Hot-pressing manufacturing method for flexible microwave devices

Abstract

This invention relates to a method for manufacturing a flexible microwave device using a polyimide film as a substrate. The polyimide is polymerized from an aromatic diamine monomer, γ-aminopropyltriethoxysilane, and an aromatic dianhydride monomer. Two polyimide films, with their convex and concave sides respectively, are stretched and stacked face-to-face in a flat state using hot pressing to form a single conductive layer. This ensures close contact between the two silver conductive layers, creating a single conductive layer located within the hot-pressed polyimide film. Therefore, regardless of bending, crumpling, wrinkling, or friction, the silver conductive layer remains protected by the polyimide film, preventing thinning and cracking due to external friction, thus further enhancing its bending resistance, wear resistance, and peel resistance.

Description

Technical Field

[0001] This invention belongs to the field of flexible microwave devices, specifically relating to a method for manufacturing a flexible microwave device that is easily thermo-pressed, specifically a method for manufacturing a flexible microwave antenna / filter. Background Technology

[0002] In our prior application CN2022100007490, we disclosed a method for manufacturing a bend-resistant flexible microwave device. The core of this method lies in fabricating identical patterned metal antennas on two polyimide films of identical size and shape. Specifically, one polyimide film is bent to create a patterned metal antenna on its convex side; the other polyimide film is bent to create a patterned metal antenna on its concave side. The patterned metal antennas on both films are identical in size and shape, resulting in two identical flexible microwave antennas / filters with patterned silver metal on their polyimide film surfaces. The two polyimide films with patterned metal layers are then stacked face-to-face in the same orientation (with the patterned silver metal layers facing each other) in a flat state, followed by hot pressing to obtain the final flexible microwave antenna / filter. This flexible microwave device can withstand tens of thousands of bends without significantly reducing its electrical performance. However, it was found that under certain bending and torsion composite conditions, the hot pressing effect was not very good, and after thousands of bending cycles, the two hot-pressed polyimide films may experience partial separation / peeling. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide a method for manufacturing a flexible microwave device, thereby further improving the bending resistance and peel resistance of the flexible microwave device. The flexible microwave device is a flexible microwave antenna or a flexible microwave filter.

[0004] The technical solution in this invention is as follows:

[0005] Identical patterned metal antennas are fabricated on two polyimide films of identical size and shape. Specifically, one polyimide film is bent to create a patterned metal antenna on its convex side; the other polyimide film is bent to create a patterned metal antenna on its concave side; the patterned metal antennas on the two films are identical in size and shape; thus, a flexible microwave antenna / filter with patterned silver metal on the surface of two identical polyimide films is obtained.

[0006] The two polyimide films with patterned metal layers are stacked face-to-face in the same orientation in a flat state (the faces with patterned silver metal layers are bonded together), and then hot-pressed to obtain the final flexible microwave antenna / filter.

[0007] In particular, in order to enhance the bonding performance and greatly improve the peel resistance during the hot pressing of two layers of polyimide film, we have made further improvements to the polyimide film in this invention. Specifically, a small amount of γ-aminopropyltriethoxysilane is added during the preparation of the polyimide film, which can form certain chemical bonds during the hot pressing of two layers of polyimide film, thereby enhancing the bonding performance and greatly improving the peel resistance.

[0008] Typically, polyimides are synthesized primarily from dianhydrides and diamines. Compared to many other heterocyclic polymers, such as polybenzimidazole, polybenzothiazole, and polyquinoline, these two monomers have a wider range of raw material sources and are easier to synthesize. There are numerous varieties of dianhydrides and diamines, and different combinations can yield polyimides with different properties.

