High-strength and high-toughness aluminum nitride ceramic and preparation method thereof

Abstract

The invention discloses a high-strength and high-toughness aluminum nitride ceramic and a preparation method thereof, and relates to the technical field of ceramics, a sol-gel method is adopted to coat the surface of aluminum nitride with a stable shell layer to form a core-shell structure, meanwhile, the low lattice mismatch rate of a core-shell interface is utilized to reduce thermal resistance, and toughness and thermal conductivity are both considered; according to the external magnetic field tape casting method, the magnetic dipole moment orientation principle is utilized, an external magnetic field is applied in the tape casting stage, the in-plane mechanical property is improved, and the fracture toughness is improved through the magnetism of aluminum nitride whiskers; a reinforcement is introduced to improve the mechanical property and corrosion resistance of the aluminum nitride ceramic material, multi-granularity powder is compounded, large-particle aluminum nitride powder is used as a sintering and heat-conducting framework material, and high activity provided by submicron particles is utilized to promote sintering, so that the sintering temperature of aluminum nitride can be remarkably reduced, and the performance is greatly improved; and the aluminum nitride substrate expands more application fields on a future packaging circuit.

Description

Technical Field

[0001] This invention relates to the field of ceramic technology, specifically to a high-strength, high-toughness aluminum nitride ceramic and its preparation method. Background Technology

[0002] Since the beginning of the 21st century, every major breakthrough in semiconductor technology has had a profound impact on human society. In the rapid development of electronic packaging and microelectronics technologies, material properties have gradually become a key factor determining technological innovation. As electronic components continue to evolve towards higher power density and miniaturization, packaging substrate materials face unprecedented performance challenges. This has led the industry to place higher demands on the thermal conductivity, high-temperature stability, and long-term reliability of packaging materials. To meet the development needs of modern electronic devices, high-performance ceramic substrate materials must possess excellent heat dissipation capabilities, stable physicochemical properties, and reasonable production costs.

[0003] Currently, mainstream ceramic substrate materials include alumina, beryllium oxide, aluminum nitride, and silicon nitride. Among them, alumina substrates still hold an important position in the market due to their mature preparation process and relatively low production cost. However, even alumina materials with a purity of up to 99.6% have thermal conductivity that is insufficient for the heat dissipation requirements of high-power devices. While beryllium oxide materials possess ideal thermal conductivity and dielectric properties, the highly toxic nature of its raw materials necessitates strict protective measures during production, significantly increasing manufacturing costs and posing safety hazards, thus severely limiting its application.

[0004] In comparison, aluminum nitride ceramics exhibit significant advantages: excellent thermal conductivity, low dielectric loss, a coefficient of thermal expansion matching silicon, non-toxic and environmentally friendly properties, and good mechanical strength, making them an ideal choice for next-generation semiconductor packaging materials. However, as a typical covalent compound, aluminum nitride faces significant challenges in its sintering densification process. Traditional solid-state sintering requires high-temperature environments, resulting in high production costs. With the development of liquid-phase sintering technology, the addition of rare earth oxides or alkaline earth metal compounds has successfully lowered the sintering temperature, significantly promoting the densification process. Aluminum nitride substrates prepared using this process exhibit excellent thermal conductivity and have been widely used in high-power power modules, hybrid integrated circuits, and other fields, particularly excelling in power electronic systems such as automotive lighting, smart grids, and high-power ultraviolet LEDs.

[0005] However, existing aluminum nitride ceramics still have significant shortcomings. The high-temperature sintering process used to pursue higher thermal conductivity can easily lead to abnormal grain growth. At the same time, excessive addition of sintering aids can introduce lattice oxygen defects, which significantly reduces the mechanical properties of the material and its bending strength is low. This poor mechanical property severely restricts the application of aluminum nitride substrates in high-reliability power electronic modules. Under long-term thermal cycling and power impact conditions, substrate deformation or even fracture may occur.

[0006] To address the aforementioned issues, this invention provides a high-strength, high-toughness aluminum nitride ceramic and its preparation method, which can be widely applied in fields such as hybrid integrated circuit power electronic power modules, microwave and millimeter-wave power devices, and high-power power supply modules. In particular, ceramic substrates prepared using its high thermal conductivity are widely used in power electronics fields such as locomotives, electric vehicles, wind power generation, and smart grids. Summary of the Invention

[0007] The purpose of this invention is to provide a high-strength, high-toughness aluminum nitride ceramic and its preparation method, so as to solve the problems raised in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing high-strength and high-toughness aluminum nitride ceramics includes the following steps:

[0010] S1: Mix the reinforcing agent, dispersant, and mixed solvent, and then ultrasonically treat the mixture to obtain a reinforcing slurry;

[0011] S2: Aluminum nitride powder and sintering aid are mixed to obtain inorganic powder; polyvinyl butyral, plasticizer, dispersant and mixed solvent are added to the inorganic powder, and the mixture is fully ball-milled and mixed. Reinforcing slurry is added and ball-milled to obtain casting slurry;

[0012] S3: Vacuum degassing and sieving of the cast slurry; casting and cutting to obtain raw ceramic tiles;

[0013] S4: The cut raw ceramic pieces are sealed with a film and subjected to warm isostatic pressing to obtain the shaped blank;

[0014] S5: The obtained molded blank is subjected to debinding treatment in an air atmosphere to obtain a debinding sheet;

[0015] S6: The obtained sheet is placed in a vacuum graphite furnace and sintered under a flowing nitrogen atmosphere to obtain a composite ceramic substrate. The substrate is then ground on both sides to obtain high-strength and high-toughness aluminum nitride ceramic.

[0016] Furthermore, in step S1, the reinforcing body is one of aluminum nitride whiskers, zirconium oxide powder, and silicon nitride powder; the aluminum nitride whiskers are long columnar single crystals with a diameter of 0.5-1.5 μm and an aspect ratio of 1:10, 1:30, or 1:100.

