Silicon nitride ceramic substrate, its preparation method, and preparation method of doctor blade slurry

Abstract

The present invention discloses a silicon nitride ceramic substrate, a preparation method thereof, and a preparation method of a casting slurry. The preparation method of the casting slurry includes the following steps: Step 1, slurry preparation: adding the pretreated silicon nitride powder to an organic solvent and mixing, then adding a sintering aid, a binder, a toughening agent, and a dispersant, and ball milling in a ball mill for 12 - 24 hours to prepare a uniform and stable slurry; Step 2, casting forming. By optimizing the preparation method of the silicon nitride casting slurry, the stability and dispersibility of the slurry are improved, thereby ensuring the quality of the casting film. And by using specific sintering aids, organic solvents, binders, and dispersants, and controlling parameters such as the stirring speed and ball milling time during the preparation process, the silicon nitride powder is uniformly dispersed in the slurry, with high consistency and stability, easy control of the casting thickness, simple drying regime, and relatively high green body strength and toughness.

Description

Technical Field

[0001] The present invention relates to the field of ceramic materials, and in particular to a silicon nitride ceramic substrate and a preparation method thereof, and a preparation method of a tape-casting slurry. Background Art

[0002] High-thermal-conductivity silicon nitride ceramic substrates are key thermal management materials for ensuring the safe operation of high-power power electronic devices. Power electronic devices are the core units for power conversion and control in power equipment, with applications spanning energy, transportation, and basic industries. The development trends for power electronic devices are high power, high frequency, and integration. Power levels can reach kilowatts or even tens of gigahertz. Due to their high energy density, they generate significant heat, leading to continuously rising operating temperatures, severely impacting device stability and lifespan. Heat dissipation has become a critical issue that needs to be addressed urgently. Commonly used substrate materials include alumina and aluminum nitride. Alumina, due to its low thermal conductivity, cannot effectively dissipate heat. While aluminum nitride ceramics have high thermal conductivity, they suffer from poor mechanical properties and are prone to cracking due to thermal shock during use. Silicon nitride ceramics, with their combination of high thermal conductivity and high reliability, are currently a very attractive candidate.

[0003] Currently, in the field of electronic ceramic materials technology, silicon nitride ceramic substrates, with their exceptional thermal conductivity, strength, and insulation properties, hold a prominent position in key applications such as electronic packaging and power modules. However, current silicon nitride ceramic substrate preparation technology still faces numerous challenges, such as insufficient slurry stability and uneven casting thickness. These challenges hinder the preparation of silicon nitride ceramic substrates, resulting in performance and quality that fail to meet application requirements. Therefore, it is necessary to develop a solution to address these issues. Summary of the Invention

[0004] In view of this, the present invention aims to address the deficiencies in the prior art, and its main purpose is to provide a silicon nitride ceramic substrate and a preparation method thereof, as well as a method for preparing a tape-cast slurry, which can effectively solve the problems of the existing silicon nitride ceramic substrate being difficult to prepare and the performance and quality being unable to meet the requirements of use.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a tape casting slurry comprises the following steps:

[0007] Step 1: Slurry preparation: Add organic solvent to pre-treated silicon nitride powder, then add sintering aid, binder, toughening agent and dispersant, and ball mill in a ball mill for 12-24 hours to prepare a uniform and stable slurry;

[0008] Step 2: Casting and forming: Pour the slurry from Step 1 into the trough of the casting machine, control the thickness of the slurry with a doctor blade to form a uniform film on the casting belt. The casting speed is 0.2 - 1.5 m / min, and the cast film is naturally dried at room temperature for 12 - 18 hours to form a preliminary cured silicon nitride substrate blank.

[0009] As a preferred embodiment, the pretreatment of the silicon nitride powder includes the following steps:

[0010] (1) Pre-sintering: Place the above-mentioned silicon nitride powder in a reducing atmosphere for pre-sintering. The pre-sintering temperature is 800 - 1000 °C, and the pre-sintering time is 3 - 5 hours;

[0011] (2) Crushing treatment: Crush the pre-sintered silicon nitride powder so that the average particle size of the silicon nitride powder is 0.4 - 1.6 μm;

[0012] (3) Surface modification treatment: Use a silane coupling agent to perform surface modification treatment on the crushed silicon nitride powder: Add the silicon nitride powder to an ethanol solution containing the silane coupling agent. The addition amount of the silane coupling agent is 1% - 3% of the mass of the silicon nitride powder, the concentration of the ethanol solution is 70% - 90%, and then stir and react at a temperature of 50 - 70 °C for 4 - 6 hours.

[0013] As a preferred embodiment, the reducing atmosphere is a nitrogen-hydrogen mixed gas, in which the volume fraction of hydrogen is 5% - 15%.

[0014] As a preferred embodiment, the addition amounts of the sintering aid, binder, toughening agent, and dispersant are 5% - 8%, 4% - 6%, 3% - 7%, and 2% - 4% of the mass of the silicon nitride powder, respectively.

[0015] As a preferred embodiment, the sintering aid is a mixture of yttrium oxide, alumina, and magnesia, and the mass ratio of yttrium oxide, alumina, and magnesia is 1.5 - 2.5:0.8 - 1.2:0.8 - 1.2.

