CN115361771A

CN115361771A - Flexible circuit board, manufacturing method thereof and electronic device

Info

Publication number: CN115361771A
Application number: CN202210151195.4A
Authority: CN
Inventors: 高野祥司; 松田文彦; 成泽嘉彦; 重冈赳志
Original assignee: Nippon Mektron KK
Current assignee: Nippon Mektron KK
Priority date: 2021-05-17
Filing date: 2022-02-15
Publication date: 2022-11-18
Also published as: JP2022176786A; TW202247714A

Abstract

The invention provides a flexible circuit board which can transmit both analog signals and digital signals and can be easily built in a shell of electronic equipment such as a smart phone in a bending state, a manufacturing method thereof and the electronic equipment. The flexible circuit board according to an embodiment includes a signal line region, a connector region, a bent region, one or more analog signal lines that transmit analog signals and are formed to extend in a longitudinal direction of the signal line region, one or more digital signal lines that transmit digital signals and are formed to extend in the longitudinal direction of the signal line region, and a ground layer that covers the analog signal lines with an insulating layer, the bent region connects the signal line region and the connector region, and at least one of the number of wiring layers and the number of insulating layers is smaller than that of the signal line region.

Description

Flexible circuit board, method of manufacturing the same, and electronic apparatus

Technical Field

The invention relates to a flexible circuit board, a manufacturing method thereof and an electronic device.

Background

In recent years, the number of antenna connection cables in electronic devices such as smartphones has increased due to the spread of the fifth generation mobile communication system (5G). Further, miniaturization of housings such as smart phones is also advancing. Therefore, a flexible circuit board in which antenna connection cables are further wired at high density is required.

In the 5G system, electric waves of the SUB6 band and electric waves of the millimeter wave band are applied, and electric waves of the frequency band of the current fourth generation mobile communication system (4G) are also applied. Therefore, in the 5G system, the number of antenna connection cables increases. Conventionally, a coaxial cable for transmitting an analog signal and a cable for transmitting a digital signal are built in a housing as separate cables. However, in the 5G system, as the number of antenna connection cables increases, it is required to combine these two types of cables into a multilayer flexible circuit board.

Further, a general multilayer flexible circuit board is described in japanese patent laid-open No. 5204871 and japanese patent laid-open No. 2004-311927.

As described above, with the spread of 5G systems, the number of antennas in electronic devices such as smartphones has increased. In the 5G system, in addition to a cable for transmitting an analog signal such as a wireless signal, a cable for transmitting a digital signal received by a digital terminal such as a USB and a cable for transmitting power of a power supply are also required. These cables are arranged in such a manner as to straddle the upper surface of the battery. On the other hand, the number of cases in which a coil for wireless power supply or the like is disposed on the upper surface of the battery is increasing. Therefore, the cable disposed on the upper surface of the battery is required to save space. In addition, a method of disposing a cable other than the upper surface of the battery is also required, for example, disposing a cable on a side surface of a housing of a smartphone or the like.

Disclosure of Invention

The present invention has been made in view of the above-described technical understanding, and an object of the present invention is to provide a flexible circuit board that can transmit both analog signals and digital signals and can be easily built into a housing of an electronic device such as a smartphone in a bent state, a method of manufacturing the same, and an electronic device incorporating the flexible circuit board.

A flexible circuit board according to a first aspect of the present invention includes a signal line region, a connector region, a bend region, one or more analog signal lines that are formed to extend in a longitudinal direction of the signal line region and transmit analog signals, one or more digital signal lines that are formed to extend in the longitudinal direction of the signal line region and transmit digital signals, and a ground layer that is formed to cover the analog signal lines with an insulating layer, the bend region connects the signal line region and the connector region, and at least one of the number of wiring layers and the number of insulating layers is smaller than that of the signal line region.

In the flexible circuit board, at least one of the number of wiring layers and the number of insulating layers in the connector region is smaller than that in the signal line region.

A flexible circuit board according to a second aspect of the present invention includes a signal line region, a connector region, a bending region, one or more analog signal lines that transmit analog signals and are formed to extend in a longitudinal direction of the signal line region, one or more digital signal lines that transmit digital signals and are formed to extend in the longitudinal direction of the signal line region, and a ground layer that is formed to cover the analog signal lines via an insulating layer, the bending region connects the signal line region and the connector region, and a space in which the wiring layer and the insulating layer are not provided is provided in the bending region.

In the flexible circuit board, the space further includes a notch in a region on one side or both sides in a thickness direction of the flexible circuit board, and a direction of the notch is a direction having a component in a width direction orthogonal to a longitudinal direction of the signal line region.

In addition, in the flexible circuit board, when the flexible circuit board is viewed in a plan view, a region of one side or both sides of the space in a thickness direction of the flexible circuit board is formed in a meander shape (meander shape) or a crank shape (crack shape).

In addition, in the flexible circuit board, an interlayer connection channel connected to the analog signal line or the digital signal line is provided in the connector region.

In addition, in the flexible circuit board, the interlayer connection channel has: a plated through hole connected to the analog signal line or the digital signal line; and a filled via (filled via) connected to the plated through hole through a conductive layer.

In addition, in the flexible circuit board, a connector part is mounted in the connector area, the connector part being electrically connected to the analog signal line and the digital signal line through the interlayer connection channel.

The electronic device of the present invention includes: a housing; the flexible circuit board is arranged in the shell; 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.

In the electronic device, the flexible circuit board is disposed so as to pass between a side surface of the case and the battery.

In addition, in the electronic apparatus, the flexible circuit board is disposed so as to pass through between the battery and the back surface or the front surface of the housing.

A method for manufacturing a flexible circuit board according to a first aspect of the present invention includes the steps of: preparing a first single-sided metal-clad 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 provided on the first main surface of the first insulating substrate; and a first protective film layer provided on the second main face of the first insulating substrate through a first adhesive layer; patterning the first metal foil to form a first conductive pattern; forming a first bottomed hole that penetrates the first protective film layer, the first adhesive layer, and the first insulating base material and reaches the first metal foil; filling a first conductive paste into the first bottomed hole; stripping the first protective film layer to obtain a first wiring base material; preparing a first double-sided metal-clad laminate having: a second insulating base material having a third main surface and a fourth main surface on the opposite side of the third main surface; a second metal foil provided on the third main surface of the second insulating substrate; and a third metal foil provided on the fourth main surface of the second insulating substrate; patterning the second metal foil to form a second conductive pattern; forming a second bottomed hole penetrating the second insulating base material and reaching the second metal foil; depositing a first metal plating layer on the side wall and the bottom surface of the second bottomed hole; patterning the third metal foil to form a third conductive pattern; forming a second adhesive layer on the third metal foil in such a manner that the third conductive pattern of the third metal foil is embedded and the first metal plating layer deposited on the second bottomed hole; forming a first cover material layer on the second adhesive layer; forming a third adhesive layer having a first opening portion on the first cover material layer; forming a second protective film layer on the third adhesive layer so as to fill the first opening of the third adhesive layer; forming a third bottomed hole that penetrates the second protective film layer, the third adhesive layer, the first cover material layer, and the second adhesive layer and reaches the third metal foil; filling a second conductive paste into the third bottomed hole; stripping the second protective film layer to obtain a second wiring base material; preparing a second double-sided metal-clad laminate, the second double-sided metal-clad laminate having: a third insulating base material having a fifth main surface and a sixth main surface on the opposite side of the fifth main surface; a fourth metal foil provided on the fifth main surface of the third insulating base material; and a fifth metal foil provided on the sixth main face of the third insulating base material; patterning the fourth metal foil to form a fourth conductive pattern; patterning the fifth metal foil to form a fifth conductive pattern; forming a fourth bottomed hole penetrating through the third insulating base material and reaching the fifth metal foil; depositing a second metal plating layer on the fourth bottomed hole side wall and the bottom surface; forming a first through hole penetrating through the third insulating base material and the fifth metal foil to obtain a third wiring base material; the first wiring base material is laminated on the second wiring base material in such a manner that the first conductive paste is brought into contact with the second conductive pattern, and the third wiring base material is laminated on the second wiring base material in such a manner that the second conductive paste is brought into contact with the third conductive pattern.

