Flexible printed circuits, circuit board assemblies, and electronic devices

Abstract

This application discloses a flexible printed circuit, a circuit board assembly, and an electronic device. The flexible printed circuit includes a bent portion and a soldering portion connected to the bent portion. The flexible printed circuit includes a plurality of conductive layers and a plurality of insulating layers, and the insulating layers are disposed between two adjacent conductive layers. The plurality of conductive layers includes a first soldering layer, a second soldering layer, and a trace layer. Both the first soldering layer and the second soldering layer are located in the soldering portion. The first soldering layer is one surface layer of the soldering portion, and the first soldering layer is formed by a plurality of first pads arranged at intervals from each other. The second soldering layer is the other surface layer of the soldering portion, and the second soldering layer is formed by a plurality of second pads arranged at intervals from each other. The trace layer is located between the first soldering layer and the second soldering layer and extends from the soldering portion to the bent portion. The first pads and the second pads are connected by using through-hole conductors and are connected to the trace layer. The pad pitch in the soldering portion of the flexible printed circuit is relatively small, whereby the surface area of the soldering portion is reduced and miniaturization can be facilitated.

Description

Technical Field

[0001] This application claims the priority of Chinese Patent Application No. 202210758071.2, titled "FLEXIBLE PRINTED CIRCUIT, CIRCUIT BOARD ASSEMBLY, AND ELECTRONIC DEVICE", filed with the State Intellectual Property Office of China on June 30, 2022, the entire content of which is incorporated herein by reference.

[0002] This application relates to the field of circuit connection structure technology, and particularly to flexible printed circuits, circuit board assemblies, and electronic devices.

Background Art

[0003] Currently, with the continuous development of electronic devices such as mobile phones, printed circuit boards (PCBs, also called printed circuit boards) and flexible printed circuits (FPCs) are widely applied in electronic devices. The flexible printed circuit and the printed circuit board can be soldered to each other by using the FPC on board (FOB) technology on the board, and signal and / or power transmission can be realized.

[0004] However, conventional flexible printed circuits have a large pad spacing, which requires a large soldering space to be secured on both the flexible printed circuit and the printed circuit board. As a result, the size of the circuit board assembly becomes large, making it difficult to implement the miniaturization and multifunctionality of electronic devices.

Summary of the Invention

[0005] This application provides a flexible printed circuit. The pad spacing in the soldering portion of the flexible printed circuit is relatively small, thereby reducing the surface area of ​​the soldering portion and making miniaturization easier. This application further provides a circuit board assembly including the above-mentioned flexible printed circuit, and an electronic device including the above-mentioned circuit board assembly.

[0006] According to a first aspect, the present application provides a flexible printed circuit including a bend and a soldered portion connected to the bend. The flexible printed circuit includes a plurality of conductive layers and a plurality of insulating layers, the insulating layers being positioned between two adjacent conductive layers. The plurality of conductive layers include a first soldering layer, a second soldering layer, and a trace layer. Both the first and second soldering layers are located in the soldered portion. The first soldering layer is one surface layer of the soldered portion and is formed by a plurality of first pads spaced apart from each other. The second soldering layer is the other surface layer of the soldered portion and is formed by a plurality of second pads spaced apart from each other. The trace layer is located between the first and second soldering layers and extends from the soldered portion to the bend. The first pad and the second pad are connected by using through-hole conductors, which are connected to the trace layer.

[0007] In this application, the first and second soldering layers are used as two surface layers of the soldered portion, with only the first pad placed on the first soldering layer and no traces, and only the second pad placed on the second soldering layer and no traces. Therefore, the soldered portion does not require a protective layer (or referred to as a solder mask layer) on the outside of the first and second soldering layers, and there is no need to place a solder mask opening structure. This makes it possible to implement a solder mask-free design, and the pad spacing in the soldered portion (i.e., the spacing between two adjacent first pads and the spacing between two adjacent second pads) is not limited by structures such as traces and solder mask openings. Compared to the pad spacing in the prior art, the pad spacing is significantly reduced, thereby reducing the surface area of ​​the soldered portion and making it possible to miniaturize flexible printed circuits. In addition, the traces of a flexible printed circuit are placed on a trace layer, forming the inner layer structure of the flexible printed circuit, and are covered by an insulating or protective layer. This helps to improve the circuit reliability of the flexible printed circuit.

[0008] In addition, compared to conventional products, the flexible printed circuit in this application arranges multiple pads separately on the soldering layer. The soldering layer may increase the number of conductive layers. However, since the thickness of the conductive layers is extremely small, for example, the thickness of the current copper foil layer is typically 0.25 micrometers, the overall increase in thickness of the flexible printed circuit in this application is small and controllable, and does not cause any obvious adverse effects or obvious obstacles to the miniaturization of both the circuit board assembly and the electronic device using the flexible printed circuit.

[0009] A through-hole conductor can be a conductive layer structure formed on the through-hole wall, or a conductive pillar structure filled inside the through-hole.

[0010] In possible implementations, the trace layer includes a conductor block and traces. The conductor block is located at the soldering portion. One end of the trace is connected to the conductor block, and the other end of the trace extends to the bend portion. Pads are connected to the conductor block by using through-hole conductors. The first and second pads are connected to the conductor block by using through-hole conductors. The first and second pads may be electrically connected to another part or component of the flexible printed circuit by using the conductor block and traces.

[0011] In possible implementations, the shape of the conductor block may be the same as or similar to the shape of the first pad.

[0012] In possible implementations, the area of ​​the conductor block is the same as the area of ​​the first pad. Compared to the pad spacing in conventional solutions, the pad spacing in this application can be reduced by approximately 22%. In a structure in which multiple pads are arranged in an array, the surface area of ​​the soldering portion of the flexible printed circuit in this application may be approximately 40% smaller than the surface area of ​​the soldering portion of conventional products. The significantly reduced surface area of ​​the soldering portion can facilitate the miniaturization of flexible printed circuits and both the circuit board assembly and electronic devices using the flexible printed circuit.

[0013] In possible implementations, the area of ​​the conductor block is smaller than the area of ​​the first pad. In this implementation, the first and second pads are connected to the conductor block by using through-hole conductors, so the locations of the first and second pads are limited by the arrangement of the conductor block. The area of ​​the conductor block is smaller than the area of ​​the first pad, and thus the area of ​​the conductor block can be set to a small value when the internal connection requirement (i.e., the conductor block is connected to the through-hole conductor) is met. In this way, when the trace layer satisfies the trace arrangement requirement, the spacing between two adjacent conductor blocks can be relatively small. In that case, the center-to-center distance between two adjacent first pads is relatively small. This makes it possible to further reduce the pad spacing in the soldering area, facilitating the miniaturization of flexible printed circuits.

[0014] In possible implementations, there are multiple trace layers, and multiple conductor blocks connected to multiple first pads are located on different trace layers. Conductor blocks connected to at least two of the multiple first pads may be located on different trace layers.

[0015] A trace layer placed on a conductor block must also accommodate traces connected to that conductor block. Therefore, when multiple conductor blocks connected to multiple first pads are centrally located on a particular trace layer of a flexible printed circuit, the trace layer has relatively high trace placement requirements. As a result, the space on the trace layer is insufficient, and trace placement is difficult. When conductor blocks connected to at least two of the multiple first pads are located on different trace layers, the traces connected to the conductor blocks can also be distributed across different trace layers. This reduces the difficulty of routing the trace layer and improves routing flexibility.

[0016] In possible implementations, there are one or more trace layers, with multiple punctured regions in each trace layer. Multiple through-hole conductors pass through the multiple punctured regions in each trace layer in a one-to-one correspondence. Support blocks are placed in the multiple punctured regions of each trace layer. Through-hole conductors pass through and connect to the support blocks. When there is one trace layer, the support block is a conductor block. Alternatively, when there are multiple trace layers, the support block is a conductor block or a bottom pad.

[0017] In this implementation, support blocks (conductor blocks or lower pads) are placed in the punctured regions of each trace layer of the flexible printed circuit, so the overall support structure of each punctured region of the flexible printed circuit is stable and less likely to collapse. In addition, the thickness of multiple punctured regions of the flexible printed circuit can be consistent. This facilitates batch punching and metal filling, improving the production efficiency and yield of flexible printed circuits.

[0018] In possible implementations, the insulating layers include a first insulating layer and a second insulating layer. The first insulating layer is located between a first soldering layer and an adjacent trace layer, extending from the soldering portion to the bend portion, with a portion of the first insulating layer located at the bend portion forming one surface layer of the bend portion. The second insulating layer is located between a second soldering layer and an adjacent trace layer, extending from the soldering portion to the bend portion, with a portion of the second insulating layer located at the bend portion forming the other surface layer of the bend portion.

[0019] In possible implementations, the conductive layers further include a first routing layer and a second routing layer. Both the first and second routing layers are located in the bend. The first routing layer and the first soldering layer are located on the same layer, and the second routing layer and the second soldering layer are located on the same layer. The flexible printed circuit further includes a first protective layer and a second protective layer. Both the first and second protective layers are located in the bend. The first protective layer is located on the side of the first routing layer away from the trace layer. The second protective layer is located on the side of the second routing layer away from the trace layer. The first and second protective layers are the two surface layers of the bend.

[0020] In this implementation, the first and second routing layers are located in the bent portion of the flexible printed circuit. The first routing layer, the second routing layer, and the trace layer can all be configured for trace placement. Therefore, the flexible printed circuit can better meet routing requirements such as multiple transmission channels.

[0021] In possible implementations, at least one insulating layer of the flexible printed circuit forms an air gap at the bend. In this way, the structures of the flexible printed circuit located on either side of the air gap can move relatively independently, improving the bending performance of the bend in the flexible printed circuit.

[0022] According to a second aspect, the present application further provides a flexible printed circuit including a bend and a soldered portion connected to the bend. The flexible printed circuit includes a plurality of conductive layers, a plurality of insulating layers, and a first protective layer. The insulating layers are arranged between two adjacent conductive layers. The plurality of conductive layers include a soldering layer and a trace layer. The soldering layer is located at the soldering portion and is one surface layer of the soldering portion, and is formed by a plurality of pads spaced apart from each other. The trace layer is located on the side of the soldering layer and extends from the soldering portion to the bend. The pads are connected to the trace layer by using through-hole conductors. The first protective layer is located on the side of the trace layer away from the soldering layer. The first protective layer extends from the soldering portion to the bend. A portion of the first protective layer located at the soldering portion forms the other surface layer of the soldering portion. A portion of the first protective layer located at the bend portion forms one surface layer of the bend.

