Electromagnetic shield film and circuit board

Abstract

The application discloses an electromagnetic shielding film and a circuit board, wherein the electromagnetic shielding film comprises an insulating layer, a metal layer and a glue film layer which are sequentially arranged in layers, and the glue film layer is provided with conductive particles; in the thickness direction of the electromagnetic shielding film, the gravity center of at least part of the conductive particles is close to the metal layer, and one end of the conductive particles away from the metal layer has a sharp structure. By arranging the conductive particles in the glue film layer, and by making the gravity center of at least part of the conductive particles close to the metal layer and one end of at least part of the conductive particles away from the metal layer have a sharp structure, the conductive particles have better piercing performance when being pressed, the contact degree between the conductive particles and between the conductive particles and the ground layer of the circuit board can be improved, and thus 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] With the rapid development of the electronics industry, electronic products are becoming increasingly miniaturized, lightweight, and assembled with high density, greatly driving the development of flexible circuit boards (PCBs), thereby enabling the integration of components and wire connections. Flexible circuit boards can be widely used in industries such as mobile phones, LCD displays, communications, and aerospace.

[0003] Driven by the international market, functional flexible circuit boards (FPCBs) dominate the flexible circuit board market, and an important indicator for evaluating the performance of FPCBs is electromagnetic interference shielding (EMI shielding). With the integration of functions in communication devices such as mobile phones, their internal components are rapidly increasing in frequency and speed. Driven by these high frequencies and speeds, the resulting problems of internal and external electromagnetic interference, signal attenuation during transmission, insertion loss, and jitter are becoming increasingly serious.

[0004] Existing electromagnetic shielding films commonly used on 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 a 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 connection with the ground plane of the circuit board and diverting interference charges to the ground plane, thereby 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 and consequently poor shielding effect. To solve the problem of poor piercing performance and improve the grounding performance of the electromagnetic shielding film, it is urgent to develop an electromagnetic shielding film and circuit board with good piercing performance and excellent grounding effect. Summary of the Invention

[0005] The purpose of this invention is to provide an electromagnetic shielding film that can improve the grounding performance of the electromagnetic shielding film.

[0006] To achieve the above objectives, embodiments of the present invention provide an electromagnetic shielding film, comprising an insulating layer, a metal layer, and an adhesive film layer stacked sequentially, wherein the adhesive film layer contains conductive particles;

[0007] In the thickness direction of the electromagnetic shielding film, at least a portion of the conductive particles have their centers of gravity close to the metal layer, and at least a portion of the conductive particles have a spike structure at the end away from the metal layer.

[0008] As an improvement to the above scheme, at least 50-90% of the conductive particles have their center of gravity close to the metal layer.

[0009] As an improvement to the above scheme, the vertical distance from the center of gravity of the conductive particles to the surface of the metal layer near the adhesive film layer is ≤1.5μm.

[0010] As an improvement to the above scheme, at least 50-90% of the conductive particles have a spike structure at the end away from the metal layer.

[0011] As an improvement to the above scheme, the height of the conductive particles is 10-80% of the thickness of the adhesive film layer.

[0012] As an improvement to the above solution, the weight percentage of the conductive particles in the adhesive film layer is 5%-50%.

[0013] As an improvement to the above scheme, the conductive particles contain thiol groups on their surface.

[0014] As an improvement to the above scheme, the film layer contains alkenyl and / or alkynyl groups.

[0015] As an improvement to the above scheme, the thickness of the metal layer is 0.1-5 μm.

[0016] 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 metal layer away from the insulating layer is electrically connected to the ground layer of the circuit board body.

[0017] 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 hot pressing, these conductive particles conduct electricity between the metal layer and the circuit board ground layer, thereby directing interference charges to the circuit board ground layer. The beneficial effect of this invention is that by ensuring at least a portion of the conductive particles have their centers of gravity close to the metal layer, and that at least a portion of the conductive particles have a spiked structure at their ends away from the metal layer, the conductive particles exhibit better piercing performance during pressing. This improves the contact between conductive particles and between the conductive particles and the circuit board ground layer, thereby enhancing the grounding performance of the electromagnetic shielding film. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the first electromagnetic shielding film provided in the embodiments of the present invention;

[0019] Figure 2 This is a schematic diagram of the structure of the second type of electromagnetic shielding film provided in an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram of the structure of the third type of electromagnetic shielding film provided in the embodiments of the present invention;

[0021] Figure 4 This is a schematic diagram of the structure of a circuit board provided in an embodiment of the present invention.

