Silicon nitride ceramic substrate and preparation method thereof, and preparation method of tape casting slurry

Abstract

The invention discloses a silicon nitride ceramic substrate and a preparation method thereof, and a preparation method of tape casting slurry, and the preparation method of the tape casting slurry comprises the following steps: step 1, slurry preparation: adding an organic solvent into pretreated silicon nitride powder, mixing, then adding a sintering aid, a binder, a flexibilizer and a dispersant, and carrying out ball milling in a ball mill for 12-24 hours to obtain slurry; uniform and stable slurry is prepared; and step 2, tape casting. By optimizing the preparation method of the silicon nitride tape-casting slurry, the stability and dispersity of the slurry are improved, so that the quality of a tape-casting film is ensured, and silicon nitride powder is uniformly dispersed in the slurry by adopting a specific sintering aid, an organic solvent, a binding agent and a dispersing agent and controlling parameters such as stirring speed and ball-milling time in the preparation process, so that the silicon nitride tape-casting slurry is prepared. Consistency and stability are high, the casting thickness is easy to control, the drying system is simple, and the green body strength and toughness are high.

Description

Technical Field

[0001] The 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 substrate is a key thermal management material to ensure the safe operation of high-power power electronic devices. Power electronic devices are the core units of power conversion and control in power equipment, and their application areas cover various fields such as energy, transportation, and basic industries. High power, high frequency, and integration are the development direction of power electronic devices. Its power can reach KW level or even more than tens of GW. Due to the high energy density and severe heat generation, the operating temperature continues to rise, seriously affecting the working stability and life of the device. The heat dissipation problem has become a key issue that needs to be solved urgently. Currently, the commonly used substrate materials are aluminum oxide and aluminum nitride. Aluminum oxide cannot effectively dissipate heat due to its low thermal conductivity; and although aluminum nitride ceramics have high thermal conductivity, they are prone to cracking due to thermal shock during use due to poor mechanical properties. Silicon nitride ceramics have the advantages of high thermal conductivity and high reliability, and are currently a very advantageous candidate material.

[0003] At present, in the field of electronic ceramic material technology, silicon nitride ceramic substrates occupy an important position in key application fields such as electronic packaging and power modules due to their excellent high thermal conductivity, high strength, and high insulation properties. However, the current silicon nitride ceramic substrate preparation technology still faces many challenges, such as insufficient slurry stability and uneven casting thickness, which make the preparation of silicon nitride ceramic substrates difficult and the performance and quality cannot meet the needs of use. Therefore, it is necessary to study a solution to solve the above problems. Summary of the invention

[0004] In view of this, the present invention aims at the deficiencies in the prior art, and its main purpose is to provide a silicon nitride ceramic substrate and a preparation method thereof, and a method for preparing a tape-casting slurry, which can effectively solve the problems that the existing silicon nitride ceramic substrates are difficult to prepare and the performance and quality cannot meet the needs of use.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A method for preparing a tape casting slurry comprises the following steps: Step 1, slurry preparation: add organic solvent to the pretreated silicon nitride powder, 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; Step 2, tape casting: Pour the slurry from step 1 into the material trough of the tape casting machine, control the thickness of the slurry by a scraper, and form a uniform film on the tape casting belt at a casting speed of 0.2-1.5 m / min. The film after tape casting is naturally dried at room temperature for 12-18 hours to initially solidify it to form a silicon nitride substrate blank.

[0006] As a preferred embodiment, the pretreatment of the silicon nitride powder comprises the following steps: (1) Pre-sintering: The silicon nitride powder is placed in a reducing atmosphere for pre-sintering at a temperature of 800-1000°C for 3-5 hours; (2) Crushing treatment: The pre-sintered silicon nitride powder is crushed to an average particle size of 0.4-1.6 μm; (3) Surface modification: The crushed silicon nitride powder is surface modified by using a silane coupling agent: the silicon nitride powder is added to an ethanol solution containing a silane coupling agent, the amount of the silane coupling agent added is 1%-3% of the mass of the silicon nitride powder, the concentration of the ethanol solution is 70%-90%, and then stirred at a temperature of 50-70°C for 4-6 hours.

