A method for preparing a high-thermal-conductivity aluminum nitride substrate

Abstract

The application relates to the field of aluminum nitride ceramic substrates, and provides a preparation method of a high-thermal-conductivity aluminum nitride substrate, which solves the defects of low thermal conductivity and insufficient mechanical strength of the aluminum nitride substrate obtained by using the preparation method of the prior art. The preparation method comprises the following preparation processes: (1) raw material preparation; (2) raw material mixing; (3) flow casting; (4) aging; (5) pre-pressing treatment; (6) sintering; and (7) post-treatment.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride ceramic substrates, and more particularly to a method for preparing a high thermal conductivity aluminum nitride substrate. Background Technology

[0002] Aluminum nitride (AlN) ceramics are widely recognized as ideal materials for next-generation high-performance electronic packaging and heat dissipation substrates due to their excellent thermal conductivity (theoretically up to 320 W / (m·K)), good electrical insulation, and a coefficient of thermal expansion matching that of silicon. However, the actual thermal conductivity of commercially available products is often far lower than the theoretical value, and there is an irreconcilable contradiction between mechanical properties and thermal conductivity, which severely restricts its application in high-end power devices, high-density integration, and other fields. The fundamental reasons for the low thermal conductivity of aluminum nitride substrates are mainly twofold: intrinsic material defects and limitations in the fabrication process.

[0003] First, oxygen impurities are the most significant factor reducing the intrinsic thermal conductivity of aluminum nitride. Commercially available AlN powder readily forms an alumina layer on its surface. During sintering, oxygen atoms dissolve into the AlN lattice, becoming strong phonon scattering centers. To reduce oxygen content, the industry commonly uses rare earth oxides (such as Y₂O₃ and CaO) as sintering aids, which react to generate grain boundary phases such as yttrium aluminates to "fix" oxygen atoms. However, traditional mechanical mixing methods struggle to ensure uniform coating of the sintering aids on the AlN particle surface, resulting in insufficient oxygen fixation in localized areas and a still high residual oxygen in the lattice, limiting the improvement of thermal conductivity. Even with high-purity powder, if process control is inadequate, the thermal conductivity typically only reaches 180-220 W / (m·K). Furthermore, existing preparation processes often require high-temperature sintering, but prolonged high-temperature sintering alone can easily lead to abnormal grain growth, resulting in a grain structure with uneven size and wide distribution (e.g., some grains are much larger than 20 μm, while some areas are still fine-grained). Although increasing grain size can reduce the number of grain boundaries and improve thermal conductivity, excessively large grains and a sharp reduction in grain boundaries will significantly weaken the mechanical strength of the material. Summary of the Invention

[0004] Therefore, in view of the above problems, the present invention provides a method for preparing a high thermal conductivity aluminum nitride substrate, which solves the defects of low thermal conductivity and insufficient mechanical strength of aluminum nitride substrates obtained by the preparation methods of the prior art.

[0005] To achieve the above objectives, the present invention employs the following technical solution: a method for preparing a high thermal conductivity aluminum nitride substrate, comprising the following preparation process:

[0006] (1) Preparation of raw and auxiliary materials: Prepare the following raw and auxiliary materials: aluminum nitride powder with a purity of ≥99.99%, sintering aid Y2O3 with a purity of ≥99.99%, and anhydrous ethanol; wherein, the aluminum nitride powder is composed of 60wt%-80wt% of coarse powder with an average particle size D50 of 0.8μm-1.5μm and 20wt%-40wt% of fine powder with an average particle size D50 of 0.3μm-0.6μm;

[0007] (2) Mixing of raw and auxiliary materials: The aluminum nitride powder, Y2O3 and anhydrous ethanol are fed into a planetary ball mill at a weight ratio of 1:(0.01-0.05):(0.9-1.1) for ball milling. The grinding balls used in the ball mill are aluminum nitride grinding balls. The ball-to-material ratio is controlled at 2:1-3:1. The ball milling is carried out at a speed of 300-400 rpm for 5-8 hours to obtain a slurry. Then the slurry is spray-dried and granulated to obtain a composite powder. Then the composite powder is pre-sintered in a flowing nitrogen atmosphere at 1400℃-1550℃ for 1-2 hours.

