Composite thermal pad and preparation method therefor, and heat dissipation device

Abstract

The present application relates to the technical field of thermal interface materials, and relates to a composite thermal pad and a preparation method therefor, and a heat dissipation device. The composite thermal pad comprises: a graphene layer, oriented in a thickness direction, the graphene layer having a first surface and a second surface in the thickness direction, the first surface being used for being attached to a heat dissipation apparatus; and a liquid metal sheet layer, arranged on the second surface of the graphene layer, capable of bending towards side surfaces of the graphene layer, and covering at least part of the side surfaces of the graphene layer. The liquid metal sheet layer sequentially comprises a first alloy layer, an intermediate layer, and a second alloy layer from top to bottom; the materials of the first alloy layer and the second alloy layer are the same or different, the intermediate layer is made of a sheet-like thermally conductive material, and the sheet-like thermally conductive material comprises a solid metal foil or a third alloy; and the melting point temperature of the intermediate layer is higher than that of the first alloy layer and that of the second alloy layer. The composite thermal pad of the present application has high thermal conductivity and also has high compressibility and high repeatability.

Description

A composite thermally conductive pad and its preparation method, and a heat sink

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 2024119697302, filed on December 30, 2024, entitled "A Composite Thermal Pad and its Preparation Method, and a Heat Sink", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of thermal interface materials technology, and in particular to a composite thermally conductive pad and its preparation method, and a heat sink. Background Technology

[0004] As chip power continues to increase, the requirements for the thermal interface material between the heatsink probe and the chip are becoming increasingly stringent. The thermal interface material is a critical component connecting the heatsink and the chip, and its performance directly affects the chip's heat dissipation efficiency and lifespan. Before chips leave the factory, they need to undergo performance testing, thus placing high demands on the thermal conductivity and reusability of the thermal interface material.

[0005] Currently, the thermal interface materials used in existing chip testing scenarios mainly include indium reticulated wafers and carbon fiber pads. While these materials possess some thermal conductivity, their thermal resistance is only around 0.15℃*cm. 2 The above / W is difficult to meet the testing requirements of high-power chips. Currently, thermal interface materials with good thermal conductivity have poor strength and reusability; while thermal interface materials with high reusability have insufficient thermal conductivity and compressibility. Therefore, many high-performance materials cannot meet the requirements for reusability, requiring the interface material to be replaced for each test, which not only increases testing costs but also wastes time and resources.

[0006] Application content

[0007] To address the shortcomings of existing technologies, the objectives of this application include providing a composite thermally conductive pad and its preparation method, as well as a heat sink, to improve compressibility and repeatability while maintaining thermal conductivity.

[0008] The embodiments of this application are implemented as follows:

[0009] In a first aspect, embodiments of this application provide a composite thermally conductive pad, comprising: a graphene layer oriented along its thickness direction, the graphene layer having a first surface and a second surface in the thickness direction, the first surface being used to adhere to a heat dissipation device; a liquid metal sheet layer disposed on the second surface of the graphene layer, and capable of bending toward the side of the graphene layer and covering at least a portion of the side of the graphene layer; wherein the liquid metal sheet layer comprises, from top to bottom, a first alloy layer, an intermediate layer, and a second alloy layer, the first alloy layer and the second alloy layer being made of the same or different materials, the intermediate layer being a sheet-like thermally conductive material, the sheet-like thermally conductive material including a solid metal foil or a third alloy; the melting point temperature of the intermediate layer being higher than that of the first alloy layer and the second alloy layer.

[0010] In the above technical solution, the composite thermally conductive pad includes a graphene layer and a liquid metal sheet layer oriented along the thickness direction. The graphene layer has a first surface and a second surface along the thickness direction. The first surface is used to adhere to the heat dissipation device, and the liquid metal sheet layer is disposed on the second surface of the graphene layer. The graphene layer, after being oriented along the thickness direction, forms a unidirectional material with high thermal conductivity. Simultaneously, it has a high compressibility, which can significantly absorb the gap tolerance at the contact surface with the heat dissipation device, thereby achieving efficient heat conduction. The liquid metal sheet layer includes upper and lower alloy layers and an intermediate layer. The intermediate layer has high strength and can provide support, improving repeatability. Its surface alloy layer melts into a liquid state at a certain temperature. The fluidity and compressibility of the liquid state are much higher than those of the solid state. Therefore, after melting, it can achieve a tight bond with the interface, acting as an interface filler, thereby reducing thermal resistance and improving heat conduction. Therefore, this application, by combining a graphene layer and a liquid metal sheet layer, can improve both thermal conductivity and compressibility.

[0011] In some embodiments of this application, the temperature difference between the melting point of the intermediate layer and the temperature difference between the first alloy layer is at least 50°C; or, the temperature difference between the melting point of the intermediate layer and the temperature difference between the second alloy layer is at least 50°C.

[0012] By creating a temperature difference of at least 50°C between the melting point of the surface layer and the intermediate layer of the liquid metal sheet, the atomic diffusion ability between the surface alloy and the intermediate metal can be weakened, which helps to reduce thermal resistance.

[0013] In some embodiments of this application, the solid metal foil includes one or more of indium foil, platinum foil, copper foil, silver foil, aluminum foil, and zinc foil; and / or, the third alloy includes one or more of Cu-Al alloy, Cu-Sn alloy, and Cu-In alloy.

