Anti-interference superconducting composite film and preparation method thereof

Abstract

The invention relates to the technical field of conductive composite films, and particularly discloses an anti-interference superconducting composite film and a preparation method thereof.The preparation method comprises the steps that firstly, diamine and dianhydride are used for synthesizing a polyimide film containing p-aryl ester and large-volume side groups, the polyimide film is foamed to serve as a base film, then, a chromium-aluminum metal transition layer is deposited on the base film, and the anti-interference superconducting composite film is obtained; according to the anti-interference superconducting composite film, copper diffusion of a conductive layer is prevented while adhesion force is enhanced, then the conductive layer composed of copper nanowires and reduced graphene is prepared on the transition layer, finally, an anti-PIM interface layer and a packaging layer are prepared on the conductive layer, the anti-interference superconducting composite film is formed, and the whole composite film is made of a non-magnetic material and has no grain boundary and lattice defects, so that the anti-interference superconducting composite film has good anti-interference performance. A non-linear current path is avoided, non-linear contact is reduced, PIM is remarkably reduced, and PIM interference caused by magnetic impurities is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive composite films, in particular to an anti-interference superconducting composite film and a preparation method thereof. Background Art

[0002] Passive intermodulation (PIM) interference occurs when two or more high-frequency signals pass through passive components such as antennas, cables, and connectors. Due to component defects such as poor contact, oxidation, and metal debris, these signals combine to create new signals. These new signals then enter the receiving frequency band and affect the original signals, causing signal distortion. This interference often occurs in wireless communication systems, particularly in multi-band, high-power modern communication scenarios such as cellular, satellite, and indoor distributed systems. PIM interference not only overwhelms useful signals, reducing receiver sensitivity and causing mutual interference between multiple systems, but also increases bit error rates, leading to frequent packet loss, and reducing data transmission efficiency, resulting in a poor user experience. Therefore, the development of conductive films that are both PIM-resistant and highly conductive can address intermodulation interference in multi-band, high-power scenarios and contribute to the development of the information and communications industry. Summary of the Invention

[0003] The purpose of the present invention is to provide an interference-resistant superconducting composite film and a preparation method thereof. The composite film has good conductivity and a certain anti-interference ability, which solves the problem of PIM interference generated in multi-frequency and high-power scenarios and affects signal transmission.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions: An anti-interference superconducting composite film comprises the following structures from bottom to top: a base layer, a transition layer, a conductive layer, an anti-PIM interface layer and an encapsulation layer, wherein the base layer is a 15-20 μm thick polyimide foam film, the transition layer is an 8-10 nm thick chromium-aluminum metal layer, the conductive layer is a 2-4 μm thick copper-graphite composite conductive layer, the anti-PIM interface layer is a 4-6 nm thick amorphous carbon layer, and the encapsulation layer is a 10-20 nm thick silicon nitride layer.

[0005] A method for preparing an interference-resistant superconducting composite film, specifically comprising: Step 1: using dimethylaniline, benzaldehyde, diaminodiphenyl ether and p-phenylene trimellitic dianhydride as raw materials, synthesizing a phenyl polyimide film, and then foaming it with carbon dioxide to obtain a polyimide foam film; Step 2: depositing chromium and aluminum on the polyimide foam film to form a transition layer to obtain a transition polyimide film; Step 3: drying the conductive paste containing reduced graphene and copper nanowires to form a copper-graphite composite conductive layer, and then hot-pressing the copper-graphite composite conductive layer and the transition polyimide film to obtain a conductive polyimide film; Step 4: depositing an amorphous carbon layer on the conductive polyimide film to obtain an anti-PIM film, and depositing silicon nitride on the surface of the anti-PIM film to form a silicon nitride layer to obtain an anti-interference superconducting composite film.

[0006] As a limitation of the present invention, the step 1 is specifically as follows: Add KH-550 silane coupling agent and deionized water to ethanol, stir evenly, add nano-silica, react at 70-80°C for 3-4 hours, centrifuge after the reaction is complete, wash with ethanol, dry at 80-90°C for 2-3 hours, and after drying, ultrasonically disperse the product in ethanol to obtain an amino-modified nano-silica dispersion; The phenyl polyimide film is immersed in an amino-modified nano-silica dispersion, taken out after ultrasonic treatment for 20-30 minutes, and dried at 70-80°C for 0.5-1h. The film is then foamed with carbon dioxide, with the foaming pressure set at 12-15MPa, the foaming temperature at 55-65°C, and the foaming time being 1-2h. After the foaming is completed, the pressure is quickly released to obtain a polyimide foam film.

[0007] Nano-silica is modified with a silane coupling agent, so that the modified nano-silica serves as a nucleation site during formation, inhibiting macroporous defects in the foaming film, improving the pore uniformity of the foaming film, and solving the problem of uneven pore distribution in the foaming film.

[0008] As a limitation of the present invention, the mass ratio of the KH-550 silane coupling agent to the nano-silica is 1:(8-12); in the amination nano-silica dispersion, the mass ratio of the product to ethanol is 1:(8-10); when heating for imidization, a step-by-step heating process is adopted, and the heating process is: heating at 80-90°C for 4-6h, heating at 120-130°C for 1-2h, heating at 160-170°C for 1-2h, heating at 200-210°C for 1-2h, heating at 250-260°C for 0.5-1h, and heating at 300-310°C for 20-30min.

[0009] As described in the present invention, the preparation method of phenyl polyimide film is: Under argon protection, dimethylaniline and benzaldehyde are mixed, stirred evenly, and then heated to 100-110°C. Concentrated hydrochloric acid and dimethoxyethanol are slowly added. After the addition is complete, the temperature is raised to 125-135°C and the reaction is carried out for 8-12 hours. After 8-12 hours, sodium hydroxide alcohol solution is added and filtered to obtain a diamine intermediate; Under nitrogen protection, the diamine intermediate, diaminodiphenyl ether and N,N-dimethylacetamide are mixed and stirred in an ice-water bath for 20-30 minutes to fully dissolve the diamine intermediate. Then, p-phenylene trimellitic dianhydride is added and stirred for 20-24 hours under nitrogen protection to obtain a polyamic acid solution. The polyamic acid is applied to a glass plate, dried at room temperature for 3-5 hours, and then heated for imidization. After heating, it is cooled to room temperature and peeled off from the glass plate to obtain a phenyl polyimide film.

[0010] Under the catalysis of concentrated hydrochloric acid, the carbonyl carbon in benzaldehyde undergoes a substitution reaction with the benzene ring of dimethylaniline to generate a diamine monomer (tetramethyldiaminotriphenylmethane) containing a bulky phenylmethyl group. The diamine monomer further undergoes a condensation reaction with diaminodiphenyl ether and p-phenylene diphenyl trimellitic acid dianhydride. Diaminodiphenyl ether provides a flexible chain segment, and p-phenylene diphenyl trimellitic acid dianhydride provides a rigid biphenyl structure. After condensation, the polyamide acid undergoes a closed-loop dehydration reaction to convert it into a polyimide containing p-aryl ester and bulky side groups, which has good heat resistance and mechanical properties.

