Graphene-based thermal interface pad having a curved surface and method for manufacturing the pad

Abstract

A polymer infiltrated graphene-enhanced thermal interface pad (100, 200) comprising a plurality of strips (102) of polymer infiltrated graphene-based film extending in the plane of the pad, wherein a thickness of the thermal interface 5 pad is different across the area of the pad.

Description

[0001] GRAPHENE-BASED THERMAL INTERFACE PAD HAVING A CURVED

[0002] SURFACE AND METHOD FOR MANUFACTURING THE PAD

[0003] Field of the Invention

[0004] The present invention relates to the field of microelectronics packaging, and especially to thermal interface materials in which heat dissipation is a crucial issue.

[0005] Background of the Invention

[0006] The rapid advancement of electronic technology, particularly in emerging fields such as artificial intelligence (Al), data centers, and autonomous driving, has necessitated the development of increasingly powerful processors and integrated circuits. These components generate substantial amounts of heat during operation, posing a significant challenge for thermal management. Efficient cooling is critical to maintaining the performance, reliability, and longevity of these high-power electronic devices. Overheating can lead to reduced performance, malfunction, and even permanent damage, making thermal management a key focus in the design and development of modem electronic systems.

[0007] Traditional thermal interface materials (TIMs) such as thermal pastes, gels, and phase change materials have been widely used to enhance heat dissipation in electronic components. These materials fill the microscopic gaps between heat-generating components and heatsinks, providing a better thermal path and thereby improving overall thermal conductivity. However, these conventional TIMs have several limitations that impact their long-term effectiveness and reliability. For instance, thermal pastes and gels can suffer from "pumping out" due to thermal cycling and mechanical stresses, leading to a decrease in thermal performance over time. Phase change materials, while effective initially, can degrade and age, further reducing their ability to manage heat in the long term.

[0008] In response to these challenges, advanced materials with superior thermal properties are being explored to improve thermal management in electronic systems. Graphene, known for its exceptional thermal conductivity and mechanical stability, has emerged as a promising candidate for nextgeneration TIMs. Graphene-based TIMs have the potential to outperform traditional materials by offering enhanced thermal conductivity, durability, and reliability. Despite these advantages, integrating graphene into practical TIM solutions that can adapt to the physical and thermal demands of high-power applications remains a challenge.

[0009] One critical issue in high-power electronics applications is the warpage of electronics components, which can negatively impact the thermal interface and reduce the effectiveness of heat transfer. There is thus a need for a thermal interface material that not only provides superior thermal conductivity but also maintains efficient heat transfer despite the warping of electronics components. Accordingly, there is a need for further improvement of graphene-based thermal interface materials.

[0010] Summary

[0011] In view of the desired properties of thermal interface materials, it is an object of the present invention to provide an improved high thermal conductivity interface material and a method for manufacturing the material.

[0012] According to a first aspect of the invention, there is provided a polymer infiltrated graphene-enhanced thermal interface pad comprising: a plurality of strips of polymer infiltrated graphene-based film extending in the plane of the pad, wherein a thickness of the thermal interface pad is different across the area of the pad.

[0013] Graphene-based films have been shown to have very high in-plane thermal conductivity, in excess of 1000-3000 W / mK, and the present invention aims to implement graphene-based films infiltrated with a polymer material to form a graphene enhanced thermal interface pad having a high thermal conductivity in the vertical direction.

[0014] The mechanical and thermal properties of the thermal interface pad can be controlled for example by controlling the ratio between polymer and graphene-based film in the pad. In practice, there may be a trade-off between the mechanical and thermal properties of the film where a larger proportion of polymer would improve the mechanical properties while reducing overall thermal conductivity.

