A method for preparing a high-strength aluminum nitride substrate

Abstract

The application discloses a preparation method of a high-strength aluminum nitride substrate and relates to the technical field of aluminum nitride substrate preparation. The method comprises the following steps: preparing modified aluminum nitride powder; adding a non-oxygen composite sintering aid composed of fluorides and borides to the modified aluminum nitride powder to obtain a mixture; the adding amount of the composite sintering aid is 0.5wt%-5wt% of the total mass of the modified aluminum nitride powder; the mixture, a binder and a dispersant are mixed in a planetary ball mill to obtain a uniform slurry; the slurry is subjected to flow casting to form a green porcelain embryo, and then, glue removal treatment is performed under the protection of flowing inert gas to remove the binder; the green porcelain embryo after glue removal is placed in an atmosphere sintering furnace to perform a multi-stage temperature rising sintering procedure to form a ceramic body; and the sintered ceramic body is subjected to heat treatment and then cooled to obtain the aluminum nitride substrate. The application reduces the lattice thermal resistance of the aluminum nitride substrate and improves the mechanical strength of the aluminum nitride substrate.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride substrate preparation technology, specifically a method for preparing a high-strength aluminum nitride substrate. Background Technology

[0002] Aluminum nitride ceramics possess excellent physical and chemical properties such as thermal conductivity, heat resistance, thermal shock resistance, and electrical insulation. They are also non-toxic, and their coefficient of thermal expansion is similar to that of silicon. As such, they are an ideal substrate material for high-density electronic packaging and have great application prospects in the field of LED lighting.

[0003] Aluminum nitride, as a strongly covalent compound, has a low self-diffusion coefficient and weak sintering driving force, making it extremely difficult to densify pure aluminum nitride powder under normal pressure. To achieve sintering densification of aluminum nitride ceramics, the industry commonly employs the introduction of sintering aids. Currently, the most mainstream and widely studied sintering aid system is rare earth metal oxides, especially Y₂O₃. Its mechanism involves the reaction of Y₂O₃ with the alumina (Al₂O₃) on the surface of aluminum nitride particles at high temperatures, generating a low-melting-point yttrium aluminate liquid phase (such as Y₃Al₅O₃). 12 YAlO3) promotes material transport and particle rearrangement through liquid-phase sintering, thereby achieving densification.

[0004] However, this technical approach has several inherent and insurmountable bottlenecks:

[0005] First, the grain boundary phase generated by the reaction of Y2O3 and Al2O3 promotes densification, but it itself acts as a phonon scattering center, which seriously reduces the thermal conductivity of the material. Although some grain boundary phases can be crystallized by extending the high-temperature holding time, the residual amorphous phase or defects will still make the actual thermal conductivity much lower than the theoretical value.

[0006] Secondly, the grain boundary phase generated by oxide additives is usually a weak point in the mechanical properties of the material. Under stress, cracks tend to propagate along the grain boundaries, which limits the further improvement of the bending strength of the aluminum nitride substrate. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a high-strength aluminum nitride substrate, so as to solve the problems mentioned in the background art.

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

[0009] A method for preparing a high-strength aluminum nitride substrate includes the following steps:

[0010] Step 1: Preparation of modified aluminum nitride powder, including the following sub-steps:

[0011] S11. Disperse aluminum nitride powder in anhydrous ethanol or deionized water to form a suspension with a solid content of 20wt%-40wt%.

[0012] S12. Add a mixed solution of yttrium-containing compound and fluorine-containing compound to the suspension. The molar ratio of yttrium to fluorine in the mixed solution is 1:1.5-1:3. Stir at 60℃-80℃ for 2-4 hours to carry out the surface reaction.

[0013] S13. The solid material in the mixed solution after reaction is filtered, washed and dried. Then the dried solid material is heat-treated in an atmosphere sintering furnace at 400℃-600℃ for 1 hour-3 hours under an inert atmosphere to obtain modified aluminum nitride powder.

