Polymer-impregnated graphene-reinforced thermal interface pad and method for manufacturing the same

Abstract

A method for manufacturing a thermal interface film, including the following steps: A stack (100) of graphene-based films (101) is provided (200); A stack of graphene-based films is pressed (202) between a first mold (102, 402) and a second mold (104, 404) to form a compressed film (106), wherein at least one of the first and second molds has a profiled surface; The process involves impregnating a compressed film with a polymer (108) (204) to form an impregnated film (110); Curing the impregnated film (110) (206); and The cured impregnated film is cut perpendicular to the plane of the graphene-based film (208) to form a graphene-reinforced thermal interface pad (116).

Description

Technical Field

[0001] The present invention relates to the field of microelectronics packaging, and more particularly to thermal interface materials where heat dissipation is a critical issue.

Background Art

[0002] As the latest electronic devices and systems continue to be developed, the increase in their power density has also caused an increase in the operating temperature. Therefore, effective thermal management has become extremely important for removing the large amount of heat required to ensure high performance and long-life reliability. The thermal conductivity of conventional thermal interface materials (TIMs), which are very important elements for heat dissipation, is often less than 10 W / mK at most, and usually about 4 or 5 W / mK in the vertical direction. Therefore, in order to solve this problem, a great deal of effort has been made in the development of high-performance TIMs based on carbon materials (e.g., graphite nanoplatelets, carbon nanotubes, and carbon fibers).

[0003] However, there is still room for further improvement in thermal interface materials strengthened with graphene.

Summary of the Invention

Problems to be Solved by the Invention

[0004] In view of the above and other drawbacks of the prior art, an object of the present invention is to provide an improved high thermal conductivity interface material and a method for manufacturing such a material.

Means for Solving the Problems

[0005] According to a first aspect of the present invention, there is provided a method for manufacturing a thermal interface pad, the method comprising the following steps: Providing a stack of graphene-based films (200); Placing the above stack of graphene-based films into a first profiled mold; The above stack of graphene-based films is pressed between a first mold and a second mold to form a compressed film, wherein at least one of the first mold and the second mold has a non-flat profiled surface; Impregnating the above-mentioned compressed film with a polymer to form an impregnated film; Curing the above-mentioned impregnated film; and The cured impregnated film is cut perpendicular to the plane of the graphene-based film to form a graphene-reinforced thermal interface pad, wherein the strips of graphene film of the graphene-reinforced thermal interface pad follow at least one of the non-flat profiles of the first and second molds in the plane of the pad.

[0006] Graphene-based films have been shown to sometimes possess very high in-plane thermal conductivity exceeding 1000-3000 W / mK, and the present invention aims to form a graphene-reinforced thermal interface pad having high thermal conductivity in the vertical direction by mounting a graphene-based film impregnated with a polymer material. The term "pad" should be interpreted as meaning that the spread in the xy plane is substantially greater than the thickness of the material. Thus, the vertical direction is considered to be the direction perpendicular to the xy plane of the film, i.e., the z direction. The described thermal interface pad can be formed as a pad or patch of a size suitable for placement, for example, between a heat-generating electrical component and a cooling element.

[0007] In particular, the present invention is based on the recognition that the mechanical properties of a thermal interface pad can be improved by forming a thermal interface pad in which a stack (lamination) of graphene-based films is arranged to follow a profile rather than being flat. In particular, the flexibility of the pad is improved, thereby allowing for further bending and / or stretching of the pad without damaging the pad and without delamination of the graphene-based film layers.

[0008] Furthermore, the softness of the thermal interface pad can be improved by up to 2 to 5 times compared to thermal interface materials based on non-layered and / or planar structures. In other words, the compressibility of thermal interface pads manufactured by the described method is higher than that of thermal interface pads that do not use profiled molds. The increased softness helps to increase the contact area and fill small gaps between the thermal interface pad and the surface of the component.

[0009] The mechanical and thermal properties of a thermal interface pad can be controlled, for example, by controlling the ratio of polymer to graphene-based film within it. In practice, there may be a trade-off between the mechanical and thermal properties of the film; a higher proportion of polymer improves mechanical properties but decreases overall thermal conductivity.

