Electromagnetic shielding film and circuit board

Abstract

The invention discloses an electromagnetic shielding film and a circuit board, the electromagnetic shielding film comprises a shielding layer, a first surface of the shielding layer is provided with a projection structure, and after the electromagnetic shielding film is laminated with a circuit board substrate provided with an OSP grounding structure through the projection structure, under a preset grounding window size, the grounding resistance of the electromagnetic shielding film is less than 800m omega. The electromagnetic shielding film can be ensured to maintain proper grounding resistance on the OSP grounding structures of different circuit board substrates, so that the grounding effect of the electromagnetic shielding film on the OSP grounding structures of the circuit board substrates is relatively good, and the electromagnetic shielding requirement of the circuit board can be met.

Description

Technical Field

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

[0002] Driven by four major trends in the electronics industry—lead-free production, high reliability, low cost, and high-density interconnects—OSP (Organic Solderability Preservatives) technology has gradually gained popularity as an important supplement and alternative to traditional nickel-gold processes. The OSP layer itself does not participate in soldering; it merely protects the metal surfaces of the circuit board before soldering. At the high temperatures of reflow soldering, the OSP layer decomposes and volatilizes, allowing the solder to directly form a strong intermetallic compound with the pure metal. This results in high solder joint strength and excellent reliability, fundamentally eliminating the "black disk" problem of chemical nickel-gold processes. Furthermore, the OSP layer is extremely thin, forming only a molecular-level protective film on the metal surface, almost completely preserving the original morphology of the metal foil.

[0003] Given the high cost and complexity of the electroless nickel-gold process, and the extremely low cost and simple process of the OSP process (which typically only requires dipping or spraying a layer of OSP solution onto a cleaned metal surface), some manufacturers use an OSP layer instead of the electroless nickel-gold process to treat the metal foil surface to form the grounding layer of the circuit board. However, existing electromagnetic shielding films struggle to achieve stable grounding on grounding layers with OSP layers, preventing interference signals from being properly discharged from the grounding layer and thus failing to meet the electromagnetic shielding requirements of the circuit board. Summary of the Invention

[0004] This invention provides an electromagnetic shielding film and a circuit board to solve the technical problem that existing electromagnetic shielding films have poor grounding effect on grounding layers with OSP layers, thus failing to meet the electromagnetic shielding requirements of circuit boards.

[0005] To address the aforementioned technical problems, a first aspect of the present invention provides an electromagnetic shielding film, comprising a shielding layer, wherein a first surface of the shielding layer is provided with a raised structure, and after the electromagnetic shielding film is pressed together with a circuit board substrate having an OSP grounding structure through the raised structure, the grounding resistance of the electromagnetic shielding film is less than 800mΩ under a preset grounding window size.

[0006] As a preferred embodiment, the roughness Rz of the first surface is 1μm~15μm, and the interface expansion area ratio Sdr of the first surface is 5%~3000%.

[0007] As a preferred embodiment, the sharpness Sku of each protrusion in the protrusion structure is 2.8~20; and / or, in the sliced ​​state, within a preset observation range, the ratio between the number of protrusions in the protrusion structure with a height-to-width ratio of 1.5~13 and the total number of protrusions is greater than 60%.

[0008] As a preferred embodiment, in the sliced ​​state, the protrusions in the protrusion structure are non-uniformly distributed on the first surface, and the interval between two adjacent protrusions in the protrusion structure is 5μm~50μm.

[0009] As a preferred embodiment, it further includes an insulating layer and an adhesive film layer; the adhesive film layer is disposed on the first surface, and the insulating layer is disposed on the second surface of the shielding layer opposite to the first surface; The difference between the thickness of the adhesive film layer and the height of each protrusion in the protrusion structure is 0.1 μm to 5 μm; and / or, the ratio between the thickness of the adhesive film layer and the height of each protrusion in the protrusion structure is 0.02 to 3.

[0010] As a preferred embodiment, the film surface resistance R of the first surface... m The electromagnetic shielding film on the OSP grounding structure has a grounding resistance R0 that satisfies the following relationship: R0 = A0 × R m +A1; where A0 ranges from -3 to 0, and A1 ranges from 280 to 330.

[0011] A second aspect of the present invention provides a circuit board, including a circuit board substrate and an electromagnetic shielding film as described in any of the first aspects. The circuit board substrate includes a cover film layer, a ground layer and an OSP layer. The cover film layer is disposed on one side of the ground layer and has a grounding window. The OSP layer is disposed at the bottom of the grounding window and covers the ground layer. The electromagnetic shielding film passes through the OSP layer through the grounding window and is connected to the ground layer.

[0012] As a preferred embodiment, the diameter of the grounding window is 0.4 mm to 2.5 mm; and / or, the thickness of the OSP layer before lamination is 5 nm to 100 nm.

[0013] As a preferred embodiment, in any sliced ​​state at any angle, the number of grounding points where the protruding structures on the shielding layer of the electromagnetic shielding film contact the grounding layer is greater than 5; and / or, In the sliced ​​state, the insertion depth of the protrusion inserted into the ground layer in the protrusion structure is 0.02μm~3μm.

[0014] As a preferred embodiment, the grounding resistance R0 and the diameter x of the grounding window satisfy the following relationship: R0 = b1 × x 2-b2×x+b3; where b1 ranges from 28 to 33, b2 ranges from -200 to -160, and b3 ranges from 300 to 400.

