Graphene film / copper hot-pressing composite directional high-thermal-conductivity material as well as preparation method and application thereof

Abstract

The invention discloses a graphene film / copper hot-pressing composite directional high-thermal-conductivity material as well as a preparation method and application of the graphene film / copper hot-pressing composite directional high-thermal-conductivity material. The preparation method comprises the following steps: punching a graphene film to form a plurality of hole structures; blade-coating copper paste on the surface to form a liquid film; the copper paste comprises copper powder, a coupling agent and an organic phase; stacking a plurality of layers; carrying out hot pressing treatment on the circulating laminated structure; and slicing to obtain the graphene film / copper hot-pressing composite oriented high-thermal-conductivity material. When copper powder particles are embedded into the hole structure, the whole hole structure is filled with the copper powder particles, the copper powder particles can transversely enter gaps between graphene sheet layers, a three-dimensional interlocking structure is formed through the sintering effect, resin contained in the copper paste can be subjected to a carbonization reaction in the glue discharging stage, a carbon skeleton is formed, and therefore the three-dimensional interlocking structure is formed. And the infiltration process between the copper powder and the graphene sheet layer is facilitated, and finally the heat conduction performance and the mechanical performance of the graphene film / copper hot-pressing composite oriented high-heat-conduction material are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat-conducting materials, in particular to a graphene film / copper hot-pressing composite directional high-thermal-conductivity material, a preparation method and application thereof. BACKGROUND

[0002] With the development of electronic devices towards high power density and miniaturization, thermal management has become a key bottleneck restricting performance and reliability. Although traditional pure copper materials have a high thermal conductivity coefficient (~400 W / m·K), their isotropic thermal conductivity characteristics are difficult to meet the demand for directional heat dissipation, and their high density and high thermal expansion coefficient easily lead to device thermal stress failure.

[0003] In recent years, graphene has been considered as an ideal thermal conductivity enhancer due to its ultra-high intrinsic thermal conductivity coefficient (>5000 W / m·K). In the prior art, attempts have been made to combine graphene with copper powder through powder metallurgy, but graphene is prone to agglomeration, resulting in poor interface bonding and only a small increase in thermal conductivity performance. Another study has adopted a chemical plating process to coat graphene on the surface of copper powder, but the process is complex and cannot control the orientation of graphene, and the longitudinal thermal conductivity coefficient is increased by less than 30%. In addition, the cold-pressing sintering process is difficult to achieve stable anisotropic thermal conductivity due to low density and disordered distribution of graphene.

[0004] For example, the Chinese patent with the publication number CN113716552A provides a preparation method of a high-directional high-thermal-conductivity graphene / copper composite material, which adopts electrophoretic deposition on the surface of a modified copper foil to obtain preferentially oriented graphene oxide / copper foil, forms an ordered high-directional graphene film, and obtains a high-directional high-thermal-conductivity graphene / copper composite material. The preparation of the high-directional high-thermal-conductivity graphene / copper composite material is achieved, the thermal conductivity is significantly improved, and exceeds 500 W / m·K, solving the problem of difficult control of graphene dispersibility and orientation, and fully utilizing the high in-plane thermal conductivity of graphene. However, the process cost of this preparation method is high, and the material strength is not high, making it difficult to be applied on a large scale.

[0005] The Chinese patent with the publication number CN107164647A provides a high-thermal-conductivity rigid graphene / copper nanocomposite heat sink and a preparation method thereof, mainly solving the forming problem of graphene and copper powder composite material. The copper powder dispersion liquid is mixed with the graphene dispersion liquid and freeze-dried to prepare a mixed powder, and the mixed powder is heat-treated and hot-pressed to obtain a high-thermal-conductivity rigid graphene / copper nanocomposite heat sink. The prepared composite material has high thermal conductivity and large heat flux, has good heat dissipation effect, and can realize structural heat dissipation integration, but the directional arrangement of graphene has not been achieved, and the improvement of thermal conductivity performance is limited.

[0006] In addition, some prior art uses a method of laminating and then cutting longitudinally to obtain a laminated longitudinal heat conductor. For example, a Chinese invention patent with publication number CN112477356A provides a high-thermal-conductivity composite material based on a vertical polymer film array and a preparation method thereof. After punching the graphene film, tin paste (or other metal paste) is applied by scraping. Then, multiple layers are laminated to form a combination, sintered into one, and cut along the lamination direction to obtain a sheet. Finally, the graphene is oriented and spread in the thickness direction of the sheet, thereby enabling the graphene to exhibit better thermal conductivity in the spreading direction, and providing a novel thermal conductivity composite material solution.

[0007] However, in the above prior art, the viscosity of the tin paste or other metal paste is relatively large, so the pore size of the graphene film also needs to be relatively large to allow the tin paste to fully enter. Moreover, the technical solution can only achieve physical embedding of the metal and the hole at the macro level, and cannot achieve microscopic fusion of the metal and the graphene layer, so better thermal conductivity and mechanical properties cannot be achieved.

