Preparation method of high-flatness silicon nitride substrate

Abstract

The invention discloses a preparation method of a high-flatness silicon nitride substrate. The preparation method comprises the following steps: preparing organic glue, ball-milling and mixing, defoaming and aging, carrying out tape casting, blanking and applying isolation powder, carrying out low-temperature flattening treatment, discharging glue in air, carrying out pressure sintering, and removing the isolation powder. The prepared silicon nitride substrate is good in flatness, low in roughness and high in mechanical property. A composite plasticizer of di (2-ethylhexyl) terephthalate and dibutyl sebacate is adopted, so that the fracture toughness of the material is improved; the polyethyleneimine and sodium tripolyphosphate composite dispersing agent is adopted, so that the roughness of the material is reduced; the cyclohexanone and white oil composite homogenizing agent is adopted, so that the warping degree of the material is reduced, and the smoothness of the material is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon nitride ceramics, and in particular relates to a method for preparing a high-flatness silicon nitride substrate. Background Art

[0002] Silicon nitride substrates have many advantages such as high strength, high hardness, high thermal conductivity, low thermal expansion coefficient, low high-temperature creep, good oxidation resistance, good thermal corrosion performance, and low friction coefficient. They have an irreplaceable position in key fields such as national defense, military industry, and electronic information. At present, the commercial application of silicon nitride substrates is mainly concentrated in the field of automotive IGBT modules. The silicon nitride substrates used in IGBT modules are relatively large in size, reaching L7.5 inches * W5.5 inches. Metallization (copper coating) on ​​such a large silicon nitride substrate places high demands on the flatness of the substrate. Silicon nitride substrates with large size and thin thickness (less than 0.5mm) are prone to warping and edge warping after sintering, which will lead to uneven thickness, poor flatness, poor bonding, and reduced cycle life of the subsequent metallization layer, which directly affects its use. The general process requires correction or surface grinding to ensure that the flatness of the substrate meets the use requirements.

[0003] Adopting a correction process to ensure the flatness of the substrate means that the substrate needs to be sintered twice. The temperature of the secondary sintering is only 500-100℃ lower than the temperature of the first sintering, which will cause the grains of the silicon nitride substrate to grow, thereby reducing the three-point bending strength of the substrate. At the same time, the secondary sintering will reduce the utilization rate of the sintering furnace and increase the energy cost, making the cost of the silicon nitride substrate, which is already expensive, even higher, which is not conducive to the market promotion of the product. The surface grinding process is used to ensure the flatness of the substrate, and a part of the processing allowance needs to be reserved on the surface of the semi-finished product. The powder cost accounts for more than 50% of the cost structure of the silicon nitride substrate, and the existence of the grinding allowance will greatly increase the cost of the substrate. At the same time, silicon nitride ceramics are brittle materials, and the processing of large-size substrates is a difficult problem in the industry. The processing process is prone to cause cracking, collapse, scratches and other quality problems on the substrate, which are as high as 10-20%. The existence of this part of the quality problems will also cause the cost of the silicon nitride substrate to become higher. Therefore, it is necessary to provide a method for manufacturing silicon nitride ceramics to solve the above problems. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a high-flatness silicon nitride substrate.

[0005] A method for preparing a high-flatness silicon nitride substrate is carried out according to the following steps:

[0006] (1) preparing organic glue: adding adhesive, plasticizer and organic solvent into a container and stirring evenly; the mass ratio of the adhesive, plasticizer and organic solvent is (10-20): (15-25): (80-120);

[0007] (2) ball milling and mixing: adding an organic solvent, silicon nitride powder, a sintering aid, a dispersant, a homogenizing agent, and a defoaming agent to a ball mill in sequence, and ball milling for 12-24 hours to obtain a mixed slurry; adding the organic glue prepared in step (1), and ball milling for another 24-36 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, sintering aid, dispersant, homogenizing agent, and defoaming agent is (80-120): (50-150): (5-15): (5-10): (5-15): (1-3); the mass ratio of the mixed slurry to the organic glue is (1-5): 1;

[0008] (3) Degassing and aging: vacuum degassing the tape casting slurry prepared in step (2) for 10-20 minutes, and stirring and aging at a speed of 5-10 rpm for 5-10 hours, controlling the viscosity to be 12000-20000 cps, the solid content to be 65-80%, and the temperature to be 15-25°C;