[0015] Compared to existing technologies, the beneficial effects of this invention are that by providing a protruding structure on the first surface of the shielding layer, the electromagnetic shielding film can be connected to the grounding layer by piercing the OSP layer in the OSP grounding structure of the circuit board substrate during the pressing process. Furthermore, within a preset grounding window size, the grounding resistance of the electromagnetic shielding film on the OSP grounding structure is less than 800mΩ. This ensures that the electromagnetic shielding film maintains a suitable grounding resistance on the OSP grounding structures of different circuit board substrates, resulting in a better grounding effect of the electromagnetic shielding film on the OSP grounding structure of the circuit board substrate, thus meeting the electromagnetic shielding requirements of the circuit board. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the first electromagnetic shielding film in an embodiment of the present invention; Figure 2 This is a schematic diagram of the spacing between two adjacent protrusions in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the second type of electromagnetic shielding film in an embodiment of the present invention; Figure 4 This is a schematic diagram of the circuit board structure in an embodiment of the present invention; Figure 5 These are electron microscope images of the circuit board in an embodiment of the present invention; Figure 6 This is a schematic diagram of the grounding resistance of the OSP grounding structure of the electromagnetic shielding film in Embodiments 1-5 and Comparative Example 1, which is pressed onto the circuit board substrate under different grounding window sizes. Among them, 1. Shielding layer; 2. Raised structure; 201. Raised; 3. Insulating layer; 4. Adhesive film layer; 5. Covering film layer; 6. Grounding layer; 7. OSP layer; 8. Grounding window. Detailed Implementation

[0017] 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. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] 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.

[0019] 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 fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. The terms "vertical," "horizontal," "left," "right," "upper," "lower," and similar expressions used in this application are for illustrative purposes only and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. The term "and / or" used in this application includes any and all combinations of one or more of the related listed items. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0020] 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.

[0021] Please see Figure 1 The first aspect of the present invention provides an electromagnetic shielding film, including a shielding layer 1. The first surface of the shielding layer 1 is provided with a protrusion structure 2. After the electromagnetic shielding film is pressed with a circuit board substrate with an OSP grounding structure through the protrusion structure 2, the grounding resistance of the electromagnetic shielding film is less than 800mΩ under a preset grounding window 8 size.

[0022] Specifically, the electromagnetic shielding film in this embodiment includes a shielding layer 1, which is made of a conductive material with good shielding performance. Therefore, when the electromagnetic shielding film is pressed against the circuit board substrate and connected to the grounding layer 6 of the circuit board substrate, it can effectively and quickly guide interference signals generated by electronic devices to the grounding layer 6 of the circuit board substrate, thus achieving electromagnetic shielding. However, when the circuit board substrate has an OSP grounding structure, since the grounding layer 6 in the OSP grounding structure is covered by the OSP layer 7, this embodiment provides a protrusion structure 2 on the first surface of the shielding layer 1. It is worth noting that this first surface is the side of the shielding layer 1 closest to the circuit board substrate when the electromagnetic shielding film is pressed together. The protrusion structure 2 has multiple protrusions 201, which can enhance the piercing force of the shielding layer 1 to pierce the OSP layer 7 and successfully connect to the grounding layer 6, achieving effective grounding.

[0023] It should be noted that the OSP grounding structure is a grounding process for flexible circuit boards. Its structure consists of a cover film layer 5 with windows covering the grounding layer 6, exposing the corresponding grounding position. An OSP layer 7 is then processed at the grounding position to form the OSP grounding structure.

[0024] Furthermore, this embodiment also specifies that after the electromagnetic shielding film is pressed against the circuit board substrate with the OSP grounding structure through the raised structure 2, the grounding resistance of the electromagnetic shielding film is less than 800mΩ under the preset grounding window 8 size. For example, the grounding resistance of the electromagnetic shielding film on the OSP grounding structure of different circuit board substrates is 10mΩ, 45mΩ, 89mΩ, 112mΩ, 143mΩ, 196mΩ, 225mΩ, 250mΩ, 300mΩ, 321mΩ, 376mΩ, 410mΩ, 43... 6mΩ, 500mΩ, 550mΩ, 600mΩ, 650mΩ, 700mΩ, 750mΩ, 785mΩ, etc., are not specifically limited in this embodiment. This ensures that the electromagnetic shielding film maintains a suitable grounding resistance on the OSP grounding structure of different circuit board substrates. In turn, the electromagnetic shielding film can achieve stable grounding on the grounding layer 6 with OSP layer 7, which has a good grounding effect and ensures that interference signals can be normally discharged from the grounding layer 6 to meet the electromagnetic shielding requirements of the circuit board.

[0025] Preferably, under the preset grounding window 8 size, the grounding resistance of the electromagnetic shielding film on the OSP grounding structure is 20mΩ~600mΩ, for example, 20mΩ, 55mΩ, 89mΩ, 105mΩ, 120mΩ, 180mΩ, 210mΩ, 250mΩ, 300mΩ, 350mΩ, 400mΩ, 450mΩ, 500mΩ, 550mΩ, 600mΩ, etc., thereby further ensuring that the grounding resistance of the electromagnetic shielding film on the OSP grounding structure of different circuit board substrates is low, so that the grounding effect of the electromagnetic shielding film on the grounding layer 6 with OSP layer 7 is better, and its electromagnetic shielding effectiveness is guaranteed.

[0026] It is worth noting that the size of the grounding window 8 in this embodiment specifically refers to the diameter of the grounding window 8, which is specifically the maximum distance between the opening contours of the grounding window 8. The grounding window 8 is preferably circular, so the size of the grounding window 8 at this time is the diameter of its circular opening.

[0027] In this embodiment, the shielding layer 1 can be made of metallic or non-metallic materials. For example, the metallic material can be any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold, or an alloy made of at least two of them, so that the shielding layer 1 is a metallic shielding layer; the non-metallic material can be graphene, carbon nanotubes, conductive carbon black, etc., and this embodiment does not make specific limitations.