[0017] Furthermore, in step S1, when the reinforcing body is aluminum nitride whiskers, the aluminum nitride whiskers are magnetized, and the steps are as follows: the aluminum nitride whiskers are immersed in an ethanol suspension containing iron nitride nanoparticles, dried after immersion treatment, and the immersion and drying are repeated 4-5 times. The temperature is raised to 200-300℃ for heat treatment for 1-2 hours to obtain magnetized aluminum nitride whiskers.

[0018] Furthermore, in the preparation of magnetized aluminum nitride whiskers, the weight ratio of aluminum nitride whiskers to an ethanol suspension containing iron nitride nanoparticles is 16:100; the solid content of iron nitride nanoparticles in the ethanol suspension containing iron nitride nanoparticles is 1-5%.

[0019] Furthermore, the aluminum nitride powder is a mixture of aluminum nitride raw powder and aluminum nitride submicron powder in a mass ratio of (40-98):(0-50); the aluminum nitride raw powder has a particle size of 1.2-1.5 μm, and the aluminum nitride submicron powder has a particle size of 0.2-0.6 μm;

[0020] Furthermore, in step S1, the mass ratio of dispersant to reinforcement is (0.5-1.5):100; the solid content of reinforcement in the reinforcement slurry is 40-60%;

[0021] Furthermore, in step S2, the mass ratio of inorganic powder, polyvinyl butyral, plasticizer, dispersant, and mixed solvent is (50-60):(5-10):(1-3):(1-3):(20-40);

[0022] Furthermore, in step S2, the mixed solvent is anhydrous ethanol, isopropanol, and toluene mixed in a volume ratio of (1-3):1:1;

[0023] Furthermore, the sintering aid is one or a combination of several of yttrium oxide, lithium carbonate, calcium oxide, calcium fluoride, yttrium fluoride, magnesium oxide, zirconium silicide, and lithium oxide;

[0024] Furthermore, the plasticizer is one of dioctyl phthalate and dibutyl phthalate;

[0025] Furthermore, the aluminum nitride powder is modified, and the preparation process is as follows:

[0026] a. Mix the metal nitrate and the aqueous ethanol solution, adjust the pH to 3-5.5 with nitric acid, heat to 60-80℃ and stir for 30-60 min to obtain the precursor solution;

[0027] b. Add aluminum nitride powder and precursor solution to a reaction vessel, add citric acid and γ-aminopropyltriethoxysilane, ultrasonically disperse for 30-60 min, stir at a constant temperature of 60-80℃ for 2-4 h, calcine and convert, cool, crush, grind and filter to obtain modified aluminum nitride powder.

[0028] Furthermore, the metal nitrate is one or a combination of Y(NO3)3 and ZrO(NO3)2;

[0029] Furthermore, the mass ratio of modified aluminum nitride powder, reinforcing agent, and sintering aid is (90-98):(0-10):(0-6);

[0030] Furthermore, the calcination conversion process is as follows: under a nitrogen atmosphere, the temperature is raised to 600-800℃ and held for 2-4 hours at a heating rate of 1-5℃ / min;

[0031] Furthermore, by weight, the raw material composition of the precursor solution is: 10-25 parts Y(NO3)3, 5-10 parts ZrO(NO3)2, and 5-25 parts aqueous ethanol solution;

[0032] Furthermore, by weight, the raw material composition of the modified aluminum nitride powder is: 30-50 parts aluminum nitride powder, 40-50 parts precursor solution, 0.3-2.0 parts citric acid, and 0.3-2.0 parts γ-aminopropyltriethoxysilane.

[0033] Furthermore, the ethanol-water solution is prepared by mixing ethanol and water in a mass ratio of 7:3;

[0034] Furthermore, the ethanol-water solution is prepared by mixing ethanol and water in a mass ratio of 1:1;

[0035] Furthermore, in step S2, the process conditions for ball milling are: rotation speed of 120-600 rpm and time of 12-24 h;

[0036] Furthermore, in step S3, the vacuum degassing process conditions are: revolution speed of 80-120 rpm, vacuum degree of -70 kPa to 90 kPa, and time of 0.5-2 h;

[0037] Furthermore, in step S3, the casting process is as follows:

[0038] 1) At the material box of the casting machine, NdFeB permanent magnets are used to construct a DC magnetic field of more than 0.5T, and the magnetic field uniformity is controlled to be 80-95%;

[0039] 2) Pour the casting slurry into the material box and keep it warm in the magnetic field for 10-60 minutes;

[0040] 3) Casting and shaping process, cutting to obtain raw ceramic tiles;

[0041] Furthermore, the casting process is as follows: the casting thickness is controlled to be 0.05-1mm, the temperature of the first zone of the casting machine is 30-40℃, and the temperature of the second zone is 40-70℃;

[0042] Furthermore, in step S4, the isostatic pressing conditions are: temperature 70-80℃, time 10-20min, and pressure 20-40Mpa.

[0043] Furthermore, in step S5, the process conditions for the glue removal treatment are: heating to 500℃-600℃ for 48-72 hours;

[0044] Furthermore, in step S6, the sintering process conditions are: heating to 1500-1850℃ for 2-6 hours.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] This invention provides a method for preparing high-strength and high-toughness aluminum nitride ceramics, which improves the fracture toughness and bending strength of aluminum nitride materials, making them more stable and reliable when used as electronic packaging substrates.

[0047] A sol-gel uniform coating mechanism was adopted, using yttrium nitrate (Y(NO3)3) as a precursor, which was dissolved in an ethanol-water mixed solvent to generate a corresponding sol through hydrolysis. The size of Y(OH)3 / Zr(OH)4 nanoparticles in the sol was controlled to achieve uniform dispersion at the molecular level. After hydroxylation of the surface of aluminum nitride powder, it was mixed with the Y(OH)3 / Zr(OH)4 sol. Through hydrogen bonding and electrostatic adsorption, the sol particles were uniformly adsorbed on the surface of aluminum nitride to form a "core-shell" structure.

