Electromagnetic shielding film and circuit board

Abstract

The invention discloses an electromagnetic shielding film and a circuit board. The electromagnetic shielding film comprises a shielding layer and an adhesive film layer which are laminated, wherein the change of the relative dielectric constant of the adhesive film layer is less than or equal to 10% when the relative humidity is changed by 5% at normal temperature within 24 hours. By using the adhesive film layer with a relatively stable dielectric constant in a humidity environment, after the shielding film covers the circuit board, the insertion loss of the shielding film is relatively stable, the use reliability of the circuit board is effectively improved, and the signal transmission quality on the circuit board is ensured.

Description

Technical Field

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

[0002] With the rapid development of the electronics industry, electronic products are further developing towards miniaturization, lightness, and high-density assembly, which greatly promotes the development of flexible circuit boards, thereby realizing the integration of component devices and wire connections. An important indicator for evaluating the performance of flexible circuit boards is electromagnetic interference shielding (EMIShielding for short). With the integration of audio components, sensor components, etc. on mobile devices such as mobile phones, the signal transmission between these components will tend to be high-frequency and high-speed. Under the drive of high frequency and high speed, the electromagnetic interference inside and outside the components, the attenuation of signals during transmission, and the problems of insertion loss and jitter are becoming increasingly serious.

[0003] In existing circuit boards, signal shielding is performed by covering the circuit board with a shielding film to reduce electromagnetic interference and other problems. Currently, the commonly used electromagnetic shielding film mainly includes a shielding layer and a film layer, which connects the shielding layer to the ground layer of the circuit board through the film layer, and then introduces the interference charge into the ground layer of the circuit board to achieve the purpose of shielding. However, after the current electromagnetic shielding film is pressed on the circuit board, due to changes in the use environment and other reasons, after a long period of use, the water vapor inside the circuit board may increase, which in turn leads to a large change in the insertion loss, which is easy to affect the reliability of the circuit board. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an electromagnetic shielding film and a circuit board. By using a film layer with a relatively stable relative dielectric constant in a humid environment, the insertion loss of the shielding film can be relatively stable after it is covered on the circuit board, thereby effectively improving the reliability of the circuit board and ensuring the quality of signal transmission on the circuit board.

[0005] In order to achieve the above-mentioned purpose, an embodiment of the present invention provides an electromagnetic shielding film, comprising a shielding layer and a film layer stacked together; wherein, at room temperature, within 24 hours, for every 5% change in relative humidity, the relative dielectric constant of the film layer changes by less than or equal to 10%.

[0006] As an improvement of the above solution, at room temperature, the relative dielectric constant of the adhesive film layer is less than or equal to 3.

[0007] As an improvement of the above solution, at room temperature, within 72 hours, for every 10% change in relative humidity, the relative dielectric constant of the adhesive film layer changes by less than or equal to 20%.

[0008] As an improvement of the above solution, the average thickness of the adhesive film layer is 1 μm to 20 μm.

[0009] As an improvement of the above solution, a side of the shielding layer close to the adhesive film layer is provided with a protruding structure, and the protruding structure is used to pierce the adhesive film layer to connect and conduct with the ground layer of the circuit board.

[0010] As an improvement of the above solution, the shielding layer has a flat surface on one side close to the adhesive film layer, the adhesive film layer includes an adhesive layer containing conductive particles, and the shielding layer is connected to the ground layer of the circuit board through the conductive particles in the adhesive film layer.

[0011] As an improvement of the above solution, the electromagnetic shielding film further comprises an insulating layer, and the insulating layer is stacked on a side of the shielding layer away from the adhesive film layer.

[0012] As an improvement of the above solution, the electromagnetic shielding film further comprises a carrier film, and the carrier film is stacked on a side of the insulating layer away from the shielding layer.

[0013] As an improvement of the above solution, the electromagnetic shielding film further comprises a protective film, and the protective film is stacked on a side of the adhesive film layer away from the shielding layer.

[0014] An embodiment of the present invention further provides a circuit board, comprising a circuit board substrate and any one of the electromagnetic shielding films described above, wherein the electromagnetic shielding film is pressed together with the circuit board substrate.

