Carrier film, electromagnetic shielding film and circuit board

Abstract

The invention discloses a carrier film, an electromagnetic shielding film and a circuit board. The absolute value of the difference value between the thermal shrinkage rate of the carrier film in the TD direction and the thermal shrinkage rate of the carrier film in the MD direction is smaller than or equal to 1%. The method can ensure that the absolute value of the difference value of the thermal shrinkage rates of the carrier film in the TD direction and the MD direction is small, so that the internal stress of the carrier film is uniformly distributed and isotropous, and therefore, after laser cutting, the deformation at the laser cutting edge is small, the heat affected area is uniform, the range of the cooled melting recondensation area is small, and the service life of the carrier film is prolonged. The adhesion phenomenon of the carrier film and the shielding film body due to a large fusion area after the hot pressing process is avoided, and the carrier film is easy to strip from the electromagnetic shielding film to avoid damage and residue.

Description

Technical Field

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

[0002] With the rapid development of the electronics industry, electronic products are further developing towards miniaturization, lightweighting, and high-density assembly, which has greatly promoted the development of flexible circuit boards. Currently, functional flexible circuit boards dominate the flexible circuit board market, and an important indicator for evaluating the performance of functional flexible circuit boards is electromagnetic interference shielding (EMI shielding).

[0003] To achieve electromagnetic shielding, current circuit boards (PCBs) typically use an electromagnetic shielding film to conduct interference charges to the PCB's ground plane. Before being laminated to the PCB substrate, this film usually undergoes laser cutting to a specific shape before being pressed onto the corresponding circuit location. After lamination, the carrier film on the surface of the electromagnetic shielding film needs to be peeled off to expose the insulating layer. However, existing electromagnetic shielding films often exhibit significant melting at the laser-cut edges, resulting in large molten re-solidification zones at the laser-cut locations during subsequent hot-pressing processes. This makes it difficult to peel the carrier film off the electromagnetic shielding film, and damage or residue is easily left during peeling. Consequently, manual removal of the remaining carrier film is required, severely impacting PCB production efficiency. Summary of the Invention

[0004] This invention provides a carrier film, an electromagnetic shielding film, and a circuit board to solve the technical problem that existing carrier films, after laser cutting, exhibit severe melting at the laser cutting edge, making it difficult to peel off from the electromagnetic shielding film after subsequent hot pressing processes, and easily resulting in damage and residue during peeling.

[0005] To solve the above-mentioned technical problems, the first aspect of the present invention provides a carrier film, wherein the absolute value of the difference between the thermal shrinkage rate of the carrier film in the TD direction and its thermal shrinkage rate in the MD direction is less than or equal to 1%.

[0006] As a preferred embodiment, the thermal shrinkage rate of the carrier membrane in the TD direction and the thermal shrinkage rate in the MD direction are both less than or equal to 2%.

[0007] As a preferred embodiment, the expansion / contraction ratio A of the carrier membrane in the TD direction and its expansion / contraction ratio B in the MD direction satisfy: B / A≤5; And / or, the expansion / contraction ratio A is less than or equal to 50. And the expansion / contraction rate B is less than or equal to 150. .

[0008] As a preferred embodiment, 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%; 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.

[0009] As a preferred embodiment, the difference between the melting point and the glass transition temperature of the carrier film is greater than or equal to 120°C.

[0010] As a preferred embodiment, the elastic modulus of the carrier membrane in the TD direction and the elastic modulus in the MD direction are both 3GPa~5GPa.

[0011] As a preferred embodiment, the absolute value of the difference between the elastic modulus of the carrier membrane in the TD direction and its elastic modulus in the MD direction is less than or equal to 1 GPa.

[0012] A second aspect of the present invention provides an electromagnetic shielding film, comprising a shielding film body and a carrier film as described in any of the first aspects; the shielding film body comprises an insulating layer, a shielding layer and an adhesive film layer, wherein the carrier film, the insulating layer, the shielding layer and the adhesive film layer are sequentially stacked.

