Electromagnetic shield film and circuit board

Abstract

This application relates to an electromagnetic shielding film and a circuit board. The electromagnetic shielding film includes an insulating layer, a barrier layer, and a shielding layer stacked sequentially; the shielding layer has a plurality of through holes extending through it in the thickness direction; wherein the ablation threshold of the barrier layer to the laser used to process the through holes is 5 to 10 times that of the shielding layer to the laser. This application can improve the insulation reliability of the shielding film.

Description

Technical Field

[0001] This application relates to the field of electronic technology, and in particular to electromagnetic shielding films and circuit boards. Background Technology

[0002] With the rapid development of 5G communication and millimeter-wave radar technology, electromagnetic shielding films are widely used to cover electronic components and circuit boards to reduce electromagnetic interference. Electromagnetic shielding films consist of an insulating layer, a shielding layer, and an adhesive film layer. The surface of the shielding layer is roughened to create raised bumps, which are used to pierce the adhesive film layer during hot pressing, thereby making contact with the grounding pads of the circuit board to form a conductive path. During the hot pressing process, air can easily be trapped between the film layers, and thermal expansion often leads to defects such as board bursting or delamination. Related technologies typically use lasers to process a perforated array of micropores through the shielding layer, allowing volatiles and residual gases to escape, thus mitigating the risk of board bursting.

[0003] However, during laser drilling, due to the thinness of the shielding layer, excess energy can easily be generated during drilling, leading to the breakdown of the insulation layer. This results in a significant reduction in the surface insulation resistance of the electromagnetic shielding film and poor insulation performance. Summary of the Invention

[0004] Based on this, this application provides an electromagnetic shielding film and a circuit board, which helps to improve the insulation reliability of the shielding film.

[0005] In a first aspect, this application provides an electromagnetic shielding film, comprising an insulating layer, a barrier layer, and a shielding layer stacked sequentially; the shielding layer has a plurality of through holes extending through it in the thickness direction; wherein the ablation threshold of the barrier layer for the laser used to process the through holes is 5 to 10 times that of the shielding layer for the laser.

[0006] In one embodiment, the thickness of the barrier layer in the thickness direction of the electromagnetic shielding film is not less than 0.2 μm and not more than 1 μm.

[0007] In one embodiment, a functional layer is further included, which is disposed on one side of the shielding layer; wherein the surface of the functional layer near the shielding layer is treated to form the barrier layer, and the untreated portion of the functional layer forms the insulating layer.

[0008] In one embodiment, the thickness of the functional layer in the thickness direction of the electromagnetic shielding film is not less than 3 μm and not more than 10 μm.

[0009] In one embodiment, the arithmetic mean deviation of the profile of the barrier layer on the side facing the shielding layer satisfies: 1μm≤Ra≤3μm.

[0010] In one embodiment, in a sliced ​​state along the thickness direction, the height difference H between the highest point of the protrusion and the lowest point of the depression on the surface of the barrier layer facing the shielding layer is: 2μm≤H≤5μm.

[0011] In one embodiment, the diameter of the through hole is not less than 10 μm and not more than 30 μm.

[0012] In one embodiment, the spacing between two adjacent through holes is not less than 30 μm and not more than 100 μm.

[0013] In one embodiment, the electromagnetic shielding film further includes an adhesive film layer, which is stacked on the side of the shielding layer facing away from the barrier layer. The surface of the shielding layer facing the adhesive film layer is provided with a plurality of protrusions. In the thickness direction of the electromagnetic shielding film, the height of the protrusions is not less than 2 μm and not more than 20 μm, and the thickness of the adhesive film layer is not less than 2 μm and not more than 20 μm.

[0014] Based on the electromagnetic shielding film of this application, by adding a barrier layer between the shielding layer and the insulating layer, and the ablation threshold of the barrier layer for the laser used to process the through hole in the shielding layer is 5 to 10 times that of the shielding layer for the laser, the barrier layer, with its significantly higher ablation threshold than the shielding layer, can absorb the remaining energy after the laser penetrates the shielding layer, thereby reducing the absorption of laser energy by the surface of the insulating layer after drilling the shielding layer. This solves the problem of the insulating layer being broken down due to excess energy during laser drilling, and is beneficial to improving the insulation reliability of the shielding film. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the electromagnetic shielding film in some embodiments of this application.

[0016] Figure 2 This is a schematic diagram of the structure of the electromagnetic shielding film in some other embodiments of this application.

[0017] Figure 3 This is a schematic diagram of the structure of the electromagnetic shielding film in some embodiments of this application.

