Electromagnetic shielding film and circuit board

Abstract

This invention discloses an electromagnetic shielding film and a circuit board. The electromagnetic shielding film comprises an insulating layer, a shielding layer, and an adhesive film layer stacked sequentially. The insulating layer includes a mask layer and a background layer. The mask layer comprises a photobleaching material having a first color; the background layer has a second color. The lightness value of the first color is lower than that of the second color, and the difference between the lightness values ​​of the first and second colors is greater than or equal to 30. The surface of the mask layer is selectively irradiated by a light source, causing irreversible photodecomposition of the photobleaching material in the irradiated area, exposing the second color of the background layer, thus forming a distinctive identification code on the mask layer that contrasts sharply with the surrounding unirradiated areas. This invention designs the insulating layer to include a background layer and a mask layer of different colors, thereby forming a distinctive identification code on the mask layer, improving the problem that laser lithography easily penetrates the shielding layer, affecting shielding effectiveness and resulting in low identification accuracy.

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] Modern electronic and communication equipment is susceptible to electromagnetic interference during signal transmission, which can affect transmission quality. Therefore, an electromagnetic shielding film is typically applied to the circuit boards inside electronic devices to shield against electromagnetic interference from both inside and outside the components, thereby ensuring the quality of signal transmission.

[0003] To facilitate product quality traceability, QR codes, text, numbers, or symbols are typically printed on the surface of the electromagnetic shielding film on circuit boards. Currently, laser engraving is commonly used to create a cutout pattern of the identification code on the insulating protective layer of the electromagnetic shielding film, and color contrast is used to display the code. However, the insulating protective layer is easily penetrated by the laser engraving process, exposing or even damaging the shielding layer. This severely affects the display effect of the identification code on the electromagnetic shielding film, making it difficult to guarantee the recognition accuracy of the code. Furthermore, damage to the shielding layer also affects the shielding effectiveness of the electromagnetic shielding film. Summary of the Invention

[0004] The purpose of this invention is to provide an electromagnetic shielding film and circuit board. The insulating layer is designed to include a background layer and a mask layer of different colors, and the brightness of the mask layer is lower than that of the background layer. When the mask layer is illuminated by a light source, the photobleaching material of the mask layer undergoes photodecomposition, revealing the color of the background layer underneath. This forms a color-contrast identification code on the mask layer, improving the problem that laser lithography can easily penetrate the shielding layer, affecting the shielding effectiveness and resulting in low identification accuracy.

[0005] To achieve the above objectives, embodiments of the present invention provide an electromagnetic shielding film, comprising an insulating layer, a shielding layer, and an adhesive film layer stacked sequentially. The insulating layer includes a mask layer and a background layer, wherein the mask layer is disposed on the side away from the shielding layer, and the background layer is disposed on the side close to the shielding layer; The mask layer includes a photobleaching material having a first color; the background layer has a second color; the lightness value of the first color is lower than the lightness value of the second color, and the difference between the lightness value of the first color and the lightness value of the second color is greater than or equal to 30. The surface of the mask layer is selectively irradiated by a light source, causing irreversible photobleaching material in the irradiated area to decompose, revealing the second color of the background layer, and forming an identification code on the mask layer that contrasts sharply with the color of the surrounding unirradiated area.

[0006] As an improvement to the above scheme, the reflectivity of the background layer in the visible light band is greater than 60%, and the reflectivity ratio of the unilluminated area of ​​the background layer to that of the mask layer is greater than 5:1.

[0007] As an improvement to the above scheme, the lightness value of the first color is less than or equal to 20, and the lightness value of the second color is greater than or equal to 70.

[0008] As an improvement to the above scheme, the photobleaching material is an azo compound or an anthraquinone derivative.

[0009] As an improvement to the above scheme, the thickness of the mask layer is 0.5 μm to 5 μm.

[0010] As an improvement to the above scheme, the thickness of the background layer is 1 μm to 10 μm.

