Electromagnetic shielding cover and circuit board

Abstract

The invention discloses an electromagnetic shielding case and a circuit board. The electromagnetic shielding case comprises a shielding case body and a metal shielding frame, the shielding case body comprises a shielding structure and a first connecting layer, the shielding structure is provided with a first surface and a second surface, the first surface is close to the first connecting layer relative to the second surface, and at any testing position, the film surface resistance R1 of the first surface and the film surface resistance R2 of the second surface meet the condition that (R2-R1) / (R1 + R2) is greater than or equal to 0.1, the shielding case body is electrically connected with the metal shielding frame. The film surface resistance of the first surface of the shielding structure in the shielding case body is smaller than that of the second surface, so that the roughness of the first surface is larger than that of the second surface, the transverse wave leakage phenomenon is effectively prevented, and the working reliability of the circuit board is improved.

Description

Technical Field

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

[0002] Electronic components susceptible to electromagnetic interference are mounted on the circuit boards of electronic devices used in consumer electronics, medical devices, and automobiles. To protect these components from electromagnetic interference, aluminum or stainless steel metal covers connected to the grounding wiring on the circuit board are typically used to cover them; one metal cover can usually cover multiple electronic components. These metal covers are manufactured using sheet metal processing, which has limitations in terms of thickness. Therefore, sheet metal-processed metal covers hinder further miniaturization or thinning of electronic devices.

[0003] Currently, flexible shielding covers are used to replace metal shielding covers, utilizing flexible materials to achieve a conformal shape with electronic components. Although this method can reduce space occupation, it cannot meet the heat dissipation requirements of electronic components. Furthermore, this type of shielding cover is only suitable for circuit boards with low electronic component height. If the electronic component is high or has sharp edges, the flexible shielding cover is easily punctured during the pressing process, causing the shielding cover to fail.

[0004] To ensure the heat dissipation of electronic components and the reliability of the shielding cover, electromagnetic shielding is currently achieved using a combination of a metal shielding frame and shielding copper foil. Holes of varying sizes are made in the metal shielding frame, and adhesive is injected to ensure heat dissipation. Then, the shielding copper foil is pressed and placed over the openings. This method avoids damage to traditional flexible shielding covers caused by the heat generated by electronic components, resulting in good shielding performance. However, the currently used shielding copper foil is a layered structure of copper foil and conductive adhesive. Electromagnetic wave leakage occurs at the contact points with the edges of the openings. Electromagnetic signals leak from within the conductive adhesive along the planar direction, creating electromagnetic interference and affecting the normal operation of nearby electronic components. Summary of the Invention

[0005] The purpose of this invention is to provide an electromagnetic shielding cover and circuit board. By setting the film resistance of the first surface of the shielding structure in the shielding cover body to be less than that of the second surface, the roughness of the first surface is greater than that of the second surface, thereby effectively preventing lateral leakage and improving the reliability of the circuit board.

[0006] To achieve the above objectives, embodiments of the present invention provide an electromagnetic shielding cover, including a shielding cover body and a metal shielding frame; the shielding cover body includes a shielding structure and a first connecting layer, the shielding structure is provided with a first surface and a second surface, the first surface is close to the first connecting layer relative to the second surface, and at any test position, the film resistance R1 of the first surface and the film resistance R2 of the second surface satisfy the following: (R2-R1) / (R1+R2)≥0.1, the shielding cover body is electrically connected to the metal shielding frame.

[0007] As an improvement to the above scheme, the film resistance R1 of the first surface and the film resistance R2 of the second surface satisfy the following condition: 0.25≤(R2-R1) / (R1+R2)≤4000.

[0008] As an improvement to the above solution, the shielding structure includes an inner core and a shielding wrapping layer, the shielding wrapping layer wrapping the outer part of the inner core, and both the first surface and the second surface are disposed on the shielding wrapping layer.

[0009] As an improvement to the above scheme, in the sliced ​​state, the shielding wrapping layer has an undulating structure, and the arithmetic mean thickness of the first surface is greater than the arithmetic mean thickness of the second surface.

