Silicon nitride ceramic substrate, method for manufacturing the same, and use thereof

Abstract

The application provides a silicon nitride ceramic substrate and a preparation method and application thereof, and relates to the technical field of inorganic materials. Specifically, an ionic dispersant solution and a non-ionic dispersant solution are prepared by condensation reflux and stirring and heating dissolution; then the two solutions are respectively mixed with silicon nitride powder and silicon powder by twice ball milling, and the slurries obtained by the twice ball milling are mixed by third ball milling to obtain third ball milling slurry; defoaming, coating, drying, cutting, lamination and static pressing are sequentially performed to obtain a silicon nitride green body; and after degassing, the silicon nitride green body is sintered in a nitrogen atmosphere to obtain the silicon nitride ceramic substrate. The application solves the technical problems that the silicon nitride powder and the silicon powder are prone to sedimentation and stratification and uneven dispersion due to the difference in density and the difference in surface characteristics, and the co-dispersion defects of the dual-phase powder are solved by designing a composite dispersant system and combining a step-by-step ball milling process, and competition adsorption and silicon powder over-grinding are avoided.

Description

Technical Field

[0001] This invention relates to the field of inorganic materials technology, and more specifically, to a silicon nitride ceramic substrate, its preparation method, and its application. Background Technology

[0002] Silicon nitride (Si3N4) ceramics are widely used in power semiconductor modules in new energy vehicles, rail transportation, and aerospace due to their excellent thermal conductivity, mechanical strength, and thermal shock resistance. As new energy vehicles develop towards higher power density and higher reliability, the performance requirements and cost control of silicon nitride ceramic substrates face greater challenges. In the preparation of silicon nitride substrates, partially replacing silicon nitride powder with silicon powder is a promising technical approach. This doped silicon powder has at least the following advantages: 1. Low cost: the price of silicon powder is far lower than that of high-purity silicon nitride powder, significantly reducing raw material costs; 2. Low oxygen content: reducing oxygen introduction into the system and contributing to improved thermal conductivity; 3. Reactive sintering characteristics: during the nitriding process, silicon powder generates Si3N4, accompanied by volume expansion, which fills pores and increases density.

[0003] However, the casting process of mixing Si powder and Si3N4 powder faces the following key technical challenges: First, sedimentation and stratification caused by density differences, as Si powder has a density of 2.33 g / cm³. 3 ) and the density of Si3N4 powder (3.18 g / cm³) 3 The differences between the two materials are significant, leading to sedimentation and stratification in the slurry, resulting in uneven distribution of the green body components. Secondly, the differences in surface properties cause dispersion difficulties; Si powder is hydrophobic, while Si3N4 powder is hydrophilic due to the presence of a SiO2 layer. These differences in surface properties result in significant differences in their dispersion behavior in solvents, making uniform co-dispersion difficult. An existing patent (CN118754679A) discloses a method for preparing silicon nitride ceramic substrates doped with silicon powder, but it does not propose a specific solution to the slurry stability problem of the Si3N4 / Si powder two-phase system.

[0004] Therefore, developing a composite dispersant combination and stepwise process for the Si3N4 powder / Si powder two-phase system to achieve high uniformity and long-term stability of the slurry will become an urgent technical problem to be solved in this field.

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

[0006] The primary objective of this invention is to provide a method for preparing silicon nitride ceramic substrates, aiming to solve the problems of slurry sedimentation and uneven dispersion caused by the difference in density and surface properties between Si powder and Si3N4 powder in the prior art.

[0007] A second objective of this invention is to provide a silicon nitride ceramic substrate.

[0008] A third objective of this invention is to provide an application of the aforementioned silicon nitride ceramic substrate.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: A method for preparing a silicon nitride ceramic substrate includes the following steps: S1 was prepared by dissolving it through reflux and stirring, resulting in ionic and nonionic dispersant solutions, respectively. S2 involves first ball milling and mixing the ionic dispersant solution and silicon nitride powder, then second ball milling and mixing the nonionic dispersant solution and silicon powder to obtain a first ball mill slurry and a second ball mill slurry, respectively; finally, the first ball mill slurry and the second ball mill slurry are ball milled and mixed in a third ball mill to obtain a third ball mill slurry. S3 sequentially degasses, coats, dries, cuts, stacks, and presses the third ball mill slurry to obtain a silicon nitride green body; S4 After removing the binder from the silicon nitride green blank, it is sintered in a nitrogen atmosphere to obtain a silicon nitride ceramic substrate.

