Electromagnetic shielding film and circuit board

Abstract

The invention discloses an electromagnetic shielding film and a circuit board, the electromagnetic shielding film comprises a first shielding layer, a flexible conductive adhesive layer and a second shielding layer which are stacked in sequence, and the flexible conductive adhesive layer is arranged between the first shielding layer and the second shielding layer, so that the bending resistance of the electromagnetic shielding film is effectively improved, interference signals are effectively weakened, and the electromagnetic shielding effect is improved. According to the electromagnetic shielding film, the shielding performance is improved, the elastic modulus of the flexible conductive adhesive layer is set between 80 MPa and 120 MPa, the elastic modulus of the flexible conductive adhesive layer is limited within a reasonable range, the bending resistance of the electromagnetic shielding film is better improved, and the electromagnetic shielding film is suitable for products needing to be folded or opened and closed for a long time and at high frequency.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and in particular to an electromagnetic shielding film and a circuit board. Background Art

[0002] With the development of miniaturization of communication equipment, there are higher and higher requirements for the miniaturization of integrated circuit boards. However, the further miniaturization of integrated circuit boards has also developed to a certain limit, so the miniaturization of communication equipment has also been restricted. In order to achieve further miniaturization of communication equipment, foldable mobile phones came into being. In order for foldable mobile phones to operate normally and avoid electromagnetic interference from the outside world and itself, it is necessary to apply an electromagnetic shielding film on the surface of the foldable mobile phone. However, the electromagnetic shielding film in the prior art is attached to a hard board and is not suitable for folding mobile phones or soft boards. Folding circuit boards or soft boards require long-term and high-frequency folding or opening and closing. Existing electromagnetic shielding films are difficult to meet such high requirements. After high-frequency folding, the internal circuits of the circuit board or soft board are often broken or damaged.

[0003] It can be seen that in order to adapt to the application requirements of existing circuit boards or flexible boards, how to improve the bending resistance of circuit boards or flexible boards is an urgent problem to be solved. Summary of the invention

[0004] The purpose of the embodiments of the present invention is to provide an electromagnetic shielding film and a circuit board, which can improve the bending resistance of the electromagnetic shielding film itself, thereby improving the bending resistance of the circuit board or flexible board containing the electromagnetic shielding film.

[0005] In order to solve the above technical problems, an embodiment of the present invention provides an electromagnetic shielding film, including a first shielding layer, a flexible conductive adhesive layer and a second shielding layer, the first shielding layer, the flexible conductive adhesive layer and the second shielding layer are stacked in sequence, and the elastic modulus of the flexible conductive adhesive layer is 80-120Mpa.

[0006] As a preferred solution, in the flexible conductive adhesive layer, the weight content of the conductive particles is 1wt%-40wt%.

[0007] As a preferred embodiment, the conductive particles are at least one of gold, silver, copper, nickel, iron and silver-coated copper.

[0008] As a preferred solution, the conductive particles in the flexible conductive adhesive layer are in at least one of a spherical, flake, star, dendrite, and cone shape.

[0009] As a preferred solution, the average thickness of the flexible conductive adhesive layer is 0.25-6 microns.

[0010] As a preferred solution, among the conductive particles in the flexible conductive adhesive layer, the number of spherical conductive particles accounts for more than 60%.

[0011] As a preferred embodiment, the conductive particles of the flexible conductive adhesive layer include silver-coated copper conductive particles, the silver-coated copper conductive particles have copper particles as cores, and the surface of the copper particles contains a silver layer of 1-50 nanometers.

[0012] As a preferred embodiment, the conductive particles of the flexible conductive adhesive layer include at least one of flake conductive particles and spherical conductive particles, and the average thickness H of the flexible conductive adhesive layer and the maximum thickness H of the flake conductive particles are 片 The maximum height D of the spherical conductive particles satisfies: D<H<3H 片 +D,H 片 <D.

[0013] As a preferred embodiment, the resin of the flexible conductive adhesive layer is at least one of polyurethane, polyester, alkyd resin, epoxy resin, acrylic resin, polyimide, polystyrene, polyvinyl acetate, polyethylene, polypropylene, polyamide, rubber, phenolic resin, urethane resin, alkyd resin and ABF resin. It should be noted that in the present invention, the average thickness of the electromagnetic shielding film is 2-20 microns.

[0014] In order to solve the same technical problem, an embodiment of the present invention further provides a circuit board, which includes the electromagnetic shielding film as described in any of the above embodiments.