[0011] As a limitation of the present invention, the mass ratio of dimethylaniline, benzaldehyde and dimethoxyethanol is (46-50):(9-11):(18-22); the mass ratio of diamine intermediate, diaminodiphenyl ether and p-phenylene trimellitic acid dianhydride is (6.4-6.8):(35-37):(92-96).

[0012] As a limitation of the present invention, in step 2, when chromium and aluminum are deposited to form a transition layer, the aluminum target power is 120-150W, the argon pressure is 0.3-0.4MPa, and the deposition time is 15-20s. After 15-20s, the chromium target power is started, the chromium target power is 180-200W, and the deposition time is 0.8-1min; before deposition, the film surface is etched and activated, the bias voltage is 180-200V, the argon flow rate is 40-50sccm, the film temperature is 55-65°C, and the etching time is 3-5min; after deposition, annealing is performed, the annealing temperature is 170-180°C, and the annealing time is 1-1.5h.

[0013] When preparing the transition layer, aluminum is first deposited as a base. Aluminum forms an aluminum-oxygen-carbon chemical bond with the carbonyl oxygen of the polyimide foam film, enhancing the adhesion of the transition layer. Depositing chromium helps form a passivation film, reducing the diffusion of copper from the conductive layer to the base layer and enhancing the stability of the film. After deposition is completed, annealing is performed to eliminate internal stress and promote the formation of aluminum-oxygen-carbon chemical bonds.

[0014] As a limitation of the present invention, the step 3 is specifically as follows: The copper nanowires were immersed in a hydrochloric acid solution for 3-5 minutes to remove the oxide film on the surface. The mixture was centrifuged after 3-5 minutes and washed with ethanol. The mixture was then added to a polyvinyl pyrrolidone alcohol solution and ultrasonically dispersed for 30-40 minutes to obtain a copper nanowire dispersion. The graphene oxide powder was added to N-methyl pyrrolidone and ultrasonically dispersed for 30-40 minutes. Ascorbic acid was added and the mixture was stirred at 80-90°C for 8-12 hours. After the reaction was completed, the mixture was evaporated and concentrated to obtain a reduced graphene dispersion. The reduced graphene dispersion and the copper nanowire dispersion are mixed, ultrasonically dispersed for 30-40 minutes, hydroxyethyl cellulose is added, and stirred evenly to obtain a conductive slurry. The conductive slurry is vacuum filtered onto a polycarbonate film, and dried at 50-60°C for 2-3 hours to form a conductive film-polycarbonate film. The polycarbonate film is peeled off, and the conductive film is covered on a polyimide film. The film is hot-pressed at 190-200°C and 4-6MPa for 5-10 minutes. After the hot pressing is completed, the film is annealed at 170-180°C under nitrogen protection for 1-1.5 hours to obtain a conductive polyimide film.

[0015] The reduced graphene and copper nanowires in the conductive layer are both non-magnetic materials, avoiding the generation of PIM interference caused by magnetic impurities; the copper nanowires form a three-dimensional conductive network in the conductive layer, reducing the lamellar structure of graphene, filling the contact gaps between copper nanowires, and reducing contact resistance; connecting isolated copper nanowires to improve conductive uniformity; reduced graphene can also isolate water and oxygen, delaying the oxidation of copper nanowires.

[0016] As a limitation of the present invention, in the copper nanowire dispersion, the mass fraction of copper nanowires is 0.5%-1.5%; in the reduced graphene dispersion, the mass fraction of reduced graphene is 1%-3%; in the conductive paste, the mass fraction of hydroxyethyl cellulose is 0.3%-0.6%, and the mass ratio of the reduced graphene dispersion to the copper nanowire dispersion is 1:(2-4).

[0017] As a limitation of the present invention, in step 4, when depositing the amorphous carbon layer, the gases used are acetylene, hydrogen and argon in a volume ratio of (4-6):1:(8-12), the film temperature during deposition is 90-100°C, the RF power is 280-300W, the intracavity pressure is 5-7Pa, and the deposition time is 50-60s; when depositing the silicon nitride layer, the gases used are silane, ammonia and nitrogen in a volume ratio of 1:(1-3):(8-12), the film temperature during deposition is 70-80°C, the RF power is 180-200W, the intracavity pressure is 20-24Pa, and the deposition time is 50-70s.

[0018] The chamber was evacuated before the two depositions, and the vacuum degree was (0.8×10 -3 )-(1×10 -3)pa, after the encapsulation layer is deposited, anneal it at 150-160℃ for 20-30min under nitrogen protection.

[0019] During the deposition process, acetylene is activated by plasma to generate active free radicals that polymerize on the surface of the material to form an amorphous carbon network. The addition of hydrogen helps to inhibit the formation of the side reaction graphite phase and improve the density of the amorphous carbon film layer; silane and ammonia are activated by plasma to generate active free radicals that polymerize on the surface of the material to form silicon nitride.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The present invention synthesizes a polyimide film containing para-arylate and bulky side groups, which has good heat resistance and mechanical properties. The polyimide film is foamed and air is introduced into the nanopores of the foamed film, significantly reducing the overall dielectric constant. The nanopores act as micro-deformation units and can disperse bending stress. The pore structure absorbs thermal stress, which is beneficial for the adhesion of other layers and reduces the risk of stress cracking during the preparation of other layers. In addition, the nanopores have the advantages of reducing weight and saving materials.

[0021] A chromium-aluminum metal transition layer is deposited on the surface of the substrate layer. The aluminum forms a chemical bond with the carbonyl oxygen on the polyimide in the substrate layer to enhance adhesion, and the chromium forms a passivation film to prevent copper from diffusing into the substrate layer, forming a high-resistance compound. A conductive layer is prepared on the transition layer, which is composed of copper nanowires and reduced graphene, providing a low-resistance path. An anti-PIM interface layer and an encapsulation layer are prepared on the conductive layer. The dense amorphous carbon anti-PIM interface layer is a non-magnetic material. Its amorphous structure has no grain boundaries and lattice defects, which avoids nonlinear current paths, reduces nonlinear contact, and significantly reduces PIM. The silicon nitride encapsulation layer is chemically inert and can isolate the inner layer from contact with water and oxygen in the environment. It has high hardness and good wear resistance, and has both good high-temperature resistance and low thermal resistance, which is beneficial to the heat dissipation of high-power devices. DETAILED DESCRIPTION

[0022] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0023] Copper nanowires (length: 30-40 μm, diameter: 40-50 nm), nanosilicon dioxide (particle size: 20 nm), graphene oxide (sheet length: 10-20 μm, thickness: 0.8-1.2 nm), chromium target (purity: ≥99.99%), aluminum target (purity: ≥99.9%).

