Preparation process of electromagnetic shielding structure of conductive foamy copper in communication equipment

Abstract

The invention relates to the technical field of preparation of a metal porous material in an electromagnetic shielding structure, in particular to a preparation process of an electromagnetic shielding structure of conductive foamy copper in communication equipment, which comprises the following steps: mixing foamy copper powder, nano silver powder, graphene and the like, adding ethanol and grinding to form a chemical bond to obtain functional slurry; the shell is subjected to plasma etching after sand blasting, soaked in a 5-8% silane solution for 10-15 minutes and dried at the temperature of 80-100 DEG C; different slurries are sprayed on three layers, the thickness is 0.15-0.3 mm in total, and pre-drying is performed for 10 minutes layer by layer at 60-80 DEG C; in a nitrogen atmosphere, carrying out heat preservation for 1-2 hours at 120-150 DEG C, carrying out heat preservation for 2-3 hours at 200-250 DEG C, carrying out heat preservation for 1-1.5 hours at 300-350 DEG C, and cooling; and immersing in 10-15% sulfuric acid for 3-5 minutes, carrying out electrodeposition on a nickel-cobalt alloy of 0.02-0.05 mm, and immersing in a silane solution to form a sealing layer. Through innovation of slurry modification, layered coating and the like, the structure is excellent in wide-frequency-band shielding effectiveness, firm in combination with a substrate, good in corrosion resistance and flexibility, adaptive to requirements of communication equipment and high in practicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of preparation of metal porous materials in electromagnetic shielding structures, in particular to a preparation process of an electrically conductive foamed copper electromagnetic shielding structure in communication equipment. BACKGROUND

[0002] With the rapid iteration of 5G and next-generation communication technology, communication equipment is developing rapidly towards high frequency, integration and miniaturization. The signal transmission rate and power of core components such as radio frequency modules and signal processors continue to increase, and electromagnetic interference problems are becoming increasingly prominent. Electromagnetic interference not only causes signal attenuation and increased error rate of the equipment, but also may cause functional disorder of adjacent components, and even threaten the safe operation of the equipment. Therefore, electromagnetic shielding has become one of the core technologies in the design of communication equipment. Electrically conductive foamed copper has become an ideal material to replace traditional metal shielding shells due to its light weight, high electrical conductivity and excellent electromagnetic shielding performance. However, it still faces many technical bottlenecks in practical application.

[0003] The existing preparation process of electrically conductive foamed copper shielding structure has obvious defects. In the functional slurry preparation process, foamed copper powder and conductive fillers are usually mixed by simple mechanical mixing, and there is a lack of effective interface modification design, which leads to poor compatibility of copper powder, nano-silver powder and other components, easy aggregation, and difficulty in forming a continuous conductive network, directly restricting the improvement of shielding effectiveness. The use of coupling agents is mostly conventional addition, without specific chemical reaction control based on the characteristics of the powder, and the interface bonding strength is weak, which is easy to delaminate under equipment vibration or temperature change.

[0004] The extensive substrate treatment process exacerbates the problem of structural stability. The traditional method of directly coating after sandblasting cannot build a stable connection bridge between the metal substrate and the shielding layer, and the bonding strength is generally low, which is difficult to adapt to the mechanical impact and thermal cycle environment in the long-term service of communication equipment. Although some processes introduce silane treatment, they do not have a supporting surface activation step such as plasma etching, and the number of hydroxyl groups on the substrate surface is insufficient, so the silane molecules cannot fully react, and the connection layer formed has poor density and is easy to become a penetration channel for water vapor and corrosive media.

[0005] The single coating and sintering process further limits the performance improvement. Single-layer coating cannot balance the electrical conductivity and flexibility of the shielding layer, and traditional sintering mostly uses constant temperature mode, which cannot simultaneously realize solvent evaporation, resin curing and interface strengthening, and is easy to have internal pores or insufficient interface bonding. The surface treatment is mostly single nickel plating or coating, and lacks composite protection design. In harsh environments such as high temperature and humidity or salt spray, the shielding layer is easy to oxidize and corrode, leading to rapid decay of electrical conductivity and shielding effectiveness.

[0006] At the device application level, the traditional shielding structure is mostly of integral design, heavy and poor in adaptability, which cannot meet the individualized shielding needs of different modules. The edge sealing mostly relies on simple conductive adhesive paste, and the sealing performance is easily affected by assembly precision. High-frequency electromagnetic waves are easily leaked from the gap, resulting in a decrease in shielding effectiveness. In addition, the existing structure has a significant shielding performance attenuation at a high frequency (above 18 GHz), which is difficult to adapt to the high-frequency needs of the next generation of communication technology.

