A method for manufacturing an aluminum nitride substrate by a water-based tape casting process

Abstract

The application relates to the technical field of aluminum nitride substrates, in particular to a preparation method of an aluminum nitride substrate through a water-based tape casting process, which comprises the following steps: step one, raw material preparation and slurry preparation; step two, slurry mixing and plasticizing; step three, vacuum degassing and aging; step four, tape casting; step five, drying; step six, green sheet stripping and cutting; and step seven, glue removal and sintering. Through a split wrapping process on aluminum nitride powder, a layer of ultra-thin film is attached to the outer surface of the aluminum nitride particles. When the tape casting process is carried out, water-based solvents can be used without causing hydrolysis of the aluminum nitride particles. Compared with organic solvents, the water-based solvents are lower in price, the production cost is lower, the damage to the environment during production and processing is reduced, production personnel are prevented from contacting toxic organic solvents, and the safety is higher.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride substrate technology, and more specifically to a method for preparing aluminum nitride substrates using a water-based casting process. Background Technology

[0002] Aluminum nitride (AlN) is a group III-V compound ceramic bonded by covalent bonds. Its crystal structure is mainly wurtzite (space group P63mc). Its theoretical thermal conductivity in a single crystal can reach 320 W / (m·K). This is due to the strong bonding between aluminum and nitrogen atoms, low atomic mass, and simple phonon spectrum, which results in a large mean free path of phonons and low thermal resistance. Aluminum nitride substrates are electronic packaging and circuit boards made primarily of aluminum nitride (AlN) ceramic. They are widely used advanced ceramic substrate materials with high thermal conductivity, low coefficient of thermal expansion, high electrical insulation, excellent mechanical properties, and chemical stability. They play a key role in modern high-power, high-frequency, and high-density electronic packaging.

[0003] Casting is a classic method for preparing large-area, thin, and flat ceramic sheets. The basic process of casting aluminum nitride substrates involves mixing ultrafine aluminum nitride powder with various additives (i.e., dispersants, binders, plasticizers, and organic solvents) to form a uniform and stable slurry with a certain viscosity. Then, a doctor blade device scrapes the slurry onto a smoothly moving carrier belt to form a thin film of uniform thickness. The wet film then enters a multi-temperature drying channel, where the solvent is slowly and uniformly evaporated, ultimately resulting in a flexible ceramic green belt. After drying, the green belt can be subjected to laser or mechanical punching, printing, lamination, etc. Finally, after debinding and high-temperature sintering, the final dense aluminum nitride ceramic substrate is obtained.

[0004] Although the aforementioned existing technologies can solve the corresponding technical problems, they still have certain drawbacks: during the molding of existing aluminum nitride substrates, aluminum nitride powder slowly hydrolyzes in water to generate aluminum hydroxide. This not only affects the sintering activity but also forms an oxide layer on the powder surface, severely reducing the thermal conductivity of the final product. Therefore, organic solvents such as toluene, xylene, methyl ethyl ketone, and isopropanol are used. However, although organic solvents can effectively prevent the hydrolysis of aluminum nitride powder, their high price significantly increases production costs. At the same time, the wastewater and exhaust gas generated during the production process can pollute and damage the environment and easily have adverse effects on the health of production personnel. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings and deficiencies of the prior art by providing a method for preparing aluminum nitride substrates using a water-based casting process.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing an aluminum nitride substrate using a water-based casting process, comprising the following steps:

[0007] Step 1: Raw material preparation and slurry preparation. High-purity aluminum nitride powder is subjected to a powder coating process to obtain coated aluminum nitride powder. The coated aluminum nitride powder and sintering aid are accurately weighed according to the ratio and dispersed in an aqueous solvent. Primary dispersion is carried out by ball milling or stirring. The powder coating process includes the following steps:

[0008] S1: Prepare raw materials, selecting high-purity aluminum nitride powder, N-vinylpyrrolidone-itaconic acid copolymer (NVP-IA), and ethanol;