[0013] As a preferred embodiment, the shielding layer has a plurality of raised structures on the side surface near the adhesive film layer; and / or, the adhesive film layer is provided with a plurality of conductive particles, the conductive particles being used to connect the ground terminal of the circuit board substrate and the shielding layer.

[0014] A third aspect of the present invention provides a circuit board, comprising a circuit board substrate and an electromagnetic shielding film as described in any of the second aspects, wherein the side of the electromagnetic shielding film away from the carrier film is pressed onto the circuit board substrate.

[0015] Compared with the prior art, the beneficial effect of the embodiments of the present invention is that by limiting the absolute value of the difference between the thermal shrinkage rates of the carrier film in the TD direction and the MD direction to less than or equal to 1%, it can be ensured that the absolute value of the difference between the thermal shrinkage rates of the carrier film in the TD direction and the MD direction is small, so that the internal stress distribution of the carrier film is uniform and isotropic. Thus, after laser cutting, it can ensure that the deformation at the laser cutting edge is small and the heat-affected zone is uniform, so that the range of the melt-resolidification zone after cooling is small. This avoids the phenomenon of adhesion between the carrier film and the shielding film body due to the large melt area after the hot pressing process, thereby making the carrier film easy to peel off from the electromagnetic shielding film and avoiding damage and residue. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the carrier membrane in an embodiment of the present invention; Figure 2 This is a schematic diagram of the laser cutting observation area in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the first electromagnetic shielding film in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the second type of electromagnetic shielding film in an embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of the third type of electromagnetic shielding film in this embodiment of the invention; Figure 6 This is a schematic diagram of a slice of the carrier membrane in Comparative Example 1 provided by the present invention after laser cutting; Figure 7 This is a schematic diagram of a slice of the carrier membrane in Comparative Example 1 provided by the present invention after hot pressing; Figure 8 This is a schematic diagram of a slice of the carrier membrane after laser cutting in Embodiment 3 of the present invention; Figure 9 This is a schematic diagram of a slice of the carrier membrane after hot pressing in Embodiment 3 of the present invention; Among them, 1. carrier film; 2. insulating layer; 3. shielding layer; 4. adhesive film layer; 5. raised structure; 6. conductive particles. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] In the description of this application, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

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

[0020] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0021] Please see Figure 1 The first aspect of the present invention provides a carrier membrane 1, wherein the absolute value of the difference between the thermal shrinkage rate of the carrier membrane 1 in the TD direction and its thermal shrinkage rate in the MD direction is less than or equal to 1%.

[0022] It is worth noting that in this embodiment, the carrier film 1 is stacked with the shielding film body in actual application. It is used to support and protect the various material layers in the shielding film body, provide sufficient tensile strength for the shielding film body, so that the various material layers in the shielding film body are not damaged by external contact or collision, and can prevent the shielding film body from wrinkling.

[0023] During laser cutting, most of the laser energy is absorbed by the carrier film 1 and converted into heat energy with high efficiency. This results in a rapid and high local temperature rise in the carrier film 1, which can easily lead to severe melting or even decomposition of the material at the laser cutting point. The molten polymer is fluid and diffuses and weaves into the surrounding area, forming a wide melt-resolidification zone after cooling. Therefore, during subsequent hot pressing, the large melt-resolidification zone leads to excessive molten material at the laser cutting point after hot pressing, forming a large molten area. This causes adhesion between the carrier film 1 and the shielding layer body, making subsequent tearing difficult. Moreover, the severe adhesion during tearing easily results in damage and residue, requiring manual removal of the remaining portion of the carrier film 1, which seriously affects the production efficiency of the circuit board.