[0007] In summary, the existing conductive foam copper shielding structure has problems such as uneven dispersion of functional paste, unstable substrate bonding, rough sintering process, insufficient surface protection, and poor device adaptability, resulting in low shielding effectiveness, poor stability, and short service life, which cannot meet the stringent requirements of high-end communication equipment. It is an urgent need for the industry to develop a conductive foam copper shielding structure with high shielding effectiveness, strong structural stability, and excellent environmental adaptability and a preparation technology. SUMMARY

[0008] (I) Technical problems solved In view of the deficiencies of the prior art, the present application provides a preparation process of a conductive foam copper electromagnetic shielding structure in a communication device.

[0009] (II) Technical solutions A preparation process of a conductive foam copper electromagnetic shielding structure in a communication device, comprising the following steps: S1, functional paste preparation: weighing 70-80% of foam copper powder, 5-8% of nano silver powder, 2-4% of graphene, 1-3% of carbon nanotube, 0.5-1% of lanthanide oxide, 0.5-1.5% of titanate coupling agent, and 3-6% of epoxy resin according to the weight percentage; putting the above raw materials into a planetary ball mill, adding anhydrous ethanol as a dispersion medium for grinding; and preparing a uniformly dispersed functional paste; S2, substrate gradient pretreatment: the communication device shell is made of aluminum alloy material, first subjected to sandblasting treatment, then subjected to plasma etching, argon and oxygen mixed gas is introduced, then immersed in 5-8% silane solution, silane is γ-glycidyl ether oxypropyl trimethoxysilane, taken out after soaking for 10-15 minutes, dried, and a Si-O bond connection layer is formed on the surface; S3, layered coating forming: high-pressure airless spraying is used for layered coating; the bottom layer is coated with a functional paste containing 80% foam copper powder; the middle layer is coated with a functional paste containing 5% nano silver powder; and the top layer is coated with a functional paste containing 3% graphene; and after coating, infrared pre-drying is performed at 60°C, 70°C and 80°C for 10 minutes, respectively; S4, step sintering: the coated substrate is put into an atmosphere sintering furnace, nitrogen is introduced; the temperature is raised to 120-150℃, and the temperature is kept for 1-2 hours; then the temperature is raised to 200-250℃, and the temperature is kept for 2-3 hours to promote the curing of the epoxy resin; finally, the temperature is raised to 300-350℃, and the temperature is kept for 1-1.5 hours to strengthen the interface chemical bonding, and then the temperature is naturally cooled to room temperature; S5, composite surface treatment: first, the sintered shielding layer is immersed in a 10-15% sulfuric acid solution, and surface roughening is carried out at 30℃, and then deionized water is used to clean the surface to neutral; then nickel-cobalt alloy electrodeposition is carried out; finally, the shielding layer is immersed in a 0.5-1% silane solution, and the shielding layer is immersed in the silane solution at 25℃ for 5 minutes, and then the shielding layer is dried at 80℃ to form a closed layer, and an electromagnetic shielding structure is prepared.

[0010] Preferably, the foam copper powder in S1 is also surface modified before use, the foam copper powder is immersed in a 3-5% oxalic acid solution, and anodic oxidation is carried out at a direct current voltage of 10-15V for 5-8 minutes, a uniform distribution of CuO nano arrays is formed on the surface, the particle size of the treated foam copper powder is controlled to be 50-100μm, the particle size of the nano silver powder is 20-50nm, and the length-diameter ratio of the carbon nanotube is 50-100.

[0011] Preferably, after the sand blasting treatment in S2, compressed air is used to blow the surface for 5 minutes to remove the residual abrasive, the distance between the electrode and the substrate is kept at 50-80mm during the plasma etching, and when the silane solution is prepared, deionized water and ethanol mixed solvents are used, the volume ratio is 1:9, and the solution is ultrasonically treated for 10 minutes before use to ensure complete dissolution.

[0012] Preferably, in S3, the nozzle diameter of the high-pressure airless spraying equipment is 0.8-1.2mm, the spraying angle is kept at 90 degrees perpendicular to the surface of the substrate, a laser thickness gauge is used to detect the thickness uniformity after each layer of coating is completed, the deviation is controlled to be within ±5%, and an infrared lamp with a wavelength of 2-5μm is used for infrared drying, and the irradiation distance is 300-500mm.

[0013] Preferably, in S4, the three temperature stages of the step sintering correspond to three key processes of solvent evaporation, resin curing and interface reaction respectively, and the nitrogen flow is adjusted at different stages, 1.2L / min at 120-150℃, 1.0L / min at 200-250℃, and 0.8L / min at 300-350℃, and the pressure in the furnace is kept at a micro-positive pressure of 50-100Pa.

[0014] Preferably, in S5, after the sulfuric acid solution roughening treatment, an eddy current flaw detector is used to detect the surface roughness to ensure that the surface roughness reaches Ra1.6-3.2μm, mechanical stirring with a stirring rate of 300-500r / min is used during the nickel-cobalt alloy electrodeposition, the electrolyte composition is detected every 30 minutes during the deposition process, and the consumed metal ions are supplemented, and the thickness of the film layer formed after the silane sealing treatment is controlled to be 1-3μm.

