Graphene-metal composite longitudinal thermal conductor, its preparation method and application

Abstract

This invention discloses a graphene-metal composite longitudinal thermal conductor, its preparation method, and its applications. The graphene-metal composite longitudinal thermal conductor includes a thermally conductive substrate and a metal coating. The thermally conductive substrate comprises graphene layers and metal separators alternately stacked along a first direction, with the dominant thermal conductivity direction of the graphene layers being the in-plane direction. The metal coating is applied to the surface of the thermally conductive substrate, with the normal direction of the metal coating being a second direction. The first and second directions are angled, and the metal coating is edge-bonded to the metal separator. The graphene-metal composite longitudinal thermal conductor provided by this invention utilizes metal separators to separate multiple graphene layers, significantly improving its coefficient of thermal expansion compared to longitudinal thermal conductors composed of pure graphene, thus meeting the needs of most application scenarios. Furthermore, the metal bonding between the metal coating and the metal separators significantly enhances the overall bonding strength, preventing problems such as loosening and detachment, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of thermal conductive materials technology, and in particular to a graphene-metal composite longitudinal thermal conductor, its preparation method and application. Background Technology

[0002] As people place increasingly higher demands on computing performance and electronic devices, electronic components are constantly evolving towards miniaturization and high integration, leading to a dramatic increase in the power density of electronic devices and resulting in serious heat dissipation problems. Statistics show that overheating accounts for 55% of all electronic device failures. Therefore, there is an urgent need to develop high-performance thermally conductive materials for thermal management of electronic devices, reducing the probability of malfunctions during use.

[0003] Graphene is carbon atoms arranged in sp... 2 Two-dimensional materials with a hexagonal honeycomb lattice formed by hybrid orbitals exhibit an in-plane thermal conductivity as high as 5300 W / m² at room temperature for monolayer graphene. -1 K -1 Furthermore, graphene has a low coefficient of thermal expansion, low density, and good mechanical properties, making it an ideal thermally conductive raw material. Metallic materials, such as copper, have high thermal conductivity and good processability and are widely used in heat dissipation devices. Therefore, combining graphene with metallic materials is considered an effective way to prepare high-performance heat dissipation materials.

[0004] Some existing technologies provide technical solutions for stacking carbon thermal conductive materials such as graphene with thin metal layers through winding or stacking to form composite longitudinal thermal conductors. For example, graphene and copper are prepared by winding and then bonded by sintering. However, in one type of technical solution, the metal material and graphene material cannot form a strong bond, so it is difficult to form composite thermal conductive materials with large lateral dimensions and thin longitudinal thickness, which seriously limits the application of this type of composite material. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a graphene-metal composite longitudinal heat conductor, its preparation method, and its applications.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] In a first aspect, the present invention provides a graphene-metal composite longitudinal thermal conductor, which includes a thermally conductive substrate and a metal coating.

[0008] The thermally conductive substrate includes graphene layers and metal separators alternately stacked along a first direction, wherein the dominant thermally conductive direction of the graphene layers is the in-plane direction;

[0009] The metal coating is applied to the surface of the thermally conductive substrate. The normal direction of the metal coating is the second direction. The first direction and the second direction are set at an angle, and the metal coating is bonded to the edge of the metal spacer.

[0010] Secondly, the present invention also provides a method for preparing a graphene-metal composite longitudinal thermal conductor, comprising:

[0011] A thermally conductive adhesive is formed by alternately stacking graphene layers and metal separators and slicing them in the stacking direction through adhesive bonding.

[0012] A metal coating is deposited on the end face of the adhesive thermal conductor to obtain a thermally conductive precursor, wherein the normal of the end face is set at an angle to the stacking direction of the graphene layer and the metal separator, and the metal coating forms a fixed bond with at least the edge of the metal separator.

[0013] The thermally conductive precursor is sintered to eliminate the adhesive material binding the graphene layer and the metal separator, thereby obtaining a graphene-metal composite longitudinal thermal conductor.

[0014] Furthermore, the above preparation method also includes a method for controlling the expansion coefficient of a graphene-metal composite longitudinal thermal conductor, which includes:

[0015] The thermal expansion coefficient of the graphene metal composite longitudinal heat conductor is adjusted by adjusting the proportion of metal interlayers and the thickness of each interlayer.

