High-strength aluminum nitride substrate and method for manufacturing the same

Abstract

The application provides a high-strength aluminum nitride substrate and a preparation method thereof, and belongs to the technical field of ceramic substrates. The preparation method of the high-strength aluminum nitride substrate comprises the following steps: S1: mixing modified first aluminum nitride powder, second aluminum nitride powder and a sintering aid to obtain mixed powder; S2: forming the mixed powder into a green body; S3: step-by-step sintering the green body in a nitrogen atmosphere, wherein the step-by-step sintering comprises a carbonization stage at 550-650 DEG C and a step-by-step sintering stage at 1480-1820 DEG C, and then cooling to 20-30 DEG C to obtain the aluminum nitride substrate. The bending strength of the obtained aluminum nitride substrate can reach more than 540 MPa, and the thermal conductivity can be stably maintained at more than 170 W / (m*K), thereby meeting the use requirements of high-reliability high-end electronic devices.

Description

Technical Field

[0001] This application relates to the field of ceramic substrate technology, and in particular to a high-strength aluminum nitride substrate and its preparation method. Background Technology

[0002] Aluminum nitride ceramics possess extremely high theoretical thermal conductivity (up to 320 W / (m·K)), its coefficient of thermal expansion is highly matched with that of silicon chips, and it exhibits excellent insulation properties and good mechanical strength. This makes it an ideal substrate material for high-end electronic devices such as high-power integrated circuits, IGBT modules, LED packaging, and semiconductor etching equipment. With the rapid development of third-generation semiconductor technology, the reliability requirements for substrate materials in electronic devices are becoming increasingly stringent. These requirements not only demand high thermal conductivity for rapid heat dissipation but also high mechanical strength to withstand packaging stress, thermal cycling fatigue, and mechanical vibration.

[0003] However, while the thermal conductivity of existing aluminum nitride substrates has reached a relatively high level of 170–200 W / (m·K), their bending strength is generally low, typically only 300–400 MPa. This strength level poses a serious risk of substrate cracking due to stress concentration when facing the complex service conditions of high-end power modules, greatly limiting its further promotion in high-reliability applications. Therefore, how to significantly improve the mechanical strength of aluminum nitride substrates while maintaining high thermal conductivity has become a key technical challenge that urgently needs to be solved in this field.

[0004] To improve the strength of aluminum nitride ceramics, existing technologies mainly involve toughening by introducing second-phase particles: for example, adding high-hardness, high-strength second phases such as SiC particles and TiB2 particles to the AlN matrix. However, problems such as weak interfacial bonding and severe thermal expansion mismatch often exist between the particles and the matrix, resulting in limited toughening effects. Moreover, the introduction of hard particles is often accompanied by a significant decrease in thermal conductivity. Alternatively, fluoride mineralizers can be added: such as CaF2 and YF3. The selective chemical etching of AlN crystal faces by fluoride ions at high temperatures induces anisotropic growth, forming long columnar AlN grains. However, fluorides at high temperatures generate highly corrosive gaseous fluorides (such as AlF3), severely corroding the graphite heating element and furnace structure of the sintering furnace, significantly shortening equipment lifespan, and causing environmental pollution. The prospects for industrial application are severely constrained by cost and environmental pressures.

[0005] Therefore, there is an urgent need to develop a novel aluminum nitride substrate preparation technology that can achieve a perfect balance between high strength and high thermal conductivity, while also possessing good environmental friendliness and industrial feasibility. Summary of the Invention

[0006] This application is made in view of the above-mentioned problems, and its purpose is to provide a high-strength aluminum nitride substrate and a method for preparing the same.

[0007] Specifically, the first aspect of this application provides a method for preparing a high-strength aluminum nitride substrate, comprising the following steps: S1: The first aluminum nitride powder is mixed with the composite precursor solution, and the mixture is subjected to selective surface coating treatment. After drying, a modified first aluminum nitride powder with a doped carbon layer on the surface is obtained. The modified first aluminum nitride powder, the second aluminum nitride powder, and the sintering aid are mixed to obtain a mixed powder. The composite precursor solution contains a carbon source and a soluble doped metal salt. The particle size D50 ratio of the first aluminum nitride powder to the second aluminum nitride powder is 7-15:1. S2: Shape the mixed powder into a blank; S3: The green blank is sintered in a nitrogen atmosphere in a stepwise manner, wherein the stepwise sintering includes: Carbonization stage: Hold at 550–650℃ for 1–3 hours; First sintering stage: Heat to 1480℃~1550℃ and sinter under nitrogen pressure of 0.3~0.5MPa; Second sintering stage: The temperature is raised to 1780℃~1820℃, and sintering is carried out under nitrogen pressure of 0.6~0.9MPa; The third sintering stage: the temperature is lowered to 1650℃~1700℃, and the nitrogen pressure is increased to 1.0~1.5MPa for sintering. Then it is cooled to 20℃~30℃ to obtain an aluminum nitride substrate.