[0023] In this implementation, the soldering layer is used as one of the surface layers of the soldering area, and only pads are placed on the soldering layer, not traces. Therefore, the soldering area does not need to have a protective layer (or solder mask layer) outside the soldering layer, and solder mask opening structures do not need to be placed. This makes it possible to implement a solder mask-free design, and the pad spacing in the soldering area is not limited by structures such as traces and solder mask openings. Compared to the pad spacing in conventional techniques, the pad spacing is significantly reduced, thereby reducing the surface area of ​​the soldering area and making it possible to miniaturize flexible printed circuits.

[0024] In addition, compared to conventional products, the flexible printed circuit in this application arranges multiple pads separately on the solder layer. The solder layer may increase the number of conductive layers. However, because the thickness of the conductive layers is extremely small, the overall increase in thickness of the flexible printed circuit in this application is small and controllable, and does not cause any apparent adverse effects or obvious obstacles to the miniaturization of both the circuit board assembly and the electronic device using the flexible printed circuit.

[0025] In possible implementations, the trace layer includes a conductor block and traces. The conductor block is located at the soldering portion. One end of the trace is connected to the conductor block, and the other end of the trace extends to the bend portion. Pads are connected to the conductor block by using through-hole conductors. Pads may be electrically connected to another part or component of the flexible printed circuit by using the conductor block and traces.

[0026] In possible implementations, the shape of the conductor block may be the same as or similar to the shape of the pad.

[0027] In possible implementations, the area of ​​the conductor block is the same as the area of ​​the pad. Compared to the pad spacing in conventional solutions, the pad spacing in this application can be reduced by approximately 22%. In a structure in which multiple pads are arranged in an array, the surface area of ​​the soldering portion of the flexible printed circuit in this application may be approximately 40% smaller than the surface area of ​​the soldering portion of conventional products. The significantly reduced surface area of ​​the soldering portion can facilitate the miniaturization of flexible printed circuits and both the circuit board assemblies and electronic devices using flexible printed circuits.

[0028] In a possible implementation, the area of the conductor block is smaller than the area of the pad. In this implementation, since the pad and the second pad are connected to the conductor block by using through-hole conductors, the locations of the pad and the second pad are limited by the arrangement of the conductor block. The area of the conductor block is smaller than the area of the pad, and thus, when the internal connection requirement (i.e., the conductor block is connected to the through-hole conductor) is satisfied, the area of the conductor block can be set to a small value. In this way, when the trace layer satisfies the trace arrangement requirement, the distance between two adjacent conductor blocks can be relatively small. In that case, the center spacing between two adjacent pads is relatively small. Thereby, the pad spacing in the soldering portion can be further reduced, making it possible to facilitate the miniaturization of the flexible printed circuit.

[0029] In a possible implementation, there are multiple trace layers, and the multiple conductor blocks connected to the multiple pads are located on different trace layers. The conductor blocks connected corresponding to at least two of the multiple pads can be located on different trace layers. The trace layer on which the conductor block is arranged further needs to arrange the traces connected to the conductor block. Therefore, when the multiple conductor blocks connected to the multiple pads are arranged centrally on a specific trace layer of the flexible printed circuit, the trace layer has relatively high trace arrangement requirements. As a result, the space of the trace layer is insufficient and trace arrangement is difficult. When the conductor blocks connected corresponding to at least two of the multiple pads are located on different trace layers, the traces connected to the conductor blocks can also be dispersed on different trace layers. This reduces the difficulty of routing the trace layer and improves routing flexibility.

[0030] In a possible implementation, there is one or more trace layers, and a plurality of punctured regions are provided in each trace layer. A plurality of through-hole conductors penetrate the plurality of punctured regions of each trace layer in a one-to-one correspondence. Support blocks are disposed in the plurality of punctured regions of each trace layer. The through-hole conductors penetrate the support blocks and are connected to the support blocks. When there is one trace layer, the support block is a conductor block. Alternatively, when there are a plurality of trace layers, the support block is a conductor block or a lower pad.

[0031] In this implementation, since the support blocks (conductor blocks or lower pads) are disposed in the punctured regions of each trace layer of the flexible printed circuit, the overall support structure of each punctured region of the flexible printed circuit is stable and the possibility of collapse is low. In addition, it is possible for the thicknesses of the plurality of punctured regions of the flexible printed circuit to be consistent. This facilitates batch punching and metal filling, and improves the production efficiency and yield of the flexible printed circuit.

[0032] In a possible implementation, the plurality of insulating layers includes a first insulating layer. The first insulating layer is located between the soldering layer and an adjacent trace layer and extends from the soldering portion to the bending portion. A part of the first insulating layer located in the bending portion forms the other surface layer of the bending portion.

[0033] In a possible implementation, the plurality of conductive layers further includes a routing layer. The routing layer is located in the bending portion, and the routing layer and the soldering layer are disposed on the same layer. The flexible printed circuit further includes a second protective layer. The second protective layer is located on the side of the routing layer away from the trace layer. The second protective layer is located in the bending portion and is the other surface layer of the bending portion.

[0034] In possible implementations, at least one insulating layer of the flexible printed circuit forms an air gap at the bend. In this way, the structures of the flexible printed circuit located on either side of the air gap can move relatively independently, improving the bending performance of the bend in the flexible printed circuit.

[0035] According to a third aspect, the application further provides a circuit board assembly comprising a circuit board and a flexible printed circuit as described in any one of the above descriptions. The soldering portion of the flexible printed circuit is soldered to the circuit board.

[0036] Because the pads of the soldering portion of the flexible printed circuit are structured to protrude from the surface, solder paste collapse and short circuits can be avoided during the soldering process, and the solder joint is guaranteed to have a specific height. This improves soldering quality and reliability.

[0037] In possible implementations, a circuit board assembly includes a first circuit board, a second circuit board, a flexible printed circuit, a first component, and a second component. The flexible printed circuit includes two soldering portions and a bend connecting the two soldering portions. The two soldering portions of the flexible printed circuit are soldered to the first circuit board and the second circuit board, respectively. The structure of each of the soldering portions and bends of the flexible printed circuit may use any one of the structures described above. The first circuit board may be a printed circuit board or a flexible printed circuit, and the second circuit board may be a printed circuit board or a flexible printed circuit. There may be one or more first components, which are fixed to and electrically connected to the first circuit board. There may be one or more second components, which are fixed to and electrically connected to the second circuit board. The flexible printed circuit is configured to provide an electrical connection between the first component and the second component.

[0038] The first and second circuit boards may be stacked. The bent portion of the flexible printed circuit is bent so that the circuit board assembly forms a sandwich stack structure. The entire circuit board assembly occupies a relatively small space and requires a relatively small installation space. This helps reduce installation difficulties and improve the range of application. In some other implementations, the first and second circuit boards may, alternatively, form a different relative position, such as a staggered arrangement.

[0039] In some implementations, a circuit board assembly includes a first circuit board, a second circuit board, a flexible printed circuit, a first electrical connector, a second electrical connector, a first component, and a second component. The flexible printed circuit includes soldering portions, connection portions, and bends connecting the soldering portions and connection portions. The structure of each of the soldering portions and bends of the flexible printed circuit may use any one of the above structures. The first circuit board may be a printed circuit board or a flexible printed circuit. There may be one or more first components, which are fixed to and electrically connected to the first circuit board. The soldering portions of the flexible printed circuit are soldered to the first circuit board. There may be one or more second components, which are fixed to and electrically connected to the second circuit board. The first and second electrical connectors may be male and female connectors, respectively, and the male and female connectors are paired with each other. Each of the first and second electrical connectors may be a board-to-board electrical connector or the like. The first electrical connector is fixed to the connection portion of the flexible printed circuit and electrically connected. The second electrical connector is fixed to the second circuit board and electrically connected. The first electrical connector is fixed to the second electrical connector and electrically connected. The flexible printed circuit is configured to provide an electrical connection between the first component and the second component.

[0040] The first and second circuit boards may be stacked. The bent portion of the flexible printed circuit is bent so that the circuit board assembly forms a sandwich stack structure. The entire circuit board assembly occupies a relatively small space and requires a relatively small installation space. This helps reduce installation difficulties and improve the range of application. In some other implementations, the first and second circuit boards may, alternatively, form a different relative positional relationship, for example, a staggered arrangement.

[0041] In some implementations, a circuit board assembly includes a circuit board, a flexible printed circuit, a first component, and a second component. The flexible printed circuit includes soldering portions, mounting portions, and bends connecting the soldering portions and mounting portions. The structure of each of the soldering portions and bends of the flexible printed circuit may use any one of the above structures. The circuit board may be a printed circuit board or a flexible printed circuit. There may be one or more first components, which are fixedly and electrically connected to the circuit board. The soldering portions of the flexible printed circuit are soldered to the circuit board. There may be one or more second components, which are fixed to and electrically connected to the mounting portions of the flexible printed circuit. The flexible printed circuit is configured to provide an electrical connection between the first component and the second component.

[0042] According to a fourth aspect, the present application further provides an electronic device comprising a housing and the above-mentioned circuit board assembly. The circuit board assembly is installed inside the housing. [Brief explanation of the drawing]

[0043] [Figure 1] This is a schematic diagram of the structure of a conventional flexible printed circuit. [Figure 2]This is a schematic diagram of the cross-sectional structure of the flexible printed circuit shown in Figure 1, cut along AA. [Figure 3] Figure 1 is a schematic diagram of the partial structure of the flexible printed circuit shown. [Figure 4] This is a schematic diagram of the structure in several embodiments of the flexible printed circuit according to the embodiments of this application. [Figure 5] This is a schematic diagram of the cross-sectional structure of the flexible printed circuit shown in Figure 4, cut along the barbell. [Figure 6] Figure 4 is a schematic diagram of the partial structure of the flexible printed circuit shown. [Figure 7] Figure 5 is a schematic diagram of the partial structure of the trace layer shown. [Figure 8] This is a schematic diagram of the internal structure in several other embodiments of the flexible printed circuit according to the embodiments of this application. [Figure 9] This is a schematic diagram of the internal structure in several other embodiments of the flexible printed circuit according to the embodiments of this application. [Figure 10] Figure 9 is a schematic diagram of the partial structure of the flexible printed circuit shown. [Figure 11] This is a schematic diagram of the internal structure in several other embodiments of the flexible printed circuit according to the embodiments of this application. [Figure 12] This is a schematic diagram of the internal structure in several other embodiments of the flexible printed circuit according to the embodiments of this application. [Figure 13] This is a schematic diagram of the internal structure in several other embodiments of the flexible printed circuit according to the embodiments of this application. [Figure 14] This is a schematic diagram of the internal structure in several other embodiments of the flexible printed circuit according to the embodiments of this application. [Figure 15] This is a schematic diagram of the internal structure in several other embodiments of the flexible printed circuit according to the embodiments of this application. [Figure 16] This is a schematic diagram of the internal structure in several other embodiments of the flexible printed circuit according to the embodiments of this application. [Figure 17] This is a schematic diagram of the structure in several other embodiments of the circuit board assembly according to the embodiments of this application. [Figure 18] Figure 17 is a schematic diagram of the circuit board assembly structure from a different angle. [Figure 19] Figure 17 is a schematic diagram of a partial structure of the circuit board assembly shown. [Figure 20] This is a schematic diagram of the structure in several other embodiments of the circuit board assembly according to the embodiments of this application. [Figure 21] Figure 20 is a schematic diagram of the partial structure of the circuit board assembly shown. [Figure 22] These are schematic diagrams of the structure in several embodiments of a circuit board assembly according to the embodiments of this application. [Figure 23] This is a schematic diagram of the structure in several other embodiments of the circuit board assembly according to the embodiments of this application. [Figure 24] This is a schematic diagram of the structure in several other embodiments of the circuit board assembly according to the embodiments of this application. [Modes for carrying out the invention]

[0044] The technical solutions of the embodiments in this application will be described below with reference to the attached drawings. In the description of the embodiments in this application, unless otherwise specified, " / " means "or". For example, A / B may mean A or B. The terms "and / or" in this specification merely describe an association relationship for describing the related objects, and indicate that three relationships may exist. For example, A and / or B may indicate the following three cases: that only A exists, that both A and B exist, and that only B exists. In addition, in the description of the embodiments in this application, "multiple" means two or more, or in other words, "multiple" means at least two.

