A silicon nitride tape-casting film strip and a preparation method thereof, a silicon nitride ceramic substrate and a preparation method thereof, and a vehicle power module

Abstract

The present application relates to the technical field of silicon nitride ceramics, and particularly to a silicon nitride tape casting film strip, a preparation method thereof, a silicon nitride ceramic substrate, a preparation method thereof and a vehicle power module. The present application provides a preparation method of a silicon nitride tape casting film strip. After silicon nitride tape casting slurry is tape casted, a silicon nitride tape casting film strip is obtained. The silicon nitride tape casting slurry comprises modified ceramic powder suspension, a binder and a plasticizer. The modified ceramic powder suspension comprises modified silicon nitride powder, a sintering aid and a solvent. The modified silicon nitride powder comprises silicon nitride powder whose surface is sequentially grafted and modified by a silane coupling agent and a polyphenol. The silane coupling agent contains an amino group and / or a mercapto group. The solvent comprises anhydrous ethanol, butanone and cyclohexanone. Through two-step surface grafting modification of silicon nitride powder and slurry formula optimization, the present application realizes the preparation of thick silicon nitride tape casting film strips and simplifies the preparation process of subsequent silicon nitride ceramic substrates.

Description

Technical Field

[0001] This invention relates to the field of silicon nitride ceramic technology, and in particular to a silicon nitride cast film tape and its preparation method, a silicon nitride ceramic substrate and its preparation method, and an automotive power module. Background Technology

[0002] With the rapid development of automotive electrification, users have a clear demand for improved charging efficiency. To further enhance the charging speed of electric vehicles, the vehicle voltage platform is evolving towards 800V or even higher voltages. Power semiconductor devices need to cope with the severe heat dissipation challenges brought about by higher voltage, higher frequency, and higher power density operating conditions. Compared with traditional ceramic substrates such as alumina and aluminum nitride, silicon nitride ceramic substrates exhibit more balanced and superior performance in terms of thermal conductivity, bending strength, and fracture toughness, making them an ideal heat dissipation material for automotive power semiconductors. With the large-scale application of third-generation semiconductor technology, silicon nitride ceramic substrates are now being practically used in the field of automotive power semiconductor packaging.

[0003] The manufacturing process of automotive silicon nitride ceramic substrates mainly includes steps such as mixing, slurry preparation, tape casting, slicing and stacking, static pressing, debinding, and sintering. On the one hand, the complexity of the process leads to high costs; on the other hand, multiple factors, such as raw materials, formulation composition, and process parameters, affect the final product performance of the ceramic substrate, resulting in poor batch consistency and a relatively low yield rate for mass-produced products.

[0004] The thickness of automotive silicon nitride ceramic substrates is typically 0.25~0.65mm. Optimizing the ceramic slurry formulation and casting process parameters to prepare thick silicon nitride cast films can further eliminate the slicing, stacking, and hydrostatic pressing processes in the ceramic substrate preparation process. Therefore, this is a major research direction for simplifying process steps, reducing process costs, improving batch consistency, and increasing the yield of mass-produced products. The preparation of thick silicon nitride cast films requires: further increasing the solid content of the ceramic slurry; increasing the slurry viscosity while meeting the casting operation conditions; and optimizing the solvent evaporation rate during the casting process.

[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 cast films. Through two-step grafting modification of the silicon nitride powder surface and optimization of the slurry formulation, a thick silicon nitride cast film is prepared, simplifying the subsequent preparation process of silicon nitride ceramic substrates.

[0007] The second objective of this invention is to provide a silicon nitride cast film tape.

[0008] A third objective of this invention is to provide a method for preparing a silicon nitride ceramic substrate.

[0009] The fourth objective of this invention is to provide a silicon nitride ceramic substrate.

[0010] The fifth objective of this invention is to provide a vehicle power module.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a method for preparing silicon nitride cast film tape, wherein silicon nitride cast slurry is cast and shaped to obtain silicon nitride cast film tape; The silicon nitride casting slurry includes a modified ceramic powder suspension, a binder, and a plasticizer. The modified ceramic powder suspension includes modified silicon nitride powder, sintering aid, and solvent; the modified silicon nitride powder includes silicon nitride powder whose surface has been successively modified by silane coupling agent and polyphenol grafting; the silane coupling agent contains amino groups and / or mercapto groups. The solvents include anhydrous ethanol, butanone, and cyclohexanone.

[0012] Furthermore, the preparation method of the modified ceramic powder suspension includes the following steps: S1. The silicon nitride powder and sintering aid are successively ground, dried and sieved to obtain a mixed powder; S2. Grind the mixed powder and solvent to obtain a ceramic powder suspension; S3. Mix the silane coupling agent and the ceramic powder suspension, adjust the pH to 6.5~7, and then grind to obtain a primary grafted ceramic powder suspension. S4. Mix the polyphenols and the primary grafted ceramic powder suspension, adjust the pH to 7.5~8.5, and then grind them to obtain the modified ceramic powder suspension.

[0013] Furthermore, it includes at least one of the following features (1) to (5); (1) The mass ratio of the silicon nitride powder to the sintering aid is (95~85):(5~15); (2) The average particle size of the silicon nitride powder is 0.5~1.2μm; (3) The specific surface area of ​​the silicon nitride powder is 7~20m². 2 / g; (4) The sintering aids include nitrogen-containing non-oxide sintering aids; (5) The average particle size of the sintering aid is ≤1μm.

