Hierarchical electromagnetic shielding film, preparation method thereof and flexible circuit board prepared from hierarchical electromagnetic shielding film

Abstract

The invention discloses a hierarchical electromagnetic shielding film, a preparation method thereof and a flexible circuit board prepared from the hierarchical electromagnetic shielding film, and the preparation method comprises the following steps: coating a first release film with insulating slurry to form an insulating layer, and obtaining a first intermediate film with the insulating layer; coating a binder on the second release film to form a base layer, depositing a shielding material on the base layer to form a shielding layer, coating a binder on the shielding layer to form a top sealing layer, and finally obtaining a second intermediate film with a base layer-shielding layer-top sealing layer; coating conductive slurry on the third release film to form a conductive layer and obtain a third intermediate film with the conductive layer; and enabling the insulating layer of the first intermediate film to be in contact with the top sealing layer of the second intermediate film for first-time lamination, then stripping the second release film, and enabling the insulating layer of the first intermediate film to be in contact with the conductive layer on the third intermediate film for second-time lamination. According to the invention, the overall performance problem caused by the structural defect of a certain layer of a traditional layered shielding material can be avoided, and the overall product performance and yield are ensured.

Description

Technical Field

[0001] This invention relates to the field of shielding materials technology, and in particular to a layered electromagnetic shielding film, its preparation method, and the flexible circuit board prepared therefrom. Background Technology

[0002] The encapsulated hybrid substrate is generally a multilayer substrate composed of organic substrates, ceramics, silicon interlayers, etc., used for high-density packaging; it can integrate shielding function directly inside or on the surface of the substrate through buried shielding layer or surface-mount shielding film; the shielding film is the key material or structure for achieving electromagnetic compatibility.

[0003] Layered electromagnetic shielding film is a thin film material that achieves efficient electromagnetic shielding through the precise composite of multiple layers of materials with different functions. Generally, layered electromagnetic shielding film includes a black insulating resin layer, a metal plating layer, and a conductive layer. The preparation steps are as follows: black insulating resin is coated using a PET release film coating process, a metal plating layer is applied using a vacuum evaporation process, and a conductive layer is coated again to prepare the finished product; finally, a hot-pressing process is used to bond it to a circuit board.

[0004] For example, existing products are prepared using a 50μm PET release film, coated with a 6μm insulating layer, vapor-deposited with a 230nm aluminum metal layer, and an 8μm conductive coating layer. In the existing technology, when the insulating layer is prepared and the vapor deposition process begins, the combined thickness of the 50μm release film and the 6μm insulating layer causes a series of problems, as follows: (1) In terms of cooling, the cooling roller of the vapor deposition machine cannot achieve complete heat conduction cooling. In addition, the insulation layer itself has poor heat resistance, which directly leads to various stripe burns during the vacuum deposition of metal particles. (2) In terms of the quality of the metal layer, not only is the density of the metal ions poor, but also the thickness of the insulating layer is uneven, resulting in poor uniformity of the thickness of the vacuum-deposited metal particles, which further causes the sheet resistance of the metal layer to be unstable, greatly increasing the difficulty of process control. (3) Due to the above problems, the yield rate of vacuum evaporation is extremely low, which makes it impossible for the product to enter the next conductive layer coating process, ultimately resulting in a low product output rate.

[0005] Therefore, there is an urgent need to improve the manufacturing process of layered electromagnetic shielding films in order to avoid the aforementioned problems caused by the layered structure of traditional processes. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, this invention provides a layered electromagnetic shielding film, its preparation method, and a flexible circuit board made therefrom. This invention avoids the overall performance problems caused by structural defects in a single layer of traditional layered shielding materials, ensuring overall product performance and yield.

[0007] The technical solution of the present invention is as follows: The first objective of this invention is to provide a method for preparing a layered electromagnetic shielding film, comprising the following steps: An insulating paste is coated onto the first release film to form an insulating layer, thus obtaining a first intermediate film with an insulating layer. An adhesive is applied to the second release film to form a base layer. A shielding material is deposited on the base layer to form a shielding layer. An adhesive is applied to the shielding layer to form a top sealing layer, thus obtaining a second intermediate film with a base layer-shielding layer-top sealing layer (i.e., a shielding structure). A conductive paste is coated onto the third release film to form a conductive layer, thus obtaining a third intermediate film with a conductive layer. The insulating layer of the first intermediate film is brought into contact with the top sealing layer of the second intermediate film for the first bonding. Then the second release film is peeled off, and the second release film is brought into contact with the conductive layer on the third intermediate film for the second bonding.

