Ceramic substrate, method for manufacturing the same, and use thereof

Abstract

The application relates to the field of electronic devices, in particular to a ceramic substrate and a preparation method and application thereof. The preparation method of the ceramic substrate comprises the following steps: performing casting treatment on casting slurry, drying, heat pressing treatment, vacuumizing treatment, warm isostatic pressing treatment, defatting and sintering; wherein the casting slurry comprises alpha-Si3N4, beta-Si3N4 crystal seeds, boron nitride nanotubes, sintering aids, a binder and a plasticizer. The preparation method of the ceramic substrate realizes accurate regulation and control of the microstructure of silicon nitride ceramics, and simultaneously solves the industry problem that high thermal conductivity and high toughness are difficult to be simultaneously achieved.

Description

Technical Field

[0001] This invention relates to the field of electronic devices, and more specifically, to a ceramic substrate, its preparation method, and its application. Background Technology

[0002] With the rapid development of aerospace, intelligent vehicles and other fields, power module chips are also developing towards miniaturization, high voltage, high current and high power density. This poses a great challenge to the assembly and packaging materials of components, especially the brittle ceramic substrates that provide electrical insulation and heat dissipation. Commonly used ceramic substrate materials include Al2O3, AlN, Si3N4, SiC, BN and others.

[0003] Al₂O₃ is currently the most widely used ceramic substrate material. It boasts good mechanical strength, mature processing, and a significant cost advantage, making it the most cost-effective choice. However, Al₂O₃ has low thermal conductivity; even 99% pure alumina only has a thermal conductivity of 24-30 W / (m·K), limiting its application in high-power-density devices (such as high-power IGBTs and lasers). AlN, on the other hand, has a high theoretical thermal conductivity, with actual products reaching 170-200 W / (m·K), enabling highly efficient heat dissipation from the chip and lowering the junction temperature. AlN exhibits low fracture toughness and poor resistance to mechanical and thermal shock, making it prone to cracking during processing and use. Furthermore, its high sintering temperature (around 1900℃) and tendency to form aluminate in water limit its applications. While BN possesses good overall performance, its high cost as a substrate material limits its application to research and promotion. SiC boasts high strength and thermal conductivity, but its low electrical resistance and dielectric constant, coupled with a high dielectric constant, make it unsuitable as a substrate material. BeO's use is restricted due to the toxicity of its raw material powder. In contrast, Si3N4 is a high-performance material that has rapidly developed in recent years to address the heat dissipation and reliability issues of high-power devices. By adjusting the composition ratio of sintering aids, controlling sintering time, and adding a second phase, silicon nitride ceramics with bending strength several times that of AlN can be obtained. Its potential high thermal conductivity and excellent mechanical properties make silicon nitride considered the most popular semiconductor ceramic substrate packaging material today.

[0004] As electronic devices evolve towards higher voltage, higher current, and higher power density, they generate significant heat during operation. Increased junction temperature leads to a greater on-state voltage drop in IGBTs, resulting in increased losses and heat generation, creating a vicious cycle of "heating → performance degradation → even more heat generation," potentially triggering overheat protection or causing hard breakdown. Si3N4 has a high theoretical thermal conductivity, reaching 200–300 W / (m·K) depending on the crystal phase and crystal axis orientation. However, the thermal conductivity of commercially available high-thermal-conductivity silicon nitride ceramic substrates is generally only 80–90 W / (m·K), significantly lower than the theoretical value. Improving the thermal conductivity of silicon nitride substrates is crucial to ensuring the stable, reliable, and long-term operation of high-power electronic devices (such as IGBTs and SiC chips in new energy vehicles and 5G communications) under high loads.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] This invention aims to provide a ceramic substrate, its preparation method, and its application. The method involves adding β-Si3N4 seed crystals and boron nitride nanotubes, and extending the sintering time. This significantly reduces the lattice oxygen content and improves the flexural strength of silicon nitride ceramics during the sintering process. The prepared ceramic substrate has high thermal conductivity, high strength, and high toughness.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: One aspect of the present invention relates to a method for preparing a ceramic substrate, comprising the following steps: The cast slurry undergoes casting treatment, drying, hot pressing treatment, vacuum treatment, warm isostatic pressing treatment, degreasing and sintering; The casting slurry includes: α-Si3N4 and β-Si3N4 seed crystals, boron nitride nanotubes, sintering aids, binders, and plasticizers.