[0014] By selecting the aforementioned solid metal foil or third alloy, the liquid metal sheet can be provided with good flexibility and a certain strength, maintaining its shape and thermal conductivity. Therefore, the liquid metal sheet can be bent and perforated to be fixed on the heat dissipation device for better heat conduction and reduced thermal resistance.

[0015] In some embodiments of this application, the material of the first alloy layer or the second alloy layer includes a phase transformation alloy or a low melting point alloy with a melting point temperature below 160°C.

[0016] The first or second alloy layer is made of a phase change alloy or a low-melting-point alloy with a melting point below 160°C. It melts into a liquid state at a certain temperature. The fluidity and compressibility of the liquid state are much higher than those of the solid state, allowing it to achieve a tight bond with the interface after melting, acting as an interface filler. For example, it can fill the gaps on the surface of the graphene layer, achieving a tight bond and better heat conduction, thereby reducing thermal resistance. When in contact with the chip, it can simultaneously fill the gaps on the chip surface, achieving better contact between the interface material and the chip surface, thus reducing thermal resistance and significantly improving thermal conductivity.

[0017] In some embodiments of this application, the phase transformation alloy includes one or more of Ga-In-Sn alloy, In-Sn-Bi alloy, In-Bi alloy, In-Bi-Ga, and Ga-In-Sn-Bi alloy.

[0018] The aforementioned alloys are all phase transformation alloys with melting points below 160°C. Under the bonding force of these alloys, the graphene layer and the liquid metal layer can achieve a tight bond that cannot be easily peeled off. Furthermore, these alloys can transform from a solid to a liquid or liquid-solid mixture at certain temperatures, filling gaps at the interface and thus reducing interfacial resistance. For example, the In-Sn-Bi alloy melts into a liquid metal at 60°C, allowing for a tight bond with the phase interface, thereby reducing thermal resistance.

[0019] In some embodiments of this application, the thickness of the liquid metal sheet is 20-200 μm, wherein the thickness of the first alloy layer and the second alloy layer is similar, at 5-50 μm.

[0020] In the liquid metal sheet layer, the first and second alloy layers primarily fill the interfacial gaps. Within the aforementioned thickness range, effective gap filling can be achieved, improving thermal conductivity. The intermediate layer possesses high strength and mainly serves a supporting function. Therefore, the intermediate layer is relatively thicker than the surface layer, which is more conducive to providing support and thus improving repeatability. Controlling the thickness of the liquid metal sheet layer between 20-200 μm helps reduce thermal resistance. However, when the thickness of the liquid metal sheet layer is less than 20 μm, the surface is not flat and smooth enough, making it prone to wrinkles and leading to poor contact. When the thickness is greater than 200 μm, the intermediate layer may warp due to its high modulus, increasing thermal resistance.

[0021] In some embodiments of this application, the thickness of the graphene layer is 0.3-3 mm.

[0022] When the thickness of the graphene layer is within the aforementioned range, the graphene layer can not only provide high thermal conductivity for the composite thermal pad, but also provide high compressibility.

[0023] In some embodiments of this application, liquid metal sheets cover part or all of the sides.

[0024] In some embodiments of this application, the liquid metal sheet also covers part or all of the first surface.

[0025] A liquid metal sheet is coated on the first surface of the graphene layer, allowing the first surface of the graphene layer to adhere to the heat dissipation device through the liquid metal sheet. This reduces the contact thermal resistance between the graphene layer and the heat dissipation device, and further improves the thermal conductivity.

[0026] In some embodiments of this application, a copper-plated layer or an aluminum-plated layer is provided on the side of the liquid metal sheet that is away from the second surface.

[0027] A copper or aluminum plating layer is provided on the side of the liquid metal sheet away from the second surface, so that the liquid metal sheet can contact the chip through the copper or aluminum plating layer. This not only dissipates heat from the chip, but also reduces the probability of the surface alloy material of the liquid metal sheet reacting with the gold and other materials on the chip surface, thereby improving the chip's lifespan.

[0028] Secondly, embodiments of this application provide a method for preparing a composite thermally conductive pad, comprising: growing graphene on a metal foil using chemical vapor deposition; peeling the graphene off the metal foil after growth and stacking it longitudinally to obtain graphene oriented along the thickness direction; heating and melting the materials of the first alloy layer and the second alloy layer to form liquid metal; coating the liquid metal on opposite sides of the intermediate sheet-like thermally conductive material to form the first alloy layer and the second alloy layer; then rolling the entire assembly to obtain a liquid metal sheet; heating the liquid metal sheet to molten the first alloy layer or the second alloy layer on the surface of the liquid metal sheet; placing the graphene layer above the liquid metal sheet; applying pressure to make the graphene layer and the liquid metal sheet in close contact and pushing; maintaining the pressure and cooling to obtain a composite thermally conductive pad.

[0029] In the above technical solution, the grown graphene is peeled off from the metal foil and stacked longitudinally to form graphene oriented along the thickness direction. This orientation enhances the thermal conductivity path of the graphene and improves the thermal conductivity efficiency. Then, the materials of the first alloy layer and the second alloy layer are heated and melted to form liquid metal, which is then coated on both sides of the intermediate sheet-like thermal conductive material. The high fluidity of the liquid metal allows it to penetrate into the microstructure of the sheet-like thermal conductive material, making the bond between the intermediate layer and the first alloy layer and the second alloy layer stronger, forming a liquid metal sheet. Furthermore, after heating the first alloy layer or the second alloy layer on the surface of the liquid metal sheet to a molten state, pressure is applied to make the graphene layer and the liquid metal sheet come into close contact, and then they are bonded by pushing. Subsequently, cooling is performed while maintaining pressure, which helps to form a stable interface structure, thereby improving the stability and durability of the composite thermal pad.

