High-thermal-conductivity silicon nitride substrate and preparation method thereof

Abstract

The invention provides a silicon nitride substrate with high thermal conductivity and a preparation method thereof, the preparation method adopts silicon powder with lower cost as a raw material, and particularly adopts nano silicon powder, nano magnesium oxide, nano yttrium oxide and nano titanium oxide as raw materials, so that the preparation cost of the silicon nitride substrate is effectively reduced; the obtained slurry is subjected to tape casting, drying and glue discharging in sequence, an obtained thin plate green body is subjected to air pressure sintering in a mixed reaction atmosphere of nitrogen and ammonia gas, the ammonia gas can be decomposed into nitrogen and hydrogen, the oxygen content of the silicon nitride substrate can be reduced through the reduction effect of the hydrogen, and therefore the heat-conducting property and the mechanical property of the silicon nitride substrate are improved; the thermal conductivity of the silicon nitride substrate is larger than or equal to 100 W / (m.K), the bending strength is larger than or equal to 78 MPa, and the fracture toughness is larger than or equal to 7 MPa.m < 1 / 2 >.

Description

Technical Field

[0001] The invention relates to the technical field of silicon nitride material preparation, and in particular to a high thermal conductivity silicon nitride substrate and a preparation method thereof. Background Art

[0002] Silicon nitride is a high-performance semiconductor material with good thermal conductivity, electrical insulation, high temperature resistance and chemical stability. Therefore, it is widely used in heat dissipation devices in the fields of electronics, aerospace and automobiles. However, the preparation cost of silicon nitride is relatively high, mainly due to the high price of silicon nitride raw powder. In addition, the thermal conductivity of silicon nitride is also affected by its oxygen content. The higher the oxygen content, the worse the thermal conductivity.

[0003] At present, there are two main methods for preparing silicon nitride: one is the high-temperature solid-phase reaction method, and the other is the chemical vapor deposition method. The high-temperature solid-phase reaction method is to react silicon powder and nitrogen at high temperature to generate silicon nitride. The advantage of this method is that the process is simple, but the energy consumption is high, and the purity of the obtained silicon nitride is not high; the chemical vapor deposition method is to deposit a silicon nitride film on the surface of the substrate through a chemical reaction. The advantage of this method is that the purity of the obtained silicon nitride is high, but the equipment is complex and the cost is high.

[0004] The existing silicon nitride preparation methods have the following main problems: first, the preparation cost is high, mainly due to the high price of silicon nitride raw powder; second, the thermal conductivity of the obtained silicon nitride is affected by its oxygen content. The higher the oxygen content, the worse the thermal conductivity.

[0005] Therefore, how to reduce the preparation cost and improve the thermal conductivity of silicon nitride while ensuring its quality is an important issue facing the current silicon nitride preparation technology. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a high thermal conductivity silicon nitride substrate and a preparation method thereof. The preparation method uses low-cost silicon powder as a raw material, thereby effectively reducing the preparation cost of the silicon nitride substrate, and performs gas pressure sintering in a mixed reaction atmosphere of nitrogen and ammonia. The ammonia will decompose into nitrogen and hydrogen. The reduction effect of hydrogen can reduce the oxygen content of the silicon nitride substrate, thereby improving the thermal conductivity and mechanical properties of the silicon nitride substrate. The thermal conductivity of the silicon nitride substrate is ≥100W / (m·K), the flexural strength is ≥78MPa, and the fracture toughness is ≥7MPa·m 1 / 2 .

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] One of the purposes of the present invention is to provide a method for preparing a high thermal conductivity silicon nitride substrate, the preparation method comprising the following steps:

[0009] Step S1: uniformly mixing silicon powder, sintering aid, solvent, hyperdispersant and defoamer to obtain a suspension; uniformly mixing a binder, a plasticizer and the suspension to obtain a slurry;

[0010] Step S2: sequentially tape-casting, drying, and debinding the slurry to obtain a green sheet;

[0011] Step S3: sintering the green sheet in a mixed reaction atmosphere of nitrogen and ammonia to obtain a silicon nitride substrate with high thermal conductivity.