[0009] Polyimide can be obtained by first undergoing low-temperature polycondensation of dianhydride and diamine in polar solvents such as DMF, DMAC, NMP, or THE / methanol mixtures to obtain soluble polyamic acid. After film formation or spinning, the polyamic acid is heated to around 300°C for dehydration and cyclization to transform into polyimide. Alternatively, acetic anhydride and tertiary amine catalysts can be added to polyamic acid to perform chemical dehydration and cyclization, yielding polyimide solutions and powders. Diamine and dianhydride can also undergo heating polycondensation in high-boiling-point solvents, such as phenolic solvents, to obtain polyimide in one step. Furthermore, polyimide can be obtained by reacting tetracarboxylic acid diesters with diamines; or by first converting polyamic acid into polyisoimide and then into polyimide. These methods facilitate processing, yielding low-viscosity, high-solids solutions with a low melt viscosity window during processing, making them particularly suitable for composite material manufacturing; the latter method increases solubility and does not release low-molecular-weight compounds during the conversion process.

[0010] In this invention, the polyimide is polymerized from an aromatic diamine monomer, γ-aminopropyltriethoxysilane (CAS No.: 919-30-2) and an aromatic dianhydride monomer; wherein, γ-aminopropyltriethoxysilane is used to enhance the adhesion between the two polyimide films in the subsequent hot pressing process and improve the peel resistance.

[0011] Preferably, the specific implementation is as follows: under normal temperature and inert gas conditions, aromatic diamine monomer and γ-aminopropyltriethoxysilane are dissolved in a polar solvent. After complete dissolution, aromatic dianhydride monomer is added, and the reaction is continued by stirring to obtain a precursor solution. The precursor solution is coated onto a substrate and placed in an oven at 70-185℃ for 0.5-3 hours. The substrate is then removed, and the film is peeled off the substrate. The temperature is then increased to 320-420℃ at a rate of 4-6℃ / min. After the temperature increase is complete, the film is allowed to cool naturally to room temperature to obtain a heat-pressable polyimide film.

[0012] Preferably, the molar ratio of aromatic diamine monomer to aromatic dianhydride monomer is 1:(0.97-1.03).

[0013] Preferably, γ-aminopropyltriethoxysilane (CAS No.: 919-30-2) is 0.1 to 3 wt% of the total mass of the aromatic diamine monomer and the aromatic dianhydride monomer.

[0014] Preferably, the two polyimide films are bent with the same preset radius of curvature.

[0015] Preferably, the manufacturing method of the above-mentioned flexible microwave device includes the following steps:

[0016] The flexible microwave antenna / filter was simulated using HFSS simulation software. The structural parameters were optimized through simulation to obtain the theoretically optimized size parameters of the flexible microwave antenna / filter.

[0017] The polyimide film was surface modified in KOH solution, followed by ion exchange in AgNO3 solution. After the reaction was completed, the polyimide film was washed and dried.

[0018] Using the previously obtained size parameters of the flexible microwave antenna / filter, a mask layer is printed on the dried and modified polyimide film, followed by a reduction reaction in H2O2 solution;

[0019] Finally, the two polyimide films are stacked face to face in the same orientation in a flat state (the sides with the patterned metal are attached). Before stacking, metal wire terminals are led out, and then hot-pressed to obtain the final flexible microwave antenna / filter.

[0020] It is worth noting that the manufacturing method of the flexible microwave device proposed in this invention is applicable to any flexible microwave antenna / filter, and is not limited to a certain type of flexible microwave antenna or flexible microwave filter.

[0021] In this invention, because the filter / antenna structure is chemically grown from a polyimide substrate, it exhibits excellent adhesion to the substrate and is less prone to cracking. Furthermore, since the metallic silver conductive layers prepared from the convex and concave sides of the two polyimide films are in two states—convex and concave—when they are stretched flat and then hot-pressed together, the two metallic silver conductive layers will be in close contact and merge into a single conductive layer. They are subjected to both bending compressive stress and bending tensile stress, which complement each other to a certain extent. Regardless of the direction of bending stress in the final hot-pressed flexible microwave antenna / filter, the metallic silver conductive layer will maintain tight conductivity, eliminating stress at any level. This results in stronger overall bending resistance, a higher number of fault-free bending cycles, and greater conductive reliability. This technology is simple, requires no expensive equipment or vacuum conditions, and significantly reduces manufacturing costs.