[0015] Compared with the prior art, the embodiments of the present invention provide an electromagnetic shielding film and a circuit board, wherein the electromagnetic shielding film comprises a first shielding layer, a flexible conductive adhesive layer and a second shielding layer stacked in sequence, and a flexible conductive adhesive layer is arranged between the first shielding layer and the second shielding layer, which effectively increases the bending resistance of the electromagnetic shielding film; at the same time, it can improve the bending resistance performance of the circuit board or the soft board containing the electromagnetic shielding film, and effectively weaken the interference signal, thereby improving the shielding performance, and the elastic modulus of the flexible conductive adhesive layer is set between 80-120Mpa, and the elastic modulus of the flexible conductive adhesive layer is limited within a reasonable range, so that the bending resistance of the electromagnetic shielding film is better improved, and the bending resistance performance of the circuit board or the soft board is improved, which is suitable for products that require long-term and high-frequency folding or opening and closing. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic structural diagram of an electromagnetic shielding film in an embodiment of the present invention;

[0017] Figure 2 is a schematic diagram of the structure of a circuit board in an embodiment of the present invention;

[0018] Among them, 1. the first shielding layer; 2. the flexible conductive adhesive layer; 21. the conductive particles; 3. the second shielding layer; 4. the adhesive layer; 5. the circuit board body. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] In the description of this application, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0021] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. The terms "vertical", "horizontal", "left", "right", "upper", "lower" and similar expressions used herein are only for illustrative purposes, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0022] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0023] See also Figure 1A preferred embodiment of the present invention provides an electromagnetic shielding film, comprising a first shielding layer 1, a flexible conductive adhesive layer 2 and a second shielding layer 3. The first shielding layer 1, the flexible conductive adhesive layer 2 and the second shielding layer 3 are stacked in sequence, and the elastic modulus of the flexible conductive adhesive layer 2 is 80-120Mpa.

[0024] Preferably, the material of the first shielding layer 1 and the second shielding layer 3 is at least one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. It is understandable that the material of the first shielding layer 1 and the second shielding layer 3 can be metal or alloy. In order to ensure that the first shielding layer 1 and the second shielding layer 3 have good electrical conductivity, the first shielding layer 1 and the second shielding layer 3 are made of at least one material of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. The materials of the first shielding layer 1 and the second shielding layer 3 can be the same or different, and no specific limitation is made here. At the same time, the first shielding layer 1 and the second shielding layer 3 can be a single-layer structure or a multi-layer structure, respectively. The materials between the layers of the multi-layer structure can be the same or different, and the specific layer structure can be set according to the design or application needs.

[0025] In this embodiment, in order to avoid the problem that the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film are not resistant to bending, which leads to the electromagnetic shielding film and the circuit board or soft board containing the electromagnetic shielding film being unable to meet the requirements of long-term and high-frequency folding or opening and closing, and are prone to wrinkles, curling or fractures, which affects the quality of the final product, the embodiment of the present invention sets a flexible conductive adhesive layer 2 between the first shielding layer 1 and the second shielding layer 3. The flexibility of the flexible conductive adhesive layer can improve the bending resistance of the electromagnetic shielding film itself, and at the same time improve the bending resistance of the circuit board or soft board containing the electromagnetic shielding film. Further, considering the influence of the elastic modulus of the flexible conductive adhesive layer 2 on the bending resistance, the elastic modulus of the flexible conductive adhesive layer 2 is set to 80-120Mpa, and the elastic modulus of the flexible conductive adhesive layer 2 can be 85, 90, 95, 100, 105, 110, 115, 118 or an interval composed of any two values, and its unit is Mpa. Of course, it can also be any other value between 80-120Mpa, which is not specifically limited here.