[0014] Furthermore, it includes at least one of the following features (1) to (6); (1) In the solvent, the mass ratio of anhydrous ethanol, butanone and cyclohexanone is (30~70):(70~30):(5~10); (2) The mass ratio of the mixed powder to the solvent is 100:(40~100); (3) The silane coupling agent includes at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, N-(aminoethyl)-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane and γ-mercaptopropyltriethoxysilane; (4) The mass ratio of the silane coupling agent to the mixed powder is (2~5):100; (5) The polyphenols include at least one of tannic acid, dopamine, baicalin, gallic acid, pyrogallol, catechin and epi-catechin; (6) The mass ratio of the polyphenol to the mixed powder is (2~5):100.

[0015] Furthermore, it includes at least one of the following features (1) to (7); (1) The adhesive comprises at least one of polyvinyl alcohol, polyvinyl butyral, and polyacrylic acid resin; (2) The mass ratio of the binder to the mixed powder is (5~15):100; (3) The plasticizer includes at least one of polyglycerol, polyethylene glycol, polypropylene glycol, dibutyl phthalate, dioctyl phthalate and butyl benzyl phthalate; (4) The mass ratio of the plasticizer to the mixed powder is (5~15):100; (5) The viscosity of the silicon nitride casting slurry is 1500~10000 mPa·s; (6) The casting process includes: applying silicon nitride casting slurry onto the casting substrate using a casting machine blade, and then drying the substrate to obtain the silicon nitride casting film. (7) The height of the scraper of the casting machine is 0.4~1.2mm; the speed of the casting substrate is 0.3~2m / min; the temperature of the drying treatment is 20~80℃, and the length of the heating zone is 10~40m.

[0016] The present invention also provides a silicon nitride cast film tape, which is prepared by the silicon nitride cast film tape preparation method described above.

[0017] Preferably, the thickness of the silicon nitride cast film is 0.25~1mm.

[0018] The present invention also provides a method for preparing a silicon nitride ceramic substrate, wherein the silicon nitride cast film tape described above is subjected to debinding, degreasing and sintering in sequence to obtain a silicon nitride ceramic substrate.

[0019] Furthermore, it includes at least one of the following features (1) to (4); (1) The temperature for degreasing and debinding is 500~800℃; (2) The heat preservation time for degreasing and debinding is 1~3h; (3) The sintering temperature is 1750~2000℃; (4) The holding time for sintering is 2~10h.

[0020] The present invention also provides a silicon nitride ceramic substrate, which is prepared by the silicon nitride ceramic substrate preparation method described above.

[0021] Preferably, the thickness of the silicon nitride ceramic substrate is 0.2~0.8 mm.

[0022] The present invention also provides an automotive power module, comprising the silicon nitride ceramic substrate as described above.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: The method for preparing silicon nitride cast film provided by this invention involves a two-step chemical grafting modification of the surface of silicon nitride powder with silane coupling agent and polyphenol, combined with a ternary mixed solvent system of anhydrous ethanol, butanone and cyclohexanone, to optimize the casting slurry formulation. This improves the rheological properties and increases the solid content of the casting slurry, enabling the preparation of thick cast film, further simplifying the ceramic substrate preparation process and reducing process costs. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 The present invention utilizes the reaction principle of grafting silicon nitride powder with a silane coupling agent.

[0026] Figure 2 The present invention utilizes the reaction principle of secondary grafting modification of silicon nitride powder after primary grafting modification with polyphenols.

[0027] Figure 3 The image shows the microstructure of the silicon nitride ceramic substrate in Example 3 of this invention. Detailed Implementation

[0028] 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.

[0029] In some embodiments of the present invention, a method for preparing silicon nitride cast film is provided, wherein silicon nitride cast slurry is cast and shaped to obtain silicon nitride cast film. The silicon nitride casting slurry includes a modified ceramic powder suspension, a binder, and a plasticizer. The modified ceramic powder suspension includes modified silicon nitride powder, sintering aid, and solvent; the modified silicon nitride powder includes silicon nitride powder whose surface has been successively modified by silane coupling agent and polyphenol grafting; the silane coupling agent contains amino groups and / or mercapto groups; Solvents include anhydrous ethanol, butanone, and cyclohexanone.

[0030] This invention addresses the problems of complex processes, high costs, poor batch consistency, and relatively low product yield in the current method of preparing silicon nitride ceramic substrates using silicon nitride cast films. It provides a method for preparing silicon nitride cast films by improving the rheological properties and increasing the solid content of the cast film through two-step grafting modification of the silicon nitride powder surface and optimization of the cast film slurry formulation, thereby achieving the preparation of thick cast films. Specific advantages are as follows: A two-stage grafting modification was designed utilizing the abundant silanol groups on the surface of silicon nitride powder: the first grafting modification involves molecular grafting via a condensation reaction between the silanol groups of the silane coupling agent and the silanol groups on the surface of the silicon nitride powder. For details of the reaction principle, please refer to [link to relevant documentation]. Figure 1 Secondary grafting modification utilizes the silane coupling agent organic groups (amino and / or thiol groups) on the surface of the powder after primary grafting modification to achieve chemical bonding grafting with polyphenols (after partial oxidation) through a Michael addition reaction. For the specific reaction principle, please refer to [link to relevant documentation]. Figure 2Through two grafting modifications, a large number of phenolic hydroxyl compounds were introduced onto the surface of silicon nitride ceramic powder. On the one hand, phenolic hydroxyl groups have high solubility in solvents, thereby improving the solubility of modified silicon nitride powder in solvents. On the other hand, phenolic hydroxyl compound molecules are large and have large steric hindrance, so the silicon nitride powder can be stably dispersed in solvents through the steric hindrance effect.