[0028] As a preferred embodiment, the roughness Rz of the first surface is 1μm~15μm, and the interface expansion area ratio Sdr of the first surface is 5%~3000%.

[0029] Specifically, in order to further ensure that the protrusion structure 2 provided on the first surface can penetrate the OSP layer 7 in the OSP grounding structure, this embodiment limits the roughness Rz of the first surface to 1μm~15μm. For example, the roughness Rz of the first surface is 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, etc. This embodiment does not make a specific limitation here. It is understandable that the height of the protrusions 201 in the protrusion structure 2 macroscopically manifests as the roughness of the first surface. The more uneven the height of the protrusions 201 and the larger the gap between two adjacent protrusions 201, the rougher the first surface appears. By limiting the roughness Rz of the first surface to 1μm~15μm, it is possible to ensure that the first surface is sufficiently rough. During the pressing of the electromagnetic shielding film, this can improve the success rate of the protrusion structure 2 in piercing the OSP layer 7 of the circuit board substrate, increase the number of effective grounding points with the grounding layer 6, and thus enable the electromagnetic shielding film to have lower grounding resistance and better shielding effect on the OSP grounding structure of the circuit board substrate. At the same time, the roughness Rz of the first surface is not too large, to avoid the problem that the gap between two adjacent protrusions 201 is too large, resulting in too few effective grounding points with the grounding layer 6 under the preset grounding window 8 size, which would increase the grounding resistance of the electromagnetic shielding film and affect its grounding effect.

[0030] Furthermore, this embodiment also limits the interface expansion area ratio Sdr of the first surface to 5%~3000%. For example, the interface expansion area ratio Sdr of the first surface can be 5%, 55%, 125%, 300%, 600%, 930%, 1050%, 1400%, 1800%, 2100%, 2300%, 2500%, 2700%, 2900%, 3000%, etc. This embodiment does not make a specific limitation. The interface expansion area ratio Sdr is the increase ratio of the expanded area (surface area) of the defined region to the area of ​​the defined region. It is used to quantify surface roughness or morphological characteristics. The interface expansion area ratio Sdr of a completely flat surface is 0. The rougher the surface or the more inclined it is, the larger the value of the interface expansion area ratio Sdr. This embodiment, by limiting the interface expansion area ratio Sdr of the first surface to 5%~3000%, ensures a relatively large surface roughness. This guarantees that the protrusions 2 on the first surface can effectively penetrate the OSP layer 7 of the circuit board substrate during lamination, and ensures that the number of effective grounding points of the grounding layer 6 is sufficient within the preset grounding window 8 size. This results in lower grounding resistance and better shielding effect of the electromagnetic shielding film on the OSP grounding structure of the circuit board substrate. Furthermore, setting an upper limit for the interface expansion area ratio Sdr of the first surface ensures the structural stability of the shielding layer 1 and avoids bonding force problems.

[0031] As a preferred embodiment, the sharpness Sku of each protrusion 201 in the protrusion structure 2 is 2.8~20.

[0032] Specifically, this embodiment further limits the sharpness Sku of each protrusion 201 in the protrusion structure 2 to 2.8~20. For example, the sharpness Sku of any protrusion 201 in the protrusion structure 2 can be 2.8, 3, 4, 5, 6, 7, 8, 9, 10, 11.5, 13.2, 14.4, 15.6, 17, 18, 19, 20, etc. This embodiment does not make a specific limitation. It is worth noting that the sharpness Sku is used to describe the steepness and concentration of the peaks and valleys of the surface profile. This embodiment can ensure that each protrusion 201 in the protrusion structure 2 is relatively sharp, so that it can effectively penetrate the OSP layer 7 when the electromagnetic shielding film is pressed, and make the insertion depth of the protrusion 201 deeper, which can ensure more grounding points and a larger contact area with the grounding layer 6, thereby making the electromagnetic shielding film have a lower grounding resistance and improving the shielding effectiveness.

[0033] Further, please refer to Figure 2 In the sliced ​​state, within the preset observation range, the ratio between the number of protrusions 201 with a height-to-width ratio of 1.5 to 13 and the total number of protrusions 201 is greater than 60%.

[0034] Specifically, this embodiment further limits the observation to a predetermined range within a sliced ​​state, where the ratio of the number of protrusions 201 with a height-to-width ratio of 1.5 to 13 in the protrusion structure 2 to the total number of protrusions 201 is greater than 60%. For example, the ratios of the number of protrusions 201 with height-to-width ratios of 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 13 to the total number of protrusions 201 are 62%, 68%, 71%, 75%, 80%, and 85%, respectively. 90%, 93%, 96%, 100%, etc., are not specifically limited in this embodiment. Since the proportion of the protrusions 201 with a large height-to-width ratio is higher than 60%, it can be ensured that the proportion of the sharper protrusions 201 in the protrusion structure 2 is relatively large. Therefore, when the electromagnetic shielding film is pressed, it can be ensured that a large number of protrusions 201 can penetrate the OSP layer 7 of the circuit board substrate and insert into the grounding layer 6, ensuring that there are enough grounding points between the shielding layer 1 and the grounding layer 6 and the contact area is large enough, so that the grounding resistance of the electromagnetic shielding film is small.

[0035] The method for measuring the height of the protrusion 201 in the protrusion structure 2 is as follows: in the sliced ​​state, the vertical distance between the highest point of the protrusion 201 on the side close to the first surface and the lowest point on the side away from the first surface is measured, which is the height of the protrusion 201.

