Electromagnetic shield and circuit board

Abstract

The application discloses an electromagnetic shielding cover and a circuit board. The electromagnetic shielding cover comprises a first protective layer, a first adhesive layer, a composite shielding layer and a second adhesive layer which are sequentially stacked. The composite shielding layer is connected with the first protective layer through the first adhesive layer. The elastic modulus of the composite shielding layer at room temperature is less than or equal to 0.8 GPa. The shear strength of the second adhesive layer is greater than or equal to the elastic modulus of the composite shielding layer. By limiting the elastic modulus of the composite shielding layer within 0.8 GPa, the overall rebound stress of the composite shielding layer after bending can be reduced, and the continuous load borne by the second adhesive layer can be reduced. Since the shear strength can represent cohesion, by limiting the shear strength of the second adhesive layer to be greater than or equal to the elastic modulus of the composite shielding layer, the matching relationship between the cohesion of the second adhesive layer and the corresponding bending rebound stress can be limited, so that the cohesive failure of the second adhesive layer under the action of the rebound load can be reduced, and the risk of opening and expanding of the electromagnetic shielding cover can be reduced.

Description

Technical Field

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

[0002] As electronic devices become smaller and denser, electromagnetic interference problems of components on PCBs (Printed Circuit Boards) are becoming increasingly prominent. To address this, flexible electromagnetic shielding covers are widely used in various electronic devices to reduce the impact of electromagnetic interference on components because they can be bent and wrapped around the surface of raised components, occupy little space, and have strong adaptability.

[0003] In related technologies, in actual surface mount applications, it is usually necessary to bend the flexible electromagnetic shielding cover along the edge of the component to cover the component. However, after bending and covering and after being left to stand and / or in high and low temperature environments, problems such as the shielding cover coming off at the edge of the component and the shielding cover shifting outward at the bonding position with the board are likely to occur, thus affecting the quality of the circuit board. Summary of the Invention

[0004] To address the aforementioned technical problems, this application proposes an electromagnetic shielding cover and circuit board, which can reduce the risk of the electromagnetic shielding cover delaminating or expanding outwards, thereby improving the quality of the circuit board.

[0005] In a first aspect, embodiments of this application provide an electromagnetic shielding cover, which includes a first protective layer, a first adhesive layer, a composite shielding layer and a second adhesive layer stacked sequentially, wherein the composite shielding layer is connected to the first protective layer through the first adhesive layer. At room temperature, the elastic modulus of the composite shielding layer is less than or equal to 0.8 GPa, and the shear strength of the second adhesive layer is greater than or equal to the elastic modulus of the composite shielding layer.

[0006] Optionally, the thickness ratio of the composite shielding layer in the electromagnetic shielding cover is 0.3~0.8.

[0007] Optionally, at room temperature, the shear strength of the second adhesive layer is 0.3 GPa to 15 GPa.

[0008] Optionally, the composite shielding layer includes a support core and a conductive portion, with the conductive portion wrapping around the outer surface of the support core.

[0009] Optionally, the porosity of the support core is 20% to 60%.

[0010] Optionally, the number of composite shielding layers is at least two, and the electromagnetic shielding cover further includes a third adhesive layer, with adjacent composite shielding layers bonded together by the third adhesive layer.

[0011] Optionally, the thickness of the second adhesive layer in the electromagnetic shielding cover is 0.1 to 0.5%.

[0012] Optionally, conductive particles are disposed within the first adhesive layer and / or the second adhesive layer.

[0013] Optionally, the thickness of the first protective layer in the electromagnetic shielding cover accounts for 0.2 to 0.6% of the total thickness.

[0014] Optionally, at room temperature, the elastic modulus of the first protective layer is 0.3 GPa to 1.5 GPa.

[0015] Optionally, the initial tack of the second adhesive layer is 3 N / cm to 6 N / cm.

[0016] Optionally, the electromagnetic shielding cover further includes a second protective layer, which is disposed on the side of the second adhesive layer facing away from the composite shielding layer.

[0017] Optionally, the electromagnetic shielding cover further includes a release carrier layer, which is disposed on the side of the first protective layer facing away from the first adhesive layer.

[0018] Secondly, embodiments of this application provide a circuit board, the circuit board including a circuit board body and an electromagnetic shielding cover as described in any one of the first aspects above, the electromagnetic shielding cover being pressed onto the circuit board body.