[0030] In some embodiments of this application, after rolling, the thickness of the first alloy layer formed is 5-50 μm, the thickness of the second alloy layer is 5-50 μm; and / or the metal foil includes one or more of copper foil, nickel foil, magnesium foil, iron foil, steel foil and titanium foil.

[0031] Setting the thickness of the first and second alloy layers to 5-50 μm can achieve a good gap-filling effect. Using the aforementioned metal foils is more conducive to graphene growth; for example, copper and nickel foils not only have high thermal conductivity, effectively conducting heat, but also high strength and rigidity, providing a stable substrate and preventing graphene from easily deforming or being damaged during growth and post-processing.

[0032] In some embodiments of this application, the applied pressure is 20-30 psi and the pushing speed is 0.8-1.2 mm / s.

[0033] By controlling the pressure to 20-30 psi and the pushing speed to 0.8-1.2 mm / s, the thickness of the graphene layer and the liquid metal sheet can be effectively controlled, thereby effectively reducing thermal resistance.

[0034] Thirdly, embodiments of this application provide a heat sink, including a heat dissipation device and any of the aforementioned composite thermally conductive pads, wherein the first surface of the composite thermally conductive pad is attached to the heat dissipation device.

[0035] In the above technical solution, the heat sink and the composite thermally conductive pad of this application are bonded together. The first surface of the composite thermally conductive pad is bonded to the heat dissipation device; that is, the graphene side of the composite thermally conductive pad is in close contact with the heat dissipation device. The high thermal conductivity of graphene allows heat to be rapidly transferred to the heat dissipation device. This significantly reduces thermal resistance, improves heat dissipation efficiency, and thus achieves the purpose of rapid heat dissipation.

[0036] In some embodiments of this application, in the heat sink, a liquid metal sheet covers the second surface and side of the graphene layer and extends outward, and the two ends of the extended liquid metal sheet are detachably connected to the opposite sides of the heat sink device.

[0037] The liquid metal sheet covers the second surface and sides of the graphene layer and extends outwards. In other words, the liquid metal sheet covers the outer part of the graphene layer. This not only protects the graphene layer but also improves the interfacial bonding between the graphene layer and the heat dissipation device, thereby reducing thermal resistance and improving heat dissipation efficiency. In addition, the two ends of the extended liquid metal sheet are detachably connected to the opposite sides of the heat dissipation device. Due to the high flexibility of the liquid metal sheet, the composite thermal pad can be bent and perforated, thus allowing the composite thermal pad to be firmly fixed to the heat dissipation device.

[0038] In some embodiments of this application, in the heat sink, a liquid metal sheet covers the second surface, side surface, and at least part of the first surface of the graphene layer, and the liquid metal sheet extends outward along the side surface, with the two ends of the extended liquid metal sheet being detachably connected to the opposite sides of the heat sink device.

[0039] A liquid metal sheet covers the outer portion of the graphene layer, thus protecting it. Furthermore, the first surface of the graphene layer is bonded to the heat dissipation device via the liquid metal sheet, improving the interfacial bonding between the graphene layer and the heat dissipation device, thereby reducing contact thermal resistance and improving heat dissipation efficiency. In addition, the two ends of the liquid metal sheet extending from the side are detachably connected to opposite sides of the heat dissipation device. Due to the high flexibility of the liquid metal sheet, this composite thermal pad can be bent and perforated, allowing it to be securely fixed to the heat dissipation device. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 is a schematic diagram of the composite thermal conductive pad of this application;

[0042] Figure 2 is a schematic diagram of the first structure of the heat sink of this application;

[0043] Figure 3 is a schematic diagram of the second structure of the heat sink of this application;

[0044] Figure 4 is a schematic diagram of the application scenario of the composite thermal conductive pad of this application.

[0045] Icons: 101 - First alloy layer; 102 - Intermediate layer; 103 - Second alloy layer; 104 - Plating; 200 - Graphene layer; 300 - Heat dissipation device; 400 - Screw; 500 - Chip. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0047] The following is a detailed description of a composite thermally conductive pad, its preparation method, and a heat sink according to embodiments of this application.

[0048] This application provides a composite thermally conductive pad, comprising: a graphene layer 200 oriented along its thickness direction, the graphene layer 200 having a first surface and a second surface in the thickness direction, the first surface being used to adhere to a heat dissipation device 300; a liquid metal sheet layer disposed on the second surface of the graphene layer 200, and capable of being bent toward the side of the graphene layer 200 and covering at least a portion of the side of the graphene layer 200; wherein, the liquid metal sheet layer comprises, from top to bottom, a first alloy layer 101, an intermediate layer 102, and a second alloy layer 103, the first alloy layer 101 and the second alloy layer 103 being made of the same or different materials, the intermediate layer 102 being a sheet-like thermally conductive material, the sheet-like thermally conductive material including a solid metal foil or a third alloy; the melting point temperature of the intermediate layer 102 being higher than that of the first alloy layer 101 and the second alloy layer 103.

