Multilayer composite circuit board preparation method and multilayer composite circuit board

Abstract

The present invention relates to the technical field of circuit board preparation, and discloses a method for preparing a multilayer composite circuit board and a multilayer composite circuit board, comprising: mixing a ceramic-based powder with nano-metal particles, sintering to form a heat-conducting microporous ceramic material having a continuous heat-conducting network and a microporous structure; stacking a plurality of heat-conducting microporous ceramic materials and pressing them into a composite substrate by vacuum hot pressing, forming a through thermal conduction hole on the composite substrate; stacking the composite substrates with the thermal conduction holes, setting a microporous layer for heat conduction and shock absorption between the layers of adjacent composite substrates, and forming a multilayer structure by vacuum hot pressing the stacked composite substrates and the microporous layer. The method for preparing a multilayer composite circuit board and the multilayer composite circuit board have a continuous heat-conducting network, a microporous structure and a microporous layer, which not only significantly improves the thermal conductivity, but also effectively relieves thermal stress and mechanical stress through the elastic characteristics of the microporous structure, thereby enhancing the overall stability of the multilayer composite circuit board.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit board preparation, and in particular to a method for preparing a multi-layer composite circuit board and a multi-layer composite circuit board. Background Art

[0002] With the rapid development of electronic technology, the application scope of electronic equipment continues to expand, from consumer electronics to automotive electronics to aerospace, and the performance requirements of electronic equipment are also constantly improving, especially high-performance electronic devices, such as autonomous driving systems, 5G communication equipment, and high-frequency radar systems. These applications require multi-layer composite electronic circuit boards to have not only high conductivity and reliable electrical insulation performance, but also excellent thermal management and seismic performance to ensure the stability and reliability of the equipment in high-speed operation and complex environments.

[0003] In the prior art, the preparation method of the multi-layer composite circuit board usually introduces a thermal conductive material into the multi-layer structure in order to improve the heat dissipation performance of the circuit board. However, in the traditional method, the thermal conductive material is usually dispersed in the substrate material (i.e., insulating material), resulting in a discontinuous heat conduction path. For example, when used in a radar sensor module used in an autonomous driving system, since the radar sensor module needs to be installed at the front of the vehicle, these modules need to work stably under various weather conditions (such as high temperature, low temperature and humid environment), and need to withstand severe vibration and impact during high-speed driving. When working in a high-temperature environment at the front of the vehicle, due to the low heat conduction efficiency, local overheating problems are prone to occur. Due to the large difference in thermal expansion coefficients between the thermal conductive material and the substrate material (i.e., insulating material), due to the low heat conduction efficiency of the thermal conductive material, thermal stress is easily generated during the thermal cycle, resulting in interlayer delamination or cracks, affecting the long-term stability of the substrate of the multi-layer composite circuit board. At the same time, in a high-vibration environment, the multi-layer structure of the traditional multi-layer composite circuit board is easily damaged, and the bonding strength between the thermal conductive material and the substrate material (i.e., insulating material) is insufficient, resulting in poor seismic performance. Summary of the invention

[0004] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing a multi-layer composite circuit board and a multi-layer composite circuit board. By having a continuous heat conductive network, a microporous structure and a microporous layer, not only the thermal conductivity is significantly improved, but also the elastic properties of the microporous structure effectively relieve thermal stress and mechanical stress, thereby enhancing the overall stability and seismic resistance of the multi-layer composite circuit board.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0006] Design a method for preparing a multilayer composite circuit board, including:

[0007] S100, mixing ceramic-based powder with nano-metal particles, and sintering to form a thermally conductive microporous ceramic material having a continuous thermally conductive network and a microporous structure;

[0008] S200, stacking a plurality of thermally conductive microporous ceramic materials and pressing them into a composite substrate by vacuum hot pressing, and forming a through thermal conductive hole on the composite substrate;

[0009] S300, stacking composite substrates formed with thermal vias, setting microporous layers for heat conduction and shock absorption between adjacent composite substrates, forming a multilayer structure through vacuum hot pressing of the stacked composite substrates and the microporous layers, and coating the surface of the multilayer structure to obtain a multi-layer composite circuit board substrate.

[0010] Optionally, the ceramic-based powder is at least one of aluminum oxide powder and silicon nitride powder, and the nano-metal particles are at least one of nano-copper particles and silver particles.