[0008] In one embodiment of the present invention, both the first and second bonding are performed using a hot press roller press, with the temperature of the hot press roller press controlled at 110℃-130℃, the pressure at 0.4MPa-0.6MPa, and the pressing time at 2min-5min.

[0009] In one embodiment of the present invention, the insulating slurry comprises, by weight parts: 30-50 parts of a first polymer binder, 5-15 parts of inorganic material, 0.5-3 parts of dispersant, 5-30 parts of toughening agent, 5-10 parts of plasticizer, 0.5-5 parts of silane coupling agent, and 10-15 parts of curing agent.

[0010] In one embodiment of the present invention, the first polymer binder is selected from at least one of acrylic acid, acrylate, polyurethane, epoxy resin, and phenolic resin; The inorganic material is selected from at least one of amorphous glass, silicon dioxide, aluminum oxide, talc, mica powder, and bentonite; The dispersant is selected from at least one of cationic dispersants and nonionic dispersants; The toughening agent is selected from at least one of elastomer toughening agents, toughness toughening agents, and mineral toughening agents; The plasticizer is selected from at least one of phthalates, aliphatic diesters, phospholipids, epoxy compounds, and polyester plasticizers; The curing agent is selected from at least one of aliphatic curing agents, aromatic amine curing agents, acid anhydride curing agents, latent curing agents, and imidazole curing agents.

[0011] In one embodiment of the present invention, after the insulating paste is coated on the first release film, it is first baked at 70°C-90°C for 1-3 hours, and then baked at 140°C-160°C for another 1-3 hours.

[0012] In one embodiment of the present invention, the thickness of the insulating layer is 4μm-8μm.

[0013] In one embodiment of the present invention, a shielding material is deposited by magnetron sputtering or vacuum deposition; the shielding material is selected from at least one of gold, silver, copper, aluminum, nickel, graphite, silver-coated copper, and nickel-coated carbon.

[0014] In one embodiment of the present invention, the thickness of the shielding layer is 0.2μm-2μm.

[0015] In one embodiment of the present invention, the adhesive used for the underlayer and top seal layer is selected from at least one of acrylic acid, acrylate, polyurethane, epoxy resin, phenolic resin, phenolic-chloroprene adhesive, phenolic-nitrile adhesive, epoxy resin-nitrile adhesive, rubber-modified acrylate adhesive, nitrile rubber adhesive, and A / RS system adhesive.

[0016] In one embodiment of the present invention, the thickness of the underlayer is 6μm-10μm; the thickness of the top layer is 0.5μm-1μm.

[0017] In one embodiment of the present invention, the conductive paste comprises, by weight parts: 20-30 parts of a second polymer binder, 40-50 parts of a conductive agent, 10-30 parts of a heat-resistant material, 0-0.5 parts of a lubricant, 0.5-5 parts of a flame retardant, and 0.1-0.5 parts of an antioxidant.

[0018] In one embodiment of the present invention, the second polymer binder is selected from at least one of acrylic acid, acrylate, polyurethane, epoxy resin, phenolic resin, phenolic-chloroprene binder, phenolic-nitrile binder, epoxy resin-nitrile binder, rubber-modified acrylate binder, nitrile rubber binder, and A / RS system binder.

[0019] In one embodiment of the present invention, the conductive agent is selected from at least one of gold, silver, copper, aluminum, nickel, graphite, carbon silver-coated copper, and nickel-coated carbon; The heat-resistant material is selected from at least one of alumina, aluminum nitride, silicon nitride, boron nitride, silicon-based ceramic powder, and aluminum; The lubricant is selected from at least one of organosilicon, diester, polyester alcohol, phosphate ester, and polyethylene glycol; The flame retardant is selected from at least one of tetrabromophthalic anhydride, tetrabromobisphenol A, aluminum diethylphosphite, aluminum hydroxide, triphenyl phosphate, and triphenyl polyphosphate; The antioxidant is selected from at least one of phenolic antioxidants, amine antioxidants, phosphite antioxidants, and metal complex antioxidants.

[0020] In one embodiment of the present invention, after the conductive paste is coated on the third release film, it is first baked at 70℃-90℃ for 0.5h-2h, and then baked at 140℃-160℃ for another 0.5h-2h.

[0021] In one embodiment of the present invention, the thickness of the conductive layer is 6μm-12μm.

[0022] In one embodiment of the present invention, the thicknesses of the first release film, the second release film, and the third release film are each independently 40μm-60μm.

[0023] The second objective of this invention is to provide a layered electromagnetic shielding film prepared by the above-described preparation method.

[0024] In one embodiment of the present invention, the layered electromagnetic shielding film consists of, from bottom to top, a first release film, an insulating layer, a top sealing layer, a shielding layer, a base layer, a conductive layer, and a third release film; the layers are connected by bonding.