[0018] Explanation of reference numerals in the attached figures:

[0019] 1. Electromagnetic shielding film; 10. Insulating layer; 20. Barrier layer; 30. Shielding layer; 31. Through hole; 32. Raised structure; 40. Adhesive film layer; 50. Protective layer; 60. Carrier layer. Detailed Implementation

[0020] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0021] In the description of this application, it should be understood that if terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" appear, these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0022] Furthermore, where the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, where the term "multiple" appears, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0023] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; 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; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0024] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0025] It should be noted that if an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. If so, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application are for illustrative purposes only and do not represent the only possible implementation.

[0026] With the rapid development of 5G communication and millimeter-wave radar technology, electromagnetic shielding films are widely used to cover electronic components and circuit boards to reduce electromagnetic interference. Electromagnetic shielding films consist of an insulating layer, a shielding layer, and an adhesive film layer. The surface of the shielding layer is roughened to create raised bumps, which are used to pierce the adhesive film layer during hot pressing, thereby making contact with the grounding pads of the circuit board to form a conductive path. During the hot pressing process, air can easily be trapped between the film layers, and thermal expansion often leads to defects such as board bursting or delamination. Related technologies typically use lasers to process a perforated array of micropores through the shielding layer, allowing volatiles and residual gases to escape, thus mitigating the risk of board bursting.

[0027] However, during laser drilling, due to the thinness of the shielding layer, excess energy can easily be generated during drilling, leading to the breakdown of the insulation layer. This results in a significant reduction in the surface insulation resistance of the electromagnetic shielding film and poor insulation performance.

[0028] Based on this, please refer to Figure 1 This application provides an electromagnetic shielding film 1, which includes an insulating layer 10, a barrier layer 20 and a shielding layer 30 stacked sequentially.

[0029] The insulating layer 10 can be formed by blending insulating materials such as epoxy resin, acrylic resin, polyester resin, polyethylene terephthalate (PET), and polyimide (PI) with ink, rubber, inorganic fillers, and organic fillers. The insulating layer 10 is disposed on one side surface of the shielding layer 30 to provide physical protection for the shielding layer 30 and prevent scratches, oxidation, or abrasions.

[0030] The shielding layer 30 is made of conductive material and is used to reflect and absorb electromagnetic waves to achieve electromagnetic shielding effectiveness. Conductive materials include, but are not limited to, any one of the following metals: aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, or an alloy composed of any two or more of these metals. The shielding layer 30 has multiple through-holes 31 extending through its thickness. These through-holes 31 provide gas venting channels during the lamination process between the electromagnetic shielding film 1 and the circuit board, preventing defects such as board bursting or delamination.

[0031] The barrier layer 20 is disposed between the shielding layer 30 and the insulating layer 10. The ablation threshold of the barrier layer 20 on the laser used to process the through hole 31 is 5 to 10 times that of the shielding layer 30 on the laser.

[0032] It should be noted that the laser ablation threshold (usually referring to the single-pulse ablation threshold) of the barrier layer 20 is defined as the minimum incident laser energy density required to cause irreversible removal (including vaporization, decomposition, or peeling) of the material surface, expressed in J / cm². It is a core indicator for evaluating a material's resistance to laser processing. As an example, in a 355nm nanosecond ultraviolet laser drilling scenario, the industry-standard testing method for this ablation threshold is the D²-lnE fitting method (i.e., the Liu method). This method involves measuring the square of the ablation spot diameter at different laser energy densities and linearly fitting it to the natural logarithm of the energy density to obtain the intrinsic ablation threshold of the material.

[0033] During the laser drilling process, the laser is incident from one side of the shielding layer 30. After absorbing the laser energy, the shielding layer 30 melts, vaporizes, and is removed, thereby achieving penetration of the shielding layer 30 to form a through hole 31. When the laser reaches the barrier layer 20, since the ablation threshold of the barrier layer 20 is higher than that of the shielding layer 30, the remaining laser energy is lower than the ablation threshold of the barrier layer 20, and the barrier layer 20 is not ablated and removed, thereby avoiding damage to the insulating layer 10.

[0034] This application sets the ablation threshold of the barrier layer 20 to 5 to 10 times that of the shielding layer 30, so that there is a sufficient ablation energy window between the shielding layer 30 and the barrier layer 20. This ensures that the shielding layer 30 can be effectively penetrated to form the through hole 31, while also ensuring that the barrier layer 20 is not ablated after the laser penetrates the shielding layer 30. Thus, while achieving the formation of the exhaust through hole 31, the insulation reliability of the electromagnetic shielding film 1 is effectively guaranteed.