[0010] In one embodiment, the ionic dispersant in the ionic dispersant solution includes at least one of triethyl phosphate, aliphatic phosphate, BYK-142, ammonium phosphate, sodium hexametaphosphate, and sodium tripolyphosphate.

[0011] In one embodiment, the nonionic dispersant in the nonionic dispersant solution includes at least one of polyvinylpyrrolidone, ammonium polyacrylate, Solsperse series, BYK-103, and castor oil.

[0012] In one embodiment, the mass ratio of the silicon nitride powder to the silicon powder is 60~90:10~40.

[0013] In one embodiment, the mass ratio of the ionic dispersant to the silicon nitride powder in the ionic dispersant solution is 1% to 4%, and the mass ratio of the nonionic dispersant to the silicon powder in the nonionic dispersant solution is 1% to 4%.

[0014] In one embodiment, the first ball mill includes: The silicon nitride powder, the ionic dispersant solution, the sintering aid, and the solvent are added to a ball mill jar. The ball-to-material ratio is controlled at 3-4:1, the rotation speed is 200-300 rpm, and the ball milling time is 4-8 hours.

[0015] In one embodiment, the second ball mill includes: The silicon powder, the nonionic dispersant solution, the sintering aid, and the solvent are added to a ball mill jar. The ball-to-material ratio is controlled at 2-3:1, the rotation speed is 150-200 rpm, and the ball milling time is 2-4 hours.

[0016] In one embodiment, the third ball mill includes: The first ball milling slurry, the second ball milling slurry, the binder and the plasticizer are added to the ball milling jar. The ball-to-material ratio is controlled at 2.5~3.5:1, the rotation speed is 200rpm~250rpm, and the ball milling time is 6h~10h.

[0017] In one embodiment, the coating is performed by a casting method, with a casting blade height of 0.2 mm to 0.7 mm and a casting speed of 0.1 m / min to 0.5 m / min.

[0018] A silicon nitride ceramic substrate is prepared using the preparation method described above.

[0019] The silicon nitride ceramic substrate has applications in new energy vehicles, rail transportation, or aerospace.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Reduced cost: Replacing silicon nitride powder with silicon powder reduces raw material costs while maintaining excellent overall performance, making it suitable for applications such as new energy vehicles that are sensitive to both cost and performance. (2) Improved slurry uniformity: Through the synergistic effect of composite dispersant and stepwise ball milling, Si powder and Si3N4 powder are uniformly co-dispersed in the slurry; (3) High consistency of silicon nitride green blank composition: Si powder is evenly distributed in the green blank, avoiding inconsistent sintering shrinkage and substrate warping caused by uneven composition. (4) Excellent sintering performance: The oxygen content of the powder is reduced from the raw materials, which reduces lattice defects and phonon scattering and improves thermal conductivity. Attached Figure Description

[0021] 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.

[0022] Figure 1 A flowchart of the preparation method of the present invention is provided; Figure 2 A schematic diagram of the dispersion mechanism of the present invention is provided; Figure 3 A bimodal distribution image of Embodiment 1 of the present invention is provided. Detailed Implementation

[0023] 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. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] The first aspect of this invention is to provide a method for preparing silicon nitride ceramic substrates, applicable to the specific preparation method of casting slurry and ceramic substrates of Si3N4 powder / Si powder dual-phase system. Through the synergistic effect of composite dispersant system and stepwise ball milling process, uniform co-dispersion of dual-phase powders is achieved, resulting in a stable and homogeneous casting slurry. At the same time, condensation reflux and heating stirring dissolution method accelerate the dissolution of dispersant in organic solvent, avoiding changes in slurry formulation ratio due to solvent evaporation caused by heating, thereby preparing silicon nitride ceramic substrates with uniform composition and excellent performance.

