Electromagnetic shielding film and circuit boards

Abstract

The present invention discloses an electromagnetic shielding film and a circuit board, wherein the electromagnetic shielding film comprises a shielding layer and an adhesive film layer; the adhesive film layer is provided with conductive particles and resin; the grounding resistance value of the electromagnetic shielding film after lamination and the conductive particles satisfy: y1≤3738.4x 2 ‑6947.9x+4354.7; y1 is the grounding resistance value of the electromagnetic shielding film after lamination, and x is the weight ratio of the conductive particles in the film layer, with a value of x ranging from 3% to 80%. By providing conductive particles in the film layer, when the electromagnetic shielding film is pressed onto the circuit board, the conductive particles can direct interference charges in the shielding layer into the circuit board ground layer, which is beneficial for improving the grounding performance of the electromagnetic shielding film. In addition, by fitting the relationship between the grounding resistance value of the electromagnetic shielding film after lamination and the weight ratio of the conductive particles in the film layer, it can be found that as the content of conductive particles in the film layer increases within a certain range, the grounding resistance value of the electromagnetic shielding film after lamination decreases, and the corresponding electromagnetic shielding film has better grounding performance.

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 rapid development of the electronics industry, electronic products are further developing towards miniaturization, lightweighting, and high-density assembly. This has greatly promoted the development of flexible circuit boards, thereby realizing the integration of component devices and wire connections. Flexible circuit boards are widely used in industries such as mobile phones, LCD displays, communications, and aerospace.

[0003] Driven by the international market, functional flexible circuit boards (FPCs) dominate the FPC market, and an important indicator for evaluating the performance of functional flexible circuit boards is electromagnetic interference shielding (EMI shielding). With the integration of functions in mobile phones and other communication devices, their internal components are rapidly becoming more high-frequency and high-speed. For example, in addition to the original audio transmission function, the camera function has become a necessary function in mobile phones. WLAN (Wireless Local Area Networks), GPS (Global Positioning System), and Internet access functions have become popular. Coupled with the integration of sensing components in the future, the trend of rapidly increasing components to higher frequencies and higher speeds is even more inevitable. Driven by high frequencies and high speeds, electromagnetic interference inside and outside components, signal attenuation during transmission, insertion loss, and jitter problems are becoming increasingly serious.

[0004] Currently, the electromagnetic shielding film commonly used in existing circuit boards includes an insulating layer, a shielding layer, and an adhesive film layer, which are stacked in sequence. The shielding layer has a rough surface on the side closest to the adhesive film. During use, the electromagnetic shielding film and the circuit board must be pressed together at high temperature. During the hot pressing process, the shielding layer penetrates the adhesive film layer through the rough surface, thereby electrically connecting with the ground layer of the circuit board, thereby directing interference charges into the ground layer of the circuit board, thereby achieving shielding. During the implementation of the present invention, the inventors discovered that the existing technology has the following technical problems: relying solely on the rough surface to penetrate the adhesive film layer is not effective, resulting in poor grounding performance of the electromagnetic shielding film. Summary of the Invention

[0005] The purpose of the embodiments of the present invention is to provide an electromagnetic shielding film and a circuit board, which are conducive to improving the grounding performance of the electromagnetic shielding film.

[0006] To achieve the above object, an embodiment of the present invention provides an electromagnetic shielding film, comprising a shielding layer and an adhesive film layer, wherein the adhesive film layer is provided with conductive particles and resin; the grounding resistance value of the electromagnetic shielding film after lamination and the conductive particles satisfy the following relationship: y1≤3738.4x 2 -6947.9x+4354.7; y1 is the grounding resistance value of the electromagnetic shielding film after lamination, x is the weight ratio of the conductive particles in the film layer, and the value of x is 3%-80%.

[0007] As an improvement to the above solution, in a direction perpendicular to the thickness of the electromagnetic shielding film, a distance D between two adjacent conductive particles satisfies: 0≤D≤100 μm.

[0008] As an improvement to the above solution, in the thickness direction of the electromagnetic shielding film, the distance d between two adjacent conductive particles satisfies: 0≤d≤10 μm.

[0009] As an improvement to the above solution, after the electromagnetic shielding film is pressed, at least 10% of the conductive particles are connected to a side of the adhesive film layer close to the shielding layer.

[0010] As an improvement to the above solution, after the electromagnetic shielding film is pressed, at least 10% of the conductive particles are connected to a side of the adhesive film layer away from the shielding layer.

[0011] As an improvement to the above solution, the surface of the conductive particles has a uniformly distributed spike structure.

[0012] As an improvement to the above solution, the grounding resistance value of the electromagnetic shielding film after curing and the conductive particles satisfy the following relationship: y2≤4537x 2 -8165.5x+5230.7; y2 is the grounding resistance value of the electromagnetic shielding film after curing, and x is the weight ratio of the conductive particles in the film layer.

