Flexible vapor chamber and preparation method and application thereof

Abstract

The application provides a flexible vapor chamber and a preparation method and application thereof. The preparation method comprises the following steps: first modification is performed on a first flexible copper-clad plate, so that a modified layer containing a phosphate group and a vinyl group is formed on the surface of the first flexible copper-clad plate; a liquid absorption core structure is formed on the surface of the first flexible copper-clad plate with the modified layer by using a photocuring 3D printing technology, so that an intermediate structure is obtained; second modification is performed on the intermediate structure, so that an organic-inorganic hybrid coupling agent grafted layer is formed on the surface of the intermediate structure, the grafted layer contains a phosphate group and a mercapto group, and a modified intermediate structure is obtained; a copper layer is formed on the modified intermediate structure; the modified intermediate structure with the copper layer is packaged with a second flexible copper-clad plate, then water is injected, and the opening is sealed, so that a flexible vapor chamber is obtained. The application improves the interfacial bonding force between the liquid absorption core structure and the flexible copper-clad plate and between the liquid absorption core structure and the copper layer through double interfacial chemical modification, and realizes high-strength and high-reliability connection of the interfaces of the layers of the vapor chamber.

Description

Technical Field

[0001] This invention belongs to the field of electronic heat dissipation technology, specifically relating to a flexible heat dissipation plate, its preparation method, and its application. Background Technology

[0002] With the advent of the 5G / 6G communication era and the continuous emergence of new electronic products such as foldable terminals and flexible wearable devices, the integration and power density of electronic devices are constantly increasing, creating an urgent need for "ultra-thin, flexible, and efficient" heat dissipation technology. Since the 1990s, vapor chambers, with their two-dimensional surface heat transfer advantages, have become the mainstream heat dissipation method for devices such as smartphones and tablets. Their equivalent thermal conductivity can reach 5 to 20 times that of pure copper, and their thickness can be compressed to less than 1 mm. However, while existing metal vapor chambers have excellent thermal conductivity, they are difficult to adapt to dynamic deformation requirements such as bending and folding; while polymer-based flexible vapor chambers have inherent problems such as the release of non-condensable gases at high temperatures and insufficient long-term reliability. Flexible copper clad laminates (FCCLs), which combine the flexibility and processability of polymer substrates and metal substrates, have broad application prospects in the field of flexible heat dissipation.

[0003] In recent years, the rise of high-precision 3D printing technology has opened up new avenues for the construction of ultrathin flexible vapor chamber wicks. However, there are still technical bottlenecks in combining 3D printing technology with FCCL substrates for use in ultrathin vapor chambers. For example, the bonding force between 3D printing resin and metal plating is insufficient. The surface of photocurable resin lacks active groups and has low free energy, resulting in poor interfacial bonding strength between the copper layer and resin during direct chemical or sputtered copper plating, which easily leads to plating peeling. Furthermore, the capillary performance and flow efficiency of the wick structure under ultrathin conditions are insufficient. Existing single-layer wire mesh or trench wicks cannot simultaneously achieve both capillary force and permeability within a thickness of less than 0.25 mm. In addition, it is difficult to balance interfacial bonding strength and sealing performance in the packaging process, and defects such as incomplete soldering and interfacial micropores are prone to occur in the packaging of the vapor chamber top and bottom cover. Summary of the Invention

[0004] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions:

[0005] A first aspect of the present invention provides a method for preparing a flexible heat spreader, comprising:

[0006] S1. The first flexible copper-clad laminate is modified to form a modified layer containing phosphate ester groups and vinyl groups on its surface;

[0007] S2. Using photopolymerization 3D printing technology, a liquid-absorbing core structure is formed on the surface of the first flexible copper-clad laminate with the modified layer to obtain an intermediate structure;

[0008] S3. The intermediate structure is modified a second time to form an organic-inorganic hybrid coupling agent graft layer on its surface, the graft layer containing phosphate ester groups and mercapto groups, to obtain the modified intermediate structure.

[0009] S4. A copper layer is formed on the modified intermediate structure;

[0010] S5. The modified intermediate structure with copper layer is encapsulated with the second flexible copper-clad laminate, and then water is injected and sealed to obtain a flexible heat spreader.

[0011] The preparation method provided by this invention employs a dual-interface chemical modification strategy to significantly enhance the interfacial bonding force between the photopolymer 3D-printed wick structure and the flexible copper clad laminate (FCCL) shell, as well as between the wick structure and the copper layer, achieving high-strength and high-reliability connections between the interfaces of each layer of the flexible vapor chamber. Furthermore, by forming the wick structure through 3D printing technology, the heterogeneous integration of the FCCL shell and the wick structure enables the overall ultrathin and flexible design of the vapor chamber.

[0012] In some embodiments, the first modification specifically includes: forming oxygen-containing polar groups on the first flexible copper-clad laminate, then contacting the first flexible copper-clad laminate containing oxygen-containing polar groups with a first modifying liquid of acrylate containing phosphate ester groups, followed by a first curing process to form the modified layer.

[0013] In some embodiments, the concentration of phosphate-containing acrylate in the first modified solution is 1wt%-5wt%.

[0014] In some embodiments, the first curing temperature is 60~90°C.

[0015] In some embodiments, the first curing time is 30 min to 120 min.

