Electromagnetic shielding film and circuit board

Abstract

The invention discloses an electromagnetic shielding film and a circuit board, the electromagnetic shielding film comprises a first shielding layer, an interlayer and a second shielding layer which are stacked in sequence, and the interlayer is arranged between the first shielding layer and the second shielding layer, so that the bending resistance of the electromagnetic shielding film or the circuit board or a soft board containing the electromagnetic shielding film is effectively improved; meanwhile, the shielding performance of the electromagnetic shielding film is also improved; furthermore, at least one surface of the interlayer is a non-flat surface, and the non-flat surface comprises a concave part and a convex part, so that the bending resistance of the electromagnetic shielding film or a circuit board or a soft board containing the electromagnetic shielding film is improved on the premise of ensuring the shielding performance of the electromagnetic shielding film.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and in particular to an electromagnetic shielding film and a circuit board. Background Art

[0002] With the development of miniaturization of communication equipment, there are higher and higher requirements for the miniaturization of integrated circuit boards. However, the further miniaturization of integrated circuit boards has also developed to a certain limit, so the miniaturization of communication equipment has also been restricted. In order to achieve further miniaturization of communication equipment, foldable mobile phones came into being. In order for foldable mobile phones to operate normally and avoid electromagnetic interference from the outside world and itself, it is necessary to apply a shielding film on the surface of the soft board or circuit board of the foldable mobile phone. However, the shielding film in the prior art is attached to the hard board and is not suitable for the soft board. The folding circuit board or soft board requires a long time and high frequency of folding or opening and closing. The existing shielding film is difficult to meet such high requirements, which will cause damage to the internal circuits of the circuit board or soft board.

[0003] It can be seen that in order to adapt to the application requirements of existing circuit boards or flexible boards, a shielding film that meets the performance requirements is urgently needed. Summary of the invention

[0004] The purpose of the embodiments of the present invention is to provide an electromagnetic shielding film and a circuit board, which can effectively improve the bending resistance of the electromagnetic shielding film itself or the circuit board or flexible board containing the electromagnetic shielding film; and at the same time can improve the shielding performance of the electromagnetic shielding film.

[0005] In order to solve the above technical problems, an embodiment of the present invention provides an electromagnetic shielding film, which includes a first shielding layer, an interlayer and a second shielding layer. The first shielding layer, the interlayer and the second shielding layer are stacked in sequence, and at least one side of the interlayer is an uneven surface, and the uneven surface includes concave portions and convex portions.

[0006] As a preferred solution, the vertical height difference ΔH between adjacent concave portions and convex portions in the interlayer is ≤ 8 μm.

[0007] As a preferred solution, the concave parts and the convex parts of the uneven surface of the interlayer are arranged at intervals.

[0008] As a preferred solution, the distance between adjacent recesses of the interlayer is greater than or equal to 5 μm.

[0009] As a preferred solution, within a range of 260 μm of the uneven surface of the interlayer, the number of the recesses is less than 40.

[0010] As a preferred solution, the vertical distance between the bottom end of the concave portion and the center line is 1-5 μm, and the center line is a middle line determined according to the highest points of the plurality of convex portions and the lowest points of the plurality of concave portions.

[0011] As a preferred embodiment, the ratio of the plane width D of the recess on the uneven surface of the interlayer to the depth H of the recess satisfies: 1.1≤D / H≤7.5, and the plane width D refers to the maximum width of the recess on the uneven surface or the horizontal distance between the tops of two protrusions adjacent to the recess.

[0012] As a preferred solution, the vertical distance between the top of the convex portion and the center line is 1-5 μm; the center line is a middle line determined based on the plurality of convex portions and the plurality of concave portions.

[0013] As a preferred solution, the concave portions whose bottom ends are at a vertical distance of 1-4 μm from the center line account for more than 50% of the statistical number of concave portions.

[0014] As a preferred solution, the concave portions whose bottom ends are at a vertical distance of 2-4 μm from the center line account for more than 65% of the statistical number of concave portions.

[0015] As a preferred embodiment, the concave portions whose bottom ends are 1-2 μm away from the center line at a vertical distance of 15%-30% of the statistical number of concave portions, the concave portions whose bottom ends are 2-3.5 μm away from the center line at a vertical distance of 40%-75% of the statistical number of concave portions, the concave portions whose bottom ends are 3.5-5 μm away from the center line at a vertical distance of 18%-37% of the statistical number of concave portions, and the center line is the middle line determined based on the plurality of convex portions and the plurality of concave portions.

[0016] As a preferred solution, the non-flat surface also includes a flat portion.

[0017] As a preferred solution, the electromagnetic shielding film further comprises a base layer and an adhesive layer, and the base layer, the first shielding layer, the interlayer, the second shielding layer and the adhesive layer are stacked in sequence.