[0010] As an improvement to the above solution, the inner core has at least two layers, and each inner core is wrapped with the shielding wrapping layer; the shielding structure also includes a second connecting layer, and adjacent inner cores are connected through the second connecting layer.

[0011] As an improvement to the above solution, a conductive element is provided in the first connecting layer, and adjacent shielding wrapping layers are electrically connected through the conductive element.

[0012] As an improvement to the above solution, the aspect ratio of the conductive element is 1 to 100.

[0013] As an improvement to the above solution, the inner core has a through-hole portion that runs from top to bottom, and the first connecting layer and the second connecting layer are connected through the through-hole portion.

[0014] As an improvement to the above solution, the shield body further includes an insulating layer disposed on the second surface.

[0015] This invention also provides a circuit board, the circuit board including an electromagnetic shield as described in any of the above claims, the electromagnetic shield being disposed on the surface of the circuit board.

[0016] Compared to existing technologies, the electromagnetic shielding cover and circuit board provided by this invention offer the following advantages: By setting the film resistance of the first surface of the shielding structure within the shielding cover body to be less than that of the second surface, the first surface exhibits greater unevenness, resulting in more conduction and connection points in the two-dimensional direction. This allows the shielding structure and the metal shielding frame to form a more dense ground connection, preventing electromagnetic waves from penetrating laterally between the connection layers, effectively preventing lateral wave leakage, and improving the reliability of the circuit board. Furthermore, the second surface of this invention has relatively less unevenness, eliminating the need for additional roughening and reducing production costs. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a preferred embodiment of the shielding cover body in an electromagnetic shielding cover provided by the present invention; Figure 2 This is a schematic diagram of the surface morphology of the shielding structure in an electromagnetic shielding cover provided by the present invention; Figure 3 This is a cross-sectional schematic diagram of the shielding structure in an electromagnetic shielding cover provided by the present invention; Figure 4 This is a schematic diagram of another preferred embodiment of the shielding cover body in an electromagnetic shielding cover provided by the present invention; Figure 5 This is a schematic diagram of another preferred embodiment of the shielding cover body in an electromagnetic shielding cover provided by the present invention.

[0018] The reference numerals in the attached figures are as follows: 1. Shielding structure; 110. First surface; 120. Second surface; 101. Inner core; 102. Shielding wrapping layer; 2. First connecting layer; 201. Conductive component; 3. Insulating layer; 4. Carrier film; 5. Protective film. Detailed Implementation

[0019] 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.

[0020] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0021] In the description of this application, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0022] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0023] Please see Figures 1 to 2 , Figure 1 This is a schematic diagram of a preferred embodiment of the shielding cover body in an electromagnetic shielding cover provided by the present invention. Figure 2 This is a schematic diagram of the surface morphology of the shielding structure in an electromagnetic shielding cover provided by the present invention. An embodiment of the present invention provides an electromagnetic shielding cover, including a shielding cover body and a metal shielding frame; the shielding cover body includes a shielding structure 1 and a first connecting layer 2. The shielding structure 1 is respectively provided with a first surface 110 and a second surface 120. The first surface 110 is closer to the first connecting layer 2 than the second surface 120, and at any test position, the film resistance R1 of the first surface 110 and the film resistance R2 of the second surface 120 satisfy the following condition: (R2-R1) / (R1+R2)≥0.1. The shielding cover body is electrically connected to the metal shielding frame.

[0024] Specifically, in this embodiment of the invention, the electromagnetic shielding cover includes a flexible shielding cover body and a rigid metal shielding frame, with the shielding cover body and the metal shielding frame electrically connected. The shielding cover body includes a shielding structure 1 and a first connecting layer 2. The shielding structure 1 has a first surface 110 and a second surface 120. The first surface 110 is closer to the first connecting layer 2 than the second surface 120, i.e., the first surface 110 is the lower layer and the second surface 120 is the upper layer. At any test position, the film resistance R1 of the first surface 110 and the film resistance R2 of the second surface 120 satisfy the following condition: (R2-R1) / (R1+R2)≥0.1, i.e., R2≥ R1 ≈ 1.222R1. At this point, R2 is at its minimum, approximately 1.222R1, therefore R2 > R1. This is because the conductive layer on the first surface has a large thickness and roughness, but the thickness has a greater impact on the film surface resistance. Film surface resistance, also known as sheet resistance, is a key parameter characterizing the conductivity of a material. Film surface resistance is typically measured using a DC microresistance meter. The measurement method is as follows: First, short-circuit the test clips and zero the instrument; then, clamp the test clips to both ends of the test module, place the test module with a 1kg weight on a soft substrate, and read the value after stabilization. The unit of film surface resistance is mΩ.