[0016] In some embodiments, the second modification specifically includes: forming oxygen-containing polar groups on the intermediate structure, contacting the intermediate structure with oxygen-containing polar groups on its surface with a second modifying liquid, and then performing a second curing to obtain a modified intermediate structure; wherein the modifying substance contained in the second modifying liquid is formed by Michael addition click reaction of a mercaptosilane coupling agent and an acrylate containing phosphate ester groups to form a functionalized precursor, and the functionalized precursor is hydrolyzed to obtain the precursor.

[0017] In some embodiments, an intermediate structure with oxygen-containing polar groups on its surface is immersed in the second modified liquid at a temperature of 25-40°C and maintained for 5-60 minutes, and then the second curing is performed.

[0018] In some embodiments, the second curing temperature is 60~90°C.

[0019] In some embodiments, the second curing time is 60 min to 120 min.

[0020] In some embodiments, the phosphate-containing acrylates involved in the first modified liquid and the second modified liquid include 2-methyl-2-acrylate-2-hydroxyethyl phosphate.

[0021] In some embodiments, the preparation method of the second modified liquid includes: subjecting a mixed reaction system containing a mercaptosilane coupling agent, an acrylate containing a phosphate ester group, and a nucleophilic base catalyst to a Michael addition click reaction to obtain the functionalized precursor; and hydrolyzing the functionalized precursor in a mixed solvent containing an organic solvent and water to obtain the second modified liquid.

[0022] In some embodiments, the mercaptosilane coupling agent includes one or a combination of more of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethoxysilane.

[0023] In some embodiments, the amounts of the mercaptosilane coupling agent and the phosphate-containing acrylate are such that the molar ratio of the mercapto groups in the mercaptosilane coupling agent to the double bonds in the phosphate-containing acrylate is 1.5:1 to 5:1.

[0024] In some embodiments, the nucleophilic base catalyst used in the Michael addition click reaction includes one or more combinations of triethylamine, dimethylaminopyridine, 1,8-diazacycloundecene-7-ene, and hexamethylenediamine.

[0025] In some embodiments, the reaction temperature of the Michael addition click reaction is 25°C to 60°C.

[0026] In some embodiments, the reaction time of the Michael addition click reaction is 0.5h to 10h.

[0027] In some embodiments, the functionalized precursor is hydrolyzed in a mixed solvent with a pH of 3.5 to 5.0, wherein the volume ratio of the organic solvent to water in the mixed solvent is 5 to 20: 1 to 3.

[0028] In some embodiments, the hydrolysis time is 4-8 hours.

[0029] In some embodiments, the solid content of the second modified liquid is 1wt% to 5wt%.

[0030] The principle of the dual-interface chemical modification of this invention is as follows: The phosphate ester groups (-PO4H2) on the surface of the first flexible copper-clad laminate can chelate with copper multidentate groups, and the vinyl groups can participate in free radical polymerization, thereby significantly improving the interfacial bonding force between the FCCL and the subsequent 3D printing resin. In the second modification, the Si-OH groups in the second modification solution can undergo condensation reactions with oxygen-containing polar groups (e.g., -OH, -COOH, etc.) on the intermediate structure to form strong Si-OC covalent bonds, and the phosphate ester groups form high-density hydrogen bonds with the oxygen-containing polar groups, both contributing to improved bonding force. Furthermore, the second modification can uniformly graft an extremely thin organic-inorganic hybrid coupling agent graft layer containing both thiol (-SH) and phosphate ester groups onto the surfaces of the FCCL and the wick structure. Phosphate groups, through their exposed phosphate groups, form a stable bidentate chelate coordination structure with the metallic copper surface in the copper layer, and transform the copper surface oxide layer into a dense copper phosphate conversion film, providing a high-strength Cu-OP ion-covalent mixed bond; secondly, the mercapto group, as a soft base ligand, generates a high-affinity Cu-S covalent bond with the copper atom; the multi-site anchoring of the phosphate-mercapto hybrid system significantly improves the bonding force between the photocurable resin wick structure and the copper layer.

[0031] In some embodiments, the liquid-absorbing core structure includes a lattice structure, a bump array, a vapor channel, and a support pillar; the bump array is disposed on the surface of the lattice structure and / or embedded in the lattice structure, and the support pillar is disposed in the vapor channel.

[0032] The array of protrusions in the wick structure increases the wick strength and specific surface area, introduces multi-scale channels, and accelerates condensate reflux. The supporting pillars provide mechanical support, low-resistance vapor channels, and condensation nucleation sites.

[0033] In some embodiments, the liquid-absorbing core structure adopts a gas-liquid coplanar layout. The liquid-absorbing core structure, vapor channel support pillars, and bump array are integrally formed, and the gas-liquid coplanar layout can reduce flow resistance. The interlattice gaps form capillary channels for the return of the liquid working fluid, and the open areas between the lattice units form vapor channels.

[0034] The liquid-absorbing core structure formed using high-precision photopolymerization 3D printing technology is made of photopolymerizable resin. In some embodiments, the liquid-absorbing core structure is made of acrylate photosensitive resin and / or epoxy acrylate photosensitive resin.

[0035] In some embodiments, the lattice structure is single-layer or multi-layer. Single-layer lattice structures (lattice unit size 40~60μm) are suitable for ultra-thin applications with a thickness of less than 0.2mm; multi-layer lattice structures are composed of two or more stacked lattice units (each lattice unit size 40~120μm, layers can be isomorphically or heteromorphically stacked, and designs such as alternating lattice types, gradual orientation changes, or gradient filling rates can also be adopted). Multi-layer structures can further improve porosity and capillary performance without significantly increasing the overall thickness.

