2), the mass ratio of the composite ceramic raw material, sintering aid, and anhydrous ethanol is 10:0.1~0.6:5~10.

[0012] Furthermore, the sintering aid in step (2) is composed of yttrium oxide, cerium oxide and zirconium nitride in a mass ratio of 2:1:1.

[0013] Furthermore, the process parameters for ball milling in step (2) are as follows: the ball milling medium is silicon nitride balls, the ball-to-material ratio is 2:1, the rotation speed is 200 rpm, and the time is 20~30 h.

[0014] Furthermore, the specific steps of the sintering treatment in step (2) are as follows: first, under the conditions of nitrogen gas at a pressure of 2 MPa and sintering temperature of 1700℃, the temperature is kept for 2 hours, then heated to isostatic pressure, and under the conditions of argon gas at a pressure of 200 MPa and temperature of 1800~2000℃, the temperature is kept for 1 hour.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: This invention utilizes glass fiber to replace part of the silicon nitride ceramic raw material, compounded with multi-walled carbon nanotubes and silicon nitride seed crystals. The glass fiber acts as a flux in the silicon nitride matrix, improving the rheological properties of the silicon nitride slurry through its flexibility, resulting in a cast green body with superior density uniformity compared to a pure silicon nitride system. Furthermore, the non-silica components in the glass fiber can serve as functional additives to further enhance the performance of the ceramic substrate. During sintering, silicon and nitrogen atoms precipitate onto β-Si3N4 nuclei and carbon nanotubes. The precipitation process then generates a self-purification effect, removing impurities and defects. Simultaneously, the multi-walled carbon nanotubes act as nucleation sites, refining the size of the generated β-Si3N4 grains and filling the pores in the matrix. The gaps are filled, which greatly enhances the mechanical and thermal properties of the silicon nitride ceramic substrate. Furthermore, through the reduction properties of carbon, the glass fiber and some of the silicon dioxide in the ceramic raw materials are reduced to form a silicon carbide transition layer, which further enhances the mechanical and thermal properties of the silicon nitride ceramic substrate. Next, the mixed material is subjected to shock wave activation treatment. Under the action of the shock wave, the multi-walled carbon nanotubes are transformed into a crystal form, and the lattice of the tube wall is distorted, providing active sites for subsequent chemical bonding with silicon nitride. The shock wave forms a high-pressure stress field around the carbon nanotubes, and the larger silicon nitride powder particles generate a large number of dislocation lines and dislocation groups, which in turn induce silicon nitride lattice distortion, forming carbon-silicon-nitrogen bonds and enhancing mechanical properties. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] To more clearly illustrate the method provided by the present invention, the following embodiments are provided in detail. The testing methods for various indicators of the high thermal conductivity silicon nitride ceramic substrates fabricated in the following embodiments are as follows: Thermal conductivity: The thermal conductivity of the same size examples and comparative examples was tested using a laser thermal conductivity meter (LFA-427, Laster Flash Thermal Constant Analyzer, Germany).

[0018] Mechanical properties: The bending strength of the same size examples and comparative examples was tested using a universal testing machine by the three-point bending method.

