Electromagnetic shielding film and circuit board

Abstract

The application discloses an electromagnetic shielding film and a circuit board, wherein the electromagnetic shielding film comprises a protection layer and a shielding layer which are sequentially stacked, a side surface of the protection layer is provided with a plurality of first protruding parts, and the hardness of the first protruding parts is smaller than that of the shielding layer. The first protruding parts can relieve external stress and slow down the damage of external stress to the shielding layer when the electromagnetic shielding film is bent, so that the bending performance of the electromagnetic shielding film is improved. When the electromagnetic shielding film is bent, the first protruding parts with smaller hardness than that of the shielding layer can avoid extruding and piercing the shielding layer due to too large hardness, so that the integrity of the shielding layer is ensured, and the stability of the shielding performance is ensured.

Description

TECHNICAL FIELD

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

[0002] With the development of high frequency and high density integration of 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 usually made of conductive materials such as metal plating, conductive polymers, and metal mesh. Their high conductivity allows them to reflect electromagnetic waves. When external electromagnetic waves reach the shielding film, electrons will move freely on the metal surface, generating an induced current. This induced current forms a counter-electromagnetic field within the shielding layer, which cancels out part of the external electromagnetic field and reduces its impact on the internal circuit of the PCB.

[0003] With the rapid development of communication equipment, folding electronic devices such as folding mobile phones have emerged. Applying electromagnetic shielding films to the circuit boards or soft boards of folding electronic devices not only enables folding, but also avoids electromagnetic interference from the outside and the folding electronic device. After folding multiple times, the folding electronic device may have cracks in the electromagnetic shielding film, resulting in a loss of shielding effect and making it difficult to meet the performance requirements of folding electronic devices.

[0004] Therefore, it is urgent to develop an electromagnetic shielding film with good bending performance. It not only needs to maintain stable electromagnetic shielding performance during bending, but also needs to overcome the problems of electromagnetic leakage and structural damage of existing shielding films during bending to meet the demand for high-performance electromagnetic shielding materials for the development of electronic devices. SUMMARY

[0005] Therefore, it is necessary to provide an electromagnetic shielding film that can improve the reliability of folding electronic devices after multiple bending.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides an electromagnetic shielding film, comprising a protection layer and a shielding layer which are sequentially stacked, wherein one side of the protection layer is provided with a plurality of first protrusions, and the hardness of the first protrusions is less than the hardness of the shielding layer.

[0007] Optionally, the elastic modulus of the first protrusions is less than the elastic modulus of the protection layer.

[0008] Optionally, the elastic modulus of the first protrusions is less than 1.2 GPa.

[0009] And / or, the tensile strength of the electromagnetic shielding film as a whole is greater than 15 MPa.

[0010] Optionally, in the preset observation range, the number of the first protruding parts with a ratio of protruding height to maximum width of 0.7-2 accounts for more than 50% in the slice state.

[0011] Optionally, the electromagnetic shielding film further comprises a glue film layer, and the glue film layer is arranged on the side of the shielding layer away from the protective layer.

[0012] Optionally, the glue film layer is provided with conductive particles, and the shielding layer is conductive to the circuit board body at least through the conductive particles.

[0013] Optionally, the shielding layer is in a relief shape in the thickness direction along any angle.

[0014] Optionally, the side of the glue film layer close to the shielding layer is provided with a plurality of second protruding parts, and the hardness of the second protruding parts is less than the hardness of the shielding layer.

[0015] Optionally, the electromagnetic shielding film further comprises a buffer layer, and the buffer layer is arranged on at least one side of the shielding layer.

[0016] To achieve the above-mentioned purpose, the second aspect of the present application further provides a circuit board comprising the electromagnetic shielding film of any one of the above-mentioned embodiments.

[0017] Compared with the prior art, the electromagnetic shielding film of the embodiment of the present application has the beneficial effects that: the electromagnetic shielding film comprises a protective layer and a shielding layer arranged in sequence, a plurality of first protruding parts are arranged on one side of the protective layer, so that the shielding layer is in a relief shape, the surface area of the shielding layer itself is increased, more electromagnetic reflection and absorption paths can be provided, the energy of the electromagnetic wave is greatly attenuated after multiple reflections and absorptions in the shielding layer, and the shielding effect of the electromagnetic shielding film on electromagnetic waves of different frequencies and different directions is significantly improved.

