Electromagnetic shielding film and circuit board

Abstract

The invention discloses an electromagnetic shielding film and a circuit board, and the electromagnetic shielding film comprises a protection layer and a shielding layer which are sequentially stacked, one 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 the hardness of the shielding layer. According to the electromagnetic shielding film, one side face of the protective layer is provided with the first protruding parts, so that when the electromagnetic shielding film is bent, the first protruding parts can relieve external stress, damage of the external stress to the shielding layer is relieved, and then the bending performance of the electromagnetic shielding film is improved. According to the electromagnetic shielding film, one side surface of the protection layer is provided with a plurality of first protruding parts whose hardness is smaller than that of the shielding layer, so that when the electromagnetic shielding film is bent, the shielding layer is prevented from being extruded and punctured due to overlarge hardness of the first protruding parts, thereby ensuring the integrity of the shielding layer, and further ensuring the stability of the shielding performance.

Description

Technical Field

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

[0002] With the development of high-frequency and high-density integration of electronic devices, as a key functional material for suppressing electromagnetic interference (EMI), electromagnetic shielding films are widely used in fields such as flexible circuit boards, chip packaging, and 5G communication modules. Electromagnetic shielding films are usually made of conductive materials (such as metal coatings, conductive polymers, metal meshes, etc.), and their high conductivity enables 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 will form a reverse electric field within the shielding layer, offsetting part of the external electromagnetic field and reducing the impact on the internal circuit of the PCB.

[0003] With the rapid development of communication devices, foldable electronic devices (such as foldable mobile phones) have emerged. Applying an electromagnetic shielding film on the circuit board or flexible board of a foldable electronic device can not only enable the folding of the foldable electronic device but also avoid electromagnetic interference between the outside and the foldable electronic device. After multiple folds of the foldable electronic device, cracks may appear inside the electromagnetic shielding film, resulting in the failure of the shielding function and making it difficult to meet the performance requirements of foldable 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 the bending process but also overcome problems such as electromagnetic leakage and structural damage that occur when the existing shielding film is bent to meet the requirements of continuously developing electronic devices for high-performance electromagnetic shielding materials. Summary of the Invention

[0005] Based on this, it is necessary to provide an electromagnetic shielding film aiming at the above problems, which can improve the reliability of use of foldable electronic devices after multiple bends.

[0006] To achieve the above object, a first aspect of the present invention provides an electromagnetic shielding film, including a protective layer and a shielding layer stacked in sequence. A plurality of first protrusions are provided on one side surface of the protective layer, 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 protective layer.

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

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

[0010] Optionally, within the preset observation range, the ratio of the protrusion height to the maximum width of the first protrusion in the sliced state is 0.7 to 2, and the proportion of the number thereof is more than 50%.

[0011] Optionally, the electromagnetic shielding film further includes an adhesive film layer, and the adhesive film layer is disposed on a side surface of the shielding layer away from the protective layer.

[0012] Optionally, conductive particles are provided in the adhesive film layer, and the shielding layer is electrically connected to the circuit board body at least through the conductive particles.

[0013] Optionally, a cross-section is made in the thickness direction along any angle, and the shielding layer is undulating.

[0014] Optionally, a plurality of second protrusions are provided on a side surface of the adhesive film layer close to the shielding layer, and the hardness of the second protrusions is less than the hardness of the shielding layer.

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

[0016] To achieve the above object, a second aspect of the present invention further provides a circuit board, and the circuit board includes the electromagnetic shielding film described in any one of the above embodiments.

[0017] Compared with the prior art, the beneficial effects of the embodiments of the present invention are as follows: The electromagnetic shielding film includes a protective layer and a shielding layer which are sequentially stacked. By providing a plurality of first protrusions on one side surface of the protective layer, the shielding layer is undulating, increasing the surface area of the shielding layer itself, and providing more electromagnetic reflection and absorption paths, so that the electromagnetic wave is reflected and absorbed multiple times in the shielding layer and the energy is greatly attenuated, significantly improving the shielding effect of the electromagnetic shielding film on electromagnetic waves of different frequencies and different directions.

