A high thermal conductivity flexible copper clad laminate, its preparation method and application

Abstract

This invention provides a high thermal conductivity flexible copper-clad laminate, its preparation method, and its applications. The high thermal conductivity flexible copper-clad laminate includes an insulating modified polymer film with through-holes. An organic-inorganic hybrid coupling agent graft layer is present on the surface of the film and on the walls of the through-holes. The graft layer is bonded to the modified polymer film via Si-O-C and / or Si-O-Si, and contains thiol and phosphate groups. A metallic copper structure is also included, comprising copper layers covering both sides of the modified polymer film and copper pillars filling the through-holes. The phosphate groups in the graft layer form a bidentate chelate coordination structure with copper, and the thiol groups form Cu-S covalent bonds with copper. The high thermal conductivity flexible copper-clad laminate provided by this invention exhibits excellent interfacial bonding strength and Z-direction thermal conductivity, as well as excellent flexibility and reliability.

Description

Technical Field

[0001] This invention belongs to the field of electronic materials and electronic components technology, specifically relating to a high thermal conductivity flexible copper clad laminate, its preparation method and application. Background Technology

[0002] With the rapid development of 5G communication, wearable devices, flexible displays, and high-power integrated circuits, electronic components are evolving towards miniaturization, high-density integration, and flexibility. This leads to a sharp increase in heat generation per unit area of ​​the device. If this heat cannot be dissipated in time, it will seriously affect the reliability and lifespan of the device. Flexible copper clad laminate (FCCL), as a key basic material for connecting and supporting electronic components, has its own thermal conductivity and heat dissipation capabilities becoming a bottleneck restricting the performance of the entire system.

[0003] FCCLs are typically formed by laminating a polymer insulating base film (such as polyimide (PI) or polyethylene terephthalate (PET)) with single-sided or double-sided copper foil. Existing FCCLs suffer from poor Z-axis thermal conductivity. The intrinsic thermal conductivity of the polymer base film is low (e.g., approximately 0.2 W / m·K for PI and 0.15 W / m·K for PET), meaning that heat transfer in the direction perpendicular to the board surface (Z-axis) is almost entirely blocked by the insulating layer, preventing localized hotspots from effectively dissipating to the backplane or heat sink. Existing methods to improve the Z-axis thermal conductivity of FCCLs include filling the polymer with thermally conductive fillers, which severely degrades the film's mechanical flexibility; or using laser drilling followed by electroplating to fill the holes, but this faces problems such as poor adhesion between the hole walls and the copper layer, and easy breakage of the plating inside the holes. Furthermore, these methods are relatively complex and have low reliability. In addition, existing FCCLs also suffer from insufficient interfacial adhesion.

[0004] Existing technologies typically employ methods such as plasma treatment, chemical roughening, or coating with coupling agents to improve adhesion. However, these methods cannot effectively achieve high-strength bonding between the polymer film and the copper layer in adhesive-free FCCL (two-layer FCCL), especially after thermal shock or dynamic bending, which can easily lead to problems such as delamination and blistering.

[0005] Therefore, developing an FCCL material that combines high Z-thermal conductivity with excellent interfacial bonding is one of the technical challenges that urgently needs to be solved in this field. Summary of the Invention

[0006] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions:

[0007] A first aspect of the present invention provides a high thermal conductivity flexible copper-clad laminate, comprising:

[0008] A modified polymer membrane, wherein the modified polymer membrane is insulating and has through holes; the surface of the modified polymer membrane and the pore walls of the through holes have an organic-inorganic hybrid coupling agent graft layer, the graft layer is bonded to the modified polymer membrane through Si-OC and / or Si-O-Si covalent bonds, and the graft layer contains thiol and phosphate ester groups;

[0009] The metallic copper structure includes copper layers covering both sides of the modified polymer film and copper pillars filling the through holes. The phosphate groups in the grafted layer form a bidentate chelate coordination structure with copper, and the thiol groups form Cu-S covalent bonds with copper.

[0010] The high thermal conductivity flexible copper-clad laminate of this invention features copper pillars formed within the vias of a polymer film. Since the thermal conductivity of copper (approximately 398 W / m·K) is much higher than that of the polymer film substrate, heat can bypass the low thermal conductivity of the polymer film and be directly conducted from the heating surface to the back heat sink via the copper pillars. This provides a metallic highway for heat transfer in the Z-direction (perpendicular to the board surface), thus exhibiting excellent Z-direction thermal conductivity. Simultaneously, this high thermal conductivity flexible copper-clad laminate constructs a molecular bridge based on strong chemical bonding between the polymer film and the metal layer. The phosphate ester groups and thiol groups at the grafted layer ends can form extremely strong coordination and covalent bonds with copper atoms, with a bonding strength far exceeding physical adsorption or weak hydrogen bonding, endowing this high thermal conductivity flexible copper-clad laminate with excellent interfacial bonding strength.

