Flexible circuit boards, their manufacturing methods, and electronic devices

Abstract

This invention provides a flexible circuit board capable of transmitting both analog and digital signals and easily integrated into the housing of electronic devices such as smartphones in a bent state, a method for manufacturing the same, and an electronic device thereof. The flexible circuit board of this embodiment includes a signal line region, a connector region, a bending region, one or more analog signal lines, one or more digital signal lines, and a ground layer. The one or more analog signal lines are formed extending along the long side of the signal line region to transmit analog signals. The one or more digital signal lines are formed extending along the long side of the signal line region to transmit digital signals. The ground layer is formed by covering the analog signal lines with an insulating layer. The bending region connects the signal line region and the connector region. Compared to the signal line region, the number of wiring layers and the number of insulating layers are both less.

Description

[Technical Field]

[0001] This invention relates to flexible circuit boards, methods for manufacturing the same, and electronic devices. [Previous Technology]

[0002] In recent years, due to the widespread adoption of fifth-generation mobile communication systems (5G), the number of antenna connection cables in electronic devices such as smartphones has increased. Furthermore, the miniaturization of smartphone casings is also progressing. Therefore, there is a growing demand for flexible circuit boards with even higher density wiring for antenna connection cables.

[0003] In 5G systems, radio waves in the SUB6 band and millimeter-wave band are used, as well as radio waves in the frequency bands of the current fourth-generation mobile communication system (4G). Therefore, the number of antenna connection cables increases in 5G systems. Previously, coaxial cables for transmitting analog signals and cables for transmitting digital signals were built into the housing as separate cables. However, in 5G systems, with the increase in the number of antenna connection cables, it is required to combine these two types of cables into a multi-layer flexible circuit board.

[0004] In addition, conventional multilayer flexible circuit boards are described in Japanese Patent Publication No. 5204871 and Japanese Patent Publication No. 2004-311927.

[0005] As mentioned earlier, with the widespread adoption of 5G systems, the number of antennas in electronic devices such as smartphones is increasing. In 5G systems, in addition to cables transmitting analog signals such as wireless signals, cables transmitting digital signals received by digital terminals such as USB, and cables transmitting power, are also required. These cables are typically arranged across the top surface of the battery. Furthermore, there is an increasing trend of placing coils for wireless power supply, etc., on the top surface of the battery. Therefore, it is necessary to save space by arranging cables on the top surface of the battery. Additionally, methods are also being sought to place the cables outside the top surface of the battery, such as arranging them on the side of the casing of smartphones, etc. [Summary of the Invention]

[0006] The present invention is based on the above-described technical understanding. One of the objectives of the present invention is to provide a flexible circuit board capable of transmitting both analog and digital signals and easily embedded in the housing of electronic devices such as smartphones in a bent state, a method for manufacturing the same, and an electronic device incorporating the flexible circuit board.

[0007] The flexible circuit board of the first aspect of the present invention includes a signal line region, a connector region, a bending region, one or more analog signal lines, one or more digital signal lines, and a ground layer. The one or more analog signal lines are formed to extend along the long side direction of the signal line region to transmit analog signals. The one or more digital signal lines are formed to extend along the long side direction of the signal line region to transmit digital signals. The ground layer is formed to cover the analog signal lines with an insulating layer. The bending region connects the signal line region and the connector region. Compared with the signal line region, the number of wiring layers and the number of insulating layers are at least one less.

[0008] In addition, in the flexible circuit board, the connector region has at least one less wiring layer and one less insulating layer compared to the signal line region.

[0009] The flexible circuit board of the second aspect of the present invention includes a signal line region, a connector region, a bending region, one or more analog signal lines, one or more digital signal lines, and a ground layer. The one or more analog signal lines are formed to extend along the long side of the signal line region to transmit analog signals. The one or more digital signal lines are formed to extend along the long side of the signal line region to transmit digital signals. The ground layer is formed to cover the analog signal lines with an insulating layer. The bending region connects the signal line region and the connector region. The interior of the bending region has a space where no wiring layer or insulating layer is provided.

[0010] In addition, in the flexible circuit board, there is a cut in one or both sides of the region in the thickness direction of the flexible circuit board in the space, and the direction of the cut is a direction having a width direction component orthogonal to the long side direction of the signal line region.

[0011] In addition, in the flexible circuit board, when viewed from above, one or both sides of the flexible circuit board in the thickness direction of the space are formed into a meander shape or a crack shape.

[0012] In addition, in the flexible circuit board, an interlayer connection channel is provided in the connector area to connect with the analog signal line or the digital signal line.

[0013] In addition, in the flexible circuit board, the interlayer connection channel has: plated through-holes connected to the analog signal lines or the digital signal lines; and filled vias connected to the plated through-holes through a conductive layer.

[0014] In addition, in the flexible circuit board, a connector component is installed in the connector area, and the connector component is electrically connected to the analog signal line and the digital signal line through the interlayer connection channel.

[0015] The electronic device of the present invention includes: a housing; the flexible circuit board disposed within the housing; a first module disposed within the housing; a second module disposed within the housing; and a battery disposed within the housing between the first module and the second module.

[0016] In addition, in the electronic device, the flexible circuit board is configured between the battery and the side of the housing.

[0017] Additionally, in the electronic device, the flexible circuit board is configured between the battery and the back or front of the housing.

[0018] A method for manufacturing a flexible circuit board according to a first aspect of the present invention includes the following steps: preparing a first single-sided metal foil laminate, the first single-sided metal foil laminate having: a first insulating substrate having a first main surface and a second main surface opposite to the first main surface; a first metal foil disposed on the first main surface of the first insulating substrate; and a first protective film layer disposed on the second main surface of the first insulating substrate through a first adhesive layer; patterning the first metal foil to form a first conductive pattern; forming a first bottom hole, the first bottom hole penetrating the first protective film layer, the first adhesive layer and the first insulating substrate and reaching the first metal foil; and inserting a hole into the first bottom hole. A first conductive paste is filled in; the first protective film layer is peeled off to obtain a first wiring substrate; a first double-sided metal foil laminate is prepared, the first double-sided metal foil laminate having: a second insulating substrate having a third main surface and a fourth main surface opposite to the third main surface; a second metal foil disposed on the third main surface of the second insulating substrate; and a third metal foil disposed on the fourth main surface of the second insulating substrate; the second metal foil is patterned to form a second conductive pattern; a second bottom hole is formed, the second bottom hole penetrating the second insulating substrate and reaching the second metal foil; a first metal plating layer is deposited on the sidewall and bottom surface of the second bottom hole; the third metal foil is patterned to form a second conductive pattern. A third conductive pattern is formed; a second adhesive layer is formed on the third metal foil by embedding the third conductive pattern of the third metal foil and depositing the first metal plating layer on the second bottom hole; a first cover material layer is formed on the second adhesive layer; a third adhesive layer having a first opening is formed on the first cover material layer; a second protective film layer is formed on the third adhesive layer by filling the first opening of the third adhesive layer; a third bottom hole is formed, the third bottom hole penetrating the second protective film layer, the third adhesive layer, the first cover material layer and the second adhesive layer and reaching the third metal foil; a second conductive paste is filled into the third bottom hole; peeling... A second wiring substrate is obtained by removing the second protective film layer; a second double-sided metal foil laminate is prepared, the second double-sided metal foil laminate having: a third insulating substrate having a fifth main surface and a sixth main surface opposite to the fifth main surface; a fourth metal foil disposed on the fifth main surface of the third insulating substrate; and a fifth metal foil disposed on the sixth main surface of the third insulating substrate; the fourth metal foil is patterned to form a fourth conductive pattern; the fifth metal foil is patterned to form a fifth conductive pattern; a fourth bottom hole is formed, the fourth bottom hole penetrating the third insulating substrate and reaching the fifth metal foil; a second metal plating layer is deposited on the sidewall and bottom surface of the fourth bottom hole;A first through-hole is formed penetrating the third insulating substrate and the fifth metal foil to obtain a third wiring substrate; the first wiring substrate is laminated onto the second wiring substrate in such a manner that the first conductive paste contacts the second conductive pattern, and the third wiring substrate is laminated onto the second wiring substrate in such a manner that the second conductive paste contacts the third conductive pattern.

[0019] A method for manufacturing a flexible circuit board according to a second aspect of the present invention includes the following steps: preparing a first single-sided metal foil laminate, the first single-sided metal foil laminate having: a first insulating substrate having a first main surface and a second main surface opposite to the first main surface; a first metal foil disposed on the first main surface of the first insulating substrate; and a first protective film layer disposed on the second main surface of the first insulating substrate through a first adhesive layer; patterning the first metal foil to form a first conductive pattern; forming a first bottom hole, the first bottom hole penetrating the first protective film layer, the first adhesive layer and the first insulating substrate and reaching the first metal foil; and inserting a first bottom hole into the first bottom hole. A first conductive paste is filled in; the first protective film layer is peeled off to obtain a first wiring substrate; a first double-sided metal foil laminate is prepared, the first double-sided metal foil laminate having: a second insulating substrate having a third main surface and a fourth main surface opposite to the third main surface; a second metal foil disposed on the third main surface of the second insulating substrate; and a third metal foil disposed on the fourth main surface of the second insulating substrate; the second metal foil is patterned to form a second conductive pattern; a second bottom hole is formed, the second bottom hole penetrating the second insulating substrate and reaching the second metal foil; a first metal plating layer is deposited on the sidewall and bottom surface of the second bottom hole; the third metal foil is patterned to form a second conductive pattern. A third conductive pattern is formed; a second adhesive layer is formed on the third metal foil by embedding the third conductive pattern of the third metal foil and depositing the first metal plating layer on the second bottom hole; a first cover material layer is formed on the second adhesive layer; a third adhesive layer having a first opening is formed on the first cover material layer; a second protective film layer is formed on the third adhesive layer by filling the first opening of the third adhesive layer; a third bottom hole is formed, the third bottom hole penetrating the second protective film layer, the third adhesive layer, the first cover material layer and the second adhesive layer and reaching the third metal foil; a second conductive paste is filled into the third bottom hole; peeling... A second wiring substrate is obtained by removing the second protective film layer; a second double-sided metal foil laminate is prepared, the second double-sided metal foil laminate having: a third insulating substrate having a fifth main surface and a sixth main surface opposite to the fifth main surface; a fourth metal foil disposed on the fifth main surface of the third insulating substrate; and a fifth metal foil disposed on the sixth main surface of the third insulating substrate; the fourth metal foil is patterned to form a fourth conductive pattern; the fifth metal foil is patterned to form a fifth conductive pattern; a fourth bottom hole is formed, the fourth bottom hole penetrating the third insulating substrate and reaching the fifth metal foil; a second metal plating layer is deposited on the sidewall and bottom surface of the fourth bottom hole;A fourth adhesive layer is formed on the fourth metal foil by embedding the third conductive pattern of the fourth metal foil and depositing the second metal plating layer on the fourth bottom hole; a second cover material layer is formed on the fourth adhesive layer; a third protective film layer is formed on the second cover material layer; a fourth protective film layer is formed on the third protective film layer; a fifth bottom hole is formed, the fifth bottom hole penetrating the fourth protective film layer, the third protective film layer, the second cover material layer, and the third adhesive layer and reaching the fourth metal foil; a third conductive paste is filled into the fifth bottom hole; the third protective film layer and the fourth protective film layer are peeled off to obtain a third wiring substrate; the first wiring substrate is laminated onto the second wiring substrate in such a way that the first conductive paste contacts the second conductive pattern, and the third wiring substrate is laminated onto the second wiring substrate in such a way that the second conductive paste contacts the third conductive paste.