[0012] The preparation method of the present invention uses low-cost silicon powder as a raw material, thereby effectively reducing the preparation cost of the silicon nitride substrate, and performs pressure sintering in a mixed reaction atmosphere of nitrogen and ammonia. The ammonia will decompose into nitrogen and hydrogen. The reduction effect of hydrogen can reduce the oxygen content of the silicon nitride substrate, thereby improving the thermal conductivity and mechanical properties of the silicon nitride substrate. The thermal conductivity of the silicon nitride substrate is ≥100W / (m·K), the flexural strength is ≥78MPa, and the fracture toughness is ≥7MPa·m 1 / 2 .

[0013] As a preferred technical solution of the present invention, in step S1, the silicon powder is surface treated before mixing, including: mixing the silicon powder and ultrapure water in a mass ratio of 1:(4-6), adding hydrofluoric acid at a rate of 6-10 ml of hydrofluoric acid per 100 g of silicon powder, reacting at 30-50° C. for 4-8 hours, filtering, washing and drying in sequence to obtain the surface-treated silicon powder.

[0014] In the surface treatment of the present invention, the mass ratio of silicon powder to ultrapure water is 1:(4-6), for example 1:4, 1:4.5, 1:5, 1:5.5 or 1:6, etc., the reaction temperature is 30-50°C, for example 30°C, 35°C, 40°C, 45°C or 50°C, etc., and the reaction time is 4-8h, for example 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h, etc.

[0015] As a preferred technical solution of the present invention, in step S1, the sintering aid includes magnesium oxide, yttrium oxide and titanium oxide, and the mass ratio of silicon powder, magnesium oxide, yttrium oxide and titanium oxide is 1:(0.05-0.2):(0.03-0.1):(0.01-0.1), for example, 1:0.05:0.03:0.01, 1:0.1:0.05:0.05 or 1:0.2:0.1:0.1, etc.

[0016] As a preferred technical solution of the present invention, in step S1, the particle size of the silicon powder is 400-600nm, for example, 400nm, 450nm, 500nm, 550nm or 600nm, and the particle size of the sintering aid is 150-200nm, for example, 150nm, 160nm, 170nm, 180nm, 190nm or 200nm, and the sintering aid includes magnesium oxide, yttrium oxide and titanium oxide, and the particle sizes of the three respectively meet 150-200nm.

[0017] It should be noted that the preparation method of the present invention can obtain a silicon nitride substrate with high purity and good quality. This is because the present invention uses nano-level raw materials, such as nano-silicon powder, nano-magnesium oxide, nano-yttrium oxide and nano-titanium oxide. These raw materials have small particle size and high activity, which are conducive to improving the completeness of the reaction, thereby obtaining a high-quality silicon nitride substrate.

[0018] As a preferred technical solution of the present invention, in step S1, the solvent includes a mixture of any one or more of ethanol, n-butanol, acetone or butanone in any proportion; the amount of the solvent is 50-80wt% of the total mass of the silicon powder and the sintering aid, for example, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt% or 80wt%, etc.

[0019] In step S1, the amount of the super dispersant is 0.1-0.8wt% of the total mass of silicon powder and sintering aid, such as 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt% or 0.8wt%, etc. The preparation method of the present invention can effectively interact with the powder particles and the dispersion medium at the same time through the super dispersant to achieve a stable dispersion state, prevent the powder particles from precipitating or agglomerating in the solvent, thereby maintaining the stable uniformity of the slurry, and then improving the thermal conductivity of the silicon nitride substrate. The super dispersant of the present invention can be selected from KMT-3017 water-based dispersant of Foshan Corning New Materials Co., Ltd., RD-9774 dispersant of Tianjin Ruike, or similar products of other companies.

[0020] In step S1, the defoamer is a waterborne polyurethane coating defoamer, and the amount of the defoamer is 0.3-0.5wt%, such as 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt% or 0.5wt%, etc. The defoamer of the present invention can prevent agglomeration, eliminate bubbles generated by grinding, and facilitate molding. The DT-9825 defoamer of Datian Chemical can be selected.