[0049] In this application, "covering at least part of the side surface of the graphene layer 200" means that the liquid metal sheet 200 can cover a portion of the side surface of the graphene layer 200 or cover all of the side surface of the graphene layer 200.

[0050] As shown in Figures 1 and 2, the composite thermal pad includes a graphene layer 200 oriented along the thickness direction and a liquid metal sheet layer. The graphene layer 200 has a first surface and a second surface along the thickness direction. The first surface is used to adhere to the heat dissipation device 300. The liquid metal sheet layer is disposed on the second surface of the graphene layer 200. After the graphene layer 200 is oriented along the thickness direction, it forms a unidirectional material with high thermal conductivity. At the same time, it has a high compressibility, which makes the composite thermal pad have a high compressibility, which can greatly absorb the gap tolerance of the contact surface with the heat dissipation device 300, thereby achieving efficient heat conduction.

[0051] Referring to Figure 1, the liquid metal sheet can be bent towards the side of the graphene layer 200 and cover at least part of the side of the graphene layer 200, thus protecting the graphene. Furthermore, since the first surface of the graphene is in contact with the heat dissipation device 300 (i.e., the heat dissipation device 300 is located below the liquid metal sheet), the high flexibility of the liquid metal sheet allows it to be bent. Therefore, the liquid metal sheet can be made into a bent and perforated shape, covering the second surface and both sides of the graphene. Perforations are made at the ends extending to the sides of the graphene, thus fixing the liquid metal sheet to the heat dissipation device 300, which facilitates better heat conduction.

[0052] Alternatively, referring to Figure 3, the liquid metal sheet is bent to cover the side of the graphene layer 200 and extends outward along the side. The two ends of the extended liquid metal sheet are detachably connected to opposite sides of the heat dissipation device. Furthermore, a liquid metal sheet is also coated on the first surface of the graphene layer 200. The graphene layer 200 adheres to the heat dissipation device 300 through the liquid metal sheet, which facilitates better heat conduction.

[0053] In this application, the liquid metal sheet covering the first surface and the liquid metal sheets covering the sides and the first surface can be an integral structure or separate structures. The first surface of the graphene layer 200 can be in contact with the first alloy layer 101 of the liquid metal sheet or with the second alloy layer 103; this application does not impose any restrictions. In this application, the liquid metal sheets can cover a portion of the first surface of the graphene layer 200 or cover the entire first surface of the graphene layer 200; this application does not impose any restrictions.

[0054] The liquid metal sheet has a sandwich structure, comprising an identical first alloy layer 101 and a second alloy layer 103, with an intermediate layer 102 being a sheet-like thermally conductive material, including a solid metal foil or a third alloy. The intermediate layer 102 of this sandwich structure possesses high strength, providing support and improving repeatability. Its surface alloy layer melts into a liquid state at a certain temperature. The fluidity and compressibility of the liquid state are far greater than those of the solid state, allowing for a tight bond with the interface after melting, acting as an interface sealer, thereby reducing thermal resistance and improving heat conduction. Therefore, thanks to the high performance and high strength of this liquid metal sheet sandwich structure, the repeatability of the thermal pad is improved.

[0055] In this embodiment, the temperature difference between the melting point of the intermediate layer 102 and the temperature difference between the first alloy layer 101 is at least 50°C; or, the temperature difference between the melting point of the intermediate layer 102 and the temperature difference between the second alloy layer 103 is at least 50°C.

[0056] In other words, the melting point of the liquid metal sheet surface layer must be at least 50°C lower than that of the intermediate layer 102. Setting such a melting point difference can reduce the atomic diffusion ability between the alloy in the surface layer and the metal in the intermediate layer 102. If the melting points of the surface layer and the intermediate layer 102 are close, there may be a situation where the atoms in different layers are very active during operation, which may easily cause mutual diffusion, leading to an increase in the melting point of the metal in the surface layer, and thus an increase in thermal resistance.

[0057] As an example, the temperature difference between the melting point of the intermediate layer 102 and the first alloy layer 101 includes, but is not limited to, 50°C, 55°C, 60°C, 70°C, 80°C, 100°C, 110°C, and 120°C.

[0058] As an example, the solid metal foil includes, but is not limited to, one or more of indium foil, platinum foil, copper foil, silver foil, aluminum foil, and zinc foil; the third alloy includes, but is not limited to, one or more of Cu-Al alloy, Cu-Sn alloy, and Cu-In alloy.

[0059] The material of the first alloy layer 101 or the second alloy layer 103 includes, but is not limited to, phase transformation alloys or low-melting-point alloys with a melting point temperature below 160°C. For example, the material of the first alloy layer 101 or the second alloy layer 103 may independently include, but is not limited to, one or more of Ga-In-Sn alloys, In-Sn-Bi alloys, In-Bi alloys, In-Bi-Ga, and Ga-In-Sn-Bi alloys.

[0060] The materials of the first alloy layer 101 and the second alloy layer 103 may be the same or different. For example, the materials of the first alloy layer 101 and the second alloy layer 103 are both Ga-In-Sn-Bi. Alternatively, as an example, the material of the first alloy layer 101 is Ga-In-Sn-Bi, and the material of the second alloy layer 103 is an In-Sn-Bi alloy.