[0007] As a preferred embodiment, the reducing atmosphere is a nitrogen-hydrogen mixed gas, wherein the volume fraction of hydrogen is 5%-15%.

[0008] As a preferred solution, the added 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.

[0009] As a preferred solution, 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 1.5-2.5:0.8-1.2:0.8-1.2.

[0010] As a preferred embodiment, the organic solvent is a mixture of ethanol, butanone, toluene, ethyl acetate and isopropanol, and 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.

[0011] As a preferred solution, the binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; and the dispersant is ammonium polyacrylate.

[0012] 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: Heating stage: heating from room temperature to 1000-1100°C at a heating rate of 3-8°C / min, and keeping at this temperature for 3 hours; Intermediate insulation stage: heat up to 1300-1450℃, keep warm for 2-3 hours; High temperature sintering stage: continue to heat up to 1650-1750℃ and keep warm for 5-7 hours; 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.

[0013] A silicon nitride ceramic substrate is prepared by using the above-mentioned method for preparing a silicon nitride ceramic substrate.

[0014] 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: 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 tape casting 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.

[0015] 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

[0016] The present invention discloses a method for preparing a tape casting slurry, comprising the following steps: Step 1: Slurry preparation: Add organic solvent to the pretreated 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. The pretreatment of silicon nitride powder includes the following steps: (1) Pre-sintering: The silicon nitride powder is placed in a reducing atmosphere for pre-sintering at a temperature of 800-1000°C for 3-5 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride and 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 combined oxygen in the silicon nitride and preliminarily activate the silicon nitride powder.

[0017] (2) Crushing treatment: The pre-sintered silicon nitride powder is crushed to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 0.4-1.6 μm. The crushing treatment can be carried out by ball milling or mechanical crushing, etc., without limitation.

[0018] (3) Surface modification: The crushed silicon nitride powder is surface modified by using a silane coupling agent: the silicon nitride powder is added to an ethanol solution containing a silane coupling agent, the amount of the silane coupling agent added is 1%-3% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 70%-90% (volume fraction). Then, the mixture is stirred and reacted at a temperature of 50-70°C for 4-6 hours to allow the silane coupling agent to fully coat the surface of the silicon nitride powder, thereby improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0019] The organic solvent is a mixture of ethanol, butanone, toluene, ethyl acetate and isopropanol, and 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 silicon nitride powder and dissolving polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity regulating effect of butanone, the uniformity improving effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization regulating effect of isopropanol work together to provide an ideal solvent environment for preparing high-quality casting slurry.

[0020] The addition amount of the sintering aid, binder, toughening agent and dispersant is 5%-8%, 4%-6%, 3%-7% and 2%-4% of the mass of 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 1.5-2.5:0.8-1.2:0.8-1.2. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystal; and the dispersant is ammonium polyacrylate. This synergistic effect can enhance the adhesion of the slurry while improving the dispersibility of silicon nitride powder, making the cast film more solid.

[0021] Step 2, tape casting: Pour the slurry from step 1 into the material trough of the tape casting machine, control the thickness of the slurry by a scraper, and form a uniform film on the tape casting belt at a casting speed of 0.2-1.5 m / min. The film after tape casting is naturally dried at room temperature for 12-18 hours to initially solidify it to form a silicon nitride substrate blank.

[0022] The present invention also discloses a method for preparing a silicon nitride ceramic substrate, wherein a silicon nitride substrate green body prepared by the aforementioned method for preparing a tape casting slurry is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used 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: Heating stage: Heating from room temperature to 1000-1100°C at a heating rate of 3-8°C / min, and keeping at this temperature for 3 hours.

[0023] Intermediate insulation stage: heat up to 1300-1450℃ and keep warm for 2-3 hours.

[0024] High temperature sintering stage: continue to heat up to 1650-1750℃ and keep warm for 5-7 hours.

[0025] 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.

[0026] The present invention further discloses a silicon nitride ceramic substrate, which is prepared by adopting the preparation method of the silicon nitride ceramic substrate.