[0011] As an improvement to the above scheme, the optical density of the mask layer in the initial state is greater than 2.

[0012] As an improvement to the above scheme, the arithmetic mean roughness of the light-irradiated surface of the mask layer is less than or equal to 0.1 μm.

[0013] As an improvement to the above scheme, the thickness uniformity deviation of the insulating layer is within ±3%, and the glass transition temperature of the insulating layer is not lower than 80°C.

[0014] This invention also provides a circuit board, including a printed circuit board and an electromagnetic shielding film as described in any of the above embodiments. The electromagnetic shielding film is bonded to the printed circuit board through an adhesive film layer, and the shielding layer of the electromagnetic shielding film has protrusions for piercing the adhesive film layer to make contact and conduction with the ground layer of the printed circuit board.

[0015] Compared with the prior art, the beneficial effects of the electromagnetic shielding film and circuit board provided by the embodiments of the present invention are as follows: the insulating layer is designed to include a mask layer and a background layer, wherein the mask layer includes a photobleaching material with a first color; the background layer has a second color; the lightness value of the first color is lower than the lightness value of the second color, and the difference between the lightness values ​​of the first color and the second color is greater than or equal to 30; the surface of the mask layer is selectively irradiated by a light source, so that the photobleaching material in the irradiated area undergoes irreversible photodecomposition, revealing the second color of the bottom background layer, thereby forming an identification code on the mask layer that contrasts sharply with the surrounding unirradiated area, thus improving the problem that laser lithography can easily penetrate the shielding layer, affecting the shielding effectiveness and resulting in low identification accuracy. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a preferred embodiment of an electromagnetic shielding film provided by the present invention; Figure 2 This is a schematic diagram of another preferred embodiment of an electromagnetic shielding film provided by the present invention; The reference numerals in the attached figures are as follows: 1. Insulating layer; 101. Mask layer; 102. Background layer; 2. Shielding layer; 3. Adhesive film layer; 4. Protective film. 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0019] 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.

[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 , Figure 1This is a schematic diagram of a preferred embodiment of an electromagnetic shielding film provided by the present invention. The embodiment of the present invention provides an electromagnetic shielding film comprising an insulating layer 1, a shielding layer 2, and an adhesive film layer 3 stacked sequentially. The insulating layer 1 includes a mask layer 101 and a background layer 102, the mask layer 101 being disposed on the side away from the shielding layer 2, and the background layer 102 being disposed on the side closer to the shielding layer 2. The mask layer 101 includes a photobleaching material and has a first color; the background layer 102 has a second color; the lightness value of the first color is lower than the lightness value of the second color, and the difference between the lightness value of the first color and the lightness value of the second color is greater than or equal to 30. The surface of the mask layer 101 is selectively irradiated by a light source, so that the photobleaching material in the irradiated area undergoes irreversible photodecomposition, revealing the second color of the background layer 102, and forming an identification code on the mask layer 101 that contrasts sharply with the color of the surrounding unirradiated area.

[0022] Specifically, in this embodiment of the invention, the insulating layer 1 includes a mask layer 101 and a background layer 102 of different colors. The mask layer 101 is disposed on the side away from the shielding layer 2, and the background layer 102 is disposed on one side of the shielding layer 2. The mask layer 101 includes a photobleaching material and has a first color; the background layer 102 has a second color. The lightness value of the first color of the mask layer is lower than the lightness value of the second color of the background layer, and the difference in lightness value between the two layers is greater than or equal to 30.

[0023] By selectively irradiating the surface of the mask layer 101 with a light source, the photobleaching material in the irradiated area undergoes irreversible photodecomposition, revealing the second color of the background layer 102, thus forming an identification code on the mask layer 101 with a color contrasting sharply with the surrounding unirradiated area. By controlling an external light source to irradiate the surface of the mask layer 101 according to a specific pattern trajectory, the photobleaching material in the irradiated area of ​​the mask layer 101 undergoes an irreversible photochemical reaction, revealing the second color in the underlying background layer 102, thereby forming an identification code pattern, such as a machine-readable QR code, on the mask layer 101 with a color contrasting sharply with the surrounding unirradiated area. This embodiment of the invention further limits the brightness difference between the two layers to greater than or equal to 30, which can effectively display a QR code with high contrast on the insulating layer.