[0036] In some embodiments, the lattice structure includes a body-centered cubic lattice and / or a close-packed hexagonal lattice.

[0037] The design of a three-dimensional porous liquid-absorbing core structure with a regular array of bumps in a body-centered cubic and / or close-packed hexagonal lattice can construct a multi-scale porous structure, achieving a balance between high porosity, high capillary force, and low flow resistance in an ultra-thin space.

[0038] In some embodiments, the lattice filling rate of the liquid-absorbing core structure is 40%~70%, the lattice unit size is 40μm~120μm, and the lattice edge diameter is 10μm~40μm.

[0039] In some embodiments, the bump array contains bumps with a diameter of 30 μm to 80 μm, a bump height of 140 μm to 200 μm (which can be consistent with the height of the crystal lattice structure), and a distance of 80 μm to 200 μm between adjacent bumps. The shape of the bumps is preferably cylindrical, conical, or hemispherical.

[0040] In some embodiments, the support columns are arranged in an array within the vapor channel. The support columns are formed by integral printing.

[0041] In some embodiments, the diameter of the support pillar is 40μm~100μm, the height is 140μm~200μm (which can be consistent with the height of the crystal lattice structure), and the distance between adjacent support pillars is 150μm~400μm. The shape of the support pillar can be cylindrical or prismatic.

[0042] In some embodiments, the method of forming oxygen-containing polar groups on the first flexible copper-clad laminate and / or on the intermediate structure includes oxygen-containing plasma treatment.

[0043] In some embodiments, the preparation method further includes: subjecting the second flexible copper-clad laminate to oxygen-containing plasma treatment, and then encapsulating it with a modified intermediate structure having a copper layer. Specifically, the inner surface of the second flexible copper-clad laminate facing the liquid absorbent core structure can be treated with oxygen-containing plasma during encapsulation to enhance the bonding force in subsequent encapsulation processes.

[0044] Oxygen-containing plasma treatment of the above structure can introduce oxygen-containing polar functional groups such as carboxyl (-COOH) and hydroxyl (-OH) on its surface, and increase its surface roughness and surface energy, thereby removing surface contaminants.

[0045] The process conditions for plasma treatment are only required to introduce oxygen-containing polar functional groups such as carboxyl groups (-COOH) and hydroxyl groups (-OH) onto the surface of the structure, and are not particularly limited. For example, oxygen-containing plasma treatment can be atmospheric or vacuum plasma treatment, the gas used can be oxygen or a mixture of argon and oxygen, the treatment power can be 50W~200W, and the treatment time can be 5min~20min.

[0046] In some embodiments, the method for forming the copper layer in step S4 includes chemical copper plating or magnetron sputtering, and forming the copper layer can impart superhydrophilicity to the wick.

[0047] In some embodiments, the thickness of the copper layer is 0.5 μm to 5 μm.

[0048] In some embodiments, the encapsulation method is vacuum thermopress diffusion bonding encapsulation.

[0049] For example, the vacuum thermopress diffusion soldering encapsulation specifically includes: aligning and assembling a first flexible copper-clad laminate (lower cover plate) with a metallized liquid wick structure and a second flexible copper-clad laminate (upper cover plate), and placing them into a vacuum thermopress diffusion soldering apparatus for encapsulation. The encapsulation process parameters are: vacuum degree of 5×10⁻⁶. -3 Below Pa, the hot-pressing temperature is 200℃~400℃, the pressure is 1MPa~10MPa, and the holding time is 30min~120min. Then, the working fluid (preferably deionized water) is injected through the pre-reserved injection port on the heat spreader, with the injection volume being 30%~70% of the cavity volume. After evacuating to remove non-condensable gases, the injection port is sealed by laser welding or mechanical sealing to complete the preparation of the ultrathin heat spreader.

[0050] In some embodiments, the first flexible copper clad laminate and the second flexible copper clad laminate are preferably adhesive-free flexible copper clad laminates, such as adhesive-free flexible copper clad laminates with polyimide-based film.

[0051] A second aspect of the present invention provides a flexible heat spreader, which is prepared by the method for preparing a flexible heat spreader as described in any of the technical solutions.

[0052] In some embodiments, the total thickness of the flexible heat spreader is less than 0.25 mm, making it an ultra-thin heat spreader.

[0053] In some embodiments, the equivalent thermal conductivity of the flexible heat spreader is above 6000 W / (m·K).

[0054] In some embodiments, the peel strength between the copper layer and the resin matrix of the absorbent core structure is 1.5 N / mm or higher.

[0055] A third aspect of the present invention provides the application of the aforementioned flexible heat spreader in the manufacture of electronic devices.

[0056] A fourth aspect of the present invention provides an electronic device comprising the flexible heat spreader described in any of the technical solutions.

[0057] In some embodiments, the electronic device includes a foldable terminal, a wearable device, a tablet computer, or a smartphone.