[0008] The method for preparing the ceramic substrate described above enables precise control over the microstructure of silicon nitride ceramics, and simultaneously solves the industry problem of balancing high thermal conductivity and high strength and toughness.

[0009] Another aspect of the present invention relates to a ceramic substrate prepared by the method described above.

[0010] The ceramic substrate has high thermal conductivity, high strength, and high toughness.

[0011] Another aspect of the present invention relates to an electronic device packaging structure, including the aforementioned ceramic substrate.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method for preparing the ceramic substrate provided by this invention introduces β-Si3N4 seed crystals with specific morphology as growth templates and combines them with a much longer sintering time than conventional methods to construct a bimodal structure composed of coarse long columnar grains and fine equiaxed grains in situ within the material, thereby significantly reducing phonon scattering and improving thermal conductivity. At the same time, boron nitride nanotubes (BNNTs) are introduced as a second-phase reinforcement, which effectively toughens the material through crack deflection, bridging and other mechanisms, overcoming the problem of strength reduction that may be caused by grain coarsening. This method achieves precise control of the microstructure of silicon nitride ceramics and simultaneously solves the industry problem of the difficulty in achieving both high thermal conductivity and high strength and toughness.

[0013] (2) The ceramic substrate provided by this invention has a thermal conductivity of up to 110 W / (m·K), which is far higher than the general level of current commercial products. This can greatly improve the heat dissipation efficiency of high-power devices and prevent thermal failure. At the same time, its bending strength can still be maintained at a high level, and its fracture toughness is excellent, ensuring the mechanical reliability and long life of the substrate under harsh working conditions. This product has both excellent thermal and mechanical properties, making it an ideal substrate material for high-end power module packaging in fields such as new energy vehicles and 5G communications. Attached Figure Description

[0014] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0015] Figure 1 The image shows the microstructure of a ceramic substrate provided in an embodiment of the present invention. Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0017] One aspect of the present invention relates to a method for preparing a ceramic substrate, comprising the following steps: The cast slurry undergoes casting treatment, drying, hot pressing treatment, vacuum treatment, warm isostatic pressing treatment, degreasing and sintering; The casting slurry includes: α-Si3N4 and β-Si3N4 seed crystals, boron nitride nanotubes, sintering aids, binders, and plasticizers.

[0018] Silicon nitride (SiN4) primarily relies on phonon thermal conductivity. The presence of lattice defects such as vacancies and stacking faults, as well as intergranular impurities, intensifies phonon scattering, reducing the thermal conductivity of SiN4. Lattice oxygen is the most significant factor affecting the thermal conductivity of SiN4. By adding rod-shaped β-SiN4 seeds to α-SiN4 raw material powder and extending the sintering time from the traditional 5 hours to approximately 40 hours, a bimodal structure composed of fine equiaxed crystals and a small number of coarse, long columnar β-SiN4 grains was successfully formed. These coarse columnar grains act as high-speed heat conduction channels within the material; when their diameter reaches or exceeds 2 µm, their intrinsic thermal conductivity can reach as high as 175–191 W / (m·K). Heat (phonons) tend to be transported along the interior of these low-defect, coarse β-SiN4 grains. Compared to a structure composed of numerous fine grains with densely packed grain boundaries, phonon scattering is significantly reduced, resulting in a substantial improvement in heat transfer efficiency, macroscopically manifested as an increase in the material's thermal conductivity.