[0025] Furthermore, the film resistance R1 of the first surface 110 ranges from 10 to 28 mΩ. The film resistance R2 of the second surface 120 ranges from 18 to 45 mΩ.

[0026] For example, in this embodiment of the invention, the film resistance R1 of the first surface is set to 18mΩ and the film resistance R2 of the second surface is set to 22Ω, satisfying (22... 18) / (22+18)=0.1. If the film resistance R2 of the second surface is 30Ω, it satisfies (30) 18) / (30 + 18) = 0.25 > 0.1.

[0027] Furthermore, to achieve the constraint relationship between the film resistance of the first and second surfaces, the shielding structure in this embodiment of the invention uses conductive non-woven fabric. After applying adhesive to the lower layer of the conductive non-woven fabric (i.e., the first surface), some non-conductive particles remain. The presence of these non-conductive particles significantly increases the roughness of the first surface. Subsequently, a sputtered metal layer is applied to the roughened first surface. During this process, not only is the thickness of the lower metal layer increased, but the surface of the resulting metal layer also exhibits a rough morphology due to the influence of the rough underlying surface, thereby achieving the aforementioned film resistance requirement.

[0028] It should be noted that, in this embodiment of the invention, the shielding structure 1 can be a metal foil or a composite material of non-metal and metal. Examples include copper foil, iron foil, aluminum foil, gold foil, silver foil, tin foil, nickel foil, chromium foil, or an alloy foil formed from two or more elements. The first connecting layer 2 is any one of fluororubber, modified polyimide, or conductive adhesive containing conductive particles.

[0029] This invention, through an embodiment of the invention, sets the film resistance of the first surface of the shielding structure in the shielding cover body to be less than that of the second surface. This results in a relatively larger unevenness on the first surface, creating more conduction and connection points in the two-dimensional direction. Consequently, the shielding structure and the metal shielding frame form a denser grounding network, reducing gaps in the connection layers. Furthermore, the roughness of the first surface allows for the formation of a dense lateral shielding network, which absorbs, reflects, and attenuates laterally leaked electromagnetic waves, preventing lateral penetration between connection layers and effectively preventing lateral wave leakage, thus improving the reliability of the circuit board. Additionally, this invention, through an embodiment of the invention, sets the unevenness of the second surface to be relatively small, eliminating the need for additional roughening and reducing production costs.

[0030] In another preferred embodiment, the film resistance R1 of the first surface 110 and the film resistance R2 of the second surface 120 satisfy the following condition: 0.25 ≤ (R2-R1) / (R1+R2) ≤ 4000.

[0031] Specifically, the embodiments of the present invention further define the relationship between the film surface resistance of the first surface 110 and the film surface resistance of the second surface 120 of the shielding structure 1, that is, the film surface resistance R1 of the first surface 110 and the film surface resistance R2 of the second surface 120 satisfy: 0.25≤(R2-R1) / (R1+R2)≤4000. This ensures that the roughness of the first surface is within a range that can both guarantee sufficient contact and avoid local defects, thereby optimizing the shielding performance. At the same time, the upper and lower limits can balance production costs.

[0032] Optionally, the shielding structure can be a single-layer structure or a composite structure.

[0033] In another preferred embodiment, the shielding structure 1 includes an inner core 101 and a shielding wrapping layer 102, the shielding wrapping layer 102 wrapping the inner core 101, and the first surface 110 and the second surface 120 are both disposed on the shielding wrapping layer 102.

