Composite heat-conducting gasket and preparation method and application thereof

Abstract

The application provides a composite heat-conducting gasket, a preparation method and application thereof. The composite heat-conducting gasket comprises at least two layers of foamed graphene film layers stacked in sequence, and a liquid metal sheet is arranged between adjacent foamed graphene film layers; the liquid metal sheet comprises a first low-temperature alloy layer, a flexible high-thermal-conductivity alloy layer and a second low-temperature alloy layer which are stacked. The heat-conducting gasket provided by the application adopts a liquid metal sheet with a sandwich structure to replace an adhesive, greatly improves the bonding strength of the composite heat-conducting gasket, solves the problem of insufficient bonding strength of the adhesive in the prior art, and ensures the stability and reliability of the heat-conducting gasket in a high-performance heat dissipation application scenario.

Description

Technical Field

[0001] This invention belongs to the field of thermal conductivity and heat dissipation technology, and relates to a thermally conductive pad, specifically a composite thermally conductive pad and its preparation method and application. Background Technology

[0002] With the advent of the 5G era, the operating frequency of electronic chips is constantly increasing, and electronic products are gradually developing towards lightweight and highly integrated designs, leading to a significant increase in the heat generated by these devices. Excess heat, if not dissipated in time, can severely impact the performance of electronic components, and in severe cases, reduce their lifespan or even cause them to fail. To improve the heat dissipation performance of electronic products and effectively transfer the heat generated by electronic components, the industry has begun to use thermal interface materials as thermal conductive media for heat dissipation.

[0003] Graphene, a novel carbon material with a single-layer two-dimensional honeycomb lattice structure composed of stacked carbon atoms, possesses excellent thermal conductivity, making it a rational material for fabricating thermal interface materials. The theoretical thermal conductivity of graphene can reach 5300 W / (m·K), which is dozens of times higher than that of common metals. Currently, graphene thermal conductive films developed using graphene as a raw material have achieved a thermal conductivity of up to 2000 W / (m·K), exhibiting better thermal conductivity than conventional graphene films. This makes it a novel thermal interface material applicable to chip heat dissipation in applications with high heat flux densities.

[0004] However, existing graphene and liquid metal thermal pads still have the following drawbacks: (1) Existing graphene and liquid metal thermal pads often use adhesives during composite bonding, which are not strong enough to meet the high-performance heat dissipation requirements; traditional thermal pads have limited thermal conductivity, which is difficult to meet the high heat conduction requirements of chip heat dissipation with high heat flux density; (2) During the cutting process of graphene thermal pads, powder is easily shed from the sides. This powder has good conductivity. If it falls on the circuit board, it can easily cause a short circuit and damage electronic products; (3) Existing graphene thermal pads still need to improve the interlayer bonding strength, which is difficult to achieve long-term stability and reliability; (4) Existing graphene thermal pads still have certain limitations in terms of thermal resistance, which is difficult to effectively reduce thermal resistance without increasing the thickness; (5) Existing graphene thermal pads are difficult to balance between thermal conductivity and mechanical strength, which is difficult to meet the dual requirements of thermal conductivity and mechanical strength for high-performance heat dissipation application scenarios.

[0005] Several invention patents have been developed to address the issues of insufficient strength, high thermal resistance, and low thermal conductivity in graphene thermal pads. For example, CN 216491732U discloses a graphene thermal pad comprising multiple layers of sequentially stacked graphene films, with an adhesive coating between adjacent layers. This patent achieves a graphene thermal pad with high thermal conductivity by stacking multiple graphene films and using an adhesive to bond adjacent layers. However, in practical applications, this patent still suffers from insufficient adhesive bonding strength. CN 116922877A discloses a graphene composite longitudinal thermally conductive film, in which the layers of the graphene film are connected in both the horizontal and vertical directions using a welding agent, comprising a graphene film and a welding agent. While this patent uses a welding agent to improve interlayer bonding strength, its thermal conductivity and reliability still need further improvement.

[0006] In summary, it is necessary to provide a novel graphene thermal pad to solve the problems of insufficient bonding strength, high thermal resistance, low thermal conductivity, and easy powder shedding during the cutting process of existing graphene and liquid metal thermal pads. Summary of the Invention

[0007] To address the problems of insufficient bonding strength, high thermal resistance, low thermal conductivity, and easy powder shedding during the cutting process of existing graphene and liquid metal thermal pads, this invention provides a composite thermal pad, its preparation method, and its application.

[0008] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a composite thermally conductive pad, the composite thermally conductive pad comprising at least two layers of foamed graphene film stacked sequentially, and a liquid metal sheet disposed between adjacent foamed graphene film layers. The liquid metal sheet comprises a first cryogenic alloy layer, a flexible high thermal conductivity alloy layer, and a second cryogenic alloy layer stacked together.

