Shielding film and circuit board

Abstract

The invention relates to the technical field of electromagnetic films, in particular to a shielding film and a circuit board. The shielding film provided by the invention comprises a substrate layer and a shielding layer which are stacked, the number N of breakpoints of the shielding layer is more than or equal to 1 and less than or equal to 20 within the distance of 260 [mu] m, and the maximum width of the breakpoints is less than or equal to 5 [mu] m. By limiting the number of the breakpoints and the shielding film within the width range of the breakpoints, the shielding film has high segment difference resistance, meanwhile, the bending resistance of a circuit board or an FPC board containing the shielding film can be improved, and a good electromagnetic shielding effect can be kept.

Description

Technical Field

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

[0002] With the rapid development of 3C devices, how to prevent interference from magnetic fields and electromagnetic waves, and avoid functional disorders and information transmission errors caused by magnetic fields and electromagnetic waves, shielding films are usually used to protect against electromagnetic interference formed by conductive bodies. At present, shielding films mostly use metals to form shielding layers, but in recent years, the miniaturization of 3C devices has placed higher requirements on the performance of shielding films, especially when facing folding mobile phones, which not only need to avoid electromagnetic interference generated by the outside world and themselves, but also have more stringent requirements on other properties of shielding films such as resistance to high step differences. Therefore, shielding films suitable for hard boards are difficult to meet the above requirements, that is, improving the resistance to high step differences of shielding films and their bending assistance performance is an urgent problem to be solved. Summary of the invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the defect of the shielding film in the prior art that the shielding film has poor high step difference resistance, thereby providing a shielding film and a circuit board.

[0004] Another technical problem to be solved by the present invention is to overcome the poor bending resistance of the circuit board or FPC board containing the shielding film in the prior art, thereby providing a shielding film and a circuit board.

[0005] The present invention provides a shielding film, comprising a stacked base layer and a shielding layer, wherein within a distance of 260 μm, the number of breakpoints of the shielding layer is 1 ≤ N ≤ 20, the maximum width of the breakpoint is less than or equal to 5 μm, and N is the number of breakpoints.

[0006] See also Figure 1 The breakpoints of the present invention are locations where the shielding layer is broken as shown in the scanning electron microscope slice diagram. During the experiment, the researchers found that a small number of breakpoints can make the shielding film have good resistance to step difference, and at the same time, it also has a certain auxiliary improvement effect on the bending resistance of the circuit board or FPC containing the shielding film, while having little effect on the shielding effectiveness of the electromagnetic shielding.

[0007] In the present invention, by limiting the number of breakpoints and the maximum width of the breakpoints, on the one hand, the bending resistance of the circuit board or FPC board containing the shielding film can be improved, and the circuit board or FPC board containing the shielding film can be ensured to remain intact after being bent multiple times; on the other hand, the high step difference resistance of the shielding film can be improved, and it can be ensured that when the shielding film is attached to the surface of the electronic components with high step difference on the circuit board, the shielding layer can still maintain a high shielding effectiveness and a low resistance. In the study, it was found that when the number of breakpoints in the shielding layer within a distance of 260μm is less than or equal to 20, and at the same time, the maximum width of the breakpoint is less than or equal to 5μm, not only the high step difference resistance performance can be improved, but also the bending resistance of the circuit board or FPC board containing the shielding film can be improved, and at the same time, the shielding effectiveness of the shielding film is lost very little. However, if the number of breakpoints is greater than 20 and the maximum width of the breakpoint is too large, the bending resistance and height difference resistance of the shielding layer will be reduced, resulting in a sharp decrease in the shielding effectiveness of the shielding layer and a sharp increase in the resistance value of the shielding film. The present invention is limited to a distance range of 260 μm, the number of breakpoints is 1, 3, 5, 6, 7, 10, 11, 15, 18 or 20 or an interval consisting of any two values, and the maximum width of the breakpoint is less than or equal to 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, which can meet the above technical effects. Figure 1 The breakpoint refers to the shielding layer being in a broken state when observed under an electron microscope or the brightness of the shielding layer here is significantly lower than the brightness of the adjacent part.

[0008] In some embodiments, the number and width of the breakpoints are measured under the field of view of a scanning electron microscope, and the magnification is mainly 2000-10000 times, preferably 2000 or 3000 times, which can be set according to actual conditions. The above-mentioned number of breakpoints can also be counted by optical microscopy or FIB, and the specific detection method is not limited.