[0019] The bimodal structure requires a longer sintering time, allowing atoms more time to diffuse and rearrange. This helps to remove impurities (such as oxygen) or enrich them at the grain boundaries, making the crystal structure of the β-Si3N4 grains more complete and pure. It also reduces the scattering of phonons by lattice defects and improves the thermal conductivity of the silicon nitride substrate.

[0020] While the formation of a bimodal structure can significantly improve the thermal conductivity of the material, excessively developed coarse grains (long columnar β-Si3N4) may become new crack sources, leading to a decrease in fracture strength. Therefore, it is necessary to add a second phase to improve the strength of the silicon nitride substrate. This invention employs the addition of boron nitride nanotubes (BNNTs) to toughen silicon nitride. The principle is that the introduction of BNNTs can change the stress distribution at the crack tip, transferring the maximum stress at the crack tip to the nanotube itself, thereby reducing the stress concentration at the crack tip of the silicon nitride ceramic. This stress transfer acts as a shield for the crack tip, adding a barrier to the crack tip and significantly improving the resistance of the composite material to crack propagation, which macroscopically manifests as an increase in the fracture strength of the material.

[0021] When a crack appears in a silicon nitride matrix and begins to propagate, boron nitride nanotubes (BNNTs) can effectively hinder crack propagation through crack deflection and crack bridging mechanisms. When a crack encounters high-strength boron nitride nanotubes (BNNTs) during its propagation, its propagation path will be deflected and it will no longer travel in a straight line, thereby increasing the total surface area required for crack propagation and consuming more energy.

[0022] This invention provides a method for preparing silicon nitride ceramic substrates with high thermal conductivity and high toughness. By adding β-Si3N4 seeds, boron nitride nanotubes and extending the sintering time, the lattice oxygen content of silicon nitride ceramics during sintering can be significantly reduced and the bending strength can be improved, thereby preparing silicon nitride substrates with both high thermal conductivity and high strength.

[0023] Hot pressing can be performed using conventional parameters in this field.

[0024] Furthermore, the mass ratio of the α-Si3N4, the β-Si3N4 seed crystals, and the boron nitride nanotubes is 75~85:10~15:1~5, including but not limited to 75:15:1, 78:14:2, 80:12:3, 83:11:4, or 85:10:5. α-Si3N4 serves as the matrix to ensure the main body of the material. Adding a certain amount of β-Si3N4 seed crystals is sufficient to induce the formation of an effective bimodal thermal conductivity structure, while excessive amounts impair strength. Adding a certain amount of BNNTs can achieve the best toughening effect without significantly hindering thermal conductivity. The three components work synergistically to significantly improve fracture toughness while maintaining high thermal conductivity.

[0025] Furthermore, the β-Si3N4 seed crystals include rod-shaped β-Si3N4 seed crystals. The unique morphology of the rod-shaped seed crystals allows them to serve as templates during sintering, epitaxially growing coarse, long columnar β-Si3N4 grains. These grains have fewer grain boundaries and defects, providing a low-scattering path for phonon transport, thereby significantly improving the intrinsic thermal conductivity of the material.

[0026] Furthermore, the sintering temperature is 1745~1755℃, including but not limited to any one of 1745℃, 1747℃, 1749℃, 1751℃, 1753℃ or 1755℃ or any range between two of them.

[0027] Furthermore, the sintering time is 38~42h, including but not limited to any one of 38h, 39h, 40h, 41h or 42h or a range between any two.

[0028] Furthermore, the sintering pressure is 22~28MPa, including but not limited to a point value or a range between any two of 22h, 24h, 26h or 28h.

[0029] Precise control of sintering temperature and pressure ensures the stability of densification and grain growth; ultra-long sintering time promotes full atomic diffusion, which is conducive to the full growth of columnar crystals to improve thermal conductivity, and also causes oxygen impurities to agglomerate at the grain boundaries, purifying the crystal lattice, ultimately achieving high performance in synergy.