[0024] It should be noted that the embodiments of the present invention use external light source irradiation, which has lower energy than laser irradiation, has no risk of breakdown, can effectively ensure shielding effectiveness, and the resulting identification code is clear and reliable.

[0025] In a preferred embodiment, the mask layer 101 of the present invention comprises a photobleaching material and a polymer matrix. In the mask layer 101, the photobleaching material accounts for 5% to 20% of the total solid mass, the polymer matrix accounts for 60% to 85% of the total solid mass, and other auxiliary additives are also included.

[0026] Furthermore, in the embodiments of the present invention, the photobleaching material must meet the following requirements: 1) It exhibits strong absorption at processing wavelengths (such as 365nm); 2) The photodecomposition reaction is highly efficient and thorough; 3) The decomposition products are colorless or very light in color; 4) Good compatibility with polymer matrix.

[0027] Therefore, in the embodiments of the present invention, the photobleaching material is preferably an azo compound or anthraquinone derivative, which undergoes irreversible photooxidation or photoreduction reactions under light to fade, has high photodecomposition efficiency, and the decomposition products are colorless.

[0028] It should be noted that azo compounds (AZO) are a class of organic compounds with an azo group (─N=N─) as the core structure, with the general formula R─N=N─R', where R and R' can be aliphatic or aromatic hydrocarbon groups. Azo compounds have cis and trans geometric isomers, with the trans isomer being more stable than the cis isomer. The two isomers can interconvert under light or heating conditions. Anthraquinone derivatives include anthraquinones and their products and dimers with different degrees of reduction, such as anthraquinones, oxyanthraquinones, anthrones, dianthraquinones, dianthraquinones, etc., as well as the glycosides of these compounds.

[0029] In this embodiment of the invention, the polymer matrix is ​​a film-forming material that carries all functional materials, and it must satisfy the following: 1) Good light transmittance (especially for processing wavelengths); 2) Strong bonding force with fillers; 3) Insulation after curing.

[0030] Therefore, in the embodiments of the present invention, the polymer matrix is ​​preferably epoxy resin, polyimide, acrylate resin, polyurethane, etc.

[0031] In this embodiment of the invention, when preparing the mask layer 101, the photobleaching material and the polymer matrix precursor are uniformly mixed to form a slurry. Dispersants, leveling agents, and other additives are also added to ensure uniform dispersion and thickness. The slurry is then coated and cured to form the mask layer 101. The polymer matrix precursor is the initial material used to prepare the polymer matrix, typically an organic polymer or a mixture thereof, which can be converted into the target material under specific conditions (such as high-temperature pyrolysis). The proportions of each component meet the aforementioned mixing ratio range.

[0032] For example, the mass percentage of the photobleaching material is 5%, the mass percentage of the polymer matrix is ​​85%, and the mass percentage of the auxiliary additives is 10%.

[0033] For example, the mass percentage of the photobleaching material is 10%, the mass percentage of the polymer matrix is ​​80%, and the mass percentage of the auxiliary additives is 10%.

[0034] For example, the mass percentage of the photobleaching material is 15%, the mass percentage of the polymer matrix is ​​70%, and the mass percentage of the auxiliary additives is 15%.

[0035] For example, the mass percentage of the photobleaching material is 20%, the mass percentage of the polymer matrix is ​​60%, and the mass percentage of the auxiliary additives is 20%.

