Carrier film, electromagnetic shielding film and circuit board

Abstract

The invention discloses a carrier film, an electromagnetic shielding film and a circuit board, the carrier film is provided with a first surface and a second surface which are opposite to each other, the second surface is used for being connected with a shielding film body, and the glossiness of the first surface at a 45-degree test angle is 50-100 GU. According to the laser cutting device, it can be guaranteed that the reflectivity of the first surface is not too low, so that the laser absorptivity of the first surface is effectively reduced, and the situation that the first surface absorbs too much laser energy in the laser cutting process, and consequently a large-range fusion recondensation area is generated is avoided; the adhesion phenomenon between the carrier film and the shielding film body due to a large melting area after the hot pressing process is avoided, so that the carrier film is easy to strip from the electromagnetic shielding film to avoid damage and residue; and meanwhile, it can be guaranteed that the reflectivity of the first surface is not too high, and it is guaranteed that laser cutting machining of the carrier film can be effectively completed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic information materials, and in particular to a carrier film, an electromagnetic shielding film and a circuit board. BACKGROUND

[0002] With the rapid development of electronic industry, electronic products further develop towards miniaturization, light weight and high density assembly, which greatly promotes the development of flexible circuit boards. At present, functional flexible circuit boards dominate the market of flexible circuit boards, and an important indicator for evaluating the performance of functional flexible circuit boards is electromagnetic shielding (EMI Shielding).

[0003] The current circuit board realizes electromagnetic shielding function by covering a layer of electromagnetic shielding film to guide interference charges into the ground layer of the circuit board. Before being pressed on the circuit board substrate, the electromagnetic shielding film usually needs to be cut into a specific shape by laser cutting and then be pressed on the corresponding circuit position. After the electromagnetic shielding film is pressed on the circuit board substrate, the carrier film on the surface of the electromagnetic shielding film needs to be torn off to expose the insulating layer. However, after the existing electromagnetic shielding film is cut by laser cutting, the melting phenomenon of the carrier film on the surface at the edge of the laser cutting is more serious, so that after the electromagnetic shielding film is hot-pressed on the circuit board substrate, it is difficult to tear off the carrier film on the surface from the electromagnetic shielding film, and the carrier film is easily damaged and left over when tearing off, so that the residual part of the carrier film needs to be manually torn off again, which seriously affects the production efficiency of the circuit board. SUMMARY

[0004] The present application provides a carrier film, an electromagnetic shielding film and a circuit board to solve the technical problem that the existing carrier film after laser cutting has a serious melting phenomenon at the edge of the laser cutting, which makes it difficult to tear off from the electromagnetic shielding film after the subsequent hot-pressing process and easily damaged and left over when tearing off.

[0005] To solve the above technical problem, the first aspect of the embodiment of the present application provides a carrier film, which has opposite first and second surfaces, the second surface is used to connect with the body of the shielding film, and the glossiness of the first surface at a test angle of 45 degrees is 50GU-100GU.

[0006] As a preferred scheme, the extreme difference of the glossiness of the first surface is less than or equal to 5GU.

[0007] As a preferred scheme, in the sliced state, the change rate of the sliced area of the carrier film in the laser cutting observation area before and after laser cutting is less than or equal to 5%. The laser cutting observation area is a slice area between the preset laser cutting line and the observation area boundary line in a slice state.

[0008] Preferably, the roughness Ra of the first surface is 20-50 nm; and / or, the ratio between the actual surface area of the first surface and its projected area is less than 1.1.

[0009] Preferably, the thickness range of the carrier film is less than or equal to 1 μm.

[0010] Preferably, the L value of the first surface in the Lab color space is 65-85.

[0011] Preferably, a transition layer with an optical thickness less than the wavelength of incident laser light is arranged on the first surface.

[0012] The second aspect of the embodiment of the present application provides an electromagnetic shielding film, comprising a shielding film body and the carrier film according to any one of the first aspect; the shielding film body comprises an insulating layer, a shielding layer and a film layer arranged in sequence; the second surface of the carrier film is connected with the surface of the insulating layer away from the shielding layer.

[0013] Preferably, the surface of the shielding layer close to the film layer is a non-flat surface; and / or, a plurality of conductive particles are arranged in the film layer, and the conductive particles are used to connect the ground end of the circuit board substrate and the shielding layer.

[0014] The third aspect of the embodiment of the present application provides a circuit board, comprising a circuit board substrate and the electromagnetic shielding film according to any one of the second aspect, and the side of the electromagnetic shielding film away from the carrier film is pressed on the circuit board substrate.