[0030] Furthermore, the casting speed of the casting process is 1~5m / min, including but not limited to the point value of any one of 1m / min, 3m / min or 5m / min or the range between any two.

[0031] Furthermore, the temperature of the isostatic pressing treatment is 65~75℃, including but not limited to any one of 65℃, 67℃, 69℃, 71℃, 73℃ or 75℃ or any range between two of them.

[0032] Furthermore, the soaking time of the isostatic pressing is 8 to 12 minutes (for example, it can be any one of 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes or any range between two), and the holding time is 8 to 12 minutes (for example, it can be any one of 8 minutes, 9 minutes, 10 minutes, 11 minutes or 12 minutes or any range between two).

[0033] Further, based on parts by weight, the cast slurry comprises: 75-85 parts of α-Si3N4 (e.g., any point value or a range between any two of 75, 78, 80, 83, or 85 parts), 10-15 parts of β-Si3N4 seed crystals (e.g., any point value or a range between any two of 10, 11, 12, 13, or 15 parts), and 1-5 parts of boron nitride nanotubes (e.g., any point value or a range between any two of 1, 2, 4, or 5 parts). The range of values ​​between), 7 to 11 parts of sintering aid (e.g., the point value or the range between any two of 7, 8, 9, 10 or 11 parts), 8 to 12 parts of binder (e.g., the point value or the range between any two of 8, 9, 10, 11 or 12 parts), and 10 to 14 parts of plasticizer (e.g., the point value or the range between any two of 10, 11, 12, 13 or 14 parts).

[0034] Furthermore, the sintering aid comprises MgO and Y2O3 in a mass ratio of 2~3:5~8 (e.g., but not limited to 2:8, 2.5:7, or 3:5). Rare earth metal ions have a high affinity for oxygen. When oxygen impurities diffuse into the grain boundary region, they react chemically with the rare earth additives to form a rare earth silicon oxide or nitrogen oxide glass phase, thereby "fixing" the oxygen at the grain boundary.

[0035] This invention does not specifically limit the type of adhesive; conventional adhesives in the art can be used to implement this invention. In some specific embodiments, the adhesive includes at least one of polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), or polyvinyl alcohol (PVA).

[0036] This invention does not specifically limit the type of plasticizer; conventional plasticizers in the art can be used to implement this invention. In some specific embodiments, the plasticizer includes at least one of dibutyl phthalate (DBP), diethyl phthalate (DEP), or dioctyl phthalate (DOP).

[0037] Furthermore, the method for preparing the cast slurry includes: The mixture of powder raw materials, solvent and dispersant is subjected to one ultrasonic dispersion and one ball milling; the ball milling allows the solvent to fully wet the powder and promotes better dispersion of the powder. The binder and plasticizer are added to the mixture after the first ball milling, followed by a second ultrasonic dispersion and a second ball milling.

[0038] Furthermore, the mass ratio of the powder raw material, the solvent, and the dispersant is 55~60:8~12:8~12, including but not limited to 55:12:8, 53:10:10, or 60:8:12.

[0039] Furthermore, the powder raw materials include: the α-Si3N4, the β-Si3N4 seed crystals, the boron nitride nanotubes, and the sintering aid.

[0040] Furthermore, the solvent includes, but is not limited to, anhydrous ethanol.

[0041] Furthermore, the dispersant includes, but is not limited to, triethyl phosphate.

[0042] Furthermore, the ball milling speed is 440~460 r / min (for example, it can be any one of 440 r / min, 445 r / min, 450 r / min, 455 r / min or 460 r / min or any range between two), and the time is 40~50 min (for example, it can be any one of 40 min, 42 min, 44 min, 46 min, 48 min or 50 min or any range between two).

[0043] Furthermore, the speed of the secondary ball milling is 440~460 r / min (for example, it can be any one of 440 r / min, 445 r / min, 450 r / min, 455 r / min or 460 r / min or any range between two), and the time is 40~50 min (for example, it can be any one of 40 min, 42 min, 44 min, 46 min, 48 min or 50 min or any range between two).