[0008] In the carbonization stage of this invention, the carbon source undergoes pyrolysis and carbonization, forming a uniform doped carbon layer on the surface of large-diameter aluminum nitride particles. During the subsequent high-temperature sintering process, this carbon layer induces some AlN grains to preferentially grow along specific crystal planes through in-situ carbon fixation. Simultaneously, the metal elements doped into the carbon layer are uniformly precipitated as sintering aids, avoiding matrix defects caused by the agglomeration of traditional sintering aids. In the third sintering stage, while cooling to 1650–1700°C, the pressure is increased to 1.0–1.5 MPa. Utilizing a dual-particle-size powder packing structure with a particle size ratio of 7:1–15:1, pressure-induced filling of the smaller-diameter second aluminum nitride powder is induced, achieving low-temperature densification without mechanical hot pressing.

[0009] Further, in step S1, the particle size D50 of the first aluminum nitride powder is 2.0 to 3.5 μm, the particle size D50 of the second aluminum nitride powder is 0.2 to 0.5 μm, and the weight ratio of the first aluminum nitride powder to the second aluminum nitride powder is 75 to 85: 10 to 20.

[0010] Furthermore, the soluble doped metal salt in the composite precursor solution is yttrium nitrate.

[0011] Furthermore, the carbon source mentioned in step S1 is glucose.

[0012] Further, the process of selective surface coating in step S1 is as follows: glucose and soluble doped metal salt are added together to anhydrous ethanol and stirred until completely dissolved to obtain a precursor solution; the first aluminum nitride powder is added to the precursor solution and stirred in a water bath at 40-60°C until the solvent evaporates, and then vacuum dried at 80-100°C to obtain modified first aluminum nitride powder with a uniformly coated carbon source.

[0013] Furthermore, the sintering aid is yttrium oxide or a mixture of yttrium oxide and magnesium oxide.

[0014] Further, the weight parts of each raw material mentioned in step S1 are: 75-85 parts of modified first aluminum nitride powder, 10-20 parts of second aluminum nitride powder, 2-5 parts of yttrium oxide, and 0.2-0.8 parts of magnesium oxide.

[0015] Furthermore, prior to the step-by-step sintering described in step S3, the process also includes: Carbonization stage: Hold at 550–650℃ for 1–3 hours; Furthermore, the carbonization stage is carried out at a heating rate of 0.5–1 °C / min from room temperature to 550–650 °C, with a nitrogen pressure of 0.12–0.15 MPa.

[0016] Furthermore, in the first sintering stage: the temperature is increased to 1480℃ to 1550℃ at a rate of 8 to 10℃ / min, and held for 0.5 to 2 hours.

[0017] Furthermore, in the second sintering stage, the temperature is increased to 1780℃~1820℃ at a rate of 10~15℃ / min and held for 1~2 hours.

[0018] Furthermore, in the third sintering stage, the temperature is reduced to 1650℃~1700℃ at a cooling rate of 3~6℃ / min, and held at that temperature for 4~8 hours.

[0019] Further, in step S2, the mixed powder is dry-pressed into a blank under a pressure of 150-200 MPa, and the blank is then subjected to cold isostatic pressing under a pressure of 180-250 MPa.

[0020] A second aspect of this application provides a high-strength aluminum nitride substrate, which is prepared by the method described above.

