Electromagnetic shielding film and circuit board
By designing the non-flat surface structure of the convex and concave parts in the electromagnetic shielding film, the segment difference resistance and shielding efficiency of the electromagnetic shielding film are improved, and the problem of insufficient segment difference resistance in the folded state is solved, achieving high efficiency electromagnetic shielding effect and long life of the equipment.
Patent Information
- Application Number
- CN202411382450.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-30
- Publication Date
- 2025-01-03
AI Technical Summary
The existing electromagnetic shielding films have insufficient resistance to segment differences in the folded state, which can easily damage or lose conduction ability, resulting in a decrease in service life of electronic equipment.
An electromagnetic shielding film is arranged with a base film and a shielding layer stacked. The shielding layer consists of a non-flat surface composed of a convex portion and a concave portion. The vertical height difference between the convex portion and the concave portion is less than or equal to 15 μm. The thickness of the thinnest part of the concave portion is greater than or equal to the average shielding layer. 3/10 of the thickness is formed by physical deposition, chemical deposition or electroplating processes to enhance bending resistance and grounding properties.
It improves the high-band difference resistance and shielding performance of the electromagnetic shielding film, and the shielding efficiency reaches more than 60DB, adapts to the application requirements of electronic devices such as folding mobile phones and extends the service life of the equipment.
Smart Images
Figure CN119255587A_ABST
Abstract
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] Electromagnetic shielding film is a key material used to reduce electromagnetic interference. It is widely used in various electronic devices, such as mobile phones, computers, etc. With the rapid development of folding screens, the requirements for electromagnetic shielding films are getting higher and higher. In order to allow folding mobile phones to operate normally and avoid electromagnetic interference from the outside world and themselves, it is necessary to apply electromagnetic shielding films on the circuit board surface of folding mobile phones and other electronic devices to ensure that the electronic devices can also maintain good electromagnetic shielding effects when folded.
[0003] However, some of the current electromagnetic shielding films not only have insufficient ability to withstand step differences, but are also prone to damage and cracks due to repeated folding, and may even lose their conductive ability, reducing the service life of electronic equipment.
[0004] Therefore, there is an urgent need for a high-performance electromagnetic shielding film that has both efficient shielding performance and strong resistance to high step difference. Summary of the invention
[0005] In view of this, the present invention provides an electromagnetic shielding film and a circuit board, so that the circuit board or FPC board containing the electromagnetic shielding film has better bending resistance and the electromagnetic shielding film has better step resistance.
[0006] In a first aspect, the present invention provides an electromagnetic shielding film, comprising: a base film and a shielding layer, wherein the shielding layer and the base film are stacked.
[0007] The base film includes but is not limited to: polyimide polyester film, polyimide film, polyurethane film, polycarbonate film, among which polyimide polyester film has excellent mechanical strength and heat resistance; polyimide film has good high temperature resistance and electrical insulation properties; polyurethane film has good elasticity and chemical resistance; polycarbonate film has good impact strength, transparency and processing properties.
[0008] The shielding layer includes but is not limited to 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 can be made of any one of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold, and the alloy shielding layer can be made of any two or more of aluminum, titanium, zinc, iron, nickel, chromium, cobalt, copper, silver and gold. The shielding layer can be a single-layer structure or a multi-layer structure, and the multi-layer structure shielding layer is a superposition of several identical shielding layers or different shielding layers.
[0009] The side of the shielding layer away from the base film is a non-flat surface composed of protrusions and recesses, and the vertical height difference between adjacent protrusions and recesses is greater than 1 and less than or equal to 15μm, for example, it can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm or an interval consisting of any two values; the thickness of the thinnest part of the recess is greater than or equal to 3 / 10 of the average thickness of the shielding layer, for example, the ratio can be 3 / 10, 1 / 3, 1 / 2, 5 / 6, 1, 1.2, 1.5, 2, 2.2, 2.5, 3, 3.2, 3.4, 4 or an interval consisting of any two values; wherein the average thickness of the shielding layer is a plurality of vertical distances between the upper surface and the lower surface of the shielding layer, that is, the average value of the thickness of the shielding layer.
[0010] The concave and convex portions of the shielding layer are formed on the surface of the base film layer by at least one of physical deposition, chemical deposition, and electroplating processes.
