A method for preparing a high flatness silicon nitride substrate

Abstract

The application discloses a preparation method of a high-flatness silicon nitride substrate. The silicon nitride substrate is prepared through the steps of configuring an organic glue, ball milling mixing, defoaming aging, flow casting, punching and coating isolation powder, low-temperature flattening treatment, air glue removal, pressure sintering and isolation powder removal. The silicon nitride substrate prepared by the method has good flatness, low roughness and high mechanical properties. Bis(2-ethylhexyl) terephthalate and dibutyl sebacate are used as a composite plasticizer to improve the fracture toughness of the material; polyethylene imine and sodium tripolyphosphate are used as a composite dispersant to reduce the roughness of the material; cyclohexanone and white oil are used as a composite homogenizing agent to reduce the warpage of the material and improve the flatness of the material.

Description

Technical Field

[0001] This invention belongs to the field of silicon nitride ceramic technology, specifically relating to a method for preparing a silicon nitride substrate with high flatness. Background Technology

[0002] Silicon nitride substrates possess numerous advantages, including high strength, high hardness, high thermal conductivity, low coefficient of thermal expansion, low high-temperature creep, good oxidation resistance, good hot corrosion resistance, and low coefficient of friction, making them irreplaceable in key fields such as national defense, military industry, and electronic information. Currently, the commercial application of silicon nitride substrates is mainly concentrated in automotive IGBT modules. IGBT modules use large silicon nitride substrates, reaching L7.5 inches * W5.5 inches. Metallizing (copper plating) on ​​such large silicon nitride substrates places high demands on substrate flatness. Large-sized and thin (less than 0.5 mm) silicon nitride substrates are prone to warping and edge warping after sintering, leading to uneven thickness, poor flatness, poor adhesion, and reduced cycle life in subsequent metallization layers, directly affecting their use. Typical processes require correction or surface grinding to ensure the substrate flatness meets usage requirements.

[0003] Using a correction process to ensure substrate flatness means performing a second sintering. The second sintering temperature is only 500-100°C lower than the first, which causes silicon nitride substrate grain growth, thus reducing the substrate's three-point bending strength. Simultaneously, the second sintering reduces the utilization rate of the sintering furnace and increases energy costs, further increasing the already high cost of silicon nitride substrates and hindering product market promotion. Using surface grinding to ensure substrate flatness requires leaving a certain processing allowance on the surface of the semi-finished product. Powder costs account for more than 50% of the cost of silicon nitride substrates, and the existence of grinding allowances will significantly increase the substrate cost. Furthermore, silicon nitride ceramics are brittle materials, and processing large-size substrates is a challenge in the industry. The processing process easily leads to quality problems such as cracking, chipping, and scratches, with these quality problems accounting for 10-20%, which also increases the cost of silicon nitride substrates. Therefore, it is necessary to provide a manufacturing method for silicon nitride ceramics to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a silicon nitride substrate with high flatness.

[0005] A method for preparing a silicon nitride substrate with high flatness, comprising the following steps: (1) Preparation of organic adhesive: Add adhesive, plasticizer and organic solvent into a container and stir evenly; the mass ratio of the adhesive, plasticizer and organic solvent is (10-20):(15-25):(80-120); (2) Ball milling: Organic solvent, silicon nitride powder, sintering aid, dispersant, homogenizer and defoamer are added to a ball mill in sequence and ball milled for 12-24 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and ball milled for another 24-36 hours to obtain a cast slurry; the mass ratio of the organic solvent, silicon nitride powder, sintering aid, dispersant, homogenizer and defoamer is (80-120):(50-150):(5-15):(5-10):(5-15):(1-3); the mass ratio of the mixed slurry to the organic adhesive is (1-5):1; (3) Degassing and aging: The casting slurry prepared in step (2) is degassed under vacuum for 10-20 min and aged at a speed of 5-10 rpm for 5-10 h, with the viscosity controlled at 12000-20000 cps, the solid content at 65-80%, and the temperature at 15-25℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube; the process parameters for this step are: casting speed 0.1-0.2 m / min, temperature of zone 1 of casting drying chamber 25-35℃, temperature of zone 2 of casting drying chamber 55-75℃, and temperature of zone 3 of casting drying chamber 65-105℃; (5) Punching and applying isolation powder: Select the punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.05-0.1MPa and the powder application temperature is 55-85℃. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 85-100℃, and the time is 3-5h. (7) Air debinding: Place the leveled green body into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 550-650℃, total time: 15-25h, and heating rate <5℃ / min between 220-350℃. (8) Pressure sintering: The debinding product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1750-1850℃, sintering time: 20-35h, pressure: 0.5-1.0MPa, and the heating rate at 1650-1700℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic.