[0021] The present invention has the following beneficial effects: This invention selectively coats large-particle-size aluminum nitride powder, and after drying, obtains modified aluminum nitride powder with a doped carbon layer on the surface. Impurities are purified by carbothermic reduction of the nano-carbon layer generated after carbonization. Simultaneously, the particle size distribution of the dual-size aluminum nitride powder is combined with a variable-temperature and variable-pressure stepwise sintering process. This achieves high densification of aluminum nitride ceramics without introducing additional second-phase toughening particles or using corrosive fluoride mineralizers. This effectively improves the bending strength of the aluminum nitride substrate without negatively impacting its thermal conductivity. The resulting aluminum nitride substrate exhibits a bending strength exceeding 540 MPa and a stable thermal conductivity above 170 W / (m·K), balancing excellent mechanical and thermal properties. It is environmentally friendly, compatible with existing conventional hot-pressing sintering equipment, and has promising industrial application prospects, meeting the requirements of high-reliability, high-end electronic devices. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0023] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0024] An embodiment of the first aspect of this application provides a method for preparing a high-strength aluminum nitride substrate, comprising the following steps: S1: The first aluminum nitride powder is mixed with the composite precursor solution, and the mixture is subjected to selective surface coating treatment. After drying, a modified first aluminum nitride powder with a doped carbon layer on the surface is obtained. The modified first aluminum nitride powder, the second aluminum nitride powder, and the sintering aid are mixed to obtain a mixed powder. The composite precursor solution contains a carbon source and a soluble doped metal salt. The particle size D50 ratio of the first aluminum nitride powder to the second aluminum nitride powder is 7-15:1. S2: Shape the mixed powder into a blank; S3: The green blank is sintered in a nitrogen atmosphere in a stepwise manner, wherein the stepwise sintering includes: Carbonization stage: Hold at 550–650℃ for 1–3 hours; First sintering stage: Heat to 1480℃~1550℃ and sinter under nitrogen pressure of 0.3~0.5MPa; Second sintering stage: The temperature is raised to 1780℃~1820℃, and sintering is carried out under nitrogen pressure of 0.6~0.9MPa; The third sintering stage: the temperature is lowered to 1650℃~1700℃, and the nitrogen pressure is increased to 1.0~1.5MPa for sintering. Then it is cooled to 20℃~30℃ to obtain an aluminum nitride substrate.

[0025] In this embodiment, the aluminum nitride powder, yttrium oxide, magnesium oxide, and carbon source in step S1 are all commercially available industrial-grade raw materials. The particle size D50 of the first aluminum nitride powder is 2.0–3.5 μm, and the particle size D50 of the second aluminum nitride powder is 0.2–0.5 μm. Glucose is selected as the carbon source.

[0026] The soluble doped metal salt in the composite precursor solution is yttrium nitrate; the preferred mass ratio of the carbon source to the metal element in the doped metal salt is 10:1. The composite precursor solution selectively coats large-particle-size aluminum nitride powder, and after subsequent carbonization, a uniformly doped carbon layer with metal elements is obtained on the particle surface. This avoids agglomeration when the doped metal elements precipitate and also utilizes the in-situ generated carbon to purify impurities in the matrix.

[0027] The selective surface coating process described in step S1 is as follows: glucose and a soluble doped metal salt (preferably yttrium nitrate) are added together to anhydrous ethanol and stirred until completely dissolved to obtain a precursor solution; the first aluminum nitride powder is added to the precursor solution and stirred in a water bath at 40–60°C until the solvent evaporates, and then vacuum dried at 80–100°C to obtain modified first aluminum nitride powder with a uniformly coated carbon source. This step ensures that the carbon source and the doped metal salt are uniformly coated only on the surface of the large-particle-size first aluminum nitride powder, achieving precise selective coating and providing a reaction basis for subsequent in-situ induced grain growth.

[0028] The specific weight proportions of each raw material are as follows: 75-85 parts modified aluminum nitride powder, 10-20 parts modified aluminum nitride powder, 2-5 parts yttrium oxide, and 0.2-0.8 parts magnesium oxide. The aluminum nitride powder has a D50 of 2.5 μm, and the aluminum nitride powder has a D50 of 0.35 μm. The components exhibit synergistic effects: the large-particle-size aluminum nitride powder achieves good packing density, while the small-particle-size aluminum nitride powder fills the gaps between large particles, increasing the initial density of the green body and laying the foundation for obtaining a high-density matrix during subsequent sintering. Yttrium oxide and magnesium oxide, as sintering aids, react with the alumina on the surface of the aluminum nitride powder to generate an aluminate liquid phase, promoting densification during sintering, reducing the required sintering temperature, and preventing excessive grain growth.

[0029] The mixing steps for each raw material are as follows: Modified aluminum nitride powder (first type), aluminum nitride powder (second type), yttrium oxide, and magnesium oxide powder are weighed according to the specified weight ratio and added to a ball mill. Using anhydrous ethanol as the medium and silicon nitride balls as the grinding media, the mixture is ball-milled for 16–24 hours to obtain a uniform slurry. The slurry is then subjected to closed-circuit spray granulation under nitrogen protection, with an inlet temperature of 200–250℃ and an outlet temperature of 80–110℃, to obtain granulated powder with good flowability.

[0030] In this embodiment, step S2 involves dry-pressing the mixed powder into a preform under a pressure of 150–200 MPa. After vacuum sealing the dry-pressed preform, it is then subjected to cold isostatic pressing under a pressure of 180–250 MPa to obtain a preform with uniform density and sufficient strength. This preform has high density, uniform internal structure, and no obvious macroscopic defects, providing a good foundation for subsequent sintering to obtain a high-performance substrate.

