Silicon nitride substrate and sintering method and application thereof

Abstract

The invention belongs to the technical field of silicon nitride ceramic substrates, and particularly relates to a high-thermal-conductivity and high-breaking-strength silicon nitride substrate and a sintering method and application thereof. In order to simultaneously improve the thermal conductivity and the breaking strength of the existing silicon nitride ceramic substrate and ensure the stability and the consistency of the performance during the production of the silicon nitride substrate, the method comprises the following steps: coating the surface of a silicon nitride ceramic biscuit subjected to tape casting with isolation powder, carrying out nitrogen or air atmosphere glue removal treatment, and then sintering; in the sintering process, the cooling process is optimized, a multi-temperature heat preservation platform is arranged above the liquid phase conversion temperature, grain growth and grain boundary composition of the silicon nitride ceramic are regulated and controlled, grain size distribution of the silicon nitride ceramic is made to be more uniform, the grain boundary structure is made to be more optimized, and the heat conductivity coefficient and breaking strength of the substrate are remarkably improved. Meanwhile, the uniformity of a temperature field in the sintering furnace can be greatly improved through the sintering method, it is ensured that the product can reach the consistent performance standard in different areas, and the stability and reliability of the product are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon nitride ceramic substrates, and in particular relates to a silicon nitride substrate with high thermal conductivity and high flexural strength, a sintering method and an application thereof. Background Art

[0002] With the rapid development of modern electronic technology, electronic devices continue to move towards miniaturization, high performance, and high power density. Silicon nitride ceramic substrates, due to their excellent insulation properties, high thermal conductivity, and good chemical stability, have been widely used in the field of electronic packaging.

[0003] In high-tech fields such as 5G communications, new energy vehicles, and aerospace, the performance requirements for silicon nitride ceramic substrates are very stringent: first, they must have a high thermal conductivity to efficiently dissipate the large amount of heat generated by electronic devices and ensure stable operation of the devices; second, high flexural strength is also necessary to ensure that the substrate can maintain structural integrity and avoid breakage and other failures in complex working environments and under mechanical stress.

[0004] Currently, improvements in the performance of silicon nitride ceramic materials have hit a bottleneck due to limitations in sintering furnace pressure thresholds and the limited nature of sintering processes. While its thermal conductivity is stable at 80 W / (m•K) and its flexural strength is approximately 700 MPa, these materials meet current market standards but struggle to demonstrate significant advantages in the fiercely competitive market. Under extreme operating conditions, such as strong vibration, mechanical shock, or complex stress environments, cracks are prone to propagation and even breakage, severely limiting the reliability and service life of electronic devices.

[0005] Moreover, due to the temperature gradient in the space inside the sintering furnace, the silicon nitride ceramic products produced in the same batch show a certain degree of discreteness in performance, making it difficult to effectively guarantee the consistency of product performance.

[0006] Therefore, there is an urgent need to develop a new type of silicon nitride substrate with high thermal conductivity, high flexural strength, and stable and consistent performance. Summary of the Invention

[0007] In order to simultaneously improve the thermal conductivity and flexural strength of existing silicon nitride ceramic substrates and ensure the stability and consistency of performance during the production of silicon nitride substrates, the present invention provides a new type of silicon nitride substrate with high thermal conductivity and high flexural strength, as well as its sintering method and application.

[0008] To achieve the above application objectives, the technical solutions adopted in this application are as follows: In a first aspect, the present invention provides a method for sintering a silicon nitride substrate, comprising the following steps: After coating the surface of the tape-cast silicon nitride ceramic green body with isolation powder, the surface is subjected to a debinding treatment in a nitrogen or air atmosphere, and then sintered to obtain a silicon nitride substrate. The sintering process is performed in the following order: (1) Under vacuum, heat the sample from room temperature to 500-800°C at a rate of 5-10°C / min and keep the temperature for 20-120 min; (2) Under 0.3-1.0 MPa nitrogen, heat the sample to 1000-1500°C at a rate of 2-5°C / min and hold for 60-180 min; (3) Under 0.5-3.0 MPa nitrogen, heat the sample to 1700-1950°C at a rate of 5-10°C / min and hold for 180-500 min; (4) Under nitrogen at 0.5-3.0 MPa, cool the temperature down to 1300-1700°C at a rate of 3-8°C / min and keep it at that temperature for 10-120 min. If the temperature is lowered to 1450-1700°C, keep it at that temperature for 10-120 min, then cool it down to 1400°C at a rate of 3-8°C / min and cool it naturally. (5) Cool naturally to room temperature under 0.3-0.5 MPa nitrogen.