[0022] Aromatic diamine monomers and aromatic dianhydride monomers possess relatively flexible structures. These molecular structures reveal freely rotating chemical bonds, resulting in polyimide films with excellent flexibility. The prepared polyimide films maintain high thermal stability and low melting temperatures, allowing for bonding of two layers at high temperatures. γ-aminopropyltriethoxysilane can be used to enhance the adhesion between the two polyimide films in subsequent hot-pressing processes, improving peel resistance.

[0023] Naturally, the present invention also possesses other superior technical effects of the prior application CN2022100007490, which will not be repeated here.

[0024] The inventors have now explained the working principle, technical solution, and technical effects of this invention. Relevant figures can be found in the prior application CN2022100007490, and will not be repeated here. Omitting the figures does not affect the completeness of the technical solution. Detailed Implementation

[0025] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the specific embodiments, structures, features, and effects proposed according to the present invention are described in detail below. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. All drawings mentioned in this invention are from the specification of the prior application CN2022100007490.

[0026] As a specific embodiment, a flexible dual-notch ultra-wideband antenna is obtained based on surface modification and in-situ self-metallization processes; the specific structure of this antenna is not a core aspect of this invention, and its detail is irrelevant. As a preferred embodiment, the flexible dual-notch ultra-wideband antenna is obtained based on surface modification and in-situ self-metallization processes, as detailed below:

[0027] Before formally manufacturing the flexible microwave antenna, the design and simulation are first carried out according to the expected performance indicators. The flexible dual-notch ultra-wideband antenna is simulated using HFSS simulation software. The structural parameters are optimized through simulation to obtain the theoretically optimized size parameters of the flexible dual-notch ultra-wideband antenna.

[0028] The flexible microwave antenna with the completed structural design was fabricated using a room-temperature wet process.

[0029] Preparation of polyimide films:

[0030] The polyimide is polymerized from an aromatic diamine monomer, γ-aminopropyltriethoxysilane, and an aromatic dianhydride monomer. The specific preparation method of the polyimide film is as follows: Under normal temperature and inert gas conditions, the aromatic diamine monomer and γ-aminopropyltriethoxysilane are dissolved in a polar solvent. After complete dissolution, the aromatic dianhydride monomer is added, and the reaction is continued by stirring to obtain a precursor solution. The precursor solution is coated onto a substrate and placed in an oven at 70-185℃ for 0.5-3 hours. The substrate is removed, and the film is peeled off the substrate. The temperature is then increased to 320-420℃ at a rate of 4-6℃ / min. After the temperature increase is completed, the film is naturally cooled to room temperature to obtain a heat-pressable polyimide film.

[0031] The aromatic diamine monomer includes

[0032]

[0033]

[0034] One or more of them.

[0035] The aromatic dianhydride monomer includes

[0036]

[0037]

[0038] One or more of them.

[0039] These molecular structures reveal that they all contain freely rotating chemical bonds, resulting in polyimide films with excellent flexibility.

[0040] The polar solvent is one or more of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and m-cresol.

[0041] Two pieces of polyimide film of identical size and shape are cut and selected;

[0042] One of the polyimide films is bent according to a preset radius of curvature. The convex side of the polyimide film is surface modified in KOH solution. Then, the convex side is ion exchanged in AgNO3 solution under the same bending state. After the reaction is completed, the polyimide film is cleaned and dried.

[0043] Another polyimide film is bent with the same preset radius of curvature. The concave side of the polyimide film is surface modified in KOH solution. Then, the concave side is ion exchanged in AgNO3 solution under the same bending state. After the reaction is completed, the polyimide film is cleaned and dried.

[0044] Identical mask layers were printed in the same direction on two modified and dried polyimide films, followed by a reduction reaction in H2O2 solution to obtain two flexible dual-notch ultrawideband antennas with metallized polyimide film surface patterns. The antennas were then cleaned and dried.