[0031] Based on the excellent dispersibility of modified silicon nitride powder, the silicon nitride casting slurry formulation was further optimized, eliminating the need for additional dispersants. Furthermore, by increasing the solubility of modified silicon nitride powder in solvents, the amount of solvent used in the casting slurry could be further reduced while still meeting the viscosity requirements for casting, thus enabling the preparation of high-solids-content casting slurries. High solids content is fundamental for preparing thick cast films. Simultaneously, to avoid drying stress cracking during the drying process of thick cast films, the slurry solvent system was further optimized: anhydrous ethanol and methyl ethyl ketone (MEK) are commonly used solvents for silicon nitride slurries, effectively dissolving silicon nitride powder, plasticizers, binders, and other slurry components. However, the low azeotropic point of anhydrous ethanol and MEK leads to rapid evaporation during drying. In thick film casting, excessively rapid drying can cause significant internal stress in the cast film, easily leading to drying stress cracking. This invention introduces cyclohexanone, a high-boiling-point solvent, into a binary solvent of anhydrous ethanol and butanone. Cyclohexanone has high solubility for organic components such as plasticizers and binders, which is beneficial for the dissolution of silicon nitride slurry. At the same time, its high boiling point means that adding a small amount of cyclohexanone can effectively control the overall solvent evaporation rate of the film during the drying process, thereby improving problems such as cracking during the drying process.

[0032] The method for preparing silicon nitride cast film tapes increases the thickness of the silicon nitride cast film tapes, allowing thicker cast film tapes to be directly used in the debinding and grouting process during the preparation of silicon nitride ceramic substrates. This eliminates the two preparation process steps of cast film tape slicing and stacking and static pressing, thereby simplifying the silicon nitride substrate preparation process and reducing process costs. At the same time, the simplification of process steps reduces process factors that affect the performance of ceramic substrate products, improving batch consistency and product qualification rate.

[0033] In some embodiments of the present invention, the preparation method of the modified ceramic powder suspension includes the following steps: S1. The silicon nitride powder and sintering aid are successively ground, dried and sieved to obtain a mixed powder; S2. Grind the mixed powder and solvent to obtain a ceramic powder suspension; S3. Mix the silane coupling agent and the ceramic powder suspension, adjust the pH to 6.5~7, and then grind to obtain a primary grafted ceramic powder suspension. S4. Mix the polyphenol and the primary grafted ceramic powder suspension, adjust the pH to 7.5~8.5, and then grind to obtain the modified ceramic powder suspension.

[0034] In some embodiments of the present invention, in step S1, the mass ratio of silicon nitride powder to sintering aid is (95~85):(5~15); typically, but not limitingly, for example, the mass ratio of silicon nitride powder to sintering aid can be 95:5, 90:10, 85:15, and any value between any two of them.

[0035] In some embodiments of the present invention, in step S1, the average particle size (D50) of the silicon nitride powder is 0.5 to 1.2 μm; typically, but not limitingly, for example, the average particle size of the silicon nitride powder can be 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, and any value between any two of these.

[0036] In some embodiments of the present invention, in step S1, the specific surface area (BET) of the silicon nitride powder is 7~20 m². 2 / g; typically, but not limitingly, the specific surface area of ​​silicon nitride powder can be 7m². 2 / g, 10m 2 / g, 15m 2 / g、20m 2 / g and any value between any two of them.

[0037] In some embodiments of the present invention, in step S1, the sintering aid includes a nitrogen-containing non-oxide sintering aid; preferably, the sintering aid includes at least one of magnesium silicon nitride, magnesium nitride, and yttrium nitride.

[0038] In some embodiments of the present invention, in step S1, the average particle size (D50) of the sintering aid is ≤1 μm; typically, but not limitingly, for example, the average particle size of the sintering aid can be 0.5 μm, 0.7 μm, 1 μm, and any value between any two thereof.

[0039] In some embodiments of the present invention, in step S2, the mass ratio of anhydrous ethanol, butanone, and cyclohexanone in the solvent is (30~70):(70~30):(5~10); typically, but not limitingly, for example, the mass ratio of anhydrous ethanol, butanone, and cyclohexanone can be 30:70:5, 70:30:10, 50:50:8, and any value between any two of these.

[0040] In some embodiments of the present invention, in step S2, the water content of the solvent is ≤0.5wt%.

[0041] The solvent is a ternary mixture of anhydrous ethanol, butanone (MEK), and cyclohexanone. Anhydrous ethanol and MEK are commonly used solvents for silicon nitride slurries, effectively dissolving silicon nitride powder, plasticizers, binders, and other slurry components. However, the binary solvent system of anhydrous ethanol and MEK has a low azeotropic point and evaporates quickly during drying. In thick-film casting, excessively rapid drying can cause significant internal stress in the cast film, leading to cracking. Cyclohexanone has high solubility for plasticizers, binders, and other organic components, which is beneficial for dissolving silicon nitride slurries. Furthermore, its high boiling point allows for effective control of the overall solvent evaporation rate during drying, thus mitigating cracking issues.