[0009] The silicon nitride ceramic green body is obtained by mixing silicon nitride powder, sintering aid, dispersant, defoamer, organic solvent, binder and plasticizer, ball milling the mixture, and then tape casting and cutting.

[0010] Preferably, the silicon nitride powder is α-phase silicon nitride powder.

[0011] More preferably, the particle size of the α-phase silicon nitride powder is 0.5 to 1 μm.

[0012] Preferably, the sintering aid is a binary mixture of alkaline earth metal oxide and rare earth oxide in a mass ratio of 3-10:1-5.

[0013] More preferably, the alkaline earth metal oxide is magnesium oxide or calcium oxide.

[0014] More preferably, the rare earth oxide is yttrium oxide, ytterbium oxide or lanthanum oxide.

[0015] Preferably, the dispersant is castor oil phosphate.

[0016] Preferably, the defoaming agent is one of n-butanol, polydimethylsiloxane and alkylphenol polyoxyethylene ether.

[0017] Preferably, the organic solvent is a mixture of ethanol and butanone in a mass ratio of 4 to 5:1.

[0018] Preferably, the binder is at least one of polyethylene glycol, polyvinyl butyral, and methyl acrylate.

[0019] Preferably, the plasticizer is at least one of phthalate, polyethylene glycol and glycerol.

[0020] Preferably, the mass ratio of the silicon nitride powder, sintering aid, dispersant, defoamer, organic solvent, binder and plasticizer is 1-1.2: 0.05-0.12: 0.01-0.03: 0.01-0.02: 0.9-1.1: 0.09-0.20: 0.08-0.15.

[0021] Before debinding, the silicon nitride ceramic green bodies are stacked between two firing plates, and a layer of isolation powder is provided between adjacent silicon nitride green bodies.

[0022] Preferably, the silicon nitride ceramic green body has a thickness of 0.2 to 1.0 mm, and the number of stacked layers is 3 to 15.

[0023] Preferably, the support plate is made of boron nitride and has a thickness of 1 to 10 mm.

[0024] Preferably, the isolation powder is boron nitride, and the powder is applied by printing, spraying, or dry application. More preferably, the weight of the applied powder is 0.1 to 0.6 g / pcs.

[0025] Among them, the debinding gas flow rate is 100~700 L / min, and the gas pressure in the furnace is -5~-20Pa.

[0026] Preferably, the air used for debinding needs to be purified and dried.

[0027] Preferably, the purity of nitrogen used for debinding is ≥99.99%.

[0028] Among them, under air atmosphere, the debinding temperature is 400-600 ℃.

[0029] Among them, under nitrogen atmosphere, the debinding temperature is 500-700 °C.

[0030] Preferably, the debinding heating rate is 0.1 to 3°C / min, and the maximum temperature holding time is 60 to 180 minutes.

[0031] The sintering container is a boron nitride crucible, and preferably, the crucible has a porosity of 15-45%.

[0032] In a second aspect, the present invention provides a silicon nitride substrate prepared by the above sintering method.

[0033] The thermal conductivity of the silicon nitride substrate is 85 to 90 W / (m•K), and the flexural strength is 860 to 920 MPa.

[0034] Among them, the difference in thermal conductivity of different silicon nitride substrates sintered in the same furnace is less than 2 W / (m•K), and the difference in flexural strength is less than 70 MPa.

[0035] In a third aspect, the present invention provides an application of the silicon nitride substrate for preparing heat dissipation devices in the fields of electronics, aerospace, or automobiles.