[0036] The method for measuring the width of protrusion 201 in protrusion structure 2 is as follows: in the slice state, measure the maximum horizontal distance between the left and right contours of protrusion 201, which is the width of protrusion 201.

[0037] It is worth noting that the observation range mentioned above can be the entire slice surface or any area of ​​any size within the slice surface. For example, the width of the observation range can be 0.2mm to 2mm, and the length of the observation range can be 0.2mm to 10mm, as long as the number of observed protrusions 201 is greater than 10. This embodiment does not specifically limit the observation range. Thus, this embodiment can ensure that the protrusions 201 with a height-to-width ratio of 1.5 to 13 are evenly distributed. When the electromagnetic shielding film is pressed, it can ensure that there are enough relatively sharp protrusions 201 in each grounding window 8 to pierce through the OSP layer 7 and insert into the grounding layer 6.

[0038] As a preferred embodiment, in the sliced ​​state, each protrusion 201 in the protrusion structure 2 is non-uniformly distributed on the first surface, and the interval between two adjacent protrusions 201 in the protrusion structure 2 is 5μm~50μm.

[0039] Specifically, in the sliced ​​state, this embodiment further limits the distribution of each protrusion 201 in the protrusion structure 2 to non-uniform distribution on the first surface, thereby further ensuring that the first surface is relatively rough, so that the electromagnetic shielding film has a lower grounding resistance and a better shielding effect in the OSP grounding structure. In addition, this embodiment also limits the spacing between two adjacent protrusions 201 in the protrusion structure 2 to 5μm~50μm, for example, the spacing between two adjacent protrusions 201 is 5μm, 10μm, 16μm, 21μm, 27μm, 30μm, 35μm, 40μm, 45μm, 50μm, etc., which are not specifically limited in this embodiment. It is worth noting that if the spacing between two adjacent protrusions 201 is too large, there will be too few grounding points in contact with the grounding layer 6 under the preset grounding window 8 size, thereby increasing the grounding resistance of the electromagnetic shielding film on the OSP grounding structure and reducing its shielding effect. Conversely, if the spacing between two adjacent protrusions 201 is too small, the protrusions 201 will clump together, making it easy for holes to appear during the electroplating of the shielding layer 1, resulting in a broken and discontinuous appearance in the sliced ​​state, which will also affect the grounding resistance of the electromagnetic shielding film. Therefore, this embodiment limits the spacing between two adjacent protrusions 201 in the protrusion structure 2 to 5μm~50μm, which ensures that the spacing between two adjacent protrusions 201 is appropriate. While ensuring that the roughness of the first surface is sufficiently large, it also ensures that there are enough grounding points in contact with the grounding layer 6 under the preset grounding window 8 size, resulting in a smaller grounding resistance of the electromagnetic shielding film on the OSP grounding structure and avoiding the appearance of holes during the electroplating of the shielding layer 1.

[0040] It is worth noting that in this embodiment, the interval between two adjacent protrusions 201 is the lateral distance between the lowest points of the two adjacent protrusions 201, and the lowest point of the protrusion 201 is the point on the outer contour of the protrusion 201 that is farthest from the first surface. Figure 2 The spacing between the two sets of protrusions 201 is shown, with a difference of 14.7 μm and 6.97 μm, respectively.

[0041] As a preferred embodiment, the electromagnetic shielding film further includes an insulating layer 3 and an adhesive film layer 4; the adhesive film layer 4 is disposed on the first surface, and the insulating layer 3 is disposed on the second surface of the shielding layer 1 opposite to the first surface; the difference between the thickness of the adhesive film layer 4 and the height of each protrusion 201 in the protrusion structure 2 is 0.1μm~5μm.

[0042] Specifically, please see Figure 3 In this embodiment, the electromagnetic shielding film further includes an insulating layer 3 and an adhesive film layer 4. The insulating layer 3 provides insulation and protection for the shielding layer 1, and also prevents wear on the shielding layer 1, thus extending the lifespan of the electromagnetic shielding film; while the adhesive film layer 4 improves the bonding stability between the electromagnetic shielding film and the circuit board substrate. This embodiment further limits the difference between the thickness of the adhesive film layer 4 and the height of each protrusion 201 in the protrusion structure 2 to 0.1μm~5μm. For example, the difference between the thickness of the adhesive film layer 4 and the height of any protrusion 201 in the protrusion structure 2 can be 0.1μm, 0.5μm, 0.8μm, 1.3μm, 1.8μm, 2μm, 2.6μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, etc. This embodiment does not make a specific limitation here, so as to ensure that the difference between the thickness of the adhesive film layer 4 and the height of the protrusion 201 in the protrusion structure 2 is not too large. When the electromagnetic shielding film is pressed, it is ensured that the protrusion structure 2 can pierce the adhesive film layer 4 and the OSP layer 7 and insert into the grounding layer 6, thereby ensuring the bonding force between the electromagnetic shielding film and the circuit board substrate and the grounding effect of the electromagnetic shielding film at the same time. It is worth noting that this embodiment does not limit the thickness of the adhesive film layer 4 to be greater than the height of each protrusion 201 in the protrusion structure 2. In the protrusion structure 2, there may be some protrusions 201 whose height is greater than the thickness of the adhesive film layer 4, that is, the protrusions 201 are set to protrude from the adhesive film layer 4.