[0011] Optionally, the S100 specifically includes:

[0012] S110, mixing the aluminum oxide powder and the nano copper particles, and uniformly dispersing them by mechanical stirring to form a preliminary mixture;

[0013] S120, placing the preliminary mixture in an electrostatic spraying device, preparing the preliminary mixture into uniform particles by low-pressure electrostatic spraying, wherein the particle size is between 100 and 300 microns, and then placing the uniform particles in a cold isostatic pressing device, performing pre-pressing molding at a pressure of 100 to 200 MPa to obtain a powder blank;

[0014] S130, placing the powder blank in a mixing device, spraying the polymethacrylate solution evenly on the surface of the powder blank through a fine mist nozzle, and then placing the powder blank sprayed with the polymethacrylate solution in a drying oven for drying at a temperature range of 50° C. to 70° C., wherein the solvent gradually evaporates and the polymethacrylate is evenly attached to the surface of the powder blank;

[0015] S140, placing the powder blank with polymethacrylate attached thereto in a high-temperature sintering furnace, and sintering by increasing the temperature in stages. During the sintering process, the nano-copper particles are combined with the alumina powder in the alumina powder by liquid phase diffusion to form a heat conduction path, and the oxidation of the particles is suppressed under the protection of nitrogen. The polymethacrylate volatilizes at a high temperature, so that the powder blank forms a uniformly distributed microporous structure, and the pore size of the micropores is controlled between 5 and 20 microns, thereby obtaining a heat-conducting microporous ceramic material;

[0016] S150, placing the sintered thermally conductive microporous ceramic material in a low-temperature annealing furnace, and annealing it at a temperature range of 500° C. to 700° C. for 1 to 2 hours to release the residual stress of the thermally conductive microporous ceramic material during the sintering process.

[0017] Optionally, the S110 specifically includes:

[0018] S111, placing the aluminum oxide powder in an ultrasonic oscillation device, washing it with deionized water to remove adsorbed impurities on the surface of the aluminum oxide powder, placing the washed aluminum oxide powder in a drying oven, and drying it at a constant temperature of 80° C. to 120° C. for 4 to 6 hours;

[0019] S112, selecting nano copper particles with a particle size ranging from 20 to 50 nanometers, placing them in a silane coupling agent solution, and mechanically stirring them for 30 to 60 minutes to form an active coating on the surface of the nano copper particles, and subjecting the nano copper particles with the active coating to low temperature drying treatment to obtain surface activated nano copper particles;

[0020] S113. Dry-mix the cleaned alumina powder and the surface-activated nano-copper particles in a mass ratio of 1:0.2-0.5 using a high-energy ball mill. The milling time of the high-energy ball mill is controlled at 6 to 8 hours. Zirconia ceramic balls are used as the ball milling medium to form a preliminary mixture.

[0021] Optionally, the S140 specifically includes:

[0022] S141, placing the powder blank with polymethacrylate attached thereto in a high-temperature sintering furnace, and performing an initial heating stage, wherein the temperature is increased from room temperature to 600° C. at a heating rate of 5° C. per minute, and maintained for 1 hour;

[0023] S142, after the initial heating stage, an intermediate heating stage is performed, in which the temperature is increased from 600° C. to 900° C. at a heating rate of 10° C. per minute and maintained for 2 hours;

[0024] S143, after the intermediate heating stage is completed, a high temperature sintering stage is performed, in which the temperature is raised from 900° C. to 1300° C. at a heating rate of 8° C. per minute and maintained for 3 to 4 hours, so that the nano copper particles form a continuous heat conduction network in the alumina powder through liquid phase diffusion;

[0025] S144. During the high-temperature sintering stage, a nitrogen protective atmosphere is maintained in the high-temperature sintering furnace to prevent oxidation of the nano-copper particles, and the polymethacrylate is volatilized at high temperature, so that the powder blank forms a uniformly distributed microporous structure;

[0026] S145. After the high temperature sintering stage is completed, a slow cooling stage is performed, in which the temperature is slowly lowered to room temperature at a cooling rate of 5° C. per minute.

[0027] Optionally, before S200, an insulating material is mixed with an electrical insulating filler to obtain an insulating coating material, and the insulating coating material is coated on the surfaces of a plurality of thermally conductive microporous ceramic materials. S200 specifically includes:

[0028] S210, stacking a plurality of thermally conductive microporous ceramic materials and placing them into a vacuum hot press, and hot pressing the stacked plurality of thermally conductive microporous ceramic materials into a composite substrate by the vacuum hot press;

[0029] S220, drilling holes on the composite substrate by using a laser drilling device to form thermal via holes penetrating the composite substrate, and performing ultrasonic cleaning on the composite substrate with the thermal via holes to remove debris and impurities generated during the drilling process;

[0030] S230, after cleaning the composite substrate with the thermal via hole formed thereon, metallizing the inner wall of the thermal via hole to uniformly form a copper film having thermal conductivity and electrical connection performance on the inner wall of the thermal via hole;

[0031] S240, after a copper film is formed on the inner wall of the thermal via hole, the composite substrate is placed in a high-temperature annealing furnace and annealed at 300° C. to 500° C. for 1 hour. During the annealing process, the copper film on the inner wall of the thermal via hole is combined with the continuous heat conduction network formed by the nano copper particles in the composite substrate to form a continuous heat conduction path.

