Graphene interface modified diamond copper composite material and preparation method and application thereof

Abstract

The invention provides a graphene interface modified diamond copper composite material and a preparation method and application thereof. The graphene interface modified diamond copper composite material comprises, by volume, 50%-65% of hydrophilic oxidized diamond particles, 0.5%-5% of graphene oxide and the balance copper powder. The diamond and the graphene form a diamond (at) GO core-shell structure of the graphene-coated diamond. Graphene is used as an interface modifier, a diamond-graphene-copper gradient interface structure is constructed, a dispersed composite three-dimensional uniform composite mode is adopted, and the transmission efficiency of phonons on an interface is greatly enhanced through the two-dimensional ultrahigh heat conduction characteristic and the interface bridging effect of graphene, so that the transmission efficiency of the phonons on the interface is greatly improved. Therefore, the composite material with ultrahigh heat conductivity and low thermal expansion is prepared; especially, the graphene-coated diamond fully utilizes the two-dimensional characteristic of graphene to reduce the interface thermal resistance. The product is mainly used for a heat dissipation bottom plate of a SiC power module, and is widely applied to the fields of new energy automobiles, rail transit, intelligent power grids, industrial motor driving and the like.

Description

Technical Field

[0001] This application belongs to the field of electronic packaging heat dissipation materials technology, and particularly relates to a graphene interface modified diamond copper composite material, its preparation method and application. Background Technology

[0002] With the development of power electronics technology towards higher power density, miniaturization, and higher frequency, wide-bandgap semiconductors, represented by SiC, have been widely used. However, the large amount of heat generated by SiC chips during operation has become a key bottleneck limiting their performance and reliability.

[0003] Currently, copper, aluminum, molybdenum copper alloy (MoCu), and tungsten copper alloy (WCu) are commonly used in the industry as materials for module heat dissipation base plates. Although copper has good thermal conductivity (387 W / (m·K)), its coefficient of thermal expansion (CTE, 17×10⁻⁶) is low. -6 / K) and SiC chip (CTE, 4.5×10 -6 The severe mismatch between the chip and the substrate ( / K) generates enormous stress during thermal cycling, which may lead to loosening and cracking of the connection between the chip and the substrate after long-term use, affecting the lifespan of the module. Although existing technologies have introduced diamond-copper composite materials (Diamond / Cu), utilizing diamond's ultra-high thermal conductivity (>1000 W / (m·K)) and low CTE (2×10⁻⁶ W / (m·K))... -6 While using / K) to improve performance, the following inherent drawbacks still exist: 1. High interfacial thermal resistance: Diamond and copper have poor physical compatibility and extremely low interfacial wettability, making interfacial thermal resistance a bottleneck restricting the improvement of overall thermal conductivity. Although metallization treatments such as tungsten (W) and molybdenum (Mo) plating are used to improve the bonding, the brittle carbides formed at the interface are prone to failure under thermal stress, and the process is complex.

[0004] 2. Performance and reliability are difficult to balance: Increasing the diamond content is necessary to improve thermal conductivity, but a high volume fraction will make it difficult to densify the material, reduce mechanical properties, and result in a low yield of finished products.

[0005] 3. High cost: Traditional processes are difficult to further reduce material costs and energy consumption while ensuring performance.

[0006] Therefore, developing a novel diamond-copper composite material that can significantly reduce interfacial thermal resistance and possess excellent comprehensive performance has become an urgent technological need in this field. Summary of the Invention

[0007] This application is made in view of the above-mentioned issues, and its purpose is to provide a graphene-modified diamond-copper composite material, which effectively reduces the interfacial thermal resistance between diamond and copper matrix, breaks through the overall thermal conductivity of composite material, improves thermal conductivity, ensures good thermal expansion matching and sufficient mechanical strength between composite material and SiC chip, and has a simple preparation method, controllable cost, and is easy to scale up for production, as well as its preparation method and application.

[0008] The first aspect of this application provides a graphene-modified diamond-copper composite material, comprising diamond particles, graphene, and copper powder, wherein the volume fraction of the diamond particles is 50%–65%, the volume fraction of the graphene is 0.5%–5%, and the balance is copper powder; the diamond particles are hydrophilic diamond oxide particles, the graphene is graphene oxide, and the copper powder is electrolytic copper powder; the diamond and graphene form a graphene-coated diamond "diamond@GO" core-shell structure.

[0009] In any embodiment, the diamond particles have a particle size of 50 to 200 μm. If the particle size is too small, the total interfacial area will increase dramatically, resulting in excessive phonon scattering and interfacial thermal resistance, which will lead to a decrease in thermal conductivity. If the particle size is too large, the copper liquid will not be able to fully fill the pores between the large particles during sintering, resulting in a decrease in density and macroscopic defects, which will impair thermal conductivity and mechanical strength.

[0010] In any embodiment, the thickness of the interface layer formed by the graphene is 1 to 2 nm.