[0024] Example 1: A method for preparing an interference-resistant superconducting composite film, specifically: Step 1: Under argon protection, 48.5 g of dimethylaniline and 10.6 g of benzaldehyde were mixed, stirred evenly, and then heated to 100 ° C. 4.2 mL of 37 wt% concentrated hydrochloric acid and 20 g of dimethoxyethanol were slowly added. After the addition was complete, the temperature was raised to 125 ° C and the reaction was allowed to react for 12 hours. After 12 hours, 2 g / 500 mL of sodium hydroxide alcohol solution was added to terminate the reaction. The mixture was filtered to obtain a diamine intermediate; Step 2: Under nitrogen protection, 66g of diamine intermediate, 360g of diaminodiphenyl ether and 4000g of N,N-dimethylacetamide were mixed and stirred in an ice-water bath for 30min to fully dissolve the diamine intermediate, and then 940g of p-phenylene trimellitic dianhydride was added. The mixture was stirred for 24h under nitrogen protection to obtain a polyamic acid solution. The polyamic acid was applied to a glass plate, dried at room temperature for 4h, and then heated at 80°C for 6h, 120°C for 2h, 160°C for 2h, 200°C for 2h, 250°C for 1h, and 300°C for 30min for imidization. After cooling to room temperature, the film was removed from the glass plate to obtain a phenyl polyimide film; Step 3: Add 10g KH-550 silane coupling agent and 1g deionized water to 89g ethanol, stir evenly, add 100g nano-silica, react at 70°C for 4h, centrifuge after the reaction is completed, wash with ethanol, and dry at 80°C for 3h. After drying, ultrasonically disperse the product in ethanol at a mass ratio of 1:9 to obtain an amino-nano-silica dispersion; Step 4: Immerse the phenyl polyimide film in the amino-modified nano-silica dispersion, take it out after ultrasonication for 30 minutes, dry it at 70°C for 1 hour, and then spread it flat in an autoclave. Use carbon dioxide to foam the film. Set the foaming pressure to 13 MPa, the foaming temperature to 60°C, and the foaming time to 2 hours. After the foaming is completed, quickly release the pressure to obtain a 20 μm thick polyimide foam film; Step 5: Place the polyimide foam film into the chamber of the magnetron sputtering equipment and fix it on the bracket. Then close the chamber and evacuate it to a vacuum degree of less than 5×10 -5 Pa, then introduced argon, set the bias voltage to 200V, the argon flow rate to 50sccm, the film temperature to 65℃, and etched for 3min. After the etching was completed, the aluminum target power was started, the aluminum target power was set to 150W, the argon pressure was adjusted to 0.4MPa, and the deposition time was 15s. After 15s, the chromium target power was started, the chromium target power was set to 200W, and the deposition time was 1min. The other conditions remained unchanged. After the deposition was completed, it was taken out and annealed at 180℃ for 1h under nitrogen protection to obtain a transitional polyimide film, wherein the thickness of the chromium-aluminum metal layer was 10nm; Step 6: Immerse the copper nanowires in a 5% hydrochloric acid solution for 5 minutes to remove the oxide film on the surface. Centrifuge for 5 minutes, wash with ethanol, and then add them to a 1% polyvinyl pyrrolidone alcohol solution. Ultrasonic dispersion is performed for 30 minutes to obtain a copper nanowire dispersion. Add graphene oxide powder to N-methyl pyrrolidone, ultrasonically disperse for 30 minutes, and then add ascorbic acid in an amount equal to the mass of the graphene oxide powder. Stir and react at 80°C for 12 hours. After the reaction is completed, evaporate and concentrate to obtain a 5 mg / mL reduced graphene dispersion. The reduced graphene dispersion and the copper nanowire dispersion are mixed in a mass ratio of 1:3, ultrasonically dispersed for 30 minutes, and 0.5% of the total mass of the mixed solution. Hydroxyethyl cellulose is added and stirred to obtain a conductive slurry. Step 7: The conductive slurry was vacuum filtered onto a polycarbonate film and dried at 60°C for 2 hours to form a copper-graphite composite conductive layer-polycarbonate film. The polycarbonate film was peeled off and the copper-graphite composite conductive layer was covered on a transition polyimide film. The film was hot-pressed at 200°C and 5 MPa for 10 minutes. After the hot-pressing was completed, the film was annealed at 180°C under nitrogen protection for 1 hour to obtain a conductive polyimide film. The thickness of the copper-graphite composite conductive layer was 3 μm. Step 8: Place the conductive polyimide film into the chamber of the plasma chemical vapor deposition equipment, close the chamber, and evacuate to 1×10 -3 pa, argon was introduced to pretreat the film, the film temperature was set to 100 ° C, the argon pressure was 10 Pa, the RF power was 100 W, the pretreatment time was 2 min, and after the pretreatment was completed, a mixture of acetylene and hydrogen was introduced for deposition to form an amorphous carbon layer with a thickness of 5 nm. The RF power was adjusted to 300 W, the pressure in the chamber was 5 Pa, the deposition time was 1 min, and after the deposition was completed, the vacuum was pumped to 1×10 -3 pa, and then a mixture of silane, ammonia and nitrogen was introduced for deposition to form a 15nm thick silicon nitride layer. The RF power was adjusted to 200W, the gas pressure in the cavity was 20Pa, the film temperature was 80℃, and the deposition time was 1min. After the deposition was completed, the film was annealed at 150℃ for 30min under nitrogen protection to obtain an interference-resistant superconducting composite film.

