Laminated graphene-based thermally conductive films and pads and methods of making the same

Abstract

A graphene-based thermally conductive film comprises a plurality of graphene film strips, wherein the graphene film strips are arranged so that graphene sheets of the graphene film are aligned in a direction perpendicular to a plane (Y'Z') of the thermally conductive film, wherein the thermally conductive film comprises: a plurality of first area portions (214a, c), which comprise graphene film strips having a first rotation alignment in the plane of the thermally conductive film; and a plurality of second area portions (214b, d), which comprise graphene film strips having a second rotation alignment in the plane of the thermally conductive film, wherein the second rotation alignment is different from the first rotation alignment.

Description

Field of the Invention

[0001] The present invention relates to laminated graphene-based thermally conductive films and methods for making the films. Specifically, the present invention relates to thermally conductive films comprising graphene film portions having different orientations. The thermally conductive films can be formed into pads for use as thermal interface materials in electronic components. Background Art

[0002] With the continuous development of modern electronic devices and systems, their ever-increasing power density has led to higher operating temperatures. Therefore, effective thermal management has become extremely important to remove the large amounts of heat required to ensure high performance and long-life reliability. Traditional thermal interface materials (TIMs) are components that are very important for heat dissipation. Their thermal conductivity is usually less than a maximum of 10W / mK, and is usually around 4W / mK or 5W / mK in the vertical direction. Therefore, in order to solve this problem, people have worked hard to develop high-performance TIMs based on carbon materials (such as graphite nanosheets, carbon nanotubes and carbon fibers).

[0003] Extensive research has been devoted to improving the thermal conductivity of graphene-based thermally conductive adhesives by increasing the graphene loading in them. However, when the graphene content is too high, it becomes impractical for the manufacturing process.

[0004] Graphene, an allotrope of carbon consisting of only one layer of atoms arranged in a two-dimensional hexagonal lattice, possesses many unique properties, such as ultrafast electron mobility, ultrahigh mechanical strength, and exceptional thermal performance (in-plane thermal conductivity = 5000 W / mK). Furthermore, graphene must be arranged into specific structures to achieve diverse functions, particularly in electronic devices.

[0005] For TIMs, high thermal conductivity in the perpendicular direction is required. Therefore, graphene must be assembled into a vertically aligned structure to facilitate heat dissipation in the direction normal to the contacting solid interface. Vertically aligned graphite films have been reported to be prepared by compacting aligned graphite sheets. However, this type of material is difficult to manufacture in an automated and cost-effective manner. Furthermore, due to the high stiffness and weak interlayer bonding strength of graphite, vertically assembled graphite composites exhibit high hardness and are brittle in directions perpendicular to the assembly direction. Consequently, the film's poor mechanical properties can be an obstacle to implementation in certain applications.

[0006] Therefore, improved methods for forming vertically aligned graphene-based films are needed to increase the availability of thermal interface materials with high out-of-plane thermal conductivity. Summary of the Invention

[0007] In view of the above and other shortcomings of the prior art, an object of the present invention is to provide an improved graphene-based thermally conductive film and a method for manufacturing the thermally conductive film.

[0008] According to a first aspect of the present invention, a method for manufacturing a laminated graphene-based thermally conductive film comprising vertically aligned graphene is provided. The method comprises: providing a laminated film comprising a plurality of graphene film layers separated by an adhesive, the graphene film comprising graphene sheets aligned with the graphene film plane, wherein the plane of the graphene film is a first plane defined by a first axis and a second axis perpendicular to the first axis; forming a plurality of blocks of the laminated film by cutting the laminated film perpendicular to the second plane, the second plane being defined by a second axis and a third axis perpendicular to each of the first and second axes; rotating a subset of the plurality of blocks about the first axis; and attaching the plurality of blocks to each other using an adhesive to form a block consisting of a plurality of graphene film layers having a first rotation alignment about the first axis. A method of forming a thermally conductive film comprising: forming a first plurality of regions and a second plurality of regions having a second rotational alignment about a first axis, the second rotational alignment being different from the first rotational alignment; applying pressure and heat to the block to cure an adhesive, thereby forming a block from the plurality of regions comprising graphene film; and cutting the block along a plane of the block, the plane being defined as perpendicular to the first axis, thereby forming a thermally conductive film having graphene sheets aligned perpendicularly to the plane of the thermally conductive film, such that the first plurality of regions of the thermally conductive film include graphene film having a first rotational alignment about the first axis, and the second plurality of regions of the thermally conductive film include graphene film having a second rotational alignment about the first axis.