[0014] Step 2: Using modified aluminum nitride powder as the main raw material, add a non-oxygen composite sintering aid composed of fluorine compounds and borides to obtain a mixture; wherein, the amount of composite sintering aid added is 0.5wt%-5wt% of the total mass of modified aluminum nitride powder. The mixture is then mixed with binder, plasticizer, and dispersant in a planetary ball mill to obtain a uniform slurry.

[0015] Step 3: The slurry is cast into a green ceramic blank, and then debinding is performed under the protection of flowing inert gas to remove the binder and plasticizer.

[0016] Step 4: Place the debinding raw ceramic blank in an atmosphere sintering furnace with a protective gas atmosphere, and perform a multi-stage heating and sintering process to form a ceramic body;

[0017] Step 5: The sintered ceramic body is heat-treated to optimize the grain boundary structure, and then cooled to obtain an aluminum nitride substrate.

[0018] Furthermore, in sub-step S12, the yttrium-containing compound is one of Y(NO3)3·6H2O or Y(CH3COO)3·4H2O, and the fluorine-containing compound is one of NH4F or HF.

[0019] Furthermore, in step two, the fluorine compound is at least one of AlF3, YF3, and CaF2, and the boride is at least one of B4C, BN, and TiB2, wherein the mass ratio of the fluorine compound to the boride is 1:0.5-1:2.

[0020] Furthermore, in step two, the planetary ball mill uses zirconia microspheres with a diameter of 0.1 mm to 0.5 mm as the grinding medium, and ball mills at a speed of 300 r / min to 500 r / min for 10 to 30 hours. The D50 particle size of the slurry after ball milling is 0.2 μm to 0.4 μm.

[0021] Furthermore, in step four, the multi-stage heating and sintering process includes:

[0022] During the low-temperature activation stage, the green ceramic blanks in the atmosphere sintering furnace are heated to 800℃-1000℃ at a rate of 3℃ / min-5℃ / min under a nitrogen atmosphere and held at that temperature for 0.5 hours-2 hours.

[0023] During the intermediate-temperature densification stage, the temperature is continued to rise to 1500℃-1650℃ at a rate of 8℃ / min-12℃ / min under a nitrogen atmosphere, and then held for 1 hour-4 hours.

[0024] During the high-temperature purification stage, the atmosphere inside the atmosphere sintering furnace is switched to a nitrogen-hydrogen mixture containing 1 vol%-5 vol% hydrogen, and the temperature is increased to 1750℃-1850℃ at a rate of 5℃ / min-8℃ / min, and held for 2-5 hours.

[0025] Furthermore, during the intermediate-temperature densification stage, a uniaxial mechanical pressure of 5MPa-20MPa is applied to the green ceramic blank to perform gas pressure sintering or hot pressure sintering.

[0026] Furthermore, the specific heat treatment process in step five is as follows: under vacuum or nitrogen atmosphere, the ceramic body is cooled to 1100℃-1300℃ at a rate of 2℃ / min-4℃ / min and held at that temperature for 1 hour-3 hours, and then cooled to room temperature in an atmosphere sintering furnace.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] The method for preparing this high-strength aluminum nitride substrate completely avoids the technical path of generating aluminate grain boundary phases due to the use of Y2O3 by employing a non-oxygen composite sintering aid. This non-oxygen aid system promotes densification without introducing strong phonon scattering centers, thereby significantly reducing lattice thermal resistance and improving the mechanical strength of the aluminum nitride substrate.