[0032] Optionally, the S230 specifically includes:

[0033] S231, immersing the cleaned composite substrate in a chemical plating solution containing copper ions, and uniformly depositing a copper film having thermal conductivity and electrical connection properties on the inner wall of the thermal via hole;

[0034] S232, electroplating the thermal via hole on which a layer of copper film is deposited, and the thickness of the copper film on the inner wall of the thermal via hole is further increased by electroplating.

[0035] Optionally, the S300 specifically includes:

[0036] S310, mixing the polyurethane particles and the carbon fiber filler according to a mass ratio to obtain a composite material for preparing a microporous layer;

[0037] S320, placing the composite material for preparing the microporous layer in a mold for pre-pressing to obtain the microporous layer;

[0038] S330, placing the microporous layer between adjacent layers of the composite substrate, bonding the microporous layer to the adjacent composite substrate by coating the surface of the microporous layer with silicone-based adhesive, and then performing vacuum hot pressing to form a multi-layer structure, performing corrosion-resistant coating on the surface of the multi-layer structure, and obtaining a multi-layer composite circuit board substrate.

[0039] A multi-layer composite circuit board is prepared by the multi-layer composite circuit board preparation method as described above, and the multi-layer composite circuit board comprises:

[0040] Thermally conductive microporous ceramic material, made by hot pressing a mixture of alumina powder and nano copper particles, used for lamination and vacuum hot pressing to form a composite substrate;

[0041] A continuous heat-conducting network and microporous structure are formed in the thermally conductive microporous ceramic material to provide a heat conduction path and absorb external mechanical shock;

[0042] Thermal vias are provided on the surface of the composite substrate and are connected to the continuous thermal conductive network to form a continuous thermal conductive path to improve thermal conductivity and electrical connection performance;

[0043] The microporous layer is disposed between the composite substrates to optimize shock absorption performance and thermal stability.

[0044] The present invention provides a method for preparing a multi-layer composite circuit board and a multi-layer composite circuit board, which have the following beneficial effects:

[0045] The preparation method of the multilayer composite circuit board and the multilayer composite circuit board are characterized by mixing ceramic-based powder with nano-metal particles, and then sintering the nano-metal particles to form a continuous heat-conducting network structure and a microporous structure in the ceramic-based powder, which not only provides a good heat conduction path and improves the overall thermal conductivity, but also enhances the mechanical strength, adhesion and anti-seismic ability of the material through the microporous structure. The thermal vias enable each layer of the heat-conducting microporous ceramic material to be closely combined, ensuring the effective transfer of heat between the layers of the heat-conducting microporous ceramic material, and achieving high thermal conductivity, high strength, high insulation and high anti-seismic performance of the multilayer composite circuit board. The microporous layer in the multilayer structure formed by the composite substrate further enhances the anti-seismic performance and environmental resistance of the circuit board, so that it can maintain a reliable and stable working state under complex working conditions. Finally, the corrosion resistance of the material is enhanced through surface coating treatment, the multilayer composite circuit board is endowed with excellent electrical insulation performance, and the service life of the multilayer composite circuit board is extended. By optimizing the heat conduction path, enhancing the interlayer bonding and shock absorption, the situation of uneven heat conduction, poor structural stability and insufficient anti-seismic performance is effectively avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0047] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical contents disclosed by the present invention.

[0048] Figure 1 This is one of the flow diagrams of the method for preparing a multilayer composite circuit board of Example 1. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. All other embodiments obtained by ordinary technicians in the field without making creative work based on the embodiments of the present invention shall fall within the scope of protection of the present invention.

[0050] Embodiment 1:

[0051] See also Figure 1 The present invention provides a technical solution: a method for preparing a multilayer composite circuit board, comprising:

[0052] S100, mixing ceramic-based powder with nano-metal particles, and sintering to form a thermally conductive microporous ceramic material having a continuous thermally conductive network and a microporous structure;

[0053] S200, stacking a plurality of thermally conductive microporous ceramic materials and pressing them into a composite substrate by vacuum hot pressing, and forming a through thermal conductive hole on the composite substrate;

[0054] S300, stacking composite substrates formed with thermal vias, providing microporous layers for heat conduction and shock absorption between adjacent composite substrates, forming a multilayer structure by vacuum hot pressing the stacked composite substrates and the microporous layers, and performing surface coating on the multilayer structure to obtain a multilayer composite circuit board substrate;

[0055] The ceramic-based powder is at least one of aluminum oxide powder and silicon nitride powder, and the nano-metal particles are at least one of nano-copper particles and silver particles;

