Electromagnetic shielding film and circuit board

Abstract

The invention discloses an electromagnetic shielding film and a circuit board, the electromagnetic shielding film comprises a protective layer and a shielding layer which are sequentially stacked, filler particles are arranged in the protective layer, and the outer contour of the filler particles is arc-shaped. According to the electromagnetic shielding film, the filler particles with the circular-arc-shaped outer contours are arranged in the protective layer, so that edges and corners of the filler are reduced, the anti-tearing effect of the electromagnetic shielding film is improved, and meanwhile, when the filler particles with the circular-arc-shaped outer contours are pressed, stress of the protective layer is dispersed, stress concentration of the filler is avoided, friction force among the filler particles is reduced, and the anti-tearing effect of the electromagnetic shielding film is improved. The electromagnetic shielding film is not easy to relatively slide and displace, so that the pulling and damage to the electromagnetic shielding film are reduced, the damage probability is reduced, the damage problem is solved, and meanwhile, the stability of the shielding performance is ensured.

Description

Technical Field

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

[0002] With the advancement of high-frequency and high-density integration in electronic devices, electromagnetic shielding films, as key functional materials for suppressing electromagnetic interference (EMI), are widely used in flexible circuit boards, chip packaging, and 5G communication modules. Electromagnetic shielding films are typically made of conductive materials (such as metal plating, conductive polymers, and metal mesh). Their high conductivity enables them to reflect electromagnetic waves. When external electromagnetic waves reach the shielding film, electrons move freely on the metal surface, generating an induced current. This induced current creates a reverse electric field within the shielding layer, partially offsetting the external electromagnetic field and reducing its impact on the PCB's internal circuits.

[0003] In the modern electronics manufacturing industry, the complexity and functional requirements of flexible printed circuit boards (FPCs) continue to increase, especially in multi-layer boards and high-frequency signal transmission applications. To ensure signal integrity, reduce electromagnetic interference (EMI), and improve product reliability, the PCB lamination process is particularly challenging. In areas with high height differences, such as coverlay film and etched pads, the height difference causes the shielding film to stretch and deform during lamination, which can easily lead to shielding film damage. Therefore, preventing EMI damage during lamination presents a major challenge.

[0004] Therefore, it is urgent to develop an electromagnetic shielding film that can meet the requirements of high step difference. It not only needs to maintain stable electromagnetic shielding performance after lamination, but also ensure that it will not break after lamination to meet the demand for high-performance electromagnetic shielding materials in the continuous development of electronic devices. Summary of the Invention

[0005] Based on this, it is necessary to provide an electromagnetic shielding film to address the above problems, which can maintain excellent performance after lamination and solve the problem of lamination breakage.

[0006] To achieve the above objectives, a first aspect of the present invention provides an electromagnetic shielding film comprising a protective layer and a shielding layer stacked in sequence, wherein filler particles are provided in the protective layer, and the outer contour of the filler particles is arc-shaped.

[0007] Optionally, the filler particles are spherical and / or ellipsoidal in shape.

[0008] Optionally, the specific surface area of ​​the filler particles is less than or equal to 1.2.

[0009] Optionally, in the slicing state, the minimum gap between any two adjacent filler particles is 2-5 μm.

[0010] Optionally, the maximum particle size of the filler particles is in the range of 0.5 to 5 μm.

[0011] Optionally, the ratio of the maximum particle size of the filler particles to the average thickness of the protective layer is in the range of 0.3 to 0.7.

[0012] Optionally, within a unit volume, the number of filler particles 11 with a maximum particle size of 1 to 4 μm accounts for more than 60%.

[0013] Optionally, the ratio of the thickness of the shielding layer to the thickness of the protective layer is 0.1-0.8.

[0014] Optionally, when sliced ​​at any angle along the thickness direction, the shielding layer is undulating.

[0015] Optionally, the electromagnetic shielding film further includes an adhesive film layer, which is arranged on a side of the shielding layer away from the protective layer, and a thickness ratio of the adhesive film layer to the shielding layer is 1.2-20.