[0006] The adhesive is one or more of polyvinyl butyral, ethyl cellulose, paraffin, and dextrin.

[0007] The plasticizer is a mixture of di(2-ethylhexyl) terephthalate and dibutyl sebacate in a mass ratio of 1:1.

[0008] The organic solvent is one or more of toluene, xylene, isopropanol, ethanol, and ethyl acetate.

[0009] The sintering aid is one or more of the following: magnesium silicon nitride, lithium oxide, lanthanum fluoride, titanium dioxide, samarium trifluoride, gadolinium fluoride, and cerium tetrafluoride.

[0010] The dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:1.

[0011] The homogenizing agent is a mixture of cyclohexanone and white oil in a mass ratio of 3:1.

[0012] The defoamer is one or more of n-octanol, cyclopentanol, silicone oil, and polydimethylsiloxane.

[0013] The raw material composition and ratio of the isolation powder in step (5) are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: (0.015-0.025): (3-5).

[0014] The beneficial effects of this invention are as follows: The silicon nitride substrate prepared by this invention has good flatness, low roughness, and high mechanical properties. The use of a composite plasticizer of di(2-ethylhexyl) terephthalate and dibutyl sebate improves the fracture toughness of the material; the use of a composite dispersant of polyethyleneimine and sodium tripolyphosphate reduces the roughness of the material; and the use of a composite homogenizing agent of cyclohexanone and white oil reduces the warpage of the material and improves its flatness. Detailed Implementation

[0015] To facilitate understanding of the present invention, a more comprehensive description will be given below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention. Example 1

[0016] A method for preparing a silicon nitride substrate with high flatness, comprising the following steps: (1) Preparation of organic adhesive: Polyvinyl butyral, plasticizer and organic solvent are added to a container and stirred evenly; the mass ratio of polyvinyl butyral, plasticizer and organic solvent is 15:20:100; the plasticizer is a mixture of di(2-ethylhexyl) terephthalate and dibutyl sebacate in a mass ratio of 1:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; (2) Ball milling and mixing: Organic solvent, silicon nitride powder, magnesium silicon nitride, dispersant, homogenizer, and n-octanol are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and the mixture is milled for another 30 hours to obtain a cast slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, dispersant, homogenizer, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; the dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:1; the homogenizer is a mixture of cyclohexanone and white oil in a mass ratio of 3:1; (3) Degassing and aging: The casting slurry prepared in step (2) is degassed under vacuum for 15 min and aged at 8 rpm for 7 h, with the viscosity controlled at 18000 cps, the solid content at 70%, and the temperature at 20℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.5 m / min, temperature of zone 1 of the casting drying chamber 30℃, temperature of zone 2 of the casting drying chamber 60℃, and temperature of zone 3 of the casting drying chamber 85℃. (5) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: 0.02: 4. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 90℃, and the time is 4h. (7) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 600℃, total time: 20h, and heating rate <5℃ / min between 300℃. (8) Pressure sintering: The debinding product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1800℃, sintering time: 28h, pressure: 0.8MPa, and the heating rate at 1680℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic. Example 2