[0015] The claimed thermal interface pad significantly enhances thermal management for high-power electronics devices by incorporating a thermal interface pad with varying thickness across the area of the pad. This design effectively addresses the challenge of warpage, a common issue in electronics components due to thermal cycling and mechanical stresses. When electronics components warp, maintaining consistent thermal contact with traditional flat thermal interface materials becomes difficult, which may lead to reduced cooling efficiency and potentially to overheating. The varying thickness of the thermal interface pad allows it to adapt to physical deformations, ensuring continuous and effective heat transfer regardless of the warpage. The adaptability of the thermal interface pad results in improved cooling performance, preventing hot spots and ensuring the stability and longevity of the electronic components.

[0016] Moreover, the strategic variation in thickness which can be tailored to fit the requirements of a particular application, ensures that the thermal interface pad can provide enhanced thermal contact where it is most needed. Thicker regions of the pad can compensate for gaps caused by warping, maintaining a robust thermal interface and optimal heat dissipation. This design ensures that even as the electronics components experience physical changes, the thermal interface pad continues to perform reliably, effectively managing heat and maintaining consistent thermal performance. By addressing the challenges posed by component warpage, the invention significantly improves the reliability and effectiveness of thermal management in high-power electronics applications, extending the operational life and performance of these systems.

[0017] According to an example embodiment, the thermal interface pad has a convex surface along at least one direction of the plane of the pad. A technical benefit of the described embodiment includes improved conformability to warped surfaces of electronics components, ensuring consistent thermal contact and enhancing heat transfer efficiency even under physical deformation.

[0018] Furthermore, the incorporation of a convex surface, enhances the adaptability of the thermal interface pad by providing a design that naturally conforms to the warped surfaces of electronics components. The central area of the pad, being thicker, ensures robust thermal contact with the core heatgenerating regions, while the thinner edges accommodate the warped areas, maintaining optimal thermal transfer throughout the entire surface. This strategic thickness variation not only mitigates the effects of warpage but also optimizes heat dissipation across the entire contact area, leading to improved cooling efficiency. By addressing the challenges posed by component warpage, various embodiments of the invention significantly enhance the thermal management capabilities of electronics systems, ensuring consistent performance and reliability even under demanding operational conditions.

[0019] According to an example embodiment, the thermal interface pad has a convex surface where edges of the thermal interface pad have a first thickness which is lower than a thickness of a central area portion of the thermal interface pad. A technical benefit of the described embodiment includes optimized thermal performance by maintaining a robust contact at the central, more critical heat-generating areas while adapting to variations at the edges, thereby preventing hot spots and ensuring uniform cooling.

[0020] According to an example embodiment, the thermal interface pad has a fully convex top surface and a flat bottom surface. A technical benefit of the described embodiment includes maximized thermal contact area with the heat source while maintaining stable and even distribution of pressure across the pad, leading to efficient heat dissipation and improved mechanical stability.

[0021] According to an example embodiment, the thermal interface pad has a gradually increasing thickness from at least one edge of the thermal interface pad to a central portion of the thermal interface pad. A technical benefit of the described embodiment includes enhanced adaptability to surface irregularities, ensuring that the pad maintains effective thermal contact across its entire area, thus improving overall thermal management and performance. According to an example embodiment, the thermal interface pad has a gradually increasing thickness from all edges of the thermal interface pad to a central portion of the thermal interface pad. A technical benefit of the described embodiment includes providing a more uniform thermal interface that compensates for warping in multiple directions, ensuring that the central portion, which typically generates more heat, is well-managed and efficiently cooled.

[0022] According to an example embodiment, the thermal interface pad comprises a first area portion having a first thickness and a second area portion having a second thickness, the first thickness being larger than the second thickness. A technical benefit of the described embodiment includes the ability to tailor the thermal pad's thickness to specific thermal management needs, where different areas of an electronics component may require varying levels of heat dissipation, thus optimizing cooling performance.

[0023] According to an example embodiment, the first area portion is mainly located in a central area portion of the thermal interface pad and the second area portion is mainly located in a peripheral area portion of the thermal interface pad. A technical benefit of the described embodiment includes concentrated thermal management in the central area, which typically generates more heat, while the peripheral area is designed to ensure overall structural integrity and effective heat distribution.