[0011] In some embodiments, the grafted layer is formed by modifying and curing a polymer film with oxygen-containing active groups on its surface using an interface modification liquid. The modifying substance contained in the interface modification liquid is formed by Michael addition click reaction of a mercaptosilane coupling agent and an acrylate monomer containing a phosphate ester group to form a functionalized precursor, and the functionalized precursor is obtained by hydrolysis.

[0012] In some embodiments, the oxygen-containing active groups include one or more of -OH, -COOH, and -C=O.

[0013] In some embodiments, the mercaptosilane coupling agent includes one or a combination of more of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethoxysilane.

[0014] In some embodiments, the phosphate-containing acrylate monomer includes 2-methyl-2-acrylate-2-hydroxyethyl phosphate.

[0015] In some embodiments, the modified polymer film has an array of through-holes, and the copper structure has an array of copper pillars filled within these through-holes. The copper pillars formed by the regularly spaced array of through-holes further enhance the Z-thermal conductivity of the flexible copper-clad laminate. Simultaneously, the array of through-holes provides a strong mechanical interlocking effect, which, combined with the strong interfacial bonding force imparted by the modification treatment, creates a dual enhancement mechanism that results in excellent mechanical properties for the high thermal conductivity flexible copper-clad laminate.

[0016] In some embodiments, the copper pillars completely fill the through holes, that is, the copper pillars densely fill the through holes.

[0017] In some embodiments, the aperture of a single hole in the array of vias is 10μm to 500μm, the hole spacing is 100μm to 2000μm, and the aperture ratio is 10% to 40%.

[0018] In some embodiments, the array of through holes is arranged in a staggered pattern of equally spaced regular hexagons, with the centers of three adjacent through holes forming an equilateral triangle.

[0019] In some embodiments, the center distance between the vias in the array is 1.5 to 4 times the aperture diameter.

[0020] The aforementioned array of through-holes allows the polymer film to maintain isotropic bending mechanical reliability while possessing a vertical heat conduction path. The small and regularly distributed apertures of the array of through-holes minimize disruption to the mechanical continuity of the polymer film. After lamination, the through-holes are filled with highly ductile pure copper, which deforms in tandem with the polymer film during dynamic bending, reducing the likelihood of cracking. Compared to existing technologies that add a large amount of rigid thermally conductive filler to the polymer matrix, the high thermal conductivity flexible copper-clad laminate of this invention exhibits superior flexibility and reliability. The copper pillars of the metallic copper structure cooperate with the array of through-holes, thus possessing a corresponding arrangement and structural features.

[0021] In some embodiments, the copper layers covering both sides of the modified polymer film in the metallic copper structure are connected to the copper pillars filling the through-holes, giving the metallic copper structure continuity. The copper layers on both sides and the copper filling the through-holes of the polymer film achieve thermal connectivity, forming a three-dimensional heat dissipation network with high lateral diffusion and high vertical conduction characteristics.

[0022] In some embodiments, the polymer film can be made of any suitable polymer known in the art for preparing flexible copper-clad laminates, such as, but not limited to, polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), etc.

[0023] In some embodiments, the thickness of the polymer film can be 12.5~125μm, preferably 12.5μm-25μm.

[0024] A second aspect of the present invention provides a method for preparing a highly thermally conductive flexible copper-clad laminate, comprising:

[0025] An insulating polymer film with through-pores is provided, wherein the surface of the polymer film has oxygen-containing active groups;

[0026] The interface modification liquid is brought into contact with the polymer film and then cured to obtain a modified polymer film; the modifying substance contained in the interface modification liquid is formed by Michael addition click reaction of mercaptosilane coupling agent and phosphate ester-containing acrylate monomer to form a functionalized precursor, and the functionalized precursor is hydrolyzed to obtain the product.

[0027] A metallic copper structure is formed on the modified polymer film, comprising a copper layer covering both sides of the modified polymer film and copper pillars filling the through-holes, to obtain a flexible copper-clad laminate with high thermal conductivity.