[0021] In step S1, the binder is polyvinyl butyral, and the amount of the binder is 2-8wt% of the total mass of silicon powder and sintering aid, such as 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt% or 8wt%.

[0022] In step S1, the plasticizer is butyl benzyl phthalate, and the amount of the plasticizer is 1-4wt% of the total mass of silicon powder and sintering aid, such as 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt% or 4wt%.

[0023] As a preferred technical solution of the present invention, in step S2, the casting tape speed of the tape casting is 0.4-4.0m / min, for example, 0.4m / min, 1.0m / min, 1.5m / min, 2.0m / min, 2.5m / min, 3.0m / min, 3.5m / min or 4.0m / min, and the thickness of the thin plate green embryo obtained by the tape casting is 0.4-0.6mm, for example, 0.4mm, 0.45mm, 0.5mm, 0.55mm or 0.6mm, etc.

[0024] As a preferred technical solution of the present invention, in step S2, the debinding is carried out in a nitrogen atmosphere, firstly heating to 680-750°C at a rate of 3-8°C / min, keeping the temperature for 5-10h, and then naturally cooling to room temperature.

[0025] In the debinding process of the present invention, the heating rate is 3-8°C / min, for example, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min or 8°C / min.

[0026] In the debinding process of the present invention, the target temperature for heating is 680-750°C, for example, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C or 750°C.

[0027] The debinding process of the present invention is heat-insulated for 5-10 hours, such as 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours.

[0028] As a preferred technical solution of the present invention, in step S3, in the mixed reaction atmosphere of nitrogen and ammonia, the volume ratio of nitrogen to ammonia is 1:(0.1-1), for example, 1:0.1, 1:0.3, 1:0.5, 1:0.6, 1:0.8 or 1:1, and the gas pressure is maintained at 5-10MPa, for example, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa or 10MPa, etc.

[0029] As a preferred technical solution of the present invention, in step S3, the gas pressure sintering includes: first heating to 750-850°C at a rate of 10-15°C / min, and keeping warm for 1-3h; then heating to 1000-1500°C at a rate of 8-12°C / min, and keeping warm for 8-12h; finally heating to 1800-1900°C at a rate of 2-5°C / min, and keeping warm for 8-12h; and naturally cooling to room temperature.

[0030] In the gas pressure sintering described in the present invention, the heating rate of the first stage is 10-15°C / min, for example, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min or 15°C / min, etc., the target temperature of the first stage is 750-850°C, for example, 750°C, 760°C, 780°C, 800°C, 810°C, 830°C or 850°C, etc., and the insulation time of the first stage is 1-3h, for example, 1h, 1.5h, 2h, 2.5h or 3h, etc.

[0031] In the gas pressure sintering described in the present invention, the heating rate of the second stage is 8-12°C / min, for example, 8°C / min, 9°C / min, 10°C / min, 11°C / min or 12°C / min, etc., the target temperature of the second stage is 1000-1500°C, for example, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C or 1500°C, etc., and the insulation time of the second stage is 8-12h, for example, 8h, 9h, 10h, 11h or 12h, etc.

[0032] In the gas pressure sintering described in the present invention, the heating rate of the third stage is 2-5°C / min, for example, 2°C / min, 3°C / min, 4°C / min or 5°C / min, etc., the target temperature of the third stage is 1800-1900°C, for example, 1800°C, 1810°C, 1830°C, 1850°C, 1870°C, 1880°C or 1900°C, etc., and the insulation time of the third stage is 8-12h, for example, 8h, 9h, 10h, 11h or 12h, etc.

[0033] A second object of the present invention is to provide a silicon nitride substrate with high thermal conductivity, which is prepared by the preparation method described in the first object.