[0009] The composite thermal pad provided by this invention uses a liquid metal sheet with a sandwich structure to replace the adhesive, which greatly improves the bonding strength of the composite thermal pad and solves the problem of insufficient bonding strength of the adhesive in the prior art, ensuring the stability and reliability of the thermal pad in high-performance heat dissipation application scenarios. More specifically, the liquid metal sheet utilizes a sandwich structure design, significantly improving the thermal conductivity and heat transfer efficiency of the thermal pad, meeting the high heat transfer requirements of chip heat dissipation fields with high heat flux densities. In addition, the thermal pad of this invention adopts a design similar to vertical graphene pads, combined with a sandwich structure alloy sheet, effectively solving the problem of powder shedding during the cutting or use of graphene thermal pads, avoiding the risk of short circuits to the circuit board caused by conductive powder, and improving the service life and safety of electronic products.

[0010] As a preferred embodiment of the present invention, the thickness of the foamed graphene film is 0.2~0.9mm, for example, it can be 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm or 0.9mm, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; preferably 0.3~0.5mm.

[0011] Preferably, the thickness of the first cryogenic alloy layer and the second cryogenic alloy layer is independently 3~10μm, for example, it can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; preferably 3~5μm.

[0012] Preferably, the thickness of the flexible high thermal conductivity alloy layer is 10~100μm, for example, it can be 10μm, 20μm, 40μm, 60μm, 80μm or 100μm, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; preferably 20~50μm.

[0013] Preferably, the thickness of the liquid metal sheet is 20~120μm, for example, it can be 20μm, 40μm, 60μm, 80μm, 100μm or 120μm, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; preferably 30~60μm.

[0014] In this invention, the thickness of the composite thermal pad is cut according to the actual working conditions, and its thickness is generally 0.2~0.5mm, for example, it can be 0.2mm, 0.3mm, 0.4mm or 0.5mm, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] As a preferred embodiment of the present invention, the materials of the first low-temperature alloy layer and the second low-temperature alloy layer are independently selected from any one of In-Bi alloy, In-Sn-Bi alloy, Ga-In alloy or Ga-In-Sn alloy.

[0016] Preferably, the In content in the In-Bi alloy is 50~80wt%, for example, it can be 50wt%, 60wt%, 70wt% or 80wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] Preferably, the In-Bi alloy is selected from In 66 Bi 34 In 80 Bi 20 or In 50 Bi 50 Any one of them.

[0018] Preferably, the In-Sn-Bi alloy contains 50-52 wt% In, for example, 50 wt%, 51 wt%, or 52 wt%, but is not limited to the listed values; other values ​​not listed within the range are also applicable. The Sn content is 25-40 wt%, for example, 25 wt%, 30 wt%, 35 wt%, or 40 wt%, but is not limited to the listed values; other values ​​not listed within the range are also applicable. The balance is Bi.

[0019] Preferably, the In-Sn-Bi alloy is selected from In 52 Sn 30 Bi 18 In 52 Sn 36 Bi 12 In 51 Sn 25 Bi 24 or In 51 Sn 34 Bi 15 Any one of them.

[0020] Preferably, the Ga content in the Ga-In alloy is 4~8wt%, for example, it can be 4wt%, 5wt%, 6wt%, 7wt% or 8wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the Ga-In alloy comprises Ga5In. 95 .

[0022] Preferably, the Ga content in the Ga-In-Sn alloy is 5~10wt%, for example, it can be 5wt%, 6wt%, 8wt% or 10wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; the Sn content is 8~12wt%, for example, it can be 8wt%, 10wt% or 12wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; the balance is In.

[0023] Preferably, the Ga-In-Sn alloy comprises Ga 8.5 In 81.5 Sn 10 .

[0024] Preferably, the material of the flexible high thermal conductivity alloy layer is selected from any one of In, Ag, Cu-In alloy, Ag-In alloy or Sn-In alloy.

[0025] Preferably, the Cu content in the Cu-In alloy is 70~85wt%, for example, it can be 70wt%, 75wt%, 80wt% or 85wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the Cu-In alloy is selected from Cu 82 In 18 Cu 80 In 20 Cu 75 In 25 or Cu 70 In 30 Any one of them.

[0027] Preferably, the Ag content in the Ag-In alloy is 80~90wt%, for example, it can be 80wt%, 82wt%, 84wt%, 86wt%, 88wt% or 90wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the Ag-In alloy is selected from Ag. 90 In 10 Ag 85 In 15 or Ag 80 In 20 Any one of them.

[0029] Preferably, the Sn content in the Sn-In alloy is 30~40wt%, for example, it can be 30wt%, 32wt%, 34wt%, 36wt%, 38wt% or 40wt%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the Sn-In alloy is selected from In. 70 Sn 30 or In 60 Sn 40 .