[0025] The method for preparing the silicon nitride ceramic substrate according to the present invention mainly includes the following steps: S1 was prepared by dissolving it through reflux and stirring, resulting in ionic and nonionic dispersant solutions, respectively. S2 involves first ball milling and mixing the ionic dispersant solution and silicon nitride (Si3N4) powder, and second ball milling and mixing the nonionic dispersant solution and silicon (Si) powder to obtain a first ball mill slurry and a second ball mill slurry, respectively; the first ball mill slurry and the second ball mill slurry are then ball milled and mixed in a third process to obtain a third ball mill slurry. S3 sequentially degasses, coats, dries, cuts, stacks, and presses the third ball mill slurry to obtain a silicon nitride green body; S4 After removing the binder from the silicon nitride green blank, it is sintered in a nitrogen atmosphere to obtain a silicon nitride ceramic substrate.

[0026] like Figure 1 The diagram shows a flowchart of the preparation method of the present invention.

[0027] Based on the above preparation process, the following typical technical advantages exist: A) Surface characteristic identification and dispersant matching: Si powder and Si3N4 powder are provided, where the surface of Si powder is hydrophobic and the surface of Si3N4 powder is hydrophilic due to the presence of a SiO2 layer; ionic dispersants are selected to match the hydrophilic surface of Si3N4 powder, and nonionic dispersants are selected to match the hydrophobic surface of Si powder; at the same time, a heating and stirring dissolution method with a condenser reflux component is used to pre-dissolve the dispersant. This method avoids the problem of changing the slurry formulation ratio due to solvent evaporation caused by heating, which is beneficial to the stable dispersion of the two-phase system casting slurry.

[0028] B) Stepwise pre-dispersion: Si3N4 powder and an ionic dispersant are ball-milled under the first ball milling condition, so that the ionic dispersant is selectively adsorbed onto the surface of Si3N4 powder; Si powder and a nonionic dispersant are ball-milled under the second ball milling condition, so that the nonionic dispersant is selectively adsorbed onto the surface of Si powder; wherein, the first ball milling condition and the second ball milling condition are set with different parameters according to the difference in mechanical properties between Si3N4 powder and Si powder, so as to achieve the specific microstate achieved after the third ball milling.

[0029] Specifically, ionic dispersants form hydrogen bonds or undergo chemisorption with the SiO2 layer on the surface of Si3N4 powder through their charged active molecules. After adsorption, the negatively charged ions form an electric double layer around the particles, preventing Si3N4 particles from agglomerating through electrostatic repulsion. Nonionic dispersants, on the other hand, adsorb onto the surface of Si powder through long polymer chains. These long chains extend into the solvent, forming a steric hindrance layer that effectively prevents Si powder particles from approaching and settling. The two types of dispersants are tailored to the surface characteristics of the two powders, avoiding the problem of a single dispersant only working on one type of powder while being ineffective or even leading to competitive adsorption.

[0030] C) Co-stabilization through mixing: The products from the first and second ball milling processes are mixed and then subjected to a third ball milling. During this process, the ionic and non-ionic dispersants already adsorbed on the surface of their respective powders do not interfere with each other. They synergistically stabilize their respective powders through electrostatic repulsion and steric hindrance mechanisms, respectively, achieving uniform co-dispersion of the two-phase powders in the slurry. Figure 2 The diagram shows the state after the composite dispersion.

[0031] In a preferred embodiment, the ionic dispersant solution contains at least one of triethyl phosphate, aliphatic phosphate, BYK-142, ammonium phosphate, sodium hexametaphosphate, and sodium tripolyphosphate. In some embodiments, the solvent of this solution includes, but is not limited to, at least one of ethanol, butanone, toluene, xylene, ethyl acetate, and trichloroethylene, and the concentration of the ionic dispersant is 5 wt.% to 15 wt.%.

[0032] In a preferred embodiment, the nonionic dispersant solution includes at least one of polyvinylpyrrolidone, ammonium polyacrylate, Solsperse series, BYK-103, and castor oil; in some embodiments, the solvent of this solution includes, but is not limited to, at least one of ethanol, butanone, toluene, xylene, ethyl acetate, and trichloroethylene, and the concentration of the nonionic dispersant is 5 wt.% to 15 wt.%.