[0058] Compared with the prior art, the present invention has at least some or all of the following beneficial effects: In the preparation process of the flexible heat spreader provided by the present invention, the flexible copper-clad laminate is first modified to form a modified layer containing phosphate ester groups and vinyl groups, and then second modified to construct an organic-inorganic hybrid coupling agent graft layer with thiol and phosphate ester bifunctional groups on the surface of the intermediate structure with the 3D printed wick structure. Through the dual interface chemical modification strategy, the interfacial bonding force between the wick structure and the flexible copper-clad laminate, as well as between the wick structure and the copper layer, is significantly improved, thereby achieving high-strength and high-reliability connection of the interfaces of each layer of the heat spreader. Attached Figure Description

[0059] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0060] Figure 1 This is a flowchart of the preparation process of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of a test system for testing the equivalent thermal conductivity of a flexible heat spreader. Detailed Implementation

[0061] The invention will be more fully understood through the following detailed description of its embodiments. The detailed embodiments disclosed herein are merely illustrative, and the invention may be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims.

[0062] In addition, unless otherwise specified, all raw materials used in the following embodiments can be purchased from the market or other sources, and all production and testing equipment used are known in the art, as are the testing methods used.

[0063] Example 1

[0064] This embodiment provides a flexible heat spreader and its preparation method. Figure 1 This is a flowchart of the preparation process in this embodiment, which specifically includes the following steps:

[0065] (1) Take the first flexible copper-clad laminate (soft copper-based FCCL, the thickness of the polyimide film it contains is 25μm and the thickness of the copper foil is 12μm, and use it as the lower cover of the heat exchanger shell) and treat it with oxygen plasma. The treatment power is 100W, the treatment time is 10min, and the oxygen flow rate is 50sccm. Oxygen plasma treatment can remove surface contaminants and introduce polar functional groups such as carboxyl groups (-COOH) and hydroxyl groups (-OH), while increasing the surface roughness and surface energy.

[0066] (2) Dissolve 2-methyl-2-acrylic acid-2-hydroxyethyl ester phosphate in ethanol to prepare a 5wt% first modification solution, and apply it to the surface of the first flexible copper-clad laminate after oxygen plasma treatment by spin coating at a spin coating speed of 2000 rpm, and then heat cure at 60°C for 30 min.

[0067] (3) A liquid-absorbing core structure is 3D printed on the first flexible copper-clad laminate processed in step (2) to obtain an intermediate structure, specifically including: using a surface projection photopolymerization 3D printer, with a printing layer thickness of 15μm, and using an acrylic photosensitive resin. The liquid-absorbing core adopts a body-centered cubic lattice structure with a lattice unit size of 80μm, a lattice edge diameter of 20μm, and a lattice filling rate of 60%; it adopts a double-layer stacked structure (each layer is 75μm high, and the total height is 150μm). The regular bump array contains cylindrical bumps with a diameter of 50μm, a height of 150μm, and a spacing of 120μm. The gas channel support pillars are cylindrical with a diameter of 60μm, a height of 150μm, and a spacing of 250μm; the gas channel support pillars are distributed at 200μm intervals along the length of the heat spreader.

[0068] (4) The intermediate structure obtained above was subjected to plasma treatment using argon-oxygen mixed plasma (Ar:O2=5:1), with a treatment power of 80W and a treatment time of 8min.

[0069] (5) Preparation of the second modified solution:

[0070] At room temperature, 4.76 g (20 mmol) of 3-mercaptopropyltriethoxysilane and 2.10 g (10 mmol) of 2-methyl-2-acrylate-2-hydroxyethyl phosphate were mixed (the molar ratio of the mercapto group in 3-mercaptopropyltriethoxysilane to the double bond in 2-methyl-2-acrylate-2-hydroxyethyl phosphate was 2:1), and 0.1 g of triethylamine was added as a nucleophilic catalyst. The mixture was stirred at 40 °C for 4 hours to obtain a functionalized precursor containing thioether bonds, residual mercapto groups, silanoxy groups, and phosphate groups.

[0071] The above-mentioned functionalized precursor was added to a mixed solvent consisting of 40 mL ethanol, 8 mL deionized water, and 0.5 mL glacial acetic acid, and the pH was adjusted to 4.5. The mixture was stirred and hydrolyzed at room temperature for 2 hours to obtain a clear second modified solution with a solid content of approximately 3%. The preparation principle of the second modified solution is as follows:

[0072]

[0073] The intermediate structure treated by plasma in step (4) was immersed in the second modified liquid and soaked at 60°C for 60 minutes. After removal, the surface was rinsed with deionized water and placed in an oven to cure at 80°C for 90 minutes to obtain the modified intermediate structure. During the curing process, the Si-OH groups generated by hydrolysis undergo a condensation reaction with the -OH and -COOH groups on the surface of the intermediate structure to form a strong Si-OC covalent bond; at the same time, a uniform organic-inorganic hybrid coupling agent graft layer containing both thiol and phosphate groups is formed on its surface.

[0074] (6) Electroless copper plating: The modified intermediate structure obtained in step (5) is immersed in a commercially available electroless copper plating solution and reacted at 45°C for 60 minutes to obtain an electroless copper plating layer with a thickness of about 5 μm. Since the grafted layer is rich in phosphate ester groups and mercapto groups, the phosphate ester groups form a stable bidentate chelate coordination structure (Cu-OP bond) with the copper surface, and the mercapto groups form a high-affinity Cu-S covalent bond with the copper atoms, making the electroless copper plating layer extremely firmly bonded.

