Circuit board and multilayer circuit board

Abstract

The invention discloses a circuit board and a multilayer circuit board, one side surface of the circuit board is covered with an electromagnetic shielding film, the electromagnetic shielding film comprises an adhesive film layer and a shielding layer which are laminated, and the shielding layer is connected with a ground layer of the circuit board through the adhesive film layer; wherein the average height H from the surface of the copper circuit on the circuit board to the shielding layer is greater than or equal to 25 microns. According to the invention, the distance constraint between the shielding layer on the shielding film and the surface of the circuit is set, so that the insertion loss on the circuit board is small, and the reliability of signal transmission on the circuit board can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic information materials, and in particular to a circuit board and a multilayer 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). 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, shielding films are used to shield signals to reduce electromagnetic interference and other problems. Currently, commonly used electromagnetic shielding films mainly include a shielding layer and an adhesive film layer. The shielding layer is connected to the ground layer of the circuit board through the adhesive film layer, and then the interference charge is introduced 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 problems such as the thickness, position or unevenness of the pressing film, it is easy to cause a large insertion loss, thereby affecting the signal transmission on the circuit board. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a circuit board and a multi-layer circuit board, by setting a distance constraint between the shielding layer on the shielding film and the circuit surface to ensure that the insertion loss on the circuit board is small, which can effectively improve the reliability of signal transmission on the circuit board.

[0005] In order to achieve the above-mentioned object, an embodiment of the present invention provides a circuit board, one side of which is covered with an electromagnetic shielding film, the electromagnetic shielding film comprising a laminated adhesive film layer and a shielding layer, the shielding layer being connected to the ground layer of the circuit board through the adhesive film layer;

[0006] Wherein, an average height H from the surface of the copper circuit on the circuit board to the shielding layer is greater than or equal to 25 μm.

[0007] As an improvement of the above solution, at the same frequency, the change difference ΔA between the insertion loss A2 of the circuit board covered with the electromagnetic shielding film and the insertion loss A1 of the circuit board before covered with the electromagnetic shielding film is less than or equal to 5dB.

[0008] As an improvement of the above solution, the thickness of the shielding layer of the electromagnetic shielding film is 0.1 μm to 6 μm.

[0009] As an improvement of the above solution, the shielding layer of the electromagnetic shielding film includes a first surface close to the adhesive film layer and a second surface away from the adhesive film layer;

[0010] The minimum vertical distance between the second surface of the shielding layer and the surface of the copper circuit on the circuit board is H1, and the maximum vertical distance is H2;

[0011] The average height from the copper circuit surface on the circuit board to the shielding layer is H=(H1+H2) / 2.

[0012] As an improvement of the above solution, a protruding structure is provided on the first surface of the shielding layer, and the protruding structure is used to pierce the adhesive film layer to connect the shielding layer to the ground layer of the circuit board.

[0013] As an improvement of the above solution, the protrusion height D1 of the protrusion structure is at least 1 / 2 of the average height H from the surface of the copper circuit on the circuit board to the shielding layer.

[0014] As an improvement of the above solution, 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.

[0015] As an improvement of the above solution, a vertical height D2 of the conductive particles along the thickness direction of the adhesive film layer is at least 1 / 2 of an average height H from the surface of the copper circuit on the circuit board to the shielding layer.

[0016] As an improvement of the above solution, the electromagnetic shielding film further includes an insulating layer, and the insulating layer is arranged on the second surface of the shielding layer.

[0017] An embodiment of the present invention further provides a multi-layer circuit board, and the multi-layer circuit board includes any one of the circuit boards described above.

