Flexible composite film material, flexible composite film and preparation method and application thereof

Abstract

The application provides a flexible composite film material, a flexible composite film and a preparation method and application thereof, and belongs to the technical field of semiconductor test materials. The flexible composite film material comprises, in percentage by mass, fluorine-containing polyamide acid 47-83%, core-shell structure nano filler 5-15%, thermotropic liquid crystal polymer 10-30%, and modified aramid fiber with grafted benzoxazole structure 2-8%. The fluorine-containing polyamide acid, the core-shell structure nano filler, the thermotropic liquid crystal polymer and the modified aramid fiber in the flexible composite film material form a synergistic effect, so that the prepared flexible composite film has good flexibility, high-temperature resistance, mechanical properties and low dielectric loss characteristics, and can meet the long-term stable use requirements of flexible electronic devices and semiconductor test related scenes.

Description

Technical Field

[0001] This invention relates to the field of semiconductor testing materials technology, and in particular to a flexible composite thin film material, a flexible composite thin film, its preparation method and application. Background Technology

[0002] With the rapid development of high-frequency and high-speed electronic technologies such as mobile communication, millimeter-wave radar, and artificial intelligence chips, semiconductor chip testing is upgrading towards high frequency, miniaturization, and flexibility, which places more stringent requirements on the electrical performance, thermal stability, and processing accuracy of the insulating support material in the probe card.

[0003] High-frequency probe cards require stable signal transmission in frequency bands above 10 GHz during operation, while also withstanding temperature cycling and repeated mechanical insertion and removal during chip testing. Traditional polyimide (PI) films, due to their strong molecular polarity and high coefficient of thermal expansion, have poor thermal compatibility with the silicon wafers in the probe card, easily leading to interface polarization loss and probe thermal drift, resulting in signal attenuation and reduced testing accuracy. Although existing filler modification schemes have been optimized, problems such as numerous interface defects, high high-frequency loss, and insufficient process compatibility still exist. Summary of the Invention

[0004] In view of this, the main objective of the present invention is to provide a flexible composite film material, a flexible composite film, a method for preparing the same, and its applications, so as to at least partially solve the aforementioned technical problems.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] In one aspect of the present invention, a flexible composite film material is provided, comprising, by weight percentage (100%): 47% to 83% fluorinated polyamic acid; 5% to 15% core-shell structured nanofiller; 10% to 30% thermotropic liquid crystal polymer; and 2% to 8% modified aramid fiber grafted with benzoxazole structure.

[0007] In a second aspect of the present invention, a method for preparing a flexible composite film is provided, comprising: mixing the above-mentioned flexible composite film material, photosensitizer, and photoacid generator to obtain a photosensitive composite paste; spin-coating the photosensitive composite paste onto a substrate to form a wet film, and drying it to obtain a composite film layer; exposing and developing the composite film layer to dissolve and remove the composite film layer in the exposed areas to form a patterned film with micron-level patterns; and performing imidization curing on the patterned film in a vacuum environment using a thermo-mechanical coupling rolling process to obtain the final composite film. The precursor, wherein the thermo-mechanical coupling rolling process includes: pre-pressing the patterned film at 130℃~210℃ and 0.05MPa~0.8MPa for 0.5h~4h, cooling it to 70℃~130℃, and rolling it under 3MPa~20MPa pressure until the thickness of the patterned film is reduced by 15%~45%, then heating it to 280℃~360℃ and imidizing it under 0.5MPa~4MPa pressure; and performing plasma surface treatment on the composite film precursor to obtain a flexible composite film.

[0008] In a third aspect of the present invention, a flexible composite film is provided, which is prepared by the above-described method for preparing a flexible composite film.

[0009] In a fourth aspect of the invention, an application of the above-described flexible composite film in a probe card is provided.

[0010] The flexible composite film material provided by this invention uses a fluorinated polyamic acid to construct a low-polarity fluorinated polyimide matrix. Core-shell structured nanofillers effectively suppress interfacial polarization loss between the filler and the fluorinated polyimide matrix. Thermotropic liquid crystal polymers achieve a lower coefficient of thermal expansion for the composite film material through orientation self-reinforcement. Modified aramid fibers grafted with benzoxazole structures strengthen the interfacial bonding between the fibers and the fluorinated polyimide matrix and enhance overall mechanical stability. This results in lower signal loss and greater thermal dimensional stability at 10 GHz. Using this flexible composite film material, a photosensitive patterning and thermo-mechanical coupling rolling process is employed to prepare the flexible composite film, enabling micron-level patterning, reducing interfacial defects and internal stress, and improving the uniformity and structural stability of the flexible composite film. The resulting flexible composite film possesses low dielectric loss, a low coefficient of thermal expansion, high mechanical strength, and a smooth surface, making it suitable for the precision processing requirements of semiconductors. Applying this flexible composite film to probe cards can reduce high-frequency (10GHz) signal attenuation, suppress probe thermal drift, improve testing accuracy and insertion / removal reliability, and meet the long-term stable operation requirements of high-frequency probe cards. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0012] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0013] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0014] In the process of developing this invention, it was discovered that as semiconductor chip testing rapidly upgrades towards higher frequencies, miniaturization, and flexibility, existing insulating support materials used in probe cards are no longer adequate to meet the stringent multi-dimensional requirements of high-frequency testing scenarios above 10GHz. Traditional polyimide materials have high dielectric loss (dielectric loss factor greater than 0.06 at 10GHz) and a high coefficient of thermal expansion (coefficient of thermal expansion greater than 15 in the range of -60℃ to 160℃), resulting in poor thermal matching with silicon wafers. During high-frequency operation and temperature cycling, this easily leads to signal transmission attenuation and probe position thermal drift, directly causing a decrease in chip testing accuracy and insufficient long-term reliability. While existing modification schemes optimize the individual properties of materials, they are prone to introducing new system defects. Furthermore, the traditional film-forming-then-etching process has poor compatibility with multi-component modified systems and cannot achieve micron-level high-precision patterning. Ultimately, it is difficult to simultaneously meet the stringent multi-dimensional requirements of high-frequency probe cards for low dielectric loss, low thermal expansion, high mechanical reliability, and high-precision processing.

