Electromagnetic shielding film and circuit board

Abstract

The invention relates to the technical field of electromagnetic shielding, and discloses an electromagnetic shielding film and a circuit board, the electromagnetic shielding film comprises a metal shielding layer, the metal shielding layer comprises a first crystal grain distribution space and a second crystal grain distribution space, and the first crystal grain distribution space and the second crystal grain distribution space are adjacent in the thickness direction of the metal shielding layer; the metal shielding layer comprises a first surface and a second surface which are oppositely arranged, the first crystal grain distribution space is located in an area which extends inwards from the first surface and / or the second surface by 10%-30% of the thickness of the metal shielding layer, and the average crystal grain size of the first crystal grain distribution space is smaller than that of the second crystal grain distribution space. The first crystal grain distribution space and the second crystal grain distribution space cooperate with each other, so that the risk of fracture of the metal shielding layer is reduced, and the bending resistance and fracture resistance of the metal shielding layer are improved.

Description

Technical Field

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

[0002] The electronic components inside electronic devices will continuously emit useless electromagnetic wave signals when in operation. These useless electromagnetic wave signals will affect the normal operation of other adjacent electronic components and generate electromagnetic interference (EMI). Applying electromagnetic shielding film to electronic components can suppress the leakage of useless electromagnetic waves and at the same time shield external electromagnetic wave noise from interfering with the operation of internal circuits. Electromagnetic shielding film is widely used in flexible circuit boards, chip packaging, and 5G communication modules. With the development of communication equipment, foldable electronic devices have gradually appeared in the public's field of vision. Usually, electromagnetic shielding film is applied to the circuit board or flexible board of the foldable electronic device to avoid electromagnetic interference from the outside world and the foldable electronic device while realizing the folding function of the foldable electronic device.

[0003] However, as the foldable electronic device is folded multiple times, the metal shielding layer in the electromagnetic shielding film breaks, causing the electromagnetic shielding film to fail, thereby affecting the normal use of the foldable electronic device. Summary of the Invention

[0004] In view of this, the present invention provides an electromagnetic shielding film and a circuit board to improve the bending resistance of the metal shielding layer.

[0005] In the first aspect, the present invention provides an electromagnetic shielding film, comprising a metal shielding layer, the metal shielding layer comprising a first grain distribution space and a second grain distribution space, the first grain distribution space and the second grain distribution space being adjacent to each other along the thickness direction of the metal shielding layer; the metal shielding layer comprising a first surface and a second surface arranged opposite to each other, the first grain distribution space being located in an area extending inward from the first surface and / or the second surface by 10% to 30% of the thickness of the metal shielding layer, and the average grain size of the first grain distribution space being smaller than the average grain size of the second grain distribution space.

[0006] When the electromagnetic shielding film is bent, part of the thickness at the bending position is subjected to tensile stress (prone to cracking), and part of the thickness is subjected to compressive stress (prone to plastic deformation). In the present invention, the first grain distribution space and the second grain distribution space are adjacent to each other along the thickness direction of the metal shielding layer. The high strength of the first grain distribution space is used to resist tensile stress, and the high plasticity of the second grain distribution space is used to adapt to compressive deformation. This can achieve the matching of stress gradient and structural gradient. At the same time, the forces on the first grain distribution space and the second grain distribution space in the thickness direction are complementary, and can undergo cooperative deformation, effectively reducing the local stress concentration phenomenon caused by the single overall structure when bending, and can reduce the risk of surface cracks when the electromagnetic shielding film is bent, thereby reducing the risk of failure of the electromagnetic shielding film. Even if cracks appear in the first grain distribution space of the electromagnetic shielding film when bending, the second grain distribution space can effectively disperse the stress through plastic deformation, thereby delaying the crack from extending to the second grain distribution space, maintaining the strength and electromagnetic shielding capability of the metal shielding layer for a certain period of time, delaying the overall failure time of the electromagnetic shielding film, and extending the service life of the electromagnetic shielding film. Furthermore, cracks in the first grain distribution space during bending release stress within the metal shielding layer, protecting the integrity of the grains within the second grain distribution space. This maintains the strength and electromagnetic shielding capability of the metal shielding layer for a certain period of time. Furthermore, the arrangement of the first and second grain distribution spaces can enhance the electromagnetic shielding capability of the electromagnetic shielding layer.

[0007] In some optional embodiments, the ratio of the average grain size of the first grain distribution space to the average grain size of the second grain distribution space is 0.02 to 0.8. By limiting the ratio of the average grain sizes of the two distribution spaces to the above range, on the one hand, it is beneficial for the first grain distribution space to have a higher tensile strength and the second grain distribution space to have a higher plasticity, and on the other hand, it reduces the risk of stress concentration caused by a large difference in the average grain size of the first grain distribution space and the second grain distribution space, so that the first grain distribution space and the second grain distribution space are optimized in mechanical properties, further improving the bending resistance and fracture resistance of the metal shielding layer, thereby further improving the structural stability of the electromagnetic shielding film.

[0008] In some optional embodiments, the average grain size of the first grain distribution space is 30 nm to 300 nm; and / or the average grain size of the second grain distribution space is 400 nm to 1500 nm. Limiting the average grain size of the first grain distribution space to the above ranges facilitates the first grain distribution space to have higher tensile strength. Limiting the average grain size of the second grain distribution space to the above ranges facilitates the second grain distribution space to have higher plasticity.

[0009] In some optional embodiments, the metal shielding layer includes a first sublayer and a second sublayer stacked together, the first sublayer forming a first grain distribution space, and the second sublayer forming a second grain distribution space. The orthographic projections of the first sublayer and the second sublayer on the first surface coincide with or substantially coincide with the first surface, and each sublayer is substantially entirely distributed within the metal shielding layer. When the electromagnetic shielding layer is bent, the sublayers can deform cooperatively, such that any position of the metal shielding layer has good bending resistance, thereby improving the bending flexibility of the foldable electronic device. Furthermore, when installed in the foldable electronic device, there is no need to consider the bending position of the foldable electronic device, resulting in lower installation precision requirements and easier installation.