[0029] By modifying the surface of aluminum nitride powder with fluorine compounds, the alumina layer on the powder surface is actively removed or transformed before sintering. This not only reduces the initial oxygen content of the entire system, laying the foundation for obtaining high thermal conductivity, but also the in-situ generated YF3 modified layer itself is a highly efficient sintering aid, achieving uniform distribution of the aid at the nanoscale, avoiding local enrichment, and improving sintering activity. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] A method for preparing a high-strength aluminum nitride substrate includes the following steps:

[0033] Step 1: Preparation of modified aluminum nitride powder, wherein the preparation method of modified aluminum nitride powder is as follows:

[0034] Aluminum nitride powder with a particle size of 2 μm is dispersed in a solvent to form a suspension with a solid content of 20 wt%-40 wt%; wherein, the preferred solid content is a suspension with 40 wt%, and the solvent can be anhydrous ethanol or deionized water, preferably anhydrous ethanol;

[0035] Then, a mixed solution containing yttrium and fluorine compounds is added to the suspension, wherein the molar ratio of yttrium to fluorine in the mixed solution is 1:1.5-1:3, and the mixture is stirred at 60℃-80℃ for 2-4 hours to carry out a surface reaction; preferably, the molar ratio of yttrium to fluorine in the mixed solution is 1:2, and the mixture is stirred at 70℃ for 3 hours to carry out a surface reaction.

[0036] Finally, the solid material in the reaction mixture is filtered, washed and dried, and the dried solid material is heat-treated in an atmosphere sintering furnace at 400℃-600℃ under an inert atmosphere for 1-3 hours to obtain modified aluminum nitride powder; preferably, the dried solid material is heat-treated in an atmosphere sintering furnace at 500℃ under a nitrogen atmosphere for 2 hours to obtain modified aluminum nitride powder.

[0037] In this scheme, the yttrium-containing compound is one of Y(NO3)3·6H2O or Y(CH3COO)3·4H2O, preferably Y(NO3)3·6H2O, and the fluorine-containing compound is one of NH4F or HF, preferably NH4F.

[0038] Step 2: Using modified aluminum nitride powder as the main raw material, a non-oxygen composite sintering aid composed of fluorine compounds and borides is added to obtain a mixture. The amount of composite sintering aid added is 0.5wt%-5wt% of the total mass of modified aluminum nitride powder; preferably, the amount of composite sintering aid added is 3wt% of the total mass of modified aluminum nitride powder. The mixture, binder (such as cyclohexanone and anhydrous ethanol mixed at a mass ratio of 3:1), and dispersant (such as phosphate ester or amine dispersant, added at 2wt% of the total mass of the mixture) are placed in a planetary ball mill with zirconia microspheres of 0.1mm-0.5mm in diameter as the grinding medium and ball-milled at a speed of 300r / min-500r / min for 10-30 hours. The D50 particle size of the slurry after ball milling is controlled to be 0.2μm-0.4μm to obtain a uniform slurry with a solid content of 50wt%-65wt%. The viscosity of the slurry is controlled between 500 mPa·s and 1500 mPa·s to meet the requirements of casting molding. The fluorine compound is at least one selected from AlF3, YF3, and CaF2. In this design, the fluorine compound is preferably AlF3, and the boride is at least one selected from B4C, BN, and TiB2, preferably B4C. The mass ratio of the fluorine compound to the boride is 1:0.5-1:2; preferably, the mass ratio is 1:2.

[0039] Step 3: The slurry is cast into a green ceramic blank, and then debinding is performed under the protection of flowing nitrogen gas to remove the binder and plasticizer. The debinding process adopts a stepped heating regime: the temperature is increased from room temperature to 200℃ at 2℃ / min and held for 1 hour, then increased to 400℃ at 1℃ / min and held for 2 hours, and finally increased to 600℃ at 3℃ / min and held for 3 hours. This ensures that the binder and plasticizer are fully decomposed and volatilized, and avoids cracking or deformation of the green ceramic blank due to internal stress concentration.