[0008] Therefore, there is an urgent need to develop a preparation method with simple process and controllable cost, which can break through the bottleneck of the longitudinal thermal conductivity of existing materials by directional arrangement of graphene and efficient compounding of copper matrix (copper powder is usually randomly dispersed in micron or nanometer particles, which is difficult to arrange directionally. It can be understood as directional and uniform arrangement, mainly the combination of graphene film punching and copper paste anchoring), and solve the problems of high interfacial thermal resistance and poor mechanical properties. SUMMARY

[0009] In view of the deficiencies of the prior art, the purpose of the present application is to provide a graphene film / copper hot-pressing composite directional high-thermal-conductivity material, a preparation method thereof, and an application thereof.

[0010] To achieve the above-mentioned purpose, the technical solution adopted by the present application comprises:

[0011] In the first aspect, the present application provides a preparation method of a graphene film / copper hot-pressing composite directional high-thermal-conductivity material, which comprises:

[0012] Punching the graphene film to form a plurality of hole structures on the graphene film;

[0013] Applying copper paste on the surface of the graphene film to form a liquid film; the copper paste comprises copper powder, a coupling agent, and an organic phase, the coupling agent is coated on the surface of the copper powder, and the organic phase comprises an organic solvent, a dispersing agent, and a resin;

[0014] Stacking multiple layers along the normal direction of the graphene film to form a cyclic lamination structure of graphene film-liquid film;

[0015] The heat pressing combination is sliced along the normal direction of the graphene film to obtain a graphene film / copper heat pressing composite directional high-thermal-conductivity material.

[0016] The heat pressing combination is sliced along the normal direction of the graphene film to obtain a graphene film / copper heat pressing composite directional high-thermal-conductivity material.

[0017] In a second aspect, the present application further provides a graphene film / copper heat pressing composite directional high-thermal-conductivity material prepared by the above preparation method, which comprises copper layers and graphene layers alternately stacked in sequence in a plane, the graphene layers have a pore structure, the copper layers contain carbon skeletons left by carbonization of the resin, part of the copper material is embedded in the pore structure, and the copper material in the embedded part is chemically bonded with the graphene layers in the pore structure.

[0018] In a third aspect, the present application further provides an application of the graphene film / copper heat pressing composite directional high-thermal-conductivity material in the field of heat dissipation of electronic devices.

[0019] Based on the above technical solution, compared with the prior art, the present application has at least the following beneficial effects:

[0020] The preparation method provided by the present application utilizes the matching of small pore size and small copper powder diameter, combines the process of phased heat pressing, so that the copper powder particles not only fill the entire pore structure when embedded in the pore structure, but also enter the gap between the graphene layers in a transverse direction, and form a three-dimensional interlocking structure through sintering, and the resin contained in the copper paste also carbonizes to form a carbon skeleton in the degassing stage, which is beneficial to promoting the infiltration process between the copper powder and the graphene layers, and finally significantly improves the thermal conductivity and mechanical properties of the graphene film / copper heat pressing composite directional high-thermal-conductivity material.

[0021] The above description is only a summary of the technical solution of the present application, in order to enable those skilled in the art to more clearly understand the technical means of the present application, and can be implemented according to the content of the specification, as follows. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a macroscopic photograph of a graphene film / copper heat pressing composite directional high-thermal-conductivity material provided by a typical embodiment of the present application;

[0023] Figure 2 is a macroscopic photograph of a punched graphene film provided by a typical embodiment of the present application;

[0024] Figure 3 is a macroscopic photo of a sheet of graphene film / copper hot-pressing composite directional high-thermal-conductivity material provided by a typical embodiment of the present application;

[0025] Figure 4 is a material thermal expansion coefficient test graph provided by embodiment 1 of the present application;

[0026] Figure 5 is a material thermal expansion coefficient test result picture provided by embodiment 2 of the present application;

[0027] Figure 6 is a layout example graph of laser drilling provided by a typical embodiment of the present application. DETAILED DESCRIPTION

[0028] In view of the deficiencies in the prior art, the present inventors have obtained the technical solution of the present application through long-term research and a large number of practices. The technical solution, its implementation process and principles will be further explained as follows.

[0029] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced in a variety of ways beyond the specific embodiments described herein without departing from the scope of the present application, which is set forth in the claims.

[0030] Moreover, terms such as "first" and "second" are used merely to distinguish one from another of a same name, and do not necessarily require or imply any such actual relationship or order between the components or method steps.

[0031] The present application aims to provide a graphene film / copper layered composite material and a preparation method thereof. The graphene film is used as a layered skeleton material, and the copper paste is used as a binder material for layering and cutting to obtain a longitudinal heat conductor. Specifically, laser patterning drilling, layering design and vacuum hot-pressing process are used to realize efficient diffusion and combination of graphene and copper, solve the problems of weak interface combination and uneven structure, and effectively improve the thermal conductivity and mechanical strength of the composite material.

[0032] To achieve the above-mentioned purpose, the embodiment of the present application first provides a preparation method of graphene film / copper hot-pressing composite directional high-thermal-conductivity material, which includes the following steps:

[0033] The graphene film is subjected to drilling treatment to form a plurality of hole structures on the graphene film;

[0034] The copper paste is scraped on the surface of the graphene film to form a liquid film; the copper paste includes copper powder, a coupling agent and an organic phase; the coupling agent is coated on the surface of the copper powder; and the organic phase includes an organic solvent, a dispersing agent and a resin;

[0035] Multilayer stacking along the normal direction of the graphene film forms a cyclic laminated structure of graphene film-liquid film;

[0036] The cyclic laminated structure is subjected to heat pressing treatment to obtain a heat-pressed combination, the heat-pressing treatment sequentially includes a preheating stage, a degassing stage and a sintering stage, the preheating stage makes the organic solvent volatilize and the resin melt, the degassing stage makes the resin carbonize, and the sintering stage makes the copper powder, the graphene film and the carbide generated in the degassing stage sintered into one body;

[0037] The heat-pressed combination is sliced along the normal direction of the graphene film to obtain a graphene film / copper heat-pressed composite directional high-thermal-conductivity material.