[0036] It should be noted that if the mass percentage of the photobleaching material is less than 5%, the concentration is too low, resulting in insufficient absorption of visible light and affecting photodecomposition efficiency. Conversely, if the mass percentage of the photobleaching material is greater than 20%, the excess molecules may not be completely decomposed by a single light irradiation, leading to incomplete bleaching, uneven dispersion, or decomposition residues. This can cause the identification code area to appear grayish, resulting in poor QR code clarity and potentially increasing costs and the risk of side reactions. Therefore, the embodiments of this invention select the above-mentioned range to ensure high light efficiency and complete decomposition during the photoreaction, resulting in clear imaging while optimizing cost-effectiveness.

[0037] When the polymer matrix comprises an ideal mass ratio of 60% to 85%, the resin and photobleaching pigment achieve optimal balance. The resin is sufficient to form a continuous, dense, and tough film, providing excellent adhesion, hardness, and durability for the coating, meeting the core requirements for insulation protection. In terms of process, the slurry has moderate viscosity and good leveling properties, enabling the stable formation of a coating with uniform thickness.

[0038] In another preferred embodiment, the background layer 102 has a reflectivity greater than 60% in the visible light band, and the reflectivity ratio of the background layer 102 to the unilluminated area of ​​the mask layer 101 is greater than 5:1.

[0039] Specifically, in this embodiment of the invention, the reflectivity of the background layer 102 in the visible light band is greater than 60%, and the reflectivity ratio of the background layer 102 to the unilluminated dark background area of ​​the mask layer is greater than 5:1. It should be noted that a reflectivity greater than 60% ensures that the QR code pattern is sufficiently bright and clean; and a reflectivity ratio greater than 5:1 (i.e., a contrast ratio as high as 500%) optically guarantees the clarity of the QR code pattern, thereby improving the recognition rate of the scanning software.

[0040] In yet another preferred embodiment, the lightness value of the first color is less than or equal to 20, and the lightness value of the second color is greater than or equal to 70.

[0041] Specifically, in this embodiment of the invention, the background layer 102 can be prepared by a polymer matrix and pigments. The pigment is filled and ground into a film to display its color, or the polymer matrix can be directly dyed without filling with pigment particles and directly coated. For example, the second color of the background layer 102 is preferably white, prepared by a polymer matrix and white filler, such as rutile titanium dioxide. The average particle size of the white filler is between 0.1 μm and 0.4 μm. This particle size range best matches the wavelength of visible light, maximizing light scattering efficiency. This ensures that after light decomposes the upper material, the exposed white area has the highest whiteness, hiding power, and contrast with the black background. At the same time, this range effectively avoids the serious agglomeration and difficulty in dispersion caused by excessively fine particles, as well as the rough coating surface and decreased whiteness caused by excessively coarse particles. Ultimately, this ensures extremely high clarity, uniformity, and machine readability of the identification code pattern.

[0042] Background layer 102 serves as a highly reflective, inert background, ensuring the highest optical contrast for the developed pattern (dark mask layer versus white QR code). Alternatively, other light-colored fillers can be used, such as light yellow, silver, light gray, or off-white. In this embodiment, the background layer 102 can also be made light-colored through direct dyeing, without the need for pigment particles; only a certain brightness difference between it and mask layer 101 is required, allowing for a degree of color customization.

[0043] In this embodiment of the invention, the mask layer 101 is generally dark-colored, preferably with the lightness value L1 of the first color of the mask layer 101 being less than or equal to 20, and the lightness value L2 of the second color of the background layer 102 being greater than or equal to 70. This embodiment of the invention uses light colors as the background layer, which are bright and have high reflectivity. These colors can form extremely high contrast with the dark mask layer, meeting the ratio requirements. This embodiment of the invention is not limited to black and white, but can also achieve multi-color high-contrast combinations such as black and yellow, black and silver, enhancing the versatility and market adaptability of the invention.

