Electromagnetic shielding film and circuit board

Abstract

The invention belongs to the technical field of electromagnetic shielding functional materials, and particularly relates to an electromagnetic shielding film and a circuit board. The electromagnetic shielding film provided by the invention comprises a substrate layer and a shielding layer which are laminated, the gram weight of the shielding layer is 0.10 g / dm < 2 >-0.50 g / dm < 2 >, the surface of the shielding layer is uneven, and the surface area ratio of the shielding layer per square centimeter is more than 1.2. By limiting the gram weight of the shielding layer and the surface area ratio of the shielding layer per square centimeter, compared with an electromagnetic shielding film of a traditional structure, the electromagnetic shielding film has higher segment difference resistance and higher adaptability, can be applied to circuit boards with different segment differences, and is particularly suitable for folding circuit boards and flexible boards, and the application range of the electromagnetic shielding film is widened. And the circuit board or the FPC board containing the electromagnetic shielding film has good bending resistance. The electromagnetic shielding film provided by the invention still has relatively high shielding effectiveness after high segment difference, and the shielding effect can reach 60 DB or above.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic shielding functional materials, and in particular relates 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 reached 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 an electromagnetic shielding film on the surface of the foldable mobile phone. However, the electromagnetic shielding film in the prior art is attached to a hard board and is not suitable for folding mobile phones or soft boards. Folding circuit boards or soft boards require long-term and high-frequency folding or opening and closing, and existing electromagnetic shielding films are difficult to meet such high requirements.

[0003] It can be seen that in order to meet the application requirements of foldable circuit boards or flexible boards, the electromagnetic shielding film's resistance to step difference and high-efficiency shielding effectiveness as well as the auxiliary circuit board or FPC's resistance to bending are urgent issues that need to be addressed. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the electromagnetic shielding film in the prior art, such as the step difference resistance and shielding efficiency cannot meet the use requirements of folding circuit boards, soft boards or flexible circuit boards, and to improve the bending resistance of circuit boards or FPC boards containing electromagnetic shielding films, thereby providing an electromagnetic shielding film and circuit board.

[0005] To this end, the present invention provides the following technical solutions:

[0006] The present invention provides an electromagnetic shielding film, comprising a base layer and a shielding layer stacked in layers, wherein the shielding layer has a gram weight of 0.10 g / dm 2 -0.50g / dm 2 , at least one side of the shielding layer has an uneven surface, and the surface area ratio of the shielding layer is greater than 1.2. Typically, but not limiting, the weight of the shielding layer can be 0.11 mg / m 2 , 0.13mg / m 2 , 0.15mg / m 2 , 0.20mg / m 2 , 0.23mg / m 2 , 0.25mg / m 2 , 0.30mg / m 2 , 0.32mg / m 2 , 0.35mg / m 2 , 0.40mg / m 2, 0.43mg / m 2 , 0.46mg / m 2 , 0.49mg / m 2 , 0.50mg / m 2 , or within the range formed by any of the above values; the surface area ratio of the shielding layer is 1.2-6. For example, the surface area ratio can be 1.2, 1.3, 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.5, 3.8, 4.0, 4.5, 4.8, 5.0, 5.5, 5.8, 6.0, or within the range formed by any of the above values.

[0007] In the present invention, by limiting the gram weight and surface area ratio of the shielding layer, the shielding effectiveness, step resistance performance and bending resistance performance of the electromagnetic shielding film and the circuit board or FPC board containing the electromagnetic shielding film can be guaranteed. If the gram weight is too high, stress concentration will occur in the entire electromagnetic shielding film, and the bending resistance performance of the circuit board or FPC board containing the electromagnetic shielding film and the step resistance performance of the electromagnetic shielding film will be reduced; if the gram weight is too low, the entire shielding effectiveness of the electromagnetic shielding film will be reduced and will not meet the expected requirements; the surface area ratio of the shielding layer is limited to an appropriate range. If the surface area ratio of the shielding layer is less than 1.2, delamination will occur between the shielding layer and the base layer, or between the shielding layer and the bonding layer. Preferably, in order to better bond between the layers and to make the circuit board or FPC board containing the electromagnetic shielding film have good bending resistance, the surface area ratio of the shielding layer is greater than or equal to 1.2. Preferably, the surface area ratio is controlled to be between 1.2-6.