[0015] Compared with the prior art, the electromagnetic shielding film and circuit board provided by the embodiment of the present invention have the following beneficial effects: by setting the relative dielectric constant of the adhesive film layer in the electromagnetic shielding film to be less than or equal to 10% for every 5% change in relative humidity at room temperature within 24 hours. By using an adhesive film layer with a relatively stable relative dielectric constant under a humid environment, the embodiment of the present invention can make the insertion loss of the shielding film relatively stable after it is covered on the circuit board, effectively improving the reliability of the circuit board and ensuring the quality of signal transmission on the circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of a preferred embodiment of an electromagnetic shielding film provided by the present invention;

[0017] Figure 2 It is a schematic diagram of a protruding structure puncturing and grounding in an electromagnetic shielding film provided by the present invention;

[0018] Figure 3 It is a schematic diagram of grounding of conductive particles in an electromagnetic shielding film provided by the present invention;

[0019] Figure 4It is a structural schematic diagram of a preferred embodiment of an electromagnetic shielding film provided by the present invention;

[0020] Figure 5 It is a schematic diagram of an uneven shielding layer in an electromagnetic shielding film provided by the present invention;

[0021] The reference numerals are as follows:

[0022] 1. Shielding layer; 11. Raised structure; 2. Adhesive film layer; 21. Conductive particles; 3. Insulating layer; 4. Carrier film; 5. Protective film; 6. Circuit board. DETAILED DESCRIPTION

[0023] 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. 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.

[0024] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, 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 should not be understood as a limitation on the present application.

[0025] 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.

[0026] 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.

[0027] See also Figure 1 , Figure 1The structure diagram of a preferred embodiment of an electromagnetic shielding film provided by the present invention is shown in FIG. The embodiment of the present invention provides an electromagnetic shielding film, comprising a shielding layer 1 and an adhesive film layer 2 stacked in layers; wherein, at room temperature, for every 5% change in relative humidity within 24 hours, the relative dielectric constant of the adhesive film layer 2 changes by less than or equal to 10%.

[0028] It should be noted that insertion loss is to evaluate the signal attenuation of the entire link from the start to the end of the line to ensure the quality of the signal during transmission. After the current electromagnetic shielding film is covered on the circuit board, the relative dielectric constant of the film layer may change significantly due to changes in the humidity of the use environment, which in turn affects the insertion loss on the circuit board, causing its insertion loss to gradually increase.

[0029] Based on this, an embodiment of the present invention designs a film layer 2 with a relatively stable relative dielectric constant under a humid environment. At room temperature, within 24 hours, for every 5% change in relative humidity, the relative dielectric constant of the film layer 2 changes by less than or equal to 10%. This ensures the stability of the relative dielectric constant of the film layer, thereby effectively improving the insertion loss stability of the electromagnetic shielding film during use, thereby improving the quality of signal transmission on the circuit board.

[0030] Since different time lengths have different effects on the dielectric constant in a humidity environment, the present invention sets a certain time range and limits the change of the relative dielectric constant to improve the stability of the insertion loss. The time range set here can be 24 hours, or other time lengths, such as 48 hours, 72 hours, 96 hours, etc., and the corresponding relative dielectric constant change can be limited for different time lengths, and the present invention does not limit this.

[0031] The embodiment of the present invention uses a film layer with a relatively stable relative dielectric constant in a humid environment, so that after the shielding film is covered on the circuit board, its insertion loss is relatively stable, which effectively improves the reliability of the circuit board and ensures the quality of signal transmission on the circuit board.

[0032] Among them, the relative dielectric constant refers to the ratio of the capacitance of a capacitor of the same size made with the material itself as the medium to that made with a vacuum as the medium.

[0033] In another preferred embodiment, at room temperature, the relative dielectric constant of the adhesive film layer 2 is less than or equal to 3.

[0034] Specifically, generally, a higher relative dielectric constant may lead to a greater insertion loss. The embodiment of the present invention further selects a film layer 2 with a lower relative dielectric constant, which can reduce the energy loss suffered by electromagnetic waves when passing through the film layer 2. At the same time, in high-speed signal transmission, the relative dielectric constant of the film layer 2 is crucial to the integrity of the signal. Too high a relative dielectric constant may cause signal distortion, delay or attenuation, affecting the performance of the system. Therefore, the embodiment of the present invention sets the relative dielectric constant of the film layer 2 to be no more than 3, which can effectively reduce the insertion loss on the circuit board and improve the reliability of the line transmission signal.

[0035] In another preferred embodiment, at room temperature, within 72 hours, for every 10% change in relative humidity, the relative dielectric constant of the adhesive film layer 2 changes by less than or equal to 20%.

[0036] Specifically, since the humidity may change more with the use time, the embodiment of the present invention further limits the change of the relative dielectric constant in the adhesive film layer 2. At room temperature, within 72 hours, for every 10% change in relative humidity, the relative dielectric constant of the adhesive film layer 2 changes by less than or equal to 20%. In this way, an adhesive film layer 2 is designed that can still make the relative dielectric constant change more stably in a relatively long humidity environment, further improving the stability of the insertion loss of the circuit board covered with the electromagnetic shielding film, and preventing the insertion loss of the circuit board from decaying too quickly after long-term use, thereby affecting its reliability.

