Aluminum nitride ceramic substrate and preparation method and application thereof

Abstract

The invention discloses an aluminum nitride ceramic substrate and a preparation method and application thereof. The aluminum nitride ceramic substrate comprises a substrate body, and the substrate body is made of aluminum nitride ceramic with the relative density larger than or equal to 98.5%. At least one group of micro-channels are arranged in the substrate main body, and the micro-channels are parallel to the substrate main body; the micro-channel is provided with a working medium inlet and a working medium outlet; a covalent ceramic coating is arranged on the inner wall of the micro-channel; the material of the covalent ceramic coating comprises at least one of hexagonal boron nitride, silicon carbide or a boron-carbon-nitrogen compound. The aluminum nitride ceramic substrate has the advantages of low leakage, low dielectric loss, corrosion resistance and long-term reliability.

Description

Technical Field

[0001] This application relates to heat dissipation technology for electronic ceramics and power device packaging, specifically to an aluminum nitride ceramic substrate, its preparation method, and its application. Background Technology

[0002] With the increase in power density of devices such as silicon carbide (SiC) / gallium nitride (GaN), the heat flux density at the packaging interface has reached 100~1000 W·cm. -2 While traditional aluminum nitride (AlN) substrates possess high thermal conductivity and insulation, they typically require an external cold plate or a thickened copper layer for heat dissipation, resulting in long thermal paths, high thermal resistance, and a significant risk of thermal cycling failure. Furthermore, existing AlN substrates suffer from leakage risks, increased dielectric losses, and poor reliability. Summary of the Invention

[0003] To address the aforementioned issues, this application aims to provide an aluminum nitride ceramic substrate, its preparation method, and its applications. The aluminum nitride ceramic substrate of this application achieves high thermal conductivity and insulation, while also improving heat dissipation, chemical corrosion resistance, reducing dielectric loss, and enhancing long-term reliability.

[0004] In a first aspect, this application provides an aluminum nitride ceramic substrate.

[0005] The aluminum nitride ceramic substrate of this application includes a substrate body, wherein the substrate body is aluminum nitride ceramic with a relative density ≥98.5%; the substrate body has at least one set of microchannels, which are parallel to the substrate body; and the microchannels have a working fluid inlet and a working fluid outlet. A covalent ceramic coating is disposed on the inner wall of the microchannels, and the material of the covalent ceramic coating includes at least one of hexagonal boron nitride, silicon carbide, or a boron-carbon-nitrogen composite. In the above scheme, this application uses aluminum nitride ceramic with a relative density ≥98.5% as the substrate body, so that the substrate body of the aluminum nitride ceramic substrate of this application has a dense aluminum nitride ceramic skeleton structure. This achieves high thermal conductivity and insulation, reduces the leakage risk of the aluminum nitride ceramic substrate, and improves the overall wear resistance of the aluminum nitride ceramic substrate. This application incorporates at least one set of closed-loop microchannels within the substrate body. These microchannels serve as cooling (or heat dissipation) channels for the flow of dielectric coolant, achieving heat dissipation of the aluminum nitride ceramic substrate without the need for an external cold plate or thickened copper layer. This integrates high thermal conductivity, high insulation, and heat dissipation into a single design. Furthermore, the inner walls of the microchannels are coated with a covalent ceramic coating made of at least one of hexagonal boron nitride, silicon carbide, or a boron-carbon-nitrogen composite material. This coating helps reduce the likelihood of corrosion or hydrogen evolution when the inner walls of the microchannels come into contact with the dielectric coolant, thereby improving the reliability of the aluminum nitride ceramic substrate, particularly its long-term reliability. Moreover, testing has shown that the aluminum nitride ceramic substrate of this application maintains water flow without leakage under an internal pressure of 5 bar, demonstrating low leakage, low dielectric loss, corrosion resistance, and long-term reliability.

[0006] In some embodiments, the thickness H of the covalent ceramic coating satisfies 50nm ≤ H ≤ 500nm. Preferably, 50nm ≤ H ≤ 300nm. More preferably, 80nm ≤ H ≤ 200nm.

[0007] In some embodiments, the microchannels employ at least one flow path topology among serpentine, parallel inline, and distribution-convergence.

[0008] In some embodiments, the cross-sectional shape of the microchannel includes at least one of near-rectangular, rounded rectangular, elliptical, and trapezoidal shapes.

[0009] In some embodiments, the cross-sectional diameter of the microchannel is R, and 30µm≤R≤500µm.

[0010] In some embodiments, the center-to-center distance of the microchannels is L, and 200µm≤L≤1000µm.

[0011] In some embodiments, the aluminum nitride ceramic substrate satisfies at least one of the following conditions: (1) the thickness uniformity of the covalent ceramic coating at room temperature is TU, and TU≤1.5; (2) the dielectric loss tangent of the covalent ceramic coating at a frequency of 10 GHz is tanδ, and tanδ≤3×10 -3 (3) The room temperature thermal conductivity of the substrate body is ≥170 W·m. -1 ·K -1 .

[0012] In some embodiments, a metallization layer is disposed on the surface of the substrate body, and the metal in the metallization layer includes at least copper; the thickness of the metallization layer is D, and 50µm≤D≤600µm.

[0013] In some embodiments, the thickness of the substrate body is 0.2 mm to 1.2 mm. Preferably, the thickness of the substrate body is 0.3 mm to 0.8 mm.

[0014] In some embodiments, the minimum remaining ceramic thickness of the channel wall is 'a', and 'a' ≥ 80 µm. Preferably, 'a' ≥ 120 µm.

[0015] Secondly, any of the above-mentioned methods for preparing aluminum nitride ceramic substrates includes the following steps: Step 1, Template Forming: Using the sacrificial template method, a corresponding sacrificial template pattern is formed on the aluminum nitride ceramic membrane according to the size and shape of the target microchannel, resulting in an aluminum nitride ceramic membrane with the sacrificial template pattern.

[0016] Step 2, Lamination: Based on the number of target microchannel groups, the corresponding number of aluminum nitride ceramic films with sacrificial template patterns obtained in Step 1 are aligned, laminated, and stacked to obtain a laminated structure.

[0017] Step 3, Pre-firing: Under a protective gas atmosphere, the stacked structure is pre-firing to remove the sacrificial template in the stacked structure and obtain a pre-firing structure with microchannels.

[0018] Step 4, sintering: The pre-sintered structure is sintered at a temperature of 1500℃~1800℃ to obtain dense aluminum nitride ceramic with microchannels.

[0019] Step 5, deposition of covalent ceramic coating: Using a deposition method, a precursor corresponding to at least one of hexagonal boron nitride, silicon carbide, or boron-carbon-nitrogen composite materials is used as the deposition raw material to deposit a covalent ceramic coating on the inner wall of the microchannel, thereby obtaining the aluminum nitride ceramic substrate.

[0020] In the above-described scheme, this application obtains an aluminum nitride ceramic substrate through template forming, stacking, pre-firing, sintering, and deposition of a covalent ceramic coating. Therefore, the preparation method of this application is easy to operate and is conducive to the mass production of aluminum nitride ceramic substrates.

[0021] Thirdly, the application of any of the above-mentioned aluminum nitride ceramic substrates in electronic devices.

[0022] In the above solution, the electronic device includes a power semiconductor module, a high heat flux LED, an RF power amplifier, or a data center cold plate replacement. The power semiconductor module includes any one of a silicon carbide (SiC) power semiconductor module, a gallium nitride (GaN) power semiconductor module, and an IGBT power semiconductor module.

[0023] In some embodiments, when the aluminum nitride ceramic substrate of this application is applied to electronic devices, a sealing structure is provided between the working fluid inlet of the microchannel and the output end of the external cooling system, and between the working fluid outlet of the microchannel and the input end of the external cooling system, to achieve sealing. This allows the dielectric coolant provided by the external cooling system to flow in the microchannel of the aluminum nitride ceramic substrate. Without the need for an external cold plate or a thickened copper layer, effective heat dissipation can be achieved through its own microchannel. Compared with traditional solid aluminum nitride substrates, the thermal path is greatly shortened. Furthermore, the junction-liquid thermal resistance of the aluminum nitride ceramic substrate of this application is reduced by more than 40% compared with that of traditional solid aluminum nitride substrates of the same thickness, effectively reducing the thermal resistance of the aluminum nitride ceramic substrate and effectively reducing the risk of thermal cycling failure.

