Millimeter-scale heat-conducting graphite plate, preparation method and application thereof

Abstract

The application discloses a preparation method of a millimeter-level heat-conducting graphite plate, and the method comprises the following steps: stacking artificial graphite films (4-20 um) and PS small balls (10-1000 nm) layer by layer to a certain thickness (0.1-0.5 mm); micro-thermal bonding and fixing at 100-150 degrees to form a multi-level structure material with gaps, so as to facilitate the exchange of electrolyte; using the above assembled material as an electrode, cooperating with a copper sulfate solution (0.1-2 mol / L) to carry out water electroplating, and electroplating copper in the gap between the graphite films (the electroplating time is 4-20 min), and the average thickness of the metal layer is 20-100 nm; after drying, hot pressing is carried out, the pressure is 0.2-2 MPa, the temperature is (500-700 DEG C), the high-temperature maintaining time is 5-30 min, and finally the prepared millimeter-level graphite plate is connected by single-crystal copper (copper is the metal most matched with the graphite structure lattice) nanometer film, the thermal resistance is small, the interface is stable, and the millimeter-level graphite plate can be widely used in high-flux heat management, such as heat dissipation of super-high-frequency mobile phones, computers and tablet computers.

Description

Technical Field

[0001] This invention relates to the field of thermal conductivity, and more particularly to a millimeter-scale thermally conductive graphite plate, its preparation method, and its application. Background Technology

[0002] Artificial graphite films using polymers as precursors possess excellent crystalline structure and superior electrical and thermal conductivity, making them widely used in heat dissipation for electronic devices. Currently, most commercially available artificial graphite films are made from polyimide, with thicknesses ranging from 4 to 100 μm. The polyimide precursor requires biaxial stretching to ensure high polymer orientation and high crystallinity in the sintered graphite film. As the thickness increases, the orientation and crystallinity of the polyimide film decrease, leading to a sharp decline in the thermal conductivity of the sintered graphite film, which fails to meet the high thermal flux requirements of high-frequency electronic devices for thermal management materials.

[0003] Currently, thick graphite plates can be made by grinding pyrolytic graphite, but they have the following problems: First, the controllability at the sub-millimeter and millimeter scales is poor; second, large-size fabrication is difficult; third, the flatness of high thermal conductivity graphite plates is difficult to guarantee, resulting in high internal stress; and fourth, the cost is high. Therefore, they are not suitable for widespread commercial application in thermal management.

[0004] Layer-by-layer composites of graphite films and metallic copper hold promise as an effective means to achieve the aforementioned high thermal flux for several reasons: First, metallic copper has high thermal conductivity and excellent lattice matching with the graphene surface, facilitating excellent interfacial heat transport; the nanometer-thickness of the metal layer can lower its own crystallization temperature and significantly suppress its volume fraction, without significantly reducing the thermal conductivity of the graphite film itself; third, graphite films and copper can be layer-by-layer composites, allowing for arbitrary control of the composite material thickness or improvement of thermal flux. The synergistic effect of these three factors ultimately enables high thermal conductivity and high flux thermal management. However, graphene's smooth surface, low surface energy, and poor solution affinity make it difficult for metal atoms to adhere. Therefore, the insertion of copper atoms onto the graphite film surface and between graphite films, especially in industrial-scale, uniform insertion, presents significant challenges, thus limiting the application of graphite films in high-flux thermal management materials. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing and applying millimeter-scale thermally conductive graphite plates. This application utilizes PS microspheres to form slits, ensuring sufficient wetting and exchange of the electrolyte. The resulting current polarization effect, along with the confinement and template effect of the slits, greatly promotes metal electroplating on the smooth surface of the artificial graphite film, eliminating the surface activity requirements of conventional graphite material electroplating. This results in an integrated millimeter-scale thermally conductive graphite plate using a high thermal conductivity copper single-crystal thin film as a binder.

[0006] The objective of this invention is achieved through the following technical solution: a method for preparing a millimeter-scale thermally conductive graphite plate, comprising the following steps:

[0007] (1) The artificial graphite film and the PS layer are stacked alternately and then bonded and fixed by micro-heating at 100-150℃ to form a multi-level structural material; the PS layer is composed of PS microspheres;

[0008] (2) The multi-level structure material prepared in step (1) is used as the cathode, and a mixed solution of copper sulfate and sulfuric acid is used as the electrolyte for electroplating. Copper is electroplated in the slits between the graphite films of the multi-level structure material. The slit effect and polarization effect of the material greatly promote the rapid growth of copper atoms.