[0009] (4) Tape casting: The slurry prepared in step (3) is subjected to tape casting by a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.1-0.2 m / min, the temperature of the first zone of the tape casting drying chamber is 25-35°C, the temperature of the second zone of the tape casting drying chamber is 55-75°C, and the temperature of the first zone of the tape casting drying chamber is 65-105°C;

[0010] (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 coating line via a conveyor belt for powder coating. The powder coating pressure is 0.05-0.1Mpa and the powder coating temperature is 55-85°C;

[0011] (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 85-100°C, and the time is 3-5h;

[0012] (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; process parameters of this step: debinding temperature 550-650°C, total time: 15-25h, heating rate <5°C / min between 220-350°C;

[0013] (8) Pressure sintering: placing the debinded product into a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1750-1850°C, sintering time: 20-35h, pressure: 0.5-1.0Mpa, and a heating rate of 1650-1700°C in the heating stage of <1°C / min;

[0014] (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

[0015] The adhesive is one or more of polyvinyl butyral, ethyl cellulose, paraffin and dextrin.

[0016] The plasticizer is a mixture of di(2-ethylhexyl) terephthalate and dibutyl sebacate in a mass ratio of 1:1.

[0017] The organic solvent is one or more of toluene, xylene, isopropanol, ethanol and ethyl acetate.

[0018] The sintering aid is one or more of magnesium silicon nitride, lithium oxide, lanthanum fluoride, titanium dioxide, samarium trifluoride, gadolinium fluoride, and cerium tetrafluoride.

[0019] The dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:1.

[0020] The homogenizing agent is a mixture of cyclohexanone and white oil in a mass ratio of 3:1.

[0021] The defoaming agent is one or more of n-octanol, cyclopentanol, silicone oil and polydimethylsiloxane.

[0022] The raw material components and proportions of the isolation powder in step (5) are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1: (0.015-0.025): (3-5).

[0023] Beneficial effects of the present invention: The silicon nitride substrate prepared by the present invention has good flatness, low roughness and high mechanical properties. The composite plasticizer of di(2-ethylhexyl) terephthalate and dibutyl sebacate is used to improve the fracture toughness of the material; the composite dispersant of polyethyleneimine and sodium tripolyphosphate is used to reduce the roughness of the material; the composite homogenizer of cyclohexanone and white oil is used to reduce the warpage of the material and improve the flatness of the material. DETAILED DESCRIPTION

[0024] In order to facilitate the understanding of the present invention, the present invention will be described more fully below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0025] Example 1

[0026] A method for preparing a high-flatness silicon nitride substrate is carried out according to the following steps:

[0027] (1) preparing an organic glue: adding polyvinyl butyral, a plasticizer, and an organic solvent into a container and stirring them evenly; the mass ratio of the polyvinyl butyral, the plasticizer, and the 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;

[0028] (2) Ball milling and mixing: adding an organic solvent, silicon nitride powder, magnesium silicon nitride, a dispersant, a homogenizing agent, and n-octanol to a ball mill in sequence, and ball milling for 18 hours to obtain a mixed slurry; adding the organic glue prepared in step (1), and ball milling for another 30 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, a dispersant, a homogenizing agent, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic glue 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 homogenizing agent is a mixture of cyclohexanone and white oil in a mass ratio of 3:1;

[0029] (3) Degassing and aging: The casting slurry prepared in step (2) was subjected to vacuum degassing for 15 min, and stirred and aged for 7 h at a speed of 8 rpm, with the viscosity controlled at 18,000 cps, the solid content at 70%, and the temperature at 20°C;

[0030] (4) Tape casting: The slurry prepared in step (3) is tape cast using a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.5 m / min, the temperature of the first zone of the tape casting drying chamber is 30° C., the temperature of the second zone of the tape casting drying chamber is 60° C., and the temperature of the first zone of the tape casting drying chamber is 85° C.;

[0031] (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 a powder coating line via a conveyor belt for powder coating. The powder coating pressure is 0.08 MPa and the powder coating temperature is 65° C. The raw material components and ratios of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4;

[0032] (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 90°C, and the time is 4 hours;

[0033] (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; the process parameters of this step are: debinding temperature 600°C, total time: 20h, heating rate at 300°C <5°C / min;