[0009] In order to further improve the step resistance performance of the shielding film, the present invention limits the distance between adjacent breakpoints of the shielding layer to be greater than or equal to 2μm. If the distance between adjacent breakpoints is less than 2μm, it will cause a large amount of stress concentration in the shielding layer, which is not conducive to the improvement of the bending resistance and step resistance performance of the circuit board or FPC board containing the shielding film. When the breakpoint distance is greater than or equal to 2μm, the shielding film can show better performance. Exemplarily, the straight-line distance between the breakpoints can be 2μm, 3μm, 5μm, 8μm, 10μm, 15μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, etc. or an interval consisting of any two values, which can improve the step resistance performance of the shielding film and also improve the bending resistance of the circuit board or FPC board containing the shielding film. Preferably, in order to stabilize the bending resistance and step resistance performance of the circuit board or FPC board, the straight-line distance between the breakpoints can be controlled within 150μm.

[0010] In order to achieve better technical effects, the shielding film has better resistance to step difference and electromagnetic shielding performance, and the circuit board or FPC board containing the shielding film has a certain optimization of bending resistance. In some embodiments, the number of breakpoints with a maximum width of 0.1-3.5μm accounts for more than 70% of the total number of breakpoints. The number of breakpoints with a maximum width of 0.1-3.5μm accounts for 50%, 60%, 65%, 70%, 75%, 80%, 90%, 95%, 100% of the total number of breakpoints, or an interval consisting of any two values.

[0011] In order to further improve the shielding film's resistance to step difference and electromagnetic shielding effectiveness, and to improve the bending resistance of the circuit board or FPC board containing the shielding film, in some embodiments, the number of breakpoints with a maximum width of 0.1μm-1.5μm accounts for 30%-75% of the total number of breakpoints, and the number of breakpoints with a width of 1.5μm-5μm accounts for 35%-85% of the total number of breakpoints, wherein the number of breakpoints with a width of 0-1.5μm and a width of 1.5μm-5μm accounts for less than or equal to 100% of the total number of breakpoints. Exemplarily, the number of breakpoints with a maximum width of 0.1μm-1.5μm accounts for 30%, 45%, 60%, 65% and 70% of the total number of breakpoints or an interval consisting of any two values; the number of breakpoints with a width of 1.5μm-5μm accounts for 35%, 40%, 50%, 55%, 60%, 70%, 85% of the total number of breakpoints or an interval consisting of any two values. The proportion of the number of breakpoints of different widths is specifically limited, thereby optimizing the shielding film's resistance to step difference and electromagnetic shielding effectiveness, and at the same time, the bending resistance of the circuit board or FPC board containing the shielding film is also improved to a certain extent.

[0012] In order to make the shielding film's resistance to step difference and electromagnetic shielding effectiveness more stable, the circuit board or FPC board containing the shielding film also has more stable bending resistance. In some embodiments, the number of breakpoints with a maximum width of 0.1-1.0μm accounts for 5%-30% of the total number of breakpoints, the number of breakpoints with a maximum width of 1.0μm-2.0μm accounts for 45%-85% of the total number of breakpoints, and the number of breakpoints with a maximum width of 2.0μm-5μm accounts for 10%-40% of the total number of breakpoints, among which the number of breakpoints with a maximum width of 0.1μm-1.0μm, a maximum width of 1.0μm-2.0μm, and a maximum width of 2.0μm-5μm accounts for less than or equal to 100% of the total number of breakpoints. Exemplarily, the number of breakpoints with a maximum width of 0.1 μm-1.0 μm can account for 5%, 10%, 15%, 20% and 30% of the total number of breakpoints or an interval consisting of any two values; the number of breakpoints with a maximum width of 1.0 μm-2.0 μm can account for 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% of the total number of breakpoints or an interval consisting of any two values; the number of breakpoints with a maximum width of 2.0 μm-5 μm can account for 10%, 15%, 20%, 30%, 35% and 40% of the total number of breakpoints or an interval consisting of any two values. The quantitative distribution of the maximum widths of different breakpoints is specifically defined, thereby optimizing the shielding film's resistance to step difference, resistance to bending, and electromagnetic shielding effectiveness.