[0010] In some optional embodiments, the first sublayer comprises two layers, with the second sublayer positioned between the two opposing first sublayers. This structure ensures that the first sublayer of the metal shielding film has high strength to withstand high tensile stress, while the second sublayer has high plasticity to withstand high compressive stress. Under various bending conditions, the first sublayer has a low risk of cracking, while the second sublayer can reduce the risk of brittle fracture by dispersing stress through coordinated deformation, further enhancing the metal shielding layer's bending resistance.

[0011] In some optional embodiments, in the metal shielding layer, the total thickness of the second sublayer is greater than the total thickness of the first sublayer. The larger total thickness of the second sublayer allows the plastic region in the metal shielding layer to occupy a larger proportion, providing a larger volume to coordinate deformation and absorb bending energy, which is more conducive to delaying the expansion of cracks appearing in the first grain distribution space to the second grain distribution space. At the same time, the second sublayer having a larger average grain size and a larger total thickness is conducive to the electromagnetic shielding film maintaining a larger electromagnetic shielding capability. The total thickness of the first sublayer is relatively small, which ensures a certain tensile strength while allowing the metal shielding layer to have an appropriate degree of freedom in bending, thereby further optimizing the bending resistance of the electromagnetic shielding film.

[0012] In some optional embodiments, the ratio of the total thickness of the second sublayer to the total thickness of the first sublayer is 2 to 30. This total thickness ratio can fully utilize the plasticity advantage of the second sublayer and the tensile strength advantage of the first sublayer. During the bending process, the stress transfer within the metal shielding layer is more uniform, effectively avoiding structural damage caused by excessive local stress, further improving the mechanical properties of the electromagnetic shielding film, further improving the bending resistance of the electromagnetic shielding film, and extending its service life.

[0013] In some optional embodiments, the material of the first grain distribution space is different from the material of the second grain distribution space, thereby facilitating the selection of materials or optimization of material properties according to the functional requirements of different distribution spaces.

[0014] In some optional embodiments, at the same temperature, the ratio of the electrical conductivity of the material in the first grain distribution space to the electrical conductivity of the material in the second grain distribution space is 0.5 to 2. The above limitation, while ensuring the overall electromagnetic shielding performance of the metal shielding layer, reduces the risk of uneven current distribution and thus additional stress concentration caused by excessive differences in the electrical conductivity between the first grain distribution space and the second grain distribution space. A reasonable electrical conductivity ratio facilitates the uniform conduction of current across the distribution spaces of the metal shielding layer during bending, reduces the impact of changes in electrical properties on structural performance, helps maintain the electromagnetic shielding performance and structural stability of the electromagnetic shielding film in a bent state, and indirectly improves its bending resistance.

[0015] In some optional embodiments, the difference in electrical conductivity between the material of the second grain distribution space and the material of the first grain distribution space at room temperature is 2MS / m to 40MS / m. The above limitation reduces the risk of additional stress concentration caused by uneven current distribution due to excessive difference in electrical conductivity between the first grain distribution space and the second grain distribution space, while ensuring the overall electromagnetic shielding performance of the metal shielding layer. A reasonable conductivity difference is conducive to the uniform conduction of current in each distribution space of the metal shielding layer during bending, reducing the impact of changes in electrical properties on structural performance, helping to maintain the electromagnetic shielding performance and structural stability of the electromagnetic shielding film in a bent state, and indirectly improving its bending resistance.

[0016] In some optional embodiments, the electrical conductivity of the material in the first grain distribution space at room temperature is 14 MS / m-65 MS / m.

[0017] In some optional embodiments, the thickness of the metal shielding layer is 0.5 μm to 5 μm. By limiting the thickness of the metal shielding layer to the above range, the metal shielding layer has good tensile strength, flexibility and shielding effect, making the electromagnetic shielding film suitable for foldable electronic devices.

[0018] In some optional embodiments, the electromagnetic shielding film includes a metal shielding unit, which includes a plurality of metal shielding layers stacked in sequence along the thickness direction of the electromagnetic shielding film, thereby facilitating improvement of the high-frequency shielding capability of the electromagnetic shielding film.

[0019] In some optional embodiments, the metal shielding unit includes a first metal shielding layer and a second metal shielding layer, the first metal shielding layer is more than two layers, the second metal shielding layer is located between two oppositely arranged first metal shielding layers, and the thickness of the second metal shielding layer is greater than the thickness of the first metal shielding layer.

[0020] In some optional embodiments, the thickness of the metal shielding unit is 0.5 μm to 5 μm. By limiting the thickness of the metal shielding unit to the above range, the metal shielding unit has good tensile strength, flexibility and shielding effect, making the electromagnetic shielding film suitable for foldable electronic devices.

[0021] In some optional embodiments, both the first surface and the second surface are undulating surfaces. The undulating structure can increase the surface area of ​​the metal shielding layer, thereby improving electromagnetic shielding performance. When the electromagnetic shielding film is bent, the undulating structure of the metal shielding layer helps guide tensile deformation, providing more space and degrees of freedom for deformation, and effectively dissipating bending stress, reducing the risk of excessive stress concentration in a specific area. This significantly enhances the adaptability and stability of the metal shielding layer during bending, improving the metal shielding layer's bending resistance.

[0022] In some optional embodiments, the electromagnetic shielding film further includes an adhesive film layer, the adhesive film layer being located on one side of the metal shielding layer and extending parallel to the metal shielding layer. The adhesive film layer not only ensures a reliable connection between the electromagnetic shielding film and the circuit board body but also provides a certain degree of cushioning and stress dispersion when the electromagnetic shielding film is bent.

[0023] In some optional embodiments, the surface of the metal shielding layer facing the adhesive film layer has a metal protrusion, and the metal protrusion penetrates the adhesive film layer; or, conductive particles are dispersed in the adhesive film layer.

[0024] When the electromagnetic shielding film is bent, the metal protrusions or the conductive particles dispersed within the film layer can adapt to the changing bend angle through self-deformation, ensuring the reliability of the ground connection and providing a certain degree of flexibility in the ground connection between the metal shielding layer and the circuit board body. Furthermore, the conductive particles dispersed within the film layer within the metal protrusions can also disperse the stress of the metal shielding layer during bending to a certain extent, reducing the risk of stress concentration at the connection point, thereby improving the grounding stability and bending resistance of the electromagnetic shielding film in the bent state.