[0024] This application does not limit the specific structural type of the ceramic-metal transition sealing structure, as long as it can achieve the sealing of the microchannel. For example, in some embodiments, the sealing structures at the working fluid inlet and outlet of the microchannel can be the same or different, and the sealing structures at the working fluid inlet and outlet can be selected from any one of, but not limited to, active brazing rings, glass solder seals, or metal solder plugs. Based on the above scheme, the helium leak detection rate of the aluminum nitride ceramic substrate of this application can be ≤1×10⁻⁶. -9 Pa·m 3 ·s -1 . Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a process flow diagram of the method for preparing the aluminum nitride ceramic substrate of this application.

[0027] Figure 2 This is a top view of the serpentine parallel connection used in Example 1-1.

[0028] Figure 3 This is a schematic diagram of the substrate structure with a covalent ceramic coating deposited in Example 1-1.

[0029] Figure 4 for Figure 3 A magnified view of a portion at point A.

[0030] Figure 5 A schematic diagram of the cross-sectional structure of substrate 1 in Example 1-1.

[0031] Figure 6 This is a schematic diagram of the structure of substrate 2 in Example 1-1.

[0032] Figure 7 for Figure 6 A magnified view of a section at point B.

[0033] Figure 8 This is a schematic diagram of an aluminum nitride ceramic substrate with pads on its upper surface.

[0034] Figure 9 This is a schematic diagram of the structure of the device formed by the aluminum nitride ceramic substrate and the power chip in this application.

[0035] Figure 10 This is a top view of the allocation-aggregation topology used in Examples 3-6.

[0036] Figure 11 This is a schematic diagram of the aluminum nitride ceramic substrate in Examples 3-6. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0038] In the description of this application, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings, and are used only for ease of description and simplification of operation. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. In addition, the terms "first" and "second" are used only for descriptive distinction and have no special meaning.

[0039] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions. Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included. Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0041] It should be emphasized that the preparation methods or operation steps not specifically described in this application all refer to the prior art in this field, which should be known by those skilled in the art, and therefore will not be described again in this application.

[0042] This application investigates and analyzes the reasons for the leakage risk, increased dielectric loss, and poor reliability of existing AlN substrates. The main reasons are found to be twofold: First, the relatively low density of existing AlN substrates leads to leakage risks during actual operation. Second, the channels in existing AlN substrates are mainly open pores. These open pores easily absorb air, moisture, or impurities from the packaging process (such as solder residue and flux). These impurities have dielectric properties far lower than the AlN matrix, forming "loss centers" within the AlN matrix, exacerbating energy loss in the alternating electric field and increasing dielectric loss. Especially when moisture seeps into the open pores, it forms "conductive channels," reducing the insulation resistance and breakdown field strength of the AlN substrate. Furthermore, these open pores make the inner walls prone to corrosion or hydrogen evolution when in contact with the dielectric coolant, thus affecting the reliability of the AlN substrate, especially its long-term reliability. To address these problems, this application provides an aluminum nitride ceramic substrate, its preparation method, and its applications.

[0043] In a first aspect, this application provides an aluminum nitride ceramic substrate.

[0044] The aluminum nitride ceramic substrate of this application includes a substrate body 100, which is aluminum nitride ceramic with a relative density of ≥98.5%. Based on the above scheme, the substrate body 100 of the aluminum nitride ceramic substrate of this application has a dense aluminum nitride ceramic skeleton structure, which not only achieves high thermal conductivity and insulation, but also reduces the leakage risk of the aluminum nitride ceramic substrate and improves the overall wear resistance of the aluminum nitride ceramic substrate. The substrate body 100 of this application has at least one set of microchannels 200 inside; the microchannels 200 are parallel to the substrate body 100, and the microchannels 200 have a working fluid inlet 201 and a working fluid outlet 202. In the above scheme, the working medium inlet 201 and the working medium outlet 202 are used to supply the flow of the working medium (dielectric coolant), so that the microchannel 200 in the substrate body 100 can be used as a cooling channel for the flow of dielectric coolant. Without the need for an external cold plate or thickened copper layer, heat dissipation of the aluminum nitride ceramic substrate can be achieved, so that the aluminum nitride ceramic substrate of this application realizes an integrated design of high thermal conductivity, high insulation and heat dissipation.

[0045] The microchannel 200 of this application has a covalent ceramic coating 300 on its inner wall. The covalent ceramic coating 300 helps reduce the possibility of corrosion or hydrogen evolution occurring on the inner wall of the microchannel 200 after contact with the dielectric coolant, thereby improving the overall reliability of the aluminum nitride ceramic substrate, especially its long-term reliability. Furthermore, the covalent ceramic coating 300 in this application is made of at least one of hexagonal boron nitride (h-BN), silicon carbide (SiC), or a boron-carbon-nitrogen (BCN) composite. Based on the above, the covalent ceramic coating 300 (such as SiC or h-BN) has extremely high covalent bond energies (approximately 301 kJ / mol for Si-C and approximately 280 kJ / mol for NB). At room temperature to medium-high temperatures, it does not react with most chemical media, thus improving the chemical corrosion resistance (i.e., chemical inertness) of the inner wall of the microchannel 200 and reducing interfacial friction and dielectric loss.

[0046] In summary, the aluminum nitride ceramic substrate of this application achieves an integrated design that combines high thermal conductivity, high insulation, and heat dissipation. It also reduces the risk of leakage and dielectric loss, and decreases the possibility of corrosion or hydrogen evolution after the microchannel 200 comes into contact with the dielectric coolant, thus improving the reliability of the aluminum nitride ceramic substrate, especially its long-term reliability. Furthermore, testing shows that the aluminum nitride ceramic substrate of this application maintains water flow without leakage under an internal pressure of 5 bar. The aluminum nitride ceramic substrate of this application exhibits low leakage, low dielectric loss, corrosion resistance, and long-term reliability.

[0047] In some embodiments, the cross-sectional diameter of the microchannel 200 is R, and 30µm≤R≤500µm, which can further improve the heat dissipation performance of the aluminum nitride ceramic substrate while achieving the above-mentioned effects. For example, the cross-sectional diameter R of the microchannel 200 is 30µm, 50µm, 100µm, 150µm, 200µm, 250µm, 300µm, 350µm, 400µm, 450µm, 500µm, or a range between any two of the above values.

[0048] In some preferred embodiments, 50µm≤R≤300µm, based on the above scheme, can better improve the heat dissipation performance of the aluminum nitride ceramic substrate. In some more preferred embodiments, 80µm≤R≤200µm, based on the above scheme, can further improve the heat dissipation performance of the aluminum nitride ceramic substrate.

[0049] In some embodiments, the substrate body 100 is aluminum nitride ceramic with a relative density of ≥99.0%. Based on the above scheme, the aluminum nitride ceramic substrate of this application can have a denser aluminum nitride ceramic skeleton structure, which is beneficial to better reduce the leakage risk of the aluminum nitride ceramic substrate and better improve the overall wear resistance of the aluminum nitride ceramic substrate, which is beneficial to further reduce the leakage risk and dielectric loss of the aluminum nitride ceramic substrate.

[0050] This application does not limit the specific thickness of the covalent ceramic coating 300. The thickness can be set according to the material used, as long as the desired effect of this application is achieved. For example, in some embodiments, the thickness H of the covalent ceramic coating 300 is 50nm ≤ H ≤ 500nm. It is understood that the thickness of the covalent ceramic coating 300 on the inner wall of the microchannel 200 all satisfy the range of 50nm ≤ H ≤ 500nm. Based on the above scheme, the thickness of the covalent ceramic coating 300 is within a suitable range, which can prevent the covalent ceramic coating from peeling off due to the scouring of dielectric coolant during actual use. This effectively prevents the dielectric coolant from entering the aluminum nitride substrate and damaging the substrate, thereby improving the chemical corrosion resistance of the inner wall of the microchannel 200 while reducing interfacial friction and dielectric loss. It should be noted that the term "chemical corrosion resistance" in this application includes resistance to acid corrosion, alkali corrosion, and salt spray corrosion.

