JP7596211B2 - Flexible circuit board, its manufacturing method, and electronic device - Google Patents

Description

The present invention relates to a flexible circuit board and a manufacturing method thereof, and to an electronic device, and more specifically to a flexible circuit board in which the bending region has a reduced-layer structure or a hollow structure, a manufacturing method thereof, and to an electronic device provided with the flexible circuit board.

In recent years, the spread of fifth-generation mobile communication systems (5G) has led to an increase in the number of antenna connection cables inside electronic devices such as smartphones. In addition, the housings of smartphones and other devices are becoming smaller. For this reason, there is a demand for flexible circuit boards in which antenna connection cables are wired at even higher densities.

In the 5G system, SUB6 and millimeter wave radio waves are applied, and radio waves in the frequency band of the previous fourth generation mobile communication system (4G) are also applied. Therefore, the number of antenna connection cables will increase in the 5G system. Conventionally, coaxial cables that transmit analog signals and cables that transmit digital signals were built into the housing as separate units. However, as the number of antenna connection cables increases in the 5G system, it is required to integrate these two types of cables into a multi-layer flexible circuit board.
In addition, Patent Documents 1 and 2 describe general multilayer flexible circuit boards.

Patent No. 5204871 JP 2004-311927 A

As mentioned above, with the spread of 5G systems, the number of antennas in electronic devices such as smartphones is increasing. In addition to cables that transmit analog signals such as wireless signals, cables that transmit digital signals received by digital terminals such as USB, and cables that transmit power from power sources are also required. These cables are arranged so as to straddle the top surface of the battery. Meanwhile, coils used for wireless power supply, etc. are increasingly being arranged on the top surface of the battery. For this reason, there is a demand for reducing the space required for cables arranged on the top surface of the battery. There is also a demand for methods of arranging cables other than on the top surface of the battery, such as arranging the cables on the side of the housing of a smartphone, etc.

The present invention was made based on the above technical recognition, and aims to provide a flexible circuit board capable of transmitting both analog and digital signals and capable of being easily installed in a bent state inside the housing of an electronic device such as a smartphone, a manufacturing method thereof, and an electronic device.

The flexible circuit board according to the first aspect of the present invention comprises:
A flexible circuit board for electrically connecting a first module having a wireless communication antenna for receiving an analog signal and a digital terminal for receiving a digital signal to a second module for performing signal processing of the analog signal and the digital signal, the flexible circuit board being provided with a signal line region, a connector region, and a bending region for connecting the signal line region and the connector region;
one or more analog signal lines extending in a longitudinal direction of the signal line region and transmitting analog signals received from the wireless communication antenna;
one or more digital signal lines extending in the longitudinal direction of the signal line region and transmitting digital signals received from the digital terminals;
a ground layer formed so as to cover the analog signal line via an insulating layer;
Equipped with
The bent region is characterized by having a reduced-layer structure in which the number of wiring layers and/or insulating layers is smaller than that of the signal line region.

In addition, in the flexible circuit board,
The connector region may also have a reduced-layer structure having fewer wiring layers and/or insulating layers than the signal line region.

A flexible circuit board according to a second aspect of the present invention comprises:
A flexible circuit board for electrically connecting a first module having a wireless communication antenna for receiving an analog signal and a digital terminal for receiving a digital signal to a second module for performing signal processing of the analog signal and the digital signal, the flexible circuit board being provided with a signal line region, a connector region, and a bending region for connecting the signal line region and the connector region;
one or more analog signal lines extending in a longitudinal direction of the signal line region and transmitting analog signals received from the wireless communication antenna;
one or more digital signal lines extending in the longitudinal direction of the signal line region and transmitting digital signals received from the digital terminals;
a ground layer formed so as to cover the analog signal line via an insulating layer;
Equipped with
The bent region has a hollow structure in which a hollow region is provided in which neither a wiring layer nor an insulating layer is provided.

In addition, in the flexible circuit board,
A cut having a width direction component perpendicular to the longitudinal direction of the signal line region may be provided in an area on one or both sides of the hollow region in the thickness direction of the flexible circuit board.

In addition, in the flexible circuit board,
The flexible circuit board may have a hollow region on one or both sides in a thickness direction of the flexible circuit board, the hollow region being formed in a meander shape or a crank shape in a plan view of the flexible circuit board.

In addition, in the flexible circuit board,
An interlayer connection path connected to the analog signal line or the digital signal line may be provided in the connector region.

In addition, in the flexible circuit board,
The interlayer connection path may include a plated through hole connected to the analog signal line or the digital signal line, and a filled via connected to the plated through hole via a conductive layer.

In addition, in the flexible circuit board,
A connector component electrically connected to the analog signal lines and the digital signal lines via the interlayer connection paths may be mounted in the connector region.