[0013] In order to optimize the above technical effects and improve the step resistance and bending resistance of the shielding film, in some embodiments, the extension line of the line between the centers of adjacent breakpoints passes through at least two centers of the adjacent breakpoints. By limiting the distribution of the breakpoints in the shielding layer, it is possible to ensure that the horizontal position of the breakpoints remains uniform. If the extension line of the line between the centers of adjacent breakpoints passes through less than two centers of the adjacent breakpoints, it means that the distribution of the breakpoints is too messy or chaotic, which will cause the step resistance of the shielding film and the bending resistance of the circuit board or FPC board containing the shielding film to decrease, thereby reducing the bending resistance. Exemplarily, the number of centers of adjacent breakpoints that the extension line of the line between the centers of adjacent breakpoints passes through is 2, 3, 4, 6, 8 or more than 10. Among them, the more the extension line of the line between the centers of adjacent breakpoints passes through the centers of adjacent breakpoints, the more the breakpoints are on the same horizontal line, which will lead to better bending resistance of the circuit board or FPC board containing the shielding film and better step resistance of the shielding film.

[0014] Alternatively, in some embodiments, the vertical distance between the centers of adjacent breakpoints is less than or equal to 7μm. Exemplarily, the vertical distance between the centers of adjacent breakpoints can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, or an interval consisting of any two values. Limiting the vertical distance between the centers of adjacent breakpoints is also to make the horizontal positions between the breakpoints as close as possible, thereby reducing stress concentration, which in turn leads to a reduction in the bending resistance of the circuit board or FPC board containing the shielding film and the shielding film's resistance to breakage. Among them, the center of the breakpoint refers to the center point of the line connecting the two ends of the breakpoint in the slice diagram.

[0015] In some embodiments, the average thickness of the shielding layer is 1-9 μm. Preferably, the thickness of the base layer can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or an interval consisting of any two values. The average thickness of the shielding layer refers to the average thickness of the shielding layer measured after excluding the breakpoint.

[0016] In some embodiments, 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. The metal shielding layer includes a single metal shielding layer and / or an alloy shielding layer; 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.

[0017] In some embodiments, the thickness of the base layer is 2-20 μm. Preferably, the thickness of the base layer can be 2 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 20 μm, or an interval consisting of any two values.

[0018] Preferably, the base layer includes, but is not limited to, polystyrene resins, vinyl acetate resins, polyester thermoplastic resins, polyethylene resins, polyamide resins, rubber resins, acrylic resins, phenolic resins, epoxy resins, polyimide resins, carbamate resins, melamine resins, alkyd resins, and ABF resins. Any base layer that can meet the requirements of the carrier is within the scope of the present invention, and will not be listed in detail here. Exemplarily, the film layer is selected from modified epoxy resins, modified acrylic resins, polyethylene terephthalate, polybutylene terephthalate, polyethylene, polyethylene naphthalate, polystyrene, polyvinyl chloride, polysulfone, polyphenylene sulfide, polyetheretherketone, polyphenylene oxide, polytetrafluoroethylene, liquid crystal polymers, polyoxadiazole, epoxy glass cloth, and BT resin. Other base layers that can meet the performance requirements are within the scope of the present invention, and will not be listed in detail here.

[0019] The shielding layer is stacked with a bonding layer on a surface away from the base layer. Preferably, the bonding layer includes at least one of vinyl acetate, polyester, polyethylene, polyamide, rubber, acrylate, phenolic, epoxy, polyimide, urethane, melamine, alkyd, ABF and other resins.

[0020] The thickness of the bonding layer is 2-20 μm. The thickness of the bonding layer can be 2 μm, 5 μm, 7 μm, 10 μm, 12 μm, 15 μm, 20 μm, or an interval consisting of any two values.

[0021] In some embodiments, the bonding layer contains conductive particles or does not contain conductive particles.

[0022] Preferably, when the adhesive layer does not contain conductive particles, grounding can be achieved by piercing the adhesive layer through the protrusions arranged on the surface of the shielding layer away from the base layer, and the insertion loss of the circuit board can be reduced. When the adhesive layer contains conductive particles, the conductive particles can enhance the grounding effect of the shielding film and improve the shielding effectiveness. The conductive particles can be conductive particles separated from each other or large-particle conductive particles 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 agglomerated, the piercing strength can be increased.

[0023] In order to solve the same technical problem, the present invention also provides a circuit board, which includes the shielding film described in any of the above solutions, and the circuit board has good electromagnetic shielding performance.

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

[0025] The present invention provides a shielding film, comprising a stacked base layer and a shielding layer, wherein within a distance of 260 μm, the number of breakpoints of the shielding layer is less than or equal to 20, and the maximum width of the breakpoints is less than or equal to 5 μm. The shielding film has a step resistance performance within the above parameter range, and the circuit board or FPC board containing the shielding film has good bending resistance performance and can also maintain a good electromagnetic shielding effect.