[0051] For example, the thickness H of the covalent ceramic coating 300 is 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, or any two of the above values. For instance, in some preferred embodiments, 50 nm ≤ H ≤ 300 nm. Based on the above scheme, the chemical corrosion resistance of the inner wall of the microchannel 200 can be better improved, and the interfacial friction and dielectric loss can be reduced. In some more preferred embodiments, 80 nm ≤ H ≤ 200 nm. Based on the above scheme, the chemical corrosion resistance of the inner wall of the microchannel 200 can be further improved, and the interfacial friction and dielectric loss can be reduced. Specifically, in some embodiments, when the covalent ceramic coating 300 includes h-BN, its c-axis orientation factor is ≥ 0.5, and the thickness H of the covalent ceramic coating 300 satisfies 80 nm ≤ H ≤ 150 nm. Based on the above scheme, the fluid shear and wall chemical reaction of the aluminum nitride ceramic substrate of this application can be further reduced. Specifically, in some embodiments, when the covalent ceramic coating 300 includes SiC, its microhardness is ≥20 GPa, and the thickness H of the covalent ceramic coating 300 satisfies 100 nm ≤ H ≤ 300 nm. Based on the above scheme, the wear resistance and pressure resistance of the aluminum nitride ceramic substrate of this application can be further improved.

[0052] In this application, the channel center distance of the microchannels 200 is L. It should be noted that the term "channel center distance" in this application refers to the distance between the centers of two adjacent microchannels 200 in a serpentine or parallel distribution of microchannels 200. This application considers that when L is too large (exceeding 1000µm), the flow channel density of the microchannels 200 will be low, which is not conducive to heat dissipation of the aluminum nitride ceramic substrate; while when L is too small (below 200µm), the flow channel density of the microchannels 200 will be too large, affecting the strength of the aluminum nitride substrate. This will not only reduce the reliability of the aluminum nitride ceramic substrate, but also increase the difficulty of microchannel design and fabrication. Therefore, based on the above considerations, in some embodiments, 200µm≤L≤1000µm. Based on the above scheme, the heat dissipation performance and long-term reliability of the aluminum nitride ceramic substrate of this application can be improved. For example, the channel center distance L of the microchannel 200 is 200µm, 300µm, 400µm, 500µm, 600µm, 700µm, 800µm, 900µm, 1000µm, or any two of the above values. For instance, in some embodiments, 300µm≤L≤700µm. Based on the above scheme, the heat dissipation performance and long-term reliability of the aluminum nitride ceramic substrate of this application can be better improved.

[0053] This application does not limit the specific flow path topology of the microchannel 200, as long as it can achieve the effect of this application. For example, in some embodiments, the microchannel 200 adopts at least one of the following flow path topologies: serpentine, parallel inline, and distribution-convergence. Based on the above schemes, the heat dissipation performance of the aluminum nitride ceramic substrate can be further improved without affecting the structural strength of the aluminum nitride ceramic substrate. In some embodiments, the microchannels 200 can be partitioned and connected in parallel in the same substrate, and the working fluid inlet 201 and working fluid outlet 202 of the microchannel 200 are respectively located at the edge or end face of the substrate body 100.

[0054] This application does not limit the specific shape of the microchannel 200, as long as it can achieve the effect of this application. For example, in some embodiments, the cross-sectional shape of the microchannel 200 includes at least one of near-rectangular, rounded rectangular, elliptical, and trapezoidal shapes.

[0055] In some embodiments, the thickness uniformity of the covalent ceramic coating 300 at room temperature is TU, and TU ≤ 1.5. Based on the above scheme, it is beneficial to ensure that the covalent ceramic coating 300 uniformly covers the inner wall of the microchannel 200, thereby better improving the chemical corrosion resistance and wear resistance of the inner wall of the microchannel 200, thus better reducing dielectric loss, and better improving the reliability of the aluminum nitride ceramic substrate. It is understood that the term "room temperature" in this application refers to 23℃±2℃, TU is an abbreviation for Thickness Uniformity, and TU = maximum thickness / minimum thickness.

[0056] In some embodiments, the dielectric loss tangent of the covalent ceramic coating 300 at a frequency of 10 GHz is tanδ, and tanδ ≤ 3 × 10⁻⁶. -3 Based on the above scheme, it is beneficial to better reduce the dielectric loss of aluminum nitride ceramic substrates.

[0057] In some embodiments, the room temperature thermal conductivity of the substrate body 100 is ≥170 W·m. -1 ·K -1 Based on the above scheme, it is beneficial to improve the heat dissipation performance of the aluminum nitride ceramic substrate and reduce the risk of thermal cycling failure. In some preferred embodiments, the room temperature thermal conductivity of the substrate body 100 is ≥200 W·m. -1 ·K -1 Based on the above scheme, it is beneficial to further improve the heat dissipation performance of aluminum nitride ceramic substrates and further reduce the risk of thermal cycling failure of aluminum nitride ceramic substrates.

[0058] Considering the application requirements of the aluminum nitride ceramic substrate in electronic devices, in some embodiments, a metallization layer 400 is provided on the surface of the substrate body 100, so that the metallization layer 400 and the substrate body 100 form a heat dissipation-electrical interconnection integrated substrate, so as to achieve the performance matching of the ceramic material's "insulation / high thermal conductivity" and the electronic device's "electrical conductivity / interconnection".

[0059] This application does not limit the specific material of the metallization layer 400, as long as it can achieve the effects of this application. In some embodiments, the material of the metallization layer 400 includes at least copper. Based on the above solution, metallic copper not only has low resistivity but also good conductivity, and the metallization layer 400 including the copper layer can act as a "conductive bridge" to realize the electrical connection between electronic devices and external circuits. In some embodiments, the thickness of the metallization layer 400 is D, and 50µm≤D≤600µm. Based on the above solution, it is possible to improve conductivity while taking into account the heat dissipation and reliability of the aluminum nitride ceramic substrate. Exemplarily, the thickness D of the metallization layer 400 is 50µm, 100µm, 150µm, 200µm, 250µm, 300µm, 350µm, 400µm, 450µm, 500µm, 550µm, 600µm or any two of the above values. For example, in some preferred embodiments, 150µm≤D≤400µm, based on the above scheme, it is possible to improve conductivity while better balancing the heat dissipation and reliability of the aluminum nitride ceramic substrate.

[0060] In some embodiments, to facilitate the application of the aluminum nitride ceramic substrate of this application in electronic devices, the working fluid inlet 201 and working fluid outlet 202 of the microchannel 200 of this application are respectively provided with sealing structures 500 to facilitate sealing connection with the pipe interface of the external cooling system. This application does not limit the specific structural type of the ceramic-metal transition sealing structure 500, as long as it can achieve the sealing of the microchannel 200. For example, in some embodiments, the sealing structures 500 at the working fluid inlet 201 and the working fluid outlet 202 of the microchannel 200 can be the same or different, and the sealing structures 500 at the working fluid inlet 201 and the working fluid outlet 202 of the microchannel 200 can be selected from any one of, including but not limited to, active brazing rings, glass brazing filler metal seals, or metal brazing plugs. Based on the above solutions, the aluminum nitride ceramic substrate of this application can avoid dielectric coolant leakage at the interface during actual application, has the advantage of low leakage, and its helium leak detection rate meets ≤1×10 -9 Pa·m 3 ·s -1 .

[0061] This application does not limit the specific thickness of the substrate body 100. The appropriate thickness can be selected according to the needs of the actual application scenario. For example, in some embodiments, the thickness of the substrate body 100 is 0.2mm to 1.2mm. Based on the above solution, the aluminum nitride ceramic substrate of this application can balance thermal conductivity, mechanical reliability, and high-voltage insulation. Exemplarily, the thickness of the substrate body 100 is 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1mm, 1.2mm, or any two of the above values. For example, in some preferred embodiments, the thickness of the substrate body 100 is 0.3mm to 0.8mm. Based on the above solution, the aluminum nitride ceramic substrate of this application can better balance thermal conductivity, mechanical reliability, and high-voltage insulation.

[0062] In some embodiments, the minimum remaining ceramic thickness of the channel wall is 'a', and 'a' ≥ 80µm. Based on the above scheme, this application can better balance the heat dissipation performance and mechanical reliability of the aluminum nitride ceramic substrate. It should be noted that the term "minimum remaining ceramic thickness of the channel wall" in this application refers to the ceramic thickness between the top of the microchannel 200 and the upper surface of the aluminum nitride ceramic substrate along the thickness direction of the aluminum nitride ceramic substrate, or the ceramic thickness between the bottom of the microchannel 200 and the lower surface of the aluminum nitride ceramic substrate.

[0063] In some preferred embodiments, a ≥ 120 µm. Based on the above scheme, this application can further balance the heat dissipation performance and mechanical reliability of the aluminum nitride ceramic substrate.

[0064] Secondly, any of the above-mentioned methods for preparing aluminum nitride ceramic substrates includes the following steps: Step 1, Template Forming: Using the sacrificial template method, a corresponding sacrificial template pattern is formed on the aluminum nitride ceramic film according to the size and shape of the target microchannel 200, resulting in an aluminum nitride ceramic film with the sacrificial template pattern.