[0025] Example 2: A method for preparing an interference-resistant superconducting composite film, specifically: Step 1: Under argon protection, 48.5 g of dimethylaniline and 10.6 g of benzaldehyde were mixed, stirred evenly, and then heated to 100 ° C. 4.2 mL of 37 wt% concentrated hydrochloric acid and 20 g of dimethoxyethanol were slowly added. After the addition was complete, the temperature was raised to 125 ° C and the reaction was allowed to react for 12 hours. After 12 hours, 2 g / 500 mL of sodium hydroxide alcohol solution was added to terminate the reaction. The mixture was filtered to obtain a diamine intermediate; Step 2: Under nitrogen protection, 66g of diamine intermediate, 360g of diaminodiphenyl ether and 4000g of N,N-dimethylacetamide were mixed and stirred in an ice-water bath for 30min to fully dissolve the diamine intermediate, and then 940g of p-phenylene trimellitic dianhydride was added. The mixture was stirred for 24h under nitrogen protection to obtain a polyamic acid solution. The polyamic acid was applied to a glass plate, dried at room temperature for 4h, and then heated at 80°C for 6h, 120°C for 2h, 160°C for 2h, 200°C for 2h, 250°C for 1h, and 300°C for 30min for imidization. After cooling to room temperature, the film was removed from the glass plate to obtain a phenyl polyimide film; Step 3: Add 10g KH-550 silane coupling agent and 1g deionized water to 89g ethanol, stir evenly, add 100g nano-silica, react at 70°C for 4h, centrifuge after the reaction is completed, wash with ethanol, and dry at 80°C for 3h. After drying, ultrasonically disperse the product in ethanol at a mass ratio of 1:9 to obtain an amino-nano-silica dispersion; Step 4: Immerse the phenyl polyimide film in the amino-modified nano-silica dispersion, take it out after ultrasonication for 30 minutes, dry it at 70°C for 1 hour, and then spread it flat in an autoclave. Use carbon dioxide to foam the film. Set the foaming pressure to 13 MPa, the foaming temperature to 60°C, and the foaming time to 2 hours. After the foaming is completed, quickly release the pressure to obtain a 20 μm thick polyimide foam film; Step 5: Place the polyimide foam film into the chamber of the magnetron sputtering equipment and fix it on the bracket. Then close the chamber and evacuate it to a vacuum degree of less than 5×10 -5 Pa, then argon gas was introduced, the bias voltage was set to 200V, the argon flow rate was 50sccm, the film temperature was 65℃, and the etching was completed for 3min. After the etching was completed, the aluminum target power supply was started, the aluminum target power was set to 150W, the argon pressure was adjusted to 0.4MPa, and the deposition time was 15s. After 15s, the chromium target power supply was started, the chromium target power was set to 200W, and the deposition time was 50s. The other conditions remained unchanged. After the deposition was completed, the film was taken out and annealed at 180℃ for 1h under nitrogen protection to obtain a transitional polyimide film, wherein the thickness of the chromium-aluminum metal layer was 8nm; Step 6: Immerse the copper nanowires in a 5% hydrochloric acid solution for 5 minutes to remove the oxide film on the surface. Centrifuge for 5 minutes, wash with ethanol, and then add them to a 1% polyvinyl pyrrolidone alcohol solution. Ultrasonic dispersion is performed for 30 minutes to obtain a copper nanowire dispersion. Add graphene oxide powder to N-methyl pyrrolidone, ultrasonically disperse for 30 minutes, and then add ascorbic acid in an amount equal to the mass of the graphene oxide powder. Stir and react at 80°C for 12 hours. After the reaction is completed, evaporate and concentrate to obtain a 5 mg / mL reduced graphene dispersion. The reduced graphene dispersion and the copper nanowire dispersion are mixed in a mass ratio of 1:4, ultrasonically dispersed for 30 minutes, and 0.5% of the total mass of the mixed solution of hydroxyethyl cellulose is added and stirred to obtain a conductive slurry. Step 7: The conductive slurry was vacuum filtered onto a polycarbonate film and dried at 60°C for 2 hours to form a copper-graphite composite conductive layer-polycarbonate film. The polycarbonate film was peeled off and the copper-graphite composite conductive layer was covered on a transition polyimide film. The film was hot-pressed at 200°C and 5 MPa for 10 minutes. After the hot-pressing was completed, the film was annealed at 180°C under nitrogen protection for 1 hour to obtain a conductive polyimide film, wherein the thickness of the copper-graphite composite conductive layer was 2 μm. Step 8: Place the conductive polyimide film into the chamber of the plasma chemical vapor deposition equipment, close the chamber, and evacuate to 1×10 -3 pa, argon was introduced to pretreat the film, the film temperature was set to 100 ° C, the argon pressure was 10 Pa, the RF power was 100 W, the pretreatment time was 2 min, and after the pretreatment was completed, a mixture of acetylene and hydrogen was introduced for deposition to form an amorphous carbon layer with a thickness of 4 nm. The RF power was adjusted to 300 W, the pressure in the chamber was 5 Pa, the deposition time was 50 s, and after the deposition was completed, the vacuum was pumped to 1×10 -3 pa, and then a mixture of silane, ammonia and nitrogen was introduced for deposition to form a 13nm thick silicon nitride layer. The RF power was adjusted to 200W, the gas pressure in the cavity was 20Pa, the film temperature was 80℃, and the deposition time was 50s. After the deposition was completed, the film was annealed at 150℃ for 30min under nitrogen protection to obtain an interference-resistant superconducting composite film.

[0026] Example 3: A method for preparing an anti-interference superconducting composite film, specifically: Step 1: Under argon protection, 48.5 g of dimethylaniline and 10.6 g of benzaldehyde were mixed, stirred evenly, and then heated to 100 ° C. 4.2 mL of 37 wt% concentrated hydrochloric acid and 20 g of dimethoxyethanol were slowly added. After the addition was complete, the temperature was raised to 125 ° C and the reaction was allowed to react for 12 hours. After 12 hours, 2 g / 500 mL of sodium hydroxide alcohol solution was added to terminate the reaction. The mixture was filtered to obtain a diamine intermediate; Step 2: Under nitrogen protection, 66g of diamine intermediate, 360g of diaminodiphenyl ether and 4000g of N,N-dimethylacetamide were mixed and stirred in an ice-water bath for 30min to fully dissolve the diamine intermediate, and then 940g of p-phenylene trimellitic dianhydride was added. The mixture was stirred for 24h under nitrogen protection to obtain a polyamic acid solution. The polyamic acid was applied to a glass plate, dried at room temperature for 4h, and then heated at 80°C for 6h, 120°C for 2h, 160°C for 2h, 200°C for 2h, 250°C for 1h, and 300°C for 30min for imidization. After cooling to room temperature, the film was removed from the glass plate to obtain a phenyl polyimide film; Step 3: Add 10g KH-550 silane coupling agent and 1g deionized water to 89g ethanol, stir evenly, add 100g nano-silica, react at 70°C for 4h, centrifuge after the reaction is completed, wash with ethanol, and dry at 80°C for 3h. After drying, ultrasonically disperse the product in ethanol at a mass ratio of 1:9 to obtain an amino-nano-silica dispersion; Step 4: Immerse the phenyl polyimide film in the amino-modified nano-silica dispersion, take it out after ultrasonication for 30 minutes, dry it at 70°C for 1 hour, and then spread it flat in an autoclave. Use carbon dioxide to foam the film. Set the foaming pressure to 13 MPa, the foaming temperature to 60°C, and the foaming time to 2 hours. After the foaming is completed, quickly release the pressure to obtain a 20 μm thick polyimide foam film; Step 5: Place the polyimide foam film into the chamber of the magnetron sputtering equipment and fix it on the bracket. Then close the chamber and evacuate it to a vacuum degree of less than 5×10 -5 Pa, then introduced argon, set the bias voltage to 200V, the argon flow rate to 50sccm, the film temperature to 65℃, and etched for 3min. After the etching was completed, the aluminum target power was started, the aluminum target power was set to 150W, the argon pressure was adjusted to 0.4MPa, and the deposition time was 15s. After 15s, the chromium target power was started, the chromium target power was set to 200W, and the deposition time was 1min. The other conditions remained unchanged. After the deposition was completed, it was taken out and annealed at 180℃ for 1h under nitrogen protection to obtain a transitional polyimide film, wherein the thickness of the chromium-aluminum metal layer was 10nm; Step 6: Immerse the copper nanowires in a 5% hydrochloric acid solution for 5 minutes to remove the oxide film on the surface. Centrifuge for 5 minutes, wash with ethanol, and then add them to a 1% polyvinyl pyrrolidone alcohol solution. Ultrasonic dispersion is performed for 30 minutes to obtain a copper nanowire dispersion. Add graphene oxide powder to N-methyl pyrrolidone, ultrasonically disperse for 30 minutes, and then add ascorbic acid in an amount equal to the mass of the graphene oxide powder. Stir and react at 80°C for 12 hours. After the reaction is completed, evaporate and concentrate to obtain a 5 mg / mL reduced graphene dispersion. The reduced graphene dispersion and the copper nanowire dispersion are mixed in a mass ratio of 1:3, ultrasonically dispersed for 30 minutes, and 0.5% of the total mass of the mixed solution. Hydroxyethyl cellulose is added and stirred to obtain a conductive slurry. Step 7: The conductive slurry was vacuum filtered onto a polycarbonate film and dried at 60°C for 2 hours to form a copper-graphite composite conductive layer-polycarbonate film. The polycarbonate film was peeled off and the copper-graphite composite conductive layer was covered on a transition polyimide film. The film was hot-pressed at 200°C and 5 MPa for 10 minutes. After the hot-pressing was completed, the film was annealed at 180°C under nitrogen protection for 1 hour to obtain a conductive polyimide film. The thickness of the copper-graphite composite conductive layer was 4 μm. Step 8: Place the conductive polyimide film into the chamber of the plasma chemical vapor deposition equipment, close the chamber, and evacuate to 1×10 -3 pa, argon was introduced to pretreat the film, the film temperature was set to 100 ° C, the argon pressure was 10 Pa, the RF power was 100 W, the pretreatment time was 2 min, and after the pretreatment was completed, a mixture of acetylene and hydrogen was introduced for deposition to form an amorphous carbon layer with a thickness of 5 nm. The RF power was adjusted to 300 W, the pressure in the chamber was 5 Pa, the deposition time was 1 min, and after the deposition was completed, the vacuum was pumped to 1×10 -3 pa, and then a mixture of silane, ammonia and nitrogen was introduced for deposition to form an 18nm thick silicon nitride layer. The RF power was adjusted to 200W, the gas pressure in the cavity was 20Pa, the film temperature was 80℃, and the deposition time was 70s. After the deposition was completed, the film was annealed at 150℃ for 30min under nitrogen protection to obtain an interference-resistant superconducting composite film.