[0034] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0035] (1) The preparation method of the present invention mainly uses nano silicon powder, nano magnesium oxide, nano yttrium oxide and nano titanium oxide as raw materials, the prices of these raw materials are relatively low, thereby effectively reducing the preparation cost of the silicon nitride substrate. Compared with the existing silicon nitride preparation method, the preparation method of the present invention is more economical;

[0036] (2) The preparation method of the present invention performs pressure sintering in a mixed reaction atmosphere of nitrogen and ammonia. Ammonia will decompose into nitrogen and hydrogen. The reduction effect of hydrogen can reduce the oxygen content of the silicon nitride substrate, thereby improving the thermal conductivity and mechanical properties of the silicon nitride substrate. The thermal conductivity of the silicon nitride substrate is ≥100W / (m·K), the flexural strength is ≥78MPa, and the fracture toughness is ≥7MPa·m 1 / 2 ;

[0037] (3) The preparation method of the present invention is simple and easy to implement, avoiding the complex steps such as high-temperature solid-phase reaction or chemical vapor deposition required in the existing silicon nitride preparation method, thereby greatly simplifying the preparation process, improving production efficiency and reducing production costs. DETAILED DESCRIPTION

[0038] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0039] The material models of the embodiments of the present invention are as follows: silicon powder, particle size 500nm, purity 99.999%; magnesium oxide, particle size 200nm; yttrium oxide, particle size 180nm; titanium oxide, particle size 180nm; hydrofluoric acid, concentration 50wt%, analytical grade, domestic chemical plant; ethanol, n-butanol, acetone, butanone, analytical grade, domestic chemical plant; hyperdispersant, Foshan Corning New Materials Co., Ltd., KMT-3017 water-based dispersant; defoamer, Datian Chemical DT-9825.

[0040] Example 1

[0041] This embodiment provides a method for preparing a high thermal conductivity silicon nitride substrate, the preparation method comprising the following steps:

[0042] Step S1: 500g silicon powder, 25g magnesium oxide, 15g yttrium oxide and 5g titanium oxide are put into a ball mill, that is, the mass ratio of silicon powder, magnesium oxide, yttrium oxide and titanium oxide is 1:0.05:0.03:0.01, 400g ethanol, 4.25g super dispersant and 2.5g defoamer are added, and ball milling is performed, with silicon nitride balls as ball milling media, the ball-to-material ratio is 3:1, the ball milling time is 12h, and the ball milling speed is 400r / min to obtain a suspension; 42.5g polyvinyl butyral and 17g butyl benzyl phthalate are added to the suspension, and secondary ball milling is performed, with silicon nitride balls as ball milling media, the ball-to-material ratio is 3:1, the ball milling time is 12h, and the ball milling speed is 400r / min to obtain a slurry;

[0043] Wherein, in step S1, the silicon powder is surface treated before mixing, including: mixing 500g of silicon powder and 2500g of deionized water, adding 40ml of hydrofluoric acid, reacting at 40°C for 6h, filtering, washing and drying in sequence to obtain silicon powder after surface treatment;

[0044] Step S2: tape-casting the slurry at a tape casting speed of 0.4 m / min to obtain a thin plate blank with a thickness of 0.4 mm, drying at 70° C. for 4 h, placing it in nitrogen for debinding, heating it to 680° C. at a speed of 4° C. / min, keeping it warm for 6 h, and then naturally cooling it to room temperature to obtain a thin plate blank after debinding;

[0045] Step S3: The debinding thin plate green body is subjected to gas pressure sintering in a mixed reaction atmosphere of nitrogen and ammonia, wherein the volume ratio of nitrogen to ammonia in the mixed reaction atmosphere is 7:3, and the gas pressure is maintained at 6MPa; the process conditions of gas pressure sintering are: firstly, the temperature is increased to 800°C at a rate of 10°C / min, and kept warm for 3h; then, the temperature is increased to 1300°C at a rate of 8°C / min, and kept warm for 8h; finally, the temperature is increased to 1850°C at a rate of 2°C / min, and kept warm for 8h; naturally cooled to room temperature; and a high thermal conductivity silicon nitride substrate is obtained.

