Electromagnetic shielding film and circuit board

Abstract

The invention discloses an electromagnetic shielding film and a circuit board, the electromagnetic shielding film comprises a shielding layer, the shielding layer is provided with a plurality of holes, and the residual rate Y of the shielding layer and the elongation E of the electromagnetic shielding film meet the following relation: Y = AE + B, wherein the residual rate Y is the weight ratio between the shielding layer after opening and the shielding layer before opening; the elongation E is the ratio of the maximum elongation to the initial length of the electromagnetic shielding film; a and B are constants, A ranges from-25 to-15, and B ranges from 1 to 3; the relational expression calculation is dimensionless. According to the invention, the residual rate of the shielding layer is restrained by using the elongation rate of the electromagnetic shielding film, and the residual rate of the shielding layer is prevented from being too large or too small, so that the electromagnetic shielding film has certain deformation capability when covering the circuit board substrate; water vapor on the surface of the circuit board can be effectively discharged through the holes in the shielding layer, and the short circuit probability of the circuit board is reduced.

Description

Technical Field

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

[0002] As electronic products gradually develop towards miniaturization, lightness, and high-density assembly, flexible circuit boards are widely used in industries such as mobile phones, liquid crystal displays, communications, and aerospace. Among them, functional flexible circuit boards dominate the flexible circuit board market, and electromagnetic interference shielding (EMI shielding) is an important indicator for evaluating the performance of functional flexible circuit boards. However, driven by the rapid high-frequency and high-speed trend of internal components of mobile phones and other communication equipment, the problems of electromagnetic interference, signal attenuation, insertion loss, and jitter of the internal components of electronic equipment are becoming increasingly serious.

[0003] In the prior art, the electromagnetic shielding film laminated on the circuit board usually includes a shielding layer and an adhesive film layer. When performing electromagnetic shielding, the shielding layer is first connected to the ground layer of the circuit board through the adhesive film layer, and then the interference charge is introduced into the ground layer of the circuit board, thereby achieving shielding. However, currently, after the electromagnetic shielding film is laminated on the circuit board substrate, it is easy to affect the reliability of the circuit board, such as the occurrence of short circuit problems between circuits, which seriously affects the use quality of the circuit board. Summary of the invention

[0004] The present invention provides an electromagnetic shielding film and a circuit board to solve the technical problem that a circuit board short circuit easily occurs after the existing electromagnetic shielding film is pressed onto a circuit board substrate, and can effectively improve the use quality of the circuit board.

[0005] In order to solve the above technical problems, a first aspect of an embodiment of the present invention provides an electromagnetic shielding film, including a shielding layer, wherein a plurality of holes are formed on the shielding layer, and a residual rate Y of the shielding layer and an elongation rate E of the electromagnetic shielding film satisfy the following relationship: Y=AE+B;

[0006] Wherein, the residual rate Y is the weight ratio between the shielding layer after the opening and the shielding layer before the opening;

[0007] The elongation E is the ratio of the maximum elongation of the electromagnetic shielding film to its initial length;

[0008] A and B are both constants, the value range of A is -25 to -15, and the value range of B is 1 to 3; the above relationship is dimensionless.

[0009] As a preferred solution, the range of the residual rate Y is 40% to 80%, and the range of the elongation E is 5% to 20%.

[0010] As a preferred solution, the thickness D of the shielding layer is 0.3 μm to 3.5 μm.

[0011] As a preferred solution, the elastic modulus of the electromagnetic shielding film is 1500MPa to 3000MPa.

[0012] As a preferred solution, the shape of the hole includes a regular shape and / or an irregular shape.

[0013] As a preferred solution, it also includes an adhesive film layer, and the adhesive film layer and the shielding layer are stacked.

[0014] As a preferred solution, a protruding structure is provided on one side of the shielding layer close to the adhesive film layer, and the adhesive film layer includes an adhesive layer that does not contain conductive particles.

[0015] As a preferred solution, a side of the shielding layer close to the adhesive film layer is a flat surface, and the adhesive film layer includes an adhesive layer containing conductive particles.

[0016] As a preferred solution, it also includes an insulating layer, which is arranged on a surface of the shielding layer on a side away from the adhesive film layer.

[0017] A second aspect of an embodiment of the present invention provides a circuit board, comprising a circuit board substrate and an electromagnetic shielding film as described in any one of the first aspects; the electromagnetic shielding film is pressed together with the circuit board substrate.