[0019] Example 1 (1) Glass fibers were immersed in a 5wt% hydrogen fluoride solution at a bath ratio of 1:10, sonicated at 21kHz for 30min, and then washed with deionized water until the pH of the washing solution was neutral. The glass fibers were dried at 80℃ for 5h to obtain low-sodium glass fibers. Multi-walled carbon nanotubes and low-sodium glass fibers were subjected to ultrasonic-assisted ball milling with the following process parameters: ultrasonic frequency of 30kHz, milling medium of silicon nitride balls, ball-to-material ratio of 10:1, rotation speed of 300rpm, and time of 1h. Then silicon nitride ceramic raw materials and silicon nitride seed crystals were added to obtain composite ceramic raw materials. The mass ratio of the multi-walled carbon nanotubes, low-sodium glass fibers, silicon nitride ceramic raw materials, and silicon nitride seed crystals was 1:5:70:0.5. The silicon nitride seed crystals were β-Si3N4 with a particle size of 2μm. (2) Argon-protected shock waves with a flow rate of 5 L / min were used to treat the composite ceramic raw materials. The process parameters of the shock waves were: pressure of 15.7 GPa and pulse frequency of 20 Hz. The raw materials were then ball-milled with sintering aids and anhydrous ethanol. The process parameters were: silicon nitride balls as the milling medium, ball-to-material ratio of 2:1, rotation speed of 200 rpm, and time of 20 h. The raw materials were dried at 80 ℃ for 2 h, placed in a mold and pressed. The loading pressure was 30 MPa and the holding time was 2 min. The raw materials were then subjected to cold isostatic pressing to eliminate the defects in the green body. The pressure gradient of the part is 300 MPa, and finally sintering is carried out. First, under nitrogen gas at a pressure of 2 MPa and a sintering temperature of 1700℃, it is held for 2 hours, then heated to isostatic pressing and held at argon gas at a pressure of 200 MPa and a temperature of 1800℃ for 1 hour to obtain a high thermal conductivity silicon nitride ceramic substrate; the mass ratio of the composite ceramic raw material, sintering aid and anhydrous ethanol is 10:0.1:5; the sintering aid is composed of yttrium oxide, cerium oxide and zirconium nitride, and their mass ratio is 2:1:1.

[0020] Example 2 (1) Glass fibers were immersed in a 5wt% hydrogen fluoride solution at a bath ratio of 1:10, sonicated at 21kHz for 30min, and then washed with deionized water until the pH of the washing solution was neutral. The glass fibers were dried at 80℃ for 5h to obtain low-sodium glass fibers. Multi-walled carbon nanotubes and low-sodium glass fibers were subjected to ultrasonic-assisted ball milling with the following process parameters: ultrasonic frequency of 35kHz, milling medium of silicon nitride balls, ball-to-material ratio of 15:1, rotation speed of 400rpm, and time of 2h. Then, silicon nitride ceramic raw materials and silicon nitride seed crystals were added to obtain composite ceramic raw materials. The mass ratio of multi-walled carbon nanotubes, low-sodium glass fibers, silicon nitride ceramic raw materials, and silicon nitride seed crystals was 2:8:75:1.5. The silicon nitride seed crystals were β-Si3N4 with a particle size of 3μm. (2) Argon-protected shock wave with a flow rate of 5 L / min was used to treat the composite ceramic raw material. The process parameters of the shock wave were: pressure of 23.8 GPa and pulse frequency of 30 Hz. Then, it was mixed with sintering aid and anhydrous ethanol by ball milling. The process parameters were: silicon nitride balls as the milling medium, ball-to-material ratio of 2:1, rotation speed of 200 rpm, time of 25 h, drying at 80 ℃ for 3 h, and then pressing in a mold with a loading pressure of 30 MPa and a holding time of 2 min. After cold isostatic pressing, the impurities in the green body were eliminated. The pressure gradient of the part is 300 MPa, and finally sintering is carried out. First, under nitrogen gas at a pressure of 2 MPa and a sintering temperature of 1700℃, it is held for 2 hours, then heated to isostatic pressing and held at argon gas at a pressure of 200 MPa and a temperature of 1900℃ for 1 hour to obtain a high thermal conductivity silicon nitride ceramic substrate; the mass ratio of the composite ceramic raw material, sintering aid and anhydrous ethanol is 10:0.4:8; the sintering aid is composed of yttrium oxide, cerium oxide and zirconium nitride, and their mass ratio is 2:1:1.

