Circuit board and preparation method therefor, and electronic component and electronic device

Abstract

Provided in the present application are a circuit board and a preparation method therefor, and an electronic component and an electronic device. The circuit board comprises a transmission region and a connection region. The transmission region is a flexible circuit board and comprises a first circuit board layer and a second circuit board layer, wherein the first circuit board layer and the second circuit board layer are arranged spaced apart from each other, and the edges of the first circuit board layer are connected to the edges of the second circuit board layer by means of connecting walls, such that a cavity is formed between the first circuit board layer and the second circuit board layer. The cavity in the circuit board results in better flexibility in the transmission region, which is a flexible circuit board. The circuit board comprises a signal line, wherein a partial region of the signal line is located on the surface of the second circuit board layer facing the cavity, and thus one side surface of the signal line is exposed in the cavity, thereby reducing the insertion loss of a signal transmission path, and improving the signal transmission efficiency and rate. The thickness of the connection region is less than the thickness of the transmission region. The circuit board in the present application takes into account multiple performance indicators such as insertion loss, impedance and flexibility.

Description

Circuit board and manufacturing method thereof, electronic component and electronic equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of the People's Republic of China on March 22, 2024, with application number 202410350444.1 and invention name "Circuit board and preparation method thereof, electronic components and electronic equipment", the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of electronic equipment, and in particular to a circuit board and a preparation method thereof, an electronic component and an electronic device. Background Art

[0004] Flexible circuit boards (FPCs) have the advantages of high density and thinness. FPCs can be soldered to printed circuit boards (PCBs) to connect the FPCs to the PCBs and realize signal transmission on the boards.

[0005] With technological advancements, signal transmission rates are increasing, and system density is also increasing. To meet these high-speed and high-density system requirements, signal transmission path losses must be minimized. As a crucial carrier in signal transmission paths, reducing insertion loss in flexible printed circuits (FPCs) is a key development direction. Furthermore, the flexibility of FPCs in the flex zone is a crucial performance indicator, significantly impacting the reliability of connections within these zones. Summary of the Invention

[0006] The present application provides a circuit board and a preparation method thereof, an electronic component and an electronic device. The circuit board in the present application can take into account multiple performance indicators such as insertion loss, impedance and flexibility.

[0007] In the first aspect, the present application provides a circuit board. The circuit board includes a transmission area and a connection area. The connection area is provided with a plurality of pins for achieving electrical connection with other structures. The transmission area is a flexible circuit board, so that the circuit board can be bent in the transmission area as required. The transmission area includes a first circuit board layer and a second circuit board layer, the first circuit board layer and the second circuit board layer are arranged at intervals, and the edge of the first circuit board layer is connected to the edge of the second circuit board layer by a connecting wall, so that a cavity is formed between the first circuit board layer and the second circuit board layer. The circuit board has a cavity inside, so that the transmission area of ​​the flexible circuit board has better flexibility. The circuit board includes a signal line, and part of the signal line is located on the surface of the second circuit board layer facing the cavity. Then one side of the surface of the signal line is exposed in the cavity, which is equivalent to the medium on one side of the signal line being air, which can reduce the insertion loss of the signal transmission path and improve the signal transmission efficiency and rate.

[0008] In addition, the thickness of the above-mentioned connection area is less than the thickness of the transmission area. The thinner thickness of the connection area of ​​the circuit board can reduce the impedance. However, the thinner thickness of the connection area will also lead to greater insertion loss, while the thicker thickness of the transmission area can reduce the insertion loss, so that the insertion loss of the entire signal transmission path of the circuit board is lower. Correspondingly, the thicker thickness of the transmission area of ​​the circuit board will also lead to increased impedance, but the lower impedance of the connection area can make the impedance of the entire signal transmission path of the circuit board lower. In addition, the flexibility of the circuit board is also strongly related to the thickness of the circuit board. During use, the flexibility of the circuit board is usually required to be higher in bending. In this application, the thickness of the connection area is thinner, so the flexibility is higher, making the circuit board more flexible during use. Therefore, the circuit board in the technical solution of this application takes into account multiple performance indicators such as insertion loss, impedance and flexibility, and has obvious advantages especially for high-density and high-speed electronic equipment.

[0009] There are various technical options for configuring the connecting wall forming the cavity. For example, in one embodiment, the connecting wall is continuously disposed around the perimeter of the cavity between the first and second circuit board layers. This allows the cavity to be relatively airtight, allowing the signal lines with their surfaces facing the cavity to be located within the enclosed cavity. This helps protect the signal lines and prevents dust and water vapor from entering during transportation, storage, and use, thereby improving the service life of the signal lines and enhancing signal transmission performance.

[0010] In a further technical solution, a support structure is provided between the first and second circuit board layers. This support structure supports the first and second circuit board layers within the cavity, enhancing the overall strength of the circuit board and making it less susceptible to damage. This structure also helps maintain the cavity at a certain height and prevents collapse, ensuring that the air medium adjacent to the signal line maintains a fixed and stable thickness, improving impedance continuity and thereby enhancing the efficiency and quality of signal transmission on the circuit board. The support structure's orthographic projection on the surface of the second circuit board layer is spaced a certain distance from the signal line, reducing its impact on the impedance of the signal line and thereby improving the efficiency and quality of signal transmission on the circuit board.

[0011] There are also multiple options for the specific form of the support structure. In one technical solution, the support structure may be a support wall, the extension direction of which is the same as the extension direction of the signal line. The distance between the support wall and the signal line is consistent along the extension direction, and the positional relationship between the support wall and the signal line is relatively fixed, which is conducive to improving impedance continuity.

[0012] The supporting structure includes a plurality of supporting columns, at least some of which are arranged along the extension direction of the signal line to support the first circuit board layer and the second circuit board layer.

[0013] When the above-mentioned support structure is specifically arranged, one end of the support structure can be connected to the first circuit board layer, and the other end of the support structure can be connected to the second circuit board layer, thereby improving the overall structural stability of the circuit board.

[0014] In one technical solution, the circuit board includes a dielectric layer that supports the metal layer and insulates adjacent metal layers. The thickness of the dielectric layer adjacent to the cavity is greater than or equal to 150μm. Due to the cavity, the circuit board can be thicker in the transmission area with minimal impact on the board's flexibility. Therefore, increasing the thickness of the dielectric layer reduces signal loss during signal transmission, improving the circuit board's signal transmission efficiency.

[0015] The connection area includes a bending zone and a pin zone. The bending zone is a flexible circuit board, located between the pin zone and the transmission zone, and contains multiple pins. The pin zone is used for fastening to other components, and the bending zone is used to bend the circuit board. The flexible circuit board facilitates bending in the bending zone with good visual alignment.

[0016] The pin area is used for fastening to other components and can be either a flexible or rigid circuit board. A flexible circuit board allows the entire circuit board to be flexible. A rigid circuit board, on the other hand, creates a rigid-flexible hybrid circuit board, with the majority of the board being flexible and the pin areas at both ends being rigid. Using a rigid circuit board in the pin area facilitates denser pin density, thereby increasing the signal density of the circuit board.

[0017] When preparing signal lines, the cross-sectional area of ​​the signal line in the connection zone can be made smaller than the cross-sectional area of ​​the same signal line in the transmission zone. The smaller cross-sectional area of ​​the signal line in the connection zone allows for a higher pin density in the pinmap, which helps reduce the area of ​​the connection zone. Since the signal line is thinner in the connection zone, insertion loss and impedance are higher; the signal line is thicker in the transmission zone, insertion loss and impedance are lower. This optimizes the insertion loss and impedance of the entire signal line, resulting in lower insertion loss and lower impedance overall.