[0027] The present invention is further described in detail below with multiple embodiments and comparative examples: Example 1 This embodiment discloses a method for preparing a tape casting slurry, comprising the following steps: Step 1: Slurry preparation: Add organic solvent to the pretreated silicon nitride powder, add sintering aid, binder, toughening agent and dispersant, and ball mill for 12 hours in a ball mill to prepare a uniform and stable slurry. The pretreatment of silicon nitride powder includes the following steps: (1) Pre-sintering: The silicon nitride powder is placed in a reducing atmosphere for pre-sintering at a temperature of 900°C for 4 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride and preliminarily activate the silicon nitride powder. The reducing atmosphere is a nitrogen-hydrogen mixed gas, in which the volume fraction of hydrogen is 10%, so as to better remove some impurities and some combined oxygen in the silicon nitride and preliminarily activate the silicon nitride powder.

[0028] (2) Crushing treatment: The pre-sintered silicon nitride powder is crushed to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 0.5 μm. The crushing treatment can be carried out by ball milling or mechanical crushing, etc., without limitation.

[0029] (3) Surface modification: The crushed silicon nitride powder is surface modified by using a silane coupling agent: the silicon nitride powder is added to an ethanol solution containing a silane coupling agent, the amount of the silane coupling agent added is 2% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 88% (volume fraction). The mixture is stirred and reacted at 60°C for 6 hours to allow the silane coupling agent to fully coat the surface of the silicon nitride powder, thereby improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0030] The organic solvent is a mixture of ethanol, butanone, toluene, ethyl acetate and isopropanol, and the volume ratio of ethanol, butanone, toluene, ethyl acetate and isopropanol is 2.5:2.2:1.2:0.6:0.7. While ensuring the wetting of silicon nitride powder and dissolving polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity regulating effect of butanone, the uniformity improving effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization regulating effect of isopropanol work together to provide an ideal solvent environment for preparing high-quality casting slurry.

[0031] The added 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, aluminum oxide, and magnesium oxide, and the mass ratio of yttrium oxide, aluminum oxide, and magnesium oxide is 2:1:1.2. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; and the dispersant is ammonium polyacrylate. This synergistic effect can enhance the adhesion of the slurry while improving the dispersibility of silicon nitride powder, making the cast film more solid.

[0032] Step 2, tape casting: Pour the slurry from step 1 into the material trough of the tape casting machine, control the thickness of the slurry by a scraper, and form a uniform film on the tape casting belt at a casting speed of 0.2 m / min. The film after tape casting is naturally dried at room temperature for 14 hours to initially solidify it to form a silicon nitride substrate blank.

[0033] This embodiment also discloses a method for preparing a silicon nitride ceramic substrate, wherein a silicon nitride substrate green body prepared by the aforementioned method for preparing a tape casting slurry is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used as a sintering atmosphere, wherein the volume fraction of nitrogen is 85% and the volume fraction of hydrogen is 15%; and sintering is performed according to the following sintering curve: Heating stage: the temperature was raised from room temperature to 1000°C at a heating rate of 3°C / min and kept at this temperature for 3 hours.

[0034] Intermediate insulation stage: heat to 1400℃ and keep warm for 2 hours.

[0035] High temperature sintering stage: continue to heat up to 1700℃ and keep warm for 6 hours.

[0036] Cooling stage: After sintering, the temperature is lowered to room temperature at a rate of 3°C / min to obtain a silicon nitride ceramic substrate.

[0037] This embodiment further discloses a silicon nitride ceramic substrate, which is prepared by using the aforementioned method for preparing a silicon nitride ceramic substrate.

[0038] Example 2 This embodiment discloses a method for preparing a tape casting slurry, comprising the following steps: Step 1: Slurry preparation: Add organic solvent to the pretreated silicon nitride powder, add sintering aid, binder, toughening agent and dispersant, and ball mill for 15 hours in a ball mill to prepare a uniform and stable slurry. The pretreatment of silicon nitride powder includes the following steps: (1) Pre-sintering: The silicon nitride powder is placed in a reducing atmosphere for pre-sintering at a temperature of 800°C for 5 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride and 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 preliminarily activate the silicon nitride powder.

[0039] (2) Crushing treatment: The pre-sintered silicon nitride powder is crushed to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 0.8 μm. The crushing treatment can be carried out by ball milling or mechanical crushing, etc., without limitation.