[0045] In the description of embodiments of this application, the terms “installation,” “connection,” and “arrangement” should be understood broadly unless otherwise stated or limited. For example, “connection” may be a detachable connection, a non-detachable connection, a direct connection, or an indirect connection via an intermediate medium.

[0046] Terms such as “first,” “second,” etc., are intended solely for explanatory purposes and should not be understood as an indication of relative importance or an implicit indication of the quantity of technical features that are implied or shown. Therefore, features limited by “first” or “second” may explicitly indicate or implicitly include one or more such features.

[0047] Please refer to Figures 1 to 3. Figure 1 is a schematic diagram of the structure of a conventional flexible printed circuit 20 used in a flexible printed circuit structure on a substrate. Figure 2 is a schematic diagram of the cross-sectional structure of the flexible printed circuit 20 shown in Figure 1, cut along AA. Figure 3 is a schematic diagram of a partial structure of the flexible printed circuit 20 shown in Figure 1.

[0048] A conventional flexible printed circuit board 20 includes two soldering portions 20a and a bendable portion 20b connecting the two soldering portions 20a, the bendable portion 20b being able to change shape, for example, bendable. The flexible printed circuit board 20 includes a first protective layer 201, a first conductive layer 202, an insulating layer 203, a second conductive layer 204, and a second protective layer 205, which are stacked in a continuous manner. The first protective layer 201 and the second protective layer 205 are also insulating layers and are sometimes called solder mask layers. The first protective layer 201 and the second protective layer 205 are the two surface layers of the flexible printed circuit board 20. The first conductive layer 202 includes a plurality of pads 2021 and a plurality of traces 2022. The first protective layer 201 is provided with a plurality of openings 2011 to expose the plurality of pads 2021.

[0049] One or more traces 2022 are typically positioned between two adjacent pads 2021. When one trace 2022 is positioned between two adjacent pads 2021, the center distance between the two adjacent pads 2021 includes the radius R of the two pads 2021, two distances S between the edge of the opening 2011 of the first protective layer 201 and the pad 2021, two distances S1 and S2 between the edge of the opening 2011 and the trace 2022, and the width W of the trace 2022. In other words, center distance between two adjacent pads 2021 = 2R + 2S + S1 + S2 + W. For some products, taking minimum values ​​as an example, considering the general processing capacity of current flexible printed circuits 20 in the industry, R is 0.15 mm, S is 0.075 mm, both S1 and S2 are 0.075 mm, and W is 0.1 mm. In this case, the pad spacing is greater than 0.7 mm. Such large pad spacing leads to a large surface area of ​​the soldering portion 20a and a large volume of the flexible printed circuit 20.

[0050] This application provides a flexible printed circuit. A soldering layer, on which only pads are placed and traces are not, is added to the soldering portion of the flexible printed circuit, and a solder mask-less design is used, thereby the pad spacing of the soldering layer is not limited by structures such as traces and solder mask openings. The pad spacing is significantly reduced, thereby reducing the surface area of ​​the soldering portion and making it possible to miniaturize the flexible printed circuit. This application further provides a circuit board assembly including the above flexible printed circuit, and an electronic device including the above circuit board assembly.

[0051] Please refer to Figures 4 to 6. Figure 4 is a schematic diagram of the structure of several embodiments of the flexible printed circuit 1 according to the embodiments of this application. Figure 5 is a schematic diagram of the cross-sectional structure of the flexible printed circuit 1 shown in Figure 4, cut along BB. Figure 6 is a schematic diagram of the partial structure of the flexible printed circuit 1 shown in Figure 4.

[0052] In some embodiments, the flexible printed circuit 1 includes a bendable portion 1a and a soldered portion 1b connected to the bendable portion 1a. The flexible printed circuit 1 may be an integrally formed mechanical part, and the bendable portion 1a and the soldered portion 1b are two parts of the flexible printed circuit 1. The bendable portion 1a can change shape, for example, it can be bent, thereby allowing the flexible printed circuit 1 to change shape. The flexible printed circuit 1 may be soldered to another component (e.g., a printed circuit board) by using the soldered portion 1b, in other words, the soldered portion 1b is configured to connect to another component to realize an electrical connection to that component. There may be two soldered portions 1b. The two soldered portions 1b may be connected to the two ends of the bendable portion 1a, respectively. The two soldered portions 1b may be soldered to different components, respectively. The flexible printed circuit 1 can realize an electrical connection between different components.

[0053] The flexible printed circuit 1 includes a plurality of conductive layers 11 and a plurality of insulating layers 12. The plurality of conductive layers 11 and the plurality of insulating layers 12 are stacked, and the insulating layers 12 are placed between two adjacent conductive layers 11. The conductive layers 11 are configured to provide a conductive function and may be manufactured from a conductive material such as copper foil. The insulating layers 12 are configured to provide an insulating function and may be manufactured from an insulating material such as polyimide (PI). The insulating layers 12 can electrically insulate adjacent conductive layers 11.

[0054] A bonding layer (not shown in the figure) may be placed between the conductive layer 11 and the insulating layer 12 to achieve mutual fixation, or a bonding layer may not be placed, and the conductive layer 11 and the insulating layer 12 may be in direct contact with each other and fixed together. The decision of whether or not to place a bonding layer between the conductive layer 11 and the adjacent insulating layer 12 may be the same or different. The method and structure for fixing multiple conductive layers 11 and multiple insulating layers 12 are not strictly limited in this embodiment of the present application.

[0055] For example, the multiple conductive layers 11 include a first soldering layer 111, a second soldering layer 112, and a trace layer 113.

[0056] Both the first soldering layer 111 and the second soldering layer 112 are conductive layers, and are configured to solder another component to achieve an electrical connection between the flexible printed circuit 1 and this other component. Both the first soldering layer 111 and the second soldering layer 112 are located on the soldering portion 1b. The first soldering layer 111 is one surface layer of the soldering portion 1b, and the first soldering layer 111 is formed by a plurality of first pads 1111 that are spaced apart from each other. In this embodiment of the present application, the spacing of the two structures means that the two structures are separated by a certain distance and a gap is formed between the two structures. The plurality of first pads 1111 may be arranged in an array or in another arrangement. The second soldering layer 112 is the other surface layer of the soldering portion 1b, and the second soldering layer 112 is formed by a plurality of second pads 1121 that are spaced apart from each other. The plurality of second pads 1121 may be arranged in an array or in another arrangement. In this embodiment of the present application, the surface layer of the soldering portion 1b is the outermost layer structure of the soldering portion 1b, and the “outside” of the flexible printed circuit 1 is the orientation closer to the external space.

[0057] The trace layer 113 is a conductive layer, and at least traces are placed on the trace layer 113 to enable electrical signal transmission through the traces. The electrical signals may include, but are not limited to, one or more of power signals, ground signals, and data signals. The trace layer 113 is located between the first soldering layer 111 and the second soldering layer 112 and extends from the soldering portion 1b to the bending portion 1a. There may be one or more trace layers 113. When there are multiple trace layers 113, an insulating layer is placed between two adjacent trace layers 113.

[0058] The first pad 1111 and the second pad 1121 are connected by using a through-hole conductor 13, and the through-hole conductor 13 is connected to the trace layer 113. In this case, the first pad 1111 and the second pad 1121 can be electrically connected by using the through-hole conductor 13, and can also be electrically connected to the trace layer 113 by using the through-hole conductor 13.

[0059] For example, the number of first pads 1111 and the number of second pads 1121 may be the same. Multiple first pads 1111 and multiple second pads 1121 may be arranged in a one-to-one correspondence, and the corresponding first pads 1111 and second pads 1121 are connected by using through-hole conductors 13. The corresponding first pads 1111 and second pads 1121 may be the same or similar in shape and size. The through-hole conductors 13 may be a conductive layer structure formed in the through-hole wall, or a conductive pillar structure filled in the through-hole. This is not strictly limited to this embodiment of the present application.

[0060] In some other embodiments, the number of first pads 1111 and the number of second pads 1121 may differ. Some first pads 1111 and some second pads 1121 may be arranged in correspondence, or some first pads 1111 and all second pads 1121 may be arranged in correspondence, or all first pads 1111 and some second pads 1121 may be arranged in correspondence. The corresponding first pads 1111 and second pads 1121 may also be connected by using through-hole conductors 13.

[0061] For example, the multiple insulating layers 12 include a first insulating layer 121 and a second insulating layer 122. The first insulating layer 121 is located between the first soldering layer 111 and the adjacent trace layer 113 and extends from the soldering portion 1b to the bent portion 1a. A portion of the first insulating layer 121 located at the soldering portion 1b insulates the first soldering layer 111 from the adjacent trace layer 113. A portion of the first insulating layer 121 located at the bent portion 1a forms one surface layer of the bent portion 1a and forms a protective layer configured to protect the internal structure of the bent portion 1a.

[0062] The second insulating layer 122 is located between the second soldering layer 112 and the adjacent trace layer 113, and extends from the soldering portion 1b to the bent portion 1a. A portion of the second insulating layer 122 located at the soldering portion 1b insulates the second soldering layer 112 from the adjacent trace layer 113. A portion of the second insulating layer 122 located at the bent portion 1a forms the other surface layer of the bent portion 1a, forming a protective layer configured to protect the internal structure of the bent portion 1a.

[0063] Please refer to Figures 5 to 7. Figure 7 is a schematic diagram of the substructure of the trace layer 113 shown in Figure 5.