[0016] As a preferred embodiment, the organic solvent is a mixture of ethanol, methyl ethyl ketone, toluene, ethyl acetate, and isopropyl alcohol, and the volume ratio of ethanol, methyl ethyl ketone, toluene, ethyl acetate, and isopropyl alcohol is 2.5 - 3.5:1.5 - 2.5:0.8 - 1.2:0.5 - 1:0.5 - 1.

[0017] As a preferred embodiment, the binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; the dispersant is ammonium polyacrylate.

[0018] A method for preparing a silicon nitride ceramic substrate comprises placing a silicon nitride substrate green body prepared by a tape casting slurry preparation method into a sintering furnace, using a nitrogen-hydrogen mixed gas as a sintering atmosphere, wherein the volume fraction of nitrogen is 85-90% and the volume fraction of hydrogen is 10-15%, and sintering is performed according to the following sintering curve:

[0019] Heating stage: heating from room temperature to 1000-1100°C at a rate of 3-8°C / min, and keeping at this temperature for 3 hours;

[0020] Intermediate insulation stage: heating to 1300-1450℃, insulation for 2-3 hours;

[0021] High temperature sintering stage: continue to heat up to 1650-1750℃ and keep warm for 5-7 hours;

[0022] Cooling stage: After sintering, the temperature is lowered to room temperature at a rate of 3-4°C / min to obtain a silicon nitride ceramic substrate.

[0023] A silicon nitride ceramic substrate is prepared by adopting the above-mentioned preparation method of the silicon nitride ceramic substrate.

[0024] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, it can be seen from the above technical solution that:

[0025] 1. By optimizing the preparation method of silicon nitride tape casting slurry, the stability and dispersibility of the slurry are improved, thereby ensuring the quality of the cast film. In addition, by using specific sintering aids, organic solvents, binders and dispersants, and controlling parameters such as stirring speed and ball milling time during the preparation process, the silicon nitride powder is evenly dispersed in the slurry, with high consistency and stability, easy control of tape casting thickness, simple drying system, and high green strength and toughness.

[0026] 2. Through a special silicon nitride powder pretreatment process, the thermal conductivity and insulation of the silicon nitride ceramic substrate are improved while the microstructure of the silicon nitride ceramic substrate is improved, making the grains finer and more uniform. The prepared silicon nitride substrate has excellent properties such as high thermal conductivity, high strength, and high insulation, which can meet the needs of electronic packaging, power modules and other fields. DETAILED DESCRIPTION

[0027] The present invention discloses a method for preparing a tape casting slurry, comprising the following steps:

[0028] Step 1: Slurry preparation: Add organic solvent to the pre-treated silicon nitride powder, then add sintering aid, binder, toughening agent and dispersant, and ball mill for 12-24 hours to prepare a uniform and stable slurry. The pretreatment of silicon nitride powder includes the following steps:

[0029] (1)Pre-sintering: The above-mentioned silicon nitride powder is placed in a reducing atmosphere for pre-sintering. The pre-sintering temperature is 800 - 1000 °C, and the pre-sintering time is 3 - 5 hours. This can effectively remove some impurities and some bound oxygen in the silicon nitride, and at the same time preliminarily activate the silicon nitride powder. The reducing atmosphere is a nitrogen-hydrogen mixed gas, in which the volume fraction of hydrogen is 5% - 15%, so as to better remove some impurities and some bound oxygen in the silicon nitride and better preliminarily activate the silicon nitride powder.

[0030] (2)Crushing treatment: The pre-sintered silicon nitride powder is subjected to crushing treatment to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 0.4 - 1.6 μm. Crushing treatment can be carried out by means such as ball milling or mechanical crushing, without limitation.

[0031] (3)Surface modification treatment: The crushed silicon nitride powder is subjected to surface modification treatment with a silane coupling agent. The silicon nitride powder is added to an ethanol solution containing a silane coupling agent. The addition amount of the silane coupling agent is 1% - 3% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 70% - 90% (volume fraction). Then, it is stirred and reacted at a temperature of 50 - 70 °C for 4 - 6 hours, so that the silane coupling agent is fully coated on the surface of the silicon nitride powder, improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0032] The organic solvent is a mixture of ethanol, butanone, toluene, ethyl acetate and isopropanol. The volume ratio of ethanol, butanone, toluene, ethyl acetate and isopropanol is 2.5 - 3.5:1.5 - 2.5:0.8 - 1.2:0.5 - 1:0.5 - 1. While ensuring the wetting of the silicon nitride powder and the dissolution of polyvinyl butyral (PVB), it improves the stability and consistency of the slurry. The rapid solubility of ethanol, the viscosity adjustment effect of butanone, the uniformity improvement effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization adjustment effect of isopropanol cooperate with each other, providing an ideal solvent environment for the preparation of high-quality casting slurries.

[0033] The addition amounts of the sintering aid, binder, toughening agent and dispersant are 5% - 8%, 4% - 6%, 3% - 7% and 2% - 4% of the mass of the silicon nitride powder respectively. The sintering aid is a mixture of yttrium oxide, alumina and magnesia, and the mass ratio of yttrium oxide, alumina and magnesia is 1.5 - 2.5:0.8 - 1.2:0.8 - 1.2. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; the dispersant is ammonium polyacrylate. This synergistic effect can improve the dispersibility of the silicon nitride powder while enhancing the adhesiveness of the slurry, making the casting film more firm.