[0018] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0019] (1) By opening a plurality of holes on the shielding layer, the air permeability of the circuit board can be increased after the electromagnetic shielding film is pressed onto the circuit board substrate, so that the water vapor on the surface of the circuit board can be discharged through the holes on the shielding layer, thereby reducing the moisture accumulated on the surface of the circuit board and significantly reducing the probability of short circuit on the circuit board.

[0020] (2) By limiting the constraint relationship between the residual rate of the shielding layer and the elongation rate of the electromagnetic shielding film, the elongation rate of the electromagnetic shielding film can be used to constrain the residual rate of the shielding layer, thereby preventing the residual rate of the shielding layer from being too large or too small. This ensures that the electromagnetic shielding film has a certain deformation ability when covering the circuit board substrate, while ensuring that the water vapor on the surface of the circuit board can be effectively discharged through the holes in the shielding layer, thereby reducing the probability of short circuit in the circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic structural diagram of a first electromagnetic shielding film provided by an embodiment of the present invention;

[0022] Figure 2is an electron microscope image of an opening on the surface of the shielding layer in an embodiment of the present invention;

[0023] Figure 3 is a schematic diagram of the fitting relationship between the elongation of the electromagnetic shielding film and the residual rate of the shielding layer when the thickness of the shielding layer is 3.5 μm in an embodiment of the present invention;

[0024] Figure 4 is a schematic diagram of the fitting relationship between the elongation of the electromagnetic shielding film and the residual rate of the shielding layer when the thickness of the shielding layer is 0.3 μm in an embodiment of the present invention;

[0025] Figure 5 is a schematic structural diagram of a second electromagnetic shielding film provided by an embodiment of the present invention;

[0026] Figure 6 is a schematic structural diagram of a third electromagnetic shielding film provided by an embodiment of the present invention;

[0027] Figure 7 is a schematic structural diagram of a fourth electromagnetic shielding film provided by an embodiment of the present invention;

[0028] Figure 8 is a schematic diagram of the fitting relationship between the elongation of the electromagnetic shielding film and the residual rate of the shielding layer in Examples 1 to 5 of the present invention;

[0029] Among them, 100, electromagnetic shielding film; 101, shielding layer; 102, film layer; 103, insulating layer; 104, protruding structure; 105, hole. DETAILED DESCRIPTION

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] See also Figure 1 According to a first aspect of an embodiment of the present invention, an electromagnetic shielding film 100 is provided, comprising a shielding layer 101, wherein a plurality of holes 105 are formed on the shielding layer 101, and a residual rate Y of the shielding layer 101 and an elongation rate E of the electromagnetic shielding film 100 satisfy the following relationship: Y=AE+B;

[0035] The residual rate Y is the weight ratio of the shielding layer 101 after the opening to the shielding layer 101 before the opening;

[0036] The elongation E is the ratio of the maximum elongation of the electromagnetic shielding film 100 to its initial length;

[0037] A and B are both constants, the value range of A is -25 to -15, and the value range of B is 1 to 3; the above relationship is dimensionless.

[0038] Specifically, after the electromagnetic shielding film 100 is pressed onto the circuit board substrate, the adhesive film layer 102 and the shielding layer 101 on the circuit board surface have a certain degree of sparseness, that is, there are small gaps on the adhesive film layer 102 and the shielding layer 101, so that the water vapor accumulated on the circuit board surface during use can be slowly discharged through the shielding layer 101, and in this embodiment, a plurality of holes 105 are opened on the shielding layer 101, such as Figure 2As shown, after the electromagnetic shielding film 100 is pressed onto the circuit board, water vapor on the surface of the circuit board can be discharged through the holes 105 on the shielding layer 101, which better reduces the moisture accumulated on the surface of the circuit board, reduces the relative humidity on the surface of the circuit board, and effectively avoids short circuits between copper circuits.