[0036] Beneficial Effects: The present invention prepares a silicon nitride substrate by mixing silicon nitride with other additives, followed by tape casting, binder removal, and sintering. During the silicon nitride sintering process, the cooling process is optimized, and multiple temperature platforms are set above the liquidus transition temperature to regulate the grain growth and grain boundary composition of the silicon nitride ceramic. This results in a more uniform grain size distribution and an optimized grain boundary structure, significantly improving the thermal conductivity and flexural strength of the substrate. Furthermore, this sintering method significantly improves the uniformity of the temperature field within the sintering furnace, ensuring that the product achieves consistent performance standards across different regions, thereby enhancing product stability and reliability. Experiments have confirmed that the silicon nitride substrates prepared by the present invention have a thermal conductivity of 85-90 W / (m·K) and a flexural strength of 860-920 MPa. The difference in thermal conductivity between different silicon nitride substrates sintered in the same furnace is less than 2 W / (m·K), and the difference in flexural strength is less than 70 MPa. Therefore, the silicon nitride substrates prepared by the present invention have great application prospects in the electronics, aerospace, and automotive fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the sintering method of the high thermal conductivity and high strength silicon nitride substrate of the present invention; Figure 2 This is an SEM image of the surface of the silicon nitride substrate prepared in Example 1; Figure 3 This is an SEM image of the surface of the silicon nitride substrate prepared in Comparative Example 1. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clear, the application is further described in detail below in conjunction with the embodiments. Unless otherwise defined, all scientific and technical terms used herein have the same meanings as understood by ordinary technicians in this field.

[0039] In one embodiment of the present invention, a method for sintering a silicon nitride substrate is provided, comprising the following steps: After coating the surface of the tape-cast silicon nitride ceramic green body with isolation powder, the surface is subjected to a debinding treatment in a nitrogen or air atmosphere, and then sintered to obtain a silicon nitride substrate. The sintering process is performed in the following order: (1) Under vacuum, heat the sample from room temperature to 500-800°C at a rate of 5-10°C / min and keep the temperature for 20-120 min; (2) Under 0.3-1.0 MPa nitrogen, heat the sample to 1000-1500 °C at a rate of 2-5 °C / min and hold for 60-180 min; (3) Under 0.5-3.0 MPa nitrogen, heat the sample to 1700-1950 °C at a rate of 5-10 °C / min and hold for 180-500 min; (4) Under nitrogen at 0.5-3.0 MPa, cool the temperature down to 1300-1700 °C at a rate of 3-8 °C / min and keep it at that temperature for 10-120 min. If the temperature is reduced to 1450-1700 °C, keep it at that temperature for 10-120 min, then cool it down to 1400 °C at a rate of 3-8 °C / min and cool it naturally. (5) Cool naturally to room temperature under 0.3-0.5 MPa nitrogen.

[0040] During the silicon nitride sintering process, the present invention optimizes the cooling process and controls the cooling process as follows: under 0.5-3.0 MPa nitrogen, the temperature is lowered to 1300-1700°C at a cooling rate of 3-8°C / min, and the temperature is kept at this temperature for 10-120 minutes; If the temperature is lowered to 1450℃~1700℃, keep it warm for 10~120 min, then lower it to 1400℃ at a cooling rate of 3~8℃ / min and then cool naturally.

[0041] The applicant has found through research that if no insulation platform is added during the cooling process or the insulation time is too short, the following disadvantages will occur: 1. The nucleation rate of silicon nitride ceramics is significantly improved, and the grain growth time is insufficient, which easily leads to the formation of small grains with uneven size distribution; 2. The columnar crystals of silicon nitride ceramics are not fully developed; 3. The glass phase at the grain boundaries of silicon nitride ceramics cannot be fully crystallized, and a large amount of amorphous phase remains at the grain boundaries.

[0042] The above shortcomings are not conducive to obtaining silicon nitride ceramics with high thermal conductivity, high flexural strength and good performance consistency.