A method for manufacturing a flexible circuit board according to a second aspect of the present invention includes the steps of: preparing a first single-sided metal-clad 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 provided on the first main surface of the first insulating substrate; and a first protective film layer provided on the second main face of the first insulating substrate through a first adhesive layer; patterning the first metal foil to form a first conductive pattern; forming a first bottomed hole that penetrates the first protective film layer, the first adhesive layer, and the first insulating base material and reaches the first metal foil; filling the first bottomed hole with a first conductive paste; stripping the first protective film layer to obtain a first wiring base material; preparing a first double-sided metal-clad laminate, the first double-sided metal-clad laminate having: a second insulating base material having a third main surface and a fourth main surface on the opposite side of the third main surface; a second metal foil provided on the third main surface of the second insulating substrate; and a third metal foil provided on the fourth main surface of the second insulating substrate; patterning the second metal foil to form a second conductive pattern; forming a second bottomed hole penetrating the second insulating base material and reaching the second metal foil; depositing a first metal plating layer on the side wall and the bottom surface of the second bottomed hole; patterning the third metal foil to form a third conductive pattern; forming a second adhesive layer on the third metal foil in such a manner that the third conductive pattern of the third metal foil is buried and the first metal plating layer having the second bottomed hole is deposited; forming a first cover material layer on the second adhesive layer; forming a third adhesive layer having a first opening portion on the first cover material layer; forming a second protective film layer on the third adhesive layer so as to fill the first opening of the third adhesive layer; forming a third bottomed hole that penetrates the second protective film layer, the third adhesive layer, the first cover material layer, and the second adhesive layer and reaches the third metal foil; filling a second conductive paste into the third bottomed hole; stripping the second protective film layer to obtain a second wiring substrate; preparing a second double-sided metal-clad laminate, the second double-sided metal-clad laminate having: a third insulating base material having a fifth main surface and a sixth main surface on the opposite side of the fifth main surface; a fourth metal foil provided on the fifth main surface of the third insulating base material; and a fifth metal foil provided on the sixth main surface of the third insulating substrate; patterning the fourth metal foil to form a fourth conductive pattern; patterning the fifth metal foil to form a fifth conductive pattern; forming a fourth bottomed hole penetrating through the third insulating base material and reaching the fifth metal foil; depositing a second metal plating layer on the fourth bottomed hole side wall and the bottom surface; forming a fourth adhesive layer on the fourth metal foil in such a manner that the third conductive pattern of the fourth metal foil is embedded and the second metal plating layer deposited in the fourth bottomed hole; forming a second cover material layer on the fourth adhesive layer; forming a third protective film layer on the second covering material layer; forming a fourth protective film layer on the third protective film layer; forming a fifth bottomed hole penetrating the fourth protective film layer, the third protective film layer, the second cover material layer, and the third adhesive layer to reach the fourth metal foil; filling a third conductive paste into the fifth bottomed hole; stripping the third protective film layer and the fourth protective film layer to obtain a third wiring base material; the first wiring base material is laminated on the second wiring base material in such a manner that the first conductive paste is brought into contact with the second conductive pattern, and the third wiring base material is laminated on the second wiring base material in such a manner that the second conductive paste is brought into contact with the third conductive paste.

In addition, in the method of manufacturing a flexible circuit board, the second conductive pattern includes an analog signal line.

In addition, in the manufacturing method of the flexible circuit board, the fifth conductive pattern includes a digital signal line.

The flexible circuit board of the present invention can transmit both analog signals and digital signals at high speed and with low loss, and can be easily built in a housing of an electronic device in a bent state.

Drawings

Fig. 1 is a plan view of a flexible circuit board of an embodiment.

Fig. 2 is an enlarged plan view of the area a of fig. 1.

Fig. 3 is a schematic cross-sectional view taken along line B-B of fig. 2.

Fig. 4 is a sectional view of steps for explaining the method of manufacturing the flexible circuit board according to the first embodiment.

Fig. 5A is a sectional view of the process for explaining the method of manufacturing the flexible circuit board according to the first embodiment, which follows fig. 4.

FIG. 5B is a view for explaining a method of manufacturing a flexible circuit board according to the first embodiment, which follows FIG. 5A

Fig. 5C is a sectional view of the process following fig. 5B for explaining the method of manufacturing the flexible circuit board according to the first embodiment.

Fig. 6 is a sectional view of the steps following fig. 5C for explaining the method of manufacturing the flexible circuit board according to the first embodiment.

Fig. 7 is a sectional view of the steps following fig. 6 for explaining the method of manufacturing the flexible circuit board according to the first embodiment.

Fig. 8 is a schematic sectional view taken along line B-B of fig. 2 of the second embodiment.

Fig. 9A is a process cross-sectional view for explaining a method of manufacturing a flexible circuit board according to the second embodiment.

Fig. 9B is a sectional view of the process following fig. 9A for explaining the method of manufacturing the flexible circuit board according to the second embodiment.

Fig. 9C is a sectional view of the process following fig. 9B for explaining the method of manufacturing the flexible circuit board according to the second embodiment.

Fig. 10 is a sectional view of the steps following fig. 9C for explaining the method of manufacturing the flexible circuit board according to the second embodiment.

Fig. 11A is a schematic perspective view of the region C of fig. 2 of the third embodiment.

Fig. 11B is a schematic perspective view of a region C of fig. 2 of the fourth embodiment (meandering shape).

Fig. 11C is a schematic perspective view of a region C of fig. 2 of the fourth embodiment (crank shape).

Fig. 12 is a plan view of a flexible circuit board according to a modification.

Fig. 13A is a schematic perspective view of an electronic apparatus of the fifth embodiment.

Fig. 13B is a schematic top view and a schematic cross-sectional view of an electronic apparatus according to a sixth embodiment.

Description of the reference numerals

10. Single-side metal foil clad laminate

20. 30 double-sided metal foil clad laminate

11. 21, 31 insulating base material

12. 22, 23, 32, 33 metal foil

13. 24, 25, 34 adhesive layer

14. 26, 35 protective film

12a, 22a, 23a, 32a, 33a landing

12b, 23b ground plane (wiring)

22i wiring (analog signal line)

32b wiring

33i wiring (digital signal line)

51. 52, 53 conductive paste

61. 62 metal plating

71. 72 layer of covering material

100. Flexible circuit board

101. 102, 103 wiring base material

110. 110a connector area

120. Signal line region

130. 130A, 130B bend region

200. First module

300. Second module

400. Battery with a battery cell

500. Shell body

A1 Opening part

H1, H2, H3, H4, H5 pore

HS space

ST1, ST2 slits

W-shaped window part

UE electronic equipment

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals are given to components having the same functions. The drawings are schematic, and the relationship between the thickness and the planar size (aspect ratio), the ratio of the thicknesses of the respective layers, and the like do not necessarily match those of reality.

< integral Structure of Flexible Circuit Board 100 >

First, the overall structure of the flexible circuit board 100 according to the embodiment will be described with reference to fig. 1. Fig. 1 shows a top view of a 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 electrically connects a first module 200 (see fig. 13A) having a wireless communication antenna for receiving an analog signal and a digital terminal for receiving a digital signal, and a second module 300 (see fig. 13A) for performing signal processing of the analog signal and the digital signal, the first module 200 being configured to receive the analog signal and the digital signal.

The connector regions 110 are disposed at both end portions of the signal line region 120. One connector area 110 is connected to an antenna module that transmits and receives analog signals such as radio signals, and the other connector area 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 in the longitudinal direction thereof, and includes analog signal lines and digital signal lines. The analog signal line transmits analog signals such as wireless signals, and the digital signal line transmits digital signals.

In addition, the antenna module may have a digital terminal for receiving a digital signal. 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, one connector area 110 is electrically connected to the first module 200, and the other connector area 110 is electrically connected to the second module 300. The analog signal lines and the digital signal lines included in the signal line region 120 electrically connect one of the connector regions 110 to the other. In other words, the first module 200 and the second module 300 are electrically connected through the connector region 110 and the signal line region 120 of the flexible circuit board 100.

Next, the bending region 130 will be described with reference to fig. 2. Fig. 2 is an enlarged top view of the area a of fig. 1, which illustrates an end portion of the flexible circuit board 100 in an enlarged manner. The bending region 130 connects the connector region 110 and the signal line region 120. The analog signal lines and the digital signal lines are included even in the bending region 130. As will be described in detail later, the bending region 130 has a reduced-layer structure in which the number of wiring layers and/or the number of insulating layers is smaller than that of the signal line region 120. Alternatively, the bending region 130 has a hollow structure in which a wiring layer and an insulating layer are not provided in the bending region 130.

(first embodiment)

< Structure of Flexible Circuit Board 100 >

Next, a cross-sectional structure of the flexible circuit board 100 according to the first embodiment will be described with reference to fig. 3. Fig. 3 is a schematic cross-sectional view taken along line B-B of fig. 2. In fig. 3, the left side of the figure shows a region corresponding to the connector region 110, and the right side of the figure shows a region corresponding to the signal line region 120. Also, the bending region 130 is located between the connector region 110 and the signal line region 120. The bending region 130 has a reduced layer structure. That is, the bending region 130 of the flexible circuit board 100 of the first embodiment has a reduced layer structure in which the number of wiring layers and/or the number of insulating layers is smaller than those of the connector region 110 and the signal line region 120.

In more detail, 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 (the wirings 12b, 22i, and 23 b) as wiring layers, and the signal line region 120 has conductive patterns (the wirings 12b, 22i, 23b, 32b, and 33 i) as wiring layers. Therefore, the bending region 130 has a reduced layer structure in which the number of wiring layers is two layers smaller than that of 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 (the insulating substrate 11 and the adhesive layer 13), a second insulating layer (the insulating substrate 21), and a third insulating layer (the adhesive layer 24 and the cover material layer 71). On the other hand, the signal line region 120 includes a first insulating layer (insulating base material 11 and adhesive layer 13), a second insulating layer (insulating base material 21), a third insulating layer (adhesive layer 24 and cover material layer 71), and a fourth insulating layer (insulating base material 31). Therefore, the bending region 130 has a reduced-layer structure in which the number of insulating layers is one layer less than that of the signal line region 120.

As described above, the bending region 130 has a reduced layer structure in which the number of wiring layers and insulating layers is smaller than that of the signal line region 120. Therefore, the bending region 130 can relax stress at the time of bending as compared with the signal line region 120. Therefore, when the flexible circuit board 100 is built into a housing of an electronic device such as a smartphone, it becomes easy to build the flexible circuit board 100 in a bent state (hereinafter, sometimes referred to as bent built-in). Specifically, in the case where the flexible circuit board 100 is built into the housing in a bent state, the flexible circuit board 100 is bent at the bent region 130 and built into the housing. At this time, the bending region 130 relatively relaxes the stress, and thus can be bent relatively easily. This makes it possible to easily incorporate the flexible circuit board 100 into the housing by bending.

In the flexible circuit board 100, the analog signal line is disposed on the wiring 22i, and the digital signal line is disposed on the wiring 33i. As described above, both the analog signal lines and the digital signal lines are incorporated in the flexible circuit board 100. Thus, by using the flexible circuit board 100, both the analog signal line and the digital signal line can be arranged, and space saving in the housing of the electronic device can be achieved.