[0008] (3) Casting: Add binder, plasticizer and solvent to the powder after pre-sintering treatment in step (2), and obtain casting slurry after high-speed stirring and vacuum degassing. Then send it to the casting machine for casting to obtain green body.

[0009] (4) Place the green body obtained in step (3) in an environment with a temperature of 23℃-28℃ and a humidity of 45-55% for 48h-72h;

[0010] (5) Pre-flattening treatment: The green billet is flattened under a pressure of 5MPa-15MPa for 10min-30min;

[0011] (6) Sintering: After the green blanks processed in step (5) are punched, stacked and debinded, they are placed in a graphite furnace protected by nitrogen with a purity of more than 99.999% for sintering. When stacking, isolation powder is used to separate the two adjacent green blanks. During sintering, the temperature is raised to 1880℃-1920℃ at a rate of 5℃ / min-10℃ / min and held at this temperature for 15h-20h, and then cooled with the furnace.

[0012] (7) Post-processing: Double-sided grinding and polishing to remove the isolation powder and obtain a high thermal conductivity aluminum nitride substrate.

[0013] Furthermore: the binder is polyvinyl butyral, the plasticizer is polyethylene glycol, and the solvent is anhydrous ethanol.

[0014] Furthermore, the separating powder is α-Al2O3 powder with a particle size of 1μm-3μm.

[0015] Further: Step (5) pre-flattening treatment is carried out in an environment 10°C-20°C lower than the glass transition temperature of the adhesive.

[0016] Further: In step (6), the specific process of descaling is as follows: the temperature is increased from room temperature to 300℃ at 0.5℃ / min; then increased to 500℃ at 0.2℃ / min, and kept at 400℃ and 500℃ for 2 hours respectively; finally, the temperature is increased to 650℃ at 1℃ / min and kept at 2 hours.

[0017] Further: The sintering process in step (6) adopts a two-step gradient sintering method: first, the temperature is rapidly increased to 1920℃-1950℃ at a rate of 15℃ / min-20℃ / min, and then the temperature is reduced to 1850℃-1880℃ and held at this temperature for 12h-24h.

[0018] Furthermore, after step (7), an annealing process is performed in a flowing nitrogen atmosphere at a temperature of 1550℃-1700℃ for 2-4 hours.

[0019] Furthermore: the amount of the binder is 3%-5% of the weight of the composite powder, the amount of the plasticizer is 1%-2% of the weight of the composite powder, and the amount of the solvent is 40%-60% of the weight of the composite powder.

[0020] By adopting the aforementioned technical solution, the beneficial effects of the present invention are as follows:

[0021] 1. The method for preparing the high thermal conductivity aluminum nitride substrate of this application uses aluminum nitride powder of two types with coarse and fine particle sizes as the main raw material. The fine powder can effectively fill the gaps between the coarse powder, improve the packing density and sintering activity of the green blank, and combined with the subsequent pre-sintering treatment, Y2O3 reacts with surface Al2O3 in advance to generate a uniform grain boundary phase precursor, which avoids the local enrichment of the second phase during the sintering process from the source, and lays the foundation for the high thermal conductivity of the aluminum nitride substrate.

[0022] 2. In the raw material mixing and pre-sintering steps, ball milling achieves uniform dispersion and coating of Y2O3. Subsequent spray drying granulation and pre-sintering treatments enable Y2O3 to undergo a sufficient solid-state reaction with the Al2O3 on the surface of AlN powder, forming a uniformly distributed grain boundary phase precursor. This avoids the migration and local enrichment of Y2O3 during the final high-temperature sintering, promoting the formation of a uniform grain boundary structure from the source.

[0023] 3. Aging and pre-pressing treatment can fully release the internal stress generated during the casting process and eliminate the curling and deformation of the green blank, resulting in a green body with high flatness and low internal stress. This reduces the risk of cracking and warping during the subsequent sintering process and improves the product qualification rate.