[0016] Thirdly, the present invention also provides an application of graphene-metal composite longitudinal thermal conductor in the field of heat dissipation of electronic products.

[0017] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include:

[0018] The graphene-metal composite longitudinal heat conductor provided by this invention utilizes metal separators to separate multiple graphene layers. Compared with longitudinal heat conductors composed of pure graphene, its coefficient of thermal expansion is significantly improved to meet the needs of most application scenarios. Furthermore, the overall bonding strength of the graphene-metal composite longitudinal heat conductor is significantly improved through the metal bonding effect between the metal coating and the metal separator, preventing problems such as loosening and detachment, and has broad application prospects.

[0019] Furthermore, the thermal expansion coefficient of the graphene-metal composite longitudinal heat conductor can be adjusted by changing the proportion of metal spacer layers and the thickness of a single layer, thus more flexibly and accurately meeting the needs of specific application scenarios.

[0020] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a graphene-metal composite longitudinal heat conductor provided in a typical embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the preparation process of a graphene-metal composite longitudinal heat conductor provided in a typical embodiment of the present invention;

[0023] Figure 3 This is a thermal expansion test curve of a graphene-metal composite longitudinal thermal conductor provided in a typical embodiment of the present invention.

[0024] Figure 4 This is a thermal expansion test curve of a graphene-metal composite longitudinal thermal conductor provided in a typical comparative case of the present invention.

[0025] Figure 5 This is a thermal expansion test curve of a graphene-metal composite longitudinal thermal conductor provided in a typical comparative case of the present invention. Detailed Implementation

[0026] Several techniques exist in this field for stacking graphene with metals, but these composites typically provide lateral thermal conductivity rather than longitudinal thermal conductivity. For example, some traditional techniques involve stacking graphene and copper layers and then pressing them at high temperatures to obtain graphene-metal composite materials with high in-plane thermal conductivity. However, materials prepared using these methods suffer from low longitudinal thermal conductivity, which is insufficient for the rapidly increasing heat dissipation demands of practical applications. Therefore, compared to existing technologies, a thermally conductive material with high longitudinal thermal conductivity, low coefficient of thermal expansion, and good mechanical properties is needed.

[0027] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0029] This invention provides a graphene-metal composite longitudinal thermal conductor, which includes a thermally conductive substrate and a metal coating. The thermally conductive substrate includes graphene layers and metal separators alternately stacked along a first direction, wherein the dominant thermally conductive direction of the graphene layers is in-plane. The metal coating is applied to the surface of the thermally conductive substrate, and the normal direction of the metal coating is a second direction. The first and second directions are angled together, and the metal coating is bonded to the edge of the metal separator.

[0030] In some implementations, the first direction and the second direction are perpendicular.

[0031] As a typical example of the above technical solution, the graphene-metal composite longitudinal heat conductor provided by the present invention has the following specific structure: Figure 1 As shown, a graphene layer and a metal separator are stacked vertically along the transverse direction (the direction shown in the illustration is the correct direction, but it does not mean that the direction is still transverse when not placed in this state). The two form a sheet-like thermally conductive substrate. At least one of the upper and lower end faces of the thermally conductive substrate is deposited with a metal coating. The main function of the metal coating is to form at least a number of metal separators into a multi-layered structure that is integrally connected through metal-metal bonding. The graphene layer is sandwiched between two adjacent metal separators. Whether it is through physical bonding or chemical bonding, this stacked structure is solidified into a whole with a certain overall bonding force.

[0032] It should be noted that, Figure 1 For ease of representation, only one side of the metal bonding layer is depicted on the top surface. However, in actual fabrication, depending on the process, this metal bonding layer can completely encapsulate the graphene thermally conductive substrate (e.g., electroless plating can achieve full coverage of all six sides), or it can selectively cover two end faces (e.g., electroplating, where the current direction can be controlled to select the deposition surface). Even in some physical sputtering deposition processes, it can be... Figure 1 The drawing only covers the topmost layer (deposited facing the target). However, regardless of the coverage method, the metal bonding layer needs to cover at least one end face to form a bond between the graphene and the metal layer.