[0018] Compared with the prior art, the beneficial effects of a circuit board and a multilayer circuit board provided by the embodiments of the present invention are: an electromagnetic shielding film is covered on one side of the circuit board, the electromagnetic shielding film includes a laminated adhesive film layer and a shielding layer, and the shielding layer is connected to the ground layer of the circuit board through the adhesive film layer; wherein the average height H from the copper circuit surface on the circuit board to the shielding layer is greater than or equal to 25μm. The embodiments of the present invention set a distance constraint between the shielding layer and the circuit surface on the shielding film to ensure that the insertion loss on the circuit board is small, which can effectively improve the reliability of signal transmission on the circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of a preferred embodiment of a circuit board provided by the present invention;

[0020] Figure 2 It is a schematic diagram of a structure in which a shielding layer of a circuit board provided by the present invention is flat;

[0021] Figure 3 It is a schematic diagram of a structure in which a shielding layer of a circuit board provided by the present invention is non-flat;

[0022] Figure 4 It is a structural schematic diagram of a protrusion structure in a circuit board provided by the present invention;

[0023] Figure 5 It is a schematic diagram of the structure of conductive particles in a circuit board provided by the present invention;

[0024] Figure 6 is a structural schematic diagram of another preferred embodiment of a circuit board provided by the present invention;

[0025] The reference numerals are as follows:

[0026] 1. Circuit board; 11. Flexible copper clad laminate; 12. Cover film; 2. Adhesive film layer; 21. Conductive particles; 3. Shielding layer; 31. Raised structure; 4. Insulating layer. DETAILED DESCRIPTION

[0027] 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.

[0028] 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.

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

[0030] In the description of 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.

[0031] See also Figure 1 , Figure 1 1 is a schematic diagram of a preferred embodiment of a circuit board provided by the present invention. The embodiment of the present invention provides a circuit board, wherein one side of the circuit board 1 is covered with an electromagnetic shielding film, wherein the electromagnetic shielding film comprises a laminated adhesive film layer 2 and a shielding layer 3, wherein the shielding layer 3 is connected to the ground layer of the circuit board 1 through the adhesive film layer 2;

[0032] Wherein, an average height H from the surface of the copper circuit on the circuit board 1 to the shielding layer 3 is greater than or equal to 25 μm.

[0033] It should be noted that insertion loss is the evaluation of the signal attenuation of the entire link from the starting point to the end point of the line, ensuring the quality of the signal during transmission. The current circuit board is covered with an electromagnetic shielding film, and the insertion loss is relatively large. This is partly due to the fact that the thickness of the metal layer (i.e., the shielding layer) or the thickness of the film layer has a greater impact. Studies have found that the thicker the film layer or the metal layer, the less insertion loss it will have if other conditions remain unchanged. However, when the electromagnetic shielding film is pressed, the film layer will be deformed by pressing and the thickness will be affected, making it impossible to accurately observe its impact on the insertion loss. Therefore, after pressing, the embodiment of the present invention uses the average distance H from the circuit surface to the metal layer to characterize the thickness difference of the above-mentioned metal layer and the film layer relative to the circuit board. This feature can effectively observe the impact of thickness on insertion loss.

[0034] Based on this, the embodiment of the present invention has verified through a large number of experiments that in conventional low-frequency tests, such as 1 / GHz, when the average height H from the copper circuit surface on the circuit board to the shielding layer is not less than 25μm, the insertion loss of the circuit board after covering the electromagnetic shielding film is relatively small, which can reach within -3dB; in conventional medium-frequency tests, such as 5 / GHz, when the average height H from the copper circuit surface on the circuit board to the shielding layer is not less than 25μm, the insertion loss of the circuit board after covering the electromagnetic shielding film is relatively small, which can reach within -8dB; in conventional high-frequency tests, such as 10 / GHz, when the average height H from the copper circuit surface on the circuit board to the shielding layer is not less than 25μm, the insertion loss of the circuit board after covering the electromagnetic shielding film is relatively small, which can reach within -12dB. Therefore, the embodiment of the present invention sets the average height H from the copper circuit surface on the circuit board to the shielding layer to be not less than 25μm, which can effectively reduce the insertion loss of the circuit board after covering the electromagnetic shielding film, so as to improve the reliability of signal transmission on the circuit board.

