Electromagnetic shielding film and circuit board

Abstract

The invention discloses an electromagnetic shielding film and a circuit board, the electromagnetic shielding film comprises an insulating layer, a metal layer and an adhesive film layer which are stacked in sequence, and conductive particles are arranged in the adhesive film layer; in the thickness direction of the electromagnetic shielding film, the gravity centers of at least one part of the conductive particles are close to the metal layer, and the ends, away from the metal layer, of the conductive particles are provided with spine structures. The conductive particles are arranged in the adhesive film layer, the gravity centers of at least one part of the conductive particles are close to the metal layer, and the ends, far away from the metal layer, of at least one part of the conductive particles are provided with the spine structures, so that the conductive particles have better puncture performance during pressing; the contact degree between conductive particles and between the conductive particles and a circuit board ground layer can be improved, so that the grounding performance of the electromagnetic shielding film is improved.

Description

Technical Field

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

[0002] With the rapid development of the electronics industry, electronic products are further moving towards miniaturization, light weight, and high-density assembly, which greatly promotes the development of flexible printed circuit boards, thus realizing the integration of component devices and wire connections. Flexible printed circuit boards can be widely used in industries such as mobile phones, liquid crystal displays, communications, and aerospace.

[0003] Driven by the international market, functional flexible printed circuit boards dominate the flexible printed circuit board market. An important indicator for evaluating the performance of functional flexible printed circuit boards is electromagnetic shielding (Electromagnetic Interference Shielding, abbreviated as EMI Shielding). With the integration of functions of communication devices such as mobile phones, their internal components are rapidly becoming high-frequency and high-speed. Under the drive of high frequency and high speed, problems such as electromagnetic interference inside and outside components, signal attenuation during transmission, insertion loss, and jitter are gradually becoming serious.

[0004] The commonly used electromagnetic shielding film for existing circuit boards includes an insulating layer, a shielding layer, and an adhesive film layer stacked in sequence. One side of the shielding layer close to the adhesive film layer has roughness. During use, the electromagnetic shielding film needs to be hot-pressed with the circuit board at a high temperature. During the hot-pressing process, the shielding layer pierces the adhesive film layer through the rough side to be electrically connected to the ground layer of the circuit board, and then the interfering charges are introduced into the ground layer of the circuit board, thereby achieving shielding. The inventor of the present invention found the following technical problems in the process of implementing the present invention: The piercing effect of only relying on the method of setting roughness to pierce the adhesive film layer is not good, resulting in poor grounding performance of the electromagnetic shielding film and poor shielding effect. To solve the piercing effect of the electromagnetic shielding film and improve its grounding performance, it is urgently necessary to develop an electromagnetic shielding film and a circuit board with good piercing performance and good grounding effect. Summary of the Invention

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

[0006] To achieve the above purpose, the embodiments of the present invention provide an electromagnetic shielding film, including an insulating layer, a metal layer, and an adhesive film layer stacked in sequence, and conductive particles are provided in the adhesive film layer;

[0007] In the thickness direction of the electromagnetic shielding film, the center of gravity of at least a part of the conductive particles is close to the metal layer, and one end of at least a part of the conductive particles away from the metal layer has a spiky structure.

[0008] As an improvement to the above solution, the centers of gravity of at least 50 - 90% of the conductive particles are close to the metal layer.

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

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

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

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

[0013] As an improvement to the above solution, the surface of the conductive particle contains a mercapto group.