[0043] If a heat preservation platform is added during the cooling process, but the heat preservation time is too long, there will be the following disadvantages: 1. The silicon nitride ceramic grains continue to grow, forming abnormally coarse grains, which makes it easier for cracks to extend along the grain boundaries; 2. The number of grain boundaries of silicon nitride ceramics is reduced, the grain boundary phase is unevenly distributed, and the uniformity of the material is destroyed; 3. Excessive diffusion of sintering aids in silicon nitride ceramics changes the chemical composition of the grain boundary phase and even generates low-melting-point phases, which reduces the high-temperature stability of the material.

[0044] The above shortcomings are also not conducive to obtaining silicon nitride ceramics with high thermal conductivity, high flexural strength and good performance consistency.

[0045] Therefore, the present invention establishes multiple temperature holding platforms above the liquidus transition temperature to regulate the grain growth and grain boundary composition of the silicon nitride ceramic, resulting in a more uniform grain size distribution and optimized grain boundary structure, significantly improving the thermal conductivity and flexural strength of the substrate. Furthermore, this sintering method significantly improves the uniformity of the temperature field within the sintering furnace, ensuring consistent performance across different product zones, thereby enhancing product stability and reliability.

[0046] Specific examples will be listed below to explain the scheme of the present invention. Those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product specifications. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0047] Example 1 Step S1: Silicon nitride powder (α-phase silicon nitride powder with a particle size of 0.5-1 μm), magnesium oxide, yttrium oxide, castor oil phosphate, n-butanol, ethanol, butanone, polyvinyl butyral, and glycerol are ball-milled in a mass ratio of 1:0.06:0.02:0.01:0.012:0.8:0.2:0.12:0.10. A 0.45 mm thick silicon nitride ceramic green tape is prepared by tape casting. Green sheets with a size of 200 x 150 mm are cut. Each green sheet is then coated with a layer of 0.35 g of boron nitride powder using a screen printing process. Four green sheets are stacked between two 3 mm thick boron nitride setters. Step S2: introducing nitrogen at a flow rate of 400 L / min, raising the temperature to 560°C at a rate of 1.2°C / min, and maintaining the temperature for 120 min. During the process, the pressure in the furnace was controlled at -15 Pa. Under these conditions, debinding was performed to obtain a debinded silicon nitride ceramic blank. Step S3: Place the silicon nitride ceramic binder blank together with the upper and lower setters into a boron nitride crucible with a porosity of 30-35%, place the crucible in a graphite treatment box, and place it in a gas pressure sintering furnace for sintering. The sintering is divided into several stages: (1) Under a vacuum pressure of 10-15 Pa, heat the sample from room temperature to 700 °C at a rate of 8 °C / min and keep the temperature for 80 min. (2) Under a nitrogen pressure of 1.0 MPa, heat the sample from 700 °C to 1500 °C at a heating rate of 3 °C / min and hold for 180 min; (3) Under a nitrogen pressure of 1.0 MPa, heat the sample from 1500 °C to 1880 °C at a rate of 5 °C / min and hold for 180 min. (4) Under a nitrogen pressure of 0.7 MPa, cool the temperature from 1880 °C to 1450 °C at a rate of 5 °C / min and hold for 60 min; (5) Cool naturally to room temperature under a nitrogen pressure of 0.4 MPa.

[0048] The silicon nitride ceramic substrate prepared in Example 1 had a thermal conductivity of 86 W / (m•K) and a flexural strength of 905 MPa. The difference in thermal conductivity between different substrates sintered in the same furnace was less than 2 W / (m•K), and the difference in flexural strength was less than 70 MPa.