[0022] Among them, 1. Insulating layer; 2. Metal layer; 3. Adhesive film layer; 4. Carrier layer; 5. Protective film layer; 6. Circuit board body; 31. Conductive particles. Detailed Implementation

[0023] 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.

[0024] 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.

[0025] 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.

[0026] See Figure 1 This invention provides an electromagnetic shielding film, comprising an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31. In the thickness direction of the electromagnetic shielding film, at least a portion of the conductive particles 31 have their centers of gravity close to the metal layer, and at least a portion of the conductive particles 31 have a spiked structure at their ends away from the metal layer 2. "The centers of gravity of the conductive particles 31 are close to the metal layer" means that regardless of their placement, the distance between the center of gravity of the conductive particles 31 and the metal layer 2 is minimized. Preferably, a portion of the surface of the conductive particles 31 is in contact with the metal layer 2.

[0027] In this embodiment of the invention, by providing conductive particles 31 in the adhesive film layer 3, and having at least a portion of the conductive particles 31 with their center of gravity close to the metal layer 2, and at least a portion of the conductive particles 31 having a spike structure at one end away from the metal layer 2, the conductive particles 31 have better piercing performance during pressing, which can improve the contact degree between the conductive particles 31 and between the conductive particles 31 and the circuit board ground layer, thereby improving the grounding performance of the electromagnetic shielding film and thus successfully guiding the interference charge into the circuit board ground layer.

[0028] In this embodiment of the invention, the conductive particle 31 has a spike structure at the end away from the metal layer 2. For example, the conductive particle 31 may be teardrop-shaped, with a spike structure at the end away from the metal layer 2 and the center of gravity of the conductive particle 31 at the end closer to the metal layer 2. The spike structure can more easily pierce the adhesive in the adhesive film layer 3. Therefore, by setting the end of the conductive particle 31 away from the metal layer 2 as a spike structure, the piercing performance of the conductive particle 31 can be improved, allowing more conductive particles 31 to come into contact with each other. At the same time, it allows the conductive particles to effectively contact the circuit board ground layer, improving the grounding performance of the electromagnetic shielding film, thereby successfully guiding the interference charge to the circuit board ground layer.

[0029] As a preferred embodiment, at least 50-90% of the conductive particles 31 have their centers of gravity close to the metal layer 2. When a certain proportion of the conductive particles 31 have their centers of gravity close to the metal layer 2, the higher density of conductive particles 31 can pierce the adhesive film layer 3, increasing the piercing density of the adhesive film layer 3, thereby reducing the grounding resistance of the electromagnetic shielding film. If the above proportion is too low, the piercing density of the conductive particles 31 will decrease, resulting in a higher grounding resistance of the electromagnetic shielding film. The above proportion can be any value or a range of any two values ​​from 55%, 60%, 65%, 70%, 75%, 80%, 85%, and 90%.

[0030] As a preferred embodiment, the vertical distance from the center of gravity of the conductive particle 31 to the surface of the metal layer 2 near the adhesive film layer 3 is ≤1.5μm. When the vertical distance from the center of gravity of the conductive particle 31 to the surface of the metal layer 2 near the adhesive film layer 3 is small, the contact area between the conductive particle 31 and the metal layer 2 increases, which is beneficial to improving conductivity and thus smoothly guiding interference charges to the bottom layer of the circuit board. When the conductive particle 31 is in complete contact with the metal layer 2, the conductivity is significantly improved. If the distance is too large, it will make it difficult for the conductive particle 31 to contact the metal layer 2, resulting in an increase in the grounding resistance of the electromagnetic shielding film.