[0015] Compared with the prior art, the embodiment of the present application has the beneficial effects that by limiting the glossiness of the first surface of the carrier film at a test angle of 45 degrees to be 50 GU-100 GU, the reflectivity of the first surface can be ensured not to be too low, thereby effectively reducing the laser absorption rate of the first surface, avoiding the first surface from generating a large range of fusion recondensation area due to absorbing too much laser energy in the laser cutting process, and further avoiding the phenomenon of adhesion between the carrier film and the shielding film body due to a large fusion area after the hot pressing process, so that the carrier film is easy to be peeled off from the electromagnetic shielding film to avoid damage and residue; at the same time, the reflectivity of the first surface can be ensured not to be too high to ensure that the laser cutting processing of the carrier film can be effectively completed. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a structural schematic diagram of a first carrier film in an embodiment of the present application; Figure 2 is a schematic diagram of a laser cutting observation area in an embodiment of the present application; Figure 3 is a structural schematic diagram of a second carrier film in an embodiment of the present application; Figure 4 is a structural schematic diagram of a first electromagnetic shielding film in an embodiment of the present application; Figure 5 is a structural schematic diagram of a second electromagnetic shielding film in an embodiment of the present application; Figure 6 is a structural schematic diagram of a third electromagnetic shielding film in an embodiment of the present application; Figure 7 is a schematic diagram of a section of the carrier film in Comparative Example 1 of the present application after laser cutting; Figure 8 is a schematic diagram of a section of the carrier film in Comparative Example 1 of the present application after heat pressing; Figure 9 is a schematic diagram of a section of the carrier film in Example 2 of the present application after laser cutting; Figure 10 is a schematic diagram of a section of the carrier film in Example 2 of the present application after heat pressing; wherein 1, carrier film; 2, insulating layer; 3, shielding layer; 4, adhesive film layer; 5, protruding structure; 6, conductive particle; 7, transition layer. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. The purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0018] In the description of the present application, the terms “first”, “second”, “third” and the like are only used for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with “first”, “second”, “third” and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of “a plurality of” is two or more.

[0019] In the description of the application, it is necessary to point out that, unless otherwise explicitly defined and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication inside two elements. The terms "vertical", "horizontal", "left", "right", "up", "down" and similar expressions used in the present application are for the purpose of illustration only, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. The term "and / or" used in the present application includes any and all combinations of one or more related listed items. For those skilled in the art, the specific meaning of the above terms in the present application can be understood in specific circumstances.

[0020] In the description of the application, it is necessary to point out that, unless otherwise defined, all technical and scientific terms used in the present application are the same as those commonly understood by those skilled in the art. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the present application. For those skilled in the art, the specific meaning of the above terms in the present application can be understood in specific circumstances.

[0021] Please refer to Figure 1 The first aspect of the embodiment of the present application provides a carrier film 1, which has opposite first and second surfaces, the second surface is used to connect with the shielding film body, and the glossiness of the first surface at a test angle of 45 degrees is 50GU-100GU.

[0022] It is worth noting that the carrier film 1 in the embodiment is arranged in the actual application with the shielding film body, which is used to carry and protect each material layer in the shielding film body, provides sufficient stiffness and tensile strength for the shielding film body, so that each material layer in the shielding film body is not damaged by external contact or collision, and can prevent the shielding film body from being wrinkled.

[0023] Since most of the laser energy is absorbed in the carrier film 1 during laser cutting, the conversion efficiency of laser energy into heat energy is high, which causes the local temperature of the carrier film 1 to rise rapidly and the value to be high, which easily causes the material at the laser cutting position to melt and even decompose. The molten polymer has fluidity and diffuses and infiltrates into the surrounding area, and forms a relatively wide molten recondensation area after cooling. Therefore, during subsequent hot pressing, due to the excessively large range of the molten recondensation area, excessive molten material is formed at the laser cutting position after hot pressing, forming a relatively large molten area, which further causes the carrier film 1 and the shielding film body to be bonded, causing the carrier film 1 to be difficult to tear off subsequently, and the carrier film 1 is easily damaged and left over when being torn off due to the serious bonding phenomenon, and the residual part of the carrier film 1 needs to be manually torn off again, which seriously affects the production efficiency of the circuit board.

[0024] In order to make the carrier film 1 easy to be peeled off from the electromagnetic shielding film after the laser cutting and hot pressing process, the gloss of the first surface of the carrier film 1 at a test angle of 45 degrees is 50GU-100GU in the embodiment, for example, the gloss of the first surface is tested at an incident angle and a reflection angle of 45 degrees, and the gloss is 50GU, 55GU, 58GU, 60GU, 63GU, 66GU, 68GU, 70GU, 73GU, 75GU, 77GU, 79GU, 80GU, 85GU, 90GU, 95GU, 100GU, etc., which is not specifically limited in the embodiment. It can be understood that the higher the gloss of the first surface, the higher the reflectivity of the first surface, and the lower the absorption rate of the laser. Therefore, by limiting the gloss of the first surface at a test angle of 45 degrees to 50GU-100GU, the gloss of the first surface is not too low, and the reflectivity is not too low, so that part of the laser can be reflected during the laser cutting process to effectively reduce the actual absorption of the laser energy, so that the laser energy penetrates deeper during cutting, the temperature rise of the carrier film 1 is relatively moderate, and the melting phenomenon at the laser cutting position is avoided due to the excessively high local temperature, thereby ensuring that the molten recondensation area after cooling is relatively narrow to form a clear and steep cutting / melting edge, so that the carrier film 1 can be easily torn off after the subsequent hot pressing process.