[0018] On the other hand, by arranging a plurality of first protruding parts on one side of the protective layer, the shielding layer is in a relief shape, the relief structure gives the shielding layer a certain flexibility, so that it is not easy to produce cracks in complex application scenarios such as bending and curling, and the stability of the shielding performance is ensured.

[0019] Further, by arranging a plurality of first protruding parts on one side of the protective layer, when the electromagnetic shielding film is bent, the first protruding parts can relieve external stress and slow down the damage of external stress to the shielding layer, thereby improving the bending performance of the electromagnetic shielding film.

[0020] Further, by arranging a plurality of first protruding parts with a hardness less than that of the shielding layer on one side of the protective layer, when the electromagnetic shielding film is bent, the first protruding parts can avoid extruding and piercing the shielding layer due to excessive hardness, thereby ensuring the integrity of the shielding layer and the stability of the shielding performance.BRIEF DESCRIPTION OF DRAWINGS BRIEF DESCRIPTION OF DRAWINGS

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

[0022] Figure 2 is a structural schematic diagram of a second electromagnetic shielding film provided by an embodiment of the present application;

[0023] Figure 3 is a structural schematic diagram of a third electromagnetic shielding film provided by an embodiment of the present application;

[0024] Figure 4 is a structural schematic diagram of a fourth electromagnetic shielding film provided by an embodiment of the present application;

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

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

[0027] Figure 7 is a structural schematic diagram of a seventh electromagnetic shielding film provided by an embodiment of the present application.

[0028] wherein, 1, protective layer; 2, shielding layer; 3, first protruding part; 4, bearing layer; 5, adhesive film layer; 51: conductive particles; 6, second protruding part; 7, buffer layer. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0030] In the description and claims of the specification, it is to be understood that the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", and the like refer to the orientation or position shown in the drawings, and are used only for convenience in describing the present application, and are not intended to indicate or imply that a particular orientation, construction or operation of the device or component is required, and therefore should not be construed as limiting the present application.

[0031] In addition, the terms first, second, etc. in the description and claims are only used for the purpose of distinguishing between similar technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features, nor necessarily describing the order or time sequence. The terms are interchangeable under appropriate circumstances. Thus, features defined with "first", "second" can explicitly or implicitly include at least one of the features.

[0032] Please refer to Figure 1 , Figure 1 is a structural schematic diagram of an electromagnetic shielding film according to an embodiment of the present application. The electromagnetic shielding film according to the embodiment of the present application comprises a protective layer 1 and a shielding layer 2 which are sequentially stacked, and a plurality of first protruding portions 3 are arranged on one side of the protective layer 1, and the hardness of the first protruding portions 3 is less than the hardness of the shielding layer 2.

[0033] In the embodiment of the present application, the protective layer 1 protects the shielding layer 2. The thickness of the protective layer 1 is 2-20 μm. The 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, and alkyd resin. Preferably, the thickness of the protective layer 1 is 3-10 μm.

[0034] It should be noted that when the electromagnetic shielding film is thin, a bearing layer 4 (see Figure 2 ) can be arranged on the surface of the protective layer 1 away from the shielding layer 2, so that the electromagnetic shielding film is not easy to wrinkle or break during processing and application. After the electromagnetic shielding film is pressed with the circuit board substrate, the bearing layer 4 is torn off, so the side of the bearing layer 4 close to the protective layer 1 is provided with a release agent. The thickness of the bearing layer is 38-50 μm. By limiting the thickness of the bearing layer 4 to 38-50 μm, the thickness of the bearing layer is within a suitable range, which can support the bearing without being too thin to support the bearing, and also can not be too thick to make the electromagnetic shielding film difficult to be pressed and filled into the grounding window, affecting the grounding effect.