[0015] Preferably, S6. Shielding effectiveness optimization: magnetron sputtering is carried out on the surface of the shielding structure after the composite surface treatment, the target material is a copper-graphene composite target, the graphene content is 5-8%, the sputtering power is 200-300W, the purity of the argon gas is 99.99%, the working pressure is 0.5-1Pa, the sputtering time is 5-10 minutes, and a copper-graphene composite layer with a thickness of 0.5-1μm is formed.

[0016] Preferably, the electromagnetic shielding effectiveness of the shielding structure reaches 90-100dB in the 100MHz-18GHz frequency band, reaches 85-95dB in the 18-40GHz high frequency band, and the surface resistance is 0.01-0.03Ω / sq.

[0017] Preferably, the bonding strength of the shielding structure and the substrate is 18-22MPa measured by tensile test, the thermal conductivity is 200-230W / (m·K), the salt spray test is carried out according to GB / T 10125, and there is no rust after 600-800 hours, and after being placed at 85℃ temperature and 85% relative humidity environment for 1000 hours, the performance index retention rate is more than 95%.

[0018] Preferably, the communication equipment using the electromagnetic shielding structure comprises an aluminum alloy shell, a signal mainboard and a modular shielding assembly, the shielding assembly adopts the conductive foam copper electromagnetic shielding structure, is divided into 3-5 independent shielding units according to the radio frequency module, the power module and the signal processing module on the mainboard, the edge of each unit is provided with a conductive rubber boss with a semicircular cross section, the boss has a diameter of 0.8-1.2mm, and forms a mortise and tenon connection structure with a groove on the shell, the overall thickness of the shielding assembly is 0.3-0.5mm, and the weight is reduced by 40-50% compared with a traditional metal shielding cover.

[0019] (Three) Beneficial technical effects Compared with the prior art, the beneficial effects of the present application are: 1. By introducing the controllable hydrolysis reaction of titanate coupling agent, the Ti-O-Ag chemical bond is connected between the conductive components, effectively solving the pain points of poor compatibility and easy agglomeration of copper powder, silver powder and other components in traditional slurry, forming a continuous and dense conductive network, laying a foundation for the improvement of wide-band shielding effectiveness. The anodic oxidation pretreatment of foam copper powder and the carboxylation modification of carbon nanotubes further enhance the interfacial bonding force between the components, avoid the performance decay caused by loose structure in the shielding layer, and the addition of lanthanide oxide optimizes the synergistic effect of electrical conductivity and magnetism.

[0020] 2. The step-by-step pretreatment of sandblasting, plasma etching and silane treatment creates multiple connection interfaces through surface roughening and chemical modification. The formation of the Si-O bond connection layer makes the shielding layer and the substrate more firmly bonded, completely solving the problems of insufficient bonding strength and easy delamination in traditional processes. The layered coating design precisely controls the slurry ratio and spraying parameters according to different coating functional requirements. The bottom layer ensures conductivity and bonding, the middle layer enhances shielding effectiveness, and the top layer improves flexibility and corrosion resistance, achieving balanced optimization of single structure and multiple performance goals.

[0021] 3. The three-stage sintering process precisely matches the needs of solvent evaporation, resin curing and interface strengthening, avoiding internal defects caused by traditional single-temperature sintering and ensuring the densification of the shielding layer structure. The composite surface treatment of sulfuric acid roughening, nickel-cobalt alloy electrodeposition and silane sealing creates multiple protective barriers, effectively resisting oxidation and corrosion medium erosion, solving the problem of rapid performance degradation of traditional shielding layers in harsh environments. The magnetic control sputtering optimization step further improves the shielding effectiveness of high-frequency bands.

[0022] 4. The independent shielding unit divided according to functional modules can meet the shielding needs of different components, greatly improving design flexibility. The mortise and tenon connection of the conductive rubber boss and the shell is more reliable than traditional conductive adhesive sealing, effectively reducing high-frequency electromagnetic wave gap leakage, and the lightweight structure design meets the development trend of communication equipment miniaturization and lightweight. BRIEF DESCRIPTION OF DRAWINGS

[0023] Fig. 1 is a preparation process flow chart of an electromagnetic shielding structure of conductive foam copper in communication equipment according to the present application; Fig. 2 is a comparison chart of 100MHz-18GHz shielding effectiveness and 18-40GHz shielding effectiveness of the example and the comparative example; Fig. 3 is a columnar comparison chart of thermal conductivity and salt spray resistance time of the example and the comparative example; Fig. 4 is a shielding effectiveness attenuation fitting curve of the example and the comparative example at different frequencies. DETAILED DESCRIPTION