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

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

[0016] To achieve the above object, an embodiment of the present invention further provides a circuit board, including a circuit board body and the 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 with the prior art, the electromagnetic shielding film and the circuit board provided by the embodiment of the present invention set conductive particles in the adhesive film layer, and during the hot pressing process, the metal layer and the ground layer of the circuit board are conducted through the conductive particles, so as to introduce interference charges into the ground layer of the circuit board and achieve electromagnetic shielding. The beneficial effect of the embodiment of the present invention is that by making the centers of gravity of at least a part of the conductive particles close to the metal layer, and at least a part of the conductive particles have a spike structure at one end away from the metal layer, the conductive particles have better piercing performance during pressing, which can improve the contact degree between the conductive particles and between the conductive particles and the ground layer of the circuit board, thereby improving the grounding performance of the electromagnetic shielding film. Description of the Drawings

[0018] Figure 1 is a schematic structural diagram of the first electromagnetic shielding film provided by the embodiment of the present invention;

[0019] Figure 2 is a schematic structural diagram of the second electromagnetic shielding film provided by the embodiment of the present invention;

[0020] Figure 3 It is a schematic structural diagram of the third electromagnetic shielding film provided by an embodiment of the present invention;

[0021] Figure 4 It is a schematic structural diagram of a circuit board provided by an embodiment of the present invention.

[0022] Among them, 1 is an insulating layer; 2 is a metal layer; 3 is an adhesive film layer; 4 is a carrier layer; 5 is a protective film layer; 6 is a circuit board body; 31 are conductive particles. Detailed implementation manners

[0023] 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. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0024] 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 accompanying 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 thus cannot be understood as a limitation to the embodiments of the present invention.

[0025] In addition, the terms first, second, etc. in the specification and claims are only used for the purpose of distinguishing the description of the same technical features, and cannot be understood 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 can be interchanged under appropriate circumstances. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features.

[0026] See Figure 1 , an embodiment of the present invention provides an electromagnetic shielding film, which includes an insulating layer 1, a metal layer 2, and an adhesive film layer 3 stacked in sequence, and conductive particles 31 are provided in the adhesive film layer 3; in the thickness direction of the electromagnetic shielding film, the center of gravity of at least a part of the conductive particles 31 is close to the metal layer, and one end of at least a part of the conductive particles 31 away from the metal layer 2 has a spike structure. The center of gravity of the conductive particles 31 being close to the metal layer means that no matter how the conductive particles 31 are placed, the distance between the center of gravity of the conductive particles 31 and the metal layer 2 should be the shortest. Preferably, a part of the surface of the conductive particles 31 is in contact with the metal layer 2.

[0027] In an embodiment of the present invention, by disposing conductive particles 31 in the adhesive film layer 3, and when the centers of gravity of at least a part of the conductive particles 31 are close to the metal layer 2, and at least a part of the ends of the conductive particles 31 away from the metal layer 2 have spiky structures, the conductive particles 31 have better piercing performance during lamination, which can improve the contact degree between the conductive particles 31 and between the conductive particles 31 and the contact between the conductive particles 31 and the circuit board ground layer, thereby improving the grounding performance of the electromagnetic shielding film, and then smoothly introducing interference charges into the circuit board ground layer.

[0028] In an embodiment of the present invention, the end of the conductive particle 31 away from the metal layer 2 has a spiky structure. For example, the conductive particle 31 has a water droplet-like structure, the end away from the metal layer 2 has a spiky structure, and the end close to the metal layer 2 is the position where the center of gravity of the conductive particle 31 is located. The spiky 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 spiky structure, the piercing performance of the conductive particle 31 can be improved, enabling more conductive particles 31 to come into contact with each other, and at the same time enabling the conductive particles to effectively contact the circuit board ground layer, improving the grounding performance of the electromagnetic shielding film, and thus smoothly introducing interference charges into the circuit board ground layer.

[0029] As a preferred solution, the centers of gravity of at least 50 - 90% of the conductive particles 31 are close to the metal layer 2. When the centers of gravity of a certain proportion of the conductive particles 31 are close to the metal layer 2, a higher density of conductive particles 31 can pierce the adhesive film layer 3, increasing the piercing density of the adhesive film layer 3, and thereby reducing the grounding resistance of the electromagnetic shielding film. If the above proportion is too small, the piercing density of the conductive particles 31 will be reduced, causing the grounding resistance of the electromagnetic shielding film to increase. The above proportion can be any value among 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or any interval composed of any two of these values.