[0009] The resulting thermally conductive film includes graphene sheets aligned vertically relative to the horizontal surface plane of the thermally conductive film, which means that the thermally conductive film has anisotropic thermal conductivity and has a significantly higher thermal conductivity in the direction perpendicular to the plane of the thermally conductive film than in the plane of the film.

[0010] The graphene film that forms the basis of the laminated film and subsequently forms the thermally conductive film can be considered to include a plurality of graphene layers arranged to form the graphene film. The graphene film can be formed, for example, of graphene flakes having an average lateral dimension of 2-100 μm. Therefore, it is not necessary for the graphene film to be a continuous graphene layer or to contain a continuous graphene layer. Instead, the graphene film can be composed of a stack of graphene layers, so that the graphene film can be considered a graphene-based film or an enhanced graphene film. The lateral dimensions of the graphene flakes in such a graphene film determine the number of grain boundaries in the material. Since grain boundaries significantly increase phonon scattering and thereby reduce thermal conductivity, it is necessary to increase the lateral dimensions of the graphene flakes to reduce the number of grain boundaries, thereby increasing the in-plane thermal conductivity of the graphene film.

[0011] The present invention is based on the recognition that homogeneous thermally conductive films made from a laminated structure comprising a large number of stacked graphene films may suffer from anisotropic mechanical properties in the plane of the film. In other words, the Young's modulus of the film may be different in different directions in the plane of the film. This, in turn, may cause the film to break more easily in one direction than in other directions when subjected to strain. Thermally conductive films are typically arranged to be in contact with or between components that change temperature and can therefore expand and contract with temperature changes. Therefore, there is a risk that a thermally conductive film attached to a component may break or be damaged in one direction in the plane of the film due to the thermal expansion of the component.

[0012] In order to avoid or at least reduce the risk of thermally conductive films rupturing during thermal expansion, the present invention describes a method for producing a thermally conductive film having uniform mechanical properties in the film plane while maintaining advantageously high thermal conductivity perpendicular to the film plane.

[0013] The mechanical and thermal properties of a thermally conductive film can be controlled, for example, by controlling the ratio between the binder and the graphene film in the laminated film and the ratio between the two when reassembling the blocks cut from the laminated film to form the blocks. In practice, there may be a trade-off between the mechanical and thermal properties of the film, where a larger proportion of binder will improve mechanical properties while reducing overall thermal conductivity.

[0014] From the thermally conductive film described, pads of suitable size can be cut for use as thermal interface materials to improve heat transfer and, thereby, improve cooling in electronic devices. Furthermore, the term "film" should be considered herein to describe a planar structure having a surface area in the plane of the structure that is significantly greater than the thickness of the structure, and the thickness of the film can be considered to be substantially uniform over the area of ​​the film.

[0015] According to one embodiment of the present invention, cutting the laminated film includes cutting square blocks, and rotating a subset of the plurality of blocks includes rotating every other block by 90° about a first axis. The resulting thermally conductive film will then exhibit a checkerboard pattern comprising square area portions, wherein adjacent area portions have a 90° difference along a rotational alignment of the graphene film, while still exhibiting high thermal conductivity overall in the vertical direction due to the vertically aligned graphene sheets. The size of the squares can vary from a few millimeters to potentially several centimeters. Having larger squares can simplify the manufacturing process, while overly large squares may risk causing the thermally conductive film to not have the desired mechanical properties. Therefore, the size of the squares can be determined based on the mechanical performance requirements.

[0016] According to one embodiment of the present invention, cutting the laminated film includes cutting hexagonal blocks, and rotating each block includes rotating each block by ±60° or ±120° relative to an adjacent block, such that no two adjacent blocks have the same rotational alignment about a first axis. The resulting thermally conductive film will have a hexagonal pattern, also known as a honeycomb pattern, in which different area portions have different rotational alignments and have vertically aligned graphene sheets across the entire surface area. To obtain a thermally conductive film with adjacent portions having different rotational alignments, three different rotations can be used to form three different types of area portions with different rotational alignments in the plane of the film.