[0040] (3) Surface modification: The crushed silicon nitride powder is surface modified by using a silane coupling agent: the silicon nitride powder is added to an ethanol solution containing a silane coupling agent, the amount of the silane coupling agent added is 3% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 70% (volume fraction). The mixture is stirred and reacted at 50°C for 5 hours to allow the silane coupling agent to fully coat the surface of the silicon nitride powder, thereby improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0041] The organic solvent is a mixture of ethanol, butanone, toluene, ethyl acetate and isopropanol, and the volume ratio of ethanol, butanone, 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 dissolving polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity regulating effect of butanone, the uniformity improving effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization regulating effect of isopropanol work together to provide an ideal solvent environment for preparing high-quality casting slurry.

[0042] The added 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, aluminum oxide, and magnesium oxide, and the mass ratio of yttrium oxide, aluminum oxide, and magnesium oxide is 2.2:0.9:1. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; and the dispersant is ammonium polyacrylate. This synergistic effect can enhance the adhesion of the slurry while improving the dispersibility of silicon nitride powder, making the cast film more solid.

[0043] Step 2, tape casting: Pour the slurry from step 1 into the material trough of the tape casting machine, control the thickness of the slurry by a scraper, and form a uniform film on the tape casting belt at a casting speed of 0.8 m / min. The film after tape casting is naturally dried at room temperature for 15 hours to initially solidify it to form a silicon nitride substrate blank.

[0044] This embodiment also discloses a method for preparing a silicon nitride ceramic substrate, wherein a silicon nitride substrate green body prepared by the aforementioned method for preparing a tape casting slurry is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used as a sintering atmosphere, wherein the volume fraction of nitrogen is 90% and the volume fraction of hydrogen is 10%; and sintering is performed according to the following sintering curve: Heating stage: the temperature was raised from room temperature to 1050°C at a heating rate of 8°C / min and kept at this temperature for 3 hours.

[0045] Intermediate insulation stage: heat to 1300℃ and keep warm for 3 hours.

[0046] High temperature sintering stage: continue to heat up to 1750℃ and keep warm for 7 hours.

[0047] Cooling stage: After sintering, the temperature is lowered to room temperature at a rate of 4°C / min to obtain a silicon nitride ceramic substrate.

[0048] This embodiment further discloses a silicon nitride ceramic substrate, which is prepared by using the aforementioned method for preparing a silicon nitride ceramic substrate.

[0049] Example 3 This embodiment discloses a method for preparing a tape casting slurry, comprising the following steps: Step 1: Slurry preparation: Add organic solvent to the pretreated silicon nitride powder, add sintering aid, binder, toughening agent and dispersant, and ball mill for 18 hours in a ball mill to prepare a uniform and stable slurry. The pretreatment of silicon nitride powder includes the following steps: (1) Pre-sintering: The silicon nitride powder is placed in a reducing atmosphere for pre-sintering at a temperature of 1000°C for 3 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride and 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 preliminarily activate the silicon nitride powder.

[0050] (2) Crushing treatment: The pre-sintered silicon nitride powder is crushed to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 1.0 μm. The crushing treatment can be carried out by ball milling or mechanical crushing, etc., without limitation.

[0051] (3) Surface modification: The crushed silicon nitride powder is surface modified by using a silane coupling agent: the silicon nitride powder is added to an ethanol solution containing a silane coupling agent, the amount of the silane coupling agent added is 1.5% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 85% (volume fraction). The mixture is stirred and reacted at 70°C for 4 hours to allow the silane coupling agent to fully coat the surface of the silicon nitride powder, thereby improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0052] The organic solvent is a mixture of ethanol, butanone, toluene, ethyl acetate and isopropanol, and the volume ratio of ethanol, butanone, toluene, ethyl acetate and isopropanol is 3.2:1.6:1.0:1:1. While ensuring the wetting of silicon nitride powder and dissolving polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity regulating effect of butanone, the uniformity improving effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization regulating effect of isopropanol work together to provide an ideal solvent environment for preparing high-quality casting slurry.