[0013] As an improvement to the above solution, the grounding resistance value of the electromagnetic shielding film after tinning and the conductive particles satisfy the following relationship: y3≤5602.7x 2 -10495x+6736.2; y3 is the grounding resistance value of the electromagnetic shielding film after tinning, and x is the weight ratio of the conductive particles in the film layer.

[0014] As an improvement to the above solution, a surface of the shielding layer close to the adhesive film layer is a non-flat surface.

[0015] To achieve the above objectives, an embodiment of the present invention further provides a circuit board, comprising a circuit board body and the electromagnetic shielding film as described in any of the above embodiments; the electromagnetic shielding film is pressed together with the circuit board body.

[0016] Compared to the prior art, the electromagnetic shielding film and circuit board disclosed in the embodiments of the present invention include a shielding layer and an adhesive film layer, wherein the adhesive film layer is provided with conductive particles and resin. By providing the conductive particles in the adhesive film layer, when the electromagnetic shielding film is pressed onto the circuit board, the conductive particles can guide the interference charge in the shielding layer into the circuit board ground layer, thereby improving the grounding performance of the electromagnetic shielding film. In addition, the grounding resistance value of the electromagnetic shielding film after pressing and the conductive particles satisfy the following relationship: y1≤3738.4x 2 -6947.9x + 4354.7; y1 is the grounding resistance of the electromagnetic shielding film after lamination, and x is the weight ratio of the conductive particles in the film layer. By fitting the relationship between the grounding resistance of the electromagnetic shielding film after lamination and the weight ratio of the conductive particles in the film layer, it can be concluded that: as the content of the conductive particles in the film layer increases within a certain range, the grounding resistance of the electromagnetic shielding film after lamination decreases, and the corresponding electromagnetic shielding film has better grounding performance. When the weight ratio of the conductive particles in the film layer is within a certain range, the grounding resistance of the electromagnetic shielding film after lamination can be reduced, while also reducing the cost of the conductive particles. In addition, when the content of the conductive particles in the film layer is within a certain range, delamination will not occur during the lamination process, preventing cracking of the panel. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of a first electromagnetic shielding film provided by an embodiment of the present invention;

[0018] Figure 2 is a structural schematic diagram of a second electromagnetic shielding film provided by an embodiment of the present invention;

[0019] Figure 3 is a schematic structural diagram of a third electromagnetic shielding film provided by an embodiment of the present invention;

[0020] Figure 4 is a schematic structural diagram of a fourth electromagnetic shielding film provided by an embodiment of the present invention;

[0021] Figure 5 is a schematic structural diagram of a fifth electromagnetic shielding film provided by an embodiment of the present invention;

[0022] Figure 6 is a schematic structural diagram of a sixth electromagnetic shielding film provided by an embodiment of the present invention;

[0023] Figure 7 It is a structural schematic diagram of a circuit board provided by an embodiment of the present invention.

[0024] Among them, 1. Shielding layer; 2. Film layer; 3. Insulation layer; 4. Carrier layer; 5. Protective film layer; 6. Circuit board body; 21. Conductive particles. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0026] In the description of the specification and claims, it should be understood that the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention, rather than indicating or implying that the device or component 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 embodiments of the present invention.

[0027] Furthermore, the terms "first," "second," and so on, in the specification and claims, are used solely for descriptive purposes to distinguish between identical technical features and are not to be construed as indicating or implying relative importance or implicitly specifying the number of technical features being referenced, nor do they necessarily describe a sequential or chronological order. The terms are interchangeable where appropriate. Thus, a feature qualified as "first" or "second" may explicitly or implicitly include at least one of those features.

[0028] It is worth noting that, in the embodiment of the present invention, when the electromagnetic shielding film is applied to the circuit board, it needs to go through the following process operations: 1. Press the electromagnetic shielding film onto the circuit board and tear off the carrier film, pressing temperature: 185°C, pressing time: 10min, pressure: 120kg / cm 2 ; 2. Curing electromagnetic shielding film, curing temperature: 160℃, curing time: 2H; 3. Pressing thermosetting reinforcing adhesive, pressing temperature: 185℃, pressing time: 3min, pressure: 120kg / cm 2 4. Cure the reinforcing adhesive at 160°C for 1.5 hours. 5. Soldering at 270°C for 60 seconds. The above process parameters and steps are examples only. Users can adjust the parameters in actual applications.

[0029] See also Figure 1 An embodiment of the present invention provides an electromagnetic shielding film, comprising a shielding layer 1 and an adhesive film layer 2, wherein the adhesive film layer 2 is provided with conductive particles 21 and a resin; the grounding resistance value of the electromagnetic shielding film after lamination and the conductive particles 21 satisfy the following relationship: y1≤3738.4x 2-6947.9x+4354.7; y1 is the grounding resistance value of the electromagnetic shielding film after lamination, and x is the weight ratio of the conductive particles 21 in the film layer 2. When y1=3738.4x 2 When -6947.9x+4354.7, R 2 =0.9174, R 2 It is expressed as an evaluation index of the function fitting effect, R 2 The closer it is to 1, the better the function fitting effect is.