[0027] Based on Example 1, control experiments were conducted, specifically Comparative Example 1, Comparative Example 2, and Comparative Example 3, as described below: Comparative Example 1: This comparative example relates to a method for preparing an anti-interference superconducting composite film. The difference from Example 1 lies in the deposition of the transition layer, specifically: Step 1: Under argon protection, 48.5 g of dimethylaniline and 10.6 g of benzaldehyde were mixed, stirred evenly, and then heated to 100 ° C. 4.2 mL of 37 wt% concentrated hydrochloric acid and 20 g of dimethoxyethanol were slowly added. After the addition was complete, the temperature was raised to 125 ° C and the reaction was allowed to react for 12 hours. After 12 hours, 2 g / 500 mL of sodium hydroxide alcohol solution was added to terminate the reaction. The mixture was filtered to obtain a diamine intermediate; Step 2: Under nitrogen protection, 66g of diamine intermediate, 360g of diaminodiphenyl ether and 4000g of N,N-dimethylacetamide were mixed and stirred in an ice-water bath for 30min to fully dissolve the diamine intermediate, and then 940g of p-phenylene trimellitic dianhydride was added. The mixture was stirred for 24h under nitrogen protection to obtain a polyamic acid solution. The polyamic acid was applied to a glass plate, dried at room temperature for 4h, and then heated at 80°C for 6h, 120°C for 2h, 160°C for 2h, 200°C for 2h, 250°C for 1h, and 300°C for 30min for imidization. After cooling to room temperature, the film was removed from the glass plate to obtain a phenyl polyimide film; Step 3: Add 10g KH-550 silane coupling agent and 1g deionized water to 89g ethanol, stir evenly, add 100g nano-silica, react at 70°C for 4h, centrifuge after the reaction is completed, wash with ethanol, and dry at 80°C for 3h. After drying, ultrasonically disperse the product in ethanol at a mass ratio of 1:9 to obtain an amino-nano-silica dispersion; Step 4: Immerse the phenyl polyimide film in the amino-modified nano-silica dispersion, take it out after ultrasonication for 30 minutes, dry it at 70°C for 1 hour, and then spread it flat in an autoclave. Use carbon dioxide to foam the film. Set the foaming pressure to 13 MPa, the foaming temperature to 60°C, and the foaming time to 2 hours. After the foaming is completed, quickly release the pressure to obtain a 20 μm thick polyimide foam film; Step 5: Immerse the copper nanowires in a 5% hydrochloric acid solution for 5 minutes to remove the oxide film on the surface. Centrifuge for 5 minutes, wash with ethanol, and then add them to a 1% polyvinyl pyrrolidone alcohol solution. Ultrasonic dispersion is performed for 30 minutes to obtain a copper nanowire dispersion. Add graphene oxide powder to N-methyl pyrrolidone, ultrasonically disperse for 30 minutes, and then add ascorbic acid in an amount equal to the mass of the graphene oxide powder. Stir and react at 80°C for 12 hours. After the reaction is completed, evaporate and concentrate to obtain a 5 mg / mL reduced graphene dispersion. The reduced graphene dispersion and the copper nanowire dispersion are mixed in a mass ratio of 1:3, ultrasonically dispersed for 30 minutes, and 0.5% of the total mass of the mixed solution of hydroxyethyl cellulose is added and stirred to obtain a conductive slurry. Step 6: The conductive slurry was vacuum filtered onto a polycarbonate film and dried at 60°C for 2 hours to form a copper-graphite composite conductive layer-polycarbonate film. The polycarbonate film was peeled off and the copper-graphite composite conductive layer was covered on a polyimide foam film. The film was hot-pressed at 200°C and 5 MPa for 10 minutes. After the hot pressing was completed, the film was annealed at 180°C under nitrogen protection for 1 hour to obtain a conductive polyimide film, wherein the thickness of the copper-graphite composite conductive layer was 3 μm. Step 7: Place the conductive polyimide film into the chamber of the plasma chemical vapor deposition equipment, close the chamber, and evacuate to 1×10 -3 pa, argon was introduced to pretreat the film, the film temperature was set to 100 ° C, the argon pressure was 10 Pa, the RF power was 100 W, the pretreatment time was 2 min, and after the pretreatment was completed, a mixture of acetylene and hydrogen was introduced for deposition to form an amorphous carbon layer with a thickness of 5 nm. The RF power was adjusted to 300 W, the pressure in the chamber was 5 Pa, the deposition time was 1 min, and after the deposition was completed, the vacuum was pumped to 1×10 -3 pa, and then a mixture of silane, ammonia and nitrogen was introduced for deposition to form a 15nm thick silicon nitride layer. The RF power was adjusted to 200W, the gas pressure in the cavity was 20Pa, the film temperature was 80℃, and the deposition time was 1min. After the deposition was completed, the film was annealed at 150℃ for 30min under nitrogen protection to obtain an interference-resistant superconducting composite film.