[0020] In addition, in the method for manufacturing the flexible circuit board, the second conductive pattern includes analog signal lines.

[0021] In addition, in the method for manufacturing the flexible circuit board, the fifth conductive pattern includes digital signal lines.

[0022] The flexible circuit board of the present invention can transmit analog signals and digital signals at high speed and with low loss, and can be easily built into the housing of electronic devices in a bent state.

Implementation Method

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each drawing, components having equivalent functions are given the same reference numerals. The drawings are schematic diagrams, and the relationship between thickness and planar dimensions (aspect ratio), the ratio of thicknesses of each layer, etc., may not necessarily correspond to reality.

[0025] <Overall Structure of Flexible Circuit Board 100>

[0026] First, the overall structure of the flexible circuit board 100 according to the embodiment will be described with reference to FIG1. ​​FIG1 shows a top view of the flexible circuit board 100. The flexible circuit board 100 is provided with a connector region 110, a signal line region 120, and a bending region 130. The flexible circuit board 100 is electrically connected to a first module 200 (see FIG13A) and a second module 300 (see FIG13A). The first module 200 has a wireless communication antenna for receiving analog signals and a digital terminal for receiving digital signals. The second module 300 performs signal processing on the analog signals and the digital signals.

[0027] Connector regions 110 are disposed at both ends of the signal line region 120. One connector region 110 is connected to an antenna module that transmits and receives analog signals such as wireless signals, and the other connector region 110 is connected to a signal processing module on which a signal processing chip is mounted. The signal line region 120 is formed to extend along its long side and includes analog signal lines and digital signal lines. The analog signal lines transmit analog signals such as wireless signals, and the digital signal lines transmit digital signals.

[0028] Additionally, the antenna module may also have a digital terminal for receiving digital signals. In the flexible circuit board 100 of the first embodiment, the first module 200 is an antenna module, and the second module 300 is a signal processing module. The flexible circuit board 100 electrically connects the first module 200 and the second module 300. Specifically, the connector area 110 of one side is electrically connected to the first module 200, and the connector area 110 of the other side is electrically connected to the second module 300. Moreover, the analog signal lines and digital signal lines included in the signal line area 120 are electrically connected to the connector areas 110 of the other side. In other words, the first module 200 and the second module 300 are electrically connected through the connector area 110 and the signal line area 120 of the flexible circuit board 100.

[0029] Next, the bending region 130 will be described with reference to FIG2. FIG2 is an enlarged top view of region A of FIG1, showing one end of the flexible circuit board 100. The bending region 130 connects the connector region 110 and the signal line region 120. Both analog signal lines and digital signal lines are included in the bending region 130. Details will be described later. The bending region 130 has a reduced-layer structure with fewer wiring layers and / or insulating layers compared to the signal line region 120. Alternatively, the bending region 130 has a hollow structure, wherein a hollow region without wiring layers and insulating layers is provided inside the bending region 130.

[0030] (First Embodiment)

[0031] <Structure of Flexible Circuit Board 100>

[0032] Next, the cross-sectional structure of the flexible circuit board 100 of the first embodiment will be described with reference to FIG3. FIG3 is a schematic cross-sectional view of the BB line in FIG2. In FIG3, the left side of the figure represents the area corresponding to the connector region 110, and the right side of the figure represents the area corresponding to the signal line region 120. Moreover, the bending region 130 is located between the connector region 110 and the signal line region 120. This bending region 130 has a layer reduction structure. That is, the bending region 130 of the flexible circuit board 100 of the first embodiment has a layer reduction structure with fewer wiring layers and / or fewer insulating layers compared to the connector region 110 and the signal line region 120.

[0033] More specifically, the bending region 130 has three wiring layers, and the signal line region 120 has five wiring layers. Specifically, the bending region 130 has conductive patterns (wiring 12b, 22i, and 23b) as wiring layers, and the signal line region 120 has conductive patterns (wiring 12b, 22i, 23b, 32b, and 33i) as wiring layers. Therefore, the bending region 130 has a reduced-layer structure with two fewer wiring layers than the signal line region 120. Similarly, the bending region 130 has two insulating layers, and the signal line region 120 has three insulating layers. Specifically, the bending region 130 has a first insulating layer (insulating substrate 11 and adhesive layer 13), a second insulating layer (insulating substrate 21), and a third insulating layer (adhesive layer 24 and cover material layer 71). On the other hand, the signal line region 120 has a first insulating layer (insulating substrate 11 and adhesive layer 13), a second insulating layer (insulating substrate 21), a third insulating layer (adhesive layer 24 and cover material layer 71), and a fourth insulating layer (insulating substrate 31). Therefore, the bending region 130 has a reduced-layer structure with one less insulating layer than the signal line region 120.

[0034] As described above, the bending region 130 has a reduced-layer structure with fewer wiring layers and insulating layers compared to the signal line region 120. Therefore, the bending region 130 can alleviate the stress during bending compared to the signal line region 120. Therefore, when the flexible circuit board 100 is built into the housing of an electronic device such as a smartphone, it becomes easier to build the flexible circuit board 100 in a bent state (hereinafter sometimes referred to as bent building). Specifically, when the flexible circuit board 100 is built into the housing in a bent state, the flexible circuit board 100 is bent in the bending region 130 and built into the housing. At this time, the bending region 130 relatively alleviates the stress, so it can be bent more easily. Thus, it is easy to build the flexible circuit board 100 into the housing by bending.

[0035] Furthermore, in the flexible circuit board 100, analog signal lines are arranged in wiring 22i, and digital signal lines are arranged in wiring 33i. Thus, both analog and digital signal lines are integrated into the flexible circuit board 100. Therefore, by using the flexible circuit board 100, both analog and digital signal lines can be arranged, thereby saving space within the housing of the electronic device.

[0036] Furthermore, the flexible circuit board 100 includes a ground layer formed in such a way that it covers the analog signal lines through an insulating layer. Specifically, ground layers 12b and 23b (wiring 12b and 23b) cover the wiring 22i of the analog signal lines through an insulating layer. As shown in FIG3, a first insulating layer (adhesive layer 13 and insulating substrate 11) is stacked on the wiring 22i, and the ground layer 12b (wiring 12b) is formed on the first insulating layer. Similarly, a second insulating layer (insulating substrate 21) is stacked under the wiring 22i, and the ground layer 23b (wiring 23b) is stacked under the second insulating layer. Thus, the flexible circuit board 100 includes ground layers 12b and 23b formed in such a way that they cover the analog signal lines (wiring 22i) through the first insulating layer and the second insulating layer, respectively. That is, the flexible circuit board 100 has a three-layer stripline structure.

[0037] Interlayer connection channels electrically connected to analog signal lines or digital signal lines are provided in the connector area 110 of the flexible circuit board 100. These interlayer connection channels are provided in holes H1 to H4 of the connector area 110 shown in FIG. 3 and are electrically connected to the analog signal lines or digital signal lines. For example, the interlayer connection channel provided in hole H2 is electrically connected to an analog signal line (wiring 22i). Additionally, the interlayer connection channel provided in hole H4 is electrically connected to a digital signal line (wiring 33i).

[0038] Furthermore, the interlayer connection channel of the connector region 110 can be formed by plated through-holes. Specifically, a first metal plating layer 61 is deposited into hole H2, and a second metal plating layer 62 is deposited into hole H4, forming plated through-holes respectively. In this way, the interlayer connection channel of the connector region 110 has plated through-holes (hole H2 or hole H4) that connect to analog signal lines (wiring 22i) or digital signal lines (wiring 33i).

[0039] Alternatively, the interlayer connection channel of the connector region 110 can also be formed by filled vias. More specifically, conductive paste is filled into hole H1 to form a filled via. Moreover, the filled via formed in hole H1 is connected to wiring 22i. Similarly, conductive paste is filled into hole H3 to form a filled via. Moreover, the filled via formed in hole H3 is connected to landing point 32a. Landing point 32a is connected to the plated through-hole of hole H4. The interlayer connection channel of the connector region 110 has plated through-holes and filled vias that are connected to the plated through-holes through the conductive layer (landing point 22a or 32a). Alternatively, connector components (not shown) that are electrically connected to analog signal lines and digital signal lines through the above-described interlayer connection channel can also be installed in the connector region 110.

[0040] The general configuration of the flexible circuit board 100 according to the first embodiment has been described above. According to the first embodiment, the bending region 130 of the flexible circuit board 100 has a reduced-layer structure with fewer wiring layers and fewer insulating substrate layers compared to the signal line region 120. Therefore, stress can be mitigated when bending the bending region 130. Therefore, the flexible circuit board 100 can be easily bent and integrated into the housing of electronic devices such as smartphones.

[0041] Furthermore, both the analog signal line and the digital signal line are housed in the flexible circuit board 100. Therefore, it is unnecessary to separately configure cables for the analog signal line and cables for the digital signal line within the casing of the electronic device. This saves space within the casing of electronic devices such as smartphones.