[0031] As a preferred embodiment, at least 50-90% of the conductive particles 31 have a spiked structure at the end furthest from the metal layer 2. To prevent the conductive particles 31 from failing to effectively pierce the adhesive film layer 2 and contact the circuit board ground layer during the lamination process, thereby reducing the grounding performance of the electromagnetic shielding film, at least 50-90% of the conductive particles 31 have a spiked structure at the end furthest from the metal layer 2. The spiked structure can effectively pierce the adhesive in the adhesive film layer 3, thus ensuring that the conductive particles 31 can contact the circuit board ground layer, increasing the contact area between the circuit board ground layer and the conductive particles 31, improving the grounding performance of the electromagnetic shielding film, and thus successfully guiding interference charges to the bottom layer of the circuit board.

[0032] As a preferred embodiment, the height of the conductive particles 31 is 10-80% of the thickness of the adhesive film layer 3. Since the conductive particles 31 need to fill the adhesive film layer 3, their height should not be too high. Excessive height may cause the conductive particles 31 to not only pierce the adhesive film layer 3 during the pressing process, but also potentially pierce the metal layer 2, thereby damaging the structure of the electromagnetic shielding film and affecting its electromagnetic shielding effect. Therefore, setting the height of the conductive particles 31 to 10-80% of the thickness of the adhesive film layer 3 can prevent the conductive particles 31 from piercing the metal layer 2 and thus avoid damaging the structure of the metal shielding film.

[0033] As a preferred embodiment, the weight percentage of the conductive particles in the adhesive film layer is 5%-50%. By setting the weight percentage of the conductive particles 31 in the adhesive film layer 3 to 5%-50%, the number of conductive particles 31 filling the adhesive film layer 3 is moderate. This avoids an insufficient number of conductive particles 31, which would reduce the contact between the conductive particles 31 and the metal layer 2 and the circuit board ground layer, thereby lowering the grounding performance of the electromagnetic shielding film and preventing interference charges from being smoothly conducted to the circuit board ground layer, resulting in a poorer shielding effect. Simultaneously, it also avoids an excessive number of conductive particles 31, which would result in insufficient adhesive in the adhesive film layer 3, leading to insufficient adhesion and delamination of the electromagnetic shielding film during the lamination process. Therefore, setting the weight percentage of the conductive particles 31 in the adhesive film layer 3 to 5%-50% can improve the grounding performance of the electromagnetic shielding film while preventing delamination during the lamination process. Optionally, the weight percentage of the conductive particles 31 can be any value or a range of any two values ​​from 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, to 45%.

[0034] As a preferred embodiment, the distance between the centers of gravity of any two adjacent conductive particles 31 is ≤20μm. By setting the distance between the centers of gravity of any two adjacent conductive particles 31 to ≤20μm, it is ensured that adjacent conductive particles 31 are not too far apart, preventing the phenomenon of non-contact between conductive particles 31, between conductive particles 31 and metal layer 2, or between conductive particles 31 and circuit board ground layer during the pressing process. At the same time, setting the distance between the centers of gravity of any two adjacent conductive particles 31 to ≤20μm allows the conductive particles 31 to achieve a more uniform distribution in the adhesive film layer 3, improving the grounding performance of the electromagnetic shielding film, and thus successfully conducting interference charges to the circuit board ground layer, achieving effective shielding.

[0035] As a preferred embodiment, the surface of the conductive particles 31 contains thiol groups, which may completely or partially cover the surface of the conductive particles 31. The presence of thiol groups on the surface of the conductive particles 31 improves the compatibility between the conductive particles 31 and the adhesive film layer 3, thereby allowing the conductive particles 31 to be stably fixed in the adhesive film layer 3 without changing position, resulting in good grounding stability of the electromagnetic shielding film. The thiol groups may be physically adsorbed on the surface of the conductive particles 31 or chemically bonded to the surface of the conductive particles 31; preferably, the thiol groups are chemically bonded to the surface of the conductive particles 31.

[0036] In addition, to improve grounding stability, the film layer 3 contains alkenyl and / or alkynyl groups. This allows the conductive particles 31 to react with the alkenyl and / or alkynyl groups in the film layer 3 to form chemical bonds. This makes the position of the conductive particles 31 more stable and less susceptible to external pressure and temperature, thereby maintaining the stability of the electromagnetic shielding film.