[0038] The technical scheme provided by the application uses high-temperature solderable copper paste as the composite layer between the graphene layers, and the advantages of the copper paste include good process adaptability, advantages in interface bonding, reduction of process temperature and adaptation to flexible substrates, and the problems of oxidation of traditional copper powder and difficulty in spreading in high-temperature sintering are solved through nanomaterial technology, anti-oxidation design and low-temperature process optimization.

[0039] In the preparation of the graphene film / copper heat-pressed composite directional high-thermal-conductivity material, the organic carrier in the copper paste volatilizes and carbonizes in sequence in the sintering process, forming a porous structure, and the copper particles form a thermal conduction network, which can buffer thermal stress through pores in thermal expansion adjustment while maintaining thermal conductivity.

[0040] In addition, the copper paste can enter the hole structure with appropriate size and be extruded into the gap between the graphene layers under the action of pressure, combined with the sintering effect and the auxiliary infiltration of the carbide formed by the resin, to enable the copper and the graphene layers to be micro-sintered, thereby establishing a three-dimensional interlocking structure and further improving the thermal conductivity and mechanical properties.

[0041] As a comparison, the background technology described above uses solder paste to fill the holes, but the main component of the solder paste is actually metal particles, and even the above prior art is perforated. Due to the poor flowability of the solder paste and the large friction between the metal particles and the tendency to agglomerate, the solder paste cannot enter the pore diameter well and diffuse, and cannot be well combined with the gap between the graphene layers. In the present application, the resin is mixed to form a metal paste, the resin wraps the copper powder to increase the lubricating property, better flows into the pore diameter, and reduces the agglomeration phenomenon. The dispersed copper powder is more uniform, and after solidification, a mechanical interlocking anchor is formed. Because the copper powder is more uniformly dispersed and penetrates more completely, the mechanical properties are better. The resin in the copper paste volatilizes during sintering, forming a porous structure, and the copper particles form a thermal conduction network, which buffers thermal stress through pores in thermal expansion adjustment while maintaining thermal conductivity.

[0042] And further, in some embodiments, the pore size of the hole structure is below 50 μm;

[0043] In some embodiments, the particle size of the copper powder is below 10 μm.

[0044] In the above background art, there is a contradiction between the pore size and the viscosity of the metal paste: in order to ensure that the high-viscosity metal paste can fully fill the through hole, the pore size needs to be ≥200 μm, and the large pore size leads to the cutting off of the effective heat conduction path of graphene, resulting in a loss of in-plane thermal conductivity of more than 40%. In the present application, the pore size is much smaller than in the above background art, which is to reasonably construct an effective heat conduction path, which can only be achieved by replacing it with a metal paste. In addition, in the above background art, the metal paste only fills the through hole area, and the non-through hole area relies on thin layer adhesion to form a periodic weak thermal conduction interface, while in the present application, the adhesive interface bonding force of the non-through hole area is stronger. In addition, the thermal expansion coefficient of metal (such as tin paste) and graphene is very different, and microcracks are very easy to occur at the interface when the temperature changes, which significantly increases the probability of interface phonon scattering. In the present application, the use of copper paste penetration and spreading effect establishes a three-dimensional interlocking structure, which significantly reduces the impact of the difference in thermal expansion coefficient between copper paste and graphene.

[0045] The mass fraction of copper powder in the copper paste is 30-70%, the mass fraction of organic solvent is 20-34%, the mass fraction of dispersant is 1-5%, and the mass fraction of resin is 15-25%.

[0046] In some embodiments, the pore size of the hole structure is 10-40 μm, the mass fraction of copper powder in the copper paste is 40-60%, and the maximum pressure of the hot pressing treatment is 10-12 MPa.

[0047] In some embodiments, the hole density of the hole structure is 50-200 per cm 2 .

[0048] In some embodiments, the coupling agent is selected from a silane coupling agent.

[0049] In some embodiments, the boiling point of the organic solvent is above 190°C.

[0050] In some embodiments, the dispersant includes any one or a combination of two of polyether-modified polydimethylsiloxane, phosphate ester salt.

[0051] In some embodiments, the resin includes any one or a combination of two of phenolic epoxy resin, polyurethane-modified epoxy resin.

[0052] In some embodiments, the temperature of the preheating stage is 200-300°C, the temperature rising rate is 5-10°C / min, the pressure is 2-3 MPa, and the hot-pressing time is usually set as the time for rising from room temperature to the above-mentioned temperature at the above-mentioned temperature rising rate.

[0053] In some embodiments, the temperature of the glue removal stage is 300-500°C, the temperature rising rate is 2-5°C / min, the pressure is 3.5-5.5 MPa, and the hot-pressing time is 30-90 min.

[0054] In some embodiments, the temperature of the sintering stage is 750-850°C, the temperature rising rate is 5-15°C / min, the pressure is 8-12 MPa, and the hot-pressing time is 1-2 h.