[0018] As a preferred solution, the second shielding layer has a protrusion on a side away from the first shielding layer.

[0019] In order to solve the same technical problem, an embodiment of the present invention further provides a circuit board, which includes the electromagnetic shielding film as described in any of the above embodiments.

[0020] Compared with the prior art, the embodiments of the present invention provide an electromagnetic shielding film and a circuit board, the circuit board comprising an electromagnetic shielding film, the electromagnetic shielding film comprising a first shielding layer, an interlayer and a second shielding layer stacked in sequence, the interlayer being arranged between the first shielding layer and the second shielding layer, which effectively increases the bending resistance of the electromagnetic shielding film itself or the circuit board or flexible board containing the electromagnetic shielding film, while also improving the shielding performance of the electromagnetic shielding film; further, at least one side of the interlayer is an uneven surface, the uneven surface comprising concave portions and convex portions, which improves the bending resistance of the electromagnetic shielding film itself or the circuit board or flexible board containing the electromagnetic shielding film while ensuring the shielding performance of the electromagnetic shielding film. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic structural diagram of an electromagnetic shielding film in an embodiment of the present invention;

[0022] Figure 2 is another structural schematic diagram of the electromagnetic shielding film in the embodiment of the present invention;

[0023] Figure 3 is a schematic structural diagram of the interlayer in an embodiment of the present invention;

[0024] Figure 4 is another structural schematic diagram of the electromagnetic shielding film in the embodiment of the present invention;

[0025] Figure 5 is another structural schematic diagram of the electromagnetic shielding film in the embodiment of the present invention;

[0026] Figure 6 is a schematic diagram of the structure of a circuit board in an embodiment of the present invention;

[0027] Among them, 1. first shielding layer; 2. interlayer; 21. uneven surface; 211. convex part; 212. concave part; 3. second shielding layer; 31. protrusion; 4. adhesive layer; 5. base layer; 6. circuit board body. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In the description of this application, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0030] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a connection between the two elements. The terms "vertical", "horizontal", "left", "right", "upper", "lower" and similar expressions used herein are only for illustrative purposes, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0031] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0032] See also Figure 1 and 2 The preferred embodiment of the present invention provides an electromagnetic shielding film, comprising a first shielding layer 1, an interlayer 2, and a second shielding layer 3, wherein the first shielding layer 1, the interlayer 2, and the second shielding layer 3 are stacked in sequence, and at least one side of the interlayer 2 is a non-flat surface 21, and the non-flat surface 21 includes a convex portion 211 and a concave portion 212. Figure 1 The non-flat surface 21 is arranged on one side of the interlayer 2 close to the first shielding layer 1, Figure 2 The uneven surface 21 is arranged on a side of the interlayer 2 close to the second shielding layer 3. Optionally, concave portions and convex portions may be arranged on both sides of the uneven surface 21.

[0033] It should be noted that a first shielding layer 1 and a second shielding layer 3 are arranged in the electromagnetic shielding film to improve the shielding performance of the electromagnetic shielding film, which has a better shielding effect than a single-layer shielding layer. An interlayer 2 is arranged between the first shielding layer 1 and the second shielding layer 3 to reduce stress concentration in the electromagnetic shielding film, so as to improve the bending resistance of the electromagnetic shielding film and a circuit board or a flexible board containing the electromagnetic shielding film. Furthermore, the protrusion 211 and the recess 212 have a great relationship with the step resistance and the bending resistance. By arranging the recess 212 and the protrusion 211 on at least one side of the interlayer 2, while ensuring that the electromagnetic shielding film has a step resistance, the electromagnetic shielding film itself and the circuit board or the flexible board containing the electromagnetic shielding film can also have good bending resistance, thereby enabling the electromagnetic shielding film to meet current application requirements. The shapes or sizes of different protrusions may be the same or different, and the shapes or sizes of different recesses may be the same or different.

[0034] Preferably, the interlayer 2 is non-metallic, and the non-metallic may include but is not limited to at least one of epoxy resin, polyester resin, polyurethane resin, acrylic resin, alkyd resin, polyamide resin, and polyimide resin, that is, the material of the interlayer 2 may be selected from at least one of epoxy resin, polyester resin, polyurethane resin, acrylic resin, alkyd resin, polyamide resin, and polyimide resin. In the technical means of the embodiment of the present invention, the interlayer 2 mainly plays the role of improving the bending resistance of the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film.

[0035] Preferably, the material of the first shielding layer 1 and the second shielding layer 3 is at least one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. It is understandable that the material of the first shielding layer 1 and the second shielding layer 3 can be metal or alloy. In order to ensure that the first shielding layer 1 and the second shielding layer 3 have good electrical conductivity, the first shielding layer 1 and the second shielding layer 3 are made of at least one material of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. The materials of the first shielding layer 1 and the second shielding layer 3 can be the same or different, and are not specifically limited here.