[0035] Specifically, if the ablation threshold of the barrier layer 20 is less than five times that of the shielding layer 30, the ablation energy window between them is too narrow. Under the influence of factors such as laser power fluctuations or uneven thickness of the shielding layer 30, the remaining laser energy may exceed the ablation threshold of the barrier layer 20, potentially causing the insulating layer 10 to be accidentally broken down. If the ablation threshold of the barrier layer 20 is more than ten times that of the shielding layer 30, then ultra-high ablation-resistant materials such as diamond-like carbon (DLC), high-density aluminum nitride, and special perfluorinated resins must be selected. The preparation process of these materials is complex, and the deposition rate is low, making it difficult to meet the economic requirements of mass production. At the same time, these materials are usually chemically inert and have low surface energy, resulting in weak bonding between them and the adjacent metal shielding layer 30 and insulating layer 10. During mass production, film lifting or interface delamination is likely to occur, and the risk of failure is high after multiple bending and high and low temperature cycling reliability tests. Therefore, limiting the ratio of the ablation threshold of the barrier layer 20 to the ablation threshold of the shielding layer 30 to between 5 and 10 times ensures effective protection of the insulation layer 10 by the barrier layer 20 while also taking into account the feasibility of mass production and product reliability.

[0036] Based on the aforementioned ablation threshold of the barrier layer 20 being 5 to 10 times that of the shielding layer 30, the material of the barrier layer 20 can be selected from self-modified polyimide, inorganic silicon nitride, inorganic alumina, cross-linked resin formed by hydrolysis and condensation with a silane coupling agent, etc. Among them, materials such as modified polyimide or silicon nitride rely on breaking high-bond-energy covalent bonds such as CC bonds, CN bonds, or Si-N bonds to achieve decomposition. The energy required for ablation per unit volume is much higher than that of metal materials, and their intrinsic ablation threshold can typically reach 1.0 J / cm² to 3.0 J / cm². In contrast, the intrinsic ablation threshold of the copper metal shielding layer 30 under 355nm nanosecond laser is only about 0.2 J / cm² to 0.6 J / cm². The ratio between the two falls exactly within the range of 5 to 10 times, which can meet the design requirements of this application for the ablation threshold multiple. At the same time, the above materials have good film-forming properties and interface compatibility, and are suitable for roll-to-roll continuous production processes.

[0037] Specifically, the modified polyimide can be any one of the following: a polyimide containing an ortho-hydroxybenzophenone structure, or a polyimide doped with boron nitride and aluminum nitride.

[0038] In polyimides containing an ortho-hydroxy benzophenone structure, an intramolecular hydrogen bond is formed between the ortho-hydroxy group and the carbonyl group of benzophenone. After absorbing ultraviolet light, this structure can rapidly dissipate the excited state energy in a non-radiative manner through keto-enol tautomerism, thereby reducing the accumulation of light energy converted into heat energy and delaying the material from reaching the temperature threshold for ablation removal. Therefore, its ablation threshold is relatively higher.

[0039] In polyimides doped with boron nitride and aluminum nitride, boron nitride and aluminum nitride themselves have high thermal conductivity, which can rapidly conduct and diffuse the local heat generated by laser irradiation along the in-plane direction, reduce the degree of heat accumulation per unit volume, and thus improve the material's ability to withstand laser irradiation, which is manifested as an increase in the ablation threshold.

[0040] Based on the electromagnetic shielding film 1 of this application embodiment, by adding a barrier layer 20 between the shielding layer 30 and the insulating layer 10, and the ablation threshold of the barrier layer 20 for the laser used to process the through hole 31 in the shielding layer 30 is 5 to 10 times that of the shielding layer 30 for the laser, the barrier layer 20, due to its higher laser ablation threshold than the shielding layer 30, can quickly absorb the remaining energy and terminate the etching process after the laser penetrates the shielding layer 30, thereby reducing the absorption of laser energy by the surface of the insulating layer 10 after drilling the shielding layer 30, solving the problem of the insulating layer 10 being broken down due to excess energy during laser drilling, and improving the insulation reliability of the shielding film.

[0041] In some embodiments, the thickness of the barrier layer 20 in the thickness direction of the electromagnetic shielding film 1 is not less than 0.2 μm and not more than 1 μm. Within this thickness range, the barrier layer 20 can effectively block residual laser energy and protect the insulating layer 10 from being broken down, provided that the above-mentioned ablation threshold multiple relationship is met. At the same time, this thickness setting is beneficial to controlling the overall thickness of the electromagnetic shielding film 1, avoiding an increase in the bending stiffness of the film layer due to excessive thickness of the barrier layer 20, thereby ensuring the bending adaptability and flexible processing performance of the electromagnetic shielding film 1 in flexible circuit board applications.

[0042] In some embodiments, the barrier layer 20 is prepared by one of slot coating curing, chemical vapor deposition, plasma-enhanced chemical vapor deposition, magnetron sputtering, and plasma polymerization. All of these methods can form a barrier layer 20 with a high ablation threshold on the surface of the insulating layer 10 facing the shielding layer 30, and each method has good process compatibility and thickness controllability, allowing selection based on actual mass production needs and material systems.