[0024] According to Figs. 1 to 4 , the specific embodiments of the present application are as follows: EXAMPLE

[0025] Functional slurry preparation: take the foamed copper powder 75%, nano-silver powder 6%, graphene 3%, carbon nanotube 2%, lanthanide oxide 0.8%, titanate coupling agent 1%, and epoxy resin 2.2% by weight percentage. The foamed copper powder has a particle size of 75 μm, and a CuO nano-array is formed on the surface after anodic oxidation in 3% oxalic acid solution for 6 minutes. The nano-silver powder has a particle size of 35 nm. The carbon nanotube has an aspect ratio of 75, and the tube wall is treated by carboxylation. The raw materials are added to a planetary ball mill, and anhydrous ethanol is added, with a solid-liquid ratio of 1:1.5, and grinding for 45 minutes. During the process, the titanate coupling agent is hydrolyzed to form a Ti-O-Ag bond on the surface of the powder, and a functional slurry is prepared.

[0026] Substrate gradient pretreatment: the aluminum alloy shell of the communication equipment is first subjected to sand blasting treatment, and 100-mesh aluminum oxide abrasive is selected, with a sand blasting pressure of 0.4 MPa. After treatment, the surface roughness reaches Ra 4.8 μm. The residual abrasive is removed by blowing compressed air for 5 minutes, and then plasma etching is performed for 4 minutes. Argon and oxygen mixed gas is introduced, with a volume ratio of 3:1, and the power is 120 W. The distance between the electrode and the substrate is kept at 65 mm. Then, the shell is immersed in a 6% γ-glycidoxypropyltrimethoxysilane solution. The solution is a mixed solvent of deionized water and ethanol, with a volume ratio of 1:9. Before use, it is ultrasonically treated for 10 minutes to ensure complete dissolution. After soaking for 12 minutes, it is taken out and dried in a 90°C oven for 30 minutes, and a Si-O bond connection layer is formed on the surface.

[0027] Layered coating molding: high-pressure airless spraying is used for layered coating, with a nozzle diameter of 1.0 mm, and a 90-degree angle perpendicular to the substrate surface. The bottom layer is coated with a functional slurry containing 80% foamed copper powder, with a thickness of 0.08 mm and a spraying pressure of 0.4 MPa. The middle layer is coated with a functional slurry containing 5% nano-silver powder, with a thickness of 0.07 mm and a spraying pressure of 0.3 MPa. The top layer is coated with a functional slurry containing 3% graphene, with a thickness of 0.07 mm and a spraying pressure of 0.2 MPa. During each layer coating, the nozzle is 175 mm away from the substrate, and the moving speed is 75 mm / s. After coating, the substrate is pre-baked at 60°C, 70°C, and 80°C respectively for 10 minutes using an infrared lamp with a wavelength of 2-5 μm, and the infrared lamp irradiation distance is 300-500 mm. A laser thickness gauge is used to detect the thickness uniformity, with a deviation controlled within ±3%.

[0028] Ladder sintering: Put the coated substrate into an atmosphere sintering furnace, and introduce nitrogen gas with a purity of 99.999% and a dew point of -45°C. In the first stage, the temperature is raised to 135°C at a rate of 3°C / min, the nitrogen flow rate is 1.2 L / min, and the holding time is 1.5 hours to completely volatilize the solvent. In the second stage, the temperature is raised to 225°C at a rate of 5°C / min, the nitrogen flow rate is 1.0 L / min, and the holding time is 2.5 hours to promote the curing of the epoxy resin. In the third stage, the temperature is raised to 325°C at a rate of 2°C / min, the nitrogen flow rate is 0.8 L / min, and the holding time is 1.2 hours to strengthen the interface chemical bonding. The pressure in the furnace is maintained at a slight positive pressure of 75 Pa, and the furnace is naturally cooled to room temperature.

[0029] Composite surface treatment: First, immerse the sintered shielding layer in a 12% sulfuric acid solution and soak it at 30°C for 4 minutes for surface roughening, and then wash it with deionized water until it is neutral. Use an eddy current flaw detector to detect the surface roughness to ensure that it reaches Ra 2.4 μm. Then perform nickel-cobalt alloy electrodeposition, the electrolyte contains nickel sulfate 225 g / L and cobalt sulfate 40 g / L, the current density is 2 A / dm², the temperature is 45°C, the pH value is 3.5, mechanical stirring is used at a rate of 300-500 r / min. The electrolyte composition is detected every 30 minutes during deposition and the consumed metal ions are supplemented. The deposition thickness is 0.035 mm. Finally, immerse it in a 0.8% silane solution at 25°C for 5 minutes, dry it at 80°C to form a sealing layer, and control the film thickness to be 2 μm.