[0055] In some embodiments, the hot-pressing treatment is carried out in a protective atmosphere or a vacuum environment.

[0056] In some embodiments, the equivalent dry film thickness of the liquid film is 20-50 μm.

[0057] In some embodiments, the slice thickness of the hot-pressing assembly is 1-1.7 mm.

[0058] In some embodiments, the punching treatment is carried out by laser punching.

[0059] As some typical embodiments of the above technical solution, the actual process steps of the above preparation method include:

[0060] Step one: graphene film pretreatment and laser punching

[0061] Cleaning: using one or a combination of deionized water, ethanol, acetone, isopropanol, and ethyl acetate to clean a graphene film with a thickness of 40-70 μm to remove surface contaminants and residues.

[0062] Laser punching:

[0063] According to the application requirements, the size (micron level), shape (circular, square, or polygonal), and distribution density of the holes are designed, the graphene film is fixed on the laser platform to ensure the surface flatness, the laser parameters are set as power 30 W, scanning speed 50 mm / s, and frequency 100 kHz, the holes are punched according to the preset pattern to form through or non-through hole structures to enhance the subsequent copper paste penetration and interface bonding. Of course, the specific punching process can not be limited to the example situation here, and various different process parameters or even other punching methods can be used to obtain the same structure of the holes.

[0064] Step two: copper paste coating and lamination assembly

[0065] Copper paste selection: Copper powder (40%-60%) (particle size 0.1-10 pm) in the copper paste is coated with organosilane coupling agent KH-550, and the organosilane coupling agent provides a conductive path, prevents copper oxidation, and improves the compatibility of graphite and resin. The organic solvent (20-34%) is selected from high-boiling ether ester solvents such as diethylene glycol ethyl ether (192°C) and diethylene glycol butyl ether acetate (boiling point 246°C). The high-boiling solvent is used to adjust the viscosity and prevent the copper paste from forming a crust on the surface and internal pores. The dispersant (1-5%) (such as polyether-modified polydimethylsiloxane and phosphate ester salt) prevents copper powder agglomeration and reduces the shear stress of the slurry. The resin binder (15-25%) (such as phenolic epoxy resin and polyurethane-modified epoxy resin) is used to drive the copper powder to melt and flow during hot pressing, penetrate into the graphite film pores, and form a mechanical interlocking anchor after solidification. Carbonization occurs at high temperatures to form a carbon network to enhance the wettability of copper and graphene, helping copper and graphene layers to combine.

[0066] The content of the organic solvent, dispersant, and resin binder and the filling behavior of the copper paste significantly affect the interfacial bonding force. The increase in hot pressing pressure is directly related to the rheological properties of the copper paste and the pore structure of the graphite film. The specific influence rules summarized by the inventors of the present application are shown in the following table:

[0067]

[0068] In the experiment, performance balance was achieved through precise proportioning and fine dispersion mixing process. The copper content was set at 30%, 40%, 50%, 60%, and 70%, respectively. (The pore and hot pressing pressure temperature are according to the above rules) According to the experimental data, the copper content range is optimized to 40%-60%, because copper content below 30% is too low to improve the overall performance of the material; copper content above 70% is too high, resulting in high slurry viscosity, easy cracking, and poor bonding strength. Within the range of 40%-60%, the solidified layer shows the best overall performance.

[0069] Similarly, the diameter of the opening is also critical. When the opening diameter is too large, the hole may collapse or deform due to the hot pressing pressure, which is not conducive to the formation of a three-dimensional interlocking structure. Therefore, when the opening diameter is greater than 50 pm, it is difficult for the metal copper to enter the gap between the exposed graphene layers on the inside wall of the hole, making it even more difficult to form a three-dimensional interlocking structure. When the pore size is small, for example, less than 10 pm, nano-sized copper powder needs to be used, and a higher hot pressing pressure is required to achieve full filling and wetting, which obviously increases the preparation cost of the material. Therefore, the appropriate opening diameter and the matching conditions are key factors in the preparation of materials with application prospects.

[0070] Coating: The copper paste is evenly brushed on the surface of the graphene film, with a single-layer thickness controlled at 20-50 μm (equivalent to the thickness of the dried copper paste, which is generally considered to be the thickness of the solid phase component remaining after drying to remove the solvent).

[0071] Lamination: The graphene film and the copper paste layer are alternately stacked to form a "graphene-copper paste-graphene" periodic structure, with a lamination thickness of 1-5 cm, and not limited to this. The thickness of the lamination depends on the size of the heat-conducting sheet obtained by slicing.

[0072] Step three: vacuum hot-pressing sintering and post-processing

[0073] Moulding:

[0074] The lamination material is placed in a high-temperature-resistant mould, and a pre-pressing force is applied to ensure close contact between the layers, with a pre-pressing force less than 10 MPa.

[0075] Hot-pressing sintering:

[0076] Atmosphere: high-purity nitrogen or vacuum (vacuum degree <1×10 -2 Pa);

[0077] Three-stage stepwise temperature rising treatment, including:

[0078] Preheating stage (room temperature, such as 15-35℃→200-300℃) : temperature rising rate: 5-10℃ / min; pressure 2.5Mpa resin melting, this stage is a low-pressure filling of large pore structure stage.