[0035] For example, see Figure 2 , Figure 2 It is a schematic diagram of the structure in which the shielding layer in a circuit board provided by the present invention is flat. In the embodiment of the present invention, one side of the circuit board 1 is covered with an electromagnetic shielding film, and the circuit board 1 includes a stacked flexible copper clad board 11 and a covering film 12, and a ground layer GND is provided on the flexible copper clad board 11. The electromagnetic shielding film includes a stacked adhesive film layer 2 and a shielding layer 3, and the shielding layer 3 is connected to the ground layer GND of the circuit board 1 through the adhesive film layer 2. Among them, the shielding layer 3 is flat, so the average height H from the copper circuit surface on the circuit board 1 to the shielding layer 3 can be directly obtained, and the average height H is set to be greater than or equal to 25μm. In addition, the electromagnetic shielding film may also include an insulating layer 4, and the insulating layer 4 is provided on the second surface of the shielding layer 3.

[0036] In another preferred embodiment, at the same frequency, the difference ΔA between the insertion loss A2 of the circuit board covered with the electromagnetic shielding film and the insertion loss A1 of the circuit board before covered with the electromagnetic shielding film is less than or equal to 5 dB.

[0037] Generally, the insertion loss A1 before insertion is lower, and the insertion loss A2 after insertion is larger. Assuming that at a certain frequency, A2 is -3dB and A1 is -2dB, it means that after insertion, the insertion loss increases by 1dB, that is, the change difference △A in the present invention refers to the change in relative value.

[0038] Specifically, in the embodiment of the present invention, on the basis of setting the average height from the copper circuit surface to the shielding layer on the circuit board to be within a certain range, if in the same frequency environment, before and after the circuit board is covered with the shielding film, the insertion loss on the circuit board is relatively stable, with small fluctuations within 5dB, which effectively improves the reliability of signal transmission. More preferably, the insertion loss variation can be within 1dB.

[0039] In yet another preferred embodiment, the thickness of the shielding layer 3 of the electromagnetic shielding film is 0.1 μm to 6 μm.

[0040] Specifically, within a certain range, the thicker the shielding layer 3 is, the better the shielding effect is, and the insertion loss may also be reduced. However, when the thickness of the shielding layer 3 increases to a certain extent, the improvement of its shielding effect will no longer be obvious, and the insertion loss may turn into an increase. Therefore, under the premise of ensuring the shielding effect, the embodiment of the present invention tries to set the thickness of the shielding layer 3 within a certain range to reduce the insertion loss. Exemplarily, the thickness of the shielding layer 3 is 0.1μm, 0.35μm, 0.6μm, 0.85μm, 0.7μm, 0.95μm, 1.1μm, 1.35μm, 1.6μm, 1.85μm, 2.1μm, 2.35μm, 2.6μm, 2.85μm, 3.1μm, 3.35μm, 3.6μm, 3.85μm, 4.1μm, 4.35μm, 4.6μm, 4.85μm, 5.1μm, 5.35μm, 5.6μm, 5.85μm, 6μm and / or an interval consisting of any two values.

[0041] In another preferred embodiment, the shielding layer 3 of the electromagnetic shielding film includes a first surface close to the adhesive film layer 2 and a second surface away from the adhesive film layer 2;

[0042] The minimum vertical distance between the second surface of the shielding layer 3 and the surface of the copper circuit on the circuit board 1 is H1, and the maximum vertical distance is H2;

[0043] The average height H from the copper circuit surface on the circuit board 1 to the shielding layer 3 is (H1+H2) / 2.

[0044] Specifically, see Figure 3 , Figure 3It is a schematic diagram of a structure in which the shielding layer in a circuit board provided by the present invention is uneven. In the embodiment of the present invention, since the shielding layer 3 is an uneven layer, when defining the average distance H from the shielding layer 3 to the circuit surface, the median of the two heights with the maximum and minimum undulation distances on the shielding layer 3 is calculated, and the median is used as the reference for the average distance. That is, the average height H from the copper circuit surface on the circuit board 1 to the shielding layer 3 = (H1+H2) / 2. Among them, H1 is the minimum vertical distance between the second surface of the shielding layer 3 and the copper circuit surface on the circuit board 1, and H2 is the maximum vertical distance.

[0045] In another preferred embodiment, a protruding structure 31 is provided on the first surface of the shielding layer 3 , and the protruding structure 31 is used to pierce the adhesive film layer 2 to connect the shielding layer 3 to the ground layer of the circuit board 1 .