[0031] Preferably, the thermal diffusivity of the foamed graphite film is ≥500m. 2 / s, for example, could be 500m 2 / s、502m 2 / s、504m 2 / s、506m 2 / s、508m 2 / s or 510m 2 / s, etc., but not limited to the listed values, other unlisted values ​​within the range also apply.

[0032] Preferably, the density of the foamed graphite film layer is 0.1~0.8 g / cm³. 3 For example, it could be 0.1 g / cm³. 3 0.2g / cm 3 0.4g / cm 3 0.6g / cm 3 or 0.8g / cm 3 This applies to, but is not limited to, the listed values; other unlisted values ​​within the range are also applicable.

[0033] As a preferred embodiment of the present invention, the composite thermally conductive pad further includes an edge-sealing layer and / or a protective layer.

[0034] Preferably, the edging layer is disposed around the composite thermal pad along the thickness direction of the composite thermal pad.

[0035] Preferably, the material of the edge-sealing layer is selected from PI film or graphene film.

[0036] Preferably, the thickness of the edge-sealing layer is 5~10μm, for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable; preferably 5~8μm.

[0037] Preferably, the protective layer is disposed on the upper and / or lower surface of the composite thermally conductive pad along the thickness direction of the composite thermally conductive pad.

[0038] Preferably, the protective layer includes a low-temperature alloy layer with a thickness of 3~10μm, such as 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the material of the low-temperature alloy layer is selected from any one of In-Bi alloy, In-Sn-Bi alloy, Ga-In alloy, or Ga-In-Sn alloy.

[0040] The protective layer of the present invention is made of the same material as the first low-temperature alloy layer or the second low-temperature alloy layer, which can effectively reduce the thermal resistance of the thermal pad, reduce the heat loss during the conduction process, and improve the overall thermal conduction efficiency. In addition, the present invention utilizes the edge layer to improve the lateral strength of the thermal pad and enhance the mechanical properties of the material, achieving a balance between thermal conductivity and mechanical strength, thus meeting the dual requirements of thermal conductivity and mechanical strength for high-performance heat dissipation applications.

[0041] The composite thermally conductive pad of the present invention has a vertical thermal conductivity ≥200W / (m·K), for example, it can be 200W / (m·K), 230W / (m·K), 250W / (m·K) or 300W / (m·K), but is not limited to the listed values. Other unlisted values ​​within the range are also applicable; preferably, it is 200~250W / (m·K).

[0042] Preferably, the total thermal resistance of the composite thermal pad is controlled within 0.01~0.05 cm under conditions of 40 psi and 80°C. 2 K / W, for example, could be 0.01cm 2 K / W, 0.02cm 2 K / W, 0.03cm 2 K / W, 0.04cm 2 K / W or 0.05cm 2 • K / W, etc., but not limited to the listed values; other unlisted values ​​within the range are also applicable; preferably 0.02~0.03cm 2 ·K / W.

[0043] Preferably, the composite thermally conductive pad has a transverse tensile strength ≥1MPa, such as 1MPa, 1.2MPa, 1.4MPa, 1.6MPa, 1.8MPa or 2MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] In a second aspect, the present invention provides a method for preparing a composite thermally conductive pad as described in the first aspect, the method comprising the following steps: A first low-temperature alloy layer and a second low-temperature alloy layer are coated on opposite sides of the flexible high thermal conductivity alloy layer to obtain a liquid metal sheet. The liquid metal sheet is placed on the first layer of foamed graphene film to obtain a blank; then the second layer of foamed graphene film is placed horizontally on the blank, heated and bonded, and then the liquid metal sheet is placed on the second layer of foamed graphene film again. This process is repeated until a blank with the target height is obtained. The preform is sliced ​​along the stacking direction of the foamed graphene film to obtain a composite thermal pad with a specified thickness.

[0045] It is worth noting that, before coating, the materials of the first and second low-temperature alloy layers are heated and melted to form liquid metal; and during the process of stacking the second foamed graphene film layer, the second foamed graphene film layer is disposed on one side of the first foamed graphene film layer of the blank raw material; at the same time, polishing is used to reduce the surface flatness and roughness.

[0046] As a preferred embodiment of the present invention, the preparation method further includes performing plasma surface treatment on the foamed graphene film.

[0047] Preferably, the plasma surface treatment time is 5 minutes and the speed is 10~30 mm / s, for example, it can be 10 mm / s, 15 mm / s, 20 mm / s, 25 mm / s or 30 mm / s, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] As a preferred embodiment of the present invention, the difference between the heating temperature and the melting point of the first low-temperature alloy layer and the second low-temperature alloy layer is ≤5℃, for example, it can be 5℃, 4℃, 3℃, 2℃ or 1℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the heating time is 0.5 to 5 minutes, for example, it can be 0.5 minutes, 1 minute, 2 minutes, 3 minutes, 4 minutes or 5 minutes, but it is not limited to the listed values. Other values ​​not listed within the range are also applicable.