[0043] Furthermore, the ratio between the thickness of the adhesive film layer 4 and the height of each protrusion 201 in the protrusion structure 2 is 0.02~3. For example, the ratio between the thickness of the adhesive film layer 4 and the height of any protrusion 201 in the protrusion structure 2 can be 0.02, 0.1, 0.4, 0.6, 0.9, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.7, 3, etc. This embodiment does not make a specific limitation. Thus, some protrusions 201 in the protrusion structure 2 have a height greater than the thickness of the adhesive film layer 4. These protrusions 201 are set to protrude from the adhesive film layer 4. When the electromagnetic shielding film is pressed, these protrusions 201 can be directly used to pierce the OSP layer 7 and insert into the grounding layer 6. This further ensures that the number of grounding points in contact with the grounding layer 6 is sufficient, reduces the grounding resistance of the electromagnetic shielding film, and avoids the situation where the thickness of the adhesive film layer 4 is greater than the height of each protrusion 201 in the protrusion structure 2. In this case, many protrusions 201 cannot pierce the adhesive film layer 4 and cannot continue to pierce the OSP layer 7, thus reducing the number of grounding points in contact with the grounding layer 6. Meanwhile, the ratio between the thickness of the adhesive film layer 4 and the height of each protrusion 201 in the protrusion structure 2 does not exceed 3. This ensures that the adhesive film layer 4 is not too thick, which would prevent the protrusions 201 from being pierced, while maintaining the bonding force between the electromagnetic shielding film and the circuit board substrate.

[0044] It is worth noting that the material of insulating layer 3 can be bisphenol A type epoxy resin, acrylic resin, polyester resin, etc. In addition, the resin used can also be any one or a mixture of at least two of epoxy resin, cyanate resin, polyphenylene ether resin, polybutadiene resin, styrene-butadiene resin, bismaleimide-triazine resin, bismaleimide resin, polytetrafluoroethylene resin, polyimide resin, phenolic resin, acrylic resin, liquid crystal resin, benzoxazine resin, phenolic resin, nitrile rubber, carboxyl-terminated nitrile rubber, or hydroxyl-terminated nitrile rubber, but is not limited to these, and all existing resin materials can be used. The mixture may be, for example, a mixture of epoxy resin and cyanate resin, a mixture of polyphenylene ether resin and polybutadiene resin, a mixture of styrene-butadiene resin and BT resin, a mixture of polytetrafluoroethylene resin and polyimide resin, a mixture of phenolic resin and acrylic resin, a mixture of epoxy resin, cyanate resin and polyphenylene ether resin, a mixture of polybutadiene resin, styrene-butadiene resin and BT resin, or a mixture of polytetrafluoroethylene resin, polyimide resin, phenolic resin and acrylic resin. That is, two or more resin mixtures may be used.

[0045] The material of the film layer 4 includes at least one of the following resins: vinyl acetate, polyester, polyethylene, polyamide, rubber, acrylate, phenolic, epoxy, polyimide, urethane, melamine, alkyd, ABF, etc. This embodiment does not make specific limitations.

[0046] As a preferred embodiment, the film surface resistance R of the first surface... m The electromagnetic shielding film on the OSP grounding structure has a grounding resistance R0 that satisfies the following relationship: R0 = A0 × R m +A1; where A0 ranges from -3 to 0, and A1 ranges from 280 to 330.

[0047] Specifically, in this embodiment, the film surface resistance R of the first surface is used. m To quantify the height of the protrusions 201 in the protrusion structure 2, it can be understood that the more uneven the height of the protrusions 201, and the larger the gap between two adjacent protrusions 201, the rougher the first surface is, and the higher the film resistance R of the first surface. m The larger the surface resistance R, the more uniform the height of the protrusion 201. m The smaller the value, the more uniform the height of the protrusions 201, and the larger the spacing between adjacent protrusions 201. This allows the electromagnetic shielding film to have a lower grounding resistance and a better shielding effect in the OSP grounding structure, i.e., the film surface resistance R of the first surface. m The grounding resistance R0 of the electromagnetic shielding film on the OSP grounding structure satisfies the above-mentioned negative correlation: R0 = A0 × R m +A1. By limiting the range of A0 to -3 to 0 and the range of A1 to 280 to 330, for example, A0 can be -3, -2, -1, 0, etc., and A1 can be 280, 285, 290, 295, 300, 305, 310, 320, 330, etc. This embodiment does not impose specific limitations here. Thus, when the roughness of the first surface is appropriate, such as when the roughness Rz of the first surface is 1μm to 15μm, the film surface resistance R of the first surface... m The resistance is relatively high, but it ensures that the grounding resistance R0 of the electromagnetic shielding film on the OSP grounding structure is low, so as to guarantee the shielding effect of the electromagnetic shielding film.

[0048] Please see Figure 4 The second aspect of the present invention provides a circuit board, including a circuit board substrate and an electromagnetic shielding film as described in any embodiment of the first aspect. The circuit board substrate includes a cover film layer 5, a ground layer 6 and an OSP layer 7. The cover film layer 5 is disposed on one side of the ground layer 6 and has a grounding window 8. The OSP layer 7 is disposed at the bottom of the grounding window 8 and covers the ground layer 6. The electromagnetic shielding film passes through the grounding window 8 and is connected to the ground layer 6 through the OSP layer 7.

[0049] Specifically, the circuit board substrate in this embodiment includes a cover film layer 5, a ground layer 6, and an OSP layer 7. The cover film layer 5 is a protective film applied to the surface of the circuit board substrate, providing protection, moisture and dust protection, interlayer insulation, and also serving an identification and aesthetic purpose. Multiple grounding windows 8 are formed on the cover film layer 5, extending through both the upper and lower surfaces. At the bottom of the grounding windows 8 is the ground layer 6, which covers the OSP layer 7. When the electromagnetic shielding film is pressed onto the circuit board substrate, the protrusions 2 on the first surface of its shielding layer 1 insert into the grounding windows 8 and pierce the OSP layer 7, then insert into the ground layer 6, connecting the shielding layer 1 and the ground layer 6, thus providing electromagnetic shielding for the circuit board. Figure 5 As shown in the electron microscope image, a grounding window 8 is formed in the cover film layer 5, as indicated by the white dashed box. The shielding layer 1 in the electromagnetic shielding film uses the protrusion structure 2 of its downwardly protruding surface 201 to insert into the grounding layer 6 through the grounding window 8. Since the thickness of the OSP layer 7 is at the nanometer level, it... Figure 5 Not shown in the image.