[0009] (3) After the multi-level structural material completed by electroplating in step (2) is dried, it is hot-pressed at a pressure of 0.2-2 MPa and a temperature of 500-700℃ for 5-30 minutes to obtain a millimeter-scale thermally conductive graphite plate. Under hot pressing, amorphous copper rapidly crystallizes and grows to form a uniform thickness of highly thermally conductive single crystal, thereby reducing the interlayer thermal resistance of the graphite film and increasing the thermal conductivity of the material.

[0010] In some embodiments of the present invention, the PS layer is prepared by spin coating.

[0011] In some embodiments of the present invention, the PS microspheres have a particle size ranging from 50 to 1000 nm. Microspheres of varying sizes are more conducive to solution penetration.

[0012] In some embodiments of the present invention, the thickness of the graphite film is 4-20 μm, and the thickness formed by the staggered stacking of the graphite film and the PS layer is 0.1-0.5 mm.

[0013] In some embodiments of the present invention, in step (3), the average thickness of the copper metal layer in the millimeter-scale thermally conductive graphite plate is 20-100 nm. The nanometer thickness of the metal binder reduces the atomic mobility barrier, thereby greatly reducing the crystallization temperature of the metal. On the one hand, it saves energy consumption costs in the hot pressing process, and on the other hand, the high thermal conductivity of highly crystalline copper can greatly reduce the interfacial thermal resistance between graphite films.

[0014] In some embodiments of the present invention, in step (2), the concentration of the copper sulfate solution is 0.1-2 mol / L, the concentration of the sulfuric acid solution is 0.3-6 mol / L, the electroplating voltage range is 4-5V, and the current density is 10-25 A / dm³. 2 The electroplating time is 4-20 minutes.

[0015] The present invention also relates to millimeter-scale thermally conductive graphite plates prepared by the above-described preparation method.

[0016] This invention utilizes a high thermal conductivity single-crystal copper thin film as an adhesive to bond high thermal conductivity artificial graphite together at low cost, thereby controllably increasing material throughput without significantly reducing the material's thermal conductivity. On one hand, it solves the problem of electroplating copper atoms onto smooth graphite surfaces, especially for batch intercalation electroplating; on the other hand, the electric heating and the nano-thickness of the metallic copper greatly reduce the material processing time and temperature, thus lowering costs and laying the material and technological foundation for heat dissipation in future high-frequency electronic devices.

[0017] The beneficial effects of this invention are as follows: It avoids the surface activation treatment process of hydrophobic graphite films in conventional electroplating, simplifying the process and reducing preparation costs. The thermal conductivity is close to 1500 W / mK, and the thickness reaches 0.1-0.5 mm; it can be used continuously for 10,000 hours without thermal conductivity loss. Attached Figure Description

[0018] Figure 1 To determine the horizontal thermal conductivity of materials using the laser flare method.

[0019] Figure 2 This is a schematic diagram of the slit stacking of graphite films.

[0020] Figure 3 This is a surface morphology diagram of a single graphite film in Example 1.

[0021] Figure 4 The bonding interface between the graphite film prepared in Example 1 and the 40nm metal is shown in a high-resolution TEM image.

[0022] Figure 5 An optical photograph of the 0.5 mm thick bonded graphite plate prepared in Example 1. Detailed Implementation

[0023] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0024] In the following embodiments, the thermal conductivity test method uses the laser flash method. Specifically, a heat source is injected from the bottom of the heat-conducting plate, and an infrared detector is used to detect the heat at the top. Figure 1 As shown.

[0025] The heat flux of a material is directly proportional to the product of its thickness and thermal conductivity. Therefore, the following examples will directly show the thickness and thermal conductivity values ​​of the material.

[0026] Example 1

[0027] A method for preparing a millimeter-scale thermally conductive graphite plate includes the following steps:

[0028] (1) 50nm PS microspheres, 100nm PS microspheres, 500nm PS microspheres, and 1µm PS microspheres (Transgenic Biotechnology) were mixed in equal mass ratios and dispersed in water to form a 1% (w / w) dispersion. This dispersion was then spin-coated onto a 20µm thick artificial graphite film (with a thermal conductivity of approximately 1600 W / mK) to form a PS layer. The PS coverage was controlled by adjusting the rotation speed and time to maintain a coverage area of ​​20%–30%. Another 20µm thick artificial graphite film was then placed over the PS layer, and this process was repeated, resulting in a total of 25 layers of artificial graphite film and 24 layers of PS layers stacked alternately. Figure 2 Then, it is bonded and fixed at 100℃ with slight heat to form a multi-level structural material;