[0015] Based on this, the present invention provides a flexible composite thin film material with multi-component synergistic coupling, and a preparation method adapted to the photosensitive patterning and thermo-mechanical coupling rolling process of the flexible composite thin film material system. This invention constructs a low-polarity fluorinated polyimide matrix using fluorinated polyamic acid. A core-shell structured nanofiller forms a dielectric buffer structure within the low-polarity fluorinated polyimide matrix to suppress interfacial polarization loss. The orientation self-reinforcing effect of thermotropic liquid crystal polymers during the molding process of the fluorinated polyimide matrix enables the regulation of the coefficient of thermal expansion. Modified aramid fibers grafted with benzoxazole structures simultaneously strengthen the interfacial bonding between multiple components and the overall mechanical stability of the flexible composite film material. These four components form a complementary and synergistic coupling system, simultaneously optimizing the performance of the flexible composite film material from multiple dimensions: molecular structure, interfacial state, and microstructure. Simultaneously, a photosensitive patterning and thermo-mechanical coupling rolling process adapted to this multi-component system is provided. This process fully releases the intrinsic properties of the flexible composite film material while completing the molding of micron-level patterns, ultimately producing a flexible composite film with low dielectric loss, low coefficient of thermal expansion, good mechanical properties, and compatibility with semiconductor processes. This film can fully meet the application requirements of high-frequency (above 10 GHz) probe cards.

[0016] According to one aspect of the present invention, a flexible composite film material is provided, comprising, by weight percentage (100%): 47% to 83% fluorinated polyamic acid; 5% to 15% core-shell structured nanofiller; 10% to 30% thermotropic liquid crystal polymer; and 2% to 8% modified aramid fiber grafted with benzoxazole structure.

[0017] According to some specific embodiments of the present invention, the mass percentage of fluorinated polyamic acid can be, for example, 47%, 50%, 60%, 70%, 80%, 83%, etc.; the mass percentage of core-shell structured nanofillers can be, for example, 5%, 7%, 10%, 13%, 15%, etc.; the mass percentage of thermotropic liquid crystal polymers can be, for example, 10%, 15%, 20%, 25%, 30%, etc.; and the mass percentage of modified aramid fibers grafted with benzoxazole structures can be, for example, 2%, 3%, 4%, 5%, 6%, 7%, etc.

[0018] According to embodiments of the present invention, a complementary and synergistic coupling system is formed by fluorinated polyamic acid, core-shell structured nanofillers, thermotropic liquid crystal polymers, and modified aramid fibers grafted with benzoxazole structures, thereby simultaneously optimizing the performance of flexible composite film materials from multiple aspects such as molecular structure, interface state, and microstructure.

[0019] Fluorinated polyamic acid, as a precursor to fluorinated polyimide, can form a continuous phase matrix for fluorinated polyimide materials after imidization. The fluorine atoms possess strong electronegativity and low polarizability, effectively reducing the inherent polarity of the polyimide molecular chain and decreasing molecular dipole polarization, thereby fundamentally reducing the intrinsic dielectric loss of the fluorinated polyimide matrix. Simultaneously, the fluorinated structure reduces the hygroscopicity of flexible composite film materials, preventing dielectric property degradation caused by moisture, while retaining the good heat resistance and film-forming properties of polyimide materials.

[0020] The shell of the core-shell structured nanofiller can prevent the accumulation of interfacial polarization charge between the core layer and the fluorinated polyimide matrix, effectively reducing the difference in dielectric constant between the core layer and the fluorinated polyimide matrix. This fundamentally suppresses Maxwell-Wagner-Sillars polarization (i.e., dielectric shielding effect) at the filler-matrix interface under high-frequency (above 10 GHz) electric fields, avoiding the problem of increased interfacial polarization loss caused by traditional inorganic fillers (such as silicon dioxide), and achieving a reduction in the dielectric loss factor of flexible composite thin film materials at high frequencies (above 10 GHz).

[0021] Thermotropic liquid crystal polymers, with their inherent low dielectric and low loss characteristics, can synergize with low-polarity fluorinated polyimide matrices to further optimize the dielectric properties of the system and ensure the dielectric stability of flexible composite film materials. Simultaneously, relying on their thermotropic melt flow characteristics, they can wet the surfaces of core-shell nanofillers and modified aramid fibers grafted with benzoxazole structures during subsequent thermal processing, improving the interfacial compatibility of the multi-components, reducing additional polarization losses and mechanical weaknesses caused by interfacial defects, and simultaneously regulating the thermal expansion properties of the flexible composite film material. This addresses the problem of the high coefficient of thermal expansion in the fluorinated polyimide matrix and core-shell nanofiller system.

[0022] In aramid fibers grafted with benzoxazole structures, the benzoxazole structure can form chemical bonds with fluorinated polyamic acid during imidization. During imidization, the benzoxazole structure undergoes ring-opening under the catalysis of free carboxyl groups and photoacid, generating a highly active intermediate with both primary amino and ortho-hydroxyl groups. The primary amino group and carboxyl group form amide bonds through nucleophilic addition-elimination. The amide bonds simultaneously cyclize with adjacent functional groups to generate imide bonds consistent with the main chain of the fluorinated polyimide matrix. This upgrades the interfacial bonding between the benzoxazole-grafted aramid fiber and the fluorinated polyimide matrix from physical adsorption to chemical bonding, solving the defects of weak interfacial bonding and easy interfacial separation in unmodified aramid fibers. At the same time, aramid fibers themselves have high modulus and fatigue resistance, forming a three-dimensional load-bearing network in the fluorinated polyimide matrix to bear mechanical stress and improve the material's resistance to bending and insertion / extraction fatigue.

[0023] Therefore, fluorinated polyamic acid provides a low-polarity core carrier for the fluorinated polyimide matrix in the flexible composite film material system; the core-shell structured nanofiller solves the interfacial polarization problem that is easily caused by multi-component composites in flexible composite film materials, and further reduces the dielectric loss of the system while multi-component doping; the thermotropic liquid crystal polymer simultaneously regulates the thermal expansion coefficient of the system, and its own low dielectric properties will not degrade the dielectric performance of the flexible composite film material; the modified aramid fiber with grafted benzoxazole structure simultaneously improves the brittleness problem caused by the thermotropic liquid crystal polymer, strengthens the interfacial bonding effect between the core-shell structured nanofiller and the fluorinated polyimide matrix, and the chemically bonded interface will not introduce new polarization losses.

[0024] Fluorinated polyamic acid, core-shell structured nanofillers, thermotropic liquid crystal polymers, and modified aramid fibers grafted with benzoxazole structures form a complementary and synergistic system, ultimately achieving a comprehensive and synergistic improvement in the flexible composite film material at a high frequency of 10GHz, with lower dielectric loss, coefficient of thermal expansion, and higher mechanical strength and fatigue resistance.

[0025] According to embodiments of the present invention, the fluorinated polyamic acid has a molecular weight of 30,000 g / mol to 80,000 g / mol and a fluorine content of 8% to 15%. The fluorine atoms effectively reduce molecular polarity and dipole moment, thereby enabling the flexible composite film material to possess a lower dielectric constant (Dk) and dielectric loss factor (Df), meeting the requirements for use with probe cards at 10 GHz high frequencies.