[0050] Preferably, the pressure for heating is 0.1~0.5MPa, for example, it can be 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa or 0.5MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] As a preferred embodiment of the present invention, the slicing process further includes: edge wrapping and surface polishing of the composite thermal pad with a specified thickness along its thickness direction.

[0052] Preferably, the process after slicing further includes coating the upper and / or lower surfaces of the composite thermal pad having a specified thickness with a protective layer.

[0053] Thirdly, the present invention provides an application of the composite thermal pad as described in the first aspect, wherein the composite thermal pad is used in a 5G electronic chip heat dissipation device.

[0054] The composite thermally conductive pad described in this invention has a vertical thermal conductivity ≥200 W / (m·K) and a total thermal resistance controlled within 0.01~0.05 cm. 2 • K / W, transverse tensile strength ≥1MPa; the composite thermal pad has an operating temperature range of -40℃ to 125℃, and has excellent thermal stability and thermal conductivity, and can be widely used in the field of 5G electronic chip heat dissipation.

[0055] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0056] Compared with the prior art, the present invention has the following beneficial effects: (1) By adopting a high thermal conductivity alloy + low temperature alloy layer bonding composite method, the present invention does not require the use of adhesive, which greatly improves the longitudinal strength (along the graphene film direction) of the composite thermal pad, solves the problem of insufficient strength of graphene pad in the prior art, and ensures the stability and reliability of the thermal pad in high performance heat dissipation application scenarios. (2) The liquid metal sheet described in this invention has a sandwich structure design to replace silicone adhesive, which can significantly improve the thermal conductivity and heat transfer efficiency of the thermal pad, and meet the high heat transfer requirements of the chip heat dissipation field with high heat flux density. (3) The present invention adopts a design similar to vertical graphene pads, combined with sandwich structure alloy sheets, which effectively solves the problem of powder shedding during the cutting or use of graphene thermal pads, avoids the risk of short circuit of conductive powder to circuit boards, and improves the service life and safety of electronic products. (4) By coating the surface of the composite thermal pad with a low-temperature alloy layer, the present invention effectively reduces the interfacial thermal resistance of the thermal pad, which can quickly dissipate the heat from the chip or heat source and improve the overall thermal conduction efficiency. (5) By coating the upper and lower surfaces with low-temperature alloy and supplementing with edge wrapping, the present invention significantly improves the transverse strength (perpendicular to the graphene film direction) of the thermal pad, enhances the mechanical properties of the material, achieves a balance between thermal conductivity and mechanical strength, and meets the dual requirements of thermal conductivity and mechanical strength for high-performance heat dissipation application scenarios. Attached Figure Description

[0057] Figure 1 A schematic diagram of the structure of the composite thermally conductive pad provided in a specific embodiment of the present invention; Figure 2 A schematic diagram of the structure of the liquid metal sheet provided for a specific embodiment of the present invention. Among them, 1 is a foamed graphene film layer, 2 is a liquid metal sheet, 2-1 is a first low-temperature alloy layer, 2-2 is a flexible high thermal conductivity alloy layer, 2-3 is a second low-temperature alloy layer, 3 is an edge-wrapping layer, and 4 is a protective layer. Detailed Implementation

[0058] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0059] In one specific embodiment, the present invention provides a composite thermally conductive pad, such as... Figure 1 and Figure 2 As shown, the composite thermal pad includes at least two layers of foamed graphene film 1 stacked sequentially, and a liquid metal sheet 2 is disposed between adjacent foamed graphene film layers. The liquid metal sheet comprises a first low-temperature alloy layer 2-1, a flexible high thermal conductivity alloy layer 2-2, and a second low-temperature alloy layer 2-3, which are stacked together.

[0060] The thickness of the foamed graphene film 1 is 0.2~0.9mm; the thickness of the first low-temperature alloy layer 2-1 and the second low-temperature alloy layer 2-3 is 3~10μm; the thickness of the flexible high thermal conductivity alloy layer 2-2 is 10~100μm; and the thickness of the liquid metal sheet is 20~120μm.