[0011] In the present invention, the convex part of the shielding layer is upwardly protruding, thicker, and has a thickness peak value, and the concave part of the shielding layer is downwardly protruding, thinner, and has a thickness valley value. The concave part and the convex part are the basic points for measurement. The vertical height difference between adjacent convex parts and concave parts of the shielding layer is the vertical distance between the position where the peak value of the convex part of the shielding layer is located and the position where the lowest point of the concave part of the shielding layer is located. The average thickness of the shielding layer is the average thickness determined by summing the thickness of all convex parts and the thickness of all concave parts, that is, the average value of multiple thicknesses between the non-flat upper surface and the lower surface of the shielding layer. When measuring, the more values are taken, the more accurate it is.
[0012] The electromagnetic shielding film provided in the present invention has a high step difference resistance performance compared to the electromagnetic shielding film of traditional structure, so that the circuit board or FPC board containing the electromagnetic shielding film has better bending resistance, and the electromagnetic shielding film still has a high shielding effectiveness after the high step difference, and the shielding effectiveness can reach more than 60DB, which can meet the application requirements of existing circuit boards or flexible boards and has high adaptability.
[0013] In the present invention, the convex portion of the shielding layer serves to be grounded, specifically to be grounded to the ground layer of the circuit board, thereby conducting away the charge accumulated in the electromagnetic shielding film, avoiding charge accumulation or heating of the electromagnetic shielding film, and improving the shielding effectiveness of the electromagnetic shielding film.
[0014] In the present invention, in addition to achieving the grounding effect, the convex part of the electromagnetic shielding layer has the structure of the convex part and the concave part, and the vertical height difference between the convex part and the concave part is less than or equal to 15μm and other specific parameters. The researchers unexpectedly found that the electromagnetic shielding film has good resistance to step difference while maintaining good shielding effectiveness, and the circuit board or FPC board containing the electromagnetic shielding film has better resistance to bending than conventional electromagnetic shielding films. The above structure has a function similar to storage, so that the electromagnetic shielding film can have high step difference resistance when the surface of high step difference components is pressed. In addition, the limitation of parameters such as the structure of the convex part and the concave part of the electromagnetic shielding film and the height difference between them can also absorb energy when bending, thereby improving the resistance to bending of the circuit board or FPC board containing the electromagnetic shielding film.
[0015] In the experiment, it was found that in order for the electromagnetic shielding film to maintain the above technical effects, certain conditions must be met, namely, the vertical height difference between adjacent convex and concave parts is less than or equal to 15μm; the thickness of the thinnest part of the concave part is greater than or equal to 3 / 10 of the average thickness of the shielding layer. This setting can ensure that the height difference between the concave and convex parts on the shielding layer is moderate, and at the same time can achieve the desired technical effect. If there are no concave and convex structures on the shielding layer, the electromagnetic shielding film has poor resistance to high step difference and poor grounding performance, resulting in poor electromagnetic shielding effect. It should be noted that the average thickness and height difference of the electromagnetic shielding film can be measured by slicing, and of course, it can also be measured by other measurement methods.
[0016] In order to make the circuit board or FPC board containing the electromagnetic shielding film have better bending resistance and the electromagnetic shielding film has better step resistance. In an optional embodiment, the distance between two adjacent protrusions is greater than or equal to 3μm. Among them, the distance between two adjacent protrusions is the horizontal distance between the highest positions of the protrusions of two adjacent protrusions. Further limiting the horizontal distance between two adjacent protrusions can further ensure that the electromagnetic shielding film does not lose shielding effectiveness while further optimizing the step resistance of the electromagnetic shielding film. The distance between two adjacent protrusions can be 3μm, 5μm, 8μm, 9μm, 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm or an interval consisting of any two values. This setting is mainly to avoid stress concentration and facilitate stress transfer. The distance between two adjacent protrusions can also be greater than 11μm, but needs to be less than 100μm. This setting facilitates the extraction of accumulated charges in the shielding layer of the electromagnetic shielding film, thereby maintaining better shielding effectiveness. At the same time, it can enable the circuit board or FPC board containing the electromagnetic shielding film to have better bending resistance.