[0042] In addition, compared with the signal line area 120, the bending area 130 can reduce the number of wiring layers and the number of insulating layers, thereby reducing the amount of wiring layers and insulating substrate materials required for manufacturing the flexible circuit board 100, thereby reducing manufacturing costs.

[0043] <Manufacturing Method of Flexible Circuit Board 100>

[0044] Next, the manufacturing method of the flexible circuit board 100 of the first embodiment will be described with reference to the process cross-sectional views of FIG4 to 6.

[0045] As shown in Figure 4(1), firstly, a single-sided metal foil laminate 10 is prepared. The single-sided metal foil laminate 10 has an insulating substrate 11, a metal foil 12 disposed on the upper surface of the insulating substrate 11, and a protective film layer 14 disposed on the lower surface of the insulating substrate 11 through an adhesive layer (micro-adhesive layer) 13. The metal foil 12 is formed on the insulating substrate 11 through a seed layer (not shown) formed on the main surface of the insulating substrate 11. The insulating substrate 11 can be, for example, polyimide (PI), modified polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluoropolymer (PFA, PTEE, etc.), etc., in addition to liquid crystal polymer (LCP), and is not particularly limited.

[0046] The thickness of the insulating substrate 11 is, for example, 100 μm. The metal foil 12 is, for example, silver or aluminum, other than copper. The thickness of the metal foil 12 is, for example, 12 μm. The protective film layer 14 is disposed on the lower surface of the insulating substrate 11 through the adhesive layer 13. The protective film layer 14 is, for example, an insulating film such as PET (polyethylene terephthalate). The thickness of the protective film layer 14 is, for example, 10 μm. The adhesive layer 13 has, for example, a thickness of 10 μm.

[0047] Next, as shown in (2) of FIG4, the metal foil 12 of the single-sided metal foil laminate 10 is patterned using a known photolithography method to form a first conductive pattern. The first conductive pattern includes a landing point 12a and a wiring 12b. The diameter of the landing point 12a is, for example, φ350μm. The wiring 12b functions as a ground layer in the flexible circuit board 100.

[0048] Next, as shown in (2) of FIG4, by irradiating the protective film layer 14 with a laser, the protective film layer 14, the adhesive layer 13, and the insulating substrate 11 are removed, forming a bottomed hole H1 with the landing site 12a exposed on the bottom surface. The diameter of the hole H1 is, for example, φ150~200μm. More specifically, an infrared laser, which is a carbon dioxide laser, is used to irradiate a predetermined position of the protective film layer 14 with a laser pulse to perform perforation. The beam diameter of the infrared laser is set to 150μm, which is the same as the diameter of the hole H1. In addition, the pulse width of the infrared laser is set to 10 microseconds, and the energy of each pulse of the infrared laser is set to 5mJ.

[0049] The protective film layer 14 is irradiated five times with an infrared laser as set as described above to obtain an aperture H1. Furthermore, as described above, the diameter of the infrared laser beam is approximately the same as the diameter of the aperture H1. In other words, the diameter of the infrared laser beam can be adjusted to match the diameter of the aperture H1. Therefore, it is suitable that the diameter of the infrared laser beam can be easily adjusted during the formation of the aperture H1. Additionally, UV-YAG lasers or similar lasers, not limited to infrared lasers, can also be used in the formation of the aperture H1.

[0050] After the hole H1 is pierced with an infrared laser, a desmearing process is performed. In the desmearing process, resin residue (residual film) at the boundary between the insulating substrate 11 and the landing site 12a, as well as the back treatment film (Ni or Cr, etc.) of the landing site 12a, are removed.

[0051] Next, as shown in (3) of FIG4, conductive paste 51 is filled into the interior of hole H1 by printing method such as screen printing. The conductive paste 51 is obtained by dispersing metal particles into a resin binder that is a thermosetting resin in paste form.

[0052] Next, as shown in (4) of FIG4, the protective film layer 14 is peeled off from the adhesive layer 13. As a result, a portion of the conductive paste 51 filling the hole H1 protrudes, forming a protrusion 51a. In addition, the height of the protrusion 51a is the same as the thickness of the protective film layer 14.

[0053] Through the above process, the wiring substrate 101 (first wiring substrate) is obtained.

[0054] Next, as shown in (1) of FIG5A, a double-sided metal foil laminate 20 is prepared. The double-sided metal foil laminate 20 has an insulating substrate 21, a metal foil 22 disposed on the upper surface of the insulating substrate 21, and a metal foil 23 disposed on the lower surface of the insulating substrate 21. The insulating substrate 21 can be liquid crystal polymer (LCP), for example, polyimide (PI), modified polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluoropolymer (PFA, PTEE, etc.), etc., without particular limitation.

[0055] The thickness of the insulating substrate 21 is, for example, 100 μm. The metal foils 22 and 23 are, for example, silver or aluminum, other than copper. The thicknesses of the metal foils 22 and 23 are, for example, 12 μm each. The metal foil 22 is formed on the insulating substrate 21 through a seed layer (not shown) formed on the upper surface of the insulating substrate 21. Similarly, the metal foil 23 is formed under the insulating substrate 21 through a seed layer (not shown) formed on the lower surface of the insulating substrate 21.

[0056] Next, as shown in (2) of FIG5A, the metal foil 22 of the double-sided metal foil laminate 20 is patterned using a known photolithography method to form a second conductive pattern. The second conductive pattern includes a landing point 22a and a wiring 22i. The diameter of the landing point 22a is, for example, φ350μm. The wiring 22i functions as an analog signal line in the flexible circuit board 100. That is, the second conductive pattern includes an analog signal line.

[0057] Next, as shown in (3) of FIG5A, the metal foil 23 of the double-sided metal foil laminate 20 is patterned using a known photolithography method to form a third conductive pattern. The third conductive pattern includes a landing point 23a and a wiring 23b. The diameter of the landing point 23a is, for example, φ350μm. The wiring 23b functions as a ground layer in the flexible circuit board 100.

[0058] Next, as shown in (4) of FIG5A, the landing site 23a is irradiated with a laser as a conformal mask, thereby removing the insulating substrate 21 and forming a bottomed hole H2 exposing the landing site 22a on the bottom surface. The diameter of the hole H2 is, for example, φ150~200μm. Hereinafter, the formation of the hole H2 is the same as the formation of the hole H1. That is, using an infrared laser as a carbon dioxide laser, a laser pulse is irradiated at a predetermined position of the landing site 23a and passes through the hole H2. The beam diameter of the infrared laser is set to 150μm, which is the same as the diameter of the hole H2. In addition, the pulse width of the infrared laser is set to 10 microseconds, and the energy of each pulse of the infrared laser is set to 5mJ.

[0059] For example, an infrared laser, set as described above, is irradiated five times to obtain an aperture H2. Alternatively, a UV-YAG laser or the like can be used in the formation of the aperture H2, and it is not limited to an infrared laser.

[0060] After the hole H2 is pierced with an infrared laser, a resin residue removal process is performed. During the resin residue removal process, resin residue (residual film) at the boundary between the insulating substrate 21 and the landing site 23a is removed. Additionally, during the resin residue removal process, the back treatment film (Ni or Cr, etc.) of the landing site 23a and the landing site 22a is removed.

[0061] Next, as shown in (5) of FIG5A, a first metal plating layer 61 is deposited on the sidewall and bottom surface of the hole H2. The first metal plating layer 61 is, for example, a copper plating layer. In addition, the first metal plating layer 61 can be deposited by partial plating or full-plate plating. The plating thickness of the first metal plating layer 61 is, for example, 16 μm.

[0062] Next, as shown in (1) of FIG5B, an adhesive layer 24 is formed by embedding a third conductive pattern (landing point 23a and wiring 23b) and a first metal plating layer 61 deposited in the hole H2. This adhesive layer 24 is, for example, a micro-adhesive layer with a thickness of 10 μm. Next, as shown in (2) of FIG5B, a cover material layer 71 is formed on the adhesive layer 24. The cover material layer 71 is, for example, an insulating resin film. As an insulating resin film, for example, a liquid crystal polymer (LCP) or polyimide is used. The thickness of the cover material layer 71 is, for example, 12 μm.

[0063] Next, as shown in (3) of FIG5B, an adhesive layer 25 having an opening A1 is formed on the cover material layer 71. The adhesive layer 25 is, for example, a micro-adhesive layer with a thickness of 10 μm. Next, as shown in (4) of FIG5B, a protective film layer 26 is formed on the adhesive layer 25 in such a way that it fills the opening A1 of the adhesive layer 25. The protective film layer 26 is, for example, a PET film with micro-adhesive and a thickness of 20 μm. The size of the opening A1 is, for example, 30 mm in the long side direction and 2 mm in the short side direction.

[0064] Next, as shown in (1) of FIG5C, by irradiating the protective film layer 26 with a laser, the protective film layer 26, adhesive layer 25, covering material layer 71 and adhesive layer 24 are removed, and a bottomed hole H3 with a landing point 23a exposed on the bottom surface is formed. The diameter of the hole H3 is, for example, φ150~200μm. Hereinafter, the formation of the hole H3 is the same as the formation of the hole H1. That is, using an infrared laser as a carbon dioxide laser, a laser pulse is irradiated at a predetermined position of the protective film layer 26 to perform perforation. The beam diameter of the infrared laser is set to 150μm, which is the same as the diameter of the hole H3. In addition, the pulse width of the infrared laser is set to 10 microseconds, and the energy of each pulse of the infrared laser is set to 5mJ.

[0065] Next, as shown in (2) of FIG5C, conductive paste 52 is filled into the interior of hole H3 by printing method such as screen printing. Conductive paste 52 is obtained by dispersing metal particles into a resin binder that is a thermosetting resin in paste form.

[0066] Next, as shown in (3) of FIG5C, the protective film layer 26 is peeled off from the adhesive layer 25 and the cover material layer 71. As a result, a portion of the conductive paste 52 filling the hole H3 protrudes, forming a protrusion 52a. In addition, the height of the protrusion 52a is the same as the thickness of the protective film layer 26 formed on the adhesive layer 25.

[0067] Through the above process, the wiring substrate 102 (second wiring substrate) is obtained.