[0024] 4. The sintering process adopts a two-step gradient sintering method. The first step is ultra-high temperature instantaneous treatment to achieve rapid densification and suppress the initial abnormal growth of grains. The second step is precise cooling to the optimal grain growth window and holding at that temperature for a long time to drive uniform migration of grain boundaries, thereby obtaining a large-size, highly uniform grain structure.

[0025] 5. By using the preparation method of this application, the aluminum nitride substrate obtained has a thermal conductivity of 250 W / (m·K) or higher and a bending strength of 380 MPa or higher. Attached Figure Description

[0026] Figure 1 This is a SEM image of the high thermal conductivity aluminum nitride substrate product obtained by the preparation method of Embodiment 1 of the present invention.

[0027] Figure 2 The image shows a scanning electron microscope (SEM) image of an aluminum nitride substrate prepared by the method in Comparative Example 1. Detailed Implementation Example 1

[0028] A method for preparing a high thermal conductivity aluminum nitride substrate includes the following preparation process:

[0029] (1) Preparation of raw and auxiliary materials: Prepare the following raw and auxiliary materials: aluminum nitride powder with a purity of 99.99%, sintering aid Y2O3 with a purity of 99.99%, and anhydrous ethanol; wherein, the aluminum nitride powder is composed of 60wt% coarse powder with an average particle size D50 of 0.8μm and 40wt% fine powder with an average particle size D50 of 0.3μm;

[0030] (2) Mixing of raw and auxiliary materials: The aluminum nitride powder, Y2O3 and anhydrous ethanol are fed into a planetary ball mill at a weight ratio of 1:0.01:0.9 for ball milling. The grinding balls used in the ball mill are aluminum nitride grinding balls. The ball-to-material ratio is controlled at 2:1. The ball milling is carried out at a speed of 300 rpm for 5 hours to obtain a slurry. Then the slurry is spray-dried and granulated to obtain a composite powder. Then the composite powder is pre-sintered at 1400℃ for 1 hour in a flowing nitrogen atmosphere.

[0031] (3) Casting: Add 3% polyvinyl butyral, 2% polyethylene glycol and 40% anhydrous ethanol by weight of the powder to the powder after pre-sintering treatment in step (2). After high-speed stirring and vacuum degassing, a casting slurry is obtained and sent to a casting machine for casting to obtain a green body.

[0032] (4) The green body obtained in step (3) is aged for 48 hours in an environment with a temperature of 23°C and a humidity of 45%;

[0033] (5) Pre-flattening treatment: The green blank is flattened for 10 minutes under a pressure of 5 MPa and a temperature 10°C lower than the glass transition temperature of the binder;

[0034] (6) Sintering: After the green blanks processed in step (5) are punched, stacked and debinded, they are placed in a graphite furnace protected by nitrogen with a purity of 99.9999% for sintering. When stacking, α-Al2O3 powder with a diameter of 1μm is used to separate the two adjacent green blanks. During sintering, the temperature is raised to 1880℃ at a rate of 5℃ / min and held at this temperature for 15h, and then cooled with the furnace.

[0035] The specific process of the glue removal treatment is as follows: the temperature is increased from room temperature to 300℃ at a rate of 0.5℃ / min; then increased to 500℃ at a rate of 0.2℃ / min, and held at 400℃ and 500℃ for 2 hours respectively; finally, the temperature is increased to 650℃ at a rate of 1℃ / min and held for 2 hours.

[0036] The sintering process adopts a two-step gradient sintering method: first, the temperature is rapidly increased to 1920℃ at a rate of 15℃ / min, then cooled to 1850℃, and held at this temperature for 12 hours.

[0037] (7) Post-processing: Double-sided grinding and polishing to remove the isolation powder and obtain a high thermal conductivity aluminum nitride substrate.

[0038] (8) Annealing treatment: Annealing is carried out in a flowing nitrogen atmosphere at a temperature of 1550℃ for 2 hours.