[0031] In this embodiment, the step-by-step sintering in step S3 includes: Carbonization stage: Hold at 550-650℃ for 1-3 hours; First sintering stage: heat to 1480℃~1550℃ and hold for 0.5~2 hours; Second sintering stage: Continue to raise the temperature to 1780℃~1820℃ and hold for 1~2 hours; Third sintering stage: Cool down to 1650℃~1700℃ and hold for 4~8 hours.

[0032] In this embodiment, during the carbonization stage, the temperature is increased from room temperature to 550–650°C at a rate of 0.5–1°C / min, while the nitrogen pressure is maintained at 0.12–0.15 MPa. The temperature is then held at 550–650°C for 2 hours to allow for complete pyrolysis of the carbon source, forming a uniformly distributed nano-carbon network in the green body. During this carbonization stage, the nano-carbon layer formed by the carbon source coating the surface of the first aluminum nitride powder preferentially undergoes a carbothermic reduction reaction with oxygen impurities in the mechanical strain layer generated during grinding on the surface of the second aluminum nitride powder, thus repairing surface defects.

[0033] In this embodiment, the first sintering stage involves heating to 1480℃~1550℃ at a rate of 8~10℃ / min, with a nitrogen pressure of 0.3~0.5 MPa. During this stage, a carbothermic reduction reaction occurs: Al2O3+3C+N2→ 2AlN+3CO↑. In this reaction, carbon is consumed and discharged from the furnace as CO gas along with the flowing nitrogen gas. No free carbon remains in the sintered substrate.

[0034] In this embodiment, during the second sintering stage, the temperature is increased to 1780℃ to 1820℃ at a rate of 10 to 15℃ / min, and the nitrogen pressure is increased to 0.6 to 0.9 MPa. The temperature is maintained at 1780℃ to 1820℃ for 1 to 2 hours, allowing the liquid phase to fully form and the green body to rapidly densify.

[0035] In this embodiment, the third sintering stage lowers the temperature to 1650℃-1700℃ at a cooling rate of 3-6℃ / min, and increases the nitrogen pressure to 1.0-2.0 MPa. The temperature and pressure are maintained for 4-8 hours. This step utilizes the stacking structure of the dual-particle-size powders to induce pressure-induced filling of the smaller-particle-size second aluminum nitride powder, further filling the remaining micropores inside the matrix. This achieves low-temperature densification without mechanical hot pressing. Simultaneously, the holding process promotes the full expulsion of grain boundary phases, reduces internal porosity, and increases matrix density, ultimately yielding an aluminum nitride sintered body with high thermal conductivity and high strength. After the holding period, the body is cooled to room temperature in the furnace, removed, and cut to obtain the desired aluminum nitride substrate.

[0036] Finally, after the heat preservation period, the temperature is cooled to 800°C at a rate of ≤5°C / min, followed by natural furnace cooling to 20°C~30°C. The sintered body is then removed and cut, ground, and polished as needed to obtain the finished aluminum nitride substrate.

[0037] An embodiment of the second aspect of this application provides a high-strength aluminum nitride substrate, which is prepared by the method described above.

[0038] Example The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0039] The raw material sources for the following examples and comparative examples are: Aluminum nitride powder: manufactured by Forsmann Technology (Beijing) Co., Ltd., with D50=2.5μm and D50=0.35μm; Yttrium oxide: Manufacturer: Zibo Ruibokang Rare Earth Materials Co., Ltd., purity 99.99%, D50=0.8μm; Magnesium oxide: Manufacturer: Langfang Qianyao Technology Co., Ltd., Purity: 99.99%, D50: 0.5μm Glucose: Analytical grade, purity ≥99.7%.