[0021] Example 3 (1) Glass fiber was immersed in 5wt% hydrogen fluoride solution at a bath ratio of 1:10, sonicated at 21kHz for 30min, and then washed with deionized water until the pH of the washing solution was neutral. It was then dried at 80℃ for 5h to obtain low sodium glass fiber. Multi-walled carbon nanotubes and low sodium glass fiber were subjected to ultrasonic-assisted ball milling with the following process parameters: ultrasonic frequency of 40kHz, ball milling medium of silicon nitride balls, ball-to-material ratio of 20:1, rotation speed of 500rpm, and time of 3h. Then silicon nitride ceramic raw material and silicon nitride seed crystals were added to obtain composite ceramic raw material. The mass ratio of multi-walled carbon nanotubes, low sodium glass fiber, silicon nitride ceramic raw material and silicon nitride seed crystals was 3:10:80:2. The silicon nitride seed crystals were β-Si3N4 with a particle size of 5μm. (2) Argon-protected shock waves with a flow rate of 5 L / min were used to treat the composite ceramic raw materials. The process parameters of the shock waves were: pressure of 30.6 GPa and pulse frequency of 50 Hz. The raw materials were then ball-milled with sintering aids and anhydrous ethanol. The process parameters were: silicon nitride balls as the milling medium, ball-to-material ratio of 2:1, rotation speed of 200 rpm, and time of 30 h. The raw materials were dried at 80 ℃ for 4 h, placed in a mold and pressed. The loading pressure was 30 MPa and the holding time was 2 min. The raw materials were then subjected to cold isostatic pressing to eliminate the internal defects of the green body. The pressure gradient is 300 MPa, and the final sintering process is carried out. First, under nitrogen gas at a pressure of 2 MPa and a sintering temperature of 1700℃, the temperature is held for 2 hours. Then, it is heated to isostatic pressure and held at argon gas at a pressure of 200 MPa and a temperature of 2000℃ for 1 hour to obtain a high thermal conductivity silicon nitride ceramic substrate. The mass ratio of the composite ceramic raw material, sintering aid, and anhydrous ethanol is 10:0.6:10. The sintering aid is composed of yttrium oxide, cerium oxide, and zirconium nitride, with a mass ratio of 2:1:1.

[0022] Example 4 (1) Glass fibers were immersed in a 5wt% hydrogen fluoride solution at a bath ratio of 1:10, sonicated at 21kHz for 30min, and then washed with deionized water until the pH of the washing solution was neutral. The glass fibers were dried at 80℃ for 5h to obtain low-sodium glass fibers. Multi-walled carbon nanotubes and low-sodium glass fibers were subjected to ultrasonic-assisted ball milling with the following process parameters: ultrasonic frequency of 35kHz, milling medium of silicon nitride balls, ball-to-material ratio of 15:1, rotation speed of 400rpm, and time of 2h. Then silicon nitride ceramic raw materials and silicon nitride seed crystals were added to obtain composite ceramic raw materials. The mass ratio of the multi-walled carbon nanotubes, low-sodium glass fibers, silicon nitride ceramic raw materials, and silicon nitride seed crystals was 0.5:8:75:1.5. The silicon nitride seed crystals were β-Si3N4 with a particle size of 3μm. (2) Argon-protected shock wave with a flow rate of 5 L / min was used to treat the composite ceramic raw material. The process parameters of the shock wave were: pressure of 23.8 GPa and pulse frequency of 30 Hz. Then, it was mixed with sintering aid and anhydrous ethanol by ball milling. The process parameters were: silicon nitride balls as the milling medium, ball-to-material ratio of 2:1, rotation speed of 200 rpm, time of 25 h, drying at 80 ℃ for 3 h, and then pressing in a mold with a loading pressure of 30 MPa and a holding time of 2 min. After cold isostatic pressing, the impurities in the green body were eliminated. The pressure gradient of the part is 300 MPa, and finally sintering is carried out. First, under nitrogen gas at a pressure of 2 MPa and a sintering temperature of 1700℃, it is held for 2 hours, then heated to isostatic pressing and held at argon gas at a pressure of 200 MPa and a temperature of 1900℃ for 1 hour to obtain a high thermal conductivity silicon nitride ceramic substrate; the mass ratio of the composite ceramic raw material, sintering aid and anhydrous ethanol is 10:0.4:8; the sintering aid is composed of yttrium oxide, cerium oxide and zirconium nitride, and their mass ratio is 2:1:1.