[0036] By adopting the technical means of the embodiment of the present invention, an interlayer 2 is arranged between the first shielding layer 1 and the second shielding layer 3, so as to improve the bending resistance of the electromagnetic shielding layer itself and the circuit board or flexible board containing the electromagnetic shielding film. Furthermore, considering the influence of the surface condition of the interlayer 2 on the overall structure of the electromagnetic shielding film and the bending resistance of the circuit board or flexible board containing the electromagnetic shielding film, at least one side of the interlayer 2 is arranged to be an uneven surface 21, and the uneven surface 21 includes a convex portion 211 and a concave portion 212. While ensuring the shielding performance of the electromagnetic shielding film, the bending resistance of the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film is improved, so that the electromagnetic shielding film meets the requirements of long-term and high-frequency folding or opening and closing; at the same time, the debonding between the layers of the electromagnetic shielding film itself is reduced, which is suitable for products with high requirements for bending resistance. Only the convexity whose vertical distance between the top of the convexity 211 of the interlayer 2 and the midline is greater than 0.8 microns can be called the convexity 211; only the concaveity whose vertical distance between the bottom of the concave 212 of the interlayer 2 and the midline is greater than 0.8 microns can be called the concave 212. Specifically, the vertical distance of the convexity can be determined by obtaining a slice diagram of the electromagnetic shielding film or shielding layer, and measuring the vertical distance of the convexity using the slice diagram. The midline is the midline between the lowest point of all the concave parts and the highest point of all the convex parts in the view to be tested.

[0037] As a preferred embodiment, the vertical height difference ΔH between adjacent convex portions 211 and concave portions 212 on the same surface of the interlayer 2 is ≤8 μm.

[0038] Please note that Figure 3 In the interlayer 2 shown, the vertical height difference ΔH between adjacent convex portions 211 and concave portions 212 is the vertical distance between the top of the adjacent convex portions 211 and the bottom of the concave portions 212 on the same surface of the interlayer 2; the thickness at the thinnest part of the concave portion refers to the thickness at the thinnest part of the interlayer, such as the distance from the bottom of the concave portion in the interlayer 2 to the other surface, such as Figure 3 H min The average thickness of the interlayer 2 is obtained by measuring the vertical distances between the two surfaces at multiple different positions of the interlayer 2 and averaging them. The height difference ΔH and the thickness at the thinnest part of the concave portion can be measured by sectioning using a scanning electron microscope or other detection methods, and the specific detection method is not limited here.

[0039] In the embodiment of the present invention, the vertical height difference ΔH between adjacent concave and convex parts and the relationship between the thickness of the thinnest concave part of the interlayer and the average thickness of the interlayer are taken into consideration, and the vertical height difference ΔH between adjacent convex parts 211 and concave parts 212 is set to be less than or equal to 8 microns, and the thickness of the thinnest part of the interlayer is greater than or equal to 3 / 4 of the average thickness of the interlayer 2. The vertical height difference ΔH between adjacent convex parts 211 and concave parts 212 can be specifically an interval consisting of any two values ​​between 2, 4, 6, 8 or less than or equal to 8 microns, and the unit is microns. Of course, the vertical height difference ΔH between adjacent convex parts 211 and concave parts 212 can also be any other value less than or equal to 8 microns, which is not specifically limited here.

[0040] By adopting the technical means of the embodiment of the present invention, the vertical height difference ΔH between the adjacent convex parts 211 and concave parts 212 in the interlayer 2 and the thickness of the thinnest part of the concave part of the interlayer 2 are limited. Such a setting can ensure that the electromagnetic shielding film's resistance to fracture difference is improved while ensuring the stability of the electromagnetic shielding film's own structure; at the same time, the electromagnetic shielding film and the circuit board or soft board containing the electromagnetic shielding film have improved bending resistance, making the electromagnetic shielding film suitable for products that require long-term and high-frequency folding or opening and closing. The overall average thickness of the electromagnetic shielding film is 5 microns to 25 microns. The average thickness of the first shielding layer 1 and the second shielding layer 3 are 0.5 microns to 6 microns respectively; the average thickness of the interlayer 2 is 0.2 microns to 8 microns.

[0041] As a preferred embodiment, the convex portions 211 and the concave portions 212 of the uneven surface of the interlayer 2 are arranged with intervals therebetween.

[0042] By adopting the technical means of the embodiment of the present invention and arranging the convex parts 211 and the concave parts 212 at intervals, the parameters of different parts of the interlayer can be balanced, thereby achieving balanced performance of various parts of the manufactured electromagnetic shielding film.

[0043] As a preferred embodiment, the distance between adjacent recesses 212 of the interlayer 2 is greater than or equal to 5 μm.