[0033] Therefore, the graphene-metal composite longitudinal heat conductor provided by the present invention regulates the thermal expansion coefficient of the graphene-metal composite longitudinal heat conductor by inserting a metal separator, making it suitable for the needs of most application scenarios, and also providing sufficient overall bonding strength so as not to be easily damaged or loosened.

[0034] In some embodiments, the metal spacer and / or metal plating layer is made of any one or a combination of two or more of copper, aluminum, and silver. Of course, the above material selection is a preferred range in the embodiments considering thermal conductivity, and the specific material of the metal bonding layer is not limited to this; any material that can achieve bonding and meets the thermal conductivity requirements is acceptable.

[0035] In some embodiments, the metal coating includes a transition layer and a main coating; the transition layer is disposed between the thermally conductive substrate and the main coating to enhance the adhesion between the thermally conductive substrate and the main coating.

[0036] In some implementations, the thickness of the graphene layer is 25-100 μm.

[0037] In some implementations, the thickness of the metal spacer is 10-50 μm.

[0038] In some implementations, the thickness of the metal coating is 1-50 μm.

[0039] In some embodiments, the thickness of the thermally conductive substrate is 0.5-5 mm.

[0040] Based on the above structural characteristics, in some embodiments, the thermal conductivity of the graphene-metal composite longitudinal heat conductor provided by the present invention in the thickness direction is 420-700 W / mK.

[0041] In some embodiments, the overall coefficient of thermal expansion of the graphene-metal composite longitudinal thermal conductor provided by the present invention is 5-15 ppm / ℃.

[0042] See Figure 2 As shown, a second aspect of the present invention also provides a method for preparing the graphene-metal composite longitudinal thermal conductor provided in any of the above embodiments, comprising the following steps:

[0043] A thermally conductive adhesive is formed by alternately stacking graphene layers and metal separators and slicing them in the stacking direction through adhesive bonding.

[0044] A metal coating is deposited on the end face of the adhesive thermal conductor to obtain a thermally conductive precursor, wherein the normal of the end face is set at an angle to the stacking direction of the graphene layer and the metal separator, and the metal coating forms a fixed bond with at least the edge of the metal separator.

[0045] The thermally conductive precursor is sintered to eliminate the adhesive material binding the graphene layer and the metal separator, thereby obtaining a graphene-metal composite longitudinal thermal conductor.

[0046] Regarding the fabrication of longitudinal heat conductors, conventional technologies typically employ one approach: bonding multiple graphene layers together with an adhesive to form a longitudinally aligned unit, followed by transverse slicing to obtain a sheet-like heat conductor. However, adhesives often have a high coefficient of thermal expansion, and their height occupies almost the entire thickness of the heat conductor, resulting in a significantly higher coefficient of thermal expansion for this longitudinal heat conductor. In many applications, thermal expansion becomes a significant and pressing issue. While this invention addresses this problem by considering directly eliminating the adhesive through sintering, the resulting heat conductor has an excessively low coefficient of thermal expansion and is extremely prone to interlayer separation, making it difficult to apply (many applications require the thermal expansion coefficient of the heat dissipation material to match its surrounding structure, with a specific optimal range, rather than demanding the lowest possible coefficient). Through continuous research and improvement, the inventors of this invention have ultimately utilized the combined effect of a metal coating and a metal separator to better integrate the heat conductor and to more finely control the coefficient of thermal expansion, thus obtaining the aforementioned graphene-metal composite longitudinal heat conductor.

[0047] Another type of technical solution provides a structure with some similarities. It obtains a longitudinal heat conductor by winding and stacking copper foil and carbon materials such as graphene and then sintering them. However, this method is difficult to apply for large-area heat dissipation. The sintering method combines carbon materials and metals, but the bonding performance between carbon materials and metals is poor, making it impossible to prepare large-sized composite materials. The preparation method of this invention first prepares the material by bonding, which can produce large-sized structures according to requirements. Then, the thermal expansion caused by the adhesive material is removed by sintering. Finally, the interlayer metal separators and the surface metal coatings are used to make the composite material into a whole. The method is completely different from the above-mentioned existing technologies, and the purpose of adding the interlayer metal separators is also different.