[0025] A third objective of this invention is to provide a flexible circuit board containing the aforementioned layered electromagnetic shielding film.

[0026] This invention can effectively avoid the overall performance problems caused by structural defects in a certain layer of traditional layered shielding materials, ensuring overall product performance and yield, and facilitating mass production.

[0027] The improved performance and yield of layered electromagnetic shielding films are beneficial for enhancing the performance and yield of flexible circuit boards.

[0028] The beneficial technical effects of this invention are as follows: The preparation method provided by this invention allows the insulating layer, shielding layer, and conductive layer to be prepared and used independently, and the yield of each structure can be controlled. They are then integrated after a bonding process, avoiding the overall yield problem caused by the performance defects of a certain layer in traditional products. This ensures the overall product performance and yield, and is conducive to achieving mass production.

[0029] Specifically, the method for preparing the layered electromagnetic shielding film provided by the present invention has the following advantages: (1) The shielding layer can be prepared separately. By changing the thickness of the shielding layer and the type / amount of the shielding material, the insulation and shielding effect of the membrane material can be flexibly adjusted, and damage to the membrane material can be avoided. (2) Conductive adhesive layers can be prepared separately. By changing their thickness and material type / amount, additional properties such as product flexibility and thermal shock resistance can be customized according to customer needs. (3) The performance of the prepared product can be adjusted individually for each layer according to customer needs to improve product strength; (4) The prepared products can avoid the problems of subsequent processes being unable to be connected and difficult to mass-produce due to defects in the structure and performance of a certain layer (poor coating uniformity, low bonding force, metal layer burn, poor density, etc.), and avoid problems such as low output and low yield. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the layered electromagnetic shielding film of the present invention; In the figure, 101-first release film; 102-insulating layer; 103-top seal layer; 104-shielding layer; 105-underlay layer; 106-conductive layer; 107-third release film. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0033] To address the issues of poor product performance and low yield in existing manufacturing processes for layered electromagnetic shielding films, the inventors have improved the manufacturing process of layered electromagnetic shielding films. Each layer can be prepared and used independently, and the yield of each layer can be controlled. Through bonding, the problems caused by a single layer in traditional products are eliminated, which helps to improve the overall product performance and yield.

[0034] A layered electromagnetic shielding film, the structure of which is as follows: Figure 1 As shown, from bottom to top, the layers are: first release film 101, insulating layer 102, top sealing layer 103, shielding layer 104, base layer 105, conductive layer 106, and third release film 107; each layer is connected by bonding.

[0035] A method for preparing a layered electromagnetic shielding film includes the following steps: S1. Preparation of a first intermediate film with an insulating layer An insulating slurry is coated onto the first release film, and after film formation, a first intermediate film with an insulating layer is obtained. The specific composition of the insulating slurry is not limited, and existing insulating slurry formulations used to prepare the insulating layer in layered electromagnetic shielding films are all within the protection scope of this invention.

[0036] It should be noted that the function of the insulating layer is as follows: (1) Electrical insulation can prevent external current or signal interference from penetrating the shielding film, avoid contact with the internal metal shielding layer to cause short circuit or signal crosstalk, and ensure that the shielding layer only works against specific electromagnetic interference (EMI); (2) Optical shielding: black pigment can absorb visible light, avoid reflection of metal shielding layer, and meet the requirements of appearance concealment in certain application scenarios (such as electronic display devices); (3) Mechanical protection, as an outer structure, provides a certain degree of wear resistance and environmental resistance (such as anti-oxidation and moisture-proof), and protects the internal metal shielding layer from physical damage or chemical corrosion.

[0037] In a preferred embodiment, the insulating grout comprises, by weight parts: 30-50 parts of a first polymer binder, 5-15 parts of inorganic material, 0.5-3 parts of dispersant, 5-30 parts of toughening agent, 5-10 parts of plasticizer, 0.5-5 parts of silane coupling agent, and 10-15 parts of curing agent. Optimizing the composition of the insulating grout helps improve the insulation effect of the insulating layer.

[0038] Specifically, in the raw material composition of the insulating grout, the amount of the first polymer binder can be 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, etc.; the amount of inorganic materials can be 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, etc.; the amount of dispersant can be 0.5 parts, 1.0 parts, 2.0 parts, 3.0 parts, 4.0 parts, 5.0 parts, etc.; the amount of toughening agent can be 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, etc.; the amount of plasticizer can be 5 parts, 8 parts, 10 parts, etc.; the amount of silane coupling agent can be 0.5 parts, 1.0 parts, 2.0 parts, 3.0 parts, 4.0 parts, 5.0 parts, etc.; and the amount of curing agent can be 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, etc. In the formulation of the insulating grout, the first polymer binder is selected from at least one of acrylic acid, acrylate, polyurethane, epoxy resin, and phenolic resin, and the first polymer binder can be any one or more of the above. The inorganic material is selected from at least one of amorphous glass, silicon dioxide, alumina, talc powder, mica powder, and bentonite, and the inorganic material can be any one or more of the above.