[0075] (7) Take the second flexible copper-clad laminate (soft copper-based FCCL, containing a polyimide film thickness of 25μm and a copper foil thickness of 12μm, used as the top cover of the heat spreader shell), and treat it with oxygen plasma at a power of 100W, a treatment time of 10min, and an oxygen flow rate of 50sccm. The modified intermediate structure with a copper layer obtained in step (6) and the second flexible copper-clad laminate treated with oxygen plasma are then encapsulated by vacuum thermopressing diffusion bonding. The process conditions include: a vacuum degree of 5×10⁻⁶. -4 Pa, hot pressing temperature 280℃, pressure 5MPa, heat and pressure holding for 60min.

[0076] (8) Water injection and sealing: Inject water into the structure formed by sealing in step (7), the water volume is 60% of the cavity volume, and evacuate to 10. -2 After Pa, laser sealing is performed to obtain a flexible heat spreader.

[0077] The total thickness of the flexible heat exchange plate obtained in this embodiment is 0.22 mm, which is an ultra-thin flexible heat exchange plate.

[0078] Tests showed that the equivalent thermal conductivity of the flexible heat spreader reached 6500 W / (m·K), and its performance retention rate was over 90% after 100 bending cycles.

[0079] Example 2

[0080] Example 2 is basically the same as Example 1, except that the liquid absorption core structure is different. The liquid absorption core structure of Example 2 is a combination of close-packed hexagonal lattice and body-centered cubic lattice, stacked in three heterogeneous layers. The bottom layer (near the first flexible copper-clad laminate) is a close-packed hexagonal lattice, the top layer (near the second flexible copper-clad laminate) is a body-centered cubic lattice, and the middle layer is a close-packed hexagonal lattice; the lattice filling rate is 55%. The total thickness of the flexible heat spreader obtained in Example 2 is 0.20 mm.

[0081] The rest is the same as in Example 1, and will not be described again here.

[0082] Example 3

[0083] Example 3 is essentially the same as Example 1, except that the liquid-absorbing core structure is different. The liquid-absorbing core structure in Example 3 is a body-centered cubic lattice structure with a lattice unit size of 40 μm, a lattice edge diameter of 10 μm, and a lattice filling rate of 40%. The regular bump array contains cylindrical bumps with a diameter of 30 μm, a height of 140 μm, and a spacing of 80 μm. The gas channel support pillars are cylindrical with a diameter of 40 μm, a height of 140 μm, and a spacing of 150 μm; the gas channel support pillars are distributed at 150 μm intervals along the length of the heat spreader. The total thickness of the flexible heat spreader obtained in Example 3 is 0.25 mm.

[0084] The rest is the same as in Example 1, and will not be described again here.

[0085] Example 4

[0086] Example 4 is essentially the same as Example 1, except that the liquid-absorbing core structure is different. The liquid-absorbing core structure in Example 4 is a close-packed hexagonal structure with a lattice unit size of 60 μm, a lattice edge diameter of 20 μm, and a lattice filling rate of 50%. The regular bump array contains cylindrical bumps with a diameter of 50 μm, a height of 160 μm, and a spacing of 80 μm. The gas channel support pillars are cylindrical with a diameter of 40 μm, a height of 140 μm, and a spacing of 150 μm; the gas channel support pillars are distributed at 150 μm intervals along the length of the heat spreader. The total thickness of the flexible heat spreader obtained in Example 3 is 0.25 mm.

[0087] The rest is the same as in Example 1, and will not be described again here.

[0088] Example 5

[0089] Example 5 is basically the same as Example 1, except that step (5) is slightly different:

[0090] The preparation method of the second modified liquid in Example 5 includes: mixing 3-mercaptopropylmethyldimethoxysilane and 2-methyl-2-acrylate-2-hydroxyethyl phosphate at room temperature, wherein the amounts of both are such that the molar ratio of the thiol group in 3-mercaptopropyltriethoxysilane to the double bond in 2-methyl-2-acrylate-2-hydroxyethyl phosphate is 5:1; adding 0.1 g of dimethylaminopyridine as a nucleophilic catalyst; and stirring the reaction at 60 °C for 0.5 h to obtain a functionalized precursor containing thioether bonds, residual thiol groups, siloxy groups, and phosphate groups.

[0091] The above-mentioned functionalized precursor was added to a mixed solvent consisting of 30 mL ethanol, 15 mL deionized water and 0.5 mL glacial acetic acid, and the pH of the mixed solvent was adjusted to 3.5. The mixture was stirred and hydrolyzed at room temperature for 8 h to obtain the second modified solution.

[0092] The intermediate structure treated with plasma in step (4) was immersed in the second modified liquid at 25°C for 60 minutes. After removal, the surface was rinsed with deionized water and placed in an oven to cure at 60°C for 120 minutes to obtain the modified intermediate structure.

[0093] The rest is the same as in Example 1, and will not be described again here.

[0094] Example 6

[0095] Example 6 is basically the same as Example 1, except that step (5) is slightly different:

[0096] At room temperature, 3-mercaptopropyltrimethoxysilane and 2-methyl-2-acrylate-2-hydroxyethyl phosphate were mixed, with the amounts of both being such that the molar ratio of the thiol group in 3-mercaptopropyltriethoxysilane to the double bond in 2-methyl-2-acrylate-2-hydroxyethyl phosphate was 1.5:1. 0.1 g of 1,8-diazacycloundecene-7-ene was added as a nucleophilic catalyst, and the mixture was stirred at 25 °C for 10 h to obtain a functionalized precursor containing thioether bonds, residual thiol groups, silanoxy groups, and phosphate groups.