[0061] The materials of the first low-temperature alloy layer 2-1 and the second low-temperature alloy layer 2-3 are independently selected from any one of In-Bi alloy, In-Sn-Bi alloy, Ga-In alloy or Ga-In-Sn alloy; The flexible high thermal conductivity alloy layer 2-2 is made of any one of In, Ag, Cu-In alloy, Ag-In alloy or Sn-In alloy; The thermal diffusivity of the foamed graphene film is ≥500 μm. 2 / s, density is 0.1~0.8g / cm³ 3 ; The composite thermal pad also includes an edge layer 3 and / or a protective layer 4; Along the thickness direction of the composite thermal pad, the edge layer 3 is disposed around the perimeter of the composite thermal pad, and the protective layer 4 is disposed on the upper surface and / or lower surface of the composite thermal pad. The material of the edge-sealing layer 3 is selected from PI film or graphene film; the thickness of the edge-sealing layer 3 is 5~10μm; the protective layer 4 includes a low-temperature alloy layer with a thickness of 3~10μm.

[0062] In another specific embodiment, the method for preparing the above-mentioned composite thermally conductive pad includes the following steps: A first low-temperature alloy layer and a second low-temperature alloy layer are coated on opposite sides of the flexible high thermal conductivity alloy layer to obtain a liquid metal sheet. The liquid metal sheet is placed on the first layer of foamed graphene film to obtain a blank; then the second layer of foamed graphene film is placed horizontally on the blank, heated and bonded, and then the liquid metal sheet is placed on the second layer of foamed graphene film again. This process is repeated until a blank with the target height is obtained. The blank is sliced ​​along the stacking direction of the foamed graphene film, and the cut surface is polished to obtain a composite thermal pad with a specified thickness. Finally, the composite thermal pad with the specified thickness is edge-wrapped and surface-polished on all four sides in the thickness direction; and / or a protective layer is applied to the upper and / or lower surfaces of the composite thermal pad with the specified thickness. Wherein, the difference between the heating temperature and the melting point of the first low-temperature alloy layer and the second low-temperature alloy layer is ≤5℃; the time is 0.5~5min; and the pressure is 0.1~0.5MPa.

[0063] It should be noted that the following embodiments are for illustrative purposes only and do not constitute a limitation of the present invention. For example, in the present invention, the material of the flexible high thermal conductivity alloy layer is selected from any one of In, Ag, Cu-In alloy, Ag-In alloy, or Sn-In alloy. The present invention only uses In, Ag, Cu... 82 In 18 The examples provided are not intended to imply that the present invention can only use In, Ag, and Cu. 82 In 18In this invention, In, Ag, Cu 82 In 18 It can also be replaced with Ag-In alloy or Sn-In alloy, and other structures and raw materials of the present invention can be understood in the same way.

[0064] Unless otherwise specified, the raw materials involved in the following specific embodiments of the present invention are all conventional materials in the art and can be obtained by purchasing commercially available products.

[0065] Example 1 This embodiment provides a composite thermally conductive pad, such as Figure 1 and Figure 2 As shown, the composite thermal pad includes at least two layers of foamed graphene film 1 stacked sequentially, and a liquid metal sheet 2 is disposed between adjacent foamed graphene film layers. The liquid metal sheet comprises a first low-temperature alloy layer 2-1, a flexible high thermal conductivity alloy layer 2-2, and a second low-temperature alloy layer 2-3, which are stacked together.

[0066] The thickness of the foamed graphene film 1 is 0.3 mm; the thickness of the first low-temperature alloy layer 2-1 and the second low-temperature alloy layer 2-3 is 5 μm each; the thickness of the flexible high thermal conductivity alloy layer 2-2 is 20 μm; and the thickness of the liquid metal sheet is 30 μm. The first low-temperature alloy layer 2-1 and the second low-temperature alloy layer 2-3 are both made of In. 66 Bi 34 The flexible high thermal conductivity alloy layer 2-2 is made of In. The thermal diffusivity of the foamed graphene film is 510 m. 2 / s; density is 0.5g / cm³ 3 ; The composite thermal pad also includes an edge-sealing layer 3 and a protective layer 4; Along the thickness direction of the composite thermal pad, the edge layer 3 is disposed around the perimeter of the composite thermal pad, and the protective layer 4 is disposed on the upper and lower surfaces of the composite thermal pad. The edge-sealing layer 3 is made of PI film; the thickness of the edge-sealing layer 3 is 5 μm. The protective layer 4 includes a low-temperature alloy layer made of In. 66 Bi 34 The thickness is 5μm.

[0067] The method for preparing the composite thermal pad described in this embodiment includes the following steps: A first low-temperature alloy layer and a second low-temperature alloy layer are coated on opposite sides of the flexible high thermal conductivity alloy layer to obtain a liquid metal sheet. The liquid metal sheet is placed on the first layer of foamed graphene film to obtain a blank; then the second layer of foamed graphene film is placed horizontally on the blank, heated and bonded, and then the liquid metal sheet is placed on the second layer of foamed graphene film again. This process is repeated until a blank with the target height is obtained. The blank body is edged along its thickness direction, then sliced ​​along the stacking direction of the foamed graphene film, and a protective layer is coated on the upper and lower surfaces to obtain a composite thermal pad with a specified thickness. The temperature difference between the heating and bonding temperature and the melting point of the first and second low-temperature alloy layers is ≤5℃, the time is 1min, and the pressure is 0.1MPa; and the melting point of the first and second low-temperature alloy layers is 72℃.

