Electromagnetic shield film and circuit board

Abstract

The application discloses an electromagnetic shielding film and a circuit board, wherein the electromagnetic shielding film comprises a shielding layer and a film layer, and the film layer is provided with conductive particles; the ratio of the roughness Ra of the shielding layer on the side close to the film layer to the weight proportion of the conductive particles in the film layer is greater than or equal to 0.2; the average cross-sectional area of part of the conductive particles in 0-1 / 2H is greater than the average cross-sectional area in 1 / 2H-H, wherein H is the height of the conductive particles. In the application, when the electromagnetic shielding film is pressed, the shielding layer can be effectively connected with the ground layer of the circuit board, so that the grounding performance of the electromagnetic shielding film is improved.

Description

Technical Field

[0001] This invention relates to the field of electronic technology, and in particular to an electromagnetic shielding film and circuit board. Background Technology

[0002] In recent years, to prevent malfunctions caused by interference from externally received electromagnetic waves or mutual electromagnetic interference between internal electronic components, electromagnetic shielding films are commonly used to cover important electronic components and circuit boards, thereby reducing electromagnetic interference. Currently, commonly used electromagnetic shielding films for circuit boards consist of an insulating layer, a shielding layer, and an adhesive film layer stacked sequentially. The side of the shielding layer closest to the adhesive film layer has roughness. During use, the electromagnetic shielding film needs to be pressed onto the circuit board at high temperature. During this hot-pressing process, the shielding layer pierces the adhesive film layer through its roughened side, thus making electrical connections with the ground plane of the circuit board, thereby guiding interference charges into the ground plane of the circuit board and achieving shielding. In the process of implementing this invention, the inventors discovered the following technical problem in the prior art: relying solely on roughness to pierce the adhesive film layer is ineffective, resulting in poor grounding performance of the electromagnetic shielding film. Summary of the Invention

[0003] The purpose of this invention is to provide an electromagnetic shielding film that can improve the grounding performance of the electromagnetic shielding film.

[0004] To achieve the above objectives, embodiments of the present invention provide an electromagnetic shielding film, comprising a shielding layer and an adhesive film layer, wherein conductive particles are disposed in the adhesive film layer;

[0005] The ratio of the roughness Ra of the shielding layer on the side near the adhesive film layer to the weight ratio of the conductive particles in the adhesive film layer is greater than or equal to 0.2; the average cross-sectional area of ​​some of the conductive particles in the range of 0-1 / 2H is greater than the average cross-sectional area in the range of 1 / 2H-H, where H is the height of the conductive particles.

[0006] As an improvement to the above solution, the roughness Ra of the shielding layer on the side near the adhesive film layer is 0.1-5 micrometers.

[0007] As an improvement to the above solution, the ratio of the roughness Ra of the shielding layer on the side near the adhesive film layer to the weight ratio of the conductive particles in the adhesive film layer is 0.2-100.

[0008] As an improvement to the above solution, one end of some of the conductive particles contacts the side of the adhesive film layer away from the shielding layer; and one end of some of the conductive particles contacts the side of the adhesive film layer close to the shielding layer.

[0009] As an improvement to the above scheme, the side with the larger average cross-section of some of the conductive particles contacts the side of the adhesive film layer that is closer to the shielding layer.

[0010] As an improvement to the above scheme, at least some of the conductive particles are provided with spike structures.

[0011] As an improvement to the above scheme, the average particle size of the conductive particles is 0.1-50 μm.

[0012] As an improvement to the above solution, the conductive particle material is selected from at least one of copper, aluminum, zinc, nickel, silver, iron, cobalt, and titanium.

[0013] As an improvement to the above solution, the surface of the shielding layer is a non-flat surface.

[0014] To achieve the above objectives, embodiments of the present invention also provide a circuit board, including a circuit board body and an electromagnetic shielding film as described in any of the above embodiments; the electromagnetic shielding film is pressed together with the circuit board body; the side of the shielding layer near the adhesive film layer is electrically connected to the ground plane of the circuit board body.