In addition, the flexible circuit board 100 has a ground layer formed so as to cover the analog signal lines with an insulating layer. Specifically, the ground layers 12b and 23b (the wirings 12b and 23 b) cover the wiring 22i simulating the signal line via the insulating layer. As shown in fig. 3, the first insulating layer (the adhesive layer 13 and the insulating base material 11) is laminated on the wiring 22i, and the ground layer 12b (the wiring 12 b) is formed on the first insulating layer. Similarly, a second insulating layer (insulating base material 21) is laminated under the wiring 22i, and a ground layer 23b (wiring 23 b) is laminated under the second insulating layer. In this way, the flexible circuit board 100 includes the ground layers 12b and 23b formed so as to cover the analog signal lines (the wirings 22 i) with the first insulating layer and the second insulating layer, respectively. That is, the flexible circuit board 100 has a three-layer strip line structure.

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. Interlayer connection vias are provided in the holes H1 to H4 of the connector region 110 shown in fig. 3, and are electrically connected to analog signal lines or digital signal lines. For example, the interlayer connection channel provided in the hole H2 is electrically connected to the analog signal line (wiring 22 i). In addition, the interlayer connection via provided in the hole H4 is electrically connected to the digital signal line (wiring 33 i).

Additionally, the interlayer connection channels of the connector region 110 may be comprised of plated through holes. In detail, the first metal plating layer 61 is deposited to the hole H2, and the second metal plating layer 62 is deposited to the hole H4, to form plated through holes, respectively. In this way, the interlayer connection channel of the connector region 110 has a plated through hole (hole H2 or hole H4) connected to the analog signal line (wiring 22 i) or the digital signal line (wiring 33 i).

In addition, the interlayer connection channels of the connector regions 110 may also be formed by filled vias. More specifically, the hole H1 is filled with a conductive paste to form a filled via hole. The filled via formed in the hole H1 is connected to the wiring 22i. Similarly, hole H3 is also filled with a conductive paste to form a filled via. Also, the filled via formed in the hole H3 is connected to the land 32 a. The land 32a is connected to the plated through hole of the hole H4. The interlayer connection channels of the connector region 110 have plated through holes and filled vias connected to the plated through holes by a conductive layer (

landings

22a or 32 a). In addition, a connector component (not shown) electrically connected to the analog signal line and the digital signal line through the interlayer connection channel described above may be attached to the connector region 110.

The schematic configuration of the flexible circuit board 100 according to the first embodiment is explained above. According to the first embodiment, the bending region 130 of the flexible circuit board 100 has a layer-reducing structure in which the number of wiring layers and the number of insulating base materials are smaller than those of the signal line region 120. Therefore, stress when bending the bending region 130 can be relaxed. Therefore, the flexible circuit board 100 can be easily bent and incorporated into the housing of the electronic device such as the smartphone.

In addition, both the analog signal lines and the digital signal lines are housed in the flexible circuit board 100. Thus, it is not necessary to separately dispose a cable for an analog signal line and a cable for a digital signal line in a housing of the electronic apparatus. Therefore, space saving in the case of an electronic device such as a smartphone can be achieved.

In addition, since the number of wiring layers and the number of insulating layers can be reduced in the bending region 130 compared to the signal line region 120, the number of wiring layers and insulating base materials required for manufacturing the flexible circuit board 100 can be reduced, and manufacturing cost can be reduced.

< method for manufacturing flexible circuit board 100 >

Next, a method for manufacturing the flexible circuit board 100 according to the first embodiment will be described with reference to process cross-sectional views of fig. 4 to 6.

As shown in fig. 4 (1), first, a single-sided metal foil-clad laminate 10 is prepared. The single-sided metal foil-clad laminate 10 includes an insulating base 11, a metal foil 12 provided on the upper surface of the insulating base 11, and a protective film layer 14 provided on the lower surface of the insulating base 11 via an adhesive layer (micro adhesive layer) 13. The metal foil 12 is formed on the insulating substrate 11 via a seed layer (not shown) formed on the main surface of the insulating substrate 11. The insulating base material 11 may be, for example, polyimide (PI), modified Polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluorine resin (PFA, PTEE, etc.), or the like, in addition to the Liquid Crystal Polymer (LCP), and is not particularly limited.

The thickness of the insulating base material 11 is, for example, 100 μm. The metal foil 12 is, for example, silver or aluminum, in addition to copper. The thickness of the metal foil 12 is, for example, 12 μm. The protective film layer 14 is provided on the lower surface of the insulating substrate 11 via the adhesive layer 13. The protective film layer 14 is an insulating film such as PET (polyethylene terephthalate), for example. The thickness of the protective film layer 14 is, for example, 10 μm. The adhesive layer 13 is, for example, 10 μm thick.

Next, as shown in fig. 4 (2), the metal foil 12 of the single-sided metal foil-clad laminate 10 is patterned by a known photolithography method to form a first conductive pattern. The first conductive pattern includes a land 12a and a wiring 12b. The diameter of the land 12a is, for example, 350 μm. The wiring 12b functions as a ground layer in the flexible circuit board 100.

Next, as shown in fig. 4 (2), the protective film layer 14 is irradiated with a laser beam to remove the protective film layer 14, the adhesive layer 13, and the insulating base 11, thereby forming a bottomed hole H1 in which the land 12a is exposed on the bottom surface. The diameter of the hole H1 is, for example, 150 to 200 μm. More specifically, the hole is punched by irradiating a predetermined position of the protective film layer 14 with a laser pulse using an infrared laser which is a carbon dioxide laser. The beam diameter of the infrared laser was set to 150 μm, which was the same as the diameter of the hole H1. The pulse width of the infrared laser light was set to 10 microseconds, and the energy per pulse of the infrared laser light was set to 5mJ.

The hole H1 is obtained by irradiating the protective film layer 14 with the laser beam of the infrared laser set as described above, for example, 5 times. As described above, the beam diameter of the infrared laser beam is substantially the same as the diameter of the hole H1. In other words, the beam diameter of the infrared laser light may be adjusted so as to match the diameter of the hole H1. Therefore, it is preferable that the beam diameter of the infrared laser beam be easily adjusted in forming the hole H1. In addition, a UV-YAG laser or the like may be used for forming the hole H1, and the laser is not limited to an infrared laser.

After the hole H1 was drilled with an infrared laser, desmear treatment was performed. In the desmear process, resin residues (residual films) at the boundary between the insulating base material 11 and the land 12a and the back surface treatment film (Ni, cr, or the like) of the land 12a are removed.

Next, as shown in fig. 4 (3), the inside of the hole H1 is filled with the conductive paste 51 by a printing method such as screen printing. The conductive paste 51 is obtained by dispersing metal particles in a resin binder which is a paste-like thermosetting resin.

Next, as shown in fig. 4 (4), the protective film layer 14 is peeled off from the pressure-sensitive adhesive layer 13. Thereby, a part of the conductive paste 51 filled in the hole H1 protrudes to form a protruding portion 51a. The height of the projection 51a is about the same as the thickness of the protective film layer 14.

Through the above steps, the wiring base material 101 (first wiring base material) is obtained.

Next, as shown in fig. 5A (1), a double-sided metal foil-clad laminate 20 is prepared. The double-sided metal foil-clad laminate 20 includes an insulating base 21, a metal foil 22 provided on the upper surface of the insulating base 21, and a metal foil 23 provided on the lower surface of the insulating base 21. The insulating base material 21 may be, for example, polyimide (PI), modified Polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluorine resin (PFA, PTEE, etc.), or the like, in addition to the Liquid Crystal Polymer (LCP), and is not particularly limited.

The thickness of the insulating base material 21 is, for example, 100 μm. The metal foils 22 and 23 are, for example, silver and aluminum, in addition to copper. The thicknesses of the metal foil 22 and the metal foil 23 are, for example, 12 μm, respectively. The metal foil 22 is formed on the insulating base 21 via a seed layer (not shown) formed on the upper surface of the insulating base 21. Similarly, the metal foil 23 is formed under the insulating base 21 by a seed layer (not shown) formed on the lower surface of the insulating base 21.

Next, as shown in fig. 5A (2), the metal foil 22 of the double-sided metal foil-clad laminate 20 is patterned by a known photolithography method to form a second conductive pattern. The second conductive pattern includes a land 22a and a wiring 22i. The diameter of the landing site 22a is, for example, 350 μm. 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.

Next, as shown in fig. 5A (3), the metal foil 23 of the double-sided metal foil-clad laminate 20 is patterned by a known photolithography method to form a third conductive pattern. The third conductive pattern includes a land 23a and a wiring 23b. The diameter of the landing 23a is, for example, 350 μm. The wiring 23b functions as a ground layer in the flexible circuit board 100.

Next, as shown in fig. 5A (4), the insulating base material 21 is removed by irradiating laser light using the land portions 23a as a conformal mask (conformal mask), and a bottomed hole H2 in which the land portion 22a is exposed on the bottom surface is formed. The diameter of the holes H2 is, for example, 150 to 200. Mu.m. Hereinafter, the formation of the hole H2 is the same as that of the hole H1. That is, an infrared laser as a carbon dioxide laser is used to irradiate a laser pulse to a predetermined position of the land 23a and pass through the hole H2. The beam diameter of the infrared laser was set to 150 μm, which was the same as the diameter of the hole H2. The pulse width of the infrared laser beam was set to 10 microseconds, and the energy per pulse of the infrared laser beam was set to 5mJ.