[0097] The above-mentioned functionalized precursor was added to a mixed solvent consisting of 40 mL ethanol, 3 mL deionized water and 0.5 mL glacial acetic acid, and the pH of the mixed solvent was adjusted to 5. The mixture was stirred and hydrolyzed at room temperature for 4 h to obtain the second modified solution.

[0098] The intermediate structure treated with plasma in step (4) was immersed in the second modified liquid at 40°C for 5 minutes. After removal, the surface was rinsed with deionized water and placed in an oven at 90°C for 60 minutes to cure, thus obtaining the modified intermediate structure.

[0099] The rest is the same as in Example 1, and will not be described again here.

[0100] Example 7

[0101] Example 7 is basically the same as Example 1, except that steps (1) and (2) are slightly different, specifically including:

[0102] (1) Take the first flexible copper clad laminate (soft copper-based FCCL, the thickness of the polyimide film it contains is 25μm and the thickness of the copper foil is 12μm) and treat it with oxygen plasma. The treatment power is 50W, the treatment time is 5min, and the oxygen flow rate is 50sccm.

[0103] (2) Dissolve 2-methyl-2-acrylic acid-2-hydroxyethyl ester phosphate in ethanol to prepare a 1wt% solution, and coat it onto the surface of the first flexible copper-clad laminate after oxygen plasma treatment by spin coating at a spin coating speed of 2000 rpm, and then heat cure at 60°C for 120 min.

[0104] The rest is the same as in Example 1, and will not be described again here.

[0105] Example 8

[0106] Example 8 is basically the same as Example 1, except that steps (1) and (2) are slightly different, specifically including:

[0107] (1) Take the first flexible copper clad laminate (soft copper-based FCCL, the thickness of the polyimide film it contains is 25μm and the thickness of the copper foil is 12μm) and treat it with oxygen plasma. The treatment power is 200W, the treatment time is 20min, and the oxygen flow rate is 50sccm.

[0108] (2) Dissolve 2-methyl-2-acrylic acid-2-hydroxyethyl ester phosphate in ethanol to prepare a 3wt% solution, and coat it onto the surface of the first flexible copper-clad laminate after oxygen plasma treatment by spin coating at a spin coating speed of 2000 rpm, and then heat cure at 90°C for 60 min.

[0109] The rest is the same as in Example 1, and will not be described again here.

[0110] Example 9

[0111] Example 9 is essentially the same as Example 1, except that a 5 μm thick copper layer is formed on the modified intermediate structure using vacuum magnetron sputtering. The rest of the process is the same as in Example 1 and will not be repeated here.

[0112] Example 10

[0113] Example 10 is basically the same as Example 1, except that a regular array of bumps is not formed when 3D printing the liquid-absorbing core structure. The rest is the same as in Example 1, and will not be described again here.

[0114] Comparing Examples 1 and 10, it was found that the equivalent thermal conductivity of the flexible heat spreader in Example 10 was approximately 4800 W / (m·K), which is about 26% lower than that in Example 1 (6500 W / (m·K)). This indicates that the regular array of bumps can increase the specific surface area and enhance capillary reflux.

[0115] Comparative Example 1

[0116] The only difference between Comparative Example 1 and Example 1 is that the 2-methyl-2-acrylate-2-hydroxyethyl phosphate modification in step (2) is not performed, and the second modification solution treatment in step (5) is not performed. Specifically, the following steps are included:

[0117] (1) Take the first flexible copper clad laminate (soft copper-based FCCL, the thickness of the polyimide film it contains is 25μm and the thickness of the copper foil is 12μm) and treat it with oxygen plasma. The treatment power is 100W, the treatment time is 10min, and the oxygen flow rate is 50sccm.

[0118] (2) A liquid-absorbing core structure is 3D printed on the first flexible copper-clad laminate processed in step (1) to obtain an intermediate structure, specifically including: using a surface projection photopolymerization 3D printer, with a printing layer thickness of 15μm, and using an acrylic photosensitive resin. The liquid-absorbing core adopts a body-centered cubic lattice structure with a lattice unit size of 80μm, a lattice edge diameter of 20μm, and a lattice filling rate of 60%; it adopts a double-layer stacked structure (each layer is 75μm high, and the total height is 150μm). The regular bump array contains cylindrical bumps with a diameter of 50μm, a height of 150μm, and a spacing of 120μm. The gas channel support pillars are cylindrical with a diameter of 60μm, a height of 150μm, and a spacing of 250μm; the gas channel support pillars are distributed at 200μm intervals along the length of the heat spreader.

[0119] (3) The intermediate structure obtained in step (2) above is subjected to plasma treatment using argon-oxygen mixed plasma (Ar:O2=5:1), with a treatment power of 80W and a treatment time of 8min.

[0120] (4) Chemical copper plating: The structure obtained in step (3) is immersed in a commercially available chemical copper plating solution and reacted at 45°C for 60 minutes to obtain a chemical copper plating layer with a thickness of about 5 μm.