[0017] According to a second aspect of the present invention, there is provided a method for manufacturing a laminated graphene-based thermally conductive film comprising vertically aligned graphene. The method comprises: providing a laminated film comprising a plurality of graphene film layers separated by an adhesive, the graphene film comprising graphene sheets aligned with the graphene film plane, wherein the plane of the graphene film is a first plane defined by a first axis and a second axis perpendicular to the first axis; forming a first heat sink structure from the laminated film, the first heat sink structure having a base plate and a plurality of columns extending in the direction of the first axis with gaps between the columns in a second plane defined by a second axis and a third axis perpendicular to each of the first and second axes; forming a second heat sink structure from the laminated film, the second heat sink structure having a base plate and a plurality of columns extending in the direction of the first axis in a second plane, wherein the columns of the second heat sink structure have an arrangement and a cross-section corresponding to the gaps between the columns of the first heat sink structure, the second plane being defined by a second axis and a third axis perpendicular to each of the first and second axes; rotating the second heat sink structure around the first axis ; connecting the second heat sink structure to the first heat sink structure by an adhesive so that the columns of the second heat sink structure fill the gaps between the columns of the first heat sink structure, and so that the rotational alignment of the first heat sink structure about the first axis is different from the rotational alignment of the second heat sink structure about the first axis; removing the base plates of the first heat sink structure and the second heat sink structure to form a block, which consists of a first plurality of blocks having a first rotational alignment about the first axis and a second plurality of blocks having a second rotational alignment about the first axis, the second rotational alignment being different from the first rotational alignment; and cutting the block along a block plane, which plane is defined as perpendicular to the first axis, to form a thermally conductive film having graphene sheets aligned perpendicularly to the plane of the thermally conductive film, so that the first plurality of regional portions of the thermally conductive film include graphene films having a first rotational alignment about the first axis, and the second plurality of regional portions of the thermally conductive film include graphene films having a second rotational alignment about the first axis.

[0018] The term "heatsink structure" here refers to the shape of the structure, not its specific function. As is well known, heat sinks have a base plate and posts or fins extending from the base plate. In the present context, a heatsink structure includes a base plate and individual posts extending from the base plate.

[0019] According to a third aspect of the present invention, there is provided a graphene-based thermally conductive film comprising a plurality of graphene film strips, wherein the graphene film strips are arranged so that the graphene sheets of the graphene film are aligned in a direction perpendicular to the plane of the thermally conductive film, wherein the thermally conductive film comprises: a plurality of first area portions comprising graphene film strips having a first rotational alignment in the plane of the thermally conductive film; and a plurality of second area portions comprising graphene film strips having a second rotational alignment in the plane of the thermally conductive film, wherein the second rotational alignment is different from the first rotational alignment.

[0020] The graphene-based thermally conductive film exhibits uniform mechanical properties in both directions of the film plane, and is therefore less sensitive to tensile stress and resulting strain that may occur due to thermal expansion of the material to which the thermally conductive film is attached.

[0021] According to one embodiment of the present invention, the plurality of first and second area portions have a rectangular shape. In addition, each first area portion comprises a graphene film strip that is rotated 90° in the plane of the thermally conductive film compared to each second area portion.

[0022] According to one embodiment of the present invention, the plurality of first and second area portions have a hexagonal shape. Subsequently, each first area portion comprises a graphene film strip rotated by ±60° or ±120° in the plane of the thermally conductive film compared to each second area portion.

[0023] According to one embodiment of the present invention, an electronic assembly is provided, comprising: an electronic component; a cooling device configured to dissipate heat from the electronic component; and a graphene-based thermally conductive film according to any of the preceding embodiments, the graphene-based thermally conductive film being sandwiched between the electronic component and the cooling device. The cooling device may be, for example, a heat sink.

[0024] The functions and features of this second and third aspect of the invention are largely similar to those described above in relation to the first aspect of the invention.

[0025] Further features and advantages of the present invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following, without departing from the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] These and other aspects of the present invention will now be described in more detail with reference to the accompanying drawings showing exemplary embodiments of the invention, in which:

[0027] Figure 1 is a flow chart outlining the general steps of a method according to one embodiment of the present invention;

[0028] Figure 2A -J schematically shows the steps according to one embodiment of the present invention;

[0029] Figure 3 is a flow chart outlining the general steps of a method according to one embodiment of the present invention;

[0030] Figure 4A -F schematically shows the steps of a method according to one embodiment of the present invention;

[0031] Figure 5 A thermally conductive film according to one embodiment of the present invention is schematically shown.

[0032] Detailed Description of Exemplary Embodiments

[0033] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. However, the present invention can be embodied in many different forms and should not be limited to the embodiments described herein; rather, these embodiments are provided so that they are thorough and complete and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout the text.