[0065] In step 1 above, it should be noted that this application does not limit the size and shape of the microchannel 200; a corresponding sacrificial template pattern can be formed according to actual needs. For example, in some embodiments, when the microchannel 200 adopts at least one of the following flow path topologies: serpentine, parallel inline, or distribution-convergence, a corresponding sacrificial template pattern is formed according to the corresponding flow path topology. In other embodiments, when the cross-sectional shape of the microchannel 200 includes at least one of the following: near-rectangular, rounded rectangular, elliptical, or trapezoidal, a corresponding sacrificial template pattern is formed according to the corresponding cross-sectional shape and the corresponding flow path topology.

[0066] This application does not limit the specific location of the working fluid inlet 201 and working fluid outlet 202 of the microchannel 200, as long as it can facilitate the entry and exit of the cooling dielectric fluid. For example, in some embodiments, the working fluid inlet 201 and working fluid outlet 202 of the microchannel 200 are respectively located at the edge or end face of the substrate.

[0067] This application does not limit the specific forming method of the sacrificial template on the aluminum nitride ceramic film, as long as the effect of this application can be achieved. For example, in some embodiments, the forming method of the sacrificial template on the aluminum nitride ceramic film includes, but is not limited to, screen printing, inkjet printing, hot pressing, photolithography, direct writing, or micro-extrusion. When screen printing is used, the mesh size of the screen is 250-400 mesh. This application does not limit the specific type of sacrificial template used, as long as the effect of this application can be achieved. For example, in some embodiments, the sacrificial template used in this application includes, but is not limited to, combustible polymers, so that it can be removed in the subsequent pre-firing step, leaving only the corresponding microchannel 200 structure. This application also does not limit the specific type of combustible sacrificial template, as long as the effect of this application can be achieved. For example, in some embodiments, the combustible polymer used in this application includes, but is not limited to, at least one of polyvinyl alcohol, polyacrylate, polylactic acid, and expandable fibers. This application also does not limit the specific template height formed by the sacrificial template; the appropriate height can be selected according to the actual application scenario requirements of the aluminum nitride ceramic substrate. For example, in some embodiments, the height of the sacrificial template is 20µm to 400µm. It should be noted that, considering the potential thickness shrinkage of the ceramic material during sintering, the thickness of the sacrificial template is set according to the material's shrinkage rate when adding the sacrificial template, and the thickness of the sacrificial template is generally between 1.1 and 1.3 times the designed thickness, depending on the material. This application does not limit the specific preparation method of the aluminum nitride ceramic film, as long as it achieves the function of this application. For example, the aluminum nitride ceramic film of this application can be obtained by casting, or by other commonly used preparation methods in the art. Exemplarily, in some embodiments, the aluminum nitride ceramic film is obtained through the following steps: mixing AlN powder with an organic carrier and a binder to obtain a slurry with a solid content ≥60wt%; casting the slurry to obtain an aluminum nitride ceramic green sheet with a thickness of 50µm to 300µm, and drying it until the solvent content is ≤1wt%, thus obtaining the aluminum nitride ceramic film. This application does not limit the specific type of organic carrier, as long as it helps to uniformly disperse the AlN powder. For example, in some embodiments, the organic carrier includes, but is not limited to, at least one of polyvinyl butyral (PVB), polyethylene glycol (PEG), dibutyl phthalate (DBP), and acrylic acid systems.

[0068] It should also be noted that the center distance of the microchannel 200 is adjusted by adjusting the spacing of the template traces of the sacrificial template pattern.

[0069] Step 2, Lamination: Based on the number of groups of target microchannels 200, the corresponding number of aluminum nitride ceramic films and the aluminum nitride ceramic films with sacrificial template patterns obtained in Step 1 are aligned, laminated, and stacked to obtain a laminated structure.

[0070] In step 2 above, it should be noted that this application does not limit the specific number of layers; the layers can be stacked according to actual needs. In some embodiments, the alignment error during stacking is ≤30µm, which can improve the accuracy of microchannel 200 formation, enhance the controllability of aluminum nitride ceramic substrate product performance stability, and facilitate the mass production of aluminum nitride ceramic substrates of this application. This application does not limit the specific lamination process parameters, as long as the effect of this application can be achieved. For example, in some embodiments, the lamination pressure during lamination is 5MPa~50MPa, the temperature is 60℃~120℃, and the time is 10min~30min, which helps to improve the bonding effect between layers, so that the resulting stacked structure can form a dense aluminum nitride ceramic with microchannel 200 through subsequent pre-firing and sintering.

[0071] Step 3, Pre-firing: Under a protective gas atmosphere, the laminated structure is pre-firing to remove the sacrificial template in the laminated structure and obtain a pre-firing structure with microchannels 200.

[0072] In step 3 above, it should be noted that this application does not limit the specific gas used for protection, as long as it ensures the safe conduct of the pre-firing process. For example, in some embodiments, the protection gas includes, but is not limited to, inert gas or nitrogen. This application does not limit the specific pre-firing temperature; the appropriate pre-firing temperature is selected based on the actual sacrificial template material used, so that the sacrificial template pattern in the laminated structure is eliminated during the pre-firing process. For example, in some embodiments, the pre-firing temperature is 500℃~900℃. In some embodiments, the pre-firing heating rate is 0.5℃·min. -1 ~2℃·min -1 This facilitates uniform heating of the laminated structure. In some embodiments, the preheating time is 0.5h to 3h to improve the glue removal effect of the sacrificial template pattern in the laminated structure.

[0073] Step 4, sintering: The pre-sintered structure is sintered at a temperature of 1500℃~1800℃ to densify the pre-sintered structure and obtain dense aluminum nitride ceramic with microchannels 200.

[0074] In step 4 above, it should be noted that by limiting the sintering temperature to 1500℃~1800℃, this application enables the sintering temperature to meet the critical sintering temperature of aluminum nitride. At this sintering temperature, the atomic diffusion activation energy of aluminum nitride is reduced, the surface diffusion and grain boundary diffusion rates are significantly accelerated, the particle necks grow rapidly, the pores are "squeezed" closed, and the particle rearrangement is more complete, thereby increasing the packing density and achieving the densification of aluminum nitride, forming a dense aluminum nitride ceramic with a relative density ≥98.5%.

[0075] This application does not limit the specific holding time at the sintering temperature. The holding time can be adjusted according to the actual selected sintering temperature, as long as the desired effect is achieved. For example, in some embodiments, when the sintering temperature is in the range of 1500℃ to 1800℃, the holding time is 0.5h to 3h, which is beneficial for better densification of aluminum nitride, forming dense aluminum nitride ceramics with a relative density ≥98.5%. In some preferred embodiments, the sintering temperature is 1600℃ to 1750℃. Based on the above scheme, the sintering temperature is close to the optimal sintering temperature, allowing aluminum nitride to achieve better densification at this temperature, forming dense aluminum nitride ceramics with a relative density ≥99.0%.

[0076] Step 5, deposition of covalent ceramic coating 300: Using a deposition method, a precursor corresponding to at least one of hexagonal boron nitride, silicon carbide or boron-carbon-nitrogen composite is used as the deposition material. It is introduced into the microchannel 200 through the fluid interface of the microchannel 200 and a covalent ceramic coating 300 is deposited on the inner wall of the microchannel 200 to obtain an aluminum nitride ceramic substrate.

[0077] In step 5 above, this application uses a deposition method to prepare the covalent ceramic coating 300. This facilitates the formation of a continuous, non-porous, and dense covalent ceramic coating 300, which completely covers the inner wall of the microchannel 200, effectively preventing external substances, such as corrosive media (acids, alkalis, water vapor, organic solvents, etc.) that may be present in the dielectric coolant, from contacting the substrate 100. It is understood that, due to the non-selective recognition effect of the deposition method, while the covalent ceramic coating 300 is deposited and formed on the inner wall of the microchannel 200, a covalent ceramic coating 300 is also formed on the surface of the substrate 100, thereby further improving the barrier effect between the substrate 100 and corrosive media (acids, alkalis, water vapor, organic solvents, etc.), and better improving the corrosion resistance of the aluminum nitride ceramic substrate. It should be noted that this application does not limit the specific deposition method of the covalent ceramic coating 300, as long as it can achieve the effect of this application. For example, in some embodiments, the deposition method of the covalent ceramic coating 300 includes, but is not limited to, chemical vapor deposition (CVD) or atomic layer deposition (ALD).