[0019] In summary, the embodiments of this application have at least the following beneficial effects: The electromagnetic shielding cover of this application embodiment includes a first protective layer, a first adhesive layer, a composite shielding layer, and a second adhesive layer stacked sequentially. The composite shielding layer is connected to the first protective layer through the first adhesive layer. The elastic modulus of the composite shielding layer at room temperature is less than or equal to 0.8 GPa, and the shear strength of the second adhesive layer is greater than or equal to the elastic modulus of the composite shielding layer. Thus, by limiting the elastic modulus of the composite shielding layer to a low modulus range of less than 0.8 GPa, the overall rebound stress of the composite shielding layer after bending can be reduced, thereby reducing the continuous load on the second adhesive layer. In addition, since shear strength can characterize cohesion, by limiting the shear strength of the second adhesive layer to be no less than the elastic modulus of the composite shielding layer, the matching relationship between the cohesion of the second adhesive layer and the corresponding bending rebound stress can be limited. This can reduce the cohesive failure of the second adhesive layer under the action of rebound load, thereby reducing the risk of delamination and outward expansion of the electromagnetic shielding cover, and thus improving the quality of the circuit board. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the electromagnetic shielding cover provided in an embodiment of this application; Figure 2 This is a schematic diagram of an electron microscope image provided in an embodiment of this application; Figure 3 This is a schematic diagram of the electromagnetic shielding cover provided in an embodiment of this application; Figure 4 This is a schematic diagram of the electromagnetic shielding cover provided in an embodiment of this application; Figure 5 This is a schematic diagram of the electromagnetic shielding cover provided in an embodiment of this application; Figure 6 This is a schematic diagram of the electromagnetic shielding cover provided in an embodiment of this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments / examples are only a part of the embodiments / examples of this application, and not all of the embodiments / examples. Based on the embodiments / examples in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0022] 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, "multiple" means two or more. In the description of this application, the term "comprising" and its variations are open-ended, meaning "including but not limited to." The term "based on" means "at least partially based on." The term "according to" means "at least partially according to." The term "one embodiment / example" means "at least one embodiment / example"; the term "another embodiment / example" means "at least one additional embodiment / example"; the term "some embodiments / examples" means "at least some embodiments / examples."

[0023] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0024] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this application is for the purpose of describing specific embodiments only and is not intended to limit the application. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0025] The following explains some terms and concepts used in the embodiments of this application: The elastic modulus is a physical quantity that characterizes a material's resistance to deformation during the elastic deformation stage; it can be defined as the ratio of stress to strain. In the embodiments of this application, the elastic modulus can refer to the stiffness index of the corresponding layered structure when it undergoes bending deformation at room temperature. In the embodiments of this application, the elastic modulus can be Young's modulus, or other types of elastic modulus can also be used; this application is not limited to this specific type.

[0026] In this embodiment, shear strength can be lap shear strength. Since the adhesive layer is typically difficult to separate from the substrate in its finished state, and it is difficult to directly test the cohesive force of the pure adhesive, this application uses lap shear strength as a direct quantitative characterization index of the adhesive layer's cohesive force. For example, according to GB / T7124 standard, lap samples can be prepared by directly bonding the adhesive layer of the finished shielding cover to the FR-4 circuit board substrate, and the tensile shear strength of the prepared lap sample can be tested at room temperature (25℃). When the adhesive layer failure mode after tensile peeling is 100% cohesive failure, that is, when adhesive remains on both the FR-4 circuit board substrate and the shielding layer side, and the adhesive layer itself tears, the measured shear strength value can be used as a direct reflection of the adhesive layer's cohesive force, thus eliminating the need for separate adhesive layer sample preparation.

[0027] In related technologies, flexible electromagnetic shielding covers can adopt a three-layer stacked structure of an insulating layer, a metal shielding layer, and an adhesive layer. The shielding layer can be made of conductive non-woven fabric, metal foil, or other materials. The insulating layer can be made of conventional resin, PI (Polyimide Film), PET (Polyethylene Terephthalate Film), or other materials. The adhesive layer can be made of general-purpose pressure-sensitive adhesive.

[0028] However, on the one hand, the elastic modulus of the insulating layer and conductive nonwoven fabric shielding layer is often relatively high. For example, the elastic modulus of PI film is usually between 2.5 GPa and 3.5 GPa. This makes it easy for such insulating layers and conductive nonwoven fabric shielding layers to generate continuous and high elastic rebound force after bending. The rebound force load acts on the adhesive layer interface for a long time. On the other hand, the cohesive force of adhesive layers such as general pressure-sensitive adhesives is often relatively low, making it difficult to resist the continuous load of structural rebound for a long time. Eventually, the cohesive damage of the adhesive layer occurs, resulting in residual adhesive, stringing, delamination, etc., which can easily lead to the shielding cover falling off and failing to meet the reliability requirements.

[0029] In view of this, embodiments of this application propose an electromagnetic shielding cover and circuit board, which aims to at least partially solve the problems existing in the above-mentioned related technologies.

[0030] Firstly, embodiments of this application provide an electromagnetic shielding cover, see [link to relevant documentation]. Figure 1 The diagram shows a schematic of the structure of an electromagnetic shielding cover provided in an embodiment of this application. The electromagnetic shielding cover includes a first protective layer 1, a first adhesive layer 2, a composite shielding layer 3 and a second adhesive layer 4 stacked in sequence. The composite shielding layer 3 is connected to the first protective layer 1 through the first adhesive layer 2. At room temperature, the elastic modulus of the composite shielding layer 3 is less than or equal to 0.8 GPa, and the shear strength of the second adhesive layer 4 is greater than or equal to the elastic modulus of the composite shielding layer 3. For example, room temperature can be 25°C, and the second adhesive layer 4 can be a pressure-sensitive adhesive or a thermosetting adhesive layer.