[0026] According to embodiments of the present invention, the core-shell structured nanofiller includes a core layer and a shell layer covering the core layer. The core layer of the core-shell structured nanofiller is any one of silicon dioxide, titanium dioxide, and alumina, and the shell layer is boron nitride (BN). The core layer is selected from inorganic ceramic materials with high modulus, heat resistance, and high-frequency insulation stability. The thermal stability of the core layer is adaptable to the imidization processing window of fluorinated polyimide and provides rigid support to help reduce the coefficient of thermal expansion of the flexible composite film material. The dielectric constant of the boron nitride shell can match that of the fluorinated polyimide matrix, enabling the construction of a dielectric constant buffer layer between the core layer with a higher dielectric constant and the fluorinated polyimide matrix with a lower dielectric constant. This fundamentally suppresses polarization loss at the interface between the filler and the fluorinated polyimide matrix at high frequencies (10 GHz). Furthermore, the hexagonal boron nitride layered structure can be aligned parallel to the electric field direction, forming a physical barrier that hinders charge migration across the interface, further suppressing polarization loss. Additionally, active groups that may exist on the surface of boron nitride, such as amino (-NH2) and hydroxyl (-OH), can form hydrogen bonds with the polyimide molecular chains, strengthening the interfacial bonding between the core-shell structured nanofiller and the fluorinated polyimide matrix, reducing the interface defect state density, and minimizing additional losses and mechanical weaknesses caused by interface defects.

[0027] The particle size of the core-shell structured nanofiller is 50nm~100nm, for example, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, etc.; the mass ratio of the core layer to the shell layer is (5~7):3, for example, 5:3, 6:3, 7:3, etc.; the thickness of the shell layer is 2nm~5nm, for example, 2nm, 3nm, 4nm, 5nm, etc. When the thickness of the shell layer is less than 2nm, a continuous and complete dielectric gradient buffer layer cannot be formed on the surface of the core layer, resulting in insufficient blocking and shielding effect on the polarization charge at the core layer interface, making it difficult to effectively suppress dielectric loss at high frequencies (10GHz); when the thickness of the shell layer is greater than 5nm, it easily leads to an imbalance in the specific surface area of ​​the core-shell structured nanofiller, resulting in decreased dispersibility in the fluorinated polyimide matrix and possible agglomeration, while also reducing the effective proportion of the core layer and weakening the auxiliary control effect of the core layer on the thermal expansion coefficient and mechanical properties of the flexible composite film material.

[0028] According to embodiments of the present invention, core-shell structured nanofillers can be prepared, for example, by the following methods.

[0029] (1) Core layer pretreatment: The inorganic ceramic material of the core layer is dispersed in anhydrous ethanol solution, and an aminosilane coupling agent is added. The mixture is refluxed at 80°C for 4 hours to complete the silanization modification. Amino (-NH2) active sites are introduced on the surface of the core layer to obtain the pretreated core layer powder, which provides stable binding sites for the uniform and continuous growth of the subsequent shell layer.

[0030] (2) In-situ growth of the shell: In-situ polymerization-pyrolysis method is adopted. Boric acid and urea are prepared into a precursor solution at a mass ratio of 1: (10~15). The precursor solution is fully mixed with the pretreated core layer powder and ultrasonically dispersed so that the precursor solution is uniformly adsorbed on the surface of the pretreated core layer powder. After drying, it is placed in a tube furnace and heat-treated at 800℃~1000℃ for 2h in an inert atmosphere of nitrogen (N2). A boron nitride shell layer with a thickness of 2nm~5nm is formed in-situ on the core layer surface to obtain the core-shell structure powder precursor.

[0031] (3) Surface modification: The core-shell structured powder precursor was subjected to secondary surface modification treatment with silane coupling agent to further regulate the surface energy, improve its interfacial compatibility with the fluorinated polyimide matrix, inhibit agglomeration, and finally obtain the core-shell structured nanofiller.

[0032] According to embodiments of the present invention, the thermotropic liquid crystal polymer is a rod-shaped liquid crystal polymer with rigid chains. The molecular chains of the thermotropic liquid crystal polymer itself have a relatively compact and regular molecular stacking structure, low intrinsic polarizability, and stable dielectric loss. It can synergistically optimize the high-frequency dielectric properties with the fluorinated polyimide matrix and improve the dielectric stability under wide temperature conditions. At the same time, the rigid chain structure has good heat resistance and creep resistance, which can effectively suppress the thermal motion of the molecular chains of the fluorinated polyimide matrix under high temperature conditions, reduce the overall thermal expansion coefficient of the system, and improve the problems of high thermal expansion and poor thermal matching with silicon wafers of traditional polyimides. In addition, the rod-shaped molecular chains can achieve orientation alignment under the action of spin coating shear force, and further constrain thermal expansion deformation along the film plane direction during the subsequent film forming process, thereby achieving stable control of the thermal expansion coefficient.

[0033] According to embodiments of the present invention, the molecular weight of the thermotropic liquid crystal polymer is 20,000 g / mol to 50,000 g / mol, for example, 20,000 g / mol, 30,000 g / mol, 40,000 g / mol, 50,000 g / mol, etc., to ensure that the molecular shear orientation and processing fluidity are balanced under the spin-coating shear force in the subsequent flexible composite film preparation process; the melting temperature is 280℃ to 320℃, for example, 280℃, 290℃, 300℃, 310℃, 320℃, etc.; the thermotropic liquid crystal polymer may contain repeating units of biphenyl / hydroxybenzoate structure.

[0034] According to embodiments of the present invention, the thermotropic liquid crystal polymer can be, for example, the Vectra series from Celanese, USA, or similar fluorinated thermotropic liquid crystal polymers.

[0035] According to embodiments of the present invention, the grafting rate of the modified aramid fiber with grafted benzoxazole structure is 2%~5%, for example, 2%, 3%, 4%, 5%, etc., which ensures that the modified aramid fiber with grafted benzoxazole structure forms a stable chemical bond with the fluorinated polyimide matrix and core-shell structured nanofiller, avoiding interface separation, reducing polarization loss, and ensuring stable dielectric properties; the fiber length is <50μm, for example, 49μm, 45μm, 40μm, 30μm, 20μm, etc.; the single filament diameter is <1μm, for example, 0.9μm, 0.7μm, 0.5μm, 0.3μm, etc. μm, 0.1μm, etc., can effectively avoid interference between modified aramid fibers and other components, and are compatible with subsequent thermal processing without affecting photolithography accuracy; aspect ratio of 30~50:1, such as 30:1, 35:1, 40:1, 45:1, 50:1, etc., can form a stable load-bearing network, enhance the overall rigidity of flexible composite film materials, reduce micro-defects, and improve the bending and fatigue resistance of the flexible composite film prepared in the subsequent process, avoiding film forming defects caused by modified aramid fibers that are too long (e.g., length greater than 50μm) or too thick (e.g., single filament diameter greater than 1μm).