[0043] In some embodiments, the electromagnetic shielding film 1 further includes a functional layer disposed on one side of the shielding layer 30. The surface of the functional layer near the shielding layer 30 is treated to form a barrier layer 20, while the untreated portion of the functional layer forms an insulating layer 10. In this example, the functional layer can be formed by blending and compounding with any one or more insulating resin materials such as epoxy resin, acrylic resin, polyester resin, polyethylene terephthalate (PET), and polyimide (PI) with additives such as ink, rubber, inorganic fillers, and organic fillers. The barrier layer 20 is formed by in-situ modification of the surface of the functional layer facing the shielding layer 30, while the unmodified portion of the functional layer forms the insulating layer 10. That is, the barrier layer 20 and the insulating layer 10 are integrally formed from the same functional layer through surface modification, and there is no independent interface between them, which is beneficial for improving the bonding strength between the film layers and simplifying the manufacturing process.

[0044] Optionally, in-situ modification treatment includes, but is not limited to, at least one of low-energy ion implantation, ultraviolet cross-linking curing, and nano-inorganic particle doping. As an example, fluorine ion implantation can be used to modify the surface of the polyimide functional layer to improve its resistance to ultraviolet lasers; or deep ultraviolet cross-linking can be used to treat the surface of the epoxy resin functional layer to improve its surface density and laser energy reflection capability. All of the above modification methods can increase the ablation threshold of the functional layer surface material, enabling it to meet the multiple requirements of the ablation threshold of the barrier layer 20 in this application, while maintaining the integrated structure with the underlying unmodified insulating layer 10.

[0045] In some embodiments, the in-situ modification treatment is performed to a depth of 1 μm. At this depth, the resulting barrier layer 20 has sufficient thickness to provide effective laser protection without excessively occupying the overall thickness of the functional layer, thereby effectively improving the insulation and mechanical properties of the unmodified portion of the functional layer, i.e., the insulating layer 10.

[0046] In some embodiments, the arithmetic mean deviation of the profile of the barrier layer 20 toward the shielding layer 30 satisfies: 1μm≤Ra≤3μm.

[0047] It should be noted that the profile arithmetic mean deviation (Ra) refers to the arithmetic mean of the absolute values ​​of the deviations of each point on the measured surface profile from the baseline (centerline) within the sampling length. Its unit is micrometer (μm), and it is used to quantify the micro-roughness of the surface of the barrier layer 20 facing the shielding layer 30.

[0048] In the electromagnetic shielding film 1 of this application, the shielding layer 30 is formed on the surface of the barrier layer 20 by electroplating or chemical deposition. Therefore, the surface microstructure of the barrier layer 20 facing the shielding layer 30 is transferred to the surface of the shielding layer 30 through conformal growth. By limiting the arithmetic mean deviation Ra of the profile of the barrier layer 20 on this side to a range of not less than 1 μm and not more than 3 μm, it is beneficial to ensure that the surface of the conformally formed shielding layer 30 has a suitable roughness base, thereby providing favorable conditions for subsequent roughening treatment to form an effective protrusion structure 32, and thus ensuring the grounding conductivity between the electromagnetic shielding film 1 and the grounding pad of the circuit board.

[0049] In some embodiments, in a sliced ​​state along the thickness direction, the height difference H between the highest point of the protrusion and the lowest point of the depression on the surface of the barrier layer 20 facing the shielding layer 30 is: 2μm≤H≤5μm.

[0050] It should be noted that the height difference H is the maximum peak-valley height of the microscopic profile of the barrier layer 20 surface, which characterizes the degree of undulation of the surface in the vertical direction.

[0051] In the electromagnetic shielding film 1 of this application, the shielding layer 30 is typically formed on the surface of the barrier layer 20 facing the shielding layer 30 by electroplating or chemical deposition. Therefore, the microscopic profile of the barrier layer 20's surface on this side is transferred to the surface of the shielding layer 30 through conformal growth. If the height difference H is less than 2 μm, the surface of the barrier layer 20 is too flat, and the surface of the shielding layer 30 formed by subsequent electroplating will lack sufficient microscopic undulations. This makes it difficult to form a raised structure 32 with sufficient height and sharp tip during subsequent roughening, thus affecting the ability of the raised structure 32 to pierce the adhesive film layer 40 and form reliable electrical contact with the circuit board grounding layer during hot pressing. This application, by setting the height difference H to not less than 2 μm, ensures that the surface of the shielding layer 30 after reshaping has suitable initial roughness, providing the necessary structural basis for subsequent roughening, thereby facilitating the formation of a raised structure 32 with sufficient piercing capability and ensuring reliable grounding conductivity.