[0056] In step S100, a ceramic-based powder is mixed with nano-metal particles, and sintered to form a thermally conductive microporous ceramic material having a continuous thermal conductive network and a microporous structure. Specifically, alumina powder or silicon nitride powder is used as the ceramic-based powder, and the nano-metal particles are selected from nano-copper particles or nano-silver particles. By precisely controlling the sintering parameters, the nano-metal particles form a continuous thermal conductive network in the ceramic matrix, and a microporous structure is generated at the same time. The microporous structure not only significantly improves the thermal conductivity of the material, but also provides good mechanical strength and stability. The continuous thermal conductive network is an interconnected network structure formed by a high thermal conductivity material (such as nano-metal particles) in a matrix material (such as a ceramic-based powder). During the sintering process, the nano-metal particles form a continuous thermal conductive path through liquid phase or solid phase diffusion, which significantly improves the overall thermal conductivity of the material. In traditional multiphase composite materials, the matrix material with poor thermal conductivity and the high thermal conductivity are There will be interfacial thermal resistance between fillers, which will significantly reduce the thermal conductivity of the material. The continuous thermal conductive network reduces the interfacial thermal resistance by forming a good interface bond, ensuring that heat can be efficiently transferred from one particle to another, thereby improving the overall thermal conductivity. The continuous thermal conductive network provides a clear transfer path for heat, reducing the loss of heat randomly diffused in the matrix material, allowing heat to be transferred in a concentrated manner, thereby improving the thermal conductivity efficiency. The air or other filling materials in the pores formed by the microporous structure can transfer heat through convection and radiation, further improving the thermal conductivity efficiency. The microporous structure has certain elastic properties, which can effectively release the stress caused by thermal expansion, avoid cracks or delamination of the material during the thermal cycle, and ensure the structural stability of the material. The reduction of thermal expansion stress helps to maintain the integrity of the thermal conductive network and avoid the breakage of the thermal conductive path due to stress concentration, thereby improving the long-term thermal conductivity of the material.

[0057] In step S200, the prepared thermally conductive microporous ceramic materials are stacked and arranged, and pressed by a vacuum hot press under high temperature and high pressure to ensure that each layer of material is tightly combined to form an integrated composite substrate. Subsequently, a through thermal conductive hole is formed on the composite substrate by a drilling device to ensure that heat can be efficiently transferred in the multi-layer structure, thereby further optimizing the heat dissipation performance and overall mechanical strength of the circuit board;

[0058] In step S300, a microporous layer material for heat conduction and shock absorption is filled between adjacent composite substrates, and the interlayer materials are tightly combined through a hot pressing process in a vacuum environment to form a multi-layer composite structure with excellent thermal conductivity and shock absorption effects. Finally, the multi-layer structure is surface coated to enhance its environmental resistance and protection capabilities, and finally a high-performance multi-layer composite circuit board substrate is obtained. This design not only improves the thermal conductivity of the circuit board, but also effectively relieves thermal expansion and mechanical stress, thereby improving the overall seismic resistance and long-term reliability.

[0059] In this embodiment, as a preferred solution, S100 specifically includes:

[0060] S110, mixing the aluminum oxide powder and the nano copper particles, and uniformly dispersing them by mechanical stirring to form a preliminary mixture;

[0061] S120, placing the preliminary mixture in an electrostatic spraying device, preparing the preliminary mixture into uniform particles by low-pressure electrostatic spraying, wherein the particle size is between 100 and 300 microns, and then placing the uniform particles in a cold isostatic pressing device, performing pre-pressing molding at a pressure of 100 to 200 MPa to obtain a powder blank;

[0062] S130, placing the powder blank in a mixing device, spraying the polymethacrylate solution evenly on the surface of the powder blank through a fine mist nozzle, and then placing the powder blank sprayed with the polymethacrylate solution in a drying oven for drying at a temperature range of 50° C. to 70° C., wherein the solvent gradually evaporates and the polymethacrylate is evenly attached to the surface of the powder blank;

[0063] S140, placing the powder blank with polymethacrylate attached in a high-temperature sintering furnace, and sintering by increasing the temperature in stages. During the sintering process, the nano copper particles are combined with the alumina powder in the alumina powder by liquid phase diffusion to form a heat conduction path, and the oxidation of the particles is suppressed under the protection of nitrogen. At the same time, volatile polymethacrylate is added to the powder blank. The polymethacrylate volatilizes at a high temperature, so that the powder blank forms a uniformly distributed microporous structure, and the pore size of the micropores is controlled to be between 5 and 20 microns, so as to obtain a heat-conducting microporous ceramic material. By adjusting the content and particle distribution of polymethacrylate, the microporous structure is ensured to be uniform and stable. This microporous structure not only provides a heat conduction path, but also can absorb external mechanical shock to achieve a shock absorption effect.