[0035] It is worth noting that in the embodiment of the present application, the side of the protective layer 1 is provided with a plurality of first protruding parts 3. By providing a plurality of first protruding parts 3 on one side of the protective layer 1, the shielding layer 2 is in a undulating shape, the surface area of the shielding layer 2 itself is increased, more electromagnetic reflection and absorption paths can be provided, the energy of the electromagnetic wave is greatly attenuated after multiple reflections and absorptions in the shielding layer 2, and the shielding effect of the electromagnetic shielding film on electromagnetic waves of different frequencies and different directions is significantly improved. Secondly, the undulating structure gives the shielding layer a certain flexibility and ductility, so that it is not easy to produce cracks in complex application scenarios such as bending and curling, and the stability of the shielding performance is ensured. By providing a plurality of first protruding parts 3 on one side of the protective layer 1, the first protruding parts 3 can relieve external stress and slow down the damage of external stress to the shielding layer 2 when the electromagnetic shielding film is bent, thereby improving the bending performance of the electromagnetic shielding film.

[0036] Further, in the embodiment of the present application, the hardness of the first protruding part 3 is less than the hardness of the shielding layer 2. By providing a plurality of first protruding parts 3 with a hardness less than the hardness of the shielding layer 2 on one side of the protective layer 1, when the electromagnetic shielding film is bent, the first protruding parts 3 avoid extruding and piercing the shielding layer 2 due to excessive hardness, thereby ensuring the integrity of the shielding layer and further ensuring the stability of the shielding performance. Preferably, the material of the first protruding part 3 can be the same as or different from the protective layer 1, and the material of the first protruding part 3 can be at least one of polyester, rubber, polyolefin thermoplastic elastomer, thermoplastic polyurethane, polyether ester, polyamide, styrene, alkyd resin, epoxy resin, acrylic resin, polyimide, polyvinyl acetate, polyethylene, polypropylene and polyamide.

[0037] It should be noted that the elastic modulus of the first protruding part 3 is less than the elastic modulus of the protective layer 1. By setting the elastic modulus of the first protruding part 3 to be less than the elastic modulus of the protective layer 1, the first protruding part 3 has better elastic deformation ability. When subjected to external force, the first protruding part 3 preferentially deforms elastically, absorbs and disperses external force, reduces the direct effect of external force on the protective layer 1 and the shielding layer 2, and reduces the risk of damage to the electromagnetic shielding film caused by external force. At the same time, good elasticity helps the first protruding part 3 to tightly adhere to the shielding layer 2, maintains stable connection between the two, and ensures the structural integrity and excellent shielding performance of the electromagnetic shielding film.

[0038] Preferably, the elastic modulus of the first protruding part 3 is less than 1.2 GPa. By limiting the elastic modulus of the first protruding part 3 to be less than 1.2 GPa, it is ensured that the first protruding part 3 has appropriate elasticity and flexibility, and in actual application, the rigidity of the first protruding part 3 will not be too large due to the too high elastic modulus of the first protruding part 3, which cannot effectively absorb external force, so as to cause the electromagnetic shielding film to be squeezed and pierced in the bending application scenario, thereby causing the shielding performance to be greatly reduced; nor will the first protruding part 3 be deformed too much due to the too low elastic modulus of the first protruding part 3, thereby losing the protection and lamination effect on the shielding layer 2. Therefore, by limiting the elastic modulus of the first protruding part 3 to be less than 1.2 GPa, the external force can be effectively buffered, and the original state can be quickly restored after the external force disappears, thereby maintaining the close lamination with the shielding layer 2, so as to improve the mechanical properties and use stability of the electromagnetic shielding film.