[0030] As a preferred solution, the vertical distance from the center of gravity of the conductive particle 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is ≤ 1.5 μm. When the vertical distance from the center of gravity of the conductive particle 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is small, the contact area between the conductive particle 31 and the metal layer 2 becomes larger, which is beneficial to improving the conductivity, and then smoothly introducing interference charges into 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 above distance is too large, it will lead to difficulty in the contact between the conductive particle 31 and the metal layer 2, causing the grounding resistance of the electromagnetic shielding film to increase.

[0031] As a preferred solution, at least 50 - 90% of the ends of the conductive particles 31 away from the metal layer 2 have spiky structures. 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 ends of the conductive particles 31 away from the metal layer 2 are provided with spiky structures. The spiky structures can effectively pierce the adhesive in the adhesive film layer 3, 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 then smoothly introducing interference charges into the bottom layer of the circuit board.

[0032] As a preferred solution, 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 be filled in the adhesive film layer 3, their height should not be too high. If it is too high, it may cause the conductive particles 31 to not only pierce the adhesive film layer 3 but also further pierce the metal layer 2 during the lamination process, thus destroying 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 not damage the structure of the metal shielding film.

[0033] As a preferred solution, the weight ratio of the conductive particles in the adhesive film layer is 5% - 50%. By setting the weight ratio of the conductive particles 31 in the adhesive film layer 3 to 5% - 50%, the number of conductive particles 31 filled in the adhesive film layer 3 is moderate. There will be no situation where the number of conductive particles 31 is too small, resulting in a reduction in the contact between the conductive particles 31 and the metal layer 2 and the circuit board ground layer, reducing the grounding performance of the electromagnetic shielding film, and further causing the interference charges to not be smoothly introduced into the circuit board ground layer, resulting in a poor shielding effect. At the same time, there will also be no situation where the number of conductive particles 31 is too large, resulting in too little adhesive in the adhesive film layer 3, making the viscosity of the adhesive film layer 3 insufficient and causing delamination of the electromagnetic shielding film during the lamination process. Therefore, setting the weight ratio of the conductive particles 31 in the adhesive film layer 3 to 5% - 50% can improve the grounding performance of the electromagnetic shielding film and prevent delamination during the lamination process. Optionally, the weight ratio of the conductive particles 31 can be any value among 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or any interval composed of any two of these values.

[0034] As a preferred solution, the distance between the centers of gravity of any two adjacent conductive particles 31 is ≤ 20 μm. By setting the distance between the centers of gravity of any two adjacent conductive particles 31 to be ≤ 20 μm, it is ensured that the adjacent conductive particles 31 are not too far apart, and there will be no phenomenon that the conductive particles 31 cannot come into contact with each other, between the conductive particles 31 and the metal layer 2, or between the conductive particles 31 and the 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 be ≤ 20 can enable the conductive particles 31 to be more evenly distributed in the adhesive film layer 3, improve the grounding performance of the electromagnetic shielding film, and then smoothly introduce interference charges into the circuit board ground layer to achieve effective shielding.

[0035] As a preferred solution, the surface of the conductive particle 31 contains a thiol group, which completely covers the surface of the conductive particle 31 or may partially cover the surface of the conductive particle 31. Due to the presence of the thiol group on the surface of the conductive particle 31, the compatibility between the conductive particle 31 and the adhesive film layer 3 is improved, and then the conductive particle 31 can be stably fixed in the adhesive film layer 3 without changing its position, and thus the grounding stability of the electromagnetic shielding film is good. Among them, the thiol group can be physically adsorbed on the surface of the conductive particle 31 or bonded to the surface of the conductive particle 31 through a chemical bond. Preferably, the thiol group is bonded to the surface of the conductive particle 31 through a chemical bond.

[0036] In addition, for better grounding stability performance, the adhesive film layer 3 contains alkenyl and / or alkynyl groups, which can enable the conductive particle 31 to react with the alkenyl and / or alkynyl groups in the adhesive film layer 3 to form chemical bonds, so that the position of the conductive particle 31 is more stable and not easily affected by external pressure and temperature, and thus the performance of the electromagnetic shielding film is maintained stable.