[0044] It should be noted that in the SEM slice image, multiple tiny concave parts will be gathered together to form a large concave part. In the actual process, the concave parts gathered together are generally considered to be one concave part. Similarly, in the SEM slice image, multiple tiny convex parts will be gathered together to form a large convex part. In the actual process, the convex parts gathered together are generally considered to be one convex part. The distance between adjacent concave parts 212 generally refers to the horizontal distance between the bottom ends of adjacent concave parts 212.

[0045] In an embodiment of the present invention, in order to make the electromagnetic shielding film and the circuit board or flexible board containing the electromagnetic shielding film more resistant to bending, the embodiment of the present invention takes into account the distribution of the recesses 212 in the interlayer 2, and sets the distance between adjacent recesses 212 of the interlayer 2 to be greater than or equal to 5 microns, which can be 5, 6, 7, 8, 10, 20, 30, 40, 50, 60 or any two values ​​greater than or equal to 5.

[0046] By adopting the technical means of the embodiment of the present invention, on the basis of setting the protrusions 211 and the recesses 212 on the surface of the interlayer 2, the distribution of the recesses 212 on the interlayer 2 is limited, so that the distance between adjacent recesses 212 will not be too close, thereby improving the step resistance of the electromagnetic shielding film and the bending resistance of the electromagnetic shielding film itself and the electromagnetic shielding film, thereby meeting the application scenarios of the electromagnetic shielding film with high performance requirements.

[0047] As a preferred embodiment, within a range of 260 μm of the uneven surface 21 of the interlayer 2 , the number of the recesses 212 is less than 40.

[0048] In the embodiment of the present invention, in order to make the electromagnetic shielding film and the circuit board or flexible board containing the electromagnetic shielding film have better effects, the distribution of the concave portions 212 is also considered. Under the detection instrument, within the range of 260 microns of the length of the interlayer 2, the number of concave portions on one side of the interlayer 2 is less than 40. That is, within the range of 260 microns of the uneven surface 21, the number of the concave portions 212 can be 5, 8, 10, 20, 30, 40 or an interval consisting of any two values ​​less than 40.

[0049] By adopting the technical means of the embodiment of the present invention, the distribution of the recesses 212 is limited, so that the number of the recesses 212 within a unit range will not be too large, thereby achieving the stability of the overall structure between the electromagnetic shielding film layers. At the same time, the step difference resistance performance of the electromagnetic shielding film and the bending resistance of the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film are improved, thereby meeting application requirements, making the electromagnetic shielding film suitable for products that require long-term and high-frequency folding or opening and closing.

[0050] As a preferred embodiment, the vertical distance between the bottom of the concave portion 212 and the center line is 1-5 μm, and the center line is a middle line determined according to the bottoms of the plurality of concave portions 212 and the tops of the plurality of convex portions 211 .

[0051] It should be noted that the center line is determined based on multiple convex parts 211 and multiple concave parts 212. The more convex parts 211 and concave parts 212 are taken, the higher the accuracy is. Preferably, all convex parts 211 and concave parts 212 in the measurement field of view are selected to draw the center line.

[0052] In the embodiment of the present invention, in order to achieve a better effect of the electromagnetic shielding film, the depth of the concave portion 212 is taken into consideration, and the vertical distance between the bottom end of the concave portion 212 and the center line is set to 1-5 microns, which can be 1 micron, 2 microns, 3 microns, 5 microns, or an interval consisting of any two values. It can be understood that the minimum vertical distance between the bottom end of the concave portion and the center line is 1, and a value lower than the minimum value of the above range does not belong to the concave portion.

[0053] By adopting the technical means of the embodiment of the present invention, the depth of the recess 212 is limited, so as to ensure the bending resistance of the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film, the step resistance of the electromagnetic shielding film and the stability of the structure of the electromagnetic shielding film itself, meet the application requirements, and make the electromagnetic shielding film suitable for products that need to be folded or opened and closed for a long time and at a high frequency. If the depth of the recess 212 is too small, the structure of the electromagnetic shielding film will be unstable, and bulging or delamination will occur; if the depth of the recess 212 is too large, the bending resistance of the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film will decrease.

[0054] As a preferred embodiment, the ratio of the plane width D of the recess 212 of the uneven surface 21 of the interlayer 2 to the depth H of the recess 212 satisfies: 1.1≤D / H≤7.5, and the plane width D refers to the maximum width of the recess 212 at the uneven surface 21 or the horizontal distance between the tops of two protrusions adjacent to the recess.

[0055] It should be noted that the measurement of the plane width D is generally carried out by making slices and then measuring the maximum width of the recess 212, or using other available detection instruments to directly measure the maximum width of the recess 212. Similarly, the depth H of the recess 212 is measured. The measurement method of the plane width D and the depth H of the recess 212 is not limited to the above specific method.