[0026] By adopting the technical means of the embodiment of the present invention, a flexible conductive adhesive layer 2 is arranged between the first shielding layer 1 and the second shielding layer 3, and multi-layer shielding is performed on the electromagnetic interference signals on both sides of the electromagnetic shielding membrane, thereby effectively weakening the electromagnetic interference signals on both sides of the electromagnetic shielding membrane. The flexible conductive adhesive layer 2 contains conductive particles 21, which can realize the electrical connection between the first shielding layer 1 and the second shielding layer 3. The excess charge is introduced into the formation through the first shielding layer 1, the conductive adhesive layer 2 and the second shielding layer 3, thereby improving the shielding performance of the electromagnetic shielding membrane. The additional flexible conductive adhesive layer 2 improves the bending resistance of the electromagnetic shielding membrane itself and the circuit board or soft board containing the electromagnetic shielding membrane. Furthermore, the elastic modulus of the flexible conductive adhesive layer 2 is set to 80-120Mpa, and the elastic modulus of the flexible conductive adhesive layer 2 is limited within a reasonable range, so that the bending resistance of the electromagnetic shielding membrane is better improved, which is suitable for products that require long-term and high-frequency folding or opening and closing. The elastic modulus of the flexible conductive adhesive layer 2 cannot be too high. If the elastic modulus is too high, the rigidity of the flexible conductive adhesive layer 2 will be too high, thereby reducing the bending resistance of the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film; at the same time, the elastic modulus of the flexible conductive adhesive layer 2 cannot be too low. If the elastic modulus is too low, the stress transfer between the first shielding layer 1 and the second shielding layer 3 of the electromagnetic shielding film will be hindered, thereby reducing the bending resistance of the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film.

[0027] As a preferred embodiment, in the flexible conductive adhesive layer 2, the weight content of the conductive particles is 1wt%-40wt%.

[0028] In an embodiment of the present invention, the influence of the content of the conductive particles 21 in the flexible conductive adhesive layer 2 on the shielding performance of the electromagnetic shielding film and the elastic modulus of the flexible conductive adhesive layer is taken into consideration, and the weight content of the conductive particles is set to 1wt%-40wt%. The weight content of the conductive particles can specifically be 5, 10, 16, 27, 30, 35, 38 or 40 or an interval consisting of any two values, and the unit is wt%, wherein wt% is a unit representing the weight ratio or the proportion of a substance in a mixture. Of course, the weight content of the conductive particles can also be any other value between 1wt% and 40wt%, which is not specifically limited here. In the present invention, the content of conductive particles needs to be limited to a specific range. If the content of conductive particles is too high, it will be detrimental to the improvement of the bending resistance of the electromagnetic shielding film and the circuit board or flexible board containing the electromagnetic shielding film. This is mainly because excessive content of conductive particles can easily cause stress concentration and uneven force between the first shielding layer 1 and the second shielding layer 3, which reduces the bending resistance of the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film. If the content of conductive particles is too low, the conductivity between the first shielding layer 1 and the second shielding layer 3 is reduced, which is not conducive to the grounding conduction of the accumulated charge between the first shielding layer 1 and the second shielding layer 3. Other means may need to be used to improve the grounding performance.

[0029] By adopting the technical means of the embodiment of the present invention, the content of the conductive particles 21 in the flexible conductive adhesive layer 2 is limited, which can effectively control the content of the conductive particles 21 within a reasonable range, effectively realize the electrical connection between the first shielding layer 1 and the second shielding layer 3, ensure the shielding performance of the electromagnetic shielding film, and at the same time ensure that the elastic modulus of the flexible conductive adhesive layer 2 can fall within the range of 80-120Mpa, thereby ensuring the bending resistance of the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film, so that the electromagnetic shielding film or the circuit board or soft board containing the shielding film is suitable for products that require long-term and high-frequency folding or opening and closing.

[0030] As a preferred embodiment, the conductive particles 21 are at least one of gold, silver, copper, nickel, iron and silver-coated copper. The conductive particles 21 in the flexible conductive adhesive layer 2 are conductive particles, and the flexible conductive adhesive layer 2 may include conductive particles 21 of various materials. The conductive particles 21 are used to electrically connect the first shielding layer 1 and the second shielding layer 3, effectively guide the excess charge, and improve the shielding performance of the electromagnetic shielding film.

[0031] As a preferred embodiment, the conductive particles 21 in the flexible conductive adhesive layer 2 are in at least one of a spherical shape, a flake shape, a star shape, a dendrite shape, and a cone shape.

[0032] It should be noted that due to differences in process and parameters, the conductive particles 21 can be spherical, flaky, star-shaped, dendrite-shaped, conical, etc., but are not limited to the above specific shapes, as long as they can play a positive role in improving the shielding performance of the electromagnetic shielding film.

[0033] As a preferred embodiment, the average thickness of the flexible conductive adhesive layer 2 is 0.25-6 microns.

[0034] In an embodiment of the present invention, taking into account the bending requirements of the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film, it is preferred to set the average thickness of the flexible conductive adhesive layer 2 to be between 0.25 and 6 microns. The average thickness of the flexible conductive adhesive layer 2 can specifically be 0.25, 0.5, 1, 2, 3, 4, 5, 6 or a range consisting of any two values, and the unit is microns. Of course, it can also be any other value between 0.25 microns and 6 microns, which is not specifically limited here.