[0048] An external magnetic field is used to impregnate and magnetize aluminum nitride whiskers. Utilizing the principle of "magnetic dipole moment orientation," an external magnetic field is applied during the casting stage to align the whiskers along the direction of force, thereby improving in-plane mechanical properties. Due to the Fe3N coating and trace amounts of Fe and other impurities, the aluminum nitride whiskers are magnetic. By utilizing the magnetism of the aluminum nitride whiskers, a magnetic dipole moment is generated in the magnetic field, resulting in oriented alignment of the whiskers. The whiskers are oriented along the in-plane direction, extending the crack propagation path. The "pull-out work" of oriented whiskers for cracks is improved compared to random distribution, enhancing the "bridging-pull-out" effect and improving fracture toughness.

[0049] The method in the existing example CN105777169B involves high-temperature sintering. However, at high temperatures, some whiskers transform from a whisker state to a crystalline state, leading to toughening failure and a lack of performance improvement. The composite material prepared using the low-temperature sintering methods in Examples 1 and 2 employs a multi-particle-size powder blending approach. Large-particle aluminum nitride powder serves as the sintering and thermal conductivity framework material, while the high activity provided by submicron particles promotes sintering. This significantly reduces the sintering temperature of aluminum nitride and prevents some whiskers from transforming into a crystalline state at high temperatures. This mixing method effectively avoids the agglomeration of the reinforcement, resulting in a more uniform distribution of the reinforcement in the slurry and a substantial improvement in performance. This allows aluminum nitride substrates to expand into more application areas in future packaging circuits.

[0050] By leveraging the high fracture toughness, strength, modulus, and corrosion resistance of the reinforcement, the mechanical properties and corrosion resistance of aluminum nitride ceramic materials are improved. This prevents warping, deformation, and even cracking of the substrate during prolonged exposure to thermal shock and power cycling. This enhances the reliability and stability of the aluminum nitride substrate, and the method is easily scalable for industrial production.

[0051] The thermal conductivity, mechanical properties, and dielectric constant of aluminum nitride ceramic sheets are significantly improved through process optimizations such as sol-gel uniform coating mechanism, external magnetic field casting method, multi-particle size powder compounding, and addition of reinforcing agents. It is also easy to realize industrial production and can be widely used in the field of aluminum nitride ceramics. Specific implementation methods

[0052] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] Example 1: A method for preparing aluminum nitride ceramics, comprising the following steps:

[0054] S1: Mix aluminum nitride raw powder and sintering aid to obtain inorganic powder; add polyvinyl butyral, dibutyl phthalate, dispersant and mixed solvent to the inorganic powder, ball mill and mix thoroughly, add reinforcing slurry, ball mill and mix at 300 rpm for 18 h to obtain casting slurry;

[0055] S3: Degas the cast slurry at a revolution speed of 80 rpm and a vacuum degree of -90 kPa for 1 hour, then sieve it; cast it into a film and cut it to obtain raw ceramic tiles;

[0056] S4: The cut green ceramic pieces are sealed with a film. The vacuum time is 2 minutes, the heating temperature is 150℃, and the heating time is 1 minute. After sealing, they are placed in an isostatic pressing chamber and heated to 70℃ and pressure is 30 MPa for 20 minutes to obtain the shaped blank.

[0057] S5: Heat the obtained molded blank to 550℃ in air and keep it at that temperature for 56 hours to remove the glue and obtain a glue removal sheet;

[0058] S6: The obtained sheet was placed in a graphite crucible and sintered at 1780°C for 4 hours under a flowing nitrogen atmosphere to obtain an aluminum nitride ceramic.

[0059] In step S2, the mass ratio of inorganic powder, polyvinyl butyral, plasticizer, dispersant, and mixed solvent is 60:7.2:1.2:1.8:29.8; the mass ratio of aluminum nitride raw powder and sintering aid in the inorganic powder is 96:4.

[0060] In step S2, the mixed solvent is anhydrous ethanol, isopropanol, and toluene mixed in a volume ratio of 2:1:1;

[0061] The aluminum nitride powder has a particle size of 1.2 μm; the sintering aid is yttrium oxide;

[0062] In step S3, the casting process is as follows: the casting thickness is controlled to be 0.25 mm, the temperature of the casting machine is 40°C in zone one and 70°C in zone two.

[0063] Example 2: A method for preparing high-strength and high-toughness aluminum nitride ceramics, the steps of which are as follows:

[0064] S1: Mix the reinforcing agent, dispersant and mixed solvent, and ultrasonically treat with an ultrasonic frequency of 20kHz and an ultrasonic power of 2kW for 1h to obtain the reinforcing slurry;

[0065] S2: Aluminum nitride powder and sintering aid are mixed to obtain inorganic powder; polyvinyl butyral, dibutyl phthalate, dispersant and mixed solvent are added to the inorganic powder, and the mixture is ball-milled for 17 hours at a speed of 300 rpm. Then, the reinforcing slurry is added and ball-milled at 120 rpm for 1 hour to obtain the casting slurry.

[0066] S3: The cast slurry is degassed under vacuum at 80 rpm and -90 kPa for 1 hour, then sieved; cast in a magnetic field and cut to obtain raw ceramic tiles;

[0067] S4: The cut green ceramic pieces are sealed with a film. The vacuum time is 2 minutes, the heating temperature is 150℃, and the heating time is 1 minute. After sealing, they are placed in an isostatic pressing chamber and heated to 70℃ and pressure is 30 MPa for 20 minutes to obtain the shaped blank.