[0017] In order to make the electromagnetic shielding film have better shielding effectiveness and better resistance to high step difference, the circuit board or FPC board containing the electromagnetic shielding film has stronger bending resistance. In an optional embodiment, within the range of 260 μm in the length direction of the shielding layer, the number of concave and convex parts whose thickness at the thinnest part of the concave and convex part is less than or equal to 2 / 3 of the average thickness of the shielding layer is less than 30. In this way, the thickness of the shielding layer can be kept relatively uniform over the entire length range to ensure better shielding effectiveness, avoid the decrease in the shielding effectiveness of the thinnest thickness of the concave and convex part, and affect the overall electromagnetic shielding performance, and such a setting can make the circuit board or FPC board containing the electromagnetic shielding film have better bending resistance and high step difference resistance of the electromagnetic shielding film. Exemplarily, within the range of 260 μm in the length direction of the shielding layer, the number of concave parts whose thickness at the thinnest part of the concave part is less than or equal to 2 / 3 of the average thickness of the shielding layer is 10, 15, 20, 25, 30 or an interval consisting of any two values, and can also be less than 10. Limiting the number of recesses whose thickness at the thinnest point is less than or equal to 2 / 3 of the average thickness of the shielding layer is to avoid breakage when the electromagnetic shielding film has a high step difference, thereby causing the electromagnetic shielding film to fail in shielding, or to ensure that the circuit board or FPC board containing the electromagnetic shielding film has good bending resistance.
[0018] In order to make the circuit board or FPC board containing the electromagnetic shielding film have stronger bending resistance and the electromagnetic shielding film has better resistance to high step difference. In an optional embodiment, the ratio of the horizontal width D of the bottom of the convex portion to the vertex height H of the convex portion is 0.2≤D / H≤8. The ratio of the horizontal width D of the convex portion to the vertex height H of the convex portion can be, for example, 0.2, 0.8, 1, 2, 3, 4, 5, 7, 8 or an interval consisting of any two values. In the present invention, the horizontal width D of the bottom of the convex portion can be measured under the slice of the electromagnetic shielding film, and the horizontal distance corresponding to the lowest adjacent point of a single convex portion can be the horizontal width of the bottom of the convex portion. The vertex height H of the convex portion is the vertical height of the vertex of the convex portion and the lowest bottom adjacent to the convex portion, wherein the measurement of the vertex height H does not include the thickness at the vertex of the convex portion.
[0019] In an optional embodiment, the thickness of the top of the protrusion is 1 μm-10 μm. Exemplarily, the thickness of the top of the protrusion can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or an interval consisting of any two values. In this way, the grounding conductivity of the electromagnetic shielding film can be better, thereby maintaining the shielding effectiveness of the electromagnetic shielding film. At the same time, it helps to improve the step resistance performance of the electromagnetic shielding film and the bending resistance performance of the circuit board or FPC board containing the electromagnetic shielding film.
[0020] In an optional embodiment, the number of convex parts whose maximum thickness at the top of the convex part is 1-1.8 times the average thickness of the shielding layer accounts for 30%-85% of the total number of convex parts; illustratively, the proportion can be 30%, 40%, 50%, 60%, 70%, 80%, 85% or an interval consisting of any two values. The number of convex parts whose thickness at the top of the convex part is 1.8-4 times the average thickness of the shielding layer accounts for 30%-90% of the total number of convex parts. illustratively, the proportion can be 30%, 40%, 50%, 60%, 70%, 80%, 90% or an interval consisting of any two values. Among them, the total proportion of the number of convex parts whose maximum thickness at the top of the convex part is 1-4 times the average thickness of the shielding layer accounts for less than or equal to 100%.
[0021] In an optional embodiment, the number of convex parts whose maximum thickness at the top of the convex part is 1-1.5 times the average thickness of the shielding layer accounts for 10%-60% of the total number of convex parts; exemplary, the proportion can be 10%, 20%, 30%, 40%, 50%, 60% or an interval consisting of any two values. The number of convex parts whose maximum thickness at the top of the convex part is 1.5-2.0 times the average thickness of the shielding layer accounts for 30%-80% of the total number of convex parts; exemplary, the proportion can be 30%, 40%, 50%, 60%, 70%, 80% or an interval consisting of any two values. The number of convex parts whose maximum thickness at the top of the convex part is 2.0-4.0 times the average thickness of the shielding layer accounts for 5%-25% of the total number of convex parts; exemplary, the proportion can be 5%, 10%, 15%, 20%, 25% or an interval consisting of any two values. The total number of protrusions whose maximum thickness at the top of the protrusions is 1-4 times the average thickness of the shielding layer accounts for less than or equal to 100% of the total number of protrusions. Further limiting the above proportion can effectively improve the step resistance and shielding effectiveness of the electromagnetic shielding film and the bending resistance of the circuit board or FPC board containing the electromagnetic shielding film.