[0010] With respect to the present invention, at least one of the non-planar profiled surfaces of the first and second types should be interpreted as a macroscopic profiled surface having a shape that is subsequently transferred to a stack of graphene-based films. Typically, the surface is visibly non-planar.

[0011] According to one embodiment of the present invention, the first mold has a concave or undulating profile. The second mold may be flat or may have a profile that reflects the profile of the first mold. If the first mold has a concave profile, the second mold may have a corresponding convex profile, so that the resulting compressed film has a curved or "U-shaped" surface profile that follows the profiles of the first and second molds. From a curved mold, a thermal interface pad is obtained in which curved strips of graphene-based film are laminated on the plane of the pad, which results in improved mechanical properties of the thermal interface.

[0012] Furthermore, in embodiments in which the first mold has an undulating or corrugated profile, the second mold may have a corresponding corrugated profile, thereby causing the resulting compressed film to have an undulating or corrugated surface profile.

[0013] According to one embodiment of the present invention, the first and / or second molds preferably have a minimum radius in the range of 5 cm to 50 cm. The appropriate radius can be selected, for example, based on the thickness and mechanical properties of the graphene-based film used as the starting material, and also based on the number of layers of the film. If the radius is too small, it may lead to film breakage, while if the radius is too large, the desired effect in terms of improving mechanical properties may not be obtained.

[0014] According to one embodiment of the present invention, the first mold has a repeating triangular profile, and the second mold may be flat or have a corresponding triangular profile shifted by half a period, so that the resulting compressed film has triangular surface profiles on both sides of the film. The angle between adjacent triangles is preferably in the range of 20° to 150°, where the appropriate angle can be selected based on the properties of the graphene-based film. As with curved profiles, if the angle is too small, there is a risk of the film breaking, and if the angle between adjacent triangles is too large, the favorable mechanical effects may not be realized.

[0015] According to one embodiment of the present invention, the first mold is a cylindrical mold. In this case, the cylindrical mold may have a triangular or undulating profile to achieve a desired profile of the compressed film. Furthermore, each of the first and second molds may be a mold with a cylindrical profile, thereby allowing a stack of graphene-based films to be pressed between two cylindrical rolls.

[0016] According to one embodiment of the present invention, pressing a stack of graphene-based films between a first mold and a second mold involves applying a pressure in the range of 1 MPa to 30 MPa.

[0017] According to one embodiment of the present invention, impregnating a compressed film with a polymer includes using vacuum impregnation. Furthermore, the polymer has a molecular weight in the range of 10,000 g / mol to 500,000 g / mol.

[0018] According to one embodiment of the present invention, curing involves heating the impregnated film to a temperature in the range of 80°C to 200°C and maintaining that temperature for a period of time in the range of 1 hour to 4 hours to solidify the polymer.

[0019] According to one embodiment of the present invention, cutting a cured impregnated film advantageously involves using wire cutting or blade cutting. The advantage of using wire cutting or blade cutting is that it provides a low surface roughness, which is important for thermal interface pads used for heat conduction between two planes.

[0020] According to one embodiment of the present invention, this method further includes coating the edges of the thermal interface pad with a polymer such as silicone, acrylic, polyurethane, polyethylene, polyimide, parylene, or epoxy material. By coating the edges, wear of the pad is avoided and the mechanical properties of the thermal interface pad are further improved.

[0021] According to one embodiment of the present invention, this method further includes coating the edges of a graphene-reinforced thermal interface pad with a polymer or epoxy material having a viscosity in the range of 1,000 to 1,000,000 mPa·s. The edge coating can improve the tensile strength of the interface pad in the direction perpendicular to the alignment direction by 20% to 100% compared to a thermal interface pad without edge coating. As a result, the coating prevents delamination of the thermal interface pad, reduces the risk of edge wear, and further reduces the amount of particles released from the thermal interface pad.