[0009] S2: Solution preparation, dissolve the N-vinylpyrrolidone-itaconic acid copolymer in ethanol to form a polymer solution;

[0010] S3: Impregnation coating, aluminum nitride powder is added to the above solution and ultrasonically dispersed using an ultrasonic dispersion device to ensure that the aluminum nitride powder is completely impregnated by the solution;

[0011] S4: Drying and curing. Solvents are removed by spray drying using a spray dryer, allowing the polymer to form a film on the powder surface and cure, resulting in aluminum nitride powder with a polymer film.

[0012] S5: The aluminum nitride powder with polymer film is sent into a vacuum oven for post-drying to obtain coated aluminum nitride powder.

[0013] The step of feeding the aluminum nitride powder with a polymer film into a vacuum oven for post-drying to obtain the finished aluminum nitride powder coated with the polymer film includes a secondary coating process, which includes the following steps:

[0014] Q1: Prepare the raw materials for the secondary coating process, including aluminum nitride powder, ethanol, deionized water, ammonia, and tetraethyl orthosilicate. Mix tetraethyl orthosilicate with deionized water and ethanol to obtain an ethanol solution containing tetraethyl orthosilicate. Mix deionized water with the remaining ethanol to obtain a dispersion.

[0015] Q2: Dispersion, ultrasonically disperse the coated aluminum nitride powder in the dispersion liquid;

[0016] Q3: Hydrolysis, while stirring, add ammonia dropwise to adjust the pH to alkaline;

[0017] Q4: Polycondensation, slowly add an ethanol solution containing tetraethyl orthosilicate, and stir continuously at a constant temperature for several hours to allow the tetraethyl orthosilicate to hydrolyze and condense on the surface of the aluminum nitride powder to form a SiO2 sol layer.

[0018] Q5: Centrifuge, wash several times with ethanol to remove impurities, and then dry at 80-120℃ to obtain secondary coated aluminum nitride powder;

[0019] Step 2: Slurry mixing and plasticizing. Add the binder and plasticizer sequentially to the fully dispersed slurry. Perform ball milling for 12-24 hours.

[0020] Step 3: Vacuum degassing and aging. Place the well-mixed slurry in a vacuum degassing device to remove air bubbles introduced during stirring and ball milling. Then, let the slurry stand and age for 12-48 hours under constant temperature conditions.

[0021] Step 4: Casting and forming. Adjust the parameters of the casting machine, pour the aged slurry into the casting machine hopper, and form a continuous, uniformly thick wet film on the uniformly moving carrier film through a scraper or mold.

[0022] Step 5: Drying. The wet film enters the drying zone along with the carrier film, where the solvent slowly evaporates under controlled temperature and humidity conditions.

[0023] Step 6: Peeling and cutting the green sheet. After complete drying, a green sheet with a certain strength and flexibility is formed. Peel it off from the carrier film and cut it using a precision punching machine or laser cutting machine to obtain green sheets of a specific size.

[0024] Step 7: Debinding and Sintering. The green sheet is placed in a sintering furnace and debinding is performed first. Under air or a protective atmosphere, it is heated to 400-600℃ at a precisely controlled heating rate and held for a sufficient time to allow the organic additives in the green sheet to completely decompose and volatilize. Then, sintering is carried out in a high-temperature, inert or reducing gas-filled environment to densify the aluminum nitride particles and form an aluminum nitride ceramic substrate.

[0025] A further improvement is made to the debinding and sintering process. The green sheet is placed in a sintering furnace and first undergoes debinding. Under air or a protective atmosphere, it is heated to 400-600°C at a precisely controlled heating rate and held for a sufficient time to allow the organic additives in the green sheet to completely decompose and volatilize. Subsequently, sintering is carried out in a high-temperature, inert, or reducing gas-filled environment to densify the aluminum nitride particles and form a ceramic substrate with high thermal conductivity and high strength. Afterwards, the process includes subsequent processing and testing. The sintered aluminum nitride ceramic substrate is subjected to planar grinding and polishing, and then metallized. Finally, the density, thermal conductivity, warpage, surface roughness, and dielectric properties of the aluminum nitride ceramic substrate are comprehensively tested.