[0008] In the present invention, the surface area ratio of the shielding layer refers to the ratio of the surface area measured on the uneven side of the shielding layer per square centimeter to per square centimeter. Since the surface of the shielding layer is uneven, the ratio must be greater than 1. The surface area ratio can be tested by a profilometer or set by other instruments.

[0009] In some optional embodiments, the nickel content of the shielding layer accounts for 0.4wt%-7wt% of the weight of the electromagnetic shielding film. Typically, but not limiting, the nickel content of the shielding layer can be 0.4wt%, 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, 2.0wt%, 3.0wt%, 4.0wt%, 5.0wt%, 6.0wt%, 7.0wt%, or within the range of any of the above values. Setting the nickel content of the shielding layer can improve the adhesion between the base layer and the shielding layer, thereby preventing the shielding layer from delaminating from the base layer. At the same time, the nickel content needs to be appropriate. If the nickel content is too low, the base layer and the shielding layer will not have a good bonding effect. If the nickel content is too high, the shielding layer will become brittle, which will weaken the bending resistance of the circuit board or FPC board containing the electromagnetic shielding film and the step resistance of the electromagnetic shielding film.

[0010] In some optional embodiments, the chromium content of the shielding layer accounts for 0.5wt%-10wt% of the weight of the electromagnetic shielding film. Typically, but not limiting, the chromium content of the shielding layer can be 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, 2.0wt%, 3.0wt%, 4.0wt%, 5.0wt%, 6.0wt%, 7.0wt%, 8.0wt%, 9.0wt%, 10.0wt%, or within the range of any of the above values. Setting the chromium content of the shielding layer can improve the adhesion between the base layer and the shielding layer, thereby preventing the shielding layer from delaminating from the base layer. At the same time, the chromium content needs to be appropriate. If the chromium content is too low, the base layer and the shielding layer will not have a good bonding effect. If the chromium content is too high, the shielding layer will become brittle, which will in turn lead to a weakened ability to resist step differences.

[0011] In some optional embodiments, with the test point as the center, the difference between the gram weight of the shielding layer tested within a radius of 5 cm from the test point and the gram weight at the test point is within 8%. Typically, but not limitingly, the difference between the gram weight of the shielding layer tested within a radius of 5 cm from the test point and the gram weight at the test point can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or within the range composed of any of the above values. In the present invention, the difference between the gram weight of the shielding layer tested within a radius of 5 cm from the test point and the gram weight at the test point is within the above range, which can make the overall shielding layer more uniform, thereby maintaining the shielding effectiveness of the shielding layer stable, and at the same time, can stabilize the step resistance of the electromagnetic shielding film and the bending resistance of the circuit board or FPC board containing the electromagnetic shielding film. The test point of the present application is randomly selected and can be any point on the shielding layer.

[0012] In some optional embodiments, with the test point as the center, the difference between the surface area ratio of the shielding layer tested within a radius of 5 cm from the test point and the measured value at the test point is within 10%. Typically, but not limitingly, the difference between the surface area ratio of the shielding layer tested within a radius of 5 cm from the test point and the measured value at the test point can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or within the range composed of any of the above values. In the present invention, the difference between the surface area ratio of the shielding layer tested within a radius of 5 cm from the test point and the measured value at the test point is within the above range, which can make the surface of the shielding layer more uniform, thereby maintaining the shielding effectiveness of the shielding layer stable, and at the same time, can stabilize the step resistance of the electromagnetic shielding film and the bending resistance of the circuit board or FPC board containing the electromagnetic shielding film.