The hole H2 is obtained by irradiating the laser beam with the infrared laser beam set as described above 5 times, for example. Further, for forming the hole H2, a UV-YAG laser or the like may be used, and the laser is not limited to an infrared laser.

After the hole H2 was drilled with an infrared laser, desmear treatment was performed. In the desmear process, resin residue (residual film) at the boundary between the insulating base material 21 and the land 23a is removed. In the desmear process, the back surface treatment films (Ni, cr, or the like) of the

land portions

23a and 22a are removed.

Next, as shown in (5) of fig. 5A, the first metal plating layer 61 is deposited on the side walls and the 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 may be deposited by partial plating or full plate plating. The plating thickness of the first metal plating layer 61 is, for example, 16 μm.

Next, as shown in (1) of fig. 5B, the adhesive layer 24 is formed so that the third conductive pattern (the land 23a and the wiring 23B) and the first metal plating layer 61 deposited in the hole H2 are embedded. The adhesive layer 24 is, for example, a micro-adhesive layer having a thickness of 10 μm. Next, as shown in fig. 5B (2), 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 the insulating resin film, for example, liquid Crystal Polymer (LCP) or polyimide is used. The thickness of the covering material layer 71 is, for example, 12 μm.

Next, as shown in fig. 5B (3), the adhesive layer 25 having the opening A1 is formed on the cover material layer 71. The adhesive layer 25 is, for example, a micro-adhesive layer having a thickness of 10 μm. Next, as shown in fig. 5B (4), a protective film layer 26 is formed on the pressure-sensitive adhesive layer 25 so as to fill the openings A1 of the pressure-sensitive adhesive layer 25. The protective film layer 26 is, for example, a 20 μm thick PET film with a micro adhesive. The size of the opening A1 is, for example, 30mm in the longitudinal direction and 2mm in the short-side direction.

Next, as shown in fig. 5C (1), the protective film layer 26, the adhesive layer 25, the cover material layer 71, and the adhesive layer 24 are removed by irradiating the protective film layer 26 with laser light, and the holes H3 with the bottoms exposed with the lands 23a are punched out. The diameter of the hole H3 is, for example, 150 to 200 μm. Hereinafter, the formation of the hole H3 is the same as that of the hole H1. That is, an infrared laser beam, which is a carbon dioxide laser beam, is used to irradiate a predetermined position of the protective film layer 26 with a laser pulse, thereby performing perforation. The beam diameter of the infrared laser was set to 150 μm, which was the same as the diameter of the hole H3. The pulse width of the infrared laser beam was set to 10 microseconds, and the energy per pulse of the infrared laser beam was set to 5mJ.

Next, as shown in fig. 5C (2), the inside of the hole H3 is filled with the conductive paste 52 by a printing method such as screen printing. The conductive paste 52 is obtained by dispersing metal particles in a resin binder which is a paste-like thermosetting resin.

Next, as shown in fig. 5C (3), the protective film layer 26 is peeled off from the adhesive layer 25 and the cover material layer 71. Thereby, a part of conductive paste 52 filled in hole H3 protrudes, and protrusion 52a is formed. The height of the protruding portion 52a is approximately the same as the thickness of the protective film layer 26 formed on the pressure-sensitive adhesive layer 25.

Through the above steps, the wiring base material 102 (second wiring base material) is obtained.

Next, as shown in fig. 6 (1), a double-sided metal foil-clad laminated plate 30 is prepared. The double-sided metal foil-clad laminate 30 includes an insulating base 31, a metal foil 32 provided on an upper surface of the insulating base 31, and a metal foil 33 provided on a lower surface of the insulating base 31. The insulating base material 31 may be, for example, polyimide (PI), modified Polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluorine resin (PFA, PTEE, etc.), or the like, in addition to the Liquid Crystal Polymer (LCP), and is not particularly limited.

The thickness of the insulating base material 31 is, for example, 50 μm. The metal foils 32 and 33 are, for example, silver and aluminum, in addition to copper. The thicknesses of the metal foil 32 and the metal foil 33 are, for example, 12 μm, respectively. The metal foil 32 is formed on the insulating base material 31 via a seed layer (not shown) formed on the upper surface of the insulating base material 31. Similarly, the metal foil 33 is formed under the insulating base material 31 by a seed layer (not shown) formed on the lower surface of the insulating base material 31.

By making the thickness of the insulating base material 31 50 μm thinner, the line width of the signal line can be reduced. In more detail, the line width of the signal line (wiring 33 i) that matches the characteristic impedance represented by Z0= √ (L/C) can be reduced. Where L is the inductance per unit length and C is the line-to-line capacitance. In this way, by making the thickness of the insulating base material 31 thin, the line width of the signal line can be reduced, and therefore the width of the flexible circuit board 100 can be reduced. Therefore, space saving can be achieved when the flexible circuit board 100 is built into a housing of an electronic device such as a smartphone.

Next, as shown in (2) of fig. 6, the metal foil 32 is patterned to form a fourth conductive pattern including the land 32a as a conformal mask. Thereafter, as shown in fig. 6 (3), the insulating base material 31 is removed by irradiating laser light using the land 32a as a conformal mask, and a bottomed hole H4 in which the land 33a is exposed on the bottom surface is formed. The diameter of the holes H4 is, for example, 150 to 200 μm. The hole H4 is formed in the same manner as the hole H1. That is, an infrared laser beam, which is a carbon dioxide laser beam, is used to irradiate the opening of the mask with a laser pulse and pass through the hole H4. The beam diameter of the infrared laser was set to 150 μm, which was the same as the diameter of the hole H4. As shown in fig. 6 (2), the metal foil 33 is patterned to form a fifth conductive pattern (a land 33a and a wiring 33 i). The diameter of the land 33a is, for example, 350 μm. 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.

After the hole H4 was drilled with an infrared laser, desmear treatment was performed. In the desmear process, resin residue (residual film) at the boundary between the land 33a and the insulating base material 31 is removed. In the desmear treatment, the back surface treatment film (Ni, cr, or the like) of the land 33a is removed.

Next, as shown in (4) of fig. 6, a second metal plating layer 62 is deposited on the side walls and bottom surface of the hole H4. The second metal plating layer 62 is, for example, a copper plating layer. In addition, 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 16 μm, for example.

Next, as shown in fig. 6 (5), the metal foil 32, the insulating base 31, and a part of the land 33a are removed by a knife die or the like to form the window W. The size of the window W is, for example, about the same as the size of the opening A1 of the pressure-sensitive adhesive layer 25 shown in fig. 5B (3), and is, for example, 30mm in the longitudinal direction and 2mm in the short-side direction.

Through the above steps, the wiring base material 103 (third wiring base material) is obtained.

In the above-described steps, the metal foil of each of the

wiring base materials

101, 102, and 103 may be subjected to roughening treatment. The roughening treatment can improve the strength of the adhesion between the metal foil and the insulating base material.

A process of laminating the wiring base 101, the wiring base 102, and the wiring base 103 obtained in the above-described process will be described below with reference to fig. 7.

First, the wiring base material 101 is laminated on the wiring base material 102. Specifically, the protruding portion 51a of the conductive paste 51 of the wiring base material 101 is laminated so as to be in contact with the land portion 22a of the wiring base material 102.

Next, the laminate composed of the wiring base material 101 and the wiring base material 102 obtained in the above-described steps is laminated on the wiring base material 103. Specifically, the protruding portion 52a of the conductive paste 52 of the wiring base material 102 is laminated so as to be in contact with the land portion 32a of the wiring base material 103. By doing so, the wiring base material 101, the wiring base material 102, and the wiring base material 103 are electrically connected to each other. The order of laminating the

wiring base materials

101, 102, and 103 is not limited to the above-described order.

In the above-described lamination step of forming a laminate composed of the wiring base material 101, the wiring base material 102, and the wiring base material 103, a vacuum press apparatus or a vacuum lamination apparatus is used. The laminate is heated and pressed by the vacuum pressing apparatus or the vacuum laminating apparatus. For example, the laminate is heated at about 200 ℃ 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 lower by about 50 ℃ or more than the temperature at which the Liquid Crystal Polymer (LCP) constituting the insulating

substrates

11, 21, and 31 softens.

When a vacuum press apparatus is used in the lamination step, the laminate is heated and pressed under the above-described conditions for about 30 to 60 minutes. The heat curing of the

adhesive layers

13, 24, and 25 and the heat curing of the

conductive pastes

51 and 52 are also completed by the heating and pressing of the laminated body by the vacuum pressing apparatus.

On the other hand, when a vacuum lamination apparatus is used in the lamination step, the laminate is heated and pressed under the above-described conditions for about several minutes. Therefore, after the laminate is heated and pressed by the vacuum laminating apparatus, the laminate is moved to an oven apparatus and post-curing treatment is performed. In the post-curing treatment, for example, the laminate is heated at about 200 ℃ for about 60 minutes. By this post-curing treatment, the thermosetting of the

adhesive layers

13, 24, and 25 and the thermosetting of the

conductive pastes

51 and 52 are also completed.

Next, if necessary, surface treatment and solder resist may be performed on the first conductive pattern and the fifth conductive pattern exposed to the outside, and the outer shape may be processed.

Through the above steps, the flexible circuit board 100 having the cross-sectional structure shown in fig. 3 is obtained.

As described above, according to the method of manufacturing a flexible circuit board of the first embodiment, the flexible circuit board 100 in which the bending region 130 has a reduced layer structure in which the number of wiring layers and/or the number of insulating layers is smaller than that of the signal line region 120 can be obtained. Therefore, the bending region 130 can relax stress at the time of bending as compared with the signal line region 120, and the flexible circuit board 100 can be easily incorporated into the bending of the housing of the electronic device such as the smartphone.