[0023] Example 5 (1) Glass fibers were immersed in a 5wt% hydrogen fluoride solution at a bath ratio of 1:10, sonicated at 21kHz for 30min, and then washed with deionized water until the pH of the washing solution was neutral. The glass fibers were dried at 80℃ for 5h to obtain low-sodium glass fibers. Multi-walled carbon nanotubes and low-sodium glass fibers were subjected to ultrasonic-assisted ball milling with the following process parameters: ultrasonic frequency of 35kHz, milling medium of silicon nitride balls, ball-to-material ratio of 15:1, rotation speed of 400rpm, and time of 2h. Then, silicon nitride ceramic raw materials and silicon nitride seed crystals were added to obtain composite ceramic raw materials. The mass ratio of the multi-walled carbon nanotubes, low-sodium glass fibers, silicon nitride ceramic raw materials, and silicon nitride seed crystals was 2:8:75:0.1. The silicon nitride seed crystals were β-Si3N4 with a particle size of 3μm. (2) Argon-protected shock wave with a flow rate of 5 L / min was used to treat the composite ceramic raw material. The process parameters of the shock wave were: pressure of 23.8 GPa and pulse frequency of 30 Hz. Then, it was mixed with sintering aid and anhydrous ethanol by ball milling. The process parameters were: silicon nitride balls as the milling medium, ball-to-material ratio of 2:1, rotation speed of 200 rpm, time of 25 h, drying at 80 ℃ for 3 h, and then pressing in a mold with a loading pressure of 30 MPa and a holding time of 2 min. After cold isostatic pressing, the impurities in the green body were eliminated. The pressure gradient of the part is 300 MPa, and finally sintering is carried out. First, under nitrogen gas at a pressure of 2 MPa and a sintering temperature of 1700℃, it is held for 2 hours, then heated to isostatic pressing and held at argon gas at a pressure of 200 MPa and a temperature of 1900℃ for 1 hour to obtain a high thermal conductivity silicon nitride ceramic substrate; the mass ratio of the composite ceramic raw material, sintering aid and anhydrous ethanol is 10:0.4:8; the sintering aid is composed of yttrium oxide, cerium oxide and zirconium nitride, and their mass ratio is 2:1:1.

[0024] Example 6 (1) Glass fibers were immersed in a 5wt% hydrogen fluoride solution at a bath ratio of 1:10, sonicated at 21kHz for 30min, and then washed with deionized water until the pH of the washing solution was neutral. The glass fibers were dried at 80℃ for 5h to obtain low-sodium glass fibers. Multi-walled carbon nanotubes and low-sodium glass fibers were subjected to ultrasonic-assisted ball milling with the following process parameters: ultrasonic frequency of 35kHz, milling medium of silicon nitride balls, ball-to-material ratio of 15:1, rotation speed of 400rpm, and time of 2h. Then, silicon nitride ceramic raw materials and silicon nitride seed crystals were added to obtain composite ceramic raw materials. The mass ratio of multi-walled carbon nanotubes, low-sodium glass fibers, silicon nitride ceramic raw materials, and silicon nitride seed crystals was 2:8:75:1.5. The silicon nitride seed crystals were β-Si3N4 with a particle size of 3μm. (2) Argon-protected shock waves with a flow rate of 5 L / min were used to treat the composite ceramic raw materials. The process parameters of the shock waves were: pressure of 8 GPa and pulse frequency of 30 Hz. Then, the raw materials were mixed with sintering aids and anhydrous ethanol by ball milling. The process parameters were: silicon nitride balls as the milling medium, ball-to-material ratio of 2:1, rotation speed of 200 rpm, and time of 25 h. The raw materials were dried at 80 ℃ for 3 h, placed in a mold and pressed. The loading pressure was 30 MPa and the holding time was 2 min. The raw materials were then subjected to cold isostatic pressing to eliminate the internal defects of the green body. A pressure gradient of 300 MPa was applied, followed by sintering. First, the substrate was sintered at 1700°C under nitrogen at 2 MPa for 2 hours, then subjected to isostatic pressing under argon at 1900°C under 200 MPa for 1 hour, yielding a high thermal conductivity silicon nitride ceramic substrate. The mass ratio of the composite ceramic raw material, sintering aid, and anhydrous ethanol was 10:0.4:8. The sintering aid consisted of yttrium oxide, cerium oxide, and zirconium nitride in a mass ratio of 2:1:1.