[0026] A further improvement is that, after selecting high-purity aluminum nitride powder, N-vinylpyrrolidone-itaconic acid copolymer (NVP-IA), and ethanol for the raw material preparation, a glove box is also prepared and filled with inert gas, and the raw materials are sent into the glove box for storage and retrieval.

[0027] A further improvement is that the impregnation coating involves adding aluminum nitride powder to the above solution and performing an ultrasonic dispersion process using an ultrasonic dispersion device to completely impregnate the aluminum nitride powder with the solution. Afterward, the ultrasonically dispersed suspension is transferred to a constant temperature magnetic stirrer, sealed with a sealing film, and reacted for 2-4 hours at 50-60°C with continuous stirring.

[0028] A further improvement is that the step of feeding the aluminum nitride powder with the polymer film into a vacuum oven for post-drying to obtain the finished coated aluminum nitride powder includes grinding and sieving, grinding with a mortar and pestle, and passing through a sieve to obtain the final uniformly coated composite powder, i.e. coated aluminum nitride powder.

[0029] A further improvement is that the preparation of the secondary coating process raw materials includes coating aluminum nitride powder, ethanol, deionized water, ammonia, and tetraethyl orthosilicate. Tetraethyl orthosilicate is mixed with deionized water and ethanol to obtain an ethanol solution containing tetraethyl orthosilicate. Deionized water is then mixed with the remaining ethanol to obtain a dispersion. The process also includes preparing a glove box, drying the glove box, filling it with inert gas, and placing the coated aluminum nitride powder into the glove box for use.

[0030] A further improvement is that the centrifugation is followed by washing with ethanol several times to remove impurities, and then drying at 80-120°C. After drying, the powder is placed in a muffle furnace or tube furnace and heated to 500-600°C at a rate of 2-5°C / min in an air or oxygen atmosphere, and held at that temperature for 1-2 hours.

[0031] The beneficial effects of this invention after adopting the above technical solution are as follows: By performing a separate coating process on aluminum nitride powder, the outer surface of the particles is coated with an ultra-thin film formed by N-vinylpyrrolidone-itaconic acid copolymer. This allows the use of water-based solvents during the casting process. Using water-based solvents prevents the coated aluminum nitride powder from directly contacting the water in the solvent, thus preventing hydrolysis of the aluminum nitride powder and affecting the quality of the finished product. While ensuring the quality of the finished product, the use of water-based solvents is cheaper than organic solvents, resulting in lower production costs. It also reduces environmental damage during production and processing, and avoids contact with toxic organic solvents for production personnel, thus enhancing safety. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0034] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. Example 1:

[0035] See Figure 1 As shown, the technical solution adopted in this specific embodiment is: a method for preparing an aluminum nitride substrate using a water-based casting process, comprising the following steps:

[0036] Step 1: Raw material preparation and slurry preparation. High-purity aluminum nitride powder is processed by powder coating to obtain coated aluminum nitride powder. The coated aluminum nitride powder and sintering aid are accurately weighed in proportion and dispersed in a water-based solvent. Primary dispersion is carried out by ball milling or stirring. Specifically, a planetary ball mill or high-speed mixer is used to ball mill or stir for 2-4 hours at a speed of 200-400 rpm for primary dispersion.