[0015] Compared to existing technologies, the electromagnetic shielding film and circuit board provided in this invention achieve electromagnetic shielding by incorporating conductive particles in the adhesive film layer. During the lamination process of the electromagnetic shielding film, these conductive particles conduct electricity between the shielding layer and the circuit board ground layer, thereby guiding interference charges into the circuit board ground layer. By setting some of the conductive particles to have an average cross-sectional area between 0 and 1 / 2H that is larger than the average cross-sectional area between 1 / 2H and H, the conductive particles exhibit better piercing performance during lamination, thus improving the contact between the conductive particles and the shielding layer. The ratio of the roughness Ra of the shielding layer near the adhesive film layer to the weight ratio of the conductive particles in the adhesive film layer is greater than or equal to 0.2. This ensures a moderate distribution of conductive particles in the adhesive film layer, preventing an insufficient number of conductive particles that would reduce contact between the conductive particles and the shielding layer and the circuit board ground layer, thereby reducing the interference charge introduced into the circuit board ground layer and lowering the grounding performance of the electromagnetic shielding film. This improves the grounding performance of the electromagnetic shielding film. Simultaneously, it prevents conductive particles from excessively occupying the adhesive space of the adhesive film layer, allowing the adhesive in the adhesive film layer to be effectively contained by the side of the shielding layer near the adhesive film layer. It also reduces the likelihood of excessive adhesive material moving to the edge of the circuit board, causing significant adhesive overflow at the edge between the electromagnetic shielding film and the circuit board. This results in a good appearance for the circuit board after the shielding film is laminated. In addition, when one end of some of the conductive particles contacts the side of the adhesive film layer away from the shielding layer, the contact area between the circuit board ground layer and the conductive particles can be increased. And when one end of some of the conductive particles contacts the side of the adhesive film layer close to the shielding layer, the contact area between the shielding layer and the conductive particles can be increased, thereby improving the grounding performance of the electromagnetic shielding film. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the first electromagnetic shielding film provided in the embodiments of the present invention;

[0017] Figure 2 This is a partial enlarged view of the electromagnetic shielding film provided in an embodiment of the present invention;

[0018] Figure 3 This is a schematic diagram of the structure of the second type of electromagnetic shielding film provided in an embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of the structure of the third type of electromagnetic shielding film provided in the embodiments of the present invention;

[0020] Figure 5 This is a schematic diagram of the structure of the fourth type of electromagnetic shielding film provided in the embodiments of the present invention;

[0021] Figure 6 This is a schematic diagram of the structure of the fifth type of electromagnetic shielding film provided in the embodiments of the present invention;

[0022] Figure 7 This is a schematic diagram of the structure of a circuit board provided in an embodiment of the present invention.

[0023] Among them, 1. shielding layer; 2. adhesive film layer; 3. insulating layer; 4. carrier layer; 5. protective film layer; 6. circuit board body; 21. conductive particles. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of the specification and claims, it should be understood that the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present invention, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the embodiments of the present invention.

[0026] Furthermore, the terms "first," "second," etc., used in the specification and claims are used only to distinguish the description of the same technical features and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated, nor necessarily the order of description or chronological sequence. Where appropriate, the terms are interchangeable. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature.

[0027] See Figures 1-2 An embodiment of the present invention provides an electromagnetic shielding film, comprising a shielding layer 1 and an adhesive film layer 2, wherein conductive particles 21 are disposed in the adhesive film layer 2; the ratio of the roughness Ra of the shielding layer near the adhesive film layer to the weight ratio of the conductive particles in the adhesive film layer is greater than or equal to 0.2; the average cross-sectional area of ​​some of the conductive particles 21 in the range of 0-1 / 2H is greater than the average cross-sectional area in the range of 1 / 2H-H, where H is the height of the conductive particles 21.

[0028] In this embodiment of the invention, by providing conductive particles 21 in the adhesive film layer 2, the conductive particles 21 conduct electricity between the shielding layer 1 and the circuit board ground layer during the pressing of the electromagnetic shielding film, thereby guiding interference charges into the ground layer of the circuit board and achieving electromagnetic shielding. By setting a portion of the conductive particles 21 to have an average cross-sectional area between 0 and 1 / 2H that is greater than the average cross-sectional area between 1 / 2H and H, the conductive particles 21 have better piercing performance during pressing, which can improve the contact degree between the conductive particles 21 and the shielding layer 1.

[0029] It is worth noting that the height "0~H" of the conductive particles 21 described in this embodiment of the invention is not directional. Figure 2 The orientation of "0 to H" is merely an example. The conductive particle 21 is "0" at the end closer to the shielding layer 1 and "H" at the end farther from the shielding layer 1; or, the conductive particle 21 is "0" at the end farther from the shielding layer 1 and "H" at the end closer to the shielding layer 1, both of which are within the protection scope of this invention.