[0034] For details, please refer to Figure 3 , Figure 3This is a cross-sectional schematic diagram of the shielding structure in an electromagnetic shielding cover provided by the present invention. In this embodiment, the shielding structure 1 includes an inner core 101 and a shielding wrapping layer 102 covering the outer surface of the inner core 101. The first surface 110 and the second surface 120 of the shielding structure 1 are both formed on the shielding wrapping layer. The inner core is made of a non-conductive material, possessing higher bending performance and corrosion resistance, capable of withstanding external pressure, vibration, or environmental erosion, providing stable support for the shielding wrapping layer. The shielding wrapping layer, a coating layer formed of conductive material, prevents external interference from entering the internal circuitry by reflecting or absorbing electromagnetic waves, while also preventing internal signal leakage.

[0035] The inner core can be made of fiber cloth, woven fabric, or non-woven fabric. Specifically, the non-woven fabric formed by thermal bonding involves heating and melting the fiber material, forming weld points at the fiber intersections, and then solidifying and fusing them to form a planar material. In a sliced ​​state, it exhibits an uneven surface with the original fiber material. The shielding layer can be formed by using conductive materials through single or combined methods such as vacuum sputtering, spraying, chemical deposition, or electroplating. For example, the conductive materials may contain elements such as copper, silver, nickel, aluminum, zinc, chromium, or other elements.

[0036] In another preferred embodiment, in the microscopic state of the slice, the shielding wrapping layer 102 has an undulating structure, and the arithmetic mean thickness of the first surface 110 is greater than the arithmetic mean thickness of the second surface 120.

[0037] Specifically, in this embodiment of the invention, the thickness of the first surface 110 and the thickness of the second surface 120 of the shielding structure 1 are further defined, that is, the arithmetic mean thickness of the first surface 110 is greater than the arithmetic mean thickness of the second surface 120. This results in a larger thickness of the lower layer, which on the one hand ensures the shielding effect, on the other hand improves the grounding effect, and further prevents leakage. Here, the arithmetic mean thickness is a parameter describing the uniformity of thickness, referring to the arithmetic mean of the thickness of all measurement points on the first or second surface within a unit area, where thickness refers to the vertical distance between the highest and lowest points. Figure 3 As shown, the shielding structure 1 includes two inner cores 101, each of which is wrapped with a shielding wrapping layer 102. The thickness of the first surface 110 of the lower shielding wrapping layer 102 is greater than the thickness of the second surface 120 of the upper shielding wrapping layer 102. Furthermore, in this embodiment, the shielding wrapping layer has an undulating structure in a sliced ​​state, which enhances shielding effectiveness by increasing the reflection path and absorption area of ​​electromagnetic waves within the shielding wrapping layer, thereby improving the attenuation capability against electromagnetic interference (EMI). For example, in high-frequency electromagnetic fields, the undulating structure can form multiple reflections, effectively reducing the intensity of transmitted waves. In addition, the undulating structure can also disperse stress concentration, improving the shock and vibration resistance of the shielding wrapping layer.

[0038] In another preferred embodiment, the inner core 101 has at least two layers, and each inner core 101 is wrapped with a shielding wrapping layer 102; the shielding structure 1 also includes a second connecting layer, and adjacent inner cores 101 are connected through the second connecting layer.

[0039] Specifically, such as Figure 3 As shown, in this embodiment of the invention, the inner core 101 of the shielding structure 1 has at least two layers, wherein the outer surface of each inner core 101 is covered with a shielding wrapping layer 102. Furthermore, the shielding structure 1 also includes a second connecting layer, through which adjacent inner cores 101 are connected. For example, in this embodiment of the invention, the inner core is made of non-woven fabric, and the shielding structure includes two layers of non-woven fabric, each with an outer surface covered with a shielding wrapping layer. The two layers of non-woven fabric are connected by the second connecting layer, forming a four-layer shielding structure in a vertical state. This two-layer flexible conductive non-woven fabric structure has the advantages of being easily bent and having good shape recovery, and can improve shielding effectiveness.