[0064] S150, placing the sintered thermally conductive microporous ceramic material in a low-temperature annealing furnace, and annealing it at a temperature range of 500° C. to 700° C. for 1 to 2 hours to release the residual stress of the thermally conductive microporous ceramic material during the sintering process, and further improve the thermal conductivity and structural stability of the thermally conductive microporous ceramic material;

[0065] In step S110, a certain proportion of alumina powder and nano-copper particles are added to a mixing container, and stirred by a high-speed mechanical stirring device to ensure that the nano-copper particles are evenly distributed in the alumina powder. Through mechanical stirring, the nano-copper particles can form a preliminary dispersion in the alumina matrix, laying the foundation for forming a thermal conductive network in the subsequent sintering process. In step S120, the preliminary mixture is placed in an electrostatic spraying device, and the preliminary mixture is prepared into uniform particles by low-pressure electrostatic spraying. The particle size is controlled between 100 and 300 microns, and the uniformity of the particles is ensured by the action of electrostatic force. Subsequently, these uniform particles are placed in a cold isostatic pressing device and pre-pressed at a pressure of 100 to 200 MPa to obtain a powder blank with a dense structure. This process uses high-pressure pressing to make the contact between the particles closer. In step S140, the powder blank is placed in a high-temperature sintering furnace and sintered by separation. The temperature is raised in stages for sintering. During the sintering process, the nano copper particles are combined with the alumina matrix in the alumina powder through liquid phase diffusion to form a continuous heat conduction path. To prevent the nano copper particles from oxidizing, the sintering is carried out under a nitrogen protective atmosphere. In addition, during the sintering process, volatile polymethacrylate is added to the powder blank. The polymethacrylate volatilizes at high temperature to form a uniformly distributed microporous structure. The pore size of the microporous structure is controlled between 5 and 20 microns. By adjusting the content and particle distribution of polymethacrylate, the uniformity and stability of the microporous structure are ensured. This microporous structure not only provides an excellent heat conduction path, but also can absorb external mechanical shock to achieve a shock absorption effect. The purpose of annealing is to release the residual stress of the thermally conductive microporous ceramic material during the sintering process, further improve the thermal conductivity and structural stability of the material, and gradually release the stress inside the material by controlling the temperature and time to improve the overall performance of the material.

[0066] The polymethacrylate powder is added to ethanol or acetone in a certain mass ratio (e.g., 5% to 10% mass concentration), and is fully dissolved by mechanical stirring or ultrasonic treatment at room temperature to form a uniform polymethacrylate solution. The pre-pressed powder blank is placed in a rotating mixing device, and the prepared polymethacrylate solution is evenly sprayed on the surface of the powder blank through a fine mist nozzle. The rotating mixing device rotates at an appropriate speed (i.e., 30 to 50 RPM), preferably 40 RPM, to ensure that the polymethacrylate solution can evenly cover each particle of the powder blank. The spraying process In the process, the spraying time and spraying amount are controlled to ensure that each gram of powder blank evenly absorbs a certain amount of polymethacrylate solution (for example, each gram of powder blank absorbs 0.1 to 0.5 ml of polymethacrylate solution), and the mixing time is controlled within 30 to 60 minutes to ensure that the polymethacrylate solution is completely and evenly distributed on the surface of the powder blank. The powder blank sprayed with the polymethacrylate solution is transferred to a low-temperature drying oven and dried at a temperature range of 50°C to 70°C for 2 to 4 hours. During the drying process, the solvent gradually evaporates and the polymethacrylate is evenly attached to the surface of the powder blank.

[0067] In this embodiment, as a preferred solution, S110 specifically includes:

[0068] S111, placing the aluminum oxide powder in an ultrasonic oscillation device, washing it with deionized water to remove adsorbed impurities on the surface of the aluminum oxide powder, placing the washed aluminum oxide powder in a drying oven, and drying it at a constant temperature of 80° C. to 120° C. for 4 to 6 hours to ensure that the aluminum oxide powder is dry and the surface is clean, so as to facilitate subsequent uniform mixing with nano-metal particles;

[0069] S112, selecting nano copper particles with a particle size range of 20 to 50 nanometers, placing them in a silane coupling agent solution, and mechanically stirring them for 30 to 60 minutes to form an active coating on the surface of the nano copper particles to enhance the interface bonding performance between the particles and the ceramic base powder. The nano copper particles with the active coating are subjected to low temperature drying to obtain surface activated nano copper particles;

[0070] S113. The cleaned alumina powder and the surface-activated nano-copper particles are dry-mixed in a mass ratio of 1:0.2 to 0.5 using a high-energy ball mill. The milling time of the high-energy ball mill is controlled at 6 to 8 hours. Zirconia ceramic balls are used as the milling medium to form a preliminary mixture to ensure uniform mixing. During the ball milling process, the rotation speed (300 to 400 rpm) and temperature are controlled to avoid particle agglomeration and ensure uniform distribution of the ceramic-based powder and the nano-metal particles.