[0034] Step 2. Tape casting: Pour the slurry from Step 1 into the trough of the tape casting machine, control the thickness of the slurry with a doctor blade, form a uniform film on the tape casting belt, the tape casting speed is 0.2 - 1.5 m / min, and the cast film is naturally dried at room temperature for 12 - 18 hours to form a preliminary cured silicon nitride substrate blank.

[0035] The present invention also discloses a method for preparing a silicon nitride ceramic substrate. Put the silicon nitride substrate blank prepared by using the aforementioned method for preparing a tape casting slurry into a sintering furnace, use a nitrogen-hydrogen mixed gas as the sintering atmosphere, where the volume fraction of nitrogen is 85 - 90%, and the volume fraction of hydrogen is 10 - 15%; sinter according to the following sintering curve:

[0036] Heating stage: Heat from room temperature to 1000 - 1100 °C at a heating rate of 3 - 8 °C / minute, and hold at this temperature for 3 hours.

[0037] Intermediate holding stage: Heat up to 1300 - 1450 °C and hold for 2 - 3 hours.

[0038] High-temperature sintering stage: Continue to heat up to 1650 - 1750 °C and hold for 5 - 7 hours.

[0039] Cooling stage: After sintering, cool down to room temperature at a cooling rate of 3 - 4 °C / minute to obtain a silicon nitride ceramic substrate.

[0040] The present invention also discloses a silicon nitride ceramic substrate prepared by using the aforementioned method for preparing a silicon nitride ceramic substrate.

[0041] The following further elaborates on the present invention with multiple examples and comparative examples:

[0042] Example 1

[0043] This example discloses a method for preparing a tape casting slurry, including the following steps:

[0044] Step 1. Slurry preparation: Add an organic solvent to the pretreated silicon nitride powder and mix, then add a sintering aid, a binder, a toughening agent, and a dispersant, and ball mill in a ball mill for 12 hours to prepare a uniform and stable slurry. The pretreatment of the silicon nitride powder includes the following steps:

[0045] (1) Pre-sintering: Place the above-mentioned silicon nitride powder in a reducing atmosphere for pre-sintering, the pre-sintering temperature is 900 °C, and the pre-sintering time is 4 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride, and at the same time preliminarily activate the silicon nitride powder; the reducing atmosphere is a nitrogen-hydrogen mixed gas, where the volume fraction of hydrogen is 10%, so as to better remove some impurities and some combined oxygen in the silicon nitride and better preliminarily activate the silicon nitride powder.

[0046] (2) Crushing treatment: The pre-sintered silicon nitride powder is subjected to crushing treatment to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 0.5 μm. Ball milling or mechanical crushing can be used for the crushing treatment, without limitation.

[0047] (3) Surface modification treatment: The crushed silicon nitride powder is subjected to surface modification treatment with a silane coupling agent: The silicon nitride powder is added to an ethanol solution containing the silane coupling agent. The addition amount of the silane coupling agent is 2% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 88% (volume fraction). Then, it is stirred and reacted at a temperature of 60 °C for 6 hours to make the silane coupling agent fully coat the surface of the silicon nitride powder, improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0048] The organic solvent is a mixture of ethanol, methyl ethyl ketone, toluene, ethyl acetate and isopropanol, and the volume ratio of ethanol, methyl ethyl ketone, toluene, ethyl acetate and isopropanol is 2.5:2.2:1.2:0.6:0.7. While ensuring the wetting of the silicon nitride powder and the dissolution of polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity adjustment effect of methyl ethyl ketone, the uniformity improvement effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization adjustment effect of isopropanol cooperate with each other to provide an ideal solvent environment for the preparation of high-quality casting slurry.

[0049] The addition amounts of the sintering aid, binder, toughening agent and dispersant are 6%, 5%, 4% and 3% of the mass of the silicon nitride powder respectively. The sintering aid is a mixture of yttrium oxide, alumina and magnesia, and the mass ratio of yttrium oxide, alumina and magnesia is 2:1:1.2. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystal; the dispersant is ammonium polyacrylate. This synergistic effect can improve the dispersibility of the silicon nitride powder while enhancing the adhesiveness of the slurry, making the cast film more firm.

[0050] Step 2. Casting and forming: Pour the slurry in Step 1 into the trough of the casting machine, control the thickness of the slurry through a doctor blade, form a uniform film on the casting belt, the casting speed is 0.2 m / min, and the cast film is naturally dried at room temperature for 14 hours to make it preliminarily cured to form a silicon nitride substrate blank.

[0051] This embodiment also discloses a preparation method of a silicon nitride ceramic substrate. The silicon nitride substrate blank prepared by using the preparation method of a casting slurry described above is put into a sintering furnace, and a nitrogen-hydrogen mixed gas is used as the sintering atmosphere, in which the volume fraction of nitrogen is 85% and the volume fraction of hydrogen is 15%; sintering is carried out according to the following sintering curve:

[0052] Heating stage: Heat from room temperature to 1000 °C at a heating rate of 3 °C per minute and hold at this temperature for 3 hours.

[0053] Intermediate holding stage: Heat to 1400 °C and hold for 2 hours.

[0054] High-temperature sintering stage: Continue to heat to the temperature of 1700 °C and hold for 6 hours.

[0055] Cooling stage: After sintering, cool to room temperature at a cooling rate of 3 °C per minute to obtain a silicon nitride ceramic substrate.

