An electromagnetic shielding film with high shielding performance and its production process

Abstract

The present invention relates to the technical field of electromagnetic shielding films for flexible circuit boards, and specifically to an electromagnetic shielding film with high shielding performance and a production process thereof. The key points of the technical solution are: it includes an insulating layer, a metal shielding layer and a conductive adhesive layer arranged in sequence, one side of the insulating layer is in a network shape, and the side where the metal shielding layer is connected to the insulating layer is in a network shape that matches the insulating layer. The electromagnetic shielding film with high shielding performance and the production process of the present invention have a unique shielding body structure, which makes the shielding effectiveness of the electromagnetic shielding film of the present invention as high as 75db. At the same time, the metal shielding layer filled on one side of the grid-shaped insulating layer, due to its special grid-shaped process characteristics, is different from the rigid flat metal shielding layer structure characteristics of the past, which can make the metal shielding layer more resistant to bending and flexing, and embody excellent flexibility. In addition, compared with similar products, the process of the present invention is simple and easy to implement, the cost is relatively lower, and it is more mass-producible.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding films for flexible circuit boards, and in particular to an electromagnetic shielding film with high shielding performance and a production process thereof. Background Art

[0002] With the rapid development of modern electronic industrialization, a large number of electronic and electrical equipment are widely used in industrial production and people's daily life, which greatly promotes the development of industrial technology and improves people's quality of life. However, electronic and electrical equipment will radiate a large amount of electromagnetic waves during use, which causes considerable harm to the normal operation of electronic equipment and the living environment of human beings. Therefore, preventing electromagnetic wave pollution has become one of the major hotspots of scientific research today. The harm of electromagnetic radiation to electronic equipment is mainly manifested in the interference of electromagnetic waves on electronic equipment or electronic components, or the radiation of electromagnetic waves to digital transmission systems causing information leakage. The harm of electromagnetic waves to human health is manifested in various diseases induced by long-term electromagnetic wave radiation. Therefore, how to effectively suppress the interference of electromagnetic wave radiation on electronic and electrical equipment and protect humans from the harm of electromagnetic wave radiation has become one of the important tasks of scientific research and industrial product development in the 21st century.

[0003] The simplest and most effective way to suppress electromagnetic radiation is to use shielding materials to suppress electromagnetic wave radiation. Shielding materials reflect electromagnetic waves through the impedance difference between them and the air, or use their own electromagnetic induction to achieve eddy current attenuation of electromagnetic waves to achieve the purpose of absorption. At present, for the flexible circuit board industry, electromagnetic shielding film is mainly used to suppress electromagnetic noise radiation from different signals between boards.

[0004] The shielding effectiveness of electromagnetic shielding films in the prior art is generally around 40-60dB. For example, the Chinese invention patent with patent application publication number CN106003916A discloses an electromagnetic shielding film, and the shielding effectiveness of each embodiment recorded in its specification is between 50-60dB. In order to enhance the shielding effect of the electromagnetic shielding film, some electromagnetic shielding film manufacturers achieve the purpose of high shielding by increasing the thickness of its adhesive layer and metal layer. For example, the Chinese utility model patent with patent authorization announcement number CN207070596U discloses a technical solution of arranging the metal shielding layer into multiple layers in its specification. However, this, on the one hand, leads to the complexity of the process, and at the same time, it also greatly increases the material and production costs. On the other hand, the thicker metal layer, due to its enhanced rigidity, leads to the problem of brittle fracture of the metal layer of the electromagnetic shielding film after multiple bending of the flexible circuit board, thereby resulting in a decrease in shielding effectiveness and an increase in grounding resistance.

[0005] Based on this, this patent application is made. Summary of the invention

[0006] In view of the shortcomings of the prior art, one of the design objectives of the present invention is to provide an electromagnetic shielding film with relatively thin thickness, high electromagnetic shielding performance and good anti-bending performance.