[0025] In some optional embodiments, the electromagnetic shielding film further comprises an insulating layer, located on the side of the metal shielding layer facing away from the adhesive film layer. The insulating layer protects the metal shielding layer from damage such as friction and scratches, thereby reducing stress concentration and the risk of crack propagation caused by surface damage. Furthermore, the insulating layer can buffer external forces acting on the metal shielding layer to a certain extent, ensuring more uniform force distribution when the metal shielding layer is bent, thereby improving the bending resistance and service life of the electromagnetic shielding film.

[0026] In a second aspect, the present invention provides a circuit board, which includes a circuit board body and the electromagnetic shielding film provided in the first aspect, wherein the electromagnetic shielding film is arranged on the surface of the circuit board body and connected to the circuit board body. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in related technologies, the following briefly introduces the drawings required for use in the specific embodiments or related technical descriptions. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 It is a schematic structural diagram of an electromagnetic shielding film provided according to an embodiment of the present invention.

[0029] Figure 2 for Figure 1 Schematic diagram of the cross-sectional structure of a metal shielding layer.

[0030] Figure 3 for Figure 1 Schematic diagram of the cross-sectional structure of another metal shielding layer.

[0031] Figure 4 for Figure 1 A cross-sectional scanning electron microscope image of a metal shielding layer.

[0032] Figure 5 Schematic diagram of the cross-sectional structure of a bending test sample according to an embodiment of the present invention.

[0033] Description of reference numerals:

[0034] 1-electromagnetic shielding film; 11-metal shielding layer; 111-first grain distribution space; 112-second grain distribution space; 113-metal protrusion; 12-adhesive film layer; 13-insulating layer; 14-protective film; 15-carrier film; 2-PI film; 3-copper sheet. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0036] In the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion about the concepts of the present invention. The accompanying drawings illustrate various schematic diagrams of structures according to embodiments of the present invention. These figures are not drawn to scale; certain details are exaggerated and may be omitted for clarity. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions based on actual needs. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be an intervening layer / element between them. Furthermore, if a layer / element is "on" another layer / element in one orientation, it may be "below" the other layer / element when the orientation is reversed.

[0037] Electromagnetic shielding films usually contain a metal shielding layer, whose high conductivity enables it to reflect electromagnetic waves. When external electromagnetic waves reach the electromagnetic shielding film, electrons will move freely on the metal surface, thereby generating an induced current. This induced current will form a reverse electric field inside the metal shielding film. The reverse electric field can offset part of the external electromagnetic field, thereby reducing the impact on the internal circuit of the circuit board. For high-frequency electromagnetic waves, when high-frequency electromagnetic waves reach the electromagnetic shielding film, the metal shielding layer will produce an eddy current effect, that is, the high-frequency electromagnetic waves induce closed currents (eddy currents) inside the metal. The eddy currents will generate a reverse magnetic field to offset the original electromagnetic waves, making it impossible to penetrate the metal shielding layer and achieve electromagnetic shielding. However, the current metal shielding layer has limited bending resistance. As foldable electronic devices are repeatedly folded, the metal shielding layer will break and lose its electromagnetic shielding capability.

[0038] Based on this, the first aspect of the present invention provides an electromagnetic shielding film. Figure 1 It is understood that the electromagnetic shielding film 1 includes a metal shielding layer 11. Figure 2 or Figure 3 It is understood that the metal shielding layer 11 includes a first grain distribution space 111 and a second grain distribution space 112, and the first grain distribution space is adjacent to the second grain distribution space along the thickness direction of the metal shielding layer; the metal shielding layer includes a first surface and a second surface arranged opposite to each other, and the first grain distribution space is located in an area extending inward from the first surface and / or the second surface by 10% to 30% of the thickness of the metal shielding layer, and the average grain size of the first grain distribution space is smaller than the average grain size of the second grain distribution space.

[0039] The first grain distribution space has a smaller average grain size. According to the Hall-Petch effect, the smaller the grain, the higher the yield strength of the material, so that the first grain distribution space has a higher tensile strength, which can reduce the risk of crack initiation when the first grain distribution space is subjected to tensile stress; at the same time, the smaller the grain, the higher the grain boundary density, so that the first grain distribution space can effectively hinder dislocation movement and crack propagation; the first grain distribution space also has a higher hardness, which is beneficial to improving the overall hardness and structural stability of the electromagnetic shielding film, so that the electromagnetic shielding film can be used in wear-resistant scenarios.

[0040] The second grain distribution space has a larger average grain size. The larger the grain, the smaller the grain boundary density, which makes the second grain distribution space have higher plasticity and can absorb energy through coordinated deformation, thereby reducing the risk of brittle fracture of the second grain distribution space due to compressive stress.

[0041] When the electromagnetic shielding film is bent, part of its thickness at the bending position is subjected to tensile stress (prone to cracking), and part of its thickness is subjected to compressive stress (prone to plastic deformation). In the present invention, the first grain distribution space and the second grain distribution space are adjacent along the thickness direction of the metal shielding layer. The high strength of the first grain distribution space is used to resist tensile stress, and the high plasticity of the second grain distribution space is used to adapt to compressive deformation. This can achieve matching of stress gradient and structural gradient. At the same time, the forces on the first grain distribution space and the second grain distribution space in the thickness direction complement each other, and can produce cooperative deformation, effectively reducing the local stress concentration phenomenon caused by the single overall structure during bending, which can reduce the risk of surface cracks initiating when the electromagnetic shielding film is bent, and reduce the risk of electromagnetic shielding film failure.

[0042] Even if cracks appear in the first grain distribution space of the electromagnetic shielding film during bending, the second grain distribution space can effectively disperse stress through plastic deformation, thereby delaying the propagation of cracks into the second grain distribution space. This maintains the strength and electromagnetic shielding capability of the metal shielding layer for a certain period of time, delaying the failure of the electromagnetic shielding film as a whole, and extending the service life of the electromagnetic shielding film. Furthermore, cracks in the first grain distribution space during bending can release stress within the metal shielding layer, which helps protect the integrity of the grains in the second grain distribution space, thereby maintaining the strength and electromagnetic shielding capability of the metal shielding layer for a certain period of time.