[0037] In another preferred embodiment, the average thickness of the adhesive film layer 2 is 1 μm to 20 μm.

[0038] Specifically, the thickness of the adhesive film layer 2 affects the propagation and attenuation of electromagnetic waves therein. A suitable thickness of the adhesive film layer 2 can reduce the insertion loss to a certain extent. Within a certain range, the thicker the adhesive film layer 2, the smaller the insertion loss of the circuit board. However, it cannot be too thick. An overly thick adhesive film layer 2 may cause other problems, such as increased weight, reduced flexibility, and poor bonding effect of the circuit board. Therefore, the embodiment of the present invention sets the average thickness of the adhesive film layer 2 to 1 μm to 20 μm, which can optimize the insertion loss of the circuit board without having a significant impact on other properties of the electromagnetic shielding film. Exemplarily, the average thickness of the film layer 2 is 1 μm, 1.5 μm, 3 μm, 4.5 μm, 5 μm, 6.5 μm, 7 μm, 8.5 μm, 9 μm, 10.5 μm, 11 μm, 12.5 μm, 13 μm, 14.5 μm, 17 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm and / or an interval consisting of any two values.

[0039] See also Figure 5 , Figure 5 Schematic diagram of an uneven shielding layer in an electromagnetic shielding film provided by the present invention. Figure 5As shown, since the shielding layer 1 may be uneven and have certain undulations, the adhesive film layer 2 generated by coating the adhesive thereon may also be prone to unevenness. Therefore, it is generally more accurate to use the average thickness to characterize its thickness, and the average thickness of the adhesive film layer 2 is obtained as follows: N vertical lines are sampled between one side of the adhesive film layer 2 close to the shielding layer 1 and the other side away from the shielding layer 1, and the average value of the N vertical lines is the average thickness of the adhesive film layer 2, where N is greater than or equal to 10.

[0040] In another preferred embodiment, a protruding structure 11 is provided on one side of the shielding layer 1 close to the adhesive film layer 2 , and the protruding structure 11 is used to pierce the adhesive film layer 2 and connect with the ground layer of the circuit board 6 .

[0041] Specifically, see Figure 2 , Figure 2 It is a schematic diagram of a raised structure piercing the ground in an electromagnetic shielding film provided by the present invention. In the embodiment of the present invention, a raised structure 11 is provided on one side of the shielding layer 1 close to the adhesive film layer 2, so that when the electromagnetic shielding film is pressed together, the adhesive film layer 2 is squeezed, and the raised structure 11 pierces the adhesive film layer 2 under the pressing force to connect with the ground layer GND of the circuit board 6. Among them, the adhesive film layer 2 includes an adhesive layer that does not contain conductive particles, which is bonded to one side of the shielding layer 1 through the adhesive layer to cover the raised structure.

[0042] In another preferred embodiment, the shielding layer 1 has a flat surface close to the adhesive film layer 2 , the adhesive film layer 2 includes an adhesive layer containing conductive particles, and the shielding layer 1 is connected to the ground layer of the circuit board through the conductive particles of the adhesive film layer 2 .

[0043] Specifically, see Figure 3 , Figure 3 It is a schematic diagram of the grounding of conductive particles in an electromagnetic shielding film provided by the present invention. When the electromagnetic shielding film is pressed together in the embodiment of the present invention, if there is no protruding structure, the film layer 2 is provided with conductive particles 21, so that after pressing together, the shielding layer 1 is connected to the ground layer GND of the circuit board 6 through the conductive particles 21.

[0044] It should be noted that the conductive particles 21 include graphene nanosheets, carbon nanotubes (CNTs), ferroferric oxide (Fe3O4), silver nanowires (AgNWs), pure silver, silver-plated copper, silver-plated aluminum, silver-plated nickel, etc. These conductive particles 21 can significantly improve the conductivity and electromagnetic shielding effectiveness of the film layer. For example, silver nanowires are widely used in the preparation of electromagnetic shielding films due to their excellent conductivity and transparency.

[0045] In order to firmly bind the conductive particles 21 to the adhesive film layer 2, it is usually necessary to add an adhesive, i.e., an adhesive layer. Common adhesives include silicone, silicone fluoride, EPDM, or carbon fluoride-silicon fluoride, etc. These adhesives have good adhesion and stability, and can ensure the uniform distribution and long-term stability of the conductive particles in the adhesive film layer.