[0007] The above technical purpose of the present invention is achieved through the following technical scheme: an electromagnetic shielding film with high shielding performance, comprising an insulating layer, a metal shielding layer and a conductive adhesive layer arranged in sequence, one side of the insulating layer is in a network shape, and the side of the metal shielding layer connected to the insulating layer is in a network shape that is compatible with the insulating layer.

[0008] By adopting the above technical scheme, compared with the existing technology, the electromagnetic shielding film with high shielding performance provided by the present invention has one side of the insulating layer designed to be grid-shaped, and one side of the metal shielding layer is filled in the grid gap of the insulating layer to become a grid-shaped metal shielding layer. A conductive adhesive layer is arranged on the side of the metal shielding layer away from the insulating layer. Due to its special grid-shaped characteristics, it is different from the rigid flat metal shielding layer structure characteristics in the past, which can make the metal shielding layer more resistant to bending and folding, and reflect excellent flexibility. The grid-shaped metal shielding layer and the conductive adhesive layer connect and ground the circuit board circuit. In addition, the grid-shaped metal shielding layer and the conductive adhesive layer together form a continuous, complete, three-dimensional grid-shaped electromagnetic wave shielding body structure, which can reflect electromagnetic waves twice or suppress them in the grid-shaped shielding layer, and the conductive adhesive layer then draws away and releases the excess charge. The unique shielding body structure makes the shielding effectiveness of the electromagnetic shielding film of the present invention as high as 75db. The grid-shaped metal layer structure can avoid the adverse effects of brittle fracture of the metal layer when bending. The anti-bending performance of the electromagnetic shielding film is more prominent, reflecting excellent flexibility. The function of the insulating layer is to prevent charge overflow and reduce the occurrence of creepage, short circuit, etc.

[0009] Preferably, the electromagnetic shielding film further comprises a carrier film, and the carrier film is arranged on a side of the mesh insulation layer away from the metal shielding layer.

[0010] By adopting the above technical solution, the carrier film can play a supporting role and provide protection for the insulation layer during transportation or processing.

[0011] Preferably, the carrier film is made of a non-silicon release film, and the carrier film is a polyester film or a polyimide film.

[0012] By adopting the above technical solution, the main function of selecting polyester film or polyimide film is to facilitate better connection between the carrier film and the insulating layer. The non-silicone release film composed of polyester film or polyimide coated with non-silicone release agent has better release and separation effect than the release film of the silicone system formed by coating with silicone release agent. If the carrier film uses a release film of the silicone system, the silicone release agent needs to be attached to the insulating layer. At this time, there is a risk of silicon transfer, that is, a certain amount of silicon molecules are transferred to the surface of the insulating layer. These silicon molecules will cause the printing performance of the surface of the insulating layer to decrease, which is not conducive to printing the insulating layer. However, when using a non-silicone release film, there is no such risk.

[0013] Preferably, the carrier film has a thickness between 30 μm and 80 μm.

[0014] Preferably, the electromagnetic shielding film further comprises a protective film, and the protective film is arranged on a side of the conductive adhesive layer away from the metal shielding layer.

[0015] By adopting the above technical solution, the protective film has a protective effect on the conductive adhesive layer and can be used as a subsequent processing protection for the product. In addition, it can also prevent foreign matter or impurities from contaminating the conductive adhesive layer.

[0016] Preferably, the protective film is a release film of an organosilicon system.

[0017] By adopting the above technical solution, the cost price of the release film of the silicone system is about 1-2 yuan / square meter, which is relatively low and can meet the performance requirements of the protective film in all aspects.

[0018] Preferably, the protective film is a polyester film or a polyimide film.

[0019] By adopting the above technical solution, polyester film or polyimide film is easily available on the market and is a better protective film material.

[0020] Preferably, the protective film has a thickness of 50 μm-80 μm.

[0021] Preferably, the insulating layer is made of resin material.

[0022] By adopting the above technical solution, the insulating layer made of resin can be processed into a grid-shaped side surface, and the other side surface can be well bonded with the carrier film. The grid-shaped side surface processed by resin has the advantages of good compliance and filling performance compared with the grid-shaped side surface processed by other materials, and has good reflow resistance.