[0034] Figure 1 is a flow chart outlining the general steps of a method according to one embodiment of the present invention, and the method will be further referenced to schematically showing the method steps. Figure 2A -J describes.

[0035] Figure 2A -D shows an exemplary method for forming a laminate film 206. The method includes providing a first graphene film 200 and providing 102 a second graphene film 202, such as Figure 2AAs shown. A graphene film suitable for use in this context can be formed by the following steps: providing graphene oxide sheets 203 in an aqueous suspension; providing a substrate; dispensing the suspension onto the substrate; heating the suspension on the substrate to form a graphene film by self-assembly; separating the graphene film from the substrate; thermally annealing the graphene film in an inert environment at a temperature ranging from 2800°C to 3300°C; and pressing the graphene film at a pressure ranging from 50 MPa to 300 MPa. This method provides a method for large-scale production of free-standing graphene films (GFs) with ultra-high in-plane thermal conductivity. Further details of graphene films with high in-plane thermal conductivity and methods for manufacturing the same can be found in PCT / SE2017 / 050185.

[0036] like Figure 2A As shown, the graphene film 200 includes a graphene sheet 203 aligned with the plane of the graphene film 200, wherein the plane of the graphene film is a first plane, represented herein as the XY plane, defined by a first axis X and a second axis Y perpendicular to the first axis X in a three-dimensional Cartesian coordinate system having first, second, and third axes represented as X, Y, and Z, respectively. The graphene film 200 is actually rotationally symmetric within the XY plane, i.e., about the Z axis. The graphene film 200 may also be referred to as an enhanced graphene film, a graphene-based film, etc., because it is not only composed of graphene itself.

[0037] The graphene films 200, 202 may also include multiple graphene layers having a turbostratic alignment between adjacent graphene layers. It has been found that graphene films having a turbostratic alignment between adjacent graphene layers can exhibit improved in-plane thermal conductivity compared to other known graphene-based materials and graphite heat dissipation materials. More details of graphene films comprising multiple graphene layers having a turbostratic alignment between adjacent graphene layers can be found in PCT / SE2018 / 000009. In addition, although the present invention is described with reference to graphene-based films, it is also possible to start from laminated films based on other materials (such as hexagonal boron nitride, MXenes, aluminum nitride, AlO2 or SiO2) instead of graphene and manufacture the thermally conductive film in the manner described by the method protected in this application. The material needs to be electrically insulating and preferably also has high thermal conductivity. It is also advantageous if a laminate film based on this material has anisotropic thermal conductivity in the same way as described for the graphene film comprising graphene sheets.

[0038] In order to improve the adhesive strength between the first and second graphene films 200 , 202 , a nanoparticle layer may be provided on the surfaces of the first and second graphene films 200 , 202 . Figure 2A Further shown is an adhesive 204 disposed on the first graphene film 200 .

[0039] The nanoparticle layer advantageously includes acicular nanoparticles configured to anchor the first graphene film 200 to the second graphene film 202 by improving the adhesion between the respective graphene films 200, 202 and the adhesive 204. The acicular nanoparticles may be composed of an elongated structure having a length of 5 nm to 100 nm and an aspect ratio between length and width of 5:1 to 50:1.

[0040] However, the nanoparticles that can be used for anchoring can also include a plurality of more or less randomly connected needle-like nanostructures, for example, to form spider-like nanostructures. In addition, the nanoparticles of the type mentioned can be formed, for example, from Al2O3, SiO2, Fe2O3, NiO2, Cr2O3, ZnO, Ag, Al, Cu, Ni, Cr, Ti, Mo, Fe, Mg and / or Li. Both the nanoparticles and the binder can be printed, dispensed or sprayed onto the graphene film.

[0041] Once the nanoparticles and binder 204 are deposited on the first graphene film 200, the second graphene film 202 is attached to the first graphene film 200 via the binder 204 and the nanoparticle layer, and the resulting layered film 205 is formed as shown in FIG. Figure 2B As shown. The nanoparticles will be anchored to the irregular and uneven portions of the graphene film surface, and the adhesive 204 will in turn form a bond with the graphene film surface and the nanoparticles. As a result, the adhesion between the first and second graphene films 200, 202 is significantly improved compared to using only the adhesive.