[0039] In the formulation of the insulating grout, the dispersant is selected from at least one of cationic and nonionic dispersants. The dispersant can be a cationic dispersant, a nonionic dispersant, or a mixture of the two. Examples of cationic dispersants include alkyl trimethylammonium salts, dialkyl dimethylammonium salts, pyridine quaternary ammonium salts, and alkylamine salts; examples of nonionic dispersants include polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone.

[0040] In the formulation of the insulating grout, the toughening agent is selected from at least one of elastomer toughening agents, toughening agents, and mineral toughening agents. The toughening agent can be any one or more of these. Specifically, the elastomer toughening agent can be chlorinated polyethylene, methyl methacrylate-butadiene-styrene copolymer, acrylate copolymer, styrene-butadiene block copolymer, EVA, etc.; the toughening agent can be chloroprene rubber, etc.; and the mineral toughening agent can be carbonate, cellulose, etc.

[0041] In the formulation of the insulating grout, the plasticizer is selected from at least one of phthalate esters, aliphatic diester esters, phospholipid esters, epoxy compounds, and polyester plasticizers. The plasticizer can be any one or more of these. Specifically, phthalate esters can be dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dioctyl phthalate, diisononyl phthalate, etc.; aliphatic diester esters can be adipate esters, azelaic esters, sebacic esters, etc.; phospholipid esters can be triphenyl phosphate, tricresyl phosphate, diphenyl octyl phosphate, etc.; epoxy compounds can be epoxidized oils, epoxy tetrahydrophthalate, etc.; and polyester plasticizers can be aromatic hyperbranched polyesters, etc.

[0042] In the formulation of the insulating grout, the curing agent is selected from at least one of aliphatic curing agents (including aliphatic amine curing agents), aromatic amine curing agents, acid anhydride curing agents, latent curing agents, and imidazole curing agents. The curing agent can be any one or more of these. Specifically, aliphatic curing agents can be ethylenediamine, diethylenetriamine, triethylenetetramine, hexamethylenediamine, etc.; aromatic amine curing agents can be diaminodiphenylmethane, diaminodiphenyl sulfone, m-phenylenediamine, etc.; acid anhydride curing agents can be phthalic anhydride, hexahydrophthalic anhydride, etc.; latent curing agents can be dicyandiamide, etc.; and imidazole curing agents can be 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, etc.

[0043] In actual operation, the insulating slurry is prepared and mixed evenly according to its formula. Then, the resulting insulating slurry is applied to the first release film and baked at 70℃-90℃ for 1-3 hours to achieve preliminary curing. After that, it is baked at 140℃-160℃ for 1-3 hours to achieve complete curing.

[0044] Specifically, during the initial curing stage, the baking temperature can be 70℃, 75℃, 80℃, 85℃, 90℃, etc., and the baking time can be 1h, 2h, 3h, etc.; during the complete curing stage, the baking temperature can be 140℃, 145℃, 150℃, 155℃, 160℃, etc., and the baking time can be 1h, 2h, 3h, etc.

[0045] By adjusting the coating thickness of the insulating slurry, the thickness of the resulting insulating layer can be 4μm-8μm, such as 4μm, 5μm, 6μm, 7μm, 8μm, etc. The thickness of the insulating layer within the above range is beneficial to improving the insulation effect.

[0046] The thickness of the first release film used is 40μm-60μm, such as 40μm, 45μm, 50μm, 55μm, 60μm, etc.

[0047] S2. Preparation of a second intermediate membrane with a shielding structure A resin adhesive or rubber adhesive is coated onto the second release film as a base layer. A shielding material is deposited on the base layer to form a shielding layer. Finally, a resin adhesive or rubber adhesive is coated onto the shielding layer as a top sealing layer. The resulting shielding structure consists of a base layer, a shielding layer, and a top sealing layer, forming a second intermediate film with a shielding structure. This base layer-shielding layer-top sealing layer shielding structure can protect the integrity of the metal layer while providing shielding performance and mechanical properties as required.

[0048] In some embodiments, the adhesives used for the underlayer and top seal layer are selected from at least one of acrylic acid, acrylate, polyurethane, epoxy resin, phenolic resin, phenolic-chloroprene adhesive, phenolic-nitrile adhesive, epoxy resin-nitrile adhesive, rubber-modified acrylate adhesive, nitrile rubber adhesive, and A / RS system adhesives. The adhesives used to prepare the underlayer and top seal layer can be any one or more of the above, and all of the above adhesives are commercially available raw materials.

