Flexible vapor chamber and preparation method
By combining a stepped edge-shrinking structure with pure copper laser welding for sealing, along with Murata's cooling core and composite cover design, the sealing and bending resistance issues of flexible heat spreaders are solved, achieving ultra-thinness and efficient heat dissipation, making them suitable for flexible electronic devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-17
- Publication Date
- 2026-03-27
AI Technical Summary
Existing flexible heat spreaders have insufficient sealing performance, poor bending resistance, and complicated manufacturing processes, making it difficult to achieve ultra-thinness and high heat dissipation efficiency.
It adopts a sealing method that combines a stepped edge reduction structure with pure copper laser welding. Combined with Murata cooling core and composite cover plate design, it eliminates the need for traditional support structure, optimizes the heat diffusion path by using tree-like branched steam channels, and optimizes the process through precision stamping, laser welding and other processes.
It improves sealing and flexibility, enhances bending resistance, achieves ultra-thin design and efficient heat dissipation, and is suitable for mass production.
Smart Images
Figure CN121751585A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of thermal management device technology, specifically a flexible heat spreader and its preparation method. Background Technology
[0002] Flexible vapor chambers (VCs) are core components for solving the heat dissipation problem of flexible electronic devices, and must simultaneously meet three major requirements: "flexibility and bendability," "ultra-thinness," and "high heat dissipation efficiency." In existing technologies (such as US18501538A1), the sealing of flexible VCs mostly relies on adhesive bonding or simple edge welding, which results in insufficient sealing and poor bending resistance. The internal support structure is mostly a complex etched groove or metal mesh, which leads to cumbersome manufacturing processes and makes it difficult to further reduce the thickness.
[0003] To address the aforementioned issues, this invention innovates in three aspects: sealing structure, core components, and material combinations. It circumvents the scope of existing patent protection through differentiated design while simultaneously improving product performance. Summary of the Invention
[0004] In view of the above situation and to overcome the defects of the prior art, the present invention provides a flexible heat spreader and its preparation method, which effectively solves the problems raised in the background art.
[0005] To achieve the above objectives, the present invention provides the following technical solution: a flexible heat spreader, comprising an upper cover plate, a lower cover plate, a Murata cooling core, and a phase change working fluid, wherein both the upper cover plate and the lower cover plate are composite structures of copper foil layer and PI film, and both edges are provided with a stepped edge shrinkage structure that shrinks inward, wherein the stepped edge shrinkage structure includes at least two steps, and the steps of the upper cover plate and the lower cover plate interlock with each other; The composite structure of the upper cover plate and the lower cover plate both include a first copper foil layer, a PI film (102) and a second copper foil layer, and a stepped staggered structure is provided between the first copper foil layer, the PI film and the second copper foil layer (103); The interlocking area of the stepped edge-shrinking structure is formed by pure copper laser welding to create a sealing structure, so that the upper cover plate and the lower cover plate enclose a closed cavity. The Murata cooling core is fixed in the closed cavity, and its upper and lower surfaces are respectively attached to the inner surfaces of the upper cover plate and the lower cover plate, and an annular steam channel is formed between the Murata cooling core and the inner wall of the closed cavity. The enclosed cavity is filled with a phase change working fluid, and the copper foil layers of the upper and lower cover plates are provided with etched channel structures for liquid phase reflux of the phase change working fluid.
[0006] Preferably, the width of each step in the stepped edge-shrinking structure is 0.05-0.3mm, and the step height is 1 / 3-1 / 2 of the thickness of the upper or lower cover plate; the diameter of the laser spot for pure copper welding is 0.1-0.5mm, and the welding depth does not exceed 2 / 3 of the thickness of the upper or lower cover plate.
[0007] Preferably, the copper foil layer of the upper cover plate and the lower cover plate is an oxygen-free copper foil with a thickness of 10-30μm, and its inner surface is provided with a nano-porous copper coating with a porosity of 40-60% and a pore size of 50-500nm.
[0008] Preferably, the thickness of the Murata cooling core is 100-300 μm, and the width of the annular steam channel between its edge and the inner wall of the enclosed cavity is 0.2-1 mm.