[0042] In some embodiments of the present invention, in step S2, the mass ratio of the mixed powder to the solvent is 100:(40~100); typically, but not limitingly, for example, the mass ratio of the mixed powder to the solvent can be 100:40, 100:60, 100:100, and any value between any two of these.

[0043] In some embodiments of the present invention, in step S2, grinding includes ball milling; preferably, ball milling includes planetary ball milling or rolling ball milling, the ball milling speed is ≥200 rpm, and the ball milling time is ≥1 h.

[0044] In some embodiments of the present invention, in step S3, the silane coupling agent includes at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, N-(aminoethyl)-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-mercaptopropyltriethoxysilane.

[0045] In some embodiments of the present invention, in step S3, the mass ratio of the silane coupling agent to the mixed powder is (2~5):100; typically, but not limitingly, for example, the mass ratio of the silane coupling agent to the mixed powder can be 2:100, 3:100, 5:100, and any value between any two of these.

[0046] In some embodiments of the present invention, in step S3, a silane coupling agent is added to a ceramic powder suspension, the pH is adjusted to 6.5-7, and then ball milling is performed to obtain a primary grafted ceramic powder suspension; typically, but not limitingly, for example, the pH is adjusted to 6.5, 6.7, 7, and any value between any two of these.

[0047] Add the silane coupling agent to the ceramic powder suspension and adjust the pH to 6.5-7 to ensure that the overall solution is weakly acidic or neutral, so as to avoid the rapid hydrolysis and condensation of the silane coupling agent in strong acid or strong alkali solutions, which could lead to self-condensation polymerization.

[0048] In some embodiments of the present invention, in step S3, the ball milling includes planetary ball milling or rolling ball milling, the ball milling speed is ≥200 rpm, and the ball milling time is ≥2h.

[0049] Rapid ball milling ensures that silane molecules and silicon nitride powder come into full contact and react, while avoiding self-condensation reactions between silane molecules (the number of silane molecules on the surface of silicon nitride powder is much greater than the number of silane molecules in the silane coupling agent; high-speed ball milling increases the probability of contact between silane molecules and silicon nitride powder while greatly reducing the probability of contact between silane molecules). Providing a longer reaction time further allows the silane coupling agent to be fully grafted onto the surface of the silicon nitride powder.

[0050] In some embodiments of the present invention, in step S4, the polyphenols include at least one of tannic acid, dopamine, baicalin, gallic acid, pyrogallol, catechin, and epi-catechin.

[0051] In some embodiments of the present invention, in step S4, the mass ratio of polyphenols to mixed powders is (2~5):100; typically, but not limitingly, for example, the mass ratio of polyphenols to mixed powders can be 2:100, 3:100, 5:100, and any value between any two of these.

[0052] In some embodiments of the present invention, in step S4, polyphenols are added to a primary grafted ceramic powder suspension, the pH is adjusted to 7.5-8.5, and then ball milling is performed to obtain a modified ceramic powder suspension (secondary grafted ceramic powder suspension); typically, but not limitingly, the pH is adjusted to 7.5, 8, 8.5, and any value between any two of these.

[0053] After adding polyphenols to the primary grafted ceramic powder suspension, adjust the pH to 7.5-8.5 to ensure the overall solution is weakly alkaline. Under weakly alkaline conditions, polyphenols will chemically bond with the organic groups (amino and / or thiol groups) of the silane coupling agent through Michael addition reactions, thus firmly grafting the polyphenol groups onto the surface of the ceramic powder. Polyphenols have higher solubility in the solvent, thus achieving sufficient dispersion. If the alkalinity increases, polyphenols will undergo oxidation and self-polymerization under air conditions, resulting in excessively large polyphenol molecular weights, which is detrimental to dispersion.

[0054] In some embodiments of the present invention, in step S4, the ball milling includes planetary ball milling or rolling ball milling, the ball milling speed is ≥200 rpm, and the ball milling time is ≥1 h.

[0055] In some embodiments of the present invention, the adhesive includes at least one selected from polyvinyl alcohol, polyvinyl butyral, and polyacrylic acid resin.

[0056] In some embodiments of the invention, the mass ratio of binder to mixed powder is (5~15):100; typically, but not limitingly, for example, the mass ratio of binder to mixed powder can be 5:100, 10:100, 15:100, and any value between any two of these.

[0057] In some embodiments of the present invention, the plasticizer includes at least one selected from polyglycerol, polyethylene glycol, polypropylene glycol, dibutyl phthalate, dioctyl phthalate, and butyl benzyl phthalate.

[0058] In some embodiments of the invention, the mass ratio of plasticizer to mixed powder is (5-15):100; typically, but not limitingly, for example, the mass ratio of plasticizer to mixed powder can be 5:100, 10:100, 15:100, and any value between any two of these.

[0059] In some embodiments of the present invention, the method for preparing silicon nitride casting slurry includes the following steps: The binder and plasticizer are added to the modified ceramic powder suspension, ball milled and mixed, and then defoamed and the viscosity of the slurry after defoaming is controlled to obtain silicon nitride casting slurry.

[0060] In some embodiments of the present invention, ball milling includes planetary ball milling or rolling ball milling, the ball milling speed is ≥200 rpm, and the ball milling time is 24~48h.

[0061] In some embodiments of the present invention, the viscosity of the silicon nitride casting slurry is 1500 to 10000 mPa·s; typically, but not limitingly, for example, the viscosity of the silicon nitride casting slurry can be 1500 mPa·s, 5000 mPa·s, 10000 mPa·s, and any value between any two of these.