[0035] By adopting the technical means of the embodiments of the present invention, the average thickness of the flexible conductive adhesive layer is limited to a reasonable range, thereby ensuring the shielding performance of the electromagnetic shielding film and the bending resistance of the shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film.

[0036] As a preferred embodiment, among the conductive particles in the flexible conductive adhesive layer, the number of spherical conductive particles accounts for more than 60%.

[0037] In the embodiment of the present invention, it is taken into consideration that the effects of conductive particles 21 of different shapes on the performance of the electromagnetic shielding film are different. Spherical conductive particles have a better effect in improving the shielding and bending resistance of the electronic electromagnetic shielding film, and the formation process of the spherical conductive particles is relatively mature. The number ratio of spherical conductive particles is set to reach more than 60% in all conductive particles 21, which can make the performance of the mass-produced flexible conductive adhesive layer 2 stable and meet the requirements of bending resistance and shielding performance. The number of spherical conductive particles accounts for 60%, 67%, 73%, 85%, 94% or 100% of the conductive particles. Of course, it can also be any other value between 60% and 100%, which is not specifically limited here.

[0038] By adopting the technical means of the embodiment of the present invention, the shape and proportion of the conductive particles 21 are limited, thereby ensuring the stability and reliability of the shielding performance of the electromagnetic shielding film.

[0039] As a preferred embodiment, the conductive particles of the flexible conductive adhesive layer include silver-coated copper conductive particles, the silver-coated copper conductive particles have copper particles as the core, and the surface of the copper particles contains a silver layer of 1-50 nanometers. For example, the thickness of the silver layer on the surface of the copper particles is 2, 5, 15, 25, 35, 45, 50 nanometers or an interval consisting of any two values. Of course, it can also be any other value between 1-50 nanometers, which is not specifically limited here.

[0040] As a preferred embodiment, the conductive particles of the flexible conductive adhesive layer include at least one of flake conductive particles and spherical conductive particles, and the average thickness H of the flexible conductive adhesive layer and the maximum thickness H of the flake conductive particles are 片 The maximum height D of the spherical conductive particles satisfies: D<H<3H 片 +D,H 片 <D.

[0041] In the embodiment of the present invention, it is considered that the conductive particles 21 of different shapes have different effects on the shielding and bending resistance of the electromagnetic shielding film. The sheet-shaped conductive particles and the spherical conductive particles have better performance in improving the shielding effectiveness of the electromagnetic shielding film, and at the same time have a certain influence on the bending resistance of the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film. The content of resin and conductive particles in the flexible conductive adhesive layer has a great influence on the bending resistance of the electromagnetic shielding film. By setting the average thickness H of the flexible conductive adhesive layer and the maximum thickness H of the sheet-shaped conductive particles, the bending resistance of the electromagnetic shielding film can be greatly improved. 片 The maximum height D of the spherical conductive particles satisfies: D<H<3H 片 +D,H 片 <D relationship, so that the electromagnetic shielding film meets the shielding performance, and the bending resistance of the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film also meets the application requirements.

[0042] As a preferred embodiment, the resin of the flexible conductive adhesive layer is at least one of polyurethane, polyester, alkyd resin, epoxy resin, acrylic resin, polyimide, polystyrene, polyvinyl acetate, polyethylene, polypropylene, polyamide, rubber, phenolic resin, urethane resin, alkyd resin and ABF resin. It can be understood that the flexible conductive adhesive layer is composed of resin and conductive particles, and the resin of the flexible conductive adhesive layer can be a single resin or can be composed of two, three or more resins, which is used to improve the bending resistance of the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film.

[0043] In addition, the electromagnetic shielding film of the present invention further includes a base layer, which is arranged on the other side of the first shielding layer 1 or the second shielding layer 3. The base layer includes, but is not limited to, at least one of polystyrene resin, vinyl acetate resin, polyester resin, polyethylene resin, polyamide resin, rubber, acrylic resin, phenolic resin, epoxy resin, polyimide resin, carbamate resin, melamine resin, alkyd resin, and ABF resin. The base layers that can meet the carrier function are all within the requirements of this scheme and are not listed in detail here. Exemplarily, the film layer is selected from modified epoxy resin, modified acrylic resin, polyethylene terephthalate, polybutylene terephthalate, polyethylene, polyethylene naphthalate, polystyrene, polyvinyl chloride, polysulfone, polyphenylene sulfide, polyetheretherketone, polyphenylene ether, polytetrafluoroethylene, liquid crystal polymer, polyoxadiazole, epoxy glass cloth, and BT resin. Other base layers that can meet the performance requirements are within the requirements of this scheme and are not listed in detail here.