[0028] The Si-OH groups in the interface modification solution undergo a condensation reaction with the oxygen-containing active groups on the polymer film surface, forming a Si-OC or Si-O-Si network after curing. Simultaneously, a uniform organic-inorganic hybrid coupling agent graft layer containing both thiol and phosphate groups is formed on the film surface and inside the pore walls. The phosphate and thiol groups in this graft layer enhance the chemical affinity with the metallic copper structure, imparting excellent interfacial bonding to the high thermal conductivity flexible copper-clad laminate. Copper pillars filling the through-holes of the polymer film improve its Z-direction thermal conductivity.

[0029] In some embodiments, the preparation method of the interface-modified liquid includes:

[0030] The functionalized precursor was prepared by Michael addition click reaction of a mixed reaction system containing a mercaptosilane coupling agent, an acrylate monomer containing a phosphate ester group, and a nucleophilic base catalyst.

[0031] The functionalized precursor is hydrolyzed in a mixed solvent containing organic solvent and water to obtain the interface-modified liquid.

[0032] In some embodiments, the mercaptosilane coupling agent includes one or a combination of more of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethoxysilane.

[0033] In some embodiments, the phosphate-containing acrylate monomer includes 2-methyl-2-acrylate-2-hydroxyethyl phosphate.

[0034] In some embodiments, the amounts of the mercaptosilane coupling agent and the phosphate-containing acrylate monomer satisfy the following: the molar ratio of the mercapto group in the mercaptosilane coupling agent to the double bond in the phosphate-containing acrylate monomer is 1.5:1 to 5:1.

[0035] 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. The molar ratio of the nucleophilic base catalyst to the phosphate-containing acrylate monomer is (0.001~0.2):1.

[0036] In some embodiments, the reaction temperature of the Michael addition click reaction is 25°C to 60°C.

[0037] In some embodiments, the reaction time of the Michael addition click reaction is 0.5 to 10 hours.

[0038] In some embodiments, the functionalized precursor is hydrolyzed in a mixed solvent with a pH of 3.5 to 5.0.

[0039] In some embodiments, the volume ratio of the organic solvent to water in the mixed solvent is 5~20:1~3.

[0040] In some embodiments, the hydrolysis time is 4-8 hours.

[0041] In some embodiments, the solid content of the interface modification liquid is 1wt% to 5wt%.

[0042] In some embodiments, the polymer film is immersed in the interface modification liquid at a temperature of 25~40°C and maintained for 5min~60min, and then cured.

[0043] In some embodiments, the curing temperature is 60°C to 150°C.

[0044] In some embodiments, the curing time is 60 min to 120 min.

[0045] In some embodiments, the method for preparing the metallic copper structure specifically includes: depositing a copper seed layer on the surface of the modified polymer film and the pore walls of the through holes to form an intermediate film; stacking copper foils on both sides of the intermediate film and vacuum hot pressing to form the metallic copper structure.

[0046] In some embodiments, the method for preparing the metallic copper structure specifically includes: depositing a copper seed layer on the surface of the modified polymer film and the pore walls of the through holes to form an intermediate film; bonding a copper foil to one side of the intermediate film by vacuum hot pressing, and electroplating copper using the bonded copper foil as a cathode, so that copper fills the through holes from one side of the copper foil to form copper pillars, and forming a copper layer on the other side of the film where the copper foil is not bonded, thereby forming the metallic copper structure.

[0047] After modification with an interface-modifying solution, the polymer film surface contains a large number of thiol and phosphate groups. The phosphate groups, through their exposed phosphate groups, form a stable bidentate chelate coordination structure with the copper seed layer, transforming the copper oxide layer into a dense copper phosphate conversion film, providing high-strength Cu-OP ion-covalent mixed bonds. Secondly, the thiol groups, acting as soft-base ligands, form high-affinity Cu-S covalent bonds with copper atoms. The multi-site anchoring of the phosphate-thiol hybrid system gives the polymer film excellent peel resistance to the metallic copper structure.

[0048] In some embodiments, the vacuum hot pressing process conditions include: a hot pressing temperature of 180~350℃, a pressure of 3MPa~10MPa, and a time of 30min~90min. The hot pressing temperature can be determined based on the glass transition temperature (Tg) of the selected polymer film; for example, 300~350℃ for PI film and 180~220℃ for PET film.