[0031] In some examples, at room temperature, the elastic modulus of the composite shielding layer 3 can be 0.1 GPa to 0.8 GPa, for example, it can be 0.2 GPa to 0.5 GPa, or the elastic modulus of the composite shielding layer 3 can be other values ​​less than or equal to 0.8 GPa, such as any one or any two of the following values ​​forming a range: 0.1 GPa, 0.2 GPa, 0.25 GPa, 0.3 GPa, 0.35 GPa, 0.4 GPa, 0.45 GPa, 0.5 GPa, 0.6 GPa, 0.7 GPa, 0.8 GPa, etc.

[0032] In some examples, the composite shielding layer 3 may be made of at least one of the following metals: copper, silver, gold, zinc, and aluminum; for example, any one of copper, silver, gold, zinc, and aluminum; or an alloy of at least two of copper, silver, gold, zinc, and aluminum. Furthermore, the composite shielding layer 3 may also be made of non-metallic materials such as PET fibers.

[0033] In some examples, the composite shielding layer 3 may contain a fiber structure, which may employ a high-loft, low-area-density fiber structure to reduce the rigidity rebound of the composite shielding layer 3 due to bending. For example, see [link to relevant documentation]. Figure 2 In electron microscopy images, the fiber structure 31 can be represented as an irregular mesh-like plane formed by pressing together multiple fibers, with pores between adjacent fibers.

[0034] In some examples, the composite shielding layer 3 may contain a metal surface layer, which may be formed by sputtering a nanoscale metal layer, so that the composite shielding layer 3 is conductive as a whole and forms a shielding effect.

[0035] In some examples, the first protective layer 1 can be an insulating layer. For instance, an insulating layer prepared from at least modified flexible polyimide (F-PI) and / or high-toughness copolymer PET film can be used as the first protective layer 1, so that the first protective layer 1 can have both electronic-grade insulation properties and low resilience characteristics. Furthermore, the first protective layer 1 can also be an insulating layer formed using materials such as rubber, pigments, epoxy resin, and / or fillers. For example, when using a single material, epoxy resin can be cured to form an insulating layer, or rubber can be vulcanized to form an insulating layer; when using composite materials, epoxy resin and fillers can be combined to form a thermally conductive insulating layer, or epoxy resin, rubber toughening agent, and fillers can be combined to form a high-reliability encapsulation layer as an insulating layer.

[0036] In some examples, at least a portion of the surface of the composite shielding layer 3 facing the second adhesive layer 4 can be formed as a rough surface, which can be formed by plasma roughening treatment of the at least portion of the surface. In this embodiment, by defining this rough surface, the interfacial bonding force between the composite shielding layer 3 and the second adhesive layer 4 can be improved, thereby ensuring to a certain extent that the failure mode is preferentially cohesive failure of the second adhesive layer 4, rather than debonding at the contact interface between the composite shielding layer 3 and the second adhesive layer 4.

[0037] For example, the roughness Rz of the rough surface of the composite shielding layer 3 facing the second adhesive layer 4 can be 0.4μm-16μm, for example, the range formed by any one or any two of the following values: 0.4μm, 0.45μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, etc.

[0038] For example, the roughness Sdr of the rough surface of the composite shielding layer 3 facing the second adhesive layer 4 can be 0.5%-600%, for example, the range formed by any one or any two of the following values: 0.5%, 1%, 10%, 20%, 50%, 80%, 100%, 150%, 200%, 300%, 400%, 500%, 550%, 570%, 580%, 590%, 600%.

[0039] In this embodiment of the application, by placing the first adhesive layer 2 between the first protective layer 1 and the composite shielding layer 3, the risk of delamination between the first protective layer 1 and the composite shielding layer 3 can be effectively reduced. In some examples, the first adhesive layer 2 can be a polyurethane primer layer; the thickness of the first adhesive layer 2 can be 1μm to 3μm, for example, the range formed by any one or any two of the following values: 1μm, 1.2μm, 1.4μm, 1.5μm, 1.6μm, 1.8μm, 2μm, 2.2μm, 2.4μm, 2.5μm, 2.6μm, 2.8μm, 3μm, etc.; the interlayer 180° peel strength of the first adhesive layer 2 can be ≥0.8N / 25mm, for example, the range formed by any one or any two of the following values: 0.85N / 25mm, 0.9N / 25mm, 0.95N / 25mm, 1N / 25mm, 1.1N / 25mm, 1.2N / 25mm, 1.3N / 25mm, 1.4N / 25mm, 1.5N / 25mm, etc.

[0040] In some examples, the total thickness of the electromagnetic shielding cover can be 50μm to 150μm, for example, 70μm to 100μm, or the total thickness of the electromagnetic shielding cover can be any one or any two of the following values: 50μm, 60μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, etc., so that the electromagnetic shielding cover can be adapted to the mounting space of high-density components. However, it is understood that in other examples, the total thickness of the electromagnetic shielding cover is not limited to 50μm to 150μm. For example, other embodiments of this application limit the thickness ratio of the composite shielding layer 3 in the electromagnetic shielding cover and provide examples of the thickness of the composite shielding layer 3. In this case, the total thickness of the electromagnetic shielding cover can be a value adapted to the other embodiments.

[0041] In one optional embodiment, the thickness ratio of the composite shielding layer 3 in the electromagnetic shielding cover is 0.3~0.8.