[0024] According to an example embodiment, the polymer-infiltrated graphene-enhanced thermal interface pad further comprises a coating polymer material such as epoxy, polyurethane, silicone or arcylics arranged at the edges of the polymer-infiltrated graphene-enhanced thermal interface pad. A technical benefit of the described embodiment includes enhanced durability and protection of the edges from mechanical wear and environmental factors, thereby extending the lifespan of the thermal interface pad and maintaining its thermal performance over time. a method for manufacturing a thermal interface pad, the method comprising: providing a stack of graphene-based films; arranging the stack of graphenebased films in a first profiled mould; pressing the stack of graphene-based films between a first mould and a second mould to form a compressed film, wherein at least one of the first and second mould has a profiled surface; infiltrating a polymer in the compressed film to form an infiltrated film; curing the infiltrated film;

[0025] According to a second aspect of the invention, it is provided a method for manufacturing a graphene-enhanced thermal interface pad, the method comprising: providing a stack of graphene-based films; infiltrating a polymer in the compressed film to form an infiltrated film; curing the infiltrated film to form a cured infiltrated film; cutting the cured infiltrated film to form a pad preform; and pressing the pad preform between a first mould and a second mould, wherein at least the first mould has a curved surface, such that a thermal interface pad having a surface profile corresponding to the curved surface the first mould is formed.

[0026] The described methos offers several advantages for manufacturing thermal interface pads. Pressing the preform between a curved first mould and a second mould which may be flat result in a thermal interface pad with a variable thickness profile, allowing it to conform to surface irregularities and warping in electronic components. This adaptability enhances the ability of the thermal interface pad to maintain consistent thermal contact, thereby improving overall heat transfer efficiency and preventing the formation of hot spots that could lead to overheating and potential component failure.

[0027] Moreover, the method allows for the customization of the moulds, enabling the production of thermal interface pads tailored to specific applications and thermal management needs. The variation in thickness can ensure that thicker central regions provide robust thermal contact with primary heat-generating areas, while thinner edges accommodate any warping or unevenness, ensuring optimal heat dissipation across the entire surface. This process not only enhances the performance and reliability of the thermal interface pad but also improves its longevity, making it suitable for long-term use in high-power electronic applications. The method is efficient and scalable, facilitating large-scale production and integration into existing manufacturing workflows. Consequently, the described manufacturing method results in thermal interface pads that meet the demanding requirements of modem electronics, ensuring high performance, durability, and reliability.

[0028] According to one embodiment of the invention, the method further comprises coating edges of the graphene-enhanced thermal interface pad using a polymer having a viscosity in the range of 1000 to 100000 mPa s. The coating of the edges may improve the tensile strength of the interface pad in the direction perpendicular to the aligned direction by 20% up to 100% compared to thermal interface pad without edge-coating. The coating thereby prevents delamination of the thermal interface pad and also reduces the risk of fraying of the edges as well as reducing the amount of particles being released by the thermal interface pad.

[0029] According to one embodiment of the invention, the thermal interface pad has a thermal conductivity in a direction perpendicular to the plane of the film in the range of 25 W / mK to 200 W / mK. The thermal conductivity in the direction through the plane of the thermal interface pad is a key parameter in determining the efficiency of the thermal interface pad as a thermal interface material arranged to transport heat away from a component generating heat.

[0030] Further effects and features of this second aspect of the present invention are largely analogous to those described above in connection with the first aspect of the invention.

[0031] Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention. Brief Description of the Drawings

[0032] 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:

[0033] Fig. 1 schematically illustrates a thermal interface pad according to an embodiment of the invention;

[0034] Fig. 2 schematically illustrates a thermal interface pad according to an embodiment of the invention; and

[0035] Fig. 3 is a flow chart outlining steps of a method according to an embodiment of the invention.