[0040] Step 4: Place the debinding raw ceramic blank in an atmosphere sintering furnace with a protective gas atmosphere, and perform a multi-stage heating and sintering process to form a ceramic body;

[0041] Multi-stage sintering includes a low-temperature activation stage, a medium-temperature densification stage, and a high-temperature purification stage, specifically:

[0042] In the low-temperature activation stage, the green ceramic blank in the atmosphere sintering furnace is heated to 800℃-1000℃ in a nitrogen atmosphere at a rate of 3℃ / min-5℃ / min and held for 0.5 hours-2 hours; preferably, it is heated to 900℃ at a rate of 4℃ / min and held for 2 hours.

[0043] During the intermediate-temperature densification stage, the temperature is further increased to 1500℃-1650℃ at a rate of 8℃ / min-12℃ / min under a nitrogen atmosphere, and held for 1 hour-4 hours; preferably, the temperature is increased to 1550℃ at a rate of 10℃ / min and held for 3 hours.

[0044] During the high-temperature purification stage, the atmosphere inside the atmosphere sintering furnace needs to be switched to a nitrogen-hydrogen mixture containing 1 vol%-5 vol% hydrogen, and the temperature is increased to 1750℃-1850℃ at a rate of 5℃ / min-8℃ / min, and held for 2-5 hours; preferably, the atmosphere inside the atmosphere sintering furnace is switched to a nitrogen-hydrogen mixture containing 5 vol% hydrogen, and the temperature is increased to 1800℃ at a rate of 8℃ / min, and held for 4 hours.

[0045] In addition, during the intermediate-temperature densification stage, a uniaxial mechanical pressure of 5MPa-20MPa is applied to the green ceramic blank for hot pressing sintering; preferably, a uniaxial mechanical pressure of 15MPa is applied to the green ceramic blank for hot pressing sintering to promote particle rearrangement and grain boundary migration, thereby increasing density.

[0046] Step 5: The sintered ceramic body is heat-treated to optimize the grain boundary structure, and then cooled to obtain an aluminum nitride substrate.

[0047] The specific heat treatment process involves cooling the ceramic body to 1100℃-1300℃ at a rate of 2℃ / min-4℃ / min under a nitrogen atmosphere, and holding it at that temperature for 1 hour-3 hours. This process ensures uniform distribution of the second phase at the grain boundaries and inhibits abnormal grain growth. The ceramic body is then cooled to room temperature in a nitrogen atmosphere sintering furnace to obtain an aluminum nitride substrate. Preferably, the ceramic body is cooled to 1200℃ at a rate of 3℃ / min and held at that temperature for 2 hours to obtain the aluminum nitride substrate.

[0048] Example 2

[0049] Unlike Example 1, step one in Example 1 is omitted, and the modified aluminum nitride powder is replaced with aluminum nitride powder with a particle size of 2μm. The remaining implementation steps are the same as in Example 1, and finally an aluminum nitride substrate is obtained.

[0050] Example 3

[0051] Unlike Example 1, step 2 in Example 1 is omitted, and the non-oxygen composite sintering aid composed of AlF3 and B4C is replaced with conventional Y2O3. The remaining implementation steps are the same as in Example 1, and finally an aluminum nitride substrate is obtained.

[0052] Example 4

[0053] Unlike Example 1, in the sintering process of step four, multi-stage heating sintering is adopted, but the hot pressing sintering process is removed. The remaining implementation steps are the same as in Example 1, and finally an aluminum nitride substrate is obtained.

[0054] Example 5

[0055] Unlike Example 1, in step four, the atmosphere inside the sintering furnace during the high-temperature purification stage is set to nitrogen. The remaining implementation steps are the same as in Example 1, and finally, an aluminum nitride substrate is obtained.

[0056] Comparative Example 1

[0057] Unlike Example 3, in the sintering process of step 4, a conventional single-step sintering process is adopted (heated to 1800°C in one step, held for 4 hours, and then cooled to room temperature). The remaining implementation steps are the same as in Example 3, and finally an aluminum nitride substrate is obtained.