[0064] In some embodiments, the trace layer 113 includes a conductor block 1131 and a trace 1132. The conductor block 1131 is located at the soldering portion 1b. One end of the trace 1132 is connected to the conductor block 1131, and the other end extends to the bend portion 1a. The first pad 1111 and the second pad 1121 are connected to the conductor block 1131 by using a through-hole conductor 13. The first pad 1111 and the second pad 1121 may be electrically connected to another part or component of the flexible printed circuit 1 by using the conductor block 1131 and the trace 1132.

[0065] In this embodiment, when the first soldering layer 111 and the second soldering layer 112 are used as two surface layers of the soldering portion 1b, only the first pad 1111 is placed on the first soldering layer 111 and no trace is placed, and only the second pad 1121 is placed on the second soldering layer 112 and no trace is placed. Therefore, a protective layer (or referred to as a solder mask layer) does not need to be placed outside the first soldering layer 111 and the second soldering layer 112 in the soldering portion 1b, and a solder mask opening structure does not need to be placed. This makes it possible to implement a solder mask-free design, and the pad spacing in the soldering portion 1b (i.e., the spacing between two adjacent first pads 1111 and the spacing between two adjacent second pads 1121) is not limited by structures such as traces and solder mask openings. Compared to the pad spacing in conventional technology, the pad spacing is significantly reduced, thereby reducing the surface area of ​​the soldering portion 1b and facilitating miniaturization of the flexible printed circuit 1. In addition, the traces of the flexible printed circuit 1 are placed on the trace layer 113, which is the inner layer structure of the flexible printed circuit 1 and is covered by an insulating layer 12 or a protective layer. This helps to improve the circuit reliability of the flexible printed circuit 1.

[0066] In addition, compared to conventional products, the flexible printed circuit 1 in this application arranges multiple pads separately on the soldering layer. The soldering layer may increase the number of conductive layers (for example, one conductive layer is added to the structure in the embodiment shown in Figure 5 compared to the structure shown in Figure 2). However, since the thickness of the conductive layer 11 is extremely small, for example, the thickness of the current copper foil layer is typically 0.25 micrometers, the overall increase in thickness of the flexible printed circuit 1 in this application is small and controllable and does not cause any obvious adverse effects or obvious obstacles to the miniaturization of both the circuit board assembly and the electronic device using the flexible printed circuit 1.

[0067] Both the conductor block 1131 and the trace 1132 are conductive components. The conductor block 1131 is configured to electrically connect the first pad 1111 and the second pad 1121 by using the through-hole conductor 13, and may be further configured to electrically connect the internal conductive structure of the flexible printed circuit 1 (e.g., the trace 1132). In this case, the flexible printed circuit 1 can be electrically connected to other components by using the first pad 1111 and the second pad 1121.

[0068] In some embodiments, the shape of the conductor block 1131 may be the same as or similar to the shape of the first pad 1111, for example, both being circular. For example, the area of ​​the conductor block 1131 is the same as the area of ​​the first pad 1111. As shown in Figure 5, the center distance between two adjacent first pads 1111 includes the radius R of the two first pads 1111, the width W of the trace 1132, and two distances S3 and S4 between the first pad 1111 and the trace 1132, in other words, the center distance between two adjacent first pads 1111 = 2R + W + S3 + S4. In some products with the same processing capacity, taking minimum values ​​as an example, R is 0.15 mm, S is 0.075 mm, both S3 and S4 are 0.075 mm, and W is 0.1 mm. In this case, the pad spacing in the soldering portion 1b is reduced to 0.55 mm. Compared to the pad spacing in conventional solutions, the pad spacing in this application can be reduced by approximately 22%. In a structure in which multiple pads are arranged in an array, the surface area of ​​the soldering portion 1b of the flexible printed circuit 1 in this application may be approximately 40% smaller than the surface area of ​​the soldering portion of conventional products. The significantly reduced surface area of ​​the soldering portion 1b can facilitate miniaturization of the flexible printed circuit 1 and both the circuit board assembly and electronic devices using the flexible printed circuit 1.

[0069] Figure 8 is a schematic diagram of the internal structure of several other embodiments of the flexible printed circuit 1 according to the embodiments of this application. The flexible printed circuit 1 shown in this embodiment may include most of the technical features of the embodiments described above. Below, we will mainly describe the differences between the flexible printed circuit 1 in the embodiments described above and that in this embodiment, skipping over the common features.

[0070] In some embodiments, the area of ​​the conductor block 1131 may be smaller than the area of ​​the first pad 1111. In this embodiment, the locations of the first pad 1111 and the second pad 1121 are limited by the arrangement of the conductor block 1131, as the first pad 1111 and the second pad 1121 are connected to the conductor block 1131 by using the through-hole conductor 13. The area of ​​the conductor block 1131 is smaller than the area of ​​the first pad 1111, and thus the area of ​​the conductor block 1131 can be set to a small value when the internal connection requirement (i.e., the conductor block is connected to the through-hole conductor 13) is met. In this way, when the trace layer 113 meets the arrangement requirement for the trace 1132, the spacing between two adjacent conductor blocks 1131 can be relatively small. In that case, the center spacing between two adjacent first pads 1111 is relatively small. This makes it possible to further reduce the pad spacing in the soldering portion 1b, which facilitates miniaturization of the flexible printed circuit 1.

[0071] Please refer to Figures 9 and 10. Figure 9 is a schematic diagram of the internal structure of several other embodiments of the flexible printed circuit 1 according to the embodiments of this application. Figure 10 is a schematic diagram of a partial structure of the flexible printed circuit 1 shown in Figure 9. The flexible printed circuit 1 shown in this embodiment may include most of the technical features of the embodiments described above. Below, we will mainly describe the differences between the flexible printed circuit 1 in the embodiments described above and that in this embodiment, skipping over the common features.

[0072] In some embodiments, the flexible printed circuit 1 may have multiple trace layers 113, for example, two, three, or four layers. In this embodiment, two layers are used as an example for explanatory and illustrative purposes. Multiple conductor blocks 1131 connected to multiple first pads 1111 may be distributed on different trace layers 113. For example, conductor blocks 1131 connected to at least two of the multiple first pads 1111 may be located on different trace layers 113. For example, the multiple first pads 1111 include a first first pad and a second first pad. The first first pad is connected to a first conductor block, and the first conductor block is located on the first trace layer. The second first pad is connected to a second conductor block, and the second conductor block is located on the second trace layer. The terms "first" and "second" above are descriptive for distinguishing two structures and do not constitute a limitation of sequence, importance, or any other limitation.

[0073] It can be understood that a trace layer 113 placed on a conductor block 1131 also needs to be provided with traces 1132 connected to the conductor block 1131. Therefore, when multiple conductor blocks 1131 connected to multiple first pads 1111 are centrally located on a particular trace layer 113 of the flexible printed circuit 1, the trace layer 113 has relatively high trace placement requirements. As a result, the space on the trace layer 113 is insufficient, and trace placement is difficult. When conductor blocks 1131 connected to at least two of the multiple first pads 1111 are located on different trace layers 113, the traces 1132 connected to the conductor blocks 1131 can also be distributed across different trace layers 113. This reduces the difficulty of routing the trace layer 113 and improves routing flexibility.

[0074] In some embodiments, the soldering portion 1b of the flexible printed circuit 1 is provided with a plurality of punctured regions, and a plurality of through-hole conductors 13 penetrate the plurality of punctured regions in a one-to-one correspondence. The first soldering layer 111, the second soldering layer 112, and the trace layer 113 are each provided with a plurality of corresponding punctured regions. A punctured region includes the space occupied by the through-hole conductors 13 and the space within a specific range around the through-hole conductors 13. For example, a plurality of first pads 1111 are arranged in a plurality of punctured regions of the first soldering layer 111, and a plurality of through-hole conductors 13 penetrate the plurality of first pads 1111 and are connected to the first pads 1111. A plurality of second pads 1121 are arranged in a plurality of punctured regions of the second soldering layer 112, and a plurality of through-hole conductors 13 penetrate the plurality of second pads 1121 and are connected to the second pads 1121.

[0075] There may be one or more trace layers 113. Each trace layer 113 is provided with multiple punctured regions. Support blocks are placed in the punctured regions, and multiple through-hole conductors 13 penetrate the multiple punctured regions in a one-to-one correspondence. The through-hole conductors 13 penetrate and are connected to the support blocks. For example, as shown in Figure 5, when there is one trace layer 113 and multiple conductor blocks 1131 connected to multiple first pads 1111 are all located on the trace layer 113, the support blocks in the punctured regions of the trace layer 113 are the conductor blocks 1131, and the through-hole conductors 13 penetrate and are connected to the conductor blocks 1131. As shown in Figure 9, when there are multiple trace layers 113 and multiple conductor blocks 1131 connected to multiple first pads 1111 are distributed on different trace layers 113, the supporting blocks in the multiple punctured regions of the trace layer 113 can be either conductor blocks 1131 or lower pads 1133 (target pads). In other words, when there are multiple trace layers 113, if conductor blocks 1131 are not placed in the punctured regions of the trace layer 113, then lower pads 1133 are placed. Both lower pads 1133 and conductor blocks 1131 are essentially conductor structures. The difference between lower pads 1133 and conductor blocks 1131 is that lower pads 1133 are not connected to traces and are a suspension structure in the transmission circuit of the flexible printed circuit 1, while conductor blocks 1131 are connected to traces 1132 and are part of the transmission circuit. The area of ​​lower pads 1133 may be larger than, smaller than, or equal to the area of ​​conductor blocks 1131. This is not strictly limited to this embodiment of the present application.

[0076] In this embodiment, since support blocks (conductor blocks 1131 or lower pads 1133) are placed in the punctured regions of each trace layer 113 of the flexible printed circuit 1, the overall support structure of each punctured region of the flexible printed circuit 1 is stable and less likely to collapse. In addition, the thickness of the multiple punctured regions of the flexible printed circuit 1 can be consistent. This facilitates batch punching and metal filling, improving the production efficiency and yield of the flexible printed circuit 1.

[0077] In the above embodiment, when the number of trace layers 113 of the flexible printed circuit 1 is relatively small (for example, one layer, two layers, or three layers), the thickness of the bent portion 1a of the flexible printed circuit 1 is extremely small, thereby ensuring bending performance, allowing the flexible printed circuit 1 to meet diverse installation environments, and thus providing better reliability. In some other embodiments, the number of trace layers 113 of the flexible printed circuit 1 may be relatively large as an alternative to meet routing requirements such as multiple transmission channels.

[0078] Figure 11 is a schematic diagram of the internal structure of several other embodiments of the flexible printed circuit 1 according to the embodiments of this application. The flexible printed circuit 1 shown in this embodiment may include most of the technical features of the embodiments described above. Below, we will mainly describe the differences between the flexible printed circuit 1 in the embodiments described above and that in this embodiment, skipping over the common features.