[0040] Example 1 A method for preparing a high-strength aluminum nitride substrate includes the following steps: S1: Preparation of modified aluminum nitride powder: 3.0 g glucose and 1.3 g yttrium nitrate were added to 800 mL of anhydrous ethanol and stirred at 400 rpm for 20 minutes on a magnetic stirrer until completely dissolved, obtaining a precursor solution. 1000 g of aluminum nitride powder (D50 = 2.0~3.5 μm) was slowly added in batches to the above precursor solution while stirring at 200 rpm to form a uniform suspension slurry. The water bath temperature was set to 50℃, the rotary evaporation speed to 60 rpm, and the vacuum degree to be maintained at -0.08~-0.1 MPa for reduced pressure rotary evaporation. Evaporation continued for 2.0 hours until the ethanol was completely evaporated. At this time, glucose was uniformly precipitated with the solvent and firmly coated on the surface of the aluminum nitride powder particles. The rotary evaporated powder was placed in a vacuum oven and dried at 90℃ under vacuum for 12 hours to obtain modified aluminum nitride powder with a uniform carbon source coating on the surface. 820g of modified first aluminum nitride powder, 120g of second aluminum nitride powder, 35g of yttrium oxide, and 5g of magnesium oxide were added to a ball mill. Using anhydrous ethanol as the medium and silicon nitride balls as the grinding media, the mixture was ball-milled at 200 rpm for 20 hours to obtain a uniform slurry. The slurry was then subjected to closed-circuit spray granulation under nitrogen protection, with an inlet temperature of 220℃ and an outlet temperature of 95℃. The granulated powder was obtained by passing the granules through a 100-mesh sieve. S2: The granulated powder is dry-pressed into a preform under a pressure of 200 MPa. After vacuum sealing the dry-pressed preform, it is subjected to cold isostatic pressing under a pressure of 220 MPa to obtain the preform. S3: The green blank is sintered in a nitrogen atmosphere in stages, including: Carbonization stage: Nitrogen pressure is maintained at 0.15 MPa, and the temperature is increased from room temperature to 600℃ at a rate of 1℃ / min and held for 2 hours; First sintering stage: Heating to 1510℃ at a rate of 8℃ / min, nitrogen pressure of 0.4MPa, and holding for 1.5 hours; Second sintering stage: continue heating to 1800℃ at a rate of 12℃ / min, increase nitrogen pressure to 0.8MPa, and hold for 2 hours; The third sintering stage: the temperature is reduced to 1670℃ at a cooling rate of 4℃ / min, and the nitrogen pressure is increased to 1.2MPa and held for 6 hours; After the heat preservation is completed, the temperature is cooled to 800°C at a rate of 5°C / min, and then naturally cooled to 25°C in the furnace. The sintered body is then removed and cut, ground, and polished as needed to obtain the finished aluminum nitride substrate.

[0041] Example 2 A method for preparing a high-strength aluminum nitride substrate includes the following steps: S1: Preparation of modified aluminum nitride powder: Same as in Example 1; 780g of modified first aluminum nitride powder, 160g of second aluminum nitride powder, 20g of yttrium oxide, and 3g of magnesium oxide were added together into a ball mill. Using anhydrous ethanol as the medium and silicon nitride balls as the grinding media, the mixture was ball-milled at 200 rpm for 18 hours to obtain a uniform slurry. The slurry was then subjected to closed-circuit spray granulation under nitrogen protection, with an inlet temperature of 220℃ and an outlet temperature of 95℃. The granulated powder was obtained by passing the granules through a 100-mesh sieve. S2: The granulated powder is dry-pressed into a preform under a pressure of 200 MPa. After vacuum sealing the dry-pressed preform, it is subjected to cold isostatic pressing under a pressure of 220 MPa to obtain the preform. S3: The green blank is sintered in a nitrogen atmosphere in stages, including: Carbonization stage: Nitrogen pressure is maintained at 0.15 MPa, and the temperature is increased from room temperature to 600℃ at a rate of 1℃ / min and held for 2 hours; First sintering stage: Heat to 1520℃ at a rate of 10℃ / min, nitrogen pressure is 0.5MPa, and hold for 1 hour; Second sintering stage: continue heating at a rate of 15℃ / min to 1820℃, increase nitrogen pressure to 0.9MPa, and hold for 1.5 hours; The third sintering stage: the temperature is reduced to 1700℃ at a cooling rate of 3℃ / min, and the nitrogen pressure is increased to 1.5MPa and held for 4 hours; After the heat preservation is completed, the temperature is cooled to 800°C at a rate of 5°C / min, and then naturally cooled to 25°C in the furnace. The sintered body is then removed and cut, ground, and polished as needed to obtain the finished aluminum nitride substrate.

[0042] Example 3 A method for preparing a high-strength aluminum nitride substrate includes the following steps: S1: Preparation of modified aluminum nitride powder: Same as in Example 1; 800g of modified first aluminum nitride powder, 130g of second aluminum nitride powder, 50g of yttrium oxide, and 8g of magnesium oxide were added together to a ball mill. Using anhydrous ethanol as the medium and silicon nitride balls as the grinding media, the mixture was ball-milled at 200 rpm for 20 hours to obtain a uniform slurry. The slurry was then subjected to closed-circuit spray granulation under nitrogen protection, with an inlet temperature of 220℃ and an outlet temperature of 95℃. The granulated powder was obtained by passing the granules through a 100-mesh sieve. S2: The granulated powder is dry-pressed into a preform under a pressure of 200 MPa. After vacuum sealing the dry-pressed preform, it is subjected to cold isostatic pressing under a pressure of 220 MPa to obtain the preform. S3: The green blank is sintered in a nitrogen atmosphere in stages, including: Carbonization stage: Nitrogen pressure is maintained at 0.15 MPa, and the temperature is increased from room temperature to 600℃ at a rate of 1℃ / min and held for 2 hours; First sintering stage: Heat to 1480℃ at a rate of 8℃ / min, nitrogen pressure of 0.3MPa, and hold for 2 hours; Second sintering stage: continue heating at a rate of 10℃ / min to 1780℃, increase nitrogen pressure to 0.6MPa, and hold for 2 hours; The third sintering stage: the temperature is reduced to 1650℃ at a cooling rate of 5℃ / min, and the nitrogen pressure is increased to 1.0MPa and held for 8 hours; After the heat preservation is completed, the temperature is cooled to 800°C at a rate of 5°C / min, and then naturally cooled to 25°C in the furnace. The sintered body is then removed and cut, ground, and polished as needed to obtain the finished aluminum nitride substrate.