[0030] Shielding effectiveness optimization: Perform magnetron sputtering on the surface of the shielding structure after composite surface treatment, the target material is a copper-graphene composite target with a graphene content of 8%. The sputtering power is 250 W, pure argon gas with a purity of 99.99% is introduced, the working pressure is 0.8 Pa, the sputtering time is 7 minutes, and a copper-graphene composite layer with a thickness of 0.8 μm is formed. Example

[0031] Functional slurry preparation: Take the foamed copper powder 70%, nano-silver powder 8%, graphene 2%, carbon nanotubes 3%, lanthanide oxide 0.5%, titanate coupling agent 1.5%, and epoxy resin 5% by weight percentage. The foamed copper powder has a particle size of 50 μm, and is anodized in a 3% oxalic acid solution for 5 minutes to form a CuO nano array on the surface. The nano-silver powder has a particle size of 20 nm. The carbon nanotubes have an aspect ratio of 50, and the tube wall is treated with carboxylation. Add the raw materials to a planetary ball mill, add anhydrous ethanol, and the solid-liquid ratio is 1:1.5, and grind for 30 minutes. During the process, the titanate coupling agent hydrolyzes and forms Ti-O-Ag bonds with the surface of the powder to obtain the functional slurry.

[0032] Substrate gradient pretreatment: The communication equipment aluminum alloy shell was first subjected to sandblasting treatment, 80 mesh alumina abrasive was selected, the sandblasting pressure was 0.3 MPa, and the surface roughness after treatment reached Ra 3.2 μm. The residual abrasive was removed by blowing compressed air for 5 minutes, and then plasma etching was performed for 3 minutes. The etching was carried out by introducing argon and oxygen mixed gas with a volume ratio of 3:1, the power was 100 W, and the distance between the electrode and the substrate was kept at 50 mm. Subsequently, it was immersed in a 5% γ-glycidoxypropyltrimethoxysilane solution, the solution was a mixed solvent of deionized water and ethanol with a volume ratio of 1:9, and was ultrasonically treated for 10 minutes before use to ensure complete dissolution. After soaking for 10 minutes, it was taken out and dried in an 80°C oven for 30 minutes, and a Si-O bond connecting layer was formed on the surface.

[0033] Layered coating forming: high-pressure airless spraying was used for layered coating, the nozzle diameter was 0.8 mm, and the 90-degree vertical distance to the substrate surface was kept. The bottom layer was coated with a functional slurry containing 80% foamed copper powder, the thickness was 0.05 mm, and the spraying pressure was 0.4 MPa. The middle layer was coated with a functional slurry containing 5% nano silver powder, the thickness was 0.05 mm, and the spraying pressure was 0.3 MPa. The top layer was coated with a functional slurry containing 3% graphene, the thickness was 0.05 mm, and the spraying pressure was 0.2 MPa. The nozzle was 150 mm away from the substrate during each layer coating, and the moving speed was 50 mm / s. After coating, the infrared lamp with a wavelength of 2-5 μm was used for pre-baking at 60°C, 70°C and 80°C respectively for 10 minutes, and the infrared lamp irradiation distance was 300-500 mm. A laser thickness gauge was used to detect the thickness uniformity, and the deviation was controlled within ±5%.

[0034] Stepwise sintering: the coated substrate was placed in a sintering furnace with a nitrogen atmosphere, and nitrogen gas with a purity of 99.999% was introduced, and the dew point was-45°C. In the first stage, the temperature was raised to 120°C at a rate of 3°C / min, the nitrogen flow was 1.2 L / min, and the temperature was kept for 1 hour to completely volatilize the solvent. In the second stage, the temperature was raised to 200°C at a rate of 5°C / min, the nitrogen flow was 1.0 L / min, and the temperature was kept for 2 hours to promote the curing of the epoxy resin. In the third stage, the temperature was raised to 300°C at a rate of 2°C / min, the nitrogen flow was 0.8 L / min, and the temperature was kept for 1 hour to strengthen the interface chemical bonding. The pressure in the furnace was maintained at a slight positive pressure of 50 Pa, and the temperature was naturally cooled to room temperature.

[0035] Composite surface treatment: the sintered shielding layer is first immersed in a 10% sulfuric acid solution, soaked at 30°C for 3 minutes for surface roughening, and then washed with deionized water until neutral. The surface roughness is detected by an eddy current flaw detector to ensure that Ra1.6μm is reached. Then nickel-cobalt alloy electrodeposition is carried out, the electrolyte contains nickel sulfate 200g / L, cobalt sulfate 30g / L, current density 1A / dm2, temperature 40°C, pH value 3, mechanical stirring is used at a rate of 300-500r / min. The electrolyte composition is detected every 30 minutes during deposition and the consumed metal ions are supplemented, the deposition thickness is 0.02mm. Finally, it is immersed in a 0.5% silane solution, soaked at 25°C for 5 minutes, dried at 80°C to form a sealing layer, and the film thickness is controlled at 1μm.