[0030] In an embodiment of the present invention, the shielding layer 1 acts as an electromagnetic shield, and the electromagnetic shielding film can be attached to the circuit board through the adhesive film layer 2. By providing conductive particles 21 in the adhesive film layer 2, when the electromagnetic shielding film is pressed onto the circuit board, the conductive particles 21 can introduce interference charges in the shielding layer 1 into the circuit board stratum, which is beneficial to improving the grounding performance of the electromagnetic shielding film. In addition, by fitting the relationship between the grounding resistance value of the electromagnetic shielding film after pressing and the content of the conductive particles 21 in the adhesive film layer 2, it can be obtained that: as the content of the conductive particles 21 in the adhesive film layer 2 increases within a certain range, the grounding resistance value of the electromagnetic shielding film after pressing is smaller, and the corresponding electromagnetic shielding film has better grounding performance.

[0031] In the embodiment of the present invention, the grounding resistance value of the electromagnetic shielding film after curing and the conductive particles 21 satisfy the following relationship: y2≤4537x 2 -8165.5x+5230.7; y2 is the grounding resistance value of the electromagnetic shielding film after curing, and x is the weight ratio of the conductive particles 21 in the film layer 2. When y2=4537x 2 When -8165.5x+5230.7, R 2 =0.9661.

[0032] For example, after the electromagnetic shielding film is pressed onto the circuit board, the circuit board with the electromagnetic shielding film pressed onto it needs to be cured. After curing, the above formula can be obtained by further fitting the grounding resistance value of the electromagnetic shielding film and the content of the conductive particles 21 in the adhesive film layer 2. By fitting the relationship between the grounding resistance value of the electromagnetic shielding film after pressing and the content of the conductive particles 21 in the adhesive film layer 2, it can be obtained that as the content of the conductive particles 21 in the adhesive film layer 2 increases within a certain range, the grounding resistance value of the electromagnetic shielding film after curing decreases, and the corresponding electromagnetic shielding film has better grounding performance.

[0033] In the embodiment of the present invention, the grounding resistance value of the electromagnetic shielding film after tinning and the conductive particles 21 satisfy the following relationship: y3≤5602.7x 2-10495x+6736.2; y3 is the grounding resistance value of the electromagnetic shielding film after tinning, and x is the weight ratio of the conductive particles 21 in the film layer 2. When y3=5602.7x 2 -10495x+6736.2, R 2 =0.8922.

[0034] For example, after the electromagnetic shielding film is pressed onto the circuit board, the circuit board, after pressing and fixing the electromagnetic shielding film, needs to be tinned. After tinning, the grounding resistance value of the electromagnetic shielding film and the content of the conductive particles 21 in the adhesive film layer 2 are further fitted to obtain the above formula. By fitting the relationship between the grounding resistance value of the electromagnetic shielding film after pressing and the content of the conductive particles 21 in the adhesive film layer 2, it can be obtained that as the content of the conductive particles 21 in the adhesive film layer 2 increases, the grounding resistance value of the electromagnetic shielding film after tinning decreases, and the corresponding electromagnetic shielding film has better grounding performance.

[0035] In the embodiment of the present invention, in a direction perpendicular to the thickness of the electromagnetic shielding film, a distance D between two adjacent conductive particles 21 satisfies: 0≤D≤100 μm.

[0036] For example, in a direction perpendicular to the thickness of the electromagnetic shielding film, the distance D between two adjacent conductive particles 21 can be 0 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc. When D = 0 μm, it indicates that the two adjacent conductive particles 21 are in contact with each other. In a direction perpendicular to the thickness of the electromagnetic shielding film, setting the distance D between two adjacent conductive particles 21 to satisfy the following: 0 ≤ D ≤ 100 μm can ensure that the conductive particles 21 are more evenly distributed in the adhesive film layer 2, and avoid the situation where many adjacent conductive particles 21 are too far apart and thus cannot contact each other when the electromagnetic shielding film is pressed onto the circuit board. This can improve the effective contact between the conductive particles 21 and the shielding layer 1, between the conductive particles 21, and between the conductive particles 21 and the circuit board ground layer, thereby improving the grounding performance of the electromagnetic shielding film. Furthermore, in the thickness direction perpendicular to the electromagnetic shielding film, the distance D between two adjacent conductive particles 21 is set to satisfy: 0≤D≤100μm, so that the conductive particles 21 are reasonably distributed in the film layer 2 and will not occupy too much of the glue-containing space of the film layer 2. The glue in the film layer 2 can be effectively accommodated by the side of the shielding layer 1 close to the film layer 2, and it is not easy for a large amount of glue to move to the edge of the circuit board, resulting in obvious glue overflow at the edge between the electromagnetic shielding film and the circuit board, thereby enabling the circuit board to have a good appearance after the shielding film is pressed.