[0018] In one technical solution, the cross-sectional area of ​​the signal line covered by the connecting wall is smaller than the cross-sectional area of ​​the same signal line in the area opposite the cavity. Because the signal line in the area covered by the connecting wall is a solid dielectric, while the dielectric in the cavity area is air, adjusting the cross-sectional area of ​​the signal line in these two areas can help reduce the overall insertion loss and impedance of the signal line and improve the impedance continuity along the signal line's extension direction.

[0019] The spacing between adjacent signal lines on the same layer in the transmission area is greater than that in the connection area. The smaller the spacing between signal lines in the connection area, the higher the pin density of the PCB pinmap is, which helps reduce the area of ​​the connection area. The smaller the spacing between signal lines in the connection area, especially between differential signal lines within a pair, the tighter the coupling between the signal lines, resulting in higher insertion loss. However, larger spacing between adjacent signal lines in the transmission area reduces insertion loss, resulting in lower overall signal line insertion loss.

[0020] The length of the bending zone along the direction from the pin zone to the transmission zone is greater than or equal to a preset value, so that the bending capacity of the circuit board in the above bending zone can meet the bending requirements.

[0021] In a specific technical solution, the above-mentioned preset value includes 60mm, which can meet the bending requirements of most electronic components, so that the circuit board can be applied to a variety of application scenarios.

[0022] To achieve a circuit board with a thicker transmission area than a connection area, the connection area can be thinned on one surface. Specifically, the circuit board includes a first side and a second side that are opposed to each other in the thickness direction. On the first side, the surface of the bending area and the surface of the transmission area are located in different planes, while on the second side, the surface of the bending area and the surface of the transmission area are located in the same plane.

[0023] Another technical solution allows the connection area of ​​the circuit board to be thinned on both sides. Specifically, the circuit board includes a first side and a second side that are separated along the thickness direction. On the first side, the surface of the bending area and the surface of the transmission area are located in different planes; on the second side, the surface of the bending area and the surface of the transmission area are located in different planes. This solution can achieve a symmetrical structure on both sides of the circuit board along the thickness direction. In this embodiment, the circuit board is symmetrical along the thickness direction, and the symmetry of the transmitted signal is also improved, which is beneficial to improving the quality of the circuit board's transmitted signals.

[0024] In the second aspect, the present application also provides a method for preparing a circuit board, which is used to prepare the circuit board provided in the first aspect above. Specifically, the preparation method includes: forming a signal line on the first metal layer on the surface of the first flexible metal-clad plate, and the surface of the first flexible metal-clad plate facing away from the first metal layer has a second metal layer; pressing the third metal layer, the first adhesive layer, the glue pad and the first flexible metal-clad plate stacked in sequence, the first adhesive layer and the glue pad are located on the same layer, the first adhesive layer covers the connection area of ​​the first flexible metal-clad plate, and the third metal layer is located on the side of the signal line facing away from the second metal layer; preparing conductive holes, the conductive holes connecting at least two layers of the first metal layer, the second metal layer and the third metal layer; splitting the third metal layer and removing the glue pad; preparing a connecting wall on the side of the first adhesive layer facing the cavity; pressing the second flexible metal-clad plate and the connecting wall stacked in sequence; the second flexible metal-clad plate includes a fourth metal layer, and the fourth metal layer is located on the surface facing away from the connecting wall. The circuit board prepared by this preparation method can take into account multiple performance indicators such as insertion loss, impedance and flexibility.

[0025] In the above-mentioned preparation method, the second flexible metal-clad plate and the connecting wall are laminated in sequence; the second flexible metal-clad plate includes a fourth metal layer, and the fourth metal layer is located on the surface away from the connecting wall, and the method previously includes: providing a blocking member in the connecting area on the surface of the third metal layer;

[0026] This is followed by: removing the blocking member.

[0027] The blocking member can block the second flexible metal-clad plate, thereby improving the accuracy of the position of the second flexible metal-clad plate.

[0028] In a third aspect, the present application further provides an electronic assembly comprising a printed circuit board and the circuit board provided in the first aspect, wherein at least one connection area of ​​the circuit board is electrically connected to the printed circuit board. The circuit board can balance multiple performance indicators such as insertion loss, impedance, and flexibility, thereby achieving high signal transmission performance for the electronic assembly.

[0029] In a fourth aspect, the present application further provides an electronic device. The electronic device includes a housing and the electronic component provided in the third aspect, wherein the electronic component is disposed in the housing. The electronic device in this embodiment has good high-density and high-speed signal transmission characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic structural diagram of an electronic device according to an embodiment of the present application;

[0031] FIG2 is a schematic structural diagram of an electronic component in an embodiment of the present application;

[0032] FIG3 is another schematic diagram of the structure of the electronic component in the embodiment of the present application;

[0033] FIG4 is another schematic diagram of the structure of the electronic component in the embodiment of the present application;

[0034] FIG5 is another schematic diagram of the structure of the electronic component in the embodiment of the present application;

[0035] FIG6 is another schematic diagram of the structure of the electronic component in the embodiment of the present application;

[0036] FIG7 is another schematic diagram of the structure of the electronic component in the embodiment of the present application;

[0037] FIG8 is another schematic diagram of the structure of the electronic component in the embodiment of the present application;

[0038] FIG9 is another schematic diagram of the structure of the electronic component in the embodiment of the present application;

[0039] FIG10 is a schematic structural diagram of a circuit board in an embodiment of the present application;

[0040] FIG11 is a schematic cross-sectional view of a circuit board according to an embodiment of the present application;

[0041] FIG12 is a schematic cross-sectional view of a circuit board according to an embodiment of the present application;

[0042] FIG13 is a schematic cross-sectional view of a circuit board according to an embodiment of the present application;

[0043] FIG14 is a schematic cross-sectional view of a circuit board according to an embodiment of the present application;

[0044] FIG15 is a schematic diagram of a top view of a circuit board in an embodiment of the present application;

[0045] FIG16 is a schematic diagram of a top view of a circuit board in an embodiment of the present application;

[0046] FIG17 is a schematic diagram of a top view of a circuit board in an embodiment of the present application;

[0047] FIG18 is a schematic diagram of a top view of a circuit board in an embodiment of the present application;

[0048] FIG19 is a schematic structural diagram of a circuit board in an embodiment of the present application;

[0049] FIG20 is a schematic structural diagram of a circuit board in an embodiment of the present application;

[0050] FIG21 is a schematic structural diagram of a circuit board in an embodiment of the present application;

[0051] FIG22 is a schematic structural diagram of a circuit board in an embodiment of the present application;

[0052] FIG23 is a schematic diagram of a top view of a circuit board in an embodiment of the present application;

[0053] FIG24 is a flow chart of a process for preparing a circuit board in an embodiment of the present application.

[0054] Reference numerals: 100 - housing; 200 - electronic component; 1 - printed circuit board; 2 - circuit board; 21 - transmission area; 211 - first circuit board layer; 212 - second circuit board layer; 22 - connection area; 221 - first connection area; 222 - second connection area; 223 - pin area; 224 - bending area; 23 - pin; 24 - signal layer; 241 - signal line; 242 - first signal layer; 243 - second signal layer; 244 - third signal layer; 245 - fourth signal layer; 25 - dielectric layer; 26 - first ground layer; 27 - second ground layer; 28 - third ground layer; 29 - first side; 210 - second side; 220 - connection wall; 230 - support structure; 3 - connector; 4 - packaging structure; L1 - first metal layer; L2 - second metal layer; L3 - third metal layer; L4 - fourth metal layer; BS1 - first adhesive layer; FL1 - first flexible metal-clad plate; FL2 - second flexible metal-clad plate; 5 - barrier element; 6 - rubber pad. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solutions and advantages of this application clearer, this application will be further described in detail below with reference to the accompanying drawings.