[0049] Specifically, phenolic-chloroprene adhesives are made by blending and modifying phenolic resin and chloroprene rubber; epoxy resin-nitrile rubber adhesives are made by physically blending and chemically modifying (such as pre-reaction) epoxy resin and nitrile rubber; rubber-modified acrylate adhesives refer to adhesives made by introducing synthetic rubber (such as chloroprene rubber, nitrile rubber, ABS resin, etc.) as a toughening component into acrylate monomers or resins; nitrile rubber adhesives are made with nitrile rubber (NBR) as the main material, combined with various additives. A / RS system adhesives are an abbreviation for Adhesive / Resin System.

[0050] In some embodiments, the shielding material is deposited using magnetron sputtering or vacuum deposition. Existing magnetron sputtering or vacuum deposition equipment can be used, and the specific deposition parameters are not limited. The shielding material is selected from at least one of gold, silver, copper, aluminum, nickel, graphite, silver-coated copper, and nickel-coated carbon. The shielding material can be any one or more of these materials, all of which can form a dense shielding layer. The shielding layer can be formed using vapor deposition, but is not limited to this method.

[0051] Furthermore, a doctor blade or automatic coating equipment can be used to coat the underlayer and top seal layer. The thickness of the underlayer is 6μm-10μm, such as 6μm, 8μm, 10μm, etc.; the thickness of the shielding layer is 0.2μm-2μm, such as 0.2μm, 0.5μm, 1.0μm, 1.5μm, 2.0μm, etc.; and the thickness of the top seal layer is 0.5μm-1μm, such as 0.5μm, 0.8μm, 1.0μm, etc. The thickness of the second release film used is 40μm-60μm, such as 40μm, 45μm, 50μm, 55μm, 60μm, etc.

[0052] S3. Preparation of a third intermediate film with a conductive layer A conductive paste is coated onto the third release film, and after curing, a third intermediate film with a conductive layer is obtained. The order of steps S1-S3 is not limited; that is, the preparation order of the first, second, and third intermediate films is not limited. In the final product structure, the conductive layer achieves charge dissipation through low-impedance connections, enhancing the overall shielding effectiveness (especially against low-frequency interference).

[0053] In some embodiments, the conductive paste comprises, by weight parts: 20-30 parts of a second polymer binder, 40-50 parts of a conductive agent, 10-30 parts of a heat-resistant material, 0-0.5 parts of a lubricant, 0.5-5 parts of a flame retardant, and 0.1-0.5 parts of an antioxidant. The conductivity of the conductive layer is improved by adjusting the amount of each component.

[0054] Specifically, in the formulation of the conductive paste, the amount of the second polymer binder can be 20 parts, 23 parts, 25 parts, 28 parts, 30 parts, etc.; the amount of the conductive agent can be 40 parts, 43 parts, 45 parts, 48 ​​parts, 50 parts, etc.; the amount of the heat-resistant material can be 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, etc.; the amount of the lubricant can be 0.0 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, etc.; the amount of the flame retardant can be 0.5 parts, 1.0 parts, 2.0 parts, 3.0 parts, 4.0 parts, 5.0 parts, etc.; and the amount of the antioxidant can be 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, etc.

[0055] In the formulation of the conductive paste, the second polymer binder is selected from at least one of acrylic acid, acrylate, polyurethane, epoxy resin, phenolic resin, phenolic-chloroprene binder, phenolic-nitrile binder, epoxy resin-nitrile binder, rubber-modified acrylate binder, nitrile rubber binder, and A / RS system binder. The second polymer binder can be any one or more of the above. All of the above binders are commercially available materials; for a detailed explanation, refer to step S2 of the instruction manual. The binder material can be at least one of oil-based and water-based binders.

[0056] In the formulation of the conductive paste, the conductive agent is selected from at least one of gold, silver, copper, aluminum, nickel, graphite, carbon-silver coated copper, and nickel-coated carbon. The conductive agent can be any one or more of the above. The heat-resistant material is selected from at least one of alumina, aluminum nitride, silicon nitride, boron nitride, silicon-based ceramic powder (containing elements such as silicon, aluminum, and titanium), and aluminum. The heat-resistant material can be any one or more of the above.

[0057] In the formulation of conductive paste, the lubricant is selected from at least one of organosilicon, diester, polyester alcohol, phosphate ester, and polyethylene glycol. The lubricant can be any one or more of the above. Specifically, organosilicon lubricants can be polydimethylsiloxane, etc.; diester lubricants can be adipate diester, polyethylene glycol diester, maleate ester and its derivatives, etc.; polyester alcohol lubricants can be polypropylene glycol, polytetrahydrofuran, etc.