[0037] Further, see Figure 2 , the conductive particles 21 exist in the adhesive film layer 2 in the form of a single layer. In the case where the thickness of the adhesive film layer 2 is relatively small, the conductive particles 21 may exist in the adhesive film layer 2 in the form of a single layer.

[0038] Furthermore, when the conductive particles 21 exist in the adhesive film layer 2 in the form of multiple layers, the distance d between two adjacent conductive particles 21 in the thickness direction of the electromagnetic shielding film satisfies: 0≤d≤10 μm.

[0039] For example, the distance d between two adjacent conductive particles 21 in the thickness direction of the electromagnetic shielding film can be 0 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. When d = 0 μm, the two adjacent conductive particles 21 are in contact with each other. The distance d between two adjacent conductive particles 21 in the thickness direction of the electromagnetic shielding film is set to satisfy the following: 0 ≤ d ≤ 10 μm. This ensures a more uniform distribution of the conductive particles 21 within the adhesive film layer 2, preventing many adjacent conductive particles 21 from being too far apart and thus unable to contact each other when the electromagnetic shielding film is pressed onto the circuit board. This improves the effective contact between the conductive particles 21 and the shielding layer 1, between the conductive particles 21, and between the conductive particles 21 and the circuit board ground layer, thereby enhancing the grounding performance of the electromagnetic shielding film. Furthermore, in the thickness direction of the electromagnetic shielding film, the distance d between two adjacent conductive particles 21 is set to satisfy: 0≤d≤10μm, so that the conductive particles 21 are reasonably distributed in the film layer 2 and will not occupy too much of the glue-containing space of the film layer 2. The glue in the film layer 2 can be effectively accommodated by the side of the shielding layer 1 close to the film layer 2, and it is not easy for a large amount of glue to move to the edge of the circuit board, resulting in obvious glue overflow at the edge between the electromagnetic shielding film and the circuit board, thereby enabling the circuit board after the shielding film is pressed together to have a good appearance.

[0040] In the embodiment of the present invention, after the electromagnetic shielding film is pressed, at least 10% of the conductive particles 21 are connected to a surface of the adhesive film layer 2 close to the shielding layer 1 .

[0041] Exemplarily, after the electromagnetic shielding film is pressed, at least 10% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%) of the conductive particles 21 are connected to the side of the shielding layer 1 close to the adhesive film layer 2. In order to avoid too little contact between the conductive particles 21 and the shielding layer 1, which results in a reduction in the interference charge introduced into the circuit board formation and a reduction in the grounding performance of the electromagnetic shielding film, at least 10% of the conductive particles 21 may be directly in contact with one end of the adhesive film layer 2 close to the shielding layer 1, or at least 10% of the conductive particles 21 may be arranged close to the side of the adhesive film layer 2 close to the shielding layer 1, thereby ensuring that after the electromagnetic shielding film is pressed, a portion of the conductive particles 21 are in contact with the shielding layer 1, thereby increasing the contact area between the conductive particles 21 and the shielding layer, thereby increasing the interference charge introduced into the circuit board formation and improving the grounding performance of the electromagnetic shielding film.

[0042] In the embodiment of the present invention, after the electromagnetic shielding film is pressed, at least 10% of the conductive particles are connected to a side of the adhesive film layer 2 away from the shielding layer 1 .

[0043] Exemplarily, after the electromagnetic shielding film is pressed, at least 10% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%) of the conductive particles 21 are connected to the side of the adhesive film layer 2 away from the shielding layer 1. In order to avoid too little contact between the conductive particles 21 and the circuit board ground layer, resulting in a reduction in the interference charge introduced into the circuit board ground layer and a reduction in the grounding performance of the electromagnetic shielding film, at least 10% of the conductive particles 21 may have one end directly in contact with the side of the adhesive film layer 2 away from the shielding layer 1, or at least 10% of the conductive particles 21 may be arranged close to the side of the adhesive film layer 2 away from the shielding layer 1, thereby ensuring that after the electromagnetic shielding film is pressed, a portion of the conductive particles 21 are in contact with the circuit board ground layer, increasing the contact area between the conductive particles 21 and the circuit board ground layer, increasing the interference charge introduced into the circuit board ground layer, and improving the grounding performance of the electromagnetic shielding film.

[0044] In the embodiment of the present invention, the surface of the conductive particles 21 has a uniformly distributed spike structure.