[0053] The added 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 nanocrystals; and the dispersant is ammonium polyacrylate. This synergistic effect can enhance the adhesion of the slurry while improving the dispersibility of silicon nitride powder, making the cast film more solid.

[0054] Step 2, tape casting: Pour the slurry from step 1 into the material trough of the tape casting machine, control the thickness of the slurry by a scraper, and form a uniform film on the tape casting belt at a casting speed of 1.5 m / min. The film after tape casting is naturally dried at room temperature for 18 hours to initially solidify it to form a silicon nitride substrate blank.

[0055] This embodiment also discloses a method for preparing a silicon nitride ceramic substrate, wherein a silicon nitride substrate green body prepared by the aforementioned method for preparing a tape casting slurry is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used as a sintering atmosphere, wherein the volume fraction of nitrogen is 88% and the volume fraction of hydrogen is 12%; and sintering is performed according to the following sintering curve: Heating stage: the temperature was raised from room temperature to 1020°C at a heating rate of 7°C / min and kept at this temperature for 3 hours.

[0056] Intermediate insulation stage: heat to 1450℃ and keep warm for 2.2 hours.

[0057] High temperature sintering stage: continue to heat up to 1650℃ and keep warm for 5 hours.

[0058] Cooling stage: After sintering, the temperature is lowered to room temperature at a rate of 3.2°C / min to obtain a silicon nitride ceramic substrate.

[0059] This embodiment further discloses a silicon nitride ceramic substrate, which is prepared by using the aforementioned method for preparing a silicon nitride ceramic substrate.

[0060] Example 4 This embodiment discloses a method for preparing a tape casting slurry, comprising the following steps: Step 1: Slurry preparation: Add organic solvent to the pretreated silicon nitride powder, then add sintering aid, binder, toughening agent and dispersant, and ball mill in a ball mill for 24 hours to prepare a uniform and stable slurry. The pretreatment of silicon nitride powder includes the following steps: (1) Pre-sintering: The silicon nitride powder is placed in a reducing atmosphere for pre-sintering at a temperature of 850°C for 3.5 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride and 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 preliminarily activate the silicon nitride powder.

[0061] (2) Crushing treatment: The pre-sintered silicon nitride powder is crushed to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 1.2 μm. The crushing treatment can be carried out by ball milling or mechanical crushing, etc., without limitation.

[0062] (3) Surface modification: The crushed silicon nitride powder is surface modified by using a silane coupling agent: the silicon nitride powder is added to an ethanol solution containing a silane coupling agent, the amount of the silane coupling agent added is 2.2% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 90% (volume fraction). The mixture is stirred and reacted at 55°C for 4.5 hours to allow the silane coupling agent to fully coat the surface of the silicon nitride powder, thereby improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0063] The organic solvent is a mixture of ethanol, butanone, toluene, ethyl acetate and isopropanol, and the volume ratio of ethanol, butanone, toluene, ethyl acetate and isopropanol is 3:1.8:0.85:0.9:0.8. While ensuring the wetting of silicon nitride powder and dissolving polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity regulating effect of butanone, the uniformity improving effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization regulating effect of isopropanol work together to provide an ideal solvent environment for preparing high-quality casting slurry.

[0064] The added 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, aluminum oxide, and magnesium oxide, and the mass ratio of yttrium oxide, aluminum oxide, and magnesium oxide is 2.3:1.2:0.9. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; and the dispersant is ammonium polyacrylate. This synergistic effect can enhance the adhesion of the slurry while improving the dispersibility of silicon nitride powder, making the cast film more solid.

[0065] Step 2, tape casting: Pour the slurry from step 1 into the material trough of the tape casting machine, control the thickness of the slurry by a scraper, and form a uniform film on the tape casting belt at a casting speed of 1.3 m / min. The film after tape casting is naturally dried at room temperature for 16 hours to initially solidify it to form a silicon nitride substrate blank.

[0066] This embodiment also discloses a method for preparing a silicon nitride ceramic substrate. The silicon nitride substrate green body prepared by the aforementioned method for preparing a tape casting slurry is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used as a sintering atmosphere, wherein the volume fraction of nitrogen is 86% and the volume fraction of hydrogen is 14%. Sintering is performed according to the following sintering curve: Heating stage: the temperature was raised from room temperature to 1080°C at a heating rate of 6°C / min and kept at this temperature for 3 hours.