[0078] In some embodiments, when the covalent ceramic coating 300 is boron nitride (h-BN), boron and nitrogen sources are used as precursors, the deposition temperature is 600℃~900℃, the deposition pressure is 10Pa~500Pa, and the deposition rate is 1nm·min. -1 ~20nm·min -1The deposition time can be adjusted according to the desired thickness of the covalent ceramic coating 300. This application does not limit the specific type of precursor, as long as it achieves the desired effect. For example, in some embodiments, the precursor may be selected from borazine (a cyclic gaseous compound containing boron and nitrogen), BCl3+NH3, or equivalents thereof.

[0079] In some embodiments, when the covalent ceramic coating 300 is SiC, the precursor is methyltrichlorosilane (MTS) + H2 or an equivalent silicon carbide source, and the deposition temperature is 700°C to 1100°C.

[0080] In some embodiments, when depositing the covalent ceramic coating 300 using atomic layer deposition (ALD), nanometer-level thickness control is achieved through pulse-purge-reaction cycles, with 200 to 3000 cycles. After deposition, annealing is performed at 800°C to 1400°C to improve the density and adhesion of the covalent ceramic coating. In some embodiments, the annealing time is 0.5 h to 2 h to further enhance the density and adhesion of the covalent ceramic coating.

[0081] Considering that in the actual sintering process, the structure of the microchannels 200 formed in the dense aluminum nitride ceramic may be either a through-hole structure or a closed structure with sealed inlets and outlets, the following considerations apply. When the microchannels 200 formed in the dense aluminum nitride ceramic are through-hole structures, subsequent covalent ceramic coating deposition can be performed directly. However, when the microchannels 200 formed in the dense aluminum nitride ceramic are closed structures, it is not conducive to directly depositing a covalent ceramic coating on the inner wall of the channel for subsequent covalent ceramic coating deposition.

[0082] Exemplarily, in some embodiments, if the microchannels 200 in the dense aluminum nitride ceramic obtained in step 4 are already closed (a closed structure), process holes need to be opened at the locations of the microchannels 200 in the dense aluminum nitride ceramic before depositing the covalent ceramic coating 300. At least two process holes are opened so that they serve as fluid interfaces (working fluid inlet 201 and working fluid outlet 202) for evacuation and precursor exchange, allowing the corresponding precursor material to enter the microchannels 200 through the process holes and deposit and form the corresponding covalent ceramic coating 300 on the inner wall of the microchannels 200. This application does not limit the specific method of opening the process holes, as long as it achieves the purpose of this application. For example, the process holes can be opened according to conventional methods in the art. In some embodiments, the aperture φ of the process holes is 0.3 mm to 1.0 mm.

[0083] For example, in some embodiments, if the microchannel 200 still maintains the preset structure, there is no need to open process holes to directly perform deposition, so that the corresponding precursor raw material can be deposited on the inner wall of the microchannel 200 and form the corresponding covalent ceramic coating 300.

[0084] In some embodiments, to facilitate the application of the aluminum nitride ceramic substrate of this application in electronic devices and to simplify the process steps in subsequent applications, this application further includes a post-processing step in addition to step 5 during the preparation of the aluminum nitride ceramic substrate. For example, in some embodiments, the post-processing step further includes step 6, sealing: sealing structures 500 are respectively provided at the working fluid inlet 201 and working fluid outlet 202 of the microchannel 200.

[0085] In the above solution, this application provides sealing structures 500 at the working fluid inlet 201 and working fluid outlet 202 of the microchannel 200, so as to seal the working fluid inlet 201 and working fluid outlet 202 of the microchannel 200 with the pipe interface of the external cooling system through the sealing structures 500, which can further improve the anti-leakage effect of dielectric coolant in the microchannel 200.

[0086] In the above scheme, if the microchannel 200 is already sealed before the covalent ceramic coating is deposited, and the covalent ceramic coating is deposited through the process orifice in step 5, then a sealing structure 500 is set at the orifice opening in step 6.

[0087] In some embodiments, a ceramic-metal sealing structure is used to seal the process orifice or fluid interface. This application does not limit the specific type of ceramic-metal transition sealing structure, as long as it can achieve the sealing of the microchannel 200. For example, in some embodiments, the sealing structures 500 at the working fluid inlet 201 and the working fluid outlet 202 of the microchannel 200 can be the same or different, such as those selected from, but not limited to, active brazing rings, glass solder seals, or metal brazing plugs. Based on the above solutions, the helium leak detection rate of the aluminum nitride ceramic substrate of this application can be ≤1×10⁻⁶. -9 Pa·m 3 ·s -1 .

[0088] Considering that the aluminum nitride ceramic substrate also needs to meet the "conductivity / interconnection" requirement with electronic devices when used, in some embodiments, the post-processing steps also include step 7, preparation of metallization layer 400: a metallization layer 400 is formed on the surface of the aluminum nitride ceramic substrate obtained in step 6.

[0089] This application does not limit the specific method of forming the metallization layer 400, as long as it can achieve the effect of this application. For example, in some embodiments, the metallization layer 400 is formed by AMB (Active Metal Brazing) or DBC (Direct Bonded Copper). It should be noted that AMB is a metallization technology that achieves ceramic-metal bonding through solder containing active elements. The key to this method is to use solder containing active elements such as Ti, Zr, or lanthanides. The active elements will chemically react with the ceramic surface to form a stable transition layer at the interface, thereby allowing the solder to fully wet the ceramic surface. After cooling, a high-strength bond between the ceramic and the copper foil is achieved. The process steps are as follows: first, clean the ceramic substrate and uniformly coat the surface with a thin layer of active metal solder, then attach the copper foil, and then heat it in a vacuum environment or inert atmosphere at 800℃~950℃ to melt the solder and wet the interface. After cooling, the solder solidifies to form a solid connection, and finally, the copper layer is etched by wet etching to create the desired circuit pattern. This process operates at a relatively low temperature and offers greater compatibility with ceramic substrates. DBC relies on a high-temperature eutectic reaction to achieve metallization between the ceramic and copper foil. In a high-temperature, oxygen- and nitrogen-containing atmosphere (1065℃~1083℃), a Cu / O eutectic liquid phase forms at the interface between the copper foil and the ceramic substrate. This Cu / O eutectic liquid phase reacts with alumina ceramics to generate intermediate phases such as CuAlO2, thus achieving bonding between the copper foil and the ceramic. DBC requires no additional solder; the copper foil is directly bonded to the ceramic substrate and then placed in the aforementioned high-temperature, oxygen-containing atmosphere for eutectic sintering. After sintering, the copper foil is patterned using an etching process to form a circuit that meets the application requirements. It is understandable that the material of the metallization layer 400 can be prepared using different methods according to actual needs. For example, when the metallization layer 400 only requires copper, the DBC method can be used to prepare the metallization layer 400; when the metallization layer 400 needs to include other metals, such as when the metallization layer 400 includes a Ti / Cr-Ni-Cu diffusion barrier / buffer composite layer, the AMB method can be used to prepare the metallization layer 400.

[0090] For example, a metallization layer 400 is formed using the AMB method, the active layer contains Ti or Zr, and the Cu foil thickness is 100µm~400µm.

[0091] For example, a copper metallization layer 400 is formed using the DBC method, with a shear strength of ≥30MPa at the copper-ceramic interface. Optional Cr / Ni stepped barrier layer and ENIG (Electroless Nickel Immersion Gold) / ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) surface treatment are used.

[0092] In some embodiments, this application performs surface treatment between steps 3 and 4, or in step 4, to achieve a surface roughness Ra ≤ 0.8µm, thereby optimizing the microstructure of the ceramic surface, reducing surface porosity and impurity residue, and facilitating the subsequent coverage of the metallization layer 400. This application does not limit the specific method of surface treatment, as long as it achieves the desired effect. For example, in some embodiments, the surface treatment includes sandblasting or chemical mechanical polishing (CMP).

[0093] In some embodiments, a temperature or strain sensing conductor / cavity is pre-placed within the diaphragm before lamination and communicates with external pads after metallization.

[0094] The preparation method of this application can not only achieve mass production of aluminum nitride ceramic substrates with low leakage, low dielectric loss, corrosion resistance and reliability, but also be compatible with AMB / DBC metallization to obtain a heat dissipation-electrical interconnect integrated substrate.

[0095] Thirdly, the application of any of the above-mentioned aluminum nitride ceramic substrates in electronic devices.