[0034] (8) Pressure sintering: placing the debinded product into a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1800°C, sintering time: 28h, pressure: 0.8Mpa, and a heating rate of 1680°C in the heating stage <1°C / min;

[0035] (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

[0036] Example 2

[0037] A method for preparing a high-flatness silicon nitride substrate is carried out according to the following steps:

[0038] (1) preparing an organic glue: adding ethyl cellulose, a plasticizer, and ethanol into a container and stirring them evenly; the mass ratio of the ethyl cellulose, the plasticizer, and the 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;

[0039] (2) Ball milling and mixing: ethanol, silicon nitride powder, lithium oxide, dispersant, homogenizing agent, and polydimethylsiloxane are added to a ball mill in sequence, and the mixture is ball milled for 14 hours to obtain a mixed slurry; the organic glue prepared in step (1) is added, and the mixture is ball milled for another 26 hours to obtain a casting slurry; the mass ratio of the ethanol, silicon nitride powder, lithium oxide, dispersant, homogenizing agent, and polydimethylsiloxane is 80:60:5:6:6:1; the mass ratio of the mixed slurry to the organic glue is 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;

[0040] (3) Degassing and aging: The casting slurry prepared in step (2) was subjected to vacuum degassing for 12 min, and stirred and aged for 6 h at a speed of 5 rpm, with the viscosity controlled at 12000 cps, the solid content at 65%, and the temperature at 15°C;

[0041] (4) Tape casting: The slurry prepared in step (3) is subjected to tape casting by a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.1 m / min, the temperature of the first zone of the tape casting drying chamber is 25° C., the temperature of the second zone of the tape casting drying chamber is 55° C., and the temperature of the first zone of the tape casting drying chamber is 65° C.;

[0042] (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 a powder coating line via a conveyor belt for powder coating. The powder coating pressure is 0.05 MPa and the powder coating temperature is 55° C. The raw material components and ratios of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.015:3-5;

[0043] (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 85°C, and the time is 3 hours;

[0044] (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; process parameters of this step: debinding temperature 550°C, total time: 15h, heating rate at 220°C <5°C / min;

[0045] (8) Pressure sintering: the debinded product is placed in a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1750°C, sintering time: 20h, pressure: 0.5Mpa, and the heating rate of 1650°C in the heating stage is less than 1°C / min;

[0046] (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

[0047] Example 3

[0048] A method for preparing a high-flatness silicon nitride substrate is carried out according to the following steps:

[0049] (1) preparing an organic glue: adding dextrin, a plasticizer, and isopropanol into a container and stirring evenly; the mass ratio of the dextrin, the plasticizer, and the 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;

[0050] (2) Ball milling and mixing: isopropanol, silicon nitride powder, lanthanum fluoride, dispersant, homogenizing agent, and silicone oil are added to a ball mill in sequence, and the mixture is ball milled for 24 hours to obtain a mixed slurry; the organic glue prepared in step (1) is added, and the mixture is ball milled for another 36 hours to obtain a casting slurry; the mass ratio of the isopropanol, silicon nitride powder, lanthanum fluoride, dispersant, homogenizing agent, and silicone oil is 120:150:15:10:15:3; the mass ratio of the mixed slurry to the organic glue is 4:1; 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;

[0051] (3) Degassing and aging: The casting slurry prepared in step (2) was subjected to vacuum degassing for 20 min, and stirred and aged for 10 h at a speed of 10 rpm, with the viscosity controlled at 20,000 cps, the solid content at 75%, and the temperature at 25° C.;

[0052] (4) Tape casting: The slurry prepared in step (3) is subjected to tape casting using a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.2 m / min, the temperature of the first zone of the tape casting drying chamber is 35° C., the temperature of the second zone of the tape casting drying chamber is 75° C., and the temperature of the first zone of the tape casting drying chamber is 105° C.;

[0053] (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 a powder coating line via a conveyor belt for powder coating. The powder coating pressure is 0.1 MPa and the powder coating temperature is 85° C. The raw material components and ratios of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.025:5;

[0054] (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 100°C, and the time is 5 hours;

[0055] (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; process parameters of this step: debinding temperature 650°C, total time: 25h, heating rate below 350°C <5°C / min;

[0056] (8) Pressure sintering: the debinded product is placed in a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1850°C, sintering time: 35h, pressure: 1.0Mpa, and the heating rate of 1700°C in the heating stage is less than 1°C / min;