[0067] Intermediate insulation stage: heat to 1350℃ and keep warm for 2.5 hours.

[0068] High temperature sintering stage: continue to heat up to 1680℃ and keep warm for 5.5 hours.

[0069] Cooling stage: After sintering, the temperature is lowered to room temperature at a rate of 3.5°C / min to obtain a silicon nitride ceramic substrate.

[0070] This embodiment further discloses a silicon nitride ceramic substrate, which is prepared by using the aforementioned method for preparing a silicon nitride ceramic substrate.

[0071] Example 5 This embodiment discloses a method for preparing a tape casting slurry, comprising the following steps: Step 1: Slurry preparation: Add organic solvent to the pretreated silicon nitride powder, add sintering aid, binder, toughening agent and dispersant, and ball mill for 20 hours in a ball mill to prepare a uniform and stable slurry. The pretreatment of silicon nitride powder includes the following steps: (1) Pre-sintering: The silicon nitride powder is placed in a reducing atmosphere for pre-sintering at a temperature of 950°C for 4.5 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride and preliminarily activate the silicon nitride powder. The reducing atmosphere is a nitrogen-hydrogen mixed gas, in which the volume fraction of hydrogen is 14%, so as to better remove some impurities and some combined oxygen in the silicon nitride and preliminarily activate the silicon nitride powder.

[0072] (2) Crushing treatment: The pre-sintered silicon nitride powder is crushed to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 1.6 μm. The crushing treatment can be carried out by ball milling or mechanical crushing, etc., without limitation.

[0073] (3) Surface modification: The crushed silicon nitride powder is surface modified by using a silane coupling agent: the silicon nitride powder is added to an ethanol solution containing a silane coupling agent, the amount of the silane coupling agent added is 1.8% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 75% (volume fraction). The mixture is stirred and reacted at 65°C for 5.5 hours to allow the silane coupling agent to fully coat the surface of the silicon nitride powder, thereby improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0074] The organic solvent is a mixture of ethanol, butanone, toluene, ethyl acetate and isopropanol, and the volume ratio of ethanol, butanone, toluene, ethyl acetate and isopropanol is 2.8:2.4:1.1:0.7:0.6. While ensuring the wetting of silicon nitride powder and dissolving polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity regulating effect of butanone, the uniformity improving effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization regulating effect of isopropanol work together to provide an ideal solvent environment for preparing high-quality casting slurry.

[0075] The added 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, aluminum oxide, and magnesium oxide, and the mass ratio of yttrium oxide, aluminum oxide, and magnesium oxide is 1.8:0.9:0.85. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; and the dispersant is ammonium polyacrylate. This synergistic effect can enhance the adhesion of the slurry while improving the dispersibility of silicon nitride powder, making the cast film more solid.

[0076] Step 2, tape casting: Pour the slurry from step 1 into the material trough of the tape casting machine, control the thickness of the slurry by a scraper, and form a uniform film on the tape casting belt at a casting speed of 0.5 m / min. The film after tape casting is naturally dried at room temperature for 13 hours to initially solidify it to form a silicon nitride substrate blank.

[0077] This embodiment also discloses a method for preparing a silicon nitride ceramic substrate. The silicon nitride substrate green body prepared by the aforementioned method for preparing a tape casting slurry is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used as a sintering atmosphere, wherein the volume fraction of nitrogen is 87% and the volume fraction of hydrogen is 13%. Sintering is performed according to the following sintering curve: Heating stage: the temperature was raised from room temperature to 1100°C at a heating rate of 5°C / min and kept at this temperature for 3 hours.

[0078] Intermediate insulation stage: heat to 1380℃ and keep warm for 2.8 hours.

[0079] High temperature sintering stage: continue to heat up to 1720℃ and keep warm for 6.5 hours.

[0080] Cooling stage: After sintering, the temperature is lowered to room temperature at a rate of 3.8°C / min to obtain a silicon nitride ceramic substrate.

[0081] This embodiment further discloses a silicon nitride ceramic substrate, which is prepared by using the aforementioned method for preparing a silicon nitride ceramic substrate.