[0056] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the specification and appended claims of this application, the singular expressions "a", "an", "above", "the", and "this" are intended to also include expressions such as "one or more", unless the context clearly indicates otherwise.

[0057] References in this specification to "one embodiment" or "a specific embodiment" mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present application. The terms "including," "comprising," "having," and their variations all mean "including but not limited to," unless otherwise specifically stated.

[0058] To facilitate understanding of the circuit boards, electronic components, and electronic devices provided in the embodiments of the present application, the following first introduces their application scenarios.

[0059] The electronic devices in the embodiments of the present application may be electronic devices such as information and communications technology (ICT) devices, communication devices (such as routers), computing devices (such as servers), network devices (such as switches), or storage devices (such as storage arrays), or may be electronic devices such as optical modules, vehicle-mounted devices, or terminal devices. The present application does not limit the specific type of electronic device; as long as the electronic device includes electronic components that use circuit boards to transmit signals, the technical solutions provided in the present application may be used.

[0060] For ease of description, the electronic device is described as a server in the embodiment of the present application. Figure 1 is a structural diagram of an electronic device in the embodiment of the present application. As shown in Figure 1, the above-mentioned electronic device may include a housing 100, and an electronic component 200 arranged in the housing 100. Specifically, when the above-mentioned electronic device is a cabinet server, the above-mentioned housing 100 can be understood as a cabinet of the cabinet server, and the electronic component 200 may include a node. As shown in Figure 1, the above-mentioned electronic component 200 specifically includes a printed circuit board 1 and a circuit board 2. The printed circuit board 1 is welded to the circuit board 2 to realize the electrical connection between the printed circuit board 1 and the circuit board 2, and further the physical connection and signal connection between the printed circuit board 1 and the circuit board 2 can be realized.

[0061] Specifically, there are many options for connecting the printed circuit board 1 and the circuit board 2, such as laser welding, hard connection, crimping, sintering, conductive adhesive bonding, hot bar welding, connector connection or surface mounted technology (SMT).

[0062] The above-mentioned circuit board 2 can be applied to different application scenarios, or the electronic component 200 can include different component forms. For example, Figure 2 is a structural schematic diagram of an electronic component in an embodiment of the present application. As shown in Figure 2, in a specific embodiment, the circuit board 2 in the above-mentioned electronic component 200 is used to realize a single-board jumper of a printed circuit board 1. Specifically, both ends of the circuit board 2 are soldered to the same printed circuit board 1 to realize the transmission of signals of devices at two positions in the printed circuit board 1. Figure 3 is another structural schematic diagram of an electronic component in an embodiment of the present application. As shown in Figure 3, in another specific embodiment, the above-mentioned electronic component 200 may include two printed circuit boards 1, and the two printed circuit boards 1 are roughly located in the same plane. The two ends of the circuit board 2 are respectively soldered to the two printed circuit boards 1, so that the circuit board 2 is connected between the two printed circuit boards 1, so that the signals between the two printed circuit boards 1 can be transmitted through the circuit board 2 to realize inter-board interconnection. Figure 4 is another structural schematic diagram of an electronic component in an embodiment of the present application. As shown in Figure 4, in another specific embodiment, the above-mentioned electronic component 200 may also include two printed circuit boards 1. The two printed circuit boards 1 in this embodiment are located in different planes. The two ends of the circuit board 2 are respectively welded to the two printed circuit boards 1, so that the circuit board 2 is connected between the two printed circuit boards 1, so that the signals between the two printed circuit boards 1 can be transmitted through the circuit board 2 to realize cross-board connection. Figure 5 is another structural schematic diagram of the electronic component in the embodiment of the present application. As shown in Figure 5, in another specific embodiment, one end of the circuit board 2 in the electronic component 200 is welded to the printed circuit board 1, and the other end is connected to the connector 3, so that the connector 3 and the printed circuit board 1 can be transmitted through the circuit board 2, and then the printed circuit board 1 can be connected to the external device through the connector 3, and the printed circuit board 1, the circuit board 2 and the connector 3 form an electronic module. Figure 6 is another structural schematic diagram of the electronic component in the embodiment of the present application. As shown in Figure 6, in another specific embodiment, the circuit board 2 realizes the connection between the packaging structure 4 and the printed circuit board 1, so that signals can be transmitted between the packaging structure 4 and the printed circuit board 1. Specifically, one end of the circuit board 2 is connected to the packaging structure 4, and the other end is connected to the printed circuit board 1.

[0063] FIG7 is another schematic diagram of the structure of an electronic assembly in an embodiment of the present application. As shown in FIG7 , in another specific embodiment, a circuit board 2 can be welded to the surface of a printed circuit board 1. FIG8 is another schematic diagram of the structure of an electronic assembly in an embodiment of the present application. As shown in FIG8 , in another specific embodiment, a plurality of stacked circuit boards 2 can be welded to the surface of a printed circuit board 1. In addition, a circuit board 2 can be connected to a single side of a printed circuit board 1, as shown in FIG7 and FIG8 . Alternatively, FIG9 is another schematic diagram of the structure of an electronic assembly in an embodiment of the present application. As shown in FIG9 , in another specific embodiment, circuit boards 2 can be connected to both sides of a printed circuit board 1.

[0064] FIG10 is a schematic diagram of a structure of a circuit board in an embodiment of the present application, and FIG11 is a schematic diagram of a cross-sectional structure of a circuit board in an embodiment of the present application. As shown in FIG10 and FIG11, in one embodiment, the circuit board 2 includes a transmission area 21 and a connection area 22. The connection area 22 is used to connect with other electronic devices, for example, at least one connection area 22 is used to electrically connect with a printed circuit board 1. In a specific embodiment, the circuit board 2 includes at least two connection areas 22. Specifically, each connection area 22 includes a plurality of pins 23. The plurality of pins 23 are arranged in the connection area 22 of the circuit board 2 to form a pinmap. The pins 23 are used to weld with other electronic devices to achieve the connection between the circuit board 2 and the other electronic devices, for example, the pins 23 of the connection area 22 are welded with the printed circuit board 1. It is worth noting that the transmission area 21 and the connection area 22 of the circuit board 2 are only for the convenience of describing the areas where the circuit board 2 is divided. In the actual structure of the circuit board 2, there is not necessarily a clear boundary to distinguish the transmission area 21 and the connection area 22. The main difference between the connection area 22 and the transmission area 21 is that the connection area 22 includes a plurality of pins 23 for connecting with other electronic devices, and its main function is to connect with other electronic devices.

[0065] Please continue to refer to Figures 10 and 11. From the perspective of layer structure, the above-mentioned circuit board 2 includes a signal layer 24 and a dielectric layer 25. Specifically, the above-mentioned signal layer 24 includes a signal line 241 for transmitting signals; and the dielectric layer 25 is mainly an insulator, which is used to separate different layers of signal layers 24, support the signal layer 24, and protect the signal layer 24. Specifically, the above-mentioned signal line 241 is connected to the pin 23 of the connection area 22. For example, one end of the signal line 241 is connected to the pin 23 of the bending area 224, and the other end of the signal line 241 is connected to the pin 23 of the second connection area 222. In an optional embodiment, the number of signal layers 24 of the circuit board 2 is not limited. The circuit board 2 can include 1 to 2 signal layers, or 3 to 5 signal layers, and so on. For example, the total number of layers of the circuit board 2 is 2 to 6 layers.