[0042] In this embodiment, the thickness ratio of the composite shielding layer 3 in the electromagnetic shielding cover is limited to 0.3~0.8. This allows the low modulus characteristics of the composite shielding layer 3 to be fully converted into low rebound stress while ensuring electromagnetic shielding effectiveness. This avoids the cohesive force exceeding the bonding strength due to excessive thickness of the composite shielding layer 3, or the shielding function failing due to excessive thinness. This facilitates matching the shear resistance of the second bonding layer 4, thereby improving the overall bending resistance reliability of the electromagnetic shielding cover. It is easy to understand that when the thickness ratio is less than 0.3, the relative thickness of the composite shielding layer 3 is too thin, making it difficult to form a continuous conductive and magnetic path, resulting in a decrease in shielding effectiveness, especially in low-frequency bands or high-interference environments where it is difficult to meet protection requirements. When the thickness ratio is greater than 0.8, although the composite shielding layer 3 itself has low stiffness, the corresponding total deformation energy is too large. Under thermal stress or mechanical bending, the interfacial shear force generated is likely to exceed the bearing limit of the bonding layer, thereby causing delamination or debonding.

[0043] It is understood that the thickness ratio of the composite shielding layer 3 in the electromagnetic shielding cover can be obtained by calculating the thickness ratio between the thickness of the composite shielding layer 3 and the total thickness of the electromagnetic shielding cover. For example, the thickness ratio of the composite shielding layer 3 in the electromagnetic shielding cover can be a value between 0.3 and 0.8, such as any one or any two of the following values: 0.3, 0.4, 0.5, 0.6, 0.7, 0.8.

[0044] In some examples, the thickness of the composite shielding layer 3 can be 20μm to 80μm, for example, it can be 30μm to 50μm, or the thickness of the composite shielding layer 3 can be any one of the following values ​​or any two of the following ranges: 20μm, 30μm, 35μm, 40μm, 45μm, 50μm, 60μm, 70μm, 80μm.

[0045] In one optional embodiment, the shear strength of the second adhesive layer 4 is 0.3 GPa to 15 GPa at room temperature.

[0046] In this embodiment, the room temperature shear strength of the second adhesive layer 4 is limited to 0.3GPa~15GPa. This can reduce the risk of debonding due to excessively low strength or brittle fracture due to modulus mismatch, provided that its cohesive force is sufficient to match the rebound stress of the low modulus shielding layer.

[0047] In some examples, at room temperature, the shear strength of the second adhesive layer 4 can be between 0.3 GPa and 15 GPa, for example, any one or any two of the following values ​​forming a range: 0.3 GPa, 0.4 GPa, 0.5 GPa, 0.55 GPa, 0.6 GPa, 0.65 GPa, 0.7 GPa, 0.8 GPa, 0.9 GPa, 1 GPa, 2 GPa, 3 GPa, 4 GPa, 5 GPa, 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10 GPa, 11 GPa, 12 GPa, 13 GPa, 14 GPa, 15 GPa.

[0048] In some examples, the elastic modulus of the second adhesive layer 4 at room temperature can be 0.02 GPa to 0.6 GPa, for example, 0.05 to 0.3 GPa. Alternatively, the elastic modulus of the second adhesive layer 4 can be any one or any two of the following values: 0.02 GPa, 0.05 GPa, 0.06 GPa, 0.08 GPa, 0.1 GPa, 0.15 GPa, 0.2 GPa, 0.25 GPa, 0.3 GPa, 0.4 GPa, 0.5 GPa, and 0.6 GPa. In this embodiment, by limiting the elastic modulus of the second adhesive layer 4 at room temperature to within the range of 0.02 GPa to 0.6 GPa, it can be ensured to a certain extent that the second adhesive layer 4 can deform with the bending of the structure, thereby reducing the damage to the second adhesive layer 4 caused by stress concentration.

[0049] In some examples, the material of the second adhesive layer 4 may include at least one of the following: modified acrylic pressure-sensitive adhesive and fumed silica. For example, the second adhesive layer 4 may be obtained by adding fumed silica to a modified acrylic pressure-sensitive adhesive. In this way, fumed silica can be used as a crosslinking reinforcing filler, thereby enabling the second adhesive layer 4 to improve cohesive strength while maintaining a low modulus. Exemplarily, the mass percentage of fumed silica in the second adhesive layer 4 may be 0.5wt% to 2wt%, for example, it may be any one or any two of the following values: 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%.

[0050] In other examples, the modified acrylic pressure-sensitive adhesive in the material of the second adhesive layer 4 can be replaced with other adhesive systems, which may include silicone pressure-sensitive adhesives and / or polyurethane adhesives, etc. It is understood that when other adhesive systems are used, shear strength can still be used as the corresponding cohesive strength metric.

[0051] In one optional embodiment, the composite shielding layer 3 includes a support core and a conductive portion, wherein the conductive portion is wrapped around the outer surface of the support core.