[0050] As a preferred embodiment, the diameter of the grounding window 8 is 0.4mm to 2.5mm.

[0051] Specifically, in this embodiment, the diameter of the grounding window 8 is further limited to 0.4mm to 2.5mm. For example, the diameter of the grounding window 8 is 0.4mm, 0.8mm, 1mm, 1.2mm, 1.5mm, 1.7mm, 1.9mm, 2.1mm, 2.3mm, 2.5mm, etc. This embodiment does not make a specific limitation here, so as to ensure that the size of the grounding window 8 is relatively large. During the grounding process of the electromagnetic shielding film, it is ensured that the number of protrusions 201 inserted into the grounding window 8 is sufficient. This can increase the probability of puncturing the OSP layer 7 and the number of grounding points in contact with the grounding layer 6, so that the grounding resistance of the electromagnetic shielding film in the grounding layer 6 covered by the OSP layer 7 is small and the grounding effect is good.

[0052] Furthermore, the thickness of the OSP layer 7 before lamination is 5nm to 100nm. For example, the thickness of the OSP layer 7 before lamination is 5nm, 15nm, 20nm, 30nm, 35nm, 43nm, 51nm, 62nm, 70nm, 80nm, 90nm, 100nm, etc. This embodiment does not make a specific limitation, thereby ensuring that the thickness of the OSP layer 7 before lamination is not too large, avoiding it being too thick to be punctured, thus affecting the grounding effect of the electromagnetic shielding film.

[0053] As a preferred embodiment, in any sliced ​​state at any angle, the number of grounding points where the protrusion structure 2 on the shielding layer 1 of the electromagnetic shielding film contacts the grounding layer 6 is greater than 5.

[0054] Specifically, this embodiment further limits the number of grounding points where the protrusion structure 2 on the shielding layer 1 of the electromagnetic shielding film contacts the grounding layer 6 to be greater than 5 in any sliced ​​state at any angle. For example, the number of grounding points where the protrusion structure 2 contacts the grounding layer 6 is 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, etc. This embodiment does not make a specific limitation here, thereby further ensuring that under the preset grounding window 8 size, the number of grounding points where the protrusion structure 2 on the shielding layer 1 contacts the grounding layer 6 is sufficient, which can further increase the puncture probability of the OSP layer 7 and achieve a lower grounding resistance of the electromagnetic shielding film.

[0055] Furthermore, in the sliced ​​state, the insertion depth of the protrusions 201 inserted into the grounding layer 6 in the protrusion structure 2 is 0.02μm to 3μm. For example, the insertion depths of each protrusion 201 inserted into the grounding layer 6 are 0.02μm, 0.1μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.6μm, 2μm, 2.1μm, 2.3μm, 2.5μm, 2.7μm, 3μm, etc. This embodiment does not impose specific limitations, thereby ensuring that the insertion depth of each protrusion 201 inserted into the grounding layer 6 is sufficiently deep, increasing the contact area with the grounding layer 6 and the grounding stability, thereby ensuring that the electromagnetic shielding film has a lower grounding resistance and ensuring its grounding effect. It is worth noting that the insertion depth of the protrusion 201 is the depth of the protrusion 201 along the surface of the grounding layer 6.

[0056] As a preferred embodiment, the grounding resistance R0 and the diameter x of the grounding window 8 satisfy the following relationship: R0 = b1 × x 2 -b2×x+b3; where b1 ranges from 28 to 33, b2 ranges from -200 to -160, and b3 ranges from 300 to 400.

[0057] Specifically, in this embodiment, the grounding resistance R0 and the diameter x of the grounding window 8 are defined to satisfy the following relationship: R0 = b1 × x 2The larger the diameter x of the grounding window 8, the smaller the grounding resistance R0 of the electromagnetic shielding film. Furthermore, by limiting the range of b1 to 28~33, b2 to -200~-160, and b3 to 300~400 in the above relationship, for example, b1 is 28, 29, 30, 31, 32, 33, etc., b2 is -200, -190, -180, -170, -160, etc., and b3 is 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, etc., this embodiment does not make specific limitations. Thus, when the diameter x of the grounding window 8 is 0.4mm~2.5mm, the grounding resistance R0 of the electromagnetic shielding film is small based on the above relationship, so that the electromagnetic shielding film has a good grounding effect in the grounding layer 6 covered with OSP layer 7.

[0058] The electromagnetic shielding film and circuit board provided in this embodiment of the invention, by setting a protruding structure on the first surface of the shielding layer, ensure that the electromagnetic shielding film can pierce the OSP layer in the OSP grounding structure of the circuit board substrate and connect to the grounding layer through the protruding structure during the pressing process. Under a preset grounding window size, the grounding resistance of the electromagnetic shielding film on the OSP grounding structure is less than 800mΩ. This ensures that the electromagnetic shielding film maintains a suitable grounding resistance on the OSP grounding structures of different circuit board substrates, thereby enabling the electromagnetic shielding film to have a better grounding effect on the OSP grounding structure of the circuit board substrate and meeting the electromagnetic shielding requirements of the circuit board.

[0059] To fully demonstrate the beneficial effects of the electromagnetic shielding film and circuit board provided in the embodiments of the present invention, the following description is provided in conjunction with some embodiments and comparative examples.