[0046] Specifically, see Figure 4 , Figure 4 It is a schematic diagram of the structure of a protruding structure in a circuit board provided by the present invention. In the embodiment of the present invention, a protruding structure 31 is provided on the first surface of the shielding layer 3, so that when the electromagnetic shielding film is pressed, the adhesive film layer 2 is squeezed, and the protruding structure 31 pierces the adhesive film layer 2 and connects with the ground layer of the FPC board under the pressing force. 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 3 through the adhesive layer to cover the protruding structure.

[0047] In yet another preferred embodiment, the protrusion height D1 of the protrusion structure 31 is at least 1 / 2 of the average height H from the copper circuit surface on the circuit board 1 to the shielding layer 3 .

[0048] Specifically, the embodiment of the present invention limits the protrusion height of the protrusion structure 31 provided on the first surface of the shielding layer 3, and sets the protrusion height D1 of the protrusion structure 31 to be at least 1 / 2 of the average height H from the copper circuit surface on the circuit board 1 to the shielding layer 3.

[0049] The embodiment of the present invention sets a protrusion of a certain length, so that it can effectively pierce the film layer for grounding during pressing, thereby ensuring the piercing effect.

[0050] In this embodiment, the protrusion height D1 of the protrusion structure 31 refers to the vertical distance between the top of the protrusion structure 31 protruding toward the adhesive film layer and the first surface of the shielding layer 3, see Figure 4 .

[0051] In another preferred embodiment, the adhesive film layer 2 includes an adhesive layer containing conductive particles 21 , and the shielding layer 3 is connected to the ground layer of the circuit board 1 through the conductive particles 21 of the adhesive film layer 2 .

[0052] Specifically, see Figure 5 , Figure 5 It is a schematic diagram of the structure of conductive particles in a circuit board provided by the present invention. When the electromagnetic shielding film is pressed together, if there is no protruding structure, the film layer 2 is provided with conductive particles 21, so that after pressing together, the shielding layer 3 is connected to the ground layer of the FPC board through the conductive particles 21.

[0053] 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 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.

[0054] 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.

[0055] In another preferred embodiment, the vertical height D2 of the conductive particles 21 along the thickness direction of the adhesive film layer 2 is at least 1 / 2 of the average height H from the copper circuit surface on the circuit board 1 to the shielding layer 3 .

[0056] Specifically, the embodiment of the present invention limits the length of the conductive particles 21 in the adhesive layer 2 , and sets the vertical height D2 of the conductive particles 21 along the thickness direction of the adhesive layer 2 to be at least 1 / 2 of the average height H from the copper circuit surface on the circuit board 1 to the shielding layer 3 .

[0057] The embodiment of the present invention sets the conductive particles to a certain length, so that they can effectively pierce the adhesive film layer for grounding during lamination, thereby ensuring the grounding effect.

[0058] In this embodiment, the vertical height D2 of the conductive particles 21 refers to the vertical height between the top of the conductive particles 21 protruding toward one side of the adhesive film layer and the first surface of the shielding layer 3 along the thickness direction of the adhesive film layer, see Figure 5 .

[0059] Preferably, the electromagnetic shielding film further includes an insulating layer 4 , and the insulating layer 4 is disposed on the second surface of the shielding layer 3 .

[0060] Specifically, see Figure 6 , Figure 6It is a structural schematic diagram of another preferred embodiment of a circuit board provided by the present invention. In the embodiment of the present invention, the electromagnetic shielding film also includes an insulating layer 4, and the insulating layer 4 is arranged on the second surface of the shielding layer 3. Since the insulating layer 4 has an insulating effect, it is beneficial to ensure the shielding effectiveness of the shielding layer 3. In addition, the insulating layer 4 also has a protective effect to ensure that the shielding layer 3 is not scratched or damaged during use, thereby helping to maintain the high shielding effectiveness of the shielding layer 3.

[0061] It should be noted that the insulating layer 4 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.

[0062] An embodiment of the present invention further provides a multi-layer circuit board, which includes the circuit board described in any of the above embodiments.

[0063] In order to demonstrate the beneficial effects of the circuit board and the multilayer circuit board provided by the embodiments of the present invention, several embodiments and comparative examples are described below.