[0048] The aforementioned prior art actually utilizes the low thermal expansion of carbon materials to compensate for the shortcomings of insufficient thermal expansion and thermal conductivity of metal materials. The purpose is to improve the thermal expansion and thermal conductivity of metals through composite carbon materials. However, the basis of this invention is graphene material itself. Instead, it utilizes the characteristic that the thermal expansion performance of the metal interlayer is lower than that of carbon materials (high coefficient of thermal expansion) to prevent the problem of excessively low coefficient of thermal expansion of the pure graphene layer after sintering and debinding, thereby improving the overall coefficient of thermal expansion of the carbon material.

[0049] Of course, limited by the above preparation method, the structure of the heat conductor provided by this invention should still contain traces of adhesive material sintering or carbonization residues between the graphene layer and the metal spacer layer. This may be a significant feature that distinguishes the heat conductor provided by this invention from the longitudinal heat conductors in the prior art. That is, there is a certain amount of carbonization residue of adhesive material between the graphene layer and the metal spacer layer of the graphene-metal composite longitudinal heat conductor provided by this invention, and this carbonization residue can also play an auxiliary role in connecting the two layers.

[0050] Regarding the specific preparation process and details, in some implementation schemes, the preparation method may specifically include the following process:

[0051] A transition layer is first deposited on the end face of the thermally conductive substrate;

[0052] A main plating layer is deposited on the surface of the transition layer, and the transition layer and the main plating layer constitute the metal plating layer;

[0053] In some embodiments, the metal coating is applied by any one or a combination of two or more of the following methods: chemical plating, electroplating, physical plating, and salt bath plating.

[0054] In addition, the thickness of the adhesive material layer in the adhesive heat conductor is usually 40-60μm, but it is not limited to this range, as long as it can ensure its bonding ability and the property of being sinterable and removable.

[0055] As typical examples of the above technical solutions, a fully automated laminating machine can be used to hot-press and cool graphene layers and metal foils (as metal spacers) onto epoxy films, removing the PET release film from the epoxy film surface. A robotic arm then performs multi-layer lamination, maintaining an interlayer distribution of graphene layers and metal foils, i.e., a structure of one layer of graphite and one layer of metal. A vacuum hot press is then used to vacuum hot-press the laminated graphene layers onto a copper layer, removing the gaps between the layers.

[0056] The graphene / copper composite is trimmed as needed using a single-wire cutting machine to maintain the overall dimensional uniformity of the material.

[0057] The trimmed material is sliced ​​along the stacking direction using a multi-wire cutting machine to obtain a vertically aligned graphene-metal adhesive thermal conductor.

[0058] By using a separation and cleaning composite integrated machine, the thermally conductive composite sheet is cleaned and peeled off to remove carbon powder and other residues left on the surface after cutting. Then, PET double-sided adhesive is applied to each sheet as a protective film to obtain a graphene-metal composite thermally conductive substrate.

[0059] To further improve the material integrity, the present invention also deposits a metal coating on the material surface by chemical plating (or electroplating, PVD, salt bath), the thickness of which is preferably 1 to 50 micrometers, and more preferably about 10 micrometers.

[0060] To further improve the bonding performance between the graphite layer and the copper plating layer, a transition layer such as Ni or Ti can be deposited by chemical plating (or electroplating, PVD, salt bath). The thickness of the transition layer is 0.5-5 μm, preferably about 2 μm, thereby improving the bonding strength.

[0061] During the above preparation process, the thickness of the graphene layer and the copper layer, or the number of intervals between the graphene layer and the copper layer, can be adjusted according to the actual application requirements. Here, the copper foil thickness is preferably 0.01-0.10 mm.

[0062] Furthermore, the preferred plating method in this invention is electroless plating, a surface treatment technology that offers advantages such as uniform and controllable coating, dense texture, and the ability to deposit on non-conductive surfaces. The specific process route is sensitization-activation-electroless plating. To enhance the fluidity of the plating solution and increase the contact area between the solution and the material, the electroless plating is performed under ultrasonic conditions.

[0063] The sensitization process is to form a reducing film on the material surface. For example, it can be carried out in a solution of 30 g / L SnCl2 and 50 ml / L hydrochloric acid, soaked at room temperature for 30 min, and then rinsed repeatedly with deionized water until neutral. The activating solution consists of 0.25 g / L PdCl2 and 10 ml / L hydrochloric acid. This process can reduce Pd to the material surface, which promotes the copper plating reaction. Soaked at room temperature for 30 min, and then rinsed repeatedly with deionized water until neutral.