[0025] At the same time, the gloss of the first surface is not too high, that is, the reflectivity is not too high. It can be understood that if the reflectivity of the first surface is too high, the laser during the laser cutting process is completely reflected by the first surface, which causes the carrier film 1 to be effectively cut. Therefore, while ensuring that the carrier film 1 does not absorb too much laser energy to cause the local temperature to rise too rapidly, the carrier film 1 can absorb sufficient laser energy to effectively complete the laser cutting process.

[0026] The gloss of the first surface of the carrier film 1 can be directly obtained by testing with a 45-degree gloss meter. The preferred gloss range for this first surface is 60 GU to 80 GU.

[0027] Furthermore, since this embodiment sets the gloss level of the first surface of the carrier film 1 to be 50 GU~100 GU at a test angle of 45 degrees, the absorption rate of the first surface to different wavelengths of laser is less than or equal to 2%. For example, this embodiment can achieve absorption rates of 0.3%, 0.6%, 0.8%, 1%, 1.3%, 1.5%, 1.7%, 2%, etc., depending on the gloss level of the first surface. Compared with other carrier films with a gloss level less than 50 GU, under the same laser parameters and under the premise that all can be cut, the carrier film 1 in this embodiment has a lower absorption rate of laser during laser cutting, thereby ensuring that the absorbed laser energy is lower, effectively avoiding the formation of a large melting and resolidification zone, resulting in better laser cutting effect, and ensuring that the carrier film 1 can be easily torn off after the hot pressing process.

[0028] It is worth noting that the laser wavelength used in laser cutting is usually less than or equal to 700nm, among which, violet lasers with a wavelength of about 400nm are commonly used for laser cutting.

[0029] In this embodiment, the laser absorptivity of the carrier film 1 is obtained by the integrating sphere method, that is, the laser reflectivity R and laser absorptivity A of the carrier film 1 sample are calculated based on the measured incident laser power P1 and total reflected power P2.

[0030] For the opaque carrier film 1 sample, the laser reflectivity R and laser absorptivity A are calculated using the following expressions: R = P2 / P1, A = 1 - R = 1 - (P2 / P1).

[0031] For the transparent carrier film 1 sample, another integrating sphere is needed to collect all transmitted light behind the carrier film 1 sample to obtain the transmitted power P3, and calculate the transmittance T of the carrier film 1 sample, where T=P3 / P1. Then the calculation of the laser absorptivity A needs to take into account the transmittance T of the carrier film 1 sample, that is, A=1-RT.

[0032] In one optional embodiment, the material of the carrier film 1 can be at least one of polytetrafluoroethylene, polyetheretherketone, or liquid crystal polymer, or it can be polyimide, polyethylene terephthalate, polypropylene, polyvinyl chloride, polyester, or other polymer materials. This embodiment does not specifically limit the material.

[0033] As a preferred embodiment, the gloss range of the first surface is less than or equal to 5 GU.

[0034] Specifically, this embodiment further limits the gloss range of the first surface to be less than or equal to 5 GU. For example, the gloss range of the first surface can be 5 GU, 4.5 GU, 4 GU, 3.5 GU, 3 GU, 2.5 GU, 2 GU, 1.5 GU, 1 GU, 0.5 GU, etc. This embodiment does not make a specific limitation here, so as to further ensure the gloss uniformity of the first surface, making the laser absorption rate at different positions on the first surface more stable. Under the same laser cutting parameters, it avoids the laser cutting effect being affected by the excessive difference in gloss at different positions on the first surface.

[0035] In this embodiment, when calculating the range of gloss on the first surface of the carrier film 1, at least 10 sampling points are used to ensure a small calculation error. Furthermore, the gloss uniformity can be further characterized by the ratio of the range to the average value at each sampling point.

[0036] As a preferred embodiment, in the sliced ​​state, the change rate of the sliced ​​area of ​​the carrier film 1 in the laser cutting observation area before and after laser cutting is less than or equal to 5%; The laser-cut observation area is the sliced ​​area between the preset laser cutting line and the boundary line of the observation area in the sliced ​​state; both the laser cutting line and the boundary line of the observation area are parallel to the thickness direction of the carrier film 1; the interval between the laser cutting line and the boundary line of the observation area is the preset length of the observation area.