[0033] In a preferred embodiment, the condensation reflux medium is water, the stirring and heating temperature is 50℃~90℃, and the stirring frequency is 10Hz~40Hz.

[0034] As an optional implementation, the method for preparing the solution includes: using a three-necked flask equipped with a reflux condenser as a container, placing the three-necked flask in a constant temperature heating device, installing a condenser tube at the middle neck, and inserting a magnetic stirrer inside the condenser tube; controlling the water to reflux stably in the condenser tube; and then adding the solvent and solute in sequence, and obtaining two solutions after they are fully dispersed.

[0035] In a preferred embodiment, the silicon nitride powder has a particle size range of 0.1 μm to 2 μm, and the silicon powder has a particle size range of 1 μm to 10 μm, both with a purity > 99.99%. The mass ratio of Si3N4 powder to Si powder is 60~90:10~40.

[0036] In a preferred embodiment, the mass ratio of the silicon nitride powder to the silicon powder is 60~90:10~40, including but not limited to any one or any two of the following: 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, and 90:10.

[0037] In a preferred embodiment, the mass ratio of the ionic dispersant to the silicon nitride powder in the ionic dispersant solution is 1% to 4%, and the mass ratio of the nonionic dispersant to the silicon powder in the nonionic dispersant solution is 1% to 4%.

[0038] It is understandable that, in step S2 of this invention, considering the significant differences between silicon powder and silicon nitride powder in terms of density, hardness, surface chemical properties, and dispersion behavior, the conventional one-step ball milling method cannot simultaneously meet the optimal dispersion conditions for both powders, easily leading to defects such as over-milling of silicon powder, insufficient dispersion of silicon nitride powder, and poor slurry stability. Therefore, S2 designs a three-step ball milling process: the first ball milling for pre-dispersion of silicon nitride powder, the second ball milling for pre-dispersion of silicon powder, and the third ball milling for mixing and homogenization; the three stages differ in ball-to-powder ratio, rotation speed, and time to achieve the technical goal of non-interference and coordinated stability.

[0039] In a preferred embodiment, the first ball milling includes: adding the silicon nitride powder, the ionic dispersant solution, the sintering aid, and the solvent into a ball mill jar, controlling the ball-to-material ratio at 3~4:1, rotating at 200rpm~300rpm, and milling for 4h~8h; wherein the sintering aid includes one or two of Y2O3, Y2Si2C2, MgSiN2, MgF2, MgO, Gd2O3, YbH2, and ZrH2, and the solvent includes at least one of ethanol, butanone, toluene, xylene, ethyl acetate, and trichloroethylene.

[0040] Understandably, in the first ball milling process, the silicon nitride powder naturally possesses a SiO2 layer on its surface, exhibiting a weakly acidic environment. After the ionic dispersant adsorbs onto the surface of the silicon nitride particles, the negative charge generated by its ionization forms an electric double layer around the particles. When two particles approach each other, an electrostatic repulsive force is generated between the electric double layers, preventing particle agglomeration. Furthermore, the first ball milling provides sufficient time and energy for dispersant adsorption while moderately breaking up soft agglomerates. Due to the high hardness of silicon nitride, a longer time and higher rotation speed are required to achieve uniform dispersion. This mechanism is only effective for silicon nitride powder, and its stabilizing effect on silicon powder is limited. Therefore, it is necessary to combine it with a non-ionic dispersant specifically designed for silicon powder to achieve silicon powder stabilization through a steric hindrance mechanism, thereby forming a composite dispersant synergistic stabilization system.

[0041] In a preferred embodiment, the second ball milling includes: adding the silicon powder, the nonionic dispersant solution, the sintering aid, and the solvent into a ball mill jar, controlling the ball-to-material ratio at 2-3:1, rotating at 150-200 rpm, and milling for 2-4 hours; wherein the sintering aid includes one or two of Y₂O₃, Y₂Si₂C₂, MgSiN₂, MgF₂, MgO, Gd₂O₃, YbH₂, and ZrH₂, and the solvent includes at least one of ethanol, butanone, toluene, xylene, ethyl acetate, and trichloroethylene. It is noteworthy that the sintering aid and the solvent maintain the same specific composition selection in both the first and second ball milling processes.