Further, in the flexible circuit board 100, an analog signal line is formed as the wiring 22i, and a digital signal line is formed as the wiring 33i. As shown in fig. 3, the flexible circuit board 100 incorporates an analog signal line and a digital signal line. Therefore, by incorporating the flexible circuit board 100 in the housing of an electronic device such as a smartphone, an analog signal line for transmitting an analog signal received by a wireless communication antenna and a digital signal line for transmitting a digital signal received by a digital terminal such as a USB can be collectively arranged at a time. As a result, space saving in the case of an electronic device such as a smartphone can be achieved.

In addition, since the number of wiring layers and the number of insulating layers are reduced in the bending region 130 of the flexible circuit board 100 as compared with the signal line region 120, the number of wiring layers and the number of insulating base materials required for the flexible circuit board 100 can be reduced, and the manufacturing cost can be reduced.

In addition, the flexible circuit board 100 is manufactured by laminating the wiring base material 101, the wiring base material 102, and the wiring base material 103. That is, since the flexible circuit board 100 is manufactured by laminating three wiring base materials, it is possible to relatively suppress the occurrence of positional deviation between the wiring base materials. Therefore, the yield of the manufacturing process of the flexible circuit board 100 can be improved. Further, the margin (margin) of the positional deviation can be made small, and the wiring structure of the wiring layer of the flexible circuit board 100 can be densified.

(second embodiment)

< Structure of Flexible Circuit Board 100A >

Next, the structure of the flexible circuit board 100A according to the second embodiment will be described with reference to fig. 8. The flexible circuit board 100A of the second embodiment has a hollow structure in the bending region 130, as opposed to the flexible circuit board 100 of the first embodiment having a reduced-layer structure in the bending region 130. Hereinafter, a description will be given of a portion different from the first embodiment.

Fig. 8 is a schematic cross-sectional view taken along line B-B of fig. 2. In fig. 8, the left side of the figure shows a region corresponding to the connector region 110, and the right side of the figure shows a region corresponding to the signal line region 120. The bending region 130 is located between the connector region 110 and the signal line region 120. The bending region 130 has a hollow structure. That is, as shown in fig. 7, the bending region 130 of the flexible circuit board 100A of the second embodiment has a space (hollow region) HS where neither the wiring layer nor the insulating layer is provided.

Specifically, in the bending region 130, a space HS is provided between the covering material layers 71 and 72. Therefore, the bending region 130 can relax stress at the time of bending as compared with the signal line region 120. Therefore, when the flexible circuit board 100A is built into a housing of an electronic device such as a smartphone, the flexible circuit board 100A can be easily built 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 at the bending region 130 and built into the housing. At this time, the bending region 130 can relatively relax the stress, and thus can be relatively easily bent. This makes it possible to easily incorporate the flexible circuit board 100A into the housing by bending.

In the flexible circuit board 100A, the analog signal line is constituted by the wiring 22i and the digital signal line is constituted by the wiring 33i, as in the case of the first embodiment. That is, the analog signal line and the digital signal line can be incorporated in the flexible circuit board 100A, and space in the housing can be saved.

In addition, the flexible circuit board 100A has a ground layer formed so as to cover the analog signal lines with an insulating layer. Specifically, the flexible circuit board 100A includes the ground layers 12b and 23b (the wirings 12b and 23 b) formed so as to cover the analog signal line (the wiring 22 i) with the first insulating layer (the adhesive layer 13 and the insulating base material 11) and the second insulating layer (the insulating base material 21), as in the first embodiment. That is, the flexible circuit board 100A has a three-layer strip line structure.

An interlayer connection channel to which an analog signal line or a digital signal line is connected is provided in the connector area 110 of the flexible circuit board 100A. As in the first embodiment, interlayer connection passages are provided in the holes H1 to H4 of the connector region 110 shown in fig. 8. The interlayer connection channel provided in the hole H2 is connected to the analog signal line (wiring 22 i). In addition, the interlayer connection channel provided in the hole H4 is connected to the digital signal line (the wiring 33 i).

In addition, the interlayer connection channels of the connector region 110 have plated through holes that connect with analog signal lines or digital signal lines. As in the first embodiment, the interlayer connection via of the connector region 110 has a plated through hole (hole H2 or hole H4) connected to an analog signal line (wiring 22 i) or a digital signal line (wiring 33 i).

In addition, the interlayer connection channels of the connector regions 110 may also be formed by filled vias. More specifically, similarly to the first embodiment, the holes H1, H3, and H5 are filled with the conductive paste to form filled vias. Thus, as described above, the interlayer connection channels of the connector region 110 have plated through holes, and filled vias connected to the plated through holes by the conductive layer (

landings

22a or 32 a). In addition, a connector component (not shown) electrically connected to the analog signal line and the digital signal line through the interlayer connection channel may be mounted in the connector region.

The structure of the flexible circuit board 100A according to the second embodiment is explained above. According to the second embodiment, the bending region 130 of the flexible circuit board 100A has a hollow structure obtained by providing a space HS (hollow region) in which no wiring layer and no insulating base material are provided inside the bending region 130. This can relax the stress when bending region 130 is bent. Therefore, the flexible circuit board 100A can be easily incorporated into a housing of an electronic device such as a smartphone.

In addition, both the analog signal lines and the digital signal lines are housed in the flexible circuit board 100A. Thus, it is not necessary to separately arrange a cable for an analog signal line and a cable for a digital signal line in the housing of the electronic device. Therefore, space saving in the case of an electronic device such as a smartphone can be achieved.

In addition, since the number of wiring layers and/or the number of insulating layers in the bending region 130 is reduced as compared with the signal line region 120, the number of wiring layers and the number of insulating base materials required for manufacturing the flexible circuit board 100A can be reduced, and manufacturing cost can be reduced.

< method for manufacturing flexible circuit board 100A >

Next, a method for manufacturing the flexible circuit board 100A according to the second embodiment will be described with reference to process cross-sectional views of fig. 9A to 10.

In the second embodiment, the flexible circuit board 100A is also manufactured by laminating the wiring base material 101 (first wiring base material), the wiring base material 102 (second wiring base material), and the wiring base material 103A (third wiring base material). The wiring base 101 and the wiring base 102 are manufactured in the same manner as in the first embodiment. That is, the method of manufacturing the wiring base material 101 according to the second embodiment is illustrated in fig. 4, and the method of manufacturing the wiring base material 102 is illustrated in fig. 5A to 5C, and therefore, the description thereof is omitted. A method for manufacturing the wiring base material 103A will be described below.

As shown in fig. 9A (1), a double-sided metal foil-clad laminate 30 is prepared. The double-sided metal foil-clad laminate 30 includes an insulating base 31, a metal foil 32 provided on the upper surface of the insulating base 31, and a metal foil 33 provided on the lower surface of the insulating base 31. The insulating base material 31 may be, for example, polyimide (PI), modified Polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluorine resin (PFA, PTEE, etc.), or the like, in addition to the Liquid Crystal Polymer (LCP), and is not particularly limited.

The thickness of the insulating base material 31 is, for example, 50 μm. The metal foils 32 and 33 are, for example, silver and aluminum, in addition to copper. The thicknesses of the metal foil 32 and the metal foil 33 are, for example, 12 μm, respectively. The metal foil 32 is formed on the insulating base material 31 by a seed layer (not shown) formed on the upper surface of the insulating base material 31. Similarly, the metal foil 3 is formed under the insulating base material 31 by a seed layer (not shown) formed on the lower surface of the insulating base material 31.

By making the thickness of the insulating base material 31 50 μm thinner, the line width of the signal line can be reduced. In more detail, the line width of the signal line (wiring 33 i) that matches the characteristic impedance represented by Z0= √ (L/C) can be reduced. Where L is the inductance per unit length and C is the line-to-line capacitance. By reducing the thickness of the insulating base material 31 in this way, the line width of the signal line can be reduced, and thus the width of the flexible circuit board 100A can be reduced. Thus, space saving can be achieved when the flexible circuit board 100A is built into a housing of an electronic device such as a smartphone.

Next, as shown in (2) of fig. 9A, the metal foil 32 is patterned to form a fourth conductive pattern including the land 32a functioning as a conformal mask. Then, as shown in (3) of fig. 9A, the metal foil 33 is patterned to form a fifth conductive pattern including a land 33a and a wiring 33i. The diameter of the land 33a is, for example, 350 μm. In addition, 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.

Next, as shown in fig. 9A (4), the insulating base material 31 is removed by irradiating laser light using the land 32a as a conformal mask, and a hole H4 in which the land 33a is exposed on the bottom surface is formed. The diameter of the hole H4 is, for example, 150 to 200 μm. The formation of the hole H4 is the same as that of the hole H1 of the first embodiment.

The insulating base material 31 is penetrated by an infrared laser and then desmear treatment is performed. In the desmear process, resin residue (residual film) at the boundary between the land 33a and the insulating base material 31 is removed. In the desmear treatment, the back surface treatment film (Ni, cr, or the like) of the land 33a is removed.

Next, as shown in (5) of fig. 9A, a second metal plating layer 62 is deposited on the side walls and bottom surface of the hole H4. The second metal plating layer 62 is, for example, a copper plating layer. In addition, 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 16 μm, for example.

Next, as shown in (1) of fig. 9B, the adhesive layer 34 is formed on the metal foil 32 in such a manner that the fourth conductive pattern (the land 32a, the wiring 32B) formed by patterning the metal foil 32 and the second metal plating layer 62 deposited in the hole H4 are buried. The thickness of the adhesive layer 34 is, for example, 10 μm. Next, as shown in (2) of fig. 9B, a covering material layer 72 is formed on the adhesive layer 34. The covering material layer 72 is, for example, an insulating resin film. As the insulating resin film, for example, liquid Crystal Polymer (LCP) or polyimide is used. The thickness of the covering material layer 72 is, for example, 12 μm. Next, as shown in (3) of fig. 9B, the 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.