[0037] The powder coating process includes the following steps:

[0038] S1: Prepare raw materials, selecting high-purity aluminum nitride powder, N-vinylpyrrolidone-itaconic acid copolymer (NVP-IA), and ethanol;

[0039] S2: Solution preparation, dissolving the N-vinylpyrrolidone-itaconic acid copolymer in ethanol to form a polymer solution, specifically, preparing a polymer solution with a concentration of 1-5 wt%, preferably a polymer solution of 2.8 wt%. The above-mentioned N-vinylpyrrolidone-itaconic acid copolymer is prior art, purchased from Xi'an Ruixi Biotechnology Co., Ltd., specifically an N-vinylpyrrolidone (NVP) / itaconic acid (IA) copolymer hydrogel;

[0040] S3: Impregnation coating. Add aluminum nitride powder to the above solution and perform ultrasonic dispersion using an ultrasonic dispersion device to completely impregnate the aluminum nitride powder with the solution. Specifically, perform ultrasonic dispersion for 20-30 minutes at a power of 300-500W and room temperature using an ultrasonic dispersion device to completely impregnate the aluminum nitride powder with the solution.

[0041] S4: Drying and curing. Solvents are removed by spray drying using a spray dryer, allowing the polymer to form a film and solidify on the powder surface, resulting in aluminum nitride powder with a polymer film. Specifically, spray drying is performed using a spray dryer at an inlet temperature of 120-160°C, an outlet temperature of 60-80°C, and a feed rate of 5-15 mL / min to remove solvents and allow the polymer to form a film and solidify on the powder surface, resulting in aluminum nitride powder with a polymer film.

[0042] S5: The aluminum nitride powder with polymer film is sent into a vacuum oven for post-drying to obtain coated aluminum nitride powder. Specifically, the aluminum nitride powder with polymer film is sent into a vacuum oven and post-dried for 2-4 hours at 80-100°C and a vacuum degree higher than -0.095MPa to obtain coated aluminum nitride powder.

[0043] Step 2: Slurry mixing and plasticizing. Add the binder and plasticizer sequentially to the fully dispersed slurry. Perform ball milling for 12-24 hours. Specifically, use a planetary ball mill with zirconia balls as the grinding medium, and mill at a speed of 250-350 rpm for 12-24 hours.

[0044] Step 3: Vacuum degassing and aging. Place the uniformly mixed slurry in a vacuum degassing device and degas for 20-30 minutes under a vacuum of -0.1MPa to remove air bubbles introduced during stirring and ball milling. Then, let the slurry stand and age for 12-48 hours under constant temperature conditions. Specifically, let the slurry stand and age for 12-48 hours under a constant temperature of 25±3°C.

[0045] Step 4: Casting and forming. Adjust the parameters of the casting machine, set the doctor blade gap to 0.2-1.0mm (adjust according to the target green film thickness), and the carrier film (such as polyester film) speed to 0.5-2.0m / min. Pour the aged slurry into the casting machine hopper. On the uniformly moving carrier film, a continuous and uniformly thick wet film is formed by passing through the doctor blade or mold.

[0046] Step 5: Drying. The wet film is placed in the drying zone along with the carrier film and dried for 4-8 hours under controlled temperature and humidity conditions, namely 30-40°C and 40-60%RH, to allow the solvent to evaporate slowly.

[0047] Step 6: Peeling and cutting the green sheet. After complete drying, a green strip with a certain strength and flexibility is formed. Peel it off from the carrier film and use a precision punching machine or laser cutting machine (power adjusted according to thickness) to obtain green sheets of a specific size.

[0048] Step 7: Debinding and Sintering. The green sheet is placed in a sintering furnace, i.e., an atmosphere sintering furnace (such as a tube furnace or a box furnace). First, debinding is performed. Under a flowing air atmosphere, the temperature is raised to 400-600°C at a heating rate of 0.5-2°C / min and held for 1-3 hours to allow the organic additives in the green sheet to completely decompose and volatilize. Then, under a flowing nitrogen or nitrogen-hydrogen mixed (reducing) atmosphere, the temperature is raised to 1800-1900°C at a rate of 5-10°C / min and held for 2-4 hours for sintering to densify the aluminum nitride particles and form an aluminum nitride ceramic substrate.