[0037] As a preferred solution, 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 ensured while the thickness of the electromagnetic shielding film is not made too thick.

[0038] In this embodiment, the metal layer 2 includes one or more of a metal shielding layer, a carbon nanotube shielding layer, a ferrite shielding layer, and a graphene shielding layer. Among them, the metal shielding layer includes a single-metal shielding layer and / or an alloy shielding layer; among them, the single-metal shielding layer is made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy shielding layer is made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. The composition and shape of the conductive particle 31 are not limited. For example, the material of the conductive particle 31 is made of any one or more of 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 resins, acrylics, modified rubbers, and modified thermoplastic polyimides.

[0040] See Figure 2 , a carrier layer 4 is further provided on the electromagnetic shielding film described in the embodiment of the present invention, and the carrier layer 4 is disposed on a surface of the insulating layer 1 away from the metal layer 2. The carrier layer 4 can be used to protect the insulating layer 1 so that the insulating layer 1 is not damaged by external contact, collision, etc. Among them, when the thickness of the carrier layer 4 is 50 microns, it has better protection ability and can perfectly protect the insulating layer 1 from being damaged by external contact, collision, etc. In addition, the carrier layer 4 can be used as a base film for forming the insulating layer 1, that is: the insulating layer 1 can be formed on one surface of the carrier layer 4.

[0041] See Figure 3 , the electromagnetic shielding film in this embodiment further includes a protective film layer 5, and the protective film layer 5 is disposed on a surface of the adhesive film layer 3 away from the metal layer 2. Since the protective film layer 5 has a protective effect, it can ensure that the adhesive film layer 3 is not scratched or damaged during use. Among them, the protective film layer 5 includes a PPS film layer, a PEN film layer, a polyester film layer, a polyimide film layer, a film layer formed after curing of epoxy resin ink, a film layer formed after curing of polyurethane ink, a film layer formed after curing of modified acrylic resin, or a film layer formed after curing of polyimide resin. Among them, when the electromagnetic shielding film is laminated onto a 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 preparation method of the electromagnetic shielding film includes:

[0043] 1) Prepare the carrier layer 4;

[0044] 2) Form the insulating layer 1 on one surface of the carrier layer 4;

[0045] 3) Form the metal layer 2 on a surface of the insulating layer 1 away from the carrier layer 4;

[0046] 4) Coat an adhesive on a surface of the metal layer 2 away from the insulating layer 1 to form the adhesive film layer 3;

[0047] 5) Bond the protective film layer 5 on a surface of the adhesive film layer 3 away from the metal layer 2.

[0048] See Figure 4, Another embodiment of the present invention further provides a circuit board, which includes a circuit board body 6 and the electromagnetic shielding film described in any of the above embodiments; the electromagnetic shielding film is laminated 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, flexible double-sided, flexible multi-layer board, and a rigid-flex board.

[0050] Specifically, by providing conductive particles 31 in the adhesive film layer 3, and making the center of gravity of at least a part of the conductive particles 31 close to the metal layer 2, and at least a part of the ends of the conductive particles 31 away from the metal layer 2 having a spiky structure, the conductive particles 31 have better piercing performance during lamination, 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.

[0051] For the convenience of understanding the above invention solutions, here, the following examples and comparative examples are combined for description 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 that are laminated in sequence. Conductive particles 31 are provided in the adhesive film layer 3. The weight ratio of the conductive particles 31 is 45%. The vertical distance from the center of gravity of the conductive particles 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is 1 μm. The thickness of the metal layer is 0.5 microns, the thickness of the electromagnetic shielding film is 10 microns. 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, 50% of the centers of gravity of the conductive particles 31 are close to the metal layer 2, and 50% of the ends of the conductive particles 31 away from the metal layer 2 have a spiky structure. The electromagnetic shielding film is subjected to lamination (185 °C, 10 min, 120 kg / cm2, the step height of the cover film is 38 um), curing (160 °C, 1.5 h), and thermal shock (288 °C, 10 s, 3 times) treatments and then subjected to a grounding test.

