GRAPHENE BASED HEAT SINK AND METHOD FOR MANUFACTURING THE HEAT SINK

Abstract

Heat sink and method of manufacturing a graphene based heat sink, the method comprising: providing a first and second graphene film; arranging a layer of nanoparticles on a surface of the first and second graphene film to improve an adhesion strength between the graphene films; attaching the second graphene film to the first graphene film by means of an adhesive and the layer of nanoparticles; forming a laminated graphene film comprising a number of graphene film layers by repeating the steps, wherein the laminated graphene film is formed to have an anisotropic thermal conductivity; assembling a plurality of laminated graphene films by applying pressure and heat to cure the adhesive to form a graphene block; and removing selected portions of the graphene block to form a heat sink comprising fins extending from a base plate of the heat sink.

Claims

1. A laminated graphene heat sink comprising: a base plate and a plurality of fins extending from the base plate; wherein the base plate and the fins comprise a plurality of layers of graphene film reaching from a bottom surface to a top surface of the heat sink, each layer of graphene film being separated from an adjacent layer of graphene film by an adhesive layer, and each layer of graphene film having an anisotropic thermal conductivity.

2. The heat sink according to claim 1, wherein the base plate and the fins of the heat sink are formed from a single solid graphene block comprising a plurality of layers of graphene film.

3. The heat sink according to claim 1, wherein the thermal conductivity of a fin is higher in the plane of the fin than in a direction perpendicular to the plane of the fin.

4. The heat sink according to claim 1, wherein the thermal conductivity of a fin is higher in a direction perpendicular to the plane of the fin and in a first direction of the plane of the fin compared to in a second direction of the plane of the fin.

5. The heat sink according to claim 1, wherein the graphite film comprises a plurality of graphene layers having a turbostratic alignment between adjacent graphene layers.

6. The heat sink according to claim 1, wherein a ratio of adhesive in the in the thermally conductive film is in the range of 10 wt % to 90 wt %.

7. The heat sink according to claim 1, wherein the adhesive consists of at least one of, polyurethane, silicone rubber, polyimide, epoxy resin and polyacrylic resin.

8. The heat sink according to claim 1, wherein each adhesive layer further comprises a first layer of nanoparticles arranged at a surface of a first graphene film and a second layer of nanoparticles arranged at a surface of a second graphene film adjacent to the first graphene film, wherein the nanoparticles are embedded in the adhesive.

9. The heat sink according to claim 8, wherein the first and second layer of nanoparticles comprises needle shaped nanoparticles configured to anchor the first graphene film to the second graphene film.

10. The heat sink according to claim 9, wherein the needle shaped nanoparticles comprises one of Al.sub.2O.sub.3, SiO.sub.2, Fe.sub.2O.sub.3, NiO.sub.2, Cr.sub.2O.sub.3, ZnO, Ag, Al, Cu, Ni, Cr, Ti, Mo, Fe, Mg and Li.

11. The heat sink according to claim 9, wherein the needle shaped nanoparticles have a length in the range of 5 to 100 nm.

12. A laminated graphene heat sink comprising: a base plate and a plurality of fins extending from the base plate; wherein the base plate and the fins comprise a plurality of layers of graphene film reaching from a bottom surface to a top surface of the heat sink, wherein the plurality of layers of graphene film are separated from an adjacent layer of graphene film by an adhesive layer, the adhesive layer comprising a first layer of nanoparticles arranged at a surface of a first graphene film and a second layer of nanoparticles arranged at a surface of a second graphene film adjacent to the first graphene film, wherein the nanoparticles are embedded in the adhesive, and wherein the plurality of layers of graphene film have an anisotropic thermal conductivity.

13. The heat sink according to claim 12, wherein the base plate and the fins of the heat sink are formed from a single solid graphene block comprising a plurality of layers of graphene film.

14. The heat sink according to claim 12, wherein the thermal conductivity of a fin is higher in the plane of the fin than in a direction perpendicular to the plane of the fin.