[0079] In some embodiments, the conductive layers 11 further include a first routing layer 114 and a second routing layer 115. Both the first routing layer 114 and the second routing layer 115 are located in the bent portion 1a. The first routing layer 114 and the first soldering layer 111 are located on the same layer. The first routing layer 114 is a conductive layer and has at least one or more traces to enable electrical signal transmission through the traces. The second routing layer 115 and the second soldering layer 112 are located on the same layer. The second routing layer 115 is a conductive layer and has at least one or more traces to enable electrical signal transmission through the traces. The first routing layer 114 and / or the second routing layer 115 may be electrically connected to a trace layer 113.

[0080] The flexible printed circuit 1 further includes a first protective layer 141 and a second protective layer 142. Both the first protective layer 141 and the second protective layer 142 are located on the bend portion 1a. The first protective layer 141 is located on the side of the first routing layer 114 away from the trace layer 113. The second protective layer 142 is located on the side of the second routing layer 115 away from the trace layer 113. The first protective layer 141 and the second protective layer 142 are two surface layers of the bend portion 1a. Both the first protective layer 141 and the second protective layer 142 are insulating layers and are configured to protect the internal structure of the flexible printed circuit 1. The first protective layer 141 and the second protective layer 142 are sometimes called solder mask layers.

[0081] In this embodiment, the first routing layer 114 and the second routing layer 115 are positioned in the bent portion 1a of the flexible printed circuit 1. The first routing layer 114, the second routing layer 115, and the trace layer 113 can all be configured for trace placement. Thus, the flexible printed circuit 1 can better satisfy routing requirements such as multiple transmission channels.

[0082] Figure 12 is a schematic diagram of the internal structure of several other embodiments of the flexible printed circuit 1 according to the embodiments of this application. The flexible printed circuit 1 shown in this embodiment may include most of the technical features of the embodiments described above. Below, we will mainly describe the differences between the flexible printed circuit 1 in the embodiments described above and that in this embodiment, skipping over the common features.

[0083] In some embodiments, when the flexible printed circuit 1 has two or more conductive layers 11, at least one insulating layer 12 of the flexible printed circuit 1 may form an air gap in the bent portion 1a. In other words, the bent portion 1a of the flexible printed circuit 1 forms one or more air gaps. In this way, the structures of the flexible printed circuit 1 located on both sides of the air gap can move relatively independently, improving the bending performance of the bent portion 1a of the flexible printed circuit 1.

[0084] For example, the flexible printed circuit 1 may have a four-layer substrate structure. The multiple conductive layers 11 of the flexible printed circuit 1 may include a first routing layer 114, a second routing layer 115, and two trace layers 113. An insulating layer 12 located between the two trace layers 113 may form an air gap 121 in the bent portion 1a. The insulating layer 12 located between the two trace layers 113 may include a first insulating sub-layer 122 and a second insulating sub-layer 123. Parts of the first insulating sub-layer 122 and parts of the second insulating sub-layer 123 in the soldering portion 1b may be press-fitted and fixed by using adhesive on both the first insulating sub-layer 122 and the second insulating sub-layer 123. The adhesive on both parts of the first insulating sub-layer 122 and parts of the second insulating sub-layer 123 in the bent portion 1a may be removed or omitted. The air gap 121 is formed between a portion of the first insulating sublayer 122 in the bent portion 1a and a portion of the second insulating sublayer 123 in the bent portion 1a.

[0085] In some other embodiments, when the multiple conductive layers 11 of the flexible printed circuit 1 do not include a first routing layer 114 and a second routing layer 115 but include multiple trace layers 113, one or more air gaps may be formed in the bent portion 1a, thereby improving the bending performance of the bent portion 1a of the flexible printed circuit 1.

[0086] When the flexible printed circuit 1 has two or more conductive layers 11, it may be understood that the stack structure of the flexible printed circuit 1 can be implemented in multiple ways. For example, when there are three conductive layers 11, the bent portion 1a can form a single-layer + double-layer stack structure by using one air gap, or a single-layer + single-layer + single-layer stack structure by using two air gaps. When there are four conductive layers 11, the bent portion 1a can form a double-layer + double-layer stack structure by using one air gap, or a single-layer + double-layer + single-layer stack structure by using two air gaps, or a single-layer + single-layer + single-layer + single-layer stack structure by using three air gaps. The number of conductive layers 11 of the flexible printed circuit 1 and the specific stack structure are not strictly limited in this embodiment of the present application.

[0087] Figure 13 is a schematic diagram of the internal structure of several other embodiments of the flexible printed circuit 1 according to the embodiment of this application.

[0088] In some embodiments, the flexible printed circuit 1 includes a bendable portion 1a and a soldered portion 1b connected to the bendable portion 1a. The flexible printed circuit 1 may also be a integrally formed mechanical portion, and the bendable portion 1a and the soldered portion 1b are two parts of the flexible printed circuit 1. The bendable portion 1a can change shape, for example, it can be bent, thereby allowing the flexible printed circuit 1 to change shape. The flexible printed circuit 1 may be soldered to another component (e.g., a printed circuit board) using the soldered portion 1b, in other words, the soldered portion 1b is configured to connect to another component to realize an electrical connection to that component. There may be two soldered portions 1b. The two soldered portions 1b may be connected to the two ends of the bendable portion 1a, respectively. The two soldered portions 1b may be soldered to different components, respectively. The flexible printed circuit 1 can realize an electrical connection between these different components.

[0089] In the above embodiment, the surface layers on both sides of the soldering portion 1b of the flexible printed circuit 1 form a soldering structure. In this embodiment, the surface layer on the side of the soldering portion 1b of the flexible printed circuit 1 forms a soldering structure, while the surface layer on the other side does not form a soldering structure. Specifically, it is as follows.

[0090] The flexible printed circuit 1 includes a plurality of conductive layers 15, a plurality of insulating layers 16, and a first protective layer 171. The plurality of conductive layers 15, the plurality of insulating layers 16, and the first protective layer 171 are stacked, and the insulating layers 16 are placed between two adjacent conductive layers 15. The conductive layers 15 are configured to provide a conductive function and may be manufactured from a conductive material such as copper foil. The insulating layers 16 are configured to provide an insulating function and may be manufactured from an insulating material such as polyimide (PI). The insulating layers 16 can electrically insulate adjacent conductive layers 15.

[0091] A bonding layer (not shown in the figure) may be placed between the conductive layer 15 and the insulating layer 16 to achieve mutual fixation, or a bonding layer may not be placed, and the conductive layer 15 and the insulating layer 16 may be in direct contact with each other and fixed. The decision of whether or not to place a bonding layer between the conductive layer 15 and the adjacent insulating layer 16 may be the same or different. The method and structure for fixing multiple conductive layers 15 and multiple insulating layers 16 are not strictly limited in this embodiment of the present application.

[0092] For example, the multiple conductive layers 15 include a soldering layer 151 and a trace layer 152.

[0093] The soldering layer 151 is a conductive layer and is configured to solder another component to achieve an electrical connection between the flexible printed circuit 1 and this other component. The soldering layer 151 is located on the soldering portion 1b and is one surface layer of the soldering portion 1b. The soldering layer 151 is formed by a plurality of pads 1511 that are spaced apart from each other. The plurality of pads 1511 may be arranged in an array or in another arrangement.

[0094] The trace layer 152 is a conductive layer, and at least traces are arranged on the trace layer 152 to enable electrical signal transmission through the traces. The electrical signals may include, but are not limited to, one or more of power signals, ground signals, and data signals. The trace layer 152 is located on the side of the soldering layer 151 and extends from the soldering portion 1b to the bending portion 1a. There may be one or more trace layers 152. When there are multiple trace layers 152, an insulating layer is arranged between two adjacent trace layers 152. The pad 1511 is connected to the trace layer 152 by using a through-hole conductor 18. The through-hole conductor 18 may be a conductive layer structure formed on the through-hole wall, or a conductive pillar structure filled in the through-hole. This is not strictly limited to this embodiment of the present application.

[0095] The trace layer 152 may include a conductor block 1521 and a trace 1522. The conductor block 1521 is located at the soldering portion 1b. One end of the trace 1522 is connected to the conductor block 1521, and the other end extends to the bend portion 1a. The pad 1511 of the soldering layer 151 is connected to the conductor block 1521 by using a through-hole conductor 18, and the pad 1511 may be electrically connected to another part or component of the flexible printed circuit 1 by using the conductor block 1521 and the trace 1522.

[0096] The first protective layer 171 is located on the side of the trace layer 152 that is away from the soldering layer 151. The first protective layer 171 extends from the soldering portion 1b to the bending portion 1a. A portion of the first protective layer 171 located at the soldering portion 1b forms the other surface layer of the soldering portion 1b. A portion of the first protective layer 171 located at the bending portion 1a forms one surface layer of the bending portion 1a. The first protective layer 171 is also an insulating layer, sometimes called a solder mask layer, and is configured to protect the internal structure of the flexible printed circuit 1. No soldering structure is provided on the side of the first protective layer 171 at the soldering portion 1b. The soldering portion 1b does not need to have structures such as traces and solder mask openings on the first protective layer 171. The first protective layer 171 can be a continuous and complete surface structure.

[0097] The multiple insulating layers 16 may include a first insulating layer 161. The first insulating layer 161 is located between the soldering layer 151 and the adjacent trace layer 152 and extends from the soldering portion 1b to the bent portion 1a. A portion of the first insulating layer 161 located at the bent portion 1a forms the other surface layer of the bent portion 1a. The portion of the first insulating layer 161 located at the soldering portion 1b is configured to insulate the soldering layer 151 from the trace layer 152.

[0098] In this embodiment, the soldering layer 151 is used as one surface layer of the soldering portion 1b, and only pads 1511 are placed on the soldering layer 151, with no traces. Therefore, the soldering portion 1b does not require a protective layer (or called a solder mask layer) outside the soldering layer 151, and a solder mask opening structure does not need to be placed. This makes it possible to realize a solder mask-free design, and the pad spacing in the soldering portion 1b is not limited by structures such as traces and solder mask openings. Compared to the pad spacing in the conventional art, the pad spacing is significantly reduced, thereby reducing the surface area of ​​the soldering portion 1b and making it possible to miniaturize the flexible printed circuit 1.

[0099] In addition, compared to conventional products, the flexible printed circuit 1 in this application arranges multiple pads separately on the soldering layer. The soldering layer may increase the number of conductive layers. However, since the thickness of the conductive layers is extremely small, for example, the thickness of the current copper foil layer is typically 0.25 micrometers, the overall increase in thickness of the flexible printed circuit 1 in this application is small and controllable and does not cause any obvious adverse effects or obvious obstacles to the miniaturization of both the circuit board assembly and the electronic device using the flexible printed circuit 1.