[0052] In some examples, the composite shielding layer 3 can be a conductive nonwoven fabric, wherein the supporting core can be as described above. Figure 2 The fiber structure shown can be, for example, made of PET fiber nonwoven fabric as the support core; the conductive part can be a conductive layer made of a metal material, such as the aforementioned metal surface layer. Exemplarily, the metal material can include at least one of copper, silver, gold, zinc, and aluminum, and the PET fiber nonwoven fabric can specifically be PET microfiber nonwoven fabric. Specifically, the metal material can be vacuum sputtered onto the surface of the PET fiber nonwoven fabric to form a conductive part on the surface of the PET fiber nonwoven fabric, thereby obtaining a conductive nonwoven fabric, so that the composite shielding layer 3 can achieve both conductivity and flexibility.

[0053] For example, the conductive nonwoven fabric described above can be a copper-nickel plated nonwoven fabric.

[0054] In other examples, the composite shielding layer 3 can also be made of other low-modulus conductive shielding materials such as low-modulus conductive cloth or ultra-thin metal mesh.

[0055] In some examples, the thickness of the conductive portion in the composite shielding layer 3 can be 20nm to 200nm, for example, it can be any one or any two of the following values: 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, etc.

[0056] In some examples, the average shielding effectiveness of the composite shielding layer 3 in the 1GHz~10GHz frequency band can be ≥60dB. For example, the average shielding effectiveness can be any one of the following values ​​or any two of the following ranges: 60dB, 65dB, 70dB, 75dB, 80dB, 85dB, 90dB, 95dB, 100dB, etc.

[0057] In one alternative embodiment, the porosity of the support core is 20% to 60%.

[0058] In this embodiment, limiting the porosity of the support core to 20%~60% effectively reduces the elastic modulus of the composite shielding layer 3 while ensuring sufficient structural strength and conductive continuity. This allows the elastic modulus of the composite shielding layer 3 to match the shear strength of the second adhesive layer 4, reducing the risk of delamination and outward expansion during bending. It is easy to understand that since the electromagnetic shielding path is formed by wrapping the conductive parts around the outer surface of the support core, a porosity of less than 20% usually means the surface is too dense and smooth. This can lead to insufficient adhesion of the conductive paste or plating on the conductive parts, resulting in easy peeling and breakage during bending. On the other hand, when the porosity of the support core is higher than 60%, although the overall modulus of the composite shielding layer decreases, the adhesive in the adhesive layer can easily penetrate excessively into the pores, reducing the effective bonding area and decreasing the cohesive force of the adhesive layer.

[0059] It should be noted that the support core can form a mesh-like plane in the electron microscope image. This mesh can be composed of multiple linear structures, and there can be pores between different linear structures. Thus, the porosity of the support core can refer to the area ratio of pores within the support core per unit area. For example, the support core can adopt the aforementioned fiber structure; thus, the multiple linear structures can refer to the aforementioned multiple fibers, and the mesh-like plane can refer to the aforementioned irregular mesh-like plane formed by pressing together multiple fibers. Furthermore, it can be understood that the pore area and / or porosity of the support core in the electron microscope image can be automatically obtained by image recognition software from the electron microscope image.

[0060] In some examples, the porosity of the support core can be 20% to 60%, for example, it can be any one of the following values ​​or any two of the following ranges: 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%.

[0061] In one alternative implementation, see [link to relevant documentation]. Figure 3 The number of composite shielding layers 3 is at least two, and the electromagnetic shielding cover also includes a third adhesive layer 5, with adjacent composite shielding layers 3 bonded together by the third adhesive layer 5.

[0062] In this embodiment, the third adhesive layer 5 can serve as an interlayer buffer medium between the composite shielding layers 3, allowing the two adjacent composite shielding layers 3 to undergo slight relative slippage and / or independent deformation when bent, so as to avoid the multilayer material as a whole from rigid bending, thereby effectively releasing the rebound energy accumulated by rigid bending, so that the continuous load on the second adhesive layer 4 in this embodiment can be less than the continuous load on the thicker single-layer composite shielding layer 3.

[0063] It is understood that the composite shielding layer 3 and the third adhesive layer 5 in this embodiment can be stacked alternately. For example, one layer of composite shielding layer 3, one layer of third adhesive layer 5, and another layer of composite shielding layer 3 can be stacked sequentially. Similarly, it can be deduced that there are three or more layers of composite shielding layer 3. In this case, the two outermost layers of composite shielding layer 3 can be stacked with the first adhesive layer 2 and the second adhesive layer 4 respectively.

[0064] In one optional embodiment, the thickness of the second adhesive layer 4 in the electromagnetic shield is 0.1 to 0.5%.

[0065] In this embodiment, the thickness ratio of the second adhesive layer 4 in the electromagnetic shield is limited to 0.1~0.5. The lower limit of the thickness ratio can provide a minimum stress dispersion layer to ensure that the second adhesive layer 4 has basic continuity and volume. It can evenly disperse the concentrated rebound stress generated by the bending of the composite shield 3 to the entire bonding surface of the second adhesive layer 4, reducing the risk of point-like debonding caused by the local stress peak exceeding the material cohesive limit. The upper limit of the thickness ratio can also prevent the second adhesive layer 4 from being too thick, thereby reducing the overall thickness of the shield and reducing the neutral axis offset and interlayer strain difference caused by the bending of the shield.