[0036] Shielding effectiveness optimization: after the composite surface treatment, the surface of the shielding structure is subjected to magnetron sputtering, the target material is a copper-graphene composite target with a graphene content of 8%. The sputtering power is 200W, pure argon gas with a purity of 99.99% is introduced, the working pressure is 0.5Pa, the sputtering time is 5 minutes, and a copper-graphene composite layer with a thickness of 0.5μm is formed. Example

[0037] Functional slurry preparation: foam copper powder 80%, nano-silver powder 5%, graphene 4%, carbon nanotubes 1%, lanthanide oxide 1%, titanate coupling agent 0.5%, and epoxy resin 8.5% are weighed according to the percentage by weight. The particle size of the foam copper powder is 100μm, which is anodized in a 5% oxalic acid solution for 8 minutes to form a CuO nano array on the surface. The particle size of the nano-silver powder is 50nm. The carbon nanotubes have a length-diameter ratio of 100 and the tube wall is treated with carboxylation. The raw materials are added to a planetary ball mill, anhydrous ethanol is added, the solid-liquid ratio is 1:1.5, and grinding is carried out for 60 minutes. During the process, the titanate coupling agent hydrolyzes and forms Ti-O-Ag bonds with the surface of the powder to obtain the functional slurry.

[0038] Substrate gradient pretreatment: the communication equipment aluminum alloy shell is first subjected to sandblasting treatment, 120 mesh aluminum oxide abrasive is selected, the sandblasting pressure is 0.5MPa, and the surface roughness after treatment reaches Ra6.3μm. The residual abrasive is removed by blowing with compressed air for 5 minutes, and then plasma etching is carried out for 5 minutes. Argon and oxygen mixed gas is introduced, the volume ratio is 3:1, the power is 150W, and the distance between the electrode and the substrate is kept at 80mm. Then it is immersed in an 8% γ-glycidoxypropyltrimethoxysilane solution, the solution is a deionized water and ethanol mixed solvent with a volume ratio of 1:9, and it is ultrasonically treated for 10 minutes before use to ensure complete dissolution. After soaking for 15 minutes, it is taken out and dried in a 100°C oven for 30 minutes to form a Si-O bond connecting layer on the surface.

[0039] Layered coating forming: Layered coating was performed by high pressure airless spraying. The nozzle diameter was 1.2 mm, and the spraying pressure was 0.4 MPa. The nozzle was kept 90 degrees perpendicular to the substrate surface. The functional slurry containing 80% foam copper powder was coated as the bottom layer with a thickness of 0.1 mm. The functional slurry containing 5% nano silver powder was coated as the middle layer with a thickness of 0.1 mm. The functional slurry containing 3% graphene was coated as the top layer with a thickness of 0.1 mm. The nozzle was 200 mm away from the substrate during coating, and the moving speed was 100 mm / s. After coating, the samples were pre-baked at 60°C, 70°C, and 80°C, respectively, for 10 minutes under an infrared lamp with a wavelength of 2-5 μm. The infrared lamp irradiation distance was 300-500 mm. A laser thickness gauge was used to detect the thickness uniformity, and the deviation was controlled within ±4%.

[0040] Stepwise sintering: The coated substrate was placed in a sintering furnace with a nitrogen atmosphere. The purity of the nitrogen was 99.999%, and the dew point was -45°C. In the first stage, the temperature was raised to 150°C at a rate of 3°C / min, and the nitrogen flow rate was 1.2 L / min. The sample was kept at this temperature for 2 hours to completely evaporate the solvent. In the second stage, the temperature was raised to 250°C at a rate of 5°C / min, and the nitrogen flow rate was 1.0 L / min. The sample was kept at this temperature for 3 hours to promote the curing of the epoxy resin. In the third stage, the temperature was raised to 350°C at a rate of 2°C / min, and the nitrogen flow rate was 0.8 L / min. The sample was kept at this temperature for 1.5 hours to strengthen the interface chemical bonding. The pressure in the furnace was maintained at a slight positive pressure of 100 Pa, and the sample was naturally cooled to room temperature.

[0041] Composite surface treatment: The sintered shielding layer was first immersed in a 15% sulfuric acid solution at 30°C for 5 minutes for surface roughening. Then, the sample was washed with deionized water until it was neutral. An eddy current flaw detector was used to detect the surface roughness to ensure that it reached Ra3.2 μm. Then, nickel-cobalt alloy electrodeposition was performed. The electrolyte contained 250 g / L of nickel sulfate and 50 g / L of cobalt sulfate. The current density was 3 A / dm², the temperature was 50°C, the pH value was 4, and mechanical stirring was used at a rate of 300-500 r / min. The electrolyte composition was checked every 30 minutes during the deposition process, and the consumed metal ions were replenished. The deposition thickness was 0.05 mm. Finally, the sample was immersed in a 1% silane solution at 25°C for 5 minutes and then dried at 80°C to form a sealing layer. The film thickness was controlled at 3 μm.