[0039] Furthermore, since the shapes of the holes 105 opened on the shielding layer 101 include different regular shapes and / or irregular shapes, and their areas are difficult to measure accurately, this embodiment uses the ratio between the weight of the shielding layer 101 after the holes are opened and the weight of the shielding layer 101 before the holes are opened, i.e., the residual rate, to characterize the volume occupied by the opening of the holes 105. At the same time, the elongation of the electromagnetic shielding film 100 is one of the important performance indicators of the electromagnetic shielding film 100. The elongation reflects the ability of the material to undergo plastic deformation without breaking when subjected to external forces. In this embodiment, the elongation is the ratio of the maximum elongation of the electromagnetic shielding film 100 when it is stretched to break to its initial length. In order to ensure that the electromagnetic shielding film 100 has a certain deformation ability when covered on the circuit board substrate, the electromagnetic shielding film 100 needs to have a certain elongation. Since the volume of the openings on the shielding layer 101 will affect the overall elongation of the electromagnetic shielding film 100, specifically, the smaller the residual rate of the shielding layer 101, the higher the elongation of the electromagnetic shielding film 100. In order to ensure that the elongation of the electromagnetic shielding layer 101 will not be greatly affected after the openings are made on the shielding layer 101, this embodiment stipulates that the residual rate of the shielding layer 101 and the elongation of the electromagnetic shielding film 100 satisfy the constraint relationship: Y=AE+B, thereby utilizing the elongation of the electromagnetic shielding film 100 to constrain the residual rate of the shielding layer 101, ensuring that the elongation of the electromagnetic shielding film 100 is within a suitable range while the residual rate of the shielding layer 101 is not too large or too small, thereby ensuring that the electromagnetic shielding film 100 has a certain deformation ability when covered on the circuit board substrate, while ensuring that the water vapor on the surface of the circuit board can be effectively discharged through the holes 105 on the shielding layer 101, thereby reducing the probability of short circuit on the circuit board.

[0040] This embodiment is based on a certain range of residual rate and elongation rate to determine the value range of the two constants in the above constraint relationship expression, that is, the value range of A is -25 to -15, and the value range of B is 1 to 3. For example, A can be -25, -24.3, -22.7, -21, -20.4, -19.6, -18, -17.8, -17.5, -16.9, -16, -15.5, -15, etc., and B can be 1, 1.2, 1.4, 1.6, 1.7, 1.9, 2, 2.1, 2.3, 2.5, 2.7, 2.9, 3, etc. This embodiment does not make specific limitations here, so as to determine the constraint relationship to ensure that within the more preferred elongation range of the electromagnetic shielding film 100, the residual rate of the shielding layer 101 is also within a more preferred range.

[0041] As one of the preferred embodiments, when the thickness of the shielding layer 101 is 3.5 μm, the fitting curve of the elongation of the electromagnetic shielding film 100 and the residual rate of the shielding layer 101 is as follows: Figure 3 As shown, the value of A is -19.515, the value of B is 1.8686, and the fitting coefficient R 2 is 0.9823. It can be understood that the fitting coefficient R 2 The closer it is to 1, the closer the fitted curve is to the actual situation. It can be seen that the value of A is in the preferred range of this embodiment: -25 to -15, and the value of B is also in the preferred range of this embodiment: 1 to 3, and within the preferred elongation range of the electromagnetic shielding film 100, it is ensured that the residual rate of the shielding layer 101 is also in a preferred range, thereby ensuring that the electromagnetic shielding film 100 has a certain deformation ability when covered on the circuit board substrate, while ensuring that the water vapor on the surface of the circuit board can be effectively discharged through the holes 105 on the shielding layer 101 to reduce the probability of short circuits in the circuit board, thereby improving the quality of the circuit board.

[0042] As another preferred embodiment, when the thickness of the shielding layer 101 is 0.3 μm, the fitting curve of the elongation of the electromagnetic shielding film 100 and the residual rate of the shielding layer 101 is as follows: Figure 4 As shown, the value of A is -21.491, the value of B is 1.4914, and the fitting coefficient R 2It is 0.9814. It can be seen that the value of A is in the preferred range of this embodiment: -25 to -15, and the value of B is also in the preferred range of this embodiment: 1 to 3, and within the preferred elongation range of the electromagnetic shielding film 100, it is ensured that the residual rate of the shielding layer 101 is also in a preferred range, so that while ensuring that the electromagnetic shielding film 100 has a certain deformation ability when covering the circuit board substrate, it is ensured that the water vapor on the surface of the circuit board can be effectively discharged through the holes 105 on the shielding layer 101 to reduce the probability of short circuit of the circuit board, thereby improving the use quality of the circuit board.

[0043] As a preferred solution, the range of the residual rate Y is 40% to 80%, and the range of the elongation E is 5% to 20%.

[0044] In this embodiment, the residual rate Y of the shielding layer 101 is preferably in the range of 40% to 80%. For example, the residual rate Y can be 40%, 42%, 45%, 47%, 50%, 52%, 54%, 56%, 59%, 61%, 64%, 65%, 67%, 69%, 71%, 73%, 75%, 77%, 79%, 80%, etc., which is not specifically limited in this embodiment. Within this residual rate range, it can be ensured that the volume occupied by the opening of the hole 105 will not be too small, that is, the residual rate Y is less than or equal to 80%, so as to ensure that the hole 105 on the shielding layer 101 accounts for a large proportion and ensure the exhaust efficiency of the circuit board surface. At the same time, it can be ensured that the volume occupied by the opening of the hole 105 will not be too large, that is, the residual rate Y is greater than or equal to 40%, so as to ensure the shielding effectiveness of the shielding layer 101.