[0022] In an optional embodiment, the surface of the convex portion of the shielding layer away from the base film side is provided with conductive particles. The conductive particles are mainly concentrated at the position of the convex portion, increasing the overall thickness of the convex portion, and the conductive particles can effectively improve the piercing and grounding performance of the convex portion, and ultimately can improve the shielding effectiveness of the electromagnetic shielding film. The material used for the conductive particles can be the same as that used for the shielding layer, or it can be different from the material used for the shielding layer, and the specific selection can be made according to actual needs. The measurement of the maximum thickness of the top of the convex portion includes the overall thickness of the conductive particles arranged on the surface of the convex portion.
[0023] In an optional embodiment, a bonding layer is provided on the surface of the shielding layer away from the base film, and the bonding layer contains conductive particles or does not contain conductive particles. The bonding layer containing conductive particles can effectively enhance the conductive path and improve the conductivity and shielding effectiveness of the shielding layer. If a bonding layer without conductive particles is provided, the manufacturing process is simple, which can effectively reduce the manufacturing cost and complexity.
[0024] It should be noted that the vertical distance between the lowest point of the concave part of the shielding layer (the outermost surface of the concave part of the shielding layer, the thickness of the shielding layer at the lowest point of the concave part is calculated) and the center line is 0.5-6μm, and the center line is the center line between the highest point of the convex part of the shielding layer (the inner side of the convex part of the shielding layer, the thickness at the highest point of the convex part is not calculated) and the lowest point of the concave part in the field of view of the sample to be tested (for example, the electron microscope of the sample slice). The vertical distance between the highest point of the convex part and the center line is 1-8μm.
[0025] In a second aspect, the present invention provides a circuit board, the circuit board comprising the electromagnetic shielding film in any one of the above embodiments.
[0026] Compared with the prior art, the beneficial effects of the present invention are: the electromagnetic shielding film provided by the present invention has higher resistance to high step difference than the electromagnetic shielding film of traditional structure, and the electromagnetic shielding film still has high shielding effectiveness after the high step difference, and the shielding effectiveness can reach more than 60DB. At the same time, the circuit board or FPC board of the electromagnetic shielding film has strong bending resistance, can adapt to the application requirements of existing circuit boards or FPC boards, and has high adaptability. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] 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.
[0028] Figure 1 is a schematic diagram of the composition of a specific example of an electromagnetic shielding film according to an embodiment of the present invention;
[0029] Figure 2 is a schematic diagram of a vertex height H according to an embodiment of the present invention;
[0030] Description of the drawings: 1-base film, 2-shielding layer, 21-convex part, 22-concave part. DETAILED DESCRIPTION
[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.
[0032] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0033] Example 1
[0034] See also Figure 1 FIG. 1 is a schematic diagram of the structure of an electromagnetic shielding film provided by an embodiment of the present invention. Figure 2 As shown, the apex height H of the convex portion is the vertical height between the top end a1 of the convex portion (excluding the thickness at the apex of the convex portion) and the bottom end a2 of the adjacent concave portion (including the thickness at the bottom of the concave portion).
[0035] In this embodiment, an electromagnetic shielding film is provided, including: a base film, a shielding layer and an adhesive layer, wherein the adhesive layer, the shielding layer and the base film are stacked, the base film is made of polyimide and epoxy resin, and its thickness is 7.2μm, and the shielding layer is made of copper, and its thickness is 1.5μm; the side of the shielding layer away from the base film is an uneven surface composed of convex parts and concave parts, and the concave parts and convex parts of the shielding layer are arranged at intervals. The vertical height difference between the convex parts and concave parts of adjacent shielding layers is less than or equal to 15μm; the thickness of the thinnest part of the shielding layer is greater than 3 / 10 of the average thickness of the shielding layer.
[0036] Example 2
[0037] Other technical features of this embodiment are the same as those of Embodiment 1, and in addition: the distance between two adjacent protrusions in this embodiment is greater than 8μm; within a range of 260μm in the length direction of the shielding layer, the number of concave portions whose thinnest thickness is less than or equal to 2 / 3 of the average thickness of the shielding layer is 18; the ratio of the horizontal width D of the protrusion to the vertex height H of the protrusion is D / H, which is 1≤D / H≤7; the thickness of the top of the protrusion is 2.1μm; the number of protrusions whose maximum thickness at the top of the protrusion is 1-1.8 times the average thickness of the shielding layer accounts for 44% of the total number of protrusions; the number of protrusions whose thickness at the top of the protrusion is 1.8-4 times the average thickness of the shielding layer accounts for 56% of the total number of protrusions.