[0017] A method for preparing a silicon nitride substrate with high flatness, comprising the following steps: (1) Preparation of organic adhesive: Ethyl cellulose, plasticizer and ethanol are added to a container and stirred evenly; the mass ratio of ethyl cellulose, plasticizer and ethanol is 12:16:85; the plasticizer is a mixture of di(2-ethylhexyl) terephthalate and dibutyl sebacate in a mass ratio of 1:1; (2) Ball milling and mixing: Ethanol, silicon nitride powder, lithium oxide, dispersant, homogenizer, and polydimethylsiloxane are added to a ball mill in sequence and milled for 14 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and the mixture is milled for another 26 hours to obtain a cast slurry; the mass ratio of ethanol, silicon nitride powder, lithium oxide, dispersant, homogenizer, and polydimethylsiloxane is 80:60:5:6:6:1; the mass ratio of the mixed slurry to the organic adhesive is 1:1; the dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:1; the homogenizer is a mixture of cyclohexanone and white oil in a mass ratio of 3:1; (3) Degassing and aging: The casting slurry prepared in step (2) is vacuum degassed for 12 min and aged at 5 rpm for 6 h, with the viscosity controlled at 12000 cps, the solid content at 65%, and the temperature at 15℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.1 m / min, temperature of zone 1 of the casting drying chamber 25℃, temperature of zone 2 of the casting drying chamber 55℃, and temperature of zone 3 of the casting drying chamber 65℃. (5) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.05MPa and the powder application temperature is 55℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.015:3-5. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 85℃, and the time is 3h. (7) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 550℃, total time: 15h, heating rate <5℃ / min between 220℃; (8) Pressure sintering: The debonded product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1750℃, sintering time: 20h, pressure: 0.5MPa, and the heating rate at 1650℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic. Example 3

[0018] A method for preparing a silicon nitride substrate with high flatness, comprising the following steps: (1) Preparation of organic glue: Dextrin, plasticizer and isopropanol are added to a container and stirred evenly; the mass ratio of dextrin, plasticizer and isopropanol is 20:25:120; the plasticizer is a mixture of di(2-ethylhexyl) terephthalate and dibutyl sebacate in a mass ratio of 1:1; (2) Ball milling: Isopropanol, silicon nitride powder, lanthanum fluoride, dispersant, homogenizer, and silicone oil are added to a ball mill in sequence and milled for 24 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and the mixture is milled for another 36 hours to obtain a cast slurry; the mass ratio of isopropanol, silicon nitride powder, lanthanum fluoride, dispersant, homogenizer, and silicone oil is 120:150:15:10:15:3; the mass ratio of the mixed slurry to the organic adhesive is 4:1; the dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:1; the homogenizer is a mixture of cyclohexanone and white oil in a mass ratio of 3:1; (3) Degassing and aging: The casting slurry prepared in step (2) is degassed under vacuum for 20 min and aged for 10 h by stirring at 10 rpm, with the viscosity controlled at 20000 cps, the solid content at 75%, and the temperature at 25℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.2 m / min, temperature of zone 1 of the casting drying chamber 35℃, temperature of zone 2 of the casting drying chamber 75℃, and temperature of zone 3 of the casting drying chamber 105℃. (5) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.1MPa and the powder application temperature is 85℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: 0.025: 5. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 100℃, and the time is 5h. (7) Air debinding: Place the leveled green body into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 650℃, total time: 25h, and heating rate <5℃ / min between 350℃. (8) Pressure sintering: The debinding product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1850℃, sintering time: 35h, pressure: 1.0MPa, and the heating rate at 1700℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic.

[0019] Comparative Example 1 A method for preparing a silicon nitride substrate with high flatness, comprising the following steps: (1) Preparation of organic adhesive: Polyvinyl butyral, di(2-ethylhexyl) terephthalate and organic solvent are added to a container and stirred evenly; the mass ratio of polyvinyl butyral, di(2-ethylhexyl) terephthalate and organic solvent is 15:20:100; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1. (2) Ball milling and mixing: Organic solvent, silicon nitride powder, magnesium silicon nitride, dispersant, homogenizer, and n-octanol are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and the mixture is milled for another 30 hours to obtain a cast slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, dispersant, homogenizer, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; the dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:1; the homogenizer is a mixture of cyclohexanone and white oil in a mass ratio of 3:1; (3) Degassing and aging: The casting slurry prepared in step (2) is degassed under vacuum for 15 min and aged at 8 rpm for 7 h, with the viscosity controlled at 18000 cps, the solid content at 70%, and the temperature at 20℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.5 m / min, temperature of zone 1 of the casting drying chamber 30℃, temperature of zone 2 of the casting drying chamber 60℃, and temperature of zone 3 of the casting drying chamber 85℃. (5) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: 0.02: 4. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 90℃, and the time is 4h. (7) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 600℃, total time: 20h, and heating rate <5℃ / min between 300℃. (8) Pressure sintering: The debinding product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1800℃, sintering time: 28h, pressure: 0.8MPa, and the heating rate at 1680℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic.