Next, as shown in fig. 9C (1), the protective film layer 35, the cover material layer 72, and the adhesive layer 34 are removed by irradiating the protective film layer 35 with laser light, and the holes H5 with the bottoms exposed to the lands 32a are punched out. The diameter of the hole H5 is, for example, 150 to 200. Mu.m. Hereinafter, the formation of the hole H5 is the same as that of the hole H1 of the first embodiment. That is, an infrared laser beam, which is a carbon dioxide laser beam, is used to irradiate a predetermined position of the protective film layer 35 with a laser pulse to perform perforation. The beam diameter of the infrared laser was set to 150 μm, which was the same as the diameter of the hole H5. The pulse width of the infrared laser beam was set to 10 microseconds, and the energy per pulse of the infrared laser beam was set to 5mJ.

Next, as shown in fig. 9C (2), the inside of the hole H5 is filled with the conductive paste 53 by a printing method such as screen printing. The conductive paste 53 is obtained by dispersing metal particles in a resin binder which is a paste-like thermosetting resin.

Next, as shown in (3) of fig. 9C, the protective film layer 35 is peeled off from the cover material layer 72. Thereby, a part of conductive paste 53 filled in hole H5 protrudes, and protrusion 53a is formed. The height of the protruding portion 53a is about the same as the thickness of the protective film layer 35.

Through the above steps, the wiring base material 103A is obtained.

In the above-described step, the metal foil of each wiring substrate may be subjected to roughening treatment. By the roughening treatment, the strength of adhesion between the metal foil and the insulating base material can be improved.

A step of laminating the wiring base material 101, the wiring base material 102, and the wiring base material 103A obtained in the above-described step will be described below with reference to fig. 10.

First, the wiring base material 102 is laminated on the wiring base material 101. Specifically, the protruding portion 51a of the conductive paste 51 of the wiring base material 101 is laminated so as to be in contact with the land portion 22a of the wiring base material 102.

Next, the laminate composed of the wiring base material 101 and the wiring base material 102 obtained in the above-described steps is laminated on the wiring base material 103A. Specifically, the protruding portions 52a of the conductive paste 52 and the protruding portions 53a of the conductive paste 53 are laminated so as to be in contact with each other. By doing so, the wiring base material 101, the wiring base material 102, and the wiring base material 103A are electrically connected to each other. The order of laminating the

wiring base materials

101, 102, and 103A is not limited to the above order.

In the above-described lamination step of forming a laminate composed of the wiring base material 101, the wiring base material 102, and the wiring base material 103A, a vacuum press apparatus or a vacuum lamination apparatus is used as in the first embodiment. The laminate is heated and pressed by the vacuum pressing apparatus or the vacuum laminating apparatus. For example, the laminate is heated at about 200 ℃ 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 lower by about 50 ℃ or more than the temperature at which the Liquid Crystal Polymer (LCP) of the insulating

substrates

11, 21, and 31 softens.

In the lamination step of the laminate, the laminate is heated and pressed under the above-described conditions for about 30 to 60 minutes, using a vacuum press apparatus. By heating and pressing the laminated body by the vacuum pressing apparatus, the thermosetting of the

adhesive layers

13, 24, 25, and 34 and the thermosetting of the

conductive pastes

51 and 52 are also completed.

On the other hand, in the lamination step, when a vacuum lamination apparatus is used, the laminate is heated and pressed under the above-described conditions for about several minutes. Therefore, after the flexible circuit board 100A is heated and pressurized by the vacuum laminating apparatus, the laminate is moved to an oven apparatus to be post-cured. In the post-curing treatment, for example, heating is performed at about 200 ℃ for about 60 minutes. By this post-curing process, the thermal curing of the

adhesive layers

13, 24, 25, and 34 and the thermal curing of the

conductive pastes

51 and 52 are also completed.

Next, surface treatment and solder resist of the first conductive pattern and the fifth conductive pattern exposed to the outside are performed as necessary, and outline processing is performed.

Through the above steps, the flexible circuit board 100A having the cross-sectional structure shown in fig. 8 is obtained.

As described above, according to the method of manufacturing the flexible circuit board 100A of the second embodiment, the flexible circuit board 100A having the hollow structure in which the space HS (hollow region) in which the wiring layer and the insulating layer are not provided is provided inside the bending region 130 can be obtained. Therefore, the bending region 130 can relax stress at the time of bending as compared with the signal line region 120, and the flexible circuit board 100A can be easily incorporated into the bending of the housing of the electronic device such as the smartphone.

In addition, in the flexible circuit board 100A, the analog signal line is formed as the wiring 22i and the digital signal line is formed as the wiring 33i, as in the first embodiment. As shown in fig. 8, an analog signal line and a digital signal line are built in the flexible circuit board 100A. Therefore, by incorporating the flexible circuit board 100A in a housing of a smartphone or the like, an analog signal line for transmitting an analog signal received by a wireless communication antenna and a digital signal line for transmitting a digital signal received by a digital terminal such as a USB can be collectively arranged at a time. As a result, space in the case of an electronic device such as a smartphone can be saved.

In addition, since the number of wiring layers and the number of insulating layers are reduced in the bending region 130 of the flexible circuit board 100A as compared with the signal line region 120, the number of wiring layers and the number of insulating base materials required for the flexible circuit board 100A can be reduced, and the manufacturing cost can be reduced.

In addition, the flexible circuit board 100A is manufactured by laminating the wiring base material 101, the wiring base material 102, and the wiring base material 103A. That is, since the flexible circuit board 100A is manufactured by laminating three wiring base materials, it is possible to relatively suppress occurrence of positional deviation between the wiring base materials. Therefore, the yield of the manufacturing process of the flexible circuit board 100A can be improved. Further, the margin of the positional deviation can be made small, and the wiring structure of the wiring layer of the flexible circuit board 100A can be densified.

(third embodiment)

Next, a flexible circuit board 100B according to a third embodiment will be described with reference to fig. 11A. The flexible circuit board 100B has a hollow structure in the bending region 130, as in the flexible circuit board 100A of the second embodiment. Further, the flexible circuit board 100B is provided with a notch on one side (the lower surface 130B side in fig. 11A) of the bending region 130. The following description will be focused on the differences from the second embodiment.

Fig. 11A is a schematic perspective view showing the bending region 130 of the flexible circuit board 100B. Fig. 11A is a schematic perspective view of the region C of fig. 2, showing a portion of the connector region 110, a portion of the signal line region 120, and the bend region 130.

In more detail, the bending region 130 of the flexible circuit board 100B has a space HS where no wiring layer and no insulating layer are 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 of the bending region 130 and the lower surface 130b of the bending region 130.

As shown in fig. 11A, slits ST1 and ST2 are provided as cutouts in the lower surface 130b of the bending region 130. Specifically, the slit ST1 and the slit ST2 are provided in a region on one side of the space HS in the thickness direction of the flexible circuit board 100B. The slits ST1 and ST2 may be provided on both sides of the bending region 130. That is, the slits ST1 and ST2 may be provided on the upper surface 130a and the lower surface 130b, which are both sides of the bending region 130. In fig. 11A, the slits ST1 and ST2 are provided along the width direction orthogonal to the longitudinal direction of the signal line region 120. Further, without being limited thereto, the slits ST1 and ST2 may be provided along a direction intersecting with the width direction of the bending region 130. The slits ST1 and ST2 may be provided so as to have a component in the width direction orthogonal to the longitudinal direction of the signal line region 120 of the flexible circuit board 100B.

The other structure of the flexible circuit board 100B is the same as the flexible circuit board 100A of the second embodiment, and therefore, the description is omitted. Note that the method of manufacturing the flexible circuit board 100B is also the same as the flexible circuit board 100A of the second embodiment, and therefore, the description thereof is omitted. The

wirings

22i and 33i are formed in a meandering manner so as to avoid the slits ST1 and ST2.

As described above, the bending region 130 of the flexible circuit board 100B has the space HS where the wiring layer and the insulating layer are not provided, and the slit ST1 and the slit ST2 are provided on the lower surface 130B of the bending region 130. Therefore, the bending region 130 can relax the stress at the time of bending more than the signal line region 120, and thus the flexible circuit board 100B can be more easily incorporated into the bending in the case of a smartphone or the like.

In addition, as in the second embodiment, the flexible circuit board 100B incorporates an analog signal line and a digital signal line. Thus, by disposing the flexible circuit board 100B in the housing, the analog signal lines and the digital signal lines can be collectively disposed at a time, and space in the housing of the smartphone or the like can be saved.

In addition, since the number of wiring layers and the number of insulating layers are reduced in the bending region 130 of the flexible circuit board 100B as compared with the signal line region 120, the number of wiring layers and the number of insulating base materials required for the flexible circuit board 100B can be reduced, and the manufacturing cost can be reduced.

In addition, the flexible circuit board 100B is manufactured by laminating a wiring base material 101 (first wiring base material), a wiring base material 102 (second wiring base material), and a wiring base material 103A (third wiring base material). That is, since the flexible circuit board 100B is manufactured by laminating three wiring base materials, it is possible to relatively suppress the occurrence of positional deviation between the wiring base materials. This can improve the yield of the manufacturing process of the flexible circuit board 100B. Further, the above-described margin of positional deviation can be made small, and the wiring structure of the wiring layer of the flexible circuit board 100B can be densified.