[0026] The present invention provides a shielding film, wherein the spacing between the breakpoints is greater than or equal to 2 μm. The present invention provides a shielding film, wherein the distance between adjacent breakpoints is relatively far, and a circuit board or FPC board containing the shielding film has good bending resistance and shielding film step resistance performance.

[0027] The present invention provides a shielding film, wherein the extension line of the line connecting the centers of adjacent breakpoints passes through at least two centers of adjacent breakpoints. The shielding film with the breakpoints showing the above distribution has good resistance to high step difference and bending, and also has good shielding performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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.

[0029] Figure 1 is a scanning electron microscope image of the shielding film of the present invention;

[0030] Figure 2 is a schematic diagram of the shielding film structure in Example 1 of the present invention;

[0031] Reference numerals:

[0032] 1-base layer; 2-shielding layer; 3-adhesive layer. DETAILED DESCRIPTION

[0033] 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.

[0034] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0035] Example 1

[0036] This embodiment provides a shielding film, and its structural schematic diagram is as follows Figure 2 As shown, the structure comprises a base layer 1 and a shielding layer 2 which are stacked, and a bonding layer 3 is arranged on the surface of the shielding layer away from the base layer.

[0037] The shielding layer is made of copper with a thickness of 1 μm, the base layer is made of epoxy resin and polyimide with a thickness of 6 μm, and the bonding layer is made of acrylic acid with a thickness of 6 μm.

[0038] The spacing between adjacent breakpoints in the shielding layer is greater than or equal to 2 μm. Within a distance of 260 μm, the number of breakpoints in the shielding layer is 10, and the maximum width of the breakpoints is less than or equal to 5 μm.

[0039] Example 2

[0040] This embodiment provides a shielding film, the structure, material and parameters of which are the same as those of Embodiment 1, except that within a distance of 260 μm, the number of breakpoints of the shielding layer is 20, and the maximum width of the breakpoints is less than or equal to 5 μm.

[0041] Example 3

[0042] This embodiment provides a shielding film, the structure, material and parameters of which are the same as those of Embodiment 1, except that within a distance of 260 μm, the number of breakpoints of the shielding layer is 2, and the maximum width of the breakpoints is less than or equal to 5 μm.

[0043] Example 4

[0044] This embodiment provides a shielding film, the structure, material and parameters of which are the same as those of Embodiment 1, except that the number of breakpoints with a maximum width of 0.1-3.5 μm accounts for 85% of the total number of breakpoints.

[0045] Example 5

[0046] This embodiment provides a shielding film, the structure, material and parameters of which are the same as those of the embodiment 1, except that the number of breakpoints with a maximum width of 0.1-1.5 μm accounts for 45% of the total number of breakpoints.

[0047] The number of breakpoints having a maximum width of 1.5 μm to 5 μm accounted for 55% of the total number of breakpoints.

[0048] Example 6

[0049] This embodiment provides a shielding film, comprising a stacked base layer 1 and a shielding layer, wherein a bonding layer is disposed on a surface of the shielding layer away from the base layer, the shielding layer is provided with a plurality of protrusions, and the bonding layer is provided with a plurality of conductive particles.

[0050] The shielding layer is made of silver with a thickness of 1 μm, the base layer is made of epoxy resin and polyimide with a thickness of 7 μm, and the bonding layer is made of acrylic acid and epoxy resin with a thickness of 5 μm.

[0051] The spacing between adjacent breakpoints in the shielding layer is greater than or equal to 4 μm. Within a distance of 260 μm, the number of breakpoints in the shielding layer is 7, and the maximum width of the breakpoints is less than or equal to 5 μm.

[0052] The number of breakpoints with a maximum width of 0.1-1.0 μm accounts for 17% of the total number of breakpoints, the number of breakpoints with a maximum width of 1.0 μm-2.0 μm accounts for 60% of the total number of breakpoints, and the number of breakpoints with a maximum width of 2.0 μm-5 μm accounts for 23% of the total number of breakpoints.

[0053] Example 7

[0054] This embodiment provides a shielding film, the structure, material and parameters of which are the same as those of Embodiment 5, except that the vertical distance between the centers of adjacent breakpoints is less than or equal to 7 μm.