[0024] To facilitate the peeling of the carrier film 1 from the electromagnetic shielding film after laser cutting and hot pressing, this embodiment limits the absolute value of the difference between the thermal shrinkage rate of the carrier film 1 in the TD (Transverse Direction) direction and its thermal shrinkage rate in the MD (Machine Direction, i.e., the longitudinal direction consistent with the machine's running direction) direction to be less than or equal to 1%. For example, the absolute value of the difference between the thermal shrinkage rate of the carrier film 1 in the TD direction and its thermal shrinkage rate in the MD direction is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc., and this embodiment does not impose specific limitations on this. It is worth noting that the thermal shrinkage rate can reflect the level and direction of the residual stress inside the carrier film 1. The higher and more unbalanced the internal residual stress, the greater the difference in thermal shrinkage rates in the TD and MD directions. Therefore, this embodiment limits the absolute value of the difference between the thermal shrinkage rate of the carrier film 1 in the TD direction and its thermal shrinkage rate in the MD direction to be small, so that the thermal shrinkage rate of the carrier film 1 in the TD direction is close to its thermal shrinkage rate in the MD direction. This indicates that the stretch ratio of the carrier film 1 in the transverse and longitudinal directions is similar, and the internal residual stress is comparable. This can effectively improve the melting effect at the laser cutting edge caused by the transient high temperature during laser cutting, and further ensure that the deformation at the laser cutting edge is small and the heat-affected zone is uniform. This makes the range of the melt-resolidification zone after cooling small, and avoids the phenomenon of adhesion between the carrier film 1 and the shielding film body due to the large melt area after the hot pressing process. This better ensures that the carrier film 1 is easy to peel off from the electromagnetic shielding film and avoids damage and residue.

[0025] 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.

[0026] As a preferred embodiment, the thermal shrinkage rate of the carrier membrane 1 in the TD direction and the thermal shrinkage rate in the MD direction are both less than or equal to 2%.

[0027] Specifically, in this embodiment, the thermal shrinkage rate of the carrier film 1 in the TD direction and its thermal shrinkage rate in the MD direction are both less than or equal to 2%. For example, the thermal shrinkage rate of the carrier film 1 in the TD direction can be 2%, 1.7%, 1.5%, 1.3%, 1%, 0.7%, 0.5%, 0.3%, etc., and the thermal shrinkage rate of the carrier film 1 in the MD direction can be 2%, 1.7%, 1.5%, 1.3%, 1%, 0.7%, 0.5%, 0.3%, etc. The thermal shrinkage rate of the carrier film 1 in the TD direction and its thermal shrinkage rate in the MD direction can be the same or different. The example is not specifically limited here, which can ensure that the thermal shrinkage rate of the carrier film 1 is small in both the TD direction and the MD direction, reduce the internal residual stress of the carrier film 1, and ensure that the material around the laser cutting edge does not shrink strongly during laser cutting. This can better ensure that the deformation at the laser cutting edge is small. Under the action of surface tension, the molten polymer liquid forms a relatively neat and narrow melt-resolidification zone, which effectively reduces the range of the melt-resolidification zone after cooling. This ensures that no obviously large melt area is generated after hot pressing, making the carrier film 1 easy to tear off.

[0028] In this embodiment, the test procedure for the thermal shrinkage rate of the carrier film 1 is as follows: At least five standard samples are cut from both the longitudinal (MD) and transverse (TD) sections of the carrier film 1. For example, the cut dimensions of the standard samples can be 100mm × 100mm or 120mm × 120mm. Measurement points are then precisely marked on each sample, for example, by drawing a 100mm × 100mm rectangle as a marker. Under a standard environment of 23°C and 50%RH, the initial length (L0) of the marker point is measured using an optical measuring instrument or a high-precision vernier caliper, accurate to 0.01mm. The standard samples are then placed unconstrained in an oven that has reached a set temperature. The oven temperature depends on the material; for example, 150°C is commonly used for PET (Polyethylene terephthalate), and 120°C is commonly used for PP (Polypropylene). The samples are heated for a specific time, such as 30 minutes. Furthermore, the standard samples must be able to shrink freely without any clamping or frictional obstruction. Then remove the standard sample and cool it to room temperature, being careful to lay it flat to prevent deformation. Measure the final length (L1) between the same marked points again. Finally, calculate the heat shrinkage rate using the expression: Heat shrinkage rate (%) = [(L0-L1) / L0] × 100%. Take the average heat shrinkage rate of multiple standard samples as the final value, and calculate the heat shrinkage rate in the MD direction and the TD direction respectively using the test method described above.