[0042] According to an illustrative example, a graphene film with a thickness of 10 μm is coated with an adhesive in the form of polydimethylsiloxane, which belongs to the silicone rubber group. Tetrahydrofuran is used as a solvent to adjust the viscosity of the polydimethylsiloxane. The concentration of polydimethylsiloxane in tetrahydrofuran is 25-75% by weight. A thin film coater is used for the deposition process. The coating thickness of the polydimethylsiloxane is determined by the thread depth of the coating rod. After the adhesive is applied, the graphene film is heated to about 50°C to 70°C for 1-20 minutes to remove the tetrahydrofuran. The thickness of the adhesive layer can be selected based on the desired ratio between the graphene film and the adhesive in the final laminate structure. The proportion of the adhesive in the thermally conductive film can be 10% to 90% by weight, and the adhesive can be composed of at least one of polyurethane, silicone rubber, polyimide, epoxy resin, and polyacrylic resin. This example shows a substantially solid graphene film. However, porous graphene films can also be used, in which pores or bubbles are formed in the film during manufacturing. The porous graphene membrane may include an internal cavity with a diameter of 0.1 μm to 1000 μm, preferably 1 μm to 100 μm, and more preferably 1 μm to 50 μm. In addition, holes in the form of openings that penetrate the graphene membrane may be formed by punching or the like after the membrane is formed. The diameter of the holes may be 10 μm to 500 μm, preferably 10 μm to 100 μm, the pore spacing may be 0.1 mm to 1 mm, preferably 0.1 mm to 0.5 mm, and the pore density may be 10-1000 openings per square centimeter, more preferably 10-500 openings per square centimeter.

[0043] The above description outlines a method for attaching two graphene films 200, 202 to each other. Next, a laminated film can be formed by stacking a plurality of such graphene films. Figure 2C By combining a plurality of layered films 205 as shown, or by simultaneously attaching one graphene layer to a growing stack of graphene layers attached to each other via the nanoparticles and binder 204 , a laminated film 206 of suitable thickness can be formed.

[0044] Use as Figure 2D The pressure tool 215 shown applies pressure and heat to cure the adhesive 204, thereby forming a laminate 206, forming a laminate 206 containing the desired number of layers. The pressure is 0.1 MPa to 3 MPa. The assembled laminate 206 is then placed in an oven for curing. The curing temperature is 80°C to 200°C, and the curing time is 10 minutes to 300 minutes.

[0045] The above description presents an exemplary method for forming the laminated graphene-based film 206. However, the method of the present invention is not dependent on a particular method of manufacturing the laminated film 206, and many variations and alternatives to the above examples are possible.

[0046] The first step of the present invention's method for manufacturing a laminated graphene-based thermally conductive film 212 comprising vertically aligned graphene includes providing 100 a laminated film 206 comprising a plurality of layers of graphene film 200 separated by an adhesive 204. As described above, the graphene film 200 includes graphene sheets 203 aligned with the plane of the graphene film 200 (represented herein as the XY plane). Due to the thermal properties of graphene, the thermal conductivity of the laminated film 206 is higher in the XY plane than in the Z direction perpendicular to the XY plane.

[0047] exist Figure 2E In this drawing, compared to the previous figures, the laminate film 206 is shown standing on its "edge" with the X-axis pointing upward, and the reference coordinate system is rotated accordingly. It should also be noted that the shape and size of the laminate film 206 and other features are not drawn to scale and do not necessarily represent the proportions of actual structures. The drawings are schematic in nature and are intended to clearly illustrate the relevant features of the present invention.

[0048] Once the laminate film 206 is provided, it is cut 102 into a plurality of sections 208a-d, where all sections preferably (but not necessarily) have the same shape. Preferably, the laminate film 206 is cut using wire cutting or sawing, but other methods are possible, such as laser cutting or plasma cutting, depending on the desired section shape. Here, the sections 208a-d have a square cross-section. Cutting is performed perpendicular to the YZ plane.

[0049] exist Figure 2F In the next step shown, a subset of the plurality of tiles is rotated about the X-axis 104. In the example shown with a square cross-section, every other tile is rotated 90° so that adjacent tiles have different rotational alignments about the X-axis, represented here by 208b and 208d. Due to symmetry in the XY plane, a 180° rotation would result in adjacent tiles having identical properties and is therefore undesirable.