[0052] If the height difference H is greater than 5 μm, the surface of the barrier layer 20 will have severely undulating protrusions and depressions. When the laser drills through the shielding layer 30, the incident residual laser will undergo multiple diffuse reflections at such steep microstructures, making the scattering path of the light more complex. This leads to a decrease in the total hemispherical reflectivity and an increase in the actual laser energy absorbed by the surface, thereby increasing the risk of the insulating layer 10 being broken down. In addition, the excessive peaks and valleys on the surface of the barrier layer 20 can also easily cause uneven local thickness distribution of the shielding layer 30 during the electroplating process, affecting the structural uniformity and overall conductivity reliability of the shielding layer 30.

[0053] In summary, this application controls the maximum peak-to-valley height difference H on the surface of the barrier layer 20 facing the shielding layer 30 within the range of 2μm to 5μm. This ensures that the shielding layer 30, after being reshaped, has sufficient microscopic undulations to form an effective protrusion structure 32, which is beneficial for subsequent roughening piercing and grounding functions. Simultaneously, within this range, the surface of the barrier layer 20 does not have extreme peaks or deep valleys. After laser irradiation reaches the surface of the barrier layer 20, it is mainly a single reflection, and the total hemispherical reflectivity remains at a high level, thereby effectively reducing the absorption rate of laser energy on the surface of the barrier layer 20 and preventing the insulation layer 10 from being broken down. Therefore, this application achieves a good balance between grounding reliability and laser drilling safety.

[0054] It is worth noting that laser processing energy is also one of the key parameters affecting whether the insulating layer 10 is broken down. When laser drilling is performed on the shielding layer 30, the total volume of the through hole 31 determines the amount of material to be removed, which in turn affects the total laser energy input required. Specifically, the larger the total volume of the through hole 31, the more material needs to be removed, the higher the corresponding laser energy requirement, and the higher the risk of the insulating layer 10 being damaged due to the absorption of residual energy. Based on this, the geometric parameters of the through hole 31 have been further optimized in this embodiment.

[0055] In some embodiments, the aperture D of the through-hole 31 is not less than 10 μm and not more than 30 μm. Specifically, the aperture of the through-hole 31 can be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, etc. It is understood that if the aperture of the through-hole 31 is less than 10 μm, the exhaust cross-section of a single through-hole 31 is insufficient, and gas cannot pass smoothly during the hot pressing process. This can easily lead to micropore blockage or exhaust delay due to poor exhaust, weakening its actual effect in mitigating the risk of board explosion. If the aperture of the through-hole 31 is greater than 30 μm, the amount of material removed from a single through-hole 31 increases significantly, which means that the laser energy required for single-hole forming increases, and the heat conducted from the shielding layer 30 to the insulating layer 10 increases accordingly, thus increasing the risk of breakdown.

[0056] In some embodiments, the spacing between two adjacent through holes 31 is not less than 30 μm and not more than 100 μm. It should be noted that the spacing between two adjacent through holes 31 refers to the shortest distance between the edges of the two through holes 31. Specifically, this spacing can be 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm. Specifically, if the spacing between two adjacent through holes 31 is less than 30 μm, the bridging area of ​​the shielding material between adjacent through holes 31 is too narrow, resulting in too many through holes 31 per unit area. During the drilling process, the laser heat-affected zones are prone to overlap, generating a heat accumulation effect, leading to a significant increase in local temperature and increasing the risk of the insulation layer 10 being burned through. Simultaneously, the excessively narrow material bridging area weakens the local mechanical strength of the shielding layer 30, making it prone to cracks or even breakage during subsequent bending or hot pressing, affecting the structural reliability of the product. If the spacing between two adjacent through holes 31 is greater than 100 μm, the through holes 31 are sparsely distributed, reducing exhaust efficiency.

[0057] Based on the above embodiments, by limiting the aperture D of the through hole 31 to 10μm to 30μm and the edge spacing of adjacent through holes 31 to 30μm to 100μm, it is possible to reduce the total laser energy input required for drilling while ensuring the exhaust effect and meeting the requirements of the explosion-proof plate, thereby mitigating the thermal impact of the drilling process on the insulating layer 10 from the source.

[0058] Please see Figure 2 In some embodiments, the electromagnetic shielding film 11 further includes an adhesive film layer 40 laminated on the first surface of the shielding layer 30. The material used for the adhesive film layer 40 is selected from at least one of the following groups: modified epoxy resin, acrylic resin, modified rubber, and modified thermoplastic polyimide. The above material system has slight tackiness at room temperature, facilitating pre-positioning bonding between the electromagnetic shielding film 11 and the circuit board, reducing the difficulty of the mounting operation. Simultaneously, this type of material can soften under hot pressing conditions and undergo viscous flow, fully wetting the microstructure of the circuit board surface, and forming a strong adhesive interface after curing, ensuring the long-term reliability of the bond between the shielding film and the circuit board.