[0064] The electroless plating solution consisted of 15 g / L copper sulfate pentahydrate, 15 g / L sodium potassium tartrate, 14 g / L EDTA, 0.01 g / L potassium ferrocyanide, 0.02 g / L 2,2'-bipyridine, 10 ml / L 36 wt% HCHO, and 2 ml / L OP-10. The solution temperature was 50℃, and the pH was 12.5-13.0 (adjusted with NaOH). The solution was ultrasonically soaked for 10 minutes. After completion, it was rinsed multiple times with deionized water until neutral and then dried in a vacuum oven for 24 hours. The plating thickness could be controlled by the number of electroless plating cycles.

[0065] Therefore, in some implementations, the electroless plating includes a process flow of sensitization, activation, and electroless plating.

[0066] In some embodiments, the electroless plating, electroplating, or salt bath coating is performed under ultrasonic conditions.

[0067] Regarding the specific conditions for sintering, in some embodiments, the sintering temperature is 300-500℃ and the time is 60-150h.

[0068] In some embodiments, the heating rate during the sintering process is 1-5 °C / min.

[0069] The sintering temperature and time can usually be set based on the material and decomposition temperature of the adhesive layer. For example, the sintering temperature can be appropriately reduced for some adhesive materials with low decomposition temperatures, and vice versa. Another important factor to consider is the heating rate during sintering. An excessively rapid heating rate may lead to thermal expansion stress failure, thus affecting the overall strength of the material. Therefore, in practical applications, the heating rate should be carefully controlled.

[0070] For example, the material to be dried can be placed in a tube furnace for sintering and debinding. Under an argon atmosphere (150 sccm), the temperature is increased to 400°C at 5°C / min and held for 2 hours. After completion, the material is cooled to room temperature, removed, and cleaned with deionized water. This ultimately yields a graphene / copper composite longitudinal thermal conductor with high longitudinal thermal conductivity, low coefficient of thermal expansion, and good mechanical properties.

[0071] Furthermore, a third aspect of the present invention provides the application of the graphene-metal composite longitudinal heat conductor provided in any of the above embodiments in the field of heat dissipation of electronic products.

[0072] In summary, the technical solution provided by this invention employs an interlayer stacked metal separator. The metal separator serves two purposes: firstly, to increase the coefficient of thermal expansion, and secondly, to promote the growth of the surface metal coating. The surface metal coating primarily functions as a bonding structure to achieve overall bonding and meet specific application requirements. After adhesive removal, the coefficient of thermal expansion of the heat conductor decreases excessively, which is detrimental to applications. Metals have a higher coefficient of thermal expansion than graphite; therefore, the appropriate addition of a metal separator can both bond the debonded heat conductor into a cohesive whole and appropriately increase the overall coefficient of thermal expansion of the material, thus meeting application requirements.

[0073] In this invention, the coefficient of thermal expansion can be controlled by increasing or decreasing the number or thickness of the interlayer metal separators and the thickness of the metal coating, according to actual application requirements. Compared with the research and development scheme without interlayer metal separators, this scheme can better control the coefficient of thermal expansion, highlighting its advantage of adjustable coefficient of thermal expansion, and can be more widely applied to products with different thermal expansion requirements.

[0074] Furthermore, after sintering and debinding, compared to the initial research and development scheme without interlayer metal separators (where there are no chemical bonds between the graphene and the metal coating, only pure mechanical bonds), the inclusion of interlayer metal separators is partly due to the consideration of improving the overall coefficient of thermal expansion of the final material. Without interlayer metal separators, the coefficient of thermal expansion of the resulting heat conductor is too low; simply relying on the surface metal coating to increase the coefficient of thermal expansion has a very limited effect and can also negatively impact thermal conductivity. Another aspect of the design with interlayer metal separators is that it not only improves the bonding performance between the surface coating and the longitudinal heat conductor (during plating, the interlayer metal bonds with the newly plated metal), but also provides more possibilities for controlling the coefficient of thermal expansion (by controlling the number of interlayer metal separators, the coefficient of thermal expansion can be regulated).