The electronic device according to the present invention comprises:
A housing and
The flexible circuit board is disposed within the housing; and
the first module disposed within the housing;
The second module disposed within the housing;
a battery disposed within the housing between the first module and the second module;
The present invention is characterized by comprising:

In addition, in the electronic device,
The flexible circuit board may be arranged to pass between a side surface of the housing and the battery.

In addition, in the electronic device,
The flexible circuit board may be arranged to pass between the rear or front surface of the housing and the battery.

The method for producing a flexible circuit board according to the first aspect of the present invention includes the steps of:
A step of preparing a first single-sided metal foil-clad laminate including 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 surface of the first insulating substrate via a first adhesive layer;
patterning the first metal foil to form a first conductive pattern;
forming a first bottomed hole penetrating the first protective film layer, the first adhesive layer, and the first insulating base material and reaching the first metal foil;
filling the first bottomed hole with a first conductive paste;
removing the first protective film layer to obtain a first wiring substrate;
A step of preparing a first double-sided metal foil-clad laminate including a second insulating substrate having a third main surface and a fourth main surface opposite to 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 third metal foil and the second insulating base material and reaching the second metal foil;
depositing a first metal plating on a sidewall and a bottom surface of the second blind hole;
patterning the third metal foil to form a third conductive pattern;
forming a second adhesive layer on the third metal foil so as to embed the third conductive pattern of the third metal foil and the first metal plating deposited in the second bottomed hole;
forming a first cover material layer over the second adhesive layer;
forming a third adhesive layer over the first cover material layer, the third adhesive layer having a first opening;
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 penetrating the second protective film layer, the third adhesive layer, the first cover material layer and the second adhesive layer and reaching the third metal foil;
filling the third bottomed hole with a second conductive paste;
removing the second protective film layer to obtain a second wiring substrate;
preparing a second double-sided metal foil-clad laminate having a third insulating substrate having a fifth main surface and a sixth main surface opposite to the fifth main surface, a fourth metal foil provided on the fifth main surface of the third insulating substrate, 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 the third insulating base material and reaching the fifth metal foil;
depositing a second metal plating on a sidewall and a bottom surface of the fourth blind hole;
forming a first through hole penetrating the fourth metal foil, the third insulating base material, and the fifth metal foil to obtain a third wiring base material;
laminating the first wiring base material on the second wiring base material such that the first conductive paste contacts the second conductive pattern, and laminating the third wiring base material on the second wiring base material such that the second conductive paste contacts the third conductive pattern;
The present invention is characterized by comprising:

A method for producing a flexible circuit board according to a second aspect of the present invention includes the steps of:
A step of preparing a first single-sided metal foil-clad laminate including 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 surface of the first insulating substrate via a first adhesive layer;
patterning the first metal foil to form a first conductive pattern;
forming a first bottomed hole penetrating the first protective film layer, the first adhesive layer, and the first insulating base material and reaching the first metal foil;
filling the first bottomed hole with a first conductive paste;
removing the first protective film layer to obtain a first wiring substrate;
A step of preparing a first double-sided metal foil-clad laminate including a second insulating substrate having a third main surface and a fourth main surface opposite to 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 third metal foil and the second insulating base material and reaching the second metal foil;
depositing a first metal plating on a sidewall and a bottom surface of the second blind hole;
patterning the third metal foil to form a third conductive pattern;
forming a second adhesive layer on the third metal foil so as to embed the third conductive pattern of the third metal foil and the first metal plating deposited in the second bottomed hole;
forming a first cover material layer over the second adhesive layer;
forming a third adhesive layer over the first cover material layer, the third adhesive layer having a first opening;
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 penetrating the second protective film layer, the third adhesive layer, the first cover material layer, and the second adhesive layer to reach the third metal foil;
filling the third bottomed hole with a second conductive paste;
removing the second protective film layer to obtain a second wiring substrate;
preparing a second double-sided metal foil-clad laminate having a third insulating substrate having a fifth main surface and a sixth main surface opposite to the fifth main surface, a fourth metal foil provided on the fifth main surface of the third insulating substrate, 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; and patterning the fifth metal foil to form a fifth conductive pattern.
forming a fourth bottomed hole penetrating the third insulating base material and reaching the fifth metal foil;
depositing a second metal plating on a sidewall and a bottom surface of the fourth blind hole;
forming a fourth adhesive layer on the fourth metal foil so as to embed the third conductive pattern of the fourth metal foil and the second metal plating deposited in the fourth bottomed hole;
forming a second cover material layer over the fourth adhesive layer;
forming a third protective film layer on the second cover 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 the fifth bottomed hole with a third conductive paste;
removing the third protective film and the fourth protective film layer to obtain a third wiring substrate;
laminating the first wiring base material and the second wiring base material so that the first conductive paste contacts the second conductive pattern, and laminating the third wiring base material on the second wiring base material so that the second conductive paste contacts the third conductive pattern;
The present invention is characterized by comprising:

In addition, in the method for producing a flexible circuit board,
The second conductive pattern may include an analog signal line.