[0022] According to one embodiment of the present invention, the thermal interface pad has a thermal conductivity in the direction perpendicular to the plane of the film, in the range of 25 W / mK to 200 W / mK. The thermal conductivity of the thermal interface pad in the direction perpendicular to the plane is an important parameter that determines the efficiency of the thermal interface pad as a thermal interface material positioned to dissipate heat from heat-generating components.

[0023] According to an embodiment of the second aspect of the present invention, a polymer-impregnated graphene-reinforced thermal interface pad is provided, comprising: A plurality of strips of a polymer-impregnated graphene-based film extending in the plane of the pad, wherein at least a portion of the strips are arranged in a curved or angled pattern along the direction in which the strips extend in the plane of the pad. The curved pattern may be a single curved pattern or a wavy pattern, and the angled pattern may be, for example, a triangular pattern.

[0024] According to one embodiment of the present invention, the polymer-impregnated graphene-reinforced thermal interface pad further comprises a coating in the form of a polymer or epoxy material disposed at an edge portion of the polymer-impregnated graphene-reinforced thermal interface pad.

[0025] The effects and features of this second aspect of the present invention are substantially the same as those described above in relation to the first aspect of the present invention.

[0026] Further features of the present invention and advantages according to the present invention will become apparent by considering the appended claims and the following description. It will be recognized by those skilled in the art that, without departing from the scope of the present invention, different features of the present invention can be combined to form embodiments other than those described below.

[0027] Next, these and other aspects of the present invention will be described in more detail with reference to the accompanying drawings showing examples of embodiments of the present invention.

Brief Description of the Drawings

[0028] [Figure 1A] Figures 1A to 1G are diagrams schematically showing the steps of a method according to an embodiment of the present invention. [Figure 1B] Figures 1A to 1G are diagrams schematically showing the steps of a method according to an embodiment of the present invention. [Figure 1C]Figures 1A to 1G are schematic diagrams illustrating the steps of a method according to an embodiment of the present invention. [Figure 1D] Figures 1A to 1G are schematic diagrams illustrating the steps of a method according to an embodiment of the present invention. [Figure 1E] Figures 1A to 1G are schematic diagrams illustrating the steps of a method according to an embodiment of the present invention. [Figure 1F] Figures 1A to 1G are schematic diagrams illustrating the steps of a method according to an embodiment of the present invention. [Figure 1G] Figures 1A to 1G are schematic diagrams illustrating the steps of a method according to an embodiment of the present invention. [Figure 2] Figure 2 is a flowchart illustrating the steps of a method according to an embodiment of the present invention. [Figure 3] Figure 3 is a schematic diagram showing a graphene-reinforced thermal interface pad according to an embodiment of the present invention. [Figure 4A] Figures 4A and 4B schematically show the steps of a method according to an embodiment of the present invention and a graphene-reinforced thermal interface pad. [Figure 4B] Figures 4A and 4B schematically show the steps of a method according to an embodiment of the present invention and a graphene-reinforced thermal interface pad. [Figure 5] Figure 5 is a schematic diagram showing the steps of a method according to an embodiment of the present invention. [Figure 6] Figure 6 is a schematic diagram showing the steps of a method according to an embodiment of the present invention. [Figure 7A] Figures 7A to 7C schematically show the steps of a method according to an embodiment of the present invention and a graphene-reinforced thermal interface pad. [Figure 7B] Figures 7A to 7C schematically show the steps of a method according to an embodiment of the present invention and a graphene-reinforced thermal interface pad. [Figure 7C] Figures 7A to 7C schematically show the steps of a method according to an embodiment of the present invention and a graphene-reinforced thermal interface pad. [Modes for carrying out the invention]

[0029] Next, the present invention will be described in more detail hereafter with reference to the accompanying drawings illustrating currently preferred embodiments of the invention. However, the present invention may be embodied in many different forms and should not be construed as being limited to the embodiments described herein, but rather these embodiments are provided for thoroughness and completeness and to fully convey the scope of the invention to those skilled in the art. Throughout, the same reference numerals refer to the same elements.