[0011] Phonon bridging is used to match the phonon vibrational spectra of diamond and copper, reducing interfacial thermal resistance. Studies show that phonons contribute 86.59% to the interfacial thermal conduction between graphene and copper, while electronic conduction accounts for only 13.41%. The copper matrix forms a continuous three-dimensional network, which serves as an electron-dominated thermal conduction path (conductivity >95%) and buffers thermal stress through plastic deformation.

[0012] In any embodiment, the thickness of the interface layer formed by the graphene is 2 to 4 layers.

[0013] This layer count control balances ultra-high intrinsic thermal conductivity and efficient phonon bridging. Too few layers (such as a single layer) may make it difficult to form continuous coatings in production; too many layers (>5 layers, i.e., >~3nm) will increase phonon scattering of the graphene layer itself, and the interfacial thermal resistance will increase.

[0014] In any embodiment, the diamond accounts for 50-65% of the volume fraction of the composite material.

[0015] This range allows for the control of the coefficient of thermal expansion (CTE) of the composite material within the range of 5.5–7.5 × 10⁻⁶ while ensuring high thermal conductivity. -6 / K, with SiC chip (4.5×10 -6 / K) form a good match. Too high a diamond content will make sintering densification difficult, while too low a content will not effectively reduce CTE.

[0016] In any embodiment, the graphene accounts for 0.5% to 5% of the volume fraction of the composite material.

[0017] This ratio ensures interface coverage. When the graphene volume fraction is >0.6%, a continuous interface layer can be formed, but if it exceeds 5%, agglomeration is likely to occur, which will block the heat flow path.

[0018] In any embodiment, the copper powder is electrolytic copper powder with a purity of not less than 99.9% and a particle size of 5 to 20 μm.

[0019] Electrolytic copper powder with a purity of no less than 99.9% (particle size 5–20 μm) is used, and low oxygen content is crucial for reducing interfacial thermal resistance. The oxide layer (Cu2O) on the surface of the copper powder is an extremely strong source of phonon scattering, which will severely degrade the interfacial thermal conductivity.

[0020] In any embodiment, the copper powder is high-purity oxygen-free copper with an oxygen content ≤0.001%.

[0021] In any embodiment, the coefficient of thermal expansion of the composite material is 5.5 to 7.5 × 10⁻⁶. -6 / K.

[0022] The second aspect of this application provides a method for preparing graphene-modified diamond-copper composite materials, comprising the following steps: (1) Diamond pretreatment: Diamond particles are placed in nitrated mixed acid for reflux treatment, washed, and dried to obtain hydrophilic diamond oxide particles. (2) Preparation of GO dispersion: Graphene oxide powder was dispersed in deionized water to prepare a uniform dispersion with a concentration of 1 to 5 mg / mL. This GO concentration ensures coating quality and efficiency. Too low a concentration (<1 mg / mL): Insufficient GO layers prevent effective and complete coating of all diamond particles, resulting in unmodified diamond surfaces and persistently high interfacial thermal resistance. Too high a concentration (>5 mg / mL): Excessive GO layers readily aggregate in solution, forming GO agglomerates. These agglomerates fail to effectively coat the diamond and instead become defects in subsequent processes, blocking heat flow paths. Furthermore, the larger the total surface area of ​​the coated diamond, the higher the required GO dispersion concentration.

[0023] (3) Constructing a core-shell structure: The pretreated diamond particles and GO dispersion were mixed in proportion, ultrasonically treated for 1 to 2 hours, and then mechanically stirred for 4 to 6 hours to fully coat the diamond surface and form a "diamond@GO" precursor. Then the mixture was filtered and dried at low temperature. When mixing, too few Go objects (GOs) will result in an incomplete interface finish, preventing the formation of a continuous wrapping layer. Too many GOs will cause excess GOs beyond the necessary amount for a complete wrapping layer to clump together, leading to the adverse effects described above.

[0024] Ultrasonic treatment utilizes cavitation to achieve microscopic dispersion and break up GO agglomerates; mechanical stirring provides gentle shear force, achieving macroscopic homogeneous mixing and self-assembly. These two steps are complementary and sequential. Insufficient time can lead to inadequate GO dispersion or coating, and incomplete interface modification. Excessive time may damage the GO lamellar structure or existing coating layers, introducing defects. It is crucial to control the ultrasonic power (300–500 W) and stirring speed (200–300 rpm). Inappropriate power or speed can damage the material or result in uneven mixing.

[0025] (4) Preparation of composite powder: The "diamond@GO" precursor and electrolytic copper powder are mixed in a V-type mixer for 3 to 5 hours.

[0026] (5) Reduction treatment: Place the mixed powder in a tube furnace and heat treat it at 400-600℃ for 1-2 hours under H2 / Ar (5% / 95%) atmosphere; If the heat treatment time is too short, the reduction will be insufficient; if the time is too long, the energy consumption will increase, which may cause the copper powder oxide layer to be over-reduced and then roughened again.

[0027] (6) SPS sintering: The reduced powder is loaded into a graphite mold and sintered in an SPS device. The sintering conditions are: vacuum environment, pressure 30-50 MPa, heating to 900-1000℃ at a rate of 100-200℃ / min, and holding for 5-15 minutes; the resulting composite material.