[0018] On the other hand, by providing a plurality of first protrusions on one side surface of the protective layer, the shielding layer is undulating, and the undulating structure endows the shielding layer with a certain flexibility, so that in complex application scenarios such as bending and curling, cracks are not easily generated, ensuring the stability of the shielding performance.

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

[0020] Further, by providing a plurality of first protrusions with a hardness less than that of the shielding layer on one side surface of the protective layer, when the electromagnetic shielding film is bent, it is avoided that the shielding layer is squeezed and punctured due to the too large hardness of the first protrusions, thereby ensuring the integrity of the shielding layer and further ensuring the stability of the shielding performance. Description of the Drawings

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

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

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

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

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

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

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

[0028] Among them, 1. protective layer; 2. shielding layer; 3. first protrusion; 4. carrier layer; 5. adhesive film layer; 51: conductive particles; 6. second protrusion; 7. buffer layer. Detailed Embodiments

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] In the description of the specification and claims, it should be understood that the orientation or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the embodiments of the present invention, rather than indicating or implying that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the embodiments of the present invention.

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

[0032] Please refer to Figure 1 , Figure 1 is a schematic structural diagram of an electromagnetic shielding film according to an embodiment of the present invention. The embodiment of the present invention provides an electromagnetic shielding film, which includes a protective layer 1 and a shielding layer 2 stacked in sequence. A plurality of first protrusions 3 are provided on one side surface of the protective layer 1, and the hardness of the first protrusions 3 is less than the hardness of the shielding layer 2.

[0033] In the embodiment of the present invention, the protective layer 1 serves to protect the shielding layer 2. The thickness of the protective layer 1 is 2 to 20 μm. The protective layer 1 includes 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 to 10 μm.

[0034] It should be noted that when the thickness of the electromagnetic shielding film is relatively thin, a carrier layer 4 can be provided on the surface of the protective layer 1 away from the shielding layer 2 (see Figure 2 ), so that the electromagnetic shielding film is not easily wrinkled or broken during processing and application. After the electromagnetic shielding film is laminated with the circuit board substrate, the carrier layer 4 is torn off. Therefore, a release agent is provided on one side surface of the carrier layer 4 close to the protective layer 1. The thickness of the carrier layer is 38 to 50 μm. By defining the thickness of the carrier layer 4 to be 38 to 50 μm, the thickness of the carrier layer is within a suitable range, and it will not be unable to play a supporting and carrying role because it is too thin, nor will it be difficult for the electromagnetic shielding film to be laminated and filled into the grounding opening, affecting the grounding effect.

[0035] It should be noted that in the embodiments of the present invention, several first convex portions 3 are provided on one side surface of the protective layer 1. By providing several first convex portions 3 on one side surface of the protective layer 1, the shielding layer 2 is in a wavy shape, increasing the surface area of the shielding layer 2 itself, and providing more electromagnetic reflection and absorption paths. The electromagnetic wave is reflected and absorbed multiple times in the shielding layer 2, and the energy is greatly attenuated, significantly improving the shielding effect of the electromagnetic shielding film on electromagnetic waves of different frequencies and different directions; secondly, the wavy structure endows the shielding layer with certain flexibility and ductility, so that in complex application scenarios such as bending and curling, cracks are not easily generated, ensuring the stability of the shielding performance; by providing several first convex portions 3 on one side surface of the protective layer 1, when the electromagnetic shielding film is bent, the first convex portions 3 can relieve the external stress and slow down the damage of the external stress to the shielding layer 2, thereby improving the bending performance of the electromagnetic shielding film.

[0036] Furthermore, in the embodiments of the present invention, the hardness of the first convex portion 3 is less than the hardness of the shielding layer 2. By providing several first convex portions 3 with a hardness less than that of the shielding layer 2 on one side surface of the protective layer 1, when the electromagnetic shielding film is bent, it is avoided that the first convex portion 3 has too high hardness and squeezes and punctures the shielding layer 2, thereby ensuring the integrity of the shielding layer and further ensuring the stability of the shielding performance. Preferably, the material of the first convex portion 3 can be the same as or different from that of the protective layer 1. The material of the first convex portion 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, polyamide.