[0020] Comparative Example 2 A method for preparing a silicon nitride substrate with high flatness, comprising the following steps: (1) Preparation of organic adhesive: Polyvinyl butyral, dibutyl sebacate and organic solvent are added to a container and stirred evenly; the mass ratio of polyvinyl butyral, dibutyl sebacate and organic solvent is 15:20:100; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1. (2) Ball milling and mixing: Organic solvent, silicon nitride powder, magnesium silicon nitride, dispersant, homogenizer, and n-octanol are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and the mixture is milled for another 30 hours to obtain a cast slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, dispersant, homogenizer, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; the dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:1; the homogenizer is a mixture of cyclohexanone and white oil in a mass ratio of 3:1; (3) Degassing and aging: The casting slurry prepared in step (2) is degassed under vacuum for 15 min and aged at 8 rpm for 7 h, with the viscosity controlled at 18000 cps, the solid content at 70%, and the temperature at 20℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.5 m / min, temperature of zone 1 of the casting drying chamber 30℃, temperature of zone 2 of the casting drying chamber 60℃, and temperature of zone 3 of the casting drying chamber 85℃. (5) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: 0.02: 4. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 90℃, and the time is 4h. (7) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 600℃, total time: 20h, and heating rate <5℃ / min between 300℃. (8) Pressure sintering: The debinding product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1800℃, sintering time: 28h, pressure: 0.8MPa, and the heating rate at 1680℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic.

[0021] Comparative Example 3 A method for preparing a silicon nitride substrate with high flatness, comprising the following steps: (1) Preparation of organic adhesive: Polyvinyl butyral, plasticizer and organic solvent are added to a container and stirred evenly; the mass ratio of polyvinyl butyral, plasticizer and organic solvent is 15:20:100; the plasticizer is a mixture of di(2-ethylhexyl) terephthalate and dibutyl sebacate in a mass ratio of 1:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; (2) Ball milling and mixing: Organic solvent, silicon nitride powder, magnesium silicon nitride, polyethyleneimine, homogenizer, and n-octanol are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and the mixture is milled for another 30 hours to obtain a cast slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, polyethyleneimine, homogenizer, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; the homogenizer is a mixture of cyclohexanone and white oil in a mass ratio of 3:1; (3) Degassing and aging: The casting slurry prepared in step (2) is degassed under vacuum for 15 min and aged at 8 rpm for 7 h, with the viscosity controlled at 18000 cps, the solid content at 70%, and the temperature at 20℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.5 m / min, temperature of zone 1 of the casting drying chamber 30℃, temperature of zone 2 of the casting drying chamber 60℃, and temperature of zone 3 of the casting drying chamber 85℃. (5) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: 0.02: 4. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 90℃, and the time is 4h. (7) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 600℃, total time: 20h, and heating rate <5℃ / min between 300℃. (8) Pressure sintering: The debinding product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1800℃, sintering time: 28h, pressure: 0.8MPa, and the heating rate at 1680℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic.

[0022] Comparative Example 4 A method for preparing a silicon nitride substrate with high flatness, comprising the following steps: (1) Preparation of organic adhesive: Polyvinyl butyral, plasticizer and organic solvent are added to a container and stirred evenly; the mass ratio of polyvinyl butyral, plasticizer and organic solvent is 15:20:100; the plasticizer is a mixture of di(2-ethylhexyl) terephthalate and dibutyl sebacate in a mass ratio of 1:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; (2) Ball milling and mixing: Organic solvent, silicon nitride powder, magnesium silicon nitride, sodium tripolyphosphate, homogenizer, and n-octanol are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and the mixture is milled for another 30 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, sodium tripolyphosphate, homogenizer, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; the homogenizer is a mixture of cyclohexanone and white oil in a mass ratio of 3:1; (3) Degassing and aging: The casting slurry prepared in step (2) is degassed under vacuum for 15 min and aged at 8 rpm for 7 h, with the viscosity controlled at 18000 cps, the solid content at 70%, and the temperature at 20℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.5 m / min, temperature of zone 1 of the casting drying chamber 30℃, temperature of zone 2 of the casting drying chamber 60℃, and temperature of zone 3 of the casting drying chamber 85℃. (5) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: 0.02: 4. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 90℃, and the time is 4h. (7) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 600℃, total time: 20h, and heating rate <5℃ / min between 300℃. (8) Pressure sintering: The debinding product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1800℃, sintering time: 28h, pressure: 0.8MPa, and the heating rate at 1680℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic.