[0071] In this embodiment, as a preferred solution, S140 specifically includes:

[0072] S141, placing the powder blank with polymethacrylate attached thereto in a high-temperature sintering furnace for an initial heating stage, wherein the temperature is raised from room temperature to 600° C. at a heating rate of 5° C. per minute and maintained for 1 hour. The purpose of this stage is to remove residual adsorbed gas and organic matter to ensure the purity of the material in the subsequent sintering process;

[0073] S142, after the initial heating stage, an intermediate heating stage is performed, in which the temperature is increased from 600°C to 900°C at a heating rate of 10°C per minute and maintained for 2 hours. The purpose of this stage is to promote a preliminary reaction between the ceramic matrix (i.e., alumina powder) and the nano-metal particles (i.e., nano-copper particles) to form a preliminary bonding interface;

[0074] S143, after the intermediate heating stage is completed, a high temperature sintering stage is performed, in which the temperature is raised from 900°C to 1300°C at a heating rate of 8°C per minute and maintained for 3 to 4 hours, so that the nano copper particles form a continuous heat conduction network in the alumina powder through liquid phase diffusion. This stage ensures the optimization of the material's density and thermal conductivity;

[0075] S144. During the high-temperature sintering stage, a nitrogen protective atmosphere is maintained in the high-temperature sintering furnace to prevent oxidation of the nano-copper particles. The polymethacrylate volatilizes at high temperature, so that the powder blank forms a uniformly distributed microporous structure. By adjusting the content (e.g., 0.5% to 2%) and particle size of the polymethacrylate, the pore size of the microporous structure is controlled to be between 5 and 20 microns, thereby ensuring the uniformity and stability of the microporous structure.

[0076] S145. After the high-temperature sintering stage, a slow cooling stage is carried out, in which the material is slowly cooled to room temperature at a cooling rate of 5°C per minute to avoid micro cracks inside the material due to excessive temperature differences.

[0077] In this embodiment, as a preferred solution, before S200, an insulating material is mixed with an electrical insulating filler to obtain an insulating coating material, and the insulating coating material is coated on the surfaces of a plurality of thermally conductive microporous ceramic materials. S200 specifically includes:

[0078] S210, stacking a plurality of thermally conductive microporous ceramic materials and placing them into a vacuum hot press, and hot pressing the stacked plurality of thermally conductive microporous ceramic materials into a composite substrate by the vacuum hot press;

[0079] S220, drilling holes on the composite substrate by laser drilling equipment to form thermal via holes penetrating the composite substrate, performing ultrasonic cleaning on the composite substrate with the thermal via holes to remove debris and impurities generated during the drilling process, drilling holes by laser drilling equipment, and precisely controlling laser power, pulse frequency, and focal length in laser drilling to ensure aperture consistency and verticality, and the aperture range is controlled between 50 and 200 microns;

[0080] S230, after the composite substrate with the thermal via hole is cleaned, metallizing the inner wall of the thermal via hole to uniformly form a copper film with thermal conductivity and electrical connection performance on the inner wall of the thermal via hole to improve the thermal conductivity and electrical connection performance;

[0081] Use an ultrasonic cleaning tank to immerse the composite substrate in a mixture of deionized water and an appropriate amount of chemical cleaning agent (such as hydrofluoric acid or nitric acid). The ultrasonic cleaning time is controlled within 10 to 20 minutes to ensure that the inner wall of the hole is clean and free of residue;

[0082] S240. After a copper film is formed on the inner wall of the thermal via hole, the composite substrate is placed in a high-temperature annealing furnace and annealed at 300°C to 500°C for 1 hour. During the annealing process, the copper film on the inner wall of the thermal via hole is combined with the continuous thermal conductive network formed by the nano-copper particles in the composite substrate to form a continuous thermal conductive path. The annealing treatment is used to enhance the bonding strength between the via hole and the continuous thermal conductive network to ensure efficient heat transfer.

[0083] In this embodiment, as a preferred solution, S230 specifically includes:

[0084] S231, immersing the cleaned composite substrate in a chemical plating solution containing copper ions, and uniformly depositing a copper film having thermal conductivity and electrical connection performance on the inner wall of the thermal via hole; using a chemical copper plating process, immersing the composite substrate in a chemical plating solution containing copper ions, and uniformly depositing a copper film on the inner wall of the thermal via hole by controlling the reaction temperature (50° C. to 70° C.) and time (30 to 60 minutes);

[0085] S232, electroplating the thermal via hole with a layer of copper film deposited thereon, and further increasing the thickness of the copper film on the inner wall of the thermal via hole by electroplating to ensure the thermal and electrical conductivity of the thermal via hole.