[0028] Comparative Example 2: This comparative example relates to a method for preparing an anti-interference superconducting composite film. The difference from Example 1 is that no amorphous carbon layer is deposited. Specifically: Step 1: Under argon protection, 48.5 g of dimethylaniline and 10.6 g of benzaldehyde were mixed, stirred evenly, and then heated to 100 ° C. 4.2 mL of 37 wt% concentrated hydrochloric acid and 20 g of dimethoxyethanol were slowly added. After the addition was complete, the temperature was raised to 125 ° C and the reaction was allowed to react for 12 hours. After 12 hours, 2 g / 500 mL of sodium hydroxide alcohol solution was added to terminate the reaction. The mixture was filtered to obtain a diamine intermediate; Step 2: Under nitrogen protection, 66g of diamine intermediate, 360g of diaminodiphenyl ether and 4000g of N,N-dimethylacetamide were mixed and stirred in an ice-water bath for 30min to fully dissolve the diamine intermediate, and then 940g of p-phenylene trimellitic dianhydride was added. The mixture was stirred for 24h under nitrogen protection to obtain a polyamic acid solution. The polyamic acid was applied to a glass plate, dried at room temperature for 4h, and then heated at 80°C for 6h, 120°C for 2h, 160°C for 2h, 200°C for 2h, 250°C for 1h, and 300°C for 30min for imidization. After cooling to room temperature, the film was removed from the glass plate to obtain a phenyl polyimide film; Step 3: Add 10g KH-550 silane coupling agent and 1g deionized water to 89g ethanol, stir evenly, add 100g nano-silica, react at 70°C for 4h, centrifuge after the reaction is completed, wash with ethanol, and dry at 80°C for 3h. After drying, ultrasonically disperse the product in ethanol at a mass ratio of 1:9 to obtain an amino-nano-silica dispersion; Step 4: Immerse the phenyl polyimide film in the amino-modified nano-silica dispersion, take it out after ultrasonication for 30 minutes, dry it at 70°C for 1 hour, and then spread it flat in an autoclave. Use carbon dioxide to foam the film. Set the foaming pressure to 13 MPa, the foaming temperature to 60°C, and the foaming time to 2 hours. After the foaming is completed, quickly release the pressure to obtain a 20 μm thick polyimide foam film; Step 5: Place the polyimide foam film into the chamber of the magnetron sputtering equipment and fix it on the bracket. Then close the chamber and evacuate it to a vacuum degree of less than 5×10 -5 Pa, then introduced argon, set the bias voltage to 200V, the argon flow rate to 50sccm, the film temperature to 65℃, and etched for 3min. After the etching was completed, the aluminum target power was started, the aluminum target power was set to 150W, the argon pressure was adjusted to 0.4MPa, and the deposition time was 15s. After 15s, the chromium target power was started, the chromium target power was set to 200W, and the deposition time was 1min. The other conditions remained unchanged. After the deposition was completed, it was taken out and annealed at 180℃ for 1h under nitrogen protection to obtain a transitional polyimide film, wherein the thickness of the chromium-aluminum metal layer was 10nm; Step 6: Immerse the copper nanowires in a 5% hydrochloric acid solution for 5 minutes to remove the oxide film on the surface. Centrifuge for 5 minutes, wash with ethanol, and then add them to a 1% polyvinyl pyrrolidone alcohol solution. Ultrasonic dispersion is performed for 30 minutes to obtain a copper nanowire dispersion. Add graphene oxide powder to N-methyl pyrrolidone, ultrasonically disperse for 30 minutes, and then add ascorbic acid in an amount equal to the mass of the graphene oxide powder. Stir and react at 80°C for 12 hours. After the reaction is completed, evaporate and concentrate to obtain a 5 mg / mL reduced graphene dispersion. The reduced graphene dispersion and the copper nanowire dispersion are mixed in a mass ratio of 1:3, ultrasonically dispersed for 30 minutes, and 0.5% of the total mass of the mixed solution. Hydroxyethyl cellulose is added and stirred to obtain a conductive slurry. Step 7: The conductive slurry was vacuum filtered onto a polycarbonate film and dried at 60°C for 2 hours to form a copper-graphite composite conductive layer-polycarbonate film. The polycarbonate film was peeled off and the copper-graphite composite conductive layer was covered on a transition polyimide film. The film was hot-pressed at 200°C and 5 MPa for 10 minutes. After the hot-pressing was completed, the film was annealed at 180°C under nitrogen protection for 1 hour to obtain a conductive polyimide film. The thickness of the copper-graphite composite conductive layer was 3 μm. Step 8: Place the conductive polyimide film into the chamber of the plasma chemical vapor deposition equipment, close the chamber, and evacuate to 1×10 -3 pa, argon gas is introduced to pretreat the film, the film temperature is set to 100℃, the argon pressure is 10Pa, the RF power is 100W, and the pretreatment time is 2min. After the pretreatment is completed, a mixture of silane, ammonia and nitrogen is introduced for deposition to form a 15nm thick silicon nitride layer, the RF power is adjusted to 200W, the air pressure in the cavity is 20Pa, the film temperature is 80℃, and the deposition time is 1min. After the deposition is completed, it is annealed at 150℃ for 30min under nitrogen protection to obtain an interference-resistant superconducting composite film.