[0025] Comparative Example 1 The difference between Comparative Example 1 and Example 2 lies in step (1). Step (1) is changed to: immersing glass fiber in a 5wt% hydrogen fluoride solution at a bath ratio of 1:10, sonicating at 21kHz for 30 minutes, then washing with deionized water until the pH of the washing solution is neutral, and drying at 80℃ for 5 hours to obtain low-sodium glass fiber; mixing the low-sodium glass fiber, silicon nitride ceramic raw material, and silicon nitride seed crystal to obtain a composite ceramic raw material; the mass ratio of the low-sodium glass fiber, silicon nitride ceramic raw material, and silicon nitride seed crystal is 8:75:1.5; the silicon nitride seed crystal is β-Si3N4 with a particle size of 3μm; the remaining steps are the same as in Example 2.

[0026] Comparative Example 2 The difference between Comparative Example 2 and Example 2 lies in step (1). Step (1) is changed to: immersing glass fiber in a 5wt% hydrogen fluoride solution at a bath ratio of 1:10, sonicating at 21kHz for 30 minutes, then washing with deionized water until the pH of the washing solution is neutral, and drying at 80℃ for 5 hours to obtain low-sodium glass fiber; mixing multi-walled carbon nanotubes, low-sodium glass fiber, silicon nitride ceramic raw material, and silicon nitride seed crystals to obtain a composite ceramic raw material; the mass ratio of the multi-walled carbon nanotubes, low-sodium glass fiber, silicon nitride ceramic raw material, and silicon nitride seed crystals is 2:8:75:1.5; the silicon nitride seed crystals are β-Si3N4 with a particle size of 3μm; the remaining steps are the same as in Example 2.

[0027] Comparative Example 3 The difference between Comparative Example 3 and Example 2 lies in step (2). Step (2) is changed to: ball milling and mixing composite ceramic raw materials with sintering aids and anhydrous ethanol. The process parameters are: the ball milling media is silicon nitride balls, the ball-to-material ratio is 2:1, the rotation speed is 200 rpm, the time is 25 h, drying at 80℃ for 3 h, placing it in a mold and pressing it into shape, with a loading pressure of 30 MPa and a holding time of 2 min, followed by cold isostatic pressing to eliminate the pressure gradient inside the green body, with a pressure of 300 MPa, and finally... The sintering process involves first holding the substrate at 1700°C under nitrogen pressure of 2 MPa for 2 hours, followed by isostatic pressing under argon pressure of 200 MPa for 1 hour to obtain a high thermal conductivity silicon nitride ceramic substrate. The mass ratio of the composite ceramic raw material, sintering aid, and anhydrous ethanol is 10:0.4:8. The sintering aid is composed of yttrium oxide, cerium oxide, and zirconium nitride in a mass ratio of 2:1:1. The remaining steps are the same as in Example 2.

[0028] Example of effect Table 1 below presents the performance analysis results of the high thermal conductivity silicon nitride ceramic substrates of Examples 1 to 6 and Comparative Examples 1 to 3 of the present invention.