[0023] Preferably, the resin used to make the insulating layer is one of acrylic resin, polyurethane and epoxy resin.

[0024] By adopting the above technical solution, acrylic resin, polyurethane and epoxy resin are all cheap, easily available and easy to process resins. By selecting the above resins, the production cost of the protective film is further reduced.

[0025] Preferably, the side of the outer surface of the insulating layer facing away from the grid shape provides printability.

[0026] By adopting the above technical solution, the printable side can print various ink characters.

[0027] Preferably, the thickness of the insulating layer is between 3 μm and 15 μm.

[0028] Preferably, the metal shielding layer is a composite metal layer composed of two different conductive metal materials.

[0029] By adopting the above technical solution, the double metal layer composed of different materials has more outstanding shielding performance, corrosion resistance and oxidation resistance.

[0030] Preferably, the conductive metal material may be one of nickel, chromium, copper, silver and gold.

[0031] By adopting the above technical scheme, nickel and copper have good electrical conductivity and can meet the electrical conductivity requirements of the metal layer. The cost is relatively low, and the processes of copper electroplating and nickel electroplating are relatively simple. Chromium has better wear resistance while meeting the electrical conductivity. The stability, wear resistance and electrical conductivity of gold and silver are all at a high level.

[0032] Preferably, the thickness of the metal shielding layer is 0.1 μm-5 μm.

[0033] Preferably, the conductive adhesive layer is an omnidirectional conductive adhesive layer.

[0034] By adopting the above technical solution, the omnidirectional conductive adhesive can further reflect electromagnetic waves or attenuate electromagnetic waves and improve the electromagnetic shielding performance. This is because the omnidirectional conductive adhesive layer can conduct electricity in three directions: X, Y and Z. A part of the electromagnetic waves will produce a certain amount of reflection when encountering the conductive particles in the X and Y directions. These electromagnetic waves reflected by the conductive adhesive can be absorbed again by the metal layer, thereby achieving the effect of enhancing the shielding effectiveness of the shielding film.

[0035] Preferably, the conductive adhesive layer is filled with conductive particles, and the conductive particles may be nickel, copper, silver, gold, or at least one of nickel-coated copper, silver-coated copper, and silver-coated graphite.

[0036] By adopting the above technical solution, nickel and copper have excellent conductivity and are relatively cheap. As conductive particles, they can better meet the conductive requirements and achieve the best electromagnetic shielding effect. Silver and gold, as conductive particles in the conductive glue layer, have the best conductive effect and the best conductive stability.

[0037] Preferably, the particle diameter of the conductive particles is selected between 1 μm and 20 μm, and the filling ratio of the conductive particles to the conductive adhesive can be between 10% and 40%.

[0038] By adopting the above technical solution, the particle size and filling ratio of the conductive particles are related to the overall conductive performance of the conductive adhesive layer. If the particle size of the conductive particles is too small, it is difficult for the conductive particles to cross-link with each other to realize their conductive function. If the conductive particles are too large, the conductive adhesive will not be sticky enough and cannot be well attached to the position where it needs to be attached. The filling ratio of the conductive particles to the conductive adhesive should not be too large. A too large filling ratio of the conductive particles will cause the conductive adhesive content to be too low, which will lead to insufficient viscosity of the conductive adhesive. The filling ratio of the conductive particles to the conductive adhesive should not be too small. A too small filling ratio of the conductive particles will cause the overall conductive performance of the conductive adhesive layer to be insufficient. The conductive particle filling ratio and particle size are both selected within the range recorded in the present application document, which can ensure the conductive performance of the conductive adhesive layer, thereby achieving the effect of improving the shielding effectiveness of the electromagnetic shielding film.

[0039] Preferably, the thickness of the conductive adhesive layer is between 3 μm and 20 μm.