[0045] The surface modification, ion exchange chemical reactions and steps involved in the above process are shown in Figures 1 and 2 of the prior application CN2022100007490.

[0046] Referring to Figure 6 of the prior application CN2022100007490, two polyimide films are then stacked face-to-face in the same orientation in a flat state (the metal surfaces with patterns are attached). Before stacking, metal wire terminals are led out, and then hot-pressed to form the final flexible dual-notch ultra-wideband antenna.

[0047] The obtained flexible bandpass antenna is subjected to electrical performance testing. If the test results deviate from the expected values, the parameters are adjusted, and the previous steps are returned to re-simulate and redesign or adjust the room temperature wet process parameters to remanufacture the flexible microwave antenna. If the test results meet the expected values, the parameters in the previous steps are fixed and the flexible microwave antenna is mass-produced.

[0048] The technique involves surface modification of a polyimide film (Qianfeng Company, Shanghai) in KOH solution, ion exchange in AgNO3 solution (Aladdin Company, Shanghai), and reduction reaction in H2O2 solution, ultimately achieving surface metallization of the polyimide film. All experimental steps were performed at room temperature.

[0049] The flexible dual-notch ultra-wideband antenna was simulated using HFSS simulation software, which is based on the finite element method. The simulation model of the polyimide substrate has a thickness of 50.8 μm and a dielectric constant of 3.5. Performance was optimized through simulation by improving structural parameters. The flexible microwave antenna, with the structural design completed in the above steps, was fabricated using a room-temperature wet process. The specific process is as follows:

[0050] After cleaning the polyimide film, two polyimide films were bent according to a predetermined radius of curvature. The convex and concave sides of each film were first immersed in a 4 mol / L KOH solution for 3 hours. This step ensures that the polyimide film undergoes chemical modification to polyamic acid through the cleavage of the surface imide rings. Subsequently, the convex and concave sides of the two polyimide films were immersed in 0.02 mol / L AgNO3 (99.8%) and NH3·H2O for 2 hours to ensure that K+ is replaced by Ag. + .

[0051] After cleaning and drying, the two treated polyimide films are pasted onto an A4 sheet of paper. Then, carbon ink is printed onto the polyimide films using a regular printer as a mask layer for the reduction of metallic silver. Next, the polyimide film with the mask pattern is immersed in a 30% H2O2 solution to ensure that the silver ions are completely reduced to silver.

[0052] Finally, the two polyimide films are stacked face to face in the same orientation in a flat state (the sides with the patterned metal are attached). Preferably, metal wire terminals are led out before stacking, and then hot-pressed to obtain the final flexible dual-notch ultra-wideband antenna.