15. The heat sink according to claim 12, wherein the thermal conductivity of a fin is higher in a direction perpendicular to the plane of the fin and in a first direction of the plane of the fin compared to in a second direction of the plane of the fin.

16. The heat sink according to claim 12, wherein the first and second layer of nanoparticles comprises needle shaped nanoparticles configured to anchor the first graphene film to the second graphene film.

17. The heat sink according to claim 16, wherein the needle shaped nanoparticles comprises one of Al.sub.2O.sub.3, SiO.sub.2, Fe.sub.2O.sub.3, NiO.sub.2, Cr.sub.2O.sub.3, ZnO, Ag, Al, Cu, Ni, Cr, Ti, Mo, Fe, Mg and Li.

18. The heat sink according to claim 16, wherein the needle shaped nanoparticles have a length in the range of 5 to 100 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing an example embodiment of the invention, wherein:

[0031] FIG. 1 is a flow chart outlining general steps of a method according to an embodiment of the invention;

[0032] FIGS. 2A-2F schematically illustrate steps of a method according to an embodiment of the invention;

[0033] FIG. 3 schematically illustrates a detail of a method according to an embodiment of the invention; and

[0034] FIG. 4 schematically illustrates a heat sink according to an embodiment of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0035] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Like reference characters refer to like elements throughout. FIG. 1 is a flow chart outlining general steps of a method according to an embodiment of the invention, and the method will be described with further reference to FIG. 2 schematically illustrating steps of the method.

[0036] The method comprises providing 100 a first graphene film 200 and providing 102 a second graphene film 202 as illustrated in FIG. 2A. A graphene film suitable for use in the present context can be formed by providing graphene oxide sheets in an aqueous suspension; providing a substrate; providing the suspension on the substrate; heating the suspension on the substrate to form a graphene based film by means of self assembly; detaching the graphene based film from the substrate; performing thermal annealing of the graphene based film at a temperature in the range of 2800−3300° C. in an inert ambient; and pressing the graphene based film at a pressure in the range of 50-300 MPa. By means of the above described method a large-scale achievable method of producing a freestanding graphene film (GF) with an ultra-high in-plane thermal conductivity is provided. Further details of a graphene film having a high in-plane thermal conductivity and a method for manufacturing such a film can be found in PCT/SE2017/050185.

[0037] The graphene film 200, 202 may also comprise a plurality of graphene layers having a turbostratic alignment between adjacent graphene layers. It has been found that a graphite film with turbostratic alignment between adjacent graphene layers may exhibit an improved in-plane thermal conductivity in comparison to other known graphene-based and graphite heat spreading materials. Further details of a graphene film comprising a plurality of graphene layers having a turbostratic alignment between adjacent graphene layers can be found in PCT/SE2018/000009, hereby incorporated by reference.

[0038] Next, illustrated in FIG. 2B, the method comprises arranging 104 a layer of nanoparticles 204 on a surface 206, 208 of the first and second graphene film 200, 202, wherein the nanoparticles 204 are configured to improve an adhesion strength between the first and second graphene films 200, 202. FIG. 2C illustrates the following step of arranging 106 an adhesive 210 on the first graphene film 200.

[0039] The layer of nanoparticles 204 advantageously comprises needle-shaped nanoparticles 204 configured to anchor the first graphene film 200 to the second graphene film 200 by improving the adhesion between the respective graphene film 200, 202 and the adhesive 210. The needle-shaped nanoparticles may consist of one elongated structure having a length in the range of 5 to 100 nm and an aspect ratio between length and width in the range of 5:1 to 50:1.

[0040] However, nanoparticles usable for anchoring may also comprise a plurality of more or less randomly connected needle-like nanostructures, e.g. forming a spider-like nanostructure. Moreover, the described type of nanoparticles can be formed from e.g. Al.sub.2O.sub.3, SiO.sub.2, Fe.sub.2O.sub.3, NiO.sub.2, Cr.sub.2O.sub.3, ZnO, Ag, Al, Cu, Ni, Cr, Ti, Mo, Fe, Mg and Li. Both the nanoparticles and the adhesive may be printed, dispensed or sprayed onto the graphene film.