[0054] Test result: After testing, when the electromagnetic shielding film of this example is laminated onto a circuit board with a PAD (pad) diameter of 1 mm, its grounding resistance is 450 milliohms.

[0055] Example 2:

[0056] An electromagnetic shielding film, comprising an insulating layer 1, a metal layer 2 and an adhesive film layer 3 which are sequentially stacked. Conductive particles 31 are provided in the adhesive film layer 3, and the weight ratio of the conductive particles 31 is 45%. The vertical distance from the center of gravity of the conductive particles 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is 1 μm. The thickness of the metal layer is 0.5 microns, the thickness of the electromagnetic shielding film is 10 microns. 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, the centers of gravity of 50% of the conductive particles 31 are close to the metal layer 2, and one end of 70% of the conductive particles 31 away from the metal layer 2 has a spiky structure. The electromagnetic shielding film is subjected to pressing (185 °C, 10 min, 120 kg / cm2, the step height of the cover film is 38 um), curing (160 °C, 1.5 h), and thermal shock (288 °C, 10 s, 3 times) treatments and then subjected to a grounding test.

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

[0058] Example 3:

[0059] An electromagnetic shielding film, comprising an insulating layer 1, a metal layer 2 and an adhesive film layer 3 which are sequentially stacked. Conductive particles 31 are provided in the adhesive film layer 3, and the weight ratio of the conductive particles 31 is 45%. The vertical distance from the center of gravity of the conductive particles 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is 1 μm. The thickness of the metal layer is 0.5 microns, the thickness of the electromagnetic shielding film is 10 microns. 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, the centers of gravity of 50% of the conductive particles 31 are close to the metal layer 2, and one end of 90% of the conductive particles 31 away from the metal layer 2 has a spiky structure. The electromagnetic shielding film is subjected to pressing (185 °C, 10 min, 120 kg / cm2, the step height of the cover film is 38 um), curing (160 °C, 1.5 h), and thermal shock (288 °C, 10 s, 3 times) treatments and then subjected to a grounding test.

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

[0061] Example 4:

[0062] An electromagnetic shielding film, comprising an insulating layer 1, a metal layer 2 and an adhesive film layer 3 which are stacked in sequence. Conductive particles 31 are provided in the adhesive film layer 3, and the weight ratio of the conductive particles 31 is 45%. The vertical distance from the center of gravity of the conductive particles 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is 1 μm. The thickness of the metal layer is 0.5 microns, the thickness of the electromagnetic shielding film is 10 microns. The surface of the conductive particles 31 contains mercapto groups, and the adhesive film layer 3 contains alkenyl groups. In the thickness direction of the electromagnetic shielding film, the centers of gravity of 70% of the conductive particles 31 are close to the metal layer 2, and one end of 50% of the conductive particles away from the metal layer 2 has a spiky structure. The electromagnetic shielding film is subjected to pressing (185 °C, 10 min, 120 kg / cm2, the step height of the cover film is 38 um), curing (160 °C, 1.5 h), and thermal shock (288 °C, 10 s, 3 times) treatments and then subjected to a grounding test.

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

[0064] Example 5:

[0065] An electromagnetic shielding film, comprising an insulating layer 1, a metal layer 2 and an adhesive film layer 3 which are stacked in sequence. Conductive particles 31 are provided in the adhesive film layer 3, and the weight ratio of the conductive particles 31 is 45%. The vertical distance from the center of gravity of the conductive particles 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is 1 μm. The thickness of the metal layer is 0.5 microns, the thickness of the electromagnetic shielding film is 10 microns. The surface of the conductive particles 31 contains mercapto groups, and the adhesive film layer 3 contains alkenyl groups. In the thickness direction of the electromagnetic shielding film, the centers of gravity of 70% of the conductive particles 31 are close to the metal layer 2, and one end of 70% of the conductive particles away from the metal layer 2 has a spiky structure. The electromagnetic shielding film is subjected to pressing (185 °C, 10 min, 120 kg / cm2, the step height of the cover film is 38 um), curing (160 °C, 1.5 h), and thermal shock (288 °C, 10 s, 3 times) treatments and then subjected to a grounding test.