[0037] It should be noted that the elastic modulus of the first convex portion 3 is less than the elastic modulus of the protective layer 1. By setting the elastic modulus of the first convex portion 3 to be less than the elastic modulus of the protective layer 1, the first convex portion 3 has better elastic deformation ability. When subjected to an external force, the first convex portion 3 preferentially undergoes elastic deformation, absorbs and disperses the external force, reduces the direct action of the 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 the external force; at the same time, the good elasticity helps the first convex portion 3 to closely adhere to the shielding layer 2, maintaining the stable connection between the two, and ensuring the structural integrity and excellent shielding performance of the electromagnetic shielding film.

[0038] Preferably, the elastic modulus of the first protrusion 3 is less than 1.2 GPa. By limiting the elastic modulus of the first protrusion 3 to less than 1.2 GPa, it is ensured that the first protrusion 3 has appropriate elasticity and flexibility. In practical applications, the rigidity of the first protrusion 3 will not be too large due to the elastic modulus of the first protrusion 3 being too high, and the first protrusion 3 will not be unable to effectively absorb external forces, which will cause the electromagnetic shielding film to squeeze and puncture the shielding layer 2 in the bending application scenario, resulting in a significant decrease in shielding performance; nor will the first protrusion 3 be excessively deformed due to the elastic modulus of the first protrusion 3 being too low, thereby losing the protection and bonding effect on the shielding layer 2. Therefore, the embodiment of the present invention can effectively buffer the external force by limiting the elastic modulus of the first protrusion 3 to less than 1.2 GPa, and can quickly restore to its original state after the external force disappears, maintaining a close fit with the shielding layer 2, thereby improving the mechanical properties and use stability of the electromagnetic shielding film.

[0039] Furthermore, within the preset observation range, the number of the first protrusions 3 in the sliced state whose ratio of the protrusion height to the maximum width is 0.7~2 accounts for more than 50%. By setting the ratio of the first protrusions 3 whose ratio of the protrusion height to the maximum width is 0.7~2 to more than 50%, the size ratio of the first protrusions 3 is more appropriate under the premise of meeting cost control and yield control. When subjected to force, it will not be too low or too wide to fully exert its elastic deformation capacity to absorb external force, which will cause cracking when bending, making the shielding performance of the electromagnetic shielding film worse; nor will it be too high or too wide to cause the shielding layer 2 to be pierced, thereby affecting the shielding performance of the electromagnetic shielding film. Therefore, the ratio of the height of the first protrusion 3 to the maximum width is 0.7-2 and the number accounts for more than 50%, so that the first protrusion 3 can ensure sufficient contact area to enhance the bonding effect with the shielding layer 2, while having a suitable height to provide effective buffering and protection for the shielding layer 2; the reasonable size ratio ensures that the first protrusion 3 can fully exert its elastic deformation ability to absorb external forces when subjected to force, avoid cracking of the electromagnetic shielding film, and ensure the comprehensive performance of the electromagnetic shielding film in practical applications. Optionally, the ratio of the height of the first protrusion 3 to the maximum width in the range of 0.7-2 can be any one of 50%, 60%, 65%, 75%, 80%, 90% or 100%, or an interval consisting of any two values.

[0040] It should be noted that in the embodiments of the present invention, the overall tensile strength of the electromagnetic shielding film is greater than 15 MPa. When the electromagnetic shielding film is in use, it is set on the circuit board by means of hot pressing. Since the circuit board is uneven, during the pressing process, the electromagnetic shielding film will be stretched and torn, etc. Therefore, the overall tensile strength of the electromagnetic shielding film is set to be greater than 15 MPa, so that the electromagnetic shielding film is not easily broken or damaged under the stress of stretching, tearing, etc., ensuring the integrity of the structure of the electromagnetic shielding film; during installation, transportation, etc., it can withstand a certain external force, preventing the electromagnetic shielding film from being damaged and affecting the shielding performance, thereby improving the reliability and applicability of the electromagnetic shielding film, making it widely applicable to various electronic devices and scenarios with certain strength requirements.