[0029] As a preferred embodiment, the expansion / contraction ratio A of the carrier membrane 1 in the TD direction and its expansion / contraction ratio B in the MD direction satisfy: B / A≤5.

[0030] To facilitate the peeling of the carrier film 1 from the electromagnetic shielding film after laser cutting and hot pressing, this embodiment further specifies that the expansion / contraction ratio A in the TD direction and the expansion / contraction ratio B in the MD direction of the carrier film 1 satisfy: B / A ≤ 5. For example, B / A can be 5, 4.5, 4, 3.5, 3, 2, 1, etc., which are not specifically limited in this embodiment. It is understood that the expansion / contraction ratio is a macroscopic manifestation of the residual stress, molecular orientation, and crystallinity within the material. A carrier film 1 with a small expansion / contraction ratio has a more stable internal structure and lower residual stress. During laser processing, heat is concentrated in the cutting area, resulting in a neat edge seal. A carrier film 1 with a large expansion / contraction ratio has higher residual stress. During laser processing, the heat generated not only serves for cutting but also triggers a large-scale stress release and molecular chain rearrangement, leading to severe melting and deformation of the carrier film 1 at the edge seal. This embodiment improves the carrier film 1 by limiting its expansion / contraction ratio in the TD and MD directions to be small, thereby ensuring that the internal stress distribution of the carrier film 1 is uniform and isotropic. During laser cutting, the laser energy is concentrated at the cutting edge, causing the material at the cutting edge to melt instantly. However, due to the uniform internal stress distribution and stable structure of the surrounding material, there is no strong shrinkage force. Under the action of surface tension, the molten polymer liquid forms a relatively neat and narrow melt-resolidification zone, i.e., the sealing edge. This ensures that after laser cutting, the deformation at the sealing edge is small, the heat-affected zone is uniform, and the sealing quality is good. After subsequent hot pressing, there will be no obviously large melting area that would cause the carrier film 1 to stick to the shielding film body, making the carrier film 1 easy to peel off from the electromagnetic shielding film and avoiding damage and residue.

[0031] Furthermore, the expansion / contraction ratio A is less than or equal to 50. And the expansion / contraction rate B is less than or equal to 150. .

[0032] Specifically, this embodiment further limits the expansion / contraction ratio A of the carrier membrane 1 in the TD direction to be less than or equal to 50%. And the expansion / contraction rate B in the MD direction is less than or equal to 150. For example, the expansion / contraction ratio A can be 50. 45 40 35 30 25 20 15 10 5 The expansion / contraction rate B can be 150. 140 130 120 110 100 90 80 70 60 50 40 30 20 10 In this embodiment, no specific limitations are made, thereby ensuring that the expansion and contraction rates A and B are small and do not differ too much, resulting in smaller internal residual stress in the carrier film 1. This further improves the structural stability of the material around the laser cutting edge during laser cutting, and better ensures that the deformation at the laser cutting edge is smaller after laser cutting, so that the range of the melt-resolidification zone after cooling is smaller.

[0033] In this embodiment, the method for determining the expansion and contraction rate of the carrier membrane 1 is as follows: A carrier membrane sample with dimensions of 230mm × 250mm is cut, and holes are drilled at the four corners of the carrier membrane sample, which are recorded as drilling points A, B, C, and D, respectively. The distances between drilling points A and B, C and D, A and B and D of the carrier membrane sample are measured using a two-dimensional image measuring instrument, and recorded as L, respectively. A-B L C-D L A-C L B-D Then, the carrier film 1 is laminated onto the substrate surface of FCCL (Flexible Copper Clad Laminate). The high-speed press is preheated for 10 seconds, and the pressing conditions are: pressing temperature of 150℃~300℃ and pressing pressure of 60kg / cm². 2 ~180kg / cm 2 The pressing time is 120s~240s. After pressing and curing under appropriate conditions, the distances between the perforation points A and B, C and D, A and C, and B and D of the carrier film sample are measured again using a two-dimensional image measuring instrument and denoted as F. A-B F C-D F A-C F B-D Finally, the calculation process for the expansion / contraction rate A in the TD direction and the expansion / contraction rate B in the MD direction is as follows: The rate of expansion / contraction A = [(F A-B -L A-B) / (2×L A-B )+(F C-D -L C-D ) / (2×L C-D )]×100%; The rate of expansion / contraction B = [(F A-C -L A-C ) / (2×L A-C )+(F B-D -L B-D ) / (2×L B-D )]×100%.