[0028] If the temperature is too low, the copper powder will not melt completely, resulting in poor fluidity, inability to densify, and numerous pores. If the temperature is too high, the graphene structure may be damaged (graphitization or the formation of carbides with copper), increasing the interfacial thermal resistance.

[0029] Pressure (30–50 MPa): If too low, it will not be enough to drive the molten copper to fill all the pores, resulting in low density. If too high, it may crush the diamond particles and damage the prefabricated structure.

[0030] Too slow a heating rate can lead to grain growth and an excessively long interfacial reaction time between graphene and copper, potentially forming harmful phases. Too fast a rate can result in thermal stress and uneven densification.

[0031] If the heat preservation time is too short, the densification process will not be completed. If it is too long, it will have the same drawback as "too slow heating rate".

[0032] In any embodiment, the mixing ratio of the diamond particles to the GO dispersion is 100:0.5 to 5.

[0033] When mixing, too few Go objects (GOs) will result in an incomplete interface finish, preventing the formation of a continuous wrapping layer. Too many GOs will cause excess GOs beyond the necessary amount for a complete wrapping layer to clump together, leading to the adverse effects described above.

[0034] In any embodiment, the ultrasonic power is 300-500W and the stirring speed is 200-300rpm.

[0035] Ultrasonic treatment utilizes cavitation to achieve microscopic dispersion and break up GO agglomerates; mechanical stirring provides gentle shear force, achieving macroscopic homogeneous mixing and self-assembly. These two steps are complementary and sequential. Insufficient time can lead to inadequate GO dispersion or coating, and incomplete interface modification. Excessive time may damage the GO lamellar structure or existing coating layers, introducing defects. It is crucial to control the ultrasonic power (300–500 W) and stirring speed (200–300 rpm). Inappropriate power or speed can damage the material or result in uneven mixing.

[0036] In any embodiment, the diamond pretreatment involves placing diamond particles in a round-bottom flask with a mixture of concentrated sulfuric acid (H2SO4, 98%) and concentrated nitric acid (HNO3, 68%) in a volume ratio of 3:1, wherein the solid-liquid ratio is 1g:10mL; heating and refluxing in an oil bath at 85–95°C for 2–4 hours; after the reaction is complete, allowing it to cool naturally to room temperature; then washing repeatedly with a large amount of deionized water by vacuum filtration until the filtrate is neutral; finally, drying the solid product in a vacuum drying oven at 80°C for 6–8 hours to obtain surface-oxidized hydrophilic diamond particles.

[0037] In any embodiment, the diamond particles have a particle size of 50–200 μm.

[0038] In any embodiment, the thickness of the interface layer formed by the graphene is 1 to 2 nm.

[0039] In any embodiment, the thickness of the interface layer formed by the graphene is 2 to 4 layers.

[0040] In any embodiment, the diamond volume fraction is 50–65%.

[0041] In any embodiment, the volume fraction of the graphene is 0.5% to 5%.

[0042] In any embodiment, the copper powder is electrolytic copper powder with a purity of not less than 99.9% and a particle size of 5–20 μm.

[0043] In any embodiment, the copper powder is high-purity oxygen-free copper with an oxygen content ≤0.001%.

[0044] A third aspect of this application also provides an application of graphene interface-modified diamond-copper composite material, wherein the diamond composite material prepared above is used in SiC power modules.

[0045] In any embodiment, the welding assembly of the composite base plate of the SiC power module is as follows: A welding tray is placed on the assembly table, and the graphene-diamond-copper composite base plate is placed on it. Then, the AMB positioning frame is placed flat on the base plate. Next, three SnSb5 solder pieces are placed sequentially within the AMB positioning frame. Then, the printed, sintered, and bonded AMB ceramic substrate is placed orderly on the solder pieces. Finally, the equipped SAC305 solder wire PIN positioning carrier is assembled with the welding base plate, ensuring that each PIN... The pins fall and contact the AMB surface. The tray is then horizontally transported to the loading dock, and the base plate is systematically welded using a formic acid vacuum reflow soldering oven. The reduction temperature of the preheating chamber is set to 200–220°C, preferably 210°C, and the reduction time is set to 200s. The formic acid pressure is set to 550mbar. The reduction temperature of the soldering chamber is set to 215–235°C, preferably 220°C, and the reduction time is set to 100s. The formic acid pressure is set to 450mbar, and the reflow time is 70s. The cooling temperature is set to 40°C. After soldering, the PIN carrier is removed, the AMB limiting frame is taken out, and then the product is removed. The final SiC power module is obtained through subsequent plastic shell assembly, vacuum potting, silicone gel curing, and cover plate assembly.