[0046] In yet another preferred embodiment, the electromagnetic shielding film further comprises an insulating layer 3 , and the insulating layer 3 is laminated on a side of the shielding layer 1 away from the adhesive film layer 2 .

[0047] Specifically, see Figure 4 , Figure 4 : is a schematic diagram of a preferred embodiment of an electromagnetic shielding film provided by the present invention. The electromagnetic shielding film in the embodiment of the present invention further includes an insulating layer 3, which is stacked on a side of the shielding layer 1 away from the adhesive film layer 2. The insulating layer 3 has an insulating effect, which can ensure the shielding effectiveness of the shielding layer 1; in addition, the insulating layer 3 also has a protective effect to ensure that the shielding layer 1 is not scratched or damaged during use, thereby facilitating the maintenance of the high shielding effectiveness of the shielding layer 1.

[0048] It should be noted that the insulating layer 3 includes a PPS film layer, a PEN film layer, a polyester film layer, a polyimide film layer, a film layer formed after epoxy resin ink is cured, a film layer formed after polyurethane ink is cured, a film layer formed after modified acrylic resin is cured, or a film layer formed after polyimide resin is cured, etc.

[0049] In yet another preferred embodiment, the electromagnetic shielding film further comprises a carrier film 4 , and the carrier film 4 is laminated on a side of the insulating layer 3 away from the shielding layer 1 .

[0050] Specifically, the electromagnetic shielding film in the embodiment of the present invention further includes a carrier film 4, which is stacked on a side of the insulating layer 3 away from the shielding layer 1. The carrier film 4 is used to protect the insulating layer 3, so that the insulating layer 3 is not damaged by external contact or collision. After the electromagnetic shielding film and the circuit board are pressed at high temperature, the carrier film 4 needs to be torn off.

[0051] In yet another preferred embodiment, the electromagnetic shielding film further comprises a protective film 5 , and the protective film 5 is laminated on a side of the adhesive film layer 2 away from the shielding layer 1 .

[0052] Specifically, the electromagnetic shielding film in the embodiment of the present invention further includes a protective film 5, which is stacked on a side of the adhesive film layer 2 away from the shielding layer 1. The protective film 5 has a protective function to ensure that the adhesive film layer 2 is not scratched or damaged during use. When the electromagnetic shielding film is pressed onto the circuit board, the protective film 5 must be peeled off first. Among them, the protective film 5 includes PPS film, PEN film, polyester film, polyimide film, etc.

[0053] An embodiment of the present invention further provides a circuit board, which includes a circuit board substrate and the electromagnetic shielding film described in any one of the above embodiments, wherein the electromagnetic shielding film is pressed together with the circuit board substrate.

[0054] In order to demonstrate the beneficial effects of the electromagnetic shielding film and circuit board provided by the embodiments of the present invention, several embodiments and comparative examples are described below.

[0055] Example 1

[0056] In this embodiment, an electromagnetic shielding film includes a shielding layer and an adhesive film layer stacked in layers. Wherein, at room temperature, for every 5% change in relative humidity within 24 hours, the relative dielectric constant of the adhesive film layer changes by 5%. At room temperature, the relative dielectric constant of the adhesive film layer is 3. At 1 / GHz, the insertion loss of the circuit board before and after being covered with the electromagnetic shielding film is measured, and the difference between the insertion loss of the circuit board after being covered with the electromagnetic shielding film and the insertion loss of the circuit board before being covered with the electromagnetic shielding film is obtained, △A=0.8dB.

[0057] Example 2

[0058] In this embodiment, an electromagnetic shielding film includes a protective film, an adhesive film layer, a shielding layer, an insulating layer and a carrier film which are stacked. The relative dielectric constant of the adhesive film layer is 2.5 at room temperature, and the dielectric constant of the adhesive film layer changes by 15% for every 10% change in relative humidity within 72 hours. The thickness of the adhesive film layer is 6 μm. At 5 / GHz, the insertion loss of the circuit board before and after the electromagnetic shielding film is covered is measured, and the difference between the insertion loss of the circuit board after the electromagnetic shielding film is covered and the insertion loss of the circuit board before the electromagnetic shielding film is covered is △A=2.5dB.

[0059] Comparative Example 1

[0060] In this embodiment, an electromagnetic shielding film includes a shielding layer and an adhesive film layer stacked in layers. Wherein, at room temperature, for every 5% change in relative humidity within 24 hours, the relative dielectric constant of the adhesive film layer changes by 15%. At room temperature, the relative dielectric constant of the adhesive film layer is 6. At 1 / GHz, the insertion loss of the circuit board before and after being covered with the electromagnetic shielding film is measured, and the difference between the insertion loss of the circuit board after being covered with the electromagnetic shielding film and the insertion loss of the circuit board before being covered with the electromagnetic shielding film is obtained, △A=8dB.