[0075] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0076] Example 1

[0077] The graphene layer (50μm thick) and copper foil (25μm thick) were hot-pressed and cooled with an epoxy film (40μm thick). The PET release film on the surface of the epoxy film was removed. The layers were stacked in multiple layers using a robotic arm. Then, the stacked graphene layer and copper layer were vacuum hot-pressed using a vacuum hot press (after loading, the temperature was first raised to 80 degrees and maintained for 30 minutes, then raised to 150 degrees and maintained for 30 minutes, and then vacuumed before hot pressing was performed twice at a pressure of 20t. Then, the pressure was held for 60 minutes at one-fifth of the hot pressing pressure. The entire hot pressing process was carried out under vacuum and the temperature was maintained at 150 degrees to remove air and gaps between the films, so that the materials were completely bonded without air. After vacuum hot pressing, the material thickness was 6cm).

[0078] The thermally conductive substrate is trimmed and sliced ​​using a single-wire cutter and a multi-wire cutter to obtain a slice thickness of 1 mm, and then the thermally conductive substrate is cleaned.

[0079] Electroless copper plating is performed on a thermally conductive substrate using a process route of sensitization-activation-electroless plating. To enhance the fluidity of the plating solution and increase the contact area between the solution and the material, electroless plating is conducted under ultrasonic conditions. The sensitization process aims to form a reducing film on the material surface. For example, it can be performed in a solution of 30 g / L SnCl2 and 50 ml / L hydrochloric acid, immersing the material at room temperature for 30 minutes, followed by repeated rinsing with deionized water until neutral. The activation solution consists of 0.25 g / L PdCl2 and 10 ml / L hydrochloric acid. This process reduces Pd to the material surface, promoting the copper plating reaction. The material is also immersed at room temperature for 30 minutes, followed by repeated rinsing with deionized water until neutral. The electroless plating solution consisted of 15 g / L copper sulfate pentahydrate, 15 g / L sodium potassium tartrate, 14 g / L EDTA, 0.01 g / L potassium ferrocyanide, 0.02 g / L 2,2'-bipyridine, 10 ml / L 36 wt% HCHO, and 2 ml / L OP-10. The solution temperature was 50℃, and the pH was 12.5-13.0 (adjusted with NaOH). The solution was ultrasonically immersed for 10 minutes. After completion, the solution was rinsed multiple times with deionized water until neutral and then dried in a vacuum oven for 24 hours. The coating thickness was controlled to 10 μm by repeating the electroless plating process.

[0080] The material was placed in a tube furnace for sintering and debinding. Under an argon atmosphere (150 sccm), the temperature was increased to 400℃ at a rate of 5℃ / min and held for 2 hours. After completion, the temperature was lowered to room temperature, the material was removed, and cleaned with deionized water. This resulted in a graphene / copper composite longitudinal thermal conductor with high longitudinal thermal conductivity, low coefficient of thermal expansion, and good mechanical properties.

[0081] Specifically, the measured coefficient of thermal expansion of this graphene longitudinal thermal conductor varies with temperature from 5.6 to 10.7 ppm / ℃, and its longitudinal thermal conductivity is 628 W / mK.

[0082] Comparative Example 1

[0083] This comparative example is largely the same as Example 1, with the main difference being:

[0084] The surface chemical plating process has been omitted.

[0085] The loss of the surface coating has little impact on the overall longitudinal thermal conductivity and coefficient of thermal expansion, and is almost the same as in Example 1; however, it has a significant impact on the overall bonding strength. The longitudinal thermal conductor provided in this comparative example is prone to breakage or loosening during processing, such as the collection, transfer, and stacking of finished products, resulting in a significant reduction in the yield, which is less than half.

[0086] Comparative Example 2

[0087] This comparative example is largely the same as Example 1, with the main difference being:

[0088] Instead of copper foil, it consists of multiple layers of graphene with adhesive layers stacked directly.

[0089] Comparative Example 3

[0090] This comparative example is largely the same as Example 1, with the main difference being:

[0091] The sintering process is omitted, and the final product is directly a heat conductor with adhesive material and coating.