[0034] 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.

[0035] 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%, 4.5%, 4%, 3.5%, 3%, 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. 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 a large melt area during the subsequent hot pressing process, which would make it difficult to peel off.

[0036] It is worth noting that, such as Figure 2As 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 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.

[0037] As a preferred embodiment, the difference between the melting point and the glass transition temperature of the carrier film 1 is greater than or equal to 120°C.

[0038] Specifically, this embodiment further limits the difference between the melting point and the glass transition temperature of the carrier film 1 to be greater than or equal to 120°C. For example, the difference between the melting point and the glass transition temperature of the carrier film 1 can be 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc. This embodiment does not make a specific limitation here. This results in a wider temperature range for the material of the carrier film 1 to transition from the glassy state to the molten state, indicating that the material of the carrier film 1 requires more energy to melt. During laser cutting, this allows for more time for heat to dissipate, and sufficient heat setting can effectively eliminate internal stress, reduce the thermal shrinkage rate of the carrier film 1, and reduce the melting range at the laser-cut edge of the carrier film 1. In an optional embodiment, the melting point and the glass transition temperature of the carrier film 1 can be measured by a DSC (Differential Scanning Calorimetry) instrument.

[0039] As a preferred embodiment, the elastic modulus of the carrier membrane 1 in the TD direction and the elastic modulus in the MD direction are both 3 GPa to 5 GPa.

[0040] It is worth noting that if the elastic modulus of the carrier film 1 is too low, the intermolecular forces are weak, and the chain segments are very easy to move and align on a large scale under external forces. During laser cutting, the material is not only vaporized but also melted. The molten polymer is easily stretched by the impact force or surface tension of the laser, forming rough, burr-like, and stringy cut edges, resulting in a large melting range. On the other hand, if the elastic modulus of the carrier film 1 is too high, the internal residual stress of the carrier film 1 is too high. Once the carrier film 1 is heated, such as after hot pressing or laser cutting, its internal residual stress will be released violently, and the molecular chains will shrink rapidly, resulting in a rapid and uneven change in the size of the carrier film 1 with a large expansion and contraction rate. At the same time, it will also cause severe melting and deformation of the material at the laser-cut edge.

[0041] Therefore, in this embodiment, the elastic modulus of the carrier membrane 1 in both the TD direction and the MD direction is limited to 3 GPa to 5 GPa. For example, the elastic modulus of the carrier membrane 1 in the TD direction is 3 GPa, 3.4 GPa, 3.8 GPa, 4 GPa, 4.3 GPa, 4.6 GPa, 5 GPa, etc., and the elastic modulus of the carrier membrane 1 in the MD direction is 3 GPa, 3.5 GPa, 3.7 GPa, 4 GPa, 4.2 GPa, 4.5 GPa, 4.8 GPa, 5 GPa, etc., and the elastic modulus of the carrier membrane 1 in the MD direction is 3 GPa, 3.5 GPa, 3.7 GPa, 4 GPa, 4.2 GPa, 4.5 GPa, 4.8 GPa, 5 GPa, etc. The elastic modulus in the TD direction and its elastic modulus in the MD direction may be the same or different. This embodiment does not make a specific limitation, so that the elastic modulus of the carrier film 1 in the TD direction and its elastic modulus in the MD direction are both limited to a suitable range. This makes the internal stress of the carrier film 1 smaller and the shrinkage resistance better. During laser cutting, the degree of melting at the laser cutting edge can be reduced, so that the molten area after subsequent hot pressing is reduced and adhesion is avoided. This makes it easy to peel the carrier film 1 from the electromagnetic shielding film and avoids damage and residue.