[0009] Preferably, it further includes an etched copper plate and a metal fiber mesh support layer. One side surface of the etched copper plate is etched to form a tree-like branched vapor channel, and the other side surface is flat. The upper or lower cover plate can be replaced with a PI substrate cover. The edge of the PI substrate cover and the edge of the etched copper plate are engaged by a stepped edge reduction structure, and the engagement area is sealed by pure copper welding to form a closed cavity. The metal fiber mesh support layer is disposed between the flat side of the etched copper plate and the inner surface of the PI substrate cover, and the mesh count of the metal fiber mesh is 200-500 mesh.
[0010] Preferably, the thickness of the etched copper plate is 20-80 μm, the depth of the tree-shaped branch vapor channel is 1 / 2-2 / 3 of the thickness of the etched copper plate, and the end of the tree-shaped branch vapor channel is provided with a circular manifold with a diameter of 0.1-0.3 mm; the thickness of the PI substrate cover is 8-20 μm, and its surface in contact with the etched copper plate is provided with a copper foil layer with a thickness of 1-5 μm, and the pure copper welding is achieved through the copper foil layer.
[0011] Preferably, the stepped edge reduction structure has a reduction width of 0.1-0.5 mm at the edge of the etched copper plate and a reduction width of 0.05-0.1 mm smaller at the edge of the PI substrate cover than the etched copper plate, forming a nested interlocking structure.
[0012] A method for preparing a flexible heat spreader includes the following steps: S1: A stepped edge reduction structure is processed on the edge of the copper foil using a precision stamping process. The step accuracy of the stamping die is controlled within ±0.01mm. The copper foil and PI film are then combined to form an upper cover plate and a lower cover plate, so that the first copper foil layer, PI film and second copper foil layer form a stepped misaligned structure. S2: A nano-porous copper coating is deposited on the inner surface of the lower cover plate by magnetron sputtering; S3: Fix the Murata cooling core to the center area of the lower cover plate with high-temperature resistant organic adhesive, wherein the adhesive dots have a diameter ≤0.5mm and a thickness ≤5μm; S4: Cover the upper cover plate to make the stepped edge-shrinking structure of the upper cover plate and the lower cover plate precisely interlock. Weld continuously along the interlocking area by a laser welding machine with a welding power of 50-150W and a welding speed of 10-30mm / s to form an edge-sealing structure. S5: Inject a phase change working fluid into the pre-reserved injection hole of the closed cavity. The phase change working fluid is deionized water containing 0.1-0.5wt% graphene, and the injection volume is 40-60% of the cavity volume.
[0013] A method for preparing a flexible heat spreader includes the following steps: T1: The copper plate is subjected to photolithography-etching to form a tree-like branched vapor channel and an end manifold. The etching accuracy is controlled within ±0.005mm to obtain an etched copper plate. T2: A metal fiber mesh support layer is fixed on the flat side of the etched copper plate by vacuum sintering at a temperature of 300-400℃. T3: A copper foil layer is formed on the surface of the PI substrate by electroplating, and then a stepped edge-shrinking structure is processed by laser cutting to obtain the PI substrate cover. T4: Align and mesh the PI substrate cover with the etched copper plate, and seal the edges using electron beam welding. The welding voltage is 50-100kV and the beam current is 10-50mA to form a closed cavity. T5: Inject an ethanol solution containing 0.5-1wt% carbon nanotubes as the phase change working medium, and evacuate to ≤5×10⁻⁶. -3 Pa seals the injection hole.
[0014] Preferably, the phase change working fluid is subjected to ultrasonic degassing treatment before injection, and the treatment time is 30-60 minutes.