[0042] Understandably, in the second ball milling process, the milling parameters are controlled to allow the nonionic dispersant to adsorb onto the silicon powder surface, forming a steric hindrance stabilizing layer, while simultaneously preventing over-milling of the silicon powder, which could lead to excessively fine particles, oxidation, or the introduction of impurities. The surface of silicon powder is naturally hydrophobic and lacks strongly polar groups; the long-chain molecules of the nonionic dispersant are adsorbed onto the silicon powder surface by van der Waals forces, forming a steric hindrance layer that prevents silicon powder particles from approaching each other and agglomerating. Since the hardness of silicon powder is lower than that of silicon nitride, excessive ball milling would break the silicon powder into nano-sized fine powder, increasing the specific surface area and making it easier for oxygen to adsorb onto the silicon powder surface. Simultaneously, too much fine powder would increase the slurry viscosity, affecting tape casting. Therefore, a lower ball-to-powder ratio, rotation speed, and time are used in the second ball milling process.

[0043] In a more preferred embodiment, in the first ball milling and the second ball milling, the ratio of the amount of solvent to the amount of silicon nitride powder and silicon powder is 40~55:45~60.

[0044] In a more preferred embodiment, in the first ball mill and the second ball mill, the ratio of the amount of the sintering aid to the amount of the silicon nitride powder and the amount of the silicon powder is 5~15:85~95.

[0045] In a preferred embodiment, the third ball milling includes: adding the first ball milling slurry, the second ball milling slurry, a binder, and a plasticizer to a ball milling jar, controlling the ball-to-material ratio at 2.5~3.5:1, rotating at 200rpm~250rpm, and milling for 6h~10h; wherein the binder includes at least one of polyvinyl alcohol, polyvinyl butyral, polyacrylic acid resin, and polyurethane, and the plasticizer includes at least one of polyethylene glycol, dibutyl phthalate, dioctyl phthalate, diethyl oxalate, and glycerin.

[0046] Understandably, in the first two ball milling stages, the surfaces of the two powders are completely covered by their respective dispersants, forming a stable protective layer. When the third ball milling is performed, since the two dispersants have different adhesion sites, there will be no competitive adsorption or mutual substitution, so the two powders can coexist stably. At this time, the longer mixing and ball milling provides sufficient material exchange opportunities, allowing silicon powder particles and silicon nitride particles to be uniformly interwoven in three-dimensional space, avoiding macroscopic segregation caused by density differences.

[0047] In a more preferred embodiment, the ratio of the amount of the binder to the sum of the amounts of the silicon nitride powder and the silicon powder is 5% to 15%, and the ratio of the amount of the plasticizer to the sum of the amounts of the silicon nitride powder and the silicon powder is 5% to 15%.

[0048] In a preferred embodiment, after obtaining the third ball mill slurry in step S2, the process further includes filtering it through a 100-mesh sieve to remove any large particles or grinding ball debris before proceeding to step S3.

[0049] In a preferred embodiment, the degassing is carried out under vacuum conditions, with a vacuum degree of 0.05MPa to 0.1MPa and a degassing time of 10min to 30min.

[0050] In a preferred embodiment, the coating is performed by a casting method, with a casting blade height of 0.2 mm to 0.7 mm and a casting speed of 0.1 m / min to 0.5 m / min.

[0051] In a preferred embodiment, the temperature for discharging the adhesive is 500℃~800℃, the heating rate is 0.2℃ / min~5℃ / min, and the holding time is 2h~6h.

[0052] In a preferred embodiment, the sintering temperature is 1700℃~2000℃, the heating rate is 1℃ / min~10℃ / min, and the holding time is 2h~24h.

[0053] In a preferred embodiment, the settling rate of the third ball mill slurry obtained in step S2 is 5% to 25%.