[0039] Depend on Figure 1 As can be seen, the product in this embodiment has a large grain size, and the grains are tightly bonded together without obvious pores. Example 2

[0040] A method for preparing a high thermal conductivity aluminum nitride substrate includes the following preparation process:

[0041] (1) Preparation of raw and auxiliary materials: Prepare the following raw and auxiliary materials: aluminum nitride powder with a purity of 99.994%, sintering aid Y2O3 with a purity of 99.995%, and anhydrous ethanol; wherein, the aluminum nitride powder is composed of 70wt% coarse powder with an average particle size D50 of 1.2μm and 30wt% fine powder with an average particle size D50 of 0.45μm;

[0042] (2) Mixing of raw and auxiliary materials: The aluminum nitride powder, Y2O3 and anhydrous ethanol are fed into a planetary ball mill at a weight ratio of 1:0.03:1.0 for ball milling. The grinding balls used in the ball mill are aluminum nitride grinding balls. The ball-to-material ratio is controlled at 2.5:1. The ball milling is carried out at a speed of 350 rpm for 6.5 h to obtain a slurry. Then the slurry is spray-dried and granulated to obtain a composite powder. Then the composite powder is pre-sintered at 1475℃ for 1.5 h in a flowing nitrogen atmosphere.

[0043] (3) Casting: Add 4% polyvinyl butyral, 1.5% polyethylene glycol and 50% anhydrous ethanol by weight of the powder to the powder after pre-sintering treatment in step (2). After high-speed stirring and vacuum degassing, a casting slurry is obtained and sent to a casting machine for casting to obtain a green body.

[0044] (4) Place the green body obtained in step (3) in an environment with a temperature of 25℃ and a humidity of 50% for 60 hours;

[0045] (5) Pre-flattening treatment: The green body is flattened for 20 minutes under a pressure of 10 MPa and a temperature 15°C lower than the glass transition temperature of the binder;

[0046] (6) Sintering: After the green blanks processed in step (5) are punched, stacked and debinded, they are placed in a graphite furnace protected by nitrogen with a purity of 99.9995% for sintering. When stacking, α-Al2O3 powder with a particle size of 2μm is used to separate the two adjacent green blanks. During sintering, the temperature is raised to 1900℃ at a rate of 8℃ / min and held at this temperature for 18h, and then cooled with the furnace.

[0047] The specific process of the glue removal treatment is as follows: the temperature is increased from room temperature to 300℃ at a rate of 0.5℃ / min; then increased to 500℃ at a rate of 0.2℃ / min, and held at 400℃ and 500℃ for 2 hours respectively; finally, the temperature is increased to 650℃ at a rate of 1℃ / min and held for 2 hours.

[0048] The sintering process adopts a two-step gradient sintering method: first, the temperature is rapidly increased to 1935℃ at a rate of 18℃ / min, then cooled to 1865℃, and held at this temperature for 18 hours.

[0049] (7) Post-processing: Double-sided grinding and polishing to remove the isolation powder and obtain a high thermal conductivity aluminum nitride substrate.

[0050] (8) Annealing treatment: Annealing is carried out in a flowing nitrogen atmosphere at a temperature of 1625℃ for 3 hours. Example 3

[0051] A method for preparing a high thermal conductivity aluminum nitride substrate includes the following preparation process:

[0052] (1) Preparation of raw and auxiliary materials: Prepare the following raw and auxiliary materials: aluminum nitride powder with a purity of 99.999%, sintering aid Y2O3 with a purity of 99.999%, and anhydrous ethanol; wherein, the aluminum nitride powder is composed of 80wt% coarse powder with an average particle size D50 of 1.5μm and 20wt% fine powder with an average particle size D50 of 0.6μm;

[0053] (2) Mixing of raw and auxiliary materials: The aluminum nitride powder, Y2O3 and anhydrous ethanol are fed into a planetary ball mill at a weight ratio of 1:0.05:1.1 for ball milling. The grinding balls used in the ball mill are aluminum nitride grinding balls. The ball-to-material ratio is controlled at 3:1. The ball milling is carried out at a speed of 400 rpm for 8 hours to obtain a slurry. Then the slurry is spray-dried and granulated to obtain a composite powder. Then the composite powder is pre-sintered at 1550℃ for 2 hours in a flowing nitrogen atmosphere.