[0044] This invention embodiment uses visible light to irradiate an electromagnetic shielding film to write QR codes, including the following steps: S11, Obtain the electromagnetic shielding film in its initial state; S12, Generate corresponding optical path control instructions based on the QR code pattern to be written; S13, according to the optical path control command, manipulate the light beam output by the light source to scan and illuminate the surface of the dark mask layer according to the path corresponding to the QR code pattern; S14, the photobleaching material in the irradiated area undergoes a photochemical reaction and decomposes, revealing the color of the light-colored background layer at the bottom, thereby forming a QR code pattern on the insulating layer that contrasts sharply with the color of the surrounding unirradiated area.

[0045] In step S13, the light beam output by the light source is ultraviolet light or short-wavelength visible light; the light source is an ultraviolet laser, an ultraviolet light-emitting diode array, or a digital light processing projection device; the scanning illumination method is laser point scanning, line scanning, or area array projection exposure.

[0046] In yet another preferred embodiment, the thickness of the mask layer 101 is 0.5 μm to 5 μm.

[0047] Specifically, in this embodiment of the invention, the thickness of the mask layer 101 is between 0.5 μm and 5 μm. This thickness range represents a process balance point for achieving the desired technical effect. If the mask layer 101 is too thin (<0.5 μm), the coating may be discontinuous, failing to completely cover the underlying layer, resulting in poor initial contrast and weak mechanical protection. If the mask layer 101 is too thick (>5 μm), higher light energy is required for complete decomposition and penetration, potentially leading to incomplete reaction (residual black spots) and low light writing efficiency.

[0048] In yet another preferred embodiment, the thickness of the background layer 102 is 1 μm to 10 μm.

[0049] Specifically, in this embodiment of the invention, the thickness of the background layer 102 is 1 μm to 10 μm. This thickness range is sufficient to form a rich, uniform solid-color background, providing a high-quality visual substrate for the QR code. At the same time, it forms a reasonable match with the upper mask layer 101, avoiding problems such as uneven coverage and pinhole defects caused by excessive thinness, and internal stress cracking and decreased bending resistance caused by excessive thickness. This is the preferred range for achieving a high-quality, bending-resistant, and clearly displayed QR code shielding film.

[0050] In yet another preferred embodiment, the optical density of the mask layer 101 in its initial state is greater than 2.

[0051] Specifically, in this embodiment of the invention, the optical density of the mask layer 101 in its initial state is greater than 2. Optical density (OD) is a scientific parameter that measures the light-blocking ability of a material. OD > 2.0 means that the mask layer 101 can block more than 99% of incident visible light. This ensures that the background layer 102 at the bottom of the unilluminated area is completely invisible, thus providing an absolutely uniform dark background before writing. This is a guarantee for achieving extremely high contrast and zero background interference in the pattern.

[0052] In yet another preferred embodiment, the arithmetic mean roughness of the light-irradiated surface of the mask layer 101 is less than or equal to 0.1 μm.

[0053] Specifically, in this embodiment of the invention, the arithmetic mean roughness Ra of the light-illuminated surface of the mask layer 101 is no greater than 0.1 μm, because an ultra-smooth surface is the physical basis for high-quality light writing. This embodiment of the invention limits the roughness (Ra ≤ 0.1 μm) to minimize diffuse reflection and scattering of incident light, thereby ensuring concentrated light spot energy and clear boundaries. This directly determines the edge sharpness and minimum resolvable feature size of the QR code lines formed by illumination, which is key to achieving high-resolution, high-precision patterns.

[0054] In another preferred embodiment, the thickness uniformity deviation of the insulating layer 1 is within ±3%, and the glass transition temperature of the insulating layer 1 is not lower than 80°C.

[0055] Specifically, in this embodiment of the invention, the thickness uniformity deviation of the insulating layer 1 is within ±3%, and the glass transition temperature of the insulating layer 1 is not lower than 80°C. Limiting the thickness deviation to ≤±3% ensures consistent optical path and photochemical reaction intensity throughout the entire writing area, which is the fundamental guarantee for uniform QR code depth and contrast. Uneven thickness leads to insufficient local contrast, affecting the overall recognition rate. Limiting the glass transition temperature (Tg) to ≥80°C ensures the dimensional and mechanical stability of the material under normal processing and usage temperatures. When the temperature rises, the coating will not soften or deform, firmly locking in the formed white filler distribution and preventing the QR code pattern from blurring due to thermal diffusion, ensuring the long-term thermal stability of the QR code pattern.