[0044] Another aspect of the present invention relates to a ceramic substrate prepared by the method described above.

[0045] The ceramic substrate described above boasts a thermal conductivity exceeding 110 W / (m·K), far surpassing the levels commonly found in current commercial products. This significantly improves the heat dissipation efficiency of high-power devices, preventing thermal failure. Simultaneously, it maintains high flexural strength and excellent fracture toughness, ensuring mechanical reliability and long lifespan under harsh operating conditions. This product combines superior thermal and mechanical properties, making it an ideal substrate material for high-end power module packaging in fields such as new energy vehicles and 5G communications.

[0046] Another aspect of the present invention relates to an electronic device packaging structure, including the aforementioned ceramic substrate.

[0047] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0048] Example 1 The method for preparing the ceramic substrate provided in this embodiment includes the following steps: S1. Weigh the raw materials and place them in a 70℃ oven for 120 minutes. The raw materials, by mass parts, include the following components: 78 parts of α-Si3N4, 10 parts of β-Si3N4 seed crystals, 9 parts of sintering aid and 3 parts of BNNTs powder; The sintering aids include: 2.6 parts MgO and 6.4 parts Y2O3; S2. Weigh the raw materials according to the mass ratio of anhydrous ethanol to silicon nitride balls = 1:2:3 and place them in a polyurethane ball mill jar. In order to make the ball milling more thorough, the silicon nitride ball gradation ratio is large balls (Φ5): medium balls (Φ3): small balls (Φ1) = 3:2:1. Use a planetary ball mill at a speed of 400 r / min for 24 hours. S3. After removing the silicon nitride balls by sieving the milled slurry through a sieve, dry it in an oven at 70°C for 8 hours. The dried block is then crushed in a mortar and passed through a 120-mesh sieve to obtain powder. S4. After ultrasonically dispersing the powder, anhydrous ethanol (organic solvent), and triethyl phosphate (dispersant) in a mass ratio of 58:10:10, place them in a polyurethane ball mill jar and ball mill them once at a speed of 450 r / min for 45 min using a planetary ball mill. S5. After adding DBP (plasticizer) and PVB (binder) to the ball mill, ultrasonic dispersion is performed. Then, the mixture is placed in a polyurethane ball mill jar and ball milled a second time at a speed of 450 r / min for 45 min. The mass ratio of α-Si3N4, DBP and PVB is 78:10:12. S6. The slurry is passed through a 400-mesh sieve to ensure complete removal of silicon nitride balls and impurities, and then placed in a vacuum degassing mixer for degassing treatment. The mixing time is 30 minutes, and finally a uniform slurry before casting is obtained (cast slurry). S7. Adjust the height of the scraper at the feed port of the casting machine to 30um, slowly pour the casting slurry into the feed port, and the casting speed is 3m / min. Under the action of the scraper, a ceramic film (the carrier film is PET film) is formed. After drying (temperature is 60℃), the organic solvent in it evaporates, and a ceramic film tape with a thickness of 40um is obtained. After cutting, the casting sheet is obtained. S8. The cut cast sheets are stacked and hot-pressed on a hot press, then transferred to a vacuum sealing bag for vacuum treatment, and then placed in a thermostatic press at a temperature of 70°C for 10 minutes and a holding time of 10 minutes. S9. Place the green blanks cut to a certain size on a corundum plate and degrease and sinter them in a high-temperature furnace. As the heating program starts (heating rate 10℃ / min), slowly increase the external pressure to 25MPa and keep it constant. When the temperature inside the furnace rises to 1750℃, do not apply additional dynamic pressure. After holding at the temperature for 40 hours, start cooling. Set the cooling rate to 8℃ / min and maintain a constant pressure of 25MPa until the furnace temperature drops to 1000℃ and unload. S10. The mechanical properties and thermal conductivity of the silicon nitride substrate after gas pressure sintering were tested. The test results are shown in Table 1.