[0049] Under high temperature and pressure conditions, the phosphate ester groups in the grafted layers on the polymer film surface and pore walls form strong coordination bonds with the copper atoms on the copper foil surface and in the copper seed layer; simultaneously, the thiol groups also form strong Cu-S bonds with the copper surface. These multidentate chemical bonds, combined with the mechanical interlocking anchoring effect provided by the metallization layer on the pore walls, enable an atomic / molecular-level super-strong bond between the copper foil, the copper layer inside the pores, and the polymer matrix.

[0050] In the scheme of laminating copper foil on both sides, the copper seed layer inside the hole undergoes sintering and densification during hot pressing, fusing with the copper foil on both sides to form a pure copper heat-conducting pillar penetrating the polymer film. In the scheme of laminating copper foil on one side and combining it with electroplating, the copper foil on one side is used as the cathode, and the other side of the polymer film without copper foil is immersed in the copper plating solution. The copper layer on that side is thickened to the target thickness through electrodeposition. At the same time, the electroplating process also further fills and thickens the copper layer inside the through hole, realizing the formation of the copper layer on the other side and the reliable encapsulation of the through hole.

[0051] In some embodiments, the method for depositing the copper seed layer can be any known suitable method, such as physical vapor deposition (e.g., magnetron sputtering) or chemical plating.

[0052] In some embodiments, the thickness of the copper seed layer is 0.5 μm to 5 μm.

[0053] In some embodiments, the electroplating solution used for copper plating only needs to be capable of copper plating, such as copper sulfate pentahydrate (CuSO4·5H2O) with a concentration of 150 g / L to 220 g / L, or sulfuric acid (H2SO4) with a concentration of 50 g / L to 70 g / L. The electroplating current density can be 2 A / dm³. 2 ~4A / dm 2The time can be from 30 minutes to 180 minutes.

[0054] In some embodiments, the thickness of the copper foil is 8μm to 70μm, preferably 12μm to 35μm.

[0055] In some embodiments, the modified polymer film has an array of through-holes. For example, the array of through-holes can be formed on the polymer film by laser drilling or mechanical die-cutting. The further arrangement and structural features of the array of through-holes have been described in detail in the first aspect of the present invention, and will not be repeated here.

[0056] In some embodiments, the polymer film is subjected to plasma activation treatment to give its surface oxygen-containing active groups (e.g., -OH, -COOH, -C=O, etc.), and the plasma activation treatment can also increase the surface roughness of the polymer film. The plasma activation treatment can be atmospheric or vacuum plasma treatment, and the gas used can be a mixture of argon and oxygen.

[0057] The high thermal conductivity flexible copper-clad laminate described in the first aspect of this invention can be prepared using the preparation method provided in the second aspect of this invention. Furthermore, the preparation method provided by this invention is highly compatible with existing flexible copper-clad laminate roll-to-roll production lines, allowing for continuous operation of polymer film treatment, metallization, and lamination.

[0058] A third aspect of the present invention provides a high thermal conductivity flexible copper clad laminate, which is prepared by the preparation method of the high thermal conductivity flexible copper clad laminate described in any of the technical solutions.

[0059] The fourth aspect of the present invention provides the application of the high thermal conductivity flexible copper-clad laminate described in any of the technical solutions in the fabrication of electronic devices.

[0060] In some embodiments, the electronic device includes a flexible LED light strip, a local hotspot heat dissipation component for a flexible circuit board, a heat dissipation substrate for a wearable device chip, or a heat dissipation connector for a battery module.

[0061] Compared with the prior art, the present invention has at least some or all of the following beneficial effects: The present invention uses a specific interface modifying liquid to chemically modify the surface of the polymer film to significantly improve the interfacial bonding force between it and the metallic copper structure; at the same time, through holes are opened on the polymer film and a copper pillar thermal conduction path is constructed through the polymer film, thereby improving the Z thermal conductivity of the flexible copper clad laminate, and the resulting flexible copper clad laminate also maintains excellent flexibility and reliability. Attached Figure Description

[0062] 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.

[0063] Figure 1 This is a flowchart of the preparation process of Embodiment 1 of the present invention;

[0064] Figure 2 This is a schematic diagram of the layout of the array of through holes on the PI film in Embodiment 1 of the present invention;

[0065] Figure 3 This is a flowchart of the preparation process of Embodiment 2 of the present invention. Detailed Implementation

[0066] The invention will be more fully understood through the following detailed description of 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.

[0067] 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.