[0043] In summary, the first grain distribution space can inhibit the initiation of surface cracks and extend the fatigue life of the electromagnetic shielding film; the second grain distribution space provides a plastic barrier to prevent crack penetration and maintain the electromagnetic shielding capability of the metal shielding layer. The first and second grain distribution spaces work together to reduce the risk of fracture in the metal shielding layer, improve the bending and fracture resistance of the metal shielding layer, extend the service life of the electromagnetic shielding film, and thus improve the reliability of foldable electronic devices after multiple bending. At the same time, the provision of the first and second grain distribution spaces can improve the electromagnetic shielding capability of the electromagnetic shielding layer.

[0044] In the present invention, the extension direction of the first surface and the second surface is parallel to the extension direction of the metal shielding layer. The first grain distribution space and the second grain distribution space are adjacent along the thickness direction of the metal shielding layer, which means that the orthographic projection of the first grain distribution space on the first surface is located within the orthographic projection of the second grain distribution space on the first surface, or the orthographic projection of the second grain distribution space on the first surface is located within the orthographic projection of the first grain distribution space on the first surface, or the orthographic projection of the second grain distribution space on the first surface coincides with the orthographic projection of the first grain distribution space on the first surface.

[0045] In some optional embodiments, the ratio of the average grain size of the first grain distribution space to the average grain size of the second grain distribution space is 0.02 to 0.8, for example, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, etc., or a range consisting of any of the above values. By limiting the ratio of the average grain sizes of the two distribution spaces to the above range, on the one hand, it is beneficial for the first grain distribution space to have a higher tensile strength and the second grain distribution space to have a higher plasticity, and on the other hand, it reduces the risk of stress concentration caused by excessive difference in the average grain size of the first grain distribution space and the second grain distribution space, so that the first grain distribution space and the second grain distribution space are optimized in mechanical properties, further improving the bending resistance and fracture resistance of the metal shielding layer, thereby further improving the structural stability of the electromagnetic shielding film. Preferably, the ratio of the average grain size in the first grain distribution space to the average grain size in the second grain distribution space is 0.15 to 0.4.

[0046] Specifically, the average grain size of the first grain distribution space can be 30 nm to 300 nm, for example, 30 nm, 60 nm, 90 nm, 120 nm, 150 nm, 180 nm, 210 nm, 240 nm, 270 nm, 300 nm, or a range consisting of any of the above values. By limiting the average grain size of the first grain distribution space to the above range, the first grain distribution space is conducive to having a higher tensile strength. Preferably, the average grain size of the first grain distribution space is 100 nm to 260 nm.

[0047] Specifically, the average grain size of the second grain distribution space can be 400nm to 1500nm, for example, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, 1100nm, 1200nm, 1300nm, 1400nm, 1500nm, etc., or a range consisting of any of the above values. By limiting the average grain size of the second grain distribution space to the above range, it is beneficial for the second grain distribution space to have higher plasticity. Preferably, the average grain size of the second grain distribution space is 860nm to 1250nm.

[0048] In the present invention, the orthographic projection of the first grain distribution space on the first surface coincides with at least a partial area of ​​the first surface, and the orthographic projection of the second grain distribution space on the first surface coincides with at least a partial area of ​​the first surface.

[0049] In some optional embodiments, the first grain distribution space and / or the second sublayer are regionally distributed in the metal shielding layer, that is, the first grain distribution space and / or the second sublayer are not distributed in the metal shielding layer as a whole, but are distributed corresponding to common bending positions of the folding electronic device to improve the reliability of the folding electronic device during multiple bending. Taking into account that the bending states of different positions of the folding electronic device may be different, some areas of the same surface are subjected to tensile stress and some areas are subjected to compressive stress, in special cases, part of the first grain distribution space is set close to the first surface and part of the first grain distribution space is set close to the second surface, and correspondingly, part of the second grain distribution space is set close to the first surface and part of the second grain distribution space is set close to the second surface.

[0050] In some other optional embodiments, reference Figure 2 or Figure 3It is understood that the metal shielding layer may include a first sublayer and a second sublayer stacked together, the first sublayer constituting a first grain distribution space, and the second sublayer constituting a second grain distribution space. That is, the orthographic projections of the first sublayer and the second sublayer on the first surface coincide with or substantially coincide with the first surface, and each sublayer is substantially distributed in the metal shielding layer. When the electromagnetic shielding layer is bent, each sublayer can deform cooperatively, so that any position of the metal shielding layer has good bending resistance, thereby improving the bending flexibility of the folding electronic device. When installed in the folding electronic device, there is no need to consider the bending position of the folding electronic device, and the installation precision requirement is low, which is convenient for installation. The first sublayer and the second sublayer can be formed by an electroplating process, which is low in cost.

[0051] In some embodiments, reference Figure 2 It is understood that the number of the first sublayer and the second sublayer in the metal shielding layer can both be one. Generally, when an electromagnetic shielding film is bent, the thickness of the portion near one surface at the bend is subjected to compressive stress, while the thickness of the portion near the opposite surface is subjected to tensile stress. The above structure enables the first surface and the second surface to withstand relatively large compressive and tensile stresses, respectively, reducing the risk of fracture of the electromagnetic shielding film.

[0052] In other embodiments, considering that the foldable electronic device may be bent repeatedly during use, that is, the bending state of the same position of the electromagnetic shielding film may be different at different times, and the stress on the same local area of ​​the same surface at different times may change repeatedly between tensile stress and compressive stress. Figure 3 It is understood that the first sublayer in the metal shielding layer can be two layers, and the second sublayer is located between the two first sublayers arranged oppositely. The above structure enables the first sublayer (i.e., the outer layer) of the metal shielding film to have a higher strength to withstand a larger tensile stress, and the second sublayer (inner layer) to have a higher plasticity to withstand a larger compressive stress. Under different bending states, the outer layer has a lower risk of cracking, and the inner layer can reduce the risk of brittle fracture by coordinating deformation and dispersing stress, further improving the bending resistance of the metal shielding layer; even if cracks appear in the outer layer during bending, the inner layer can also delay the crack expansion to the inside through plastic deformation. At the same time, cracks in the outer layer can release the stress in the metal shielding layer, which is beneficial to protecting the integrity of the inner layer grains, thereby delaying the overall failure time of the electromagnetic shielding film and extending the service life of the electromagnetic shielding film.