[0066] In a specific embodiment, the signal layer 24 may be a copper layer, a silver layer, or a gold layer to reduce signal loss during transmission via the signal layer 24 and improve signal transmission speed. The dielectric layer 25 may be a low-loss dielectric, for example, the dielectric layer 25 may be made of at least one of modified polyimide (MPI), liquid crystal polymer (LCP), polyfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), and polytetrafluoroethylene (PTFE). These materials are flexible and produce low signal loss, further reducing insertion loss during signal transmission via the circuit board 2.

[0067] In one embodiment, the above-mentioned signal layer is a copper layer, and the copper layer adopts copper loss reduction technology at least in the transmission area 21 to reduce the loss of the signal transmission path. For example, the signal line 241 can be processed by silver plating or polishing to improve the efficiency of signal transmission of the signal line 241.

[0068] In the embodiment provided herein, the thickness of the connection region 22 is less than that of the transmission region 21. The thinner thickness of the connection region 22 of the circuit board 2 reduces impedance. However, a thinner thickness of the connection region 22 also results in higher insertion loss, while a thicker thickness of the transmission region 21 reduces insertion loss, resulting in lower insertion loss for the entire signal transmission path of the circuit board 2. Accordingly, a thicker thickness of the transmission region 21 of the circuit board 2 also results in higher impedance, but the lower impedance of the connection region 22 reduces the impedance for the entire signal transmission path of the circuit board 2. Furthermore, the flexibility of the circuit board 2 is strongly correlated with its thickness. During use, high flexibility is generally required for the circuit board 2 to bend 22. In this embodiment, the thinner thickness of the connection region 22 results in higher flexibility, making the circuit board 2 more flexible during use. Therefore, the circuit board 2 of the technical solution of this application balances multiple performance indicators, including insertion loss, impedance, and flexibility, offering significant advantages, particularly for high-density, high-speed electronic devices, such as those with speeds above 112G.

[0069] In an optional embodiment, the thickness of all the connection areas 22 of the circuit board 2 may be smaller than the thickness of the transmission area 21 , or the thickness of some of the connection areas 22 may be smaller than the thickness of the transmission area 21 .

[0070] Please continue to refer to Figure 10. In one embodiment, the transmission area 21 includes a first circuit board layer 211 and a second circuit board layer 212. The first circuit board layer 211 can be a single-layer structure or a multi-layer structure, and the number of layers included in the second circuit board layer 212 is not limited. It can be understood that the transmission area 21 of the circuit board 2 includes at least two parts in the layer structure. The first circuit board layer 211 and the second circuit board layer 212 are spaced apart, and the edge of the first circuit board layer 211 is connected to the edge of the second circuit board layer 212 by a connecting wall 220, so that a cavity is formed between the first circuit board layer 211 and the second circuit board layer 212. The circuit board 2 in this solution has a cavity inside, which makes the transmission area 21 of the circuit board 2 more flexible.

[0071] Referring to Figures 10 and 11 , a portion of the signal line 241 of the circuit board 2 is located on the surface of the second circuit board layer 212 facing the cavity. This exposes one side of the signal line 241 within the cavity, effectively connecting one side of the signal line 241 to air. This reduces insertion loss in the signal transmission path and improves signal transmission efficiency and speed.

[0072] Continuing with Figure 11, in one embodiment, the connecting wall 220 is continuously disposed around the perimeter of the cavity between the first circuit board layer 211 and the second circuit board layer 212. This can be understood as forming a ring-shaped structure, with the connecting wall 220, the first circuit board layer 211, and the second circuit board layer 212 enclosing a sealed cavity. In this embodiment, the signal line 241, with its surface facing the cavity, is located within the sealed cavity, which helps protect the signal line 241 and prevents dust and water vapor from entering during transportation, storage, and use, thereby improving the service life of the signal line 241 and enhancing signal transmission efficiency.

[0073] FIG12 is a schematic cross-sectional view of a circuit board according to an embodiment of the present application. Referring to FIG12 , in some embodiments, the connecting walls 220 may be located only at the two ends of the cavity, primarily connecting the transmission area 21 and the connection area 22, and connecting the first circuit board layer 211 and the second circuit board layer 212. This solution facilitates improved flexibility of the circuit board 2.

[0074] FIG13 is a schematic cross-sectional view of a circuit board according to an embodiment of the present application. Referring to FIG13 , in one embodiment, a support structure 230 is provided between the first circuit board layer 211 and the second circuit board layer 212. The orthographic projection of the support structure 230 on the surface of the second circuit board layer 212 is spaced a certain distance from the signal line 241. The support structure 230 supports the first and second circuit board layers 211, 212 within the cavity. This structure, particularly when the circuit board 2 is relatively large and the cavity is relatively large, can support the first and second circuit board layers 211, 212 within the cavity, thereby enhancing the overall strength of the circuit board 2 and making it less susceptible to damage. Furthermore, this structure helps maintain the cavity at a certain height and prevents collapse, thereby maintaining a constant and stable thickness of the air medium adjacent to the signal line 241, improving impedance continuity and, consequently, enhancing the efficiency and quality of signal transmission by the circuit board 2. In addition, the support structure 230 and the signal line 241 do not overlap, and the support structure 230 and the signal line 241 are separated by a certain distance, which can reduce the impact of the support structure 230 on the impedance of the signal line 241, thereby improving the efficiency and quality of signal transmission of the circuit board 2.

[0075] In specific embodiments, the shape, number, and size of the support structures 230 are not limited and can be selected from a variety of options. For example, referring to Figure 13 , in one embodiment, the support structures 230 are support walls. Specifically, the support structures 230 are planar or strip-shaped. The support walls extend in the same direction as the signal lines 241, thereby maintaining a relatively fixed positional relationship between the support walls and the signal lines 241, which helps improve impedance continuity.

[0076] In one embodiment, the distance between the support wall and the adjacent signal line 241 is the same at any position along the extension direction, which is beneficial for further improving impedance continuity and enhancing the quality and rate of signal transmission by the signal line 241. Specifically, the distance between the support wall and the adjacent signal line 241 refers to the distance between the side of the support wall facing the adjacent signal line 241 and the edge of the adjacent signal line 241 facing the support wall, along the direction perpendicular to the extension direction of the signal line 241. Alternatively, in some embodiments, it can also be understood that there is a gap between the support wall and the signal line 241, and the distance is the width of the gap along the direction perpendicular to the extension direction of the signal line 241.

[0077] In one embodiment, both ends of the support wall along the extension direction are connected to the connecting wall 220. This improves the structural stability of the support wall and makes the impedance of the portion of the signal line 241 within the cavity more continuous along the extension direction.

[0078] Figure 14 is a schematic diagram of a cross-sectional structure of a circuit board in an embodiment of the present application. Please refer to Figure 14. In one embodiment, the above-mentioned support structure 230 includes a plurality of support columns, and at least some of the plurality of support columns are arranged along the extension direction of the signal line 241 to support the first circuit board layer 211 and the second circuit board layer 212.

[0079] Furthermore, the support structure 230 has one end connected to the first circuit board layer 211 and the other end connected to the second circuit board layer 212 along the thickness of the circuit board, thereby enhancing the overall structural stability of the circuit board. In some embodiments, the support structure 230 may have one end connected to the first circuit board layer 211 and the other not connected to the second circuit board layer 212. Alternatively, one end may be connected to the second circuit board layer 212 and the other not connected to the first circuit board layer 211. The specific design can be tailored to the actual product requirements.