[0061] For example, the melting point of the first alloy layer 101 is lower than that of the second alloy layer 103. Because the first alloy layer 101 has a lower melting point, it can melt at a lower temperature when in contact with a heat source such as the chip 500, filling the interface between the liquid metal sheet and the heat source.

[0062] Further, as an example, please continue to refer to FIG3. A plating layer 104 is provided on the side of the liquid metal sheet layer facing away from the second surface. The plating layer 104 can be a copper plating layer or an aluminum plating layer. For example, when the second alloy layer 103 of the liquid metal layer is in contact with the second surface of the graphene layer 200, a copper plating layer or an aluminum plating layer can be provided on the side of the first alloy layer 101 of the liquid metal layer facing away from the second alloy layer 103. By using the composite thermal pad provided in this embodiment to dissipate heat from heat sources such as the chip 500, and by providing a copper plating layer or an aluminum plating layer between the chip 500 and the first alloy layer 101, the probability of materials such as gold on the surface of the chip 500 reacting with the alloy material of the first alloy layer 101 can be reduced, thereby improving the service life of the chip 500.

[0063] In this application, the thickness of the liquid metal sheet is 20-200 μm, wherein the thickness of the first alloy layer 101 and the second alloy layer 103 is similar, at 5-50 μm.

[0064] That is, the thickness of the intermediate layer 102 is 10-190μm. For example, the thickness of the intermediate layer 102 includes, but is not limited to, 10μm, 20μm, 30μm, 40μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm or 190μm.

[0065] The similarity of the thicknesses of the first alloy layer 101 and the second alloy layer 103 means that the thicknesses of the first alloy layer 101 and the second alloy layer 103 are the same within the aforementioned range, or that the thicknesses of the first alloy layer 101 and the second alloy layer 103 are different within the aforementioned range. For example, the thicknesses of the first alloy layer 101 and the second alloy layer 103 that are independent of each other include, but are not limited to, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, or 50μm.

[0066] In this application, the thickness of the graphene layer 200 is 0.3-3 mm.

[0067] As an example, the thickness of the graphene layer 200 includes, but is not limited to, 0.3 mm, 0.5 mm, 0.8 mm, 1 mm, 1.3 mm, 1.7 mm, 2 mm, 2.2 mm, 2.6 mm, 2.8 mm, and 3 mm.

[0068] The preparation method of the above-mentioned composite thermal conductive pad is described below.

[0069] A method for preparing a composite thermally conductive pad includes the following steps:

[0070] (1) Preparation of graphene layer 200

[0071] Graphene was grown on a metal foil using chemical vapor deposition (CVD), and then the graphene was peeled off from the metal foil and stacked longitudinally to obtain a graphene layer 200 oriented along the thickness direction.

[0072] The metal foil includes, but is not limited to, one or more of copper foil, nickel foil, magnesium foil, iron foil, steel foil, and titanium foil.

[0073] (2) Preparation of liquid metal sheets

[0074] The materials of the first alloy layer 101 and the second alloy layer 103 are heated and melted to form liquid metal. The liquid metal is then coated on both sides of the sheet-like thermally conductive material of the intermediate layer 102 to form the first alloy layer 101 and the second alloy layer 103. The entire assembly is then pressed to obtain a liquid metal sheet.

[0075] After rolling, the thickness of the first alloy layer 101 formed is 5-50 μm, and the thickness of the second alloy layer 103 is 5-50 μm.

[0076] The first alloy layer 101 and the second alloy layer 103 mainly serve to fill gaps. Therefore, if the thickness is too thin, it will not have the effect of filling gaps, and if the thickness is too thick, it will overflow during the subsequent rolling process, thus affecting the heat conduction effect. Therefore, the thickness of the first alloy layer 101 and the second alloy layer 103 is set to 5-50μm, which can not only have the effect of filling gaps, but also facilitate heat conduction.

[0077] (3) Combining graphene layer 200 and liquid metal sheet

[0078] The liquid metal sheet in step (2) is heated so that the first alloy layer 101 or the second alloy layer 103 on the surface of the liquid metal sheet is in a molten state. Then the graphene layer 200 in step (1) is placed above the liquid metal sheet, pressure is applied to make the graphene layer 200 and the liquid metal sheet come into close contact, and the pressure is maintained for cooling to obtain a composite thermal conductive pad.

[0079] Furthermore, after placing the graphene layer 200 above the liquid metal sheet in step (1) and pressing it, a layer of liquid metal sheet prepared in step (2) can be attached to the first surface of the graphene layer 200, heated, and pressure is applied to the liquid metal sheet to make the graphene layer 200 and the liquid metal sheet come into close contact, and then pressed. After maintaining the pressure and cooling, a composite thermal pad with liquid metal sheet covering both surfaces of the graphene layer 200 is obtained.

[0080] Furthermore, a coating 104 can be deposited on the side of the liquid metal sheet facing away from the second surface. The coating 104 can be a copper layer or an aluminum layer. The deposition method can be magnetron sputtering or electron beam evaporation.

[0081] In the preparation of the liquid metal sheet, the applied pressure is 20-30 psi and the pushing speed is 0.8-1.2 mm / s.