[0068] Example 2 This embodiment provides a composite thermally conductive pad, which differs from Embodiment 1 only in that: This embodiment omits the protective layer disposed on the upper surface of the composite thermally conductive pad having a specified thickness.

[0069] Example 3 This embodiment provides a composite thermally conductive pad, which differs from Embodiment 1 only in that: This embodiment omits the protective layer 4 disposed on the upper and lower surfaces of the composite thermally conductive pad having a specified thickness.

[0070] The preparation method of the composite thermal pad described in this embodiment is the same as that in Embodiment 1.

[0071] Example 4 This embodiment provides a composite thermally conductive pad, which includes at least two layers of foamed graphene film 1 stacked sequentially, and a liquid metal sheet 2 is disposed between adjacent foamed graphene film layers. The liquid metal sheet comprises a first low-temperature alloy layer 2-1, a flexible high thermal conductivity alloy layer 2-2, and a second low-temperature alloy layer 2-3, which are stacked together.

[0072] The thickness of the foamed graphene film 1 is 0.3 mm; the thickness of the first low-temperature alloy layer 2-1 and the second low-temperature alloy layer 2-3 is 3 μm; the thickness of the flexible high thermal conductivity alloy layer 2-2 is 50 μm; and the thickness of the liquid metal sheet is 56 μm.

[0073] The first low-temperature alloy layer 2-1 and the second low-temperature alloy layer 2-3 are both made of In. 66 Bi 34 The flexible high thermal conductivity alloy layer 2-2 is made of Ag. The thermal diffusivity of the foamed graphene film is 520 m. 2 / s; density is 0.5g / cm³ 3 .

[0074] The method for preparing the composite thermal pad described in this embodiment includes the following steps: A first low-temperature alloy layer and a second low-temperature alloy layer are coated on opposite sides of the flexible high thermal conductivity alloy layer to obtain a liquid metal sheet. The liquid metal sheet is placed on the first layer of foamed graphene film to obtain a blank; then the second layer of foamed graphene film is placed horizontally on the blank, heated and bonded, and then the liquid metal sheet is placed on the second layer of foamed graphene film again. This process is repeated until a blank with the target height is obtained. The blank is sliced ​​along the stacking direction of the foamed graphene film, and the cut surface is polished to obtain a composite thermal pad with a specified thickness. The melting point of the first and second low-temperature alloy layers is 72°C; the heating bonding temperature is 72±5°C, the time is 2 min, and the pressure is 0.1 MPa.

[0075] Example 5 This embodiment provides a composite thermally conductive pad, which includes at least two layers of foamed graphene film 1 stacked sequentially, and a liquid metal sheet 2 is disposed between adjacent foamed graphene film layers. The liquid metal sheet includes a first low-temperature alloy layer 2-1, a flexible high thermal conductivity alloy layer 2-2, and a second low-temperature alloy layer 2-3 stacked together; The thickness of the foamed graphene film 1 is 0.5 mm; the thickness of the first low-temperature alloy layer 2-1 and the second low-temperature alloy layer 2-3 is 10 μm; the thickness of the flexible high thermal conductivity alloy layer 2-2 is 100 μm; and the thickness of the liquid metal sheet is 120 μm. The first low-temperature alloy layer 2-1 and the second low-temperature alloy layer 2-3 are both made of In. 66 Bi 34 The flexible high thermal conductivity alloy layer 2-2 is made of Cu. 82 In 18 ; The thermal diffusivity of the foamed graphene film is 550 μm. 2 / s; density is 0.7g / cm³ 3 .

[0076] The method for preparing the composite thermal pad described in this embodiment includes the following steps: A first low-temperature alloy layer and a second low-temperature alloy layer are coated on opposite sides of the flexible high thermal conductivity alloy layer to obtain a liquid metal sheet. The liquid metal sheet is placed on the first layer of foamed graphene film to obtain a blank; then the second layer of foamed graphene film is placed horizontally on the blank, heated and bonded, and then the liquid metal sheet is placed on the second layer of foamed graphene film again. This process is repeated until a blank with the target height is obtained. The blank is sliced ​​along the stacking direction of the foamed graphene film, and the cut surface is polished to obtain a composite thermal pad with a specified thickness. The melting point of the first and second low-temperature alloy layers is 72°C; the heating bonding temperature is 72±5°C, the time is 3 minutes, and the pressure is 0.2 MPa.