[0068] S5: Heat the obtained molded blank to 550℃ in air and keep it at that temperature for 56 hours to remove the glue and obtain a glue removal sheet;

[0069] S6: The obtained sheet is placed in a vacuum graphite furnace and sintered at 1650℃ for 5 hours under a flowing nitrogen atmosphere to obtain a composite ceramic substrate. The substrate is then ground on both sides to obtain high-strength and high-toughness aluminum nitride ceramic.

[0070] In step S1, the reinforcing material is aluminum nitride whiskers. The aluminum nitride whiskers are magnetized as follows: the aluminum nitride whiskers are immersed in an ethanol suspension containing iron nitride nanoparticles, dried after immersion, and the immersion and drying are repeated 5 times. The mixture is then heat-treated at 350°C for 2 hours to obtain magnetized aluminum nitride whiskers. In the preparation of magnetized aluminum nitride whiskers, the weight ratio of aluminum nitride whiskers to the ethanol suspension containing iron nitride nanoparticles is 16:100; the solid content of the ethanol suspension containing iron nitride nanoparticles is 2%.

[0071] The aluminum nitride whiskers are long columnar single crystals with a diameter of 1.0 μm and an aspect ratio of 1:10;

[0072] In step S1, the mass ratio of dispersant to reinforcement is 1.5:100; the solid content of reinforcement in the reinforcement slurry is 60%.

[0073] In step S2, the mass ratio of inorganic powder, polyvinyl butyral, plasticizer, dispersant, and mixed solvent is 60:7.5:1.5:1.5:29.5.

[0074] In step S2, the mixed solvent is anhydrous ethanol, isopropanol, and toluene mixed in a volume ratio of 2:1:1;

[0075] The aluminum nitride powder is a mixture of aluminum nitride raw powder and aluminum nitride submicron powder in a mass ratio of 45:45; the aluminum nitride raw powder has a particle size of 1.2 μm, and the aluminum nitride submicron powder has a particle size of 0.5 μm.

[0076] The aluminum nitride powder is modified, and the preparation process of the modified aluminum nitride powder is as follows:

[0077] a. Mix the ethanol-water solution of Y(NO3)3, adjust the pH to 4.5 with nitric acid, heat to 60℃ and stir for 30 min to obtain the precursor solution;

[0078] b. Add aluminum nitride powder and precursor solution to a reaction vessel, add citric acid and γ-aminopropyltriethoxysilane, ultrasonically disperse at a frequency of 24kHz and a power of 500W for 30min, stir at a constant temperature of 60℃ for 2h, heat to 600℃ and hold for 2h under a nitrogen atmosphere at a heating rate of 5℃ / min, cool, pulverize, grind and filter to obtain modified aluminum nitride powder;

[0079] The precursor solution, by weight, comprises 24.5 parts Y(NO3)3 and 44.5 parts an aqueous ethanol solution; the aqueous ethanol solution is prepared by mixing ethanol and water in a mass ratio of 7:3; the modified aluminum nitride powder comprises 30 parts aluminum nitride powder, 69 parts precursor solution, 0.5 parts citric acid, and 0.5 parts γ-aminopropyltriethoxysilane.

[0080] In step S2, the mass ratio of the modified aluminum nitride powder, the reinforcing agent, and the sintering aid is 93:3:4;

[0081] The sintering aid is a mixture of calcium oxide and lithium oxide in a mass ratio of 2:2.

[0082] In step S3, the casting process is as follows:

[0083] 1) At the material box of the casting machine, a 0.5T DC magnetic field is constructed using NdFeB permanent magnets, with a magnetic field uniformity of 90%;

[0084] 2) Pour the casting slurry into the material box and keep it warm in the magnetic field for 30 minutes;

[0085] 3) The thickness of the cast film is controlled at 0.25mm. The temperature of the casting machine is 40℃ in zone one and 70℃ in zone two for casting.

[0086] Example 3: A method for preparing high-strength and high-toughness aluminum nitride ceramics, the steps of which are as follows:

[0087] S1: Mix the reinforcing agent, dispersant and mixed solvent, and ultrasonically treat with an ultrasonic frequency of 30kHz and an ultrasonic power of 2kW for 1h to obtain the reinforcing slurry;

[0088] S2: Aluminum nitride powder and sintering aid are mixed to obtain inorganic powder; polyvinyl butyral, dibutyl phthalate, dispersant and mixed solvent are added to the inorganic powder, and the mixture is ball-milled for 17 hours at a speed of 300 rpm. Then, the reinforcing slurry is added and ball-milled at 120 rpm for 1 hour to obtain the casting slurry.

[0089] S3: Degas the cast slurry at a revolution speed of 80 rpm and a vacuum degree of -90 kPa for 1 hour, then sieve it; cast it into a film and cut it to obtain raw ceramic tiles;

[0090] S4: The cut green ceramic pieces are sealed with a film. The vacuum time is 2 minutes, the heating temperature is 150℃, and the heating time is 1 minute. After sealing, they are placed in an isostatic pressing chamber and heated to 70℃ and pressure is 30 MPa for 20 minutes to obtain the shaped blank.

[0091] S5: The obtained molded blank is heated to 550℃ and held for 56 hours in an air and nitrogen debinding furnace with a volume ratio of 1:1 to obtain a debinding sheet.

[0092] S6: The obtained sheet is placed in an atmospheric pressure sintering furnace and heated to 1700℃ and held for 5 hours under a flowing nitrogen atmosphere to obtain a composite ceramic substrate. The substrate is then ground on both sides to obtain a high-strength and high-toughness aluminum nitride ceramic.

[0093] In step S1, the reinforcement is aluminum nitride whiskers; the aluminum nitride whiskers are long columnar single crystals with a diameter of 1.0 μm and an aspect ratio of 1:30;

[0094] In step S1, the mass ratio of dispersant to reinforcement is 1.5:100; the solid content of reinforcement in the reinforcement slurry is 60%.

[0095] In step S2, the mass ratio of inorganic powder, polyvinyl butyral, plasticizer, dispersant, and mixed solvent is 60:7.5:1.5:1.5:29.5.