[0082] By applying pressure and pushing the material, the thickness of each layer in the graphene and liquid metal sheets can be effectively controlled, keeping the graphene thickness between 0.3-3 mm and the liquid metal sheet thickness between 20-200 μm. The first alloy layer 101 and the second alloy layer 103 have similar thicknesses, ranging from 5-50 μm. By controlling the pushing pressure and speed within the above ranges, the thickness of the composite thermal pad can be effectively adjusted, thereby effectively reducing thermal resistance. This application also provides a heat sink, including a heat dissipation device 300 and any of the aforementioned composite thermal pads, wherein the first surface of the composite thermal pad is attached to the heat dissipation device 300.

[0083] As shown in Figure 2, the graphene layer 200 is covered by a liquid metal sheet. The first surface of the graphene layer 200 is attached to the heat dissipation device 300, and the second surface is tightly bonded to the liquid metal sheet.

[0084] Referring to Figure 2, the liquid metal sheet covers the second surface and side of the graphene layer 200 and extends outward, and the two ends of the extended liquid metal sheet are detachably connected to the opposite sides of the heat dissipation device 300.

[0085] Alternatively, referring to Figure 3, a liquid metal sheet covers the second surface and sides of the graphene layer 200 and extends outwards, with both ends of the extended liquid metal sheet detachably connected to opposite sides of the heat dissipation device 300. Furthermore, a liquid metal sheet is also disposed between the first surface of the graphene layer 200 and the heat dissipation device 300.

[0086] The composite thermally conductive pad of this application has the advantages of high strength and good flexibility. Therefore, it can be bent and drilled according to the shape of the heat dissipation device 300 and then fixed with screws or other fixing components. The operation is simple and time-saving.

[0087] As an example, the liquid metal sheet can be fixed to the heat dissipation device 300 by means of screws 400 or the like (as shown in Figure 4).

[0088] The heat sink of this application can be used to dissipate heat from chip 500, and its usage diagram is shown in Figure 4. As can be seen from Figure 4, the graphene layer 200 at the bottom of the composite thermal pad is in contact with the heat dissipation device 300, and the liquid metal sheet layer at the top is in contact with chip 500. The alloy layer on the surface of the liquid metal sheet is not easily damaged during contact and separation from chip 500 due to its low bonding force, and the other side is tightly bonded to the graphene pad. Therefore, it can maintain a low thermal resistance during repeated use, and the graphene layer 200 can be repeatedly tested without damage due to the support and protection of the liquid metal sheet layer; however, after repeated testing, the surface of the alloy layer on the surface of the liquid metal sheet layer will be gradually contaminated by impurities or slightly oxidized, resulting in performance degradation. When the degradation reaches an unusable value, it can be easily replaced.

[0089] Furthermore, when a gold plating layer is provided on the surface of the chip 500, the liquid metal sheet layer on the top of the composite thermal pad comes into contact with the chip 500 through a copper plating layer or an aluminum plating layer, etc., to prevent the gold or other materials on the surface of the chip 500 from directly contacting and reacting with the alloy material on the surface of the liquid metal sheet layer.

[0090] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0091] Example 1

[0092] This embodiment provides a composite thermally conductive pad, including the following steps:

[0093] (1) Preparation of graphene layer 200

[0094] Graphene was grown on copper foil using chemical vapor deposition (CVD), then the graphene was peeled off the copper foil and stacked longitudinally to obtain a graphene layer 200 oriented along the thickness direction, with the thickness of the graphene layer 200 controlled to be 0.3 mm.

[0095] (2) Preparation of liquid metal sheets

[0096] Weigh the components according to the following ratio: In-32wt.%Bi-16.5wt.%Sn (i.e., In mass percentage 51.5%, Bi mass percentage 32%, Sn mass percentage 16.5%), then heat and melt them to form liquid metal. The liquid metal is then coated on opposite sides of a 0.05mm thick copper foil to form a first alloy layer 101 with a thickness of 0.015mm and a second alloy layer 103 with a thickness of 0.015mm, respectively. Subsequently, the entire assembly is rolled flat on a hot roller to achieve uniform thickness of the liquid metal sheet, resulting in a liquid metal sheet with a total thickness of 0.08mm and a surface layer thickness of 0.015mm on one side.

[0097] (3) Combining graphene layer 200 and liquid metal sheet

[0098] The liquid metal sheet in step (2) is placed on a heating table and heated so that the first alloy layer 101 or the second alloy layer 103 on the surface of the liquid metal sheet is in a molten state. Then the graphene layer 200 in step (1) is placed above the liquid metal sheet, and a pressure of 30 psi is applied to make the graphene layer 200 in close contact with the liquid metal sheet. The pressure is pushed at 1.0 mm / s, and the pressure is maintained for cooling to obtain a composite thermal conductive pad.

[0099] Example 2

[0100] This embodiment is basically the same as Embodiment 1, except that the thickness of the graphene layer 200 is 0.5 mm.

[0101] Example 3

[0102] This embodiment is basically the same as Embodiment 1, except that: a 0.12mm thick copper foil is selected, and the total thickness of the final liquid metal sheet is 0.15mm.

[0103] Example 4

[0104] This embodiment is basically the same as Embodiment 1, except that the thickness of the graphene layer 200 is 0.4 mm.

[0105] Example 5

[0106] This embodiment is basically the same as Embodiment 1, except that: the total thickness of the liquid metal sheet is 0.11 mm, and a copper foil with a thickness of 0.08 mm is selected, that is, the thickness of the intermediate layer 102 is 0.08 mm.