[0037] As a preferred embodiment, the thickness of the metal layer 2 is 0.1-5 μm. By setting the thickness of the metal layer 2 to 0.1-5 μm, the electromagnetic shielding effect of the electromagnetic shielding film can be guaranteed without making the electromagnetic shielding film too thick.

[0038] In this embodiment, the metal layer 2 includes one or more of the following: a metal shielding layer, a carbon nanotube shielding layer, a ferrite shielding layer, and a graphene shielding layer. The metal shielding layer includes a single-metal shielding layer and / or an alloy shielding layer; wherein the single-metal shielding layer is made of any one of the following materials: aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold; and the alloy shielding layer is made of any two or more of the following materials: aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. The composition and shape of the conductive particles 31 are not limited; for example, the conductive particles 31 may be made of any one or more of the following materials: copper, aluminum, titanium, zinc, iron, nickel, chromium, cobalt, silver, and gold.

[0039] In this embodiment, the material used for the adhesive film layer 3 is selected from at least one of the following: modified epoxy resin, acrylic resin, modified rubber, and modified thermoplastic polyimide.

[0040] See Figure 2 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 1 away from the metal layer 2. The carrier layer 4 protects the insulating layer 1 from damage caused by external contact or impact. A thickness of 50 micrometers for the carrier layer 4 provides excellent protection, effectively preventing damage to the insulating layer 1 from external contact or impact. Furthermore, the carrier layer 4 can serve as a base film for forming the insulating layer 1; that is, the insulating layer 1 can be formed on one side of the carrier layer 4.

[0041] See Figure 3 In this embodiment, the electromagnetic shielding film further includes a protective film layer 5, which is disposed on the side of the adhesive film layer 3 away from the metal layer 2. The protective film layer 5 provides protection, ensuring that the adhesive film layer 3 is not scratched or damaged during use. The protective film layer 5 may be 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.

[0042] Specifically, when the electromagnetic shielding film includes a carrier layer 4, an insulating layer 1, a metal layer 2, an adhesive film layer 3, and a protective film layer 5, the method for preparing the electromagnetic shielding film includes:

[0043] 1) Prepare carrier layer 4;

[0044] 2) An insulating layer 1 is formed on one side of the carrier layer 4;

[0045] 3) A metal layer 2 is formed on the side of the insulating layer 1 that is away from the carrier layer 4;

[0046] 4) Apply adhesive to the side of the metal layer 2 away from the insulating layer 1 to form an adhesive film layer 3;

[0047] 5) Attach the protective film layer 5 to the side of the adhesive film layer 3 that is away from the metal layer 2.

[0048] See Figure 4Another 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 metal layer 2 away from the insulating layer 1 is electrically connected to the ground layer of the circuit board body 6.

[0049] 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.

[0050] Specifically, by setting conductive particles 31 in the adhesive film layer 3, and placing at least a portion of the conductive particles 31 with their center of gravity close to the metal layer 2, and having at least a portion of the conductive particles 31 with a spike structure at one end away from the metal layer 2, the conductive particles 31 have better piercing performance during pressing, which can improve the contact between the conductive particles 31 and between the conductive particles 31 and the circuit board ground layer, thereby improving the grounding performance of the electromagnetic shielding film.

[0051] To facilitate understanding of the above-mentioned invention, the following embodiments and comparative examples are used for illustration and the results are tested.

[0052] Example 1:

[0053] An electromagnetic shielding film includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31, which constitute 45% of the film's weight. The center of gravity of each conductive particle 31 is 1 μm perpendicular to the surface of the metal layer 2 near the adhesive film layer 3. The metal layer has a thickness of 0.5 μm, and the electromagnetic shielding film has a thickness of 10 μm. The surface of the conductive particles 31 contains thiol groups, and the adhesive film layer 3 contains alkenyl groups. Along the thickness direction of the electromagnetic shielding film, 50% of the conductive particles 31 have their centers of gravity close to the metal layer 2, and the ends of 50% of the conductive particles 31 furthest from the metal layer 2 have spike structures. The electromagnetic shielding film was subjected to pressing (185℃, 10 min, 120 kg / cm², cover film step height 38 μm), curing (160℃, 1.5 h), and thermal shock (288℃, 10 s, 3 times) before grounding testing.