[0062] In some embodiments of the present invention, the casting process includes: applying silicon nitride casting slurry onto a casting substrate using a casting machine blade, and then drying the substrate to obtain a silicon nitride casting film.

[0063] In some embodiments of the present invention, the method for preparing silicon nitride cast film tape specifically includes the following steps: Adjust the height of the squeegee in the casting machine, pour the silicon nitride casting slurry into the casting machine trough, and adjust the speed of the casting substrate to make the silicon nitride casting slurry evenly coated on the casting substrate. Then, perform drying treatment to obtain silicon nitride casting film tape.

[0064] In some embodiments of the invention, the height of the casting machine squeegee is 0.4 to 1.2 mm; typically, but not limitingly, for example, the height of the casting machine squeegee can be 0.4 mm, 0.8 mm, 1.2 mm, and any value between any two of these.

[0065] In some embodiments of the present invention, the material of the cast substrate includes PET.

[0066] In some embodiments of the present invention, the speed of the casting baseband is 0.3 to 2 m / min; typically, but not limitingly, for example, the speed of the casting baseband can be 0.3 m / min, 1 m / min, 2 m / min and any value between any two of these.

[0067] In some embodiments of the invention, the drying temperature is 20 to 80°C; typically, but not limitingly, the drying temperature can be 20°C, 50°C, 80°C, or any value between any two of these.

[0068] In some embodiments of the present invention, the length of the heating zone for drying is 10 to 40 m; typically, but not limitingly, for example, the length of the heating zone for drying can be 10 m, 30 m, 40 m, or any value between any two of these.

[0069] In some embodiments of the present invention, a silicon nitride cast film tape is also provided, which is prepared by the above-described method for preparing silicon nitride cast film tape.

[0070] In some embodiments of the present invention, the thickness of the silicon nitride cast film is 0.25 to 1 mm; typically, but not limitingly, for example, the thickness of the silicon nitride cast film can be 0.25 mm, 0.5 mm, 0.75 mm, 1 mm, and any value between any two of these.

[0071] In some embodiments of the present invention, a method for preparing a silicon nitride ceramic substrate is also provided, wherein the silicon nitride cast film is sequentially degreased and sintered to obtain a silicon nitride ceramic substrate.

[0072] During the debinding and degreasing process of silicon nitride cast film, organic matter fully decomposes and volatilizes under high temperature conditions. However, the silane contained in the silane coupling agent reacts at high temperature to generate silicon oxide, which is then retained in the silicon nitride green body. It can act as a sintering aid during the sintering process, facilitating the dissolution, migration, and precipitation of silicon nitride in the liquid phase sintering process. However, excessively high oxygen content will significantly reduce the thermal conductivity of the silicon nitride ceramic substrate. Therefore, adding only nitrogen-containing non-oxide sintering aids to the ceramic powder can, on the one hand, control the oxygen content at a low level, which helps to improve thermal conductivity; on the other hand, it can further increase the N / O ratio in the sintering aid system, thereby controlling the liquid phase viscosity during the sintering process, promoting the formation of a microscopic bimodal distribution, and improving the overall performance of the silicon nitride ceramic substrate.

[0073] In some embodiments of the invention, the degreasing temperature is 500-800°C; typically, but not limitingly, the degreasing temperature can be 500°C, 650°C, 800°C, or any value between any two of these.

[0074] In some embodiments of the present invention, the heat preservation time for degreasing is 1 to 3 hours; typically, but not limitingly, for example, the heat preservation time for degreasing can be 1 hour, 2 hours, 3 hours, or any value between any two of these.

[0075] In some embodiments of the present invention, the heating and / or cooling rate of the degreasing process is 0.1~3℃ / min.

[0076] In some embodiments of the invention, the sintering temperature is 1750~2000°C; typically, but not limitingly, for example, the sintering temperature can be 1750°C, 1850°C, 2000°C, and any value between any two of these.

[0077] In some embodiments of the present invention, the holding time for sintering is 2 to 10 hours; typically, but not limitingly, for example, the holding time for sintering can be 2 hours, 6 hours, 10 hours, or any value between any two of these.

[0078] In some embodiments of the present invention, the heating and / or cooling rate of sintering is 1~10°C / min.

[0079] In some embodiments of the present invention, the sintering atmosphere includes nitrogen, and the sintering gas pressure is 1~10 MPa.

[0080] In some embodiments of the present invention, a silicon nitride ceramic substrate is also provided, which is prepared by the above-described method for preparing silicon nitride ceramic substrates.

[0081] In some embodiments of the present invention, the thickness of the silicon nitride ceramic substrate is 0.2 to 0.8 mm; typically, but not limitingly, for example, the thickness of the silicon nitride ceramic substrate can be 0.2 mm, 0.5 mm, 0.8 mm, and any value between any two of these.

[0082] In some embodiments of the present invention, the flexural strength of the silicon nitride ceramic substrate is ≥750MPa; preferably, the flexural strength of the silicon nitride ceramic substrate is ≥800MPa.

[0083] In some embodiments of the present invention, the thermal conductivity of the silicon nitride ceramic substrate is ≥80 W / (m²). K); Preferably, the thermal conductivity of the silicon nitride ceramic substrate is ≥90W / (m²). K).

[0084] In some embodiments of the present invention, an automotive power module is also provided, comprising the aforementioned silicon nitride ceramic substrate.