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

[0067] Example 6:

[0068] An electromagnetic shielding film, comprising an insulating layer 1, a metal layer 2 and an adhesive film layer 3 which are sequentially laminated. Conductive particles 31 are provided in the adhesive film layer 3, and the weight ratio of the conductive particles 31 is 45%. The vertical distance from the center of gravity of the conductive particles 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is 1 μm. The thickness of the metal layer is 0.5 microns, the thickness of the electromagnetic shielding film is 10 microns. The surface of the conductive particles 31 contains mercapto groups, and the adhesive film layer 3 contains alkenyl groups. In the thickness direction of the electromagnetic shielding film, the centers of gravity of 70% of the conductive particles 31 are close to the metal layer 2, and one end of 90% of the conductive particles 31 away from the metal layer 2 has a spiky structure. The electromagnetic shielding film is subjected to pressing (185 °C, 10 min, 120 kg / cm2, the step height of the cover film is 38 um), curing (160 °C, 1.5 h), and thermal shock (288 °C, 10 s, 3 times) treatments and then subjected to a ground test.

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

[0070] Example 7:

[0071] An electromagnetic shielding film, comprising an insulating layer 1, a metal layer 2 and an adhesive film layer 3 which are sequentially laminated. Conductive particles 31 are provided in the adhesive film layer 3, and the weight ratio of the conductive particles 31 is 45%. The vertical distance from the center of gravity of the conductive particles 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is 1 μm. The thickness of the metal layer is 0.5 microns, the thickness of the electromagnetic shielding film is 10 microns. The surface of the conductive particles 31 contains mercapto groups, and the adhesive film layer 3 contains alkenyl groups. In the thickness direction of the electromagnetic shielding film, the centers of gravity of 90% of the conductive particles 31 are close to the metal layer 2, and one end of 50% of the conductive particles 31 away from the metal layer 2 has a spiky structure. The electromagnetic shielding film is subjected to pressing (185 °C, 10 min, 120 kg / cm2, the step height of the cover film is 38 um), curing (160 °C, 1.5 h), and thermal shock (288 °C, 10 s, 3 times) treatments and then subjected to a ground test.

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

[0073] Example 8:

[0074] An electromagnetic shielding film, comprising an insulating layer 1, a metal layer 2 and an adhesive film layer 3 which are sequentially laminated. Conductive particles 31 are provided in the adhesive film layer 3, and the weight ratio of the conductive particles 31 is 45%. The vertical distance from the center of gravity of the conductive particles 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is 1 μm. The thickness of the metal layer is 0.5 microns, the thickness of the electromagnetic shielding film is 10 microns, the surface of the conductive particles 31 contains mercapto groups, and the adhesive film layer 3 contains alkenyl groups; in the thickness direction of the electromagnetic shielding film, the centers of gravity of 90% of the conductive particles 31 are close to the metal layer 2, and one end of 70% of the conductive particles 31 away from the metal layer 2 has a spiky structure. The electromagnetic shielding film is subjected to pressing (185 °C, 10 min, 120 kg / cm2, the step height of the cover film is 38 um), curing (160 °C, 1.5 h), and thermal shock (288 °C, 10 s, 3 times) treatments and then subjected to a grounding test.