[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. Innovative sealing structure: The combination of stepped edge reduction structure and laser welding / electron beam welding is adopted, which is significantly different from the existing flat edge sealing or glue bonding, improving sealing performance and flexibility, and avoiding patent conflicts from a structural point of view. 2. Simplified core components: Design 1 uses Murata cooling core as the heat transfer core, eliminating the traditional complex support structure. This is different from the existing "cover plate + independent support + working fluid channel" design, highlighting its innovation. Design 2 optimizes the heat diffusion path through tree-like branched steam channels and end-of-line confluence cavity, improving heat dissipation efficiency. 3. Breakthrough in material combination: The first copper foil layer, PI film and second copper foil layer of the composite cover plate are combined, and the composite structure of PI substrate and etched copper plate in Design 2, combined with metal fiber mesh support, achieves ultra-thinness while differentiating itself from the existing all-metal structure, with better flexibility and temperature resistance. 4. Strong process controllability: Through process optimization such as precision stamping, laser welding, electron beam welding, ultrasonic degassing, and vacuum sintering, product consistency and stability are ensured, making it suitable for mass production. Attached Figure Description
[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.
[0017] In the attached diagram: Figure 1 This is a schematic diagram of the overall assembly structure of the flexible heat spreader of the present invention; Figure 2 This is a schematic diagram of the stepped edge-shrinking composite layer structure of the cover plate of the present invention; Figure 3 This is a schematic diagram of the closed structure after the cover plate of the present invention has been welded; Figure 4 This is a schematic diagram of the assembly interface structure of the flexible heat spreader of the present invention; Figure 5 This is a schematic diagram of the appearance of the flexible heat spreader of the present invention; In the diagram, 10 is the upper cover plate; 30 is the lower cover plate; 50 is the liquid injection hole; 60 is the stepped edge reduction structure; 601 is the edge sealing structure; 101 is the first copper foil layer; 102 is the PI film; 103 is the second copper foil layer; 104 is the etched channel structure; 200 is the Murata cooling core; 40 is the flexible folding position; and 70 is the mounting position. Detailed Implementation
[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0019] The flexible heat spreader of the present invention includes two differentiated structural designs, both based on the core components and connection relationships shown in the accompanying drawings, as detailed below: Design 1: Simplified structure based on Murata cooling core (capillary cooling core) The flexible heat exchanger design includes an upper cover plate 10, a lower cover plate 30, a Murata cooling core 200, and a phase change working fluid.
[0020] The upper cover plate 10 and the lower cover plate 30 have completely identical structures, both being composite structures of the first copper foil layer 101, the PI film 102, and the second copper foil layer 103, with a stepped staggered structure between them to reserve space for subsequent edge sealing; the edges of the upper cover plate 10 and the lower cover plate 30 are processed by precision stamping to form at least two levels of stepped edge reduction structure 60, with each step width being 0.05-0.3mm and the step height being 1 / 3-1 / 2 of the cover plate thickness. This structure allows the edges of the upper cover plate 10 and the lower cover plate 30 to form a precise nesting and interlocking, providing a stable structural foundation for sealing.
[0021] The copper foil layers of the upper cover plate 10 and the lower cover plate 30 are made of oxygen-free copper foil with a thickness of 10-30 μm. A nano-porous copper coating with a porosity of 40-60% and a pore size of 50-500 nm is deposited on the inner surface using magnetron sputtering. This significantly enhances the reflux capability of the phase change working fluid and solves the problem of liquid retention after flexible bending. An etched channel structure 104 is provided on the copper foil layer of the upper cover plate 10 or the lower cover plate 30 to further assist in the reflux of the liquid working fluid.
[0022] The Murata cooling core 200, serving as the core heat transfer unit, has a thickness of 100-300μm. It is fixed to the central area of the lower cover plate 30 by applying high-temperature resistant organic adhesive dots with a diameter ≤0.5mm and a thickness ≤5μm, ensuring both stability and heat transfer performance. The upper and lower surfaces of the Murata cooling core 200 are tightly fitted to the inner surfaces of the upper cover plate 10 and the lower cover plate 30, respectively, and the edges form annular vapor channels with a width of 0.2-1mm with the inner wall of the closed cavity, providing a channel for the flow of phase change working fluid vapor.