[0054] In a preferred embodiment, the silicon nitride ceramic substrate obtained in step S4 has a smooth surface, good flexibility, and is free from macroscopic structural defects such as cracks, wrinkles, and bubbles; its thermal conductivity is 110 W / (m·K)~140 W / (m·K), its flexural strength is 600 MPa~800 MPa, and its fracture toughness is 6.5 MPa·m. 1 / 2 ~8.5MPa·m 1 / 2 .

[0055] A second aspect of the present invention is to provide a silicon nitride ceramic substrate prepared by the preparation method described in the first aspect. It is understood that, in addition to the preparation method described in the first aspect, other conventional or unconventional preparation processes may also be involved.

[0056] A third aspect of the present invention is to provide the use of the aforementioned silicon nitride ceramic substrate in new energy vehicles, rail transportation or aerospace.

[0057] Example 1 (1) Dissolution of the composite dispersant: Place a three-necked flask in a constant-temperature heating apparatus, install a condenser at the middle neck, and seal the left and right necks with glass stoppers. Add a magnetic stirrer to the three-necked flask. Add 15g of a binary azeotropic mixture of ethanol and butanone (ethanol:butanone mass ratio of 2:3; this mass ratio will be used for all ethanol and butanone azeotropic mixtures mentioned below) through the side neck into the three-necked flask. Raise the temperature to 60°C, turn on the magnetic stirrer, set the speed to 20Hz, and then slowly add 1.5g of triethyl phosphate. Stop the stirring once the mixture is completely dissolved to obtain a triethyl phosphate solution. Similarly, dissolve 0.5g of polyvinylpyrrolidone in 5g of the same solvent in the same manner to obtain a polyvinylpyrrolidone solution.

[0058] (2) Distributed ball milling process: (2.1) Pre-dispersion of silicon nitride powder: 75g of Si3N4 powder (0.7μm, purity >99.99%), sintering aid, ionic dispersant solution (triethyl phosphate solution, net weight of triethyl phosphate 1.5g) and 45g of mixed solvent ethanol and butanone binary azeotropic mixture were added to the ball mill jar. The ball-to-powder ratio was controlled at 3:1 (mass ratio). The planetary ball mill speed was set to 300rpm and the ball milling time was 8 hours.

[0059] (2.2) Pre-dispersion of silicon powder: Add 25g of Si powder (5μm, purity >99.99%), sintering aid, nonionic dispersant solution (polyvinylpyrrolidone solution, PVP net weight 0.5g) and 15g of mixed solvent to another ball mill jar. The ball-to-powder ratio is 2:1, the ball milling speed is set to 200 rpm, and the ball milling time is 3 hours.

[0060] The sintering aids include Y2O3 (4.47g) and MgO (3.82g), and the ratio of the sintering aids used in steps (2.1) and (2.2) is 3:1.

[0061] (2.3) Ball milling for mixing and homogenization: The silicon nitride pre-dispersed slurry (containing 75g of Si3N4 powder) prepared in (2.1) and the silicon powder pre-dispersed slurry (containing 25g of silicon powder) prepared in (2.2) were poured into the same ball mill jar, and 8g of binder polyvinyl butyral and 8g of plasticizer dibutyl phthalate were added. The ball mill speed was set to 250 rpm and the ball-to-material ratio was 2.5:1. The mixture was ball milled for 10 hours.

[0062] (3) Casting: The slurry after ball milling is degassed for 15 minutes under a vacuum of 0.05 MPa. After degassed, the slurry is coated onto the base belt using a casting machine with a squeegee height of 0.6 mm and a casting speed of 0.3 m / min. After drying, a flexible green belt is formed. The green belt is then cut, stacked, and statically pressed to obtain a silicon nitride green body.

[0063] (4) Gas pressure sintering: The silicon nitride green body was subjected to debinding treatment at 600°C, 1°C / min, and held for 6 hours. Then, under a nitrogen atmosphere, the sintering temperature was 1900°C, the gas pressure was 1MPa, and the temperature was increased to the preset temperature at a rate of 10°C / min, followed by holding for 4 hours for gas pressure sintering treatment, to obtain the silicon nitride ceramic substrate of this embodiment.