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

[0076] Example 9:

[0077] An electromagnetic shielding film, comprising an insulating layer 1, a metal layer 2 and an adhesive film layer 3 which are sequentially laminated. Conductive particles 31 are provided in the adhesive film layer 3, and the weight ratio of the conductive particles 31 is 45%. The vertical distance from the center of gravity of the conductive particles 31 to the surface of the metal layer 2 close to the adhesive film layer 3 is 1 μm. The thickness of the metal layer is 0.5 microns, the thickness of the electromagnetic shielding film is 10 microns, the surface of the conductive particles 31 contains mercapto groups, and the adhesive film layer 3 contains alkenyl groups; in the thickness direction of the electromagnetic shielding film, the centers of gravity of 90% of the conductive particles 31 are close to the metal layer 2, and one end of 90% of the conductive particles 31 away from the metal layer 2 has a spiky structure. The electromagnetic shielding film is subjected to pressing (185 °C, 10 min, 120 kg / cm2, the step height of the cover film is 38 um), curing (160 °C, 1.5 h), and thermal shock (288 °C, 10 s, 3 times) treatments and then subjected to a grounding test.

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

[0079] Comparative Example 1:

[0080] An electromagnetic shielding film, comprising an insulating layer 1, a metal layer 2 and an adhesive film layer 3 which are sequentially stacked. Conductive particles 31 are provided in the adhesive film layer 3; the weight ratio of the conductive particles 31 is 45%, the thickness of the metal layer is 0.5 microns, and the thickness of the electromagnetic shielding film is 10 microns. In the thickness direction of the electromagnetic shielding film, the conductive particles 31 are irregularly distributed in the adhesive film layer 3, and the conductive particles 31 have no obvious spike structure. The electromagnetic shielding film is subjected to pressing (185°C, 10 min, 120 kg / cm2, the step height of the cover film is 38 um), curing (160°C, 1.5 h), and thermal shock (288°C, 10 s, 3 times) treatments and then subjected to a ground test.

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

[0082] As shown in Table 1 below, the ground resistances of the electromagnetic shielding films of the above-mentioned Embodiment 1 - Embodiment 9 and Comparative Example 1 are presented.

[0083] Table 1. Ground Resistances of the Electromagnetic Shielding Films of Embodiment 1 - Embodiment 9 and Comparative Example 1

[0084]

[0085] It can be seen that by applying the electromagnetic shielding film of this embodiment, the ground performance of the electromagnetic shielding film can be improved.

[0086] In summary, by providing conductive particles 31 in the adhesive film layer 3; in the thickness direction of the electromagnetic shielding film, at least a part (50%, 70%, 90%) of the centers of gravity of the conductive particles 31 are located in the upper half of the conductive particles, and at least a part (50%, 70%, 90%) of the ends of the conductive particles 31 far from the metal layer 2 have spike structures, 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 ground performance of the electromagnetic shielding film.

[0087] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. An electromagnetic shielding film, characterized in that, It includes an insulating layer, a metal layer, and a film layer that are stacked in sequence, and conductive particles are provided in the film layer; In the thickness direction of the electromagnetic shielding film, the centers of gravity of at least a part of the conductive particles are close to the metal layer, and one end of at least a part of the conductive particles away from the metal layer has a spiky structure.

2. The electromagnetic shielding film according to claim 1, wherein The centers of gravity of at least 50 - 90% of the conductive particles are close to the metal layer.

3. The electromagnetic shielding film according to claim 2, wherein, The vertical distance from the center of gravity of the conductive particle to the surface of the metal layer close to the film layer is ≤ 1.5 μm.

4. The electromagnetic shielding film according to claim 1, characterized in that, One end of at least 50 - 90% of the conductive particles away from the metal layer has a spiky structure.

5. The electromagnetic shielding film according to claim 1, wherein The height of the conductive particle is 10 - 80% of the thickness of the film layer.

6. The electromagnetic shielding film according to any one of claims 1 to 5, characterized in that The weight ratio of the conductive particles in the film layer is 5% - 50%.

7. The electromagnetic shielding film according to claim 1, wherein The surface of the conductive particle contains a mercapto group.

8. The electromagnetic shielding film according to claim 7, wherein The film layer contains alkenyl and / or alkynyl groups.

9. The electromagnetic shielding film according to claim 1, wherein The thickness of the metal layer is 0.1 - 5 μm.

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