[0092] Figure 3 The graph shows the thermal expansion coefficient test results of the graphene-metal composite longitudinal heat conductor provided in Example 1 above. It can be seen that its thermal expansion coefficient is within a moderate range, neither too high nor too low; and Figure 4 The thermal expansion coefficient test curves of the copper foil-free thermal conductor provided in Comparative Example 2 are shown. It can be seen that without the interlayer metal separator, relying solely on the graphene layer and a thin metal coating results in an excessively low thermal expansion coefficient. This leads to thermal stress problems in some applications due to the inability to match the thermal expansion of other structures (of course, such a low thermal expansion coefficient structure may be appropriate for some extremely specialized applications). Figure 5 The thermal expansion coefficient test curve of the unsintered thermal conductor provided in Comparative Example 3 is shown. It can be seen that because the adhesive material with strong thermal expansion characteristics was not removed, the thermal expansion coefficient of the resulting product is too large, which will lead to the same thermal stress problem.

[0093] Example 2

[0094] This embodiment is largely the same as Embodiment 1, with the main difference being:

[0095] The electroless copper plating process is replaced with an electroplating copper plating process, and the specific electroplating conditions are as follows:

[0096] A copper plate was used as the anode, and the electrolyte consisted of 200 g / L copper sulfate pentahydrate and 55 g / L sulfuric acid; the current density was 3 Adm. -2 During electroplating, the electroplating solution is continuously stirred to ensure uniform distribution; the coating thickness is controlled by the electroplating time.

[0097] The resulting graphene-metal composite longitudinal heat conductor has essentially the same properties as the example.

[0098] Furthermore, this embodiment also made various substitutions for the metal coating method, such as physical coating (PVD: magnetron sputtering, ion beam evaporation, thermal evaporation, etc.) and salt bath coating, etc., all of which achieved equivalent results. This shows that the method and structure provided by the present invention are not specifically limited to one or more specific preparation methods, but are based on the basic inventive concept provided by the present invention.

[0099] Example 3

[0100] This embodiment is largely the same as Embodiment 1, with the main difference being:

[0101] The dimensions of each layer were adjusted: the graphene layer was 100 μm thick, the copper separator was 50 μm thick, the copper plating was 5 μm thick, and the thermally conductive substrate slice was 2 mm thick.

[0102] Within the aforementioned size range, the obtained graphene-metal composite longitudinal thermal conductor exhibits equally excellent thermal conductivity, thermal expansion, and overall bonding properties.

[0103] Example 4

[0104] This embodiment is largely the same as Embodiment 1, with the main difference being:

[0105] The dimensions of each layer were adjusted: the graphene layer thickness was 25 μm, the copper separator thickness was 10 μm, the copper plating thickness was 50 μm, and the thermally conductive substrate slice thickness was 0.5 mm.

[0106] Within the aforementioned size range, the obtained graphene-metal composite longitudinal thermal conductor exhibits equally excellent thermal conductivity, thermal expansion, and overall bonding properties.

[0107] Example 5

[0108] This embodiment is largely the same as Embodiment 1, with the main difference being:

[0109] The copper foil is replaced with silver foil, and the copper plating is also replaced with silver-plated metal. The remaining structural and dimensional characteristics remain unchanged.

[0110] Since different metals have different thermal conductivity and thermal expansion properties, the relevant properties of the graphene metal composite longitudinal heat conductor provided in this embodiment also show some corresponding changes, which is normal. However, it still has similar excellent thermal conductivity, thermal expansion and overall bonding performance, which will not be elaborated further here.

[0111] Furthermore, this embodiment also replaced various metal materials, such as aluminum foil and aluminized metal, and the same pattern was observed in all cases.

[0112] Example 6

[0113] This embodiment is largely the same as Embodiment 1, with the main difference being:

[0114] The adhesive material was replaced with acrylate thermally conductive adhesive, and the sintering temperature was adjusted to 450℃ and the sintering time was adjusted to 1.5h.

[0115] It is still possible to obtain a graphene-metal composite longitudinal heat conductor with basically similar performance.

[0116] In addition, this embodiment also replaces a variety of adhesive materials. Under the premise of ensuring that the adhesive material can be removed by sintering, the sintering conditions are adjusted accordingly, and a graphene metal composite longitudinal heat conductor with excellent performance can be obtained.