[0058] Comparative Example 2

[0059] Unlike Example 1, in the sintering process of step four, a conventional single-step sintering process is used, while the remaining implementation steps are the same as in Example 1, and finally an aluminum nitride substrate is obtained.

[0060] Comparative Example 3

[0061] Unlike Example 1, in the sintering process of step four, a conventional single-step sintering process is used, and the modified aluminum nitride powder is replaced with aluminum nitride powder with a particle size of 2μm. The remaining implementation steps are the same as in Example 1, and finally an aluminum nitride substrate is obtained.

[0062] The aluminum nitride substrates obtained in each embodiment and comparative example were cut into ten 120mm × 120mm squares. The relative density, average grain size, three-point bending strength, thermal conductivity, grain boundary oxygen content, dielectric constant, and breakdown strength were all tested according to GB / T 1409 and GB / T 1408.1, respectively, according to GB / T 25995, GB / T 31566, GB / T 6569, GB / T 5598, GB / T 5598, GB / T 1408.1, GB / T 1409, and GB / T 1408.1, respectively. The data are shown in Table 1, where each data point in Table 1 represents the average value of the test data.

[0063] Table 1:

[0064] project Relative density (%) Average grain size (μm) Three-point bending strength (MPa) Thermal conductivity (W / m·K) Grain boundary oxygen content (at%) Dielectric constant (1MHz) Breakdown strength (kV / mm) Example 1 99.7 2.8 720 205 0.8 8.9 35 Example 2 99.4 3.5 650 195 1.5 9.0 32 Example 3 99.1 6.5 480 178 3.2 9.3 28 Example 4 99.3 3.0 680 198 0.9 9.0 33 Example 5 99.5 3.2 690 185 1.8 9.1 31 Comparative Example 1 97.5 8.0 350 160 3.8 9.5 22 Comparative Example 2 98.0 4.5 520 175 1.9 9.2 26 Comparative Example 3 96.8 5.0 400 165 2.5 9.4 24

[0065] The following conclusions can be drawn from Table 1:

[0066] Example 1 employed modified aluminum nitride powder, non-oxygen composite sintering aid (AlF3+B4C), and all core technologies of multi-stage hot pressing sintering, achieving optimal comprehensive performance. Its flexural strength of 720 MPa and thermal conductivity of 205 W / (m·K) reached extremely high levels, while also exhibiting the lowest grain boundary oxygen content and the highest breakdown strength, demonstrating the superior effectiveness of this scheme in microstructure control, grain boundary purification, and defect elimination.

[0067] Compared with Example 2, which used unmodified raw powder, Example 1 showed significant improvements in strength, thermal conductivity and grain boundary purity. This indicates that the surface YF3 modified layer effectively reduced the initial oxygen content and provided more uniform and active sintering kinetics in the early stage of sintering.

[0068] In Example 3 using conventional Y2O3, the formation of a grain boundary glass phase resulted in coarse grains, and the strength (480 MPa) and thermal conductivity (178 W / (m·K)) were significantly inferior to those in Example 1.

[0069] As can be seen from Example 4, hot pressing further eliminates porosity by applying mechanical pressure, allowing the density and strength of Example 1 to reach their peak.

[0070] Example 5 uses pure nitrogen in the high-temperature range, and its thermal conductivity and grain boundary purity are significantly lower than those in Example 1. This demonstrates the irreplaceable role of the reducing atmosphere of a nitrogen-hydrogen mixture in removing oxygen impurities and purifying grain boundaries at high temperatures.