[0050] Since only a subset of the blocks are rotated, and since the original coordinate system is defined relative to the plane of the graphene film 200, a new coordinate system must be defined to describe the following steps, such as Figure 2G As shown in FIG. , the X-axis remains unchanged, but a new plane is defined here as the Y'Z' plane. In the new coordinate system, the graphene sheet 203 is aligned with the X-axis, so at a macroscopic level, the thermal conductivity in the X-direction is higher than in the Y' and Z' directions.

[0051] Then, if Figure 2HAs shown, a plurality of blocks 208a-d are attached to each other 106 using an adhesive to form a block 210, which is composed of a first plurality of blocks 208a,c having a first rotational alignment about a first axis (X) and a second plurality of blocks 208b,d having a second rotational alignment about the first axis (X), the second rotational alignment being different from the first rotational alignment.

[0052] The adhesive is cured 108 to form a block 210 from the plurality of blocks comprising the graphene film. Forming the block 210 may also include using a pressing tool. In addition, the different blocks may be placed in a suitable holder to facilitate alignment of the different blocks, dispensing of the adhesive, pressing, and curing.

[0053] Figure 2I The final step shown includes cutting 110 the block 210 along its Y'Z' plane defined by a plane perpendicular to the X axis, thereby forming a thermally conductive film 212 having graphene sheets aligned perpendicular to the plane of the thermally conductive film (here, the Y'Z' plane). The block 210 is cut into slices of appropriate thickness. The thermally conductive film 212 is shown in FIG. Figure 2J , wherein it can be seen that the first plurality of region portions 214a, c of the thermally conductive film 212 include graphene films having a first rotation alignment around the X-axis, and the second plurality of region portions 214b, d of the thermally conductive film 212 include graphene films having a second rotation alignment around the X-axis.

[0054] After cutting, the surface of the thermally conductive film 212 may be polished to make the surface smooth. The surface roughness of the final thermally conductive film is 212, preferably less than 1 μm.

[0055] With reference to the above-described manufacturing method, the remaining portions of the graphene film are actually thin strips attached to each other by adhesive, wherein the strips are aligned in different directions within the plane of the thermally conductive film 212 . Figure 2E The block of laminated film 206 shown has higher mechanical strength in the Y direction than in the Z direction because tensile stress in the Z direction may cause delamination. Therefore, if a thin film is produced by cutting the laminated film along the YZ plane, the mechanical strength of the resulting film will be non-uniform in the YZ plane, which may be undesirable in some applications.

[0056] Figure 2JThus, a graphene-based thermally conductive film 212 is described, comprising a plurality of graphene film strips arranged such that the graphene sheets of the graphene film are aligned in a direction perpendicular to the Y'Z' plane of the thermally conductive film 212. The thermally conductive film 212 includes: a plurality of first area portions 214a, c, which include graphene film strips having a first rotational alignment in the Y'Z' plane of the thermally conductive film; and a plurality of second area portions 214b, d, which include graphene film strips having a second rotational alignment in the Y'Z' plane of the thermally conductive film 212, the second rotational alignment being different from the first rotational alignment. In the illustrated example, the graphene strips of the first area portions 214a, c are aligned with the Y' axis, and the graphene strips of the second area portions 214b, d are aligned with the Z' axis and are therefore rotated 90° relative to the graphene strips of the first area portions 214a, c. The illustrated thermally conductive film 212 includes only a small number of area portions for ease of understanding. It will be readily apparent to those skilled in the art that the film may be formed over a large area and have a large number of distinct area portions, for example, arranged in a checkerboard pattern.

[0057] Figure 3 is a flow chart outlining the general steps of a method according to one embodiment of the present invention, and the method will be further referenced to schematically showing the method steps. Figure 4A -F describes.

[0058] In most cases, the method is similar to the method described above with reference to Figures 2-3. The method includes providing 300 a laminated film 206 comprising a plurality of graphene film 200 layers in the same manner as described above.

[0059] A first heat sink structure 400 is formed 302 from the laminate film 206 having a base plate 402 in the YZ plane and a plurality of posts 403 extending in the X direction with gaps between the posts, as shown. Figure 4A In one embodiment, the pillars 403 have a square cross-section, and the gaps have the same size and shape as the pillars 403, whereby the gaps and pillars 403 form a checkerboard pattern when viewed from above (ie, in the x-direction).