[0036] Detailed Description of Embodiments

[0037] 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.

[0038] Fig. 1 schematically illustrates a polymer infiltrated graphene-enhanced thermal interface pad 100 according to an embodiment of the invention. The thermal interface pad 100 comprises a plurality of strips 102 of polymer infiltrated graphene-based film extending in the plane of the pad 100, wherein a thickness of the thermal interface pad 100 is different across the area of the pad 100. In the illustrated example, the strips 102 extend along the y-direction of the pad 100 where the xy-plane define the plane of the pad 100 and the z- axis defines the thickness-direction of the pad 100.

[0039] That the material is referred to as a pad should be interpreted to mean that the extension in an xy-plane is substantially larger than the thickness of the material. Accordingly, a vertical direction is seen as the direction perpendicular to the xy-plane of the film, i.e. the z-direction. The described thermal interface pad can be formed as pads or patches of appropriate size to be arranged for example between a heat-generating electrical component and a cooling element. Furthermore, the shape of the pad may be rectangular, square, circular, or it may be provided in an arbitrary shape. A free-form shaped thermal interface pad is possible since the pad can be cut to a suitable shape by conventional cutting methods.

[0040] Moreover, the strips 102 may have any orientation in the plane (xy- plane) of the pad. The strips 102 may thereby be aligned along the x- direction, along the y-direction, or at an angle between the x-direction and y- direction. The thermal interface pad 100 thereby has a convex surface 104 along the x-direction direction of the plane of the pad 100 so that first and second edges 106, 108 of the thermal interface pad have a first thickness which is lower than a thickness of a central area portion 110 of the thermal interface pad.

[0041] Fig. 2 schematically illustrate an example embodiment of a circular thermal interface pad 202 having a fully convex surface, i.e. where the thickness of the edge 204 of the thermal interface pad 202 is lower than a thickness of the central portion 206 of the interface pad.

[0042] Even though the illustrated thermal interface pads have one curved surface and one flat surface, it is equally possible to provide an interface pad where both surfaces are curved, having the same or different curvatures. Moreover, in some applications, the warpage properties of an electronics component can be assumed to be known, and the shape and thickness variation of the thermal interface pad can thereby be adapted to the known warpage properties.

[0043] The manufacturing of graphene-based films is described elsewhere and only a general description will therefore be provided herein. For example, a graphene-based film suitable for use in the present context can be formed by providing graphene oxide sheets in an aqueous suspension; providing a substrate; dispensing the suspension on the substrate; heating the suspension on the substrate to form a graphene film by means of self- assembly; detaching the graphene film from the substrate; performing thermal annealing of the graphene film at a temperature in the range of 2800-3200°C in an inert ambient. By means of the above-described method, a large-scale method of producing a freestanding graphene-based film (GF) with an ultra- high in-plane thermal conductivity is provided. It should however be noted that graphene based films manufactured by other method may also be used in the describe method as long as the graphene-based film has a sufficiently high in-plane thermal conductivity. Moreover, that the film is graphene-based means that there is a portion of graphene in the film, and that the graphene facilitates advantageous properties such as high thermal conductivity. The graphene-based films may comprise a number of additional components such as the polymers, nanoparticles, etc. to reach the desired mechanical and thermal properties of a thermal interface pad.

[0044] The method for manufacturing a thermal interface pad, the method comprises providing 300a stack of graphene-based films; infiltrating 302 a polymer in the compressed film to form an infiltrated film; curing 304 the infiltrated film to form a cured infiltrated film; cutting 306 the cured infiltrated film to form a pad preform; and pressing 308 the pad preform between a first mould and a second mould, wherein at least the first mould has a curved surface, such that a thermal interface pad having a surface profile corresponding to the curved surface the first mould is formed.