[0085] In some embodiments of the present invention, a new energy vehicle is also provided, including the above-mentioned vehicle power module.

[0086] Example 1 The method for preparing a silicon nitride ceramic substrate provided in this embodiment includes the following steps: S1. 90 parts of silicon nitride powder and 10 parts of sintering aid are sequentially ball-milled, dried, and sieved to obtain a mixed powder; wherein the average particle size (D50) of the silicon nitride powder is 0.5 μm, and the specific surface area (BET) is 20 m². 2 / g, the sintering aid is magnesium silicon nitride powder, and the average particle size (D50) of magnesium silicon nitride powder is 1μm; S2. Mix 100 parts of the above-mentioned mixed powder with 40 parts of solvent, and then ball mill to obtain a ceramic powder suspension; wherein, the solvent is anhydrous ethanol, butanone and cyclohexanone in a mass ratio of 30:70:5, the ball milling is carried out by a planetary ball mill, the ball milling speed is 200 rpm, and the ball milling time is 1 hour. S3. Add 5 parts of silane coupling agent to the above ceramic powder suspension, adjust the pH to 6.5, and then ball mill to obtain a primary grafted ceramic powder suspension; wherein, the silane coupling agent is γ-aminopropyltriethoxysilane, the ball milling is carried out using a planetary ball mill, the ball milling speed is 200 rpm, and the ball milling time is 2 hours. S4. Add 5 parts of polyphenol to the above-mentioned primary grafted ceramic powder suspension, adjust the pH to 8.5, and then ball mill to obtain modified ceramic powder suspension; wherein, the polyphenol is tannic acid, the ball milling is carried out by a planetary ball mill, the ball milling speed is 200 rpm, and the ball milling time is 1 hour. S5. Add 15 parts of binder and 15 parts of plasticizer to the above modified ceramic powder suspension, ball mill and mix, defoam and control the viscosity of the slurry after defoaming to obtain a silicon nitride casting slurry with a viscosity of 10000 mPa·s; wherein, the binder is polyvinyl butyral, the plasticizer is polyethylene glycol, the ball milling is carried out using a planetary ball mill, the ball milling speed is 200 rpm, and the ball milling time is 24 h; S6. Adjust the height of the squeegee of the casting machine to 1.2mm, pour the above silicon nitride casting slurry into the casting machine trough, adjust the speed of the PET casting substrate to 0.3m / min, so that the silicon nitride casting slurry is evenly coated on the PET casting substrate, and then dry it at 20℃. The length of the drying heating zone is 10m, and a silicon nitride casting film with a thickness of 1mm is obtained. S7. The silicon nitride cast film is sequentially degreased and sintered to obtain a silicon nitride ceramic substrate with a thickness of 0.8 mm. The degreasing temperature is 800℃, the holding time is 1 h, and the heating and / or cooling rate is 0.1℃ / min. The sintering temperature is 2000℃, the holding time is 2 h, and the heating and / or cooling rate is 1℃ / min. The sintering is carried out in a nitrogen atmosphere with a gas pressure of 1 MPa.

[0087] Example 2 The method for preparing a silicon nitride ceramic substrate provided in this embodiment includes the following steps: S1. 90 parts of silicon nitride powder and 10 parts of sintering aid are sequentially ball-milled, dried, and sieved to obtain a mixed powder; wherein the average particle size (D50) of the silicon nitride powder is 1.2 μm, and the specific surface area (BET) is 7 m². 2 / g, the sintering aid is magnesium nitride powder, and the average particle size (D50) of magnesium nitride powder is 0.7μm; S2. Mix 100 parts of the above-mentioned mixed powder with 100 parts of solvent, and then ball mill to obtain a ceramic powder suspension; wherein, the solvent is anhydrous ethanol, butanone and cyclohexanone in a mass ratio of 70:30:10, the ball milling is carried out using a rolling ball mill, the ball milling speed is 300 rpm, and the ball milling time is 2 hours. S3. Add 2 parts of silane coupling agent to the above ceramic powder suspension, adjust the pH to 7, and then ball mill to obtain a primary grafted ceramic powder suspension; wherein, the silane coupling agent is γ-mercaptopropyltrimethoxysilane, the ball milling is carried out using a rolling ball mill, the ball milling speed is 300 rpm, and the ball milling time is 3 hours. S4. Add 2 parts of polyphenol to the above-mentioned primary grafted ceramic powder suspension, adjust the pH to 7.5, and then ball mill to obtain modified ceramic powder suspension; wherein, the polyphenol is dopamine, the ball milling is carried out using a rolling ball mill, the ball milling speed is 300 rpm, and the ball milling time is 2 hours. S5. Add 5 parts of binder and 5 parts of plasticizer to the above modified ceramic powder suspension, ball mill and mix, defoam, and control the viscosity of the slurry after defoaming to obtain a silicon nitride casting slurry with a viscosity of 2000 mPa·s; wherein, the binder is polyacrylic acid resin, the plasticizer is dibutyl phthalate, the ball milling is carried out using a rolling ball mill, the ball milling speed is 300 rpm, and the ball milling time is 36 h; S6. Adjust the height of the squeegee of the casting machine to 0.4mm, pour the above silicon nitride casting slurry into the casting machine trough, adjust the speed of the PET casting substrate to 2m / min, so that the silicon nitride casting slurry is evenly coated on the PET casting substrate, and then dry it at 80℃. The length of the drying heating zone is 40m, and a silicon nitride casting film with a thickness of 0.25mm is obtained. S7. The silicon nitride cast film is sequentially degreased and sintered to obtain a silicon nitride ceramic substrate with a thickness of 0.2 mm. The degreasing temperature is 500℃, the holding time is 3h, and the heating and / or cooling rate is 3℃ / min. The sintering temperature is 1750℃, the holding time is 10h, and the heating and / or cooling rate is 10℃ / min. The sintering is carried out in a nitrogen atmosphere with a gas pressure of 10MPa.