[0066] It is understood that the thickness ratio of the second adhesive layer 4 in the electromagnetic shielding cover can be obtained by calculating the thickness ratio between the thickness of the second adhesive layer 4 and the total thickness of the electromagnetic shielding cover. For example, the thickness ratio of the second adhesive layer 4 in the electromagnetic shielding cover can be a value between 0.1 and 0.5, such as any one of the following values ​​or any two of the following ranges: 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5.

[0067] In some examples, the thickness of the second adhesive layer 4 can be 10μm to 50μm, for example, 15μm to 30μm, or the thickness of the second adhesive layer 4 can be any one or any two of the following values: 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm. Thus, in this embodiment, by limiting the thickness of the second adhesive layer 4 to within 10μm to 50μm, the thickness of the second adhesive layer 4 can be made moderate so that the second adhesive layer 4 can balance adhesion and wettability with cohesive stability.

[0068] In one alternative implementation, see [link to relevant documentation]. Figure 4 Conductive particles 6 are provided in the first adhesive layer 2 and / or the second adhesive layer 4.

[0069] In some examples, the proportion of conductive particles 6 in the second adhesive layer 4 can be 0.1wt% to 0.5wt%, for example, it can be any one or any two of the following values: 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%. In this embodiment, grounding can be achieved by setting conductive particles 6 in the second adhesive layer 4, thereby improving the shielding effect of the electromagnetic shielding cover.

[0070] In some examples, the conductive particles 6 may include spherical conductive particles 6, i.e. conductive microspheres, or conductive particles of other shapes, such as spiked conductive particles, etc. The embodiments of this application are not limited to this.

[0071] In some examples, the material of the conductive particle 6 can be selected from at least one of copper, aluminum, zinc, nickel, silver, iron, cobalt, and titanium.

[0072] In one optional embodiment, the thickness of the first protective layer 1 in the electromagnetic shielding cover is 0.2 to 0.6%.

[0073] In this embodiment, the thickness ratio of the first protective layer 1 is limited to 0.2~0.6. This ensures that it provides sufficient structural support and surface protection for the low-modulus composite shielding layer 3, while avoiding instability due to excessive thinness or increased overall bending stiffness of the shielding due to excessive thickness.

[0074] In some examples, the thickness of the first protective layer 1 can be between 10 μm and 50 μm, such as 12 μm to 25 μm, to balance insulation withstand voltage and flexibility. For example, the thickness of the first protective layer 1 can be any one of the following values ​​or a range formed by any two of them: 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm.

[0075] In some examples, the insulation breakdown strength of the first protective layer 1 can be ≥5kV / mm, and the temperature resistance rating can be ≥120℃ to meet the reliability requirements of electronic packaging. For example, the insulation breakdown strength of the first protective layer 1 can take any one or any two of the following values ​​within a range: 5kV / mm, 6kV / mm, 7kV / mm, 8kV / mm, 9kV / mm, 10kV / mm, 15kV / mm, 20kV / mm, 25kV / mm, 30kV / mm, 35kV / mm, 40kV / mm, and the temperature resistance rating of the first protective layer 1 can take any one or any two of the following values ​​within a range: 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃.

[0076] In one optional embodiment, the elastic modulus of the first protective layer 1 is 0.3 GPa to 1.5 GPa at room temperature.

[0077] In this embodiment, the elastic modulus of the first protective layer 1 is limited to 0.3GPa~1.5GPa. This ensures that it provides sufficient structural support and surface protection for the low-modulus composite shielding layer 3, while avoiding the overall rebound stress of the shielding cover being increased due to excessive elastic modulus, or the first protective layer 1 losing its restraining ability due to excessively low elastic modulus.

[0078] In some examples, the elastic modulus of the first protective layer 1 at room temperature can be between 0.3 GPa and 1.5 GPa, for example, between 0.5 GPa and 1.0 GPa, to reduce bending rebound force. For instance, at room temperature, the elastic modulus of the first protective layer 1 can be a value between 0.3 GPa and 1.5 GPa, such as any one or any two of the following values ​​forming a range: 0.3 GPa, 0.4 GPa, 0.5 GPa, 0.6 GPa, 0.7 GPa, 0.8 GPa, 0.9 GPa, 1 GPa, 1.1 GPa, 1.2 GPa, 1.3 GPa, 1.4 GPa, 1.5 GPa, etc.

[0079] In one alternative embodiment, the initial tack of the second adhesive layer 4 is 3 N / cm to 6 N / cm.

[0080] In this embodiment, the initial tack of the second adhesive layer 4 is limited to 3N / cm to 6N / cm, which can ensure that it can reliably position the low modulus composite shielding layer 3, prevent slippage and expansion in the early stage of bonding, and avoid local stress damage or loss of repositioning ability caused by excessive adhesion.

[0081] In some examples, the initial tack of the second adhesive layer 4 can be 3 N / cm to 6 N / cm, for example, it can be any one of the following values ​​or any two of the following ranges: 3 N / cm, 3.5 N / cm, 4 N / cm, 4.5 N / cm, 5 N / cm, 5.5 N / cm, 6 N / cm, etc.

[0082] In one alternative implementation, see [link to relevant documentation]. Figure 5 The electromagnetic shielding cover further includes a second protective layer 7, which is disposed on the side of the second adhesive layer 4 facing away from the composite shielding layer 3.