[0029] Comparative Example 3: This comparative example relates to a method for preparing an anti-interference superconducting composite film. The difference from Example 1 is that the conductive layer does not contain reduced graphene, specifically: Step 1: Under argon protection, 48.5 g of dimethylaniline and 10.6 g of benzaldehyde were mixed, stirred evenly, and then heated to 100 ° C. 4.2 mL of 37 wt% concentrated hydrochloric acid and 20 g of dimethoxyethanol were slowly added. After the addition was complete, the temperature was raised to 125 ° C and the reaction was allowed to react for 12 hours. After 12 hours, 2 g / 500 mL of sodium hydroxide alcohol solution was added to terminate the reaction. The mixture was filtered to obtain a diamine intermediate; Step 2: Under nitrogen protection, 66g of diamine intermediate, 360g of diaminodiphenyl ether and 4000g of N,N-dimethylacetamide were mixed and stirred in an ice-water bath for 30min to fully dissolve the diamine intermediate, and then 940g of p-phenylene trimellitic dianhydride was added. The mixture was stirred for 24h under nitrogen protection to obtain a polyamic acid solution. The polyamic acid was applied to a glass plate, dried at room temperature for 4h, and then heated at 80°C for 6h, 120°C for 2h, 160°C for 2h, 200°C for 2h, 250°C for 1h, and 300°C for 30min for imidization. After cooling to room temperature, the film was removed from the glass plate to obtain a phenyl polyimide film; Step 3: Add 10g KH-550 silane coupling agent and 1g deionized water to 89g ethanol, stir evenly, add 100g nano-silica, react at 70°C for 4h, centrifuge after the reaction is completed, wash with ethanol, and dry at 80°C for 3h. After drying, ultrasonically disperse the product in ethanol at a mass ratio of 1:9 to obtain an amino-nano-silica dispersion; Step 4: Immerse the phenyl polyimide film in the amino-modified nano-silica dispersion, take it out after ultrasonication for 30 minutes, dry it at 70°C for 1 hour, and then spread it flat in an autoclave. Use carbon dioxide to foam the film. Set the foaming pressure to 13 MPa, the foaming temperature to 60°C, and the foaming time to 2 hours. After the foaming is completed, quickly release the pressure to obtain a 20 μm thick polyimide foam film; Step 5: Place the polyimide foam film into the chamber of the magnetron sputtering equipment and fix it on the bracket. Then close the chamber and evacuate it to a vacuum degree of less than 5×10 -5 Pa, then introduced argon, set the bias voltage to 200V, the argon flow rate to 50sccm, the film temperature to 65℃, and etched for 3min. After the etching was completed, the aluminum target power was started, the aluminum target power was set to 150W, the argon pressure was adjusted to 0.4MPa, and the deposition time was 15s. After 15s, the chromium target power was started, the chromium target power was set to 200W, and the deposition time was 1min. The other conditions remained unchanged. After the deposition was completed, it was taken out and annealed at 180℃ for 1h under nitrogen protection to obtain a transitional polyimide film, wherein the thickness of the chromium-aluminum metal layer was 10nm; Step 6: Immerse the copper nanowires in a 5% hydrochloric acid solution for 5 minutes to remove the oxide film on the surface. Centrifuge for 5 minutes and wash with ethanol. Then, add the copper nanowires to a 1% polyvinyl pyrrolidone alcohol solution and ultrasonically disperse for 30 minutes to obtain a copper nanowire dispersion. Add 0.5% hydroxyethyl cellulose to the total mass of the dispersion and stir evenly to obtain a conductive slurry. Step 7: The conductive slurry was vacuum filtered onto a polycarbonate film and dried at 60°C for 2 hours to form a copper-graphite composite conductive layer-polycarbonate film. The polycarbonate film was peeled off and the copper-graphite composite conductive layer was covered on a transition polyimide film. The film was hot-pressed at 200°C and 5 MPa for 10 minutes. After the hot-pressing was completed, the film was annealed at 180°C under nitrogen protection for 1 hour to obtain a conductive polyimide film. The thickness of the copper-graphite composite conductive layer was 3 μm. Step 8: Place the conductive polyimide film into the chamber of the plasma chemical vapor deposition equipment, close the chamber, and evacuate to 1×10 -3 pa, argon was introduced to pretreat the film, the film temperature was set to 100 ° C, the argon pressure was 10 Pa, the RF power was 100 W, the pretreatment time was 2 min, and after the pretreatment was completed, a mixture of acetylene and hydrogen was introduced for deposition to form an amorphous carbon layer with a thickness of 5 nm. The RF power was adjusted to 300 W, the pressure in the chamber was 5 Pa, the deposition time was 1 min, and after the deposition was completed, the vacuum was pumped to 1×10 -3 pa, and then a mixture of silane, ammonia and nitrogen was introduced for deposition to form a 15nm thick silicon nitride layer. The RF power was adjusted to 200W, the gas pressure in the cavity was 20Pa, the film temperature was 80℃, and the deposition time was 1min. After the deposition was completed, the film was annealed at 150℃ for 30min under nitrogen protection to obtain an interference-resistant superconducting composite film.

[0030] Detection experiment: Superconducting composite film samples required for the test were prepared according to the preparation methods in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively, and the performance of the conductive composite film was tested.

[0031] Combined performance test: A universal material testing machine was used to test the peel strength of the sample. The sample was cut into 150mm×25mm strips. A blade was used to pre-peel 20mm at one end of the strip sample to form a peeling starting point. The upper clamp of the testing machine was used to fix the peeling starting point, and the lower clamp was used to fix the base of the strip sample. The peeling speed was set to 50mm / min. When the sample surface was completely peeled off, the testing machine was stopped and the peel strength was calculated.

[0032] Conductivity test: Use a four-probe tester to test the surface square resistance of the superconducting composite film sample. Lay the conductive film flat on an insulating substrate, use four probes to vertically contact the film surface, input a constant current of 10mA, record the voltage reading, calculate the surface square resistance of the sample, and move the probe to measure multiple points and take the average value (test 5 locations).

[0033] Anti-PIM performance test: A PIM analyzer was used to measure the PIM level of each superconducting composite film sample. First, the background noise was tested. The test frequencies were set to f1 = 935 MHz and f2 = 960 MHz. A dual-frequency signal was input at a power of 43 dBm, and the background noise was recorded. Then, silver electrodes were printed on the surface of the conductive film and fixed to the test fixture. The electrodes were connected to a low-PIM cable. The test frequency was set again, and a dual-frequency signal was input. IM3 products were detected, and the higher IM3 value was taken as the PIM level.

[0034] Insertion loss performance test: A vector network analyzer (VNA) was used to test the insertion loss of each superconducting composite film sample. After printing silver electrodes on the surface of the conductive film, a VNA was connected to the input end of the sample. The VNA frequency range was set to 26.5-40 GHz, the number of scan points was 1601, and the IF bandwidth was 1 kHz. The insertion loss of the sample was calculated.

[0035] Conclusion: It can be seen from the test data that the peel strength, surface square resistance, insertion level and insertion loss of the conductive composite film prepared by the preparation method of the superconducting composite film in the embodiment are better than those of the comparative examples. The conductive composite film prepared by the preparation method of the anti-interference superconducting composite film provided by the present invention has good conductive performance and anti-PIM interference function, small insertion loss, good bonding performance, and is suitable for multi-frequency and high-power working environments.

[0036] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. An anti-interference superconducting composite film, characterized in that: From bottom to top, it includes the following structures: a base layer, a transition layer, a conductive layer, an anti-PIM interface layer and an encapsulation layer. The base layer is a 15-20 μm thick polyimide foam film, the transition layer is an 8-10 nm thick chromium-aluminum metal layer, the conductive layer is a 2-4 μm thick copper-graphite composite conductive layer, the anti-PIM interface layer is a 4-6 nm thick amorphous carbon layer, and the encapsulation layer is a 10-20 nm thick silicon nitride layer.