[0068] Example 1

[0069] This embodiment provides a high thermal conductivity flexible copper-clad laminate and its preparation method. Figure 1 This is a flowchart of the preparation process in this embodiment, which specifically includes the following steps:

[0070] (1) Selection of base film and preparation of array vias:

[0071] A 25 μm thick polyimide (PI) film was selected as the insulating substrate. An array of through-holes was fabricated on the PI film using a UV laser drilling machine. The hole diameter (D) was 50 μm, the hole spacing (P) was 200 μm, and the holes were arranged in a staggered, equally spaced hexagonal pattern, with an open area ratio of approximately 10%. This arrangement ensures that the centers of three adjacent micropores form an equilateral triangle, guaranteeing the material's isotropic bending reliability in the XY plane. Figure 2 This is a schematic diagram of the layout of the PI film array through-holes in this embodiment, where the aperture (D) is 50 μm and the hole spacing (P) is 200 μm.

[0072] (2) Plasma activation treatment:

[0073] The PI film with arrayed through holes obtained in step (1) is placed in a vacuum plasma treatment device, and a mixture of argon and oxygen (argon to oxygen volume ratio of 4:1) is introduced. The mixture is treated for 5 minutes at a power of 200W to introduce a large number of active groups such as -OH, -COOH, and -C=O on the surface of the PI film and the inner surface of the pore wall. At the same time, the surface roughness of the PI film is moderately increased.

[0074] (3) Preparation of interface-modified liquid

[0075] Click chemistry reaction (Michael addition): 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, with the amounts of both satisfying a molar ratio of 2:1 between the thiol group in 3-mercaptopropyltriethoxysilane and the double bond in 2-methyl-2-acrylate-2-hydroxyethyl phosphate. 0.1 g of triethylamine was added as a nucleophilic catalyst, and the reaction was stirred at 40 °C for 4 h to obtain a functionalized precursor containing thioether bonds, residual thiol groups, silanoxy groups, and phosphate groups.

[0076] 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 of the mixed solvent was adjusted to 4.5. The mixture was stirred and hydrolyzed at room temperature for 2 h to obtain a clear interface-modified solution with a solid content of about 3 wt%.

[0077] The preparation principle of the interface modification liquid is as follows:

[0078]

[0079] (4) Immerse the PI film with arrayed through-holes activated in step (2) into the above interface modification solution and soak it at 60°C for 60 minutes. Then take it out, rinse the surface with deionized water, and place it in an oven to cure at 120°C for 90 minutes. During the curing process, the Si-OH groups generated by hydrolysis react with the -OH and -COOH on the surface of the PI film to form a strong Si-OC covalent bond. At the same time, a uniform organic-inorganic hybrid coupling agent graft layer containing both mercapto groups and phosphate ester groups is formed on the surface of the PI film and inside the pore wall, thus obtaining a modified PI film with arrayed through-holes.

[0080] (5) Preparation of metallic copper structure:

[0081] A modified PI film with arrayed through-holes was immersed in a commercially available electroless copper plating solution and reacted at 45°C for 20 minutes to deposit a copper seed layer with a thickness of approximately 1.5 μm on the entire surface of the PI film and the walls of the through-holes. Because the grafted layer of the organic-inorganic hybrid coupling agent is rich in phosphate ester groups and mercapto groups at its ends, 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 copper atoms, resulting in an extremely strong bond to the copper seed layer.

[0082] Next, double-sided copper-clad vacuum hot pressing is performed: A 18μm thick rolled copper foil is aligned on each side of the PI film with the copper seed layer prepared above, and placed in a vacuum hot press. The temperature is set at 320℃, the pressure at 6MPa, and the hot pressing time at 60 minutes. During the hot pressing process, the copper seed layer inside the hole undergoes sintering and densification, and achieves metallurgical bonding with the copper foil on both sides at the interface through strong Cu-OP and Cu-S chemical bonds and atomic diffusion, forming a pure copper heat-conducting pillar penetrating the PI film. After cooling, it is removed to obtain a high thermal conductivity flexible copper-clad laminate.

[0083] Example 2

[0084] This embodiment provides a high thermal conductivity flexible copper-clad laminate and its preparation method. Figure 3 This is a flowchart of the preparation process in this embodiment. The only difference from Embodiment 1 is that step (5), which involves preparing the metallic copper structure, is different. Specifically, it includes:

[0085] A modified PI film with arrayed through holes was immersed in a commercially available electroless copper plating solution and reacted at 45°C for 20 minutes to deposit a copper seed layer with a thickness of about 1.5 μm on the entire surface of the PI film and the walls of the through holes.