[0083] In this embodiment, by providing the second protective layer 7, the side of the second adhesive layer 4 facing away from the composite shielding layer 3 can be effectively protected. Furthermore, during the winding of the electromagnetic shielding cover, without the second protective layer 7, the second adhesive layer 4 and the first protective layer would adhere together. Since the composite shielding layer has a low elastic modulus, a soft overall structure, and is sensitive to pressure, the adhesive in the second adhesive layer 4 is prone to cold flow and penetration to the surface of the directly contacting first protective layer, causing irreversible adhesion. The second protective layer 7 in this embodiment prevents the side of the second adhesive layer 4 facing away from the composite shielding layer 3 from adhering to the first protective layer during the winding of the electromagnetic shielding cover, thereby improving the smoothness of unwinding and reducing residual adhesive left during unwinding.

[0084] In some examples, the material of the second protective layer 7 may include at least one of the following: protective film, PET, polyethylene, polypropylene, polyimide, etc.

[0085] In one alternative implementation, see [link to relevant documentation]. Figure 6 The electromagnetic shielding cover further includes a release carrier layer 8, which is disposed on the side of the first protective layer 1 facing away from the first adhesive layer 2.

[0086] Understandably, due to the low elastic modulus of the composite shielding layer, its overall structure is relatively soft and its resistance to indentation is weak. During the winding process of the electromagnetic shielding cover, interlayer pressure can easily cause microscopic relative sliding between the surface of the first protective layer and adjacent layers, resulting in scratches. In this embodiment, by setting a release carrier layer as a sacrificial medium with high hardness and low coefficient of friction, the sliding friction can be transferred to the surface of the release carrier layer, preventing the first protective layer from being scratched during winding, transportation, and use. The release carrier layer can then be torn off when in use.

[0087] In some examples, the material of the release carrier layer 8 may include at least one of the following: PET, polyolefin film, fluoroplastic film, etc.

[0088] Secondly, embodiments of this application provide a circuit board, the circuit board including a circuit board body and an electromagnetic shielding cover as described in any one of the first aspects above, the electromagnetic shielding cover being pressed onto the circuit board body.

[0089] In some examples, the electromagnetic shield can be integrally formed by thermo-pressing and can be bent and attached to the raised components on the surface of the circuit board to reduce the impact of electromagnetic interference on the components.

[0090] In some examples, the layered structure in the electromagnetic shielding cover, from the side furthest from the circuit board body to the side where it is mounted or close to the circuit board body, can be as follows: first protective layer 1, first adhesive layer 2, composite shielding layer 3 and second adhesive layer 4.

[0091] In some examples, the circuit board can be a PCB, an FPC (Flexible Printed Circuit), or a rigid-flex board, etc.

[0092] To better illustrate the technical effects, specific embodiments and comparative examples are used below to explain the technical effects of this application.

[0093] Example 1 An electromagnetic shielding cover includes a first protective layer, a first adhesive layer, a composite shielding layer and a second adhesive layer stacked sequentially, wherein the composite shielding layer is connected to the first protective layer through the first adhesive layer. At room temperature, the elastic modulus of the first protective layer is 0.8 GPa, the elastic modulus of the composite shielding layer is 0.4 GPa, the shear strength of the second adhesive layer is 0.55 GPa, and the elastic modulus of the second adhesive layer is 0.2 GPa.

[0094] Comparative Example 1 An electromagnetic shielding cover includes a first protective layer, a first adhesive layer, a composite shielding layer and a second adhesive layer stacked sequentially, wherein the composite shielding layer is connected to the first protective layer through the first adhesive layer. At room temperature, the elastic modulus of the first protective layer is 3.0 GPa, the elastic modulus of the composite shielding layer is 1.8 GPa, the shear strength of the second adhesive layer is 0.2 GPa, and the elastic modulus of the second adhesive layer is 0.8 GPa.

[0095] Comparative Example 2 An electromagnetic shielding cover includes a first protective layer, a first adhesive layer, a composite shielding layer and a second adhesive layer stacked sequentially, wherein the composite shielding layer is connected to the first protective layer through the first adhesive layer. At room temperature, the elastic modulus of the first protective layer is 0.8 GPa, the elastic modulus of the composite shielding layer is 1.8 GPa, the shear strength of the second adhesive layer is 0.2 GPa, and the elastic modulus of the second adhesive layer is 0.8 GPa.

[0096] Comparative Example 3 An electromagnetic shielding cover includes a first protective layer, a first adhesive layer, a composite shielding layer and a second adhesive layer stacked sequentially, wherein the composite shielding layer is connected to the first protective layer through the first adhesive layer. At room temperature, the elastic modulus of the first protective layer is 0.8 GPa, the elastic modulus of the composite shielding layer is 0.4 GPa, the shear strength of the second adhesive layer is 0.2 GPa, and the elastic modulus of the second adhesive layer is 0.8 GPa.

[0097] Tests were conducted on the above embodiments and comparative examples, and the test items are as follows: 1. Bending and outward expansion test: The shielding cover is attached to the analog chip component with a protrusion height of 10mm on the surface of FR-4, and the four sides are bent at 90° to cover it. After standing at room temperature for 72 hours, the maximum outward displacement of the edge of the shielding cover is measured and recorded as the outward expansion amount.