[0056] In the embodiment of the present invention, in order to achieve better technical effects, the correlation between the plane width and depth of the recess 212 is taken into consideration, and the ratio of the plane width D of the recess 212 of the non-flat surface 21 of the interlayer 2 to the depth H of the recess 212 satisfies 1.1≤D / H≤7.5. The ratio can be 1.3, 1.5, 1.7, 2.0, 3.0, 4.0, 5.0, 6.0 or 7.4, or an interval consisting of any two values, which is not specifically limited here.

[0057] By adopting the technical means of the embodiment of the present invention, the ratio between the plane width and the depth of the recess 212 is limited, thereby improving the bending resistance of the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film, as well as the step resistance of the electromagnetic shielding film and its own structural stability, meeting application requirements, and making the electromagnetic shielding film suitable for products that require long-term and high-frequency folding or opening and closing.

[0058] As a preferred embodiment, the vertical distance between the top of the convex portion 211 and the center line is 1-5 μm; the center line is a middle line determined according to the plurality of concave portions 212 and the plurality of convex portions 211 .

[0059] In the embodiment of the present invention, in order to achieve a better technical effect, the height of the convex portion 211 is taken into consideration, and the vertical distance between the top of the convex portion 211 and the midline is set to 1-5 microns, which can be 1, 2, 3, 4, 5 or an interval consisting of any two values, and the unit is microns, or any value between 1 micron and 5 microns, which is not specifically limited here. It can be understood that a convex portion means that the vertical distance from the top of the convex portion to the midline is at least greater than 1 micron, and if the vertical distance from the top of the convex portion to the midline is less than the minimum value, it is not considered a convex portion.

[0060] By adopting the technical means of the embodiment of the present invention, the height of the protrusion 211 is limited, thereby improving the step difference resistance of the electromagnetic shielding film and the bending resistance of the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film, ensuring the stability of the structure of the electromagnetic shielding film itself, avoiding the detachment and peeling between layers, meeting the application requirements, and making the electromagnetic shielding film suitable for products that require long-term and high-frequency folding or opening and closing.

[0061] As a preferred embodiment, the concave portions 212 whose bottom ends are at a vertical distance of 1-4 μm from the center line account for more than 50% of the statistical number of concave portions.

[0062] It should be understood that, ideally, the number of concave statistics is the same as the actual total number of concave parts. However, in practice, affected by detection technology, it can be considered that the number of concave statistics refers to the number of all concave parts obtained through measurement.

[0063] In the embodiment of the present invention, the existence of the concave portion 212 has a great relationship with the step resistance and the bending resistance of the electromagnetic shielding film. The vertical distance of the bottom end of the concave portion 212 from the center line is 1-4 microns, which can make the electromagnetic shielding film have better interlayer structural stability, and at the same time make the shielding film have better step resistance performance, and the bending resistance of the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film is further improved. In setting the number of concave portions, more than 50% of the bottom ends of the concave portions 212 have a vertical distance of 1-4 microns from the center line, and the specific value of the vertical distance can be 1, 2, 3, 4 microns, or an interval composed of any two values, which is not specifically limited here. It should be noted that more than 50% refers to 50%, 60%, 70%, 80%, 90%, 100% or an interval composed of any two numbers.

[0064] By adopting the technical means of this embodiment, the proportion of the recessed portions 212 whose bottom ends are 1-4 microns away from the center line in all the recessed portions is limited to a certain range. While ensuring the shielding performance and step resistance performance of the electromagnetic shielding film, the bending resistance of the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film is improved.

[0065] As a preferred embodiment, the concave portions whose bottom ends are at a vertical distance of 2-4 μm from the center line account for more than 65% of the statistical number of concave portions.

[0066] In the embodiment of the present invention, the vertical distance between the bottom end of the concave portion 212 and the center line is 2-4 microns, which can bring better resistance to step difference and bending resistance of the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film. In setting the number of concave portions, more than 65% of the bottom ends of the concave portions 212 have a vertical distance from the center line of 2-4 microns, and the specific value of the vertical distance can be 2, 3 or 4 microns, or an interval consisting of any two values, which is not specifically limited here. It should be noted that more than 65% refers to 70%, 75%, 80%, 85%, 90%, 100% or an interval consisting of any two numbers.

[0067] By adopting the technical means of this embodiment, the proportion of the recess 212 whose bottom end is 2-4 microns away from the center line in all the recesses is limited to a certain range. While ensuring the shielding performance of the electromagnetic shielding film, the step difference resistance performance of the electromagnetic shielding film, the electromagnetic shielding film itself and the bending resistance of the circuit board or flexible board containing the electromagnetic shielding film are optimized.