[0080] In a specific embodiment, the thickness of the dielectric layer adjacent to the cavity in the dielectric layer of the circuit board is greater than or equal to 150 μm. Due to the setting of the cavity, the thickness of the circuit board in the transmission area 21 can be set to be thicker, while having little impact on the flexibility of the circuit board. In this embodiment, the thickness of the dielectric layer is thickened, and the loss of the signal transmitted by the signal line 241 is lower, which is beneficial to improving the efficiency of signal transmission of the circuit board. In a specific embodiment, the thickness of the dielectric layer adjacent to the cavity can be any one of 160 μm, 180 μm, 185 μm, 190 μm, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm or 260 μm.

[0081] Continuing with reference to FIG11 , the cross-sectional area of ​​the signal line 241 in the connection region 22 is smaller than the cross-sectional area of ​​the same signal line 241 in the transmission region 21 , that is, the signal line 241 in the connection region 22 is thinner than the same signal line 241 in the transmission region 21 . In one embodiment, the thinner signal line 241 in the connection region 22 occupies less space, allowing the pins 23 of the circuit board 2 to be arranged at a higher density on the pinmap, which is beneficial for reducing the area of ​​the connection region 22 , reducing the size of the electronic device, and improving the integration of the electronic device. While the thinner signal line 241 in the connection region 22 has greater insertion loss and higher impedance, the thicker signal line 241 in the transmission region 21 has less insertion loss and lower impedance, thereby optimizing the insertion loss and impedance of the entire signal line 241 , resulting in less insertion loss and lower impedance for the signal line 241 as a whole.

[0082] In a specific embodiment, when the signal line 241 has the same thickness, the cross-sectional area is mainly affected by the line width. It can also be understood that the line width of the signal line 241 in the bending area 224 is smaller than the line width of the same signal line 241 in the transmission area 21. The line width of the signal line 241 in the second connection area 222 is smaller than the line width of the same signal line 241 in the transmission area 21.

[0083] Referring to Figures 13 and 14 , in one embodiment, the cross-sectional area of ​​the signal line 241 covered by the connection wall 220 is smaller than the cross-sectional area of ​​the same signal line 241 in the area opposite the cavity. Because the signal line 241 in the area covered by the connection wall 220 is a solid dielectric, while the dielectric in the cavity area is air, adjusting the cross-sectional area of ​​the signal line 241 in these two areas can help reduce the overall insertion loss and impedance of the signal line 241 and improve the impedance continuity of the signal line 241 along its extension direction.

[0084] Similarly, when the thickness of the above-mentioned signal line 241 is the same, the above-mentioned cross-sectional area is mainly affected by the line width. It can also be understood that the line width of the signal line 241 in the area covered by the connecting wall 220 is smaller than the line width of the same signal line 241 in the area opposite to the cavity.

[0085] Continuing with FIG11 , adjacent signal lines 241 on the same layer have greater spacing in the transmission area 21 than in the connection area 22 , meaning the signal lines 241 are denser in the connection area 22 and more sparse in the transmission area 21 . In a specific embodiment, when multiple signal lines 241 on the same layer are arranged in the connection area 22 , the spacing between adjacent signal lines 241 is smaller, occupying less space. This allows the pins 23 of the circuit board 2 to be arranged at a higher density, which is beneficial for reducing the area of ​​the connection area 22 , reducing the size of the electronic device, and improving the integration of the electronic device. The smaller spacing between signal lines 241 in the connection area, especially between a pair of differential signal lines, results in tight coupling between the signal lines 241 , which can result in greater insertion loss. However, the larger spacing between adjacent signal lines 241 in the transmission area 21 can reduce insertion loss, resulting in lower overall insertion loss for the signal lines 241 . This embodiment further optimizes the relationship between the area of ​​the connection region 22 of the circuit board 2 and insertion loss. This reduces insertion loss even when the circuit board 2 has a smaller connection region 22, thereby increasing the signal transmission rate of the circuit board 2 to meet the high-density and high-speed requirements of electronic devices. In one embodiment, the density of adjacent signal lines 241 on the same layer in the transmission region 21 is lower than in the bending region 224.

[0086] In the embodiment provided herein, the cross-sectional area of ​​a signal line 241 in the connection region 22 is smaller than the cross-sectional area of ​​the same signal line 241 in the transmission region 21. Adjacent signal lines 241 on the same layer are spaced farther apart in the transmission region 21 than in the connection region 22. The signal lines 241 in the connection region 22 are arranged thinner and denser, facilitating the placement of denser pins 23 in the connection region 22, thereby reducing the area of ​​the connection region 22 and, in turn, the area of ​​the circuit board 2. In this embodiment, the signal lines 241 in the connection region 22 are tightly coupled with thin wire widths, resulting in a higher impedance of the circuit board 2 in the connection region 22. The thin thickness of the connection region 22 of the circuit board 2 can reduce impedance. However, the thin thickness of the connection region 22 can also result in higher insertion loss. The thicker transmission region 21 of the circuit board 2 and the proximity of the signal lines 241 to the cavity can reduce insertion loss, resulting in lower insertion loss for the entire signal transmission path of the circuit board 2. Correspondingly, the thicker thickness of the transmission of the circuit board 2 will also lead to increased impedance, but the impedance of the bending area 224 is smaller, which can make the impedance of the entire signal transmission path of the circuit board 2 smaller. In addition, the transmission area 21 has a larger area for routing relative to the connection area 22. Therefore, the signal line 241 is thicker and has a larger spacing in the transmission area 21. The thick line in the transmission area 21 is loosely coupled, which can reduce the impedance of the circuit board 2 in the connection area 22. In addition, the thickness of the connection area 22 in the present application is thinner, so it is more flexible, making the circuit board 2 more flexible during use. Therefore, the circuit board 2 in the technical solution of the present application takes into account multiple performance indicators such as insertion loss, impedance and flexibility, especially for high-density and high-speed electronic equipment, such as electronic equipment with a speed of more than 112G, it has more obvious advantages.

[0087] The embodiment of the present application realizes the division of different areas on the same low-loss circuit board 2. The connection area 22 at the end of the circuit board 2 can support a tight coupling design with thin traces. By setting a thinner bending area 224, the connection area 22 can maintain a low target impedance requirement even when the signal lines 241 are thin and dense. The design of a loose coupling design with thick traces in the middle transmission area 21 can ensure lower loss performance in the longer transmission area 21. This solution solves both the impedance problem of the connection area 22 and the overall insertion loss problem.

[0088] Continuing with Figures 10 and 11 , in one embodiment, the connection region 22 includes a pin region 223 and a bending region 224. The pins 23 of the circuit board are located in the pin region 223, and a pinmap is formed in the pin region 223. The bending region 224 is located between the pin region 223 and the transmission region 21. Specifically, with respect to the side of the circuit board facing a connection region 22, the transmission region 21, bending region 224, and pin region 223 are arranged in that order.

[0089] The length of the bending zone 224 along the direction from the pin area 223 toward the transmission area 21 is greater than or equal to a preset value. The length of the bending zone 224 along the extension direction of the circuit board 2 is greater than or equal to a preset value. The thinner the connection area 22 is, the more flexible it is, making it easier to adjust the shape of the circuit board 2 to the actual product's position. Only the area outside the pins 23, namely the bending zone 224, can bend when the pins 23 are fixed to other components. The length of the bending zone 224 along the direction from the pin area 223 toward the transmission area 21 is greater than or equal to a preset value, ensuring that the bending capacity of the circuit board 2 in the bending zone 224 meets bending requirements. The preset value is selected based on the bending requirements of the circuit board 2 in the direction toward the connection area 22 and the flexibility of the circuit board 2 in the bending zone 224. For example, the greater the bending requirements, the greater the bending angle, or the longer the bending distance, the larger the preset value. Conversely, the weaker the bending requirements, the smaller the preset value. For example, the worse the flexibility of the connection area 22 is, the larger the preset value is set to. Conversely, the better the flexibility of the connection area 22 is, the smaller the preset value is set to.