[0049] Example 2 The difference between this embodiment and Embodiment 1 is that the amount of α-Si3N4 is 79 parts and the amount of BNNTs powder is 2 parts.

[0050] Example 3 The difference between this embodiment and Embodiment 1 is that the amount of α-Si3N4 is 80 parts and the amount of BNNTs powder is 1 part.

[0051] Example 4 The method for preparing the ceramic substrate provided in this embodiment includes the following steps: S1. Weigh the raw materials and place them in a 70℃ oven for 120 minutes. The raw materials, by mass parts, include the following components: 75 parts of α-Si3N4, 15 parts of β-Si3N4 seed crystals, 7 parts of sintering aid and 1 part of BNNTs powder; Sintering aids include: 2 parts MgO and 5 parts Y2O3; S2~S4. Same as Example 1; S5. After adding DBP (plasticizer) and PVB (binder) to the ball mill, ultrasonic dispersion is performed. Then, the mixture is placed in a polyurethane ball mill jar and ball milled a second time at a speed of 450 r / min for 45 min. The mass ratio of α-Si3N4, DBP and PVB is 75:8:10. S6~S7. Same as in Example 1; S8. The cut cast sheets are stacked and hot-pressed on a hot press, then transferred to a vacuum sealing bag for vacuum treatment, and then placed in a thermostatic press at a temperature of 65°C for 8 minutes and a holding time of 8 minutes. S9. Place the green blanks cut to a certain size on a corundum plate and degrease and sinter them in a high-temperature furnace. As the heating program starts (heating rate 10℃ / min), slowly increase the external pressure to 28MPa and keep it constant. When the temperature inside the furnace rises to 1745℃, do not apply additional dynamic pressure. After holding at the temperature for 38 hours, start cooling. Set the cooling rate to 8℃ / min and maintain a constant pressure of 28MPa until the furnace temperature drops to 1000℃ and unload. S10. Same as Example 1.

[0052] Example 5 The method for preparing the ceramic substrate provided in this embodiment includes the following steps: S1. Weigh the raw materials and place them in a 70℃ oven for 120 minutes. The raw materials, by mass parts, include the following components: 85 parts of α-Si3N4, 13 parts of β-Si3N4 seed crystals, 11 parts of sintering aid and 5 parts of BNNTs powder; Sintering aids include: 3 parts MgO and 8 parts Y2O3; S2~S4. Same as Example 1; S5. After adding DBP (plasticizer) and PVB (binder) to the ball mill, ultrasonic dispersion is performed. Then, the mixture is placed in a polyurethane ball mill jar and ball milled a second time at a speed of 450 r / min for 45 min. The mass ratio of α-Si3N4, DBP and PVB is 85:12:14. S6~S7. Same as in Example 1; S8. The cut cast sheets are stacked and hot-pressed on a hot press, then transferred to a vacuum sealing bag for vacuum treatment, and then placed in a thermostatic press at a temperature of 75°C for 12 minutes and a holding time of 12 minutes. S9. Place the green blanks cut to a certain size on a corundum plate and degrease and sinter them in a high-temperature furnace. As the heating program starts (heating rate 10℃ / min), slowly increase the external pressure to 22MPa and keep it constant. When the temperature inside the furnace rises to 1755℃, do not apply additional dynamic pressure. After holding at the temperature for 42 hours, start cooling. Set the cooling rate to 8℃ / min and maintain a constant pressure of 22MPa until the furnace temperature drops to 1000℃ and unload. S10. Same as Example 1.

[0053] Comparative Example 1 The difference between this comparative example and Example 1 is that no BNNTs were added, the amount of α-Si3N4 was 76 parts, and the amount of β-Si3N4 seed crystals was 15 parts.

[0054] Comparative Example 2 The difference between this comparative example and Example 1 is that no BNNTs were added, and the amount of α-Si3N4 used was 81 parts.