[0100] In some embodiments, the shape of the conductor block 1521 may be the same as or similar to the shape of the pad 1511, for example, both being circular. For example, the area of ​​the conductor block 1521 is the same as the area of ​​the pad 1511. As shown in Figure 13, the center distance between two adjacent pads 1511 includes the radius R of the two pads 1511, the width W of the trace, and two distances S3 and S4 between the pad 1511 and the trace, in other words, center distance between two adjacent pads 1511 = 2R + W + S3 + S4. In some products, the same processing capacity and minimum values ​​are used as an example. R is 0.15 mm, S is 0.075 mm, both S3 and S4 are 0.075 mm, and W is 0.1 mm. In this case, the pad spacing is reduced to 0.55 mm. Compared to the pad spacing in conventional solutions, the pad spacing in this application can be reduced by only about 22%. In a structure in which multiple pads 1511 are arranged in an array, the surface area of ​​the soldering portion 1b of the flexible printed circuit 1 in this application may be approximately 40% smaller than the surface area of ​​the soldering portion of conventional products. The significantly reduced surface area of ​​the soldering portion 1b can facilitate miniaturization of the flexible printed circuit 1 and both the circuit board assembly and electronic devices using the flexible printed circuit 1.

[0101] In some other embodiments, the area of ​​the conductor block 1521 may be smaller than the area of ​​the pad 1511. In this embodiment, the location of the pad 1511 is limited by the arrangement of the conductor block 1521, since the pad 1511 is connected to the conductor block 1521 by using the through-hole conductor 18. The area of ​​the conductor block 1521 is smaller than the area of ​​the pad 1511, and thus the area of ​​the conductor block 1521 can be set to a small value when the internal connection requirement (i.e., the conductor block 1521 is connected to the through-hole conductor 18) is met. In this way, when the trace layer 152 satisfies the trace arrangement, the spacing between two adjacent conductor blocks 1521 can be relatively small. In that case, the center spacing between two adjacent pads 1511 is relatively small. This makes it possible to further reduce the pad spacing in the soldering portion 1b, which facilitates miniaturization of the flexible printed circuit 1.

[0102] Figure 14 is a schematic diagram of the internal structure of several other embodiments of the flexible printed circuit 1 according to the embodiments of this application. The flexible printed circuit 1 shown in this embodiment may include most of the technical features of the embodiments described above. Below, we will mainly describe the differences between the flexible printed circuit 1 in the embodiments described above and that in this embodiment, skipping over the common features.

[0103] In some embodiments, the flexible printed circuit 1 may have multiple trace layers 152, for example, two, three, or four layers. In this embodiment, two layers are used as an example for explanation and illustration. Two conductor blocks 1521 connected to two adjacent pads 1511 may be located on different trace layers 152. Multiple conductor blocks 1521 connected to multiple pads 1511 may be distributed on different trace layers 152. For example, conductor blocks 1521 connected to at least two of the multiple pads 1511 may be located on different trace layers 152. For example, the multiple pads 1511 include a first pad and a second pad. The first pad is connected to a first conductor block, and the first conductor block is located on the first trace layer. The second pad is connected to a second conductor block, and the second conductor block is located on the second trace layer. The terms "first" and "second" above are merely descriptive to distinguish between the two structures and do not constitute a limitation of sequence, importance, or any other limitation.

[0104] It may be understood that a trace layer 152 placed on a conductor block 1521 also needs to accommodate traces 1522 connected to the conductor block 1521. Therefore, when multiple conductor blocks 1521 connected to multiple pads 1511 are centrally located on a particular trace layer 152 of the flexible printed circuit 1, the trace layer 152 has relatively high trace placement requirements. As a result, the space on the trace layer 152 is insufficient, and trace placement is difficult. When conductor blocks 1521 connected to at least two of the multiple pads 1511 are located on different trace layers 152, the traces 1522 connected to the conductor blocks 1521 can also be distributed across different trace layers 152. This reduces the difficulty of routing the trace layer 152 and improves routing flexibility.

[0105] In some embodiments, the soldering portion 1b of the flexible printed circuit 1 is provided with a plurality of punctured regions, and a plurality of through-hole conductors 18 penetrate the plurality of punctured regions in a one-to-one correspondence. The soldering layer 151 and the trace layer 152 are each provided with a plurality of corresponding punctured regions. A punctured region includes the space occupied by the through-hole conductors 18 and the space within a specific range around the through-hole conductors 18. For example, a plurality of pads 1511 are arranged in a plurality of punctured regions of the soldering layer 151, and a plurality of through-hole conductors 18 penetrate the plurality of pads 1511 and are connected to the pads 1511.

[0106] There may be one or more trace layers 152. Each trace layer 152 is provided with multiple punctured regions. Support blocks are placed in the punctured regions, and multiple through-hole conductors 18 penetrate the multiple punctured regions in a one-to-one correspondence. The through-hole conductors 18 penetrate and are connected to the support blocks. For example, as shown in Figure 13, when there is one trace layer 152 and multiple conductor blocks 1521 connected to multiple pads 1511 are all located on the trace layer 152, the support blocks in the punctured regions of the trace layer 152 are the conductor blocks 1521, and the through-hole conductors 18 penetrate and are connected to the conductor blocks 1521. As shown in Figure 14, when there are multiple trace layers 152 and multiple conductor blocks 1521 connected to multiple pads 1511 are distributed on different trace layers 152, the supporting blocks in the multiple punctured regions of the trace layer 152 can be either the conductor blocks 1521 or the lower pad 1523 (target pad). In other words, when there are multiple trace layers 152, if the conductor blocks 1521 are not placed in the punctured regions of the trace layer 152, the lower pad 1523 is placed there. Both the lower pad 1523 and the conductor block 1521 are essentially conductor structures. The difference between the lower pad 1523 and the conductor block 1521 is that the lower pad 1523 is not connected to the traces and is a suspension structure in the transmission circuit of the flexible printed circuit 1, while the conductor block 1521 is connected to the traces 1522 and is part of the transmission circuit. The area of ​​the lower pad 1523 may be larger than, smaller than, or equal to the area of ​​the conductor block 1521. This is not strictly limited to this embodiment of the present application.

[0107] In this embodiment, since support blocks (conductor blocks 1521 or lower pads 1523) are placed in the punctured regions of each trace layer 152 of the flexible printed circuit 1, the overall support structure of each punctured region of the flexible printed circuit 1 is stable and less likely to collapse. In addition, the thickness of the multiple punctured regions of the flexible printed circuit 1 can be consistent. This facilitates batch punching and metal filling, improving the production efficiency and yield of the flexible printed circuit 1.

[0108] When there are multiple trace layers 152, it may be understood that some of the multiple through-hole conductors 18 do not necessarily penetrate all of the trace layers 152, but may penetrate some of them. For example, as shown in Figure 14, there are two trace layers 152, some through-hole conductors 18 penetrate both trace layers 152, and some through-hole conductors 18 penetrate one trace layer 152. In this case, the number of punctured areas of the different trace layers 152 may differ, and consequently, the number of support blocks placed in the punctured areas may differ. The through-hole conductors 18 do not penetrate all of the trace layers 152. Trace layers 152 not penetrated by the through-hole conductors 18 may contain support areas. The support areas are placed in correspondence with the punctured areas of the other trace layers 152 penetrated by the through-hole conductors 18. Support blocks may also be placed in the support areas to improve the support strength of the flexible printed circuit 1 corresponding to the through-hole conductors 18.

[0109] In the above embodiment, when the number of trace layers 152 of the flexible printed circuit 1 is relatively small (for example, one layer, two layers, or three layers), the thickness of the bent portion 1a of the flexible printed circuit 1 is extremely small, thereby ensuring bending performance, allowing the flexible printed circuit 1 to meet diverse installation environments, and it may be understood that reliability is better. In some other embodiments, the number of trace layers 152 of the flexible printed circuit 1 may be relatively large as an alternative to meet routing requirements such as multiple transmission channels.

[0110] Figure 15 is a schematic diagram of the internal structure of several other embodiments of the flexible printed circuit 1 according to the embodiments of this application. The flexible printed circuit 1 shown in this embodiment may include most of the technical features of the embodiments described above. Below, we will mainly describe the differences between the flexible printed circuit 1 in the embodiments described above and that in this embodiment, skipping over the common features.

[0111] In some embodiments, the conductive layers 15 further include a routing layer 153 located on the bent portion 1a, and the routing layer 153 and the soldering layer 151 are arranged on the same layer. The routing layer 153 is a conductive layer and has at least one or more traces arranged thereon to enable electrical signal transmission through the traces. The routing layer 153 is manufactured from a conductive material such as copper foil. The routing layer 153 may be electrically connected to the trace layer 152.

[0112] The flexible printed circuit 1 further includes a second protective layer 172. The second protective layer 172 is located on the side of the routing layer 153 that is away from the trace layer 152. The second protective layer 172 is located on the bend portion 1a and is the other surface layer of the bend portion 1a. The second protective layer 172 is an insulating layer configured to protect the internal structure of the flexible printed circuit 1 and is sometimes called a solder mask layer.

[0113] In this embodiment, the routing layer 153 is located in the bent portion 1a of the flexible printed circuit 1. Both the routing layer 153 and the trace layer 152 can be configured for trace placement. Thus, the flexible printed circuit 1 can better satisfy routing requirements such as multiple transmission channels.

[0114] Figure 16 is a schematic diagram of the internal structure of several other embodiments of the flexible printed circuit 1 according to the embodiments of this application. The flexible printed circuit 1 shown in this embodiment may include most of the technical features of the embodiments described above. Below, we will mainly describe the differences between the flexible printed circuit 1 in the embodiments described above and that in this embodiment, skipping over the common features.

[0115] In some embodiments, when the flexible printed circuit 1 has two or more conductive layers 15, at least one insulating layer 16 of the flexible printed circuit 1 may form an air gap in the bent portion 1a. In other words, the bent portion 1a of the flexible printed circuit 1 forms one or more air gaps. In this way, the structures of the flexible printed circuit 1 located on both sides of the air gap can move relatively independently, improving the bending performance of the bent portion 1a of the flexible printed circuit 1.

[0116] For example, the flexible printed circuit board 1 may have a three-layer structure. The multiple conductive layers 15 of the flexible printed circuit board 1 may include a routing layer 153 and two trace layers 152. An insulating layer 16 located between the two trace layers 152 may form an air gap 161 in the bent portion 1a. The insulating layer 16 located between the two trace layers 152 may include a first insulating sublayer 162 and a second insulating sublayer 163. Parts of the first insulating sublayer 162 and parts of the second insulating sublayer 163 in the soldering portion 1b may be press-fitted and fixed by using adhesive on both the first insulating sublayer 162 and the second insulating sublayer 163. The adhesive on both parts of the first insulating sublayer 162 and parts of the second insulating sublayer 163 in the bent portion 1a may be removed or omitted. The air gap 161 is formed between a portion of the first insulating sublayer 162 and a portion of the second insulating sublayer 163 in the bent portion 1a. The air gap may also be formed between the routing layer 153 and the trace layer 152.