[0086] A 18μm thick rolled copper foil is aligned and covered on one side of the PI film with a copper seed layer. The foil is then placed in a vacuum hot press at 320℃, 6MPa, and for 60 minutes. Next, using this copper foil as the cathode, the exposed side of the PI film (with the electroless copper seed layer) is immersed in a copper plating solution (containing 220g / L copper sulfate pentahydrate and 70g / L sulfuric acid). Electroplating is performed at a current density of 2 A / dm² for 50 minutes, forming an 18μm thick copper layer on this side. Simultaneously, the electroplating process further fills and thickens the copper within the vias, forming densely packed copper pillars within the vias. This results in a three-dimensional and continuous metallic copper structure on the side of the PI film and within the vias, achieving reliable encapsulation.

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

[0088] Example 3

[0089] The only difference between Example 3 and Example 1 is that: in step (1) of Example 3, a PET film with a thickness of 25 μm is used, and an array of through holes is prepared by mechanical die cutting with a hole diameter of 150 μm and a hole spacing of 450 μm; and in step (5), the vacuum hot pressing temperature is 200℃, the pressure is 4 MPa, and the time is 40 min.

[0090] The rest is the same as in Example 1, and will not be described again here.

[0091] Example 4

[0092] The only difference between Example 4 and Example 1 is that in step (1) of Example 4, an array of through holes is prepared on the PI film with a pore diameter of 500 μm, a pore spacing of 2000 μm, and an opening rate of about 40%.

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

[0094] Example 5

[0095] Example 5 is basically the same as Example 1, except that the preparation method of the interface modification liquid is as follows:

[0096] Click-through chemical reaction (Michael addition): 3-mercaptopropylmethyldimethoxysilane and 2-methyl-2-acrylate-2-hydroxyethyl phosphate were mixed at room temperature, with the amounts of both satisfying a molar ratio of thiol group in 3-mercaptopropyltriethoxysilane to double bond in 2-methyl-2-acrylate-2-hydroxyethyl phosphate of 5:1. 0.1 g of dimethylaminopyridine was added as a nucleophilic catalyst, and the mixture was stirred at 60 °C for 0.5 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 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 interface modified solution.

[0098] The PI film with arrayed through-holes activated in step (2) was immersed in the above interface modification solution and treated at 25°C for 60 minutes. Then it was taken out, the surface was rinsed with deionized water, and cured in an oven at 60°C for 120 minutes.

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

[0100] Example 6

[0101] Example 6 is basically the same as Example 1, except that the preparation method of the interface modification liquid is as follows:

[0102] Click-through chemical reaction (Michael addition): 3-mercaptopropyltrimethoxysilane and 2-methyl-2-acrylate-2-hydroxyethyl phosphate were mixed at room temperature, with the amounts of both satisfying a molar ratio of thiol group in 3-mercaptopropyltriethoxysilane to double bond in 2-methyl-2-acrylate-2-hydroxyethyl phosphate of 1.5:1. 0.1 g of 1,8-diazacycloundecene-7-ene was added as a nucleophilic catalyst, and the reaction was stirred at 20 °C for 10 h to obtain a functionalized precursor containing thioether bonds, residual thiol groups, silanoxy groups, and phosphate groups.

[0103] 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 interface modified solution.

[0104] The activated PI film with arrayed through-holes from step (2) was immersed in the above interface modification solution and treated at 40°C for 5 minutes. Then it was taken out, the surface was rinsed with deionized water, and cured in an oven at 150°C for 60 minutes.

[0105] The rest is the same as in Example 1, and will not be described again here.

[0106] Comparative Example 1

[0107] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses the same 25μm PI film and 18μm rolled copper foil as Example 1, but does not perform pore opening treatment and interface modification liquid modification; the PI film is only subjected to plasma activation treatment, and then commercially available epoxy resin adhesive is used to bond the copper foil to both sides of the PI film to make a traditional three-layer flexible copper clad laminate.

[0108] Comparative Example 2

[0109] The only difference between Comparative Example 2 and Example 1 is that the interface modification solution of Comparative Example 2 does not use 2-methyl-2-acrylate-2-hydroxyethyl phosphate for click chemical reaction, but only hydrolyzes 3-mercaptopropyltriethoxysilane in the same mixed solvent to obtain silane hydrolysate.

[0110] The rest is the same as in Example 1, and will not be described again here.