[0037] Specifically, this embodiment further limits the change rate of the sliced ​​area of ​​the carrier film 1 in the laser cutting observation area before and after laser cutting to less than or equal to 5% in the sliced ​​state. For example, the change rate of the sliced ​​area of ​​the carrier film 1 in the laser cutting observation area before and after laser cutting is 5%, 4.7%, 4.4%, 4%, 3.8%, 3.3%, 2.7%, 2.5%, 2%, 1.5%, 1%, 0.5%, etc., which are not limited in this embodiment. It can be understood that the laser cutting observation area is the sliced ​​area between the preset laser cutting line and the boundary line of the observation area in the sliced ​​state, that is, the sliced ​​area around the edge of the laser cutting. If the change rate of the sliced ​​area in the laser cutting observation area before and after laser cutting is large, it indicates that the deformation at the laser cutting point is large, and a large melting and resolidification zone is formed after laser cutting. This can easily cause the carrier film 1 to stick to the shielding film body after the subsequent hot pressing process. Therefore, this embodiment limits the change rate of the sliced ​​area of ​​the carrier film 1 in the laser cutting observation area before and after laser cutting to less than or equal to 5% under the slicing state. This ensures that the deformation at the laser cutting point is small and the range of the melt-resolidification zone formed after laser cutting is small. This avoids the phenomenon of adhesion between the carrier film 1 and the shielding film body due to the large melting area during the subsequent hot pressing process, which would make it difficult to peel off the carrier film 1.

[0038] It is worth noting that, such as Figure 2 As shown, in the slicing state, a perpendicular line is drawn 100 μm away from the set laser cutting line. This perpendicular line is the boundary line of the observation area, and the length L of the observation area is 100 μm. The slicing area between the laser cutting line and the boundary line of the observation area is the laser-cut observation area. Before laser cutting, the slice area S in the laser-cut observation area is a constant value, which can be calculated by multiplying the length L of the observation area by the thickness D of the carrier film 1. After laser cutting, due to the melting and resolidification phenomenon at the cut edge, the slice area S1 in the laser-cut observation area is now the actual contour area of ​​the sliced ​​area in the laser-cut observation area. Due to its irregular shape, its area can be automatically identified by the visual statistical software ImageJ. The final change rate of the slice area before and after laser cutting is (S1-S) / S.

[0039] As a preferred embodiment, the roughness Ra of the first surface is 20nm~50nm.

[0040] Specifically, this embodiment further limits the roughness Ra of the first surface to 20nm~50nm. For example, the roughness Ra of the first surface can be 20nm, 22nm, 25nm, 27nm, 29nm, 32nm, 35nm, 38nm, 41nm, 45nm, 47nm, 50nm, etc., and this embodiment does not make a specific limitation. It is understood that if the roughness Ra of the first surface is too large, there will be too many microscopic protrusions and depressions on the first surface. When the laser is incident, diffuse reflection will occur, and some scattered light will be reflected and refracted by the film surface twice or even multiple times. This increases the residence time of the laser on the first surface, which can easily lead to excessive laser energy being absorbed by the surface material, thereby easily forming a large melting and resolidification zone after laser cutting. If the roughness Ra of the first surface is too small, the first surface will be too flat and the reflectivity will be too high, resulting in a low absorption rate of the laser during laser cutting, making it impossible to effectively carry out the laser cutting process. Therefore, by limiting the roughness Ra of the first surface to 20nm~50nm, this embodiment can ensure that the roughness Ra of the first surface is moderate, so that its gloss at a test angle of 45 degrees can meet 50GU~100GU. While ensuring that the laser cutting process can be carried out effectively, it also ensures that the laser energy absorbed by the first surface during the laser cutting process is not too high, avoiding excessive melting due to excessive local laser energy concentration at the laser cutting point. Furthermore, it ensures that the range of the melt resolidification zone after cooling is small, thereby making the melted area at the laser cutting edge smaller after the hot pressing process, making it easier to peel off the carrier film 1.

[0041] Furthermore, the ratio between the actual surface area and the projected area of ​​the first surface is less than 1.1.

[0042] It is understandable that when measuring the actual surface area of ​​the first surface, the surface area of ​​its microscopic protrusions and depressions will be considered. In this embodiment, the ratio between the actual surface area and the projected area of ​​the first surface is limited to less than 1.1. For example, the ratio between the actual surface area and the projected area of ​​the first surface is 1.05, 1.06, 1.07, 1.08, 1.09, etc. This embodiment does not make a specific limitation here, so that the ratio between the actual surface area and the projected area of ​​the first surface is small, which can ensure that the first surface is a surface with a low profile, that is, the roughness of the first surface is not too large, thereby reducing the absorption rate of the first surface for laser. After laser cutting, it can avoid the formation of a large melting and resolidification zone, and ensure that the carrier film 1 is still easy to tear off after hot pressing.