[0117] In some other embodiments, the flexible printed circuit 1 includes multiple conductive layers 15, but does not include a routing layer 153, but does include multiple trace layers 152. 。 One or more air gaps may be formed in the bent portion 1a, thereby improving the bending performance of the bent portion 1a of the flexible printed circuit 1.

[0118] When the flexible printed circuit 1 has two or more conductive layers 15, it may be understood that the stack structure of the flexible printed circuit 1 can be implemented in multiple ways. For example, when there are three conductive layers 15, the bent portion 1a can form a single-layer + double-layer stack structure by using one air gap, or a single-layer + single-layer + single-layer stack structure by using two air gaps. When there are four conductive layers 15, the bent portion 1a can form a double-layer + double-layer stack structure by using one air gap, or a single-layer + double-layer + single-layer stack structure by using two air gaps, or a single-layer + single-layer + single-layer stack structure by using three air gaps. The number of conductive layers 15 of the flexible printed circuit 1 and the specific stack structure are not strictly limited in this embodiment of the present application.

[0119] In some other embodiments, the flexible printed circuit 1 may include two routing layers 153, for example, a first routing layer and a second routing layer. Both the first and second routing layers are located in the bend portion 1a. The first routing layer and the soldering layer 151 are arranged on the same layer. The second routing layer is located on the side of the first protective layer 171 away from the trace layer 152. In this embodiment, the flexible printed circuit 1 may further include a second protective layer and a third protective layer. Both the second and third protective layers are located in the bend portion 1a. The second protective layer is located on the side of the first routing layer away from the trace layer 152. The third protective layer is located on the side of the second routing layer away from the trace layer 152. In this embodiment, a portion of the first protective layer 171 located in the bend portion 1a is no longer a surface layer of the bend portion 1a, but is an internal layer structure of the bend portion 1a.

[0120] In some of the embodiments described above, the flexible printed circuit 1 may include two soldering portions 1b and a bend portion 1a. The bend portion 1a is connected between the two soldering portions 1b. The two soldering portions 1b are soldered to different components. The flexible printed circuit 1 provides electrical connections between these different components.

[0121] In some other embodiments, the flexible printed circuit 1 may, alternatively, include a solder portion 1b and a bend portion 1a, and may further include a connection portion. The bend portion 1a may be connected between the solder portion 1b and the connection portion. The connection portion may be configured to secure an electrical connector. The electrical connector may include, but is not limited to, a board-to-board (BTB) connector. When the solder portion 1b and the electrical connector are connected to different components, the flexible printed circuit 1 can provide electrical connections between these different components. The design of the solder portion 1b and the bend portion 1a of the flexible printed circuit 1 may be the same as or similar to those in the above embodiments and will not be described in detail again here.

[0122] In some other embodiments, the flexible printed circuit 1 may, alternatively, include a solder portion 1b, a bend portion 1a, and a mounting portion. The bend portion 1a may be connected between the solder portion 1b and the mounting portion. The mounting portion may be configured to mount a component. The component may be a chip and / or an auxiliary component of a chip. When the solder portion 1b of the flexible printed circuit 1 is fixed to another component and electrically connected, the component mounted on the mounting portion of the flexible printed circuit 1 is electrically connected to the corresponding component. When the mounting portion of the flexible printed circuit 1 mounts a component, the flexible printed circuit 1 and this component together form a Flexible Printed Circuit Assembly (FPCA). The design of the solder portion 1b and the bend portion 1a of the flexible printed circuit 1 may be the same as or similar to those in some of the embodiments described above and will not be described in detail again here.

[0123] Please refer to Figures 17 to 19. Figure 17 is a schematic diagram of the structure of several embodiments of the circuit board assembly 10 according to the embodiments of this application. Figure 18 is a schematic diagram of the structure of the circuit board assembly 10 shown in Figure 17 from a different angle. Figure 19 is a schematic diagram of a partial structure of the circuit board assembly 10 shown in Figure 17.

[0124] In some embodiments, the circuit board assembly 10 includes a circuit board 2 and a flexible printed circuit 1. The soldering portion 1b of the flexible printed circuit 1 is soldered to the circuit board 2, and the bending portion 1a can change shape depending on the installation environment. The circuit board 2 may be a printed circuit board or a flexible printed circuit. A plurality of pads 21 are arranged on the circuit board 2. The plurality of pads 21 of the circuit board 2 correspond to the pad structure of the soldering portion 1b of the flexible printed circuit 1 (i.e., the first pad 1111 and the second pad 1121).

[0125] The soldered portion 1b may be fixed to the circuit board 2 and electrically connected by using surface mount technology (SMT), hotbar soldering technology, or another method. Figure 19 may be understood to use the structure of the flexible printed circuit 1 shown in Figure 9 as an example. The flexible printed circuit 1 of the circuit board assembly 10 in this embodiment may, as an alternative, use a different flexible printed circuit structure in which both surface layers of the soldered portion 1b include the soldering structure in the above embodiment, for example, the structure shown in Figures 5, 8, 11, or 12.

[0126] When the soldering portion 1b of the flexible printed circuit 1 is fixed to the circuit board 2 by hot press soldering, solder paste and solder flux may be pre-applied on the pads of the soldering portion 1b (i.e., the first pad 1111 and the second pad 1121) and the pad 21 of the circuit board 2. Soldering is then performed between the pads by heating using a pulsed heat head to achieve electrical conduction between the flexible printed circuit 1 and the circuit board 2. When the soldering portion 1b of the flexible printed circuit 1 is fixed to the circuit board 2 by surface mounting technology, the flexible printed circuit 1 may be soldered to the circuit board 2 as a component, or the circuit board 2 may be soldered to the flexible printed circuit 1 as a component, thereby achieving electrical conduction between the flexible printed circuit 1 and the circuit board 2.

[0127] In this embodiment, the pads of the soldering portion 1b of the flexible printed circuit 1 (i.e., the first pad 1111 and the second pad 1121) protrude from the surface, so that solder paste collapse and short circuits can be avoided during the soldering process, and the solder joint is guaranteed to have a specific height. This improves soldering quality and reliability.

[0128] Please refer to Figures 20 and 21. Figure 20 is a schematic diagram of the structure of several other embodiments of the circuit board assembly 10 according to the embodiments of this application. Figure 21 is a schematic diagram of a partial structure of the circuit board assembly 10 shown in Figure 20.

[0129] In some embodiments, the circuit board assembly 10 includes a circuit board 2 and a flexible printed circuit 1. The soldering portion 1b of the flexible printed circuit 1 is soldered to the circuit board 2, and the bending portion 1a can change shape depending on the installation environment. The circuit board 2 may be a printed circuit board or a flexible printed circuit. A plurality of pads 21 are arranged on the circuit board 2. The plurality of pads 21 of the circuit board 2 correspond to the structure of the pads 1511 of the soldering portion 1b of the flexible printed circuit 1.

[0130] The soldered portion 1b may be fixed to the circuit board 2 and electrically connected by using surface mount technology (SMT) or by another means. Figure 21 may be understood to use the structure of the flexible printed circuit 1 shown in Figure 14 as an example. The flexible printed circuit 1 of the circuit board assembly 10 in this embodiment may, as an alternative, use a different flexible printed circuit structure in which one surface layer of the soldered portion 1b includes a soldered structure, and the other surface layer does not include the soldered structure in the above embodiment, for example, the structure shown in Figures 13, 15, or 16.

[0131] When the soldered portion 1b of the flexible printed circuit 1 is fixed to the circuit board 2 by using surface mounting technology, the flexible printed circuit 1 may be soldered to the circuit board 2 as a component, or the circuit board 2 may be soldered to the flexible printed circuit 1 as a component, thereby achieving electrical conduction between the flexible printed circuit 1 and the circuit board 2.

[0132] In some embodiments, the circuit board assembly 10 shown in Figures 17 to 21 may further include one or more components, one or more of which may be soldered to the circuit board 2 and / or to the flexible printed circuit 1. When the circuit board 2 is a printed circuit board and the components are mounted on the circuit board 2, the circuit board 2 and the components together may form a Printed Circuit Board Assembly (PCBA).

[0133] In some embodiments, the circuit board assembly 10 shown in Figures 17 to 21 may further include electrical connectors. The electrical connectors may be fixed to the flexible printed circuit 1 and electrically connected so that the flexible printed circuit 1 can be electrically connected to other components by using the electrical connectors.

[0134] Several embodiments of the circuit board assembly 10 are described below.

[0135] Figure 22 is a schematic diagram of the structure of several embodiments of the circuit board assembly 10 according to the embodiments of this application.

[0136] In some embodiments, the circuit board assembly 10 includes a first circuit board 22, a second circuit board 23, a flexible printed circuit 1, a first component 31, and a second component 32. The flexible printed circuit 1 includes two soldering portions 1b and a bend portion 1a connecting the two soldering portions 1b. The two soldering portions 1b of the flexible printed circuit 1 are soldered to the first circuit board 22 and the second circuit board 23, respectively. For the structure of each of the soldering portions 1b and bend portion 1a of the flexible printed circuit 1, refer to any of the structures in the embodiments described above. The first circuit board 22 may be a printed circuit board or a flexible printed circuit, and the second circuit board 23 may be a printed circuit board or a flexible printed circuit. There may be one or more first components 31, which are fixed to and electrically connected to the first circuit board 22. There may be one or more second components 32, which are fixed to and electrically connected to the second circuit board 23. The flexible printed circuit 1 is configured to provide an electrical connection between the first component 31 and the second component 32.

[0137] The first circuit board 22 and the second circuit board 23 may be stacked. The bent portion 1a of the flexible printed circuit 1 is bent so that the circuit board assembly 10 forms a sandwich stack structure. The entire circuit board assembly 10 occupies a relatively small space and requires a relatively small installation space. This helps reduce installation difficulties and improve the scope of application. In some other embodiments, the first circuit board 22 and the second circuit board 23 may, alternatively, form a different relative positional relationship, for example, a staggered arrangement.

[0138] Figure 23 is a schematic diagram of the structure of several other embodiments of the circuit board assembly 10 according to the embodiments of this application.