[0013] In some optional embodiments, a bonding layer is laminated on the surface of the shielding layer away from the base layer.

[0014] Preferably, the adhesive layer includes at least one of resins selected from the group consisting of vinyl acetate, polyester, polyethylene, polyamide, rubber, acrylate, phenolic, epoxy, polyimide, urethane, melamine, alkyd, ABF and the like.

[0015] In some optional embodiments, the bonding layer contains conductive particles or does not contain conductive particles.

[0016] In some optional embodiments, when the adhesive layer contains conductive particles, the shielding layer introduces interference charges into the stratum of the circuit board through the conductive particles and / or the uneven surface of the shielding layer. The conductive particles can be conductive particles separated from each other, or they can be large-particle conductive particles that are agglomerated; when the conductive particles are conductive particles separated from each other, the grounding conductivity of the adhesive layer can be further improved; and when the conductive particles are large-particle conductive particles that are agglomerated, the puncture strength can be increased. When the adhesive layer contains conductive particles, the conductive particles can enhance the grounding effect of the electromagnetic shielding film and improve the shielding effectiveness. When the adhesive layer does not contain conductive particles, the interference charges are introduced into the stratum of the circuit board through the uneven surface of the shielding layer.

[0017] In some optional embodiments, the surface of the shielding layer away from the base layer is provided with a protrusion 4 (schematic diagram as shown in FIG. Figure 2 shown).

[0018] In some optional embodiments, the protrusions may be formed by at least one of electroplating, physical vapor deposition, or chemical vapor deposition. The protrusions formed in the present invention serve to enhance the piercing effect, so that the grounding effect of the electromagnetic shielding film is more stable. In addition, the protrusions are mainly concentrated on the convex parts of the uneven surface, which increases the undulation of the uneven surface, thereby enhancing the piercing and grounding effects and improving the shielding effectiveness of the electromagnetic shielding film.

[0019] In some optional embodiments, the thickness of the base layer is 2-20 μm; typically, but not limitedly, the thickness of the base layer can be 2 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 20 μm, or within the range of any of the above values;

[0020] And / or, the thickness of the bonding layer is 2-20 μm; typically but not limitedly, the thickness of the bonding layer may be 2 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 20 μm, or within a range consisting of any of the above values.

[0021] In the present invention, the materials of the shielding layer and the base layer are conventional in the field, typically non-limiting, and the shielding layer includes one or more of a metal shielding layer, a carbon nanotube shielding layer, a ferrite shielding layer, and a graphene shielding layer. Among them, the metal shielding layer includes a single metal shielding layer and / or an alloy shielding layer; wherein the single metal shielding layer is made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold, and the alloy shielding layer is made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver, and gold. The base layer includes, but is not limited to, polystyrene-based thermoplastic resins, vinyl acetate-based thermoplastic resins, polyester-based thermoplastic resins, polyethylene-based thermoplastic resins, polyamide-based thermoplastic resins, rubber-based thermoplastic resins, acrylic-based thermoplastic resins, phenolic-based thermosetting resins, epoxy-based thermosetting resins, thermoplastic polyimide-based thermosetting resins, urethane-based thermosetting resins, melamine-based thermosetting resins, alkyd-based thermosetting resins, and ABF resins. Any resin that can satisfy the carrier function is within the requirements of this solution and is not listed in detail here. Exemplarily, the base layer is selected from modified epoxy resin, modified acrylic resin, polyethylene terephthalate, polybutylene terephthalate, polyethylene, polyethylene naphthalate, polystyrene, polyvinyl chloride, polysulfone, polyphenylene sulfide, polyetheretherketone, polyphenylene ether, polytetrafluoroethylene, liquid crystal polymer, polyoxadiazole, epoxy glass cloth, BT resin, and other base layers that can meet the performance requirements are within the scope of the requirements of this solution and are not listed in detail here.