[0040] The second object of the present invention is to provide a production process for an electromagnetic shielding film, which is simple and easy to implement, has a relatively lower cost, and is more mass-producible.

[0041] The above technical objectives of the present invention are achieved through the following technical solutions, a production process of an electromagnetic shielding film, and the specific process steps include the following points:

[0042] Step a, coating an insulating resin on one side of the carrier film to form a grid-shaped insulating layer;

[0043] Step b, electroplating a conductive metal on one side of the mesh-shaped insulating layer to form a mesh-shaped metal shielding layer;

[0044] Step c, coating a conductive adhesive on the side of the mesh metal shielding layer facing away from the insulating layer to form a conductive adhesive layer;

[0045] Step d: forming a protective film on the surface of the conductive adhesive layer facing away from the metal shielding layer in a bonding manner.

[0046] Through the above technical solution, an electromagnetic shielding film with good shielding performance can be produced at a relatively low cost, and can be suitable for industrial mass production needs.

[0047] In summary, the present invention has the following beneficial effects:

[0048] First, the present invention has better electromagnetic shielding effectiveness, which can reach 70-75dB;

[0049] Secondly, the metal shielding layer of the present invention has more outstanding anti-bending performance and excellent flexibility;

[0050] Thirdly, the process of the present invention is simple and easy to implement, with relatively lower cost and better mass production capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a structural schematic diagram of this embodiment;

[0052] Figure 2 It is a schematic diagram of the structure when the ground resistance of the electromagnetic shielding film is detected.

[0053] In the figure: 1. Carrier film; 2. Grid insulation layer; 3. Metal shielding layer; 4. Conductive adhesive layer; 5. Protective film; 6. Test hole; 7. CVL covering film; 8. Flexible copper clad laminate. DETAILED DESCRIPTION

[0054] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0055] like Figure 1 As shown, the electromagnetic shielding film with high shielding performance provided by the present invention has the following product structures: a carrier film 1, a grid-shaped insulating layer 2, a grid-shaped metal shielding layer 3, a conductive adhesive layer 4, and a protective film 5.

[0056] The carrier film 1 of this embodiment uses a non-silicon release film, and its film material can be one of polyester film, polyimide film, etc. The carrier film uses a non-silicon release film of polyester film or polyimide film. The main function is to facilitate the formation of the insulating layer 2. The insulating layer in this embodiment is made of resin, and the insulating layer made of resin can be better connected to the surface of the polyester film or polyimide film. In addition, the carrier film can also play a supporting role and provide protection for the transportation or processing process of the insulating layer 2. Preferably, the thickness of the carrier film can be between 30μm and 80μm, and optimally, it can be 47~53μm.

[0057] The insulating layer 2 is in a grid shape and is coated on either side of the carrier film 1. Preferably, the resin used to make the insulating layer can be one of acrylic resin, polyurethane resin or epoxy resin. The acrylic resin, polyurethane resin or epoxy resin here can also be modified by adding curing agent, antifreeze agent, leveling agent and other substances according to actual use. The main function of the insulating layer 2 is to prevent charge overflow and reduce the occurrence of creepage, short circuit and the like. Considering its subsequent processing, the side of the outer surface of the insulating layer 2 that is away from the grid shape provides printability, which is convenient for printing various ink characters. Preferably, the thickness of the insulating layer can be between 3μm and 15μm, and most preferably, it can be 6~8μm.

[0058] The metal shielding layer 3 is electroplated on one side of the grid-shaped insulating layer 2 to form a grid-shaped metal layer structure. The grid-shaped metal layer structure can avoid the adverse effect of brittle fracture of the metal shielding layer 3 when bending. The anti-bending performance of the electromagnetic shielding film is more prominent, reflecting excellent flexibility. Among them, the conductive metal material of the metal shielding layer can be at least one of nickel, chromium, copper, silver, gold or nickel-chromium alloy, nickel-silver alloy, copper-nickel alloy, and copper-silver alloy. Preferably, the metal shielding layer adopts a double-layer structure composed of two different conductive metal materials, and its shielding performance, corrosion resistance and oxidation resistance are more prominent. The electroplating method can be formed by chemical plating, vacuum magnetron sputtering plating, vacuum evaporation plating, electromagnetic plating or a composite process thereof. Preferably, the thickness of the metal shielding layer is between 0.1μm and 5μm, and most preferably, it can be 0.3μm.