[0023] In terms of sealing technology, after the stepped edge-shrinking structure 60 of the upper cover plate 10 and the lower cover plate 30 are engaged, they are continuously welded along the engagement area by a laser welding machine to form the edge sealing structure 601. The laser welding spot diameter is 0.1-0.5mm, the welding depth does not exceed 2 / 3 of the cover plate thickness, the welding power is 50-150W, and the welding speed is 10-30mm / s. This dual sealing of "physical engagement + metallurgical combination" improves the sealing performance by more than 30% compared with the existing flat edge welding or glue sealing. The stress distribution in the welding area is uniform, and the bending resistance reaches more than 10,000 times (bending test with a radius of 5mm).
[0024] The sealed cavity is filled with deionized water containing 0.1-0.5 wt% graphene as the phase change working fluid, with the injection volume being 40-60% of the cavity volume. Before injection, the phase change working fluid undergoes ultrasonic degassing for 30-60 minutes and is injected through a pre-reserved injection hole. Afterward, the cavity is evacuated to a vacuum level ≤1×0. -3 Pa, then seal the injection hole with a laser for 50.
[0025] This design eliminates the need for the complex steam chamber support structure of traditional VC, and the overall thickness can be controlled within 300μm, which is 20-40% thinner than existing technologies. Design 2: Ultra-thin structure based on PI substrate and etched copper plate This design is an optional structural variation of the aforementioned flexible heat spreader. The core is to replace one of the cover plates with a combination of a PI substrate cover and an etched copper plate, specifically including an etched copper plate, a PI substrate cover, a metal fiber mesh support layer, and a phase change working fluid.
[0026] The etched copper plate uses 20-80μm thick copper. Through photolithography and etching, a tree-like branched vapor channel is formed on one side of the surface, while the other side is flat. The depth of the tree-like branched vapor channel is 1 / 2-2 / 3 of the thickness of the etched copper plate. The end is provided with a circular confluence cavity with a diameter of 0.1-0.3mm. Compared with the existing parallel trenches, the heat diffusion efficiency is improved by 15%, which is more adaptable to the changes in heat flow distribution during flexible bending. The etching accuracy is controlled within ±0.005mm to ensure the consistency of the channel structure.
[0027] The PI substrate cover is 8-20μm thick. The surface in contact with the etched copper plate is electroplated to form a 1-5μm thick copper foil layer for pure copper welding and sealing. Its edges are laser-cut to form a stepped edge reduction structure 60. The reduction width at the edge of the etched copper plate is 0.1-0.5mm, and the reduction width at the edge of the PI substrate cover is 0.05-0.1mm smaller than that of the etched copper plate, forming a nested interlocking structure to ensure tight sealing.
[0028] A metal fiber mesh support layer, with a mesh size of 200-500, is placed between the planar side of the etched copper plate and the inner surface of the PI substrate cover. It is fixed to the etched copper plate by vacuum sintering at 300-400℃. This support layer replaces the traditional etched support pillars, reducing the obstruction to flexibility while ensuring structural strength, and the bending radius can be reduced to below 3mm.
[0029] After the PI substrate cover is aligned and interlocked with the etched copper plate, the edges are sealed using electron beam welding at a voltage of 50-100kV and a beam current of 10-50mA to form a closed sealing strip. The sealed cavity is then filled with an ethanol solution containing 0.5-1wt% carbon nanotubes as the phase change working medium, with an injection volume of 40-60% of the cavity volume. Before injection, the cavity undergoes ultrasonic degassing for 30-60 minutes, and after injection, a vacuum of ≤5×0 ppm is applied. -3 Pa, then seal the injection hole 50.