[0029] Table 1

[0030] A comparison of the experimental data from the embodiments and comparative examples in Table 1 reveals that this invention utilizes glass fiber to replace part of the silicon nitride ceramic raw material, combined with multi-walled carbon nanotubes and silicon nitride seed crystals. The glass fiber acts as a flux in the silicon nitride matrix, improving the rheological properties of the silicon nitride slurry through its flexibility, resulting in a higher density uniformity in the cast green body compared to the pure silicon nitride system. Furthermore, the non-silica components in the glass fiber can serve as functional additives to further enhance the performance of the ceramic substrate. During sintering, silicon and nitrogen atoms precipitate onto the β-Si3N4 nuclei and carbon nanotubes. Simultaneously, the multi-walled carbon nanotubes act as nucleation sites, refining the size of the generated β-Si3N4 grains and significantly increasing the yield. The mechanical and thermal properties of the silicon nitride ceramic substrate are enhanced by the reduction properties of carbon, which reduces the silicon dioxide in the glass fiber and some of the ceramic raw materials to form a silicon carbide transition layer, thereby further improving the mechanical and thermal properties of the silicon nitride ceramic substrate. Then, the mixed material is subjected to shock wave activation treatment. Under the action of the shock wave, the multi-walled carbon nanotubes are transformed into a crystal form and the lattice of the tube wall is distorted, providing active sites for subsequent chemical bonding with silicon nitride. The shock wave forms a high-pressure stress field around the carbon nanotubes, and the larger silicon nitride powder particles generate a large number of dislocation lines and dislocation groups, which in turn induce silicon nitride lattice distortion and form carbon-silicon-nitrogen bonds, enhancing the mechanical properties.

[0031] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a silicon nitride ceramic substrate with high thermal conductivity, characterized in that, Includes the following steps: (1) Multi-walled carbon nanotubes and glass fibers were subjected to ultrasonic-assisted ball milling, and then silicon nitride ceramic raw materials and silicon nitride seed crystals were added to obtain composite ceramic raw materials; (2) Argon-protected shock wave is used to treat composite ceramic raw materials, and then ball milling and mixing with sintering aid and anhydrous ethanol. After drying, the raw materials are placed in a mold, first pressed and then cold isostatically pressed, and finally sintered to obtain a high thermal conductivity silicon nitride ceramic substrate. The mass ratio of the multi-walled carbon nanotubes, glass fiber, silicon nitride ceramic raw material, and silicon nitride seed crystals is 1~3:5~10:70~80:0.5~2; The glass fiber is low-sodium glass fiber; The mass ratio of the composite ceramic raw material, sintering aid, and anhydrous ethanol is 10:0.1~0.6:5~10; The process parameters of the shock wave are: pressure of 15.7~30.6 GPa and pulse frequency of 20~50 Hz. The specific steps of the sintering process are as follows: first, under nitrogen gas at a pressure of 2 MPa and a sintering temperature of 1700℃, the mixture is held for 2 hours; then, under isostatic pressing, under argon gas at a pressure of 200 MPa and a temperature of 1800~2000℃, the mixture is held for 1 hour.

2. The method for preparing a high thermal conductivity silicon nitride ceramic substrate according to claim 1, characterized in that, The silicon nitride seed crystals mentioned in step (1) are β-Si3N4 with a particle size of 2~5μm.

3. The method for preparing a high thermal conductivity silicon nitride ceramic substrate according to claim 1, characterized in that, The process parameters for ultrasonic-assisted ball milling in step (1) are: ultrasonic frequency of 30~40kHz, milling medium of silicon nitride balls, ball-to-material ratio of 10~20:1, rotation speed of 300~500rpm, and time of 1~3h.

4. The method for preparing a high thermal conductivity silicon nitride ceramic substrate according to claim 1, characterized in that, The sintering aid in step (2) consists of yttrium oxide, cerium oxide and zirconium nitride in a mass ratio of 2:1:

1.

5. The method for preparing a high thermal conductivity silicon nitride ceramic substrate according to claim 1, characterized in that, The process parameters for ball milling in step (2) are: the milling medium is silicon nitride balls, the ball-to-material ratio is 2:1, the rotation speed is 200 rpm, and the time is 20~30 h.

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