[0016] Optionally, conductive particles are provided in the adhesive film layer, and the shielding layer is used to be grounded to the circuit board through the conductive particles.

[0017] To achieve the above-mentioned object, a second aspect of the present invention provides a circuit board, which includes the electromagnetic shielding film described in any one of the above-mentioned embodiments.

[0018] Compared with the prior art, the beneficial effect of the embodiments of the present invention is that: by providing filler particles with an arc-shaped outer contour in the protective layer, it is beneficial to ensure the protective effect and insulation effect of the protective layer. At the same time, the filler particles with an arc-shaped outer contour reduce the edges and corners of the filler. During pressing, the stress of the protective layer is dispersed, stress concentration of the filler is avoided, and the friction between the filler particles is reduced, so that the electromagnetic shielding film is not prone to relative sliding and displacement, thereby reducing the pulling and damage to the electromagnetic shielding film, reducing the probability of breakage, solving the breakage problem, and improving the tear resistance of the electromagnetic shielding film. At the same time, the stability of the shielding performance is guaranteed.

[0019] On the other hand, by further limiting the maximum particle size of the filler particles to 1~4μm accounting for more than 60%, and limiting the ratio of the maximum particle size of the filler particles to the average thickness of the protective layer 1 to 0.3~0.7, it can ensure that the protective layer has sufficient mechanical strength to resist external forces and reduce the risk of breakage. At the same time, it can reduce the risk of filler particles tearing the electromagnetic shielding film at the break position, thereby ensuring the stability of the shielding performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic structural diagram of a first electromagnetic shielding film provided by an embodiment of the present invention;

[0021] Figure 2 is a structural schematic diagram of a second electromagnetic shielding film provided by an embodiment of the present invention;

[0022] Figure 3 is a schematic structural diagram of a third electromagnetic shielding film provided by an embodiment of the present invention;

[0023] Figure 4 is a schematic structural diagram of a fourth electromagnetic shielding film provided by an embodiment of the present invention;

[0024] Figure 5 It is a schematic structural diagram of the fifth electromagnetic shielding film provided by an embodiment of the present invention.

[0025] Among them, 1: protective layer; 2: shielding layer; 11: filler particles; 3: bearing layer; 4: film layer; 41: conductive particles. DETAILED DESCRIPTION

[0026] 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.

[0027] 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.

[0028] 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.

[0029] See Figure 1 , Figure 1The figure is a schematic structural diagram of an electromagnetic shielding film according to an embodiment of the present invention. The present invention provides an electromagnetic shielding film comprising a protective layer 1 and a shielding layer 2 stacked in sequence. The protective layer 1 is provided with filler particles 11 having an arc-shaped outer profile. The inclusion of filler particles 11 with an arc-shaped outer profile within the protective layer 1 helps ensure both protective and insulating properties. Furthermore, the filler particles 11 with an arc-shaped outer profile reduce the filler's sharp corners. Such mixing within the protective layer 1 prevents the filler's sharp corners from penetrating the protective layer and damaging the shielding layer in the circuit board's discontinuity region during lamination, leading to tearing of the shielding layer 2 and thus affecting the shielding performance of the electromagnetic shielding film. Furthermore, the filler particles with an arc-shaped outer profile disperse stress within the protective layer 1 during lamination, preventing stress concentration within the filler particles and reducing friction between the filler particles. This reduces relative sliding and displacement of the electromagnetic shielding film, thereby reducing pulling and damage to the electromagnetic shielding film, lowering the probability of breakage and addressing the problem, while also ensuring the stability of the shielding performance. Preferably, the filler particles are spherical and / or ellipsoidal in shape.

[0030] In this embodiment of the present invention, filler particles 11 are provided in protective layer 1. Filler particles 11 enhance the mechanical properties of protective layer 1, such as strength, hardness, and wear resistance. During lamination, they prevent slippage and displacement, making protective layer 1 less susceptible to tearing and ensuring the stability of the electromagnetic shielding film's shielding performance. Filler particles 11 are made of at least one of talc, calcium carbonate, titanium dioxide, kaolin, silicon dioxide, and aluminum oxide.