[0056] The thickness uniformity is calculated as follows: Thickness uniformity = (thickness range / average thickness) × 100%.

[0057] It should be noted that when calculating thickness uniformity, the sample is sliced, the maximum and minimum thicknesses are measured within the slice area, the thickness range is calculated, and at least 10 samples are taken to calculate the average thickness. The thickness uniformity is obtained by the ratio of the thickness range to the average thickness.

[0058] The method for preparing an electromagnetic shielding film provided in this embodiment of the invention includes the following steps: S21, Obtain a peelable carrier film, coat a precursor solution containing photobleaching material and polymer matrix onto the carrier film, and cure the coating to form a mask layer 101 on the carrier film. S22, on the other side of the mask layer 101, a precursor solution containing pigment and polymer matrix is ​​coated and cured to form a background layer 102 on the mask layer 101. S23, on the other side of the background layer 102, a shielding layer 2 is formed by magnetron sputtering, evaporation coating or electroplating process; S24, an adhesive film layer 3 is formed by coating the shielding layer 2.

[0059] In the application of the electromagnetic shielding film of this invention, after hot pressing, the electromagnetic shielding film needs to be peeled off from the carrier film before the surface of the insulating layer is irradiated with a light source to form a QR code. Therefore, the carrier film should protect the surface of the insulating layer and also provide a certain degree of opacity to prevent it from being affected by external light before the code is colored and displayed. That is, the light transmittance of the carrier film is low, not more than 20%, and it is preferably dark-colored to better protect the surface of the insulating layer before the code is colored and displayed, so as to avoid affecting normal use.

[0060] In this embodiment of the invention, the electromagnetic shielding film achieves its shielding effect by piercing the adhesive film layer 3 on one side of the shielding layer 2 to make contact with the ground layer of the circuit board. Therefore, in step S23, when the shielding layer 2 is formed by electroplating or sputtering, the side near the adhesive film layer 3 is a non-flat surface with multiple protruding copper nodules. These protrusions pierce the adhesive film layer 3 to ground. Furthermore, any excess adhesive film layer 3 formed on this side can be filled into the recess between two protrusions after lamination, thereby preventing board bursting.

[0061] In this embodiment of the invention, the adhesive film layer 3 may also be provided with conductive particles, which, together with the piercing surface of the shielding layer 2, are grounded to increase the grounding contact efficiency. The conductive particles include one or more of metal particles, carbon nanotube particles, and ferrite particles. Furthermore, the metal particles include single-metal particles and / or alloy particles; wherein the single-metal particles are made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy particles are made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold; due to differences in processing methods and parameters, the conductive particles can be in the form of clusters, ice crystals, stalactites, dendrites, etc., and this embodiment of the invention does not specifically limit their shape.

[0062] Furthermore, in this embodiment of the invention, the shielding layer 2 is a single layer or multiple layers, and includes a single metal shielding layer and / or an alloy shielding layer. The single metal shielding layer is made of any one of the following materials: aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. The alloy shielding layer is made of any two or more of the following materials: aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold.

[0063] Please see Figure 2 , Figure 2 This is a schematic diagram of another preferred embodiment of an electromagnetic shielding film provided by the present invention.

[0064] The electromagnetic shielding film in this embodiment of the invention also includes a protective film 4. The protective film 4 is adhered to the side of the adhesive film layer 3 away from the shielding layer 2. Before pressing the electromagnetic shielding film, the protective film 4 is first peeled off, and then the bonding process begins. The protective film 4 serves to protect the adhesive film layer 3, preventing dust and dirt, and avoiding any impact on the adhesiveness of the adhesive film layer 3.