[0045] In addition, the elongation E of the electromagnetic shielding film 100 is preferably in the range of 5% to 20%. For example, the elongation E can be 5%, 6%, 8%, 9%, 11%, 12%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., which is not specifically limited in this embodiment. Within this elongation range, the electromagnetic shielding film 100 can be prevented from being easily broken due to too small elongation when covering the circuit board substrate, so that the electromagnetic shielding film 100 has a certain deformation ability. At the same time, under the constraint relationship between the residual rate of the shielding layer 101 and the elongation of the electromagnetic shielding film 100, the residual rate Y of the shielding layer 101 can be constrained within the range of 40% to 80%, ensuring that the shielding layer 101 has a certain open pore volume to achieve the purpose of effectively discharging water vapor.

[0046] As a preferred solution, the thickness D of the shielding layer 101 is 0.3 μm to 3.5 μm.

[0047] Specifically, the thickness of the shielding layer 101 will affect the shielding effectiveness of the electromagnetic shielding film 100. If the thickness of the shielding layer 101 is too thin, the shielding effectiveness of the electromagnetic shielding film 100 will be low. However, if the thickness of the shielding layer 101 is too thick, the overall thickness of the electromagnetic shielding film 100 will be too large. In the present embodiment, the thickness D of the shielding layer 101 is further limited to 0.3μm to 3.5μm. For example, the thickness D of the shielding layer 101 can be 0.3μm, 0.5μm, 0.7μm, 0.9μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.7μm, 1.9μm, 2.1μm, 2.3μm, 2.5μm, 2.7μm, 3.1μm, 3.3μm, 3.4μm, 3.5μm, etc. The present embodiment does not make any specific limitation here, so as to ensure that the thickness of the shielding layer 101 will not be too thin, resulting in low shielding effectiveness of the electromagnetic shielding film 100, nor will it be too thick, resulting in excessive overall thickness of the electromagnetic shielding film 100.

[0048] As a preferred solution, the elastic modulus of the electromagnetic shielding film 100 is 1500 MPa to 3000 MPa.

[0049] It is worth noting that the elastic modulus is a physical quantity that measures the material's ability to resist elastic deformation when subjected to external forces. Specifically, the elastic modulus describes the ratio of stress to strain of a material under a unidirectional stress state. For the electromagnetic shielding film 100, the larger its elastic modulus, the smaller the elastic deformation it produces under the same stress, that is, the stronger the rigidity of the material. Since the elastic modulus is directly related to the material's ability to resist deformation, a higher elastic modulus also means that the electromagnetic shielding film 100 has better durability and fatigue resistance, and can maintain better shielding effect and stability during long-term use. However, an excessively high elastic modulus also makes the electromagnetic shielding film 100 more difficult to bend, cut or fit onto an irregular surface. In situations where frequent bending or folding is required, an electromagnetic shielding film 100 with an excessively high elastic modulus may produce stress concentration at the bend, causing material fatigue or even fracture. At the same time, the electromagnetic shielding film 100 with too low elastic modulus is relatively soft and easy to deform, but in actual application, it may cause the electromagnetic shielding film 100 to be unable to maintain a stable shape and position, thereby changing the contact state between it and the shielded object. If the contact is not tight or there is a gap, it may cause the leakage of electromagnetic waves, indirectly affecting the shielding effect. In addition, materials with too low elastic modulus often have lower wear and tear resistance. During long-term use, the electromagnetic shielding film 100 with too low elastic modulus may lose its original shielding effect due to wear or tear. Therefore, in this embodiment, the elastic modulus of the electromagnetic shielding film 100 is limited to 1500MPa to 3000MPa. For example, the elastic modulus of the electromagnetic shielding film 100 can be 1500MPa, 1650MPa, 1700MPa, 1742MPa, 1785MPa, 1896MPa, 1923MPa, 2014MPa, 2100MPa, 2250MPa, 2300MPa, 2471MPa, 2555MPa, 2700MPa. Pa, 2830MPa, 2900MPa, 2966MPa, 3000MPa, etc., which are not specifically limited in this embodiment. Therefore, during the use of the electromagnetic shielding film 100, the electromagnetic shielding film 100 can maintain a good shielding effect and stability, avoid stress concentration due to too high elastic modulus, effectively avoid the electromagnetic shielding film 100 from breaking, and avoid deformation due to too low elastic modulus, so that the electromagnetic shielding film 100 can maintain a stable shape and position.