[0054] (3) Casting: Add 5% polyvinyl butyral, 2% polyethylene glycol and 60% anhydrous ethanol by weight of the powder to the powder after pre-sintering treatment in step (2). After high-speed stirring and vacuum degassing, a casting slurry is obtained and sent to a casting machine for casting to obtain a green body.

[0055] (4) Place the green body obtained in step (3) in an environment with a temperature of 28°C and a humidity of 55% for 72 hours;

[0056] (5) Pre-flattening treatment: The green compact is flattened for 30 minutes under a pressure of 15 MPa and a temperature 20°C lower than the glass transition temperature of the binder;

[0057] (6) Sintering: After the green blanks processed in step (5) are punched, stacked and debinded, they are placed in a graphite furnace protected by nitrogen with a purity of 99.9999% for sintering. When stacking, α-Al2O3 powder with a particle size of 3μm is used to separate the two adjacent green blanks. During sintering, the temperature is raised to 1920℃ at a rate of 10℃ / min and held at this temperature for 20h, and then cooled with the furnace.

[0058] The specific process of the glue removal treatment is as follows: the temperature is increased from room temperature to 300℃ at a rate of 0.5℃ / min; then increased to 500℃ at a rate of 0.2℃ / min, and kept at 400℃ and 500℃ for 2 hours respectively; finally, the temperature is increased to 650℃ at a rate of 1℃ / min and kept at 650℃ for 2 hours.

[0059] The sintering process adopts a two-step gradient sintering method: first, the temperature is rapidly increased to 1950℃ at a rate of 20℃ / min, then cooled to 1880℃, and held at this temperature for 24 hours;

[0060] (7) Post-processing: Double-sided grinding and polishing to remove the isolation powder and obtain a high thermal conductivity aluminum nitride substrate;

[0061] (8) Annealing treatment: Annealing is carried out in a flowing nitrogen atmosphere at a temperature of 1700℃ for 4 hours.

[0062] Comparative Example 1

[0063] Referring to Example 1, the difference between this comparative example and Example 1 is as follows: the aluminum nitride powder used in step (1) has a purity of 99.9% and an average particle size D50 of 1.0 μm; zirconium oxide grinding balls are used in step (2) ball milling, omitting the pre-sintering treatment step; dry pressing is used instead of step (3); and the binder removal in step (4) is directly performed using a single high-temperature long-time sintering mode. The specific preparation process of this comparative example is as follows:

[0064] A method for preparing an aluminum nitride substrate includes the following preparation process:

[0065] (1) Preparation of raw materials and auxiliary materials: Prepare aluminum nitride powder with a purity of 99.9% (average particle size D50 is 1.0μm), sintering aid Y2O3 with a purity of 99.9%, and anhydrous ethanol;

[0066] (2) Mixing and granulation of raw materials and auxiliary materials: The aluminum nitride powder, Y2O3 and anhydrous ethanol are fed into a ball mill at a weight ratio of 1:0.03:1.0. Zirconia grinding balls are used with a ball-to-material ratio of 2:1. The mixture is ball-milled at 300 rpm for 4 hours to obtain a slurry. The slurry is then spray-dried and granulated to obtain a composite powder.

[0067] (3) Dry pressing: The composite powder obtained in step (2) is dry pressed at a pressure of 100 MPa to obtain a green blank;

[0068] (4) Debinding and sintering: The green blank is placed in an air atmosphere furnace and heated to 600°C at 1°C / min and held for 2 hours to remove the binder; then the debinded green blank is placed in a graphite furnace protected by ordinary nitrogen (purity 99.9%), heated to 1900°C at 5°C / min and held at this temperature for 20 hours, and then cooled with the furnace.

[0069] (5) Post-processing: The sintered body is ground and polished on both sides to obtain an aluminum nitride substrate.

[0070] The tests showed that the thermal conductivity of the aluminum nitride substrates in Examples 1 to 3 was above 250 W / (m·k), and the bending strength was above 380 MPa.