[0042] Shielding effectiveness optimization: A copper-graphene composite target with a graphene content of 8% was used for magnetron sputtering on the surface of the composite surface treated shielding structure. The sputtering power was 300 W, the purity of the argon gas was 99.99%, the working pressure was 1 Pa, and the sputtering time was 10 minutes. A copper-graphene composite layer with a thickness of 1 μm was formed.

[0043] Comparative example The slurry is prepared by using traditional process: taking 85% of foamed copper powder, 10% of nano silver powder and 5% of epoxy resin by weight percentage, adding anhydrous ethanol and grinding for 45 minutes. The aluminum alloy shell of communication equipment is only sandblasted with roughness Ra4.8 μm, directly sprayed with 0.22 mm slurry in single layer, sprayed at 0.3 MPa, pre-dried at 80℃ for 30 minutes. Sintered at 250℃ for 3 hours in nitrogen atmosphere, without stepwise temperature control. The surface is only treated by nickel plating with thickness of 0.035 mm, without silane blocking and magnetron sputtering steps. The communication equipment uses an integrated shield, and the edge is sealed with conductive glue.

[0044] The shielding performance of the examples and the comparative examples is compared as follows: Table 1

[0045] The sludge carbon application performance and process economy indicators of the examples and the comparative examples are compared as follows: Table 2

[0046] The shielding performance attenuation of the examples and the comparative examples at different frequencies is compared as follows: Table 3

[0047] It can be seen from the data of the three tables that the conductive foamed copper electromagnetic shielding structure prepared by the preparation process has significantly better core performance than the traditional process product. In terms of shielding performance, the shielding performance of the examples reaches 90-100 dB in the 100 MHz-18 GHz frequency band, and reaches 85-95 dB in the 18-40 GHz high frequency band, the surface resistance is as low as 0.01-0.03 Ω / sq, and the performance attenuation is only 1-3 dB after 180° bending 50 times, which is much better than the shielding performance, surface resistance and bending attenuation of the comparative examples; in terms of structure and environmental performance, the bonding strength and thermal conductivity of the examples are higher, the salt spray resistance time is as long as 600-800 hours, and the performance retention rate is more than 95% after 1000 hours in 85℃ / 85% humidity environment, and the corresponding indicators of the comparative examples are obviously different; in terms of frequency adaptability, the attenuation rate of the examples is only 1.0%-3.2% in the whole frequency band of 1-40 GHz, and the comparative examples is 5.8%-12.3%, especially in the high frequency band. In addition, the performance of the examples can be precisely controlled by adjusting the process parameters, which further proves the superiority and practicality of the preparation process.

[0048] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A process for the preparation of an electromagnetic shielding structure in a communication device using electrically conductive copper foam, characterized in that, Comprise the following steps: S1, functional slurry preparation: weigh the raw materials according to the percentage by weight, wherein the raw materials include: foamed copper powder 70-80%, nano-silver powder 5-8%, graphene 2-4%, carbon nanotubes 1-3%, lanthanide oxide 0.5-1%, titanate coupling agent 0.5-1.5%, epoxy resin 3-6%; Put the raw materials into a planetary ball mill, add anhydrous ethanol as a dispersion medium for grinding; Prepare a uniformly dispersed functional slurry; S2, substrate gradient pretreatment: the communication equipment shell is made of aluminum alloy material, first sand blasting treatment, then plasma etching, argon and oxygen mixed gas is introduced, then immersed in 5-8% silane solution, silane is γ-glycidyl ether propyl trimethoxysilane, soaked for 10-15 minutes, then taken out and dried, a Si-O bond connection layer is formed on the surface; S3, layered coating forming: high pressure airless spraying is used for layered coating; The bottom layer is coated with a functional slurry containing 80% foamed copper powder; The middle layer is coated with a functional slurry containing 5% nano-silver powder; The top layer is coated with a functional slurry containing 3% graphene; After coating, infrared pre-drying is carried out at 60℃, 70℃ and 80℃ respectively for 10 minutes; S4, step sintering: put the coated substrate into the atmosphere sintering furnace, introduce nitrogen; Heat to 120-150℃, keep for 1-2 hours; Then heat to 200-250℃, keep for 2-3 hours to promote the curing of the epoxy resin; Finally, heat to 300-350℃, keep for 1-1.5 hours to strengthen the interface chemical bonding, and naturally cool to room temperature; S5, composite surface treatment: first immerse the sintered shielding layer in 10-15% sulfuric acid solution, soak at 30℃ for surface roughening, and then wash with deionized water until neutral; Then nickel-cobalt alloy electrodeposition is carried out; Finally, immerse in 0.5-1% silane solution, soak at 25℃ for 5 minutes, and dry at 80℃ to form a closed layer, thereby obtaining an electromagnetic shielding structure.