[0030] This design utilizes the high flexibility (elongation at break > 30%) and temperature resistance (long-term operating temperature -50 to 150°C) of the PI substrate, combined with an ultra-thin etched copper plate, to achieve an overall thickness of ≤ 100 μm, which is 50% thinner than traditional thin VC. Example 1: Flexible heat spreader based on Murata cooling core (capillary cooling core) Upper cover plate 10 and lower cover plate 30: The copper foil layer is 20μm thick oxygen-free copper foil, the PI film thickness is adapted, and the edge is processed with a two-level stepped edge reduction structure 60, each step is 0.1mm wide and 7μm high; Murata Cooling Core 200: Selected FCB300 series, 200μm thick, fixed to the lower cover plate 30 by high temperature resistant organic adhesive, with adhesive dots diameter of 0.3mm; Welding parameters: laser power 100W, spot diameter 0.3mm, welding speed 20mm / s, forming a sealing structure 601; Phase change working fluid: deionized water containing 0.3 wt% graphene, injected at 50% of the cavity volume, ultrasonically degassed for 45 min, cavity vacuum degree 5 × 10⁻⁶. -4 Pa; Performance indicators: Overall thickness 240μm, heat dissipation power ≥5W / cm² with a bending radius of 5mm, and bending resistance 12,000 cycles. Example 2: Flexible heat spreader based on PI substrate and etched copper plate Etched copper plate: 50μm thick copper, tree-like branched vapor channels 104 ohms deep 30μm, end manifold diameter 0.2mm, etching accuracy ±0.005mm; PI substrate cover: 15μm thick PI, with a 3μm thick copper foil layer electroplated on the side in contact with the etched copper plate, and a stepped edge shrinkage structure with a shrinkage width of 0.3mm, which is 0.08mm smaller than the shrinkage width of the etched copper plate; Metal fiber mesh support layer: 300 mesh copper fiber mesh, vacuum sintered at 350℃ for 1 hour and fixed to the flat side of the etched copper plate; Welding parameters: Electron beam welding, voltage 80kV, beam current 30mA, forming a sealing strip with a width of 0.4mm; Phase change working fluid: ethanol solution containing 0.8 wt% carbon nanotubes, injected at 45% of the cavity volume, ultrasonically degassed for 50 min, cavity vacuum degree 8 × 10⁻⁶. -4 Pa; Performance indicators: Overall thickness 80μm, heat dissipation power ≥3W / cm² with bending radius 3mm, and bending resistance 15,000 cycles.
[0031] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A flexible heat spreader, comprising an upper cover plate (10), a lower cover plate (30), a Murata cooling core (200), and a phase change working fluid, characterized in that: The upper cover plate (10) and the lower cover plate (30) are both composite structures of copper foil layer and PI film, and the edges are provided with stepped edge shrinkage structure (60) that shrinks inward. The stepped edge shrinkage structure (60) includes at least two steps, and the steps of the upper cover plate (10) and the lower cover plate (30) interlock with each other. The composite structure of the upper cover plate (10) and the lower cover plate (30) both include a first copper foil layer (101), a PI film (102), and a second copper foil layer (103), and a stepped staggered structure is provided between the first copper foil layer (101), the PI film (102), and the second copper foil layer (103); The interlocking area of the stepped edge-shrinking structure (60) is formed by pure copper laser welding to form an edge-sealing structure (601), so that the upper cover plate (10) and the lower cover plate (30) enclose a closed cavity. The Murata cooling core (200) is fixed in the closed cavity, and its upper and lower surfaces are respectively attached to the inner surfaces of the upper cover plate (10) and the lower cover plate (30), and an annular steam channel is formed between the Murata cooling core (200) and the inner wall of the closed cavity. The enclosed cavity is filled with a phase change working fluid, and the copper foil layers of the upper cover plate (10) and the lower cover plate (30) are provided with an etched channel structure (104) for liquid phase reflux of the phase change working fluid.
2. The flexible heat spreader according to claim 1, characterized in that: The width of each step of the stepped edge-shrinking structure (60) is 0.05-0.3mm, and the step height is 1 / 3-1 / 2 of the thickness of the upper cover plate (10) or the lower cover plate (30); the diameter of the laser spot of the pure copper laser welding is 0.1-0.5mm, and the welding depth does not exceed 2 / 3 of the thickness of the upper cover plate (10) or the lower cover plate (30).
3. A flexible heat spreader according to claim 1, characterized in that: The copper foil layers of the upper cover plate (10) and the lower cover plate (30) are oxygen-free copper foils with a thickness of 10-30μm, and their inner surfaces are provided with a nano-level porous copper coating. The porosity of the porous copper coating is 40-60%, and the pore size is 50-500nm.
4. A flexible heat spreader according to claim 1, characterized in that: The thickness of the Murata cooling core (200) is 100-300μm, and the width of the annular steam channel between its edge and the inner wall of the closed cavity is 0.2-1mm.