[0053] Optionally, in the metal shielding layer, the total thickness of the second sublayer may be greater than the total thickness of the first sublayer. It can be understood that when there are multiple first sublayers in the metal shielding layer, the total thickness of the second sublayer is the sum of the thicknesses of the multiple first sublayers; when there are multiple second sublayers in the metal shielding layer, the total thickness of the second sublayer is the sum of the thicknesses of the multiple second sublayers; when the metal shielding layer contains a single first sublayer, the total thickness of the second sublayer is the thickness of the single first sublayer; and when the metal shielding layer contains a single second sublayer, the total thickness of the second sublayer is the thickness of the single second sublayer.

[0054] The second sublayer can undergo plastic deformation when the electromagnetic shielding film is bent. The large total thickness of the second sublayer allows the plastic area in the metal shielding layer to occupy a larger proportion, providing a larger volume to coordinate deformation and absorb bending energy, thereby better adapting to bending deformation, absorbing and dispersing most of the bending stress, and being more conducive to delaying the expansion of cracks that appear in the first grain distribution space to the second grain distribution space. At the same time, the large total thickness of the second sublayer means that the electromagnetic shielding function of the electromagnetic shielding film mainly comes from the second sublayer, and the high plasticity of the second sublayer also makes the probability of cracking lower than that of the first sublayer. It can be seen that the second sublayer has a larger average grain size and a larger total thickness, which is conducive to the electromagnetic shielding film maintaining a larger electromagnetic shielding capability. In addition, the large total thickness of the second sublayer can also improve the overall stiffness of the electromagnetic shielding film and reduce the risk of fracture due to excessive local deformation.

[0055] The first sublayer's reduced overall thickness ensures a certain degree of tensile strength while allowing the metal shielding layer adequate bending freedom, further optimizing the electromagnetic shielding film's flexural resistance. Furthermore, the first sublayer's reduced overall thickness helps reduce the film's overall weight. Furthermore, the first sublayer's higher strength compensates for the increased localized stresses associated with its reduced overall thickness.

[0056] Optionally, in the metal shielding layer, the ratio of the total thickness of the second sublayer to the total thickness of the first sublayer can be 2 to 30. For example, the ratio of the total thickness of the second sublayer to the total thickness of the first sublayer can be 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, etc., or a range consisting of any of the above values. The above total thickness ratio can give full play to the plasticity advantage of the second sublayer and the tensile strength advantage of the first sublayer. During the bending process, the stress transfer in the metal shielding layer is more uniform, effectively avoiding structural damage caused by excessive local stress, further improving the mechanical properties of the electromagnetic shielding film, further improving the bending resistance of the electromagnetic shielding film and extending its service life. Preferably, the ratio of the total thickness of the second sublayer to the total thickness of the first sublayer is 4-10.

[0057] In some optional embodiments, the thickness of the metal shielding layer can be 0.5 μm to 5 μm, such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or the like, or a range consisting of any of the above values, preferably 0.8 μm to 1.5 μm. By limiting the thickness of the metal shielding layer to the above range, the metal shielding layer has good tensile strength, flexibility, and shielding effect, making the electromagnetic shielding film suitable for foldable electronic devices.

[0058] In the present invention, the material of the metal shielding layer includes but is not limited to at least one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. The material of the first grain distribution space and the material of the second grain distribution space may be the same or different. Preferably, the material of the first grain distribution space is different from the material of the second grain distribution space, which is conducive to selecting materials or optimizing material properties according to the functional requirements of different distribution spaces. For example, the second grain distribution space uses a material with good plasticity (such as copper), and the first grain distribution space uses a material with greater tensile strength (such as silver and / or nickel), so that the metal shielding layer has excellent bending resistance.

[0059] In some optional embodiments, at the same temperature, the ratio of the electrical conductivity of the material in the first grain distribution space to the electrical conductivity of the material in the second grain distribution space is 0.5 to 2, such as 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, etc., or a range consisting of any of the above values. The above limitation reduces the risk of additional stress concentration caused by uneven current distribution due to excessive difference in conductivity between the first grain distribution space and the second grain distribution space, while ensuring the overall electromagnetic shielding performance of the metal shielding layer. A reasonable conductivity ratio is conducive to the uniform conduction of current in each distribution space of the metal shielding layer during bending, reducing the impact of changes in electrical properties on structural performance, helping to maintain the electromagnetic shielding performance and structural stability of the electromagnetic shielding film in a bent state, and indirectly improving its bending resistance. Preferably, at the same temperature, the ratio of the electrical conductivity of the material in the first grain distribution space to the electrical conductivity of the material in the second grain distribution space is 0.8-1.5.

[0060] In some optional embodiments, the difference in electrical conductivity between the material of the second grain distribution space and the material of the first grain distribution space at room temperature is 2MS / m to 40MS / m, such as 2MS / m, 4MS / m, 8MS / m, 12MS / m, 16MS / m, 20MS / m, 24MS / m, 28MS / m, 32MS / m, 36MS / m, 40MS / m, etc., or a range consisting of any of the above values. The above limitation reduces the risk of additional stress concentration caused by uneven current distribution due to excessive difference in electrical conductivity between the first grain distribution space and the second grain distribution space, while ensuring the overall electromagnetic shielding performance of the metal shielding layer. A reasonable conductivity difference is conducive to the uniform conduction of current in each distribution space of the metal shielding layer during bending, reducing the impact of changes in electrical properties on structural performance, helping to maintain the electromagnetic shielding performance and structural stability of the electromagnetic shielding film in a bent state, and indirectly improving its bending resistance. Preferably, the difference between the electrical conductivity of the material in the second grain distribution space and the electrical conductivity of the material in the first grain distribution space at room temperature is 10 MS / m-20 MS / m.