[0139] In some embodiments, the circuit board assembly 10 includes a first circuit board 22, a second circuit board 23, a flexible printed circuit 1, a first electrical connector 41, a second electrical connector 42, a first component 31, and a second component 32. The flexible printed circuit 1 includes a soldering portion 1b, a connecting portion 1c, and a bend portion 1a connecting the soldering portion 1b and the connecting portion 1c. For the structure of each of the soldering portion 1b and the bend portion 1a of the flexible printed circuit 1, refer to any of the structures in the embodiments described above. The first circuit board 22 may be a printed circuit board or a flexible printed circuit. There may be one or more first components 31, which are fixed to and electrically connected to the first circuit board 22. The soldering portion 1b of the flexible printed circuit 1 is soldered to the first circuit board 22. There may be one or more second components 32, which are fixed to and electrically connected to the second circuit board 23. The first electrical connector 41 and the second electrical connector 42 may be male and female connectors, respectively, and the male and female connectors are paired with each other. Each of the first electrical connector 41 and the second electrical connector 42 may be a board-to-board electrical connector or the like. The first electrical connector 41 is fixed to and electrically connected to the connection portion 1c of the flexible printed circuit 1. The second electrical connector 42 is fixed to and electrically connected to the second circuit board 23. The first electrical connector 41 is fixed to and electrically connected to the second electrical connector 42. The flexible printed circuit 1 is configured to realize an electrical connection between the first component 31 and the second component 32.

[0140] The first circuit board 22 and the second circuit board 23 may be stacked. The bent portion 1a of the flexible printed circuit 1 is bent so that the circuit board assembly 10 forms a sandwich stack structure. The entire circuit board assembly 10 occupies a relatively small space and requires a relatively small installation space. This helps reduce installation difficulties and improve the scope of application. In some other embodiments, the first circuit board 22 and the second circuit board 23 may, alternatively, form a different relative positional relationship, for example, a staggered arrangement.

[0141] Figure 24 is a schematic diagram of the structure of several other embodiments of the circuit board assembly 10 according to the embodiments of this application.

[0142] In some embodiments, the circuit board assembly 10 includes a circuit board 2, a flexible printed circuit 1, a first component 31, and a second component 32. The flexible printed circuit 1 includes a soldering portion 1b, a mounting portion 1d, and a bend portion 1a connecting the soldering portion 1b and the mounting portion 1d. For the structure of the soldering portion 1b and the bend portion 1a of the flexible printed circuit 1, refer to any of the structures in the embodiments described above. The circuit board 2 may be a printed circuit board or a flexible printed circuit. There may be one or more first components 31, which are fixed to the circuit board 2 and electrically connected. The soldering portion 1b of the flexible printed circuit 1 is soldered to the circuit board 2. There may be one or more second components 32, which are fixed to the mounting portion 1d of the flexible printed circuit 1 and electrically connected. The flexible printed circuit 1 is configured to provide an electrical connection between the first component 31 and the second component 32.

[0143] Embodiments of this application further provide an electronic device including a housing and a circuit board assembly. The circuit board assembly may use any of the structures in the above embodiments, and the circuit board assembly is installed inside the housing. The electronic device may be, but is not limited to, an electronic product such as a mobile phone, tablet computer (pad), portable game console, palmtop computer (personal digital assistant, PDA), notebook computer, ultra-mobile personal computer (UMPC), handheld computer, netbook, in-car media playback device, wearable electronic device, virtual reality (VR) terminal device, or augmented reality (AR) terminal device.

[0144] For example, when the electronic device is a mobile phone or a tablet computer, and the circuit board assembly uses the structure of the circuit board assembly 10 shown in Figure 22 or Figure 23, the first circuit board 22 and the second circuit board 23 may be a main board and a sub-board, respectively, the first component 31 may include a processor, and the second component 32 may include a radio frequency chip.

[0145] For example, when the electronic device is a wearable electronic device, such as a smartwatch or smart band, and the circuit board assembly uses the structure of the circuit board assembly 10 shown in Figure 23, the first circuit board 22 may be a circuit board for a heart rate module, the first component 31 may include a heart rate detection sensor, the second circuit board 23 may be a main board, and the second component 32 may include a processor or the like.

[0146] For example, if the electronic device is a Bluetooth headset and the circuit board assembly 10 uses the structure of the circuit board assembly 10 shown in Figure 24, the circuit board 2 may be a main board, the first component 31 may include a processor, and the second component 32 may include a microphone (MIC) and / or its auxiliary components.

[0147] The structures of circuit board assemblies are diverse, and it may be understood that there are also diverse applications of circuit board assemblies in electronic devices of different forms, types, and sizes. This is not strictly limited to this embodiment of the present application.

[0148] The embodiments described above are intended to illustrate the technical solutions of this application and are not intended to limit this application. Although this application has been described in detail with reference to the embodiments described above, those skilled in the art should understand that modifications may still be made to the technical solutions described in the embodiments above, or that some of their technical features may be replaced with equivalent substitutions, without departing from the scope of the technical solutions of the embodiments of this application.

Claims

1. A flexible printed circuit including a bent portion and a soldered portion connected to the bent portion, The flexible printed circuit includes a plurality of conductive layers and a plurality of insulating layers, the insulating layers being arranged between two adjacent conductive layers. The plurality of conductive layers include a first soldering layer, a second soldering layer, and a trace layer. Both the first soldering layer and the second soldering layer are located on the soldering portion, the first soldering layer is one surface layer of the soldering portion and is formed by a plurality of first pads spaced apart from each other, the second soldering layer is the other surface layer of the soldering portion and is formed by a plurality of second pads spaced apart from each other, The trace layer is located between the first soldering layer and the second soldering layer and extends from the soldering portion to the bending portion, the first pad and the second pad are connected using a through-hole conductor, and the through-hole conductor is connected to the trace layer. The plurality of insulating layers include a first insulating layer, the first insulating layer is located between the first soldering layer and the adjacent trace layer, and extends from the soldering portion to the bent portion, and a portion of the first insulating layer located in the bent portion forms one of the surface layers of the bent portion. Flexible printed circuit board.

2. The trace layer includes a conductor block and a trace, the conductor block being located at the soldering portion, one end of the trace being connected to the conductor block, the other end of the trace extending to the bend portion, and the first pad and the second pad being connected to the conductor block using the through-hole conductor. The flexible printed circuit according to claim 1.

3. The area of ​​the conductor block is smaller than the area of ​​the first pad. The flexible printed circuit according to claim 2.

4. There are multiple trace layers, and the multiple conductor blocks connected to the multiple first pads are located on different trace layers. The flexible printed circuit according to claim 2.

5. There is one or more trace layers, and multiple punctured regions are provided on each trace layer, and multiple through-hole conductors penetrate the multiple punctured regions of each trace layer in a one-to-one correspondence. Support blocks are arranged in the plurality of punctured regions of each trace layer, and the through-hole conductors penetrate the support blocks and are connected to the support blocks. When there is one trace layer, the support block is the conductor block, or when there are multiple trace layers, the support block is the conductor block or the lower pad. The flexible printed circuit according to claim 2.

6. The plurality of insulating layers include a second insulating layer, The second insulating layer is located between the second soldering layer and the adjacent trace layer, and extends from the soldering portion to the bent portion, and a portion of the second insulating layer located in the bent portion forms the other surface layer of the bent portion. The flexible printed circuit according to claim 1.

7. The plurality of conductive layers further include a first routing layer and a second routing layer, both of which are located in the bent portion, the first routing layer and the first soldering layer are arranged on the same layer, and the second routing layer and the second soldering layer are arranged on the same layer. The flexible printed circuit further includes a first protective layer and a second protective layer, both of which are located in the bent portion, the first protective layer being located on the side of the first routing layer away from the trace layer, the second protective layer being located on the side of the second routing layer away from the trace layer, and the first and second protective layers being two surface layers of the bent portion. The flexible printed circuit according to claim 1.

8. At least one insulating layer of the flexible printed circuit forms an air gap in the bent portion. The flexible printed circuit according to claim 7.

9. A flexible printed circuit including a bent portion and a soldered portion connected to the bent portion, The flexible printed circuit includes a plurality of conductive layers, a plurality of insulating layers, and a first protective layer, wherein the insulating layer is arranged between two adjacent conductive layers. The plurality of conductive layers include a soldering layer and a trace layer, the soldering layer is located on the soldering portion, the soldering layer is one surface layer of the soldering portion, the soldering layer is formed by a plurality of pads spaced apart from each other, the trace layer is located on the side of the soldering layer and extends from the soldering portion to the bend portion, the pads are connected to the trace layer using through-hole conductors, The first protective layer is located on the side of the trace layer away from the soldering layer, the first protective layer extends from the soldering portion to the bend portion, a portion of the first protective layer located at the soldering portion forms the other surface layer of the soldering portion, and a portion of the first protective layer located at the bend portion forms one surface layer of the bend portion. The plurality of insulating layers include a first insulating layer, the first insulating layer is located between the soldering layer and the adjacent trace layer, and extends from the soldering portion to the bent portion, and a portion of the first insulating layer located in the bent portion forms the other surface layer of the bent portion. Flexible printed circuit board.

10. The trace layer includes a conductor block and a trace, the conductor block being located at the soldering portion, one end of the trace being connected to the conductor block, the other end of the trace extending to the bend portion, and the pad being connected to the conductor block using the through-hole conductor. The flexible printed circuit according to claim 9.

11. The area of ​​the conductor block is smaller than the area of ​​the pad. The flexible printed circuit according to claim 10.

12. There are multiple trace layers, and multiple conductor blocks connected to the multiple pads are located on different trace layers. The flexible printed circuit according to claim 10.

13. There is one or more trace layers, and multiple punctured regions are provided on each trace layer, and multiple through-hole conductors penetrate the multiple punctured regions of each trace layer in a one-to-one correspondence. Support blocks are arranged in the plurality of punctured regions of each trace layer, and the through-hole conductors penetrate the support blocks and are connected to the support blocks. When there is one trace layer, the support block is the conductor block, or when there are multiple trace layers, the support block is the conductor block or the lower pad. The flexible printed circuit according to claim 10.

14. The plurality of conductive layers further include a routing layer, the routing layer is located in the bent portion, and the routing layer and the soldering layer are arranged on the same layer. The flexible printed circuit further includes a second protective layer, the second protective layer being located on the side of the routing layer away from the trace layer, and the second protective layer being located in the bend portion and being the other surface layer of the bend portion. The flexible printed circuit according to claim 9.

15. At least one insulating layer of the flexible printed circuit forms an air gap in the bent portion. The flexible printed circuit according to claim 14.

16. A circuit board assembly comprising a circuit board and a flexible printed circuit according to any one of claims 1 to 15, wherein the soldering portion of the flexible printed circuit is soldered to the circuit board.

17. An electronic device comprising a housing and a circuit board assembly, wherein the circuit board assembly comprises a circuit board and the flexible printed circuit described in any one of claims 1 to 15, the soldering portion of the flexible printed circuit being soldered to the circuit board, and the circuit board assembly being installed inside the housing.

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