[0050] As a preferred solution, the shape of the hole 105 includes a regular shape and / or an irregular shape.

[0051] It is worth noting that the present embodiment does not specifically limit the shape of the hole 105 on the shielding layer 101, and the shape of the hole 105 may include different regular shapes, different irregular shapes, or different regular shapes and irregular shapes at the same time. Further, the shape of the hole 105 on the shielding layer 101 is preferably a regular shape, so as to facilitate the production of the electromagnetic shielding film 100, and the regular geometric shape facilitates the measurement of the maximum width of the hole 105 and the hole spacing.

[0052] In one of the optional embodiments, the holes 105 on the shielding layer 101 include blind holes and / or through holes, that is, the holes 105 on the shielding layer 101 may all be blind holes, may all be through holes, or may include both blind holes and through holes. Preferably, the holes 105 on the shielding layer 101 are all set as through holes. If the holes 105 on the shielding layer 101 include blind holes, the bottom surface of the blind holes is made of a material with low density, such as copper, which can be achieved by sputtering a thin layer of copper on the blind holes. Since the bottom surface of the blind holes has a certain degree of sparseness, the water vapor accumulated on the surface of the circuit board can be discharged through the bottom surface of the blind holes. Preferably, the sealing surface of the blind holes is arranged on the side away from the circuit board substrate, and the opening end thereof is arranged on the side close to the circuit board substrate, so as to effectively enhance the water vapor discharge effect.

[0053] As a preferred solution, the shape of the hole 105 includes at least one of a circle, an ellipse, a rectangle, a rhombus, a triangle, and a regular polygon.

[0054] Specifically, the present embodiment limits the shape of the hole 105 to a regular geometric figure, thereby facilitating the production of the electromagnetic shielding film 100, and the regular geometric figure facilitates the measurement of the maximum width and the hole spacing of the hole 105. It is worth noting that the shape of the hole 105 in the present embodiment can be one of a circle, an ellipse, a rectangle, a rhombus, a triangle, and a regular polygon, and can also include two or more of these geometric figures. For example, the shape of the hole 105 on the shielding layer 101 can be a circle, an ellipse, a rectangle, a rhombus, a triangle, or a regular polygon, and can also include a circle and an ellipse, or include a rectangle, a rhombus and a circle, or include a circle, a triangle and a regular polygon, or include a circle, an ellipse, a rectangle, a rhombus, a triangle, and a regular polygon at the same time. This embodiment will not be repeated here.

[0055] See also Figure 5 As a preferred solution, it further includes a film layer 102 , and the film layer 102 and the shielding layer 101 are stacked.

[0056] Specifically, the adhesive film layer 102 in this embodiment is arranged between the shielding layer 101 and the circuit board substrate. The material of the adhesive film layer 102 is generally a polymer matrix, including polyethylene terephthalate, polyethylene, polyvinyl alcohol, cycloolefin copolymer, etc. These materials have good flexibility, transparency and processing performance, and are ideal substrates for preparing flexible transparent electromagnetic shielding film 100.

[0057] As a preferred solution, a protruding structure 104 is provided on one side of the shielding layer 101 close to the adhesive film layer 102 , and the adhesive film layer 102 includes an adhesive layer that does not contain conductive particles.

[0058] Specifically, Figure 6 As shown, in this embodiment, a protruding structure 104 is provided on one side of the shielding layer 101 close to the adhesive film layer 102. In order to ensure that the electromagnetic shielding film 100 can be tightly bonded to the circuit board substrate after being pressed together, the adhesive film layer 102 further includes an adhesive layer that does not contain conductive particles. When the electromagnetic shielding film 100 is pressed together with the circuit board substrate, the protruding structure 104 on the shielding layer 101 can pierce the adhesive film layer 102 so that the shielding layer 101 can be connected to the ground layer of the circuit board substrate, thereby ensuring that the interference charge is normally discharged and realizing the electromagnetic shielding function.