[0054] Test results: After testing, the electromagnetic shielding film of this embodiment has a grounding resistance of 450 milliohms when it is pressed onto a circuit board with a PAD (pad) diameter of 1mm.

[0055] Example 2:

[0056] An electromagnetic shielding film includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31, which constitute 45% of the film's weight. The center of gravity of each conductive particle 31 is 1 μm perpendicular to the surface of the metal layer 2 near the adhesive film layer 3. The metal layer has a thickness of 0.5 μm, and the electromagnetic shielding film has a thickness of 10 μm. The surface of the conductive particles 31 contains thiol groups, and the adhesive film layer 3 contains alkenyl groups. Along the thickness direction of the electromagnetic shielding film, 50% of the conductive particles 31 have their centers of gravity close to the metal layer 2, and 70% of the conductive particles 31 have a spiked structure at their ends away from the metal layer 2. The electromagnetic shielding film was subjected to pressing (185℃, 10 min, 120 kg / cm², cover film step height 38 μm), curing (160℃, 1.5 h), and thermal shock (288℃, 10 s, 3 times) before grounding testing.

[0057] Test results: After testing, the electromagnetic shielding film of this embodiment has a grounding resistance of 372 milliohms when it is pressed onto a circuit board with a PAD (pad) diameter of 1mm.

[0058] Example 3:

[0059] An electromagnetic shielding film includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31, which constitute 45% of the film's weight. The center of gravity of each conductive particle 31 is 1 μm perpendicular to the surface of the metal layer 2 near the adhesive film layer 3. The metal layer has a thickness of 0.5 μm, and the electromagnetic shielding film has a thickness of 10 μm. The surface of the conductive particles 31 contains thiol groups, and the adhesive film layer 3 contains alkenyl groups. Along the thickness direction of the electromagnetic shielding film, 50% of the conductive particles 31 have their centers of gravity close to the metal layer 2, and 90% of the conductive particles 31 have a spiked structure at their ends away from the metal layer 2. The electromagnetic shielding film was subjected to pressing (185℃, 10 min, 120 kg / cm², cover film step height 38 μm), curing (160℃, 1.5 h), and thermal shock (288℃, 10 s, 3 times) before grounding testing.

[0060] Test results: After testing, the electromagnetic shielding film of this embodiment has a grounding resistance of 299 milliohms when it is pressed onto a circuit board with a PAD (pad) diameter of 1mm.

[0061] Example 4:

[0062] An electromagnetic shielding film includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31, which constitute 45% of the film's weight. The center of gravity of each conductive particle 31 is 1 μm perpendicular to the surface of the metal layer 2 near the adhesive film layer 3. The metal layer has a thickness of 0.5 μm, and the electromagnetic shielding film has a thickness of 10 μm. The surface of the conductive particles 31 contains thiol groups, and the adhesive film layer 3 contains alkenyl groups. In the thickness direction of the electromagnetic shielding film, 70% of the conductive particles 31 have their centers of gravity close to the metal layer 2, and 50% of the conductive particles have a spiked structure at their ends away from the metal layer 2. The electromagnetic shielding film was subjected to pressing (185℃, 10 min, 120 kg / cm², cover film step height 38 μm), curing (160℃, 1.5 h), and thermal shock (288℃, 10 s, 3 times) before grounding testing.

[0063] Test results: After testing, the electromagnetic shielding film of this embodiment has a grounding resistance of 364 milliohms when it is pressed onto a circuit board with a PAD (pad) diameter of 1mm.

[0064] Example 5:

[0065] An electromagnetic shielding film includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31, which constitute 45% of the film's weight. The center of gravity of each conductive particle 31 is 1 μm perpendicular to the surface of the metal layer 2 near the adhesive film layer 3. The metal layer has a thickness of 0.5 μm, and the electromagnetic shielding film has a thickness of 10 μm. The surface of the conductive particles 31 contains thiol groups, and the adhesive film layer 3 contains alkenyl groups. Along the thickness direction of the electromagnetic shielding film, 70% of the conductive particles 31 have their centers of gravity close to the metal layer 2, and 70% of the conductive particles 31 have a spiked structure at their ends away from the metal layer 2. The electromagnetic shielding film was subjected to pressing (185℃, 10 min, 120 kg / cm², cover film step height 38 μm), curing (160℃, 1.5 h), and thermal shock (288℃, 10 s, 3 times) before grounding testing.