[0057] (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

[0058] Comparative Example 1

[0059] A method for preparing a high-flatness silicon nitride substrate is carried out according to the following steps:

[0060] (1) preparing an organic glue: adding polyvinyl butyral, di(2-ethylhexyl) terephthalate, and an organic solvent into a container and stirring them evenly; the mass ratio of the polyvinyl butyral, di(2-ethylhexyl) terephthalate, and the organic solvent is 15:20:100; and the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1;

[0061] (2) Ball milling and mixing: adding an organic solvent, silicon nitride powder, magnesium silicon nitride, a dispersant, a homogenizing agent, and n-octanol to a ball mill in sequence, and ball milling for 18 hours to obtain a mixed slurry; adding the organic glue prepared in step (1), and ball milling for another 30 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, a dispersant, a homogenizing agent, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic glue 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 homogenizing agent is a mixture of cyclohexanone and white oil in a mass ratio of 3:1;

[0062] (3) Degassing and aging: The casting slurry prepared in step (2) was subjected to vacuum degassing for 15 min, and stirred and aged for 7 h at a speed of 8 rpm, with the viscosity controlled at 18,000 cps, the solid content at 70%, and the temperature at 20°C;

[0063] (4) Tape casting: The slurry prepared in step (3) is tape cast using a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.5 m / min, the temperature of the first zone of the tape casting drying chamber is 30° C., the temperature of the second zone of the tape casting drying chamber is 60° C., and the temperature of the first zone of the tape casting drying chamber is 85° C.;

[0064] (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 a powder coating line via a conveyor belt for powder coating. The powder coating pressure is 0.08 MPa and the powder coating temperature is 65° C. The raw material components and ratios of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4;

[0065] (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 90°C, and the time is 4 hours;

[0066] (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; the process parameters of this step are: debinding temperature 600°C, total time: 20h, heating rate at 300°C <5°C / min;

[0067] (8) Pressure sintering: placing the debinded product into a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1800°C, sintering time: 28h, pressure: 0.8Mpa, and a heating rate of 1680°C in the heating stage <1°C / min;

[0068] (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

[0069] Comparative Example 2

[0070] A method for preparing a high-flatness silicon nitride substrate is carried out according to the following steps:

[0071] (1) preparing an organic glue: adding polyvinyl butyral, dibutyl sebacate, and an organic solvent into a container and stirring them evenly; the mass ratio of the polyvinyl butyral, dibutyl sebacate, and the organic solvent is 15:20:100; and the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1;

[0072] (2) Ball milling and mixing: adding an organic solvent, silicon nitride powder, magnesium silicon nitride, a dispersant, a homogenizing agent, and n-octanol to a ball mill in sequence, and ball milling for 18 hours to obtain a mixed slurry; adding the organic glue prepared in step (1), and ball milling for another 30 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, a dispersant, a homogenizing agent, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic glue 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 homogenizing agent is a mixture of cyclohexanone and white oil in a mass ratio of 3:1;

[0073] (3) Degassing and aging: The casting slurry prepared in step (2) was subjected to vacuum degassing for 15 min, and stirred and aged for 7 h at a speed of 8 rpm, with the viscosity controlled at 18,000 cps, the solid content at 70%, and the temperature at 20°C;

[0074] (4) Tape casting: The slurry prepared in step (3) is tape cast using a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.5 m / min, the temperature of the first zone of the tape casting drying chamber is 30° C., the temperature of the second zone of the tape casting drying chamber is 60° C., and the temperature of the first zone of the tape casting drying chamber is 85° C.;

[0075] (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 a powder coating line via a conveyor belt for powder coating. The powder coating pressure is 0.08 MPa and the powder coating temperature is 65° C. The raw material components and ratios of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4;

[0076] (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 90°C, and the time is 4 hours;

[0077] (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; the process parameters of this step are: debinding temperature 600°C, total time: 20h, heating rate at 300°C <5°C / min;

[0078] (8) Pressure sintering: placing the debinded product into a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1800°C, sintering time: 28h, pressure: 0.8Mpa, and a heating rate of 1680°C in the heating stage <1°C / min;

[0079] (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

[0080] Comparative Example 3

[0081] A method for preparing a high-flatness silicon nitride substrate is carried out according to the following steps:

[0082] (1) preparing an organic glue: adding polyvinyl butyral, a plasticizer, and an organic solvent into a container and stirring them evenly; the mass ratio of the polyvinyl butyral, the plasticizer, and the 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;

[0083] (2) ball milling and mixing: adding an organic solvent, silicon nitride powder, magnesium silicon nitride, polyethyleneimine, a homogenizing agent, and n-octanol to a ball mill in sequence, and ball milling for 18 hours to obtain a mixed slurry; adding the organic glue prepared in step (1), and ball milling for another 30 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, polyethyleneimine, a homogenizing agent, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic glue is 3:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; the homogenizing agent is a mixture of cyclohexanone and white oil in a mass ratio of 3:1;

[0084] (3) Degassing and aging: The casting slurry prepared in step (2) was subjected to vacuum degassing for 15 min, and stirred and aged for 7 h at a speed of 8 rpm, with the viscosity controlled at 18,000 cps, the solid content at 70%, and the temperature at 20°C;

[0085] (4) Tape casting: The slurry prepared in step (3) is tape cast using a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.5 m / min, the temperature of the first zone of the tape casting drying chamber is 30° C., the temperature of the second zone of the tape casting drying chamber is 60° C., and the temperature of the first zone of the tape casting drying chamber is 85° C.;

[0086] (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 a powder coating line via a conveyor belt for powder coating. The powder coating pressure is 0.08 MPa and the powder coating temperature is 65° C. The raw material components and ratios of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4;

[0087] (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 90°C, and the time is 4 hours;

[0088] (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; the process parameters of this step are: debinding temperature 600°C, total time: 20h, heating rate at 300°C <5°C / min;

[0089] (8) Pressure sintering: placing the debinded product into a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1800°C, sintering time: 28h, pressure: 0.8Mpa, and a heating rate of 1680°C in the heating stage <1°C / min;

[0090] (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

[0091] Comparative Example 4

[0092] A method for preparing a high-flatness silicon nitride substrate is carried out according to the following steps:

[0093] (1) preparing an organic glue: adding polyvinyl butyral, a plasticizer, and an organic solvent into a container and stirring them evenly; the mass ratio of the polyvinyl butyral, the plasticizer, and the 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;

[0094] (2) ball milling and mixing: adding an organic solvent, silicon nitride powder, magnesium silicon nitride, sodium tripolyphosphate, a homogenizing agent, and n-octanol to a ball mill in sequence, and ball milling for 18 hours to obtain a mixed slurry; adding the organic glue prepared in step (1), and ball milling for another 30 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, sodium tripolyphosphate, a homogenizing agent, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic glue is 3:1; the organic solvent is a mixture of toluene and isopropanol in a volume ratio of 1:1; the homogenizing agent is a mixture of cyclohexanone and white oil in a mass ratio of 3:1;

[0095] (3) Degassing and aging: The casting slurry prepared in step (2) was subjected to vacuum degassing for 15 min, and stirred and aged for 7 h at a speed of 8 rpm, with the viscosity controlled at 18,000 cps, the solid content at 70%, and the temperature at 20°C;

[0096] (4) Tape casting: The slurry prepared in step (3) is tape cast using a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.5 m / min, the temperature of the first zone of the tape casting drying chamber is 30° C., the temperature of the second zone of the tape casting drying chamber is 60° C., and the temperature of the first zone of the tape casting drying chamber is 85° C.;

[0097] (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 a powder coating line via a conveyor belt for powder coating. The powder coating pressure is 0.08 MPa and the powder coating temperature is 65° C. The raw material components and ratios of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4;

[0098] (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 90°C, and the time is 4 hours;

[0099] (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; the process parameters of this step are: debinding temperature 600°C, total time: 20h, heating rate at 300°C <5°C / min;

[0100] (8) Pressure sintering: placing the debinded product into a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1800°C, sintering time: 28h, pressure: 0.8Mpa, and a heating rate of 1680°C in the heating stage <1°C / min;

[0101] (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

[0102] Comparative Example 5

[0103] A method for preparing a high-flatness silicon nitride substrate is carried out according to the following steps:

[0104] (1) preparing an organic glue: adding polyvinyl butyral, a plasticizer, and an organic solvent into a container and stirring them evenly; the mass ratio of the polyvinyl butyral, the plasticizer, and the 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;