[0059] In some embodiments, the height of the raised structure 32 is not less than 2 μm and not more than 20 μm in the thickness direction of the electromagnetic shielding film 11, and the thickness of the adhesive film layer 40 is not less than 2 μm and not more than 20 μm. Specifically, if the thickness of the adhesive film layer 40 is less than 2 μm, it is easy to lead to insufficient bonding strength and difficulty in providing reliable interfacial bonding force; if the thickness of the adhesive film layer 40 is greater than 20 μm, it increases the thickness of the adhesive film layer 40 that the raised structure 32 needs to penetrate, and may not be able to effectively contact the grounding pad due to insufficient piercing stroke. At the same time, the height of the raised structure 32 needs to be adapted to the thickness of the adhesive film layer 40 to ensure that the raised structure 32 can completely penetrate the adhesive film layer 40 and form reliable contact with the grounding pad of the circuit board during the hot pressing process.

[0060] Please see Figure 3 Furthermore, in some embodiments, the electromagnetic shielding film 11 further includes a protective layer 50, which is disposed on the surface of the adhesive film layer 40 away from the shielding layer 30. The protective layer 50 is used to protect the adhesive film layer 40 during the winding and transportation of the electromagnetic shielding film 11, preventing the adhesive film layer 40 from being contaminated or damaged. In use, after peeling off the protective layer 50, the electromagnetic shielding film 11 is pressed onto the surface of the circuit board.

[0061] As an example, this application provides a method for preparing the electromagnetic shielding film 11 described above, which specifically includes the following steps:

[0062] S1: Provides a carrier layer of 60;

[0063] The carrier layer 60 can be a release film. Specifically, the release film is a polyester film (PET) or polypropylene film (PP) treated with silicone oil or fluorine, used to carry the functional layers in subsequent processes and to be easily peeled off when the finished product is used.

[0064] S2: Prepare insulating layer 10;

[0065] An insulating layer 10 is formed on the release film through a coating process. An insulating adhesive is prepared by blending insulating substrates such as polyethylene terephthalate (PET) and polyimide (PI) with black ink, and then uniformly coated onto the surface of the carrier layer 60. After drying and curing, the insulating layer 10 is formed. The thickness of the insulating layer 10 is controlled between 3 μm and 10 μm.

[0066] S3: Prepare barrier layer 20;

[0067] A barrier layer 20 is formed on the surface of the insulating layer 10 away from the carrier layer 60. Specifically, the barrier layer 20 can be formed in any of the following ways:

[0068] Method 1: The surface of the insulating layer 10 is treated with an in-situ modification method to transform the surface layer into a barrier layer 20. The in-situ modification treatment includes, but is not limited to, at least one of low-energy ion implantation, ultraviolet cross-linking curing, and nano-inorganic particle doping. After the in-situ modification treatment, the surface layer of the insulating layer 10 is transformed into the barrier layer 20, and its ablation threshold is increased to meet the requirement of the present application for a multiple of the ablation threshold of the barrier layer 20; the unmodified portion of the insulating layer 10 retains its original insulating properties. Preferably, the depth of the in-situ modification treatment is 1 μm.

[0069] Method 2: A barrier layer 20 is formed on the surface of the insulating layer 10 away from the carrier layer 50 by coating. Specifically, the barrier layer material is prepared into a coating liquid and uniformly coated onto the surface of the insulating layer 10 by methods such as slot coating, doctor blade coating, or roller coating. After curing, the barrier layer 20 is formed. The barrier layer material includes, but is not limited to, any one of modified polyimide, silicon nitride, and alumina. The curing method is selected from thermosetting or ultraviolet curing depending on the material system.

[0070] Both of the above methods can form a barrier layer 20 with a high ablation threshold on the side of the insulating layer 10 facing the shielding layer, and have good process compatibility and thickness controllability, which can be selected according to mass production requirements and material system.

[0071] S4: Prepare shielding layer 30;

[0072] A shielding layer 30 is prepared on the surface of the barrier layer 2020 away from the insulating layer 10. Specifically, a conductive seed layer is deposited on the surface of the insulating layer 10 by physical vapor deposition (PVD) sputtering. The seed layer is made of copper or a copper-nickel alloy and serves as a conductive substrate for subsequent electroplating. Then, a deposited metal layer is thickened on the seed layer by electroplating. The electroplating material is copper or a copper alloy containing one or more alloying elements selected from nickel, tin, and chromium. After electroplating, the thickness of the shielding layer 30 is controlled between 1 μm and 6 μm. In other embodiments, rolled copper foil or electrolytic copper foil can also be directly adhered to the surface of the insulating layer 10 by hot pressing or bonding to form the shielding layer 30.

[0073] Subsequently, the exposed surface of the shielding layer 30 is subjected to a micro-roughening treatment to form a grounding protrusion structure 32. Specifically, the protrusion structure 32 is formed on the first surface by chemical etching, mechanical polishing, electroplating nodules, or laser etching. The protrusion structure 32 can be a micro-bump, a ridge, or a pointed cone, with a height of 2μm to 20μm.