[0086] In this embodiment, as a preferred solution, S300 specifically includes:

[0087] S310, mixing the polyurethane particles and the carbon fiber filler in a mass ratio to obtain a composite material for preparing a microporous layer; the elastic polymer particles are decomposed in a subsequent sintering process to form a microporous structure with a certain elasticity, and the shock-absorbing reinforcing filler further optimizes the shock-absorbing performance and thermal stability of the microporous layer, and the mixed material is uniformly mixed in a vacuum environment for 3 to 5 hours to ensure uniform distribution of the components;

[0088] S320, placing the composite material for preparing the microporous layer in a mold for pre-pressing to obtain the microporous layer;

[0089] S330, placing a microporous layer between adjacent layers of a composite substrate, bonding the microporous layer to the adjacent composite substrate by coating a silicon-based adhesive on the surface of the microporous layer, and then performing vacuum hot pressing to form a multi-layer structure, performing a corrosion-resistant coating on the surface of the multi-layer structure, and obtaining a multi-layer composite circuit board substrate;

[0090] The thermal via hole is opened on the composite substrate, and the microporous layer is provided with a secondary via hole corresponding to the thermal via hole. A copper film with thermal conductivity and electrical connection performance is deposited on the secondary via hole and the thermal via hole and electroplated. The thickness of the copper film on the inner wall of the thermal via hole is further increased by electroplating to ensure the thermal and electrical conductivity of the thermal via hole.

[0091] Alternatively, secondary conductive holes may be opened in the microporous layer corresponding to the thermal conductive holes. When the microporous layer is placed between adjacent layers of the composite substrate, the microporous layer is coated with silicone-based adhesive on the surface of the microporous layer to bond with the adjacent composite substrate and then vacuum hot pressed to form a multi-layer structure. A copper layer is then coated on part of the microporous layer of the multi-layer structure to form a connected conductive path.

[0092] The present invention also provides a multilayer composite circuit board, which is prepared by the multilayer composite circuit board preparation method as described above, and the multilayer composite circuit board comprises:

[0093] Thermally conductive microporous ceramic material, made by hot pressing a mixture of alumina powder and nano copper particles, used for lamination and vacuum hot pressing to form a composite substrate;

[0094] A continuous heat-conducting network and microporous structure are formed in the thermally conductive microporous ceramic material to provide a heat conduction path and absorb external mechanical shock;

[0095] Thermal vias are provided on the surface of the composite substrate and are connected to the continuous thermal conductive network to form a continuous thermal conductive path to improve thermal conductivity and electrical connection performance;

[0096] The microporous layer is disposed between the composite substrates to optimize shock absorption performance and thermal stability.

[0097] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a multilayer composite circuit board, characterized in that: include: S100, mixing ceramic-based powder with nano-metal particles, and sintering to form a thermally conductive microporous ceramic material having a continuous thermally conductive network and a microporous structure; S200, stacking a plurality of thermally conductive microporous ceramic materials and pressing them into a composite substrate by vacuum hot pressing, and forming a through thermal conductive hole on the composite substrate; S300, stacking composite substrates formed with thermal vias, providing microporous layers for heat conduction and shock absorption between adjacent composite substrates, forming a multilayer structure by vacuum hot pressing the stacked composite substrates and the microporous layers, and performing surface coating on the multilayer structure to obtain a multilayer composite circuit board substrate; S100 specifically includes: S110, mixing the ceramic-based powder and the nano-metal particles, and uniformly dispersing them by mechanical stirring to form a preliminary mixture; S120, placing the preliminary mixture in an electrostatic spraying device, preparing the preliminary mixture into uniform particles by low-pressure electrostatic spraying, wherein the particle size is between 100 and 300 microns, and then placing the uniform particles in a cold isostatic pressing device, performing pre-pressing molding at a pressure of 100 to 200 MPa to obtain a powder blank; S130, placing the powder blank in a mixing device, spraying the polymethacrylate solution evenly on the surface of the powder blank through a fine mist nozzle, and then placing the powder blank sprayed with the polymethacrylate solution in a drying oven for drying at a temperature range of 50° C. to 70° C., wherein the solvent gradually evaporates and the polymethacrylate is evenly attached to the surface of the powder blank; S140. Place the powder blank with polymethacrylate attached in a high-temperature sintering furnace and perform sintering by increasing the temperature in stages. During the sintering process, the nano-metal particles are combined with the ceramic-based powder through liquid-phase diffusion in the ceramic-based powder to form a heat conduction path, and the oxidation of the particles is suppressed under the protection of nitrogen. The polymethacrylate volatilizes at high temperature to form a uniformly distributed microporous structure in the powder blank. The pore size of the micropores is controlled between 5 and 20 microns to obtain a thermally conductive microporous ceramic material.

2. The method for preparing a multilayer composite circuit board according to claim 1, characterized in that: The ceramic-based powder is at least one of aluminum oxide powder and silicon nitride powder, and the nano-metal particles are at least one of nano-copper particles and silver particles.

3. The method for preparing a multilayer composite circuit board according to claim 2, characterized in that: The S110 specifically includes: S111, placing the aluminum oxide powder in an ultrasonic oscillation device, washing it with deionized water to remove adsorbed impurities on the surface of the aluminum oxide powder, placing the washed aluminum oxide powder in a drying oven, and drying it at a constant temperature of 80° C. to 120° C. for 4 to 6 hours; S112, selecting nano copper particles with a particle size ranging from 20 to 50 nanometers, placing them in a silane coupling agent solution, and mechanically stirring them for 30 to 60 minutes to form an active coating on the surface of the nano copper particles, and subjecting the nano copper particles with the active coating to low temperature drying treatment to obtain surface activated nano copper particles; S113. Dry-mix the cleaned alumina powder and the surface-activated nano-copper particles in a mass ratio of 1:0.2-0.5 using a high-energy ball mill. The milling time of the high-energy ball mill is controlled at 6 to 8 hours. Zirconia ceramic balls are used as the ball milling medium to form a preliminary mixture.