[0045] The manufacturing steps up to and including the formation of the pad preform have been described elsewhere by the same applicant and will not be discussed in detail here. In short, the pad preform is a thermal interface pad having a uniform thickness, where strips of a graphene-based film run along the length of the pad and where the plane of the graphene-based film is perpendicular to the plane of the pad to achieve high thermal conductivity through the pad, i.e. in the z-direction as illustrated in Figs. 1-2.

[0046] By pressing 308 the pad preform between first and second moulds, a desired thickness variation of the final thermal interface pad can be achieved. The moulds may be configured in many different ways for example by using additive manufacturing for making the molds. Moreover, the second mould may have a flat surface, or the second mould may also have a curved surface.

[0047] The method of manufacturing a thermal interface pad may further comprise coating edges of the thermal interface pad using a polymer or an epoxy, silicone, urethane or acrylic material which preferably has a viscosity in the range of 1000 to 100000 mPa s. A coating may for example be applied by dipping the pad in a coating material. The coating improves the tensile strength of the pad in the plane of the pad. Depending on the type of coating, the tensile strength may be improved by 20% for a silicone coating and with an improvement of up to 100% for a coating. The coating also prevents particle fall-off from the pad and reduces the risk of delamination.

[0048] Even though the invention has been described with reference to specific 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.

Claims

CLAIMS1 . A polymer infiltrated graphene-enhanced thermal interface pad (100, 200) comprising: a plurality of strips (102) of polymer infiltrated graphene-based film extending in the plane of the pad, wherein a thickness of the thermal interface pad is different across the area of the pad.

2. The thermal interface pad according to claim 1 , wherein the thermal interface pad has a convex surface (104) along at least one direction of the plane of the pad.

3. The thermal interface pad according to claim 1 or 2, wherein the thermal interface pad has a convex surface where edges of the thermal interface pad have a first thickness which is lower than a thickness of a central area portion of the thermal interface pad.

4. The thermal interface pad according to claim 1 , wherein the thermal interface pad has a fully convex top surface (202) and a flat bottom surface.

5. The thermal interface pad according to claim 1 , wherein the thermal interface pad has a gradually increasing thickness from at least one edge of the thermal interface pad to a central portion of the thermal interface pad.

6. The thermal interface pad according to claim 5, wherein the thermal interface pad has a gradually increasing thickness from all edges of the thermal interface pad to a central portion of the thermal interface pad.

7. The thermal interface pad according to claim 1 , wherein the thermal interface pad comprises a first area portion having a first thicknessand a second area portion having a second thickness, the first thickness being larger than the second thickness.

8. The thermal interface pad according to claim 7, wherein the first area portion is mainly located in a central area portion of the thermal interface pad and the second area portion is mainly located in a peripheral area portion of the thermal interface pad9. The polymer infiltrated graphene-enhanced thermal interface pad according to any one of the preceding claims, further comprising a coating polymer material arranged at edges of the polymer infiltrated graphene-enhanced thermal interface pad.

10. Method for manufacturing a graphene-enhanced thermal interface pad, the method comprising: providing (300) a stack of graphene-based films; infiltrating (302) a polymer in the compressed film to form an infiltrated film; curing (304) the infiltrated film to form a cured infiltrated film; cutting (306) the cured infiltrated film to form a pad preform; and pressing (308) the pad preform between a first mould and a second mould, wherein at least the first mould has a curved surface, such that a thermal interface pad having a surface profile corresponding to the curved surface the first mould is formed.11 . The method according to claim 10, wherein the first mould has a concave surface profile in one direction.

12. The method according to claim 10, wherein the first mould has a fully concave surface profile.

13. The method according to any one of the preceding claims, further comprising arranging a spacer between the first mold and the second mold, the spacer defining the minimum thickness of the thermal interface pad.

14. The method according to any one of the preceding claims, further comprising coating edges of the thermal interface pad using a polymer material.

15. The method according to any one of the preceding claims, further comprising coating edges of the thermal interface pad using a polymer material having a viscosity in the range of 1000 to 100000 mPa s

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