[0074] S5: Machining through hole 31;

[0075] Multiple through holes 31 are fabricated on the shielding layer 30 using ultraviolet or infrared lasers. Specifically, a 355nm ultraviolet nanosecond laser can be used to drill holes in the shielding layer 30. The diameter D of the first through hole 31 is controlled between 10μm and 30μm, and the spacing between the edges of two adjacent through holes 31 is controlled between 30μm and 100μm.

[0076] S6: Prepare adhesive film layer 40;

[0077] An adhesive is applied to the surface of the perforated shielding layer 30, and then pre-cured to form an adhesive film layer 40. The adhesive can be a modified epoxy resin, acrylic resin, modified rubber resin, or modified thermoplastic polyimide resin.

[0078] S7: Post-baking curing and slitting;

[0079] The finished product is then baked and cured to achieve the required degree of cross-linking of the adhesive film layer (40%). Finally, it is cut into specified widths to obtain the finished electromagnetic shielding film 11.

[0080] To verify the grounding reliability of the electromagnetic shielding film 11 provided in the above embodiments of this application, the following experimental data are also provided. It should be noted that the following experimental data are merely exemplary verification results of various embodiments of this application and are not intended to limit the scope of protection of this application in any way.

[0081] Multiple samples of the same batch of coated wafers were drilled under uniform laser energy parameters. After drilling, the samples were sliced, and the cross-sectional morphology of the slices was observed using a scanning electron microscope.

[0082] Evaluation criteria: Observe and record whether there are signs of damage such as breakdown, carbonization or cracking at the corresponding holes on the 10 sides of the insulation layer.

[0083] The laser-drilled sheet is further coated with an adhesive film layer 40 to form the finished electromagnetic shielding film 11; then the finished film is pressed onto the FPC grounding pad with the following pressing parameters: temperature 180℃, pressure 3MPa, and time 60s.

[0084] The samples after lamination were subjected to thermal shock testing. The test conditions were as follows: the samples were placed in a tin bath at 260℃ for tin immersion test, each immersion lasted 10 seconds, and the immersion was repeated 3 times.

[0085] Evaluation metric: Observe whether bubbles form on the surface of the insulation layer.

[0086]

[0087] Among them, Comparative Example 1 is an electromagnetic shielding film 1 without a barrier layer 20; Comparative Example 2 is an electromagnetic shielding film 1 with a barrier layer 20 ablation threshold multiple exceeding 10 times; Comparative Example 3 is an electromagnetic shielding film 1 with a barrier layer 20 ablation threshold multiple less than 5 times; Examples 1 and 2 are electromagnetic shielding films 1 of the present application, and their barrier layer 20 ablation threshold multiples all fall within the range of 5 times to 10 times.

[0088] The data in the table above shows that:

[0089] In Comparative Example 1, no barrier layer 20 was provided between the insulating layer 10 and the shielding layer 30. After laser drilling, the sections were observed under an electron microscope, and the breakdown rate of the holes was statistically analyzed. The breakdown rate of the insulating layer 10 was high, reaching over 92%. This indicates that in the absence of the barrier layer 20, the residual energy of the laser after penetrating the shielding layer 30 directly acts on the insulating layer 10, resulting in large-area damage to the insulating layer 10.

[0090] In Comparative Example 2, a barrier layer 20 is provided between the insulating layer 10 and the shielding layer 30, and the ablation threshold of this barrier layer 20 is 13 times that of the metal layer. After laser drilling, the breakdown rate of the insulating layer 10 is low, less than 10%, indicating that the excessively high ablation threshold can indeed effectively block residual laser energy. However, after thermal shock testing, blistering occurred on the surface of the insulating layer 10. Cross-sectional observation showed that the blistering was due to local separation between the insulating layer 10 and the shielding layer 30, resulting in localized bonding abnormalities. The reason for this is that the excessively high ablation threshold means that the material of the barrier layer 20 must have extremely high heat resistance and chemical inertness. Such materials have weak interfacial bonding with the adjacent shielding layer 30 and insulating layer 10, leading to interlayer separation after thermal shock. This results in a high risk of delamination in repeated bending or high-temperature applications.

[0091] In Comparative Example 3, a barrier layer 20 is provided between the insulating layer 10 and the shielding layer 30, but the ablation threshold of this barrier layer 20 is three times that of the metal layer. After laser drilling, the breakdown rate of the insulating layer 10 is high, exceeding 60%, indicating that when the ablation threshold is too low, the barrier layer 20 cannot effectively block the residual laser energy after penetrating the shielding layer 30, and the insulating layer 10 still faces a high risk of breakdown. However, due to its low ablation threshold, the interfacial bonding force between the barrier layer 20 material and the adjacent layers is good, and no blistering of the insulating layer 10 occurs after the thermal shock test.