[0036] According to embodiments of the present invention, the modified aramid fiber grafted with a benzoxazole structure can specifically be poly(p-phenylene terephthalamide) (PPTA) or poly(m-phenylene isophthalamide) (PMIA). The modified aramid fiber grafted with a benzoxazole structure can be prepared by the following method: a 1wt%~3wt% ethanol solution is prepared using a silane coupling agent containing a benzoxazole structure (such as a silicon-containing benzoxazine monomer), and refluxed at 80°C under nitrogen protection for 4 hours, controlling the grafting rate at 2%~5% to ensure a balance between interfacial reinforcement and fiber dispersibility; after the reaction, the fiber is washed three times with ethanol to remove unreacted silane coupling agent, and then vacuum dried at 60°C for 2 hours; after grafting modification, the surface contact angle of the modified aramid fiber grafted with a benzoxazole structure can be increased from approximately 45° to approximately 75°, effectively improving its compatibility with the fluorinated polyimide matrix.

[0037] According to an embodiment of a second aspect of the present invention, a method for preparing a flexible composite film is provided, comprising the following steps 1 to 5.

[0038] Step 1: Mix the above-mentioned flexible composite film material, photosensitizer, and photoacid generator to obtain a photosensitive composite slurry.

[0039] Step 2: Spin-coat the photosensitive composite paste onto the substrate to form a wet film, and then dry it to obtain the composite film layer.

[0040] Step 3: Expose and develop the composite film to dissolve and remove the composite film in the exposed area, forming a patterned thin film with micron-level patterns.

[0041] Step 4: In a vacuum environment, the patterned film is imidized and cured using a thermo-mechanical coupling rolling process to obtain a composite film precursor. The thermo-mechanical coupling rolling process includes: pre-pressing the patterned film at 130℃~210℃ and 0.05MPa~0.8MPa for 0.5h~4h, cooling it to 70℃~130℃, and then rolling it under a pressure of 3MPa~20MPa until the thickness of the patterned film is reduced by 15%~45%. Subsequently, the temperature is raised to 280℃~360℃ and imidized and cured under a pressure of 0.5MPa~4MPa.

[0042] Step 5: Perform plasma surface treatment on the composite film precursor to obtain a flexible composite film.

[0043] According to an embodiment of the present invention, the thermo-mechanical coupling rolling process can be implemented as follows: The patterned film is pre-compressed at any temperature of 130°C, 150°C, 170°C, 200°C, 210°C, etc., with any pressure of 0.05MPa, 0.1MPa, 0.2MPa, 0.4MPa, 0.6MPa, 0.8MPa, etc., for a pre-compressing time of 0.5h, 1h, 2h, 3h, 4h, etc., to partially imidize the fluorinated polyamic acid in the patterned film and reduce the viscosity of the system; after cooling to 70°C, 90°C, 100°C, 110°C, 120°C, etc., After reaching any temperature such as 130℃, the film is rolled or flat-pressed 2 to 15 times under any mechanical pressure such as 3MPa, 5MPa, 10MPa, 15MPa, 20MPa, etc., controlling the reduction of the patterned film thickness by any reduction ratio such as 15%, 20%, 30%, 40%, 45%, etc., to increase the fiber volume fraction inside the patterned film; then the temperature is raised to any temperature such as 280℃, 300℃, 320℃, 340℃, 360℃, etc., and complete imidization curing is completed under any pressure condition such as 0.5MPa, 1MPa, 2MPa, 3MPa, 4MPa, etc.

[0044] According to the preparation method of the flexible composite film of the present invention, the flexible composite film material, photosensitizer, and photoacid generator are uniformly mixed, and the composite film layer is exposed and developed to dissolve and remove the composite film layer in the exposed area, forming a patterned film with micron-level patterns. This method can directly prepare uniform and high-precision micron-level insulating layer patterns on the substrate surface. Compared with traditional dry etching and wet etching patterning processes, the preparation method of the present invention does not require additional complex post-processing steps such as etching, effectively simplifying the preparation process and shortening the production cycle. At the same time, the subsequent use of a thermo-mechanical coupling rolling process enables optimized control of the entire process of raw material mixing, film forming, and pattern curing. This effectively avoids the problems of core-shell structure nanofiller damage, benzoxazole-grafted modified aramid fiber damage, and performance degradation of flexible composite film materials caused by acid and alkali corrosion and plasma bombardment during traditional etching processes.

[0045] According to embodiments of the present invention, the photosensitizer is a photosensitizer containing a diazononaphthoquinone structure, such as a photosensitizer containing a diazononaphthoquinone-4-sulfonate structure, and the addition amount is 1% to 3% of the mass of the flexible composite film material; the photoacid generating agent includes any one of triarylthionium salt, diaryliodoonium salt, alkyl sulfonate, and trifluoromethanesulfonate, and the addition amount is 1% to 3% of the mass of the flexible composite film material. By selecting a photosensitizer containing a diazononaphthoquinone structure and controlling its addition amount, a photochemical reaction can occur under exposure conditions. Combined with the synergistic effect of the photoacid generating agent, it can more precisely catalyze the polarity change in the exposed area, achieving controllable dissolution and development. Good photosensitivity efficiency can be obtained at a low addition amount without significantly increasing the dielectric loss and dielectric constant of the material, thus avoiding affecting the high-frequency insulation performance. Simultaneously, the wet film thickness is controlled to 12μm to 35μm to adapt to the penetration depth (approximately 40μm) of 300nm to 400nm ultraviolet light (e.g., 365nm) exposure, ensuring complete photolysis of the exposed area and no penetration of the unexposed area. It can ensure that light can fully penetrate the film layer, achieve complete and uniform exposure and development, and obtain micron-level pattern structures with more precise dimensions. At the same time, it can meet the requirements of the insulating layer thickness of high-frequency probe cards, avoiding problems such as insufficient exposure and pattern distortion caused by excessively thick film layers (such as exceeding 35μm), or insufficient withstand voltage and easy breakage caused by excessively thin film layers (such as less than 12μm). The overall ratio and thickness parameters are well matched, taking into account the photolithography pattern accuracy, thin film dielectric insulation performance, mechanical stability and high-frequency signal transmission stability, and adapting to the needs of high-precision patterning processing and high-frequency testing applications.