[0049] Example 2 Step S1: Silicon nitride powder (α-phase silicon nitride powder with a particle size of 0.5-1 μm), magnesium oxide, yttrium oxide, castor oil phosphate, n-butanol, ethanol, butanone, polyvinyl butyral, and glycerol are ball-milled in a mass ratio of 1:0.06:0.02:0.01:0.012:0.8:0.2:0.12:0.10. A 0.50 mm thick silicon nitride ceramic green tape is prepared by tape casting. Green sheets with a size of 200 x 150 mm are cut. Each green sheet is then coated with a layer of 0.15 g of boron nitride powder by spraying. Six green sheets are stacked between two 5 mm thick boron nitride setters. Step S2: introducing air at a flow rate of 500 L / min, raising the temperature to 540°C at a rate of 1.5°C / min, and maintaining the temperature for 120 min. During the process, the pressure in the furnace was controlled at -15 Pa. Debinding was performed under these conditions to obtain a debinded silicon nitride ceramic blank. Step S3: Place the silicon nitride ceramic binder blank together with the upper and lower setters into a boron nitride crucible with a porosity of 30-35%, place the crucible in a graphite treatment box, and then place it in a gas pressure sintering furnace; sintering is divided into several stages: (1) Under a vacuum pressure of 10-15 Pa, heat the sample from room temperature to 700 °C at a rate of 7 °C / min and keep the temperature for 80 min. (2) Under a nitrogen pressure of 0.8 MPa, heat the sample from 700 °C to 1500 °C at a heating rate of 2 °C / min and hold for 180 min; (3) Under a nitrogen pressure of 1.5 MPa, heat the sample from 1500 °C to 1870 °C at a rate of 5 °C / min and hold for 180 min. (4) Under a nitrogen pressure of 0.9 MPa, cool the temperature from 1870 °C to 1350 °C at a rate of 5 °C / min and hold for 40 min; (5) Cool naturally to room temperature under a nitrogen pressure of 0.4 MPa.

[0050] The silicon nitride ceramic substrate prepared in Example 2 had a thermal conductivity of 85 W / (m•K) and a flexural strength of 917 MPa. The difference in thermal conductivity between different substrates sintered in the same furnace was less than 1 W / (m•K), and the difference in flexural strength was less than 50 MPa.

[0051] Example 3 Step S1: Silicon nitride powder (α-phase silicon nitride powder with a particle size of 0.5-1 μm), magnesium oxide, yttrium oxide, castor oil phosphate, n-butanol, ethanol, butanone, polyvinyl butyral, and glycerol are ball-milled in a mass ratio of 1:0.06:0.02:0.01:0.012:0.8:0.2:0.12:0.10. A 0.42 mm thick silicon nitride ceramic green tape is prepared by tape casting. Green sheets with a size of 200 x 150 mm are cut. Each green sheet is then coated with a layer of 0.30 g of boron nitride powder using a dry coating process. Ten green sheets are stacked between two 5 mm thick boron nitride setters.

[0052] Step S2: introducing nitrogen at a flow rate of 600 L / min, raising the temperature to 560°C at a rate of 1.2°C / min, and maintaining the temperature for 120 min. During the process, the pressure in the furnace was controlled at -15 Pa. Debinding was performed under these conditions to obtain a debinded silicon nitride ceramic blank. Step S3: Place the silicon nitride ceramic binder blank together with the upper and lower setters into a boron nitride crucible with a porosity of 30-35%, place the crucible in a graphite treatment box, and then place it in a gas pressure sintering furnace; sintering is divided into several stages: (1) Under a vacuum pressure of 10-15 Pa, heat the sample from room temperature to 700 °C at a rate of 8 °C / min and keep the temperature for 80 min. (2) Under a nitrogen pressure of 1.0 MPa, heat the sample from 700 °C to 1500 °C at a heating rate of 4 °C / min and hold for 180 min; (3) Under a nitrogen pressure of 2.0 MPa, heat the sample from 1500 to 1880 °C at a heating rate of 6 °C / min and hold for 180 min. (4) Under a nitrogen pressure of 1.5 MPa, the temperature was cooled from 1880 °C to 1700 °C at a cooling rate of 5 °C / min, kept at that temperature for 30 min, and then cooled from 1700 °C to 1400 °C at a cooling rate of 5 °C / min. If the temperature was cooled naturally from 1700 °C to room temperature, the following results would occur: above the liquidus temperature, the cooling rate of the ceramic would be too fast, the nucleation rate would be significantly increased, and a large number of fine grains would be generated; the temperature consistency would be poor, the grain size would be uneven, and the amorphous phase at the grain boundary would be unevenly distributed.