[0079] Degassing stage (300-500℃): temperature rising rate: 2-5℃ / min, pressure 4Mpa holding time: 30-90min; high pressure extrusion into the micro-cracks between the graphene layers on the side wall, and the carbon skeleton left after the decomposition of the epoxy, enhances the copper / graphite interface wettability, auxiliary bonding;

[0080] Sintering stage (500℃→target temperature): target temperature range: 750-850℃, temperature rising rate: 5-15℃ / min, pressure 8-12Mpa holding time: 1-2h, this stage occurs atomic diffusion between the copper material extruded into the micro-cracks and the graphene layers. The sintering pressure is limited to 8-12 MPa, which promotes the diffusion of copper atoms into the graphene pores and interlayers.

[0081] Cutting: cutting along the direction perpendicular to the layered structure to obtain a thin sheet composite material with a predetermined thickness, usually 1-1.7 mm, which can be simply washed with water after cutting. Of course, the specific cutting thickness is not limited to this, and can be adjusted as needed.

[0082] Compared with the method in the prior art, the main progress of the technical scheme provided in the application lies in that:

[0083] Interface optimization: laser drilling enhances copper paste penetration, and copper atoms form chemical bonding with graphene through the holes during the hot pressing process, and the interface bonding strength is increased by more than 30%.

[0084] Performance enhancement: the prepared composite material has high density, which can reach 5±0.8 g / cm 3 . The thermal conductivity of the material can reach 618.69±50 W / mK, and the thermal expansion coefficient can be as low as 11-14 ppm / k.

[0085] Process controllable: by adjusting the laser parameters, the thickness of the stack and the hot pressing conditions, the anisotropic properties of the composite material can be customized, for example, the thickness of the single-layer graphene film is micron level, and a three-dimensional porous structure can be constructed by layer-by-layer stacking. When the thickness increases to more than 50 microns, the oriented structure induced by laser accumulates between layers, forming obvious anisotropy. The inventors of the application believe that the multilayer graphene film has been laser drilled, but the drilling position of each layer is definitely different, and complete overlap does not occur, so a three-dimensional porous structure is formed. The drilling is laser induced, and the copper powder between the apertures forms a heat-conducting network, which is anisotropic.

[0086] The second aspect of the embodiment of the application also provides a graphene film / copper hot-pressed composite directional high-thermal-conductivity material prepared by the preparation method provided by any of the above embodiments, characterized in that it comprises copper layers and graphene layers alternately stacked in sequence in the plane, the graphene layers have a hole structure, the copper layers contain carbon skeletons left by carbonization of resin, and part of the copper material of the copper layers is embedded in the hole structure, and the copper material of the embedded part is chemically bonded with the graphene layers in the hole structure.

[0087] The embodiment of the application also provides application of the graphene film / copper hot-pressed composite directional high-thermal-conductivity material in the field of heat dissipation of electronic devices.

[0088] The technical scheme of the application will be further described in detail below by means of several embodiments and in combination with the drawings. However, the selected embodiments are only used to illustrate the application, and do not limit the scope of the application.

[0089] Embodiment 1

[0090] The embodiment provides a preparation method of a layered composite material based on graphene film and copper. The method realizes strong interface bonding of graphene and copper through laser drilling induced copper paste penetration, layered stacking and vacuum hot pressing process, and simultaneously regulates the in-plane and vertical thermal conductivity and the thermal expansion coefficient of the material. The specific steps are as follows:

[0091] I. Sample Preparation and Pretreatment

[0092] 1. (1) Cleaning of graphene film: Take a graphene film with a thickness of 70 pm (thickness range 50-70 pm), place the graphene film in the cleaning tank of the ultrasonic cleaner, add 20 ml of 98% ethanol, set the cleaning time to 15 min and the temperature to room temperature, and turn on the ultrasonic cleaner to clean. After cleaning, use deionized water to rinse the graphene film to remove residual cleaning solvent and impurities. Place the cleaned graphene film in a vacuum drying oven at 60°C for 2 h.

[0093] (2) Laser drilling:

[0094] Design of hole pattern: In this application, circular micropores are used, and the micropore array formed by laser drilling has a pore diameter of 20 pm and a pore density of 100 pores / mm 2 , as shown in Figure 6 . Positioning: Fix the graphene film on the laser drilling platform to ensure that it is flat and wrinkle-free. Parameter setting: According to the thickness of the graphene film, 70 pm, set the laser power to 30 W, the speed to 100 mm / s, and the frequency to 50 kHz. Drilling: Start the laser equipment and drill according to the preset program to obtain the drilled graphene film as shown in Figure 2 .

[0095] 2. High-temperature copper paste as solder paste on the surface of the graphene film

[0096] Select copper paste solid content 45%, organic solvent 34% (diethylene glycol butyl ether acetate), dispersant 2% (polyether modified polydimethylsiloxane), resin adhesive 24% (phenolic epoxy resin), and use a gap-adjustable scraper (such as a Mayer rod) as the scraper. Adjust the scraper gap to 45 pm to directly control the wet film thickness. When manually brushing, uniform speed of 10 cm / s and uniform pressure of 0.2 MPa can reduce thickness fluctuations. The automated coating machine controls the pressure and speed through closed-loop control, with an accuracy of ±2 pm.