[0055] Comparative Example 1

[0056] This comparative example provides a shielding film, whose structure, material and parameters are the same as those of Example 1, except that within a distance of 260 μm, the number of breakpoints of the shielding layer is 30, and the maximum width of the breakpoints is 1 μm.

[0057] Comparative Example 2

[0058] This comparative example provides a shielding film, whose structure, material and parameters are the same as those of Example 1, except that within a distance of 260 μm, the number of breakpoints of the shielding layer is 15, and the maximum width of the breakpoints is greater than or equal to 6 μm.

[0059] Experimental example

[0060] The electromagnetic shielding performance, bending resistance, and high step resistance of the shielding films of Examples 1-7 and Comparative Examples 1-2 were tested, and the results are as follows:

[0061] 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 corresponding to the step height, and test the grounding resistance of the electromagnetic shielding film. The grounding resistance shall not exceed 1 ohm, and it shall be deemed to be failed if it exceeds 1 ohm; 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 the circuit) 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 when the resistance change of the bending line exceeds 10%, the test is stopped. The test results are shown in Table 1.

[0062] Table 1 Performance parameters of shielding film

[0063] Group Electromagnetic shielding performance / dB Bending resistance / times High step resistance / μm Example 1 Greater than 62 More than 12000 Greater than 75 Example 2 More than 60 More than 12000 Greater than 75 Example 3 Greater than 63 More than 12000 Greater than 75 Example 4 Greater than 62 More than 13000 Greater than 75 Example 5 Greater than 63 More than 13000 Greater than 75 Example 6 Greater than 65 More than 13000 Greater than 75 Example 7 Greater than 63 More than 13000 Greater than 75 Comparative Example 1 45 8926 50 Comparative Example 2 48 10210 50

[0064] It can be seen that the shielding film provided by the present invention has good bending resistance, high step resistance and electromagnetic shielding performance.

[0065] 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 therefrom are still within the scope of protection of the invention.

Claims

1. A shielding film, characterized in that: It comprises a base layer and a shielding layer which are stacked, wherein within a horizontal distance of 260 μm, the number of breakpoints of the shielding layer is 1 ≤ N ≤ 20, the maximum width of the breakpoints is less than or equal to 5 μm, and N is the number of breakpoints.

2. The shielding film according to claim 1, characterized in that The distance between adjacent breakpoints is greater than or equal to 2 μm.

3. The shielding film according to claim 2, characterized in that The number of breakpoints with a maximum width of 0.1 μm-3.5 μm accounts for more than 70% of the total number of breakpoints.

4. The shielding film according to claim 3, characterized in that The number of breakpoints with a maximum width of 0.1 μm to 1.5 μm accounts for 30% to 75% of the total number of breakpoints. The number of breakpoints with a maximum width of 1.5 μm to 5 μm accounts for 35% to 85% of the total number of breakpoints, The sum of the number of breakpoints whose maximum width is 0.1 μm-1.5 μm and the number of breakpoints whose maximum width is 1.5 μm-5 μm accounts for less than or equal to 100% of the total number of breakpoints.

5. The shielding film according to claim 4, characterized in that The number of breakpoints with a maximum width of 0.1-1.0 μm accounts for 5%-30% of the total number of breakpoints, The number of breakpoints with a maximum width of 1.0 μm-2.0 μm accounts for 45%-85% of the total number of breakpoints, The number of breakpoints with a maximum width of 2.0 μm to 5 μm accounts for 10% to 40% of the total number of breakpoints, The sum of the number of breakpoints with a maximum width of 0.1-1.0 μm, the number of breakpoints with a maximum width of 1.0 μm-2.0 μm and the number of breakpoints with a maximum width of 2.0 μm-5 μm accounts for less than or equal to 100% of the total number of breakpoints.

6. The shielding film according to claim 4 or 5, characterized in that: An extension line of a line connecting the centers of adjacent breakpoints passes through at least two centers of adjacent breakpoints; and / or, A vertical distance between centers of adjacent breakpoints is less than or equal to 7 μm.

7. The shielding film according to claim 6, characterized in that The thickness of the shielding layer is 1-9 μm, The thickness of the base layer is 2-20 μm.

8. The shielding film according to claim 7, characterized in that A bonding layer is stacked on the surface of the shielding layer away from the base layer, and the thickness of the bonding layer is 2-20 μm.

9. The shielding film according to claim 8, characterized in that The bonding layer contains conductive particles or does not contain conductive particles; and / or, A protrusion is arranged on the surface of the shielding layer away from the base layer.

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

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