[0061] Optionally, the electrical conductivity of the material in the first grain distribution space at room temperature is 14MS / m-65MS / m, such as 14MS / m, 20MS / m, 25MS / m, 30MS / m, 35MS / m, 40MS / m, 45MS / m, 50MS / m, 55MS / m, 60MS / m, 65MS / m, etc., or a range consisting of any of the above values, preferably 15MS / m-46MS / m.

[0062] In some optional embodiments, both the first surface and the second surface are undulating surfaces (not shown). That is, the metal shielding layer is wavy in any cross-section parallel to the thickness direction of the electromagnetic shielding film, and the metal shielding layer has an undulating structure. The undulating structure can increase the surface area of ​​the metal shielding layer, thereby improving the electromagnetic shielding performance. When the electromagnetic shielding film is bent, the undulating structure of the metal shielding layer is conducive to guiding the tensile deformation, can provide more space and freedom for its deformation, and can effectively disperse the bending stress, reduce the risk of excessive concentration of stress in a certain local area, significantly enhance the adaptability and stability of the metal shielding layer during the bending process, and improve the bending resistance of the metal shielding layer. The thickness of the metal shielding layer with an undulating structure refers to the average value of the shortest distance from any n measuring points on the first surface to the second surface along the thickness direction of the electromagnetic shielding film.

[0063] In some optional embodiments, the electromagnetic shielding film includes a metal shielding unit (not shown), which includes a plurality of metal shielding layers stacked in sequence along the thickness direction of the electromagnetic shielding film, which is beneficial to improving the high-frequency shielding capability of the electromagnetic shielding film. Specifically, high-frequency electromagnetic waves have a significant skin effect. Most of the materials inside the metal shielding layer with a single-layer structure cannot participate in the shielding due to the skin effect, resulting in material waste; while in the metal shielding layer with a multi-layer structure, the thickness of each layer is close to or less than the skin depth, so each surface layer can independently carry high-frequency current, which is equivalent to increasing the effective shielding area and improving the reflection and absorption efficiency in the high-frequency band. At the same time, electromagnetic waves can be reflected and refracted at the interface of each layer of the metal shielding layer with a multi-layer structure, and each reflection is accompanied by energy loss, thereby significantly improving the total absorption efficiency.

[0064] Optionally, the metal shielding unit may include a first metal shielding layer and a second metal shielding layer, the first metal shielding layer is more than two layers, the second metal shielding layer is located between two oppositely arranged first metal shielding layers, and the thickness of the second metal shielding layer is greater than that of the first metal shielding layer.

[0065] Optionally, the thickness of the metal shielding unit is 0.5 μm to 5 μm, such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a range consisting of any of the above values, preferably 1 μm to 2 μm. By limiting the thickness of the metal shielding unit to the above range, the metal shielding unit has good tensile strength, flexibility, and shielding effect, making the electromagnetic shielding film suitable for foldable electronic devices.

[0066] In some optional embodiments, combined with Figure 1 As shown, the electromagnetic shielding film 1 also includes: an adhesive film layer 12, which is located on one side of the metal shielding layer 11, and the extension direction of the adhesive film layer 12 is parallel to the extension direction of the metal shielding layer 11. The adhesive film layer 12 not only achieves a reliable connection between the electromagnetic shielding film and the circuit board body, but also plays a certain buffering and stress dispersion role when the electromagnetic shielding film is bent. Specifically, the adhesive film layer 12 can absorb part of the bending stress, preventing the stress from directly acting on the connection part between the metal shielding layer 11 and the circuit board body, reducing the risk of connection failure or damage to the metal shielding layer 11 due to stress concentration at the connection part, thereby improving the connection stability and overall bending resistance of the electromagnetic shielding film in the bent state. Exemplarily, the material of the adhesive film layer 12 includes but is not limited to epoxy resin. The adhesive film layer has two surfaces arranged opposite to each other, and the thickness of the adhesive film layer refers to the average value of the shortest distance from any p measurement points on one surface to the other surface along the thickness direction of the electromagnetic shielding film.

[0067] refer to Figure 1It is understood that in some embodiments, the metal shielding layer 11 has a metal protrusion 113 on one surface facing the film layer 12 , and the metal protrusion passes through the film layer 12 , and the metal protrusion is used to be grounded to the circuit board body. Figure 4 This is a scanning electron microscope image of a cross-section of a metal shielding layer. When the electromagnetic shielding film is bent, the metal protrusions deform to adapt to the changing bend angle, ensuring a reliable ground connection and providing flexibility in the ground connection between the metal shielding layer 11 and the circuit board body. Furthermore, the presence of the metal protrusions disperses stress on the metal shielding layer 11 during bending, reducing the risk of stress concentration at the connection point. This improves the grounding stability and bending resistance of the electromagnetic shielding film when bent.

[0068] In other embodiments, conductive particles are dispersed within the adhesive film layer 12, and the metal shielding layer 11 is grounded to the circuit board body at least via the conductive particles. When the electromagnetic shielding film is bent, the conductive particles dispersed within the adhesive film layer 12 can deform to maintain a conductive path between the metal shielding layer 11 and the circuit board body, ensuring continuity and stability of the grounding. Furthermore, the conductive particles can also disperse stress on the metal shielding layer 11 during bending, reducing the risk of stress concentration damaging the adhesive film layer 12 or reducing its conductivity, thereby improving the grounding performance and bending resistance of the electromagnetic shielding film when bent.

[0069] In some other embodiments, the metal shielding layer 11 has a metal protrusion on a surface facing the adhesive film layer 12 , and the metal protrusion penetrates the adhesive film layer 12 , and conductive particles are dispersed in the adhesive film layer 12 .