[0068] As a preferred embodiment, the convex-concave portions 212 whose bottom end of the concave portion 212 is 1-2 μm away from the center line account for 15%-30% of the statistical number of concave portions, the concave portions 212 whose bottom end is 2-3.5 μm away from the center line account for 40%-75% of the statistical number of concave portions, and the concave portions 212 whose bottom end is 3.5-5 μm away from the center line account for 18%-37% of the statistical number of concave portions. The center line is a middle line determined based on the bottom ends of the multiple concave portions 212 and the top ends of the multiple convex portions 211.

[0069] In the embodiment of the present invention, the influence of the proportion of the concave portions 212 with different vertical distances from the bottom end to the center line on the step resistance of the electromagnetic shielding film and the bending resistance of the electromagnetic shielding film itself and the circuit board or the flexible board containing the electromagnetic shielding film is taken into consideration, and the vertical distance of the bottom end of the concave portion 212 from the center line is limited, and the proportion information is also limited. The proportion of the concave portion 212 with a vertical distance of 1-2 μm from the bottom end of the concave portion 212 to the center line in the statistical number of concave portions can be any value between 15% and 30%, such as 15%, 20%, 25% or 30%, and the concave portion 212 The proportion of the concave portion 212 whose bottom end is 2-3.5 μm away from the center line in the statistical number of concave portions can be any value between 40% and 75%, such as 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75%, and the proportion of the concave portion 212 whose bottom end is 3.5-5 μm away from the center line in the statistical number of concave portions can be any value between 18% and 37%, such as 19%, 20%, 25%, 30% or 35%, and the specific numerical value of the proportion is not specifically limited here. The sum of the above proportions is less than or equal to 100%.

[0070] By adopting the technical means of the embodiment of the present invention, the vertical distance between the bottom end of the recess 212 and the center line is limited, and the proportion information is also limited. Under the condition of ensuring the shielding performance of the electromagnetic shielding film, the step difference resistance performance of the electromagnetic shielding film, the electromagnetic shielding film itself and the bending resistance of the circuit board or flexible board containing the electromagnetic shielding film are further optimized, making the electromagnetic shielding film suitable for products that require long-term and high-frequency folding or opening and closing.

[0071] As a preferred embodiment, please refer to Figure 4 The electromagnetic shielding film further comprises an adhesive layer 4 and a base layer 5, wherein the base layer 5, the first shielding layer 1, the interlayer 2, the second shielding layer 3 and the adhesive layer 4 are stacked in sequence.

[0072] In the embodiment of the present invention, the adhesive layer 4 mainly plays a bonding role, thereby improving the adhesion between two adjacent material layers. In order to improve the adhesion between the second shielding layer 3 and the circuit board body 6, the adhesive layer 4 is arranged on the surface of the second shielding layer 3 away from the first shielding layer 1, which enhances the bonding force between the electromagnetic shielding film and the circuit board body 6, so that the electromagnetic shielding film and the circuit board body are not prone to blistering and delamination, avoiding separation and other problems, and ensuring the peeling strength between the second shielding layer 3 and the circuit board body 6. The base layer 5 mainly plays a supporting and protective role. The base layer 5 or the adhesive layer 4 is mainly selected from at least one of vinyl acetate, polyester, polyethylene, polyamide, rubber, acrylate, phenolic, epoxy, polyimide, urethane, melamine, alkyd, ABF and other resins.

[0073] As a preferred embodiment, please refer to Figure 5 The second shielding layer 3 has a protrusion 31 away from the first shielding layer side 1, and the second shielding layer 3 is electrically connected to the ground layer of the circuit board body 6 through the adhesive layer 4, thereby ensuring the connection between the first shielding layer 1 and the second shielding layer 3 and the circuit board body 6, thereby achieving the introduction of interference charges in the first shielding layer 1 and the second shielding layer 3 into the ground, avoiding the accumulation of interference charges to form an interference source affecting the normal operation of the circuit board, the protrusion 31 is conducive to piercing the adhesive layer 4, and can also increase the amount of glue between the second shielding layer and the circuit board body 6, thereby increasing the bonding strength between the two, making it difficult for the electromagnetic shielding film to be separated from the circuit board body 6.