[0105] (2) Ball milling and mixing: adding an organic solvent, silicon nitride powder, magnesium silicon nitride, a dispersant, cyclohexanone, and n-octanol to a ball mill in sequence, and ball milling for 18 hours to obtain a mixed slurry; adding the organic glue prepared in step (1), and ball milling for another 30 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, a dispersant, cyclohexanone, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic glue 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;

[0106] (3) Degassing and aging: The casting slurry prepared in step (2) was subjected to vacuum degassing for 15 min, and stirred and aged for 7 h at a speed of 8 rpm, with the viscosity controlled at 18,000 cps, the solid content at 70%, and the temperature at 20°C;

[0107] (4) Tape casting: The slurry prepared in step (3) is tape cast using a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.5 m / min, the temperature of the first zone of the tape casting drying chamber is 30° C., the temperature of the second zone of the tape casting drying chamber is 60° C., and the temperature of the first zone of the tape casting drying chamber is 85° C.;

[0108] (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 a powder coating line via a conveyor belt for powder coating. The powder coating pressure is 0.08 MPa and the powder coating temperature is 65° C. The raw material components and ratios of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4;

[0109] (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 90°C, and the time is 4 hours;

[0110] (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; the process parameters of this step are: debinding temperature 600°C, total time: 20h, heating rate at 300°C <5°C / min;

[0111] (8) Pressure sintering: placing the debinded product into a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1800°C, sintering time: 28h, pressure: 0.8Mpa, and a heating rate of 1680°C in the heating stage <1°C / min;

[0112] (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

[0113] Comparative Example 6

[0114] A method for preparing a high-flatness silicon nitride substrate is carried out according to the following steps:

[0115] (1) preparing an organic glue: adding polyvinyl butyral, a plasticizer, and an organic solvent into a container and stirring them evenly; the mass ratio of the polyvinyl butyral, the plasticizer, and the 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;

[0116] (2) Ball milling and mixing: adding an organic solvent, silicon nitride powder, magnesium silicon nitride, a dispersant, white oil, and n-octanol to a ball mill in sequence, and ball milling for 18 hours to obtain a mixed slurry; adding the organic glue prepared in step (1), and ball milling for another 30 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, magnesium silicon nitride, a dispersant, white oil, and n-octanol is 100:120:10:8:10:2; the mass ratio of the mixed slurry to the organic glue 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;

[0117] (3) Degassing and aging: The casting slurry prepared in step (2) was subjected to vacuum degassing for 15 min, and stirred and aged for 7 h at a speed of 8 rpm, with the viscosity controlled at 18,000 cps, the solid content at 70%, and the temperature at 20°C;

[0118] (4) Tape casting: The slurry prepared in step (3) is tape cast using a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.5 m / min, the temperature of the first zone of the tape casting drying chamber is 30° C., the temperature of the second zone of the tape casting drying chamber is 60° C., and the temperature of the first zone of the tape casting drying chamber is 85° C.;

[0119] (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 a powder coating line via a conveyor belt for powder coating. The powder coating pressure is 0.08 MPa and the powder coating temperature is 65° C. The raw material components and ratios of the isolation powder are: boron nitride powder: polyvinyl butyral: anhydrous ethanol = 1:0.02:4;

[0120] (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 90°C, and the time is 4 hours;

[0121] (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; the process parameters of this step are: debinding temperature 600°C, total time: 20h, heating rate at 300°C <5°C / min;

[0122] (8) Pressure sintering: placing the debinded product into a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1800°C, sintering time: 28h, pressure: 0.8Mpa, and a heating rate of 1680°C in the heating stage <1°C / min;

[0123] (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

[0124] Experimental Example 1:

[0125] The fracture toughness of the silicon nitride substrates prepared in Examples 1-3 and Comparative Examples 1-2 was tested by indentation method, the applied load was 196N, each group of experiments was measured three times in parallel, and SPSS24.0 software was used for statistical analysis. The quantitative data results were expressed as The data were expressed as mean ± standard deviation. The Kolmogorov-Smirnov test was used for normality test. For data that met the normal distribution, the t-test was used to compare the mean differences between the two groups. The difference was considered statistically significant when P < 0.05.