[0096] In step S2, the mixed solvent is anhydrous ethanol, isopropanol, and toluene mixed in a volume ratio of 2:1:1;

[0097] The aluminum nitride powder is a mixture of aluminum nitride raw powder and aluminum nitride submicron powder in a mass ratio of 45:45; the aluminum nitride raw powder has a particle size of 1.2 μm, and the aluminum nitride submicron powder has a particle size of 0.5 μm.

[0098] The aluminum nitride powder is modified, and the preparation process of the modified aluminum nitride powder is as follows:

[0099] a. Mix Y(NO3)3 and an aqueous ethanol solution, adjust the pH to 4.5 with nitric acid, heat to 60℃ and stir for 30 min to obtain the precursor solution;

[0100] b. Add aluminum nitride powder and precursor solution to a reaction vessel, add citric acid and γ-aminopropyltriethoxysilane, ultrasonically disperse at a frequency of 24kHz and a power of 500W for 30min, stir at a constant temperature of 60℃ for 2h, heat to 600℃ and hold for 2h under a nitrogen atmosphere at a heating rate of 5℃ / min, cool, pulverize, grind and filter to obtain modified aluminum nitride powder;

[0101] The precursor solution, by weight, comprises 24.5 parts Y(NO3)3 and 44.5 parts an aqueous ethanol solution; the aqueous ethanol solution is prepared by mixing ethanol and water in a mass ratio of 7:3; the modified aluminum nitride powder comprises 30 parts aluminum nitride powder, 69 parts precursor solution, 0.5 parts citric acid, and 0.5 parts γ-aminopropyltriethoxysilane.

[0102] In step S2, the mass ratio of the modified aluminum nitride powder, the reinforcing agent, and the sintering aid is 94:3:3;

[0103] The sintering aid is a mixture of calcium fluoride and lithium oxide in a mass ratio of 2:1.

[0104] In step S3, the casting process is as follows:

[0105] The thickness of the cast film is controlled at 0.25mm. The temperature of the casting machine is 40℃ in zone one and 70℃ in zone two for casting.

[0106] Example 4: A method for preparing high-strength and high-toughness aluminum nitride ceramics, the steps of which are as follows:

[0107] S1: Mix the reinforcing agent, dispersant and mixed solvent, and ultrasonically treat with an ultrasonic frequency of 30kHz and an ultrasonic power of 2kW for 1h to obtain the reinforcing slurry;

[0108] S2: Add polyvinyl butyral, dibutyl phthalate, dispersant and mixed solvent to inorganic powder, ball mill and mix thoroughly, add reinforcing slurry, ball mill and mix at 300 rpm for 18 h to obtain cast slurry;

[0109] S3: Degas the cast slurry at a revolution speed of 80 rpm and a vacuum degree of -90 kPa for 1 hour, then sieve it; cast it into a film and cut it to obtain raw ceramic tiles;

[0110] S4: The cut green ceramic pieces are sealed with a film. The vacuum time is 2 minutes, the heating temperature is 150℃, and the heating time is 1 minute. After sealing, they are placed in an isostatic pressing chamber and heated to 70℃ and pressure is 30 MPa for 20 minutes to obtain the shaped blank.

[0111] S5: Transfer the obtained molded blank to a debinding furnace with a volume ratio of 1:1 of air and nitrogen mixed atmosphere, heat it to 550℃ and hold it for 56 hours to debind and obtain a debinding sheet;

[0112] S6: Place the obtained coated graphite crucible with aluminum nitride, boron nitride and aluminum oxide in a mass ratio of 1:1:1 as the embedded powder system, and then place it in a gas pressure sintering furnace at 1800℃ for 4 hours under a nitrogen atmosphere of 1.5 MPa to obtain a composite ceramic substrate. Grind both sides to obtain high-strength and high-toughness aluminum nitride ceramic.

[0113] In step S1, the mass ratio of dispersant to reinforcement is 1.5:100; the solid content of reinforcement in the reinforcement slurry is 60%; the reinforcement is zirconia powder.

[0114] In step S2, the mass ratio of inorganic powder, polyvinyl butyral, plasticizer, dispersant, and mixed solvent is 60:7:1.5:2:29.5.

[0115] In step S2, the mixed solvent is anhydrous ethanol, isopropanol, and toluene mixed in a volume ratio of 2:1:1;

[0116] In step S2, the inorganic powder is a modified aluminum nitride powder and a reinforcing agent compounded at a mass ratio of 98:2; the aluminum nitride powder is raw aluminum nitride powder; the particle size of the raw aluminum nitride powder is 1.2 μm.

[0117] The preparation process of the modified aluminum nitride powder is as follows:

[0118] a. In a constant temperature stirred tank, ZrO(NO3)2, Y(NO3)3 and ethanol aqueous solution are mixed, the pH is adjusted to 3, and the mixture is stirred at 60℃ for 30 min to obtain the precursor solution.

[0119] b. Add aluminum nitride powder to an ultrasonic reactor, then add precursor solution, citric acid, and γ-aminopropyltriethoxysilane. Disperse ultrasonically at 500W power and 24kHz frequency for 30min, stir at 60℃ for 2h, and hold at 600℃ for 2h under nitrogen atmosphere at a heating rate of 5℃ / min. Cool, pulverize, grind, and filter to obtain modified aluminum nitride powder.

[0120] By weight, the precursor solution comprises: 21.75 parts Y(NO3)3, 9 parts ZrO(NO3)2, and 39.4 parts a mixed solution of ethanol and water; the ethanol-water solution is prepared by mixing ethanol and water in a mass ratio of 1:1; the modified aluminum nitride powder comprises: 29.15 parts aluminum nitride powder, 70.15 parts precursor solution, 0.35 parts citric acid, and 0.35 parts γ-aminopropyltriethoxysilane.