[0096] In the above solution, the electronic devices include power semiconductor modules, high heat flux LEDs, RF power amplifiers, or data center cold plate replacements. The power semiconductor modules include any one of SiC power semiconductor modules, GaN power semiconductor modules, and IGBT power semiconductor modules.

[0097] In the above-described solution, the aluminum nitride ceramic substrate of this application is used in electronic devices. The microchannels 200 within the aluminum nitride ceramic substrate can be used for dielectric coolant flow. Furthermore, because the aluminum nitride ceramic substrate of this application has a closed-loop microchannel structure with a covalent ceramic coating on the inner wall of the microchannel, the dielectric coolant only contacts the covalent ceramic coating on the inner wall of the microchannel, without directly contacting the substrate body 100. This effectively prevents corrosive media (acids, alkalis, water vapor, organic solvents, etc.) that may be present in the dielectric coolant from contacting the substrate body 100, thus effectively avoiding damage to the substrate body 100 from these media. The dielectric coolant is powered externally to circulate in the microchannels. The external driving component can continuously provide low-temperature (<35°C) flowing dielectric coolant through external cooling or natural cooling.

[0098] In some embodiments, the dielectric cooling liquid includes at least one of a fluorinated liquid and pure water.

[0099] It should be emphasized that the junction-liquid relationship formed between the aluminum nitride ceramic substrate and the dielectric cooling liquid in this application is... 10 at 40~125℃ 4 After the second thermal cycle, the microchannels remained leak-free and the metallization layer did not peel up.

[0100] The following examples and comparative examples illustrate the implementation of this application in more detail.

[0101] Example 1-1 Please see Figure 1 This embodiment provides an aluminum nitride ceramic substrate, the preparation method of which is as follows: Step 1, Template Forming: Step 1.1, Preparation of aluminum nitride ceramic film: AlN powder is mixed with an organic carrier to obtain a slurry with a solid content of 60 wt%; the slurry is cast to obtain an aluminum nitride ceramic green sheet with a thickness of 100 µm, and dried until the solvent content is ≤1 wt%, thus obtaining the aluminum nitride ceramic film. The oxygen content of the AlN powder is ≤0.6 wt%, D 50 The size ranges from 0.5µm to 2µm, and the organic carrier is polyvinyl butyral and polyethylene glycol (mass ratio 1:1).

[0102] Step 1.2, Forming the template pattern: Using polyacrylic acid resin (molecular weight 400,000~650,000) as the sacrificial template, micro-extrusion molding is used to shape the sacrificial template according to... Figure 2The serpentine parallel pattern shown (the parts extending on both sides serve as the working medium inlet 201 and the working medium outlet 202, respectively) has a rectangular cross-sectional shape for the microchannel 200. The template width of the sacrificial template is adjusted to 120µm and the height to 80µm, and the channel center distance is 400µm. The aluminum nitride ceramic membrane is obtained by placing the corresponding sacrificial template pattern on the aluminum nitride ceramic membrane.

[0103] Step 2, Lamination: Eight aluminum nitride ceramic films and two aluminum nitride ceramic films with sacrificial template patterns obtained in Step 1 are aligned and laminated, and the alignment error during lamination is controlled to be ≤30µm; then, under the lamination process adjustment of lamination pressure of 30MPa and temperature of 100℃, the lamination is pressed for 20min to obtain a 10-layer laminated structure.

[0104] Step 3, Pre-firing: Under a nitrogen (N2) atmosphere, the laminated structure obtained in Step 2 is pre-fired at 1°C / min. -1 After the temperature is raised to 600℃, it is kept at a pre-calcination temperature of 600℃ for 1 h to remove the sacrificial template in the laminated structure and obtain a pre-calcined structure with microchannels 200 inside.

[0105] Step 4, Sintering: Continue heating to 1650℃ and hold the pre-sintered structure at 1650℃ for 2 hours to densify it, obtaining dense aluminum nitride ceramic with 200 microchannels inside. Furthermore, testing showed that the relative density of the dense aluminum nitride ceramic in this embodiment is 99.1%, and its room temperature thermal conductivity is >170 W·m. -1 ·K -1 The thickness of the dense aluminum nitride ceramic (i.e., the substrate body 100) with microchannels 200 inside is 0.8 mm.

[0106] Step 5, Deposition of the covalent ceramic coating: Two process holes are formed in the dense aluminum nitride ceramic obtained in Step 4, connecting them to the microchannels 200 inside the ceramic. These process holes serve as the working fluid inlet 201 and outlet 202, respectively. The two process holes are then connected to the deposition equipment via external piping. This embodiment uses chemical vapor deposition (CVD) with BCl3 and NH3 as precursors to provide boron and nitrogen sources. During CVD, the gas flow rate of BCl3 is 5 sccm, the gas flow rate of NH3 is 25 sccm, the carrier gas is 2 SLM of N2, the deposition temperature is 800℃, the deposition time is 40 min, and the deposition thickness is 100 nm. Therefore, the covalent ceramic coating 300 in this embodiment is an h-BN coating. The resulting product structure is as follows... Figure 3 and Figure 4 As shown, Figure 4 for Figure 3 A magnified view of the area at point A, by Figure 3 and Figure 4 It can be seen that a covalent ceramic coating 300 is formed on the inner wall of the microchannel 200 through chemical vapor deposition.

[0107] Step 6, Sealing: An active brazed ring 500 is used as the sealing structure to seal the two process holes created above, resulting in the following... Figure 5 The aluminum nitride ceramic substrate shown is denoted as substrate 1. (The text appears to be incomplete and requires further context.) Figure 5 As can be seen, the active brazing ring is used as the sealing structure 500 for sealing. The middle part of the active brazing ring is a hollow structure so that the microchannel 200 can be connected to the pipeline of the external cooling system through the active brazing ring to form a closed microchannel 200, which effectively avoids or reduces leakage of dielectric coolant when it flows in the microchannel 200.

[0108] Step 7, Preparation of metallization layer 400: Using the DBC method, copper foil with a thickness of 300µm is directly bonded to the upper and lower surfaces of the substrate 1 obtained in step 6. Heating is performed in air at 1070℃ to melt the copper foil and wet the interface. Cooling to room temperature forms metallization layer 400 on the surface of the aluminum nitride ceramic substrate, resulting in... Figure 6 and Figure 7 The surface-metallized aluminum nitride ceramic substrate shown is denoted as substrate 2. Figure 7 for Figure 6 A magnified view at point B, by Figure 6 and Figure 7 As can be seen, the metallization layer 400 is formed on both the upper and lower surfaces of the substrate 1 by the preparation method of this application.

[0109] The surface-metallized aluminum nitride ceramic substrate obtained above is processed as follows: Figure 8 As shown, pads 600 are provided on the upper surface, and power chips (SiC chips) 700 are mounted through the pads 600. Pure water is used as the dielectric coolant 800. The working fluid inlet 201 and working fluid outlet 202 on the surface-metallized aluminum nitride ceramic substrate are connected to an external cooling system supplying pure water through a sealing structure 500, allowing pure water to enter the microchannels 200 of the aluminum nitride ceramic substrate, resulting in... Figure 9 The device shown.

[0110] Examples 1-2 to 1-6, and Comparative Examples 1-1 to 1-2 The difference from Example 1-1 is that the thickness H of the covalent ceramic coating is adjusted according to Table 1, specifically by adjusting the deposition rate or deposition time. In Comparative Example 1-1, the aluminum nitride ceramic substrate is a conventional solid substrate with a cold plate. In Comparative Example 1-2, step 5 of depositing the covalent ceramic coating is not performed; that is, the microchannels 200 in the aluminum nitride ceramic substrate of Comparative Example 1-2 do not contain a covalent ceramic coating.

[0111] This application tested the thickness uniformity TU of the aluminum nitride ceramic substrates of Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-2 at room temperature, and all met the requirement of TU≤1.5, indicating that the preparation method of this application can form a uniformly distributed covalent ceramic coating on the inner wall of the microchannel 200.

[0112] This application also tested the heat dissipation performance, chemical corrosion resistance, dielectric loss and long-term reliability of the aluminum nitride ceramic substrates of Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-2, and the test results are summarized in Table 1.

[0113] Testing and evaluation methods: (a) Testing of structural parameters 1) Relative density test: The relative density test refers to the test of the volume density of aluminum nitride ceramic substrate (GB / T 39975-2021) and then calculates the relative density of aluminum nitride ceramic substrate according to the following formula: Relative density = volume density / theoretical density of aluminum nitride × 100%.