[0030] In an embodiment of the present invention, see Figure 3 The ratio of the roughness Ra of the shielding layer 1 near the adhesive film layer 2 to the weight percentage of the conductive particles 21 in the adhesive film layer 2 is 0.2-100. This ratio ensures a moderate distribution of conductive particles in the adhesive film layer, preventing insufficient contact between the conductive particles and the shielding layer and the circuit board ground plane. Simultaneously, it prevents the conductive particles 21 from excessively occupying the adhesive space of the adhesive film layer 2. This allows the adhesive in the adhesive film layer 2 to be effectively contained by the side of the shielding layer 1 near the adhesive film layer 2, reducing the likelihood of excessive adhesive overflow at the edge between the electromagnetic shielding film and the circuit board. Consequently, the circuit board after laminating the shielding film has a good appearance.

[0031] In this embodiment of the invention, the surface roughness Ra of the side of the shielding layer 1 near the adhesive film layer 2 is 0.1-5 micrometers. When the surface roughness Ra of the side of the shielding layer 1 near the adhesive film layer 2 is 0.1-5 micrometers, the adhesive film layer 2 will squeeze the adhesive into the recess on the lower surface of the shielding layer 1 during the pressing process, avoiding the phenomenon of board bursting due to small adhesive capacity, which in turn leads to grounding failure.

[0032] In this embodiment of the invention, the conductive particles 21 account for 5% to 50% of the weight of the adhesive film layer 2. By setting the weight percentage of the conductive particles 21 in the adhesive film layer 2 to 5% to 50%, the number of conductive particles 21 filling the adhesive film layer 2 is moderate. This avoids situations where the number of conductive particles 21 is too small, resulting in reduced contact between the conductive particles 21 and the shielding layer 1 and the circuit board ground layer, thus reducing the interference charge introduced into the circuit board ground layer and lowering the grounding performance of the electromagnetic shielding film. Simultaneously, it also avoids situations where the number of conductive particles 21 is too large, resulting in insufficient adhesive in the adhesive film layer 2, leading to insufficient adhesion and delamination of the electromagnetic shielding film during lamination. Furthermore, it also avoids situations where excessive conductive particles 21 cause the adhesive film layer 2 to become brittle, making it prone to breakage when laminating the electromagnetic shielding film to the circuit board. Therefore, setting the weight percentage of the conductive particles 21 in the adhesive film layer 2 to 5% to 50% can improve the grounding performance of the electromagnetic shielding film while preventing delamination during lamination.

[0033] It is worth noting that when the roughness Ra of the shielding layer 1 near the adhesive film layer 2 is 0.1 micrometers, and the weight percentage of the conductive particles 21 in the adhesive film layer 2 is 5%, the ratio of the roughness Ra of the shielding layer near the adhesive film layer to the weight percentage of the conductive particles in the adhesive film layer is 2; when the roughness Ra of the shielding layer 1 near the adhesive film layer 2 is 0.1 micrometers, and the weight percentage of the conductive particles 21 in the adhesive film layer 2 is 50%, the ratio of the roughness Ra of the shielding layer near the adhesive film layer to the weight percentage of the conductive particles in the adhesive film layer is... The roughness Ra of the shielding layer 1 near the adhesive film layer 2 is 5 micrometers, and the weight percentage of the conductive particles 21 in the adhesive film layer 2 is 5%, the ratio of the roughness Ra of the shielding layer near the adhesive film layer to the weight percentage of the conductive particles in the adhesive film layer is 100; when the roughness Ra of the shielding layer 1 near the adhesive film layer 2 is 5 micrometers, and the weight percentage of the conductive particles 21 in the adhesive film layer 2 is 50%, the ratio of the roughness Ra of the shielding layer near the adhesive film layer to the weight percentage of the conductive particles in the adhesive film layer is 10.

[0034] In embodiments of the present invention, at least 10% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%) of the conductive particles 21 have an average cross-sectional area in the 0-1 / 2H region that is greater than the average cross-sectional area in the 1 / 2H-H region. When the horizontal cross-sectional areas of the conductive particles 21 in the 0-1 / 2H region and the 1 / 2H-H region are not equal, the conductive particles 21 can be teardrop-shaped, conical, tower-shaped, pyramid-shaped, or other shapes; when the horizontal cross-sectional areas of the conductive particles 21 in the 0-1 / 2H region and the 1 / 2H-H region are equal, the conductive particles 21 can be cylindrical, cuboid, cube-shaped, or other shapes.

[0035] In this embodiment of the invention, 50% of the conductive particles 21 may have a larger horizontal cross-sectional area at 0-1 / 2H compared to 1 / 2H-H, and 50% of the conductive particles 21 may have a larger horizontal cross-sectional area at 1 / 2H-H compared to 0-1 / 2H. Alternatively, 50% of the conductive particles 21 may have a larger horizontal cross-sectional area at 0-1 / 2H compared to 1 / 2H-H, and 20% of the conductive particles 21 may have a larger horizontal cross-sectional area at 1 / 2H-H compared to 0-1 / 2H. In this case, 30% of the conductive particles 21 may have the same horizontal cross-sectional area at 0-1 / 2H and 1 / 2H-H. It is worth noting that the above proportions are only examples, and other proportions are also possible. The specific proportions can be adjusted according to the needs of those skilled in the art.