[0066] Test results: After testing, the electromagnetic shielding film of this embodiment has a grounding resistance of 328 milliohms when it is pressed onto a circuit board with a PAD (pad) diameter of 1mm.

[0067] Example 6:

[0068] An electromagnetic shielding film includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31, which constitute 45% of the film's weight. The center of gravity of each conductive particle 31 is 1 μm perpendicular to the surface of the metal layer 2 near the adhesive film layer 3. The metal layer has a thickness of 0.5 μm, and the electromagnetic shielding film has a thickness of 10 μm. The surface of the conductive particles 31 contains thiol groups, and the adhesive film layer 3 contains alkenyl groups. Along the thickness direction of the electromagnetic shielding film, 70% of the conductive particles 31 have their centers of gravity close to the metal layer 2, and 90% of the conductive particles 31 have a spiked structure at their ends away from the metal layer 2. The electromagnetic shielding film was subjected to pressing (185℃, 10 min, 120 kg / cm², cover film step height 38 μm), curing (160℃, 1.5 h), and thermal shock (288℃, 10 s, 3 times) before grounding testing.

[0069] Test results: After testing, the electromagnetic shielding film of this embodiment has a grounding resistance of 263 milliohms when it is pressed onto a circuit board with a PAD (pad) diameter of 1mm.

[0070] Example 7:

[0071] An electromagnetic shielding film includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31, which comprise 45% of the film's weight. The center of gravity of each conductive particle 31 is 1 μm perpendicular to the surface of the metal layer 2 near the adhesive film layer 3. The metal layer has a thickness of 0.5 μm, and the electromagnetic shielding film has a thickness of 10 μm. The conductive particles 31 contain thiol groups on their surface, and the adhesive film layer 3 contains alkenyl groups. Along the thickness direction of the electromagnetic shielding film, 90% of the conductive particles 31 have their centers of gravity close to the metal layer 2, and 50% of the conductive particles 31 have a spiked structure at their ends away from the metal layer 2. The electromagnetic shielding film was subjected to pressing (185℃, 10 min, 120 kg / cm², cover film step height 38 μm), curing (160℃, 1.5 h), and thermal shock (288℃, 10 s, 3 times) before grounding testing.

[0072] Test results: After testing, the electromagnetic shielding film of this embodiment has a grounding resistance of 284 milliohms when it is pressed onto a circuit board with a PAD (pad) diameter of 1mm.

[0073] Example 8:

[0074] An electromagnetic shielding film includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31, which constitute 45% of the film's weight. The center of gravity of each conductive particle 31 is 1 μm perpendicular to the surface of the metal layer 2 near the adhesive film layer 3. The metal layer has a thickness of 0.5 μm, and the electromagnetic shielding film has a thickness of 10 μm. The surface of the conductive particles 31 contains thiol groups, and the adhesive film layer 3 contains alkenyl groups. Along the thickness direction of the electromagnetic shielding film, 90% of the conductive particles 31 have their centers of gravity close to the metal layer 2, and 70% of the conductive particles 31 have a spiked structure at their ends away from the metal layer 2. The electromagnetic shielding film was subjected to pressing (185℃, 10 min, 120 kg / cm², cover film step height 38 μm), curing (160℃, 1.5 h), and thermal shock (288℃, 10 s, 3 times) before grounding testing.

[0075] Test results: After testing, the electromagnetic shielding film of this embodiment has a grounding resistance of 215 milliohms when it is pressed onto a circuit board with a PAD (pad) diameter of 1mm.

[0076] Example 9:

[0077] An electromagnetic shielding film includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31, which constitute 45% of the film's weight. The center of gravity of each conductive particle 31 is 1 μm perpendicular to the surface of the metal layer 2 near the adhesive film layer 3. The metal layer has a thickness of 0.5 μm, and the electromagnetic shielding film has a thickness of 10 μm. The surface of the conductive particles 31 contains thiol groups, and the adhesive film layer 3 contains alkenyl groups. Along the thickness direction of the electromagnetic shielding film, 90% of the conductive particles 31 have their centers of gravity close to the metal layer 2, and 90% of the conductive particles 31 have a spiked structure at their ends away from the metal layer 2. The electromagnetic shielding film was subjected to pressing (185℃, 10 min, 120 kg / cm², cover film step height 38 μm), curing (160℃, 1.5 h), and thermal shock (288℃, 10 s, 3 times) before grounding testing.