[0121] In step S3, the casting process is as follows: the casting thickness is controlled to be 0.25 mm, the temperature of the casting machine is 40°C in zone one and 70°C in zone two.

[0122] Example 5: A method for preparing high-strength and high-toughness aluminum nitride ceramics, the steps of which are as follows:

[0123] S1: Mix the reinforcing agent, dispersant, and mixed solvent, and sonicate at an ultrasonic frequency of 30kHz and an ultrasonic power of 1.5kW for 2 hours to obtain the reinforcing slurry;

[0124] S2: Mix aluminum nitride powder and sintering aid to obtain inorganic powder; add polyvinyl butyral, dibutyl phthalate, dispersant and mixed solvent to the inorganic powder, ball mill and mix thoroughly, add reinforcing slurry, ball mill and mix at 300 rpm for 18 h to obtain casting slurry;

[0125] S3: Degas the cast slurry at a revolution speed of 80 rpm and a vacuum degree of -90 kPa for 1 hour, then sieve it; cast it into a film and cut it to obtain raw ceramic tiles;

[0126] S4: The cut green ceramic pieces are sealed with a film. The vacuum time is 2 minutes, the heating temperature is 150℃, and the heating time is 1 minute. After sealing, they are placed in an isostatic pressing chamber and heated to 70℃ and pressure is 30 MPa for 20 minutes to obtain the shaped blank.

[0127] S5: Heat the obtained molded blank to 550℃ in air and keep it at that temperature for 56 hours to remove the glue and obtain a glue removal sheet;

[0128] S6: The obtained sheet is placed in a pneumatic sintering furnace and sintered at 1800℃ under a nitrogen atmosphere at 1.5MPa for 5 hours to obtain a composite ceramic substrate. The substrate is then ground on both sides to obtain a high-strength and high-toughness aluminum nitride ceramic.

[0129] In step S1, the reinforcing agent is a mixture of silicon nitride powder, magnesium oxide, and zirconium silicide in a mass ratio of 5.5:0.15:0.35; the silicon nitride powder has a particle size of 0.5 μm.

[0130] In step S1, the mass ratio of dispersant to reinforcement is 1.5:100; the solid content of reinforcement in the reinforcement slurry is 60%.

[0131] In step S2, the mass ratio of inorganic powder, polyvinyl butyral, plasticizer, dispersant, and mixed solvent is 60:7:1.5:2:29.5.

[0132] In step S2, the mixed solvent is anhydrous ethanol, isopropanol, and toluene mixed in a volume ratio of 2:1:1;

[0133] In step S2, the mass ratio of the aluminum nitride powder, the reinforcing body, and the sintering aid is 90:6:4; the sintering aid is yttrium oxide.

[0134] The aluminum nitride powder is raw aluminum nitride powder; the particle size of the raw aluminum nitride powder is 1.2 μm;

[0135] In step S3, the casting process is as follows: the casting thickness is controlled to be 0.25 mm, the temperature of the casting machine is 40°C in zone one and 70°C in zone two.

[0136] Comparative Example 1: Using Example 1 as the control group, the preparation of the inorganic powder was different, but other processes were normal: The preparation of the inorganic powder included the following steps:

[0137] a. Mix Y(NO3)3 and an aqueous ethanol solution, adjust the pH to 4.5 with nitric acid, heat to 60℃ and stir for 30 min to obtain the precursor solution;

[0138] b. Add aluminum nitride powder and precursor solution to a reaction vessel, add citric acid and γ-aminopropyltriethoxysilane, ultrasonically disperse at a frequency of 24kHz and a power of 500W for 30min, stir at a constant temperature of 60℃ for 2h, heat to 600℃ and hold for 2h under a nitrogen atmosphere at a heating rate of 5℃ / min, cool, pulverize, grind and filter to obtain modified aluminum nitride powder;

[0139] The aluminum nitride powder is aluminum nitride raw powder; the aluminum nitride raw powder has a particle size of 1.2 μm, and the aluminum nitride submicron powder has a particle size of 0.5 μm;

[0140] The precursor solution, by weight, comprises 24.5 parts Y(NO3)3 and 44.5 parts aqueous ethanol solution; the aqueous ethanol solution is prepared by mixing ethanol and water in a mass ratio of 7:3; the modified aluminum nitride powder comprises 30 parts aluminum nitride powder, 69 parts precursor solution, 0.5 parts citric acid, and 0.5 parts γ-aminopropyltriethoxysilane.

[0141] Comparative Example 2: Using Example 2 as the control group, the casting process was not carried out in a magnetic field. The casting thickness was controlled at 0.25 mm, the temperature of the casting machine was 40°C in Zone 1 and 70°C in Zone 2, and other processes were normal.

[0142] Comparative Example 3: Using Example 4 as the control group, the addition method of zirconium oxide and yttrium oxide was adjusted. The inorganic powder was aluminum nitride powder, the reinforcing zirconium oxide and the sintering aid were compounded in a mass ratio of 94:2:4. The sintering aid was yttrium oxide. Other processes were normal.