[0023] Comparative Example 5 A method for preparing a silicon nitride substrate with high flatness, comprising the following steps: (1) Preparation of organic adhesive: Polyvinyl butyral, plasticizer and organic solvent are added to a container and stirred evenly; the mass ratio of polyvinyl butyral, plasticizer and organic solvent is 15:20:100; the plasticizer is a mixture of di(2-ethylhexyl) terephthalate and dibutyl sebacate in a mass ratio of 1:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; (2) Ball milling and mixing: Organic solvent, silicon nitride powder, magnesium silicon nitride, dispersant, cyclohexanone, and n-octanol are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and the mixture is milled for another 30 hours to obtain a cast slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, dispersant, cyclohexanone, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; the dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:1; (3) Degassing and aging: The casting slurry prepared in step (2) is degassed under vacuum for 15 min and aged at 8 rpm for 7 h, with the viscosity controlled at 18000 cps, the solid content at 70%, and the temperature at 20℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.5 m / min, temperature of zone 1 of the casting drying chamber 30℃, temperature of zone 2 of the casting drying chamber 60℃, and temperature of zone 3 of the casting drying chamber 85℃. (5) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: 0.02: 4. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 90℃, and the time is 4h. (7) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 600℃, total time: 20h, and heating rate <5℃ / min between 300℃. (8) Pressure sintering: The debinding product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1800℃, sintering time: 28h, pressure: 0.8MPa, and the heating rate at 1680℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic.

[0024] Comparative Example 6 A method for preparing a silicon nitride substrate with high flatness, comprising the following steps: (1) Preparation of organic adhesive: Polyvinyl butyral, plasticizer and organic solvent are added to a container and stirred evenly; the mass ratio of polyvinyl butyral, plasticizer and organic solvent is 15:20:100; the plasticizer is a mixture of di(2-ethylhexyl) terephthalate and dibutyl sebacate in a mass ratio of 1:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; (2) Ball milling and mixing: Organic solvent, silicon nitride powder, magnesium silicon nitride, dispersant, white oil, and n-octanol are added to a ball mill in sequence and milled for 18 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and the mixture is milled for another 30 hours to obtain a cast slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, dispersant, white oil, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic adhesive is 3:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; the dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:1; (3) Degassing and aging: The casting slurry prepared in step (2) is degassed under vacuum for 15 min and aged at 8 rpm for 7 h, with the viscosity controlled at 18000 cps, the solid content at 70%, and the temperature at 20℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube. The process parameters for this step are: casting speed 0.5 m / min, temperature of zone 1 of the casting drying chamber 30℃, temperature of zone 2 of the casting drying chamber 60℃, and temperature of zone 3 of the casting drying chamber 85℃. (5) Punching and applying isolation powder: Select a punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.08MPa and the powder application temperature is 65℃. The raw material composition and ratio of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: 0.02: 4. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 90℃, and the time is 4h. (7) Air debinding: The leveled green body is placed into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 600℃, total time: 20h, and heating rate <5℃ / min between 300℃. (8) Pressure sintering: The debinding product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1800℃, sintering time: 28h, pressure: 0.8MPa, and the heating rate at 1680℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of the sintered silicon nitride ceramic.

[0025] Experimental Example 1: The fracture toughness of silicon nitride substrates prepared in Examples 1-3 and Comparative Examples 1-2 was tested using the indentation method. The applied load was 196 N, and each experiment was performed in triplicate. Statistical analysis was performed using SPSS 24.0 software. The results of the quantitative data are expressed as x ± s (mean ± standard deviation). The Kolmogorov-Smirnov test was used to test the normality of the data. For normally distributed data, the difference between the means of two groups was compared using the t-test, and P < 0.05 was considered statistically significant.

[0026] The test results are shown in Table 1: Table 1

[0027] Note: * indicates P<0.05 compared to Example 1 group.

[0028] Experimental Example 2: The surface roughness of the silicon nitride substrates prepared in Examples 1-3 and Comparative Examples 3-4 was tested. The surface roughness was measured by selecting at least five test points on both sides of the silicon nitride substrate, and the average roughness of all test points was taken as the test result. All test points included a central point located in the center, with the remaining test points located around the central point and close to the edges of the silicon nitride substrate. The test results are shown in Table 2. Table 2

[0029] Note: * indicates P<0.05 compared to Example 1 group.