[0068] Next, as shown in (1) of FIG6, a double-sided metal foil laminate 30 is prepared. The double-sided metal foil laminate 30 has an insulating substrate 31, a metal foil 32 disposed on the upper surface of the insulating substrate 31, and a metal foil 33 disposed on the lower surface of the insulating substrate 31. The insulating substrate 31 can be liquid crystal polymer (LCP), for example, polyimide (PI), modified polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluoropolymer (PFA, PTEE, etc.), etc., without particular limitation.

[0069] The thickness of the insulating substrate 31 is, for example, 50 μm. The metal foils 32 and 33 are, for example, silver or aluminum, other than copper. The thicknesses of the metal foils 32 and 33 are, for example, 12 μm each. The metal foil 32 is formed on the insulating substrate 31 through a seed layer (not shown) formed on the upper surface of the insulating substrate 31. Similarly, the metal foil 33 is formed under the insulating substrate 31 through a seed layer (not shown) formed on the lower surface of the insulating substrate 31.

[0070] By making the thickness of the insulating substrate 31 thinner at 50 μm, the line width of the signal lines can be reduced. More specifically, the line width of the signal lines (wiring 33i) that match the characteristic impedance expressed as Z0 = √(L / C) can be reduced. Here, L is the inductance per unit length, and C is the inter-line capacitance. In this way, by making the thickness of the insulating substrate 31 thinner, the line width of the signal lines can be reduced, and therefore the width of the flexible circuit board 100 can be reduced. Therefore, when the flexible circuit board 100 is built into the housing of electronic devices such as smartphones, space can be saved.

[0071] Next, as shown in FIG6(2), the metal foil 32 is patterned to form a fourth conductive pattern including the landing portion 32a, which serves as a conformal mask. Subsequently, as shown in FIG6(3), the landing portion 32a is irradiated with a laser as a conformal mask, thereby removing the insulating substrate 31 and forming a bottomed hole H4 with the landing portion 33a exposed on the bottom surface. The diameter of the hole H4 is, for example, φ150~200μm. The hole H4 is formed in the same manner as the hole H1. That is, using an infrared laser, which is a carbon dioxide laser, a laser pulse is irradiated onto the opening of the conformal mask and passes through the hole H4. The beam diameter of the infrared laser is set to 150μm, which is the same as the diameter of the hole H4. In addition, as shown in FIG6(2), the metal foil 33 is patterned to form a fifth conductive pattern (landing portion 33a and wiring 33i). The diameter of the landing portion 33a is, for example, φ350μm. Additionally, wiring 33i functions as a digital signal line in the flexible circuit board 100. That is, the fifth conductive pattern includes digital signal lines.

[0072] After the H4 hole is pierced with an infrared laser, a resin residue removal process is performed. During the resin residue removal process, resin residue (residual film) at the boundary between the landing site 33a and the insulating substrate 31 is removed. Additionally, the back treatment film (Ni or Cr, etc.) of the landing site 33a is removed during the resin residue removal process.

[0073] Next, as shown in (4) of FIG6, a second metal plating layer 62 is deposited on the sidewall and bottom surface of the hole H4. The second metal plating layer 62 is, for example, a copper plating layer. Alternatively, the second metal plating layer 62 is deposited by partial plating or full-plate plating. The plating thickness of the second metal plating layer 62 is, for example, 16 μm.

[0074] Next, as shown in (5) of FIG6, the metal foil 32, the insulating substrate 31 and a portion of the landing area 33a are removed using a die or the like to form the window portion W. The size of the window portion W is, for example, the same as the size of the opening A1 of the adhesive layer 25 shown in (3) of FIG5B, for example, 30 mm in the long side direction and 2 mm in the short side direction.

[0075] Through the above process, the wiring substrate 103 (third wiring substrate) is obtained.

[0076] In addition, in the above-described process, the metal foils of each wiring substrate 101, 102, and 103 can be roughened. Through roughening treatment, the bonding strength between the metal foil and the insulating substrate can be improved.

[0077] Hereinafter, the process of laminating the wiring substrate 101, wiring substrate 102 and wiring substrate 103 obtained in the above process will be described with reference to FIG7.

[0078] First, the wiring substrate 101 is laminated onto the wiring substrate 102. Specifically, the lamination is performed such that the protrusions 51a of the conductive paste 51 of the wiring substrate 101 come into contact with the landing portion 22a of the wiring substrate 102.

[0079] Next, the laminate obtained in the above process, consisting of wiring substrate 101 and wiring substrate 102, is laminated onto wiring substrate 103. Specifically, the lamination is performed such that the protrusions 52a of the conductive paste 52 of wiring substrate 102 contact the landing portions 32a of wiring substrate 103. By doing so, electrical layers of wiring substrate 101, wiring substrate 102, and wiring substrate 103 are electrically connected. Furthermore, the order in which wiring substrates 101, 102, and 103 are laminated is not limited to the order described above.

[0080] In the above-described lamination process for forming a laminate composed of wiring substrate 101, wiring substrate 102, and wiring substrate 103, a vacuum pressurizing device or a vacuum lamination device is used. The laminate is heated and pressurized using this vacuum pressurizing device or vacuum lamination device. For example, the laminate is heated at approximately 200°C and pressurized with a pressure of several MPa (e.g., 2.0 MPa). The temperature at which the flexible circuit board 100 is heated is, for example, a temperature approximately 50°C or more lower than the softening temperature of the liquid crystal polymer (LCP) constituting the insulating substrates 11, 21, and 31.

[0081] When a vacuum pressurizing device is used in the lamination process, the laminate is heated and pressurized for about 30 to 60 minutes under the above conditions. By using the vacuum pressurizing device to heat and pressurize the laminate, the thermal curing of adhesive layers 13, 24 and 25, as well as the thermal curing of conductive pastes 51 and 52, are also completed.

[0082] On the other hand, when a vacuum lamination apparatus is used in the lamination process, the laminate is heated and pressurized for several minutes under the conditions described above. Therefore, after the laminate is heated and pressurized by the vacuum lamination apparatus, it is moved into an oven apparatus for post-curing. In the post-curing process, for example, the laminate is heated at approximately 200°C for approximately 60 minutes. Through this post-curing process, the thermal curing of adhesive layers 13, 24, and 25, as well as the thermal curing of conductive pastes 51 and 52, are also completed.

[0083] Next, as needed, the surface treatment and solder resist of the first and fifth conductive patterns exposed to the outside can be performed, and the shape can be processed.

[0084] Through the above process, a flexible circuit board 100 with the cross-sectional structure shown in Figure 3 is obtained.

[0085] As described above, according to the manufacturing method of the flexible circuit board of the first embodiment, a flexible circuit board 100 with a reduced-layer structure in which the bending region 130 has fewer wiring layers and / or fewer insulating layers compared to the signal line region 120 can be obtained. Therefore, the bending region 130 can alleviate the stress during bending compared to the signal line region 120, thereby making it easier to bend and embed the flexible circuit board 100 into the housing of an electronic device such as a smartphone.

[0086] Furthermore, in the flexible circuit board 100, analog signal lines are formed as wiring 22i, and digital signal lines are formed as wiring 33i. As shown in FIG3, analog signal lines and digital signal lines are built into the flexible circuit board 100. Therefore, by building the flexible circuit board 100 into the housing of electronic devices such as smartphones, analog signal lines that transmit analog signals received by wireless communication antennas and digital signal lines that transmit digital signals received by digital terminals such as USB can be centrally configured at one time. As a result, space can be saved within the housing of electronic devices such as smartphones.

[0087] In addition, the bending region 130 of the flexible circuit board 100 reduces the number of wiring layers and the number of insulating layers compared to the signal line region 120. Therefore, the amount of wiring layers and insulating substrate material required for the flexible circuit board 100 can be reduced, thereby reducing manufacturing costs.

[0088] Furthermore, the flexible circuit board 100 is manufactured by stacking wiring substrate 101, wiring substrate 102, and wiring substrate 103. That is, the flexible circuit board 100 is manufactured by stacking three wiring substrates, thus relatively suppressing positional misalignment between the wiring substrates. Therefore, the yield of the manufacturing process of the flexible circuit board 100 can be improved. Moreover, the margin of the aforementioned positional misalignment can be made smaller, thereby enabling a high-density wiring structure in the wiring layer of the flexible circuit board 100.

[0089] (Second Embodiment)

[0090] <Structure of Flexible Circuit Board 100A>

[0091] Next, the structure of the flexible circuit board 100A according to the second embodiment will be described with reference to FIG8. Compared to the flexible circuit board 100 of the first embodiment, which has a reduced-layer structure in the bending region 130, the flexible circuit board 100A of the second embodiment has a hollow structure in the bending region 130. Hereinafter, the differences from the first embodiment will be described.

[0092] Figure 8 is a schematic cross-sectional view of the BB line in Figure 2. In Figure 8, the left side of the figure represents the area corresponding to the connector area 110, and the right side of the figure represents the area corresponding to the signal line area 120. The bending area 130 is located between the connector area 110 and the signal line area 120. This bending area 130 has a hollow structure. That is, as shown in Figure 7, the bending area 130 of the flexible circuit board 100A of the second embodiment has a space (hollow area) HS where neither the wiring layer nor the insulating layer is provided.

[0093] Specifically, in the bending region 130, a space HS is provided between the cover material layer 71 and the cover material layer 72. Therefore, the bending region 130 can alleviate the stress during bending compared to the signal line region 120. Therefore, when the flexible circuit board 100A is built into the housing of an electronic device such as a smartphone, the flexible circuit board 100A can be easily built into the housing in a bent state. Specifically, when the flexible circuit board 100A is built into the housing in a bent state, the flexible circuit board 100A is bent in the bending region 130 and built into the housing. At this time, the bending region 130 can relatively alleviate the stress, so it can be bent relatively easily. Thus, the flexible circuit board 100A can be easily bent and built into the housing.

[0094] Similar to the first embodiment, in the flexible circuit board 100A, analog signal lines are composed of wiring 22i, and digital signal lines are composed of wiring 33i. That is, analog signal lines and digital signal lines can be built into the flexible circuit board 100A, thereby saving space within the housing.

[0095] Furthermore, the flexible circuit board 100A has a ground layer formed by covering the analog signal lines through an insulating layer. Specifically, similar to the first embodiment, the flexible circuit board 100A has ground layers 12b and 23b (wiring 12b and 23b) formed by covering the analog signal lines (wiring 22i) through a first insulating layer (adhesive layer 13 and insulating substrate 11) and a second insulating layer (insulating substrate 21). That is, the flexible circuit board 100A has a three-layer stripline structure.