[0056] This embodiment also discloses a silicon nitride ceramic substrate, which is prepared by using the preparation method of the aforementioned silicon nitride ceramic substrate.

[0057] Example 2

[0058] This embodiment discloses a preparation method of a casting slurry, which includes the following steps:

[0059] Step 1. Slurry preparation: Add the pretreated silicon nitride powder to an organic solvent and mix, then add a sintering aid, a binder, a toughening agent and a dispersant, and ball mill in a ball mill for 15 hours to prepare a uniform and stable slurry. The pretreatment of the silicon nitride powder includes the following steps:

[0060] (1) Pre-sintering: Place the above-mentioned silicon nitride powder in a reducing atmosphere for pre-sintering. The pre-sintering temperature is 800 °C and the pre-sintering time is 5 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride, and at the same time preliminarily activate the silicon nitride powder; the reducing atmosphere is a nitrogen-hydrogen mixed gas, in which the volume fraction of hydrogen is 12%, so as to better remove some impurities and some combined oxygen in the silicon nitride and better preliminarily activate the silicon nitride powder.

[0061] (rushing treatment: Perform crushing treatment on the pre-sintered silicon nitride powder to make its particle size more uniform. Crush the silicon nitride powder to an average particle size of 0.8 μm. Crushing treatment can be carried out by means such as ball milling or mechanical crushing, without limitation.

[0062] (3) Surface modification treatment: Use a silane coupling agent to perform surface modification treatment on the crushed silicon nitride powder: Add the silicon nitride powder to an ethanol solution containing a silane coupling agent. The addition amount of the silane coupling agent is 3% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 70% (volume fraction). Then stir and react at a temperature of 50 °C for 5 hours to make the silane coupling agent fully coat the surface of the silicon nitride powder, improving the dispersibility of the silicon nitride powder and the compatibility with other additives.

[0063] The organic solvent is a mixture of ethanol, methyl ethyl ketone, toluene, ethyl acetate and isopropanol, and the volume ratio of ethanol, methyl ethyl ketone, toluene, ethyl acetate and isopropanol is 3.5:2.5:0.9:0.8:0.9. While ensuring the wetting of silicon nitride powder and the dissolution of polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity adjustment effect of methyl ethyl ketone, the uniformity improvement effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization adjustment effect of isopropanol cooperate with each other to provide an ideal solvent environment for the preparation of high-quality casting slurries.

[0064] The addition amounts of the sintering aid, binder, toughening agent and dispersant are 8%, 6%, 7% and 2.5% of the mass of the silicon nitride powder respectively. The sintering aid is a mixture of yttrium oxide, alumina and magnesia, and the mass ratio of yttrium oxide, alumina and magnesia is 2.2:0.9:1. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; the dispersant is ammonium polyacrylate. This synergistic effect can improve the dispersibility of silicon nitride powder while enhancing the adhesiveness of the slurry, making the cast film more firm.

[0065] Step 2, casting and forming: Pour the slurry in Step 1 into the trough of the casting machine, control the thickness of the slurry through a doctor blade, form a uniform film on the casting belt, the casting speed is 0.8 m / min, and the cast film is naturally dried at room temperature for 15 hours to form a silicon nitride substrate blank through preliminary curing.

[0066] This embodiment also discloses a method for preparing a silicon nitride ceramic substrate. The silicon nitride substrate blank prepared by using the method for preparing a casting slurry described above is put into a sintering furnace, and a nitrogen-hydrogen mixed gas is used as the sintering atmosphere, wherein the volume fraction of nitrogen is 90% and the volume fraction of hydrogen is 10%; sintering is carried out according to the following sintering curve:

[0067] Heating stage: Heat from room temperature to 1050 °C at a heating rate of 8 °C / minute and hold at this temperature for 3 hours.

[0068] Intermediate holding stage: Heat up to 1300 °C and hold for 3 hours.

[0069] High-temperature sintering stage: Continue to heat up to 1750 °C and hold for 7 hours.

[0070] Cooling stage: After sintering, cool down to room temperature at a cooling rate of 4 °C / minute to obtain a silicon nitride ceramic substrate.

[0071] This embodiment also discloses a silicon nitride ceramic substrate prepared by using the method for preparing a silicon nitride ceramic substrate described above.

[0072] Example 3

[0073] This embodiment discloses a method for preparing a casting slurry, which includes the following steps:

[0074] Step 1. Slurry preparation: Add the pretreated silicon nitride powder to an organic solvent and mix, then add a sintering aid, a binder, a toughening agent, and a dispersant, and ball mill for 18 hours in a ball mill to prepare a uniform and stable slurry. The pretreatment of the silicon nitride powder includes the following steps:

[0075] (1) Pre-sintering: Place the above-mentioned silicon nitride powder in a reducing atmosphere for pre-sintering. The pre-sintering temperature is 1000 °C and the pre-sintering time is 3 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride, and at the same time preliminarily activate the silicon nitride powder; the reducing atmosphere is a nitrogen-hydrogen mixed gas, in which the volume fraction of hydrogen is 15%, so as to better remove some impurities and some combined oxygen in the silicon nitride and better preliminarily activate the silicon nitride powder.

[0076] (2) Crushing treatment: The pre-sintered silicon nitride powder is subjected to crushing treatment to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 1.0 μm, and methods such as ball milling or mechanical crushing can be used for crushing treatment, without limitation.