[0044] In addition, the electromagnetic shielding film of the present invention contains an adhesive layer, and an adhesive layer is laminated on the surface of the first shielding layer 1 or the second shielding layer 3 away from the base layer. Preferably, the adhesive layer includes at least one of polyvinyl acetate, polyester, polyethylene, polypropylene, polyamide, rubber, acrylic, phenolic resin, epoxy resin, polyimide, urethane resin, melamine resin, alkyd resin, ABF and other resins. The adhesive layer may or may not contain conductive particles. Among them, the overall thickness of the electromagnetic shielding film in the present invention is 5-25 microns.

[0045] The various properties of the electromagnetic shielding film were tested respectively using specific examples. The parameters and test results of the electromagnetic shielding film are specifically shown in Table 1.

[0046] Test Example 1

[0047] An electromagnetic shielding film comprises a base layer, a first shielding layer, a flexible conductive adhesive layer, a second shielding layer and an adhesive layer which are stacked in sequence, the elastic modulus of the flexible conductive adhesive layer is 80 MPa, the content of conductive particles is 8 wt%, the first shielding layer and the second shielding layer are made of copper, the overall average thickness of the electromagnetic shielding film is 12 microns, the average thickness of the first shielding layer is 0.9 microns, and the average thickness of the second shielding layer is 2.0 microns.

[0048] Test Example 2

[0049] The other conditions of this test example are the same as those of test example 1, except that the elastic modulus of the flexible conductive adhesive layer is 120 MPa.

[0050] Test Example 3

[0051] The other conditions of this test example are the same as those of test example 1, except that the elastic modulus of the flexible conductive adhesive layer is 100 MPa.

[0052] Test Example 4

[0053] The other conditions of this test example are the same as those of the test example 3, except that the number of spherical conductive particles accounts for 80%.

[0054] Test Example 5

[0055] The other conditions of this test example are the same as those of test example 4, except that the average thickness H of the flexible conductive adhesive layer and the maximum thickness H of the flake conductive particles 片 The maximum height D of the spherical conductive particles satisfies: D<H<3H 片 +D,H 片 <D.

[0056] Test Example 6

[0057] An electromagnetic shielding film comprises a base layer, a first shielding layer and an adhesive layer which are stacked in sequence, wherein the thickness of the first shielding layer is the same as that of test example 1.

[0058] Test Example 7

[0059] The other conditions of this test example are the same as those of test example 1, except that the elastic modulus of the flexible conductive adhesive layer is 130 MPa.

[0060] Table 1

[0061] Shielding effectiveness test / DB Folding resistance test / times Test Example 1 Greater than 63 Greater than 9200 Test Example 2 Greater than 63 Greater than 9200 Test Example 3 Greater than 63 Greater than 9200 Test Example 4 Greater than 63 Greater than 9200 Test Example 5 Greater than 63 More than 9500 Test Example 6 Approx. 52 Approx. 8,200 Test Example 7 Greater than 63 Approx. 7,400

[0062] It can be seen from Table 1 that when the total elongation at break of the electromagnetic shielding film is 80-120Mpa, the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film have good bending resistance and still have high shielding effectiveness after a high step difference, with the shielding effectiveness reaching above 63DB.

[0063] It should be noted that in order to improve the accuracy of the test results, each set of data is tested multiple times, and the multiple test results are combined to obtain the final test result.

[0064] The test method for the bending resistance of the electromagnetic shielding film is as follows: the bending resistance is to attach two electromagnetic shielding films of the same model to be tested to the two surfaces of the bending plate (the bending plate contains circuits) and press them (pre-pressing time 10 seconds, molding time 180 seconds, molding pressure 120kg, pressing temperature 185°C); bake and cure after pressing (baking temperature 160°C, baking time 90min); the strip width is 1.5cm, the bending conditions are: R angle 0.8mm, speed 60 rpm, angle ±135 degrees, load 500g, when the resistance of the bending circuit changes by more than 10%, stop the test. The shielding effectiveness of the electromagnetic shielding film is tested in accordance with GB / T30142-2013.

[0065] It can be seen from the above table that the electromagnetic shielding film provided by the embodiment of the present invention has good electromagnetic shielding effectiveness, and the bending resistance of the electromagnetic shielding film itself or the circuit board or flexible board containing the electromagnetic shielding film is greatly improved.