[0055] Comparative Example 3 The difference between this comparative example and Example 1 is that no BNNTs were added, and the sintering time was 20 hours.

[0056] Comparative Example 4 The difference between this comparative example and Example 1 is that no BNNTs were added, and the sintering time was 5 hours.

[0057] Comparative Example 5 The difference between this comparative example and Example 1 is that β-Si3N4 seed crystals and BNNTs were not added, and the amount of α-Si3N4 used was 91 parts.

[0058] Table 1

[0059] Figure 1 This is a microstructure morphology diagram of a ceramic substrate.

[0060] This invention creates a bimodal microstructure by adding β-Si3N4 seeds and extending the sintering time. This structure consists of fine matrix grains and exceptionally large grains (diameter greater than 2 μm). The number of internal grain boundaries in these large grains is significantly reduced, providing a longer and smoother mean free path for phonon transport, greatly reducing phonon scattering at grain boundaries, thereby improving the material's thermal conductivity. Furthermore, these large β-Si3N4 grains themselves possess high intrinsic thermal conductivity, reaching 175–191 W / (m·K).

[0061] Rare earth metal ions have a high affinity for oxygen. When oxygen impurities diffuse into the grain boundary region, they react chemically with rare earth additives to form rare earth silicon oxides or nitrogen oxide glass phases, thereby "fixing" the oxygen at the grain boundaries. This invention extends the sintering time, causing oxygen impurities in the lattice to further segregate towards the grain boundaries, thus purifying the grains themselves, reducing the concentration of lattice defects, and improving the thermal conductivity of the material.

[0062] As a nanoscale reinforcing phase, BNNTs effectively hinder crack propagation and absorb fracture energy through various physical mechanisms such as crack deflection, bridging, fiber pull-out, and stress shielding, thereby significantly improving the fracture toughness and damage resistance of materials.

[0063] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a ceramic substrate, characterized in that, Includes the following steps: The cast slurry undergoes casting treatment, drying, hot pressing treatment, vacuum treatment, warm isostatic pressing treatment, degreasing and sintering; The casting slurry includes: α-Si3N4 and β-Si3N4 seed crystals, boron nitride nanotubes, sintering aids, binders, and plasticizers.

2. The method for preparing a ceramic substrate according to claim 1, characterized in that, The mass ratio of the α-Si3N4, the β-Si3N4 seed crystals, and the boron nitride nanotubes is 75~85:10~15:1~5.

3. The method for preparing a ceramic substrate according to claim 1, characterized in that, The β-Si3N4 seed crystals include rod-shaped β-Si3N4 seed crystals.

4. The method for preparing a ceramic substrate according to claim 1, characterized in that, The sintering temperature is 1745~1755℃; And / or, the sintering time is 38~42h.

5. The method for preparing a ceramic substrate according to claim 1, characterized in that, The sintering pressure is 22~28MPa.

6. The method for preparing a ceramic substrate according to claim 1, characterized in that, The casting speed of the casting process is 1~5m / min.

7. The method for preparing a ceramic substrate according to claim 1, characterized in that, The temperature for the isostatic pressing process is 65~75℃; And / or, the soaking time for the isostatic pressing is 8-12 minutes, and the holding time is 8-12 minutes.

8. The method for preparing a ceramic substrate according to claim 2, characterized in that, The casting paste comprises, by weight parts: 75-85 parts of α-Si3N4, 10-15 parts of β-Si3N4 seed crystals, 1-5 parts of boron nitride nanotubes, 7-11 parts of sintering aid, 8-12 parts of binder and 10-14 parts of plasticizer; Preferably, the sintering aid comprises MgO and Y2O3 in a mass ratio of 2~3:5~8.

9. A ceramic substrate prepared by the method of preparing a ceramic substrate as described in any one of claims 1 to 8.

10. An electronic device packaging structure, characterized in that, Includes the ceramic substrate as described in claim 9.

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