[0077] (3) Surface modification treatment: Use a silane coupling agent to perform surface modification treatment on the crushed silicon nitride powder: Add the silicon nitride powder to an ethanol solution containing a silane coupling agent. The addition amount of the silane coupling agent is 1.5% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 85% (volume fraction). Then stir and react at a temperature of 70 °C for 4 hours to make the silane coupling agent fully coat the surface of the silicon nitride powder, improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0078] The organic solvent is a mixture of ethanol, methyl ethyl ketone, toluene, ethyl acetate, and isopropyl alcohol, and the volume ratio of ethanol, methyl ethyl ketone, toluene, ethyl acetate, and isopropyl alcohol is 3.2:1.6:1.0:1:1. While ensuring the wetting of the silicon nitride powder and the dissolution of polyvinyl butyral (PVB), it improves the stability and consistency of the slurry. The rapid solubility of ethanol, the viscosity adjustment effect of methyl ethyl ketone, the uniformity improvement effect of toluene, the auxiliary dissolution effect of ethyl acetate, and the volatilization adjustment effect of isopropyl alcohol cooperate with each other to provide an ideal solvent environment for the preparation of high-quality casting slurry.

[0079] The addition amounts of the sintering aid, binder, toughening agent, and dispersant are 7%, 4.5%, 6%, and 4% of the mass of the silicon nitride powder respectively. The sintering aid is a mixture of yttrium oxide, aluminum oxide, and magnesium oxide, and the mass ratio of yttrium oxide, aluminum oxide, and magnesium oxide is 2.5:1.1:1.1. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystal; the dispersant is ammonium polyacrylate. This synergistic effect can improve the dispersibility of the silicon nitride powder while enhancing the adhesiveness of the slurry, making the cast film more firm.

[0080] Step 2, casting forming: Pour the slurry obtained in Step 1 into the trough of the casting machine, control the thickness of the slurry through a doctor blade, form a uniform film on the casting belt, the casting speed is 1.5 m / min, and the cast film is naturally dried at room temperature for 18 hours to form a preliminary cured silicon nitride substrate blank.

[0081] This embodiment also discloses a preparation method of a silicon nitride ceramic substrate. The silicon nitride substrate blank prepared by using the preparation method of a casting slurry described above is put into a sintering furnace, and a nitrogen-hydrogen mixed gas is used as the sintering atmosphere, wherein the volume fraction of nitrogen is 88% and the volume fraction of hydrogen is 12%; sintering is carried out according to the following sintering curve:

[0082] Heating stage: Heat from room temperature to 1020 °C at a heating rate of 7 °C / minute, and hold at this temperature for 3 hours.

[0083] Intermediate holding stage: Heat up to 1450 °C and hold for 2.2 hours.

[0084] High-temperature sintering stage: Continue to heat up to 1650 °C and hold for 5 hours.

[0085] Cooling stage: After sintering, cool down to room temperature at a cooling rate of 3.2 °C / minute to obtain a silicon nitride ceramic substrate.

[0086] This embodiment also discloses a silicon nitride ceramic substrate, which is prepared by using the preparation method of a silicon nitride ceramic substrate described above.

[0087] Example 4

[0088] This embodiment discloses a preparation method of a casting slurry, including the following steps:

[0089] Step 1, slurry preparation: Add the pretreated silicon nitride powder to an organic solvent and mix, then add a sintering aid, a binder, a toughening agent, and a dispersant, and ball mill in a ball mill for 24 hours to prepare a uniform and stable slurry. The pretreatment of the silicon nitride powder includes the following steps:

[0090] (1)Pre-sintering: The above-mentioned silicon nitride powder is placed in a reducing atmosphere for pre-sintering. The pre-sintering temperature is 850 °C and the pre-sintering time is 3.5 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride, and at the same time preliminarily activate the silicon nitride powder. The reducing atmosphere is a nitrogen-hydrogen mixed gas, in which the volume fraction of hydrogen is 8%, so as to better remove some impurities and some combined oxygen in the silicon nitride and better preliminarily activate the silicon nitride powder.

[0091] (2)Crushing treatment: The pre-sintered silicon nitride powder is subjected to crushing treatment to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 1.2 μm, and methods such as ball milling or mechanical crushing can be used for crushing treatment, not limited thereto.

[0092] (3)Surface modification treatment: The crushed silicon nitride powder is subjected to surface modification treatment with a silane coupling agent: The silicon nitride powder is added to an ethanol solution containing a silane coupling agent. The addition amount of the silane coupling agent is 2.2% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 90% (volume fraction). Then, it is stirred and reacted at a temperature of 55 °C for 4.5 hours to make the silane coupling agent fully coat the surface of the silicon nitride powder, improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0093] The organic solvent is a mixture of ethanol, methyl ethyl ketone, toluene, ethyl acetate and isopropyl alcohol, and the volume ratio of ethanol, methyl ethyl ketone, toluene, ethyl acetate and isopropyl alcohol is 3:1.8:0.85:0.9:0.8. While ensuring the wetting of the silicon nitride powder and the dissolution of polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity adjustment effect of methyl ethyl ketone, the uniformity improvement effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization adjustment effect of isopropyl alcohol cooperate with each other, providing an ideal solvent environment for the preparation of high-quality casting slurries.