[0031] In this embodiment of the present invention, protective layer 1 functions as a protective shielding layer 2. Protective layer 1 has a thickness of 2 to 20 μm. Protective layer 1 comprises at least one of polyurethane, polyester, epoxy resin, acrylic resin, polyimide, polystyrene, polyvinyl acetate, polyethylene, polypropylene, polyamide, rubber, phenolic resin, urethane resin, alkyd resin, and ink. Preferably, protective layer 1 has a thickness of 3 to 10 μm.

[0032] It should be noted that, see Figure 1 When the electromagnetic shielding film is thin, a carrier layer 3 can be provided on the surface of the protective layer 1 away from the shielding layer 2. This prevents the electromagnetic shielding film from wrinkling or breaking during processing and application. After the electromagnetic shielding film is laminated to the circuit board substrate, the carrier layer 3 is removed. Therefore, a release agent is provided on the side of the carrier layer 3 closest to the protective layer 1. The carrier layer has a thickness of 38-50 μm. By limiting the thickness of the carrier layer 3 to 38-50 μm, the thickness of the carrier layer is within an appropriate range. It is neither too thin to provide support nor too thick to make it difficult for the electromagnetic shielding film to be laminated and filled into the grounding window, affecting the grounding effect.

[0033] In an embodiment of the present invention, the specific surface area of ​​the filler particles 11 is less than or equal to 1.2. By further limiting the specific surface area of ​​the filler particles 11 to less than or equal to 1.2, the surface of the filler particles 11 is not too rough. During lamination, the friction between the filler particles 11 is reduced, which disperses the stress of the protective layer 1 and avoids stress concentration in the filler particles. As a result, the electromagnetic shielding film is less likely to experience relative sliding and displacement, reducing pulling and damage to the electromagnetic shielding film, lowering the probability of breakage, and solving the problem of breakage, while ensuring the stability of the shielding performance. Exemplary examples include the specific surface areas of the filler particles 11 of 1.0, 0.9, 0.8, 0.6, 0.5, and 0.4.

[0034] It is worth noting that in the embodiments of the present invention, the minimum gap between any two adjacent filler particles 11, when observed in a sliced ​​state, is 2-5 μm. By further limiting the minimum gap between adjacent filler particles 11 to an appropriate range, on the one hand, it is prevented that a too small minimum gap would result in an excessive number of filler particles 11 per unit volume, which would increase the mutual friction between adjacent filler particles 11 during lamination, causing the electromagnetic shielding film to be relatively prone to relative sliding and displacement, thereby increasing the risk of damage. On the other hand, it is prevented that a too large minimum gap would result in too few filler particles 11 per unit volume, which would prevent the mechanical properties of the protective layer 1 from being effectively enhanced, causing sliding and displacement during lamination, which would easily tear the protective layer 1 and affect the stability of the electromagnetic shielding performance. Therefore, limiting the minimum gap between adjacent filler particles 11 to 2-5 μm not only enhances the mechanical properties of the protective layer 1 and reduces the risk of damage to the electromagnetic shielding film, but also reduces the mutual friction between adjacent filler particles 11, making the electromagnetic shielding film less susceptible to relative sliding and displacement, reducing the risk of damage and ensuring the stability of the electromagnetic shielding performance. Optionally, the minimum gap may be any one value of 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.6 μm or 5 μm, or an interval consisting of any two values.