[0090] In an optional embodiment, the preset value may be 60 mm, and the length of the bending zone 224 along the extension direction of the circuit board 2 is greater than or equal to 60 mm, which can meet the bending requirements of most electronic components, making the circuit board 2 applicable to a variety of application scenarios. For example, in some embodiments, the preset value may include 65 mm, 68 mm, 70 mm, 75 mm, 80 mm, 82 mm, 85 mm, 90 mm, 95 mm, 98 mm, 100 mm, 110 mm, 120 mm, 125 mm, 130 mm, 135 mm, 140 mm, 145 mm, or 150 mm.

[0091] In one embodiment of the present application, the bending region 224, pin region 223, and transmission region 21 of the circuit board are all flexible circuit boards. The flexibility of the circuit board 2 is relatively uniform in the connection region 22, and the flexibility of the connection region 22 is consistent, indicating good flexibility. Specifically, the thickness of the bending region 224 is the same as that of the pin region 223. In a specific embodiment, the thickness of the bending region 224 can be less than or equal to 0.3, thereby ensuring good flexibility.

[0092] Figure 15 is a schematic diagram of a top view of the circuit board in an embodiment of the present application, and Figure 16 is a schematic diagram of a structure of the circuit board in an embodiment of the present application. As shown in Figures 15 and 16, in one embodiment, the rigidity of the above-mentioned pin area 223 is greater than the rigidity of the bending area 224, and the above-mentioned pin area 223 includes a rigid circuit board. The circuit board 2 is a flexible and rigid circuit board, most of which is flexible, and the pin areas 223 at both ends have a certain rigidity. This flexible and rigid circuit board is also applicable to the technical solution provided in this application. Providing a rigid circuit board in the pin area 223 is conducive to preparing relatively dense pins in the pin area 223, thereby increasing the density of signal transmission of the circuit board. In a possible embodiment, the above-mentioned pin area 223 includes a rigid circuit board layer, and the rigid circuit board layer is sandwiched on both sides of the flexible circuit board. When preparing the above-mentioned circuit board, the flexible pin area 223, the bending area 224 and the transmission area 21 are first prepared, and then the rigid circuit board layers on both sides are prepared.

[0093] Continuing with FIG10 , in one embodiment, the circuit board 2 further includes a first ground layer 26 and a second ground layer 27, with the signal layer 24 located between the first ground layer 26 and the second ground layer 27. A dielectric layer 25 is located between the first ground layer 26 and the signal layer 24, and a dielectric layer 25 is also located between the second ground layer 27 and the signal layer 24. The first ground layer 26 and the second ground layer 27 serve as ground layers or shielding layers for the circuit board 2.

[0094] The specific form of the pinmap of the circuit board 2 in the pin area 223 of the present application has multiple options. For example, as shown in Figure 11, in one embodiment, the pins 23 of the above-mentioned pinmap of the circuit board 2 in the connection area 22 are arranged in a matrix (box). Figure 17 is a schematic diagram of the top structure of the circuit board in the embodiment of the present application. As shown in Figure 17, in one embodiment, the pins 23 of the above-mentioned pinmap of the circuit board 2 in the pin area 223 are staggered (stagger) arranged. Figure 18 is a schematic diagram of the top structure of the circuit board in the embodiment of the present application. As shown in Figure 18, in one embodiment, the pins 23 of the above-mentioned pinmap of the circuit board 2 in the pin area 223 are irregularly arranged. In this embodiment, the spacing (Pin pitch) of the pins 23 in the pinmap of the pin area 223 is 0.4mm~1mm, and the density of the pins 23 is relatively large. Specifically, the above-mentioned Pin pitch refers to the distance between the centers of two adjacent pins 23.

[0095] There are multiple options for the specific form of the circuit board 2 in the embodiment of the present application. Figure 19 is a structural schematic diagram of the circuit board in the embodiment of the present application, and Figure 20 is a structural schematic diagram of the circuit board in the embodiment of the present application. In one possible embodiment, as shown in Figure 19, the above-mentioned circuit board 2 can be a one-to-one type circuit board 2, that is, the circuit board 2 is used to realize signal transmission between two points. In this embodiment, the circuit board 2 can only include two connection areas 22, a first connection area 221 and a second connection area 222, and the first connection area 221 and the second connection area 222 are respectively located at the two ends of the circuit board 2. As shown in Figure 20, in one possible embodiment, the above-mentioned circuit board 2 can be a one-to-many type circuit board 2, that is, the circuit board 2 is used to realize signal transmission between one point and multiple points. In this embodiment, the circuit board 2 includes multiple connection areas 22, one of which is located at one end of the circuit board 2, and at least two connection areas 22 are located at the other end of the circuit board 2.

[0096] FIG21 is a schematic diagram of the structure of a circuit board in an embodiment of the present application. As shown in FIG21 , in one embodiment, the signal layer 24 of the circuit board 2 includes a first signal layer 242 and a second signal layer 243, and a third ground layer 28 is provided between the first signal layer 242 and the second signal layer 243. The first signal layer 242 has a cavity on the side facing away from the second signal layer 243, and the second signal layer 243 has another cavity on the side facing away from the first signal layer 242. The circuit board 2 in this embodiment has a large number of signal layers 24, so the area of ​​the signal layer 24 used to prepare the signal line 241 is large, thereby increasing the number of signal lines 241. This solution can improve the integration of the circuit board 2, allowing the circuit board 2 to transmit a large number of signals.

[0097] FIG22 is a schematic diagram of the structure of a circuit board in an embodiment of the present application. As shown in FIG22 , in one embodiment, the signal layer 24 of the circuit board 2 includes a third signal layer 244 and a fourth signal layer 245, and two fourth ground layers are provided between the third signal layer 244 and the fourth signal layer 245. Specifically, a dielectric layer 25 is provided between the two fourth ground layers, so that one of the fourth ground layers can serve as a reference ground layer for the third signal layer 244, and the other fourth ground layer can serve as a reference ground layer for the fourth signal layer 245. More importantly, the fourth ground layer can serve as a shielding layer between the third signal layer 244 and the fourth signal layer 245 to reduce crosstalk between the third signal layer 244 and the fourth signal layer 245, which is beneficial to improving the signal transmission rate of the circuit board 2. The transmission area 21 of the circuit board is relatively thick, which is beneficial to further improving the signal transmission rate of the signal line 241.

[0098] When preparing the circuit boards shown in Figures 21 and 22, the flexible metal-clad plate required to prepare the circuit board 2 shown in Figure 21 can be reduced by one piece compared to the flexible metal-clad plate required to prepare the circuit board 2 shown in Figure 22, so as to reduce costs.

[0099] Please continue to refer to Figures 21 and 22. There are many options for achieving the solution of making the thickness of the connection area 22 smaller than the thickness of the transmission area 21. For example, as shown in Figure 21, the thickness of the connection area 22 can be reduced on both sides of the circuit board 2, so that the surface of the connection area 22 and the surface of the transmission area 21 on one side of the circuit board 2 are located in different planes, and the surface of the connection area 22 and the surface of the transmission area 21 on the other side are also located in different planes; or, as shown in Figure 22, the thickness of the connection area 22 can also be reduced on one side of the circuit board 2, so that the surface of the connection area 22 and the surface of the transmission area 21 on one side of the circuit board 2 are located in different planes, and the surface of the connection area 22 and the surface of the transmission area 21 on the other side are also located in the same plane.