[0058] In the formulation of the conductive paste, the flame retardant is selected from at least one of tetrabromophthalic anhydride, tetrabromobisphenol A, diethylaluminum hypophosphite, aluminum hydroxide, triphenyl phosphate, and polyphenyl phosphate. The flame retardant can be any one or more of the above. The antioxidant is selected from at least one of phenolic antioxidants (such as antioxidant 1010, antioxidant 1076, etc.), amine antioxidants (such as antioxidant 1135, antioxidant 5057, etc.), phosphite antioxidants (such as antioxidant 168, antioxidant 618, etc.), and metal complex antioxidants (such as citric acid, etc.). The antioxidant can be any one or more of the above.

[0059] In actual operation, the conductive paste is coated onto the third release film and baked at 70℃-90℃ for 0.5h-2h to achieve preliminary curing. Then, it is baked at 140℃-160℃ for another 0.5h-2h to achieve complete curing. Specifically, during preliminary curing, the baking temperature can be 70℃, 75℃, 80℃, 85℃, 90℃, etc., and the baking time can be 0.5h, 1.0h, 2.0h, etc.; during the complete curing stage, the baking temperature can be 140℃, 145℃, 150℃, 155℃, 160℃, etc., and the baking time can be 0.5h, 1.0h, 2.0h, etc.

[0060] In some embodiments, the thickness of the conductive layer is controlled to be 6μm-12μm by controlling the coating thickness of the conductive paste, such as 6μm, 8μm, 10μm, 12μm, etc. The thickness of the third release film used is 40μm-60μm, such as 40μm, 45μm, 50μm, 55μm, 60μm, etc.

[0061] S4, Integration The first, second, and third intermediate films can be laminated simultaneously or separately, with the first and third release films exposed on the outer side of the layered structure for protection, resulting in... Figure 1 The structure shown.

[0062] The preparation method provided in this invention allows each layer of the structure to be prepared individually and can be adjusted according to market demand. In particular, the shielding layer can be individually adjusted to protect the metal shielding layer according to customer needs, and additional mechanical and flexibility properties required by the customer can be added.

[0063] In some embodiments, the insulating layer on the first intermediate film is first bonded to the side of the second intermediate film away from the second release film, then the second release film is peeled off, and then a second bonding is performed with the conductive layer on the third intermediate film. This two-step bonding process helps to obtain products with higher appearance uniformity and further improves the overall performance of the product.

[0064] In some embodiments, the insulating layer of the first intermediate film is brought into contact with the top sealing layer of the second intermediate film for a first bonding, then the second release film is peeled off, and then brought into contact with the conductive layer on the third intermediate film for a second bonding.

[0065] In some embodiments, both the first and second bonding processes are performed using a hot press roller. The temperature of the hot press roller is controlled at 110℃-130℃, such as 110℃, 120℃, 130℃, etc.; the pressure applied by the press roller is 0.4MPa-0.6MPa, such as 0.4MPa, 0.5MPa, 0.6MPa, etc.; and the pressing time is 2min-5min, such as 2min, 3min, 4min, 5min, etc.

[0066] Example 1 A method for preparing a layered electromagnetic shielding film, comprising the following steps: (1) Preparation of a first intermediate film with an insulating layer Material weighing: Accurately weigh the following according to the formula ratio: 45 parts of first polymer binder (epoxy resin), 10 parts of alumina, 3 parts of dispersant (polyethylene glycol), 15 parts of toughening agent (styrene-butadiene block copolymer), 9 parts of plasticizer (dioctyl phthalate), 2 parts of silane coupling agent, and 15 parts of curing agent (triethylenetetramine).

[0067] Mixing: Add all ingredients to the mixing equipment and stir at 1200r / m for 30 minutes to ensure uniform mixing and form a stable insulating slurry.

[0068] Coating: Using an automatic coating equipment, the insulating paste is evenly coated onto a 50μm thick PET release film, with the coating thickness controlled at 8μm. The coating speed and pressure are adjusted to ensure uniform coating.

[0069] Preliminary curing: Place the coated sample in an oven and bake at 80°C for 2 hours.

[0070] Final curing: Increase the temperature to 150°C and continue baking for 2 hours to ensure the quality and heat resistance of the insulation layer.

[0071] (2) Preparation of a second intermediate membrane with a shielding structure Material preparation: Polyurethane was selected as the resin binder and aluminum as the shielding material.

[0072] Undercoat coating: Apply an ultra-thin layer of resin as the undercoat on another PET release film, with a thickness controlled at 1μm. Use a doctor blade or automatic coating equipment for this operation.