[0030] Experimental Example 3: The warpage (mm / 25.4mm) of the silicon nitride substrates prepared in Examples 1-3 and Comparative Examples 5-6 was tested. The test results are shown in Table 3. Table 3

[0031] Note: * indicates P<0.05 compared to Example 1 group.

[0032] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a silicon nitride substrate with high flatness, characterized in that, Follow these steps: (1) Preparation of organic adhesive: Add adhesive, plasticizer and organic solvent into a container and stir evenly; the mass ratio of the adhesive, plasticizer and organic solvent is (10-20):(15-25):(80-120); (2) Ball milling: Organic solvent, silicon nitride powder, sintering aid, dispersant, homogenizer and defoamer are added to a ball mill in sequence and ball milled for 12-24 hours to obtain a mixed slurry; the organic adhesive prepared in step (1) is added and ball milled for another 24-36 hours to obtain a cast slurry; the mass ratio of the organic solvent, silicon nitride powder, sintering aid, dispersant, homogenizer and defoamer is (80-120):(50-150):(5-15):(5-10):(5-15):(1-3); the mass ratio of the mixed slurry to the organic adhesive is (1-5):1; (3) Degassing and aging: The casting slurry prepared in step (2) is degassed under vacuum for 10-20 min and aged at a speed of 5-10 rpm for 5-10 h, with the viscosity controlled at 12000-20000 cps, the solid content at 65-80%, and the temperature at 15-25℃. (4) Casting: The slurry prepared in step (3) is cast using a casting machine, and the green body is wrapped with a paper tube; the process parameters for this step are: casting speed 0.1-0.2 m / min, temperature of zone 1 of casting drying chamber 25-35℃, temperature of zone 2 of casting drying chamber 55-75℃, and temperature of zone 3 of casting drying chamber 65-105℃; (5) Punching and applying isolation powder: Select the punching die according to the drawing requirements, cut the green blank prepared in step (4), and transport it to the powder application line by conveyor belt for powder application. The powder application pressure is 0.05-0.1MPa and the powder application temperature is 55-85℃. (6) Low-temperature flattening treatment: The powdered silicon nitride green blanks are stacked alternately on the firing plate, and the weight plate is placed on the stacked silicon nitride green blanks; the weight plate is a boron nitride plate, the flattening temperature is 85-100℃, and the time is 3-5h. (7) Air debinding: Place the leveled green body into an intermittent furnace for debinding; the process parameters for this step are: debinding temperature 550-650℃, total time: 15-25h, and heating rate <5℃ / min between 220-350℃. (8) Pressure sintering: The debinding product is placed into the sintering furnace for sintering; the process parameters for this step are: sintering temperature 1750-1850℃, sintering time: 20-35h, pressure: 0.5-1.0MPa, and the heating rate at 1650-1700℃ during the heating stage is <1℃ / min. (9) Removal of isolation powder: Remove the isolation powder from the surface of the sintered silicon nitride ceramic using dust removal equipment; The plasticizer is a mixture of di(2-ethylhexyl) terephthalate and dibutyl sebacate in a mass ratio of 1:1; The dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:1; The homogenizing agent is a mixture of cyclohexanone and white oil in a mass ratio of 3:

1.

2. The method for preparing a high-flatness silicon nitride substrate according to claim 1, characterized in that, The adhesive is one or more of polyvinyl butyral, ethyl cellulose, paraffin, and dextrin.

3. The method for preparing a high-flatness silicon nitride substrate according to claim 1, characterized in that, The organic solvent is one or more of toluene, xylene, isopropanol, ethanol, and ethyl acetate.

4. The method for preparing a high-flatness silicon nitride substrate according to claim 1, characterized in that, The sintering aid is one or more of the following: magnesium silicon nitride, lithium oxide, lanthanum fluoride, titanium dioxide, samarium trifluoride, gadolinium fluoride, and cerium tetrafluoride.

5. The method for preparing a high-flatness silicon nitride substrate according to claim 1, characterized in that, The defoamer is one or more of n-octanol, cyclopentanol, silicone oil, and polydimethylsiloxane.

6. The method for preparing a high-flatness silicon nitride substrate according to claim 1, characterized in that, The raw material composition and ratio of the isolation powder in step (5) are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: (0.015-0.025): (3-5).

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