[0043] As a preferred embodiment, the gloss, roughness Ra, and absorption rate of the first surface satisfy a fitting relationship: A =0.03× R +0.05× G-1 ;in, A This indicates the absorption rate; R This represents the roughness Ra; G This refers to the gloss level.

[0044] It is worth noting that in this embodiment, the gloss, roughness Ra, and laser absorption rate of the first surface are defined to satisfy the following relationship: A =0.03× R +0.05× G -1 This can further limit the laser absorption rate of the first surface to a more preferred range, so that it can absorb enough laser energy to achieve laser cutting, while avoiding the formation of a large melting and resolidification zone due to excessive laser energy absorption.

[0045] Furthermore, the calculation of the above-mentioned fitting relationship expression is dimensionless.

[0046] As a preferred embodiment, the thickness range of the carrier membrane 1 is less than or equal to 1 μm.

[0047] Specifically, in this embodiment, the thickness difference of the carrier film 1 is further limited to less than or equal to 1 μm. For example, the thickness difference of the carrier film 1 is 1 μm, 0.8 μm, 0.6 μm, 0.4 μm, 0.2 μm, 0.1 μm, etc. This embodiment does not make a specific limitation here, so as to ensure the overall thickness of the carrier film 1 is uniform and avoid excessive gloss difference at different positions of the first surface due to excessive thickness difference, which would affect the laser cutting effect.

[0048] In this embodiment, when calculating the thickness range of the carrier film 1, at least 10 sampling points are used to ensure a small calculation error. Furthermore, the thickness uniformity can be further characterized by the ratio of the range to the average value at each sampling point.

[0049] As a preferred embodiment, the L value of the first surface in the Lab color space is 65~85.

[0050] Specifically, the Lab color space consists of three elements: illuminance (L) and a and b related to color. The L value represents illuminance, and its value ranges from 0 to 100. The higher the L value, the higher the reflectivity of the material surface and the lower the laser absorption rate.

[0051] In this embodiment, the L value of the first surface in the Lab color space is limited to 65-85. For example, the L value of the first surface is 65, 67, 70, 72, 75, 77, 79, 82, 84, 85, etc. This embodiment does not make a specific limitation. This ensures that the L value of the first surface is moderate, and it is light gray, beige, etc. On the one hand, the first surface will not be too dark due to the L value being too low, and the laser absorption rate will not be too high. This ensures that the absorption rate of the first surface for different wavelengths of laser is less than or equal to 2%, which further avoids the formation of a large melting and resolidification zone at the laser cutting point of the carrier film 1 due to excessive absorption of laser energy. On the other hand, the reflectivity of the first surface will not be too high due to the L value being too high, which avoids the first surface having too low and unstable laser absorption rate. This ensures that the laser cutting processing of the carrier film 1 can be effectively completed. If the L value is too high, it is easy to cause problems such as specular reflection and surface contamination sensitivity, which will affect the stability of laser cutting. Therefore, this embodiment can simultaneously ensure the stability and safety of the laser processing process.

[0052] As a preferred embodiment, a transition layer 7 with an optical thickness less than the incident laser wavelength is provided on the first surface, which can make the transmittance of the carrier film 1 to lasers of different wavelengths greater than 94%.

[0053] Specifically, such as Figure 3 As shown, in this embodiment, a transition layer 7 is also coated on the first surface. Preferably, the transition layer 7 is a SiO2 nanoparticle layer. It can be understood that the transition layer 7 is equivalent to adding a refractive index gradient transition layer between the air and the substrate of the carrier film 1, so that when the laser is incident on the first surface of the carrier film 1, it can pass through the transition layer 7 smoothly, thereby significantly reducing the interface reflection of the laser, allowing the laser to cut vertically in most places, reducing the contact of the laser at the film surface, and effectively avoiding the generation of a large heat-affected zone in the carrier film 1 during cutting.

[0054] In this embodiment, the optical thickness of the transition layer 7 is less than the incident laser wavelength. Preferably, the optical thickness of the transition layer 7 is λ / 4, where λ is the incident laser wavelength, to reduce laser reflection by utilizing destructive interference. Furthermore, this embodiment reduces the absorption of interface defect states between the transition layer 7 and the carrier film 1 through silane modification, resulting in a transmittance of the carrier film 1 for lasers of different wavelengths greater than 94%. For example, the transmittance of the carrier film 1 for lasers of different wavelengths is 95%, 96%, 96.5%, 97%, 98%, etc. This embodiment does not specify a particular transmittance. This allows most of the laser energy to pass smoothly through the first surface of the carrier film 1, rather than being reflected or absorbed. This enables the laser absorptivity of the first surface to be controlled at an extremely low level, achieving an absorptivity of less than or equal to 2% for lasers of different wavelengths on the first surface. This ensures that the laser energy penetrates deeper during cutting, improving the laser cutting effect.