[0092] In Examples 1 and 2, a barrier layer 20 is provided between the insulating layer 10 and the shielding layer 30, and the ablation threshold of the barrier layer 20 is 6 and 9 times that of the metal layer, respectively, falling within the range of 5 to 10 times. After laser drilling, the breakdown rate of the insulating layer 10 in each example is low, less than 18% and 15%, respectively; at the same time, no blistering of the insulating layer 10 occurred after thermal shock, indicating that the interlayer bonding is good and can meet the requirements for normal use. This shows that within this range, the barrier layer 20 can effectively block residual laser energy to protect the insulating layer 10, and can also maintain good interfacial bonding with adjacent layers, ensuring the stability of the interfacial interface after thermal shock.

[0093] In summary, this application provides a barrier layer 20 between the insulating layer 10 and the shielding layer 30, and limits the ablation threshold of the barrier layer 20 to 5 to 10 times that of the metal layer. This effectively blocks the residual laser energy after it penetrates the shielding layer 30 during laser drilling, reduces the absorption of laser energy by the insulating layer 10, reduces the probability of the insulating layer 10 being broken down, and ensures the insulation performance of the shielding film. At the same time, this multiple range is conducive to the formation of a stable interface bond between the barrier layer 20 and the adjacent layers, avoiding interface separation phenomena such as blistering of the insulating layer 10 after thermal shock, and improving the interlayer bonding stability and reliability of the electromagnetic shielding film 1 after thermal shock.

[0094] Secondly, embodiments of this application also provide a circuit board, including a circuit board body and an electromagnetic shielding film 1 as described in any of the above embodiments. The circuit board includes a substrate layer, a ground layer disposed on one surface of the substrate layer, and a cover layer covering the ground layer and the surface of the substrate layer. The substrate layer includes a support structure and a circuit structure disposed on the surface of the support structure. The support structure provides mechanical support, and the circuit structure enables the transmission and connection of electrical signals. The ground layer is electrically connected to the grounding line in the circuit structure to provide a grounding potential. The cover layer covers the ground layer and the surface of the substrate layer, and the cover layer has a window to at least partially expose the ground layer, allowing the protrusion structure 32 of the electromagnetic shielding film 1 to penetrate and form an electrical connection with the ground layer. Because the circuit board is provided with the aforementioned electromagnetic shielding film 1, it has at least the aforementioned beneficial effects, which will not be elaborated further here.

[0095] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0096] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An electromagnetic shielding film, characterized in that, It includes an insulating layer, a barrier layer, and a shielding layer stacked sequentially; the shielding layer has multiple through holes extending through the thickness direction. Wherein, the ablation threshold of the barrier layer for the laser used to process the through hole is 5 to 10 times that of the shielding layer for the laser.

2. The electromagnetic shielding film according to claim 1, characterized in that, In the thickness direction of the electromagnetic shielding film, the thickness of the barrier layer is not less than 0.2 μm and not greater than 1 μm.

3. The electromagnetic shielding film according to claim 1, characterized in that, It includes a functional layer, which is disposed on one side of the shielding layer; The surface of the functional layer near the shielding layer is treated to form the barrier layer, and the untreated portion of the functional layer forms the insulating layer.

4. The electromagnetic shielding film according to claim 3, characterized in that, In the thickness direction of the electromagnetic shielding film, the thickness of the functional layer is not less than 3 μm and not more than 10 μm.

5. The electromagnetic shielding film according to claim 1, characterized in that, The arithmetic mean deviation of the profile of the barrier layer on the side facing the shielding layer satisfies: 1μm≤Ra≤3μm.

6. The electromagnetic shielding film according to claim 1, characterized in that, In the sliced ​​state along the thickness direction, the height difference H between the highest point of the protrusion and the lowest point of the depression on the surface of the barrier layer facing the shielding layer is: 2μm≤H≤5μm.

7. The electromagnetic shielding film according to claim 1, characterized in that, The diameter of the through hole is not less than 10 μm and not more than 30 μm.

8. The electromagnetic shielding film according to claim 1, characterized in that, The distance between two adjacent through holes shall be no less than 30 μm and no more than 100 μm.

9. The electromagnetic shielding film according to claim 1, characterized in that, The electromagnetic shielding film also includes an adhesive film layer, which is stacked on the side of the shielding layer facing away from the barrier layer, and the surface of the shielding layer facing the adhesive film layer is provided with a plurality of protrusion structures. In the thickness direction of the electromagnetic shielding film, the height of the raised structure is not less than 2μm and not more than 20μm, and the thickness of the adhesive film layer is not less than 2μm and not more than 20μm.

10. A circuit board, characterized in that, include: Circuit board body; as well as The electromagnetic shielding film as described in any one of claims 1 to 9; The electromagnetic shielding film is pressed onto the circuit board body, and the shielding layer is electrically connected to the grounding layer of the circuit board body.

Images