5. A flexible heat spreader according to claim 1, characterized in that: It also includes an etched copper plate and a metal fiber mesh support layer. One side of the etched copper plate is etched to form a tree-like branched steam channel, and the other side is a flat surface. The upper cover plate (10) or lower cover plate (30) can be replaced with a PI substrate cover. The edge of the PI substrate cover and the edge of the etched copper plate are engaged by a stepped edge reduction structure (60), and the engagement area is sealed by pure copper welding to form a closed cavity. The metal fiber mesh support layer is disposed between the flat side of the etched copper plate and the inner surface of the PI substrate cover. The mesh count of the metal fiber mesh is 200-500 mesh.
6. A flexible heat spreader according to claim 5, characterized in that: The thickness of the etched copper plate is 20-80μm, the depth of the tree-shaped branch vapor channel is 1 / 2-2 / 3 of the thickness of the etched copper plate, and the end of the tree-shaped branch vapor channel is provided with a circular confluence cavity with a diameter of 0.1-0.3mm; the thickness of the PI substrate cover is 8-20μm, and its surface in contact with the etched copper plate is provided with a copper foil layer with a thickness of 1-5μm, and the pure copper welding is achieved through the copper foil layer.
7. A flexible heat spreader according to claim 5, characterized in that: The stepped edge shrinkage structure (60) has a shrinkage width of 0.1-0.5 mm at the edge of the etched copper plate and a shrinkage width of 0.05-0.1 mm smaller than that at the edge of the PI substrate cover, forming a nested interlocking structure.
8. A method for preparing a flexible heat spreader, used to prepare the flexible heat spreader according to any one of claims 1-4, characterized in that, Includes the following steps: S1: A stepped edge reduction structure (60) is processed on the edge of the copper foil using a precision stamping process. The step accuracy of the stamping die is controlled within ±0.01mm. The copper foil and PI film are then combined to form an upper cover plate (10) and a lower cover plate (30), so that the first copper foil layer (101), the PI film (102) and the second copper foil layer (103) form a stepped misaligned structure. S2: A nano-porous copper coating is deposited on the inner surface of the lower cover plate (30) by magnetron sputtering; S3: Fix the Murata cooling core (200) to the center area of the lower cover plate (30) by applying high-temperature resistant organic adhesive, wherein the diameter of the adhesive dots is ≤0.5mm and the thickness is ≤5μm; S4: Cover the upper cover plate (10) so that the stepped edge-shrinking structure (60) of the upper cover plate (10) and the lower cover plate (30) are precisely engaged. Weld continuously along the engagement area by a laser welding machine with a welding power of 50-150W and a welding speed of 10-30mm / s to form an edge-sealing structure (601). S5: Inject a phase change working medium into the reserved injection hole (50) of the closed cavity. The phase change working medium is deionized water containing 0.1-0.5wt% graphene, and the injection amount is 40-60% of the cavity volume.
9. A method for preparing a flexible heat spreader, used to prepare the flexible heat spreader according to any one of claims 5-7, characterized in that, Includes the following steps: T1: The copper plate is subjected to photolithography-etching to form a tree-like branched vapor channel and an end manifold. The etching accuracy is controlled within ±0.005mm to obtain an etched copper plate. T2: A metal fiber mesh support layer is fixed on the flat side of the etched copper plate by vacuum sintering at a temperature of 300-400℃. T3: A copper foil layer is formed on the surface of the PI substrate by electroplating, and then a stepped edge-shrinking structure (60) is processed by laser cutting to obtain the PI substrate cover; T4: Align and mesh the PI substrate cover with the etched copper plate, and seal the edges using electron beam welding. The welding voltage is 50-100kV and the beam current is 10-50mA to form a closed cavity. T5: Inject an ethanol solution containing 0.5-1wt% carbon nanotubes as the phase change working medium, and evacuate to ≤5×10⁻⁶. -3 Pa seals the injection hole (50).
10. A method for preparing a flexible heat spreader according to claim 8 or 9, characterized in that: The phase change working fluid is subjected to ultrasonic degassing treatment before injection, and the treatment time is 30-60 minutes.