[0059] The conductive adhesive layer 4 is an omnidirectional conductive adhesive, which is coated on the side of the metal shielding layer 3 away from the insulating layer 2 to provide good filling properties, conductivity and bonding strength. The material can be one of epoxy resin, acrylic resin, and polyurethane resin. The epoxy resin, acrylic resin, and polyurethane resin mentioned here can be modified epoxy resin, modified acrylic resin, or modified polyurethane resin added with a curing agent, a leveling agent, and a dispersant. Preferably, the thickness of the conductive adhesive layer is between 3μm and 20μm, and most preferably, it can be 3μm. The high shielding effectiveness provided by the electromagnetic shielding film in the present invention is mainly achieved by the continuous and complete shielding structure composed of the grid-shaped metal shielding layer 3 and the omnidirectional conductive adhesive layer 4.

[0060] The protective film 5 is a release film of an organic silicon system. The protective film 5 has a protective effect on the conductive adhesive layer 4 and can provide protection for subsequent processing of the product. In addition, the protective film 5 can also prevent foreign matter, impurities, etc. from contaminating the conductive adhesive layer 4.

[0061] Combination Figure 1 As shown, the production of the electromagnetic shielding film with high shielding performance provided by the present invention

[0062] The specific production process includes the following steps:

[0063] Step a: coating insulating resin on either side of the carrier film 1, drying the solvent to solidify it, and coating to form a grid-shaped insulating layer 2.

[0064] Step b, electroplating a conductive metal on the side of the surface of the grid-shaped insulating layer 2 away from the carrier film to form a metal shielding layer 3. The conductive metal material can be at least one of nickel, chromium, copper, silver, gold or nickel-chromium alloy, nickel-silver alloy, copper-nickel alloy, copper-silver alloy and the like. Preferably, the metal shielding layer uses a metal alloy of two different materials. The metal shielding layer of the double-layer structure composed of different materials has more outstanding shielding performance, corrosion resistance and oxidation resistance, more stable performance and stronger structure. The electroplating method can be formed by chemical plating, vacuum magnetron sputtering plating, vacuum evaporation plating, electromagnetic plating or a composite process thereof.

[0065] Step c, apply conductive glue on the side of the metal shielding layer 3 away from the insulating layer, dry and solidify, and form an omnidirectional conductive glue layer 4. Of course, the conductive glue layer 4 can also be an anisotropic conductive glue layer. Preferably, the conductive glue layer 4 in the present invention adopts omnidirectional conductive glue, which can further reflect electromagnetic waves or attenuate electromagnetic waves. Among them, the conductive glue is filled with conductive particles, and the conductive particles can be nickel, copper, silver, gold, or at least one of nickel-coated copper, silver-coated copper, silver-coated graphite, etc.

[0066] Preferably, the diameter of the conductive particles of the conductive adhesive layer 4 is selected to be between 1 μm and 20 μm.

[0067] Preferably, the filling ratio of the conductive particles in the conductive adhesive layer 4 to the conductive adhesive may be between 10% and 40%.

[0068] Step d, forming a protective film 5 on the side of the conductive adhesive layer 4 away from the grid-shaped metal layer 3 in a bonding manner. The protective film 5 is a release film of an organic silicon system. The film material of the protective film 5 can be one of a polyester film, a polyimide film, etc. The protective film 5 has a protective effect on the conductive adhesive layer 4 and can be used as a subsequent processing protection for the product. In addition, it can also prevent foreign matter, impurities, etc. from contaminating the conductive adhesive layer 4.