[0060] Example 1 A circuit board includes a circuit board substrate and an electromagnetic shielding film. The electromagnetic shielding film includes a shielding layer, and a first surface of the shielding layer is provided with a raised structure. The circuit board substrate includes a cover film layer, a grounding layer and an OSP layer. The cover film layer has a grounding window with a diameter of 1 mm. After the electromagnetic shielding film is pressed against the circuit board substrate with the OSP grounding structure through the raised structure, the grounding resistance of the electromagnetic shielding film is 553 mΩ under the size of the grounding window.

[0061] Example 2 A circuit board includes a circuit board substrate and an electromagnetic shielding film. The electromagnetic shielding film includes a shielding layer, and a first surface of the shielding layer has a raised structure. The circuit board substrate includes a cover film layer, a grounding layer, and an OSP layer. The cover film layer has a grounding window with a diameter of 1.5 mm. After the electromagnetic shielding film is pressed against the circuit board substrate with the OSP grounding structure through the raised structure, the grounding resistance of the electromagnetic shielding film is 601 mΩ under the size of the grounding window.

[0062] Furthermore, the roughness Rz of the first surface is 3.5 μm, and the interfacial expansion area ratio Sdr of the first surface is 16.8%. The sharpness Sku of each protrusion in the protrusion structure is 3.6. In the sliced ​​state, the ratio of the number of protrusions with a height-to-width ratio of 1.5 to 13 to the total number of protrusions in any observation range is 75%.

[0063] Example 3 A circuit board includes a circuit board substrate and an electromagnetic shielding film. The electromagnetic shielding film includes an insulating layer, a shielding layer, and an adhesive film layer stacked thereon. The first surface of the shielding layer has a raised structure. The circuit board substrate includes a cover film layer, a grounding layer, and an OSP layer. The cover film layer has a grounding window with a diameter of 1.5 mm. After the electromagnetic shielding film is pressed against the circuit board substrate with the OSP grounding structure through the raised structure, the grounding resistance of the electromagnetic shielding film is 433 mΩ under the size of the grounding window.

[0064] Furthermore, the roughness Rz of the first surface is 3.9 μm, and the interfacial expansion area ratio Sdr of the first surface is 23.3%. The sharpness Sku of each protrusion in the protrusion structure is 3.7. In the sliced ​​state, the ratio of the number of protrusions with a height-to-width ratio of 1.5 to 13 to the total number of protrusions in the protrusion structure within any observation range is 80%. In addition, in the sliced ​​state, the interval between two adjacent protrusions in the protrusion structure is 18.6 μm.

[0065] The difference between the thickness of the adhesive film layer and the height of each protrusion in the raised structure is 2.4 μm, and the ratio between the thickness of the adhesive film layer and the height of each protrusion is 0.5.

[0066] Example 4 A circuit board includes a circuit board substrate and an electromagnetic shielding film. The electromagnetic shielding film includes an insulating layer, a shielding layer, and an adhesive film layer stacked thereon. The first surface of the shielding layer has a raised structure. The circuit board substrate includes a cover film layer, a grounding layer, and an OSP layer. The cover film layer has a grounding window with a diameter of 1 mm. After the electromagnetic shielding film is pressed against the circuit board substrate with the OSP grounding structure through the raised structure, the grounding resistance of the electromagnetic shielding film is 411 mΩ under the size of the grounding window.

[0067] Furthermore, the roughness Rz of the first surface is 5.3 μm, and the interfacial expansion area ratio Sdr of the first surface is 56%. The sharpness Sku of each protrusion in the protrusion structure is 8.6. In the sliced ​​state, the ratio of the number of protrusions with a height-to-width ratio of 1.5 to 13 to the total number of protrusions in the protrusion structure within any observation range is 65%. In addition, in the sliced ​​state, the interval between two adjacent protrusions in the protrusion structure is 20.4 μm.

[0068] The difference between the thickness of the adhesive film layer and the height of each protrusion in the raised structure is 0.5 μm, and the ratio between the thickness of the adhesive film layer and the height of each protrusion is 1.5.

[0069] Example 5 A circuit board includes a circuit board substrate and an electromagnetic shielding film. The electromagnetic shielding film includes an insulating layer, a shielding layer, and an adhesive film layer stacked thereon. The first surface of the shielding layer has a raised structure. The circuit board substrate includes a cover film layer, a grounding layer, and an OSP layer. The cover film layer has a grounding window with a diameter of 2.0 mm. After the electromagnetic shielding film is pressed against the circuit board substrate with the OSP grounding structure through the raised structure, the grounding resistance of the electromagnetic shielding film is 264 mΩ under the size of the grounding window.

[0070] Furthermore, the roughness Rz of the first surface is 3.6 μm, and the interfacial expansion area ratio Sdr of the first surface is 26%. The sharpness Sku of each protrusion in the protrusion structure is 3.9. In the sliced ​​state, the ratio of the number of protrusions with a height-to-width ratio of 1.5 to 13 to the total number of protrusions in the protrusion structure within any observation range is 75%. In addition, in the sliced ​​state, the interval between two adjacent protrusions in the protrusion structure is 31 μm.

[0071] The difference between the thickness of the adhesive film layer and the height of each protrusion in the raised structure is 3 μm, and the ratio between the thickness of the adhesive film layer and the height of each protrusion is 0.8.