[0046] According to an embodiment of the present invention, the preparation method of the photosensitive composite slurry includes: stirring and mixing fluorinated polyamic acid and core-shell structured nanofillers at 70℃~90℃ for 1h~3h, cooling to 50℃~70℃ and then adding thermotropic liquid crystal polymer and stirring for 0.5h~2h; adding modified aramid fibers grafted with benzoxazole structure and ultrasonically dispersing for 20min~40min; then adding photosensitizer and photoacid generator, stirring evenly and then performing vacuum degassing treatment to obtain the photosensitive composite slurry.

[0047] Optionally, a sensitizer, such as a coumarin derivative, can be further added to the photosensitive composite paste, which can effectively broaden the photosensitive response range of the system, expand the exposure window to about 436nm, and improve the adaptability of the process and the patterning accuracy.

[0048] According to an embodiment of the present invention, the developing process uses a 1%~3% tetramethylammonium hydroxide aqueous solution, the developing temperature is 23±1℃, and the developing time is: spraying for 50s~70s and soaking for 10s~30s, to ensure that the exposed area is completely dissolved and the unexposed area does not swell. The mildly alkaline, low-concentration developing system is gentle and controllable, and will not corrode or damage the core-shell nanofiller, the modified aramid fiber grafted with benzoxazole, or the thermotropic liquid crystal polymer components. It can effectively prevent the peeling off of the core-shell nanofiller, the breakage of the modified aramid fiber grafted with benzoxazole, and the swelling and deformation of the flexible composite film. The constant developing temperature can stabilize the developing rate, ensuring that the exposed areas are fully dissolved and removed, and the unexposed areas are not eroded, resulting in micron-level patterns with high precision and no residual defects. The segmented spraying and immersion developing method takes into account both developing uniformity and pattern shape preservation, which not only improves developing efficiency but also prevents overdevelopment from causing pattern collapse and dimensional distortion. At the same time, it is highly compatible with the diazonoquinone-containing photosensitive system, with high patterning precision and good process stability, and can meet the high-precision insulating layer preparation requirements of high-frequency probe cards.

[0049] According to an embodiment of the present invention, the exposure uses 365nm ultraviolet light with an energy of 80mJ / cm². 2 ~120mJ / cm 2 The exposure progress is controlled by endpoint detection (such as portable ozone-depleting substance spectroscopy (ODS)) to avoid overexposure leading to pattern shrinkage or underexposure leading to residue.

[0050] According to an embodiment of the present invention, the spin coating process includes: spin coating at a speed of 500 rpm to 800 rpm for 5 to 15 seconds, and then spin coating at a speed of 2000 rpm to 4000 rpm for 40 to 50 seconds. First, slow spin coating at a lower speed (500 rpm to 800 rpm) allows the photosensitive composite paste to spread fully, level and wet, eliminating air bubbles and local accumulation in the paste, ensuring that the photosensitive composite paste fully and uniformly covers the substrate, and avoiding defects such as missing paste, exposed substrate, and uneven stripes; then, spin coating at a higher speed (2000 rpm to 4000 rpm) for a longer time (40 to 50 seconds) can evenly remove excess paste, control the wet film thickness to be stable within the range of 12 μm to 35 μm, and further improve the flatness and thickness uniformity of the film layer, suppress the sedimentation of core-shell structured nanofillers, the uneven orientation of modified aramid fibers grafted with benzoxazole structure, and the defects of thickening at the edge of the film layer. The two-stage spin coating works together to ensure good wettability and film uniformity, while also allowing for more precise control of the wet film thickness. This provides a stable foundation for subsequent uniform exposure, development, and micron-level patterning, reducing exposure deviations and pattern distortion caused by uneven film thickness, and ultimately improving film dimensional accuracy, dielectric uniformity, and surface quality.

[0051] According to an embodiment of the present invention, the exposure uses 300nm~400nm ultraviolet light, for example, 365nm ultraviolet light, and the exposure energy is 80mJ / cm. 2 ~120mJ / cm 2 This band of ultraviolet light can match the photosensitive absorption bands of diazonaphthoquinone photosensitizers and onium salt photoacid generators, resulting in high photochemical reaction efficiency and rapid response; the exposure energy can be controlled at 80 J / cm². 2 ~120mJ / cm 2 This method allows for sufficient photodecomposition, acid production, and polarity reversal in the exposed area, ensuring complete dissolution and removal without residual adhesive during subsequent development, resulting in a micron-level pattern with steep and clear edges. It also avoids problems such as film hardening, excessive cross-linking, and pattern shrinkage caused by excessively high exposure energy, as well as insufficient exposure, incomplete development, and linewidth distortion caused by excessively low energy. Furthermore, this exposure condition does not damage the microstructure of core-shell nanofillers, modified aramid fibers grafted with benzoxazole, or thermotropic liquid crystal polymers.

[0052] According to an embodiment of the present invention, plasma surface treatment employs a mixed plasma of oxygen and carbon tetrafluoride, wherein the volume ratio of oxygen to carbon tetrafluoride is 2-3:1, the treatment power is 100W-300W, the treatment time is 30s-120s, and the treatment pressure is 5Pa-15Pa. Oxygen plasma can etch away residual organic matter, adhesive residue, and microscopic impurities on the film surface, introducing polar active groups such as hydroxyl and carboxyl groups to enhance surface energy and wettability. Carbon tetrafluoride plasma can moderately fluorinate the patterned film surface, reducing surface energy, improving hydrophobicity and resistance to damp heat, while suppressing surface polarization loss. When the two are used in a specific ratio (2~3:1), they work synergistically to gently clean the surface and improve interfacial adhesion without excessively etching and damaging the fillers, fibers and microstructure inside the flexible composite film. Combined with low-pressure (5Pa~15Pa), low-power (100W~300W) and short-time (30s~120s) process parameters, the surface flatness can be optimized, the surface defect state density can be reduced, and high-frequency leakage current and interfacial polarization loss can be reduced without damaging the original dielectric properties, thermal expansion properties and mechanical properties of the flexible composite film. This further improves the insulation stability, environmental reliability and subsequent assembly and bonding adhesion of the flexible composite film.

[0053] According to an embodiment of a third aspect of the present invention, a flexible composite film is provided, which is prepared by the above-described preparation method.

[0054] According to embodiments of the present invention, the flexible composite film is prepared by multi-component synergistic modification of fluorinated polyamic acid, core-shell structured nanofillers, thermotropic liquid crystal polymers, and modified aramid fibers grafted with benzoxazole structures, combined with photosensitive direct photolithography patterning, thermo-mechanical coupling rolling imidization curing, and plasma surface treatment. Micron-level insulating patterns are directly formed through photosensitive exposure and development, eliminating traditional etching steps and avoiding damage to fillers and fiber structures. The resulting patterns have high precision and good dimensional stability. The flexible composite film possesses low dielectric constant, high-frequency dielectric loss, low coefficient of thermal expansion, and high mechanical strength and heat-resistant density. Simultaneously, the flexible composite film has uniform and dense layers, few interface defects, and controllable surface properties, effectively suppressing interface polarization and signal attenuation. Its overall performance is well-compatible with high-precision semiconductor photolithography processes, exhibiting structural stability and reliable insulation under long-term temperature cycling and high-frequency operating conditions, meeting the stringent requirements of high-frequency, high-speed probe cards for insulating dielectric layers.