[0098] 2. Failure Mode Determination Test: After the expansion test, the shield is peeled off from FR-4, and the proportion of the residual adhesive area on the FR-4 surface to the surface area of ​​the second adhesive layer is observed to calculate the cohesive failure ratio.

[0099] 3. Environmental reliability test: The shielding cover is attached to the analog chip component with a protrusion height of 10mm on the surface of FR-4. After bending and covering it at 90° on all four sides, it is subjected to 100 cycles of high and low temperature from -40℃ to 85℃. The results are observed for whether the adhesive comes off or shifts.

[0100] 4. Shielding effectiveness test: The shielding cover is attached to the analog chip component with a protrusion height of 10mm on the surface of FR-4. After bending and covering it at 90° on all four sides, the average shielding effectiveness from 1 to 10GHz is obtained by testing using the flange coaxial method.

[0101] Data was collected from the above tests, and the results are shown in Table 1 below.

[0102] Table 1

[0103] As can be seen from the data in Table 1 above, the outward expansion of Example 1 is only about 1 / 10 of that of Comparative Example 1, and there is no adhesive failure. In contrast, Comparative Examples 1-3 did not show pure cohesive failure, indicating that the cohesive force is low. In addition, the shielding effectiveness of Example 1 is basically consistent with that of Comparative Examples 1-3, effectively solving the problems of adhesive failure and outward expansion after bending and mounting the shielding cover. In summary, the embodiments of this application have at least the following beneficial effects: The electromagnetic shielding cover of this application embodiment includes a first protective layer, a first adhesive layer, a composite shielding layer, and a second adhesive layer stacked sequentially. The composite shielding layer is connected to the first protective layer through the first adhesive layer. The elastic modulus of the composite shielding layer at room temperature is less than or equal to 0.8 GPa, and the shear strength of the second adhesive layer is greater than or equal to the elastic modulus of the composite shielding layer. Thus, by limiting the elastic modulus of the composite shielding layer to a low modulus range of less than 0.8 GPa, the overall rebound stress of the composite shielding layer after bending can be reduced, thereby reducing the continuous load on the second adhesive layer. In addition, since shear strength can characterize cohesion, by limiting the shear strength of the second adhesive layer to be no less than the elastic modulus of the composite shielding layer, the matching relationship between the cohesion of the second adhesive layer and the corresponding bending rebound stress can be limited. This can reduce the cohesive failure of the second adhesive layer under the action of rebound load, thereby reducing the risk of delamination and outward expansion of the electromagnetic shielding cover, and thus improving the quality of the circuit board.

[0104] The above description represents optional embodiments of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. An electromagnetic shielding cover, characterized in that, The electromagnetic shielding cover includes a first protective layer, a first adhesive layer, a composite shielding layer and a second adhesive layer stacked in sequence, wherein the composite shielding layer is connected to the first protective layer through the first adhesive layer. At room temperature, the elastic modulus of the composite shielding layer is less than or equal to 0.8 GPa, and the shear strength of the second adhesive layer is greater than or equal to the elastic modulus of the composite shielding layer.

2. The electromagnetic shielding cover according to claim 1, characterized in that, The composite shielding layer accounts for 0.3~0.8% of the thickness of the electromagnetic shielding cover; and / or, At room temperature, the shear strength of the second adhesive layer is 0.3 GPa to 15 GPa.

3. The electromagnetic shielding cover according to claim 1, characterized in that, The composite shielding layer includes a support core and a conductive part, with the conductive part wrapped around the outer surface of the support core.

4. The electromagnetic shielding cover according to claim 3, characterized in that, The porosity of the support core is 20%~60%.

5. The electromagnetic shielding cover according to claim 1, characterized in that, The number of composite shielding layers is at least two, and the electromagnetic shielding cover also includes a third adhesive layer, with adjacent composite shielding layers bonded together by the third adhesive layer.

6. The electromagnetic shielding cover according to claim 1, characterized in that, The thickness of the second adhesive layer in the electromagnetic shielding cover is 0.1~0.5%; and / or, Conductive particles are disposed within the first adhesive layer and / or the second adhesive layer.

7. The electromagnetic shielding cover according to claim 1, characterized in that, The thickness of the first protective layer in the electromagnetic shielding cover accounts for 0.2~0.6% of the total thickness; and / or, At room temperature, the elastic modulus of the first protective layer is 0.3 GPa to 1.5 GPa.

8. The electromagnetic shielding cover according to claim 1, characterized in that, The initial tack of the second adhesive layer is 3 N / cm to 6 N / cm.

9. The electromagnetic shielding cover according to claim 1, characterized in that, The electromagnetic shielding cover further includes a second protective layer, which is disposed on the side of the second adhesive layer facing away from the composite shielding layer; and / or, The electromagnetic shielding cover also includes a release carrier layer, which is disposed on the side of the first protective layer facing away from the first adhesive layer.

10. A circuit board, characterized in that, The circuit board includes a circuit board body and an electromagnetic shielding cover as described in any one of claims 1-9, wherein the electromagnetic shielding cover is pressed onto the circuit board body.

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