[0045] Exemplarily, the conductive particles 21 are provided with a spike structure. In order to prevent the conductive particles 21 from being unable to effectively penetrate the adhesive film layer 2 and contact the shielding layer 1 and the circuit board ground layer during the lamination process, resulting in a reduction in the interference charge introduced by the shielding layer 1 into the circuit board ground layer and a reduction in the grounding performance of the electromagnetic shielding film, a spike structure is provided on the conductive particles 21. The spike structure can effectively penetrate the adhesive in the adhesive film layer 2, thereby ensuring that the conductive particles 21 can contact the shielding layer 1, increasing the contact area between the shielding layer 1 and the conductive particles 21, and at the same time ensuring that the conductive particles 21 can contact the circuit board ground layer, increasing the contact area between the circuit board ground layer and the conductive particles 21, thereby increasing the interference charge introduced into the circuit board ground layer and improving the grounding performance of the electromagnetic shielding film.

[0046] In the embodiment of the present invention, the surface of the shielding layer 1 close to the adhesive film layer 2 is a non-flat surface.

[0047] For example, see Figure 3 , Figure 3 The figure shows a structure in which the side of the shielding layer 1 closest to the adhesive film layer 2 is uneven. This uneven surface includes several convex and concave portions. When the side of the shielding layer 1 closest to the adhesive film layer 2 is uneven, the adhesive film layer 2 squeezes the adhesive into the concave portion of the lower surface of the shielding layer 1 during the lamination process, preventing the small amount of adhesive that can easily cause the board to explode, leading to grounding failure.

[0048] In an embodiment of the present invention, the particle size of the conductive particles 21 is 0.1-20 μm. By setting the particle size of the conductive particles 21 to 0.1-20 μm, when the thickness of the adhesive film layer 2 is set to 1-30 μm, the conductive particles 21 can be more densely filled in the adhesive film layer 2, and there can be more contact points between the conductive particles 21, forming a conductive network with more connections, and achieving better conductive performance. Exemplarily, the particle size of the conductive particles 21 is proportional to the thickness of the adhesive film layer 2. When the thickness of the adhesive film layer 2 is thicker, the particle size of the conductive particles 21 is larger, so that the conductive particles 21 can be reasonably distributed in the adhesive film layer 2. For example, when the thickness of the adhesive film layer 2 is 1 μm, the particle size of the conductive particles 21 is 0.1 μm, and when the thickness of the adhesive film layer 2 is 30 μm, the particle size of the conductive particles 21 is 20 μm.

[0049] In an embodiment of the present invention, the weight proportion of the conductive particles 21 in the adhesive film layer 2 is 3%-80% (i.e., the value of x), for example, the weight proportion of the conductive particles 21 in the adhesive film layer 2 is 3%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or 80%. By setting the weight proportion of the conductive particles 21 in the adhesive film layer 2 to 3%-80%, the amount of the conductive particles 21 filled in the adhesive film layer 2 is moderate, and there will not be too few conductive particles 21, which will lead to reduced contact between the conductive particles 21 and the shielding layer 1 and the circuit board layer, thereby reducing the interference charge introduced into the circuit board layer and reducing the grounding performance of the electromagnetic shielding film. At the same time, there is no need to use too many conductive particles 21, which reduces the cost of the conductive particles 21. In addition, there will not be too many conductive particles 21, which will lead to too little resin content in the adhesive film layer 2, resulting in insufficient viscosity of the adhesive film layer 2 and causing delamination of the electromagnetic shielding film during the lamination process. Therefore, setting the weight proportion of the conductive particles 21 in the adhesive film layer 2 to 3%-80% can improve the grounding performance of the electromagnetic shielding film, while preventing delamination during the lamination process and preventing explosion of the board.

[0050] For example, when the weight proportion of the conductive particles 21 in the film layer 2 is 3%, 100 parts of the film layer 2 contain 3 parts of conductive particles 21; when the weight proportion of the conductive particles 21 in the film layer 2 is 40%, 100 parts of the film layer 2 contain 40 parts of conductive particles 21; when the weight proportion of the conductive particles 21 in the film layer 2 is 80%, 100 parts of the film layer contain 80 parts of conductive particles 21.

[0051] In an embodiment of the present invention, the conductive particles 21 are made of at least one material selected from copper, aluminum, zinc, nickel, silver, iron, cobalt, and titanium.

[0052] In the embodiment of the present invention, the thickness of the shielding layer 1 is 0.1-7 μm. By setting the thickness of the shielding layer 1 to 0.1-7 μm, the electromagnetic shielding effect of the electromagnetic shielding film can be ensured while the thickness of the electromagnetic shielding film will not be too thick.

[0053] In this embodiment, the material used for the adhesive film layer 2 is selected from the following: modified epoxy resin, acrylic resin, modified rubber, and modified thermoplastic polyimide.

[0054] See also Figure 4The electromagnetic shielding film of this embodiment of the present invention is further provided with an insulating layer 3. This insulating layer 3 is disposed on the side of the shielding layer 1 facing away from the adhesive film layer 2. This insulating layer 3 effectively electrically isolates the shielding layer 1 from the outside world, thereby ensuring the electromagnetic shielding effect of the shielding layer 1. The shielding layer 1 provides electromagnetic shielding. Furthermore, the adhesive film layer 2 allows the electromagnetic shielding film to be adhered to the circuit board.