[0035] Furthermore, in an embodiment of the present invention, the maximum particle size of the filler particles 11 ranges from 0.5 to 5 μm. By limiting the maximum particle size of the filler particles 11 to a suitable range, on the one hand, the filler particles 11 at the break position will not be pushed up and moved downward during pressing due to the filler particle size being too large, which will easily tear the protective layer 1 and the shielding layer 2, thereby affecting the stability of the shielding performance. On the other hand, the filler particles 11 will not agglomerate due to their small particle size, causing stress concentration in the protective layer 1 and tearing it by external force. At the same time, it may lead to the effect of enhancing the mechanical properties of the protective layer 1 being not obvious, and the probability of damage to the protective film 1 when subjected to external force increases. Therefore, limiting the maximum particle size of the filler particles 11 to the range of 0.5 to 5 μm can ensure that the protective layer 1 has sufficient mechanical strength to resist external forces and reduce the risk of damage. At the same time, it reduces the risk of the filler particles 11 tearing the electromagnetic shielding film at the break position, thereby ensuring the stability of the shielding performance. Optionally, the maximum particle size may be any one value of 0.5 μm, 1 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.4 μm or 5 μm, or an interval consisting of any two values.

[0036] Furthermore, in an embodiment of the present invention, the number of filler particles 11 with a maximum particle size of 1 to 4 μm accounts for more than 60% per unit volume. The maximum particle size of the filler particles 11 is 1 to 4 μm, which can ensure that the protective layer 1 has sufficient mechanical strength to resist external forces and reduce the risk of breakage. At the same time, it reduces the risk of the filler particles 11 tearing the electromagnetic shielding film at the break position, thereby ensuring the stability of the shielding performance. Therefore, when the number of filler particles 11 with a maximum particle size of 1 to 4 μm accounts for less than 60% per unit volume, the above-mentioned beneficial effects are not obvious. Therefore, when the number of filler particles 11 with a maximum particle size of 1 to 4 μm accounts for more than 60% per unit volume, the above-mentioned beneficial effects can be more prominent. Preferably, the number of filler particles 11 with a maximum particle size of 1 to 4 μm accounts for more than 80%.

[0037] Furthermore, in an embodiment of the present invention, the ratio of the maximum particle size of the filler particles 11 to the average thickness of the protective layer 1 is in the range of 0.3~0.7. By setting the ratio of the maximum particle size of the filler particles 11 to the average thickness of the protective layer 1 in the range of 0.3~0.7, the distribution of the filler particles 11 in the protective layer 1 is made more reasonable. On the one hand, the ratio of the two is too large, which will not cause the filler particles 11 at the break position to push upward during pressing, easily tearing the protective layer 1, thereby affecting the stability of the shielding performance. On the other hand, the ratio of the two is too small, which will cause the filler particles 11 to have an insignificant effect in improving the mechanical properties of the protective layer 1, thereby increasing the probability of damage to the protective film 1 when subjected to external force. Therefore, limiting the ratio of the maximum particle size of the filler particles 11 to the average thickness of the protective layer 1 to a range of 0.3~0.7 can ensure that the protective layer 1 has sufficient mechanical strength to resist external forces and reduce the risk of damage. At the same time, it reduces the risk of the filler particles 11 tearing the electromagnetic shielding film at the break position, thereby ensuring the stability of the shielding performance. Optionally, the ratio between the two can be any one of 0.3, 0.4, 0.5, 0.6 or 0.7, or an interval consisting of any two values.

[0038] The average thickness of the protective layer 1 is the average of the thickness at a preset measurement position, and the thickness of the protective layer 1 is the shortest distance between the two opposite side surfaces of the protective layer along the thickness direction of the shielding film.

[0039] It should be noted that in the embodiment of the present invention, the ratio of the thickness of the shielding layer 2 to the thickness of the protective layer 1 is 0.1-0.8. By limiting the ratio of the thickness of the shielding layer 2 to the thickness of the protective layer 1 to 0.1-0.8, on the one hand, the tensile strength of the entire electromagnetic shielding film will not be significantly reduced due to a too small ratio, and it will not be easy to tear when the step difference area is subjected to external forces during lamination, thereby affecting its shielding performance; on the other hand, the shielding layer 2 will not be too thick due to a too large ratio, making it difficult to press and fill the step difference area, resulting in unstable environmental reliability. Therefore, by limiting the thickness ratio of the shielding layer 2 to the thickness of the protective layer 1 to 0.1-0.8, the thickness of the shielding layer 2 is relatively moderate. During lamination, it can both ensure the filling effect in the step difference area and resist external tearing. This makes the electromagnetic shielding film have excellent environmental reliability, significantly reduces the probability of damage, and thus ensures the stability of the shielding performance. Optionally, the ratio between the two can be any one of 0.1, 0.2, 0.4, 0.5, 0.6, 0.7 or 0.8, or an interval consisting of any two values.