[0059] As one of the optional embodiments, the protruding structure 104 can extend into the adhesive film layer 102, so that the protruding structure 104 can more easily pierce the adhesive film layer 102 during the process of laminating the electromagnetic shielding film 100 with the circuit board substrate. Alternatively, the protruding structure 104 can also pierce the adhesive film layer 102, so that during the process of laminating the electromagnetic shielding film 100 with the circuit board substrate, the protruding structure 104 can be directly inserted into the ground layer of the circuit board substrate. Of course, the protruding structure 104 can also not extend into the adhesive film layer 102 but be covered by the adhesive film layer 102.

[0060] It is worth noting that the adhesive layer included in the film layer 102 in this embodiment is achieved by adding an adhesive to the film layer 102. Commonly used adhesives include silicone, silicone fluoride, EPDM (Ethylene Propylene Diene Monomer), fluorocarbon-silicon fluoride, etc. These adhesives have good adhesion and stability.

[0061] It is worth noting that the raised structure 104 in this embodiment is formed by sputtering or electroplating when the shielding layer 101 has no holes. After the raised structure 104 is formed, holes are opened on the shielding layer 101. The positions of the holes are preferably located at positions with fewer raised structures 104, so as to ensure as much as possible that after the holes are opened, the puncture grounding performance of the metal shielding film and the circuit board substrate is not affected when pressed together, thereby avoiding affecting the shielding effectiveness.

[0062] As a preferred solution, the side of the shielding layer 101 close to the adhesive film layer 102 is a flat surface, and the adhesive film layer 102 includes an adhesive layer containing conductive particles.

[0063] Specifically, in this embodiment, the side of the shielding layer 101 close to the film layer 102 is a flat surface, so that in this embodiment, the film layer 102 includes an adhesive layer containing conductive particles. Therefore, in the process of pressing the electromagnetic shielding film 100 and the circuit board substrate, because the force is mutual, when the shielding layer 101 continues to approach the film layer 102 under the action of pressure, the circuit board substrate also approaches the film layer 102 under the action of pressure, so that the film layer 102 is squeezed by two forces in opposite directions, and then the shielding layer 101 can be connected to the ground layer of the circuit board substrate through the conductive particles in the film layer 102, thereby ensuring that the interference charge is normally discharged and realizing the electromagnetic shielding function.

[0064] As one optional embodiment, the conductive particles include graphene nanosheets, carbon nanotubes, ferroferric oxide, silver nanowires, pure silver, silver-plated copper, silver-plated aluminum, silver-plated nickel, etc. These conductive particles can significantly improve the conductivity and electromagnetic shielding effectiveness of the adhesive film layer 102. For example, silver nanowires are widely used in the preparation of the electromagnetic shielding film 100 due to their excellent conductivity and transparency.

[0065] As one of the optional embodiments, the conductive particles in this embodiment can be conductive particles separated from each other, or can be large-particle conductive particles formed by agglomeration; when the conductive particles are conductive particles separated from each other, the area of ​​electrical contact can be further increased, and the uniformity of electrical contact can be improved; and when the conductive particles are large-particle conductive particles formed by agglomeration, the piercing strength can be increased.

[0066] It is worth noting that, in order to firmly combine the conductive particles in the film layer 102, the adhesive layer included in the film layer 102 in this embodiment is achieved by adding an adhesive to the film layer 102. Commonly used adhesives include silicone, silicone fluoride, EPDM (Ethylene Propylene Diene Monomer), fluorocarbon-silicon fluoride, etc. These adhesives have good adhesion and stability, and can ensure the uniform distribution and long-term stability of the conductive particles in the film layer 102.

[0067] See also Figure 7 As a preferred solution, it further includes an insulating layer 103 , and the insulating layer 103 is disposed on a surface of the shielding layer 101 away from the adhesive film layer 102 .

[0068] It is worth mentioning that, since the insulating layer 103 has an isolation effect, arranging the insulating layer 103 on one side surface of the shielding layer 101 is helpful to ensure the shielding effectiveness of the shielding layer 101; in addition, the insulating layer 103 also has a protective effect to ensure that the shielding layer 101 is not scratched or damaged during use, thereby helping to maintain the high shielding effectiveness of the shielding layer 101.

[0069] The insulating layer 103 in this embodiment includes a PPS film layer, a PEN film layer, a polyester film layer, a polyimide film layer, a film layer formed after epoxy resin ink is cured, a film layer formed after polyurethane ink is cured, a film layer formed after modified acrylic resin is cured, or a film layer formed after polyimide resin is cured, etc. This embodiment is not specifically limited here.

[0070] A second aspect of the embodiments of the present invention provides a circuit board, comprising a circuit board substrate and the electromagnetic shielding film 100 as described in any embodiment of the first aspect; the electromagnetic shielding film 100 is pressed together with the circuit board substrate.