[0061] Comparative Example 2

[0062] In this embodiment, an electromagnetic shielding film includes a protective film, an adhesive film layer, a shielding layer, an insulating layer and a carrier film which are stacked. The relative dielectric constant of the adhesive film layer is 8 at room temperature. Within 72 hours, the relative dielectric constant of the adhesive film layer changes by 43% for every 10% change in relative humidity. The thickness of the adhesive film layer is 10 μm. At 5 / GHz, the insertion loss of the circuit board before and after the electromagnetic shielding film is covered is measured, and the difference between the insertion loss of the circuit board after the electromagnetic shielding film is covered and the insertion loss of the circuit board before the electromagnetic shielding film is covered is △A=14dB.

[0063] In the embodiments 1-2 of the present invention, the electromagnetic shielding film comprises a protective film, an adhesive film layer, a shielding layer, an insulating layer and a carrier film which are stacked. The dielectric constant of the adhesive film layer and the degree of change of the dielectric constant in a humidity environment for a certain period of time are both within the preferred range defined by the present invention, and the insertion loss of the circuit board before and after the electromagnetic shielding film is covered is measured, and the difference △A between the insertion loss of the circuit board after the electromagnetic shielding film is covered and the insertion loss of the circuit board before the electromagnetic shielding film is covered is less than 3dB, which can effectively ensure that the insertion loss on the circuit board is small and improve the reliability of signal transmission on the circuit board.

[0064] In Comparative Examples 1-2, the electromagnetic shielding film includes a shielding layer and an adhesive film layer. The dielectric constant of the adhesive film layer and the degree of change of the dielectric constant in a humidity environment for a certain period of time do not conform to the preferred range specified by the present invention. The insertion loss of the circuit board before and after being covered with the electromagnetic shielding film is measured, and the difference △A between the insertion loss of the circuit board after being covered with the electromagnetic shielding film and the insertion loss of the circuit board before being covered with the electromagnetic shielding film is obtained. Both are above 7dB. It can be seen that the insertion loss is high, resulting in poor reliability of signal transmission on the circuit board.

[0065] In summary, the electromagnetic shielding film prepared by limiting the dielectric constant of the adhesive film layer and the degree of change of the dielectric constant in a humidity environment for a certain period of time as defined in the present invention can effectively reduce the insertion loss of the circuit board after being covered with the electromagnetic shielding film, and improve the reliability of signal transmission on the circuit board.

[0066] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. An electromagnetic shielding film, characterized in that: It comprises a shielding layer and an adhesive film layer which are stacked; wherein, at room temperature, within 24 hours, when the relative humidity changes by 5%, the relative dielectric constant of the adhesive film layer changes by less than or equal to 10%.

2. The electromagnetic shielding film according to claim 1, wherein At room temperature, the relative dielectric constant of the adhesive film layer is less than or equal to 3.

3. The electromagnetic shielding film according to claim 1, wherein At room temperature, within 72 hours, for every 10% change in relative humidity, the relative dielectric constant of the adhesive film layer changes by less than or equal to 20%.

4. The electromagnetic shielding film according to claim 1, wherein The average thickness of the adhesive film layer is 1 μm to 20 μm.

5. The electromagnetic shielding film according to claim 1, wherein A protruding structure is provided on one side of the shielding layer close to the adhesive film layer, and the protruding structure is used to pierce the adhesive film layer to connect and conduct with the ground layer of the circuit board.

6. The electromagnetic shielding film according to claim 1, wherein The shielding layer has a flat surface on one side close to the adhesive film layer. The adhesive film layer includes an adhesive layer containing conductive particles. The shielding layer is connected to the ground layer of the circuit board through the conductive particles in the adhesive film layer.

7. The electromagnetic shielding film according to any one of claims 1 to 6, characterized in that: The electromagnetic shielding film further comprises an insulating layer, and the insulating layer is stacked on a side of the shielding layer away from the adhesive film layer.

8. The electromagnetic shielding film according to claim 7, wherein The electromagnetic shielding film further comprises a carrier film, and the carrier film is stacked on a side of the insulating layer away from the shielding layer.

9. The electromagnetic shielding film according to claim 8, wherein The electromagnetic shielding film further comprises a protective film, and the protective film is stacked on a side of the adhesive film layer away from the shielding layer.

10. A circuit board, characterized in that: It comprises a circuit board substrate and the electromagnetic shielding film according to any one of claims 1 to 9, wherein the electromagnetic shielding film is pressed together with the circuit board substrate.

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