[0046] Example 2

[0047] This embodiment provides a method for preparing a high thermal conductivity silicon nitride substrate, the preparation method comprising the following steps:

[0048] Step S1: 500g silicon powder, 30g magnesium oxide, 20g yttrium oxide and 5g titanium oxide are put into a ball mill, that is, the mass ratio of silicon powder, magnesium oxide, yttrium oxide and titanium oxide is 1:0.06:0.04:0.01, 400g ethanol, 4.25g super dispersant and 2.5g defoamer are added, and ball milling is performed, with silicon nitride balls as ball milling media, the ball-to-material ratio is 3:1, the ball milling time is 14h, and the ball milling speed is 400r / min to obtain a suspension; 42.5g polyvinyl butyral and 17g butyl benzyl phthalate are added to the suspension, and secondary ball milling is performed, with silicon nitride balls as ball milling media, the ball-to-material ratio is 3:1, the ball milling time is 14h, and the ball milling speed is 400r / min to obtain a slurry;

[0049] Wherein, in step S1, the silicon powder is surface treated before mixing, including: mixing 500g of silicon powder and 2500g of deionized water, adding 40ml of hydrofluoric acid, reacting at 40°C for 6h, filtering, washing and drying in sequence to obtain silicon powder after surface treatment;

[0050] Step S2: tape-casting the slurry at a tape speed of 0.4 m / min to obtain a green sheet with a thickness of 0.4 mm, drying it at 75° C. for 4 h, placing it in nitrogen for debinding, heating it to 700° C. at a speed of 4° C. / min, keeping it at that temperature for 6 h, and then naturally cooling it to room temperature to obtain a green sheet after debinding;

[0051] Step S3: The debinding thin plate green body is subjected to gas pressure sintering in a mixed reaction atmosphere of nitrogen and ammonia, wherein the volume ratio of nitrogen and ammonia in the mixed reaction atmosphere is 7:3, and the gas pressure is maintained at 8MPa; the process conditions of gas pressure sintering are: firstly heating to 800°C at a rate of 10°C / min and keeping warm for 3h; then heating to 1300°C at a rate of 8°C / min and keeping warm for 10h; finally heating to 1850°C at a rate of 2°C / min and keeping warm for 10h; naturally cooling to room temperature; and obtaining a high thermal conductivity silicon nitride substrate.

[0052] Example 3

[0053] This embodiment provides a method for preparing a high thermal conductivity silicon nitride substrate, the preparation method comprising the following steps:

[0054] Step S1: 500g silicon powder, 30g magnesium oxide, 20g yttrium oxide and 5g titanium oxide are put into a ball mill, that is, the mass ratio of silicon powder, magnesium oxide, yttrium oxide and titanium oxide is 1:0.06:0.04:0.01, 400g ethanol, 4.25g super dispersant and 2.5g defoamer are added, and ball milling is performed, with silicon nitride balls as ball milling media, the ball-to-material ratio is 3:1, the ball milling time is 14h, and the ball milling speed is 420r / min to obtain a suspension; 42.5g polyvinyl butyral and 17g butyl benzyl phthalate are added to the suspension, and secondary ball milling is performed, with silicon nitride balls as ball milling media, the ball-to-material ratio is 3:1, the ball milling time is 16h, and the ball milling speed is 400r / min to obtain a slurry;

[0055] Wherein, in step S1, the silicon powder is surface treated before mixing, including: mixing 500g of silicon powder and 2500g of deionized water, adding 40ml of hydrofluoric acid, reacting at 40°C for 6h, filtering, washing and drying in sequence to obtain silicon powder after surface treatment;

[0056] Step S2: tape-casting the slurry at a tape casting speed of 0.4 m / min to obtain a thin plate blank with a thickness of 0.4 mm, drying it at 75° C. for 4 h, placing it in nitrogen for debinding, heating it to 750° C. at a speed of 4° C. / min, keeping it at that temperature for 6 h, and then naturally cooling it to room temperature to obtain a thin plate blank after debinding;

[0057] Step S3: The debinding thin plate green body is subjected to gas pressure sintering in a mixed reaction atmosphere of nitrogen and ammonia, wherein the volume ratio of nitrogen and ammonia in the mixed reaction atmosphere is 6:4, and the gas pressure is maintained at 10 MPa; the process conditions of gas pressure sintering are: firstly heating to 800°C at a rate of 10°C / min and keeping warm for 3 hours; then heating to 1300°C at a rate of 6°C / min and keeping warm for 10 hours; finally heating to 1850°C at a rate of 2°C / min and keeping warm for 12 hours; naturally cooling to room temperature; and obtaining a high thermal conductivity silicon nitride substrate.