[0030] Figures 1A to 1G schematically show a method for manufacturing a thermal interface pad 118 according to an embodiment of the present invention. Figures 1A to 1G will be further explained with reference to Figure 2, which shows a flowchart illustrating the steps of the method.

[0031] The first step in the method for manufacturing the thermal interface pad 118 includes providing a stack 100 (200) of graphene-based films, as shown in Figure 1A. The stack 100 of graphene-based films may comprise any number of films from 10 to 2000, depending on the size required for the pad to be manufactured and the thickness and size of the individual graphene-based films.

[0032] Since the manufacture of graphene-based films has been reported elsewhere, only a general description is provided herein. For example, a graphene film suitable for use in relation to the present invention can be formed by providing a graphene oxide sheet in an aqueous suspension; providing a substrate; supplying this suspension onto the substrate; heating the suspension on the substrate to form a graphene film by self-assembly; peeling the graphene film from the substrate; performing thermal annealing of the graphene film in an inert environment at a temperature in the range of 2800 to 3300°C; and pressing the graphene film at a pressure in the range of 50 to 300 MPa. The above method provides a large-scale method for manufacturing self-supporting graphene-based films (GF) having very high in-plane thermal conductivity. However, it should be noted that graphene-based films manufactured by other methods can also be used in the method herein, provided that the graphene-based film has sufficiently high in-plane thermal conductivity.

[0033] A stack 100 of graphene-based films is placed between a first mold 102 and a second mold 104. In Figure 1B, the first mold 102 has a concave shape, and the second mold 104 has a convex shape that reflects the shape of the first mold 102.

[0034] The fact that the first and / or second molds have profiled surfaces means that a surface profile exists on a scale such that the majority of the film in the film stack takes on a shape corresponding to the mold's profile.

[0035] The stack 100 of graphene-based films is then pressed (202) between a first mold 102 and a second mold 104, as shown in Figure 1C, to form a compressed film 106. Here, all films in the stack 100 can take on the curved shape of the first and second molds 102, 104. Preferably, pressing (202) involves applying a pressure in the range of 1 MPa to 30 MPa. Thereafter, the resulting compressed film 106 shown in Figure 1C has a U-shaped profile that follows the first and second molds.

[0036] The next step, schematically shown in Figure 1D, includes impregnating the compressed film with polymer 108 (204) to form an impregnated film 110. Polymer impregnation is carried out, for example, by vacuum impregnation, where the compressed film 106 is 10 -2 ~10 -6 torr(1.3 Pa ~ 1.3 × 10 ー4 The polymer 108 is placed in a sealed container 112 where a vacuum of the range of Pa is formed, and the polymer 108 is supplied into the container to impregnate the compression film, thereby forming a polymer-impregnated film 110. The polymer used for impregnation may be silicone, epoxy, acrylic, or polyurethane, or other polymers having similar properties, and the polymer preferably has a molecular weight in the range of 10,000 g / mol to 500,000 g / mol. It may also be possible to use wax or a similar material for impregnating the compression film.

[0037] Next, as shown in Figure 1E, the polymer-impregnated film 110 is cured (206) in the heating chamber 113 to solidify the polymer. Depending on the type of polymer used, the temperature and time for curing the polymer may vary. In an example embodiment, curing (206) involves heating the impregnated film to a temperature in the range of 80°C to 200°C and maintaining that temperature for a time in the range of 1 to 4 hours.

[0038] After curing, the cured impregnated film 116 is cut using a wire saw 114 in a direction perpendicular to the plane of the graphene-based film (208), as shown in Figure 1F, to form the base of the graphene-reinforced thermal interface pad 118 shown in Figure 1G. The graphene-reinforced thermal interface pad 118 may be used directly as cut from the cured impregnated film 116, or it may subsequently be cut into any suitable shape.