[0040] Optionally, the material of the second connecting layer can be any one of fluororubber, modified polyimide, or conductive adhesive containing conductive particles.

[0041] In another preferred embodiment, a conductive element 201 is provided in the first connecting layer 2, and adjacent shielding wrapping layers 102 are electrically connected through the conductive element 201.

[0042] Specifically, in this embodiment of the invention, a conductive element 201, such as a conductive particle or other conductive structure, is provided in the first connecting layer 2, so that adjacent shielding layers 102 are electrically connected through the conductive element 201. When electromagnetic waves are incident, multiple reflections and scattering occur between the conductive particles, which can prolong the propagation path of electromagnetic waves in the shielding structure, increase absorption loss, and thus enhance electromagnetic shielding performance.

[0043] In yet another preferred embodiment, the aspect ratio of the conductive element 201 is 1 to 100.

[0044] Specifically, in this embodiment of the invention, the aspect ratio of the conductive element 201 within the first connecting layer is further defined, that is, the aspect ratio of the conductive element 201 is 1 to 100. The aspect ratio is a key parameter describing the anisotropy of the conductive particle shape, defined as the ratio of the longest axis length to the shortest axis length of the particle. The aspect ratio directly affects the arrangement, contact area, and conductivity of the conductive particles in the composite material.

[0045] Furthermore, in this embodiment of the invention, the conductive particles include sheet-like conductive particles and granular conductive particles, and a mixed structure of sheet-like conductive particles and / or granular conductive particles is provided in the first connecting layer 2. For example, the aspect ratio of the sheet-like conductive particles satisfies 3:1 to 5:1, the size of the sheet-like conductive particles is 2 to 12 μm, and the angle between the sheet-like conductive particles and the thickness direction is 0 to 90°. The size of the granular conductive particles is 2 to 8 μm. The maximum spacing between any two conductive particles satisfies d1 ≤ 10 μm; where d1 represents the maximum spacing between any two conductive particles. By limiting the maximum spacing between any two conductive particles, this embodiment of the invention can ensure that the conductive particles form a relatively continuous conductive network in the first connecting layer. If the spacing between conductive particles is too large, conductive dead zones may occur, i.e., some areas lack conductive particles, and electrons cannot conduct through these areas. Limiting the maximum spacing to within 10 μm can effectively avoid the occurrence of conductive dead zones, enabling the entire first connecting layer to conduct electricity uniformly, improving the uniformity and reliability of conductivity. Furthermore, the densely distributed conductive particles enhance the adhesion between the first connecting layer and the shielding structure. Simultaneously, when the first connecting layer is subjected to external forces, the densely distributed conductive particles can better disperse stress. Due to the small spacing between the conductive particles, stress can be transferred and dispersed among multiple conductive particles, preventing localized stress concentration that could lead to cracks or separation at the interface between the first connecting layer and the shielding structure, thus affecting shielding performance.

[0046] Furthermore, when the first connecting layer 2 is provided with a mixed structure of sheet-like conductive particles and granular conductive particles, the proportion of sheet-like conductive particles in the first connecting layer 2 is 30% to 50%, and the proportion of granular conductive particles is 50% to 70%. This embodiment of the invention limits the proportion of granular conductive particles in the first connecting layer to be greater than or equal to the proportion of sheet-like conductive particles. This is because sheet-like conductive particles have a larger aspect ratio, enabling them to provide a large-area contact network, thus requiring fewer sheet-like conductive particles. Granular conductive particles, on the other hand, are smaller in size, and a larger number of granular conductive particles can fill the tiny gaps between the sheet-like conductive particles, thereby making the conductive network more dense.

[0047] Optionally, the sheet-like or granular conductive particles can be either silver-plated copper particles or nickel-plated copper particles.

[0048] In another preferred embodiment, the inner core 101 has a through-hole portion that extends from top to bottom, and the first connecting layer 2 and the second connecting layer are connected through the through-hole portion.