[0094] The addition amounts of the sintering aid, binder, toughening agent and dispersant are 6.5%, 5.5%, 5% and 3.5% of the mass of the silicon nitride powder respectively. The sintering aid is a mixture of yttrium oxide, alumina and magnesia, and the mass ratio of yttrium oxide, alumina and magnesia is 2.3:1.2:0.9. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; the dispersant is ammonium polyacrylate. This synergistic effect can enhance the dispersibility of the silicon nitride powder while enhancing the adhesiveness of the slurry, making the casting film more firm.

[0095] Step 2: Casting and forming: Pour the slurry from Step 1 into the trough of the casting machine, control the thickness of the slurry through a doctor blade, form a uniform film on the casting belt, the casting speed is 1.3 m / min, and the cast film is naturally dried at room temperature for 16 hours to make it preliminarily cured to form a silicon nitride substrate blank.

[0096] This embodiment also discloses a method for preparing a silicon nitride ceramic substrate. The silicon nitride substrate green body prepared by using the aforementioned method for preparing a casting slurry is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used as the sintering atmosphere, where the volume fraction of nitrogen is 86% and the volume fraction of hydrogen is 14%; sintering is carried out according to the following sintering curve:

[0097] Heating stage: Heat from room temperature to 1080 °C at a heating rate of 6 °C per minute and hold at this temperature for 3 hours.

[0098] Intermediate holding stage: Heat up to 1350 °C and hold for 2.5 hours.

[0099] High-temperature sintering stage: Continue to heat up to 1680 °C and hold for 5.5 hours.

[0100] Cooling stage: After sintering, cool down to room temperature at a cooling rate of 3.5 °C per minute to obtain a silicon nitride ceramic substrate.

[0101] This embodiment also discloses a silicon nitride ceramic substrate prepared by using the aforementioned method for preparing a silicon nitride ceramic substrate.

[0102] Example 5

[0103] This embodiment discloses a method for preparing a casting slurry, which includes the following steps:

[0104] Step 1. Slurry preparation: Add the pretreated silicon nitride powder to an organic solvent and mix, then add a sintering aid, a binder, a toughening agent, and a dispersant, and ball mill in a ball mill for 20 hours to prepare a uniform and stable slurry. The pretreatment of the silicon nitride powder includes the following steps:

[0105] (1) Pre-sintering: Place the above-mentioned silicon nitride powder in a reducing atmosphere for pre-sintering. The pre-sintering temperature is 950 °C and the pre-sintering time is 4.5 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride, and at the same time preliminarily activate the silicon nitride powder; the reducing atmosphere is a nitrogen-hydrogen mixed gas, where the volume fraction of hydrogen is 14%, so as to better remove some impurities and some combined oxygen in the silicon nitride and better preliminarily activate the silicon nitride powder.

[0106] (2) Crushing treatment: The pre-sintered silicon nitride powder is subjected to crushing treatment to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 1.6 μm, and crushing treatment can be carried out by means such as ball milling or mechanical crushing, without limitation.

[0107] (3) Surface modification treatment: The surface of the crushed silicon nitride powder is modified using a silane coupling agent. The silicon nitride powder is added to an ethanol solution containing the silane coupling agent. The addition amount of the silane coupling agent is 1.8% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 75% (volume fraction). Then, the mixture is stirred and reacted at a temperature of 65°C for 5.5 hours to ensure that the silane coupling agent fully coats the surface of the silicon nitride powder, improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0108] The organic solvent is a mixture of ethanol, methyl ethyl ketone, toluene, ethyl acetate, and isopropyl alcohol, and the volume ratio of ethanol, methyl ethyl ketone, toluene, ethyl acetate, and isopropyl alcohol is 2.8:2.4:1.1:0.7:0.6. While ensuring the wetting of the silicon nitride powder and the dissolution of polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity adjustment effect of methyl ethyl ketone, the uniformity improvement effect of toluene, the auxiliary dissolution effect of ethyl acetate, and the volatilization adjustment effect of isopropyl alcohol work together synergistically to provide an ideal solvent environment for the preparation of high-quality casting slurries.

[0109] The addition amounts of the sintering aid, binder, toughening agent, and dispersant are 7.5%, 4.8%, 5.5%, and 2.8% of the mass of the silicon nitride powder, respectively. The sintering aid is a mixture of yttrium oxide, alumina, and magnesia, and the mass ratio of yttrium oxide, alumina, and magnesia is 1.8:0.9:0.85. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; the dispersant is ammonium polyacrylate. This synergistic effect can improve the dispersibility of the silicon nitride powder while enhancing the adhesiveness of the slurry, making the cast film more firm.

[0110] Step 2: Casting and forming: The slurry from Step 1 is poured into the trough of the casting machine, and the thickness of the slurry is controlled by a doctor blade to form a uniform film on the casting belt. The casting speed is 0.5 m / min, and the cast film is naturally dried at room temperature for 13 hours to form a preliminary cured silicon nitride substrate blank.

[0111] This embodiment also discloses a method for preparing a silicon nitride ceramic substrate. The silicon nitride substrate blank prepared by using the method for preparing a casting slurry described above is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used as the sintering atmosphere, where the volume fraction of nitrogen is 87% and the volume fraction of hydrogen is 13%. Sintering is carried out according to the following sintering curve:

[0112] Heating stage: The temperature is raised from room temperature to 1100°C at a heating rate of 5°C / minute and held at this temperature for 3 hours.