[0078] Test results: After testing, the electromagnetic shielding film of this embodiment has a grounding resistance of 174 milliohms when it is pressed onto a circuit board with a PAD (pad) diameter of 1mm.

[0079] Comparative Example 1:

[0080] An electromagnetic shielding film includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked sequentially. The adhesive film layer 3 contains conductive particles 31. The conductive particles 31 account for 45% of the total weight. The metal layer has a thickness of 0.5 micrometers, and the electromagnetic shielding film has a thickness of 10 micrometers. The conductive particles 31 are randomly distributed in the adhesive film layer 3 along the thickness direction of the electromagnetic shielding film, and the conductive particles 31 have no obvious sharp spikes. The electromagnetic shielding film was subjected to grounding tests after being treated with pressing (185℃, 10min, 120kg / cm², cover film step height of 38µm), curing (160℃, 1.5h), and thermal shock (288℃, 10s, 3 times).

[0081] Test results: After testing, the electromagnetic shielding film of this embodiment has a grounding resistance of 1864 milliohms when it is pressed onto a circuit board with a PAD (pad) diameter of 1mm.

[0082] Table 1 below shows the grounding resistance of the electromagnetic shielding films of Examples 1-9 and Comparative Example 1.

[0083] Table 1. Grounding resistance of electromagnetic shielding films in Examples 1-9 and Comparative Example 1

[0084]

[0085] Therefore, by applying the electromagnetic shielding film described in this embodiment, the grounding performance of the electromagnetic shielding film can be improved.

[0086] In summary, the conductive particles 31 are provided in the adhesive film layer 3; in the thickness direction of the electromagnetic shielding film, at least a portion (50%, 70%, 90%) of the conductive particles 31 have their center of gravity located in the upper half of the conductive particles, and at least a portion (50%, 70%, 90%) of the conductive particles 31 have a spike structure at the end away from the metal layer 2, so that the conductive particles 31 have better piercing performance during pressing, which can improve the contact degree between the conductive particles 31 and between the conductive particles 31 and the circuit board ground layer, thereby improving the grounding performance of the electromagnetic shielding film.

[0087] 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 an insulating layer, a metal layer and an adhesive film layer stacked sequentially, wherein the adhesive film layer contains conductive particles; In the thickness direction of the electromagnetic shielding film, at least a portion of the conductive particles have their center of gravity close to the metal layer, and at least a portion of the conductive particles have a spike structure at the end away from the metal layer. The height of the conductive particles is 10-80% of the thickness of the film layer.

2. The electromagnetic shielding film as described in claim 1, characterized in that, At least 50-90% of the conductive particles have their center of gravity close to the metal layer.

3. The electromagnetic shielding film as described in claim 2, characterized in that, The vertical distance from the center of gravity of the conductive particles to the surface of the metal layer near the adhesive film layer is ≤1.5μm.

4. The electromagnetic shielding film as described in claim 1, characterized in that, At least 50-90% of the conductive particles have a spiked structure at the end away from the metal layer.

5. The electromagnetic shielding film according to any one of claims 1-4, characterized in that, The conductive particles in the adhesive film layer account for 5%-50% of the total weight.

6. The electromagnetic shielding film as described in claim 1, characterized in that, The conductive particles contain thiol groups on their surface.

7. The electromagnetic shielding film as described in claim 6, characterized in that, The film layer contains alkenyl and / or alkynyl groups.

8. The electromagnetic shielding film as described in claim 1, characterized in that, The thickness of the metal layer is 0.1-5 μm.

9. A circuit board, characterized in that, It includes a circuit board body and an electromagnetic shielding film as described in any one of claims 1-8; the electromagnetic shielding film is pressed together with the circuit board body; the side of the metal layer away from the insulating layer is electrically connected to the ground layer of the circuit board body.

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