[0042] In this embodiment, a carrier membrane 1 with a stable structure and suitable elastic modulus can be obtained by filler reinforcement or sufficient heat setting. This carrier membrane 1 can provide sufficient stiffness and stability during processing and maintain dimensional stability when heated, thereby obtaining clean and neat laser-cut edges. The elastic modulus of the carrier membrane 1 can be obtained by tensile testing using a tensile testing machine, referring to the ISO 527-3 testing standard.

[0043] As a preferred embodiment, the absolute value of the difference between the elastic modulus of the carrier membrane 1 in the TD direction and its elastic modulus in the MD direction is less than or equal to 1 GPa.

[0044] Specifically, this embodiment further limits the absolute value of the difference between the elastic modulus of the carrier film 1 in the TD direction and its elastic modulus in the MD direction to be less than or equal to 1 GPa. For example, the absolute value of the difference between the elastic modulus of the carrier film 1 in the TD direction and its elastic modulus in the MD direction is 1 GPa, 0.8 GPa, 0.7 GPa, 0.5 GPa, 0.3 GPa, 0.1 GPa, etc. This embodiment does not make a specific limitation, thereby making the difference in elastic modulus of the carrier film 1 in the TD direction and MD direction small, ensuring the internal stress balance of the carrier film 1, thereby better avoiding uneven changes in the size of the carrier film 1 during laser cutting, and ensuring clean and neat laser cut edges.

[0045] Please see Figure 3 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, wherein the carrier film 1, the insulating layer 2, the shielding layer 3 and the adhesive film layer 4 are sequentially stacked.

[0046] Specifically, in this embodiment, the electromagnetic shielding film is obtained by sequentially stacking a carrier film 1, an insulating layer 2, a shielding layer 3, and an adhesive film layer 4. 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.

[0047] The insulating layer 2 serves to insulate and protect the shielding layer 3, while also preventing wear and tear on the shielding layer 3, thus 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. Alternatively, 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 types of resins; 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.

[0048] The shielding layer 3 is used 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.

[0049] 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.

[0050] As a preferred embodiment, the shielding layer 3 has a plurality of protrusion structures 5 on the side surface near the adhesive film layer 4; Specifically, such as Figure 4 As shown, in this embodiment, the surface of the shielding layer 3 near the adhesive film layer 4 is an uneven surface. This side surface is provided with several protrusions 5. 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.

[0051] 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.

[0052] Specifically, such as Figure 5 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.

[0053] 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.

[0054] 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.

[0055] The carrier film, electromagnetic shielding film, and circuit board provided in the embodiments of the present invention have at least the following beneficial effects: (1) By limiting the absolute value of the difference between the thermal shrinkage rates of the carrier film in the TD and MD directions to less than or equal to 1%, it is possible to ensure that the absolute value of the difference between the thermal shrinkage rates of the carrier film in the TD and MD directions is small, so that the internal stress distribution of the carrier film is uniform and isotropic. Thus, after laser cutting, it is possible to ensure that the deformation at the laser cutting edge is small and the heat-affected zone is uniform, so that the range of the melt-resolidification zone after cooling is small, avoiding the phenomenon of adhesion between the carrier film and the shielding film body due to the large melt area after the hot pressing process. In this way, the carrier film can be easily peeled off from the electromagnetic shielding film to avoid damage and residue.

[0056] (2) By limiting the ratio of the expansion and contraction rate of the carrier film in the TD direction and the MD direction to less than or equal to 5, it can be ensured that the ratio of the expansion and contraction rate of the carrier film in the TD direction and the MD direction is small, which further ensures that the internal stress distribution of the carrier film is uniform and isotropic. Thus, after laser cutting, it can further ensure that the deformation at the laser cutting edge is small and the heat-affected zone is uniform, so that the range of the melt-resolidification zone after cooling is small, avoiding the phenomenon of adhesion between the carrier film and the shielding film body due to the large melt area after the hot pressing process. In this way, the carrier film can be easily peeled off from the electromagnetic shielding film to avoid damage and residue.