[0113] Intermediate holding stage: The temperature is raised to 1380°C and held for 2.8 hours.

[0114] High-temperature sintering stage: Continue to heat up to 1720 °C and hold for 6.5 hours.

[0115] Cooling stage: After sintering, cool down to room temperature at a cooling rate of 3.8 °C per minute to obtain a silicon nitride ceramic substrate.

[0116] This example also discloses a silicon nitride ceramic substrate, which is prepared by using the preparation method of the foregoing silicon nitride ceramic substrate.

[0117] Example 6

[0118] This example discloses a preparation method of a casting slurry, which includes the following steps:

[0119] Step 1. Slurry preparation: Add the pretreated silicon nitride powder to an organic solvent and mix, then add a sintering aid, a binder, a toughening agent, and a dispersant, and ball mill for 22 hours in a ball mill to prepare a uniform and stable slurry. The pretreatment of the silicon nitride powder includes the following steps:

[0120] (1) Pre-sintering: Place the above-mentioned silicon nitride powder in a reducing atmosphere for pre-sintering. The pre-sintering temperature is 860 °C and the pre-sintering time is 4 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride, and at the same time preliminarily activate the silicon nitride powder; the reducing atmosphere is a nitrogen-hydrogen mixed gas, in which the volume fraction of hydrogen is 5%, so as to better remove some impurities and some combined oxygen in the silicon nitride and better preliminarily activate the silicon nitride powder.

[0121] (2) Crushing treatment: The pre-sintered silicon nitride powder is subjected to crushing treatment to make its particle size more uniform. Crush the silicon nitride powder to an average particle size of 0.9 μm. Crushing treatment can be carried out by means such as ball milling or mechanical crushing, not limited thereto.

[0122] (3) Surface modification treatment: Use a silane coupling agent to carry out surface modification treatment on the crushed silicon nitride powder: Add the silicon nitride powder to an ethanol solution containing a silane coupling agent. The addition amount of the silane coupling agent is 1% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 80% (volume fraction). Then stir and react at a temperature of 50 °C for 4 hours to make the silane coupling agent fully coat the surface of the silicon nitride powder, improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0123] The organic solvent is a mixture of ethanol, methyl ethyl ketone, toluene, ethyl acetate and isopropanol, and the volume ratio of ethanol, methyl ethyl ketone, toluene, ethyl acetate and isopropanol is 2.6:1.5:0.8:0.5:0.5. While ensuring the wetting of silicon nitride powder and the dissolution of polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity adjustment effect of methyl ethyl ketone, the uniformity improvement effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization adjustment effect of isopropanol cooperate with each other to provide an ideal solvent environment for the preparation of high-quality casting slurries.

[0124] The addition amounts of the sintering aid, binder, toughening agent and dispersant are 5%, 4%, 3% and 2% of the mass of the silicon nitride powder respectively. The sintering aid is a mixture of yttrium oxide, alumina and magnesia, and the mass ratio of yttrium oxide, alumina and magnesia is 1.5:0.8:0.8. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; the dispersant is ammonium polyacrylate. This synergistic effect can improve the dispersibility of silicon nitride powder while enhancing the adhesiveness of the slurry, making the cast film more firm.

[0125] Step 2, casting and forming: Pour the slurry obtained in Step 1 into the trough of a casting machine, control the thickness of the slurry through a doctor blade, form a uniform film on the casting belt, the casting speed is 1.2 m / min, and the cast film is naturally dried at room temperature for 12 hours to form a silicon nitride substrate blank through preliminary curing.

[0126] This embodiment also discloses a method for preparing a silicon nitride ceramic substrate. The silicon nitride substrate blank prepared by using the aforementioned method for preparing a casting slurry is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used as the sintering atmosphere, where the volume fraction of nitrogen is 89% and the volume fraction of hydrogen is 11%; sintering is carried out according to the following sintering curve:

[0127] Heating stage: Heat from room temperature to 1060 °C at a heating rate of 4 °C per minute and hold at this temperature for 3 hours.

[0128] Intermediate holding stage: Heat up to 1410 °C and hold for 2.4 hours.

[0129] High-temperature sintering stage: Continue to heat up to 1670 °C and hold for 6 hours.

[0130] Cooling stage: After sintering, cool down to room temperature at a cooling rate of 3.3 °C per minute to obtain a silicon nitride ceramic substrate.

[0131] This embodiment also discloses a silicon nitride ceramic substrate prepared by using the aforementioned method for preparing a silicon nitride ceramic substrate.

[0132] Comparative Example 1

[0133] The difference between the comparative example and the above-mentioned Example 6 is that the silicon nitride powder in this comparative example is not pretreated, and the rest of the content of this comparative example is the same as that of Example 6, which will not be elaborated here.

[0134] Comparative Example 2

[0135] The difference between this comparative example and the above-mentioned Example 6 is that other organic solvent ratios are used in this comparative example, and the rest of the content of this comparative example is the same as that of Example 6, which will not be elaborated here.

[0136] Comparative Example 3

[0137] The difference between this comparative example and the above-mentioned Example 6 is that chitin nanocrystals are not added in this comparative example, and the rest of the content of this comparative example is the same as that of Example 6, which will not be elaborated here.