[0041] See Figure 3 , Figure 3 which is a schematic structural diagram of another electromagnetic shielding film provided by the embodiments of the present invention. In the embodiments of the present invention, the electromagnetic shielding film further includes an adhesive film layer 5, and the adhesive film layer 5 is disposed on a side surface of the shielding layer 2 away from the protective layer 1.

[0042] In the embodiments of the present invention, the adhesive 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 adhesive film layer 5, so that it is not easy for the electromagnetic shielding film and the circuit board to blister and delaminate, avoiding problems such as separation, and realizing the shielding effect. The thickness of the adhesive film layer 5 is 1 - 20 μm, and the adhesive film layer 5 is mainly selected from at least one of resins such as polyester, polyethylene, polyamide, rubber, acrylate, phenolic, epoxy, polyimide, urethane, melamine, alkyd, etc.

[0043] Preferably, as Figure 4 shown, Figure 4 which is a schematic structural diagram of another electromagnetic shielding film provided by the embodiments of the present invention. In the embodiments of the present invention, conductive particles 51 are provided in the adhesive film layer 5, and the shielding layer 2 is electrically connected to the circuit board body at least through the conductive particles 51. The conductive particles 51 in the adhesive film layer 5 build a good conductive path between the shielding layer 2 and the circuit board body, enabling the shielding layer 2 to quickly and effectively conduct the induced electromagnetic interference current to the ground, realizing reliable grounding; in addition, this grounding method significantly enhances the electrostatic discharge ability of the electromagnetic shielding film, reduces the risk of interference and damage to electronic components caused by electrostatic accumulation, and improves the electromagnetic compatibility and working stability of the circuit board and electronic devices.

[0044] In one embodiment, a cross-section is made in the thickness direction at any angle. The shielding layer 2 is undulating. Any angle means making a cross-section perpendicular to the surface of the electromagnetic shielding film at any position on the surface of the electromagnetic shielding film. The shielding layer 2 is an undulating structure at any angle, and the cross-section at any angle is undulating. The undulating shielding layer 2 increases the surface area of the shielding layer itself, can provide more electromagnetic reflection and absorption paths, enables the electromagnetic wave to be reflected and absorbed multiple times in the shielding layer 2 and then the energy is greatly attenuated, and significantly improves the shielding effect of the electromagnetic shielding film on electromagnetic waves of different frequencies and different directions; in addition, the undulating structure endows the shielding layer 2 with greater flexibility and ductility, so that it is not easy to generate cracks in complex application scenarios such as bending and curling, and ensures the stability of the shielding performance.

[0045] Combined with Figure 3 , in the embodiment of the present invention, a plurality of second protrusions 6 are provided on one side surface of the adhesive film layer 5 close to the shielding layer 2, and the hardness of the second protrusions 6 is less than the hardness of the shielding layer 2. By providing a plurality of second protrusions 6 on one side surface of the adhesive film layer 5 close to the shielding layer 2, the second protrusions 6 of the adhesive film layer 5 are fitted with the shielding layer 2, and a mechanical interlocking structure is formed 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 easy to delaminate when pasted on other components; at the same time, the hardness of the second protrusions 6 is less than the hardness of the shielding layer 2. When subjected to external force impact, the second protrusions 6 are deformed first, buffering the influence of the external force on the shielding layer 2 and preventing the shielding layer 2 from being damaged. At the same time, the second protrusions 6 with lower hardness can better adapt to different surface morphologies, 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, polyamide.

[0046] It should be noted that in the embodiment of the present invention, the hardness of the second protrusions 6 refers to the hardness of the cured second protrusions 6 after curing the adhesive film layer before pressing on the circuit board.