[0064] Example 1

[0065] In this embodiment, a circuit board is provided, one side of which is covered with an electromagnetic shielding film, wherein the electromagnetic shielding film comprises a laminated adhesive film layer and a shielding layer, wherein the shielding layer is connected to the ground layer of the circuit board through the adhesive film layer. The average height H from the surface of the copper circuit on the circuit board to the shielding layer is equal to 25 μm, and the thickness of the shielding layer of the electromagnetic shielding film is 1 μm. 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 A2 of the circuit board after being covered with the electromagnetic shielding film and the insertion loss A1 of the circuit board before being covered with the electromagnetic shielding film is obtained, △A=1.8dB.

[0066] Example 2

[0067] In this embodiment, a circuit board is provided, one side of which is covered with an electromagnetic shielding film, the electromagnetic shielding film comprising a laminated adhesive film layer, a shielding layer and an insulating layer, the shielding layer being connected to the ground layer of the circuit board through the adhesive film layer. The average height H from the surface of the copper circuit on the circuit board to the shielding layer is equal to 40 μm, and the thickness of the shielding layer of the electromagnetic shielding film is 1.5 μm. A protruding structure is provided on the first surface of the shielding layer close to the adhesive film layer, the protruding structure is used to puncture the adhesive film layer to connect the shielding layer to the ground layer of the circuit board, and the protruding height D1 of the protruding structure is 30 μm. At 5 / 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 A2 of the circuit board after being covered with the electromagnetic shielding film and the insertion loss A1 of the circuit board before being covered with the electromagnetic shielding film is obtained, and the difference △A=1.2dB.

[0068] Example 3

[0069] In this embodiment, a circuit board is provided, one side of which is covered with an electromagnetic shielding film, the electromagnetic shielding film comprising a laminated adhesive film layer, a shielding layer and an insulating layer, the shielding layer being connected to the ground layer of the circuit board through the adhesive film layer. The average height H from the copper circuit surface on the circuit board to the shielding layer is 60 μm, and the thickness of the shielding layer of the electromagnetic shielding film is 3 μm. The first surface of the shielding layer close to the adhesive film layer is a flat surface, the adhesive film layer comprises an adhesive layer containing conductive particles, the shielding layer is connected to the ground layer of the circuit board through the conductive particles of the adhesive film layer, and the vertical height D2 of the conductive particles along the thickness direction of the adhesive film layer is 50 μm. At 5 / 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 A2 of the circuit board after being covered with the electromagnetic shielding film and the insertion loss A1 of the circuit board before being covered with the electromagnetic shielding film is obtained, △A=1dB.

[0070] Comparative Example 1

[0071] In this embodiment, a circuit board is provided, one side of which is covered with an electromagnetic shielding film, wherein the electromagnetic shielding film comprises a laminated adhesive film layer and a shielding layer, wherein the shielding layer is connected to the ground layer of the circuit board through the adhesive film layer. The average height H from the surface of the copper circuit on the circuit board to the shielding layer is equal to 15 μm, and the thickness of the shielding layer of the electromagnetic shielding film is 1 μm. 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 A2 of the circuit board after being covered with the electromagnetic shielding film and the insertion loss A1 of the circuit board before being covered with the electromagnetic shielding film is obtained, and the difference △A=7dB.

[0072] Comparative Example 2

[0073] In this embodiment, a circuit board is provided, one side of which is covered with an electromagnetic shielding film, wherein the electromagnetic shielding film comprises a laminated adhesive film layer, a shielding layer and an insulating layer, wherein the shielding layer is connected to the ground layer of the circuit board through the adhesive film layer. The average height H from the surface of the copper circuit on the circuit board to the shielding layer is equal to 10 μm, and the thickness of the shielding layer of the electromagnetic shielding film is 1.5 μm. At 5 / 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 A2 of the circuit board after being covered with the electromagnetic shielding film and the insertion loss A1 of the circuit board before being covered with the electromagnetic shielding film is obtained, △A=13dB.