[0046] The preheating chamber is where the solder pad connects to the AMB. The product is slowly heated to activate the solder, evaporate the solvent, and complete the preheating process, preventing sudden boiling upon entering the high-temperature zone. The temperature and formic acid atmosphere are set to clean and activate the surface to be soldered before welding, preventing oxidation. The temperature rises rapidly above the solder melting point, causing the solder pad (SnSb5) to completely melt, wet, and form a reliable weld joint. The temperature of 220°C is above the liquidus line of SnSb5, ensuring good reflow. The beneficial effects of this application are as follows: This application utilizes graphene as an interface modifier to construct a gradient interface structure of "diamond-graphene-copper". Employing a dispersed composite three-dimensional uniform composite method, the application leverages the two-dimensional ultra-high thermal conductivity and interfacial bridging effect of graphene to significantly enhance the phonon transmission efficiency at the interface, thereby preparing a composite material with ultra-high thermal conductivity and low thermal expansion. In particular, the "graphene-coated diamond" scheme fully utilizes the two-dimensional properties of graphene to reduce interfacial thermal resistance. This can be achieved through wet mixing, directly solving the core problem of the diamond-copper interface. The product is mainly used to manufacture heat dissipation base plates for third-generation semiconductor silicon carbide (SiC) power modules and can be widely applied in fields with extremely high requirements for heat dissipation performance and reliability, such as new energy vehicles, rail transportation, smart grids, and industrial motor drives.

[0047] The composite material obtained by this application has the following characteristics: 1. Significantly reduced interfacial thermal resistance and breakthrough improvement in thermal conductivity: The interface layer formed by traditional tungsten plating has a relatively low thermal conductivity (WC, 80 W / (m·K)). This invention uses graphene (1500 W / (m·K)) with extremely high thermal conductivity as the interface layer, providing an efficient channel for phonon transport. Experimental results show that, with a diamond volume fraction of 60%, the thermal conductivity of the material of this invention can reach 770 W / (m·K), which is a significant improvement over traditional tungsten-plated diamond-coated copper materials (570 W / (m·K)) and traditional oxygen-free copper substrate materials (387 W / (m·K)) under the same conditions.

[0048] 2. Enhanced interface bonding strength and reliability: The diamond-graphene-copper composite substrate material showed no defects after 1000 thermal shocks. In contrast, after 500 thermal shocks, a traditional oxygen-free copper substrate exhibited bright, cloud-like, or linear high-gloss areas at the chip edges, clearly indicating interface delamination. Power modules using this composite substrate are expected to have a power cycle life more than twice that of modules using traditional oxygen-free copper substrates.

[0049] 3. Adjustable coefficient of thermal expansion (CTE) with better matching: By adjusting the content of diamond and graphene, the CTE of the material can be precisely controlled within the range of 5.5–7.5 × 10⁻⁶. -6 Within the range of / K, compared to SiC chips (4.5×10 -6 The excellent matching between the K and AMB ceramic substrate greatly reduces the thermal stress of the package.

[0050] 4. The preparation process is simple, low-cost, and environmentally friendly. This application abandons the complex vacuum coating equipment and adopts a technical route that combines solution self-assembly and powder metallurgy. The process is short, energy consumption is low, and it is easy to achieve large-scale production. The overall cost is reduced by about 30% compared with the traditional coating method.

[0051] 5. Excellent overall material performance: Due to the reinforcing effect of graphene, the material achieves ultra-high thermal conductivity while maintaining a bending strength of over 280 MPa, exhibiting good machinability and allowing for subsequent processing such as cutting, drilling, and grinding. Attached Figure Description

[0052] Figure 1 This is a process flow diagram of the preparation method of the graphene interface modified diamond copper composite material of this application; Figure 2 These are TEM images of the microstructures of diamond, graphene, and composite materials.

[0053] Figure 3 Here is a SEM image of the diamond particles in this application; Figure 4 This is a SEM image of the graphene in this application; Figure 5 Here is a SEM image of the copper powder particles in this application; Figure 6 This is a TEM image of the graphene-copper layered structure of this application; Figure 7 SEM image of the diamond-graphene-copper composite structure of this application. Figure 8 This is a schematic diagram of the upper surface structure of the composite substrate of the SiC power module in this application; Figure 9 This is a schematic diagram of the lower surface structure of the composite substrate of the SiC power module in this application; Figure 10 This is a three-dimensional structural diagram of the composite base plate of the SiC power module of this application; Figure 11 The images are ultrasonic scanning microscope (SAM) images of the interface before and after thermal shock testing of the composite substrate of the SiC power module in this application. Figure 12 For comparison, ultrasonic scanning microscopy (SAM) images of the interface before and after thermal shock testing of the oxygen-free copper substrate in document 1. Detailed Implementation The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the graphene interface-modified diamond-copper composite material, its preparation method, and its applications. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of providing a full understanding of this application by those skilled in the art and are not intended to limit the subject matter of the claims.

[0054] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0055] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0056] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0057] 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.

[0058] 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.

[0059] 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).