2. A method for preparing an interference-resistant superconducting composite film, characterized in that: Specifically: Step 1: using dimethylaniline, benzaldehyde, diaminodiphenyl ether and p-phenylene trimellitic dianhydride as raw materials, synthesizing a phenyl polyimide film, and then foaming it with carbon dioxide to obtain a polyimide foam film; Step 2: depositing chromium and aluminum on the polyimide foam film to form a transition layer to obtain a transition polyimide film; Step 3: drying the conductive paste containing reduced graphene and copper nanowires to form a copper-graphite composite conductive layer, and then hot-pressing the copper-graphite composite conductive layer and the transition polyimide film to obtain a conductive polyimide film; Step 4: depositing an amorphous carbon layer on the conductive polyimide film to obtain an anti-PIM film, and depositing silicon nitride on the surface of the anti-PIM film to form a silicon nitride layer to obtain an anti-interference superconducting composite film.

3. The method for preparing an interference-resistant superconducting composite film according to claim 2, wherein: Step 1 is as follows: Add KH-550 silane coupling agent and deionized water to ethanol, stir evenly, add nano-silica, react at 70-80°C for 3-4 hours, centrifuge after the reaction is complete, wash with ethanol, dry at 80-90°C for 2-3 hours, and after drying, ultrasonically disperse the product in ethanol to obtain an amino-nano-silica dispersion; The phenyl polyimide film is immersed in an amino-modified nano-silica dispersion, taken out after ultrasonic treatment for 20-30 minutes, and dried at 70-80°C for 0.5-1h. The film is then foamed with carbon dioxide, with the foaming pressure set at 12-15MPa, the foaming temperature at 55-65°C, and the foaming time being 1-2h. After the foaming is completed, the pressure is quickly released to obtain a polyimide foam film.

4. The method for preparing an interference-resistant superconducting composite film according to claim 3, wherein: The mass ratio of KH-550 silane coupling agent to nano-silica is 1:(8-12); in the amino-modified nano-silica dispersion, the mass ratio of the product to ethanol is 1:(8-10); when heating for imidization, step-by-step heating is adopted, and the heating process is: heating at 80-90°C for 4-6 hours, heating at 120-130°C for 1-2 hours, heating at 160-170°C for 1-2 hours, heating at 200-210°C for 1-2 hours, heating at 250-260°C for 0.5-1 hour, and heating at 300-310°C for 20-30 minutes.

5. The method for preparing an interference-resistant superconducting composite film according to claim 3, wherein: The preparation method of phenyl polyimide film is as follows: Under argon protection, dimethylaniline and benzaldehyde are mixed, stirred evenly, and then heated to 100-110°C. Concentrated hydrochloric acid and dimethoxyethanol are slowly added. After the addition is complete, the temperature is raised to 125-135°C and the reaction is carried out for 8-12 hours. After 8-12 hours, sodium hydroxide alcohol solution is added and filtered to obtain a diamine intermediate; Under nitrogen protection, the diamine intermediate, diaminodiphenyl ether and N,N-dimethylacetamide are mixed and stirred in an ice-water bath for 20-30 minutes to fully dissolve the diamine intermediate. Then, p-phenylene trimellitic dianhydride is added and stirred for 20-24 hours under nitrogen protection to obtain a polyamic acid solution. The polyamic acid is applied to a glass plate, dried at room temperature for 3-5 hours, and then heated for imidization. After heating, it is cooled to room temperature and peeled off from the glass plate to obtain a phenyl polyimide film.

6. The method for preparing an interference-resistant superconducting composite film according to claim 5, characterized in that: The mass ratio of dimethylaniline, benzaldehyde and dimethoxyethanol is (46-50):(9-11):(18-22); the mass ratio of diamine intermediate, diaminodiphenyl ether and p-phenylene trimellitic acid dianhydride is (6.4-6.8):(35-37):(92-96).

7. The method for preparing an interference-resistant superconducting composite film according to claim 2, wherein: In step 2, when chromium and aluminum are deposited to form a transition layer, the aluminum target power is 120-150W, the argon pressure is 0.3-0.4MPa, and the deposition time is 15-20s. After 15-20s, the chromium target power is started, the chromium target power is 180-200W, and the deposition time is 0.8-1min; before deposition, the film surface is etched and activated, the bias voltage is 180-200V, the argon flow rate is 40-50sccm, the film temperature is 55-65°C, and the etching time is 3-5min; after deposition, annealing is performed at a temperature of 170-180°C and a time of 1-1.5h.

8. The method for preparing an interference-resistant superconducting composite film according to claim 2, characterized in that: Step 3 is as follows: The copper nanowires were immersed in a hydrochloric acid solution for 3-5 minutes to remove the oxide film on the surface. The mixture was centrifuged after 3-5 minutes and washed with ethanol. The mixture was then added to a polyvinyl pyrrolidone alcohol solution and ultrasonically dispersed for 30-40 minutes to obtain a copper nanowire dispersion. The graphene oxide powder was added to N-methyl pyrrolidone and ultrasonically dispersed for 30-40 minutes. Ascorbic acid was added and the mixture was stirred at 80-90°C for 8-12 hours. After the reaction was completed, the mixture was evaporated and concentrated to obtain a reduced graphene dispersion. The reduced graphene dispersion and the copper nanowire dispersion are mixed, ultrasonically dispersed for 30-40 minutes, hydroxyethyl cellulose is added, and stirred evenly to obtain a conductive slurry. The conductive slurry is vacuum filtered onto a polycarbonate film, and dried at 50-60°C for 2-3 hours to form a conductive film-polycarbonate film. The polycarbonate film is peeled off, and the conductive film is covered on a polyimide film. The film is hot-pressed at 190-200°C and 4-6MPa for 5-10 minutes. After the hot pressing is completed, the film is annealed at 170-180°C under nitrogen protection for 1-1.5 hours to obtain a conductive polyimide film.

9. The method for preparing an interference-resistant superconducting composite film according to claim 8, characterized in that: In the copper nanowire dispersion, the mass fraction of copper nanowires is 0.5%-1.5%; in the reduced graphene dispersion, the mass fraction of reduced graphene is 1%-3%; in the conductive paste, the mass fraction of hydroxyethyl cellulose is 0.3%-0.6%, and the mass ratio of the reduced graphene dispersion to the copper nanowire dispersion is 1:(2-4).

10. The method for preparing an interference-resistant superconducting composite film according to claim 2, characterized in that: In step 4, when depositing the anti-PIM interface layer, the gases used are acetylene, hydrogen and argon in a volume ratio of (4-6):1:(8-12), the film temperature during deposition is 90-100°C, the RF power is 280-300W, the intracavity pressure is 5-7Pa, and the deposition time is 50-60s; when depositing the encapsulation layer, the gases used are silane, ammonia and nitrogen in a volume ratio of 1:(1-3):(8-12), the film temperature during deposition is 70-80°C, the RF power is 180-200W, the intracavity pressure is 20-24Pa, and the deposition time is 50-70s.

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