[0096] An interlayer connection channel for connecting to analog signal lines or digital signal lines is provided in the connector area 110 of the flexible circuit board 100A. Similar to the first embodiment, the interlayer connection channel is provided in holes H1 to H4 of the connector area 110 shown in FIG8. Furthermore, the interlayer connection channel provided in hole H2 is connected to an analog signal line (wiring 22i). Additionally, the interlayer connection channel provided in hole H4 is connected to a digital signal line (wiring 33i).

[0097] In addition, the interlayer connection channel of the connector region 110 has plated through holes for connecting to analog signal lines or digital signal lines. Similar to the first embodiment, the interlayer connection channel of the connector region 110 has plated through holes (hole H2 or hole H4) for connecting to analog signal lines (wiring 22i) or digital signal lines (wiring 33i).

[0098] Alternatively, the interlayer connection channel of the connector region 110 can also be formed by filled vias. More specifically, similar to the first embodiment, conductive paste is filled into holes H1, H3, and H5 to form filled vias. Therefore, as described above, the interlayer connection channel of the connector region 110 has plated through holes and filled vias that are connected to the plated through holes through the conductive layer (landing portion 22a or 32a). In addition, a connector component (not shown) that is electrically connected to analog signal lines and digital signal lines through the aforementioned interlayer connection channel can also be installed in the connector region.

[0099] The configuration of the flexible circuit board 100A according to the second embodiment has been described above. According to the second embodiment, the bending region 130 of the flexible circuit board 100A has a hollow structure, which is obtained by providing a space HS (hollow region) inside the bending region 130 without a wiring layer and an insulating substrate. This mitigates the stress when the bending region 130 is bent. Therefore, the flexible circuit board 100A can be easily bent and integrated into the housing of electronic devices such as smartphones.

[0100] Furthermore, both the analog signal line and the digital signal line are housed in the flexible circuit board 100A. Therefore, it is unnecessary to separately house the analog signal line cable and the digital signal line cable within the casing of the electronic device. This saves space within the casing of electronic devices such as smartphones.

[0101] In addition, compared with the signal line area 120, the bending area 130 reduces the number of wiring layers and / or the number of insulating layers, thereby reducing the amount of wiring layers and insulating substrate material required for the manufacture of the flexible circuit board 100A, thereby reducing manufacturing costs.

[0102] <Manufacturing Method of Flexible Circuit Board 100A>

[0103] Next, the manufacturing method of the flexible circuit board 100A of the second embodiment will be described with reference to the process cross-sectional views of Figures 9A to 10.

[0104] Even in the second embodiment, the flexible circuit board 100A is manufactured by stacking wiring substrate 101 (first wiring substrate), wiring substrate 102 (second wiring substrate), and wiring substrate 103A (third wiring substrate). Furthermore, the manufacturing methods for wiring substrate 101 and wiring substrate 102 are the same as in the first embodiment. That is, the manufacturing method of wiring substrate 101 in the second embodiment is shown in FIG. 4, and the manufacturing method of wiring substrate 102 is shown in FIGS. 5A to 5C, therefore, the description is omitted. The manufacturing method of wiring substrate 103A will be described below.

[0105] As shown in (1) of Figure 9A, a double-sided metal foil laminate 30 is prepared. The double-sided metal foil laminate 30 has an insulating substrate 31, a metal foil 32 disposed on the upper surface of the insulating substrate 31, and a metal foil 33 disposed on the lower surface of the insulating substrate 31. The insulating substrate 31 can be liquid crystal polymer (LCP), for example, polyimide (PI), modified polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluoropolymer (PFA, PTEE, etc.), etc., without any particular limitation.

[0106] The thickness of the insulating substrate 31 is, for example, 50 μm. The metal foils 32 and 33 are, for example, silver or aluminum, other than copper. The thicknesses of the metal foils 32 and 33 are, for example, 12 μm each. The metal foil 32 is formed on the insulating substrate 31 through a seed layer (not shown) formed on the upper surface of the insulating substrate 31. Similarly, the metal foil 3 is formed under the insulating substrate 31 through a seed layer (not shown) formed on the lower surface of the insulating substrate 31.

[0107] By making the insulating substrate 31 thinner at 50 μm, the line width of the signal lines can be reduced. More specifically, the line width of the signal lines (wiring 33i) that match the characteristic impedance expressed as Z0 = √(L / C) can be reduced. Here, L is the inductance per unit length, and C is the inter-line capacitance. In this way, by making the insulating substrate 31 thinner, the line width of the signal lines can be reduced, and therefore the width of the flexible circuit board 100A can be reduced. As a result, space can be saved when the flexible circuit board 100A is built into the housing of electronic devices such as smartphones.

[0108] Next, as shown in (2) of FIG9A, the metal foil 32 is patterned to form a fourth conductive pattern including a landing portion 32a that functions as a conformal mask. Furthermore, as shown in (3) of FIG9A, the metal foil 33 is patterned to form a fifth conductive pattern including a landing portion 33a and wiring 33i. The diameter of the landing portion 33a is, for example, φ350μm. Additionally, the wiring 33i functions as a digital signal line in the flexible circuit board 100. That is, the fifth conductive pattern includes a digital signal line.

[0109] Next, as shown in (4) of FIG9A, by irradiating the landing site 32a with a laser as a conformal mask, the insulating substrate 31 is removed, and a hole H4 is formed on the bottom surface exposing the landing site 33a. The diameter of the hole H4 is, for example, φ150~200μm. In addition, the formation of the hole H4 is the same as the formation of the hole H1 in the first embodiment.

[0110] After penetrating the insulating substrate 31 with an infrared laser, a resin residue removal process is performed. During the resin residue removal process, resin residue (residual film) at the boundary between the landing site 33a and the insulating substrate 31 is removed. Additionally, during the resin residue removal process, the back treatment film (Ni or Cr, etc.) of the landing site 33a is removed.

[0111] Next, as shown in (5) of FIG9A, a second metal plating layer 62 is deposited on the sidewall and bottom surface of the hole H4. The second metal plating layer 62 is, for example, a copper plating layer. Alternatively, the second metal plating layer 62 is deposited by partial plating or full-plate plating. The plating thickness of the second metal plating layer 62 is, for example, 16 μm.

[0112] Next, as shown in FIG9B(1), an adhesive layer 34 is formed on the metal foil 32 by embedding a fourth conductive pattern (landing point 32a, wiring 32b) formed by patterning the metal foil 32 and a second metal plating layer 62 deposited in the hole H4. The thickness of the adhesive layer 34 is, for example, 10 μm. Next, as shown in FIG9B(2), a cover material layer 72 is formed on the adhesive layer 34. The cover material layer 72 is, for example, an insulating resin film. Liquid crystal polymer (LCP) or polyimide is used as the insulating resin film, for example. The thickness of the cover material layer 72 is, for example, 12 μm. Next, as shown in FIG9B(3), a protective film layer 35 is formed on the cover material layer 72. The thickness of the protective film layer 35 is, for example, 10 μm.

[0113] Next, as shown in FIG9C (1), by irradiating the protective film layer 35 with a laser, the protective film layer 35, the covering material layer 72, and the adhesive layer 34 are removed, and a bottomed hole H5 with a landing point 32a exposed on the bottom surface is formed. The diameter of the hole H5 is, for example, φ150~200μm. Hereinafter, the formation of the hole H5 is the same as the formation of the hole H1 in the first embodiment. That is, using an infrared laser as a carbon dioxide laser, a laser pulse is irradiated at a predetermined position of the protective film layer 35 to perform perforation. The beam diameter of the infrared laser is set to 150μm, which is the same as the diameter of the hole H5. In addition, the pulse width of the infrared laser is set to 10 microseconds, and the energy of each pulse of the infrared laser is set to 5mJ.

[0114] Next, as shown in (2) of FIG9C, conductive paste 53 is filled into the interior of hole H5 by printing method such as screen printing. Conductive paste 53 is obtained by dispersing metal particles into a resin binder that is a thermosetting resin in paste form.

[0115] Next, as shown in (3) of FIG9C, the protective film layer 35 is peeled off from the cover material layer 72. As a result, a portion of the conductive paste 53 filling the hole H5 protrudes, forming a protrusion 53a. In addition, the height of the protrusion 53a is the same as the thickness of the protective film layer 35.

[0116] Through the above process, wiring substrate 103A is obtained.

[0117] In the above process, the metal foil of each wiring substrate can also be roughened. Through roughening treatment, the bonding strength between the metal foil and the insulating substrate can be improved.

[0118] Hereinafter, the process of stacking the wiring substrate 101, wiring substrate 102 and wiring substrate 103A obtained in the above process will be described with reference to FIG10.

[0119] First, the wiring substrate 102 is laminated onto the wiring substrate 101. Specifically, the lamination is performed such that the protrusions 51a of the conductive paste 51 of the wiring substrate 101 come into contact with the landing portion 22a of the wiring substrate 102.

[0120] Next, the laminate obtained in the above process, consisting of wiring substrate 101 and wiring substrate 102, is laminated onto wiring substrate 103A. Specifically, the laminate is performed such that the protrusions 52a of conductive paste 52 contact the protrusions 53a of conductive paste 53. By doing so, electrical layers of wiring substrate 101, wiring substrate 102, and wiring substrate 103A are electrically connected. Furthermore, the order in which wiring substrates 101, 102, and 103A are laminated is not limited to the order described above.

[0121] In the above-described lamination process for forming the laminate composed of wiring substrate 101, wiring substrate 102, and wiring substrate 103A, a vacuum pressurizing device or a vacuum laminating device is used, similar to the first embodiment. The laminate is heated and pressurized using this vacuum pressurizing device or vacuum laminating device. For example, the laminate is heated at approximately 200°C and pressurized at a pressure of several MPa (e.g., 2.0 MPa). The temperature at which the laminate is heated is, for example, a temperature approximately 50°C or more lower than the softening temperature of the liquid crystal polymer (LCP) of the insulating substrates 11, 21, and 31.