[0060] Next, a second heat sink structure 404 is formed, which also has a base plate 406 in the YZ plane and a plurality of pillars 405 extending in the X direction with gaps between the pillars 405. However, the pillars 405 of the second heat sink structure 404 have an arrangement and cross-section that corresponds to the gaps between the pillars 403 of the first heat sink structure 400. Correspondingly, the gaps between the pillars 405 in the second heat sink structure 404 correspond to the pillars 403 of the first heat sink structure 400. In the example shown, the pillars 405 and the gaps of the second heat sink structure 404 form a checkerboard pattern.

[0061] The next step includes rotating 306 the second heat sink structure 404 about the X-axis, and in the example presented, the second heat sink structure 404 is rotated 90°.

[0062] like Figure 4B As shown, the next step includes: attaching 308 the second heat sink structure 404 to the first heat sink structure 400 by adhesive so that the posts 405 of the second heat sink structure 404 fill the gaps between the posts 403 of the first heat sink structure 400 and so that the rotational alignment of the first heat sink structure 400 about the X-axis is different from the rotational alignment of the second heat sink structure 404 about the X-axis. Figure 4C As shown, the first and second heat sink structures 400, 404 are connected together to form a substantially solid structure 408. It may be necessary to cure the adhesive by applying heat and pressure to properly adhere the two structures 400, 404 to each other and form a solid material. The reference coordinate system is herein referenced with reference to Figure 2G The same approach is changed and the base plate now lies in the Y'Z' plane.

[0063] The base plates 402, 406 from the first and second heat sink structures 400, 404 are then removed 310, as shown in FIG. Figure 4D Thus, block 410 is composed of a first plurality of blocks having a first rotation alignment about the X-axis and a second plurality of blocks having a second rotation alignment about the X-axis, the second rotation alignment being different from the first rotation alignment.

[0064] The final steps include: Figure 4E In the same manner as shown in FIG, the block is cut 312 along the Y'Z' plane to form Figure 4F The thermally conductive film 412 shown in FIG. The thermally conductive film 412 thus has regions 214a-d comprising graphene strips of different rotational pairs about the x-axis, with the graphene sheets aligned perpendicular to the y'z' plane of the thermally conductive film, thereby making the thermal conductivity in the x-direction perpendicular to the plane of the film higher than in the y'z' plane. Thus, a manufacturing method with the potential for large-scale production is described. The heat sink structure can be formed, for example, by laser cutting. Furthermore, the pillars can be of many different geometries while still obtaining a thermally conductive film with the desired properties.

[0065] Figure 5 An exemplary embodiment of a thermally conductive film 500 comprising hexagonal area portions 502a-c is schematically shown, wherein adjacent portions have different rotational alignments, which may be achieved by rotating adjacent wetted areas by 60° or 120°.

[0066] Although the invention has been described with reference to exemplary embodiments thereof, many different alternatives, modifications, etc. will become apparent to those skilled in the art. Furthermore, it should be noted that parts of the method may be omitted, interchanged, or arranged in various ways, and the method may still perform the functions of the invention.

[0067] Moreover, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The fact that certain measures are recited in mutually different dependent claims does not mean that a combination of these measures cannot be used to advantage.

Claims

1. A method of manufacturing a laminated graphene-based thermally conductive film (212), the laminated graphene-based thermally conductive film comprising vertically aligned graphene, the method comprising: providing (100) a laminate film (206), the laminate film comprising a plurality of graphene film (200) layers separated by an adhesive (204), the graphene film (200) comprising graphene sheets (203) aligned with a graphene film plane, wherein the plane of the graphene film is a first plane (XY) defined by a first axis (X) and a second axis (Y) perpendicular to the first axis; forming (102) a plurality of sections (208a-c) of the laminated film by cutting the laminated film perpendicular to a second plane (YZ) defined by a second axis (Y) and a third axis (Z) perpendicular to each of the first and second axes; A subset of the plurality of blocks is rotated (104) about a first axis (X); attaching (106) the plurality of tiles to one another using an adhesive to form a block (210) comprised of a first plurality of tiles having a first rotational alignment about a first axis (X) and a second plurality of tiles having a second rotational alignment about the first axis (X), the second rotational alignment being different from the first rotational alignment; curing the adhesive (108) to form a block from the plurality of regions comprising the graphene film; and The block is cut (110) along a block plane (Y'Z'), which is defined as perpendicular to a first axis (X), thereby forming a thermally conductive film (212) having graphene sheets aligned perpendicular to the thermally conductive film plane (Y'Z'), such that a first plurality of area portions of the thermally conductive film include graphene films having a first rotation alignment about the first axis (X), and a second plurality of area portions of the thermally conductive film include graphene films having a second rotation alignment about the first axis (X).