2. The process for the preparation of electromagnetic shielding structure in communication equipment using electrically conductive copper foam as claimed in claim 1 wherein, Also includes surface modification treatment of foamed copper powder in S1 before use, immerse the foamed copper powder in 3-5% oxalic acid solution, anodize for 5-8 minutes using 10-15V direct current voltage, form a uniform distribution of CuO nano array on the surface, the particle size of the treated foamed copper powder is controlled within 50-100μm, the particle size of the nano-silver powder is 20-50nm, and the length-diameter ratio of the carbon nanotubes is 50-100.

3. The process for preparing electromagnetic shielding structure in communication equipment using electrically conductive copper foam as claimed in claim 1 wherein, Also includes blowing off the surface residual abrasive with compressed air for 5 minutes after sand blasting in S2, the distance between the electrode and the substrate is kept at 50-80mm during plasma etching, and the silane solution is prepared by mixing deionized water and ethanol with a volume ratio of 1:9, which is ultrasonically treated for 10 minutes before use to ensure complete dissolution.

4. The process for preparing electromagnetic shielding structure in communication equipment using electrically conductive copper foam according to claim 1, wherein, The nozzle diameter of the high pressure airless spraying equipment in S3 is 0.8-1.2mm, the spraying angle is kept at 90 degrees perpendicular to the substrate surface, the thickness uniformity is detected after each layer of coating is completed using a laser thickness gauge, the deviation is controlled within ±5%, and the infrared drying uses infrared lamps with a wavelength of 2-5μm, the irradiation distance is 300-500mm.

5. The process for preparing electromagnetic shielding structure in communication equipment using electrically conductive copper foam according to claim 1, wherein The three temperature stages of the step sintering in S4 correspond to three key processes of solvent evaporation, resin curing and interface reaction respectively, and the nitrogen flow is adjusted in different stages, 1.2L / min in 120-150℃, 1.0L / min in 200-250℃, and 0.8L / min in 300-350℃, and the pressure in the furnace is maintained at 50-100Pa of micro-positive pressure.

6. The process for preparing electromagnetic shielding structure in communication equipment using electrically conductive copper foam as claimed in claim 1 wherein, In S5, the surface roughness is detected by eddy current flaw detector after the roughening treatment of sulfuric acid solution, to ensure that it reaches Ra1.6-3.2μm, and mechanical stirring with stirring speed of 300-500r / min is used during nickel-cobalt alloy electrodeposition, and the electrolyte composition is detected every 30 minutes during the deposition process and the consumed metal ions are supplemented, and the thickness of the film layer formed after silane sealing treatment is controlled at 1-3μm.

7. The process for preparing electromagnetic shielding structure in communication equipment using electrically conductive copper foam as claimed in claim 1 wherein, It also includes S6. Shielding effectiveness optimization: magnetron sputtering is carried out on the surface of the shielding structure after composite surface treatment, the target material is copper-graphene composite target, the content of graphene is 5-8%, the sputtering power is 200-300W, the purity of argon gas is 99.99%, the working pressure is 0.5-1Pa, the sputtering time is 5-10 minutes, and a copper-graphene composite layer with a thickness of 0.5-1μm is formed.

8. The process for preparing electromagnetic shielding structure in communication equipment using electrically conductive copper foam as claimed in claim 1 wherein, The electromagnetic shielding effectiveness of the shielding structure reaches 90-100dB in the frequency band of 100MHz-18GHz, and reaches 85-95dB in the high frequency band of 18-40GHz, and the surface resistance is 0.01-0.03Ω / sq.

9. The process for preparing electromagnetic shielding structure in communication equipment using electrically conductive copper foam according to claim 1, wherein, The bonding strength between the shielding structure and the substrate is measured by tensile test as 18-22MPa, the thermal conductivity is 200-230W / (m·K), the salt spray test is carried out according to GB / T 10125, and there is no rust after 600-800 hours, and after being placed in 85℃ temperature and 85% relative humidity environment for 1000 hours, the performance index retention rate is more than 95%.

10. A communication device using the electromagnetic shielding structure produced by the production process according to any one of claims 1 to 9, characterized in that, It includes an aluminum alloy shell, a signal mainboard and a modular shielding assembly, the shielding assembly adopts the conductive foam copper electromagnetic shielding structure, and is divided into 3-5 independent shielding units according to the radio frequency module, power module and signal processing module on the mainboard, each unit edge is provided with a conductive rubber boss with a semicircular cross section, the boss diameter is 0.8-1.2mm, and the boss forms a mortise and tenon connection structure with the groove on the shell, the overall thickness of the shielding assembly is 0.3-0.5mm, and the weight is reduced by 40-50% compared with the traditional metal shielding cover.

Images