[0055] See also Figure 5 The electromagnetic shielding film described in the embodiment of the present invention is further provided with a carrier layer 4, and the carrier layer 4 is provided on the side of the insulating layer 3 away from the shielding layer 1. The carrier layer can be used to protect the insulating layer 3 so that the insulating layer 3 is not damaged by external contact or collision. Among them, when the thickness of the carrier layer is 50 microns, it has better protection ability and can well protect the insulating layer 3 from being damaged by external contact or collision. In addition, the carrier layer can be used as a base film for forming the insulating layer 3, that is, the insulating layer 3 can be formed on one side of the carrier layer 4.

[0056] See also Figure 6 , the electromagnetic shielding film in this embodiment also includes a protective film layer 5, and the protective film layer 5 is arranged on the side of the adhesive film layer 2 away from the shielding layer 1. Since the protective film layer 5 has a protective function, it ensures that the adhesive film layer 2 is not scratched or damaged during use. Among them, the protective film layer 5 includes a PPS film layer, a PEN film layer, a polyester film layer, a polyimide film layer, a film layer formed after the epoxy resin ink is cured, a film layer formed after the polyurethane ink is cured, a film layer formed after the modified acrylic resin is cured, or a film layer formed after the polyimide resin is cured. Among them, when the electromagnetic shielding film is pressed onto the circuit board, the protective film layer 5 needs to be peeled off first.

[0057] Specifically, when the electromagnetic shielding film includes a carrier layer 4, an insulating layer 3, a shielding layer 1, an adhesive film layer 2 and a protective film layer 5, the preparation method of the electromagnetic shielding film includes:

[0058] 1) preparing a carrier layer 4;

[0059] 2) forming an insulating layer 3 on one surface of the carrier layer 4;

[0060] 3) forming a shielding layer 1 on a surface of the insulating layer 3 away from the carrier layer 4;

[0061] 4) applying glue on the side of the shielding layer 1 away from the insulating layer 3 to form a glue film layer 2, and disposing conductive particles 21 in the glue film layer 2;

[0062] 5) Laminating the protective film layer 5 on the side of the adhesive film layer 2 away from the shielding layer 1 .

[0063] To facilitate understanding of the above invention, the following nine specific implementation methods are provided and tested: Specific embodiment 1

[0065] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the shielding layer 1 has a rough surface on a side close to the film layer 2, and the film layer 2 does not contain conductive particles 21; the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um) and then a grounding test is performed, and the grounding resistance obtained by the test is 5567 milliohms. Specific embodiment two:

[0067] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the film layer 2 is provided with conductive particles 21; the grounding resistance value of the electromagnetic shielding film after lamination and the conductive particles satisfy the following relationship: y1≤3738.4x 2 -6947.9x+4354.7; y1 is the grounding resistance of the electromagnetic shielding film after lamination, and x is the weight ratio of the conductive particles 21 in the film layer 2.

[0068] When the value of x is 3%, the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um) and the grounding test is carried out after treatment. The calculated grounding resistance value y1 is approximately equal to 4150 milliohms. Specific embodiment three:

[0070] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the film layer 2 is provided with conductive particles 21; the grounding resistance value of the electromagnetic shielding film after lamination and the conductive particles satisfy the following relationship: y1≤3738.4x 2 -6947.9x+4354.7; y1 is the grounding resistance value of the electromagnetic shielding film after lamination, and x is the weight ratio of the conductive particles 21 in the film layer 2 .

[0071] When the value of x is 40%, the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um) and the grounding test is carried out. The calculated grounding resistance value y1 is approximately equal to 2173 milliohms. Specific embodiment four:

[0073] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the film layer 2 is provided with conductive particles 21; the grounding resistance value of the electromagnetic shielding film after lamination and the conductive particles satisfy the following relationship: y1≤3738.4x2 -6947.9x+4354.7; y1 is the grounding resistance value of the electromagnetic shielding film after lamination, and x is the weight ratio of the conductive particles 21 in the film layer 2 .

[0074] When the value of x is 80%, the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um) and the grounding test is carried out. The calculated grounding resistance value y1 is approximately equal to 1189 milliohms. Specific embodiment five

[0076] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the shielding layer 1 has a rough surface on a side close to the film layer 2, and the film layer 2 does not contain conductive particles 21; the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um), and a grounding test is performed after curing (160°C, curing time: 2H). The grounding resistance obtained by the test is 6370 milliohms. Specific embodiment six:

[0078] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the film layer 2 is provided with conductive particles 21; the grounding resistance value of the electromagnetic shielding film after curing and the conductive particles satisfy the following relationship: y2≤4537x 2 -8165.5x+5230.7; y2 is the grounding resistance value of the electromagnetic shielding film after curing, and x is the weight ratio of the conductive particles 21 in the film layer 2.