2. The method according to claim 1, wherein Cutting the laminated film includes cutting square sections, and rotating a subset of the plurality of sections includes rotating every other section by 90° about a first axis (X).

3. The method according to claim 1, wherein Cutting the laminated film includes cutting hexagonal blocks, and rotating includes rotating each block by ±60° or ±120° compared to an adjacent block such that no two adjacent blocks have the same rotation alignment about the first axis.

4. A method as claimed in any preceding claim, wherein: Cut the laminated film using wire cutting, sawing, or laser cutting.

5. A method as claimed in any preceding claim, wherein: Curing the adhesive involves applying pressure and heat to the block.

6. A graphene-based thermally conductive film manufactured by the method according to any one of the preceding claims.

7. A method of manufacturing a laminated graphene-based thermally conductive film (212), the laminated graphene-based thermally conductive film comprising vertically aligned graphene, the method comprising: providing (300) a laminate film (206) comprising a plurality of graphene film (200) layers separated by an adhesive (204), the graphene film (200) comprising graphene sheets aligned with a graphene film plane, wherein the plane of the graphene film is a first plane (XY) defined by a first axis (X) and a second axis (Y) perpendicular to the first axis; forming (302) a first heat sink structure (400) from a laminate film, the first heat sink structure (400) having a base plate (402) and a plurality of posts (403) extending along a first axis (X) with gaps between the posts in a second plane (YZ) defined by a second axis (Y) and a third axis (Z) perpendicular to each of the first and second axes; forming (304) a second heat sink structure (404) from the laminate film, the second heat sink structure (404) having a base plate (406) and a plurality of posts (405) extending along a first axis (X) in a second plane (YZ) defined by a second axis (Y) and a third axis (Z) perpendicular to each of the first and second axes; rotating (306) the second heat sink structure about the first axis; connecting (308) the second heat sink structure to the first heat sink structure with an adhesive so that the posts of the second heat sink structure fill gaps between the posts of the first heat sink structure and so that the rotational alignment of the first heat sink structure about the first axis is different from the rotational alignment of the second heat sink structure about the first axis; removing (310) the base plates of the first and second heat sink structures to form a block (410) consisting of a first plurality of segments having a first rotational alignment about a first axis (X) and a second plurality of segments having a second rotational alignment about the first axis (X), the second rotational alignment being different from the first rotational alignment; and The block is cut (312) along a block plane (Y'Z'), which is defined as perpendicular to a first axis (X), thereby forming a thermally conductive film (212) having graphene sheets aligned perpendicular to the thermally conductive film plane (Y'Z'), such that a first plurality of area portions (214a, c) of the thermally conductive film include graphene films having a first rotation alignment about the first axis (X), and a second plurality of area portions (214b, d) of the thermally conductive film include graphene films having a second rotation alignment about the first axis (X).

8. A graphene-based thermally conductive film comprising a plurality of graphene film strips arranged so that the graphene sheets of the graphene film are aligned in a direction perpendicular to the plane (Y'Z') of the thermally conductive film, wherein: The thermally conductive film comprises: a plurality of first area portions (214a, c) comprising graphene film strips having a first rotation alignment in the plane of the thermally conductive film; and A plurality of second area portions (214b, d) comprising graphene film strips having a second rotation pair of lines in the plane of the thermally conductive film, the second rotation pair of lines being different from the first rotation pair of lines.

9. The graphene-based thermally conductive film according to claim 8, wherein: The plurality of first area portions and second area portions have a rectangular shape.

10. The graphene-based thermally conductive film according to claim 9, wherein: Each first area portion comprises a graphene film strip that is rotated by 90° in the plane of the thermally conductive film compared to each second area portion.

11. The graphene-based thermally conductive film according to claim 8, wherein: The plurality of first area portions and second area portions have a hexagonal shape.

12. The graphene-based thermally conductive film according to claim 11, wherein: Each first area portion comprises a graphene film strip that is rotated by ±60° or ±120° in the plane of the thermally conductive film compared to each second area portion.

13. An electronic component comprising: electronic components; cooling means arranged to dissipate heat from the electronic components; and The graphene-based thermally conductive film according to any one of claims 8 to 12, wherein the graphene-based thermally conductive film is sandwiched between an electronic component and a cooling device.

14. The electronic component according to claim 13, wherein The cooling device is a radiator.

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