[0043] Example 4 A method for preparing a high-strength aluminum nitride substrate includes the following steps: S1: Preparation of modified aluminum nitride powder: Same as in Example 1; 820g of modified aluminum nitride powder (first type), 180g of modified aluminum nitride powder (second type), 35g of yttrium oxide, and 5g of magnesium oxide were added to a ball mill. Using anhydrous ethanol as the medium and silicon nitride balls as the grinding media, the mixture was ball-milled at 200 rpm for 20 hours to obtain a uniform slurry. The slurry was then subjected to closed-circuit spray granulation under nitrogen protection at an inlet temperature of 220℃ and an outlet temperature of 95℃. The granulated powder was obtained by passing the granules through a 100-mesh sieve. S2: The granulated powder is dry-pressed into a preform under a pressure of 200 MPa. After vacuum sealing the dry-pressed preform, it is subjected to cold isostatic pressing under a pressure of 220 MPa to obtain the preform. S3: The green blank is sintered in a nitrogen atmosphere in stages, including: Carbonization stage: Nitrogen pressure is maintained at 0.15 MPa, and the temperature is increased from room temperature to 600℃ at a rate of 1℃ / min and held for 2 hours; First sintering stage: Heat to 1500℃ at a rate of 8℃ / min, nitrogen pressure is 0.4MPa, and hold for 1 hour; Second sintering stage: continue heating to 1800℃ at a rate of 12℃ / min, increase nitrogen pressure to 0.8MPa, and hold for 2 hours; The third sintering stage: the temperature is reduced to 1690℃ at a cooling rate of 3℃ / min, and the nitrogen pressure is increased to 1.2MPa and held for 8 hours; After the heat preservation is completed, the temperature is cooled to 800°C at a rate of 5°C / min, and then naturally cooled to 25°C in the furnace. The sintered body is then removed and cut, ground, and polished as needed to obtain the finished aluminum nitride substrate.

[0044] Example 5 A method for preparing a high-strength aluminum nitride substrate includes the following steps: S1: Preparation of modified aluminum nitride powder: Same as in Example 1; 750g of modified aluminum nitride powder (first type), 200g of modified aluminum nitride powder (second type), 35g of yttrium oxide, and 5g of magnesium oxide were added to a ball mill. Using anhydrous ethanol as the medium and silicon nitride balls as the grinding media, the mixture was ball-milled at 200 rpm for 20 hours to obtain a uniform slurry. The slurry was then subjected to closed-circuit spray granulation under nitrogen protection at an inlet temperature of 220℃ and an outlet temperature of 95℃. The granulated powder was obtained by passing the granules through a 100-mesh sieve. S2: The granulated powder is dry-pressed into a preform under a pressure of 200 MPa. After vacuum sealing the dry-pressed preform, it is subjected to cold isostatic pressing under a pressure of 220 MPa to obtain the preform. S3: The green blank is sintered in a nitrogen atmosphere in stages, including: Carbonization stage: Nitrogen pressure is maintained at 0.15 MPa, and the temperature is increased from room temperature to 600℃ at a rate of 1℃ / min and held for 2 hours; First sintering stage: Heat to 1500℃ at a rate of 8℃ / min, nitrogen pressure of 0.5MPa, and hold for 1.5 hours; Second sintering stage: Continue heating at a rate of 12℃ / min to 1800℃, increase nitrogen pressure to 0.9MPa, and hold for 2 hours; The third sintering stage: the temperature is reduced to 1680℃ at a cooling rate of 6℃ / min, and the nitrogen pressure is increased to 1.3MPa and held for 5 hours; After the heat preservation is completed, the temperature is cooled to 800°C at a rate of 5°C / min, and then naturally cooled to 25°C in the furnace. The sintered body is then removed and cut, ground, and polished as needed to obtain the finished aluminum nitride substrate.