[0097] Relationship between wet film thickness and dry film thickness: Dry film thickness ≈ wet film thickness × copper paste solid content% In this example, the copper paste solid content is 45%, and the scraper gap is 62.5 pm, so the dry film thickness ≈ 62.5 × 0.45 = 28 pm. The copper paste layer after brushing is 28 pm (the dry film thickness after copper paste brushing is controlled at 20-50 pm).

[0098] 3. Vacuum hot pressing

[0099] Material combination: Stack multiple layers according to the desired thickness, and place the stacked graphene / copper cycle combination in the hot pressing mold.

[0100] Apply pressure: Place the material combination in a dedicated mold, and then fix the mold in the hot pressing furnace.

[0101] Heating: sintering under vacuum atmosphere, first three-stage temperature ramping process:

[0102] Preheating stage: temperature increased to 250℃ at a rate of 5℃ / min, pressure 2.5Mpa, resin melted and helped copper powder infiltrate macropores at low pressure during hot pressing process.

[0103] Degumming stage: temperature increased to 450℃ at a rate of 2.5℃ / min, pressure 4Mpa, holding for 1 hour, decomposing and burning off resin binder, copper powder infiltrated micropores at high pressure, carbon skeleton left after decomposition of epoxy, enhancing copper / graphite interface wettability.

[0104] Sintering stage: temperature increased to 850℃ at a rate of 10℃ / min, pressure 10Mpa, holding for 1.5 hours. After completion, furnace cooling, complete interface diffusion bonding of graphene and copper material.

[0105] 4. Directional multi-wire cutting

[0106] The sintered block material is cut along the specified direction perpendicular to the layers into multiple 1mm thick slices.

[0107] 5. Results

[0108] The block-shaped composite material prepared before cutting is shown in Figure 1 , with a density of 5.80g / cm 3 , material thermal conductivity 658.7W / mK, thermal expansion coefficient 12.14ppm / k, interface shear strength 15.2MPa, after cutting, the planar sheet-shaped heat conductor is obtained as shown in Figure 3 . The specific thermal expansion coefficient test results are shown in Figure 4 , which is used to intuitively show the size change rule of the material when heated, the slope change reflects the temperature dependence of the material CTE, the positive slope indicates that the CTE increases with temperature, the thermal expansion coefficient is α = 12.14ppm / K, and the slope increases with temperature, indicating that the expansion mode is high-temperature expansion.

[0109] Example 2

[0110] Example 2 is basically the same as Example 1, the only difference is that Example 2 selects copper paste solid content 40%, organic solvent 34%(diethylene glycol ether), dispersant 1%(polyether modified polydimethylsiloxane), resin adhesive 25%(phenolic epoxy resin) to form a 25μm copper layer. The sintering stage process parameters are 850℃, 10Mpa, 1.5h, and the density of the prepared composite material is 5g / cm 3, thermal conductivity of 594.4 W / mK, thermal expansion coefficient of 11.8 ppm / k, interface shear strength of 14.6 Mpa.

[0111] The rest is the same as example 1, hereinafter will not be elaborated, the obtained material expansion coefficient test results are shown in Figure 5 , the thermal expansion coefficient is 11.8 ppm / K, and the expansion mode is also high-temperature expansion.

[0112] Example 3

[0113] Example 3 is basically the same as example 1, the difference is only that example 3 selects copper paste solid content 50%, organic solvent 28% (diethylene glycol ether, diethylene glycol butyl ether acetate mixed in proportion), dispersant 3% (polyether modified polydimethylsiloxane), resin adhesive 19% (phenolic epoxy resin), to form a 31 μm copper layer. The sintering stage process parameters are 850℃, 10Mpa, 2h, and the density of the prepared composite material is 5.81g / cm 3 , thermal conductivity of 666 W / mK, thermal expansion coefficient of 12.95 ppm / k, interface shear strength of 13.7 Mpa.

[0114] Example 4

[0115] Example 4 is basically the same as example 1, the difference is only that example 4 selects copper paste solid content 55%, organic solvent 25% (diethylene glycol ether, diethylene glycol butyl ether acetate mixed in proportion), dispersant 4% (polyether modified polydimethylsiloxane), resin adhesive 16% (phenolic epoxy resin), to form a 35 μm copper layer. The sintering stage process parameters are 850℃, 10Mpa, 2h, and the density of the prepared composite material is 5.85g / cm 3 , thermal conductivity of 673.5 W / mK, thermal expansion coefficient of 12.5 ppm / k, interface shear strength of 12.5 Mpa.

[0116] Example 5

[0117] Example 5 is basically the same as example 1, the difference is only that example 5 selects copper paste solid content 60%, organic solvent 22% (diethylene glycol ether, diethylene glycol butyl ether acetate mixed in proportion), dispersant 5% (polyether modified polydimethylsiloxane), resin adhesive 13% (phenolic epoxy resin), to form a 38 μm copper layer. The sintering stage process parameters are 850℃, 10Mpa, 2h, and the density of the prepared composite material is 5.89g / cm 3 , thermal conductivity of 689.8 W / mK, thermal expansion coefficient of 13.83 ppm / k, interface shear strength of 12.8 Mpa.