[0036] For example, during the hot pressing process of the electromagnetic shielding film, the forces are mutual. When the shielding layer 1 moves closer to the adhesive film layer 2 under pressure, the circuit board also moves closer to the adhesive film layer 2 under pressure, causing the adhesive film layer 2 to be squeezed by two forces in opposite directions. Therefore, when the portion of the conductive particle 21 with a larger average cross-sectional area contacts the upper or lower surface of the adhesive film layer, the conductive particle 21 can pierce the adhesive film layer 2 in both the upper and lower directions when the adhesive film layer 2 is squeezed, so as to achieve the purpose of connecting the shielding layer 1 and the circuit board ground layer.

[0037] In this embodiment of the invention, one end of a portion of the conductive particles 21 contacts the side of the adhesive film layer 2 away from the shielding layer 1. For example, at least 10% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%) of the conductive particles 21 contact one end of the adhesive film layer 2 away from the shielding layer 1. To avoid insufficient contact between the conductive particles 21 and the circuit board ground layer during the lamination process, which would reduce the interference charge introduced into the circuit board ground layer and decrease the grounding performance of the electromagnetic shielding film, at least 10% of the conductive particles 21 are in contact with one end of the adhesive film layer 2 away from the shielding layer 1. This ensures that a portion of the conductive particles 21 are in contact with the circuit board ground layer, increasing the contact area between the conductive particles 21 and the circuit board ground layer, thereby increasing the interference charge introduced into the circuit board ground layer and improving the grounding performance of the electromagnetic shielding film.

[0038] For example, the conductive particles 21 that are in contact with the side of the adhesive film layer 2 away from the shielding layer 1 can be the conductive particles 21 that have the above-mentioned "average cross-sectional area in 0-1 / 2H is greater than the average cross-sectional area in 1 / 2H-H", or conductive particles 21 that have the "average cross-sectional area in 0-1 / 2H is equal to the average cross-sectional area in 1 / 2H-H", or both.

[0039] In this embodiment of the invention, one end of a portion of the conductive particles 21 contacts the side of the adhesive film layer 2 near the shielding layer 1. For example, at least 10% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%) of the conductive particles 21 contact one end of the adhesive film layer 2 near the shielding layer 1. To avoid insufficient contact between the conductive particles 21 and the shielding layer 1 during the lamination process, which would reduce the interference charge introduced into the circuit board ground layer and decrease the grounding performance of the electromagnetic shielding film, at least 10% of the conductive particles 21 are in contact with one end of the adhesive film layer 2 near the shielding layer 1. This ensures that a portion of the conductive particles 21 are in contact with the shielding layer 1, increasing the contact area between the shielding layer 1 and the conductive particles 21, thereby increasing the interference charge introduced into the circuit board ground layer and improving the grounding performance of the electromagnetic shielding film.

[0040] For example, the conductive particles 21 that are in contact with the side of the adhesive film layer 2 that is close to the shielding layer 1 can be the conductive particles 21 that have the above-mentioned "average cross-sectional area in 0-1 / 2H is greater than the average cross-sectional area in 1 / 2H-H", or conductive particles 21 that have the "average cross-sectional area in 0-1 / 2H is equal to the average cross-sectional area in 1 / 2H-H", or both.

[0041] In this embodiment of the invention, neither end of a portion of the conductive particles 21 contacts the side of the adhesive film layer 2 away from the shielding layer 1 nor the side of the adhesive film layer 2 close to the shielding layer 1. The presence of some conductive particles 21 that do not contact both sides allows these particles to conduct electricity between the upper and lower conductive particles 21, preventing a situation where most conductive particles 21 are not conductive during lamination. Furthermore, the presence of these conductive particles 21 enhances the toughness of the adhesive film layer 2, preventing excessive adhesive buildup. This reduces the likelihood of significant horizontal movement of the adhesive film layer 2 during lamination with the circuit board, thus minimizing the problem of horizontal movement of the electromagnetic shielding film as a whole due to the horizontal movement of the insulating layer when laminating it onto the circuit board. This ensures the electromagnetic shielding film is properly laminated to the corresponding position on the circuit board.