[0060] The overall concept of this application: 1. Constructing using multi-scale heat conduction networks Diamond particles of 50–200 μm are used as the main thermally conductive framework, which has ultra-high thermal conductivity (>1500 W / m·K) and low coefficient of thermal expansion (2×10⁻⁶). -6 The graphene interfacial layer (1–2 nm thick) provides a basic heat dissipation channel for the composite material. Through phonon bridging, it matches the phonon vibrational spectrum of diamond and copper, reducing interfacial thermal resistance. Studies show that phonons contribute 86.59% to the interfacial thermal conduction between graphene and copper, while electronic conduction accounts for only 13.41%. The copper matrix forms a continuous three-dimensional network, serving as an electron-dominated heat conduction path (conductivity >95%) and buffering thermal stress through plastic deformation.

[0061] 2. Component optimization Diamond volume fraction (50–65%): This range allows for the control of the composite material's coefficient of thermal expansion (CTE) within the range of 5.5–7.5 × 10⁻⁶ while maintaining high thermal conductivity. -6 / K, with SiC chip (4.5×10 -6 / K) forms a good match. Excessive diamond content leads to difficulties in sintering densification, while insufficient content fails to effectively reduce CTE. Graphene content (0.5–5%): This percentage is derived from calculations of interface coverage. Experiments show that when the graphene volume fraction > 0.6%, a continuous interface layer can be formed, but exceeding 5% easily leads to agglomeration, which in turn blocks the heat flow path.

[0062] In one embodiment of this application, a method for preparing graphene interface-modified diamond-copper composite materials and its application in SiC power modules are proposed, specifically including the following: a. Raw material preparation and pretreatment: 1. Select synthetic diamond particles with high thermal conductivity and clean surface, typically ranging from 50 to 200 μm in size. Place the diamond particles in a round-bottom flask with a mixture of concentrated sulfuric acid (H₂SO₄, 98%) and concentrated nitric acid (HNO₃, 68%) in a volume ratio of 3:1, with a solid-liquid ratio of 1 g:10 mL. Heat the mixture under reflux in an oil bath at 85-95°C for 2-4 hours. After the reaction, allow it to cool naturally to room temperature. Wash the mixture repeatedly with a large amount of deionized water by vacuum filtration until the filtrate is neutral (pH≈7). Finally, dry the solid product in a vacuum drying oven at 80°C for 6-8 hours to obtain hydrophilic diamond particles with an oxidized surface.

[0063] This process introduces a large number of oxygen-containing functional groups (-OH, -COOH) onto the diamond surface, changing its surface from "hydrophobic" to "hydrophilic," thus providing reaction sites for subsequent binding with graphene oxide (GO).

[0064] 2. Prepare an aqueous dispersion of graphene oxide (GO) with a concentration of 1-5 mg / mL.

[0065] 3. Constructing a “diamond@graphene oxide” core-shell structure: Mix the oxidized diamond particles with GO aqueous dispersion in a certain proportion, place them in an ultrasonic bath for ultrasonic treatment for 1-2 hours, and then mechanically stir for 4-6 hours.

[0066] Under intermolecular forces, graphene oxide (GO) sheets spontaneously and uniformly coat the surface of charged diamond oxide particles, forming a stable "diamond@GO" core-shell structure, ensuring the uniformity and integrity of the coating.

[0067] The process primarily utilizes the hydrogen bonds and molecular forces between diamond oxide and the oxygen-containing functional groups on the GO surface to spontaneously and uniformly coat the surface of each diamond particle with GO sheets, forming a core-shell structure precursor called "diamond@GO". This process is a molecular-level self-assembly and requires no expensive equipment.

[0068] like Figure 1As shown, from top to bottom, the images depict the microstructure of diamond, the microstructure of graphene, and a TEM image of the composite material. The diamond microstructure reveals that diamond is a metastable allotrope of carbon, with each carbon atom in its crystal structure separated by sp... 3 The hybridized carbon atom forms covalent bonds with its four adjacent carbon atoms, which are arranged in a diamond cubic structure. As a material with exceptionally superior physical properties, diamond possesses the highest known hardness and outstanding thermal conductivity, approximately five times that of copper. The microstructure of graphene shows that the carbon atoms in graphene are arranged in a hexagonal lattice, a typical example of a hybridized splined carbon atom. 2 The interatomic spacing between adjacent atoms is 0.142 nm. Graphene possesses the most flexible and robust crystal structure. The thermal conductivity of graphene at room temperature is approximately 5000 W / m·K, which is 10 times higher than that of copper (401 W / m·K). As can be seen from the composite material of this application, diamond and graphene are uniformly distributed in strips perpendicular to the sintering pressure. The copper matrix appears white, while graphene and diamond, being allotropes of carbon, exhibit the same black color.

[0069] b. Preparation and reduction of composite powder: 1. The above-mentioned "diamond@GO" precursor and electrolytic copper powder with an average particle size of 5-20 μm are dry-mixed for 3-5 hours using a ball mill or V-type mixer to ensure uniform dispersion.

[0070] 2. Heat the mixed powder at 400-600℃ for 1-2 hours under a hydrogen / argon atmosphere.

[0071] During this process, GO is reduced to reduced graphene oxide (rGO), restoring its thermal conductivity; at the same time, the surface of the copper powder is slightly reduced and activated.