[0055] According to embodiments of the present invention, the performance of the flexible composite film satisfies at least one of the following conditions.

[0056] (1) The dielectric loss factor of the flexible composite film at 10GHz is <0.002, which has low high-frequency polarization loss, low signal transmission attenuation, and excellent high-speed high-frequency transmission stability, which can meet the signal transmission requirements of high-frequency and high-speed probe cards.

[0057] (2) The coefficient of thermal expansion in the range of -60℃ to 160℃ is <5ppm / K, the dimensional stability is good, and it is not easy to warp, deform or crack under temperature cycling conditions. It has good thermal matching with chips and substrates.

[0058] (3) Surface roughness < 0.15μm, the surface is flat and dense with few micro-defects, which can effectively reduce interface polarization, leakage current and high-frequency parasitic loss, while improving the pattern accuracy, insulation reliability and subsequent bonding and assembly interface performance.

[0059] According to an embodiment of the present invention, dielectric loss testing can be performed using the resonant cavity method, with a test frequency of 8 GHz to 12 GHz, focusing on recording the dielectric loss factor (Df) value at 10 GHz. The test sample size can be 50 mm × 50 mm × thickness (corresponding to the actual thickness of the flexible composite film used), and the test temperature is 25 ± 1 °C. Thermal expansion coefficient testing can be performed using a thermomechanical analyzer (TMA) at a heating rate of 10 °C / min within a temperature range of -60 °C to 160 °C, recording a linear expansion curve, the slope of which is the thermal expansion coefficient. Surface roughness testing can be performed using an atomic force microscope (AFM) in tapping mode, with a scanning area of ​​10 × 10 μm. 2 The surface roughness (Ra) value is calculated at a sampling frequency of 1Hz.

[0060] According to an embodiment of a third aspect of the present invention, an application of the above-described flexible composite film in a probe card is provided.

[0061] According to embodiments of the present invention, the flexible composite film of the present invention possesses low dielectric loss, low coefficient of thermal expansion, low surface roughness, and high-precision photolithography patterning capability at 10GHz high frequency. When used as an insulating dielectric layer for probe cards, it can effectively reduce high-frequency and high-speed signal transmission loss and delay, and improve signal integrity. The low wide-temperature coefficient of thermal expansion enables excellent thermodynamic matching with probes, chips, and substrates, effectively suppressing warping deformation, alignment misalignment, and poor contact problems under temperature cycling. The flat and dense surface structure can reduce interface polarization, leakage current, and parasitic capacitance, improving insulation reliability. At the same time, the material can be directly photolithographically patterned into micron-level circuit patterns without etching damage, resulting in high pattern accuracy and good structural stability. This can effectively improve the testing accuracy, high-speed response performance, and long-term reliability of high-frequency probe cards, meeting the stringent application requirements of high-end high-frequency semiconductor test probe cards.

[0062] According to some specific embodiments of the present invention, when the flexible composite film of the present invention is applied to a probe card, the following multilayer probe card complete structure and preparation process can be adopted.

[0063] The silicon wafer or glass substrate is cleaned; a first layer of flexible composite film material is spin-coated and cured using stepped temperature rise; a first metal layer is deposited and patterned using photosensitive etching; a second layer of flexible composite film material is spin-coated, and through-holes are formed by photosensitive etching, followed by deposition of a second metal layer and photolithography etching; a third layer of flexible composite film material is spin-coated and a passivation layer is deposited, followed by photolithography windowing; a seed layer is deposited and metal contacts are electroplated; a temporary support layer is attached, the substrate is peeled off, and an interface transition layer is deposited. In this invention, the flexible composite film serves as the first, second, and third insulating layers, ensuring a low dielectric loss and low coefficient of thermal expansion across the entire structure. The specific metal system used is as follows: the first layer of metal is made of chromium (Cr) or titanium (Ti), with a thickness of 5nm~30nm, to improve the bonding force between the metal and the polymer; the second layer of metal is preferably made of gold / copper (Au / Cu) system, which takes into account both conductivity and corrosion resistance. Cu can also be used and a barrier layer can be set to control costs; the electroplated metal contacts are mainly made of Cu, with 0.1wt%~0.5wt% of cobalt (Co) or phosphorus (P) added to improve anti-electromigration performance.

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. Unless otherwise specified, specific techniques or conditions in the embodiments are conventional methods and can be performed according to the techniques or conditions described in the literature in this field or according to the product instructions. It should be noted that the methods provided by this invention are conventional methods unless otherwise specified, and the reactants and reagents can be obtained from publicly available commercial sources unless otherwise specified.

[0065] Example 1

[0066] This invention provides a flexible composite film, and the preparation method of the flexible composite film is as follows.

[0067] A flexible composite film material was obtained by mixing 100g of fluorinated polyamic acid solution, 10g of core-shell structured nanofiller SiO2@BN (core layer is silicon dioxide (SiO2), shell layer is boron nitride (BN), particle size is 50nm, core-shell mass ratio is 7:3), 20g of thermotropic liquid crystal polymer LCP, and 5g of poly(p-phenylene terephthalamide) fiber grafted with benzoxazole structure (grafting rate 3%).

[0068] The flexible composite film material, 2g of diazonaphthoquinone-4-sulfonate, and 1g of triarylthionium salt were mixed evenly to obtain the photosensitive composite slurry.

[0069] Photosensitive composite paste was spin-coated onto the substrate to form a wet film with a thickness of 12 μm. The spin-coating process was as follows: spin-coating at 500 rpm for 10 s, then spin-coating at 3000 rpm for 45 s; after baking at 90℃ for 2 min, the temperature was raised to 115℃ and baked for 3 min to obtain the composite film layer.

[0070] The composite film was exposed to 365nm ultraviolet light at an exposure energy of 80mJ / cm. 2 The composite film layer in the exposed area was dissolved and removed by spraying for 60 seconds and soaking for 30 seconds, using a 2.38% tetramethylammonium hydroxide aqueous solution at a development temperature of 23±1℃ to form a patterned thin film with micron-level patterns.

[0071] In a vacuum environment, the patterned film is imidized and cured by thermo-mechanical coupling rolling to obtain a composite film precursor. The thermo-mechanical coupling rolling process includes: pre-pressing the patterned film at 150℃ and 0.1MPa for 1 hour, cooling it to 100℃, rolling it 8 times under 10MPa pressure until the thickness of the patterned film is reduced by 30%, and then heating it to 320℃ and imidizing and curing it under 2MPa pressure for 2 hours.