[0042] In this embodiment of the invention, a portion of the conductive particles 21, on the side with the larger average cross-section, contact the side of the adhesive film layer 2 near the shielding layer 1. For example, at least 10% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%) of the conductive particles 21, on the side with the larger average cross-section, contact the side of the adhesive film layer 2 near the shielding layer 1. That is, the conductive particles 21 in contact with the side of the adhesive film layer 2 near the shielding layer 1 can all be the conductive particles 21 described above that have an average cross-sectional area greater than that in the 0-1 / 2H section, or include the conductive particles 21 that have an average cross-sectional area greater than that in the 1 / 2H section and the conductive particles 21 that have an average cross-sectional area equal to that in the 1 / 2H section.

[0043] In embodiments of the invention, at least a portion of the conductive particles 21 are provided with spike structures. For example, at least 10% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%) of the conductive particles 21 are provided with spike structures. To prevent the conductive particles 21 from failing to effectively pierce the adhesive film layer 2 and contact the shielding layer 1 and the circuit board ground layer during the lamination process, thus reducing the interference charge introduced from the shielding layer 1 to the circuit board ground layer and lowering the grounding performance of the electromagnetic shielding film, at least 10% of the conductive particles 21 are provided with spike structures. The spike structures can effectively pierce the adhesive in the adhesive film layer 2, thereby ensuring that the conductive particles 21 can contact the shielding layer 1, increasing the contact area between the shielding layer 1 and the conductive particles 21. At the same time, it can also ensure that the conductive particles 21 can contact the circuit board ground layer, increasing the contact area between the circuit board ground layer and the conductive particles 21, thereby increasing the interference charge introduced to the circuit board ground layer and improving the grounding performance of the electromagnetic shielding film.

[0044] Furthermore, the spike structure is disposed at the upper end, lower end, or both ends of the conductive particle 21. For example, when one end of the conductive particle 21 is in contact with the side of the adhesive film layer 2 away from the shielding layer 1, the spike structure is disposed at the other end of the conductive particle 21; when one end of the conductive particle 21 is in contact with the side of the adhesive film layer 2 close to the shielding layer 1, the spike structure is disposed at the other end of the conductive particle 21; when neither end of the conductive particle 21 is in contact with the side of the adhesive film layer 2 away from the shielding layer 1 or the side of the adhesive film layer 2 close to the shielding layer 1, the spike structure can be disposed at both ends of the conductive particle 21.

[0045] In this embodiment of the invention, the surface roughness Ra of the shielding layer 1 away from the adhesive film layer 2 is 0.1-5 micrometers. When an insulating layer is provided on the side of the shielding layer 1 away from the adhesive film layer 2, compared to a shielding layer 1 with a flat surface structure, the insulating layer is less likely to undergo significant horizontal movement during the pressing process between the electromagnetic shielding film and the circuit board. Therefore, it is less likely to cause the electromagnetic shielding film to move horizontally as a whole due to the horizontal movement of the insulating layer when pressing the electromagnetic shielding film onto the circuit board, and the electromagnetic shielding film can be pressed onto the corresponding position on the circuit board.

[0046] In this embodiment of the invention, the conductive particles 21 are made of at least one of copper, aluminum, zinc, nickel, silver, iron, cobalt, and titanium.

[0047] In this embodiment of the invention, the height of the conductive particles 21 is 10-100% of the thickness of the adhesive film layer 2. Since the conductive particles 21 need to fill the adhesive film layer 2, their height should not be too high. Excessive height may cause the conductive particles 21 to not only pierce the adhesive film layer 2 during the pressing process, but may also further pierce the shielding layer 1, thereby damaging the structure of the electromagnetic shielding film and affecting its electromagnetic shielding effect. Therefore, setting the height of the conductive particles 21 to 10-100% of the thickness of the adhesive film layer 2 can prevent the conductive particles 21 from piercing the shielding layer 1 and thus avoid damaging the structure of the metal shielding film.

[0048] In this embodiment of the invention, the thickness of the shielding layer 1 is 0.1-7 μm. By setting the thickness of the shielding layer 1 to 0.1-7 μm, the electromagnetic shielding effect of the electromagnetic shielding film can be guaranteed without making the electromagnetic shielding film too thick.

[0049] In this embodiment of the invention, the thickness of the adhesive film layer 2 is set to 1-30 μm. By setting the thickness of the adhesive film layer 2 to 1-30 μm, the conductive particles 21 can achieve a denser filling within the adhesive film layer 2.

[0050] In this embodiment, the materials used for the adhesive film layer 2 are selected from the following: modified epoxy resins, acrylic resins, modified rubbers, and modified thermoplastic polyimides.