4. The method for preparing a multilayer composite circuit board according to claim 2, characterized in that: The S140 specifically includes: S141, placing the powder blank in a high-temperature sintering furnace for an initial heating stage, during which the temperature is raised from room temperature to 600° C. at a heating rate of 5° C. per minute and maintained for 1 hour; S142, after the initial heating stage, an intermediate heating stage is performed, in which the temperature is increased from 600° C. to 900° C. at a heating rate of 10° C. per minute and maintained for 2 hours; S143, after the intermediate heating stage is completed, a high temperature sintering stage is performed, in which the temperature is raised from 900° C. to 1300° C. at a heating rate of 8° C. per minute and maintained for 3 to 4 hours, so that the nano copper particles form a continuous heat conduction network in the alumina powder through liquid phase diffusion; S144. During the high-temperature sintering stage, a nitrogen protective atmosphere is maintained in the high-temperature sintering furnace to prevent oxidation of the nano-copper particles, and the polymethacrylate is volatilized at high temperature, so that the powder blank forms a uniformly distributed microporous structure; S145. After the high temperature sintering stage is completed, a slow cooling stage is performed, in which the temperature is slowly lowered to room temperature at a cooling rate of 5° C. per minute.

5. The method for preparing a multi-layer composite circuit board according to claim 1, characterized in that: Before S200, an insulating material is mixed with an electrical insulating filler to obtain an insulating coating material, and the insulating coating material is coated on the surfaces of a plurality of thermally conductive microporous ceramic materials. S200 specifically includes: S210, stacking a plurality of thermally conductive microporous ceramic materials and placing them into a vacuum hot press, and hot pressing the stacked plurality of thermally conductive microporous ceramic materials into a composite substrate by the vacuum hot press; S220, drilling holes on the composite substrate by using a laser drilling device to form thermal via holes penetrating the composite substrate, and performing ultrasonic cleaning on the composite substrate with the thermal via holes to remove debris and impurities generated during the drilling process; S230, after cleaning the composite substrate with the thermal via hole formed thereon, metallizing the inner wall of the thermal via hole to uniformly form a copper film having thermal conductivity and electrical connection performance on the inner wall of the thermal via hole; S240, after a copper film is formed on the inner wall of the thermal via hole, the composite substrate is placed in a high-temperature annealing furnace and annealed at 300° C. to 500° C. for 1 hour. During the annealing process, the copper film on the inner wall of the thermal via hole is combined with the continuous heat conduction network formed by the nano copper particles in the composite substrate to form a continuous heat conduction path.

6. The method for preparing a multi-layer composite circuit board according to claim 5, characterized in that: The S230 specifically includes: S231, immersing the cleaned composite substrate in a chemical plating solution containing copper ions, and uniformly depositing a copper film having thermal conductivity and electrical connection properties on the inner wall of the thermal via hole; S232, electroplating the thermal via hole on which a layer of copper film is deposited, and the thickness of the copper film on the inner wall of the thermal via hole is further increased by electroplating.

7. The method for preparing a multi-layer composite circuit board according to claim 1, characterized in that: The S300 specifically includes: S310, mixing the polyurethane particles and the carbon fiber filler according to a mass ratio to obtain a composite material for preparing a microporous layer; S320, placing the composite material for preparing the microporous layer in a mold for pre-pressing to obtain the microporous layer; S330, placing the microporous layer between adjacent layers of the composite substrate, bonding the microporous layer to the adjacent composite substrate by coating the surface of the microporous layer with silicone-based adhesive, and then performing vacuum hot pressing to form a multi-layer structure, performing corrosion-resistant coating on the surface of the multi-layer structure, and obtaining a multi-layer composite circuit board substrate.

8. A multi-layer composite circuit board, characterized in that: The multilayer composite circuit board is prepared by the method for preparing the multilayer composite circuit board according to any one of claims 1 to 7, wherein the multilayer composite circuit board comprises: Thermally conductive microporous ceramic material, made by hot pressing a mixture of alumina powder and nano copper particles, used for lamination and vacuum hot pressing to form a composite substrate; A continuous heat-conducting network and microporous structure are formed in the thermally conductive microporous ceramic material to provide a heat conduction path and absorb external mechanical shock; Thermal vias are provided on the surface of the composite substrate and are connected to the continuous thermal conductive network to form a continuous thermal conductive path to improve thermal conductivity and electrical connection performance; The microporous layer is disposed between the composite substrates to optimize shock absorption performance and thermal stability.

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