[0038] Example 3
[0039] The other technical features of this embodiment are the same as those of Embodiment 2, and in addition: the number of protrusions whose maximum thickness at the top of the protrusion is 1-1.5 times the average thickness of the shielding layer accounts for 22% of the total number of protrusions; the number of protrusions whose maximum thickness at the top of the protrusion is 1.5-2.0 times the average thickness of the shielding layer accounts for 67% of the total number of protrusions; the number of protrusions whose maximum thickness at the top of the protrusion is 2.0-4.0 times the average thickness of the shielding layer accounts for 11% of the total number of protrusions.
[0040] Comparative Example 1
[0041] This comparative example provides an electromagnetic shielding film, whose structure and the material and thickness of each structure are the same as those of Example 1, except that the vertical height difference between the convex and concave parts of adjacent shielding layers is greater than 18μm; the thickness at the thinnest point is less than 3 / 11 of the average thickness of the shielding layer.
[0042] Test example
[0043] In this test example, 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 adhere two electromagnetic shielding films of the same model to be tested to the two surfaces of the bending plate (the bending plate contains circuits) and press them together (pre-pressing time 10 seconds, molding time 180 seconds, molding pressure 120kg, pressing temperature 185°C); after pressing, bake and cure (baking temperature 160°C, 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%.
[0044] Referring to Table 1, the performance parameters between the embodiment and the comparative example are shown.
[0045] Table 1
[0046] Electromagnetic shielding effectiveness / DB Bending resistance / times Step resistance performance / μm Example 1 More than 60 More than 11000 Greater than 75 Example 2 Greater than 62 More than 15000 Greater than 75 Example 3 Greater than 62 More than 16000 Greater than 75 Comparative Example 1 Approx. 48 Approx. 8863 Approx. 50
[0047] It can be seen that the electromagnetic shielding film provided by the present invention has higher step difference resistance performance 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.
[0048] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.
Claims
1. An electromagnetic shielding film, characterized in that: include: Basement membrane; A shielding layer, the shielding layer and the base film are stacked; The side of the shielding layer away from the base film is a non-flat surface composed of protrusions and recesses, and the vertical height difference between adjacent protrusions and recesses is less than or equal to 15μm; the thickness of the thinnest part of the shielding layer is greater than or equal to 3 / 10 of the average thickness of the shielding layer; wherein the average thickness of the shielding layer is the average value of the thicknesses of multiple shielding layers between the upper surface and the lower surface of the shielding layer.
2. The electromagnetic shielding film according to claim 1, characterized in that The distance between two adjacent protrusions is greater than or equal to 3 μm.
3. The electromagnetic shielding film according to claim 1, characterized in that Within a range of 260 μm in the length direction of the shielding layer, the number of the concave and convex portions whose thinnest thickness is less than or equal to 2 / 3 of the average thickness of the shielding layer is less than 30.
4. The electromagnetic shielding film according to claim 1, characterized in that A ratio of a horizontal width D of the convex portion to a vertex height H of the convex portion is 0.2≤D / H≤8.
5. The electromagnetic shielding film according to claim 1, characterized in that The thickness of the top of the protrusion is 1 μm-10 μm.
6. The electromagnetic shielding film according to claim 1, characterized in that The number of protrusions whose maximum thickness at the top of the protrusion is 1-1.8 times the average thickness of the shielding layer accounts for 30%-85% of the total number of protrusions; the number of protrusions whose thickness at the top of the protrusion is 1.8-4 times the average thickness of the shielding layer accounts for 30%-90% of the total number of protrusions.
7. The electromagnetic shielding film according to claim 1, characterized in that The number of convex parts whose maximum thickness at the top of the convex parts is 1-1.5 times the average thickness of the shielding layer accounts for 10%-60% of the total number of convex parts; The number of convex parts whose maximum thickness at the top of the convex parts is 1.5-2.0 times the average thickness of the shielding layer accounts for 30%-80% of the total number of convex parts; The number of the protrusions whose maximum thickness at the top of the protrusion is 2.0-4.0 times the average thickness of the shielding layer accounts for 5%-25% of the total number of the protrusions.
8. The electromagnetic shielding film according to claim 1, characterized in that Conductive particles are provided on the surface of the protrusion of the shielding layer on a side away from the base film.
9. The electromagnetic shielding film according to claim 1, characterized in that A bonding layer is provided on the surface of the shielding layer away from the base film, and the bonding layer contains conductive particles.
10. A circuit board, characterized in that: The circuit board comprises the electromagnetic shielding film as described in any one of claims 1 to 9.