[0074] This embodiment tests the electromagnetic shielding film formed by the first shielding layer and the second shielding layer of commonly used materials and the interlayer of various common non-metallic materials, and limits the values ​​of various parameters of the interlayer (such as the vertical height difference between adjacent concave and convex parts, the distance between adjacent concave parts, etc.) within the range of the above-mentioned embodiments, and determines that the interlayer 2 is provided between the first shielding layer 1 and the second shielding layer 3, which can improve the bending resistance of the electromagnetic shielding layer itself and the circuit board or soft board containing the electromagnetic shielding film, and the non-flat surface with convex parts and concave parts is provided in the interlayer 2, while ensuring the shielding performance of the electromagnetic shielding film, which can improve the bending resistance of the electromagnetic shielding film itself and the circuit board or soft board containing the electromagnetic shielding film. The following is a display of some test results, and the specific test examples are as follows:

[0075] Test Example 1

[0076] An electromagnetic shielding film comprises a base layer, a first shielding layer, an interlayer, a second shielding layer and an adhesive layer which are stacked in sequence, wherein both sides of the interlayer are uneven surfaces, wherein the uneven surfaces include concave portions and convex portions, wherein the vertical height difference ΔH between adjacent concave portions and convex portions is ≤8 μm, and within a range of 260 μm of the uneven surface of the interlayer, the number of the concave portions is 15, the first shielding layer and the second shielding layer are made of copper, the overall average thickness of the electromagnetic shielding film is 11.2 μm, the average thickness of the first shielding layer is 0.9 μm, and the average thickness of the second shielding layer is 2.0 μm.

[0077] Test Example 2

[0078] This test example is the same as the other conditions of the test example 1, except that the distance between adjacent recesses of the interlayer is greater than or equal to 5 μm.

[0079] Test Example 3

[0080] The other conditions of this test example are the same as those of test example 2, except that the vertical distance between the bottom end of the concave portion and the center line is 1-5 μm.

[0081] Test Example 4

[0082] The other conditions of this test example are the same as those of test example 3, except that the ratio of the plane width D of the concave portion of the uneven surface of the interlayer to the depth H of the concave portion satisfies: 1.1≤D / H≤7.5.

[0083] Test Example 5

[0084] This test example is the same as test example 4 in other conditions, except that the concave portions whose bottom ends are 1-4 μm vertically away from the center line account for 95% of the statistical number of concave portions.

[0085] Test Example 6

[0086] This test example is the same as test example 4 in other conditions, except that the recesses whose bottom end is at a vertical distance of 1-2 μm from the center line account for 25% of the statistical number of recesses, the recesses whose bottom end is at a vertical distance of 2-3.5 μm from the center line account for 55% of the statistical number of recesses, and the recesses whose bottom end is at a vertical distance of 3.5-5 μm from the center line account for 20% of the statistical number of recesses.

[0087] Test Example 7

[0088] The other conditions of this test example are the same as those of test example 1, except that the vertical height difference ΔH between adjacent concave and convex portions in the interlayer is ≥ 9 μm.

[0089] Test Example 8

[0090] An electromagnetic shielding film comprises a base layer, a first shielding layer and an adhesive layer which are stacked in sequence, wherein the thickness of the first shielding layer is the same as that of test example 1.

[0091] Table 1

[0092] Bending resistance / times Shielding effectiveness / DB Test Example 1 Greater than 9600 Greater than 62 Test Example 2 Greater than 9800 Greater than 62 Test Example 3 Greater than 9800 Greater than 62 Test Example 4 More than 11000 Greater than 62 Test Example 5 More than 11000 Greater than 62 Test Example 6 More than 12000 Greater than 62 Test Example 7 Approx. 8700 Greater than 62 Test Example 8 Approx. 8,200 Approx. 52

[0093] It should be noted that, in order to improve the accuracy of the test results, each set of data was tested repeatedly for multiple times, and the multiple test results were combined to obtain the final test results. In the multiple repeated tests of test examples 1 to 6, the material of the interlayer was non-metallic, and the tests were conducted when the interlayer material was epoxy resin, polyester resin, polyurethane resin, acrylic resin, alkyd resin, polyamide resin, polyimide resin, and a mixed material of epoxy resin and polyester resin. In test example 7, the material of the interlayer was a mixed material of epoxy resin and polyester resin.

[0094] The test method for the bending resistance and step resistance of the electromagnetic shielding film is as follows: The steps of the MIT folding resistance test include: pressing two shielding films on a bending plate in a counter-pressing manner, the pressing conditions are 185°C, pre-pressing for 10s, molding time for 180s, and molding pressure of 120kg / cm 2 , the pressing temperature is 185℃, and the baking and curing are carried out after pressing. The baking temperature is 160℃, the baking time is 90min, the strip width is 1.5cm, the R angle is 0.8, the speed is 60 rpm, the angle is ±135°, and the load is 500g; when the bending starts, when the line resistance changes by more than 10%, the machine automatically stops the test and records the number of bending times and the failure resistance value; the shielding effectiveness is tested in accordance with GB / T30142-2013.

[0095] It can be seen from the above table that the electromagnetic shielding film provided by the embodiment of the present invention has better electromagnetic shielding performance, and the electromagnetic shielding film itself and the circuit board or flexible board containing the electromagnetic shielding film have better bending resistance.

[0096] In order to solve the same technical problem, an embodiment of the present invention further provides a circuit board, which includes the electromagnetic shielding film as described in any of the above embodiments.