[0077] Example 6 This embodiment provides a composite thermally conductive pad, which differs from Embodiment 1 only in that: In this embodiment, the thickness of both the first and second cryogenic alloy layers is adjusted to 1 μm.

[0078] The preparation method of the composite thermal pad described in this embodiment is the same as that in Embodiment 1.

[0079] Example 7 This embodiment provides a composite thermally conductive pad, which differs from Embodiment 1 only in that: In this embodiment, the thickness of both the first and second cryogenic alloy layers is adjusted to 7 μm.

[0080] The preparation method of the composite thermal pad described in this embodiment is the same as that in Embodiment 1.

[0081] Example 8 This embodiment provides a composite thermally conductive pad, which differs from Embodiment 1 only in that: In this embodiment, the thickness of both the first and second cryogenic alloy layers is adjusted to 12 μm.

[0082] The preparation method of the composite thermal pad described in this embodiment is the same as that in Embodiment 1.

[0083] Example 9 This embodiment provides a composite thermally conductive pad, which differs from Embodiment 1 only in that: In this embodiment, the thickness of the flexible high thermal conductivity alloy layer is adjusted to 5 μm.

[0084] The preparation method of the composite thermal pad described in this embodiment is the same as that in Embodiment 1.

[0085] Example 10 This embodiment provides a composite thermally conductive pad, which differs from Embodiment 1 only in that: In this embodiment, the thickness of the flexible high thermal conductivity alloy layer is adjusted to 50 μm.

[0086] The preparation method of the composite thermal pad described in this embodiment is the same as that in Embodiment 1.

[0087] Example 11 This embodiment provides a composite thermally conductive pad, which differs from Embodiment 1 only in that: In this embodiment, the thickness of the flexible high thermal conductivity alloy layer is adjusted to 120 μm.

[0088] The preparation method of the composite thermal pad described in this embodiment is the same as that in Embodiment 1.

[0089] Comparative Example 1 This comparative example provides a graphene composite thermal conductive pad, which differs from Example 1 only in that: In this comparative example, the liquid metal sheet was adjusted to be silicone of uniform thickness.

[0090] Comparative Example 2 This comparative example provides a graphene composite thermal conductive pad, which differs from Example 1 only in that: This comparative example omits the flexible high thermal conductivity alloy layer 2-2 and the second low temperature alloy layer 2-3, i.e., adjacent foamed graphene film layers are fixed by a 10μm thick low temperature alloy layer.

[0091] Performance testing: The performance of the composite thermal pads provided in the above embodiments and comparative examples was tested, and the results are shown in Table 2. The composite thermal pad has a thickness of 0.3 mm. The performance tests include: at least three tensile strength tests, thermal resistance tests, and temperature range tests. The thermal resistance is tested at a pressure of 40 psi and a temperature of 80°C. The tensile strength test temperature is room temperature, and the tensile strength test includes transverse tensile strength and longitudinal tensile strength. The tensile strength test results of the composite thermal conductive pad provided in Example 1 are shown in Table 1.

[0092] Table 1 Table 2 In Table 2, the tensile strength test results are the data range of three test results.

[0093] According to Table 2, the following points can be observed: (1) Comprehensive analysis of Examples 1-4 shows that the present invention adopts a low-temperature alloy layer bonding composite method, which eliminates the need for adhesives, greatly improves the bonding strength of the composite thermal pad, and reduces the thermal resistance. In addition, analysis of Examples 1 and 2-3 shows that the protective layer can further improve the transverse tensile strength of the gasket. (2) Comprehensive analysis of Examples 1 and 5-7 shows that as the thickness of the first low-temperature alloy layer and the second low-temperature alloy layer increases, the thermal resistance of the resulting gasket does not change much. Since the low-temperature alloy layer with appropriate thickness can fill the roughness of the foamed graphene film layer, it can optimize the connection effect with the protective layer and further slightly improve the transverse strength of the resulting gasket. If its thickness is too high, it will cause overflow after melting and pressure, which may cause short circuit risk. A comprehensive analysis of Examples 1 and 8-10 shows that as the thickness of the flexible high thermal conductivity alloy layer increases, the overall strength of the resulting gasket will increase, but the thermal resistance will decrease. This is because the higher the proportion of the alloy layer, the lower the proportion of the graphene film, and the thermal conductivity of the graphene film is 10 times that of the alloy. (3) A comprehensive analysis of Examples 1-2 and Comparative Example 1 shows that, compared with the sandwich structure liquid metal sheet provided by the present invention, using silicone as a binder will result in lower strength; A comprehensive analysis of Example 1 and Comparative Example 2 shows that if the sandwich-structured liquid metal sheet is changed to a single-layer cryogenic alloy layer, the product will be NG if the cryogenic alloy layer is exceeded.