[0122] In the lamination process of the laminate, when using a vacuum pressurizing device, the laminate is heated and pressurized for about 30 to 60 minutes under the above conditions. By using the vacuum pressurizing device to heat and pressurize the laminate, the thermal curing of adhesive layers 13, 24, 25 and 34, as well as the thermal curing of conductive pastes 51 and 52, are also completed.

[0123] On the other hand, in the lamination process, when using a vacuum lamination apparatus, the laminate is heated and pressurized for several minutes under the conditions described above. Therefore, after heating and pressurizing the flexible circuit board 100A using a vacuum lamination apparatus, the laminate is moved to an oven apparatus for post-curing. In the post-curing process, for example, it is heated at approximately 200°C for approximately 60 minutes. Through this post-curing process, the thermal curing of adhesive layers 13, 24, 25, and 34, as well as the thermal curing of conductive pastes 51 and 52, are also completed.

[0124] Next, as needed, the surface treatment and solder resist of the first and fifth conductive patterns exposed to the outside are performed, and the shape is processed.

[0125] Through the above process, a flexible circuit board 100A with the cross-sectional structure shown in FIG8 is obtained.

[0126] As shown above, according to the manufacturing method of the flexible circuit board 100A of the second embodiment, a flexible circuit board 100A with a hollow structure having a space HS (hollow region) without wiring layers and insulating layers disposed inside the bending region 130 can be obtained. Therefore, the bending region 130 can alleviate the stress during bending compared with the signal line region 120, thereby making it easy to bend and embed the flexible circuit board 100A into the housing of electronic devices such as smartphones.

[0127] Furthermore, similar to the first embodiment, in the flexible circuit board 100A, analog signal lines are formed as wiring 22i, and digital signal lines are formed as wiring 33i. As shown in FIG8, the analog signal lines and digital signal lines are built into the flexible circuit board 100A. Therefore, by building the flexible circuit board 100A into the housing of a smartphone or similar device, analog signal lines that transmit analog signals received by a wireless communication antenna and digital signal lines that transmit digital signals received by a digital terminal such as a USB can be centrally configured at once. As a result, space can be saved within the housing of electronic devices such as smartphones.

[0128] In addition, the bending region 130 of the flexible circuit board 100A reduces the number of wiring layers and the number of insulating layers compared to the signal line region 120. Therefore, the amount of wiring layers and insulating substrate material required for the flexible circuit board 100A can be reduced, thereby reducing manufacturing costs.

[0129] Furthermore, the flexible circuit board 100A is manufactured by stacking wiring substrate 101, wiring substrate 102, and wiring substrate 103A. That is, the flexible circuit board 100A is manufactured by stacking three wiring substrates, thus relatively suppressing the occurrence of positional deviation between the wiring substrates. Therefore, the yield of the manufacturing process of the flexible circuit board 100A can be improved. Moreover, the margin of the aforementioned positional deviation can be made smaller, thereby enabling a high-density wiring structure in the wiring layer of the flexible circuit board 100A.

[0130] (Third Embodiment)

[0131] Next, the flexible circuit board 100B of the third embodiment will be described with reference to FIG11A. Similar to the flexible circuit board 100A of the second embodiment, the flexible circuit board 100B has a hollow structure in the bending region 130. Furthermore, the flexible circuit board 100B has a cutout on one side of the bending region 130 (the lower surface 130b side in FIG11A). Hereinafter, the differences from the second embodiment will be described.

[0132] FIG11A is a schematic perspective view showing the bending region 130 of the flexible circuit board 100B. FIG11A is a schematic perspective view of region C of FIG2, showing a portion of the connector region 110, a portion of the signal line region 120, and the bending region 130.

[0133] More specifically, the bending region 130 of the flexible circuit board 100B has a space HS where no wiring layer or insulating layer is provided. That is, the bending region 130 has a hollow structure. In other words, a space HS as a hollow region is provided between the upper surface 130a and the lower surface 130b of the bending region 130.

[0134] As shown in FIG11A, slits ST1 and ST2, serving as cuts, are provided on the lower surface 130b of the curved region 130. Specifically, slits ST1 and ST2 are provided in a region on one side of the space HS in the thickness direction of the flexible circuit board 100B. Alternatively, slits ST1 and ST2 may also be provided on both sides of the curved region 130. That is, slits ST1 and ST2 may be provided on the upper surface 130a and lower surface 130b, which are both sides of the curved region 130. In FIG11A, slits ST1 and ST2 are provided along a width direction orthogonal to the long side direction of the signal line region 120. Alternatively, slits ST1 and ST2 may also be provided along a direction intersecting the width direction of the curved region 130. Slits ST1 and ST2 may also be provided with a width direction component orthogonal to the long side direction of the signal line region 120 of the flexible circuit board 100B.

[0135] The other structures of the flexible circuit board 100B are the same as those of the flexible circuit board 100A in the second embodiment, so the description is omitted. Furthermore, the manufacturing method of the flexible circuit board 100B is also the same as that of the flexible circuit board 100A in the second embodiment, so the description is omitted. Wiring 22i and 33i are formed in a serpentine manner to avoid slits ST1 and ST2.

[0136] As shown above, the bending region 130 of the flexible circuit board 100B has a space HS where no wiring layer or insulating layer is provided. Furthermore, slits ST1 and ST2 are provided on the lower surface 130b of the bending region 130. Therefore, the bending region 130 can further mitigate the stress during bending compared to the signal line region 120, thus making it easier to bend and integrate the flexible circuit board 100B into the housing of a smartphone or the like.

[0137] In addition, similar to the second embodiment, analog signal lines and digital signal lines are built into the flexible circuit board 100B. Therefore, by placing the flexible circuit board 100B into the housing, analog signal lines and digital signal lines can be centrally arranged at once, thereby saving space inside the housing of smartphones and the like.

[0138] In addition, the bending region 130 of the flexible circuit board 100B reduces the number of wiring layers and the number of insulating layers compared to the signal line region 120, so the amount of wiring layers and insulating substrate material required for the flexible circuit board 100B can be reduced, thereby reducing manufacturing costs.

[0139] Furthermore, the flexible circuit board 100B is manufactured by stacking wiring substrate 101 (first wiring substrate), wiring substrate 102 (second wiring substrate), and wiring substrate 103A (third wiring substrate). That is, the flexible circuit board 100B is manufactured by stacking three wiring substrates, thus relatively suppressing the positional deviation between the wiring substrates. As a result, the yield of the flexible circuit board 100B manufacturing process can be improved. Moreover, the margin of the aforementioned positional deviation can be made smaller, thereby enabling a high-density wiring structure in the wiring layer of the flexible circuit board 100B.

[0140] (Fourth Embodiment)

[0141] Next, the flexible circuit board 100C of the fourth embodiment will be described with reference to FIGS. 11B and 11C. Similar to the flexible circuit board 100A of the second embodiment, the flexible circuit board 100C has a hollow structure in the bending region 130. Furthermore, one side of the bending region 130 of the flexible circuit board 100C (the lower surface 130b side in FIGS. 11B and 11C) is provided in a meandering or crank-like shape. Hereinafter, the differences from the second embodiment will be described.

[0142] Figures 11B and 11C are schematic perspective views showing the bending region 130 of the flexible circuit board 100C. Figures 11B and 11C are schematic perspective views of region C of Figure 2, showing a portion of the connector region 110, a portion of the signal line region 120, and the bending region 130.

[0143] More specifically, the bending region 130 of the flexible circuit board 100C has a space HS where no wiring layer or insulating layer is provided, that is, the bending region 130 has a hollow structure. In other words, there is a space HS between the upper surface 130a and the lower surface 130b of the bending region 130.

[0144] First, as shown in FIG11B, the lower surface 130b of the curved region 130 has a serpentine, meandering shape. Specifically, when viewed from above the flexible circuit board 100C, the lower surface 130b of the curved region 130 is configured in a meandering shape. In other words, this meandering lower surface 130b is located in a region on one side of the space HS in the thickness direction of the flexible circuit board 100C. Alternatively, both sides of the curved region 130, namely the upper surface 130a and the lower surface 130b, may also be configured in a meandering shape.

[0145] On the other hand, as shown in FIG11C, the lower surface 130b of the curved region 130 may also have a crank shape. Specifically, when viewed from above the flexible circuit board 100C, the lower surface 130b of the curved region 130 is configured as a crank. In other words, the crank-shaped lower surface 130b is disposed in a region on one side of the space HS in the thickness direction of the flexible circuit board 100C. Alternatively, both sides of the curved region 130, namely the upper surface 130a and the lower surface 130b, may also be configured as cranks.

[0146] The other structures of the flexible circuit board 100C are the same as those of the flexible circuit board 100A in the second embodiment, so descriptions are omitted. Furthermore, the manufacturing method of the flexible circuit board 100C is the same as that of the flexible circuit board 100A in the second embodiment, so descriptions are omitted. Wiring 22i and 33i are formed along a meandering or crank-like shape.

[0147] As shown above, the bending region 130 of the flexible circuit board 100C has a space HS where no wiring layer or insulating layer is provided. Furthermore, the lower surface 130b of the bending region 130 is configured in a meandering or crank-shaped manner. Therefore, compared with the signal line region 120, the bending region 130 can further mitigate the stress during bending, thereby making it easier to bend and integrate the flexible circuit board 100C into the housing of a smartphone or the like.

[0148] In addition, similar to the second embodiment, analog signal lines and digital signal lines are built into the flexible circuit board 100C. Therefore, by placing the flexible circuit board 100C into the housing, analog signal lines and digital signal lines can be centrally arranged at one time, thereby saving space inside the housing of smartphones and the like.

[0149] In addition, the bending region 130 of the flexible circuit board 100C reduces the number of wiring layers and the number of insulating layers compared to the signal line region 120. Therefore, the amount of wiring layers and insulating substrate material required for the flexible circuit board 100C can be reduced, thereby reducing manufacturing costs.

[0150] Furthermore, the flexible circuit board 100C is manufactured by stacking wiring substrate 101 (first wiring substrate), wiring substrate 102 (second wiring substrate), and wiring substrate 103A (third wiring substrate). That is, the flexible circuit board 100C is manufactured by stacking three wiring substrates, thus relatively suppressing the occurrence of positional deviation between the wiring substrates. Therefore, the yield of the flexible circuit board 100C manufacturing process can be improved. Moreover, the margin of the aforementioned positional deviation can be made smaller, thereby enabling a high-density wiring structure in the wiring layer of the flexible circuit board 100C.