[0100] As shown in Figures 21 and 22, in a specific embodiment, for ease of description, the circuit board 2 is considered to include a first side 29 and a second side 210 that are spaced apart along the thickness direction. As shown in Figure 21, in an optional implementation, on the first side 29 of the circuit board 2, the surface of the connection area 22 and the surface of the transmission area 21 are located in different planes; on the second side 210 of the circuit board 2, the surface of the connection area 22 and the surface of the transmission area 21 are located in different planes. Specifically, the distance between the surface of the connection area 22 on the first side 29 and the surface of the transmission area 21 on the second side 210 is smaller than the distance between the surface of the transmission area 21 on the first side 29 and the surface of the transmission area 21 on the second side 210; and the distance between the surface of the connection area 22 on the second side 210 and the surface of the transmission area 21 on the first side 29 is smaller than the distance between the surface of the transmission area 21 on the second side 210 and the surface of the transmission area 21 on the first side 29. Specifically, the two sides of the circuit board 2 can be symmetrical along the thickness direction. In this embodiment, the circuit board 2 is symmetrical along the thickness direction, and the signal transmission is also symmetrical, which helps improve the signal transmission quality of the circuit board 2.

[0101] As shown in Figure 22, in one optional implementation, the thickness of the connection area 22 is reduced on one side of the circuit board 2. Specifically, on the first side 29 of the circuit board 2, the surface of the connection area 22 and the surface of the transmission area 21 are located in different planes; on the second side 210 of the circuit board 2, the surface of the connection area 22 and the surface of the transmission area 21 are located in the same plane. Specifically, the distance between the surface of the connection area 22 on the first side 29 and the surface of the circuit board 2 on the second side 210 is smaller than the distance between the surface of the transmission area 21 on the first side 29 and the surface of the circuit board 2 on the second side 210.

[0102] In a specific embodiment, the thickness h1 of the above-mentioned circuit board 2 in the above-mentioned connection area 22 is less than or equal to 0.3 mm, that is, h1≤0.3 mm. The thickness h2 of the above-mentioned circuit board 2 in the above-mentioned transmission area 21 is greater than or equal to 0.5 mm, that is, h2≥0.5 mm. In a specific embodiment, the thickness difference △h between the above-mentioned circuit board 2 in the connection area 22 and the transmission area 21 is less than or equal to 0.5 mm, that is, △h≤0.5 mm. The line width w1 of the signal line 241 in the connection area 22 is less than or equal to 50 μm, that is, w1≤50 μm. The line width w2 of the signal line 241 in the transmission area 21 is greater than or equal to 250 μm, that is, w1≥250 μm.

[0103] In the embodiment of the present application, the connection area 22 of the circuit board 2 covers the pinmap of the circuit board 2. However, along the width direction of the circuit board 2, the connection area 22 may or may not extend through the circuit board 2. Figure 23 is a schematic top view of the circuit board structure in the embodiment of the present application. As shown in Figure 23, the circuit board 2 includes an extension direction X, a width direction Y, and a thickness direction Z. The first direction X, the second direction Y, and the thickness direction are perpendicular to each other.

[0104] As shown in Figure 18 , in one embodiment, the connection region 22 extends through the width of the circuit board 2, which helps simplify the manufacturing process of the circuit board 2 and improves the flexibility of the circuit board 2 in the connection region 22. As shown in Figure 23 , in one embodiment, the connection region 22 does not extend through the circuit board 2 in the width direction. That is, the circuit board 2 further includes an additional region at the edge of the connection region 22 in the thickness direction. The thickness of the additional region is greater than that of the connection region 22. In a specific embodiment, the thickness of the additional region can be the same as that of the transmission region 21. This embodiment helps improve the strength of the circuit board 2.

[0105] Based on the same concept, the present application also provides a method for preparing a circuit board 2. FIG24 is a flow chart of a process for preparing a circuit board in an embodiment of the present application. Referring to FIG24 , the circuit board 2 includes a transmission area 21 and a connection area 22, and the transmission area 21 is connected to the connection area 22. The method for preparing the circuit board 2 provided in the present application includes the following steps:

[0106] S101 , forming a signal line 241 in a first metal layer L1 on a surface of a first flexible metal-clad plate FL1 , wherein a second metal layer L2 is formed on a surface of the first flexible metal-clad plate FL1 facing away from the first metal layer L1 ;

[0107] The flexible metal-clad laminate in the present application includes a stacked metal layer and a dielectric layer, and the metal layer can specifically be a metal foil layer. The flexible metal-clad laminate can specifically include a single-sided metal-clad laminate and a double-sided metal-clad laminate. The single-sided metal-clad laminate is a laminate having a metal layer covering one surface of the dielectric layer, and the double-sided metal-clad laminate is a laminate having metal layers covering both surfaces of the dielectric layer. The connection between the metal layer and the dielectric layer in the flexible metal-clad laminate is more reliable, and the use of the flexible metal-clad laminate to prepare the circuit board 2 is conducive to simplifying the preparation process of the circuit board 2. The above-mentioned first flexible metal-clad laminate FL1 is a double-sided metal-clad laminate. In a specific embodiment, the flexible metal-clad laminate in the present application can specifically be a flexible copper clad laminate (FCCL). In addition, the metal layer in the present application can be a copper layer, an aluminum layer, a silver layer, etc.

[0108] S102, laminating the third metal layer L3, the first adhesive layer BS1, the adhesive pad 6, and the first flexible metal-clad plate FL1 stacked in sequence. The first adhesive layer BS1 and the adhesive pad 6 are located on the same layer. The first adhesive layer BS1 covers the connection area of ​​the first flexible metal-clad plate FL1. The third metal layer L3 is located on the side of the signal line 241 facing away from the second metal layer L2.

[0109] The third metal layer L3 is secured to the side of the first flexible metal-clad sheet FL1, which has the first metal layer L1, via a first adhesive layer BS1. The provision of adhesive pads 6 prevents the first adhesive layer BS1 from covering the portion of the first flexible metal-clad sheet FL1 that would otherwise be blocked by adhesive pads 6, facilitating the fabrication of the circuit board cavity. Specifically, the first flexible metal-clad sheet FL1 is used to fabricate the first circuit board layer 211.

[0110] S103, preparing a conductive via, wherein the conductive via connects at least two layers among the first metal layer L1, the second metal layer L2, and the third metal layer L3;

[0111] The steps of preparing the conductive holes may specifically include two steps: processing the holes and electroplating the metal layer. The step of processing the holes may be completed by mechanical drilling or laser drilling. For example, the conductive holes are formed by mechanical drilling, and the aperture of the conductive holes is between 4mil and 10mil; the conductive holes are formed by laser drilling, and the aperture of the conductive holes is between 2mil and 4mil. In addition, the conductive holes may specifically be through holes or blind holes. In the process of electroplating the metal layer in the hole, the metal layer may also be electroplated on the surface of the metal layer to thicken the metal layer. Which metal layers the conductive holes are specifically connected to is prepared according to the actual routing requirements.

[0112] S104, dividing the third metal layer L3 and removing the glue pad 6;

[0113] Specifically, the third metal layer L3 can be divided by etching or laser cutting. Specifically, after cutting, the third metal layer L3 at least exposes the glue pad 6, so as to facilitate the removal of the glue pad 6. After the glue pad 6 is removed, a groove structure is formed.