[0055] Please see Figure 4 The second aspect of the present invention provides an electromagnetic shielding film, comprising a shielding film body and a carrier film 1 as described in any embodiment of the first aspect; the shielding film body comprises an insulating layer 2, a shielding layer 3 and an adhesive film layer 4 stacked sequentially; the second surface of the carrier film 1 is connected to the side surface of the insulating layer 2 away from the shielding layer 3.

[0056] Specifically, the electromagnetic shielding film in this embodiment includes a carrier film 1, an insulating layer 2, a shielding layer 3, and an adhesive film layer 4 stacked sequentially. Since the carrier film 1 needs to be peeled off from the surface of the insulating layer 2 after the electromagnetic shielding film is pressed with the circuit board substrate, the carrier film 1 and the insulating layer 2 are peelable.

[0057] It is worth noting that the insulating layer 2 provides insulation and protection for the shielding layer 3, while also preventing wear on the shielding layer 3 and extending the lifespan of the electromagnetic shielding film. The insulating layer 2 can be made of bisphenol A type epoxy resin, acrylic resin, polyester resin, etc. In addition, the resin used can be any one or a mixture of at least two of the following: 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; however, it 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.

[0058] The shielding layer 3 is used to connect with the ground layer of the circuit board to achieve effective electromagnetic interference shielding. Its material is a conductive material with good shielding performance. Optionally, the conductive material selected for the shielding layer 3 can be a metallic material, such as any one element or an alloy of at least two of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold. It can also be a non-metallic material, such as graphene, carbon nanotubes, conductive carbon black, etc. This embodiment does not make specific limitations.

[0059] The adhesive film layer 4 can improve the bonding stability between the electromagnetic shielding film and the circuit board substrate. The material of the adhesive 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.

[0060] As a preferred embodiment, the surface of the shielding layer 3 near the adhesive film layer 4 is a non-flat surface.

[0061] Specifically, such as Figure 5 As shown, in this embodiment, the shielding layer 3 has several protrusions 5 on the side surface near the adhesive film layer 4 to form an uneven surface. Thus, when the electromagnetic shielding film is hot-pressed onto the circuit board substrate, the protrusions 5 on the shielding layer 3 can pierce the adhesive film layer 4, allowing the shielding layer 3 to contact the ground layer of the circuit board and achieve electromagnetic shielding.

[0062] Furthermore, a plurality of conductive particles 6 are disposed within the adhesive film layer 4, the conductive particles 6 being used to connect the grounding terminal of the circuit board substrate and the shielding layer 3.

[0063] Specifically, such as Figure 6 As shown, the surface of the shielding layer 3 near the adhesive film layer 4 in this embodiment can also be a flat surface. In order to ensure that the shielding layer 3 can effectively achieve electromagnetic shielding, a number of conductive particles 6 are provided in the adhesive film layer 4. When the electromagnetic shielding film is hot-pressed onto the circuit board substrate, the conductive particles 6 can pierce the adhesive film layer 4, so that the shielding layer 3 can contact the ground layer of the circuit board to achieve electromagnetic shielding.

[0064] It is worth noting that the conductive particles 6 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 6 can be in the form of clusters, ice crystals, stalactites, dendrites, etc., and this embodiment does not specifically limit their shape.

[0065] A third 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 second aspect, wherein the side of the electromagnetic shielding film away from the carrier film is pressed onto the circuit board substrate.

[0066] The carrier film, electromagnetic shielding film, and circuit board provided in this invention have the following advantages: By limiting the gloss of the first surface of the carrier film to 50 GU~100 GU at a test angle of 45 degrees, the reflectivity of the first surface can be ensured to be not too low, thereby effectively reducing the laser absorption rate of the first surface. This avoids the formation of a large melting and resolidification zone on the first surface due to excessive laser energy absorption during laser cutting, and thus avoids adhesion between the carrier film and the shielding film body due to a large melting area after the hot pressing process. This makes the carrier film easy to peel off from the electromagnetic shielding film and avoids damage and residue. At the same time, it ensures that the reflectivity of the first surface is not too high, so as to ensure that the laser cutting processing of the carrier film can be effectively completed.

[0067] To better demonstrate the beneficial effects of the carrier film, electromagnetic shielding film, and circuit board in the embodiments of the present invention, the following description is provided in conjunction with some embodiments and comparative examples.