[0045] Comparative Example 1 A method for preparing a high-strength aluminum nitride substrate includes the following steps: S1: Preparation of modified aluminum nitride powder: Same as in Example 1; 820g of modified aluminum nitride powder (first type), 120g of modified aluminum nitride powder (second type), 35g of yttrium oxide, and 5g of magnesium oxide were added to a ball mill. Using anhydrous ethanol as the medium and silicon nitride balls as the grinding media, the mixture was ball-milled at 200 rpm for 20 hours to obtain a uniform slurry. The slurry was then subjected to closed-circuit spray granulation under nitrogen protection at an inlet temperature of 220℃ and an outlet temperature of 95℃. The granulated powder was obtained by passing the granules through a 100-mesh sieve. S2: The granulated powder is dry-pressed into a preform under a pressure of 200 MPa. After vacuum sealing the dry-pressed preform, it is subjected to cold isostatic pressing under a pressure of 220 MPa to obtain the preform. S3: The green blank is sintered in a nitrogen atmosphere. Under a constant pressure of 0.4 MPa nitrogen atmosphere, the temperature is increased from room temperature to 1820℃ at 5℃ / min and held for 6 hours. Then the temperature is decreased to 800℃ at 5℃ / min and then furnace cooled.

[0046] Comparative Example 2 This comparative example is basically the same as Example 1, except that the sintering in step S3 is carried out under a constant pressure nitrogen atmosphere of 0.8 MPa, with the temperature increased to 600°C at 1°C / min and held for 2 hours, then increased to 1820°C at 10°C / min and held for 6 hours, and then cooled to 800°C at 5°C / min and then furnace cooled.

[0047] Comparative Example 3 This comparative example is basically the same as Example 1, except that the first aluminum nitride powder is not modified in step S1; the raw materials include: 820g of the first aluminum nitride powder, 120g of the second aluminum nitride powder, 35g of yttrium oxide, and 5g of magnesium oxide.

[0048] Comparative Example 4 This comparative example is basically the same as Example 1, except that in step S3: the third sintering stage: the temperature is reduced to 1670°C at a cooling rate of 4°C / min, the nitrogen pressure is kept constant at 0.8 MPa, and the temperature is maintained for 6 hours.

[0049] Comparative Example 5 This comparative example is basically the same as Example 1, except that the amount of glucose used in step S1 is 2g.

[0050] Comparative Example 6 This comparative example is basically the same as Example 1, except that in step S1, only 940g of ordinary first aluminum nitride powder is used, and no second aluminum nitride powder is used.

[0051] Experimental Case The following tests were performed on the samples prepared in Examples 1-5 and Comparative Examples 1-6: Density: Archimedes' displacement method; Bending strength: Three-point bending method, span 30 mm, loading rate 0.5 mm / min; Fracture toughness: Single-sided notched beam method (SENB), notch depth 2.5 mm; Thermal conductivity: laser scintillation method, with a graphite coating sprayed onto the sample surface; The test results are shown in Table 1.

[0052]

[0053] As shown in Table 1, this invention effectively improves the flexural strength, fracture toughness, and thermal conductivity of aluminum nitride substrates by adding an appropriate amount of carbon source and combining it with a stepwise pressure sintering process. The carbon source participates in the carbothermic reduction reaction to remove oxygen-containing impurities adsorbed on the surface of the aluminum nitride powder, reducing oxygen content and promoting aluminum nitride grain growth. Simultaneously, the high-temperature, high-nitrogen-pressure treatment in the third stage of the stepwise sintering process forms a fine and uniform residual stress field inside the substrate, effectively hindering crack propagation and significantly improving the mechanical properties of the substrate. By using two different particle sizes of aluminum nitride powder, the powder packing density can be optimized, further improving the sintering density and ensuring that the substrate possesses both excellent mechanical and thermal conductivity properties. The resulting high-strength aluminum nitride substrate can meet the requirements of high-power electronic devices. The prepared aluminum nitride substrate has a flexural strength exceeding 540 MPa and a fracture toughness of 4.9 MPa·m. 1 / 2 The above-mentioned thermal conductivity is not less than 170 W / (m·K), and the overall performance is excellent, meeting the requirements of high-performance electronic devices.