[0049] To improve product performance, the debinding and sintering process involves placing the green sheet in a sintering furnace and first performing debinding. Then, under air or a protective atmosphere, the sheet is heated to 400-600°C at a precisely controlled heating rate and held for a sufficient time to allow the organic additives within the green sheet to completely decompose and volatilize. Subsequently, sintering is carried out in a high-temperature, inert, or reducing gas-filled environment to densify the aluminum nitride particles, forming a ceramic substrate with high thermal conductivity and high strength. Subsequent processing and testing include planar grinding and polishing of the sintered aluminum nitride ceramic substrate, followed by metallization. Finally, a comprehensive test is conducted on the density, thermal conductivity, warpage, surface roughness, and dielectric properties of the aluminum nitride ceramic substrate.

[0050] To isolate moisture and prevent abnormal hydrolysis of aluminum nitride powder caused by water vapor, the preparation of raw materials, including high-purity aluminum nitride powder, N-vinylpyrrolidone-itaconic acid copolymer (NVP-IA), and ethanol, also includes preparing a glove box and filling it with inert gas before sending the raw materials into the glove box for storage and retrieval.

[0051] In order to enable the polymer to adhere more evenly and fully to the outer surface of the aluminum nitride powder and to moderately evaporate the solvent to promote the precipitation and film formation of the polymer, the impregnation coating involves adding the aluminum nitride powder to the above solution and performing an ultrasonic dispersion process using an ultrasonic dispersion device to completely wet the aluminum nitride powder with the solution. Afterwards, the ultrasonically dispersed suspension is transferred to a constant temperature magnetic stirrer, sealed with a sealing film, and reacted for 2-4 hours at 50-60°C with continuous stirring.

[0052] To make the obtained aluminum nitride powder more uniform in size and reduce agglomeration, the aluminum nitride powder with polymer film is sent into a vacuum oven for post-drying to obtain finished coated aluminum nitride powder. The process also includes grinding and sieving, grinding with a mortar and mortar and passing through a sieve to obtain a final uniformly coated composite powder, i.e. coated aluminum nitride powder. Example 2:

[0053] This embodiment is prepared based on Embodiment 1. In order to make the aluminum nitride powder more stable during the water-based casting process, further reduce the probability of hydrolysis, and obtain an aluminum nitride ceramic substrate with higher strength and fewer impurities, the aluminum nitride powder with polymer film is sent into a vacuum oven for a post-drying step to obtain the finished product coated with aluminum nitride powder. After that, a secondary coating process is also included, which includes the following steps:

[0054] Q1: Prepare the raw materials for the secondary coating process, including aluminum nitride powder, ethanol, deionized water, ammonia, and tetraethyl orthosilicate. Mix tetraethyl orthosilicate with deionized water and ethanol to obtain an ethanol solution containing tetraethyl orthosilicate. Specifically, the molar ratio of tetraethyl orthosilicate:ethanol:H2O:NH3·H2O≈1:20-40:4-10:0.05-0.1 is estimated. At the same time, mix deionized water and ethanol to obtain a dispersion.

[0055] Q2: Dispersion, ultrasonically disperse the coated aluminum nitride powder in the dispersion liquid, specifically, ultrasonically disperse for 20-30 minutes at a power of 300-500W;

[0056] Q3: Hydrolysis, while stirring at 500-700 rpm, add ammonia dropwise to adjust the pH to 9-10;

[0057] Q4: Polycondensation, slowly add an ethanol solution containing tetraethyl orthosilicate using a constant pressure dropping funnel, with the addition time controlled to be more than 1 hour, and continue stirring at a constant temperature of 35-40°C for 4-6 hours, so that the tetraethyl orthosilicate hydrolyzes and condenses on the surface of the aluminum nitride powder to form a SiO2 sol layer.