[0039] Further, in a preset observation range, the number ratio of the first protruding part 3 with a protruding height to maximum width ratio of 0.7-2 is 50% or more. By setting the number ratio of the first protruding part 3 with a protruding height to maximum width ratio of 0.7-2 to be 50% or more, the size ratio of the first protruding part 3 is appropriate under the premise of cost control and yield control, and when stressed, the first protruding part 3 cannot fully play the elastic deformation capacity to absorb external force due to being too low and too wide, which can cause cracking when bending, thereby reducing the shielding performance of the electromagnetic shielding film; nor will the shielding layer 2 be pierced due to being too high or too wide, thereby affecting the shielding performance of the electromagnetic shielding film. Therefore, by setting the protruding height to maximum width ratio of the first protruding part 3 to be 0.7-2 and the number ratio to be 50% or more, the first protruding part 3 can have appropriate height to provide effective buffering and protection to the shielding layer 2 while ensuring sufficient contact area to enhance the lamination effect with the shielding layer 2; the reasonable size ratio ensures that the first protruding part 3 can fully play the elastic deformation capacity to absorb external force when stressed, thereby avoiding cracking of the electromagnetic shielding film and ensuring the comprehensive performance of the electromagnetic shielding film in actual application. Optionally, the ratio of the protruding height to the maximum width of the first protruding part 3 can be any one of 50%, 60%, 65%, 75%, 80%, 90% or 100% or an interval formed by any two of them.

[0040] It is worth mentioning that in the embodiment of the present application, the tensile strength of the electromagnetic shielding film as a whole is greater than 15 MPa. In use, the electromagnetic shielding film is arranged on the circuit board by hot pressing. Due to the unevenness of the circuit board, the electromagnetic shielding film will be stretched and torn during pressing. Therefore, the tensile strength of the electromagnetic shielding film as a whole is set to be greater than 15 MPa, so that the electromagnetic shielding film is not easy to break and damage under the stress of stretching and tearing, thereby ensuring the integrity of the electromagnetic shielding film structure; during installation and transportation, the electromagnetic shielding film can withstand certain external forces, preventing the electromagnetic shielding film from being damaged and affecting the shielding performance, thereby improving the reliability and applicability of the electromagnetic shielding film, and making it widely applicable to various electronic devices and scenes with certain strength requirements.

[0041] Referring to Figure 3 , Figure 3 is another structural schematic diagram of an electromagnetic shielding film provided by the embodiment of the present application. In the embodiment of the present application, the electromagnetic shielding film further comprises a glue film layer 5, which is arranged on the side of the shielding layer 2 away from the protective layer 1.

[0042] In the embodiment of the present application, the glue film layer 5 plays a bonding role. In the application of the circuit board, the electromagnetic shielding film is bonded to the circuit board through the glue film layer 5, so that the electromagnetic shielding film and the circuit board are not easy to bubble and separate, thereby avoiding separation and other problems and achieving shielding effect. The thickness of the glue film layer 5 is 1-20 μm. The glue film layer 5 is mainly selected from at least one of polyester, polyethylene, polyamide, rubber, acrylate, phenolic, epoxy, polyimide, urethane, melamine, alkyd and other resins.

[0043] Preferably, as Figure 4 shown, Figure 4 is another structural schematic diagram of an electromagnetic shielding film provided by the embodiment of the present application. In the embodiment of the present application, the glue film layer 5 is provided with conductive particles 51, and the shielding layer 2 is at least conductive to the circuit board body through the conductive particles 51. The conductive particles 51 in the glue film layer 5 build a good conductive path between the shielding layer 2 and the circuit board body, so that the shielding layer 2 can quickly and effectively conduct the sensed electromagnetic interference current to the ground to achieve reliable grounding. In addition, this grounding mode significantly enhances the electrostatic discharge capacity of the electromagnetic shielding film, reduces the interference and damage risk of electronic components caused by static electricity accumulation, and improves the electromagnetic compatibility and working stability of the circuit board and electronic equipment.

[0044] In one embodiment, the shielding layer 2 is in relief when a cross section is taken along a thickness direction at any angle. The term "any angle" means that a cross section is taken perpendicularly to the surface of the electromagnetic shielding film from any position on the surface of the electromagnetic shielding film, and the shielding layer 2 is in relief at any angle. The shielding layer 2 in relief at any angle 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 absorptions in the shielding layer 2, and the shielding effect of the electromagnetic shielding film on electromagnetic waves of different frequencies and different directions is significantly improved. In addition, the relief structure gives the shielding layer 2 greater flexibility and ductility, so that the shielding layer 2 is not prone to cracking in complex application scenarios such as bending and curling, and the stability of the shielding performance is ensured.