(fourth embodiment)

Next, a flexible circuit board 100C according to a fourth embodiment will be described with reference to fig. 11B and 11C. The flexible circuit board 100C has a hollow structure in the bending region 130, as in the flexible circuit board 100A of the second embodiment. Further, one side (the lower surface 130B side in fig. 11B and 11C) of the bent region 130 of the flexible circuit board 100C is provided in a meander shape or a crank shape. Hereinafter, a description will be given of a portion different from the second embodiment.

Fig. 11B and 11C are schematic perspective views showing the bending region 130 of the flexible circuit board 100C. Fig. 11B and 11C are schematic perspective views of the region C of fig. 2, showing a part of the connector region 110, a part of the signal line region 120, and the bending region 130.

In more detail, the bending region 130 of the flexible circuit board 100C has a space HS where the wiring layer and the insulating layer are not disposed, that is, the bending region 130 has a hollow structure. In other words, there is a space HS between the upper surface 130a of the bending region 130 and the lower surface 130b of the bending region 130.

First, as shown in fig. 11B, the lower surface 130B of the curved region 130 has a meandering shape. Specifically, the lower surface 130b of the bent region 130 is provided in a meandering shape in a plan view of the flexible circuit board 100C. In other words, the meander-like lower surface 130b is provided in a region on one side of the space HS in the thickness direction of the flexible circuit board 100C. The upper surface 130a and the lower surface 130b, which are both sides of the curved region 130, may be formed in a zigzag shape.

On the other hand, as shown in fig. 11C, the lower surface 130b of the curved region 130 may also have a crank shape. Specifically, the lower surface 130b of the bent region 130 is formed in a crank shape in a plan view of the flexible circuit board 100C. In other words, the crank-shaped lower surface 130b is provided in a region on one side of the space HS in the thickness direction of the flexible circuit board 100C. The upper surface 130a and the lower surface 130b, which are both sides of the curved region 130, may be formed in a crank shape.

The other structure of the flexible circuit board 100C is the same as the flexible circuit board 100A of the second embodiment, and therefore, the description is omitted. Note that, since the manufacturing method of the flexible circuit board 100C is the same as the flexible circuit board 100A of the second embodiment, the description thereof is omitted. The

wirings

22i and 33i are formed along a meandering shape or a crank shape.

As described above, the bending region 130 of the flexible circuit board 100C has the space HS where the wiring layer and the insulating layer are not provided, and further, the lower surface 130b of the bending region 130 is provided in a meander shape or a crank shape. Therefore, the bending region 130 can further relax the stress at the time of bending than the signal line region 120, and the flexible circuit board 100C can be more easily incorporated into the bending of the housing of the smartphone or the like.

In addition, as in the second embodiment, the flexible circuit board 100C incorporates an analog signal line and a digital signal line. Thus, by disposing the flexible circuit board 100C in the housing, the analog signal lines and the digital signal lines can be collectively disposed at a time, and space in the housing of the smartphone or the like can be saved.

In addition, since the number of wiring layers and the number of insulating layers are reduced in the bending region 130 of the flexible circuit board 100C as compared with the signal line region 120, the number of wiring layers and the number of insulating base materials required for the flexible circuit board 100C can be reduced, and the manufacturing cost can be reduced.

In addition, the flexible circuit board 100C is manufactured by laminating a wiring base material 101 (first wiring base material), a wiring base material 102 (second wiring base material), and a wiring base material 103A (third wiring base material). That is, since the flexible circuit board 100C is manufactured by laminating three wiring base materials, it is possible to relatively suppress the occurrence of positional deviation between the wiring base materials. Therefore, the yield of the manufacturing process of the flexible circuit board 100C can be improved. Further, the above-described margin of positional deviation can be made small, and the wiring structure of the wiring layer of the flexible circuit board 100C can be densified.

(modification example)

Next, the structure of the flexible circuit board 100D according to a modification will be described with reference to fig. 12. The flexible circuit board 100 according to the first embodiment has a reduced-thickness structure in the bending region 130, whereas the flexible circuit board 100D according to the modification has a reduced-thickness structure also in the connector region 110A. The following description will be focused on the differences from the first embodiment.

Fig. 12 is a schematic plan view of a flexible circuit board 100D of a modification. As shown in fig. 12, a flexible circuit board 100D of the modification includes a connector region 110, a connector region 110A, a signal line region 120, and a bending region 130. Fig. 12 shows a state in which the connector component 111 is attached to the connector area 110A.

Even in the flexible circuit board 100D of the modification, the bending region 130 has a layer-reduced structure. That is, the bending region 130 of the flexible circuit board 100D has a reduced layer structure in which the number of wiring layers and/or the number of insulating layers is smaller than that of the signal line region 120.

Further, in the modification, the connector region 110A has a reduced-layer structure in addition to the bent region 130. That is, the connector region 110A has a reduced layer structure in which the number of wiring layers and/or the number of insulating layers is smaller than that of the signal line region 120. In addition, the cross-sectional structure of the connector region 110A may also be the same as the bending region 130. That is, the cross-sectional structure of the connector region 110A may be the same as the cross-sectional structure of the bending region 130 shown in fig. 3. In the flexible circuit board 100D shown in fig. 12, the connector region 110A, which is one connector region, has a reduced-layer structure. In the flexible circuit board 100D of the modification, both connector regions (the connector region 110 and the connector region 110A) may have a reduced-layer structure.

The other structure of the flexible circuit board 100D is the same as the flexible circuit board 100 of the first embodiment. In addition, the manufacturing method of the flexible circuit board 100D is also the same as the flexible circuit board 100 of the first embodiment. That is, in the method of manufacturing the flexible circuit board 100D, the step of forming the reduced-thickness structure of the bending region 130 may be applied to the step of forming the reduced-thickness structure of the connector region 110A.

As described above, according to the flexible circuit board 100D of the modification, in addition to the bending region 130, the connector region 110A also has a reduced layer structure in which the number of wiring layers and/or the number of insulating layers is smaller than that of the signal line region 120. Therefore, the number of wiring layers and insulating base materials required for the flexible circuit board 100D can be further reduced, and the manufacturing cost can be further reduced.

In addition, the connector region 110A and the bending region 130 can relax stress at the time of bending as compared with the signal line region 120. Therefore, as with the flexible circuit board 100 of the first embodiment, the flexible circuit board 100D can be easily bent and incorporated into the housing of a smartphone or the like.

In addition, the flexible circuit board 100D incorporates an analog signal line and a digital signal line. Thus, by disposing the flexible circuit board 100D in the housing, the analog signal lines and the digital signal lines can be collectively disposed at a time, and space in the housing of the smartphone or the like can be saved.

In addition, the flexible circuit board 100D is manufactured by laminating the wiring base material 101 (first wiring base material), the wiring base material 102 (second wiring base material), and the wiring base material 103 (third wiring base material). That is, since the flexible circuit board 100D is manufactured by laminating three wiring base materials, it is possible to relatively suppress the occurrence of positional deviation between the wiring base materials. This can improve the yield of the manufacturing process of the flexible circuit board 100D. Further, the margin of the positional deviation can be made small, and the wiring structure of the wiring layer of the flexible circuit board 100D can be densified.

Electronic device with built-in flexible circuit board

(fifth embodiment)

Next, an embodiment of an electronic device incorporating the flexible circuit board 100 according to the first to fourth embodiments or the modification described above will be described with reference to fig. 13A. In the electronic apparatus of the present embodiment, the flexible circuit board 100 is bent and built in a side surface in a housing of the electronic apparatus.

The right side view of fig. 13A is a perspective view schematically showing a state before bending the flexible circuit board 100. The center view of fig. 13A is a perspective view schematically showing a state in which the flexible circuit board 100 is bent. As shown in the right and center views of fig. 13A, when the flexible circuit board 100 is built into a housing of an electronic device, the bending region 130 of the flexible circuit board 100 is bent into a desired shape. In fig. 13A, the flexible circuit board 100 is built in the side face inside the case of the electronic apparatus. In the right-hand drawing of fig. 13A, the connector region 110a and the bent region 130 stand upright on the signal line region 120. From this state, as shown in the center of fig. 13A, the bending region 130 is bent forward (in the direction of incorporating the flexible circuit board 100), and the connector region 110b falls forward.

Fig. 13A is a diagram schematically illustrating an electronic device UE incorporating a flexible circuit board 100 on the left side. In the electronic apparatus UE, the flexible circuit board 100 and other electronic components are built in the housing 500. Specifically, the electronic apparatus UE includes a housing 500, and the flexible circuit board 100 according to the above-described embodiment or modification is built in the housing 500. The first module 200 and the second module 300 are disposed inside the case 500, and the battery 400 is disposed between the first module 200 and the second module 300.

In the electronic apparatus UE according to the present embodiment, the first module 200 includes a wireless communication antenna for receiving an analog signal and a digital terminal for receiving a digital signal. The second module 300 performs signal processing of the analog signal and the digital signal received by the first module 200. As shown in fig. 13A, the processor 210 for overall control of the electronic device UE may be disposed in the first module 200.

The first module 200 is provided with a connector unit 220. The first module 200 is electrically connected to the connector area 110a by the connector member 220. On the other hand, the second module 300 is also provided with a connector member 310. The second module 300 is electrically connected with the connector area 110b through the connector member 310. Thus, the first module 200 is electrically connected to the second module 300 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.

As described above, in the present embodiment, the flexible circuit board 100 is built along the side surface inside the housing 500 of the electronic device UE. That is, the flexible circuit board 100 is housed in the housing 500 such that the bending region 130 is bent to fit the connector component 220 and the connector component 310 to the first module 200 and the second module 300, respectively, and the signal line region 120 extends along the side surface in the housing 500.