[0070] In some optional embodiments, the electromagnetic shielding film may further include an insulating layer 13, which is located on the side of the metal shielding layer 11 away from the adhesive film layer 12. The insulating layer 13 protects the metal shielding layer 11, protects the metal shielding layer 11 from damage such as external friction and scratches, and reduces the risk of stress concentration and crack propagation caused by surface damage. At the same time, the insulating layer 13 can buffer the external force on the metal shielding layer 11 to a certain extent, so that the metal shielding layer 11 is more evenly stressed when bent, thereby improving the bending resistance and service life of the electromagnetic shielding film. The insulating layer has two surfaces arranged relative to each other, and the thickness of the insulating layer refers to the average value of the shortest distance from any m measurement points on one surface to the other surface along the thickness direction of the electromagnetic shielding film.

[0071] In some optional embodiments, the electromagnetic shielding film may further include a buffer layer (not shown), which is located on the side of the metal shielding layer 11 facing away from the adhesive film layer 12. When the electromagnetic shielding film is bent, the buffer layer can absorb and buffer external forces (such as the extrusion stress of the adhesive film layer and the insulating layer) to further disperse the stress on the metal shielding layer 11. Its soft material properties can make the metal shielding layer 11 more evenly stressed during the bending process, reduce the risk of crack generation and expansion due to stress concentration, significantly improve the bending resistance and fatigue resistance of the electromagnetic shielding film, and extend its service life. The buffer layer can be located on the surface of the insulating layer 13 facing away from the metal shielding layer 11, or it can be located between the insulating layer 13 and the metal shielding layer 11.

[0072] In some optional embodiments, the electromagnetic shielding film may further include a protective film 14 and a carrier film 15. The protective film 14 is located on the side of the adhesive film layer 12 facing away from the metal shielding layer 11, and the carrier film 15 is located on the side of the insulating layer 13 facing away from the metal shielding layer 11. The carrier film 15 is the base for the insulating layer 13 and can be made of a polymer material such as PET. The protective film 14 is used to protect the adhesive film layer 12 and can be made of a material such as release paper.

[0073] In the present invention, the electromagnetic shielding film has a tensile strength greater than 15 MPa and has good bending resistance.

[0074] In some embodiments, the elongation of the laminated structure composed of a metal shielding layer or a metal shielding unit and an insulating layer is greater than 10%. The special metal shielding layer structure can increase the elongation of the metal shielding layer. The greater elongation can further improve the bending resistance and avoid breakage of the metal shielding layer.

[0075] A second aspect of the present invention provides a circuit board comprising a circuit board body and the electromagnetic shielding film of the first aspect, the electromagnetic shielding film being disposed on a surface of the circuit board body and connected to the circuit board body. This circuit board has all the advantages of the electromagnetic shielding film described above, which are not further elaborated here.

[0076] Specifically, the adhesive film layer can be formed on one side surface of the metal shielding layer through a coating process. After the metal shielding film is pressed onto the circuit board body, the adhesive film layer is cured to form a tight connection between the metal shielding film and the circuit board body. The circuit board body has a grounding window for grounding the metal shielding film. The metal shielding layer is electrically connected to the grounding layer of the circuit board body through the grounding window to form a ground, thereby conducting electromagnetic interference.

[0077] Circuit boards include but are not limited to flexible circuit boards (FPCs). It should be understood that the electromagnetic shielding film provided by the present invention can also be applied to other electronic components such as rigid circuit boards.

[0078] Specific embodiments are provided below to support the technical effects of this application.

[0079] Example 1

[0080] This embodiment provides an electromagnetic shielding film, which includes a carrier film, an insulating layer, a metal shielding layer, an adhesive film layer and a protective film stacked in sequence.

[0081] The metal shielding layer has an undulating structure and includes a first surface and a second surface disposed opposite each other. The region extending 0.5 μm inward from the first and second surfaces is the first sublayer, with an average grain size of 266 nm and made of Ag. The region 1.3 μm thick between the two first sublayers is the second sublayer, with an average grain size of 1.1 μm and made of Cu. Hereinafter, the thickness of the first sublayer is referred to as 0.5 μm, and the thickness of the second sublayer is referred to as 1.3 μm. The sum of the thicknesses of the first and second sublayers constitutes the thickness of the metal shielding layer.

[0082] The thickness of the insulating layer is 5.4 μm, and the material is a mixture of epoxy resin, polyimide, rubber, and ink; the thickness of the film layer is 3 μm, and the material is modified epoxy resin.

[0083] Examples 2 to 12-Comparative Examples 1 to 2

[0084] The differences between Examples 2 to 12—Comparative Examples 1 to 2 and Example 1 are detailed in Table 1.

[0085] The difference between Example 2-4 and Example 1 is only that the thickness of the first sub-layer is different, and the thickness of the second sub-layer is the same;

[0086] The difference between Examples 5-7 and Example 1 is only that the thickness of the second sub-layer is different, and the thickness of the first sub-layer is the same;

[0087] The difference between Examples 8-10 and Example 1 is only that the average grain size of the first sub-layer is different, and the average grain size of the second sub-layer is the same;

[0088] The difference between Examples 11-12 and Example 1 is only that the average grain size of the second sub-layer is different, and the average grain size of the first sub-layer is the same;

[0089] The only difference between Comparative Example 1-2 and Example 1 is that the average grain size of the second sublayer and the average grain size of the first sublayer in Comparative Example 1 are the same as the average grain size of the first sublayer in Example 1, and the average grain size of the second sublayer and the average grain size of the first sublayer in Comparative Example 2 are the same as the average grain size of the second sublayer in Example 1; the thickness of the metal shielding layer in Comparative Example 1-2 is the same as that in Example 1, the thickness of the second sublayer in Comparative Example 1-2 is the same as that of the second sublayer in Example 1, and the thickness of the first sublayer in Comparative Example 1-2 is the same as that of the first sublayer in Example 1.