[0065] This invention also provides a circuit board, which includes a printed circuit board and an electromagnetic shielding film as described in any of the above embodiments. The electromagnetic shielding film is bonded to the printed circuit board through an adhesive film layer, and the shielding layer of the electromagnetic shielding film has protrusions for piercing the adhesive film layer to make contact and conduction with the ground layer of the printed circuit board.

[0066] To demonstrate the beneficial effects of the electromagnetic shielding film and circuit board provided in the embodiments of the present invention, the following verification is performed: Measure the brightness value L of the illuminated pattern area and the unilluminated background area, and calculate the difference ΔL.

[0067] Write: The mask layer surface is irradiated with a 355nm ultraviolet laser, causing the light to decompose and reveal a QR code in the background layer color on its surface.

[0068] Color difference verification: The colorimeter measured the L value of the light-colored pattern area in the background layer to be 85, and the L value of the dark background in the unilluminated area of ​​the mask layer to be 15. ΔL =70, reflectance contrast ratio is 10:1.

[0069] Practical verification: Using a scanning device, scanning the code under 500 lux illumination, the first recognition success rate was 100%.

[0070] Therefore, the electromagnetic shielding film prepared by the two insulating layers of different colors and the defined color brightness value according to the present invention can cause irreversible photodecomposition of the photobleaching material in the irradiated area when the mask layer is irradiated by a light source, revealing the color of the bottom background layer, so as to form a color-contrast identification code on the mask layer. This effectively avoids the problem that laser lithography can easily penetrate the shielding layer and affect the shielding effectiveness, while ensuring the recognition accuracy of the identification code.

[0071] 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 in that, It includes an insulating layer, a shielding layer, and an adhesive film layer stacked in sequence; The insulating layer includes a mask layer and a background layer, wherein the mask layer is disposed on the side away from the shielding layer, and the background layer is disposed on the side close to the shielding layer; The mask layer includes a photobleaching material having a first color; the background layer has a second color; the lightness value of the first color is lower than the lightness value of the second color, and the difference between the lightness value of the first color and the lightness value of the second color is greater than or equal to 30. The surface of the mask layer is selectively irradiated by a light source, causing irreversible photobleaching material in the irradiated area to decompose, revealing the second color of the background layer, and forming an identification code on the mask layer that contrasts sharply with the color of the surrounding unirradiated area.

2. The electromagnetic shielding film as described in claim 1, characterized in that, The background layer has a reflectivity greater than 60% in the visible light band, and the reflectivity ratio of the background layer to the unilluminated area of ​​the mask layer is greater than 5:

1.

3. The electromagnetic shielding film as described in claim 1, characterized in that, The lightness value of the first color is less than or equal to 20, and the lightness value of the second color is greater than or equal to 70.

4. The electromagnetic shielding film as described in claim 1, characterized in that, The photobleaching material is an azo compound or an anthraquinone derivative.

5. The electromagnetic shielding film as described in claim 1, characterized in that, The thickness of the mask layer is 0.5 μm to 5 μm.

6. The electromagnetic shielding film as described in claim 1, characterized in that, The thickness of the background layer is 1 μm to 10 μm.

7. The electromagnetic shielding film as described in claim 1, characterized in that, The optical density of the mask layer in its initial state is greater than 2.

8. The electromagnetic shielding film as described in claim 1, characterized in that, The arithmetic mean roughness of the light-irradiated surface of the mask layer is less than or equal to 0.1 μm.

9. The electromagnetic shielding film as described in claim 1, characterized in that, The thickness uniformity deviation of the insulating layer is within ±3%, and the glass transition temperature of the insulating layer is not lower than 80°C.

10. A circuit board, characterized in that, The invention includes a printed circuit board and an electromagnetic shielding film as described in any one of claims 1 to 9, wherein the electromagnetic shielding film is bonded to the printed circuit board through an adhesive film layer, and the shielding layer of the electromagnetic shielding film has protrusions for piercing the adhesive film layer to make contact and conduction with the ground layer of the printed circuit board.

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