[0111] Comparative Example 3

[0112] The only difference between Comparative Example 3 and Example 1 is that no array of vias is prepared on the PI film in step (1). The rest is the same as in Example 1, and will not be described again here.

[0113] The flexible copper-clad laminates prepared in the above embodiments and comparative examples were subjected to performance tests, and the test methods are as follows:

[0114] 180° Peel Strength: The peel strength of the copper foil from the base film is tested according to IPC-TM-650 2.4.9 standard.

[0115] Z-direction thermal conductivity: The thermal diffusivity of the sample is measured by laser flare method, and the Z-direction thermal conductivity is calculated by combining specific heat capacity and density.

[0116] MIT bending resistance: radius of curvature R=2mm, load 500gf, record the number of bends when the resistance change exceeds 10%.

[0117] Thermal shock reliability: The flexible copper-clad laminate is placed in a high and low temperature alternating chamber, with the upper part at 150°C and the lower part at -55°C. After holding at the high temperature for 30 minutes, it is instantly transferred to the low temperature and held at the low temperature for another 30 minutes. This is one cycle. After 500 cycles, the cross-section is observed to see if delamination occurs.

[0118] The test results are shown in Table 1.

[0119] Table 1. Relevant properties of flexible copper-clad laminates obtained in the examples and comparative examples.

[0120] Comparing Example 1, Comparative Example 1, and Comparative Example 3, it was found that the Z-thermal conductivity of the flexible copper-clad laminate in Example 1 (9.5 W / m·K) is more than 20 times that of Comparative Example 1 (0.32 W / m·K) and Comparative Example 3 (0.45 W / m·K). This proves that the pure copper thermally conductive pillars formed by arrayed vias are an important structure for improving Z-thermal conductivity. Even with surface modification as in Comparative Example 3, without vias in the base film, heat still needs to pass through the low thermal conductivity PI substrate, and the Z-thermal conductivity cannot be effectively improved.

[0121] Comparing Example 1 and Comparative Example 2, the peel strength of the flexible copper-clad laminate in Example 1 (1.42 N / mm) was 73% higher than that in Comparative Example 2 (0.82 N / mm). Comparative Example 2 only used mercaptosilane treatment, and the Cu-S bonds and mechanical interlocking alone could not significantly improve the interfacial bonding strength. In contrast, Example 1 introduced an additional phosphate ester group, which, through bidentate chelate coordination, formed Cu-OP bonds with Cu-S bonds, creating a multi-site anchoring synergistic effect that significantly enhanced the interfacial bonding strength. Furthermore, Comparative Example 2 showed slight delamination after 500 thermal shocks, while Example 1 remained intact, demonstrating superior thermal shock reliability and proving the excellent ability of the strongly chemically bonded interface to resist thermal mismatch stress.

[0122] Combined with Examples 1-3 and Comparative Example 2, the MIT (Mean Transformation Tolerance) of the perforated samples all exceeded 5000 cycles, proving that the design of opening through holes did not significantly degrade the overall flexibility of the base film, thus meeting the requirements of flexible electronics applications.

[0123] Comparing Example 1 and Example 2, the method of Example 2, through electrodeposition encapsulation, makes the copper layer denser and the copper filling in the vias more saturated. Therefore, the peel strength and Z-direction thermal conductivity are slightly higher than those of Example 1, but the process steps are relatively complex. Both process paths of Example 1 and Example 2 can achieve good results.

[0124] 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.

[0125] All aspects, embodiments, features, and examples of this invention should be considered illustrative, used to explain and illustrate the invention, but not to limit it. The scope of the invention is defined only by the claims.

[0126] 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 flexible copper-clad laminate with high thermal conductivity, characterized in that, include: A modified polymer membrane, wherein the modified polymer membrane is insulating and has through holes; the surface of the modified polymer membrane and the pore walls of the through holes have an organic-inorganic hybrid coupling agent graft layer, the graft layer is bonded to the modified polymer membrane through Si-OC and / or Si-O-Si covalent bonds, and the graft layer contains thiol and phosphate ester groups; The metallic copper structure includes copper layers covering both sides of the modified polymer film and copper pillars filling the through holes. In the grafted layer, the phosphate groups form a bidentate chelate coordination structure with copper, and the thiol groups form Cu-S covalent bonds with copper. The grafted layer is formed by modifying and curing a polymer film with oxygen-containing active groups on its surface using an interface modification liquid. The modifying substance contained in the interface modification liquid is formed by Michael addition click reaction of a mercaptosilane coupling agent and an acrylate monomer containing a phosphate ester group to form a functionalized precursor, and the functionalized precursor is obtained by hydrolysis.