[0088] Example 3 The method for preparing a silicon nitride ceramic substrate provided in this embodiment includes the following steps: S1. 90 parts of silicon nitride powder and 10 parts of sintering aid are sequentially ball-milled, dried, and sieved to obtain a mixed powder; wherein the average particle size (D50) of the silicon nitride powder is 0.9 μm, and the specific surface area (BET) is 12 m². 2 / g, the sintering aid is yttrium nitride powder, and the average particle size (D50) of the yttrium nitride powder is 0.5μm; S2. Mix 100 parts of the above-mentioned mixed powder with 70 parts of solvent, and then ball mill to obtain a ceramic powder suspension; wherein, the solvent is anhydrous ethanol, butanone and cyclohexanone in a mass ratio of 50:50:8, the ball milling is carried out by a planetary ball mill, the ball milling speed is 400 rpm, and the ball milling time is 3 hours. S3. Add 4 parts of silane coupling agent to the above ceramic powder suspension, adjust the pH to 6.8, and then ball mill to obtain a primary grafted ceramic powder suspension; wherein, the silane coupling agent is γ-aminopropyltrimethoxysilane and γ-mercaptopropyltriethoxysilane in a mass ratio of 1:1, the ball milling is carried out using a planetary ball mill, the ball milling speed is 400 rpm, and the ball milling time is 4 h; S4. Add 3 parts of polyphenol to the above-mentioned primary grafted ceramic powder suspension, adjust the pH to 8, and then ball mill to obtain the modified ceramic powder suspension; wherein, the polyphenol is gallic acid and catechol in a mass ratio of 1:1, the ball milling is carried out using a planetary ball mill, the ball milling speed is 200 rpm, and the ball milling time is 4 hours. S5. Add 8 parts of binder and 12 parts of plasticizer to the above modified ceramic powder suspension, ball mill and mix, defoam and control the viscosity of the slurry after defoaming to obtain a silicon nitride casting slurry with a viscosity of 6000 mPa·s; wherein, the binder is polyacrylic acid resin and polyvinyl butyral in a mass ratio of 1:1, and the plasticizer is polypropylene glycol and dioctyl phthalate in a mass ratio of 1:1. The ball milling is carried out using a planetary ball mill at a ball milling speed of 200 rpm for 48 h. S6. Adjust the height of the squeegee of the casting machine to 0.7mm, pour the above silicon nitride casting slurry into the casting machine trough, adjust the speed of the PET casting substrate to 1m / min, so that the silicon nitride casting slurry is evenly coated on the PET casting substrate, and then dry it at 60℃. The length of the drying heating zone is 20m, and a silicon nitride casting film with a thickness of 0.5mm is obtained. S7. The silicon nitride cast film is sequentially degreased and sintered to obtain a silicon nitride ceramic substrate with a thickness of 0.32 mm. The degreasing temperature is 600℃, the holding time is 2 h, and the heating and / or cooling rate is 1℃ / min. The sintering temperature is 1950℃, the holding time is 4 h, and the heating and / or cooling rate is 3℃ / min. The sintering is carried out in a nitrogen atmosphere with a gas pressure of 3 MPa.

[0089] The microstructure of the silicon nitride ceramic substrate in this embodiment is as follows: Figure 3 As shown.

[0090] Comparative Example 1 The preparation method of the silicon nitride ceramic substrate provided in this comparative example is the same as that in Example 1, except that step S3 is omitted and no silane coupling agent is added; the viscosity of the silicon nitride casting slurry obtained in step S5 is 20000 mPa·s, which is too high to be cast.

[0091] Comparative Example 2 The preparation method of the silicon nitride ceramic substrate provided in this comparative example is the same as that in Example 1, except that step S4 is omitted and polyphenols are not added; the viscosity of the silicon nitride casting slurry obtained in step S5 is 15000 mPa·s, which is too high to be cast.

[0092] Comparative Example 3 The preparation method of the silicon nitride ceramic substrate provided in this comparative example is the same as that in Example 1, except that in step S2, the solvent is anhydrous ethanol and butanone in a mass ratio of 30:70; and the silicon nitride cast film obtained in step S6 shows cracking and cannot be sintered.

[0093] Comparative Example 4 The preparation method of the silicon nitride ceramic substrate provided in this comparative example is the same as that in Example 1, except that in step S1, the silicon nitride magnesium powder is replaced with magnesium oxide.

[0094] Test case The performance of the silicon nitride ceramic substrates of Examples 1-3 and Comparative Examples 1-4 was tested, and the results are shown in Table 1.

[0095] Test methods: The thermal conductivity and bending strength of silicon nitride ceramic substrates were tested according to the test methods described in items 6.6 and 6.7 of GB / T 45767—2025 "Silicon Nitride Ceramic Substrates"; among them, comparative examples 1 to 3 did not have silicon nitride ceramic substrates and could not be measured.