[0121] (5) Take the second flexible copper-clad laminate (soft copper-based FCCL, containing a polyimide film thickness of 25 μm and a copper foil thickness of 12 μm), and treat it with oxygen plasma at a power of 100 W for 10 min and an oxygen flow rate of 50 sccm. The structure with a copper layer obtained in step (4) and the oxygen-plasma-treated second flexible copper-clad laminate are then encapsulated by vacuum thermopressing diffusion bonding. The process conditions include: a vacuum degree of 5 × 10⁻⁶. -4 Pa, hot pressing temperature 280℃, pressure 5MPa, heat and pressure holding for 60min.

[0122] (6) Water injection and sealing: Inject water into the structure formed by sealing in step (4), the water volume is 60% of the cavity volume, and evacuate to 10. -2 After Pa, laser sealing is performed to obtain a flexible heat spreader.

[0123] During the preparation of Comparative Example 1, it was found that the copper layer could not be uniformly deposited on the surface of the resin absorbent core during electroless copper plating, resulting in numerous unplated areas. Even in the deposited areas, the peel strength between the copper layer and the resin was only 0.3 N / mm. After encapsulation, thermal performance testing showed an equivalent thermal conductivity of only about 800 W / (m·K), and after 10 thermal cycles, plating peeled off and performance degraded. This indicates that without interface modification, the resin and copper layer cannot form an effective bond.

[0124] Comparative Example 2

[0125] The only difference between Comparative Example 2 and Example 1 is that the liquid absorption core structure of Comparative Example 2 is fixed to the first flexible copper-clad laminate by diffusion welding using a stainless steel wire mesh (200 mesh, 150 μm thick) instead of a 3D printed lattice structure.

[0126] The porosity of the wire mesh absorbent core in Comparative Example 2 is approximately 60%, but it lacks three-dimensional interconnected channels and a bump array, resulting in a lower capillary limit. Testing showed an equivalent thermal conductivity of approximately 2800 W / (m·K), with a maximum heat transfer power of only 3W (compared to over 5W in Example 1). This demonstrates that traditional wire mesh structures cannot provide sufficient capillary force and permeability within ultra-thin spaces.

[0127] The flexible heat exchange plates prepared in the above embodiments and comparative examples were subjected to relevant performance tests, and the test methods are as follows: The equivalent thermal conductivity test method is as follows: The heat spreader to be tested is placed horizontally on the heating source (simulated heat source) of the test device. Thermal grease (thermal conductivity approximately 3 W / (m·K), thickness approximately 0.05 mm) is uniformly applied to the upper and lower surfaces of the heat spreader to reduce contact thermal resistance. The heating source uses a ceramic heating element, and the power is controlled by a DC power supply. The heating power Q is gradually increased from 1 W until the heat spreader shows signs of dry burning (i.e., in 1 W increments). Figure 2 This is a schematic diagram of a test system for testing equivalent thermal conductivity. The heating source is located behind the point marked T1, where T1 represents the temperature at the measurement point directly opposite the heating source, and T2 represents the temperature at the measurement point furthest from the heating source. Figure 2 In this context, "12mm" represents the distance from the temperature measuring point to the edge of the sample as 12mm. The formula for calculating the equivalent thermal conductivity is:

[0128] Equivalent thermal conductivity = Test power (W) × Measurement point distance (m) / (Cross-sectional area of ​​heat spreader (m²) 2 ) × temperature difference ΔT (K)).

[0129] Test method for copper peel strength: The copper peel strength is evaluated using the 90° peel strength test method (according to IPC-TM-650 2.4.9 standard).

[0130] Test method for maximum heat transfer power: Maximum heat transfer power is defined as the maximum heating power that the vapor chamber can withstand while maintaining normal operation (without localized dry burning or a rapid temperature rise). Using the same test platform as the "equivalent thermal conductivity test," start with a low power (e.g., 1W) and gradually increase the heating power in 1W increments (reducing the increment to 0.5W when approaching the expected limit). The power stabilization time for each step should be no less than 2 minutes. Record the evaporator and condenser temperatures and calculate the temperature difference ΔT. A temperature difference exceeding 5℃ indicates vapor chamber failure.

[0131] Table 1. Relevant performance of flexible heat spreaders in the examples and comparative examples.

[0132] As can be seen from Table 1, the flexible heat exchange plate prepared by the embodiment of the present invention has better overall performance, and can achieve ultra-thin flexible heat exchange plate while taking into account efficient heat transfer and high reliability.

[0133] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0134] All aspects, embodiments, features, and examples of this invention should be considered illustrative and used to explain and illustrate the invention, but not to limit it. The scope of the invention is defined only by the claims.

[0135] Although the invention has been described with reference to the above embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that substantially equivalents can be substituted for elements in the described embodiments. Therefore, the invention is not intended to be limited to the specific embodiments disclosed, but rather to encompass all embodiments falling within the scope defined by the claims.