[0039] The plane of the cured impregnated film 116 is defined as the xy plane in Figure 1F, and the film 116 is therefore cut in the z direction, so that the resulting polymer-impregnated graphene-reinforced thermal interface pad 118 comprises multiple strips 120 of polymer-impregnated graphene-based film extending in the plane of the pad 118, which is the xz plane using the coordinate system of Figure 1F. Although wire cutting is shown in Figure 1F, other cutting methods such as blade cutting are also possible. This allows for easy control of the thickness of the pad 118 in the range of approximately 50 μm to several millimeters.

[0040] Furthermore, at least a portion of the strip 120 is arranged in a curved or angled pattern along the direction in which the strip 120 extends, in the plane of the pad 118, and further examples of possible orientations of the graphene-based film strip 120 are described below.

[0041] In the curved mold, a thermal interface pad 118 is obtained in which curved strips 120 of graphene-based film are laminated on the plane of the pad 118, which results in improved mechanical properties of the thermal interface pad 118.

[0042] A method for manufacturing a thermal interface pad may further include coating the edges of the thermal interface pad with a polymer or epoxy material having a viscosity in the range of 1,000 to 1,000,000 mPa·s. A thermal interface pad 300 having coated edges 302 is schematically shown in Figure 3. The coating can be applied, for example, by immersing the pad in the coating material. The coating improves the tensile strength of the pad in the plane of the pad in a direction perpendicular to the direction in which the strip 120 of graphene-based film extends, which is shown as the z direction in Figure 3. Depending on the type of coating, the tensile strength can be improved by 20% with a silicone coating and by up to 100% with an epoxy coating. The coating also prevents particle shedding from the pad and reduces the risk of delamination.

[0043] At least one of the first mold 402 and the second mold 404 may have a ridged or corrugated surface profile, and in Figure 4A, both the first and second molds 402, 404 have a corrugated surface profile, resulting in a thermal interface pad 406 having strips 408 of graphene-based film aligned in a corrugated pattern on the plane of the thermal interface pad 406, as shown in Figure 4B. However, non-uniform and / or free-form surface profiles of the first and / or second molds may also be possible. The first and / or second profiled molds preferably have a minimum radius of curvature in the range of 5 cm to 50 cm, and the appropriate radius can be selected based on, for example, the thickness of the graphene-based film stack, the ratio of polymer to graphene-based film, and the desired mechanical properties of the thermal interface pad.

[0044] Furthermore, although the thermal interface pad is illustrated as a rectangular pad, the pad may be of any shape to suit any given application. Since the pad can be cut to the appropriate shape using conventional cutting methods, a free-form thermal interface pad is possible.

[0045] Figure 5 schematically illustrates an implementation in which a stack of graphene-based films 101 is pressed between the roller and the flat surface, with the first mold 502 being a roller having a profiled surface and the second mold (not shown) being a flat surface. The first mold 502 has a triangular surface with ridges extending along the axial direction of the roller. The angle between adjacent ridges is 90° here, and the distance between peaks is 150 μm, although the angle may preferably be in the range of 20° to 160°. It is also possible to provide opposing rollers so that the stack of graphene-based films 100 is pressed between two rollers.

[0046] Figure 6 shows an implementation similar to that in Figure 5, but differs in that the ridge portion of the first profiled mold 602 is positioned to extend along the circumference of the mold 602.

[0047] Figure 7A schematically shows a compressed film 702 pressed between a first profiled mold 502, 602 having a triangular surface profile and a second mold having a flat surface, and Figure 7B shows a compressed film 704 pressed between the first and second molds 502, 602, each having a triangular surface profile. The compressed films 702, 704 can be formed, for example, by using rollers 502, 602 of the type shown in Figures 5 and 6. The angles β1 and β2 indicate the corresponding opening angle β1 and peak angle β2 of the triangle in the triangular profile.

[0048] Figure 7C shows a thermal interface pad 706 with strips 708 of graphene film arranged in a triangular pattern, the shown pad can be formed from a compressed and polymer-impregnated film, as shown in Figure 7B.

[0049] While the present invention has been described with reference to its specific exemplary embodiments, many different changes, modifications, and similarities will be apparent to those skilled in the art. It should also be noted that parts of the method may be omitted, replaced, or rearranged in various ways, and the method will still be capable of performing the functions of the present invention.