[0022] The present invention also provides a circuit board, which includes the electromagnetic shielding film mentioned above.

[0023] In some optional embodiments, the circuit board is a foldable circuit board, a flexible circuit board or a soft board.

[0024] The technical solution of the present invention has the following advantages:

[0025] The electromagnetic shielding film provided by the present invention comprises a base layer and a shielding layer which are stacked, and the gram weight of the shielding layer is 0.10 g / dm 2 -0.50g / dm 2 , the surface of the shielding layer is uneven, and the surface area ratio of the shielding layer per square centimeter is greater than 1.2. By limiting the gram weight of the shielding layer and the surface area ratio of the shielding layer per square centimeter, the electromagnetic shielding film has higher resistance to step difference and bending resistance of the circuit board or FPC board containing the electromagnetic shielding film compared to the electromagnetic shielding film of the traditional structure, and has high adaptability and can be used in circuit boards with different step differences, especially suitable for folding circuit boards and flexible boards. The electromagnetic shielding film in the present invention still has a high shielding effectiveness after a high step difference, and the shielding effectiveness can reach more than 60DB. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a structural schematic diagram of an embodiment of the electromagnetic shielding film provided by the present invention;

[0028] Figure 2 It is a structural schematic diagram of another embodiment of the electromagnetic shielding film provided by the present invention;

[0029] Reference numerals:

[0030] 1. Adhesive layer; 2. Shielding layer; 3. Base layer; 4. Protrusion. DETAILED DESCRIPTION

[0031] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0032] 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.

[0033] 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.

[0034] In order to better illustrate the present application, the technical effects of the present application are illustrated by some embodiments. If no specific experimental steps or conditions are specified in the embodiments, the conventional experimental steps or conditions described in the literature in the art can be used. If the manufacturer of the reagents or instruments used is not specified, they are all conventional reagent products that can be obtained commercially.

[0035] Example 1

[0036] This embodiment provides an electromagnetic shielding film, and its structural schematic diagram is as follows Figure 1 As shown, it includes a stacked base layer 3, a shielding layer 2 and an adhesive layer 1, the surface of the shielding layer 2 is uneven, and the weight of the shielding layer is 0.31 g / dm 2 The surface area ratio of the shielding layer is 2.5; wherein the thickness of the base layer is 7 μm, and the material is epoxy resin and polyimide; the bonding layer is acrylic acid and polyester resin, and the thickness is 6.7 microns.

[0037] Example 2

[0038] This embodiment provides an electromagnetic shielding film, the material, structure, etc. are the same as those of Embodiment 1, except that the difference between the gram weight of the shielding layer tested within a radius of 5 cm from the test point and the gram weight at the test point is within 8%.

[0039] Example 3

[0040] This embodiment provides an electromagnetic shielding film, the material, structure, etc. are the same as those of Embodiment 2, except that the surface area ratio of the shielding layer tested within a radius of 5 cm from the test point differs from the measured value at the test point by less than 10%.

[0041] Example 4

[0042] This embodiment provides an electromagnetic shielding film, the material, structure, etc. are the same as those of the embodiment 3, except that the nickel content of the shielding layer accounts for 1.0 wt % of the weight of the electromagnetic shielding film.

[0043] Example 5

[0044] This embodiment provides an electromagnetic shielding film, the material, structure, etc. are the same as those of the embodiment 4, except that the Cr content of the shielding layer accounts for 1.0 wt % of the weight of the electromagnetic shielding film.

[0045] Comparative Example 1

[0046] This comparative example provides an electromagnetic shielding film, which is different from Example 1 only in that the gram weight of the shielding layer is 0.05 g / dm 2 , the material is copper, and the surface area ratio of the shielding layer is 1.5.

[0047] Comparative Example 2

[0048] This comparative example provides an electromagnetic shielding film, which is different from Example 1 in that the weight of the shielding layer is 0.4 g / dm 2 , the material is copper, and the surface area ratio of the shielding layer is 1.05.