[0040] It should be noted that, in this embodiment, the thickness of the shielding layer 2 is the average value of the minimum distances between two opposite side surfaces of the shielding layer 2 at any measurement points.

[0041] refer to Figure 3 , Figure 3This is a schematic diagram of the structure of another electromagnetic shielding film according to an embodiment of the present invention. In the electromagnetic shielding film according to the embodiment of the present invention, the shielding layer 2 is undulating when sliced ​​at any angle along the thickness direction. At any angle, that is, when a cross section is made perpendicular to the surface of the electromagnetic shielding film from any position on the surface of the electromagnetic shielding film, the shielding layer 2 has an undulating structure, and is undulating when cut at any angle. The undulating shielding layer 2 increases the surface area of ​​the shielding layer itself, and can provide more electromagnetic reflection and absorption paths, so that the energy of electromagnetic waves is greatly attenuated after multiple reflections and absorption in the shielding layer 2, significantly improving the shielding effect of the electromagnetic shielding film against electromagnetic waves of different frequencies and directions; in addition, the undulating structure gives the shielding layer 2 greater flexibility and ductility, making it difficult to tear in complex application scenarios such as bending, curling, and pulling, thereby ensuring the stability of the shielding performance.

[0042] refer to Figure 4 , Figure 4 FIG2 is a schematic structural diagram of another electromagnetic shielding film according to an embodiment of the present invention. The electromagnetic shielding film according to the embodiment of the present invention further includes an adhesive film layer 4, which is disposed on a side of the shielding layer 2 away from the protective layer 1, and the thickness ratio of the adhesive film layer 4 to the shielding layer 2 is 1.2 to 20.

[0043] In the embodiment of the present invention, the adhesive layer 4 serves as an adhesive. In circuit board applications, the electromagnetic shielding film is bonded to the circuit board via the adhesive layer 4, preventing blistering and delamination between the electromagnetic shielding film and the circuit board, thereby preventing separation and other problems, and achieving effective shielding. The adhesive layer 4 has a thickness of 1-20 μm and is primarily selected from at least one resin selected from polyesters, polyethylenes, polyamides, rubbers, acrylics, phenolics, epoxies, polyimides, urethanes, melamines, alkyds, and the like.

[0044] It should be noted that in the embodiment of the present invention, the thickness ratio of the adhesive film layer 4 to the shielding layer 2 is 1.2 to 20. By limiting the thickness ratio of the adhesive film layer 4 to the shielding layer 2 to an appropriate range, on the one hand, the ratio is not too small, resulting in a thicker shielding layer 2 and a relatively smaller adhesive film layer 4, which would cause the adhesive film layer 4 to be loosely bonded to the circuit board during lamination. During high-temperature assembly, the thicker shielding layer 2 makes it difficult for gas to be discharged, making blistering and delamination more likely to occur. On the other hand, if the adhesive film layer 4 is too thick, the grounding resistance between the electromagnetic shielding film and the circuit board increases, affecting the smooth conduction of the induced charge of the shielding layer 2 to the circuit board ground layer, which in turn affects the shielding performance of the electromagnetic shielding film. Therefore, limiting the thickness ratio of the adhesive film layer 4 to the shielding layer 2 to 1.2 to 20 can ensure high-temperature assembly and the reliability of the electromagnetic shielding film. At the same time, it enables the shielding layer 2 to quickly and effectively conduct the induced electromagnetic interference charge to the circuit board ground layer, achieving reliable grounding, significantly enhancing the electromagnetic shielding film's ability to release induced charge, reducing the risk of interference and damage to electronic components caused by induced charge accumulation, and improving the electromagnetic compatibility and operating stability of circuit boards and electronic equipment. Optionally, the ratio can be any one of 1.2, 2, 3, 4, 4.5, 5, 6, 6.6, 7, 7.8, 9, 10, 12, 13, 15, or 20, or an interval consisting of any two values.