[0072] 2. Spark plasma sintering (SPS): The reduced composite powder is loaded into a graphite mold and placed in an SPS sintering furnace. Under vacuum, a pressure of 30-50 MPa is applied, and the temperature is raised to 900-1000℃ at a rate of 100-200℃ / min, and held for 5-15 minutes.

[0073] In this process, the copper powder melts and flows rapidly, filling all the pores. At the same time, GO is reduced in situ to reduced graphene oxide (rGO), which has better thermal conductivity, and forms a tight interfacial bond with copper.

[0074] Final structure: Formation of an ideal microstructure of diamond-graphene-copper composite structure - each diamond is encapsulated in a layer of rGO and perfectly embedded in a continuous copper matrix.

[0075] The rapid sintering characteristics of SPS can suppress the destruction of the graphene structure and the excessive growth of the interfacial reaction layer. Under high temperature and pressure, copper melts and flows to fill the voids, forming a tight metallurgical-mechanical bond with the rGO layer on the diamond surface, ultimately obtaining a composite material with a density >99%.

[0076] c. Welding and assembly of the SiC power module composite base plate: Place the welding tray support on the assembly table, then place the graphene-diamond-copper composite base plate. Next, place the AMB retaining frame flat on the base plate. Then, take 3 SnSb5 solder pieces and place them sequentially within the AMB retaining frame. Next, place the printed, sintered, and bonded AMB ceramic substrates orderly on the solder pieces, ensuring they are within the retaining frame. Then, assemble the equipped SAC305 solder wire PIN positioning carrier with the welding base plate, ensuring each PIN falls and contacts the AMB surface. Horizontally transport the tray to the loading dock, and use a formic acid vacuum reflow soldering furnace for system welding of the base plate. The preheating chamber reduction temperature is set to 210℃, reduction time to 200s, and formic acid pressure to 550mbar; the welding chamber reduction temperature is set to 220℃, reduction time to 100s, formic acid pressure to 450mbar, and reflow time to 70s; the cooling temperature is set to 40℃. After soldering, the PIN carrier is removed, the AMB limiting frame is taken out, and then the product is removed. Subsequent processes include plastic casing assembly, vacuum potting, silicone gel curing, and cover plate assembly to obtain the final SiC power module. The substrate curvature and reliability are then tested.

[0077] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0078] Example 1 A method for preparing a graphene-modified diamond-copper composite material includes the following steps: 1. Diamond pretreatment: Diamond particles are placed in a concentrated H2SO4 / HNO3 mixture with a volume ratio of 3:1, refluxed at 90°C for 2 hours, washed with deionized water until neutral, and dried to obtain hydrophilic diamond oxide.

[0079] 2. Preparation of GO dispersion: Graphene oxide powder was dispersed in deionized water to prepare a uniform dispersion with a concentration of 3 mg / mL.

[0080] 3. Constructing the core-shell structure: The pretreated diamond and GO dispersion were mixed in a certain proportion, ultrasonically treated for 1.5 hours, and then mechanically stirred for 5 hours to allow GO to fully coat the diamond surface and form a "diamond@GO" precursor. The mixture was then filtered and dried at low temperature.

[0081] 4. Preparation of composite powder: The "diamond@GO" precursor and electrolytic copper powder were mixed in a V-type mixer for 4 hours.

[0082] 5. Reduction treatment: The mixed powder is placed in a tube furnace and heat-treated at 500°C for 1.5 hours under an H2 / Ar (5% / 95%) atmosphere. GO is reduced to rGO.

[0083] 6. SPS sintering: The reduced powder is loaded into a graphite mold and sintered in an SPS device. The conditions are: vacuum environment, pressure 40 MPa, heating to 950℃ at a rate of 150℃ / min, and holding at that temperature for 10 minutes.

[0084] Example 2: The steps are basically the same as in Example 1, with the key adjustment being the SPS sintering process: to promote the flow of molten copper with high diamond content, the sintering temperature was increased to 980°C, the pressure to 45 MPa, and the holding time to 12 minutes. This example demonstrates that by increasing the diamond content and optimizing the process, the thermal conductivity can be further increased and the CTE reduced. Although the density and strength decrease slightly, they still meet the usage requirements.

[0085] Example 3: The process is essentially the same as in Example 1. Due to the lower graphene content, the sonication and stirring times were extended to 2 hours and 6 hours, respectively, in the "constructing the core-shell structure" step to ensure uniform coating. Even using only 0.8% graphene, its thermal conductivity is significantly higher than that of conventional tungsten-copper / diamond composites (570 W / (m·K)), demonstrating the effectiveness of the invention at low doses and providing an option for cost-sensitive applications.

[0086] Example 4: A hot-press sintering furnace was used. Under argon protection, the temperature was increased to 920°C at a rate of 15°C / min, and a pressure of 35 MPa was applied. The holding time was 45 minutes, followed by furnace cooling. Although the thermal conductivity and density are slightly lower than those of the SPS process, hot-press sintering can still produce composite materials with excellent performance and is suitable for the fabrication of large-size parts, thus expanding the process applicability of this invention.