[0047] Referring to Figure 5 shown, Figure 5 is a schematic structural diagram of another electromagnetic shielding film provided by the embodiment of the present invention. In the embodiment of the present invention, the electromagnetic shielding film further includes a buffer layer 7, and the buffer layer 7 is laminated on at least one side surface of the shielding layer 2. The buffer layer 7 is arranged between the protective layer 1 and the shielding layer 2 (such as Figure 5 ), or the buffer layer 7 is arranged between the shielding layer 2 and the adhesive film layer 5 (such as Figure 6), or the buffer layer 7 is respectively disposed between the protective layer 1 and the shielding layer 2 and between the shielding layer 2 and the adhesive film layer 5 (such as Figure 7 ). By providing 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, thereby avoiding cracking of the electromagnetic shielding film and improving the bending resistance of the electromagnetic shielding film. When subjected to external impact or extrusion, the buffer layer 7 can effectively absorb and disperse the external force, further reducing the possibility of damage to the shielding layer 2; at the same time, the buffer layer 7 can fill the tiny gaps between the shielding layer 2 and other components, improve the fitting degree and sealing performance of the electromagnetic shielding film, reduce the leakage of electromagnetic waves, enhance the overall electromagnetic shielding effect, and enable the electromagnetic shielding film to maintain good performance in complex usage environments. 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] An embodiment of the present invention also provides a circuit board, which includes the electromagnetic shielding film of any embodiment of the present invention.

[0049] The electromagnetic shielding film and the circuit board provided by the embodiments of the present invention have the beneficial effects that: the electromagnetic shielding film includes a protective layer and a shielding layer which are sequentially stacked. By providing a plurality of first protrusions on one side surface of the protective layer, the shielding layer is in a undulating shape, increasing the surface area of the shielding layer itself, and capable of providing more electromagnetic reflection and absorption paths, so that the electromagnetic wave 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 different directions.

[0050] On the other hand, by providing a plurality of first protrusions on one side surface of the protective layer, the shielding layer is in a undulating shape, and the undulating structure endows the shielding layer with a certain flexibility, so that it is not easy to generate cracks in complex application scenarios such as bending and curling, ensuring the stability of the shielding performance.

[0051] Furthermore, by providing a plurality of first protrusions on one side surface of the protective layer, when the electromagnetic shielding film is bent, the first protrusions can relieve the external stress and slow down the damage of the external stress to the shielding layer, thereby improving the bending performance of the electromagnetic shielding film.

[0052] Furthermore, by providing a plurality of first protrusions with a hardness less than that of the shielding layer on one side surface of the protective layer, when the electromagnetic shielding film is bent, it is avoided that the shielding layer is punctured by extrusion due to the too large hardness of the first protrusions, thereby ensuring the integrity of the shielding layer and further ensuring the stability of the shielding performance.

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

[0054] Example 1:

[0055] An electromagnetic shielding film includes a protective layer 1 and a shielding layer 2 which are stacked in sequence. A plurality of first protrusions 3 are provided on one side surface of the protective layer 1, and the hardness of the first protrusions 3 is less than the hardness of the shielding layer 2. The proportion of the number of the first protrusions 3 with the ratio of the protrusion height to the maximum width being 0.7 to 2 in the sliced state is 50%.

[0056] Example 2:

[0057] The electromagnetic shielding film of this example is the same as that of Example 1, except that: the proportion of the number of the first protrusions 3 with the ratio of the protrusion height to the maximum width being 0.7 to 2 is 70%.

[0058] Example 3:

[0059] The electromagnetic shielding film of this example is the same as that of Example 1, except that: the proportion of the number of the first protrusions 3 with the ratio of the protrusion height to the maximum width being 0.7 to 2 is 80%.

[0060] Example 4:

[0061] The electromagnetic shielding film of this example is the same as that of Example 1, except that: the proportion of the number of the first protrusions 3 with the ratio of the protrusion height to the maximum width being 0.7 to 2 is 100%.

[0062] Example 5:

[0063] The electromagnetic shielding film of this example is the same as that of Example 1, except that: a buffer layer 7 is provided between the protective layer 1 and the shielding layer 2.

[0064] Example 6:

[0065] The electromagnetic shielding film of this example 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 this example is the same as that of Example 1, except that: buffer layers 7 are respectively provided between the protective 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 includes a protective layer 1 and a shielding layer 2 which are stacked in sequence. No first protrusions are provided on one side surface of the protective layer 1.

[0070] Comparative Example 2:

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

[0072] Comparative Example 3:

[0073] The electromagnetic shielding film of this comparative example is the same as that of Example 1, except that: the proportion of the number of the first convex portions 3 with the ratio of the convex height to the maximum width being 0.7 - 2 in the sliced state is 10%.