[0151] (Modified Example)

[0152] Next, the structure of the flexible circuit board 100D of the modified example will be described with reference to FIG12. The flexible circuit board 100 of the first embodiment has a reduced-layer structure in the bending region 130, while the flexible circuit board 100D of the modified example also has a reduced-layer structure in the connector region 110A. Hereinafter, the parts that differ from those of the first embodiment will be described.

[0153] FIG12 is a schematic top view of the flexible circuit board 100D of the modified example. As shown in FIG12, the flexible circuit board 100D of the modified example includes connector region 110 and connector region 110A, signal line region 120 and bending region 130. In addition, FIG12 shows the state in which connector component 111 is installed in connector region 110A.

[0154] Even in the modified flexible circuit board 100D, the bending region 130 has a reduced-layer structure. That is, the bending region 130 of the flexible circuit board 100D has a reduced-layer structure with fewer wiring layers and / or fewer insulating layers compared to the signal line region 120.

[0155] Furthermore, in the modified example, in addition to the bending region 130, the connector region 110A also has a layer-reduction structure. That is, the connector region 110A has a layer-reduction structure with fewer wiring layers and / or fewer insulating layers compared to the signal line region 120. Additionally, the cross-sectional structure of the connector region 110A can also be the same as that of the bending region 130. That is, the cross-sectional structure of the connector region 110A can be the same as the cross-sectional structure of the bending region 130 shown in FIG. 3. Furthermore, in the flexible circuit board 100D shown in FIG. 12, the connector region 110A, as one of the connector regions, has a layer-reduction structure. In the modified example, the flexible circuit board 100D may also have layer-reduction structures in both connector regions (connector region 110 and connector region 110A).

[0156] The other structures of the flexible circuit board 100D are the same as those of the flexible circuit board 100 of the first embodiment. Furthermore, the manufacturing method of the flexible circuit board 100D is also the same as that of the flexible circuit board 100 of the first embodiment. That is, in the manufacturing method of the flexible circuit board 100D, the process of forming the subtractive structure of the bending region 130 is simply applied to the process of forming the subtractive structure of the connector region 110A.

[0157] As shown above, in the modified flexible circuit board 100D, in addition to the bending region 130, the connector region 110A also has a reduced-layer structure with fewer wiring layers and / or fewer insulating layers compared to the signal line region 120. Therefore, the amount of wiring layers and insulating substrate material required for the flexible circuit board 100D can be further reduced, thereby further reducing manufacturing costs.

[0158] Furthermore, the connector region 110A and the bending region 130 can mitigate the stress during bending compared to the signal line region 120. Therefore, similar to the flexible circuit board 100 of the first embodiment, the flexible circuit board 100D can be easily bent and embedded into the housing of a smartphone or the like.

[0159] In addition, analog signal lines and digital signal lines are built into the flexible circuit board 100D. Therefore, by placing the flexible circuit board 100D into the housing, analog signal lines and digital signal lines can be centrally arranged at one time, thereby saving space inside the housing of smartphones and the like.

[0160] Furthermore, the flexible circuit board 100D is manufactured by stacking wiring substrate 101 (first wiring substrate), wiring substrate 102 (second wiring substrate), and wiring substrate 103 (third wiring substrate). That is, the flexible circuit board 100D is manufactured by stacking three wiring substrates, thus relatively suppressing the occurrence of positional deviation between the wiring substrates. As a result, the yield of the flexible circuit board 100D manufacturing process can be improved. Moreover, the margin of the aforementioned positional deviation can be made smaller, thereby enabling a high-density wiring structure in the wiring layer of the flexible circuit board 100D.

[0161] <Electronic devices with built-in flexible circuit boards>

[0162] (Fifth Embodiment)

[0163] Next, an embodiment of an electronic device incorporating the flexible circuit board 100 of the first to fourth embodiments or variations described above will be described with reference to FIG13A. In the electronic device of this embodiment, the flexible circuit board 100 is bent and incorporated into the side of the electronic device housing.

[0164] The right-hand view of Figure 13A is a perspective view schematically showing the state of the flexible circuit board 100 before bending. The central view of Figure 13A is a perspective view schematically showing the state of the flexible circuit board 100 after bending. As shown in the right-hand and central views of Figure 13A, when the flexible circuit board 100 is incorporated into the housing of the electronic device, the bending region 130 of the flexible circuit board 100 is bent into the desired shape and incorporated. In Figure 13A, the side of the flexible circuit board 100 incorporated into the housing of the electronic device is shown. In the right-hand view of Figure 13A, the connector region 110a and the bending region 130 are shown upright on the signal line region 120. From this state, as shown in the central view of Figure 13A, the bending region 130 is bent forward (in the direction of incorporating the flexible circuit board 100), resulting in the connector region 110b leaning forward.

[0165] The left side of FIG13A is a schematic diagram of an electronic device UE with a flexible circuit board 100 built in. In the electronic device UE, the flexible circuit board 100 and other electronic components are built in a housing 500. Specifically, the electronic device UE has a housing 500, in which the flexible circuit board 100 of the above-described embodiment or variation is built. Furthermore, a first module 200 and a second module 300 are disposed inside the housing 500, and a battery 400 is disposed between the first module 200 and the second module 300.

[0166] In the electronic device UE of this embodiment, the first module 200 has a wireless communication antenna for receiving analog signals and a digital terminal for receiving digital signals. The second module 300 performs signal processing on the analog and digital signals received by the first module 200. Additionally, as shown in FIG13A, a processor 210 for overall control of the electronic device UE may also be configured on the first module 200.

[0167] A connector component 220 is provided in the first module 200. The first module 200 and the connector region 110a are electrically connected through the connector component 220. On the other hand, a connector component 310 is also provided in the second module 300. The second module 300 and the connector region 110b are electrically connected through the connector component 310. Thus, the first module 200 and the second module 300 are electrically connected through the flexible circuit board 100. In other words, the flexible circuit board 100 electrically connects the first module 200 and the second module 300.

[0168] As described above, in this embodiment, a flexible circuit board 100 is built into the side of the housing 500 of the electronic device UE. That is, the flexible circuit board 100 is built into the housing 500 in such a way that the connector component 220 and the connector component 310 are bent in the bending region 130 so that the connector component 220 and the connector component 310 are respectively fitted into the first module 200 and the second module 300, and the signal line region 120 is along the side of the housing 500.

[0169] As shown above, according to this embodiment, the first module 200 and the second module 300 can be electrically connected using the flexible circuit board 100. Therefore, it is possible to save space within the housing of the electronic device UE, thus enabling the battery 400 to be made larger. In addition, since the flexible circuit board 100 can be arranged without spanning the battery 400, coils for wireless power supply, etc., can be arranged on the upper surface of the battery.

[0170] (Sixth Embodiment)

[0171] Next, another embodiment of an electronic device incorporating the flexible circuit board 100 of the first to fourth embodiments or variations described above will be described with reference to FIG13B. In this embodiment, the flexible circuit board 100 is incorporated into the bottom surface of the housing of the electronic device in a bent state with the bending region 130 bent. Hereinafter, the differences from the fifth embodiment will be described.

[0172] FIG13B is a diagram showing an electronic device UE with a flexible circuit board 100 built in. FIG13B(1) is a schematic top view of the electronic device UE, and FIG13B(2) is a schematic cross-sectional view of the electronic device UE. As shown in FIG13B(1) and FIG13B(2), the electronic device UE has a flexible circuit board 100 and other electronic components built in a housing 500. Specifically, the electronic device UE has a housing 500, and the flexible circuit board 100 of the above embodiment or variation is built in the housing 500. In addition, a first module 200 and a second module 300 are arranged inside the housing 500, and a battery 400 is arranged between the first module 200 and the second module 300.

[0173] Figure 13B (3) shows a perspective view of the flexible circuit board 100 in the state of being built into the housing 500 (the state shown in Figures 13B (1) and (2)). As shown in Figure 13B (3), the flexible circuit board 100 is bent in bending region 130B at P1 and P2, and bent in bending region 130A at P3 and P4. In other words, bending region 130A and bending region 130B are bent at two locations respectively. That is, in the flexible circuit board 100 of the first embodiment to the fourth embodiment or the modified embodiment, the stress when bending region 130 is reduced, so that both locations of bending region 130 can be bent as shown in this embodiment.

[0174] Furthermore, similar to the fifth embodiment, the first module 200 and the second module 300 can be electrically connected using the flexible circuit board 100. Therefore, it is possible to save space within the housing of the electronic device UE, thus enabling the battery 400 to be made larger. Additionally, since the flexible circuit board 100 can be arranged without spanning the upper surface of the battery 400, coils used for wireless power supply, etc., can be arranged on the upper surface of the battery.

[0175] Based on the foregoing description, those skilled in the art may conceive of additional effects and various modifications of the present invention, but the invention is not limited to the various embodiments described above. Elements spanning different embodiments can be appropriately combined. Various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the invention derived from the claims and their equivalents. [Simplified Explanation of the Diagram]

[0023] FIG1 is a top view of the flexible circuit board according to the embodiment. FIG2 is an enlarged top view of region A in FIG1. ​​FIG3 is a schematic cross-sectional view of line BB in FIG2. FIG4 is a process cross-sectional view for explaining the manufacturing method of the flexible circuit board according to the first embodiment. FIG5A is a process cross-sectional view following FIG4 for explaining the manufacturing method of the flexible circuit board according to the first embodiment. FIG5B is a process cross-sectional view following FIG5A for explaining the manufacturing method of the flexible circuit board according to the first embodiment. FIG5C is a process cross-sectional view following FIG5B for explaining the manufacturing method of the flexible circuit board according to the first embodiment. FIG6 is a process cross-sectional view following FIG5C for explaining the manufacturing method of the flexible circuit board according to the first embodiment. FIG7 is a process cross-sectional view following FIG6 for explaining the manufacturing method of the flexible circuit board according to the first embodiment. FIG8 is a schematic cross-sectional view of line BB in FIG2 according to the second embodiment. FIG9A is a process cross-sectional view for explaining the manufacturing method of the flexible circuit board according to the second embodiment. FIG9B is a process cross-sectional view following FIG9A for explaining the manufacturing method of the flexible circuit board according to the second embodiment. Figure 9C is a process cross-sectional view, following Figure 9B, illustrating the manufacturing method of the flexible circuit board according to the second embodiment. Figure 10 is a process cross-sectional view, following Figure 9C, illustrating the manufacturing method of the flexible circuit board according to the second embodiment. Figure 11A is a schematic perspective view of region C of Figure 2 according to the third embodiment. Figure 11B is a schematic perspective view of region C of Figure 2 according to the fourth embodiment (winding shape). Figure 11C is a schematic perspective view of region C of Figure 2 according to the fourth embodiment (crank shape). Figure 12 is a top view of a modified flexible circuit board. Figure 13A is a schematic perspective view of an electronic device according to the fifth embodiment. Figure 13B is a schematic top view and a schematic cross-sectional view of an electronic device according to the sixth embodiment.