[0073] Vacuum evaporation deposition: The PET release film with the underlayer is placed in the magnetron sputtering equipment, and the parameters are set (e.g., vacuum degree 1×10). -4 (Pa, power 150kw), deposit a dense and uniform aluminum shielding layer with a thickness controlled at 230nm.

[0074] Protective layer coating: Apply an ultra-thin resin of the same thickness to the shielding layer again to form a shielding structure with the main structure being a base layer, a shielding layer, and a top sealing layer.

[0075] (3) Preparation of a third intermediate film with a conductive layer Material weighing and mixing: Weigh 20 parts of the second polymer binder (epoxy resin E51), 40 parts of the conductive agent (graphite, 7 parts of nano-grade nickel powder), 10 parts of the heat-resistant material (alumina), 0.3 parts of the lubricant (silane coupling agent), 0.5 parts of the flame retardant (tetrabromophthalic anhydride), and 0.1 parts of the antioxidant (antioxidant 168) according to the proportions, and stir evenly in a high-speed mixer to form a conductive slurry.

[0076] Coating: The conductive paste is evenly coated onto the third PET release film using an automatic coating equipment, and the coating thickness is controlled to be 8μm.

[0077] Preliminary curing: Bake at 80℃ for 1 hour to allow the coating to cure initially.

[0078] Final curing: Heat to 150℃ and continue baking for 1 hour to complete the preparation of the conductive layer.

[0079] (4) Integration Prepare the composite layer: Align the layered structures prepared in steps (1) and (2).

[0080] Hot pressing conditions settings: Set the temperature of the hot press roller to 120℃, the pressure to 0.5MPa, and the time to 3 minutes.

[0081] Bonding: The two layers are bonded together for the first time using a hot press roller to ensure that each layer is tightly bonded.

[0082] Peel off the release film: Carefully peel off the PET release film from step (2).

[0083] Alignment and bonding: Align the conductive layer formed in step (3) with the previously bonded composite layer to prepare for the second bonding.

[0084] Hot pressing conditions: Same as the first bonding conditions, temperature set to 120℃, pressure 0.5MPa, time 3 minutes. The two are then bonded a second time using a hot press roller to form a complete electromagnetic shielding film product.

[0085] The above technical solution is the most complete technical solution. Other solutions only require reducing the experimental steps according to actual needs.

[0086] Referring to the process route of Example 1, the relevant parameters were controlled and the variables were changed as shown in Table 1 below, as well as Examples 2-8 and Comparative Example 1.

[0087] Table 1

[0088] Comparative Example 1 The manufacturing process is as follows: coating-evaporation-coating. A 6μm black insulating layer is formed by coating a 50μm PET release film with black insulating resin (epoxy resin). A 230nm metal coating is then prepared by vacuum evaporation. Finally, an 8μm conductive layer is coated to produce the finished product. The final product is then bonded to a circuit board using a hot-pressing process.

[0089] Test example: The electromagnetic shielding films obtained in Examples 1-11 and Comparative Example 1 were subjected to the following performance tests: (1) Electromagnetic shielding effectiveness test method: The test shall be conducted in accordance with GB / T30142 2013 standard; (2) Bending performance: Refer to standard IPC TM 650. Cut the shielding film sample into test samples with a length of 15cm and a width of 1cm and press them together (180℃, 100Kgf / cm). 2 The sample was cured for 1 hour and then placed on the MIT folding endurance tester for testing. The number of folds the shielding film was recorded with the shielding layer not being exposed as the standard. The performance test results of the electromagnetic shielding films obtained in Examples 1-11 and Comparative Example 1 are shown in Table 2 below.

[0090] Table 2

[0091] The above comparison clearly demonstrates the advantages of preparing each structure separately. The thin resin / rubber-metal-thin resin / rubber preparation method protects the metal shielding layer while improving the product's mechanical properties. Furthermore, the conductive layer structure enhances the product's mechanical properties and allows for continuous improvement based on demand, preventing issues like low yield or low production volume caused by any single step. Example 7 exhibits the best overall performance.

[0092] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a layered electromagnetic shielding film, characterized in that, Includes the following steps: An insulating paste is coated onto the first release film to form an insulating layer, thus obtaining a first intermediate film with an insulating layer. An adhesive is applied to the second release film to form a base layer. A shielding material is deposited on the base layer to form a shielding layer. An adhesive is applied to the shielding layer to form a top sealing layer, thus obtaining a second intermediate film having a base layer, a shielding layer, and a top sealing layer. A conductive paste is coated onto the third release film to form a conductive layer, thus obtaining a third intermediate film with a conductive layer. The insulating layer of the first intermediate film is brought into contact with the top sealing layer of the second intermediate film for the first bonding. Then the second release film is peeled off, and the second release film is brought into contact with the conductive layer on the third intermediate film for the second bonding.