[0053] The above description is only a preferred embodiment of the present invention and is 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 method for manufacturing a flexible microwave device by hot pressing, the flexible microwave device being a flexible microwave antenna or a flexible microwave filter, the method comprising the following steps: (1) selecting a flexible substrate as a polyimide film, wherein the polyimide is polymerized from an aromatic diamine monomer, a γ-aminopropyl triethoxysilane and an aromatic dianhydride monomer; (2) cutting two pieces of the polyimide film obtained in step (1) to have the same size and shape; bending the two pieces of the polyimide film according to the same preset radius of curvature; surface modifying a convex side of one of the two pieces of the polyimide film in a KOH solution, and then ion exchanging the convex side in an AgNO 3 solution; surface modifying a concave side of the other piece of the polyimide film in the KOH solution, and then ion exchanging the concave side in the AgNO 3 solution; and cleaning and drying the two pieces of the polyimide film after the reaction is completed; (3) printing a mask layer with the same preset pattern on the two pieces of the polyimide film obtained in step (1) in the same direction, and then performing a reduction reaction in an H 2 O 2 solution to obtain two pieces of the flexible microwave device with the same patterned silver metal surface on the polyimide film; and (4) stacking the two pieces of the polyimide film in a flat state and in the same orientation, face to face, and then hot pressing and forming. 2.The method according to claim 1, wherein the polyimide film is prepared by the following method: dissolving the aromatic diamine monomer and the γ-aminopropyl triethoxysilane in a polar solvent under normal temperature and inert gas conditions, the polar solvent being one or more of N-methyl pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide and m-cresol; after complete dissolution, adding the aromatic dianhydride monomer, continuing to stir and react to obtain a precursor glue solution; coating the precursor glue solution on a substrate, placing the substrate in an oven for constant temperature drying for a certain time, taking out the substrate, peeling off the film from the substrate, and then heating to a polymerization reaction temperature, and naturally cooling to room temperature after heating is completed to obtain a polyimide film that can be hot pressed. 3.The method according to claim 1, wherein the molar ratio of the aromatic diamine monomer to the aromatic dianhydride monomer is 1: (0.97-1.03) ; and the γ-aminopropyl triethoxysilane (CAS No. 919-30-2) is 0.1-3wt% of the total mass of the aromatic diamine monomer and the aromatic dianhydride monomer. 4.The method according to any one of claims 1-3. ​ ​ ​ In step (3), carbon ink is printed on the polyimide film as a mask layer for reduction of metallic silver; then the obtained polyimide film is immersed in an H2O2 solution, Ag + is completely reduced to metallic silver; ​ ​ ​ ​ ​ ​ ​ Step (2) is performed as follows: after cleaning, the polyimide film is first immersed in 4 mol / L KOH solution for 3 h; this step ensures that the polyimide film is chemically modified to polyamic acid by cleavage of the imide rings on the surface; then, the surface-modified side of the film is immersed in 0.02 mol / L AgNO3(99.8%) and NH3·H2O for 2 h to ensure that K+is replaced by Ag+; the film is cleaned and dried.

5. The production method according to claim 1 or 2, characterized by: The aromatic diamine monomer includes one or more of the group consisting of 6. The production method according to claim 1 or 2, characterized by: The aromatic dianhydride monomers include one or more of the following:

7. The manufacturing method of claim 2, wherein: The polyimide film is prepared as follows: aromatic diamine monomers and γ-aminopropyl triethoxysilane are dissolved in a polar solvent, and after complete dissolution, aromatic dianhydride monomers are added, and the reaction is continued with stirring to obtain a precursor glue solution; the precursor glue solution is coated on a substrate, and the substrate is placed in an oven at 70-185°C for 0.5-3 h; the substrate is removed, and the film is peeled off from the substrate; the temperature is then increased to 320-420°C at a rate of 4-6°C / min, and after the temperature is increased, the temperature is naturally cooled to room temperature to obtain a polyimide film that can be hot-pressed. In step (3), the metal wire terminals are drawn out before lamination, and then hot-pressed. Specifically, the steps include: Two pieces of polyimide film having the same size and shape are bent, and patterned metal antennas are manufactured on the outer convex side of one piece of the polyimide film and on the inner concave side of the other piece of the polyimide film; the patterned metal antennas on the two pieces of the polyimide film have the same size and shape; thus, two pieces of flexible microwave antenna / filters having patterned silver metal on the surface of the polyimide film are obtained; The two pieces of polyimide film having the patterned metal layer are laminated in a flat state, and the two pieces of polyimide film are laminated in the same orientation and face to face, that is, the surfaces having the patterned silver metal layer are attached, and then hot-pressed to obtain the final flexible microwave antenna / filters; 8. The production method according to claim 1, wherein: The polyimide is polymerized from aromatic diamine monomers, γ-aminopropyl triethoxysilane, and aromatic dianhydride monomers.

9. A method of manufacturing a flexible microwave antenna / filter with high bending resistance, characterized by, The two pieces of polyimide film are bent according to the same preset radius of curvature. ​ ​ ​ 10. The method of manufacturing a flexible microwave antenna / filter according to claim 9, wherein: ​

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