[0045] Specifically, the thickness of the adhesive film layer 4 is the average value of the shortest distances between two opposite side surfaces of the adhesive film layer 4 along the thickness direction of the electromagnetic shielding film at any measurement position.

[0046] Preferably, if Figure 5 As shown, Figure 5 : is a schematic diagram of the structure of another electromagnetic shielding film provided by an embodiment of the present invention. In this embodiment of the present invention, conductive particles 41 are provided in the adhesive film layer 4, and the shielding layer 2 is electrically connected to the circuit board body at least through the conductive particles 41. The conductive particles 41 in the adhesive film layer 4 establish a good conductive path between the shielding layer 2 and the circuit board body, enabling the shielding layer 2 to quickly and effectively conduct the induced electromagnetic interference charge to the circuit board ground layer, thereby achieving reliable grounding; in addition, this grounding method significantly enhances the induced charge release capability of the electromagnetic shielding film, reduces the risk of interference and damage to electronic components caused by induced charge accumulation, and improves the electromagnetic compatibility and operating stability of the circuit board and electronic equipment.

[0047] An embodiment of the present invention further provides a circuit board, which includes the electromagnetic shielding film according to any embodiment of the present invention.

[0048] The electromagnetic shielding film and circuit board provided by the embodiments of the present invention have the following beneficial effects: by providing filler particles with an arc-shaped outer contour in the protective layer, the edges and corners of the filler are reduced, and the tear resistance of the electromagnetic shielding film is improved. At the same time, the filler particles with an arc-shaped outer contour disperse the stress of the protective layer during pressing, avoid stress concentration of the filler, reduce the friction between the filler particles, and make the electromagnetic shielding film less likely to produce relative sliding and displacement, thereby reducing the pulling and damage to the electromagnetic shielding film, reducing the probability of breakage, solving the breakage problem, and at the same time, ensuring the stability of the shielding performance.

[0049] In order to demonstrate the beneficial effects of an electromagnetic shielding film and a circuit board provided by the embodiments of the present invention, several embodiments and comparative examples are described below.

[0050] Example 1:

[0051] An electromagnetic shielding film includes a protective layer 1, a shielding layer 2, and an adhesive layer 4, which are stacked in sequence. The protective layer 1 is composed of a mixture of ink, rubber, and epoxy resin; the shielding layer 2 is composed of a nickel-copper alloy; and the adhesive layer 4 is composed of a modified epoxy resin. The protective layer 1 is provided with ellipsoidal filler particles 11, which are made of rubber. The maximum particle size of the filler particles 11 ranges from 1 to 4 μm, accounting for 60% of the total particle size. The minimum gap between any two adjacent filler particles 11 is 4 μm. The ratio of the maximum particle size of the filler particles 11 to the average thickness of the protective layer 1 is in the range of 0.3.

[0052] Example 2:

[0053] The electromagnetic shielding film structure of this embodiment is the same as that of the first embodiment, except that the maximum particle size of the filler particles 11 of 1-4 μm accounts for 70%.

[0054] Example 3:

[0055] The electromagnetic shielding film structure of this embodiment is the same as that of the embodiment 1, except that the maximum particle size of the filler particles 11 of 1-4 μm accounts for 80%.

[0056] Example 4:

[0057] The electromagnetic shielding film structure of this embodiment is identical to that of Example 1, except that the filler particles 11 within the protective layer 1 have an arc-shaped outer contour and an ellipsoidal shape, with a specific surface area of ​​1.0. The minimum gap between adjacent filler particles 11 is 2 μm, the maximum particle size is 0.5 μm, the ratio of the maximum particle size to the average thickness of the protective layer 1 is 0.3, and the number of filler particles 1-4 μm accounts for 60%. The thickness ratio of the shielding layer 2 to the protective layer 1 is 0.1, and the shielding layer 2 is undulating. The thickness ratio of the adhesive film layer 4 to the shielding layer 2 is 1.2, and the adhesive film layer 4 contains conductive particles.