[0079] When the value of x is 3%, the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um), and the grounding test is performed after curing (160℃, curing time: 2H). The calculated grounding resistance value y2 is approximately equal to 4990 milliohms. Specific embodiment seven:

[0081] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the film layer 2 is provided with conductive particles 21; the grounding resistance value of the electromagnetic shielding film after curing and the conductive particles satisfy the following relationship: y2≤4537x 2 -8165.5x+5230.7; y2 is the grounding resistance value of the electromagnetic shielding film after curing, and x is the weight ratio of the conductive particles 21 in the film layer 2.

[0082] When the value of x is 40%, the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2, the step height of the covering film is 38um), and the grounding test is performed after curing (160℃, curing time: 2H). The calculated grounding resistance value y2 is approximately equal to 2691 milliohms. Specific embodiment eight:

[0084] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the film layer 2 is provided with conductive particles 21; the grounding resistance value of the electromagnetic shielding film after curing and the conductive particles satisfy the following relationship: y2≤4537x 2 -8165.5x+5230.7; y2 is the grounding resistance value of the electromagnetic shielding film after curing, and x is the weight ratio of the conductive particles 21 in the film layer 2.

[0085] When the value of x is 80%, the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um), and the grounding test is performed after curing (160℃, curing time: 2H). The calculated grounding resistance value y2 is approximately equal to 1602 milliohms. Specific embodiment nine

[0087] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the shielding layer 1 has a rough surface on a side close to the film layer 2, and the film layer 2 does not contain conductive particles 21; the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um), curing (160℃, curing time: 2H), and tinning (270℃, 60s) were treated and then a grounding test was performed. The grounding resistance obtained by the test was 7129 milliohms. Specific embodiment ten:

[0089] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the film layer 2 is provided with conductive particles 21; the grounding resistance value of the electromagnetic shielding film after tinning and the conductive particles satisfy the following relationship: y3≤5602.7x 2 -10495x+6736.2; y3 is the grounding resistance value of the electromagnetic shielding film after tinning, and x is the weight ratio of the conductive particles 21 in the film layer 2.

[0090] When the value of x is 3%, the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um), curing (160℃, curing time: 2H), and tinning (270℃, 60s) are treated and then the grounding test is performed. The calculated grounding resistance value y3 is approximately equal to 6426 milliohms. Specific embodiment eleven:

[0092] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the film layer 2 is provided with conductive particles 21; the grounding resistance value of the electromagnetic shielding film after tinning and the conductive particles satisfy the following relationship: y3≤5602.7x 2 -10495x+6736.2; y3 is the grounding resistance value of the electromagnetic shielding film after tinning, and x is the weight ratio of the conductive particles 21 in the film layer 2.

[0093] When the value of x is 40%, the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um), curing (160℃, curing time: 2H), and tinning (270℃, 60s) are treated and then the grounding test is performed. The calculated grounding resistance value y3 is approximately equal to 3432 milliohms. Specific embodiment 12:

[0095] An electromagnetic shielding film comprises a shielding layer 1 and a film layer 2, wherein the film layer 2 is provided with conductive particles 21; the grounding resistance value of the electromagnetic shielding film after tinning and the conductive particles satisfy the following relationship: y3≤5602.7x 2 -10495x+6736.2; y3 is the grounding resistance value of the electromagnetic shielding film after tinning, and x is the weight ratio of the conductive particles 21 in the film layer 2.

[0096] When the value of x is 80%, the electromagnetic shielding film is pressed (185°C, 10 min, 120 kg / cm 2 , the step height of the covering film is 38um), curing (160℃, curing time: 2H), and tinning (270℃, 60s) are treated and then the grounding test is performed. The calculated grounding resistance value y3 is approximately equal to 1926 milliohms.

[0097] The calculation results of the grounding resistance of the above embodiments are integrated to obtain the data in Table 1 below.

[0098] Table 1 Calculation results of ground resistance in the embodiment

[0099] <![CDATA[y1]]> <![CDATA[y2]]> <![CDATA[y3]]> x＝3％ 4150 4990 6426 x＝40％ 2173 2691 3432 x＝80％ 1189 1602 1926

[0100] In the solution of the present invention, by providing conductive particles 21 in the adhesive film layer 2, when the electromagnetic shielding film is pressed onto the circuit board, the conductive particles 21 can conduct interference charges in the shielding layer 1 into the circuit board ground layer, which is beneficial to improving the grounding performance of the electromagnetic shielding film. As can be seen from Table 1, by fitting the relationship between the grounding resistance value of the electromagnetic shielding film and the content of the conductive particles in the adhesive film layer after the electromagnetic shielding film and the circuit board are pressed, cured, and tinned, it can be obtained that as the content of the conductive particles in the adhesive film increases, the corresponding grounding resistance of the electromagnetic shielding film decreases and the grounding performance improves. Moreover, as the electromagnetic shielding film is pressed, cured, and tinned, its corresponding grounding resistance increases. This is because after curing or tinning, the conductive particles are affected by high temperature and surface oxidation occurs, which reduces the conductive performance of the conductive particles. At the same time, the expansion of the adhesive film layer may lead to poor contact between the conductive particles, between the conductive particles and the shielding layer, and between the conductive particles and the circuit board, resulting in reduced grounding performance.