[0068] Example 1 A carrier film having opposing first and second surfaces, the second surface being for connection with a shielding film body, the first surface having a gloss of 55 GU at a test angle of 45 degrees.

[0069] Example 2 A carrier film having opposing first and second surfaces, the second surface being for connection with a shielding film body, the first surface having a gloss of 64 GU at a test angle of 45 degrees.

[0070] In the sliced ​​state, the change rate of the sliced ​​area of ​​the carrier film in the laser-cut observation area before and after laser cutting was 4.6%. The laser-cut observation area is the sliced ​​region between the preset laser cutting line and the boundary line of the observation area in the sliced ​​state, and the length of the observation area is 100 μm.

[0071] Example 3 A carrier film having opposing first and second surfaces, the second surface being for connection with a shielding film body, the first surface having a gloss of 78 GU at a test angle of 45 degrees.

[0072] In the sliced ​​state, the change rate of the sliced ​​area of ​​the carrier film in the laser-cut observation area before and after laser cutting is 4%. The laser-cut observation area is the sliced ​​area between the preset laser cutting line and the boundary line of the observation area in the sliced ​​state, and the length of the observation area is 100μm.

[0073] The roughness Ra of the first surface is 20 nm, and the ratio between the actual surface area and its projected area is 1.08. The thickness range of the carrier film is 1 μm, and the gloss range of the first surface is 4.6 GU.

[0074] Example 4 A carrier film having opposing first and second surfaces, the second surface being for connection with a shielding film body, the first surface having a gloss of 83 GU at a test angle of 45 degrees.

[0075] In the sliced ​​state, the change rate of the sliced ​​area of ​​the carrier film within the laser-cut observation area before and after laser cutting is 3.5%. The laser-cut observation area is the sliced ​​region between the preset laser cutting line and the boundary line of the observation area in the sliced ​​state, with a length of 100 μm.

[0076] The roughness Ra of the first surface is 30 nm, and the ratio between the actual surface area and its projected area is 1.07. The thickness range of the carrier film is 0.8 μm, and the gloss range of the first surface is 4 GU. The L value of the first surface in the Lab color space is 69. A transition layer with an optical thickness of λ / 4, where λ is the incident laser wavelength, is disposed on the first surface.

[0077] Example 5 A carrier film having opposing first and second surfaces, the second surface being for connection with a shielding film body, the first surface having a gloss of 95 GU at a test angle of 45 degrees.

[0078] In the sliced ​​state, the change rate of the sliced ​​area of ​​the carrier film within the laser-cut observation area before and after laser cutting is 2.5%. The laser-cut observation area is the sliced ​​region between the preset laser cutting line and the boundary line of the observation area in the sliced ​​state, with a length of 100 μm.

[0079] The roughness Ra of the first surface is 40 nm, and the ratio between the actual surface area and its projected area is 1.05. The thickness range of the carrier film is 0.6 μm, and the gloss range of the first surface is 3 GU. The L value of the first surface in the Lab color space is 75. A transition layer with an optical thickness of λ / 4, where λ is the incident laser wavelength, is disposed on the first surface.

[0080] Comparative Example 1 A carrier film having opposing first and second surfaces, the second surface being for connection with a shielding film body, the first surface having a gloss of 20 GU at a test angle of 45 degrees.

[0081] Comparative Example 2 A carrier film having opposing first and second surfaces, the second surface being for connection with a shielding film body, the first surface having a gloss of 150 GU at a test angle of 45 degrees.

[0082] Electromagnetic shielding films were prepared using the carrier films from Examples 1-5 and Comparative Examples 1-2. The insulating layer, shielding layer, and adhesive film layer in the electromagnetic shielding films were all identical. They were processed using the same laser cutting parameters to cut into identical specific shapes, and then pressed onto the same circuit board substrate using the same hot-pressing parameters. The carrier film was then peeled off from the electromagnetic shielding film. During the testing process, the laser cutting effect of the carrier film and whether it could be successfully peeled off without any damage or residue were observed. The test results are shown in Table 1 below. Table 1. Carrier membrane processing details

[0083] As can be seen from Table 1 above, since the carrier films in Examples 1 to 5 all meet the requirement that the gloss of the first surface is 50 GU to 100 GU at a test angle of 45 degrees, the laser absorption rate of the first surface is effectively reduced, avoiding the formation of a large melting and resolidification zone on the first surface due to excessive laser energy absorption during laser cutting. This avoids the adhesion between the carrier film and the shielding film body due to a large melting area after the hot pressing process, making the carrier film easy to peel off from the electromagnetic shielding film and avoiding damage and residue. At the same time, it can ensure that the reflectivity of the first surface is not too high, so as to ensure that the laser cutting processing of the carrier film can be effectively completed.