[0053] (5) Cool naturally to room temperature under a nitrogen pressure of 0.4 MPa.

[0054] The silicon nitride ceramic substrate prepared in Example 3 had a thermal conductivity of 89 W / (m•K) and a flexural strength of 860 MPa. The difference in thermal conductivity between different substrates sintered in the same furnace was less than 2 W / (m•K), and the difference in flexural strength was less than 50 MPa.

[0055] Comparative Example 1 The difference between this comparative example and Example 1 is that in the sintering stage of step S3, in the cooling process steps (4) and (5), the temperature is cooled from 1880°C to 1450°C at a cooling rate of 5°C / min under a nitrogen pressure of 0.7 MPa, and then naturally cooled to room temperature at a nitrogen pressure of 0.4 MPa. There is no insulation platform during the cooling process. The other technical solutions are the same as those in Example 1. In this comparative example, the thermal conductivity of the silicon nitride ceramic substrate material is 83 W / (m•K) and the flexural strength is only 720 MPa. The difference in thermal conductivity of different substrates sintered in the same furnace is 2 W / (m•K), and the difference in flexural strength is 100 MPa.

[0056] Comparative Example 2 The difference between this comparative example and Example 2 is that in the sintering stage of step S3, in the cooling process steps (4) and (5), the temperature is cooled from 1870°C to 1350°C at a cooling rate of 5°C / min under a nitrogen pressure of 0.9 MPa, and then naturally cooled to room temperature at a nitrogen pressure of 0.4 MPa. There is no insulation platform during the cooling process. The other technical solutions are the same as those in Example 2. In this comparative example, the thermal conductivity of the silicon nitride ceramic substrate material is 84 W / (m•K) and the flexural strength is only 740 MPa. The difference in thermal conductivity of different substrates sintered in the same furnace is 2 W / (m•K), and the difference in flexural strength is 80 MPa.

[0057] Comparative Example 3 The difference between this comparative example and Example 3 is that in the sintering stage of step S3, in the cooling process steps (4) and (5), the temperature is cooled from 1880°C to 1400°C at a cooling rate of 5°C / min under a nitrogen pressure of 1.5 MPa, and then naturally cooled to room temperature at a nitrogen pressure of 0.4 MPa. There is no insulation platform during the cooling process. The other technical solutions are the same as those in Example 3. In this comparative example, the thermal conductivity of the silicon nitride ceramic substrate material is 82 W / (m•K) and the flexural strength is only 700 MPa. The difference in thermal conductivity of different substrates sintered in the same furnace is 4 W / (m•K), and the difference in flexural strength is 150 MPa.

[0058] Comparative Example 4 The difference between this comparative example and Example 3 is that in the sintering stage of step S3, in the cooling process steps (4) and (5), the temperature is cooled from 1880°C to 1200°C at a cooling rate of 5°C / min under a nitrogen pressure of 1.5 MPa, kept at this temperature for 30 minutes, and then naturally cooled to room temperature under a nitrogen pressure of 0.4 MPa. The other technical solutions are the same as those in Example 3. In this comparative example, the thermal conductivity of the silicon nitride ceramic substrate material is 84 W / (m•K) and the flexural strength is only 600 MPa. The difference in thermal conductivity of different substrates sintered in the same furnace is 2 W / (m•K), and the difference in flexural strength is 50 MPa.

[0059] Comparative Example 5 The difference between this comparative example and Example 3 is that in the sintering stage of step S3, in the cooling process steps (4) and (5), the temperature is cooled from 1880°C to 1700°C at a cooling rate of 5°C / min under a nitrogen pressure of 1.5 MPa, and kept at this temperature for 180 min. Then, the temperature is cooled from 1700°C to 1400°C at a cooling rate of 5°C / min, and then naturally cooled to room temperature at a nitrogen pressure of 0.4 MPa. The other technical solutions are the same as those in Example 3. In this comparative example, the thermal conductivity of the silicon nitride ceramic substrate material is 90 W / (m•K) and the flexural strength is 730 MPa. The difference in thermal conductivity of different substrates sintered in the same furnace is 3 W / (m•K), and the difference in flexural strength is 120 MPa.