[0057] (3) By limiting the expansion / contraction ratio A of the carrier membrane in the TD direction to less than or equal to 50 And the expansion / contraction rate B in the MD direction is less than or equal to 150. This ensures that the expansion and contraction rates A and B are small, resulting in lower residual stress inside the carrier film. This further improves the structural stability of the material around the laser cutting edge during laser cutting, and better ensures that the deformation at the laser cutting edge is smaller after laser cutting, thus minimizing the size of the molten resolidification zone after cooling.

[0058] (4) By limiting the thermal shrinkage rate of the carrier film in the TD direction and the thermal shrinkage rate in the MD direction to less than or equal to 2%, it can be ensured that the thermal shrinkage rate of the carrier film in both the TD and MD directions is small, which can reduce the internal residual stress of the carrier film and ensure that the material around the laser cutting edge will not shrink strongly during laser cutting. This can better ensure that the deformation at the laser cutting edge is small, effectively reduce the range of the melt resolidification zone after cooling, and thus ensure that no obviously large melt area is generated after hot pressing, making the carrier film easy to tear off.

[0059] (5) By limiting 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%, so that the change rate of the sliced ​​area in the laser cutting observation area before and after laser cutting is small, thereby ensuring that the deformation at the laser cutting point is small and the range of the melt-resolidification zone formed after laser cutting is small, avoiding the phenomenon of adhesion between the carrier film and the shielding film body due to the large melting area during subsequent hot pressing, which makes it difficult to peel off.

[0060] (6) By limiting the difference between the melting point of the carrier film and its glass transition temperature to be greater than or equal to 120°C, the material of the carrier film requires more energy to melt. During laser cutting, the heat can be dissipated more fully, which can reduce the thermal shrinkage rate of the carrier film and reduce the melting range at the edge of the carrier film during laser cutting.

[0061] (7) By limiting the elastic modulus of the carrier film in the TD direction and its elastic modulus in the MD direction to 3GPa~5GPa, and the absolute value of the difference between the elastic modulus in the TD direction and its elastic modulus in the MD direction to less than or equal to 1GPa, the internal stress of the carrier film is smaller, the uniformity is better and the shrinkage resistance is better, thereby better avoiding the uneven change of the size of the carrier film during laser cutting, and ensuring the cleanliness and neatness of the laser cut edge.

[0062] 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.

[0063] Example 1 A carrier membrane having a thermal shrinkage rate of 1% in the TD direction and a thermal shrinkage rate of 1.5% in the MD direction.

[0064] Example 2 A carrier membrane having a shrinkage rate A of 30 in the TD direction. Its expansion / contraction rate B in the MD direction is 135. Furthermore, its thermal shrinkage rate in the TD direction is 0.8%, and its thermal shrinkage rate in the MD direction is 1.2%.

[0065] 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 less than or equal to 4.8%. 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.

[0066] Example 3 A carrier membrane having a shrinkage rate A of 20 in the TD direction. Its expansion / contraction rate B in the MD direction is 84. Furthermore, its thermal shrinkage rate in the TD direction is 0.5%, and its thermal shrinkage rate in the MD direction is 1.5%.

[0067] 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 less than or equal to 3.6%. 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.

[0068] The difference between the melting point and the glass transition temperature of the carrier film is 140℃. Its elastic modulus in the TD direction is 3.2 GPa and its elastic modulus in the MD direction is 3.8 GPa.

[0069] Example 4 A carrier membrane having a shrinkage rate A of 38 in the TD direction. Its expansion / contraction rate B in the MD direction is 120. Furthermore, its thermal shrinkage rate in the TD direction is 0.3%, and its thermal shrinkage rate in the MD direction is 1%.

[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 is less than or equal to 2.8%. 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] The difference between the melting point and the glass transition temperature of the carrier film is 125℃. Its elastic modulus in the TD direction is 3.5GPa and its elastic modulus in the MD direction is 4GPa.

[0072] Example 5 A carrier membrane having a expansion / contraction ratio A of 15 in the TD direction. Its expansion / contraction rate B in the MD direction is 50. Furthermore, its thermal shrinkage rate in the TD direction is 1.5%, and its thermal shrinkage rate in the MD direction is 2%.