[0071] It is worth noting that the electromagnetic shielding film 100 in this embodiment is pressed against the circuit board substrate, and the ground layer of the circuit board substrate is connected to the shielding layer 101 in the electromagnetic shielding film 100, thereby ensuring that the interference charges are normally extracted.

[0072] The electromagnetic shielding film 100 and the circuit board provided by the embodiment of the present invention have the beneficial effects of at least one of the following:

[0073] (1) By opening a plurality of holes 105 on the shielding layer 101, the air permeability of the circuit board can be increased after the electromagnetic shielding film 100 is pressed onto the circuit board substrate, so that water vapor on the surface of the circuit board can be discharged through the holes 105 on the shielding layer 101, thereby reducing the moisture accumulated on the surface of the circuit board and significantly reducing the probability of a short circuit on the circuit board.

[0074] (2) By limiting the constraint relationship between the residual rate of the shielding layer 101 and the elongation rate of the electromagnetic shielding film 100, the elongation rate of the electromagnetic shielding film 100 can be used to constrain the residual rate of the shielding layer 101, thereby preventing the residual rate of the shielding layer 101 from being too large or too small. This ensures that the electromagnetic shielding film 100 has a certain deformation ability when covering the circuit board substrate, while ensuring that the water vapor on the surface of the circuit board can be effectively discharged through the holes 105 on the shielding layer 101, thereby reducing the probability of short circuit on the circuit board.

[0075] In order to demonstrate the beneficial effects of the electromagnetic shielding film and circuit board provided by the embodiments of the present invention, several embodiments and comparative examples are described below.

[0076] Example 1

[0077] An electromagnetic shielding film comprises a shielding layer, wherein the shielding layer is provided with a plurality of holes, the elongation E of the electromagnetic shielding film is 7%, the residual rate Y of the shielding layer is about 50%, the thickness of the shielding layer is 3.5 μm, and the elastic modulus of the electromagnetic shielding film is 1500 MPa.

[0078] Example 2

[0079] An electromagnetic shielding film comprises a shielding layer, wherein the shielding layer is provided with a plurality of holes, the elongation E of the electromagnetic shielding film is 6.5%, the residual rate Y of the shielding layer is about 60%, the thickness of the shielding layer is 3.5 μm, and the elastic modulus of the electromagnetic shielding film is 1750 MPa.

[0080] Example 3

[0081] An electromagnetic shielding film comprises a shielding layer, wherein the shielding layer is provided with a plurality of holes, the elongation E of the electromagnetic shielding film is 6%, the residual rate Y of the shielding layer is about 69%, the thickness of the shielding layer is 3.5 μm, and the elastic modulus of the electromagnetic shielding film is 2000 MPa.

[0082] Example 4

[0083] An electromagnetic shielding film comprises a shielding layer, a film layer and an insulating layer, wherein the film layer and the shielding layer are stacked, and the insulating layer is arranged on a side of the shielding layer away from the film layer. The side of the shielding layer close to the film layer is a flat surface, and the film layer comprises an adhesive layer containing conductive particles. The shielding layer is provided with a plurality of holes, the elongation E of the electromagnetic shielding film is 5.5%, the residual rate Y of the shielding layer is about 79%, the thickness of the shielding layer is 3.5 μm, and the elastic modulus of the electromagnetic shielding film is 2500 MPa.

[0084] Example 5

[0085] An electromagnetic shielding film comprises a shielding layer, a film layer and an insulating layer, wherein the film layer and the shielding layer are stacked, and the insulating layer is arranged on a side of the shielding layer away from the film layer. The side of the shielding layer close to the film layer is a flat surface, and the film layer comprises an adhesive layer containing conductive particles. The shielding layer is provided with a plurality of holes, the elongation E of the electromagnetic shielding film is 7.8%, the residual rate Y of the shielding layer is about 41%, the thickness of the shielding layer is 3.5 μm, and the elastic modulus of the electromagnetic shielding film is 3000 MPa.

[0086] Comparative Example 1

[0087] An electromagnetic shielding film comprises a shielding layer, a film layer and an insulating layer. The film layer and the shielding layer are stacked, the insulating layer is arranged on a side surface of the shielding layer away from the film layer, and no holes are opened on the shielding layer. The elongation E of the electromagnetic shielding film is 4%, the thickness of the shielding layer is 2μm, and the elastic modulus of the electromagnetic shielding film is 2000MPa.