[0107] Example 6

[0108] This embodiment is basically the same as Embodiment 1, except that: the total thickness of the liquid metal sheet is 0.06mm, and a copper foil with a thickness of 0.03mm is selected, that is, the thickness of the intermediate layer 102 is 0.03mm.

[0109] Example 7

[0110] This embodiment is basically the same as Embodiment 1, except that: liquid metal is coated on both sides of a 0.02mm thick copper foil to form a first alloy layer 101 with a thickness of 0.025mm and a second alloy layer 103 with a thickness of 0.015mm.

[0111] Example 8

[0112] This embodiment is basically the same as Embodiment 1, except that the liquid metal composition of the alloy layer on the side of the liquid metal sheet away from the graphene layer 200 is In-33wt.%Bi alloy. That is, the composition of the first alloy layer 101 is In-33wt.%Bi alloy, and the composition of the second alloy layer 103 is consistent with that of Embodiment 1.

[0113] Example 9

[0114] This embodiment is basically the same as Embodiment 1, except that copper is plated on one side of the liquid metal sheet away from the graphene layer 200.

[0115] Example 10

[0116] This embodiment is basically the same as Embodiment 1, except that: the side of the liquid metal sheet away from the graphene layer 200 is plated with indium on one side.

[0117] Example 11

[0118] This embodiment is basically the same as Embodiment 1, except that: in step (3), the liquid metal sheet from step (2) is placed on a heating table and heated to make the first alloy layer 101 or the second alloy layer 103 on the surface of the liquid metal sheet melted. Then, the graphene layer 200 from step (1) is placed above the liquid metal sheet, and a pressure of 30 psi is applied to make the graphene layer 200 and the liquid metal sheet come into close contact. The graphene layer is pushed at a pressure of 1.0 mm / s and the pressure is maintained for cooling. The liquid metal sheet is bent to cover the side of the graphene layer 200. The liquid metal sheet is attached to the first surface of the graphene layer 200, heated, and a pressure of 30 psi is applied to make the graphene layer 200 and the liquid metal sheet come into close contact. The graphene layer is pushed at a pressure of 1.0 mm / s and the pressure is maintained for cooling, resulting in a composite thermal pad with the first surface, side surface, and second surface of the graphene layer 200 covered with liquid metal graphene sheets.

[0119] Comparative Example 1

[0120] This comparative example is basically the same as Example 1, except that the liquid metal sheet is replaced with a copper foil of the same thickness.

[0121] Comparative Example 2

[0122] This comparative example is basically the same as Example 1, except that the liquid metal sheet is replaced with a textured indium sheet of the same thickness.

[0123] Comparative Example 3

[0124] This comparative example is pure graphene with a thickness of 0.3 mm.

[0125] Comparative Example 4

[0126] This comparative example is basically the same as Example 1, except that there is no graphene layer 200, and only liquid metal sheets are used as thermal pads.

[0127] This comparative example provides a composite thermally conductive pad, comprising the following steps:

[0128] Weigh the materials according to the ratio of In-32wt.%Bi-16.5wt.%Sn, then heat and melt them to form liquid metal. The liquid metal is then coated on opposite sides of a 0.05mm thick copper foil to form a first alloy layer 101 with a thickness of 0.015mm and a second alloy layer 103 with a thickness of 0.015mm, respectively. The entire sheet is then rolled flat on a hot roller to achieve uniform thickness of the liquid metal sheet, resulting in a liquid metal sheet with a total thickness of 0.08mm and a surface layer thickness of 0.015mm on one side.

[0129] Please refer to Table 1 for some parameters of the above embodiments and comparative examples.

[0130] Table 1

[0131] Test case

[0132] This test example measures the performance of the materials prepared in Examples 1-11 and Comparative Examples 1-4, including contact thermal resistance and cost-effectiveness index.

[0133] The contact thermal resistance measurement method is as follows: the materials prepared in Examples 1-11 and Comparative Examples 1-4 are cut into sheets of 30*30mm size and then placed on a thermal resistance meter (Ruiling Technology LW9389) for testing. The test temperature is 80℃ and the pressure is 10-50psi. The measurement is carried out in accordance with the ASTM D5470 standard.

[0134] Defining the cost-performance ratio index: For chip testing, performance (low thermal resistance) is the top priority, followed by gap tolerance filling and number of test cycles. High-power chip testing requires a thermal resistance below 0.15℃*cm. 2 / W, the standard chip testing thermal resistance requirement is 0.25℃*cm 2 / W. Assuming a material performance weight of 0.4 for high-power chip testing scenarios, with a temperature below 0.15℃*cm... 2 / W is 100 points, when the thermal resistance is higher than 0.5℃*cm 2 When the value is / W, the score is 0; the compression ratio weight is set to 0.3, with 50% or more at 50psi being 100 points and less than 20% being 0 points; the repetition count weight is 0.3, with 100 times being 100 points, and the weight is 0 when the repetition count is less than 10. The cost-effectiveness index of Example 1 is calculated as follows: performance index score is 40 points, compression index score is 49.5 / 50*100*0.3=29.7, repetition index score is 20 / 100*100*0.3=6 points, and the total score is 75.7 points; the cost-effectiveness score of Comparative Example 2 is calculated as follows: performance index is 0.15 / 0.4*100*0.4=15 points, compression index score is 46.9 / 50*100*0.3=28.1, repetition index is 80 / 100*100*0.3=24 points, and the total score is 67.1 points; calculations for other cases are shown in Table 2.