[0058] Example 5:

[0059] The electromagnetic shielding membrane structure of this embodiment is identical to that of Example 1, except that filler particles 11 within protective layer 1 have an arc-shaped outer contour, a mixture of spheres and ellipsoids, a specific surface area of ​​0.8, a minimum gap between adjacent particles of 5 μm, a maximum particle size of 5 μm, a ratio of maximum particle size to average protective layer thickness of 0.7, and 80% of the filler particles are 1-4 μm. The thickness ratio of shielding layer 2 to protective layer 1 is 0.8, and shielding layer 2 is undulating. The thickness ratio of adhesive film layer 4 to shielding layer 2 is 20, and adhesive film layer 4 contains conductive particles.

[0060] Example 6:

[0061] The electromagnetic shielding film structure of this embodiment is the same as that of embodiment 1, except that the ratio of the maximum particle size of the filler particles 11 to the average thickness of the protective layer 1 is in the range of 0.4.

[0062] Example 7:

[0063] The electromagnetic shielding film structure of this embodiment is identical to that of Example 1, except that filler particles 11 have an arc-shaped outer contour, a spherical shape, a specific surface area of ​​1.1, a gap of 3 μm between adjacent particles, a maximum particle size of 1 μm, a ratio of maximum particle size to average thickness of protective layer 1 of 0.4, and a population of filler particles 11 sized 1 to 4 μm, comprising 65%. The thickness ratio of shielding layer 2 to protective layer 1 is 0.3, shielding layer 2 is undulating, the thickness ratio of adhesive film layer 4 to shielding layer 2 is 5, and adhesive film layer 4 contains conductive particles 41.

[0064] Example 8:

[0065] The electromagnetic shielding membrane structure of this embodiment is identical to that of Example 1, except that: the filler particles are ellipsoidal, with an arc-shaped outer contour, a specific surface area of ​​1.2, a gap of 4 μm between adjacent particles, a maximum particle size of 4 μm, a ratio of the maximum particle size to the average thickness of the protective layer 1 of 0.6, and the number of filler particles between 1 and 4 μm accounts for 75%. The thickness ratio of the shielding layer 2 to the protective layer 1 is 0.6, the shielding layer 2 is undulating, the thickness ratio of the adhesive film layer 4 to the shielding layer 2 is 15, and the adhesive film layer 4 contains conductive particles 41.

[0066] Example 9:

[0067] The electromagnetic shielding film structure of this embodiment is the same as that of embodiment 1, except that the ratio of the maximum particle size of the filler particles 11 to the average thickness of the protective layer 1 is in the range of 0.7.

[0068] Comparative Example 1:

[0069] An electromagnetic shielding film comprises a protective layer 1, a shielding layer 2 and an adhesive film layer 4 which are stacked in sequence, wherein prismatic filler particles are provided in the protective layer.

[0070] Comparative Example 2:

[0071] The electromagnetic shielding film structure of this embodiment is the same as that of the first embodiment, except that the maximum particle size of the filler particles 11 of 1-4 μm accounts for 10%.

[0072] Comparative Example 3:

[0073] The electromagnetic shielding film structure of this embodiment is the same as that of embodiment 1, except that the ratio of the maximum particle size of the filler particles 11 to the average thickness of the protective layer 1 is in the range of 0.1.

[0074] Comparative Example 4:

[0075] The structure of the electromagnetic shielding film of this embodiment is the same as that of embodiment 1, except that the specific surface area of ​​the filler particles is 1.3.

[0076] The electromagnetic shielding films of Examples 1 to 9 and Comparative Examples 1 to 4 were subjected to ground resistance and damage tests. The electromagnetic shielding films were laminated onto a 38 μm thick test plate using the following lamination process: lamination at a temperature of 185°C, a lamination time of 3 minutes, and a pressure of 120 kg / cm 2 The test board was post-cured at 160°C for 1.5 hours. The test board consisted of a cover film, a grounding circuit layer, and an insulating substrate layer. The cover film had a 2mm-diameter window and was grounded to the ground beneath it. The board was observed for damage and ground resistance. The test data is shown in Table 1.