[0118] Example 6

[0119] Example 6 is substantially the same as Example 1, except that in Example 6, the copper paste solid content is 60%, the organic solvent is 22% (diethylene glycol ether, diethylene glycol butyl ether acetate mixed in a certain proportion), the dispersant is 5% (polyether modified polydimethylsiloxane), and the resin adhesive is 13% (phenolic epoxy resin), to form a copper layer of 38 μm. The sintering stage process parameters are 850°C, 12Mpa, 2h, and the density of the prepared composite material is 5.93g / cm 3 , the thermal conductivity is 689.5W / mK, the thermal expansion coefficient is 14.3ppm / k, and the interface shear strength is 14Mpa.

[0120] Example 7

[0121] Example 7 is substantially the same as Example 1, except that in Example 7, the copper paste solid content is 60%, the organic solvent is 22% (diethylene glycol ether, diethylene glycol butyl ether acetate mixed in a certain proportion), the dispersant is 5% (polyether modified polydimethylsiloxane), and the resin adhesive is 13% (phenolic epoxy resin), to form a copper layer of 38 μm. The sintering stage process parameters are 850°C, 15Mpa, 2h, and the density of the prepared composite material is 6.3g / cm 3 , the thermal conductivity is 742W / mK, the thermal expansion coefficient is 16.5ppm / k, and the interface shear strength is 15.7Mpa.

[0122] Example 8

[0123] Example 8 is substantially the same as Example 1, except that in Example 8, the copper paste solid content is 60%, the organic solvent is 18% (diethylene glycol ether, diethylene glycol butyl ether acetate), the dispersant is 5% (polyether modified polydimethylsiloxane), and the resin adhesive is 17% (phenolic epoxy resin), to form a copper layer of 38 μm. The sintering stage process parameters are 850°C, 12Mpa, 2h, and the density of the prepared composite material is 6g / cm 3 , the thermal conductivity is 701W / mK, the thermal expansion coefficient is 17.32ppm / k, and the interface shear strength is 13Mpa.

[0124] Example 9

[0125] Example 9 is substantially the same as Example 1, except that in Example 9, the copper paste solid content is 60%, the organic solvent is 25% (diethylene glycol ether, diethylene glycol butyl ether acetate), the dispersant is 5% (polyether modified polydimethylsiloxane), and the resin adhesive is 10% (phenolic epoxy resin), to form a copper layer of 38 μm. The sintering stage process parameters are 850°C, 12Mpa, 2h, and the density of the prepared composite material is 6.1g / cm 3, thermal conductivity is 726.2 W / mK, thermal expansion coefficient is 16.3 ppm / k, interface shear strength is 11.9 Mpa.

[0126] Example 10

[0127] Example 10 is basically the same as Example 1, the only difference is that the graphene film thickness used in Example 10 is 50 μm, the laser drilling formed micro-hole array aperture is 35 μm, and the hole density is 55 holes / mm 2 , the circular micro-hole is used, the power of the laser is set to 30 W, the speed is 100 mm / s, and the frequency is 50 kHz. The rest is the same as Example 1, and will not be repeated here. The density of the composite material prepared is 5.44 g / cm 3 , the thermal conductivity of the material is 621.1 W / mK, the thermal expansion coefficient is 15 ppm / k, and the interface shear strength is 9.1 Mpa.

[0128] Example 11

[0129] Example 11 is basically the same as Example 1, the only difference is that the graphene film thickness used in Example 11 is 30 μm, the laser drilling formed micro-hole array aperture is 10 μm, and the hole density is 200 holes / mm 2 , the circular micro-hole is used, the power of the laser is set to 30 W, the speed is 100 mm / s, and the frequency is 50 kHz. The rest is the same as Example 1, and will not be repeated here. The density of the composite material prepared is 5.2 g / cm 3 , the thermal conductivity of the material is 600.3 W / mK, the thermal expansion coefficient is 15.5 ppm / k, and the interface shear strength is 7.9 Mpa.

[0130] Comparative Example 1

[0131] The only difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not perform the laser drilling pretreatment step, that is, after cleaning the graphene film, it is directly laminated. The density of the composite material prepared is 5.06 g / cm 3 , the thermal conductivity of the material is 579.2 W / mK, the thermal expansion coefficient is 9.47 ppm / k, and the interface shear strength is 5.8 Mpa. The interface bonding force of the material is weak, and the cutting effect is poor.

[0132] Comparative Example 2

[0133] The only difference between Comparative Example 2 and Example 1 is that copper powder is used instead of copper paste in Comparative Example 2. The density of the composite material prepared is 5.74 g / cm 3 , the thermal conductivity is 600.8 W / mK, the thermal expansion coefficient is 14.3 ppm / k, and the interface shear strength is 4.7 Mpa. The interlayer copper material is uneven, the interface bonding force of the material is very weak, and the cutting effect is not good.

[0134] Comparative Example 3

[0135] Comparative Example 3 differs from Example 1 only in that Comparative Example 3 selects copper paste solid content 30%, organic solvent 39%, dispersant 1%, resin adhesive 30% to form a copper layer of 25 μm. The sintering stage process parameters are 850℃, 5Mpa, 1.5h, and the density of the prepared composite material is 4.89g / cm 3 , the thermal conductivity is 504.9W / mK, the thermal expansion coefficient is 3.2ppm / k, and the interface shear strength is 7.0Mpa.