[0051] See Figure 4 In this embodiment of the invention, the electromagnetic shielding film further includes an insulating layer 3. The insulating layer 3 is disposed on the side of the shielding layer 1 away from the adhesive film layer 2. The insulating layer 3 effectively isolates the shielding layer 1 from the outside environment, thereby ensuring the electromagnetic shielding effect of the shielding layer 1. The shielding layer 1 serves as an electromagnetic shield. Furthermore, the adhesive film layer 2 allows the electromagnetic shielding film to be adhered to the circuit board.

[0052] See Figure 5 In this embodiment of the invention, the electromagnetic shielding film further includes a carrier layer 4, which is disposed on the side of the insulating layer 3 away from the shielding layer 1. The carrier layer protects the insulating layer 3 from damage caused by external contact or impact. A thickness of 50 micrometers provides excellent protection, effectively preventing damage to the insulating layer 3 from external contact or impact. Furthermore, the carrier layer can serve as a base film for forming the insulating layer 3; that is, the insulating layer 3 can be formed on one side of the carrier layer 4.

[0053] See Figure 6In this embodiment, the electromagnetic shielding film further includes a protective film layer 5, which is disposed on the side of the adhesive film layer 2 away from the shielding layer 1. The protective film layer 5 provides protection, ensuring that the adhesive film layer 2 is not scratched or damaged during use. The protective film layer 5 may include a PPS film layer, a PEN film layer, a polyester film layer, a polyimide film layer, a film layer formed by curing epoxy resin ink, a film layer formed by curing polyurethane ink, a film layer formed by curing modified acrylic resin, or a film layer formed by curing polyimide resin. When pressing the electromagnetic shielding film onto the circuit board, the protective film layer 5 needs to be peeled off first.

[0054] Specifically, when the electromagnetic shielding film includes a carrier layer 4, an insulating layer 3, a shielding layer 1, an adhesive film layer 2, and a protective film layer 5, the method for preparing the electromagnetic shielding film includes:

[0055] 1) Prepare carrier layer 4;

[0056] 2) An insulating layer 3 is formed on one side of the carrier layer 4;

[0057] 3) A shielding layer 1 is formed on the side of the insulating layer 3 that is away from the carrier layer 4;

[0058] 4) Apply adhesive to the side of the shielding layer 1 away from the insulating layer 3 to form an adhesive film layer 2, and form conductive particles 21 in the adhesive film layer;

[0059] 5) Attach the protective film layer 5 to the side of the adhesive film layer 2 that is away from the shielding layer 1.

[0060] To facilitate understanding of the above-mentioned invention, the following five specific embodiments are provided and tested:

[0061] Example 1:

[0062] An electromagnetic shielding film includes a shielding layer 1 and an adhesive film layer 2. The surface roughness Ra of the shielding layer 1 near the adhesive film layer 2 is 0.1 micrometers. The weight percentage of conductive particles 21 in the adhesive film layer 2 is 5%. The ratio of the surface roughness Ra of the shielding layer near the adhesive film layer to the weight percentage of conductive particles in the adhesive film layer is 2. The electromagnetic shielding film is then subjected to pressing (185℃, 10 min, 120 kg / cm²). 2 The film was covered with a step height of 38 μm, cured (160℃, 1.5 h), and subjected to thermal shock (288℃, 10 s, 3 times) before being tested for grounding.

[0063] Test results: After the electromagnetic shielding film of this embodiment was pressed onto the circuit board, the grounding resistance between the shielding layer of the electromagnetic shielding film and the ground layer of the circuit board was less than 1212mΩ.

[0064] Therefore, by applying the electromagnetic shielding film described in this embodiment, the shielding layer can be effectively connected to the ground layer of the circuit board during the pressing of the electromagnetic shielding film, thereby improving the grounding performance of the electromagnetic shielding film.

[0065] Example 2:

[0066] An electromagnetic shielding film includes a shielding layer 1 and an adhesive film layer 2. The surface roughness Ra of the shielding layer 1 near the adhesive film layer 2 is 0.1 micrometers. The weight percentage of conductive particles 21 in the adhesive film layer 2 is 50%. The ratio of the surface roughness Ra of the shielding layer near the adhesive film layer to the weight percentage of the conductive particles in the adhesive film layer is 0.2. The electromagnetic shielding film is then subjected to pressing (185℃, 10 min, 120 kg / cm²). 2 The film was covered with a step height of 38 μm, cured (160℃, 1.5 h), and subjected to thermal shock (288℃, 10 s, 3 times) before being tested for grounding.