[0066] In order to solve the same technical problem, an embodiment of the present invention further provides a circuit board, which includes the electromagnetic shielding film as described in any of the above embodiments.

[0067] In the embodiment of the present invention, please refer to Figure 2 The circuit board includes an adhesive layer 4, a circuit board body 5 and an electromagnetic shielding film as described in any of the above embodiments. The electromagnetic shielding film is pressed against the circuit board body 5 through the adhesive layer 4 and is electrically connected to the ground layer of the circuit board body 5, thereby ensuring that the first shielding layer 1 and the second shielding layer 3 are connected to the ground layer of the circuit board body 5, thereby achieving the goal of introducing interference charges in the first shielding layer 1 and the second shielding layer 3 into the ground, avoiding the accumulation of interference charges to form an interference source that affects the normal operation of the circuit board.

[0068] Preferably, the circuit board body 5 is one of a flexible single-sided board, a flexible double-sided board, a flexible multilayer board, and a rigid-flexible board. It is worth noting that the circuit board body 5 is not limited to the above specific types and can be set according to actual conditions.

[0069] Compared with the prior art, the circuit board provided in the embodiment of the present invention includes an electromagnetic shielding film, which includes a first shielding layer 1, a flexible conductive adhesive layer 2 and a second shielding layer 3 stacked in sequence. A flexible conductive adhesive layer 2 is arranged between the first shielding layer 1 and the second shielding layer 3, which effectively increases the bending resistance of the electromagnetic shielding film, effectively weakens the interference signal, and improves the shielding performance. The elastic modulus of the flexible conductive adhesive layer 2 is set between 10 MPa and 20 MPa, and the elastic modulus of the flexible conductive adhesive layer 2 is limited within a reasonable range, so that the bending resistance of the electromagnetic shielding film is better improved, and it is suitable for products that require long-term and high-frequency folding or opening and closing. The electromagnetic shielding film in the present invention still has a high shielding effectiveness after a high step difference, and the shielding effectiveness can reach more than 60DB. On the basis of ensuring the shielding effectiveness of the electromagnetic shielding film, the bending resistance of the electromagnetic shielding film is improved.

[0070] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An electromagnetic shielding film, characterized in that: The electromagnetic shielding film comprises a first shielding layer, a flexible conductive adhesive layer and a second shielding layer. The first shielding layer, the flexible conductive adhesive layer and the second shielding layer are stacked in sequence. The elastic modulus of the flexible conductive adhesive layer is 80-120 MPa.

2. The electromagnetic shielding film according to claim 1, wherein In the flexible conductive adhesive layer, the weight content of the conductive particles is 1wt%-40wt%.

3. The electromagnetic shielding film according to claim 2, wherein: The conductive particles are at least one of gold, silver, copper, nickel, iron and silver-coated copper.

4. The electromagnetic shielding film according to claim 1, wherein The conductive particles in the flexible conductive adhesive layer are in at least one of a spherical shape, a flake shape, a star shape, a dendrite shape, and a cone shape.

5. The electromagnetic shielding film according to claim 1, wherein The average thickness of the flexible conductive adhesive layer is 0.25-6 microns.

6. The electromagnetic shielding film according to claim 5, characterized in that Among the conductive particles in the flexible conductive adhesive layer, the number of spherical conductive particles accounts for more than 60%.

7. The electromagnetic shielding film according to claim 1, wherein The conductive particles of the flexible conductive adhesive layer include silver-coated copper conductive particles. The silver-coated copper conductive particles have copper particles as cores, and the surfaces of the copper particles contain a silver layer of 1-50 nanometers.

8. The electromagnetic shielding film according to claim 1, wherein The conductive particles of the flexible conductive adhesive layer include at least one of flake-shaped conductive particles and spherical conductive particles. The average thickness H of the flexible conductive adhesive layer and the maximum thickness H of the flake-shaped conductive particles are 片 The maximum height D of the spherical conductive particles satisfies: D<H<3H 片 +D,H 片 <D.

9. The electromagnetic shielding film according to claim 7 or 8, characterized in that The resin of the flexible conductive adhesive layer is at least one of polyurethane, polyester, alkyd resin, epoxy resin, acrylic resin, polyimide, polystyrene, polyvinyl acetate, polyethylene, polypropylene, polyamide, rubber, phenolic resin, urethane resin, alkyd resin and ABF resin.

10. A circuit board, characterized in that: The circuit board includes the electromagnetic shielding film according to any one of claims 1 to 9.

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