2. The high thermal conductivity flexible copper-clad laminate according to claim 1, characterized in that, The modified polymer film has an array of through-holes, and the copper structure has an array of copper pillars filled in the array of through-holes.

3. The high thermal conductivity flexible copper-clad laminate according to claim 1, characterized in that, The mercaptosilane coupling agent includes one or a combination of more of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethoxysilane.

4. The high thermal conductivity flexible copper-clad laminate according to claim 1, characterized in that, The phosphate-containing acrylate monomers include 2-methyl-2-acrylate-2-hydroxyethyl phosphate.

5. The high thermal conductivity flexible copper-clad laminate according to claim 2, characterized in that, The aperture of each hole in the array is 10μm to 500μm, the spacing between holes is 100μm to 2000μm, and the open area ratio is 10% to 40%.

6. The high thermal conductivity flexible copper-clad laminate according to claim 2, characterized in that, The array of through holes is arranged in a staggered pattern of equally spaced regular hexagons, with the centers of three adjacent through holes forming an equilateral triangle.

7. A method for preparing a high thermal conductivity flexible copper-clad laminate, characterized in that, include: An insulating polymer film with through-pores is provided, wherein the surface of the polymer film has oxygen-containing active groups; The interface modification liquid is brought into contact with the polymer film and then cured to obtain the modified polymer film; The interface modification liquid contains a modifying substance formed by a Michael addition click reaction of a mercaptosilane coupling agent and an acrylate monomer containing a phosphate ester group to form a functionalized precursor, which is then hydrolyzed. A metallic copper structure is formed on the modified polymer film, comprising a copper layer covering both sides of the modified polymer film and copper pillars filling the through holes, to obtain a flexible copper-clad laminate with high thermal conductivity.

8. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7, characterized in that, The preparation method of the interface-modified liquid includes: The functionalized precursor was prepared by Michael addition click reaction of a mixed reaction system containing a mercaptosilane coupling agent, an acrylate monomer containing a phosphate ester group, and a nucleophilic base catalyst. The functionalized precursor is hydrolyzed in a mixed solvent containing organic solvent and water to obtain the interface-modified liquid.

9. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7 or 8, characterized in that, The mercaptosilane coupling agent includes one or a combination of more of 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropylmethyldimethoxysilane.

10. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7 or 8, characterized in that, The phosphate-containing acrylate monomers include 2-methyl-2-acrylate-2-hydroxyethyl phosphate.

11. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7 or 8, characterized in that, The amounts of the mercaptosilane coupling agent and the phosphate-containing acrylate monomer are such that the molar ratio of the mercapto group in the mercaptosilane coupling agent to the double bond in the phosphate-containing acrylate monomer is 1.5:1 to 5:

1.

12. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7 or 8, characterized in that, 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.

13. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7 or 8, 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.

14. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7 or 8, 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.

15. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7 or 8, characterized in that, The hydrolysis time is 4-8 hours.

16. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7 or 8, characterized in that, The solid content of the interface modification liquid is 1wt%~5wt%.

17. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7, characterized in that, The polymer film is immersed in the interface modification solution at a temperature of 25~40℃ and maintained for 5min~60min.

18. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7, characterized in that, The curing temperature is 60~150℃, and / or the curing time is 60min~120min.

19. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7, characterized in that, The modified polymer film has an array of through-holes.

20. The method for preparing a high thermal conductivity flexible copper-clad laminate according to claim 7, characterized in that, The specific method for preparing the copper structure includes: A copper seed layer is deposited on the surface of the modified polymer film and on the pore walls of the through-holes to form an intermediate film; Copper foils are stacked on both sides of the intermediate film and vacuum hot-pressed to form the metallic copper structure; or, copper foils are bonded to one side of the intermediate film by vacuum hot-pressing, and copper is electroplated using the bonded copper foils as cathodes, so that copper fills the through holes from one side of the copper foils to form copper pillars, and a copper layer is formed on the other side of the film where no copper foils are bonded, to form the metallic copper structure.

21. A flexible copper-clad laminate with high thermal conductivity, characterized in that, It is prepared by the method of any one of claims 7-20 for the preparation of a high thermal conductivity flexible copper-clad laminate.

22. The application of the high thermal conductivity flexible copper-clad laminate according to any one of claims 1-6 and 21 in the fabrication of electronic devices.

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