[0071] Comparative Examples 1, 2, and 3 show that all comparative examples using single-step sintering exhibit performance inferior to their counterparts using multi-stage sintering. In particular, Comparative Examples 2 and 3, even with the use of innovative modified aluminum nitride powder and oxygen-free composite sintering aids, show limited performance improvement due to the crude sintering process. This strongly demonstrates that the multi-stage activation sintering process of this invention is key to achieving high performance and must be used in conjunction with specific modified aluminum nitride powder and oxygen-free composite sintering aids to maximize its effectiveness.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-strength aluminum nitride substrate, characterized in that, Includes the following steps: Step 1: Preparation of modified aluminum nitride powder, including the following sub-steps: S11. Disperse aluminum nitride powder in anhydrous ethanol or deionized water to form a suspension with a solid content of 20wt%-40wt%. S12. Add a mixed solution of yttrium-containing compound and fluorine-containing compound to the suspension. The molar ratio of yttrium to fluorine in the mixed solution is 1:1.5-1:

3. Stir at 60℃-80℃ for 2-4 hours to carry out the surface reaction. S13. The solid material in the mixed solution after reaction is filtered, washed and dried. Then the dried solid material is heat-treated in an atmosphere sintering furnace at 400℃-600℃ for 1 hour-3 hours under an inert atmosphere to obtain modified aluminum nitride powder. Step 2: Using modified aluminum nitride powder as the main raw material, add a non-oxygen composite sintering aid composed of fluorine compounds and borides to obtain a mixture; wherein, the amount of composite sintering aid added is 0.5wt%-5wt% of the total mass of modified aluminum nitride powder. The mixture is then mixed with binder, plasticizer, and dispersant in a planetary ball mill to obtain a uniform slurry. Step 3: The slurry is cast into a green ceramic blank, and then debinding is performed under the protection of flowing inert gas to remove the binder and plasticizer. Step 4: Place the debinding raw ceramic blank in an atmosphere sintering furnace with a protective gas atmosphere, and perform a multi-stage heating and sintering process to form a ceramic body; Step 5: The sintered ceramic body is heat-treated to optimize the grain boundary structure, and then cooled 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 sub-step S12, the yttrium-containing compound is one of Y(NO3)3·6H2O or Y(CH3COO)3·4H2O, and the fluorine-containing compound is one of NH4F or HF.

3. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, In step two, the fluorine compound is at least one of AlF3, YF3, and CaF2, and the boride is at least one of B4C, BN, and TiB2, wherein the mass ratio of the fluorine compound to the boride is 1:0.5-1:

2.

4. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, In step two, the planetary ball mill uses zirconia microspheres with a diameter of 0.1 mm to 0.5 mm as the grinding medium and ball mills at a speed of 300 r / min to 500 r / min for 10 to 30 hours. The D50 particle size of the slurry after ball milling is 0.2 μm to 0.4 μm.

5. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, In step four, the multi-stage heating and sintering process includes: During the low-temperature activation stage, the green ceramic blanks in the atmosphere sintering furnace are heated to 800℃-1000℃ at a rate of 3℃ / min-5℃ / min under a nitrogen atmosphere and held at that temperature for 0.5 hours-2 hours. During the intermediate-temperature densification stage, the temperature is continued to rise to 1500℃-1650℃ at a rate of 8℃ / min-12℃ / min under a nitrogen atmosphere, and then held for 1 hour-4 hours. During the high-temperature purification stage, the atmosphere inside the atmosphere sintering furnace is switched to a nitrogen-hydrogen mixture containing 1 vol%-5 vol% hydrogen, and the temperature is increased to 1750℃-1850℃ at a rate of 5℃ / min-8℃ / min, and held for 2-5 hours.

6. The method for preparing a high-strength aluminum nitride substrate according to claim 5, characterized in that, During the intermediate-temperature densification stage, a uniaxial mechanical pressure of 5MPa-20MPa is applied to the green ceramic blank to perform gas pressure sintering or hot pressure sintering.

7. The method for preparing a high-strength aluminum nitride substrate according to claim 1, characterized in that, The specific heat treatment process in step five is as follows: under vacuum or nitrogen atmosphere, the ceramic body is cooled to 1100℃-1300℃ at a rate of 2℃ / min-4℃ / min and held at that temperature for 1 hour-3 hours, and then cooled to room temperature in an atmosphere sintering furnace.