As described above, according to the present embodiment, the first module 200 and the second module 300 can be electrically connected by the flexible circuit board 100. Therefore, space saving in the case of the electronic apparatus UE can be achieved, and therefore, the battery 400 can be increased in size. In addition, since the flexible circuit board 100 can be disposed without straddling the battery 400, a coil for wireless power supply or the like can be disposed on the upper surface of the battery.

(sixth embodiment)

Next, another embodiment of an electronic device incorporating the flexible circuit board 100 according to the first to fourth embodiments or the modified examples described above will be described with reference to fig. 13B. In the present embodiment, the flexible circuit board 100 is built in the bottom surface inside the case of the electronic apparatus in a state where the bending region 130 is bent. Hereinafter, a description will be given focusing on a part different from the fifth embodiment.

Fig. 13B is a diagram showing the electronic apparatus UE incorporating the flexible circuit board 100. Fig. 13B (1) is a schematic plan view of the electronic device UE, and fig. 13B (2) is a schematic cross-sectional view of the electronic device UE. As shown in fig. 13B (1) and 13B (2), in the electronic apparatus UE, the flexible circuit board 100 and other electronic components are incorporated in the housing 500. Specifically, the electronic apparatus UE includes a housing 500, and the flexible circuit board 100 according to the above-described embodiment or modification is built in the housing 500. The first module 200 and the second module 300 are disposed inside the case 500, and the battery 400 is disposed between the first module 200 and the second module 300.

Fig. 13B (3) is a perspective view of the flexible circuit board 100 in a state of being housed in the housing 500 (the state shown in fig. 13B (1) and (2)). As shown in (3) of fig. 13B, the flexible circuit board 100 is bent in the bent region 130B at P1 and P2, and the bent region 130A is bent at P3 and P4. In other words, the bending region 130A and the bending region 130B are bent at two locations, respectively. That is, in the flexible circuit board 100 according to the first to fourth embodiments or the modified examples, since the stress when the bending region 130 is bent can be reduced, two portions of the bending region 130 can be bent as in the present embodiment.

In addition, as in the fifth embodiment, the first module 200 and the second module 300 can be electrically connected by the flexible circuit board 100. Therefore, space can be saved in the case of the electronic apparatus UE, and the battery 400 can be increased in size. Further, since the flexible circuit board 100 can be disposed without crossing the upper surface of the battery 400, a coil for wireless power supply or the like can be disposed on the upper surface of the battery.

From the above description, those skilled in the art may conceive of additional effects and various modifications of the present invention, but the embodiments of the present invention are not limited to the above embodiments. The constituent elements across different embodiments may be appropriately combined. Various additions, modifications, and partial deletions can be made without departing from the spirit and scope of the present invention derived from the contents and equivalents thereof as defined in the claims.

Claims

1. A flexible circuit board is characterized in that a flexible circuit board is provided,

the flexible circuit board is provided with a signal line region, a connector region, a flex 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 in a longitudinal direction of the signal line region and transmit analog signals,

the one or more digital signal lines are formed so as to extend in the longitudinal direction of the signal line region, transmit digital signals,

the ground layer is formed in such a manner as to cover the analog signal line through an insulating layer,

the bending region connects the signal line region and the connector region, and at least one of the number of wiring layers and the number of insulating layers is smaller than that of the signal line region.

2. The flexible circuit board of claim 1,

the connector region is smaller in at least one of the number of wiring layers and the number of insulating layers than the signal line region.

3. A flexible circuit board is characterized in that,

the one or more analog signal lines are formed so as to extend in a longitudinal direction of the signal line region, and transmit analog signals,

the bending region connects the signal line region and the connector region, and a space in which a wiring layer and an insulating layer are not provided is provided inside the bending region.

4. The flexible circuit board of claim 3,

the space further includes a notch in a region on one side or both sides in the thickness direction of the flexible circuit board, and the notch has a direction having a component in the width direction orthogonal to the longitudinal direction of the signal line region.

5. The flexible circuit board of claim 3,

the space is formed in a zigzag shape or a crank shape in a region on one side or both sides in a thickness direction of the flexible circuit board in a plan view of the flexible circuit board.

6. The flexible circuit board according to any one of claims 1 to 5,

an interlayer connection channel connected with the analog signal line or the digital signal line is provided in the connector region.

7. The flexible circuit board of claim 6,

the interlayer connection channel has: a plated through hole connected to the analog signal line or the digital signal line; and filling the through holes, and connecting the through holes with the plated through holes through the conductive layer.

8. Flexible circuit board according to claim 6 or 7,

a connector part is mounted in the connector area, and the connector part is electrically connected with the analog signal line and the digital signal line through the interlayer connection channel.

9. An electronic device, comprising:

a housing;

the flexible circuit board of any one of claims 1 to 8, 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.

10. The electronic device of claim 9,

the flexible circuit board is disposed so as to pass between the side surface of the case and the battery.

11. The electronic device of claim 9,

the flexible circuit board is disposed so as to pass between the battery and the back surface or the front surface of the case.

12. A method for manufacturing a flexible circuit board is characterized in that,

the manufacturing method of the flexible circuit board comprises the following steps:

preparing a first single-sided metal-clad 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 provided on the first main surface of the first insulating substrate; and a first protective film layer provided on the second main face of the first insulating substrate through a first adhesive layer;

patterning the first metal foil to form a first conductive pattern;

forming a first bottomed hole that penetrates the first protective film layer, the first adhesive layer, and the first insulating base material and reaches the first metal foil;

filling a first conductive paste into the first bottomed hole;

stripping the first protective film layer to obtain a first wiring base material;

preparing a first double-sided metal-clad laminate having: a second insulating base material having a third main surface and a fourth main surface on the opposite side of the third main surface; a second metal foil provided on the third main surface of the second insulating substrate; and a third metal foil provided on the fourth main surface of the second insulating substrate;

patterning the second metal foil to form a second conductive pattern;

forming a second bottomed hole penetrating the second insulating base material and reaching the second metal foil;

depositing a first metal plating layer on the second bottomed hole side wall and the bottom surface;

patterning the third metal foil to form a third conductive pattern;

forming a second adhesive layer on the third metal foil in such a manner that the third conductive pattern of the third metal foil is buried and the first metal plating layer having the second bottomed hole is deposited;

forming a first cover material layer on the second adhesive layer;

forming a third adhesive layer having a first opening portion on the first cover material layer;

forming a second protective film layer on the third adhesive layer so as to fill the first opening of the third adhesive layer;

forming a third bottomed hole that penetrates the second protective film layer, the third adhesive layer, the first cover material layer, and the second adhesive layer and reaches the third metal foil;

filling a second conductive paste into the third bottomed hole;

stripping the second protective film layer to obtain a second wiring base material;

preparing a second double-sided metal-clad laminate, the second double-sided metal-clad laminate having: a third insulating base material having a fifth main surface and a sixth main surface on the opposite side of the fifth main surface; a fourth metal foil provided on the fifth main surface of the third insulating base material; and a fifth metal foil provided on the sixth main face of the third insulating base material;

patterning the fourth metal foil to form a fourth conductive pattern;

patterning the fifth metal foil to form a fifth conductive pattern;

forming a fourth bottomed hole penetrating through the third insulating base material and reaching the fifth metal foil;

depositing a second metal plating layer on the fourth bottomed hole sidewall and the bottom surface;

forming a first through hole penetrating through the third insulating base material and the fifth metal foil to obtain a third wiring base material; and

the first wiring base material is laminated on the second wiring base material in such a manner that the first conductive paste is brought into contact with the second conductive pattern, and the third wiring base material is laminated on the second wiring base material in such a manner that the second conductive paste is brought into contact with the third conductive pattern.

13. A method for manufacturing a flexible circuit board is characterized in that,

patterning the first metal foil to form a first conductive pattern;

filling a first conductive paste into the first bottomed hole;

patterning the second metal foil to form a second conductive pattern;

patterning the third metal foil to form a third conductive pattern;

forming a second adhesive layer on the third metal foil in such a manner that the third conductive pattern of the third metal foil is embedded and the first metal plating layer deposited on the second bottomed hole;

forming a first covering material layer on the second adhesive layer;

filling a second conductive paste into the third bottomed hole;

preparing a second double-sided metal-clad laminate, the second double-sided metal-clad laminate having: a third insulating base material having a fifth main surface and a sixth main surface on the opposite side of the fifth main surface; a fourth metal foil provided on the fifth main surface of the third insulating base material; and a fifth metal foil provided on the sixth main surface of the third insulating substrate;

patterning the fourth metal foil to form a fourth conductive pattern;

patterning the fifth metal foil to form a fifth conductive pattern;

forming a fourth adhesive layer on the fourth metal foil in such a manner that the third conductive pattern of the fourth metal foil is buried and the second metal plating layer deposited in the fourth bottomed hole is formed;

forming a second cover material layer on the fourth adhesive layer;

forming a third protective film layer on the second covering material layer;

forming a fourth protective film layer on the third protective film layer;

forming a fifth bottomed hole penetrating the fourth protective film layer, the third protective film layer, the second cover material layer, and the third adhesive layer to reach the fourth metal foil;

filling a third conductive paste into the fifth bottomed hole;

stripping the third protective film layer and the fourth protective film layer to obtain a third wiring base material; and

the first wiring base material is laminated on the second wiring base material in such a manner that the first conductive paste is brought into contact with the second conductive pattern, and the third wiring base material is laminated on the second wiring base material in such a manner that the second conductive paste is brought into contact with the third conductive paste.

14. The method of manufacturing a flexible circuit board according to claim 12 or 13,

the second conductive pattern includes an analog signal line.

15. The method of manufacturing a flexible circuit board according to any one of claims 12 to 14,

the fifth conductive pattern includes a digital signal line.