[0143] Source of raw materials used (for illustrative purposes only):

[0144] The raw materials used in this technical solution are all commercially available products: aluminum nitride whiskers (24304-00-5, 99.9%, diameter 1.0μm): Nangong Fenghui Nanotechnology Co., Ltd.; zirconium oxide powder (1314-23-4, 99.9%): Shanghai Yingcheng New Materials Co., Ltd.; silicon nitride powder (12033-89-5, 99%): Hebei Gaofu Silicon Nitride Materials Co., Ltd.; yttrium oxide (1314-36-9, 99%). Products sold by Jining Maikerui Rare Earth Co., Ltd. under product number mkr12; Calcium oxide (1305-78-8, 98%) sold by Nanjing Chemical Reagent Co., Ltd. under product number C0050570223; Lithium oxide (12057-24-8, 99%) sold by Tianmen Hengchang Chemical Co., Ltd. under product number HC0502; Polyvinyl butyral (63148-65-2, 99%) sold by Hubei Xinrunde Chemical Co., Ltd. Dibutyl phthalate (84-74-2, 99.5%): Shandong Yukang Chemical Co., Ltd.; AKM-0531 dispersant: Shanghai Jiangze New Material Co., Ltd., selling the product under model AKM-0531; Iron nitride (37245-77-5, 50nm): Hebei Lifu Optoelectronic Technology Co., Ltd.; NdFeB permanent magnet (grade N52): U-POLEMAG; Aluminum nitride powder (24304-00-5, 99.9%) % (D50 = 1.2 μm): Xiamen Juci Technology Co., Ltd.; γ-aminopropyltriethoxysilane (919-30-2, 98%): Hubei Xinkang Pharmaceutical Chemical Co., Ltd.; Y(NO3)3 (13494-98-9, 99.9%): Shandong Desheng New Materials Co., Ltd.; ZrO(NO3)2 (13826-66-9): Zibo Rongruida Powder Materials Factory; Anhydrous ethanol, isopropanol, toluene, citric acid, analytical grade, commercially available.

[0145] Performance testing: The aluminum nitride ceramics prepared in the examples and comparative examples were tested:

[0146] (1) Thermal conductivity test: A laser thermal conductivity meter was used to process aluminum nitride ceramic samples into circular pieces with a diameter of 10 mm and a thickness of 2 mm. A graphite layer was sprayed on the surface to enhance the absorption of infrared signals. The test was carried out in the range of 25 to 300 °C with high-purity nitrogen (flow rate 30 mL / min) as the protective atmosphere. Data were collected after equilibration at each temperature point for 5 min, and the thermal conductivity was calculated.

[0147] (2) Bending strength test (three-point bending method): A universal testing machine was used, referring to the standard GB / T 6569-2006. The sample was cut into strips of 3mm×4mm×36mm with a span of 30mm. The loading rate was 0.5mm / min until fracture. At least 5 samples were tested in each group, and the average value was taken to calculate the bending strength.

[0148] (3) Fracture toughness test: The sample was processed into a strip of 2mm×4mm×20mm. A notch of 0.2mm width and 2mm depth was cut at the center of the length direction (diamond wire cutting). Three-point bending load was applied with a span of 16mm and a speed of 0.05mm / min. The fracture toughness was calculated.

[0149] (4) Bulk density test (Archimedes displacement method): An electronic balance (accuracy 0.1 mg) and a density measuring kit were used. After drying, the sample was weighed (m1), immersed in deionized water and boiled to remove air bubbles. The wet weight was (m2), the suspended weight was (m3), and the density was calculated.

[0150] (5) Dielectric performance test: The sample was made into a disc with a diameter of 50 mm and a thickness of 1 mm. Gold electrodes were sputtered on both sides of the sample. The dielectric constant (Dk) and dielectric loss (Df) were measured by coaxial waveguide method under the conditions of 10 GHz frequency, 25 ℃ temperature and 50% RH humidity. The average value of three measurements was taken.

[0151] (6) Volume resistivity test: A Keithley 6517B high resistance meter was used with a DC voltage of 500V. The electrode configuration was the same as that for dielectric test. The volume resistivity was calculated.

[0152] (7) Breakdown voltage test: Refer to GB / T 1408.1-2016, with a sample thickness of 0.5 mm and a copper electrode diameter of 25 mm, increase the voltage at a rate of 1 kV / s until breakdown, and calculate the breakdown voltage.

[0153] The test results are as follows:

[0154] Table 1

[0155]

[0156] Table 2

[0157]

[0158] The analysis results are as follows:

[0159] Comparing Examples 2 and 3 with Example 1, it can be seen that the present invention utilizes the advantages of aluminum nitride whiskers—high aspect ratio, complete structure, few defects, high strength and modulus—to prepare a composite ceramic substrate. Applying an external magnetic field during the casting stage causes the whiskers to align along the direction of force, improving in-plane mechanical properties. This directional alignment helps reduce inter-whisker porosity and improve thermal conductivity. The use of a low-temperature system ensures that the aluminum nitride whiskers maintain their whisker state. The substrate prepared in Example 2 has a thermal conductivity of 180 W / (m·K), a bending strength of 400 MPa, and a fracture toughness of 4.5 MPa·m1 / 2. The substrate prepared in Example 3 has a thermal conductivity of 190 W / (m·K), a bending strength of 430 MPa, and a fracture toughness of 5.5 MPa·m1 / 2, significantly improving the toughness compared to conventional ceramics. Higher fracture toughness implies higher reliability when used in electronic packaging substrates.

[0160] Comparing Example 4 with Example 1, it can be seen that the present invention utilizes zirconia for reinforcement. Zirconia and yttrium oxide shells are coated on the surface of aluminum nitride using the sol-gel method to form a composite powder zirconia reinforcement body with an "aluminum nitride core-zirconia shell" and a liquid phase encapsulation of the "aluminum nitride core-yttrium oxide shell". Local phase transformation toughening is achieved through the nanoscale zirconia shell layer. The low lattice mismatch rate at the core-shell interface reduces thermal resistance, balancing toughness and thermal conductivity. Using gas pressure sintering and powder embedding processes, the prepared substrate has a thermal conductivity of over 160 W / (m·K), a fracture toughness of over 4 MPa·m1 / 2, and a bending strength of 600 MPa, which is more than 70% higher than the strength of conventional ceramics. The higher fracture toughness means higher reliability when used in electronic packaging substrates.