[0087] Example 5: After undergoing the same acid pickling pretreatment, diamond was directly mixed with copper powder without adding graphene, and sintered using the same SPS process as in Example 1. Under the same process and diamond content, due to the lack of graphene interfacial bridging, the interfacial thermal resistance between diamond and copper was extremely high, resulting in a significant decrease in overall thermal conductivity, even lower than some products produced by traditional processes. This fully demonstrates the indispensability of graphene interfacial modification in this invention.

[0088] Table 1. Process parameters and material thermal conductivity properties in each embodiment.

[0089] Comparative Example 1 Preparation of oxygen-free copper substrate: High-purity oxygen-free copper (oxygen content ≤0.001%) of grade C1020 was selected as the raw material. Standard thickness plates were prepared by hot pressing sintering or hot rolling. To eliminate internal stress and obtain recrystallized structure, annealing was performed in a hydrogen or vacuum atmosphere (temperature 450–550℃, time 1–2 hours). Finally, the plates were machined (grinding, cutting) to produce the base plate samples required for testing.

[0090] Comparative Example 2 Preparation of diamond-copper composite base plate: A tungsten-plating method is used to metallize the surface of diamond particles to improve their wettability with copper. The tungsten-plated diamond particles (55%–60% by volume) are then mechanically mixed with electrolytic copper powder. The mixture is then formed using hot-pressing sintering or melt infiltration. Taking hot-pressing sintering as an example: under vacuum or argon protection, the temperature is 950–980℃, the pressure is 35–45 MPa, and the holding time is 60–120 minutes. This method aims to simulate the mainstream technical route currently used in the industry to prepare high-performance diamond-copper composite materials without the use of graphene interface modification.

[0091] Figures 3-5 The images show the scanning electron microstructure of diamond particles, graphene, and copper powder particles, respectively. Figure 6 This is a transmission electron microscopy (TEM) diagram of a graphene-copper layered structure. We can see that the graphene-copper layered structure adopts a sandwich structure, rather than true original graphene dispersed within copper. Figure 7 This is a scanning electron microscope image of a diamond-graphene-copper composite structure, clearly showing each diamond particle. Figure 3 ) are all covered by a continuous or semi-continuous graphene film ( Figure 4 Encased in a continuous copper substrate, the graphene layer is embedded within the substrate. Figure 5In this process, a perfect bridge is formed between diamond and copper. Diamond particles form the main thermally conductive framework, a graphene interface layer is used to establish an efficient phonon transport channel, and finally, the copper matrix provides a continuous heat transport medium.

[0092] To objectively and quantitatively evaluate the comprehensive thermal performance of the graphene-modified diamond-copper composite substrate prepared in this application, a commercial oxygen-free copper substrate (Comparative Example 1) and a traditional tungsten-plated diamond-copper composite substrate (Comparative Example 2) were selected as reference standards. Under identical test conditions (based on GB / T 39149 standard, using the laser flash method), the thermal conductivity, coefficient of thermal expansion, and density of the three materials were precisely measured. The test comparison table is shown in Table 2.

[0093] Table 2: Comparison of thermal conductivity of different base plates

[0094] Note: The parameter testing conditions were the same for different samples in the oxygen-free copper substrate and diamond-copper composite substrate to prove repeatability and consistency.

[0095] The test results clearly show that the material of this invention successfully constructed a "diamond-graphene-copper" gradient interface structure, and its thermal conductivity surpassed that of the two reference materials. At the same time, it maintained good thermal expansion matching with the SiC chip, which fully demonstrates the effectiveness and advancement of this invention in solving the core technical problem of interface thermal resistance.

[0096] To verify its reliability, a simplified power module unit was soldered onto a substrate using sintered silver paste. A comparative thermal shock test was conducted on the diamond-graphene-copper composite substrate (corresponding to the sample in Example 1) prepared according to standards such as JESD22-A104, comparing it with a traditional oxygen-free copper substrate. The high-temperature chamber was set to +125°C, and the low-temperature chamber was set to -40°C. The residence time of the sample in both the high-temperature and low-temperature chambers was strictly controlled to be more than 15 minutes to ensure that the sample reached overall temperature equilibrium. The transition time between high and low temperatures was less than 30 seconds to generate a severe temperature shock. Figure 11 , 12 This describes the interface of the substrate material using an ultrasonic scanning microscope.

[0097] Ultrasonic scanning microscopy (SAM) image of a diamond-graphene-copper composite substrate material after 1000 thermal shocks. Figure 11 The interface region exhibits a uniform dark color, indicating the absence of defects. This is an ultrasonic scanning microscopy (SAM) image of a traditional oxygen-free copper substrate after 500 thermal shocks. Figure 12Bright, cloud-like, or linear highlighted areas are visible at the edges of the chip, clearly indicating the interface layering.

[0098] Based on the above data, the power module using the composite base plate of the present invention is expected to have a power cycle life that is more than twice that of the traditional oxygen-free copper base plate module.