[0082] Example 6 This embodiment discloses a method for preparing a tape casting slurry, comprising the following steps: Step 1: Slurry preparation: Add organic solvent to the pretreated silicon nitride powder, add sintering aid, binder, toughening agent and dispersant, and ball mill for 22 hours to prepare a uniform and stable slurry. The pretreatment of silicon nitride powder includes the following steps: (1) Pre-sintering: The silicon nitride powder is placed in a reducing atmosphere for pre-sintering at a temperature of 860°C for 4 hours, which can effectively remove some impurities and some combined oxygen in the silicon nitride and 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 preliminarily activate the silicon nitride powder.

[0083] (2) Crushing treatment: The pre-sintered silicon nitride powder is crushed to make its particle size more uniform. The silicon nitride powder is crushed to an average particle size of 0.9 μm. The crushing treatment can be carried out by ball milling or mechanical crushing, etc., without limitation.

[0084] (3) Surface modification: The crushed silicon nitride powder is surface modified by using a silane coupling agent: the silicon nitride powder is added to an ethanol solution containing a silane coupling agent, the amount of the silane coupling agent added is 1% of the mass of the silicon nitride powder, and the concentration of the ethanol solution is 80% (volume fraction). The mixture is stirred and reacted at 50°C for 4 hours to allow the silane coupling agent to fully coat the surface of the silicon nitride powder, thereby improving the dispersibility of the silicon nitride powder and its compatibility with other additives.

[0085] The organic solvent is a mixture of ethanol, butanone, toluene, ethyl acetate and isopropanol, and the volume ratio of ethanol, butanone, 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 dissolving polyvinyl butyral (PVB), the stability and consistency of the slurry are improved. The rapid solubility of ethanol, the viscosity regulating effect of butanone, the uniformity improving effect of toluene, the auxiliary dissolution effect of ethyl acetate and the volatilization regulating effect of isopropanol work together to provide an ideal solvent environment for preparing high-quality casting slurry.

[0086] The added 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, aluminum oxide, and magnesium oxide, and the mass ratio of yttrium oxide, aluminum oxide, and magnesium oxide is 1.5:0.8:0.8. The binder is polyvinyl butyral; the toughening agent is chitin nanocrystals; and the dispersant is ammonium polyacrylate. This synergistic effect can enhance the adhesion of the slurry while improving the dispersibility of silicon nitride powder, making the cast film more solid.

[0087] Step 2, tape casting: Pour the slurry from step 1 into the material trough of the tape casting machine, control the thickness of the slurry by a scraper, and form a uniform film on the tape casting belt at a casting speed of 1.2 m / min. The film after tape casting is naturally dried at room temperature for 12 hours to initially solidify it to form a silicon nitride substrate blank.

[0088] This embodiment also discloses a method for preparing a silicon nitride ceramic substrate, wherein a silicon nitride substrate green body prepared by the aforementioned method for preparing a tape casting slurry is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used as a sintering atmosphere, wherein the volume fraction of nitrogen is 89% and the volume fraction of hydrogen is 11%; and sintering is performed according to the following sintering curve: Heating stage: the temperature was raised from room temperature to 1060°C at a heating rate of 4°C / min and kept at this temperature for 3 hours.

[0089] Intermediate insulation stage: heat to 1410℃ and keep warm for 2.4 hours.

[0090] High temperature sintering stage: continue to raise the temperature to 1670℃ and keep it for 6 hours.

[0091] Cooling stage: After sintering, the temperature is lowered to room temperature at a rate of 3.3°C / min to obtain a silicon nitride ceramic substrate.

[0092] This embodiment further discloses a silicon nitride ceramic substrate, which is prepared by using the aforementioned method for preparing a silicon nitride ceramic substrate.

[0093] Comparative Example 1 The difference between the comparative example and the above-mentioned Example 6 is that the silicon nitride powder in this comparative example has not undergone a pretreatment process. The rest of the contents of this comparative example are the same as those of Example 6 and will not be repeated here.

[0094] Comparative Example 2 The difference between this comparative example and the above-mentioned Example 6 is that other organic solvent ratios are used in this comparative example. The rest of the contents of this comparative example are the same as those of Example 6 and will not be repeated here.