[0064] Examples 2-6 are basically the same as Example 1, except that the raw material mass amounts of the ball milling slurry prepared in step (2.3) are different. Specifically, the total mass of silicon powder and silicon nitride powder in the ball milling slurry is 100g. Table 1 provides the mass of silicon powder, so the mass of silicon nitride powder is the difference between 100g and the mass of silicon powder. Based on the mass of silicon powder and silicon nitride powder in Table 1, the amounts of Si3N4 powder and silicon powder raw materials introduced in steps 2.1 and 2.2 of Examples 2-6 can be derived. At the same time, the mass ratio of sintering aids in steps 2.1 and 2.2 is controlled according to the ratio of Si3N4 powder and silicon powder raw materials to ensure that the two have the same ratio value. The percentage of dispersant in Table 1 refers to the mass ratio of ionic dispersant to silicon nitride powder, and also indicates the mass ratio of nonionic dispersant to silicon powder (for example, in Example 3, it refers to 2 wt.% ionic dispersant and 2 wt.% nonionic dispersant to silicon powder). The mass of the dispersant refers to the mass of the active ingredients (triethyl phosphate and PVP) in the ionic dispersant solution in step 2.1 and the nonionic dispersant solution in step 2.2. Based on the mass percentage of dispersant in Table 1, the amount of triethyl phosphate and PVP introduced in steps 2.1 and 2.2 in Examples 2-6 can be deduced.

[0065] The percentage amounts of binder and plasticizer in Table 1 are the ratios of their respective masses to the masses of silicon powder and silicon nitride powder (100g). Based on the mass percentages of binder and plasticizer in Table 1, the amount of organic additives introduced in step 2.3 of Examples 2-6 can be derived. In addition, the casting process parameters used in step (3) are different, as shown in Table 1 below.

[0066] Table 1

[0067] Example 7: Basically the same as Example 1, except that the ionic dispersant is replaced by sodium hexametaphosphate instead of triethyl phosphate, and the nonionic dispersant is replaced by castor oil instead of polyvinylpyrrolidone.

[0068] Example 8: Basically the same as Example 1, except that the adhesive is replaced by polyvinyl butyral and polyacrylic acid resin, and the plasticizer is replaced by dibutyl phthalate and polyethylene glycol.

[0069] Comparative Example: Basically the same as Example 1, except that: the non-ionic dispersant is replaced with an ionic dispersant, the distribution ball milling process in step (2) is replaced with a one-step mixing ball milling process, and the scraper height in step (3) is replaced with 0.5 mm and the casting speed is replaced with 0.2 m / min.

[0070] Test case The settling rate of the slurry obtained in step (2) was tested; the thickness and density of the green sheet obtained in step (3) were tested; and the thermal conductivity, flexural strength, and fracture toughness of the silicon nitride ceramic substrate obtained in step (4) were tested. The results are recorded in Table 2.

[0071] Table 2

[0072] Furthermore, such as Figure 3 As shown, an SEM image of the etched surface of the silicon nitride ceramic substrate of Embodiment 1 of the present invention is provided, which shows a bimodal microstructure. This indicates that during the sintering process, uniformly distributed Si powder undergoes in-situ nitridation to generate β-Si3N4 nuclei, which compete with the β-Si3N4 nuclei transformed from α-Si3N4 for differentiated growth, ultimately resulting in a microstructure interwoven with coarse rod-shaped crystals and fine-grained matrix. This result fully demonstrates that the composite dispersant and stepwise ball milling process successfully transfer the uniformity of the macroscopic slurry to the controllability of the microscopic grain size, thereby achieving a synergistic improvement in the bridging of high-strength fine-grained matrix and high-toughness coarse-grained matrix. This provides a clear and reproducible process path for preparing high thermal conductivity and high-reliability silicon nitride substrates.