[0126] The test results are shown in Table 1:

[0127] Table 1

[0128]

[0129] Note: * represents P < 0.05 compared with the group in Example 1.

[0130] Experimental Example 2:

[0131] The surface roughness of the silicon nitride substrates prepared in Examples 1-3 and Comparative Examples 3-4 was tested. The surface roughness was tested by selecting at least 5 test points on the front and back sides of the silicon nitride substrate, and taking the average value of the roughness of all the test points as the test result. All the test points include a central point located in the center, and the remaining test points are located outside the central point and close to the corners of the silicon nitride substrate. The test results are shown in Table 2:

[0132] Table 2

[0133]

[0134] Note: * represents P < 0.05 compared with the group in Example 1.

[0135] Experimental Example 3:

[0136] The warpage (mm / 25.4 mm) 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:

[0137] Table 3

[0138]

[0139] Note: * represents P < 0.05 compared with the group in Example 1.

[0140] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a high-flatness silicon nitride substrate, characterized in that: Follow these steps: (1) preparing organic glue: adding adhesive, plasticizer and organic solvent into a container and stirring evenly; the mass ratio of the adhesive, plasticizer and organic solvent is (10-20): (15-25): (80-120); (2) ball milling and mixing: adding an organic solvent, silicon nitride powder, a sintering aid, a dispersant, a homogenizing agent, and a defoaming agent to a ball mill in sequence, and ball milling for 12-24 hours to obtain a mixed slurry; adding the organic glue prepared in step (1), and ball milling for another 24-36 hours to obtain a casting slurry; the mass ratio of the organic solvent, silicon nitride powder, sintering aid, dispersant, homogenizing agent, and defoaming agent is (80-120): (50-150): (5-15): (5-10): (5-15): (1-3); the mass ratio of the mixed slurry to the organic glue is (1-5): 1; (3) Degassing and aging: vacuum degassing the tape casting slurry prepared in step (2) for 10-20 minutes, and stirring and aging at a speed of 5-10 rpm for 5-10 hours, controlling the viscosity to be 12000-20000 cps, the solid content to be 65-80%, and the temperature to be 15-25°C; (4) Tape casting: The slurry prepared in step (3) is subjected to tape casting by a tape casting machine, and the green body is wrapped with a paper tube; the process parameters of this step are: tape casting speed 0.1-0.2 m / min, the temperature of the first zone of the tape casting drying chamber is 25-35°C, the temperature of the second zone of the tape casting drying chamber is 55-75°C, and the temperature of the first zone of the tape casting drying chamber is 65-105°C; (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 coating line via a conveyor belt for powder coating. The powder coating pressure is 0.05-0.1Mpa and the powder coating temperature is 55-85°C; (6) Low-temperature flattening treatment: The powder-coated silicon nitride green bodies are stacked on a firing plate in an alternating manner according to the front and back sides, and a weight plate is placed on the stacked silicon nitride green bodies; the weight plate is a boron nitride plate, the flattening temperature is 85-100°C, and the time is 3-5h; (7) Air debinding: Place the flattened green body into an intermittent furnace for debinding; process parameters of this step: debinding temperature 550-650°C, total time: 15-25h, heating rate <5°C / min between 220-350°C; (8) Pressure sintering: placing the debinded product into a sintering furnace for sintering; the process parameters of this step are: sintering temperature 1750-1850°C, sintering time: 20-35h, pressure: 0.5-1.0Mpa, and a heating rate of 1650-1700°C in the heating stage of <1°C / min; (9) Removal of isolation powder: Use dust removal equipment to remove the isolation powder on the surface of silicon nitride ceramics after sintering.

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

1.

4. 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.

5. 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 magnesium silicon nitride, lithium oxide, lanthanum fluoride, titanium dioxide, samarium trifluoride, gadolinium fluoride, and cerium tetrafluoride.

6. The method for preparing a high-flatness silicon nitride substrate according to claim 1, characterized in that: The dispersant is a mixture of polyethyleneimine and sodium tripolyphosphate in a mass ratio of 1:

1.

7. The method for preparing a high-flatness silicon nitride substrate according to claim 1, characterized in that: The homogenizing agent is a mixture of cyclohexanone and white oil in a mass ratio of 3:

1.

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

9. The method for preparing a high-flatness silicon nitride substrate according to claim 1, characterized in that: The raw material components and proportions 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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