[0058] Q5: Centrifugal separation, using a centrifuge at a speed of 8000-10000 rpm for 5 minutes each time, and then drying in a vacuum oven at 80-120℃ for 6-12 hours to obtain secondary coated aluminum nitride powder.

[0059] To prevent moisture in the air from contacting the aluminum nitride powder, the preparation of the secondary coating process materials includes coating aluminum nitride powder, ethanol, deionized water, ammonia, and tetraethyl orthosilicate. Tetraethyl orthosilicate is mixed with deionized water and ethanol to obtain an ethanol solution containing tetraethyl orthosilicate. Deionized water is then mixed with the remaining ethanol to obtain a dispersion. The process also includes preparing a glove box, drying the glove box, filling it with inert gas, and placing the coated aluminum nitride powder into the glove box for use.

[0060] To densify the shaped SiO2 layer and achieve better isolation between aluminum nitride powder and water-based solvents, the process involves centrifugation, washing several times with ethanol to remove impurities, drying at 80-120°C, and then placing the dried powder in a muffle furnace or tube furnace and heating it to 500-600°C at a rate of 2-5°C / min in an air or oxygen atmosphere, and holding it at that temperature for 1-2 hours.

[0061] Effects and Testing:

[0062] To verify the performance of the aluminum nitride ceramic substrate prepared by the water-based casting process described in this invention, a series of comparative tests were conducted.

[0063] 1. Experimental Design:

[0064] Comparative Example 1 (D1): A conventional organic solvent casting process was used. Aluminum nitride powder of the same purity was used, but without any encapsulation treatment, and dispersed in a toluene-isopropanol mixed solvent. The process parameters for subsequent steps (ball milling, casting, debinding, and sintering) were consistent with those of Example 1 of the present invention.

[0065] Comparative Example 2 (D2): A water-based casting process was used, but the aluminum nitride powder was not coated in any way. The aluminum nitride powder was directly dispersed in deionized water, and the remaining steps were the same as in Example 1.

[0066] Example Group (E1): The process of Example 1 (single-layer polymer encapsulation) of the present invention is adopted.

[0067] Example Group (E2): The process of Example 2 of the present invention (polymer + SiO2 double-layer encapsulation) is adopted.

[0068] 2. Test methods and results:

[0069] The following key performance tests were performed on the aluminum nitride ceramic substrates obtained after sintering the above four groups of samples. The results are taken as the average of the five samples, as shown in the table below:

[0070]

[0071] 3. Results Analysis and Conclusions:

[0072] Compared with Comparative Example 1 (traditional organic process): The substrates prepared in Examples 1 (E1) and 2 (E2) of this invention reach or even slightly exceed the levels of traditional organic solvent processes in all key performance indicators (thermal conductivity, strength, density, etc.). This fully demonstrates that the powder encapsulation process of this invention successfully overcomes the hydrolysis problem of aluminum nitride in water, making it possible to completely replace toxic organic solvents with environmentally friendly, low-cost water-based solvents without affecting the performance of the final product.

[0073] Compared with Comparative Example 2 (uncoated water-based process): Group D2, which directly used water-based solvent without coating, suffered severe hydrolysis of aluminum nitride powder, resulting in a comprehensive deterioration of the substrate's various properties after sintering (low density, sharp drop in thermal conductivity, poor strength, rough surface, and severe warping). This proves that the coating process is an indispensable key technical feature for the success of water-based tape casting in this invention.

[0074] Comparison of Example 1 and Example 2: Group E2, which uses a two-stage coating (polymer + SiO2), shows slightly better performance than Group E1, which uses only a single polymer coating, in terms of thermal conductivity, flexural strength, surface roughness, and warpage. This indicates that the two-stage coating process provides superior isolation and protection, further improving the overall performance and consistency of the substrate.

[0075] Overall benefits: While ensuring high performance, this invention completely avoids the use of toxic organic solvents such as toluene and xylene, significantly reducing production costs, eliminating health hazards to operators, and reducing emissions of volatile organic compounds (VOCs), thus having significant environmental and social benefits.