[0073] Based on the test results of the above-mentioned experimental examples, the silicon nitride ceramic substrate prepared by this invention has excellent performance. First, through the composite dispersant and stepwise ball milling, the Si powder is uniformly distributed in the green body, avoiding the problems of incomplete nitriding or concentrated reaction heat caused by local agglomeration. Second, it generates a bimodal microstructure. Because the Si powder undergoes nitriding reaction to generate β-Si3N4 crystal nuclei in situ, it has a longer nucleation time and higher growth activity. After the α-Si3N4 powder is dissolved and precipitated, a large number of β-Si3N4 crystals are formed, but the nucleation time is relatively late. The in-situ generated crystal nuclei preferentially obtain solute in the liquid phase due to their size advantage and grow rapidly along the c-axis into coarse rod-shaped grains. On the other hand, the numerous transformed crystal nuclei that nucleate later are limited by growth space and material supply and can only develop into fine equiaxed grains. Finally, a bimodal structure is formed in which a small number of coarse rod-shaped crystals are uniformly distributed in a large number of fine-grained matrices, which ensures both high strength and high toughness. Third, the Si powder undergoes a silicothermic reduction reaction with the SiO2 on the surface of the α-Si3N4 powder (SiO2+Si→2SiO↑), which actively reduces the lattice oxygen content in the system by generating SiO gas and volatilizing, thereby reducing phonon scattering and improving thermal conductivity.

[0074] 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; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a silicon nitride ceramic substrate, characterized in that, Includes the following steps: S1 was prepared by dissolving it through reflux and stirring, resulting in ionic and nonionic dispersant solutions, respectively. S2 involves first ball milling and mixing the ionic dispersant solution and silicon nitride powder, then second ball milling and mixing the nonionic dispersant solution and silicon powder to obtain a first ball mill slurry and a second ball mill slurry, respectively; finally, the first ball mill slurry and the second ball mill slurry are ball milled and mixed in a third ball mill to obtain a third ball mill slurry. S3 sequentially degasses, coats, dries, cuts, stacks, and presses the third ball mill slurry to obtain a silicon nitride green body; S4 After removing the binder from the silicon nitride green blank, it is sintered in a nitrogen atmosphere to obtain a silicon nitride ceramic substrate.

2. The preparation method according to claim 1, characterized in that, The ionic dispersant in the ionic dispersant solution includes at least one of triethyl phosphate, aliphatic phosphate, BYK-142, ammonium phosphate salt, sodium hexametaphosphate, and sodium tripolyphosphate. And / or, the nonionic dispersant in the nonionic dispersant solution includes at least one of polyvinylpyrrolidone, ammonium polyacrylate, Solsperse series, BYK-103, and castor oil.

3. The preparation method according to claim 1, characterized in that, The mass ratio of silicon nitride powder to silicon powder is 60~90:10~40.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the ionic dispersant to the silicon nitride powder in the ionic dispersant solution is 1% to 4%, and the mass ratio of the nonionic dispersant to the silicon powder in the nonionic dispersant solution is 1% to 4%.

5. The preparation method according to claim 1, characterized in that, The first ball mill includes: The silicon nitride powder, the ionic dispersant solution, the sintering aid, and the solvent are added to a ball mill jar. The ball-to-material ratio is controlled at 3-4:1, the rotation speed is 200-300 rpm, and the ball milling time is 4-8 hours.

6. The preparation method according to claim 1, characterized in that, The second ball mill includes: The silicon powder, the nonionic dispersant solution, the sintering aid, and the solvent are added to a ball mill jar. The ball-to-material ratio is controlled at 2-3:1, the rotation speed is 150-200 rpm, and the ball milling time is 2-4 hours.

7. The preparation method according to claim 1, characterized in that, The third ball mill includes: The first ball milling slurry, the second ball milling slurry, the binder and the plasticizer are added to the ball milling jar. The ball-to-material ratio is controlled at 2.5~3.5:1, the rotation speed is 200rpm~250rpm, and the ball milling time is 6h~10h.

8. The preparation method according to claim 1, characterized in that, The coating is performed by a casting method, with a casting blade height of 0.2mm~0.7mm and a casting speed of 0.1m / min~0.5m / min.

9. A silicon nitride ceramic substrate, characterized in that, It is prepared by a method comprising any one of claims 1 to 8.

10. The use of the silicon nitride ceramic substrate as described in claim 9 in new energy vehicles, rail transportation, or aerospace.

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