[0088] The above embodiment and comparative example are used to detect whether a short circuit occurs during the use of the circuit board. The pressing method for covering the electromagnetic shielding film on the circuit board substrate is: at 185°C, 120kg / cm 2 The electromagnetic shielding film was pressed onto the circuit board substrate with a pressure of 3 minutes. The test environment of the circuit board after pressing was as follows: the test temperature was 75°C, the humidity was 90% RH, the SIR test voltage was 50V, the test time was 24 hours, and the judgment standard for circuit board short circuit was: insulation resistance <100MΩ was considered to be a short circuit. The test results are shown in Table 1 below.

[0089] Table 1 Circuit board short circuit situation

[0090] Detection object Elongation of electromagnetic shielding film Shielding layer residual rate Circuit board short circuit Example 1 7％ 50％ No short circuit Example 2 6.5％ 60％ No short circuit Example 3 6％ 69％ No short circuit Example 4 5.5％ 79％ No short circuit Example 5 7.8％ 41％ No short circuit Comparative Example 1 4％ 100％ Short circuit occurs

[0091] The data of Examples 1 to 5 in Table 1 are fitted to obtain the following equation: Figure 8 The constraint relationship shown is: Y = -16.753E + 1.697, R2 = 0.9861, wherein the shielding layer of Examples 1 to 5 is provided with a plurality of holes, and the values ​​of A and B in the above relationship are all within the ranges recorded in the embodiments of the present invention. In addition, the residual rate of the shielding layer, the elongation of the electromagnetic shielding film, and the thickness of the shielding layer in Examples 1 to 5 are all within the optimized ranges recorded in the embodiments of the present invention, and no short circuit occurs. In Comparative Example 1, since there are no holes in the shielding layer, although its elongation is within a more suitable range, water vapor gradually accumulates on the surface of the circuit board during use, resulting in a short circuit in the copper circuit etched on the circuit board.

[0092] Therefore, through the verification of the above-mentioned embodiments, it can be known that the present invention can effectively utilize the elongation of the electromagnetic shielding film to constrain the residual rate of the shielding layer, thereby avoiding the residual rate of the shielding layer being too large or too small, thereby ensuring that the electromagnetic shielding film has a certain deformation ability when covering the circuit board substrate, while ensuring that the water vapor on the surface of the circuit board can be effectively discharged through the holes in the shielding layer, thereby reducing the probability of short circuit in the circuit board and improving the quality of the circuit board.

[0093] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. An electromagnetic shielding film, characterized in that: It includes a shielding layer, a plurality of holes are formed on the shielding layer, and the residual rate Y of the shielding layer and the elongation rate E of the electromagnetic shielding film satisfy the following relationship: Y=AE+B; Wherein, the residual rate Y is the weight ratio between the shielding layer after the opening and the shielding layer before the opening; The elongation E is the ratio of the maximum elongation of the electromagnetic shielding film to its initial length; A and B are both constants, the value range of A is -25 to -15, and the value range of B is 1 to 3; the above relationship is dimensionless.

2. The electromagnetic shielding film according to claim 1, wherein The range of the residual rate Y is 40% to 80%, and the range of the elongation E is 5% to 20%.

3. The electromagnetic shielding film according to claim 1, wherein The thickness D of the shielding layer is 0.3 μm to 3.5 μm.

4. The electromagnetic shielding film according to any one of claims 1 to 3, characterized in that: The elastic modulus of the electromagnetic shielding film is 1500 MPa to 3000 MPa.

5. The electromagnetic shielding film according to any one of claims 1 to 3, characterized in that: The shape of the holes includes regular shape and / or irregular shape.

6. The electromagnetic shielding film according to any one of claims 1 to 3, characterized in that: It also includes a glue film layer, and the glue film layer and the shielding layer are stacked.

7. The electromagnetic shielding film according to claim 6, wherein A protruding structure is arranged on one side of the shielding layer close to the adhesive film layer, and the adhesive film layer includes an adhesive layer without conductive particles.

8. The electromagnetic shielding film according to claim 6, wherein The side of the shielding layer close to the adhesive film layer is a flat surface, and the adhesive film layer includes an adhesive layer containing conductive particles.

9. The electromagnetic shielding film according to claim 6, wherein: It also includes an insulating layer, which is arranged on a surface of the shielding layer on one side away from the adhesive film layer.

10. A circuit board, characterized in that: It comprises a circuit board substrate and the electromagnetic shielding film as claimed in any one of claims 1 to 9; the electromagnetic shielding film is pressed together with the circuit board substrate.

Images