[0077] Table 1. Grounding resistance and damage of electromagnetic shielding films of Examples 1 to 9 and Comparative Examples 1 to 4

[0078]

[0079] It can be seen that by applying the electromagnetic shielding film of this embodiment, the probability of breakage can be effectively reduced, the breakage problem can be solved, the tear resistance of the electromagnetic shielding film can be improved, and at the same time, the stability of the shielding performance can be guaranteed.

[0080] In summary, by providing the protective layer 1 with filler particles 11 with an arc-shaped outer contour, it is beneficial to ensure the protective effect and insulation effect of the protective layer 1. At the same time, the filler particles 11 with an arc-shaped outer contour reduce the edges and corners of the filler. During pressing, the stress of the protective layer 1 is dispersed, stress concentration of the filler is avoided, and the friction between the filler particles 11 is reduced, so that the internal structure of the electromagnetic shielding film is not prone to relative sliding and displacement, thereby reducing the pulling and damage to the electromagnetic shielding film, reducing the probability of breakage, solving the breakage problem, and improving the tear resistance of the electromagnetic shielding film. At the same time, the stability of the shielding performance is guaranteed.

[0081] On the other hand, by further limiting the proportion of the maximum particle size of the filler particles 11 to 1~4μm (60%, 70%, 80%, 90% or 100%), and limiting the ratio range of the maximum particle size of the filler particles 11 to the average thickness of the protective layer 1 (0.3, 0.4, 0.5, 0.6 or 0.7), it can ensure that the protective layer 1 has sufficient mechanical strength to resist external forces and reduce the risk of breakage. At the same time, it can reduce the risk of the filler particles 11 tearing the electromagnetic shielding film at the break position, thereby ensuring the stability of the shielding performance.

[0082] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. An electromagnetic shielding film, characterized in that The electromagnetic shielding film comprises a protective layer and a shielding layer which are stacked in sequence. Filler particles are arranged in the protective layer, and the outer contour of the filler particles is arc-shaped.

2. The electromagnetic shielding film according to claim 1, wherein The filler particles are spherical and / or ellipsoidal in shape.

3. The electromagnetic shielding film according to claim 1, wherein The specific surface area of ​​the filler particles is less than or equal to 1.

2.

4. The electromagnetic shielding film according to claim 1, wherein In the sliced ​​state, the minimum gap between any two adjacent filler particles is 2-5 μm.

5. The electromagnetic shielding film according to claim 1, wherein The maximum particle size of the filler particles ranges from 0.5 to 5 μm. The electromagnetic shielding film according to claim 1 , wherein: The ratio of the maximum particle size of the filler particles to the average thickness of the protective layer is in the range of 0.3 to 0.

7.

7. The electromagnetic shielding film according to claim 1, wherein In a unit volume, the filler particles 11 with a maximum particle size of 1 to 4 μm account for more than 60%.

8. The electromagnetic shielding film according to any one of claims 1 to 7, characterized in that: The ratio of the thickness of the shielding layer to the thickness of the protective layer is 0.1-0.

8.

9. The electromagnetic shielding film according to claim 8, wherein When sliced ​​at any angle along the thickness direction, the shielding layer is undulating.

10. The electromagnetic shielding film according to claim 9, wherein The electromagnetic shielding film further includes an adhesive film layer, which is arranged on a side of the shielding layer away from the protective layer. The thickness ratio of the adhesive film layer to the shielding layer is 1.2-20.

11. The electromagnetic shielding film according to claim 10, wherein Conductive particles are provided in the adhesive film layer, and the shielding layer is used for grounding to the circuit board through the conductive particles.

12. A circuit board, characterized in that: The circuit board includes the electromagnetic shielding film according to any one of claims 1 to 11.

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