[0161] Comparing Example 5 with Example 1, it can be seen that in the process of silicon nitride-reinforced aluminum nitride, the long columnar crystal structure of β-phase silicon nitride is utilized. Through the sintering system SiO2-ZrSi2-MgO, the β-phase silicon nitride phase transformation can be enlarged and the grain boundaries thinned, significantly improving its aspect ratio. Using gas pressure sintering and powder embedding processes, the substrate prepared has a thermal conductivity of over 150 W / (m·K), a fracture toughness of over 4 MPa·m1 / 2, and a bending strength of 550 MPa, which is more than 55% higher than that of conventional ceramics. The higher fracture toughness means higher reliability when used in electronic packaging substrates.

[0162] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing high-strength, high-toughness aluminum nitride ceramics, characterized in that, The preparation method involves the following steps: S1: Mix the reinforcing agent, dispersant, and mixed solvent, and then ultrasonically treat the mixture to obtain a reinforcing slurry; S2: Aluminum nitride powder and sintering aid are mixed to obtain inorganic powder; polyvinyl butyral, plasticizer, dispersant and mixed solvent are added to the inorganic powder, and the mixture is fully ball-milled and mixed. Reinforcing slurry is added and ball-milled to obtain casting slurry; S3: Vacuum degassing and sieving of the cast slurry; casting and cutting to obtain raw ceramic tiles; S4: The cut raw ceramic pieces are sealed with a film and subjected to warm isostatic pressing to obtain the shaped blank; S5: The obtained molded blank is subjected to debinding treatment in an air atmosphere to obtain a debinding sheet; S6: The obtained sheet is placed in a vacuum graphite furnace and sintered under a flowing nitrogen atmosphere to obtain a composite ceramic substrate. The substrate is then ground on both sides to obtain high-strength and high-toughness aluminum nitride ceramic.

2. The method for preparing high-strength, high-toughness aluminum nitride ceramic according to claim 1, characterized in that, In step S1, the reinforcing body is one of aluminum nitride whiskers, zirconium oxide powder, and silicon nitride powder; the aluminum nitride powder is a mixture of aluminum nitride raw powder and aluminum nitride submicron powder in a mass ratio of (40-98):(0-50); the particle size of the aluminum nitride raw powder is 1.2-1.5μm, and the particle size of the aluminum nitride submicron powder is 0.2-0.6μm.

3. The method for preparing high-strength, high-toughness aluminum nitride ceramic according to claim 1, characterized in that, In step S1, the reinforcing material is aluminum nitride whiskers. The aluminum nitride whiskers are magnetized by the following steps: immersing the aluminum nitride whiskers in an ethanol suspension containing iron nitride nanoparticles, drying them after immersion, repeating the immersion and drying process 4-5 times, and then heat-treating them at 200-300℃ for 1-2 hours to obtain magnetized aluminum nitride whiskers.

4. The method for preparing high-strength, high-toughness aluminum nitride ceramic according to claim 1, characterized in that, In step S1, the mass ratio of dispersant to reinforcement is (0.5-1.5):100; the solid content of reinforcement in the reinforcement slurry is 40-60%; in step S2, the mass ratio of inorganic powder, polyvinyl butyral, plasticizer, dispersant and mixed solvent is (50-60):(5-10):(1-3):(1-3):(20-40).

5. The method for preparing high-strength, high-toughness aluminum nitride ceramic according to claim 1, characterized in that, In step S2, the aluminum nitride powder is modified. The preparation process is as follows: a. Mix the metal nitrate and the aqueous ethanol solution, adjust the pH to 3-5.5 with nitric acid, heat to 60-80℃ and stir for 30-60 min to obtain the precursor solution; b. Add aluminum nitride powder and precursor solution to a reaction vessel, add citric acid and γ-aminopropyltriethoxysilane, ultrasonically disperse for 30-60 min, stir at a constant temperature of 60-80℃ for 2-4 h, calcine and convert, cool, crush, grind and filter to obtain modified aluminum nitride powder.

6. The method for preparing a high-strength, high-toughness aluminum nitride ceramic according to claim 5, characterized in that, The metal nitrate is one or a combination of Y(NO3)3 and ZrO(NO3)2.

7. The method for preparing high-strength, high-toughness aluminum nitride ceramic according to claim 1, characterized in that, In step S3, the casting process is as follows: 1) At the material box of the casting machine, a DC magnetic field is constructed using NdFeB permanent magnets, and the magnetic field uniformity is controlled to be 80-95%. 2) Pour the casting slurry into the material box and let it stand in the magnetic field for 10-60 minutes; 3) Casting and shaping process, cutting to obtain raw ceramic tiles.

8. The method for preparing high-strength, high-toughness aluminum nitride ceramic according to claim 1, characterized in that, In step S2, the sintering aid is one or more of yttrium oxide, lithium carbonate, calcium oxide, calcium fluoride, yttrium fluoride, magnesium oxide, zirconium silicide, and lithium oxide; the mixed solvent is anhydrous ethanol, isopropanol, and toluene in a volume ratio of (1-3):1:1; and the plasticizer is one of dioctyl phthalate and dibutyl phthalate.

9. The method for preparing high-strength, high-toughness aluminum nitride ceramic according to claim 1, characterized in that, In step S1, the ultrasonic treatment process conditions are: ultrasonic frequency of 20kHz-40kHz, ultrasonic power of 1-2kW, and dispersion time of 1-3h; in step S2, the ball milling process conditions are: rotation speed of 120-600rpm and time of 12-24h; in step S3, the vacuum degassing process conditions are: revolution speed of 80-120rpm, vacuum degree of -70kpa-90kpa, and time of 0.5-2h; in step S4, the isostatic pressing process conditions are: temperature of 70-80℃, time of 10-20min, and pressure of 20-40MPa; in step S5, the debinding process conditions are: temperature of 500℃-600℃ and time of 48-72h; in step S6, the sintering process conditions are: temperature of 1500-1850℃ and time of 2-6h.

10. A high-strength, high-toughness aluminum nitride ceramic, characterized in that, Prepared by the preparation method according to any one of claims 1-9.

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