[0096] Table 1

[0097] As shown in Table 1, Examples 1, 2, and 3, using the process steps of the present invention, achieve high thermal conductivity and flexural strength, resulting in excellent overall performance and meeting the requirements of vehicle applications. Comparative Examples 1 and 2 lack the key process steps described in the present invention, and the grafting modification of ceramic powder failed to achieve stable dispersion, resulting in high viscosity of the ceramic slurry, which could not complete the casting process. Comparative Example 3 did not use the solvent system described in the present invention. During the casting of the thick film, the solvent evaporation rate was too fast, leading to excessive internal stress in the film and causing drying stress cracking, making it impossible to perform debinding and sintering processes. Comparative Example 4 used an oxide sintering aid, resulting in excessive oxygen content in the aid system, ultimately leading to low thermal conductivity and flexural strength of the ceramic substrate.

[0098] 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 cast film, characterized in that, Silicon nitride casting slurry is cast into silicon nitride film strips after casting. The silicon nitride casting slurry includes a modified ceramic powder suspension, a binder, and a plasticizer. The modified ceramic powder suspension includes modified silicon nitride powder, sintering aid, and solvent; the modified silicon nitride powder includes silicon nitride powder whose surface has been successively modified by silane coupling agent and polyphenol grafting; the silane coupling agent contains amino groups and / or mercapto groups. The solvents include anhydrous ethanol, butanone, and cyclohexanone.

2. The method for preparing silicon nitride cast film tape according to claim 1, characterized in that, The preparation method of the modified ceramic powder suspension includes the following steps: S1. The silicon nitride powder and sintering aid are successively ground, dried and sieved to obtain a mixed powder; S2. Grind the mixed powder and solvent to obtain a ceramic powder suspension; S3. Mix the silane coupling agent and the ceramic powder suspension, adjust the pH to 6.5~7, and then grind to obtain a primary grafted ceramic powder suspension. S4. Mix the polyphenols and the primary grafted ceramic powder suspension, adjust the pH to 7.5~8.5, and then grind them to obtain the modified ceramic powder suspension.

3. The method for preparing silicon nitride cast film tape according to claim 2, characterized in that, Includes at least one of the following features (1) to (5); (1) The mass ratio of the silicon nitride powder to the sintering aid is (95~85):(5~15); (2) The average particle size of the silicon nitride powder is 0.5~1.2μm; (3) The specific surface area of ​​the silicon nitride powder is 7~20m². 2 / g; (4) The sintering aids include nitrogen-containing non-oxide sintering aids; (5) The average particle size of the sintering aid is ≤1μm.

4. The method for preparing silicon nitride cast film tape according to claim 2, characterized in that, Includes at least one of the following features (1) to (6); (1) In the solvent, the mass ratio of anhydrous ethanol, butanone and cyclohexanone is (30~70):(70~30):(5~10); (2) The mass ratio of the mixed powder to the solvent is 100:(40~100); (3) The silane coupling agent includes at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldiethoxysilane, N-(aminoethyl)-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane and γ-mercaptopropyltriethoxysilane; (4) The mass ratio of the silane coupling agent to the mixed powder is (2~5):100; (5) The polyphenols include at least one of tannic acid, dopamine, baicalin, gallic acid, pyrogallol, catechin and epi-catechin; (6) The mass ratio of the polyphenol to the mixed powder is (2~5):

100.

5. The method for preparing silicon nitride cast film tape according to claim 2, characterized in that, Includes at least one of the following features (1) to (7); (1) The adhesive comprises at least one of polyvinyl alcohol, polyvinyl butyral, and polyacrylic acid resin; (2) The mass ratio of the binder to the mixed powder is (5~15):100; (3) The plasticizer includes at least one of polyglycerol, polyethylene glycol, polypropylene glycol, dibutyl phthalate, dioctyl phthalate and butyl benzyl phthalate; (4) The mass ratio of the plasticizer to the mixed powder is (5~15):100; (5) The viscosity of the silicon nitride casting slurry is 1500~10000 mPa·s; (6) The casting process includes: applying silicon nitride casting slurry onto the casting substrate using a casting machine blade, and then drying the substrate to obtain the silicon nitride casting film. (7) The height of the scraper of the casting machine is 0.4~1.2mm; the speed of the casting substrate is 0.3~2m / min; the temperature of the drying treatment is 20~80℃, and the length of the heating zone is 10~40m.

6. A silicon nitride cast film tape, characterized in that, The silicon nitride cast film tape was prepared by the method described in any one of claims 1 to 5. Preferably, the thickness of the silicon nitride cast film is 0.25~1mm.

7. A method for preparing a silicon nitride ceramic substrate, characterized in that, After the silicon nitride cast film tape described in claim 6 is sequentially degreased and sintered, a silicon nitride ceramic substrate is obtained.

8. The method for preparing a silicon nitride ceramic substrate according to claim 7, characterized in that, Includes at least one of the following features (1) to (4); (1) The temperature for degreasing and debinding is 500~800℃; (2) The heat preservation time for degreasing and debinding is 1~3h; (3) The sintering temperature is 1750~2000℃; (4) The holding time for sintering is 2~10h.

9. A silicon nitride ceramic substrate, characterized in that, The silicon nitride ceramic substrate was prepared using the method described in claim 7 or 8. Preferably, the thickness of the silicon nitride ceramic substrate is 0.2~0.8 mm.

10. A vehicle power module, characterized in that, Including the silicon nitride ceramic substrate as described in claim 9.

Images