[0084] In Comparative Example 1, the first surface of the carrier film exhibits excessively low gloss at a 45-degree testing angle, resulting in excessive absorption of laser light across various wavelengths. This leads to excessive laser energy absorption during laser cutting, causing significant deformation at the laser-cut edge and an overly large molten resolidation zone after cooling. Following the hot-pressing process, this excessive molten area causes adhesion between the carrier film and the shielding film, making complete separation impossible and resulting in damaged residue after removal. Similarly, in Comparative Example 2, the first surface of the carrier film exhibits excessively high gloss at a 45-degree testing angle, resulting in low absorption of laser light across various wavelengths. This leads to excessively high reflectivity and insufficient incident energy, preventing effective and rapid laser cutting. The relatively long laser energy contact time also increases the heat-affected zone. Consequently, after cutting and hot-pressing, the excessively large molten area causes adhesion, resulting in damaged residue after removal.

[0085] In addition, such as Figure 7 The image shows a schematic diagram of a slice of the carrier membrane in Comparative Example 1 after laser cutting. The red box in the image represents the laser cutting observation area. It can be seen that the width of the melt-resolidification zone after cooling reaches 27.6 μm. The change rate of the slice area within this laser cutting observation area before and after laser cutting is much greater than 10%. Figure 8The image shows a schematic diagram of a slice of the carrier film after hot pressing. The width of the molten region reaches 70.14 μm, which leads to the blurring of the boundary between the burned edge and the insulating layer. The large melting changes result in a large area of ​​adhesion.

[0086] But if Figure 9 The diagram shows a slice of the carrier membrane in Example 2 after laser cutting. The red box in the diagram represents the laser cutting observation area. It can be seen that the width of the cooled melt-resolidification zone is only 9.58 μm, much smaller than the width of the melt-resolidification zone of the carrier membrane in Comparative Example 1 after laser cutting. The change rate of the slice area within this laser cutting observation area before and after laser cutting is less than 5%. Figure 10 The diagram shows a slice of the carrier film after hot pressing. The width of the molten region is only 11.32 μm, which is much smaller than the width of the molten region of the carrier film after hot pressing in Comparative Example 1. No obvious adhesion zone is generated, and the boundary between the burned edge and the insulating layer is obvious. The melting change is not significant, which effectively improves the degree of melting after hot pressing, avoids adhesion at the burned edge, makes the carrier film easy to peel off without leaving any broken residue, eliminates the need for multiple rework and tearing, and effectively improves production efficiency.

[0087] 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. A carrier membrane, characterized in that, The carrier film has a first surface and a second surface opposite to each other, the second surface being used to connect with the shielding film body, and the first surface having a gloss of 50 GU~100 GU at a test angle of 45 degrees.

2. The carrier membrane as described in claim 1, characterized in that, The range of gloss on the first surface is less than or equal to 5 GU.

3. The carrier membrane as described in claim 1, characterized in that, In the sliced ​​state, the change rate of the sliced ​​area of ​​the carrier film in the laser-cut observation area before and after laser cutting is less than or equal to 5%; Wherein, the laser-cut observation area is the sliced ​​area between the preset laser cutting line and the boundary line of the observation area in the sliced ​​state; both the laser cutting line and the boundary line of the observation area are parallel to the thickness direction of the carrier film; the interval between the laser cutting line and the boundary line of the observation area is the preset length of the observation area.

4. The carrier membrane as described in claim 1, characterized in that, The roughness Ra of the first surface is 20nm~50nm; and / or the ratio between the actual surface area and the projected area of ​​the first surface is less than 1.

1.

5. The carrier membrane as described in claim 1, characterized in that, The thickness range of the carrier membrane is less than or equal to 1 μm.

6. The carrier membrane as described in claim 1, characterized in that, The L value of the first surface in the Lab color space is 65~85.

7. The carrier membrane as described in claim 1, characterized in that, The first surface is provided with a transition layer with an optical thickness smaller than the incident laser wavelength.

8. An electromagnetic shielding film, characterized in that, It includes a shielding film body and a carrier film as described in any one of claims 1 to 7; the shielding film body includes an insulating layer, a shielding layer and an adhesive film layer stacked sequentially; the second surface of the carrier film is connected to the side surface of the insulating layer away from the shielding layer.

9. The electromagnetic shielding film as described in claim 8, characterized in that, The surface of the shielding layer near the adhesive film layer is a non-flat surface; and / or, the adhesive film layer contains a plurality of conductive particles, which are used to connect the ground terminal of the circuit board substrate and the shielding layer.

10. A circuit board, characterized in that, It includes a circuit board substrate and an electromagnetic shielding film as described in claim 8 or 9, wherein the side of the electromagnetic shielding film away from the carrier film is pressed onto the circuit board substrate.

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