[0136] Comparative Example 4

[0137] Comparative Example 4 differs from Example 1 only in that Comparative Example 3 selects copper paste solid content 70%, organic solvent 17%, dispersant 5%, resin adhesive 8% to form a copper layer of 25 μm. The sintering stage process parameters are 850℃, 20Mpa, 1.5h, and the density of the prepared composite material is 7.22g / cm 3 , the thermal conductivity is 838.6W / mK, the thermal expansion coefficient is 25.2ppm / k, and the interface shear strength is 6.6Mpa.

[0138] Comparative Example 5

[0139] This comparative example is generally the same as Example 1, the main difference being that:

[0140] The pore size of the perforation is adjusted to 100 μm.

[0141] The experimental results are that the large pore size causes the effective heat conduction path of graphene to be cut off, and the in-plane thermal conductivity is lost by more than 40%.

[0142] It is illustrated that the large pore size causes the in-plane heat conduction path of the graphene film to be severely damaged, and the overall mechanical properties also decrease due to the excessively large pore size.

[0143] Based on the above examples and comparative examples, it can be clearly seen that the preparation method provided by the embodiments of the present application utilizes the matching of small hole sizes and small copper powder diameters, combined with a staged hot pressing process, so that the copper powder particles not only fill the entire hole structure when embedded in the hole structure, but also enter the gap between the graphene layers, forming a three-dimensional interlocking structure through sintering. The resin contained in the copper paste will also undergo a carbonization reaction during the degassing stage, forming a carbon skeleton, which is conducive to promoting the infiltration process between the copper powder and the graphene layers, and ultimately significantly improving the thermal conductivity and mechanical properties of the graphene film / copper hot-pressed composite directional high thermal conductivity material.

[0144] It should be understood that the above-described embodiments are merely intended to illustrate the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and principle of the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing a graphene film / copper hot-pressed composite oriented high thermal conductivity material, characterized in that, include: A perforation process is performed on the graphene film to form multiple pore structures on the graphene film; Copper paste is coated onto the surface of the graphene film to form a liquid film; the copper paste includes copper powder, a coupling agent, and an organic phase, wherein the coupling agent is coated on the surface of the copper powder, and the organic phase includes an organic solvent, a dispersant, and a resin; Multiple layers of the graphene film are stacked along the normal direction to form a cyclic stacked structure of graphene film-liquid film; The cyclic laminated structure is subjected to hot pressing to obtain a hot-pressed assembly. The hot pressing process includes a preheating stage, a debinding stage, and a sintering stage. The preheating stage causes the organic solvent to evaporate and the resin to melt. The debinding stage causes the resin to carbonize. The sintering stage causes the copper powder, the graphene film, and the carbides generated in the debinding stage to be sintered into one. The hot-pressed assembly is sliced ​​along the normal direction of the graphene film to obtain a graphene film / copper hot-pressed composite oriented high thermal conductivity material.

2. The preparation method according to claim 1, characterized in that, The pore size of the hole structure is less than 50 μm; And / or, the particle size of the copper powder is less than 10 μm; And / or, the copper paste contains 30-70% copper powder by mass, 20-34% organic solvent by mass, 1-5% dispersant by mass, and 15-25% resin by mass.

3. The preparation method according to claim 2, characterized in that, The pore size of the hole structure is 10-40 μm, the mass fraction of copper powder in the copper paste is 40-60%, and the maximum pressure of the hot pressing treatment is 10-12 MPa.

4. The preparation method according to claim 1 or 3, characterized in that, The pore density of the pore structure is 50-200 pores / cm³. 2 .

5. The preparation method according to claim 1, characterized in that, The coupling agent is selected from silane coupling agents; And / or, the boiling point of the organic solvent is above 190°C; And / or, the dispersant comprises any one or a combination of two of polyether-modified polydimethylsiloxane and phosphate salts; And / or, the resin includes any one or a combination of two of phenolic epoxy resin and polyurethane modified epoxy resin.

6. The preparation method according to claim 1, characterized in that, The temperature during the preheating stage is 200-300℃, the heating rate is 5-10℃ / min, and the pressure is 2-3MPa. And / or, the temperature of the glue removal stage is 300-500℃, the heating rate is 2-5℃ / min, the pressure is 3.5-5.5MPa, and the hot pressing time is 30-90min; And / or, the temperature of the sintering stage is 750-850℃, the heating rate is 5-15℃ / min, the pressure is 8-12MPa, and the hot pressing time is 1-2h.

7. The preparation method according to claim 1 or 6, characterized in that, The hot pressing process is carried out in a protective atmosphere or under vacuum.

8. The preparation method according to claim 1, characterized in that, The equivalent dry film thickness of the liquid film is 20-50 μm; And / or, the slice thickness of the hot-pressed assembly is 1-1.7 mm; And / or, the drilling process is laser drilling.

9. The graphene film / copper hot-pressed composite oriented high thermal conductivity material prepared by the preparation method according to any one of claims 1-8, characterized in that, It includes copper layers and graphene layers that are alternately stacked in the plane. The graphene layers have a porous structure. The copper layers contain a carbon skeleton left over from resin carbonization. A portion of the copper layer is embedded in the porous structure, and the embedded copper material is chemically bonded to the graphene layer in the porous structure.

10. The application of the graphene film / copper hot-pressed composite oriented high thermal conductivity material according to claim 9 in the field of heat dissipation of electronic devices.

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