[0054] Comparative Example 1, using a constant-pressure conventional sintering process, showed that the flexural strength, fracture toughness, and thermal conductivity of the resulting aluminum nitride substrate were significantly lower than those of the embodiments in this application. This demonstrates that stepwise pressure sintering is key to improving the overall performance of the aluminum nitride substrate. Comparative Example 2, not employing the stepwise pressure sintering process of this invention, maintained a constant nitrogen pressure throughout the process, which failed to effectively suppress the high-temperature decomposition of aluminum nitride, resulting in numerous internal pores and a significant decrease in the flexural strength and fracture toughness of the substrate. Comparative Example 3, where the first aluminum nitride was not modified, had a high content of impurities on the powder surface, leading to numerous grain boundary phase impurities after sintering. This hindered heat conduction and reduced grain boundary bonding strength, resulting in a significant decrease in both mechanical properties and thermal conductivity. Comparative Example 4, where the nitrogen pressure was not increased in the third sintering stage and remained constant, failed to suppress high-temperature decomposition and optimize the microstructure, resulting in significantly lower flexural strength and fracture toughness compared to Example 1. Comparative Example 5, with insufficient glucose addition, struggled to fully reduce the oxides on the powder surface, leading to a high amount of residual oxygen impurities during sintering, and both thermal conductivity and mechanical properties did not reach ideal levels. Comparative Example 6 uses only aluminum nitride powder with a single particle size, resulting in insufficient powder packing density and higher porosity after sintering. This leads to a significant decrease in flexural strength and fracture toughness compared to Example 1, which uses aluminum nitride powder with a bimodal particle size. This indicates that combining aluminum nitride raw materials with different particle size ranges can further improve powder packing density, which is more conducive to sintering densification and obtaining high-performance aluminum nitride substrates.

[0055] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a high-strength aluminum nitride substrate, characterized in that, Includes the following steps: S1: The first aluminum nitride powder is mixed with the composite precursor solution, and the mixture is subjected to selective surface coating treatment. After drying, a modified first aluminum nitride powder with a doped carbon layer on the surface is obtained. The modified first aluminum nitride powder, the second aluminum nitride powder, and the sintering aid are mixed to obtain a mixed powder. The composite precursor solution contains a carbon source and a soluble doped metal salt. The particle size D50 ratio of the first aluminum nitride powder to the second aluminum nitride powder is 7-15:

1. S2: Shape the mixed powder into a blank; S3: The green blank is sintered in a nitrogen atmosphere in a stepwise manner, wherein the stepwise sintering includes: Carbonization stage: Hold at 550–650℃ for 1–3 hours; First sintering stage: Heat to 1480℃~1550℃ and sinter under nitrogen pressure of 0.3~0.5MPa; Second sintering stage: The temperature is raised to 1780℃~1820℃, and sintering is carried out under nitrogen pressure of 0.6~0.9MPa; The third sintering stage: the temperature is lowered to 1650℃~1700℃, and the nitrogen pressure is increased to 1.0~1.5MPa for sintering. Then it is cooled to 20℃~30℃ to obtain an aluminum nitride substrate.

2. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, In step S1, the particle size D50 of the first aluminum nitride powder is 2.0-3.5 μm, the particle size D50 of the second aluminum nitride powder is 0.2-0.5 μm, and the weight ratio of the first aluminum nitride powder to the second aluminum nitride powder is 75-85:10-20. The soluble doped metal salt in the composite precursor solution is yttrium nitrate.

3. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, The carbon source mentioned in step S1 is glucose; The process of selective surface coating in step S1 is as follows: glucose and soluble doped metal salt are added together to anhydrous ethanol and stirred until completely dissolved to obtain a precursor solution; the first aluminum nitride powder is added to the precursor solution and stirred in a water bath at 40-60°C until the solvent evaporates, and then vacuum dried at 80-100°C to obtain modified first aluminum nitride powder with a uniformly coated carbon source. The sintering aid is yttrium oxide or a mixture of yttrium oxide and magnesium oxide.

4. The method for preparing a high-strength aluminum nitride substrate according to claim 3, characterized in that, The weight parts of each raw material mentioned in step S1 are as follows: 75-85 parts of modified first aluminum nitride powder, 10-20 parts of second aluminum nitride powder, 2-5 parts of yttrium oxide, and 0.2-0.8 parts of magnesium oxide.

5. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, The carbonization stage involves heating from room temperature to 550–650°C at a rate of 0.5–1°C / min, with a nitrogen pressure of 0.12–0.15 MPa.

6. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, The first sintering stage: the temperature is increased to 1480℃~1550℃ at a rate of 8~10℃ / min, and held for 0.5~2 hours.

7. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, In the second sintering stage, the temperature is increased to 1780℃~1820℃ at a rate of 10~15℃ / min and held for 1~2 hours.

8. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, The third sintering stage involves cooling the temperature to 1650℃~1700℃ at a cooling rate of 3~6℃ / min and holding it at that temperature for 4~8 hours.

9. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, In step S2, the mixed powder is dry-pressed into a blank under a pressure of 150-200 MPa, and the blank is then subjected to cold isostatic pressing under a pressure of 180-250 MPa.

10. A high-strength aluminum nitride substrate, characterized in that, Prepared by the method described in any one of claims 1-9.

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