[0067] Test results: After the electromagnetic shielding film of this embodiment was pressed onto the circuit board, the grounding resistance between the shielding layer of the electromagnetic shielding film and the ground layer of the circuit board was less than 915mΩ.

[0068] Therefore, by applying the electromagnetic shielding film described in this embodiment, the shielding layer can be effectively connected to the ground layer of the circuit board during the pressing of the electromagnetic shielding film, thereby improving the grounding performance of the electromagnetic shielding film.

[0069] Example 3:

[0070] An electromagnetic shielding film includes a shielding layer 1 and an adhesive film layer 2. The surface roughness Ra of the shielding layer 1 near the adhesive film layer 2 is 5 micrometers. The weight percentage of conductive particles 21 in the adhesive film layer 2 is 5%. The ratio of the surface roughness Ra of the shielding layer near the adhesive film layer to the weight percentage of conductive particles in the adhesive film layer is 100. The electromagnetic shielding film is then subjected to pressing (185℃, 10 min, 120 kg / cm²). 2 The film was covered with a step height of 38 μm, cured (160℃, 1.5 h), and subjected to thermal shock (288℃, 10 s, 3 times) before being tested for grounding.

[0071] Test results: After the electromagnetic shielding film of this embodiment was pressed onto the circuit board, the grounding resistance between the shielding layer of the electromagnetic shielding film and the ground layer of the circuit board was less than 943mΩ.

[0072] Therefore, by applying the electromagnetic shielding film described in this embodiment, the shielding layer can be effectively connected to the ground layer of the circuit board during the pressing of the electromagnetic shielding film, thereby improving the grounding performance of the electromagnetic shielding film.

[0073] Example 4:

[0074] An electromagnetic shielding film includes a shielding layer 1 and an adhesive film layer 2. The surface roughness Ra of the shielding layer 1 near the adhesive film layer 2 is 5 micrometers. The weight percentage of conductive particles 21 in the adhesive film layer 2 is 50%. The ratio of the surface roughness Ra of the shielding layer near the adhesive film layer to the weight percentage of conductive particles in the adhesive film layer is 10. The electromagnetic shielding film is then subjected to pressing (185℃, 10 min, 120 kg / cm²). 2 The film was covered with a step height of 38 μm, cured (160℃, 1.5 h), and subjected to thermal shock (288℃, 10 s, 3 times) before being tested for grounding.

[0075] Test results: After the electromagnetic shielding film of this embodiment was pressed onto the circuit board, the grounding resistance between the shielding layer of the electromagnetic shielding film and the ground layer of the circuit board was less than 251mΩ.

[0076] Therefore, by applying the electromagnetic shielding film described in this embodiment, the shielding layer can be effectively connected to the ground layer of the circuit board during the pressing of the electromagnetic shielding film, thereby improving the grounding performance of the electromagnetic shielding film.

[0077] Example 5:

[0078] An electromagnetic shielding film includes a shielding layer 1 and an adhesive film layer 2; the surface roughness Ra of the shielding layer 1 near the adhesive film layer 2 is 2 micrometers, and the adhesive film layer 2 does not contain conductive particles. The electromagnetic shielding film is subjected to pressing (185℃, 10 min, 120 kg / cm²). 2 The film was covered with a step height of 38 μm, cured (160℃, 1.5 h), and subjected to thermal shock (288℃, 10 s, 3 times) before being tested for grounding.

[0079] Test results: After the electromagnetic shielding film of this embodiment was pressed onto the circuit board, the grounding resistance between the shielding layer of the electromagnetic shielding film and the ground layer of the circuit board was less than 2376mΩ.

[0080] In summary, the conductive particles 21 are provided in the adhesive film layer 2; the average cross-sectional area of ​​some of the conductive particles in the range of 0-1 / 2H is greater than the average cross-sectional area in the range of 1 / 2H-H, where H is the height of the conductive particles. The ratio of the roughness Ra of the shielding layer near the adhesive film layer to the weight ratio of the conductive particles in the adhesive film layer is 0.2-100 (0.2, 2, 10, 100). This results in the conductive particles 21 having better piercing performance during pressing, which can improve the contact degree between the conductive particles 21 and the shielding layer 1, and can increase the contact area between the circuit board ground layer and the conductive particles 21, thereby improving the grounding performance of the electromagnetic shielding film. This design ensures a moderate distribution of conductive particles in the adhesive film layer, preventing insufficient particle counts that would reduce contact between the conductive particles and the shielding layer and circuit board ground layer, thereby decreasing interference charge introduced into the circuit board ground layer and reducing the grounding performance of the electromagnetic shielding film. This improves the grounding performance of the electromagnetic shielding film. Simultaneously, it prevents conductive particles from excessively occupying the adhesive space of the adhesive film layer, allowing the adhesive in the film layer to be effectively contained by the side of the shielding layer closest to the adhesive film layer. It also reduces the likelihood of excessive adhesive migration to the edge of the circuit board, leading to significant adhesive overflow at the edge between the electromagnetic shielding film and the circuit board. This results in a circuit board with a good appearance after the shielding film is laminated.