[0049] Test Case

[0050] The electromagnetic shielding films provided in each embodiment and comparative example were tested for performance, and the specific testing methods are as follows:

[0051] The shielding effectiveness of the electromagnetic shielding film is tested in accordance with GB / T30142-2013; the step resistance performance test is to press the electromagnetic shielding film on the surface of the component with the corresponding step height, and test the grounding resistance of the electromagnetic shielding film. The grounding resistance shall not exceed 1 ohm, otherwise it shall be deemed to be failed; the bending resistance is to stick two electromagnetic shielding films of the same model to be tested on the two surfaces of the bending plate (the bending plate contains circuits) and press them (pre-pressing time 10 seconds, molding time 180 seconds, molding pressure 120kg, pressing temperature 185℃); after pressing, bake and cure (baking temperature 160℃, baking time 90min); the strip width is 1.5cm, and the bending conditions are: R angle 0.8mm, speed 60 rpm, angle ±135 degrees, load 500g, and the test is stopped when the resistance change of the bending line exceeds 10%.

[0052] The specific test results are shown in the table below:

[0053] Table 1

[0054] Shielding effectiveness / DB Resistance to step difference / μm Bending / times Example 1 More than 60 Greater than 75 More than 12000 Example 2 More than 60 Greater than 75 More than 12000 Example 3 More than 60 Greater than 75 More than 12000 Example 4 More than 60 Greater than 75 More than 13000 Example 5 More than 60 Greater than 75 More than 15000 Comparative Example 1 40 Greater than 75 12204 Comparative Example 2 48 50 8960

[0055] From the data in the above table, it can be seen that the electromagnetic shielding film provided by the present invention has higher resistance to step difference than the electromagnetic shielding film of traditional structure, and the electromagnetic shielding film has higher shielding effectiveness, and the shielding effectiveness can reach more than 60DB. At the same time, the circuit board or FPC board containing the electromagnetic shielding film has strong bending resistance, can adapt to the application requirements of existing circuit boards or flexible boards, and has high adaptability.

[0056] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. An electromagnetic shielding film, characterized in that: It comprises a base layer and a shielding layer which are stacked, wherein the weight of the shielding layer is 0.10 g / dm 2 -0.50g / dm 2 , at least one surface of the shielding layer is uneven, and the surface area ratio of the shielding layer is greater than 1.

2.

2. The electromagnetic shielding film according to claim 1, characterized in that With the test point as the center, the difference between the grammage of the shielding layer tested within a radius of 5 cm from the test point and the grammage at the test point is within 8%.

3. The electromagnetic shielding film according to claim 1, characterized in that Taking the test point as the center, the difference between the surface area ratio of the shielding layer tested within a radius of 5 cm from the test point and the measured value at the test point is within 10%.

4. The electromagnetic shielding film according to claim 1, characterized in that A bonding layer is laminated on the surface of the shielding layer away from the base layer.

5. The electromagnetic shielding film according to claim 1, characterized in that The nickel content of the shielding layer accounts for 0.4wt%-7wt% of the weight of the electromagnetic shielding film.

6. The electromagnetic shielding film according to claim 1, characterized in that The chromium content of the shielding layer accounts for 0.5wt%-10wt% of the weight of the electromagnetic shielding film.

7. The electronic electromagnetic shielding film according to claim 6, characterized in that: The adhesive layer may contain conductive particles or may not contain conductive particles.

8. The electromagnetic shielding film according to claim 1, characterized in that: A protrusion is arranged on the surface of the shielding layer away from the base layer.

9. The electromagnetic shielding film according to claim 6, characterized in that The thickness of the base layer is 2-20 μm; And / or, the thickness of the bonding layer is 2-20 μm.

10. A circuit board, characterized in that: The circuit board comprises the electromagnetic shielding film according to any one of claims 1 to 9.

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