[0090] Bending performance test

[0091] The electromagnetic shielding films of Examples 1-12 and Comparative Examples 1-2 were subjected to bending performance tests according to the following steps. The test results are shown in Table 1:

[0092] S1. Press the copper sheet 3 onto both ends of the 25 μm thick and 1.5 cm wide strip PI film 2;

[0093] S2, remove the carrier film and protective film on the surface of the strip electromagnetic shielding film 1, place the adhesive film layer of the electromagnetic shielding film 1 toward the PI film 2 and the copper sheet 3, and heat the PI film 2 at a temperature of 185°C and a pressure of 120kg / cm 2 The copper sheet 3 was pressed with a pressure of 10 minutes to ensure electrical connection between the metal shielding layer of the electromagnetic shielding film 1 and cured at 160°C for 1.5 hours to obtain Figure 5 Bend test specimen shown;

[0094] S3. The test lead of the bending machine is electrically connected to the copper sheet to monitor the resistance of the copper sheet and record the initial resistance;

[0095] S4. Start the bending machine and bend the test sample. Record the number of bends until the copper sheet's resistance increases to twice its initial resistance. Bending conditions are: bending radius 0.38 mm, bending speed 150 rpm, bending angle 135°, load 0.5 kg. When the copper sheet's resistance increases to twice its initial resistance, it indicates a break in the metal shielding layer.

[0096] Table 1

[0097]

[0098] As shown in Table 1, the electromagnetic shielding film provided by the present invention has a stronger bending resistance, which is conducive to ensuring the stability of the shielding performance of the electromagnetic shielding film. At the same time, as shown in Examples 1-4, the bending resistance of the electromagnetic shielding film gradually increases with the increase of the thickness of the first sublayer, which may be due to the fact that the thicker the first sublayer, the greater its tensile strength; as shown in Examples 1, 5-7, the bending resistance of the electromagnetic shielding film gradually increases with the increase of the thickness of the second sublayer, which may be due to the fact that the thicker the second sublayer, the greater its plasticity; as shown in Examples 1, 8-10, the bending resistance of the electromagnetic shielding film gradually increases with the decrease of the average grain size of the first sublayer, which may be due to the fact that the smaller the average grain size of the first sublayer, the greater its tensile strength; as shown in Examples 1, 11-12, the bending resistance of the electromagnetic shielding film gradually increases with the increase of the average grain size of the second sublayer, which may be due to the fact that the smaller the average grain size of the second sublayer, the greater its plasticity.

[0099] In the description of this specification, the reference terms "this embodiment", "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in an appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples, unless otherwise clearly defined. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, "multiple" means at least two, such as two, three, etc., unless otherwise clearly defined.

[0100] The above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described above, and that various obvious changes, readjustments, combinations, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of protection of the present invention is determined by the scope of the appended claims.

Claims

1. An electromagnetic shielding film comprising a metal shielding layer, characterized in that: The metal shielding layer includes a first grain distribution space and a second grain distribution space, and the first grain distribution space is adjacent to the second grain distribution space along the thickness direction of the metal shielding layer; the metal shielding layer includes a first surface and a second surface arranged opposite to each other, and the first grain distribution space is located in an area extending inward from the first surface and / or the second surface by 10% to 30% of the thickness of the metal shielding layer, and the average grain size of the first grain distribution space is smaller than the average grain size of the second grain distribution space.

2. The electromagnetic shielding film according to claim 1, wherein The ratio of the average grain size of the first grain distribution space to the average grain size of the second grain distribution space is 0.02 to 0.

8.

3. The electromagnetic shielding film according to claim 1, wherein The average grain size of the first grain distribution space is 30 nm to 300 nm; and / or the average grain size of the second grain distribution space is 400 nm to 1500 nm.

4. The electromagnetic shielding film according to claim 1, wherein The metal shielding layer includes a first sublayer and a second sublayer stacked together, the first sublayer constituting the first crystal grain distribution space, and the second sublayer constituting the second crystal grain distribution space; Preferably, the first sub-layer consists of two layers, and the second sub-layer is located between two oppositely arranged first sub-layers.

5. The electromagnetic shielding film according to claim 4, wherein In the metal shielding layer, the total thickness of the second sublayer is greater than the total thickness of the first sublayer; Preferably, the ratio of the total thickness of the second sub-layer to the total thickness of the first sub-layer is 2-30.

6. The electromagnetic shielding film according to any one of claims 1 to 5, characterized in that The metal shielding layer meets one or more of the following conditions: The material of the first grain distribution space is different from the material of the second grain distribution space; At the same temperature, the ratio of the electrical conductivity of the material in the first grain distribution space to the electrical conductivity of the material in the second grain distribution space is 0.5 to 2; The difference between the electrical conductivity of the material in the second grain distribution space and the electrical conductivity of the material in the first grain distribution space at room temperature is 2MS / m to 40MS / m; The electrical conductivity of the material in the first grain distribution space at room temperature is 14MS / m-65MS / m; The thickness of the metal shielding layer is 0.5 μm to 5 μm.

7. The electromagnetic shielding film according to any one of claims 1 to 5, characterized in that The electromagnetic shielding film includes a metal shielding unit, and the metal shielding unit includes a plurality of metal shielding layers stacked in sequence along a thickness direction of the electromagnetic shielding film; Preferably, the metal shielding unit includes a first metal shielding layer and a second metal shielding layer, the first metal shielding layer is more than two layers, the second metal shielding layer is located between two oppositely arranged first metal shielding layers, and the thickness of the second metal shielding layer is greater than that of the first metal shielding layer; Preferably, the thickness of the metal shielding unit is 0.5 μm to 5 μm.

8. The electromagnetic shielding film according to any one of claims 1 to 5, characterized in that The first surface and the second surface are both undulating surfaces.

9. The electromagnetic shielding film according to any one of claims 1 to 5, characterized in that The electromagnetic shielding film further comprises: an adhesive film layer, the adhesive film layer being located on one side of the metal shielding layer, and an extending direction of the adhesive film layer being parallel to an extending direction of the metal shielding layer; Preferably, the metal shielding layer has a metal protrusion on a side facing the adhesive film layer, and the metal protrusion passes through the adhesive film layer; or, conductive particles are dispersed in the adhesive film layer; Preferably, the electromagnetic shielding film further comprises: an insulating layer, wherein the insulating layer is located on a side of the metal shielding layer away from the adhesive film layer.

10. A circuit board, characterized in that: The circuit board comprises: Circuit board body; The electromagnetic shielding film according to any one of claims 1 to 9, wherein the electromagnetic shielding film is provided on the surface of the circuit board body and connected to the circuit board body.

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