[0072] Comparative Example 1 A circuit board includes a circuit board substrate and an electromagnetic shielding film. The electromagnetic shielding film includes a shielding layer, and a raised structure is provided on the first surface of the shielding layer. The circuit board substrate includes a cover film layer, a grounding layer and an OSP layer. The cover film layer has a grounding window with a diameter of 0.4 mm. After the electromagnetic shielding film is pressed against the circuit board substrate with the OSP grounding structure through the raised structure, the grounding resistance of the electromagnetic shielding film is 5844 mΩ under the size of the grounding window.

[0073] For the circuit board in Embodiment 1 above, the grounding resistance of the electromagnetic shielding film under different grounding windows is shown in Table 1 below: Table 1 Grounding resistance test results

[0074] Furthermore, the grounding resistance of the OSP grounding structure pressed onto the circuit board substrate under different grounding window sizes in Examples 1-5 and Comparative Example 1 is as follows: Figure 6 As shown, in Figure 6In the graph, the horizontal axis represents different grounding window sizes, including those with diameters of 0.4mm, 0.5mm, 0.6mm, 0.8mm, 1mm, 1.5mm, 2mm, and 2.5mm, while the vertical axis represents the grounding resistance value. From... Figure 6 As can be seen, the electromagnetic shielding film in Comparative Example 1 exhibits significant differences in grounding resistance under different grounding window sizes. Specifically, the grounding resistance exceeds 800mΩ for grounding window sizes of 0.4mm, 0.5mm, 0.6mm, 0.8mm, 1mm, and 2mm, with the grounding resistance being particularly high at 0.4mm and 0.5mm. This results in the electromagnetic shielding film in Comparative Example 1 failing to achieve stable grounding on the grounding layer covered by the OSP layer, leading to poor grounding performance. In contrast, the electromagnetic shielding films in Examples 1-5 exhibit grounding resistances less than 800mΩ across all grounding window sizes, with a smaller range of variation. Consequently, the electromagnetic shielding films in Examples 1-5 maintain suitable and stable grounding resistance on the OSP grounding structures of different circuit board substrates, resulting in excellent grounding performance.

[0075] The shielding effectiveness of the electromagnetic shielding films in the above embodiments and comparative examples was tested, and the test results are shown in Table 2 below: Table 2 Shielding effectiveness test results

[0076] Therefore, it can be seen that since the grounding resistance of the electromagnetic shielding film in Examples 1 to 5 is less than 800mΩ on the grounding layer covered with the OSP layer, it can ensure stable grounding of the electromagnetic shielding film on the grounding layer with the OSP layer, resulting in good grounding effect and good shielding performance, which can meet the electromagnetic shielding requirements of the circuit board. In contrast, the electromagnetic shielding film in Comparative Example 1 has excessively high grounding resistance on the grounding layer covered with the OSP layer, resulting in poor grounding effect. Interference signals cannot be properly exported from the grounding layer, resulting in poor shielding performance and failing to meet the electromagnetic shielding requirements of the circuit board.

[0077] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. An electromagnetic shielding film, characterized by, The shielding layer has a first surface provided with a protruding structure, and the electromagnetic shielding film has a grounding resistance less than 800 mΩ under a preset grounding window size after being pressed with the OSP grounding structure provided line board substrate.

2. The electromagnetic shielding film according to claim 1, wherein The first surface has a roughness Rz of 1 μm to 15 μm, and the first surface has an interface extension area ratio Sdr of 5% to 3000%.

3. The electromagnetic shielding film according to claim 1, wherein Each protrusion in the protruding structure has a sharpness Sku of 2.8 to 20; and / or, in a sliced state, the ratio between the number of protrusions with a height-to-width ratio of 1.5 to 13 and the total number of protrusions in a preset observation range is greater than 60%.

4. The electromagnetic shielding film according to claim 1, wherein In a sliced state, each protrusion in the protruding structure is unevenly distributed on the first surface, and the interval between two adjacent protrusions in the protruding structure is 5 μm to 50 μm.

5. The electromagnetic shielding film according to claim 1, wherein The adhesive film layer is provided on the first surface, and the insulating layer is provided on the second surface opposite to the first surface of the shielding layer. The difference between the thickness of the adhesive film layer and the height of each protrusion in the protruding structure is 0.1 μm to 5 μm. And / or, the ratio between the thickness of the adhesive film layer and the height of each protrusion in the protruding structure is 0.02 to 3.

6. The electromagnetic shielding film according to any one of claims 1 to 5, wherein The film surface resistance R of the first surface m The ground resistance R0 of the electromagnetic shielding film on the OSP ground structure satisfies the relationship: R0=A0×R m +A1; A0 is in the range of -3 to 0, and A1 is in the range of 280 to 330.

7. A wiring board, characterized by The circuit board substrate includes a cover film layer, a grounding layer, and an OSP layer, the cover film layer is provided on one side of the grounding layer, and the cover film layer is provided with a grounding window, the OSP layer is provided at the bottom of the grounding window and covers the grounding layer, and the electromagnetic shielding film is connected with the grounding layer through the grounding window and the OSP layer.

8. The circuit board of claim 7, wherein, The diameter of the grounding window is 0.4 mm to 2.5 mm; and / or, the thickness of the OSP layer before pressing is 5 nm to 100 nm.

9. The circuit board of claim 7, wherein, In a sliced state at any angle, the number of grounding points at which the protruding structure on the shielding layer of the electromagnetic shielding film is in contact with the grounding layer is greater than 5; and / or, In a sliced state, the insertion depth of the protrusion in the protruding structure inserted into the grounding layer is 0.02 μm to 3 μm.

10. The circuit board of claim 7, wherein, The ground resistance R0 and the diameter x of the ground window satisfy the relationship: R0 = b1 x x 2 b2 x x + b3; wherein, b1 ranges from 28 to 33, b2 ranges from -200 to -160, and b3 ranges from 300 to 400.

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