[0081] See Figure 7 Another embodiment of the present invention provides a circuit board, which includes a circuit board body 6 and an electromagnetic shielding film as described in any of the above embodiments; the electromagnetic shielding film is pressed together with the circuit board body 6; the side of the shielding layer 1 near the adhesive film layer 2 is electrically connected to the ground layer of the circuit board body 6.

[0082] Preferably, the circuit board body 6 is one of a flexible single-sided board, a flexible double-sided board, a flexible multilayer board, or a rigid-flex board.

[0083] Specifically, by providing conductive particles 21 in the adhesive film layer 2, and when the average cross-sectional area of ​​some of the conductive particles in the 0-1 / 2H range is greater than the average cross-sectional area in the 1 / 2H-H range, the conductive particles 21 have better piercing performance during pressing, which can improve the contact between the conductive particles 21 and the shielding layer 1, the conductive particles 21 and the circuit board ground layer, and the conductive particles 21 and each other, thereby increasing the interference charge introduced into the circuit board ground layer and improving the grounding performance of the electromagnetic shielding film. The ratio of the roughness Ra of the shielding layer near the adhesive film layer to the weight ratio of the conductive particles in the adhesive film layer is greater than or equal to 0.2. This ensures a moderate distribution of conductive particles in the adhesive film layer, preventing insufficient contact between the conductive particles and the shielding layer and the circuit board ground layer, which would reduce the interference charge introduced into the circuit board ground layer and decrease the grounding performance of the electromagnetic shielding film. This improves the grounding performance of the electromagnetic shielding film. Simultaneously, it prevents the conductive particles from excessively occupying the adhesive space of the adhesive film layer, allowing the adhesive in the adhesive film layer to be effectively contained by the side of the shielding layer near the adhesive film layer. It also reduces the likelihood of excessive adhesive movement towards the edge of the circuit board, causing significant adhesive overflow at the edge between the electromagnetic shielding film and the circuit board. This results in a good appearance for the circuit board after the shielding film is laminated. In addition, when one end of some of the conductive particles 21 contacts the side of the adhesive film layer 2 away from the shielding layer 1, the contact area between the circuit board ground layer and the conductive particles 21 can be increased. And when one end of some of the conductive particles 21 contacts the side of the adhesive film layer 2 close to the shielding layer 1, the contact area between the shielding layer 1 and the conductive particles 21 can be increased, thereby improving the grounding performance of the electromagnetic shielding film.

[0084] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. An electromagnetic shielding film, characterized in that, It includes a shielding layer and an adhesive film layer, wherein the adhesive film layer contains conductive particles; The ratio of the roughness Ra of the shielding layer near the adhesive film layer to the weight ratio of the conductive particles in the adhesive film layer is 0.2-100; the average cross-sectional area of ​​some of the conductive particles in the range of 0-1 / 2H is greater than the average cross-sectional area in the range of 1 / 2H-H, where H is the height of the conductive particles; and one end of the aforementioned conductive particles is in contact with the side of the adhesive film layer away from the shielding layer, while the other end is not in contact with the side of the adhesive film layer near the shielding layer. The roughness Ra of the shielding layer on the side near the adhesive film layer is 0.1-5 micrometers.

2. The electromagnetic shielding film as described in claim 1, characterized in that, The side with the larger average cross-section of some of the conductive particles contacts the side of the adhesive film layer closest to the shielding layer.

3. The electromagnetic shielding film as described in claim 1, characterized in that, At least some of the conductive particles have spike structures.

4. The electromagnetic shielding film as described in claim 1, characterized in that, The average particle size of the conductive particles is 0.1-50 μm.

5. The electromagnetic shielding film as described in claim 1, characterized in that, The conductive particles are made of at least one of copper, aluminum, zinc, nickel, silver, iron, cobalt, and titanium.

6. The electromagnetic shielding film as described in claim 1, characterized in that, The surface of the shielding layer is not smooth.

7. A circuit board, characterized in that, It includes a circuit board body and an electromagnetic shielding film as described in any one of claims 1-6; the electromagnetic shielding film is pressed together with the circuit board body; the side of the shielding layer near the adhesive film layer is electrically connected to the ground plane of the circuit board body.

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