[0076] The above test data clearly confirms that the water-based cast aluminum nitride substrate preparation method provided by this invention effectively solves the core obstacle in water-based aluminum nitride processing through innovative powder encapsulation technology, successfully replacing organic solvents with water. The prepared ceramic substrate has excellent performance, fully meets the application requirements of high-end electronic packaging, and has outstanding practicality and significant progress.

[0077] This invention protects the structure of the product; the model numbers of the components are not protected by this invention, as they are common technology. Any component on the market that can achieve the functions described above can be used as an option. Therefore, the model numbers and other parameters of the components are not described in detail in this invention. The contribution of this invention lies in the scientific combination of the various components.

[0078] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions above are merely illustrative of the principles of the invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents. Any aspects not detailed in the present invention are well-known to those skilled in the art.

Claims

1. A method for preparing an aluminum nitride substrate using a water-based casting process, characterized in that: Includes the following steps: Step 1: Raw material preparation and slurry preparation. High-purity aluminum nitride powder is subjected to a powder coating process to obtain coated aluminum nitride powder. The coated aluminum nitride powder and sintering aid are accurately weighed according to the ratio and dispersed in an aqueous solvent. Primary dispersion is carried out by ball milling or stirring. The powder coating process includes the following steps: S1: Prepare raw materials, selecting high-purity aluminum nitride powder, N-vinylpyrrolidone-itaconic acid copolymer, and ethanol; S2: Solution preparation: Dissolve the N-vinylpyrrolidone-itaconic acid copolymer in ethanol to form a polymer solution; S3: Impregnation coating, aluminum nitride powder is added to the above solution and ultrasonically dispersed using an ultrasonic dispersion device to ensure that the aluminum nitride powder is completely impregnated by the solution; S4: Drying and curing. Solvents are removed by spray drying using a spray dryer, allowing the polymer to form a film on the powder surface and cure, resulting in aluminum nitride powder with a polymer film. S5: The aluminum nitride powder with polymer film is sent into a vacuum oven for a post-drying step to obtain coated aluminum nitride powder. The step of feeding the aluminum nitride powder with a polymer film into a vacuum oven for post-drying to obtain the finished aluminum nitride powder coated with polymer film includes a secondary coating process, which includes the following steps: Q1: Prepare the raw materials for the secondary coating process, including aluminum nitride powder, ethanol, deionized water, ammonia, and tetraethyl orthosilicate. Mix tetraethyl orthosilicate with deionized water and ethanol to obtain an ethanol solution containing tetraethyl orthosilicate. Mix deionized water with the remaining ethanol to obtain a dispersion. Q2: Dispersion, ultrasonically disperse the coated aluminum nitride powder in the dispersion liquid; Q3: Hydrolysis, while stirring, add ammonia dropwise to adjust the pH to alkaline; Q4: Polycondensation, slowly add an ethanol solution containing tetraethyl orthosilicate, and stir continuously at a constant temperature for several hours to allow the tetraethyl orthosilicate to hydrolyze and condense on the surface of the aluminum nitride powder to form a SiO2 sol layer. Q5: Centrifuge, wash several times with ethanol to remove impurities, and then dry at 80-120℃ to obtain secondary coated aluminum nitride powder; Step 2: Slurry mixing and plasticizing. In the fully dispersed slurry, binder and plasticizer are added in sequence, and ball milling is carried out for 12-24 hours. Step 3: Vacuum degassing and aging. Place the well-mixed slurry in a vacuum degassing device to remove air bubbles introduced during stirring and ball milling. Then, let the slurry stand and age for 12-48 hours under constant temperature conditions. Step 4: Casting and forming. Adjust the parameters of the casting machine, pour the aged slurry into the casting machine hopper, and form a continuous, uniformly thick wet film on the uniformly moving carrier film through a scraper or mold. Step 5: Drying. The wet film enters the drying zone along with the carrier film, where the solvent slowly evaporates under controlled temperature and humidity conditions. Step 6: Peeling and cutting the green sheet. After complete drying, a green sheet with a certain strength and flexibility is formed. Peel it off from the carrier film and cut it using a precision punching machine or laser cutting machine to obtain green sheets of a specific size. Step 7: Debinding and Sintering. The green sheet is placed in a sintering furnace and debinding is performed first. Under air or a protective atmosphere, it is heated to 400-600℃ at a precisely controlled heating rate and held for a sufficient time to allow the organic additives in the green sheet to completely decompose and volatilize. Then, sintering is carried out in a high-temperature, inert or reducing gas-filled environment to densify the aluminum nitride particles and form an aluminum nitride ceramic substrate.