[0117] Based on the above embodiments and comparative examples, it is clear that the graphene-metal composite longitudinal heat conductor provided by the embodiments of the present invention utilizes metal separators to separate multiple graphene layers. Compared with longitudinal heat conductors composed of pure graphene, its coefficient of thermal expansion is significantly improved to meet the needs of most application scenarios. Furthermore, the overall bonding strength of the graphene-metal composite longitudinal heat conductor is significantly improved through the metal bonding effect between the metal coating and the metal separator, preventing problems such as loosening and detachment, and has broad application prospects.

[0118] Furthermore, in this embodiment of the invention, the thermal expansion coefficient of the graphene-metal composite longitudinal heat conductor can be adjusted by changing the proportion of metal spacer layers and the thickness of a single layer, thus more flexibly and accurately meeting the needs of specific application scenarios.

[0119] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a graphene-metal composite longitudinal thermal conductor, characterized in that, include: A thermally conductive adhesive is formed by alternately stacking graphene layers and metal separators and slicing them in the stacking direction through adhesive bonding. A metal coating is deposited on the end face of the adhesive thermal conductor to obtain a thermally conductive precursor, wherein the normal of the end face is set at an angle to the stacking direction of the graphene layer and the metal separator, and the metal coating forms a fixed bond with at least the edge of the metal separator. The thermally conductive precursor is sintered to eliminate the adhesive material binding the graphene layer and the metal separator, thereby obtaining a graphene-metal composite longitudinal thermal conductor. The overall thermal expansion coefficient of the graphene-metal composite longitudinal heat conductor is 5-15 ppm / ℃.

2. The preparation method according to claim 1, characterized in that, Specifically, it includes: A transition layer is first plated on the end face of the adhesive heat conductor; A main coating is deposited on the surface of the transition layer, and the transition layer and the main coating constitute the metal coating.

3. The preparation method according to claim 2, characterized in that, The thickness of the adhesive material layer in the adhesive heat conductor is 40-60 μm.

4. The preparation method according to claim 2, characterized in that, The metal coating method includes any one or a combination of two or more of the following: chemical plating, electroplating, physical plating, and salt bath plating. The chemical plating includes a process flow of sensitization, activation, and chemical plating. The chemical plating, electroplating, or salt bath plating is performed under ultrasonic conditions.

5. The preparation method according to claim 1, characterized in that, The sintering process is carried out at a temperature of 300-500℃ for 60-150 min, with a heating rate of 1-5℃ / min.

6. A graphene-metal composite longitudinal thermal conductor prepared by the preparation method according to any one of claims 1-5, characterized in that, Including the thermally conductive substrate and the metal coating; The thermally conductive substrate includes graphene layers and metal separators alternately stacked along a first direction, wherein the dominant thermally conductive direction of the graphene layers is the in-plane direction; The metal coating is applied to the surface of the thermally conductive substrate. The normal direction of the metal coating is the second direction. The first direction and the second direction are set at an angle, and the metal coating is bonded to the edge of the metal spacer.

7. The graphene-metal composite longitudinal thermal conductor according to claim 6, characterized in that, The first direction and the second direction are perpendicular.

8. The graphene-metal composite longitudinal thermal conductor according to claim 6, characterized in that, The material of the metal spacer and / or metal plating includes any one or a combination of two or more of copper, aluminum, and silver.

9. The graphene-metal composite longitudinal thermal conductor according to claim 6, characterized in that, The metal coating includes a transition layer and a main coating; The transition layer is disposed between the thermally conductive substrate and the main coating to enhance the adhesion between the thermally conductive substrate and the main coating.

10. The graphene-metal composite longitudinal thermal conductor according to claim 6, characterized in that, The graphene layer has a thickness of 25-100 μm, the metal separator has a thickness of 10-50 μm, the metal coating has a thickness of 1-50 μm, the thermally conductive substrate has a thickness of 0.5-5 mm, and the graphene-metal composite longitudinal thermal conductor has a thermal conductivity of 420-700 W / mK in the thickness direction.

11. The application of the graphene-metal composite longitudinal thermal conductor according to any one of claims 6-10 in the field of heat dissipation of electronic products.

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