[0060] The performance test results of the above-mentioned Example 1, Example 2, Example 3 and Comparative Example 1, Comparative Example 2, Comparative Example 3 are shown in Table 1.

[0061] Table 1 Properties of silicon nitride substrates prepared in different experimental groups

[0062]

Claims

1. A method for sintering a silicon nitride substrate, characterized in that: The following steps are involved: After coating the surface of the tape-cast silicon nitride ceramic green body with isolation powder, the surface is subjected to a debinding treatment in a nitrogen or air atmosphere, and then sintered to obtain a silicon nitride substrate. The sintering process is performed in the following order: (1) Under vacuum, heat the sample from room temperature to 500-800°C at a rate of 5-10°C / min and keep the temperature for 20-120 min; (2) Under 0.3-1.0 MPa nitrogen, heat the sample to 1000-1500 °C at a rate of 2-5 °C / min and hold for 60-180 min; (3) Under 0.5-3.0 MPa nitrogen, heat the sample to 1700-1950 °C at a rate of 5-10 °C / min and hold for 180-500 min; (4) Under nitrogen at 0.5-3.0 MPa, cool the temperature down to 1300-1700 °C at a rate of 3-8 °C / min and keep it at that temperature for 10-120 min. If the temperature is reduced to 1450-1700 °C, keep it at that temperature for 10-120 min, then cool it down to 1400 °C at a rate of 3-8 °C / min and cool it naturally. (5) Cool naturally to room temperature under 0.3-0.5 MPa nitrogen.

2. The sintering method of a silicon nitride substrate according to claim 1, wherein: The silicon nitride ceramic green body is obtained by mixing silicon nitride powder, sintering aid, dispersant, defoamer, organic solvent, binder and plasticizer, performing ball milling, tape casting and cutting.

3. The sintering method of a silicon nitride substrate according to claim 2, wherein: Meet at least one of the following: The silicon nitride powder is α-phase silicon nitride powder with a particle size of 0.5 to 1 μm; The sintering aid is a binary mixture of alkaline earth metal oxide and rare earth oxide in a mass ratio of 3-10:1-5; The dispersant is castor oil phosphate; The defoaming agent is one of n-butanol, polydimethylsiloxane and alkylphenol polyoxyethylene ether; The organic solvent is a mixture of ethanol and butanone in a mass ratio of 4 to 5:1; The binder is at least one of polyethylene glycol, polyvinyl butyral, and methyl acrylate; The plasticizer is at least one of phthalate, polyethylene glycol and glycerol.

4. The sintering method of a silicon nitride substrate according to claim 3, wherein: The mass ratio of the silicon nitride powder, sintering aid, dispersant, defoamer, organic solvent, binder and plasticizer is 1-1.2: 0.05-0.12: 0.01-0.03: 0.01-0.02: 0.9-1.1: 0.09-0.20: 0.08-0.

15.

5. The sintering method of a silicon nitride substrate according to claim 1, wherein: Before debinding, the silicon nitride ceramic blanks are stacked between two firing plates, and a layer of isolation powder is placed between adjacent silicon nitride blanks; the isolation powder is boron nitride, and the powder is applied by printing, spraying or dry application.

6. The sintering method of a silicon nitride substrate according to claim 1, wherein: The debinding gas flow rate is 100~700 L / min, and the gas pressure in the furnace is -5~-20 Pa.

7. The sintering method of a silicon nitride substrate according to claim 6, wherein: In air atmosphere, the debinding temperature is 400-600 ℃; in nitrogen atmosphere, the debinding temperature is 500-700 ℃.

8. The sintering method of a silicon nitride substrate according to claim 6 or 7, wherein: The debinding heating rate is 0.1-3 ℃ / min, and the maximum temperature holding time is 60-180 min.

9. A silicon nitride substrate prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the silicon nitride substrate according to claim 9 in preparing heat dissipation devices in the fields of electronics, aerospace or automobiles.

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