[0041] Once the nanoparticles 204 and the adhesive 210 is deposited on the graphene film, the second graphene film 202 is attached 108 to the first graphene film 200 by means of the adhesive 210 and the layer of nanoparticles 204 with the resulting laminated graphene film 212 illustrated in FIG. 2D. The nanoparticles 204 will become anchored to irregularities and uneven portions of the graphene film surface, and the adhesive 210 will in turn form a bond to both the graphene film surface and to the nanoparticles. Thereby, the adhesion between the first and second graphene films 200, 202 is significantly improved compared to if only an adhesive would be used.

[0042] According to an illustrative example, a graphene film with a thickness of 10 μm was coated by an adhesive in the form of polydimethylsiloxane belonging to the group of silicone rubbers. Tetrahydrofuran was used as a solvent to adjust the viscosity of polydimethylsiloxane. The concentration of the polydimethylsiloxane in tetrahydrofuran is in the range of 25-75 wt %. The deposition process was performed using a film coater. The coating thickness of polydimethylsiloxane is defined by the thread depth of the coating bar. After coating of the adhesive, the graphene film was heated to approximately 50-70° C. for 1-20 min to remove the tetrahydrofuran. The thickness of the adhesive layer may be selected based on the desired proportion between graphene film and adhesive in the final laminate structure.

[0043] The above description outlines a method for attaching two graphene films 202, 204 to each other. Next, the method comprises forming 110 a laminated graphene film 212 comprising a predetermined number of graphene film layers by repeating the steps of arranging 104 a layer of nanoparticles, arranging 106 an adhesive and attaching 108 a graphene film. By combining a number of laminated graphene films 212 as illustrated in FIG. 2E, or by attaching one graphene layer at the time to a growing stack of graphene layers attached to each other by the described nanoparticles 204 and adhesive 210, a graphene block 214 of desirable thickness can be achieved.

[0044] The graphene block 214 comprising the desired number of layers is laminated 112 by applying pressure using a pressure tool 215 as illustrated in FIG. 2F and by heating to cure the adhesive 210, thereby forming a graphene block 214. The pressure is in the range of 0.1 to 3 MPa. The assembled graphene block 214 is subsequently put into a furnace for curing. The curing temperature is in the range of 80−200° C. and the curing time is in the range of 10 to 300 minutes.

[0045] Cutting may for example be performed using a diamond saw, even though other cutting methods also are possible.

[0046] FIG. 3 schematically illustrates a laminated graphene heat sink 300 comprising a base plate 302 and a plurality of fins 304 extending from the base plate. The fin 304 may also be referred to as a flange. The base plate 302 and the fins 304 comprise a plurality of layers of graphene film 212 reaching from a bottom surface 306 to a top surface 308 of the heat sink 300, each layer of graphene film 212 being separated from an adjacent layer of graphene film by an adhesive layer 210, and each layer of graphene film 212 having an anisotropic thermal conductivity. The heat sink 300 thus comprises vertically aligned layers of the laminated graphene film 212.

[0047] It is also possible to cut the graphene block 214 from the other side, i.e. in a direction perpendicular to the plane of the laminated graphene films 212. Moreover, the graphene block 214 may also be cut at an angle as long as the advantages of the high in-plane thermal conductivity is maintained in at least one direction.

[0048] FIG. 4 is a close up illustration of two graphene films 200, 202 attached to each other where it is shown how the nanoparticles 204 are attached to the surfaces of the two graphene films 200, 202 and embedded in the adhesive 210. Accordingly, the nanoparticles 204 will be present in the adhesive 210, which may be significantly thicker than the length of the nanoparticles 204. Even though the invention has been described with reference to exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Also, it should be noted that parts of the method may be omitted, interchanged or arranged in various ways, the method yet being able to perform the functionality of the present invention.

[0049] Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person 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 mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.