[0071] Depend on Figure 2 It can be seen that the grain size of Comparative Example 1 is relatively small but uniform and dense, but the small grain size limits the upper limit of its thermal conductivity.

[0072] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A method for preparing a high thermal conductivity aluminum nitride substrate, characterized in that, The preparation process includes the following: (1) Preparation of raw and auxiliary materials: Prepare the following raw and auxiliary materials: aluminum nitride powder with a purity of ≥99.99%, sintering aid Y2O3 with a purity of ≥99.99%, and anhydrous ethanol; wherein, the aluminum nitride powder is composed of 60wt%-80wt% of coarse powder with an average particle size D50 of 0.8μm-1.5μm and 20wt%-40wt% of fine powder with an average particle size D50 of 0.3μm-0.6μm; (2) Mixing of raw and auxiliary materials: The aluminum nitride powder, Y2O3 and anhydrous ethanol are fed into a planetary ball mill at a weight ratio of 1:(0.01-0.05):(0.9-1.1) for ball milling. The grinding balls used in the ball mill are aluminum nitride grinding balls. The ball-to-material ratio is controlled at 2:1-3:

1. The ball milling is carried out at a speed of 300rpm-400rpm for 5h-8h to obtain a slurry. Then the slurry is spray-dried and granulated to obtain a composite powder. Then the composite powder is pre-sintered at 1400℃-1550℃ for 1h-2h in a flowing nitrogen atmosphere. (3) Casting: Add binder, plasticizer and solvent to the powder after pre-sintering treatment in step (2), and obtain casting slurry after high-speed stirring and vacuum degassing. Then send it to the casting machine for casting to obtain green body. (4) Place the green body obtained in step (3) in an environment with a temperature of 23℃-28℃ and a humidity of 45%-55% for 48h-72h; (5) Pre-pressing treatment: Press the aged green billet flat under a pressure of 5MPa-15MPa for 10min-30min; (6) Sintering: After the green blanks processed in step (5) are punched, stacked and debinded, they are placed in a graphite furnace protected by nitrogen with a purity of more than 99.999% for sintering. When stacking, isolation powder is used to separate the two adjacent green blanks. During sintering, the temperature is first rapidly increased to 1920℃-1950℃ at a rate of 15℃ / min-20℃ / min, and then cooled to 1850℃-1880℃. The temperature is then maintained at this temperature for 12h-24h, and then cooled with the furnace. (7) Post-processing: Double-sided grinding and polishing to remove the isolation powder and obtain a high thermal conductivity aluminum nitride substrate.

2. The method for preparing a high thermal conductivity aluminum nitride substrate according to claim 1, characterized in that: The plasticizer is polyethylene glycol, and the solvent is anhydrous ethanol.

3. The method for preparing a high thermal conductivity aluminum nitride substrate according to claim 1, characterized in that: The separating powder is α-Al2O3 powder with a particle size of 1μm-3μm.

4. The method for preparing a high thermal conductivity aluminum nitride substrate according to claim 1, characterized in that: Step (5) Pre-flattening treatment is carried out in an environment 10°C-20°C below the glass transition temperature of the adhesive.

5. The method for preparing a high thermal conductivity aluminum nitride substrate according to claim 1, characterized in that: In step (6), the specific process of desizing is as follows: the temperature is increased from room temperature to 300℃ at 0.5℃ / min; then increased to 500℃ at 0.2℃ / min, and kept at 400℃ and 500℃ for 2 hours respectively; finally, the temperature is increased to 650℃ at 1℃ / min and kept at 2 hours.

6. The method for preparing a high thermal conductivity aluminum nitride substrate according to claim 1, characterized in that: After step (7), an annealing process is performed in a flowing nitrogen atmosphere at a temperature of 1550℃-1700℃ for 2-4 hours.

7. The method for preparing a high thermal conductivity aluminum nitride substrate according to claim 1, characterized in that: The amount of the binder is 3%-5% of the weight of the composite powder, the amount of the plasticizer is 1%-2% of the weight of the composite powder, and the amount of the solvent is 40%-60% of the weight of the composite powder.

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