[0138] The thermal conductivity, flexural strength and insulation resistance of the silicon nitride ceramic substrates prepared in the above-mentioned examples and comparative examples were tested by conventional methods, and the test results are shown in the following table:

[0139]

[0140] It can be seen from the test results that the silicon nitride ceramic substrates prepared by the present invention are superior to the comparative examples in terms of thermal conductivity, flexural strength and insulation resistance, and have good performance and quality. Compared with ordinary silicon nitride ceramic substrates, the silicon nitride ceramic substrates obtained by pretreating silicon nitride powder and adding chitin nanocrystals have high thermal conductivity, flexural strength and insulation resistance.

[0141] The design focus of the present invention is as follows: First, by optimizing the preparation method of the silicon nitride casting slurry, the stability and dispersibility of the slurry are improved, thereby ensuring the quality of the casting film. By using specific sintering aids, organic solvents, binders and dispersants, and controlling parameters such as stirring speed and ball milling time during the preparation process, the silicon nitride powder is uniformly dispersed in the slurry, with high consistency and stability, easy control of the casting thickness, simple drying system, and high green body strength and toughness. Second, through a special pretreatment process of silicon nitride powder, while improving the thermal conductivity and insulation of the silicon nitride ceramic substrate, the microstructure of the silicon nitride ceramic substrate is improved, making the grains finer and more uniform. The prepared silicon nitride substrate has excellent properties such as high thermal conductivity, high strength and high insulation, and can meet the requirements of fields such as electronic packaging and power modules.

[0142] The above is only a preferred embodiment of the present invention, and does not impose any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a casting slurry, characterized in that: It includes the following steps: Step 1, slurry preparation: Add the pretreated silicon nitride powder to an organic solvent and mix, then add a sintering aid, a binder, a toughening agent, and a dispersant, and ball mill in a ball mill for 12 - 24 hours to prepare a uniform and stable slurry; the pretreatment of the silicon nitride powder includes the following steps: (1) Pre-sintering: Place the above-mentioned silicon nitride powder in a reducing atmosphere for pre-sintering, the pre-sintering temperature is 800 - 1000 °C, and the pre-sintering time is 3 - 5 hours; (2) Crushing treatment: The pre-sintered silicon nitride powder is subjected to crushing treatment to crush the silicon nitride powder to an average particle size of 0.4 - 1.6 μm; (3) Surface modification treatment: Use a silane coupling agent to perform surface modification treatment on the crushed silicon nitride powder: Add the silicon nitride powder to an ethanol solution containing a silane coupling agent, the addition amount of the silane coupling agent is 1% - 3% of the mass of the silicon nitride powder, the concentration of the ethanol solution is 70% - 90%, and then stir and react at a temperature of 50 - 70 °C for 4 - 6 hours; The addition amounts of the sintering aid, the binder, the toughening agent, and the dispersant are 5% - 8%, 4% - 6%, 3% - 7%, and 2% - 4% of the mass of the silicon nitride powder respectively; the binder is polyvinyl butyral; the toughening agent is chitin nanocrystal; the dispersant is ammonium polyacrylate; The organic solvent is a mixture of ethanol, methyl ethyl ketone, toluene, ethyl acetate, and isopropyl alcohol, and the volume ratio of ethanol, methyl ethyl ketone, toluene, ethyl acetate, and isopropyl alcohol is 2.5 - 3.5:1.5 - 2.5:0.8 - 1.2:0.5 - 1:0.5 - 1; Step 2, tape casting: Pour the slurry from Step 1 into the trough of the tape casting machine, control the thickness of the slurry through a doctor blade, form a uniform film on the tape casting belt, the tape casting speed is 0.2 - 1.5 m / min, and the film after tape casting is naturally dried at room temperature for 12 - 18 hours to be preliminarily cured to form a silicon nitride substrate blank.

2. The preparation method of the casting slurry according to claim 1, characterized in that: The reducing atmosphere is a nitrogen-hydrogen mixed gas, in which the volume fraction of hydrogen is 5% - 15%.

3. The preparation method of the casting slurry according to claim 1, characterized in that: The sintering aid is a mixture of yttrium oxide, alumina, and magnesia, and the mass ratio of yttrium oxide, alumina, and magnesia is 1.5 - 2.5:0.8 - 1.2:0.8 - 1.

2.

4. A method for preparing a silicon nitride ceramic substrate, characterized in that: Put the silicon nitride substrate blank prepared by using the preparation method of the tape casting slurry as described in any one of claims 1 - 3 into a sintering furnace, use a nitrogen-hydrogen mixed gas as the sintering atmosphere, in which the volume fraction of nitrogen is 85% - 90%, and the volume fraction of hydrogen is 10% - 15%; sinter according to the following sintering curve: Heating stage: Heat from room temperature to 1000 - 1100 °C at a heating rate of 3 - 8 °C / minute, and keep the temperature at this temperature for 3 hours; Intermediate holding stage: Heat up to 1300 - 1450 °C and hold for 2 - 3 hours; High-temperature sintering stage: Continue to heat up to 1650 - 1750 °C and hold for 5 - 7 hours; Cooling stage: After sintering, cool down to room temperature at a cooling rate of 3 - 4 °C / minute to obtain a silicon nitride ceramic substrate.

5. A silicon nitride ceramic substrate, characterized in that: Prepared by using the preparation method of a silicon nitride ceramic substrate as described in claim 4.

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