[0050] In addition, modifications to the disclosed embodiments can be understood and implemented by those skilled in the art in practicing the claimed inventions by examining the drawings, disclosures, and accompanying claims. In the claims, the word “comprising” does not exclude other elements or processes, and the indefinite article “a” or “an” does not exclude plurals. The mere fact that certain means are described in different dependent claims does not indicate that a combination of these means cannot be used advantageously.

Claims

1. A method for manufacturing a thermal interface pad (118, 404), comprising the following steps: To provide (200) a stack (100) of graphene-based films (101); Pressing the stack of graphene-based films between a first mold (102, 402, 502, 602) and a second mold (104, 404) (202) to form a compressed film (106), wherein at least one of the first mold and the second mold has a non-flat profile surface; Impregnating the compressed film with a polymer (108) (204) to form an impregnated film (110); (206) curing the impregnated film (110); and The cured impregnated film is cut in a direction perpendicular to the plane of the graphene-based film (208) to form a graphene-reinforced thermal interface pad (118), wherein the strips of graphene film of the graphene-reinforced thermal interface pad follow the non-flat profile of at least one of the first and second molds in the plane of the pad.

2. The method according to claim 1, wherein the first mold has a concave profile.

3. The method according to claim 1, wherein the first mold has an undulating profile.

4. The method according to claim 2 or 3, wherein the first mold has a minimum radius in the range of 5 cm to 50 cm.

5. The method according to claim 1, wherein the first type has a repeating triangular profile.

6. The method according to claim 5, wherein the angle of opening between adjacent triangles is in the range of 20° to 150°.

7. The method according to any one of claims 1 to 6, wherein the first mold is a cylindrical mold.

8. The method according to any one of claims 1 to 6, wherein the second type has a profile that reflects the profile of the first type.

9. The method according to any one of claims 1 to 8, wherein one of the first mold and the second mold has a flat surface.

10. The method according to any one of claims 1 to 9, wherein pressing the stack of graphene-based films between the first mold and the second mold comprises applying a pressure in the range of 1 MPa to 30 MPa.

11. The method according to any one of claims 1 to 10, wherein impregnating the compressed film with a polymer includes using vacuum impregnation.

12. The method according to any one of claims 1 to 11, wherein curing includes heating the impregnated film to a temperature in the range of 80°C to 200°C and maintaining the temperature for a period of time in the range of 1 hour to 4 hours.

13. The method according to any one of claims 1 to 12, wherein the polymer has a molecular weight in the range of 10,000 g / mol to 500,000 g / mol.

14. The method according to any one of claims 1 to 13, wherein cutting the cured impregnated film includes using wire cutting or blade cutting.

15. The method according to any one of claims 1 to 14, further comprising coating the edges of the thermal interface pad with a polymer or epoxy material.

16. The method according to any one of claims 1 to 15, further comprising coating the edges of the thermal interface pad with a polymer or epoxy material having a viscosity in the range of 1,000 to 100,000 mPa·s.

17. The method according to any one of claims 1 to 16, wherein the thermal interface pad has a thermal conductivity in the direction perpendicular to the plane of the film, in the range of 25 W / mK to 200 W / mK.

18. A polymer-impregnated graphene-reinforced thermal interface pad (118) comprising the following: A plurality of strips (120) of polymer-impregnated graphene-based film extending in the plane of the pad, wherein at least a portion of the strips are arranged in a curved or angled pattern along the direction in which the strips extend in the plane of the pad.

19. The polymer-impregnated graphene-reinforced thermal interface pad according to claim 18, wherein the pattern of the strip is a wave-shaped pattern.

20. The polymer-impregnated graphene-reinforced thermal interface pad according to claim 18, wherein the pattern of the strip is a triangular pattern.

21. The polymer-impregnated graphene-reinforced thermal interface pad according to any one of claims 18 to 20, further comprising a coating polymer or epoxy material disposed on the edge of the polymer-impregnated graphene-reinforced thermal interface pad.

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