[0058] Example 4

[0059] This embodiment provides a method for preparing a high thermal conductivity silicon nitride substrate. Compared with the preparation method described in Example 3, the only difference is that the particle size of the silicon powder in this embodiment is no longer at the nanometer level, and the particle size of the silicon powder is 3 μm.

[0060] Example 5

[0061] This embodiment provides a method for preparing a silicon nitride substrate with high thermal conductivity. Compared with the preparation method described in Example 3, the only difference is that the hyperdispersant in step S1 is completely omitted.

[0062] Example 6

[0063] This embodiment provides a method for preparing a high thermal conductivity silicon nitride substrate. Compared with the preparation method described in Example 3, the only difference is that the surface treatment of silicon powder in step S1 is completely omitted and mixing is performed directly.

[0064] Comparative Example 1

[0065] This comparative example provides a method for preparing a silicon nitride substrate. Compared with the preparation method described in Example 3, the only difference is that the gas pressure sintering in step S3 is performed in a nitrogen atmosphere without containing ammonia.

[0066] Comparative Example 2

[0067] This comparative example provides a method for preparing a silicon nitride substrate. Compared with the preparation method described in Example 3, the only difference is that in the gas pressure sintering described in step S3, the volume ratio of nitrogen and ammonia in the mixed reaction atmosphere of nitrogen and ammonia is 1:0.05.

[0068] The silicon nitride substrates prepared in the above-mentioned embodiment and comparative example were tested for thermal conductivity, bending strength and fracture toughness, respectively. The specific test results are shown in Table 1.

[0069] Table 1

[0070]

[0071] From Table 1, we can see the following points:

[0072] (1) Comparing Example 3 with Example 4, since the particle size of the silicon powder in Example 4 is no longer at the nanometer level, but is 3 μm, the reactivity of the silicon powder is relatively low, which is not conducive to the completeness of the reaction during the gas pressure sintering process, resulting in a slight decrease in the thermal conductivity, flexural strength and fracture toughness of the silicon nitride substrate obtained in Example 4;

[0073] (2) Comparing Example 3 with Example 5, since the hyperdispersant in step S1 is completely omitted in Example 5, the dispersion state of the silicon powder is poor, and the powder particles slightly precipitate or agglomerate in the solvent, resulting in a slight decrease in the thermal conductivity, flexural strength and fracture toughness of the silicon nitride substrate obtained in Example 5;

[0074] (3) Comparing Example 3 with Example 6, since Example 6 completely omits the surface treatment of silicon powder in step S1 and directly performs mixing, the oxide film remaining on the surface of the silicon powder will increase the oxygen content of the silicon nitride substrate. Although ammonia will decompose into nitrogen and hydrogen during the subsequent gas pressure sintering process, and the reduction effect of hydrogen can reduce the oxygen content of the silicon nitride substrate, the thermal conductivity of the silicon nitride substrate obtained in Example 6 is still significantly reduced;

[0075] (4) Comparing Example 3 with Comparative Examples 1 and 2, since Comparative Example 1 performs the gas pressure sintering in step S3 under a nitrogen atmosphere and does not contain ammonia, hydrogen cannot be decomposed during the gas pressure sintering process, and the oxygen content of the silicon nitride substrate cannot be reduced, resulting in a significant decrease in the thermal conductivity, flexural strength and fracture toughness of the silicon nitride substrate obtained in Comparative Example 1. Since the volume ratio of nitrogen and ammonia in the gas pressure sintering in step S3 is set to 1:0.05 in Comparative Example 2, that is, the ammonia content is relatively low, resulting in a small amount of hydrogen generated by decomposition, and the reducing effect of hydrogen is relatively small, resulting in a slight decrease in the thermal conductivity, flexural strength and fracture toughness of the silicon nitride substrate obtained in Comparative Example 2. Moreover, although the ammonia content in gas pressure sintering can be further increased in theory, the hydrogen content generated by the decomposition of ammonia will also increase. Hydrogen, as a flammable and explosive gas, will increase the risk of safety accidents, so the ammonia content in gas pressure sintering should not be too high.