[0049] Specifically, in this embodiment of the invention, the inner core 101 of the shielding structure 1 has a through-hole portion, and the first connecting layer 2 and the second connecting layer are connected through the through-hole portion. For example, in this embodiment of the invention, the inner core is made of non-woven fabric, which is formed by interlacing and pressing multiple irregular threads into a sheet-like structure, resulting in a through-hole portion in the non-woven fabric. When the shielding structure 1 has two inner cores 101, adjacent inner cores 101 are connected by the second connecting layer. At this time, during high-temperature pressing, the fluid first connecting layer 2 and the second connecting layer communicate with each other through the through-hole portion.

[0050] In yet another preferred embodiment, the shield body further includes an insulating layer 3 disposed on the second surface 120.

[0051] For details, please refer to Figure 4 , Figure 4 This is a schematic diagram of another preferred embodiment of the shielding cover body in an electromagnetic shielding cover provided by the present invention. In this embodiment of the present invention, the second surface 120 of the shielding structure 1 is further provided with an insulating layer 3. The insulating layer 3 provides insulation and protection for the shielding structure 1, prevents the shielding structure from conducting with other parts, and also prevents glue overflow caused by the perforation of the shielding structure during the processing of the first connecting layer, and ensures stable bonding force.

[0052] In yet another preferred embodiment, the shielding cover body further includes a carrier film 4 and / or a protective film 5.

[0053] The carrier membrane 4 is disposed on the side of the insulating layer 3 away from the shielding structure 1; The protective film 5 is disposed on the side of the connecting layer 2 away from the shielding structure 1.

[0054] For details, please refer to Figure 5 , Figure 5 This is a schematic diagram of another preferred embodiment of the shielding cover body in an electromagnetic shielding cover provided by the present invention. In this embodiment, the shielding cover body further includes a carrier film 4, or a protective film 5, or both a carrier film 4 and a protective film 5. The carrier film 4 is disposed on the side of the insulating layer 3 away from the shielding structure 1, and serves to support and protect it. During production, the carrier film is coated and cured to form an insulating layer. The carrier film 4 also provides high-temperature resistance and protects the insulating layer 3 during pressing.

[0055] The protective film 5 is disposed on the side of the first connecting layer 2 away from the shielding structure 1, and serves to protect the connecting layer. The protective film 5 is generally a release film.

[0056] For example, the method for manufacturing the shielding cover body in this embodiment of the invention is as follows: An insulating layer is coated on one side of the carrier membrane, and after slitting, baking, and inspection, it proceeds to the next stage. Adhesive is applied to the side of the insulating layer away from the carrier film, and conductive nonwoven fabric is pressed together to form a shielding structure. If the shielding structure includes multiple layers of conductive nonwoven fabric, repeat the above steps of applying adhesive and pressing: apply conductive adhesive again to the surface of the already pressed conductive nonwoven fabric layer, and then press the next layer of conductive nonwoven fabric; two or more layers of conductive nonwoven fabric can be pressed according to actual needs, and conductive adhesive is applied between adjacent conductive nonwoven fabric layers. An adhesive with insulating or conductive particles is coated on the surface of the bottom conductive nonwoven fabric. After evaporation, particles are left on the first surface. A metal cladding layer is formed by vacuum sputtering on the first surface, which increases the thickness of the shielding layer in the shielding structure. After sputtering and thickening, the metal layer is coated with adhesive, and the shield body is then subjected to post-treatments such as baking. After covering the sides of the post-processing shield body with a protective film, it is rolled up.

[0057] This invention also provides a circuit board, which includes an electromagnetic shielding cover as described in any of the above embodiments. The electromagnetic shielding cover is disposed on the surface of the circuit board and is used to cover all components on the circuit board.

[0058] To demonstrate the beneficial effects of the electromagnetic shielding cover and circuit board provided in the embodiments of the present invention, the following description is provided in conjunction with several embodiments and comparative examples.

[0059] Example 1 In this embodiment, the shielding cover body includes a shielding structure and a first connecting layer. The shielding structure is provided with a first surface and a second surface, with the first surface being closer to the first connecting layer than the second surface. The film surface resistance of the first surface is R1=15mΩ, and the film surface resistance of the second surface is R2=22mΩ.