[0114] S105, preparing a connecting wall 220 on the side of the first adhesive layer BS1 facing the cavity;

[0115] In a specific embodiment, the connecting wall 220 can be fabricated using an adhesive layer. The height of the connecting wall 220 can be greater than or equal to the height of the first adhesive layer BS1. The height of the connecting wall can be specifically designed based on the required cavity height. If the cavity also includes a support structure 230, the support structure 230 can be fabricated simultaneously with the connecting wall to simplify the circuit board fabrication process.

[0116] S106 , pressing the second flexible metal-clad plate FL2 and the connecting wall 220 stacked in sequence; the second flexible metal-clad plate FL2 includes a fourth metal layer L4 , and the fourth metal layer L4 is located on a surface away from the connecting wall 220 .

[0117] The second flexible metal-clad sheet FL2 is a single-sided metal-clad sheet. Its fourth metal layer L4 is located on the surface of the circuit board. The second flexible metal-clad sheet FL2 only partially covers the transmission area 21, resulting in a thicker circuit board in the transmission area 21 than in the connection area 22. Furthermore, the second flexible metal-clad sheet FL2 serves as the second circuit board layer 212. The second flexible metal-clad sheet FL2, support walls 220, and first flexible metal-clad sheet FL1 together form a circuit board cavity.

[0118] Before the above step S106, the method includes S1061: providing a blocking member 5 on the surface of the third metal layer L3;

[0119] The blocking member 5 may be a gasket or a blocking block. The blocking member 5 may block the second flexible metal-clad plate FL2 to improve the accuracy of the position of the second flexible metal-clad plate FL2.

[0120] After the above step S106 , the process includes step S1062 : removing the blocking member 5 .

[0121] Specifically, the depth-controlled drilling and milling technology can be used to remove the blocking member 5. This solution is conducive to the second flexible metal-clad plate FL2 covering the transmission area 21 more accurately and reliably.

[0122] In a specific embodiment, the cross-sectional area of ​​the signal line 241 formed in step S101 in the connection area 22 is smaller than the cross-sectional area of ​​the same signal line 241 in the transmission area 21, and the spacing between adjacent signal lines 241 in the connection area 22 is smaller than the spacing in the transmission area 21. This reduces the insertion loss of the circuit board and optimizes the impedance of the circuit board, thereby improving the density and rate of signal transmission on the circuit board.

[0123] Obviously, those skilled in the art may make various changes and modifications to the present application without departing from the scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include these modifications and variations.

Claims

1. A circuit board, characterized in that: It includes a transmission area and a connection area, wherein the connection area is provided with a plurality of pins, wherein: The transmission area is a flexible circuit board, and the thickness of the connection area is smaller than that of the transmission area; the transmission area includes a first circuit board layer and a second circuit board layer, the first circuit board layer and the second circuit board layer are spaced apart, and the edge of the first circuit board layer is connected to the edge of the second circuit board layer by a connecting wall, so that a cavity is formed between the first circuit board layer and the second circuit board layer; The circuit board includes a signal line, and a partial area of ​​the signal line is located on a surface of the second circuit board layer facing the cavity.

2. The circuit board according to claim 1, wherein: The connecting wall is continuously arranged on a peripheral side of the cavity between the first circuit board layer and the second circuit board layer.

3. The circuit board according to claim 1 or 2, wherein: A support structure is further provided between the first circuit board layer and the second circuit board layer, and an orthographic projection of the support structure on the surface of the second circuit board layer is spaced a certain distance from the signal line.

4. The circuit board according to claim 3, wherein: The supporting structure is a supporting wall, and an extending direction of the supporting wall is the same as an extending direction of the signal line.

5. The circuit board according to claim 3 or 4, wherein: One end of the support structure is connected to the first circuit board layer, and the other end of the support structure is connected to the second circuit board layer.

6. The circuit board according to any one of claims 1 to 5, wherein: The circuit board includes a dielectric layer, and a thickness of the dielectric layer adjacent to the cavity is greater than or equal to 150 μm.

7. The circuit board according to any one of claims 1 to 6, wherein: The connection area includes a bending area and a pin area, the bending area is a flexible circuit board, the bending area is located between the pin area and the transmission area, and the plurality of pins are located in the pin area.

8. The circuit board according to claim 7, wherein: The pin area is a flexible circuit board; or, the pin area includes a rigid circuit board.

9. The circuit board according to any one of claims 1 to 8, wherein: The cross-sectional area of ​​the signal line in the connection area is smaller than the cross-sectional area of ​​the same signal line in the transmission area.

10. The circuit board according to any one of claims 1 to 9, wherein: The cross-sectional area of ​​the region of the signal line covered by the connection wall is smaller than the cross-sectional area of ​​the region of the same signal line facing the cavity.

11. The circuit board according to any one of claims 1 to 10, wherein: The distance between adjacent signal lines located in the same layer in the transmission area is greater than the distance in the connection area.

12. The circuit board according to any one of claims 1 to 11, wherein: The length of the bending area along the direction from the pin area to the transmission area is greater than or equal to a preset value.

13. The circuit board according to claim 12, wherein: The preset value includes 60 mm.

14. The circuit board according to any one of claims 1 to 13, wherein: The circuit board includes a first side and a second side that are opposite to each other in the thickness direction; on the first side, the surface of the bending zone and the surface of the transmission zone are located in different planes; on the second side, the surface of the bending zone and the surface of the transmission zone are located in the same plane.

15. The circuit board according to any one of claims 1 to 13, wherein: The circuit board includes a first side and a second side that are opposite to each other in the thickness direction; on the first side, the surface of the bending zone and the surface of the transmission zone are located in different planes; on the second side, the surface of the bending zone and the surface of the transmission zone are located in different planes.

16. A method for preparing a circuit board, characterized in that: For preparing the circuit board according to any one of claims 1 to 15, the preparation method comprises: forming a signal line on the first metal layer on the surface of the first flexible metal-clad plate, wherein the surface of the first flexible metal-clad plate facing away from the first metal layer has a second metal layer; Laminating the third metal layer, the first adhesive layer, the glue resistance pad, and the first flexible metal-clad plate stacked in sequence, wherein the first adhesive layer and the glue resistance pad are located on the same layer, the first adhesive layer covers the connection area of ​​the first flexible metal-clad plate, and the third metal layer is located on a side of the signal line facing away from the second metal layer; preparing a conductive via, wherein the conductive via connects at least two layers among the first metal layer, the second metal layer, and the third metal layer; dividing the third metal layer and removing the glue blocking pad; preparing a connecting wall on a side of the first adhesive layer facing the cavity; The second flexible metal-clad plate and the connecting wall are sequentially stacked and pressed together; the second flexible metal-clad plate includes a fourth metal layer, and the fourth metal layer is located on a surface away from the connecting wall.

17. The preparation method according to claim 16, wherein The second flexible metal-clad plate and the connecting wall are laminated in sequence; The second flexible metal-clad sheet includes a fourth metal layer, the fourth metal layer is located on a surface facing away from the connecting wall, and includes: Disposing a blocking member in the connection area on the surface of the third metal layer; Afterwards include: The blocking member is removed.

18. An electronic component, characterized in that The invention comprises a printed circuit board and the circuit board according to any one of claims 1 to 15, wherein at least one connection area of ​​the circuit board is electrically connected to the printed circuit board.

19. An electronic device, characterized in that: The electronic device comprises a housing and the electronic component according to claim 18, wherein the electronic component is arranged in the housing.

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