[0073] 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 less than or equal to 2%. 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.

[0074] The difference between the melting point and the glass transition temperature of the carrier film is 130℃. Its elastic modulus in the TD direction is 4GPa and its elastic modulus in the MD direction is 5GPa.

[0075] Comparative Example 1 A carrier membrane has a thermal shrinkage rate of 3.2% in the TD direction and a thermal shrinkage rate of 5% in the MD direction.

[0076] Electromagnetic shielding films were prepared using the carrier films from Examples 1-5 and Comparative Example 1. The insulating layer, shielding layer, and adhesive film layer in the electromagnetic shielding films were all identical. They were processed using the same laser engraving parameters to be cut into the same 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, and it was observed whether it could be successfully peeled off without any damage or residue. The test results are shown in Table 1 below. Table 1. Carrier membrane tearing status

[0077] As can be seen from Table 1 above, since the carrier films in Examples 1 to 5 all satisfy the condition that the absolute value of the difference between the thermal shrinkage rates in the TD and MD directions is less than or equal to 1%, it can be ensured that the absolute value of the difference between the thermal shrinkage rates in the TD and MD directions is small. This makes the internal stress distribution of the carrier film uniform and isotropic, thus ensuring that the deformation at the laser cutting edge is small and the heat-affected zone is uniform after laser cutting. This makes the area of ​​the melt-resolidification zone after cooling small, avoiding the phenomenon of adhesion between the carrier film and the shielding film body due to the large melt area after the hot pressing process. In this way, the carrier film can be easily peeled off from the electromagnetic shielding film to avoid damage and residue.

[0078] In Comparative Example 1, the carrier film not only exhibits excessive thermal shrinkage rates in both the TD and MD directions, but also has an absolute difference between these rates exceeding 1%. This excessive difference in thermal shrinkage rates between the TD and MD directions leads to an uneven distribution of internal stress within the carrier film. After laser cutting, the deformation at the laser-cut edge is significant, resulting in an uneven heat-affected zone. Consequently, the area of ​​the melt-re-solidification zone after cooling is excessively large. During the hot-pressing process, the excessively large melt zone causes adhesion between the carrier film and the shielding film, making it impossible to tear them apart in one go, and resulting in damage and residue after tearing.

[0079] In addition, such as Figure 6 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 7 The 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.

[0080] But if Figure 8 The diagram shows a slice of the carrier membrane in Example 3 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 9 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.

[0081] 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 absolute value of the difference between the thermal shrinkage rate of the carrier membrane in the TD direction and its thermal shrinkage rate in the MD direction is less than or equal to 1%.

2. The carrier membrane as described in claim 1, characterized in that, The thermal shrinkage rate of the carrier membrane in the TD direction and the thermal shrinkage rate in the MD direction are both less than or equal to 2%.

3. The carrier membrane as described in claim 1, characterized in that, The expansion / contraction ratio A of the carrier membrane in the TD direction and its expansion / contraction ratio B in the MD direction satisfy: B / A≤5; And / or, the expansion / contraction ratio A is less than or equal to 50. And the expansion / contraction rate B is less than or equal to 150. .

4. 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.

5. The carrier membrane as described in claim 1, characterized in that, The difference between the melting point and the glass transition temperature of the carrier film is greater than or equal to 120°C.

6. The carrier membrane as described in claim 1, characterized in that, The elastic modulus of the carrier membrane in the TD direction and the elastic modulus in the MD direction are both 3 GPa to 5 GPa.

7. The carrier membrane as described in claim 6, characterized in that, The absolute value of the difference between the elastic modulus of the carrier membrane in the TD direction and its elastic modulus in the MD direction is less than or equal to 1 GPa.

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, wherein the carrier film, the insulating layer, the shielding layer and the adhesive film layer are stacked sequentially.

9. The electromagnetic shielding film as described in claim 8, characterized in that, The shielding layer has several raised structures on the side surface near the adhesive film layer; and / or, the adhesive film layer contains several 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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