[0097] In the embodiment of the present invention, please refer to Figure 6 The circuit board includes a circuit board body 6 and an electromagnetic shielding film as described in any of the above embodiments, wherein the electromagnetic shielding film is pressed together with the circuit board body 6 through an adhesive layer 4; the second shielding layer 3 is electrically connected to the ground layer of the circuit board body 6 through the adhesive layer 4, thereby ensuring that the first shielding layer 1 and the second shielding layer 3 are connected to the ground layer of the circuit board body 6, thereby achieving the goal of introducing interference charges in the first shielding layer 1 and the second shielding layer 3 into the ground, thereby avoiding the accumulation of interference charges to form an interference source that affects the normal operation of the circuit board.

[0098] Preferably, the circuit board body 6 is one of a flexible single-sided board, a flexible double-sided board, a flexible multilayer board, and a rigid-flexible board. It is worth noting that the circuit board body 6 is not limited to the above specific types and can be set according to actual conditions.

[0099] Compared with the prior art, the circuit board provided in the embodiment of the present invention includes an electromagnetic shielding film, which includes a first shielding layer 1, an interlayer 2 and a second shielding layer 3 stacked in sequence. The interlayer 2 is arranged between the first shielding layer 1 and the second shielding layer 3, which effectively increases the bending resistance of the electromagnetic shielding film itself or the circuit board or soft board containing the electromagnetic shielding film, and also improves the shielding performance of the electromagnetic shielding film; further, at least one side of the interlayer 2 is an uneven surface 21, and the uneven surface 21 includes a convex portion 211 and a concave portion 212. On the premise of ensuring the shielding performance of the electromagnetic shielding film, the bending resistance of the electromagnetic shielding film itself or the circuit board or soft board containing the electromagnetic shielding film is improved.

[0100] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An electromagnetic shielding film, characterized in that: The electromagnetic shielding film includes a first shielding layer, an interlayer and a second shielding layer. The first shielding layer, the interlayer and the second shielding layer are stacked in sequence. At least one side of the interlayer is an uneven surface, and the uneven surface includes concave parts and convex parts.

2. The electromagnetic shielding film according to claim 1, wherein A vertical height difference ΔH between adjacent concave and convex portions in the interlayer is ≤ 8 μm.

3. The electromagnetic shielding film according to claim 1, wherein The concave parts and the convex parts of the uneven surface of the interlayer are arranged at intervals.

4. The electromagnetic shielding film according to claim 1, wherein The distance between adjacent recesses of the interlayer is greater than or equal to 5 μm.

5. The electromagnetic shielding film according to claim 1, wherein The number of the recesses is less than 40 within 260 μm of the uneven surface of the interlayer.

6. The electromagnetic shielding film according to claim 1, wherein The vertical distance between the bottom end of the concave portion and the center line is 1-5 μm, and the center line is a middle line determined according to the plurality of convex portions and the plurality of concave portions.

7. The electromagnetic shielding film according to claim 1, wherein The ratio of the plane width D of the concave portion on the uneven surface of the interlayer to the depth H of the concave portion satisfies: 1.1≤D / H≤7.5, and the plane width D refers to the maximum width of the concave portion on the uneven surface or the horizontal distance between the tops of two convex portions adjacent to the concave portion.

8. The electromagnetic shielding film according to claim 6, wherein The concave portions whose bottom ends are at a vertical distance of 1-4 μm from the center line account for more than 50% of the statistical number of concave portions.

9. The electromagnetic shielding film according to claim 6, wherein: The concave portions whose bottom ends are at a vertical distance of 2-4 μm from the center line account for more than 65% of the statistical number of concave portions.

10. The electromagnetic shielding film according to claim 1, wherein The concave portions whose bottom ends are 1-2 μm away from the center line at a vertical distance account for 15%-30% of the statistical number of concave portions, the concave portions whose bottom ends are 2-3.5 μm away from the center line at a vertical distance account for 40%-75% of the statistical number of concave portions, the concave portions whose bottom ends are 3.5-5 μm away from the center line at a vertical distance account for 18%-37% of the statistical number of concave portions, and the center line is the middle line determined based on the plurality of convex portions and the plurality of concave portions.

11. The electromagnetic shielding film according to claim 1, wherein The non-planar surface also includes a planar portion.

12. The electromagnetic shielding film according to claim 1, wherein The electromagnetic shielding film further includes a base layer and a bonding layer. The base layer, the first shielding layer, the interlayer, the second shielding layer and the bonding layer are stacked in sequence.

13. The electromagnetic shielding film according to any one of claims 1 to 12, characterized in that: The second shielding layer has a protrusion on a side away from the first shielding layer.

14. A circuit board, characterized in that: The circuit board includes the electromagnetic shielding film according to any one of claims 1 to 13.

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