Claims

1. A method for preparing a flexible heat spreader, characterized in that, include: S1. The first flexible copper-clad laminate is modified in the following ways: oxygen plasma treatment is performed on the first flexible copper-clad laminate to form oxygen polar groups, then a first modification liquid containing acrylate containing phosphate groups is brought into contact with the first flexible copper-clad laminate containing oxygen polar groups, and then a first curing is performed to form a modified layer containing phosphate groups and vinyl groups on its surface. S2. Using photopolymerization 3D printing technology, a liquid-absorbing core structure is formed on the surface of the first flexible copper-clad laminate with the modified layer to obtain an intermediate structure; S3. The intermediate structure is subjected to a second modification, comprising: subjecting the intermediate structure to oxygen-containing plasma treatment to form oxygen-containing polar groups, contacting the intermediate structure with oxygen-containing polar groups on its surface to a second modification liquid, and then performing a second curing to obtain a modified intermediate structure; wherein the modifying substance contained in the second modification liquid is formed by Michael addition click reaction of a mercaptosilane coupling agent and an acrylate containing phosphate ester groups to form a functionalized precursor, and the functionalized precursor is hydrolyzed to obtain an organic-inorganic hybrid coupling agent graft layer on the surface of the intermediate structure, wherein the graft layer contains phosphate ester groups and mercapto groups to obtain a modified intermediate structure; S4. A copper layer is formed on the modified intermediate structure; S5. The modified intermediate structure with copper layer is encapsulated with the second flexible copper-clad laminate, and then water is injected and sealed to obtain a flexible heat spreader.

2. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The phosphate-containing acrylates include 2-methyl-2-acrylate-2-hydroxyethyl phosphate.

3. The method for preparing the flexible heat spreader according to claim 1, characterized in that, The concentration of phosphate ester-containing acrylate in the first modified solution is 1wt%-5wt%.

4. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The first curing temperature is 60~90℃, and the curing time is 30~120min.

5. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The intermediate structure with oxygen-containing polar groups on its surface is immersed in the second modification liquid at a temperature of 25~40℃ and maintained for 5min~60min, and then the second curing is carried out.

6. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The second curing temperature is 60~90℃, and the curing time is 60min~120min.

7. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The preparation method of the second modified liquid includes: The functionalized precursor was prepared by Michael addition click reaction of a mixed reaction system containing a mercaptosilane coupling agent, a phosphate ester-containing acrylate, and a nucleophilic base catalyst. The functionalized precursor is hydrolyzed in a mixed solvent containing an organic solvent and water to obtain the second modified liquid.

8. The method for preparing a flexible heat spreader according to claim 7, characterized in that, The mercaptosilane coupling agent includes one or a combination of more of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethoxysilane.

9. The method for preparing a flexible heat spreader according to claim 7, characterized in that, The amounts of the mercaptosilane coupling agent and the phosphate-containing acrylate are such that the molar ratio of the mercapto groups in the mercaptosilane coupling agent to the double bonds in the phosphate-containing acrylate is 1.5:1 to 5:

1.

10. The method for preparing a flexible heat spreader according to claim 7, characterized in that, The nucleophilic base catalyst includes one or more combinations of triethylamine, dimethylaminopyridine, 1,8-diazacycloundecene-7-ene, and hexamethylenediamine.

11. The method for preparing a flexible heat spreader according to claim 7, characterized in that, The Michael addition click reaction is carried out at a temperature of 25°C to 60°C and / or for a reaction time of 0.5 h to 10 h.

12. The method for preparing a flexible heat spreader according to claim 7, characterized in that, The functionalized precursor is hydrolyzed in a mixed solvent with a pH of 3.5 to 5.0, wherein the volume ratio of organic solvent to water in the mixed solvent is 5 to 20: 1 to 3.

13. The method for preparing a flexible heat spreader according to claim 7, characterized in that, The hydrolysis time is 4-8 hours.

14. The method for preparing a flexible heat spreader according to claim 7, characterized in that, The solid content of the second modified liquid is 1wt%~5wt%.

15. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The liquid-absorbing core structure includes a crystal lattice structure, a bump array, a vapor channel, and a support pillar; the bump array is disposed on the surface of the crystal lattice structure and / or embedded in the crystal lattice structure, and the support pillar is disposed in the vapor channel.

16. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The liquid-absorbing core structure adopts a gas-liquid coplanar layout.

17. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The material of the liquid-absorbing core structure includes acrylate photosensitive resin and / or epoxy acrylate photosensitive resin.

18. The method for preparing a flexible heat spreader according to claim 15, characterized in that, The lattice structure is a single layer or multiple layers, including a body-centered cubic lattice and / or a close-packed hexagonal lattice; and / or, the lattice filling rate of the liquid-absorbing core structure is 40%~70%, the lattice unit size is 40μm~120μm, and the lattice edge diameter is 10μm~40μm.

19. The method for preparing a flexible heat spreader according to claim 15, characterized in that, The diameter of the bumps in the bump array is 30μm~80μm, the height of the bumps is 140μm~200μm, and the distance between adjacent bumps is 80μm~200μm.

20. The method for preparing a flexible heat spreader according to claim 15, characterized in that, The support columns are arranged in an array in the steam channel; and / or, the diameter of the support columns is 40μm~100μm, the height is 140μm~200μm, and the distance between adjacent support columns is 150μm~400μm.

21. The method for preparing a flexible heat spreader according to claim 1, characterized in that, In step S4, the method for forming the copper layer includes chemical copper plating or magnetron sputtering.

22. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The thickness of the copper layer is 0.5μm to 5μm.

23. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The preparation method further includes: subjecting the second flexible copper-clad laminate to oxygen-containing plasma treatment, and then encapsulating it with a modified intermediate structure having a copper layer.

24. The method for preparing a flexible heat spreader according to claim 1, characterized in that, The encapsulation method includes vacuum thermopress diffusion bonding encapsulation.

25. A flexible heat spreader, characterized in that, It is prepared by the method of any one of claims 1-24.

26. An electronic device, characterized in that, Including the flexible heat spreader as described in claim 25.

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