2. The preparation method according to claim 1, characterized in that, The first and second bonding processes are both performed using a hot press roller press. The temperature of the hot press roller press is controlled at 110℃-130℃, the pressure is 0.4MPa-0.6MPa, and the pressing time is 2min-5min.

3. The preparation method according to any one of claims 1-2, characterized in that, The insulating slurry comprises, by weight, 30-50 parts of a first polymer binder, 5-15 parts of inorganic material, 0.5-3 parts of dispersant, 5-30 parts of toughening agent, 5-10 parts of plasticizer, 0.5-5 parts of silane coupling agent, and 10-15 parts of curing agent; The first polymer binder is selected from at least one of acrylic acid, acrylate, polyurethane, epoxy resin, and phenolic resin; The inorganic material is selected from at least one of amorphous glass, silicon dioxide, aluminum oxide, talc, mica powder, and bentonite; The dispersant is selected from at least one of cationic dispersants and nonionic dispersants; The toughening agent is selected from at least one of elastomer toughening agents, toughness toughening agents, and mineral toughening agents; The plasticizer is selected from at least one of phthalates, aliphatic diesters, phospholipids, epoxy compounds, and polyester plasticizers; The curing agent is selected from at least one of aliphatic curing agents, aromatic amine curing agents, acid anhydride curing agents, latent curing agents, and imidazole curing agents.

4. The preparation method according to claim 1, characterized in that, After applying the insulating slurry to the first release film, bake it at 70℃-90℃ for 1h-3h, and then continue baking it at 140℃-160℃ for 1h-3h. The thickness of the insulating layer is 4μm-8μm.

5. The preparation method according to claim 1, characterized in that, The shielding material is deposited using magnetron sputtering or vacuum deposition; the shielding material is selected from at least one of gold, silver, copper, aluminum, nickel, graphite, silver-coated copper, and nickel-coated carbon. The thickness of the shielding layer is 0.2μm-2μm.

6. The preparation method according to claim 1, characterized in that, The adhesives used for the underlayer and top seal layer are selected from at least one of the following: acrylic, acrylate, polyurethane, epoxy resin, phenolic resin, phenolic-chloroprene adhesive, phenolic-nitrile adhesive, epoxy resin-nitrile adhesive, rubber-modified acrylate adhesive, nitrile rubber adhesive, and A / RS system adhesive. The thickness of the underlayer is 6μm-10μm; the thickness of the top layer is 0.5μm-1μm.

7. The preparation method according to claim 1, characterized in that, The conductive paste comprises, by weight, 20-30 parts of a second polymer binder, 40-50 parts of a conductive agent, 10-30 parts of a heat-resistant material, 0-0.5 parts of a lubricant, 0.5-5 parts of a flame retardant, and 0.1-0.5 parts of an antioxidant. Wherein, the second polymer adhesive is selected from at least one of acrylic acid, acrylate, polyurethane, epoxy resin, phenolic resin, phenolic-chloroprene adhesive, phenolic-nitrile adhesive, epoxy resin-nitrile adhesive, rubber-modified acrylate adhesive, nitrile rubber adhesive, and A / RS system adhesive; The conductive agent is selected from at least one of gold, silver, copper, aluminum, nickel, graphite, carbon silver-coated copper, and nickel-coated carbon; The heat-resistant material is selected from at least one of alumina, aluminum nitride, silicon nitride, boron nitride, silicon-based ceramic powder, and aluminum. The lubricant is selected from at least one of organosilicon, diester, polyester alcohol, phosphate ester, and polyethylene glycol; The flame retardant is selected from at least one of tetrabromophthalic anhydride, tetrabromobisphenol A, aluminum diethylphosphite, aluminum hydroxide, triphenyl phosphate, and triphenyl polyphosphate. The antioxidant is selected from at least one of phenolic antioxidants, amine antioxidants, phosphite antioxidants, and metal complex antioxidants.

8. The preparation method according to claim 7, characterized in that, After coating the conductive paste onto the third release film, bake it at 70℃-90℃ for 0.5h-2h, and then continue baking it at 140℃-160℃ for 0.5h-2h. The thickness of the conductive layer is 6μm-12μm; The thicknesses of the first release film, the second release film, and the third release film are each independently 40μm-60μm.

9. A layered electromagnetic shielding film prepared by the preparation method according to any one of claims 1-8.

10. A flexible circuit board, characterized in that, It contains the layered electromagnetic shielding film as described in claim 9.

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