[0114] 2) Test of cross-sectional diameter: The aluminum nitride ceramic substrate was cut along the thickness direction and its surface was tested by scanning electron microscopy to obtain the cross-sectional diameter of the microchannel 200.

[0115] 3) Testing of channel center distance: The testing method for the center distance of microchannels in the cross-section of microchannels is performed using a two-dimensional graphic measuring instrument.

[0116] 4) Thickness uniformity test: The thickness gauge is used to measure the thickness at five points: the four corners and the center of the substrate, and the thickness uniformity is calculated.

[0117] (ii) Sealing performance: 1) Helium mass spectrometry leak detection (vacuum chamber method) was used for sealing performance testing. Test result evaluation (E1): If the helium leak detection rate of the aluminum nitride ceramic substrate is ≤1×10⁻⁶, the sealing performance is considered good. -9 Pa·m 3 ·s -1 If the result is positive, denote it as Y; otherwise, denote it as N.

[0118] 2) The sealing performance was tested using a water pressure / air pressure burst test, with a pressure of 5 bar to 10 bar and a holding time of 10 minutes. Evaluation of test results (E2): If no leakage is observed after holding the pressure at 5 bar for 10 minutes, it is recorded as Y; otherwise, it is recorded as N.

[0119] Comprehensive evaluation of sealing performance (CE1): When both of the above test results are Y, the sealing performance is considered to be good and meets the requirements for low leakage sealing applications, and is recorded as Y; otherwise, it is recorded as N.

[0120] (III) Heat dissipation performance: The junction-liquid thermal resistance of the corresponding devices obtained from each embodiment and each comparative example is calculated. Specifically, the junction-liquid thermal resistance is calculated using the following method: Junction-liquid thermal resistance = (T...) j -T l ) / Pd, where T j T represents the junction temperature (°C) of the device chip. l Pd represents the average temperature (°C) of the dielectric coolant and Pd represents the actual heat dissipation power of the device. This application uses a conventional solid substrate as a reference in Comparative Example 1-1, and evaluates the heat dissipation performance of the device by the rate of reduction in thermal resistance η of the junction-liquid thermal resistance of each embodiment or comparative example relative to Comparative Example 1-1. η = |Measured thermal resistance - Fixed thermal resistance| / Fixed thermal resistance × 100%, where the measured thermal resistance is the junction-liquid thermal resistance of each embodiment or comparative example, and the fixed thermal resistance is the junction-liquid thermal resistance of Comparative Example 1-1. A larger η indicates better heat dissipation performance of the device.

[0121] Furthermore, the junction-liquid thermal resistance of Comparative Example 1-1 was tested to be 2.01 °C / W. Therefore, this application is based on Comparative Example 1-1 and describes the junction-liquid thermal resistance of other embodiments and comparative examples as the rate of thermal resistance reduction relative to Comparative Example 1-1, and the rate of thermal resistance reduction η = |measured thermal resistance - 2.01| / 2.01 × 100%.

[0122] (iv) Dielectric loss: IEC standard sheet, 10 kV / mm withstand voltage, dielectric loss tangent tanδ at 10 GHz frequency.

[0123] (v) Mechanical properties: The shear strength of the surface interface of aluminum nitride ceramics in each embodiment and comparative example was tested using a tensile tester according to the test methods in GB / T 31541-2015.

[0124] (vi) Corrosion resistance: The devices in each embodiment and comparative example were placed in an environment of 85°C, and pure water was used as the coolant to continuously circulate in the aluminum nitride ceramic substrate for 500 h. During the circulation process, the aluminum nitride ceramic substrate was observed for any abnormalities and the coating (including covalent ceramic coating and metallization layer) peeling.

[0125] Evaluation of corrosion resistance: If the coating shows no cracks or warping after 500 hours of cycling, it is considered to have excellent corrosion resistance and is denoted as Y; otherwise, it is denoted as N.

[0126] (vii) Long-term reliability: The aluminum nitride ceramic substrates in each embodiment and comparative example were subjected to thermal cycling tests, with a cycle consisting of heating to 125°C and then rapidly cooling to -40°C. The thermal cycling was performed for 10 days. 4 Afterwards, a two-dimensional microscope was used to observe whether there were cracks or warping on the surface of the aluminum nitride ceramic substrate, and the sealing performance after thermal cycling was tested.

[0127] Structural reliability evaluation (E3): When the surface of the aluminum nitride ceramic is free of cracks or warping after thermal cycling, it is considered to have long-term thermal reliability and is denoted as Y; otherwise, it is denoted as N.

[0128] Sealing performance reliability evaluation (E4): Referring to the testing and evaluation of sealing performance in (I) above, when the comprehensive evaluation result of the sealing performance of the aluminum nitride ceramic substrate after thermal cycling is Y, it is considered to have long-term sealing performance reliability and is recorded as Y; otherwise, it is recorded as N.

[0129] Long-term reliability comprehensive evaluation (CE2): When both of the above test results are Y, the sealing performance is considered to be good and meets the requirements for low leakage sealing applications, and is recorded as Y; otherwise, it is recorded as N.

[0130] Table 1

[0131] In Table 1, “\” indicates that it does not exist or is not set, and “η” is the rate of reduction of the junction-liquid thermal resistance of each embodiment or comparative example relative to Comparative Example 1-1.

[0132] In Comparative Example 1, the temperature of the solid substrate increases as the power device heats up, leading to an exponential decrease in thermal conductivity, which fails to meet the heat dissipation requirements of high-power chips. According to the test results in Table 1, the junction-liquid thermal resistance of Example 1-1 is nearly 55% lower than that of Comparative Example 1-1. Furthermore, the percentage decrease in junction-liquid thermal resistance of Examples 1-2 to 1-6 compared to Comparative Example 1-1 is within the range of 40% to 60%. This indicates that, given the presence of a covalent ceramic coating on the inner wall of the microchannel 200 and the substrate body 100 being aluminum nitride ceramic with a relative density ≥98.5%, when the cross-sectional diameter R of the microchannel 200 satisfies 30µm≤R≤500µm, this application can improve the corrosion resistance of the inner wall of the microchannel 200, reduce interfacial friction and dielectric loss, and simultaneously improve the heat dissipation performance of the aluminum nitride ceramic substrate.

[0133] Furthermore, this application found that during corrosion resistance testing, the aluminum nitride ceramic substrates of Comparative Examples 1-2 showed visible wall corrosion and flow fluctuations after 200 hours of cycling, with helium leak detection increasing to >1×10⁻⁶. -8 Pa·m 3 ·s -1 However, none of the above-mentioned situations occurred in Examples 1-1 to 1-6 of this application, indicating that when the thickness H of the covalent ceramic coating provided on the inner wall of the microchannel 200 satisfies 50nm≤H≤500nm, the chemical corrosion resistance of the inner wall of the microchannel 200 can be improved and the interfacial friction and dielectric loss can be reduced.

[0134] Furthermore, according to the test results in Table 1, when H satisfies 50nm≤H≤300nm, the chemical corrosion resistance of the inner wall of microchannel 200 can be improved more effectively, and interfacial friction and dielectric loss can be reduced. In particular, when H satisfies 80nm≤H≤200nm, the chemical corrosion resistance of the inner wall of microchannel 200 can be further improved, and interfacial friction and dielectric loss can be reduced even more effectively.

[0135] Examples 2-1 to 2-7 The difference from Example 1-1 is as follows: Adjust the cross-sectional diameter R of the microchannel 200 in the aluminum nitride ceramic substrate according to Table 1. Specifically, the cross-sectional diameter R of the microchannel 200 in the aluminum nitride ceramic substrate is adjusted by adjusting the size of the sacrificial template.

[0136] This application tested the heat dissipation performance, corrosion resistance, dielectric loss and long-term reliability of the aluminum nitride ceramic substrates of Examples 1-1, 2-1 to 2-7, and the test results are summarized in Table 2.

[0137] Table 2

[0138] In Table 2, “\” indicates that it does not exist or is not set, and “tanδ” indicates the dielectric loss tangent.