[0072] The composite film precursor was subjected to surface treatment with a mixed plasma of oxygen and carbon tetrafluoride, with a volume ratio of oxygen to carbon tetrafluoride of 3:1, a treatment power of 200W, a treatment time of 60s, and a treatment pressure of 10Pa, to obtain flexible composite film 1.

[0073] Comparative Example 1

[0074] The present invention provides a flexible composite film in a comparative example. The preparation method of the flexible composite film differs from that of Example 1 in that no core-shell structured nanofiller is added, while the remaining preparation steps are the same as those in Example 1, and a flexible composite film 2 is obtained.

[0075] Comparative Example 2

[0076] The present invention provides a flexible composite film in a comparative example. The difference between the preparation method of the flexible composite film and that of Example 1 is that the thermotropic liquid crystal polymer (LCP) is not added, while the remaining preparation steps are the same as those of Example 1, and the flexible composite film 3 is obtained.

[0077] Comparative Example 3

[0078] The present invention provides a flexible composite film in a comparative example. The preparation method of the flexible composite film differs from that of Example 1 in that: thermotropic liquid crystal polymer (LCP) and poly(p-phenylene terephthalamide) fiber grafted with benzoxazole structure are not added. The remaining preparation steps are the same as those in Example 1, and the flexible composite film 4 is prepared.

[0079] Comparative Example 4

[0080] The present invention provides a flexible composite film in a comparative example. The preparation method of the flexible composite film differs from that of Example 1 in that: no core-shell structured nanofiller and no grafted benzoxazole structured poly(p-phenylene terephthalamide) fiber are added. The remaining preparation steps are the same as those in Example 1, and a flexible composite film 5 is obtained.

[0081] Comparative Example 5

[0082] The present invention provides a flexible composite film in a comparative example. The difference between the preparation method of the flexible composite film and that of Example 1 is that the patterned film is subjected to imidization curing by a direct curing process. The direct curing process includes curing at 350°C for 2 hours. The remaining preparation steps are the same as those in Example 1, and a flexible composite film 6 is prepared.

[0083] Comparative Example 6

[0084] The present invention provides a comparative example of a commercially available homogeneous polyimide film (DuPont Kapton® HN).

[0085] Comparative Example 7

[0086] This invention provides a comparative example of a modified polyimide film, specifically the Apical modified polyimide film from Kaneka Corporation of Japan. TM NP-25, nominal thickness is 50μm.

[0087] The modified polyimide film is made of a modified polyimide resin containing ether bonds; the preparation process is biaxial stretching casting.

[0088] The flexible composite films in Examples 1 and Comparative Examples 1 to 7 of the present invention were subjected to the following performance tests to evaluate their dielectric properties, thermal dimensional stability, surface quality, molding flatness and application reliability. All test samples were pretreated for 24 hours at 25±1℃ and 50±5%RH.

[0089] (1) Dielectric loss test: The test is conducted using the resonant cavity method or the transmission line method. The test frequency is 8GHz~12GHz, covering the communication and high frequency test bands. The dielectric loss factor at 10GHz is recorded.

[0090] (2) Coefficient of thermal expansion (CTE) test: The thermomechanical analyzer (TMA) was used for the test. The heating rate was 10℃ / min, and the test temperature range was -60℃ to 160℃, covering the actual test working temperature range of the chip, to obtain the coefficient of thermal expansion of the thin film.

[0091] (3) Surface quality and reliability testing: Characterization was performed using atomic force microscopy (AFM) in tapping mode with a scanning area of ​​10 × 10 μm.2 The sampling frequency is 1Hz, and the three-dimensional morphology of the thin film surface is obtained and the surface roughness (Ra) value is calculated.

[0092] (4) Film warpage test: Using a 100mm substrate as a reference, test and record the warpage of the film to evaluate its molding flatness and process compatibility.

[0093] (5) Contact life and reliability test: The contact resistance change was recorded by using a simulated probe card insertion and removal test. The test platform consists of a micro-force probe test stage, a high-precision displacement stage and a four-probe resistance test module. The test conditions are: probe pressure 0.5mN / point, insertion and removal frequency 2Hz, ambient temperature 25℃ and relative humidity 50%RH. The failure criterion is that the contact resistance increment > 50% or fluctuation > ±10%. The service life and stability of the film under long-term probe contact are evaluated.

[0094] (6) Interface peel strength test:

[0095] The 180° peel strength test method (refer to IPC-TM-650 2.4.8 and GB / T 2790 standard) was adopted. The specific test steps are as follows: (1) Sample preparation: The flexible composite film to be tested (cut size 25mm×150mm) was bonded to the standard silicon wafer or epoxy board (FR-4) substrate by hot pressing. The bonding interface was subjected to a pressure of 0.5MPa and a temperature of 120℃ for 30min. Then it was placed in an environment of 25±1℃ and 50±5%RH for 24h to mature. (2) Sample cutting and clamping: A sample with a width of 25mm was cut along the longitudinal direction of the film with a precision cutter. A ≥20mm unbonded area was reserved at the peeling start end. The samples were fixed in a universal testing machine (such as Instron). (3) Test parameters: The test speed is set to 50 mm / min, the peel angle is strictly maintained at 180°, the test environment temperature is 25±1℃ and the relative humidity is 50±5%RH; (4) Data acquisition and calculation: Record the force-displacement curve during the peeling process, remove the non-steady-state fluctuation data at the beginning and end, and take the average force value (N) of the middle stable peeling stage. Interface peel strength (N / mm) = average peel force (N) / sample width (25mm). Five samples are tested in parallel in each group, and the arithmetic mean and standard deviation are taken as the final result.

[0096] Table 1 shows a comparison of the performance of flexible composite films in Example 1 and Comparative Examples 1 to 7 of the present invention.

[0097] Table 1

[0098]

[0099] As shown in Table 1, the flexible composite film prepared in Example 1 of this invention significantly outperforms Comparative Examples 1 to 7 in key performance aspects such as dielectric loss at 10 GHz, coefficient of thermal expansion, surface roughness, film warpage, and contact life. Example 1 exhibits a dielectric loss factor as low as 0.0018 at 10 GHz, a coefficient of thermal expansion of only 4.2 ppm / K within the range of -60℃ to 160℃, a surface roughness Ra of 0.12 μm, a film warpage of only 0.8 mm / 100 mm, a contact life greater than 10 million cycles, and a resistance change rate of only +3.8% after 10 million insertion / removal cycles. Overall, it demonstrates excellent high-frequency dielectric properties, thermal dimensional stability, surface quality, and long-term reliability, meeting the stringent requirements of high-frequency probe cards. Even compared to Comparative Example 7 (currently one of the main commercial substrates for high-frequency probe cards and encapsulation insulating support layers), the flexible composite film prepared in this invention still possesses certain comprehensive advantages in terms of low dielectric loss, low coefficient of thermal expansion matching, and surface roughness. Furthermore, as can be seen from Comparative Example 5, the present invention uses thermo-mechanical coupling rolling for imidization curing, which can effectively improve the density of flexible composite films, reduce warpage, optimize surface flatness and interfacial bonding, while extending contact life and reducing insertion and extraction resistance fluctuations.