[0029] (2) Using the multi-level structure material obtained in step (1) as the cathode, and copper sulfate solution as the electrolyte, electroplating was performed. The concentration of the copper sulfate solution was 1 mol / L, the concentration of the sulfuric acid solution was 3 mol / L, the electroplating voltage range was 4.5 V, and the current density was 15 A / dm³. 2 The electroplating time is 20 minutes. After electroplating, the image is analyzed using SEM (Selenium Electron Microscopy). Figure 4 It can be seen that Cu has formed a single crystal with a thickness of 100 nm.

[0030] (3) After the multi-level structural material is dried after electroplating in step (2), it is hot-pressed at a pressure of 0.2-2MPa and a temperature of 500-700℃ for 5-30 minutes to completely decompose the PS microspheres and allow the metal to crystallize and homogenize the metal into a metal layer with an average thickness of 20nm; finally, a millimeter-level thermally conductive graphite plate is obtained.

[0031] Figure 3 The image shown is a surface morphology diagram of a single graphite film. Figure 3 As shown, the surface of a single graphite film is smooth and flat, making it difficult to electroplate a composite copper metal layer on the surface. Figure 4 The sub-millimeter thick (approximately 0.5 mm) thermally conductive graphite plate prepared in this embodiment ( Figure 5 A high-resolution TEM image of the interface between a graphite film and a copper metal layer is shown. The image shows that copper and graphene are bonded at the atomic level, and copper exhibits single-crystal characteristics, which lays the structural foundation for the subsequent high thermal conductivity.

[0032] The horizontal thermal conductivity of the prepared graphite plate was found to be 1430 W / mK after thermal conductivity testing.

[0033] Example 2

[0034] A method for preparing a millimeter-scale thermally conductive graphite plate includes the following steps:

[0035] (1) Mix 100nm PS microspheres, 500nm PS microspheres and 800nm ​​PS microspheres (Transformer Bio) in equal mass ratio, disperse them in water to form a dispersion with a mass fraction of 2%, spin coat them onto a 4μm thick artificial graphite film (thermal conductivity of about 1600W / mK) to form a PS layer, and control the rotation speed and time to make the PS coverage rate (coverage area) between 20% and 30%; then cover the PS layer with another 4μm thick artificial graphite film, and so on, stacking them alternately to 0.11mm, and then fix them by micro-thermal bonding at 150℃ to form a multi-level structure material;

[0036] (2) Using the multi-level structural material obtained in step (1) as the cathode, and copper sulfate solution as the electrolyte, electroplating was performed. The concentration of the copper sulfate solution was 2 mol / L, the concentration of the sulfuric acid solution was 0.3 mol / L, the electroplating voltage range was 5V, and the current density was 25A / dm³. 2 The electroplating time was 4 minutes. After electroplating, SEM showed that Cu had formed a single crystal with a thickness of 20 nm.

[0037] (3) After drying the multi-level structural material completed in step (2) by electroplating, it is hot-pressed at a pressure of 0.2 MPa and a temperature of 700 °C for 30 minutes to completely decompose the PS microspheres and allow the metal to crystallize, homogenizing the metal into a metal layer with an average thickness of 100 nm; finally, a millimeter-scale thermally conductive graphite plate is obtained. The photograph of the millimeter-scale thermally conductive graphite plate obtained in this embodiment shows a thickness of approximately 0.102 mm.

[0038] The horizontal thermal conductivity of the prepared graphite plate was found to be 1390 W / mK after thermal conductivity testing.

[0039] Example 3

[0040] A method for preparing a millimeter-scale thermally conductive graphite plate includes the following steps:

[0041] (1) Mix 100nm PS microspheres, 500nm PS microspheres and 800nm ​​PS microspheres (Transformer Bio) in equal mass ratio, spin-coat them onto a 15μm thick artificial graphite film (thermal conductivity of about 1600W / mK) to form a PS layer, and control the rotation speed and time to make the PS coverage rate (coverage area) between 20% and 30%; then cover the PS layer with another 15μm thick artificial graphite film, and so on, stacking them alternately to 0.3mm, and then fix them by micro-thermal bonding at 120℃ to form a multi-level structure material;

[0042] (2) Using the multi-level structure material obtained in step (1) as the cathode, and copper sulfate solution as the electrolyte, electroplating is performed. The concentration of the copper sulfate solution is 0.1 mol / L, the concentration of the sulfuric acid solution is 6 mol / L, the electroplating voltage range is 4V, and the current density is 10A / dm³. 2 The electroplating time was 20 minutes. After electroplating, SEM showed that Cu had formed a single crystal with a thickness of 67 nm.