[0045] In combination Figure 3 In the embodiment of the present application, the adhesive film layer 5 is provided with a plurality of second protrusions 6 on the side close to the shielding layer 2, and the hardness of the second protrusions 6 is less than that of the shielding layer 2. By providing the adhesive film layer 5 with a plurality of second protrusions 6 on the side close to the shielding layer 2, the second protrusions 6 of the adhesive film layer 5 are embedded with the shielding layer 2 to form a mechanical interlocking structure after curing, which greatly enhances the bonding force between the adhesive film layer 5 and the shielding layer 2, and ensures that the electromagnetic shielding film is not prone to delamination when pasted to other components. At the same time, the hardness of the second protrusions 6 is less than that of the shielding layer 2, so that the second protrusions 6 deform first when subjected to external force impact, thereby buffering the influence of external force on the shielding layer 2 and preventing the shielding layer 2 from being damaged. In addition, the second protrusions 6 with lower hardness can better adapt to different surface topographies, improve the tightness of pasting, and ensure the overall shielding performance of the electromagnetic shielding film. Preferably, the material of the second protrusions 6 can be the same as or different from that of the adhesive film layer 5. The material of the second protrusions 6 can be at least one of polyester, rubber, polyolefin thermoplastic elastomer, thermoplastic polyurethane, polyether ester, polyamide, styrene, alkyd resin, epoxy resin, acrylic resin, polyimide, polyvinyl acetate, polyethylene, polypropylene, and polyamide.

[0046] It should be noted that, in the embodiment of the present application, the hardness of the second protrusions 6 refers to the hardness of the second protrusions 6 after the adhesive film layer is cured before being pressed onto the circuit board.

[0047] Reference Figure 5 As shown, Figure 5 is another structural schematic diagram of an electromagnetic shielding film provided by the embodiment of the present application. In the embodiment of the present application, the electromagnetic shielding film further comprises a buffer layer 7, and the buffer layer 7 is arranged on at least one side of the shielding layer 2 in a stacked manner. The buffer layer 7 is arranged between the protective layer 1 and the shielding layer 2 (as shown in Figure 5 ), or the buffer layer 7 is arranged between the shielding layer 2 and the adhesive film layer 5 (as shown in Figure 6), or, the buffer layer 7 is arranged between the protective layer 1 and the shielding layer 2 and between the shielding layer 2 and the adhesive film layer 5 (as shown in Figure 7 By arranging the buffer layer 7, the extrusion stress of the adhesive film layer 5 and the extrusion stress of the protective layer 1 are further buffered, so as to avoid the cracking of the electromagnetic shielding film and improve the bending resistance of the electromagnetic shielding film. When subjected to external force impact and extrusion, the buffer layer 7 can effectively absorb and disperse external force, further reducing the possibility of damage to the shielding layer 2; at the same time, the buffer layer 7 can fill the small gap between the shielding layer 2 and other components, improve the adhesion and sealing performance of the electromagnetic shielding film, reduce the leakage of electromagnetic waves, and enhance the overall electromagnetic shielding effect, so that the electromagnetic shielding film can still maintain good performance in complex use environment. Preferably, the thickness of the buffer layer 7 is 1-10 μm, and the buffer layer 7 is selected from at least one of polyester, rubber, polyolefin thermoplastic elastomer, thermoplastic polyurethane, polyether ester, polyamide or styrene.

[0048] The embodiments of the present application also provide a circuit board comprising the electromagnetic shielding film of any of the embodiments of the present application.

[0049] The electromagnetic shielding film and the circuit board provided by the embodiments of the present application have the beneficial effects that the electromagnetic shielding film comprises a protective layer and a shielding layer which are arranged in sequence, a plurality of first protruding parts are arranged on one side of the protective layer, so that the shielding layer is in a wavy shape, the surface area of the shielding layer itself is increased, more electromagnetic reflection and absorption paths are provided, the energy of electromagnetic waves is greatly attenuated after multiple reflections and absorptions in the shielding layer, and the shielding effect of the electromagnetic shielding film on electromagnetic waves of different frequencies and different directions is significantly improved.