2. The method for preparing an aluminum nitride substrate using a water-based casting process according to claim 1, characterized in that: The debinding and sintering process involves placing the green sheet in a sintering furnace and first debinding it. Then, under air or a protective atmosphere, the sheet is heated to 400-600°C at a precisely controlled rate and held for a sufficient time to allow the organic additives within the green sheet to completely decompose and volatilize. Subsequently, sintering is performed in a high-temperature, inert, or reducing gas-filled environment to densify the aluminum nitride particles, forming a ceramic substrate with high thermal conductivity and high strength. Subsequent processing and testing include planar grinding and polishing of the sintered aluminum nitride ceramic substrate, followed by metallization. Finally, a comprehensive test is conducted on the density, thermal conductivity, warpage, surface roughness, and dielectric properties of the aluminum nitride ceramic substrate.

3. The method for preparing an aluminum nitride substrate using a water-based casting process according to claim 1, characterized in that: The preparation of raw materials, including high-purity aluminum nitride powder, N-vinylpyrrolidone-itaconic acid copolymer, and ethanol, also includes preparing a glove box, filling the glove box with inert gas, and sending the raw materials into the glove box for storage and retrieval.

4. The method for preparing an aluminum nitride substrate using a water-based casting process according to claim 1, characterized in that: The impregnation coating process involves adding aluminum nitride powder to the above solution and performing an ultrasonic dispersion process using an ultrasonic dispersion device to completely impregnate the aluminum nitride powder with the solution. Afterward, the ultrasonically dispersed suspension is transferred to a constant temperature magnetic stirrer, sealed with a sealing film, and reacted for 2-4 hours at 50-60°C with continuous stirring.

5. The method for preparing an aluminum nitride substrate using a water-based casting process according to claim 1, characterized in that: The step of feeding the aluminum nitride powder with polymer film into a vacuum oven for post-drying to obtain finished coated aluminum nitride powder includes grinding and sieving, grinding with a mortar and mortar and passing through a sieve to obtain a final uniformly coated composite powder, i.e. coated aluminum nitride powder.

6. The method for preparing an aluminum nitride substrate using a water-based casting process according to claim 1, characterized in that: The preparation of raw materials for the secondary coating process includes coating aluminum nitride powder, ethanol, deionized water, ammonia, and tetraethyl orthosilicate. Tetraethyl orthosilicate is mixed with deionized water and ethanol to obtain an ethanol solution containing tetraethyl orthosilicate. Deionized water is then mixed with the remaining ethanol to obtain a dispersion. The process also includes preparing a glove box, drying the glove box, filling it with inert gas, and placing the coated aluminum nitride powder into the glove box for use.

7. The method for preparing an aluminum nitride substrate using a water-based casting process according to claim 1, characterized in that: The centrifugation process involves washing the powder several times with ethanol to remove impurities, followed by drying at 80-120°C. The dried powder is then placed in a muffle furnace or tube furnace and heated to 500-600°C at a rate of 2-5°C / min in an air or oxygen atmosphere, and held at that temperature for 1-2 hours.

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