[0100] By comparing Example 1 with Comparative Examples 1 to 7, it can be demonstrated that the core-shell structured nanofiller, thermotropic liquid crystal polymer, and modified aramid fiber grafted with benzoxazole structure have a synergistic effect in this invention. The orientation of the thermotropic liquid crystal polymer can induce the shell layer of the filler to be oriented in-plane, thereby reducing the dielectric loss at 10 GHz compared to the single-addition system. The modified aramid fiber grafted with benzoxazole structure and the thermotropic liquid crystal polymer can form a π-π interaction, which can improve interfacial compatibility, reduce micropore defects, and reduce the coefficient of thermal expansion after temperature cycling. After the three components are coupled, the modified aramid fiber grafted with benzoxazole structure bears the mechanical stress to reduce microcracks in the fluorinated polyimide matrix, thereby maintaining the orientation integrity of the core-shell structured nanofiller and the thermotropic liquid crystal polymer, achieving long-term stability of electrical and thermal properties, and demonstrating the comprehensive performance improvement brought about by the synergy of multiple components.

[0101] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A flexible composite thin film material, characterized in that, The flexible composite film material comprises 100% by weight, including: Fluorinated polyamic acid: 47%~83%; Core-shell structured nanofillers: 5%–15%; Thermotropic liquid crystal polymers: 10%~30%; Modified aramid fibers grafted with benzoxazole structure: 2%–8%.

2. The flexible composite film material according to claim 1, characterized in that, The fluorinated polyamic acid has a weight-average molecular weight of 30,000 g / mol to 80,000 g / mol and a fluorine content of 8% to 15%. The core-shell structured nanofiller includes a core layer and a shell layer covering the core layer, wherein the core layer is any one of silicon dioxide, titanium dioxide, and aluminum oxide, and the shell layer is boron nitride; The core-shell structured nanofiller has a particle size of 50nm~100nm, the mass ratio of the core layer to the shell layer is (5~7):3, and the thickness of the shell layer is 2nm~5nm.

3. The flexible composite thin film material according to claim 1, characterized in that, The thermotropic liquid crystal polymer is a rod-shaped liquid crystal polymer with rigid chains, a molecular weight of 20,000 g / mol to 50,000 g / mol, and a melting temperature of 280°C to 320°C.

4. The flexible composite thin film material according to claim 1, characterized in that, The grafting rate of the modified aramid fiber with grafted benzoxazole structure is 2%~5%, the fiber length is <50μm, the single filament diameter is <1μm, and the aspect ratio is 30~50:

1.

5. A method for preparing a flexible composite film, characterized in that, The preparation method includes: Mix the flexible composite film material, photosensitizer, and photoacid generator according to any one of claims 1 to 4 to obtain a photosensitive composite slurry. The photosensitive composite paste is spin-coated onto a substrate to form a wet film, and then dried to obtain a composite film layer. The composite film is exposed and developed to dissolve and remove the composite film in the exposed area, forming a patterned thin film with micron-level patterns. In a vacuum environment, the patterned film is subjected to imidization curing using a thermo-mechanical coupling rolling process to obtain a composite film precursor. The thermo-mechanical coupling rolling process includes: pre-pressing the patterned film at 130℃~210℃ and 0.05MPa~0.8MPa for 0.5h~4h, cooling it to 70℃~130℃, and then rolling it under a pressure of 3MPa~20MPa until the thickness of the patterned film is reduced by 15%~45%, followed by heating it to 280℃~360℃ and imidizing it under a pressure of 0.5MPa~4MPa. The composite film precursor is subjected to plasma surface treatment to obtain a flexible composite film.

6. The method for preparing the flexible composite film according to claim 5, characterized in that, The photosensitizer is a photosensitizer containing a diazononaphthoquinone structure, and the amount of photosensitizer added is 1% to 3% of the mass of the flexible composite film material; The photoacid generating agent includes any one of triarylthionium salt, diaryliodonium salt, alkyl sulfonate, and trifluoromethanesulfonate, and the amount of the photoacid generating agent added is 1% to 3% of the mass of the flexible composite film material; The thickness of the wet film is 12μm~35μm.

7. The method for preparing the flexible composite film according to claim 5, characterized in that, The preparation method of the photosensitive composite slurry includes: stirring and mixing fluorinated polyamic acid and core-shell structured nanofillers at 70℃~90℃ for 1h~3h, cooling to 50℃~70℃ and then adding thermotropic liquid crystal polymer and stirring for 0.5h~2h; adding modified aramid fibers grafted with benzoxazole structure and ultrasonically dispersing for 20min~40min; then adding the photosensitizer and the photoacid generator, stirring evenly and then performing vacuum degassing treatment to obtain the photosensitive composite slurry; The developing process uses a 1%~3% tetramethylammonium hydroxide aqueous solution, the developing temperature is 23±1℃, and the developing time is: 50s~70s for spraying and 10s~30s for soaking. The spin coating includes: spin coating the photosensitive composite paste on the substrate at a speed of 500 rpm to 800 rpm for 5 s to 15 s, and then spin coating at a speed of 2000 rpm to 4000 rpm for 40 s to 50 s. The exposure uses ultraviolet light in the 300nm~400nm range, with an exposure energy of 80mJ / cm². 2 ~120mJ / cm 2 ; The plasma surface treatment uses a mixed plasma of oxygen and carbon tetrafluoride, wherein the volume ratio of oxygen to carbon tetrafluoride is 2~3:1, the treatment power is 100W~300W, the treatment time is 30s~120s, and the treatment pressure is 5Pa~15Pa.

8. A flexible composite film, characterized in that, The flexible composite film is prepared by the method for preparing a flexible composite film according to any one of claims 5 to 7.

9. The flexible composite film according to claim 8, characterized in that, The performance of the flexible composite film meets at least one of the following conditions: The dielectric loss factor of the flexible composite film at a frequency of 10 GHz is <0.002; The coefficient of thermal expansion in the range of -60℃ to 160℃ is <5ppm / K; Surface roughness < 0.15 μm.

10. The application of a flexible composite film as described in claim 8 or 9 in a probe card.

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