[0050] On the other hand, by arranging a plurality of first protruding parts on one side of the protective layer, the shielding layer is in a wavy shape, the wavy structure gives the shielding layer a certain flexibility, so that it is not easy to produce cracks in complex application scenarios such as bending and curling, and the stability of the shielding performance is ensured.

[0051] Further, by arranging a plurality of first protruding parts on one side of the protective layer, when the electromagnetic shielding film is subjected to bending, the first protruding parts can relieve external stress and slow down the damage of external stress to the shielding layer, thereby improving the bending performance of the electromagnetic shielding film.

[0052] Further, by arranging a plurality of first protruding parts with a hardness less than that of the shielding layer on one side of the protective layer, when the electromagnetic shielding film is subjected to bending, the first protruding parts with a large hardness are prevented from extruding and piercing the shielding layer, so as to ensure the integrity of the shielding layer and further ensure the stability of the shielding performance.

[0053] In order to embody the beneficial effects of the electromagnetic shielding film and the circuit board provided by the embodiments of the present application, the following describes several embodiments and comparative examples.

[0054] Example 1:

[0055] An electromagnetic shielding film, comprising a protection layer 1 and a shielding layer 2 which are sequentially stacked, wherein one side of the protection layer 1 is provided with a plurality of first protrusions 3, and the hardness of the first protrusions 3 is less than the hardness of the shielding layer 2, and the ratio of the protrusion height to the maximum width of the first protrusions 3 in the slicing state is 0.7-2, and the number ratio of the first protrusions 3 is 50%.

[0056] Example 2:

[0057] The electromagnetic shielding film of the present embodiment is the same as that of Example 1, except that the ratio of the protrusion height to the maximum width of the first protrusions 3 is 0.7-2, and the number ratio of the first protrusions 3 is 70%.

[0058] Example 3:

[0059] The electromagnetic shielding film of the present embodiment is the same as that of Example 1, except that the ratio of the protrusion height to the maximum width of the first protrusions 3 is 0.7-2, and the number ratio of the first protrusions 3 is 80%.

[0060] Example 4:

[0061] The electromagnetic shielding film of the present embodiment is the same as that of Example 1, except that the ratio of the protrusion height to the maximum width of the first protrusions 3 is 0.7-2, and the number ratio of the first protrusions 3 is 100%.

[0062] Example 5:

[0063] The electromagnetic shielding film of the present embodiment is the same as that of Example 1, except that a buffer layer 7 is provided between the protection layer 1 and the shielding layer 2.

[0064] Example 6:

[0065] The electromagnetic shielding film of the present embodiment is the same as that of Example 1, except that a buffer layer 7 is provided between the shielding layer 2 and the adhesive film layer 5.

[0066] Example 7:

[0067] The electromagnetic shielding film of the present embodiment is the same as that of Example 1, except that a buffer layer 7 is provided between the protection layer 1 and the shielding layer 2, and between the shielding layer 2 and the adhesive film layer 5.

[0068] Comparative Example 1:

[0069] An electromagnetic shielding film, comprising a protection layer 1 and a shielding layer 2 which are sequentially stacked, wherein one side of the protection layer 1 is not provided with a first protrusion.

[0070] Comparative Example 2:

[0071] The electromagnetic shielding film of the present comparative example is the same as that of Example 1, except that the hardness of the first protruding portion 3 is greater than the hardness of the shielding layer 2.

[0072] Comparative Example 3:

[0073] The electromagnetic shielding film of the present comparative example is the same as that of Example 1, except that the ratio of the protruding height to the maximum width of the first protruding portion 3 in the sliced state is 0.7-2, and the number ratio is 10%.

[0074] Bending performance test:

[0075] The electromagnetic shielding covers of Examples 1-7 and Comparative Examples 1-3 were subjected to a bending performance test.

[0076] S1: Copper pieces were pressed onto both ends of a 25-micron PI film;

[0077] S2: The electromagnetic shielding film was pressed onto the 25-micron PI film at 185°C for 10 minutes and 120 kg, ensuring that the two copper pieces were electrically connected to the metal layer of the shielding film, and was cured at 160°C for 1.5 hours;

[0078] S3: The resistance of the two copper pieces was monitored using the test leads of the bending machine. When the resistance measured by the test leads increased by 100%, indicating that the metal layer had cracked, the count was stopped. The bending conditions were: bending radius 0.38 mm, bending speed 150 revolutions / minute, bending angle 135°, and weight 0.5 kg. The test results are shown in Table 1.