[0139] Tests show that the junction-liquid thermal resistance of Examples 2-1 to 2-7 decreased by 40% to 60% compared to Comparative Example 1-1. This further demonstrates that, given the substrate body 100 is aluminum nitride ceramic with a relative density ≥98.5%, when the cross-sectional diameter R of the microchannel 200 satisfies 30µm ≤ R ≤ 500µm, this application can improve the heat dissipation performance of the aluminum nitride ceramic substrate while enhancing the corrosion resistance of the inner wall of the microchannel 200 and reducing interfacial friction and dielectric loss. Moreover, the test results in Table 1 show that when the cross-sectional diameter of the microchannel 200 is 50µm to 300µm, the heat dissipation performance of the aluminum nitride ceramic substrate is improved even more. In particular, when the cross-sectional diameter of the microchannel 200 is 80µm to 200µm, the heat dissipation performance of the aluminum nitride ceramic substrate is further improved. Furthermore, according to the test results in Table 1, it can be seen that the aluminum nitride ceramic substrates of Examples 1-1 to 1-7 of this application all meet the requirement of no leakage after 10 minutes of internal pressure at 5 bar, and the helium leak detection is ≤1×10⁻⁶. -9 Pa·m 3 ·s -1 tanδ all satisfy tanδ≤3×10 -3 Furthermore, the aluminum nitride ceramic substrate of this application maintains sealing reliability and metallization reliability even after thermal cycling, which indicates that the aluminum nitride ceramic substrate has low leakage, low dielectric loss, corrosion resistance, and long-term reliability.

[0140] Examples 3-1 to 3-4 The difference from Example 1-1 is as follows: Adjust the channel center distance L according to Table 3. Specifically, adjust the channel center distance L by adjusting the spacing of the template traces of the sacrificial template graphic.

[0141] Examples 3-5 The difference from Example 1-1 is as follows: In Examples 3-5, the covalent ceramic coating material is SiC. Specifically, in Examples 3-5, the SiC covalent ceramic coating was prepared using the following method: chemical vapor deposition (CVD) with methyltrichlorosilane (MTS) + H2 as the precursor to provide the carbon and silicon sources. During CVD, the gas flow rate of MTS was 5 sccm, the gas flow rate of H2 was 25 sccm, and the deposition temperature was 900℃.

[0142] Examples 3-6 The difference from Examples 3-5 is as follows: In step 1, microchannels 200 are grouped together, and the following method is used: Figure 10 The distribution-gathering topology shown has a channel inlet manifold of 500µm and each channel of 80µm×60µm.

[0143] In step 5, the SiC deposition thickness is 180 nm.

[0144] In step 7, the metallization layer 400 is prepared using a solder with a nickel content of 15%–20%, a titanium content of 3%–6%, a silicon content of 0.06%–0.08%, and the remainder being aluminum as the active metal solder. This active metal solder is uniformly coated onto the upper and lower surfaces of the aluminum nitride ceramic substrate obtained in step 6, with a coating thickness of 5 µm. Copper foil with a thickness of 200 µm is then bonded to the coated active metal solder. The substrate is then heated in a vacuum environment at 900 °C to melt the solder and wet the interface. After cooling to room temperature, a metallization layer 400 is formed on the surface of the aluminum nitride ceramic substrate, resulting in a surface-metallized aluminum nitride ceramic substrate. The surface-metallized aluminum nitride ceramic substrates obtained in Examples 3-6 are as follows... Figure 11 As shown.

[0145] Examples 3-7 to 3-10 The difference from Example 1-1 is as follows: Adjust the thickness D of the metallization layer 400 according to Table 3. Specifically, adjust the thickness D of the metallization layer 400 by adjusting the thickness of the bonded copper foil.

[0146] This application tested the corrosion resistance, dielectric loss, and long-term reliability of the aluminum nitride ceramic substrates of Examples 3-1 to 3-10, and the test results are summarized in Table 3.

[0147] Table 3

[0148] According to the test results in Table 3, when the channel center distance L satisfies 200µm≤L≤1000µm, the heat dissipation performance and long-term reliability of the aluminum nitride ceramic substrate of this application can be improved. Furthermore, when 300µm≤L≤700µm, the heat dissipation performance and long-term reliability of the aluminum nitride ceramic substrate can be improved even further. The test results in Table 3 also show that the presence of a covalent ceramic coating, made of at least one of hexagonal boron nitride, silicon carbide, or a boron-carbon-nitrogen composite material, on the inner wall of the microchannel reduces the possibility of corrosion or hydrogen evolution after the inner wall of the microchannel comes into contact with the dielectric coolant, thus improving the reliability of the aluminum nitride ceramic substrate, especially its long-term reliability. In addition, the microchannels in this application employ at least one flow path topology among serpentine, parallel inline, and distribution-convergence, which can further improve the heat dissipation performance of the aluminum nitride ceramic substrate without affecting its structural strength.

[0149] Obviously, the above embodiments of this application are merely examples for clear illustration and are not intended to limit the implementation of this application. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection claimed by this application.

Claims

1. An aluminum nitride ceramic substrate, characterized in that, It includes a substrate body (100), wherein the substrate body (100) is aluminum nitride ceramic with a relative density ≥98.5%; The substrate body (100) has at least one set of microchannels (200) inside, the microchannels (200) being parallel to the substrate body (100); and the microchannels (200) having a working fluid inlet (201) and a working fluid outlet (202). The inner wall of the microchannel (200) is provided with a covalent ceramic coating (300), and the material of the covalent ceramic coating (300) includes at least one of hexagonal boron nitride, silicon carbide or boron-carbon-nitrogen composite.

2. The aluminum nitride ceramic substrate according to claim 1, characterized in that, The thickness of the covalent ceramic coating (300) is H, and 50nm≤H≤500nm.

3. The aluminum nitride ceramic substrate according to claim 1, characterized in that, The cross-sectional diameter of the microchannel (200) is R, and 30µm≤R≤500µm; The center-to-center distance of the microchannels (200) is L, and 200µm≤L≤1000µm.

4. The aluminum nitride ceramic substrate according to claim 1, characterized in that, The microchannel (200) adopts at least one flow path topology among serpentine, parallel inline, and distribution-gathering.

5. The aluminum nitride ceramic substrate according to claim 1, characterized in that, The cross-sectional shape of the microchannel (200) includes at least one of near-rectangular, rounded rectangular, elliptical, and trapezoidal shapes.

6. The aluminum nitride ceramic substrate according to claim 1, characterized in that, The aluminum nitride ceramic substrate satisfies at least one of the following conditions: (1) The thickness uniformity of the covalent ceramic coating (300) at room temperature is TU, and TU≤1.5; (2) The dielectric loss tangent of the covalent ceramic coating (300) at a frequency of 10 GHz is tanδ, and tanδ≤3×10 -3 ; (3) The room temperature thermal conductivity of the substrate body (100) is ≥170 W·m -1 ·K -1 .

7. The aluminum nitride ceramic substrate according to claim 1, characterized in that, The surface of the substrate body (100) is provided with a metallization layer (400), and the metal in the metallization layer (400) includes at least copper; The thickness of the metallization layer (400) is D, and 50µm≤D≤600µm.

8. The aluminum nitride ceramic substrate according to claim 1, characterized in that, The thickness of the substrate body (100) is 0.2mm to 1.2mm; The minimum remaining ceramic thickness of the channel wall is a, where a ≥ 80µm.

9. A method for preparing an aluminum nitride ceramic substrate according to any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1, Template Forming: Using the sacrificial template method, a corresponding sacrificial template pattern is formed on the aluminum nitride ceramic membrane according to the size and shape of the target microchannel, resulting in an aluminum nitride ceramic membrane with a sacrificial template pattern. Step 2, Layering: Based on the number of target microchannels, the corresponding number of aluminum nitride ceramic films and the aluminum nitride ceramic films with sacrificial template patterns obtained in step 1 are aligned, stacked, and laminated to obtain a stacked structure. Step 3, Preheating: Under a protective gas atmosphere, the laminated structure is pre-fired to remove the sacrificial template in the laminated structure and obtain a pre-fired structure with fluid channels. Step 4, sintering: The pre-fired structure is sintered at a temperature of 1500℃~1800℃ to obtain a substrate body (100), wherein the substrate body (100) is a dense aluminum nitride ceramic with microchannels (200); Step 5, Deposition of covalent ceramic coating (300): A covalent ceramic coating (300) is deposited on the inner wall of the microchannel (200) using a deposition method with a precursor corresponding to at least one of hexagonal boron nitride, silicon carbide, or boron-carbon-nitrogen composite as the deposition material, to obtain the aluminum nitride ceramic substrate.

10. The application of an aluminum nitride ceramic substrate according to any one of claims 1 to 8 in an electronic device, characterized in that, The electronic devices include power semiconductor modules, high heat flux LEDs, radio frequency power amplifiers, or data center cold plate replacements. The power semiconductor module includes any one of SiC power semiconductor module, GaN power semiconductor module and IGBT power semiconductor module.

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