Claims

1. A flexible circuit board, wherein, The flexible circuit board includes a signal line area, a connector area, a bending area, one or more analog signal lines, one or more digital signal lines, and a ground plane. The one or more analog signal lines are formed to extend along the long side of the signal line area and transmit analog signals. The one or more digital signal lines are formed to extend along the long side of the signal line area and transmit digital signals. The ground plane is formed to cover the analog signal lines through an insulating layer. The bending area connects the signal line area and the connector area. Compared with the signal line area, the number of wiring layers and the number of insulating layers are at least one less.

2. The flexible circuit board as described in claim 1, wherein, Compared to the signal line area, the connector area has at least one less wiring layer and at least one less insulation layer.

3. A flexible circuit board, wherein, The flexible circuit board includes a signal line area, a connector area, a bending area, one or more analog signal lines, one or more digital signal lines, and a ground layer. The one or more analog signal lines are formed to extend along the long side of the signal line area and transmit analog signals. The one or more digital signal lines are formed to extend along the long side of the signal line area and transmit digital signals. The ground layer is formed to cover the analog signal lines through an insulating layer. The bending area connects the signal line area and the connector area, and the interior of the bending area has a space where no wiring layer or insulating layer is provided.

4. The flexible circuit board as described in claim 3, wherein, The flexible circuit board in the space also has a cutout on one or both sides in the thickness direction, and the direction of the cutout is a width direction component that is orthogonal to the long side direction of the signal line region.

5. The flexible circuit board as described in claim 3, wherein, When viewed from above, the flexible circuit board is formed in a meandering or crank-like shape on one or both sides of the space in the thickness direction of the flexible circuit board.

6. The flexible circuit board as claimed in any one of claims 1 to 5, wherein, An interlayer connection channel is provided in the connector area, and the interlayer connection channel is connected to the analog signal line or the digital signal line.

7. The flexible circuit board as described in claim 6, wherein, The interlayer connection channel has: plated through-holes connected to the analog signal line or the digital signal line; and filled vias connected to the plated through-holes through a conductive layer.

8. The flexible circuit board as described in claim 6, wherein, A connector component is installed in the connector area, and the connector component is electrically connected to the analog signal line and the digital signal line through the interlayer connection channel.

9. The flexible circuit board as claimed in claim 7, wherein, A connector component is installed in the connector area, and the connector component is electrically connected to the analog signal line and the digital signal line through the interlayer connection channel.

10. An electronic device, comprising: case; The flexible circuit board as described in any one of claims 1 to 8 is disposed within the housing; The first module is disposed within the housing; A second module is disposed within the housing; and a battery is disposed within the housing between the first module and the second module.

11. The electronic device as claimed in claim 10, wherein, The flexible circuit board is configured between the battery and the side of the housing.

12. The electronic device as claimed in claim 10, wherein, The flexible circuit board is configured between the battery and the back or front of the housing.

13. A method for manufacturing a flexible circuit board, wherein, The manufacturing method of the flexible circuit board includes the following steps: preparing a first single-sided metal foil laminate, the first single-sided metal foil laminate having: a first insulating substrate having a first main surface and a second main surface opposite to the first main surface; and a first metal foil disposed on the first main surface of the first insulating substrate; A first protective film layer is disposed on the second main surface of the first insulating substrate through a first adhesive layer; the first metal foil is patterned to form a first conductive pattern; a first bottom hole is formed, the first bottom hole penetrating the first protective film layer, the first adhesive layer, and the first insulating substrate and reaching the first metal foil; a first conductive paste is filled into the first bottom hole; the first protective film layer is peeled off to obtain a first wiring substrate; Prepare a first double-sided metal foil laminate, the first double-sided metal foil laminate having: a second insulating substrate having a third main surface and a fourth main surface opposite to the third main surface; and a second metal foil disposed on the third main surface of the second insulating substrate; A third metal foil is disposed on the fourth main surface of the second insulating substrate; the second metal foil is patterned to form a second conductive pattern; a second bottom hole is formed, the second bottom hole penetrating the second insulating substrate and reaching the second metal foil; a first metal plating layer is deposited on the sidewall and bottom surface of the second bottom hole; the third metal foil is patterned to form a third conductive pattern; a second adhesive layer is formed on the third metal foil by embedding the third conductive pattern of the third metal foil and the first metal plating layer deposited on the second bottom hole; a first cover material layer is formed on the second adhesive layer; a third adhesive layer having a first opening is formed on the first cover material layer; a second protective film layer is formed on the third adhesive layer by filling the first opening of the third adhesive layer; a third bottom hole is formed, the third bottom hole penetrating the second protective film layer, the third adhesive layer, the first cover material layer, and the second adhesive layer and reaching the third metal foil; a second conductive paste is filled into the third bottom hole; the second protective film layer is peeled off to obtain a second wiring substrate; Prepare a second double-sided metal foil laminate, the second double-sided metal foil laminate having: a third insulating substrate having a fifth main surface and a sixth main surface opposite to the fifth main surface; and a fourth metal foil disposed on the fifth main surface of the third insulating substrate; A fifth metal foil is disposed on the sixth main surface of the third insulating substrate; the fourth metal foil is patterned to form a fourth conductive pattern; the fifth metal foil is patterned to form a fifth conductive pattern; a fourth bottom hole is formed, the fourth bottom hole penetrating the third insulating substrate and reaching the fifth metal foil; a second metal plating layer is deposited on the sidewall and bottom surface of the fourth bottom hole; a first through hole is formed penetrating the third insulating substrate and the fifth metal foil to obtain a third wiring substrate; and the first wiring substrate is laminated onto the second wiring substrate in such a way that the first conductive paste contacts the second conductive pattern, and the third wiring substrate is laminated onto the second wiring substrate in such a way that the second conductive paste contacts the third conductive pattern.

14. A method for manufacturing a flexible circuit board as described in claim 13, wherein, The second conductive pattern includes analog signal lines.

15. A method for manufacturing a flexible circuit board, wherein, The manufacturing method of the flexible circuit board includes the following steps: preparing a first single-sided metal foil laminate, the first single-sided metal foil laminate having: a first insulating substrate having a first main surface and a second main surface opposite to the first main surface; and a first metal foil disposed on the first main surface of the first insulating substrate; A first protective film layer is disposed on the second main surface of the first insulating substrate through a first adhesive layer; the first metal foil is patterned to form a first conductive pattern; a first bottom hole is formed, the first bottom hole penetrating the first protective film layer, the first adhesive layer, and the first insulating substrate and reaching the first metal foil; a first conductive paste is filled into the first bottom hole; the first protective film layer is peeled off to obtain a first wiring substrate; Prepare a first double-sided metal foil laminate, the first double-sided metal foil laminate having: a second insulating substrate having a third main surface and a fourth main surface opposite to the third main surface; and a second metal foil disposed on the third main surface of the second insulating substrate; A third metal foil is disposed on the fourth main surface of the second insulating substrate; the second metal foil is patterned to form a second conductive pattern; a second bottom hole is formed, the second bottom hole penetrating the second insulating substrate and reaching the second metal foil; a first metal plating layer is deposited on the sidewall and bottom surface of the second bottom hole; the third metal foil is patterned to form a third conductive pattern; a second adhesive layer is formed on the third metal foil by embedding the third conductive pattern of the third metal foil and the first metal plating layer deposited on the second bottom hole; a first cover material layer is formed on the second adhesive layer; a third adhesive layer having a first opening is formed on the first cover material layer; a second protective film layer is formed on the third adhesive layer by filling the first opening of the third adhesive layer; a third bottom hole is formed, the third bottom hole penetrating the second protective film layer, the third adhesive layer, the first cover material layer, and the second adhesive layer and reaching the third metal foil; a second conductive paste is filled into the third bottom hole; the second protective film layer is peeled off to obtain a second wiring substrate; Prepare a second double-sided metal foil laminate, the second double-sided metal foil laminate having: a third insulating substrate having a fifth main surface and a sixth main surface opposite to the fifth main surface; and a fourth metal foil disposed on the fifth main surface of the third insulating substrate; A fifth metal foil is disposed on the sixth main surface of the third insulating substrate; the fourth metal foil is patterned to form a fourth conductive pattern; the fifth metal foil is patterned to form a fifth conductive pattern; a fourth bottom hole is formed, the fourth bottom hole penetrating the third insulating substrate and reaching the fifth metal foil; a second metal plating layer is deposited on the sidewalls and bottom surface of the fourth bottom hole; a fourth adhesive layer is formed on the fourth metal foil by embedding the third conductive pattern of the fourth metal foil and the second metal plating layer deposited on the fourth bottom hole; a second cover material layer is formed on the fourth adhesive layer; a third protective film layer is formed on the second cover material layer; and a fourth protective film layer is formed on the third protective film layer. A fifth bottom hole is formed, the fifth bottom hole penetrating the fourth protective film layer, the third protective film layer, the second cover material layer, and the third adhesive layer and reaching the fourth metal foil; a third conductive paste is filled into the fifth bottom hole; the third protective film layer and the fourth protective film layer are peeled off to obtain a third wiring substrate; and the first wiring substrate is laminated onto the second wiring substrate in such a way that the first conductive paste contacts the second conductive pattern, and the third wiring substrate is laminated onto the second wiring substrate in such a way that the second conductive paste contacts the third conductive paste.

16. A method for manufacturing a flexible circuit board as described in claim 15, wherein, The second conductive pattern includes analog signal lines.

17. A method for manufacturing a flexible circuit board as described in any one of claims 13 to 16, wherein, The fifth conductive pattern includes digital signal lines.

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