[0079] Table 1. Bending performance test of the electromagnetic shielding films of Examples 1-7 and Comparative Examples 1-3

[0080]

[0081] As can be seen from Table 1, by applying the electromagnetic shielding film of the present example, cracks are less likely to occur in complex application scenarios such as bending and curling, ensuring the stability of the shielding performance.

[0082] In summary, by providing a plurality of first protruding portions on one side of the protective layer, the shielding layer assumes a wavy shape, increasing the surface area of the shielding layer itself and providing more electromagnetic reflection and absorption paths, so that the energy of electromagnetic waves is greatly attenuated after multiple reflections and absorptions in the shielding layer, significantly improving the shielding effect of the electromagnetic shielding film on electromagnetic waves of different frequencies and directions.

[0083] On the other hand, by providing a plurality of first protruding portions on one side of the protective layer, the shielding layer assumes a wavy shape, and the wavy structure gives the shielding layer a certain flexibility, making it less likely to crack in complex application scenarios such as bending and curling, ensuring the stability of the shielding performance.

[0084] Further, by arranging a plurality of first protrusions on one side of the protective layer, the first protrusions can relieve external stress when the electromagnetic shielding film is bent, slow down damage to the shielding layer by external stress, and thus improve the bending performance of the electromagnetic shielding film.

[0085] Further, by arranging a plurality of first protrusions on one side of the protective layer, the first protrusions can relieve external stress when the electromagnetic shielding film is bent, slow down damage to the shielding layer by external stress, and thus improve the bending performance of the electromagnetic shielding film.

[0086] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but it should be understood that any combination of the technical features that does not cause contradiction is within the scope of the present disclosure.

[0087] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that, for those skilled in the art, some modifications and improvements can be made without departing from the concept of the present application, and these are within the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the appended claims.

Claims

1. An electromagnetic shielding film, characterized in that, The electromagnetic shielding film includes a protective layer and a shielding layer stacked in sequence. The protective layer has a plurality of first protrusions on one side facing the shielding layer. The hardness of the first protrusions is less than that of the shielding layer. The elastic modulus of the first protrusions is less than 1.2 GPa. The proportion of the number of first protrusions with a height-to-maximum-width ratio of 0.7 to 2 in the sliced ​​state is more than 50%.

2. The electromagnetic shielding film according to claim 1, characterized in that, The elastic modulus of the first protrusion is less than that of the protective layer.

3. The electromagnetic shielding film according to claim 2, characterized in that, The overall tensile strength of the electromagnetic shielding film is greater than 15 MPa.

4. The electromagnetic shielding film according to claim 1, characterized in that, The electromagnetic shielding film also includes an adhesive film layer, which is disposed on the side of the shielding layer away from the protective layer.

5. The electromagnetic shielding film according to claim 4, characterized in that, The adhesive film layer contains conductive particles, and the shielding layer is connected to the circuit board body at least through the conductive particles.

6. The electromagnetic shielding film according to any one of claims 4-5, characterized in that, The shielding layer is undulating when a cross-section is taken along the thickness direction at any angle.

7. The electromagnetic shielding film according to claim 6, characterized in that, The adhesive film layer has a plurality of second protrusions on one side near the shielding layer, and the hardness of the second protrusions is less than the hardness of the shielding layer.

8. The electromagnetic shielding film according to claim 7, characterized in that, The electromagnetic shielding film further includes a buffer layer, which is stacked on at least one side of the shielding layer, and is disposed between the protective layer and the shielding layer, or... The buffer layer is disposed between the shielding layer and the adhesive film layer, or, There are at least two buffer layers, which are respectively disposed between the protective layer and the shielding layer and between the shielding layer and the adhesive film layer.

9. A circuit board, characterized in that, The circuit board includes the circuit board body and the electromagnetic shielding film as described in any one of claims 1-8.

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