[0094] In summary, the composite thermal pad provided by this invention uses a liquid metal sheet with a sandwich structure to replace the adhesive, which greatly improves the bonding strength of the composite thermal pad, solves the problem of insufficient adhesive bonding strength in the prior art, and ensures the stability and reliability of the thermal pad in high-performance heat dissipation application scenarios.

[0095] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A composite thermally conductive pad, characterized in that, The composite thermal pad includes at least two layers of foamed graphene film stacked sequentially, and a liquid metal sheet is disposed between adjacent foamed graphene film layers. The liquid metal sheet comprises a first cryogenic alloy layer, a flexible high thermal conductivity alloy layer, and a second cryogenic alloy layer stacked together.

2. The composite thermally conductive pad according to claim 1, characterized in that, The thickness of the foamed graphene film is 0.2~0.9mm, preferably 0.3~0.5mm; Preferably, the thickness of the first low-temperature alloy layer and the second low-temperature alloy layer is 3~10μm, more preferably 3~5μm; Preferably, the thickness of the flexible high thermal conductivity alloy layer is 10~100μm, and more preferably 20~50μm; Preferably, the thickness of the liquid metal sheet is 20~120μm, and more preferably 30~60μm.

3. The composite thermally conductive pad according to claim 2, characterized in that, The materials of the first and second cryogenic alloy layers are independently selected from any one of In-Bi alloy, In-Sn-Bi alloy, Ga-In alloy or Ga-In-Sn alloy; Preferably, the In content in the In-Bi alloy is 50~80 wt%; Preferably, the In-Sn-Bi alloy contains 50-52 wt% In, 25-40 wt% Sn, and the balance is Bi; Preferably, the Ga content in the Ga-In alloy is 4~8 wt%; Preferably, the Ga-In-Sn alloy contains 5-10 wt% Ga, 8-12 wt% Sn, and the balance is In; Preferably, the material of the flexible high thermal conductivity alloy layer is selected from any one of In, Ag, Cu-In alloy, Ag-In alloy or Sn-In alloy; Preferably, the Cu content in the Cu-In alloy is 70~85 wt%; Preferably, the Ag-In alloy contains 80-90 wt% Ag. Preferably, the Sn content in the Sn-In alloy is 30~40wt%.

4. The composite thermally conductive pad according to any one of claims 1-3, characterized in that, The thermal diffusivity of the foamed graphene film is ≥500 μm. 2 / s; Preferably, the density of the foamed graphene film is 0.1~0.8 g / cm³. 3 .

5. The composite thermally conductive pad according to any one of claims 1-4, characterized in that, The composite thermal pad also includes an edge-sealing layer and / or a protective layer; Preferably, the edging layer is disposed around the composite thermal pad along the thickness direction of the composite thermal pad; Preferably, the material of the edge-sealing layer is selected from PI film or graphene film; Preferably, the thickness of the edge-sealing layer is 5~10μm, more preferably 5~8μm; Preferably, the protective layer is disposed on the upper surface and / or lower surface of the composite thermally conductive pad along the thickness direction of the composite thermally conductive pad; Preferably, the protective layer comprises a low-temperature alloy layer with a thickness of 3~10μm; Preferably, the material of the low-temperature alloy layer is selected from any one of In-Bi alloy, In-Sn-Bi alloy, Ga-In alloy, or Ga-In-Sn alloy.

6. A method for preparing a composite thermally conductive pad as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: A first low-temperature alloy layer and a second low-temperature alloy layer are coated on opposite sides of the flexible high thermal conductivity alloy layer to obtain a liquid metal sheet. The liquid metal sheet is placed on the first layer of foamed graphene film to obtain a blank; then the second layer of foamed graphene film is placed horizontally on the blank, heated and bonded, and then the liquid metal sheet is placed on the second layer of foamed graphene film again. This process is repeated until a blank with the target height is obtained. The preform is sliced ​​along the stacking direction of the foamed graphene film to obtain a composite thermal pad with a specified thickness.

7. The preparation method according to claim 6, characterized in that, The difference between the heating temperature and the melting point of the first and second low-temperature alloy layers is ≤5℃. Preferably, the heating and bonding time is 0.5 to 5 minutes; Preferably, the pressure of the heating connection is 0.1~0.5MPa.

8. The preparation method according to claim 6 or 7, characterized in that, The process after slicing also includes: edge wrapping and surface polishing of the composite thermal pad with a specified thickness along its thickness direction.

9. The preparation method according to any one of claims 6-8, characterized in that, The process of slicing also includes coating the upper and / or lower surfaces of the composite thermal pad having a specified thickness with a protective layer.

10. An application of the composite thermally conductive pad as described in any one of claims 1-5, characterized in that, The composite thermal pad is used in 5G electronic chip heat dissipation devices.

Images