[0099] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A graphene-modified diamond-copper composite material, characterized in that, It comprises diamond particles, graphene, and copper powder, wherein the volume fraction of the diamond particles is 50%–65%, the volume fraction of the graphene is 0.5%–5%, and the balance is copper powder; the diamond particles are hydrophilic diamond oxide particles, the graphene is graphene oxide, and the copper powder is electrolytic copper powder; the diamond and graphene form a "diamond@GO" core-shell structure in which the diamond is coated with graphene.

2. The graphene-modified diamond-copper composite material according to claim 1, characterized in that, The diamond particles have a particle size of 50–200 μm; the copper powder is electrolytic copper powder with a purity of not less than 99.9% and a particle size of 5–20 μm.

3. The graphene-modified diamond-copper composite material according to claim 1, characterized in that, The thickness of the interface layer formed by the graphene is 1–2 nm.

4. The graphene-modified diamond-copper composite material according to claim 1, characterized in that, The thickness of the interface layer formed by the graphene is 2 to 4 layers.

5. A method for preparing a graphene-modified diamond-copper composite material, characterized in that, Includes the following steps: (1) Diamond pretreatment: Diamond particles are placed in nitrated mixed acid for reflux treatment, washed, and dried to obtain hydrophilic diamond oxide particles. (2) Preparation of GO dispersion: Graphene oxide powder was dispersed in deionized water to prepare a uniform dispersion with a concentration of 1-5 mg / mL. (3) Constructing a core-shell structure: The pretreated diamond particles and GO dispersion were mixed in proportion, ultrasonically treated for 1 to 2 hours, and then mechanically stirred for 4 to 6 hours to fully coat the diamond surface and form a "diamond@GO" precursor. Then the mixture was filtered and dried at low temperature. (4) Preparation of composite powder: The "diamond@GO" precursor and electrolytic copper powder are mixed in a V-type mixer for 3 to 5 hours. (5) Reduction treatment: Place the mixed powder in a tube furnace and heat treat it at 400-600℃ for 1-2 hours under H2 / Ar (5% / 95%) atmosphere; (6) SPS sintering: The reduced powder is loaded into a graphite mold and sintered in an SPS device. The sintering conditions are: vacuum environment, pressure 30-50 MPa, heating to 900-1000℃ at a rate of 100-200℃ / min, and holding for 5-15 minutes; the resulting composite material.

6. The preparation method of graphene interface-modified diamond-copper composite material according to claim 7, characterized in that, The mixing ratio of the diamond particles to the GO dispersion is 100:0.5 to 5.

7. The method for preparing graphene interface-modified diamond-copper composite material according to claim 7, characterized in that, The ultrasonic power is 300-500W, and the stirring speed is 200-300rpm.

8. The preparation method of graphene interface-modified diamond-copper composite material according to claim 7, characterized in that, The diamond pretreatment involves placing diamond particles in a round-bottom flask with a mixture of concentrated sulfuric acid (H2SO4, 98%) and concentrated nitric acid (HNO3, 68%) in a volume ratio of 3:1, with a solid-liquid ratio of 1g:10mL. The mixture is heated under reflux in an oil bath at 85–95°C for 2–4 hours. After the reaction, the mixture is allowed to cool naturally to room temperature. Then, the mixture is repeatedly washed with a large amount of deionized water by vacuum filtration until the filtrate is neutral. Finally, the solid product is dried in a vacuum drying oven at 80°C for 6–8 hours to obtain surface-oxidized hydrophilic diamond particles.

9. An application of a graphene interface-modified diamond-copper composite material, wherein the diamond composite material according to any one of claims 1 to 6 or the diamond composite material prepared by the manufacturing method of any one of claims 7 to 8 is used in a SiC power module.

10. The application according to claim 9, characterized in that, The welding and assembly of the composite base plate of the SiC power module is as follows: Place the welding tray support on the assembly table, place the graphene-diamond-copper composite base plate, then place the AMB limiting frame flat on the base plate, and then place 3 SnSb5 solder pads sequentially within the AMB limiting frame. Next, place the printed, sintered, and bonded AMB ceramic substrates in an orderly manner on the solder pads. Finally, assemble the equipped SAC305 solder wire PIN positioning carrier with the welding base plate, ensuring that each PIN... The pins fall and contact the AMB surface. The tray is then horizontally transported to the loading dock, and the base plate is systematically welded using a formic acid vacuum reflow soldering oven. The reduction temperature of the preheating chamber is set to 200–220°C, the reduction time to 200 seconds, and the formic acid pressure to 550 mbar. The reduction temperature of the soldering chamber is set to 215–235°C, the reduction time to 100 seconds, the formic acid pressure to 450 mbar, and the reflow time to 70 seconds. The cooling temperature is set to 40°C. After soldering, the PIN carrier is removed, the AMB limiting frame is taken out, and then the product is removed. The final SiC power module is obtained through subsequent plastic shell assembly, vacuum potting, silicone gel curing, and cover plate assembly.

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