[0095] Comparative Example 3 The difference between this comparative example and the above-mentioned Example 6 is that chitosan nanocrystals are not added in this comparative example. The rest of the contents of this comparative example are the same as those of Example 6 and will not be described again here.

[0096] The thermal conductivity, flexural strength and insulation resistance of the silicon nitride ceramic substrates prepared in the above embodiments and comparative examples were tested by conventional methods. The test results are shown in the following table:

[0097] It can be seen from the test results that the silicon nitride ceramic substrate prepared by the present invention is superior to the comparative example in terms of thermal conductivity, flexural strength and insulation resistance, and has good performance and quality. Compared with ordinary silicon nitride ceramic substrates, the silicon nitride ceramic substrate obtained by pretreating silicon nitride powder and adding chitin nanocrystals has high thermal conductivity, flexural strength and insulation resistance.

[0098] The design emphasis of the present invention is as follows: first, 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 tape casting film, and by using specific sintering aids, organic solvents, binders and dispersants, and by controlling the stirring speed, ball milling time and other parameters in 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 body strength and toughness. Secondly, through a special silicon nitride powder pretreatment process, 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 more fine and uniform, and 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.

[0099] The above description is only a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any slight modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a tape casting slurry, characterized in that: The following steps are included: Step 1, slurry preparation: add organic solvent to the pretreated silicon nitride powder, 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; Step 2, tape casting: Pour the slurry from step 1 into the material trough of the tape casting machine, control the thickness of the slurry by a scraper, and form a uniform film on the tape casting belt at a casting speed of 0.2-1.5 m / min. The film after tape casting is naturally dried at room temperature for 12-18 hours to initially solidify it to form a silicon nitride substrate blank.

2. The method for preparing the tape casting slurry according to claim 1, characterized in that: The pretreatment of the silicon nitride powder comprises the following steps: (1) Pre-sintering: The silicon nitride powder is placed in a reducing atmosphere for pre-sintering at a temperature of 800-1000°C for 3-5 hours; (2) Crushing treatment: The pre-sintered silicon nitride powder is crushed to an average particle size of 0.4-1.6 μm; (3) Surface modification: The crushed silicon nitride powder is surface modified by using a silane coupling agent: the silicon nitride powder is added to an ethanol solution containing a silane coupling agent, the amount of the silane coupling agent added is 1%-3% of the mass of the silicon nitride powder, the concentration of the ethanol solution is 70%-90%, and then stirred at a temperature of 50-70°C for 4-6 hours.

3. The method for preparing the tape casting slurry according to claim 2, characterized in that: The reducing atmosphere is a nitrogen-hydrogen mixed gas, wherein the volume fraction of hydrogen is 5%-15%.

4. The method for preparing the tape casting slurry according to claim 1, characterized in that: The added 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.

5. The method for preparing the tape casting slurry according to claim 1, characterized in that: 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 1.5-2.5:0.8-1.2:0.8-1.

2.

6. The method for preparing the tape casting slurry according to claim 1, characterized in that: The organic solvent is a mixture of ethanol, butanone, toluene, ethyl acetate and isopropanol, and 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.

7. The method for preparing the tape casting slurry according to claim 1, characterized in that: The binder is polyvinyl butyral; the toughening agent is chitin nanocrystal; and the dispersant is ammonium polyacrylate.

8. A method for preparing a silicon nitride ceramic substrate, characterized in that: The silicon nitride substrate green body prepared by the method for preparing the tape casting slurry according to any one of claims 1 to 7 is placed in a sintering furnace, and a nitrogen-hydrogen mixed gas is used as the 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: Heating stage: heating from room temperature to 1000-1100°C at a heating rate of 3-8°C / min, and keeping at this temperature for 3 hours; Intermediate insulation stage: heat up to 1300-1450℃, keep warm for 2-3 hours; High temperature sintering stage: continue to heat up to 1650-1750℃ and keep warm for 5-7 hours; 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.

9. A silicon nitride ceramic substrate, characterized in that: The silicon nitride ceramic substrate is prepared by the method for preparing the silicon nitride ceramic substrate as claimed in claim 8.

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