[0060] Example 2 Unlike Example 1, the film resistance of the first surface is R1=26mΩ and the film resistance of the second surface is R2=38mΩ, so (38-26) / (38+26)=0.1875.

[0061] Example 3 The shielding cover body includes a shielding structure and a first connecting layer. The shielding structure is provided with a first surface and a second surface, with the first surface being closer to the first connecting layer than the second surface. The shielding structure includes an inner core and a shielding wrapping layer wrapped around the inner core. The shielding wrapping layer has an undulating structure, and the arithmetic mean thickness of the first surface is greater than the arithmetic mean thickness of the second surface.

[0062] Comparative Example 1 In this embodiment, the shielding cover body includes a shielding structure and a first connecting layer stacked together.

[0063] Comparative Example 2 Unlike Comparative Example 1, the film surface resistance R1 of the shielding structure near the first surface of the first connecting layer is 25mΩ, and the film surface resistance R2 of the shielding structure away from the first connecting layer is 18mΩ.

[0064] Comparative Example 3 Unlike Comparative Example 1, the arithmetic mean thickness of the first surface of the shielding structure near the first connecting layer is less than the arithmetic mean thickness of the second surface of the shielding structure away from the first connecting layer.

[0065] Electromagnetic shielding covers provided in Examples 1-3 and Comparative Examples 1-3 were used to cover components on the surface of a circuit board, and transmission loss was tested on the fabricated fine circuitry. A vector network analyzer (VNA) was used to measure the transmission loss. The specific test environment was a 3-5 GHz operating frequency. The test results are shown in Table 1. Table 1 Test Results

[0066] As shown in Table 1 above, the electromagnetic shielding cover prepared in the embodiments of the present invention can effectively prevent the transverse leakage of electromagnetic waves from affecting the shielding performance and improve the working reliability of the circuit board.

[0067] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 cover, characterized in that, The shield includes a shield body and a metal shield frame. The shield body includes a shielding structure and a first connecting layer. The shielding structure has a first surface and a second surface. The first surface is closer to the first connecting layer than the second surface. At any test position, the film resistance R1 of the first surface and the film resistance R2 of the second surface satisfy the following condition: (R2-R1) / (R1+R2)≥0.

1. The shield body is electrically connected to the metal shield frame.

2. The electromagnetic shielding cover as described in claim 1, characterized in that, The film resistance R1 of the first surface and the film resistance R2 of the second surface satisfy the following condition: 0.25≤(R2-R1) / (R1+R2)≤4000.

3. The electromagnetic shielding cover as described in claim 1, characterized in that, The shielding structure includes an inner core and a shielding wrapping layer, with the shielding wrapping layer covering the outer part of the inner core. The first surface and the second surface are both disposed on the shielding wrapping layer.

4. The electromagnetic shielding cover as described in claim 3, characterized in that, In the sliced ​​state, the shielding wrapping layer has an undulating structure, and the arithmetic mean thickness of the first surface is greater than the arithmetic mean thickness of the second surface.

5. The electromagnetic shielding cover as described in claim 3, characterized in that, The inner core has at least two layers, and each inner core is wrapped with the shielding wrapping layer; the shielding structure also includes a second connecting layer, and adjacent inner cores are connected through the second connecting layer.

6. The electromagnetic shielding cover as described in claim 5, characterized in that, The first connecting layer is provided with a conductive element, and the adjacent shielding wrapping layers are electrically connected through the conductive element.

7. The electromagnetic shielding cover as described in claim 6, characterized in that, The aspect ratio of the conductive component is 1 to 100.

8. The electromagnetic shielding cover as described in claim 7, characterized in that, The inner core has a through-hole section running from top to bottom, and the first connecting layer and the second connecting layer are connected through the through-hole section.

9. The electromagnetic shielding cover as described in any one of claims 1-7, characterized in that, The shield body also includes an insulating layer, which is disposed on the second surface.

10. A circuit board, characterized in that, The circuit board includes an electromagnetic shielding cover as described in any one of claims 1-9, the electromagnetic shielding cover being disposed on the surface of the circuit board.

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