[0101] For each of the above embodiments, several electromagnetic shielding films (for example, 10 electromagnetic shielding films were tested in each embodiment) were used for actual testing, and the test results are shown in Table 2 below.

[0102] Table 2 Grounding resistance measurement results of the embodiment

[0103] Does it conform to formula 1? Does it conform to formula 2? Does it comply with formula 3? Example 1 Not compliant Not compliant Not compliant Example 2 conform to conform to conform to Example 3 conform to conform to conform to Example 4 conform to conform to conform to Example 5 Not compliant Not compliant Not compliant Example 6 conform to conform to conform to Example 7 conform to conform to conform to Example 8 conform to conform to conform to Embodiment 9 Not compliant Not compliant Not compliant Example 10 conform to conform to conform to Example 11 conform to conform to conform to Example 12 conform to conform to conform to

[0104] As can be seen from Table 2, by using the electromagnetic shielding film in the solution of the present invention, after the lamination, curing and tinning processes, the grounding resistance is tested and all of the above three formulas are satisfied.

[0105] See also Figure 7 Another embodiment of the present invention further provides a circuit board, which includes a circuit board body 6 and the electromagnetic shielding film described in any of the above embodiments; the electromagnetic shielding film is pressed against the circuit board body 6; and the side of the shielding layer 1 close to the adhesive film layer 2 is electrically connected to the ground layer of the circuit board body 6.

[0106] Preferably, the circuit board body 6 is one of a flexible single-sided board, a flexible double-sided board, a flexible multi-layer board, and a rigid-flexible board.

[0107] Specifically, by providing conductive particles 21 in the adhesive film layer 2, when the electromagnetic shielding film is pressed onto the circuit board, the conductive particles 21 can direct interference charges in the shielding layer 1 into the circuit board ground layer, thereby improving the grounding performance of the electromagnetic shielding film. By fitting the relationship between the grounding resistance value of the electromagnetic shielding film and the content of the conductive particles in the adhesive film layer after the electromagnetic shielding film and the circuit board are pressed, cured, and tinned, it can be found that as the content of the conductive particles in the adhesive film layer increases, the corresponding grounding resistance of the electromagnetic shielding film decreases and the grounding performance improves; and as the electromagnetic shielding film is pressed, cured, and tinned, its corresponding grounding resistance increases.

[0108] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles 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 and a film layer, wherein the film layer is provided with conductive particles and resin; the grounding resistance value of the electromagnetic shielding film after lamination and the conductive particles satisfy the following relationship: y1≤3738.4x 2 -6947.9x+4354.7; y1 is the grounding resistance value of the electromagnetic shielding film after lamination, x is the weight ratio of the conductive particles in the film layer, and the value of x ranges from 3% to 80%; The grounding resistance value of the electromagnetic shielding film after curing and the conductive particles satisfy the following relationship: y2≤4537x 2 -8165.5x+5230.7; y2 is the grounding resistance value of the electromagnetic shielding film after curing, and x is the weight ratio of the conductive particles in the film layer.

2. The electromagnetic shielding film according to claim 1, wherein In a direction perpendicular to the thickness of the electromagnetic shielding film, a distance D between two adjacent conductive particles satisfies: 0≤D≤100 μm.

3. The electromagnetic shielding film according to claim 1, wherein In the thickness direction of the electromagnetic shielding film, a distance d between two adjacent conductive particles satisfies: 0≤d≤10 μm.

4. The electromagnetic shielding film according to claim 1, wherein After the electromagnetic shielding film is pressed, at least 10% of the conductive particles are connected to a side of the adhesive film layer close to the shielding layer.

5. The electromagnetic shielding film according to claim 1, wherein After the electromagnetic shielding film is pressed, at least 10% of the conductive particles are connected to a side of the adhesive film layer away from the shielding layer.

6. The electromagnetic shielding film according to claim 1, wherein The surfaces of the conductive particles have uniformly distributed spike structures.

7. The electromagnetic shielding film according to claim 1, wherein The grounding resistance value of the electromagnetic shielding film after tinning and the conductive particles satisfy the following relationship: y3≤5602.7x 2 -10495x+6736.2; y3 is the grounding resistance value of the electromagnetic shielding film after tinning, and x is the weight ratio of the conductive particles in the film layer.

8. The electromagnetic shielding film according to claim 1, wherein The side of the shielding layer close to the adhesive film layer is a non-flat surface.

9. A circuit board, characterized in that: It comprises a circuit board body and the electromagnetic shielding film according to any one of claims 1 to 8; the electromagnetic shielding film is pressed together with the circuit board body.

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