[0074] Bending performance test:

[0075] The bending performance tests were carried out on the electromagnetic shielding covers of Examples 1 - 7 and Comparative Examples 1 - 3.

[0076] S1: Press copper sheets at both ends of a 25 - micron PI film;

[0077] S2: Press the electromagnetic shielding film on the 25 - micron PI film at 185°C * 10 min * 120 kg, ensuring electrical connection between the copper on both sides and the metal layer of the shielding film, and curing at 160°C for 1.5 h;

[0078] S3: Use the test wires of the bending machine to monitor the resistance of the copper on both sides. When the bending machine starts to count, when the resistance measured by the test wires shows a 100% increase change, it indicates that the metal layer has broken, and the counting stops. The bending conditions are: bending radius 0.38 mm, bending speed 150 revolutions per minute, bending angle 135°, load 0.5 kg, and 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 this example, in complex application scenarios such as bending and curling, cracks are not easily generated, ensuring the stability of the shielding performance.

[0082] All in all, by providing a plurality of first convex portions on one side of the protective layer, the shielding layer is in a wavy shape, increasing the surface area of the shielding layer itself, providing more paths for electromagnetic reflection and absorption, enabling the electromagnetic wave to be reflected and absorbed multiple times within the shielding layer and significantly attenuating its energy, and significantly improving the shielding effect of the electromagnetic shielding film on electromagnetic waves of different frequencies and different directions.

[0083] On the other hand, by providing a plurality of first convex portions on one side of the protective layer, the shielding layer is in a wavy shape, and the wavy structure endows the shielding layer with a certain flexibility, making it not easily generate cracks in complex application scenarios such as bending and curling, ensuring the stability of the shielding performance.

[0084] Furthermore, by providing a plurality of first protrusions on one side surface of the protective layer, when the electromagnetic shielding film is bent, the first protrusions can relieve external stress and slow down the damage of the external stress to the shielding layer, thereby improving the bending performance of the electromagnetic shielding film.

[0085] Furthermore, by providing a plurality of first protrusions with a hardness less than that of the shielding layer on one side surface of the protective layer, when the electromagnetic shielding film is bent, it is avoided that the shielding layer is squeezed and punctured due to the too large hardness of the first protrusions, thus ensuring the integrity of the shielding layer and further ensuring the stability of the shielding performance.

[0086] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0087] The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall 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 which are stacked in sequence. A plurality of first protrusions are provided on one side surface of the protective layer, and the hardness of the first protrusions is less than that of the shielding layer.

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

3. The electromagnetic shielding film according to claim 2, wherein, The elastic modulus of the first protrusions is less than 1.2 GPa; and / or, the tensile strength of the electromagnetic shielding film as a whole is greater than 15 MPa.

4. The electromagnetic shielding film according to claim 1, characterized in that, In a preset observation range, the proportion of the number of the ratio of the protrusion height to the maximum width of the first protrusions in the sliced state being 0.7 to 2 is more than 50%.

5. The electromagnetic shielding film according to claim 1, characterized in that, The electromagnetic shielding film further includes an adhesive film layer, and the adhesive film layer is disposed on the side surface of the shielding layer away from the protective layer.

6. The electromagnetic shielding film according to claim 5, characterized in that, Conductive particles are provided in the adhesive film layer, and the shielding layer is electrically connected to the circuit board body at least through the conductive particles.

7. The electromagnetic shielding film according to any one of claims 1 to 6, characterized in that, Making a cross-section along the thickness direction at any angle, the shielding layer is undulating.

8. The electromagnetic shielding film according to claim 7, wherein A plurality of second protrusions are provided on the side surface of the adhesive film layer close to the shielding layer, and the hardness of the second protrusions is less than that of the shielding layer.

9. The electromagnetic shielding film according to any one of claims 1-8, characterized in that, The electromagnetic shielding film further includes a buffer layer, and the buffer layer is stacked on at least one side surface of the shielding layer.

10. A circuit board, characterized in that, The circuit board includes a circuit board body and the electromagnetic shielding film according to any one of claims 1-9.

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