[0074] In embodiments 1-3 of the present invention, one side of the circuit board is covered with an electromagnetic shielding film, and the electromagnetic shielding film includes a laminated adhesive film layer, a shielding layer and an insulating layer, and the shielding layer is connected to the ground layer of the circuit board through the adhesive film layer. The average height H from the copper circuit surface on the circuit board to the shielding layer is set to be greater than or equal to 25μm, and the insertion loss of the circuit board before and after being covered with the electromagnetic shielding film is measured, and the change difference △A between the insertion loss A2 of the circuit board after being covered with the electromagnetic shielding film and the insertion loss A1 of the circuit board before being covered with the electromagnetic shielding film is obtained. Both are less than 5dB, which is within the preferred range defined by the present invention, and can effectively ensure that the insertion loss on the circuit board is small; at the same time, the above embodiments further set a more preferred range for the protrusion height of the protruding structure set on the first surface of the shielding layer, or the length of the conductive particles on the adhesive film layer, so that the adhesive film layer can be effectively pierced for grounding during pressing, thereby ensuring the grounding effect and improving the reliability of signal transmission on the circuit board.

[0075] In Comparative Example 1-2, one side of the circuit board is covered with an electromagnetic shielding film, and the electromagnetic shielding film includes a stacked adhesive film layer, a shielding layer and an insulating layer. The shielding layer is connected to the ground layer of the circuit board through the adhesive film layer. The average height H from the copper circuit surface on the circuit board to the shielding layer is set to be less than or equal to 20m, and the insertion loss of the circuit board before and after being covered with the electromagnetic shielding film is measured. The difference △A between the insertion loss A2 of the circuit board after being covered with the electromagnetic shielding film and the insertion loss A1 of the circuit board before being covered with the electromagnetic shielding film is much larger than 5dB, which is not within the preferred range defined by the present invention. This will result in a higher insertion loss on the circuit board, and thus lead to poor reliability of signal transmission on the circuit board.

[0076] In summary, the circuit board prepared by constraining the distance between the copper circuit surface and the shielding layer on the circuit board as defined by the present invention and limiting the height of the protruding structure of the shielding layer and the length of the conductive particles in the film layer can effectively reduce the insertion loss of the circuit board after being covered with the electromagnetic shielding film, thereby improving the reliability of signal transmission on the circuit board.

[0077] 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. A circuit board, characterized in that: One side of the circuit board is covered with an electromagnetic shielding film, the electromagnetic shielding film comprises a laminated adhesive film layer and a shielding layer, the shielding layer is connected to the ground layer of the circuit board through the adhesive film layer; Wherein, an average height H from the surface of the copper circuit on the circuit board to the shielding layer is greater than or equal to 25 μm.

2. The circuit board according to claim 1, characterized in that: At the same frequency, the difference ΔA between the insertion loss A2 of the circuit board covered with the electromagnetic shielding film and the insertion loss A1 of the circuit board before being covered with the electromagnetic shielding film is less than or equal to 5 dB.

3. The circuit board according to claim 1, characterized in that: The thickness of the shielding layer of the electromagnetic shielding film is 0.1 μm to 6 μm.

4. The circuit board according to claim 1, characterized in that: The shielding layer of the electromagnetic shielding film comprises a first surface close to the adhesive film layer and a second surface away from the adhesive film layer; The minimum vertical distance between the second surface of the shielding layer and the surface of the copper circuit on the circuit board is H1, and the maximum vertical distance is H2; The average height from the copper circuit surface on the circuit board to the shielding layer is H=(H1+H2) / 2.

5. The circuit board according to claim 4, characterized in that: A protruding structure is provided on the first surface of the shielding layer, and the protruding structure is used to pierce the adhesive film layer to connect the shielding layer to the ground layer of the circuit board.

6. The circuit board according to claim 5, characterized in that: The protrusion height D1 of the protrusion structure is at least 1 / 2 of the average height H from the copper circuit surface on the circuit board to the shielding layer.

7. The circuit board according to claim 4, characterized in that: 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.

8. The circuit board according to claim 7, characterized in that: The vertical height D2 of the conductive particles along the thickness direction of the adhesive film layer is at least 1 / 2 of the average height H from the surface of the copper circuit on the circuit board to the shielding layer.

9. The circuit board according to claim 4, characterized in that: The electromagnetic shielding film further includes an insulating layer, and the insulating layer is disposed on the second surface of the shielding layer.

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

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