[0069] Compared with the existing technology, the electromagnetic shielding film with high shielding performance provided by the present invention designs the insulating layer 2 into a grid shape, and the metal layer 3 is electroplated in the grid gap of the insulating layer 2 to form a grid-shaped metal shielding layer 3. In turn, an omnidirectional conductive adhesive layer 4 is coated on the side of the metal shielding layer 3 away from the insulating layer 2. The grid-shaped metal shielding layer 3 and the omnidirectional conductive adhesive layer 4 connect the circuit board circuit to the ground. In addition, the grid-shaped metal shielding layer 3 and the omnidirectional conductive adhesive layer 4 together form a continuous, complete, three-dimensional grid-shaped electromagnetic wave shielding body structure, which can reflect electromagnetic waves twice or suppress them in the grid-shaped shielding layer, and the conductive adhesive layer 4 then draws away and releases the excess charge. The unique shielding body structure makes the shielding effectiveness of the electromagnetic shielding film of the present invention as high as 75db. At the same time, the metal shielding layer 3 filled on one side of the grid-shaped insulating layer 2, due to its special grid-shaped process characteristics, is different from the rigid flat metal shielding layer structure characteristics of the past, which can make the metal shielding layer more resistant to bending and flexing, reflecting excellent flexibility. In addition, compared with similar products, the process of the present invention is simple and easy to implement, with relatively lower cost and better mass production.

[0070] The electromagnetic shielding film described in the present invention was sent for inspection, and the product characteristic test data obtained were as follows:

[0071] project Test results Detection Methods Shielding performance (db) 70-75db SJ20524-1995 (10MHz~3000MHz) Ground resistance (Ω) ≤1 GND φ=1mm, after tinning Bending resistance ≥25000 times Bending radius R = 1.0 mm

[0072] See also Figure 2 The grounding resistance test method is as follows: the shielding film is pressed and covered on the FPC test hole 6, and the grounding resistance of different grounding holes is tested by pressing and transferring, and then the grounding resistance is tested after baking at 160-170℃ for 1H to cure, reflow soldering or tinning.

[0073] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. An electromagnetic shielding film with high shielding performance, characterized in that: It comprises an insulating layer, a metal shielding layer and a conductive adhesive layer arranged in sequence, one side of the insulating layer is in a network shape, and the side of the metal shielding layer connected to the insulating layer is in a network shape adapted to the insulating layer; The grounding resistance of the electromagnetic shielding film is less than or equal to 1 ohm, and the bending resistance is greater than or equal to 25,000 times; The production process of the electromagnetic shielding film with high shielding performance includes the following specific process steps: Step a, coating an insulating resin on one side of the carrier film to form a grid-shaped insulating layer; Step b, electroplating a conductive metal on one side of the mesh-shaped insulating layer to form a mesh-shaped metal shielding layer; Step c, coating a conductive adhesive on the side of the mesh metal shielding layer facing away from the insulating layer to form a conductive adhesive layer; Step d, forming a protective film on the side of the conductive adhesive layer facing away from the metal shielding layer in a bonding manner; The electromagnetic shielding film further comprises a carrier film, and the carrier film is arranged on a side of the mesh insulation layer away from the metal shielding layer; The insulating layer is made of resin material, and the resin used to make the insulating layer is one of acrylic resin, polyurethane, and epoxy resin; The thickness of the insulating layer is between 3 μm and 15 μm; the metal shielding layer is a composite metal layer composed of two different conductive metal materials; The conductive metal material may be one of nickel, chromium, copper, silver, and gold; The thickness of the metal shielding layer is 0.1 μm-5 μm; The conductive adhesive layer is an omnidirectional conductive adhesive layer; The conductive adhesive layer is filled with conductive particles, which may be nickel, copper, silver, gold, or at least one of nickel-coated copper, silver-coated copper, and silver-coated graphite. The particle diameter of the conductive particles is selected between 1 μm and 20 μm, and the filling ratio of the conductive particles to the conductive adhesive is between 10% and 40%; The thickness of the conductive adhesive layer is between 3 μm and 20 μm.

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