[0135] Table 2

[0136] As shown in Table 2, comparing Examples 1, 3, 5, and 6 reveals that increasing or decreasing the thickness of the liquid metal sheet has little impact on repeatability, but it does increase thermal resistance. Comparing Example 1 with Comparative Examples 1 and 2 shows that replacing the liquid metal sheet with copper foil or indium mesh of the same thickness can increase the number of repeatable cycles, but the overall thermal resistance increases significantly. Comparing Example 1 with Comparative Examples 3 and 4 shows that using only graphene, although the thermal resistance is very low, the number of repeatable cycles is only 1-2, making it unusable. Using only the liquid metal sheet as a thermal pad achieves very low thermal resistance as measured on a thermal resistance meter, but due to its thinness and compression ratio of less than 20%, it cannot fill the contact gap tolerance between the chip and the heat sink, thus making it difficult to apply.

[0137] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A composite thermally conductive pad, wherein, include: A graphene layer oriented along the thickness direction, the graphene layer having a first surface and a second surface along the thickness direction, the first surface being used to adhere to a heat dissipation device. A liquid metal sheet is disposed on the second surface of the graphene layer and is bendable toward the side of the graphene layer, covering at least a portion of the side of the graphene layer. The liquid metal sheet layer comprises, from top to bottom, a first alloy layer, an intermediate layer, and a second alloy layer. The first alloy layer and the second alloy layer may be made of the same or different materials. The intermediate layer is a sheet-like thermally conductive material, which may include a solid metal foil or a third alloy. The melting point of the intermediate layer is higher than that of the first alloy layer and the second alloy layer.

2. The composite thermally conductive pad according to claim 1, wherein, The temperature difference between the melting point of the intermediate layer and the temperature of the first alloy layer is at least 50°C; or, the temperature difference between the melting point of the intermediate layer and the temperature of the second alloy layer is at least 50°C.

3. The composite thermally conductive pad according to claim 2, wherein, The solid metal foil includes one or more of indium foil, platinum foil, copper foil, silver foil, aluminum foil, and zinc foil; And / or, the third alloy includes one or more of Cu-Al alloy, Cu-Sn alloy and Cu-In alloy.

4. The composite thermally conductive pad according to claim 2, wherein, The material of the first alloy layer or the second alloy layer includes a phase transformation alloy or a low melting point alloy with a melting point temperature below 160°C. Optionally, the phase transformation alloy includes one or more of Ga-In-Sn alloy, In-Sn-Bi alloy, In-Bi alloy, In-Bi-Ga, and Ga-In-Sn-Bi alloy.

5. The composite thermally conductive pad according to claim 2, wherein, The thickness of the liquid metal sheet is 20-200 μm, wherein the thickness of the first alloy layer and the second alloy layer is similar, at 5-50 μm; Optionally, the thickness of the graphene layer is 0.3-3 mm.

6. The composite thermally conductive pad according to claim 1, wherein, The liquid metal sheet covers part or all of the side surface; And / or, the liquid metal layer also covers part or all of the first surface.

7. The composite thermally conductive pad according to claim 1, wherein, The liquid metal sheet has a copper plating layer or an aluminum plating layer on the side opposite to the second surface.

8. A method for preparing a composite thermally conductive pad as described in any one of claims 1-7, wherein, include: Graphene was grown on a metal foil using chemical vapor deposition. After growth, the graphene was peeled off from the metal foil and stacked longitudinally to obtain graphene oriented along the thickness direction. The materials of the first alloy layer and the second alloy layer are heated and melted to form liquid metal. The liquid metal is then coated on both sides of the sheet-like thermally conductive material in the middle layer to form the first alloy layer and the second alloy layer. The entire assembly is then rolled to obtain a liquid metal sheet. The liquid metal sheet is heated to molten state the first alloy layer or the second alloy layer on the surface of the liquid metal sheet. Then, the graphene is placed above the liquid metal sheet, pressure is applied to make the graphene and the liquid metal sheet come into close contact, and the pressure is maintained while cooling to obtain the composite thermal conductive pad.

9. The preparation method according to claim 8, wherein, After the rolling process, the thickness of the first alloy layer formed is 5-50 μm, and the thickness of the second alloy layer is 5-50 μm. Or / and, the metal foil includes one or more of copper foil, nickel foil, magnesium foil, iron foil, steel foil, and titanium foil.

10. The preparation method according to claim 8, wherein, The applied pressure is 20-30 psi, and the pushing speed is 0.8-1.2 mm / s.

11. A radiator, wherein, The device includes a heat dissipation device and a composite thermally conductive pad according to any one of claims 1-7, wherein the first surface of the composite thermally conductive pad is attached to the heat dissipation device.

12. The radiator according to claim 11, wherein, In the heat sink, the liquid metal sheet covers the second surface and the side surface of the graphene layer and extends outward, and the two ends of the extended liquid metal sheet are detachably connected to the opposite sides of the heat sink.

13. The radiator according to claim 11, wherein, In the heat sink, the liquid metal sheet covers the second surface, the side surface, and at least part of the first surface of the graphene layer, and the liquid metal sheet extends outward along the side surface, with the two ends of the extended liquid metal sheet being detachably connected to the opposite sides of the heat sink.

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