[0043] (3) After drying the multi-level structural material completed in step (2) by electroplating, hot-press it at a pressure of 2 MPa and a temperature of 500°C for 5 minutes to completely decompose the PS microspheres and allow the metal to crystallize, homogenizing the metal into a metal layer with an average thickness of 20 nm; finally, a millimeter-scale thermally conductive graphite plate is obtained. The photograph of the millimeter-scale thermally conductive graphite plate obtained in this embodiment shows a thickness of approximately 0.27 mm.

[0044] The prepared graphite plate has a horizontal thermal conductivity of 1210 W / mK after thermal conductivity testing.

[0045] Example 4

[0046] Other conditions are the same as in Example 1, except that PS microspheres with a uniform size of 500nm are used.

[0047] Electroplating was performed using the same parameters as in step 2. After electroplating, the Cu single crystal thickness reached 78 nm.

[0048] The horizontal thermal conductivity of the prepared graphite plate was found to be 1470 W / mK after thermal conductivity testing.

[0049] Comparative Example 1

[0050] A method for preparing a millimeter-scale thermally conductive graphite plate includes the following steps:

[0051] (1) Stack 20μm thick artificial graphite films until their thickness is consistent with the thickness of the composite film obtained in step 1 of Example 1, and then perform micro-heat treatment at 100°C.

[0052] (2) Using the stacked film obtained in step (1) as the cathode, electroplating was performed with copper sulfate solution as the electrolyte. The concentration of the copper sulfate solution was 1 mol / L, the concentration of the sulfuric acid solution was 3 mol / L, the electroplating voltage range was 4.5 V, and the current density was 15 A / dm³. 2 The electroplating time was 20 minutes. After electroplating, Cu could not be observed using SEM.

[0053] (3) After the multi-level structural material is dried after electroplating in step (2), it is hot-pressed at a pressure of 0.2-2MPa and a temperature of 500-700℃ for 5-30 minutes; finally, a thermally conductive graphite plate is obtained.

[0054] The horizontal thermal conductivity of the prepared graphite plate was found to be 350 W / mK after thermal conductivity testing.

Claims

1. A method for preparing a millimeter-scale thermally conductive graphite plate, characterized in that, Includes the following steps: (1) The artificial graphite film and the PS layer are stacked alternately and then bonded and fixed by micro-heating at 100-150℃ to form a multi-level structural material; the PS layer is composed of PS microspheres; (2) The multi-level structural material prepared in step (1) is used as the cathode, and copper sulfate solution is used as the electrolyte for electroplating. Copper is electroplated in the narrow gaps between the graphite films of the multi-level structural material. (3) After the multi-level structural material completed by electroplating in step (2) is dried, it is hot-pressed at a pressure of 0.2-2MPa and a temperature of 500-700℃ for 5-30 minutes to obtain a millimeter-level thermally conductive graphite plate.

2. The method according to claim 1, characterized in that, In step (1), the PS layer is prepared by spin coating.

3. The method according to claim 1, characterized in that, In step (1), the particle size of the PS microspheres is 50-1000 nm.

4. The method according to claim 1, characterized in that, In step (1), the thickness of the artificial graphite film is 4-20 μm.

5. The method according to claim 1, characterized in that, In step (1), the thickness of the artificial graphite film and the PS layer is 0.1-0.5 mm, which are stacked alternately.

6. The method according to claim 1, characterized in that, In step (3), the average thickness of the copper metal layer in the millimeter-scale thermally conductive graphite plate is 20-100 nm.

7. The method according to claim 1, characterized in that, In step (2), the concentration of the copper sulfate solution is 0.1-2 mol / L, the electroplating voltage range is 4-5V, and the current density is 10-25 A / dm³. 2 The concentration of the sulfuric acid solution is 0.3-6 mol / L, and the electroplating time is 4-20 min.

8. A millimeter-sized thermally conductive graphite plate prepared by the method of any one of claims 1-7.

9. The application of the millimeter-scale thermally conductive graphite plate as described in claim 8 as a heat dissipation material.

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