[0076] The present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a high thermal conductivity silicon nitride substrate, characterized in that: The preparation method comprises the following steps: Step S1: uniformly mixing silicon powder, sintering aid, solvent, hyperdispersant and defoamer to obtain a suspension; uniformly mixing a binder, a plasticizer and the suspension to obtain a slurry; Step S2: sequentially tape-casting, drying, and debinding the slurry to obtain a green sheet; Step S3: sintering the green sheet in a mixed reaction atmosphere of nitrogen and ammonia to obtain a silicon nitride substrate with high thermal conductivity.

2. The preparation method according to claim 1, characterized in that: In step S1, the silicon powder is surface treated before mixing, including: mixing the silicon powder and ultrapure water in a mass ratio of 1:(4-6), adding hydrofluoric acid at a rate of 6-10 ml hydrofluoric acid per 100 g silicon powder, reacting at 30-50° C. for 4-8 h, filtering, washing and drying in sequence to obtain the surface-treated silicon powder.

3. The preparation method according to claim 1 or 2, characterized in that: In step S1, the sintering aid includes magnesium oxide, yttrium oxide and titanium oxide, and the mass ratio of silicon powder, magnesium oxide, yttrium oxide and titanium oxide is 1:(0.05-0.2):(0.03-0.1):(0.01-0.1).

4. The preparation method according to claim 1 or 2, characterized in that: In step S1, the particle size of the silicon powder is 400-600 nm, and the particle size of the sintering aid is 150-200 nm.

5. The preparation method according to claim 1 or 2, characterized in that: In step S1, the solvent includes any one or more of ethanol, n-butanol, acetone or butanone in any proportion; the amount of the solvent is 50-80wt% of the total mass of the silicon powder and the sintering aid; In step S1, the amount of the superdispersant is 0.1-0.8wt% of the total mass of silicon powder and sintering aid; In step S1, the defoamer is a water-based polyurethane coating defoamer, and the amount of the defoamer is 0.3-0.5wt%; In step S1, the binder is polyvinyl butyral, and the amount of the binder is 2-8wt% of the total mass of silicon powder and sintering aid; In step S1, the plasticizer is butyl benzyl phthalate, and the amount of the plasticizer used is 1-4wt% of the total mass of silicon powder and sintering aid.

6. The preparation method according to claim 1 or 2, characterized in that: In step S2, the casting belt speed of the tape casting is 0.4-4.0 m / min, and the thickness of the thin plate green body obtained by the tape casting is 0.4-0.6 mm.

7. The preparation method according to claim 1 or 2, characterized in that: In step S2, the debinding is carried out in a nitrogen atmosphere, firstly the temperature is raised to 680-750°C at a rate of 3-8°C / min, kept at that temperature for 5-10 hours, and then naturally cooled to room temperature.

8. The preparation method according to claim 1 or 2, characterized in that: In step S3, in the mixed reaction atmosphere of nitrogen and ammonia, the volume ratio of nitrogen to ammonia is 1:(0.1-1), and the gas pressure is maintained at 5-10 MPa.

9. The preparation method according to claim 1 or 2, characterized in that: In step S3, the gas pressure sintering includes: first heating to 750-850°C at a rate of 10-15°C / min, and keeping warm for 1-3 hours; then heating to 1000-1500°C at a rate of 8-12°C / min, and keeping warm for 8-12 hours; finally heating to 1800-1900°C at a rate of 2-5°C / min, and keeping warm for 8-12 hours; and naturally cooling to room temperature.

10. A high thermal conductivity silicon nitride substrate, characterized in that: The preparation method is described in any one of claims 1 to 9.

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