In addition, in the method for producing a flexible circuit board,
The fifth conductive pattern may include a digital signal line.

The present invention provides a flexible circuit board that can transmit both analog and digital signals at high speed and with low loss, and can be easily installed in a bent state inside the housing of an electronic device, as well as a manufacturing method thereof and an electronic device.

FIG. 1 is a plan view of a flexible circuit board according to an embodiment. FIG. 2 is an enlarged plan view of region A in FIG. 1 . 3 is a schematic cross-sectional view taken along line BB in FIG. 2. 5A to 5C are cross-sectional views illustrating steps in a method for manufacturing a flexible circuit board according to the first embodiment. 5A to 5C are cross-sectional views illustrating steps in the manufacturing method of the flexible circuit board according to the first embodiment, following FIG. 4 . 5B is a cross-sectional view illustrating a process of the manufacturing method of the flexible circuit board according to the first embodiment, following FIG. 5A. 5B, which is a cross-sectional view illustrating a process of the manufacturing method of the flexible circuit board according to the first embodiment. 5C , which is a cross-sectional view illustrating a process of the manufacturing method of the flexible circuit board according to the first embodiment. 7A to 7C are cross-sectional views illustrating steps in the manufacturing method of the flexible circuit board according to the first embodiment, following FIG. 6 . FIG. 3 is a schematic cross-sectional view taken along line BB in FIG. 2 according to the second embodiment. 10A to 10C are cross-sectional views illustrating steps in a method for manufacturing a flexible circuit board according to a second embodiment of the present invention. 9B is a cross-sectional view illustrating a process of the manufacturing method of the flexible circuit board according to the second embodiment, following FIG. 9A. 9C are cross-sectional views illustrating steps in the manufacturing method of a flexible circuit board according to a second embodiment, following FIG. 9B. 9C , which is a cross-sectional view illustrating a process of the manufacturing method of the flexible circuit board according to the second embodiment. FIG. 10 is a schematic perspective view of a region C in FIG. 2 according to a third embodiment. FIG. 13 is a schematic perspective view of a region C in FIG. 2 according to a fourth embodiment (meander shape). FIG. 11 is a schematic perspective view of a region C in FIG. 2 according to a fourth embodiment (crank shape). FIG. 13 is a plan view of a flexible circuit board according to a modified example. FIG. 13 is a schematic perspective view of an electronic device according to a fifth embodiment. 13A and 13B are a schematic plan view and a schematic cross-sectional view of an electronic device according to a sixth embodiment.

Embodiments of the present invention will be described below with reference to the drawings. In each drawing, components having equivalent functions are given the same reference numerals. The drawings are schematic, and the relationship between thickness and planar dimensions (aspect ratio), the thickness ratio of each layer, etc. do not necessarily match the actual ones.

<Overall structure of flexible circuit board 100>

First, referring to FIG. 1, the overall structure of the flexible circuit board 100 according to the embodiment will be described. FIG. 1 shows a plan view of the flexible circuit board 100. The flexible circuit board 100 is provided with a connector region 110, a signal line region 120, and a bending region 130. The flexible circuit board 100 electrically connects a first module (see first module 200 in FIG. 13A) having a wireless communication antenna for receiving analog signals and a digital terminal for receiving digital signals, to a second module (see second module 300 in FIG. 13A) for performing signal processing of the analog signals and the digital signals.

The connector regions 110 are provided at both ends of the signal line region 120. One connector region 110 is connected to an antenna module that transmits and receives analog signals such as wireless signals, and the other connector region 110 is connected to a signal processing module equipped with a signal processing chip. The signal line region 120 is formed to extend in its longitudinal direction, and includes an analog signal line and a digital signal line. The analog signal line transmits analog signals such as wireless signals, and the digital signal line transmits digital signals.

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 is an antenna module, and the second module is a signal processing module. The flexible circuit board 100 electrically connects the first module and the second module. Specifically, one connector region 110 is electrically connected to the first module, and the other connector region 110 is electrically connected to the second module. The analog signal line and the digital signal line included in the signal line region 120 electrically connect the respective connector regions 110. In other words, the first module and the second module are electrically connected via 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 plan view of region A in FIG. 1, showing one end 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 bending region 130 also includes analog signal lines and digital signal lines. As will be described in detail later, the bending region 130 has a reduced-layer structure with fewer wiring layers and/or insulating layers than the signal line region 120. Alternatively, the bending region 130 has a hollow structure with a hollow region in which neither wiring layers nor insulating layers are provided.

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

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

As described above, the bending region 130 has a reduced-layer structure with fewer wiring layers and insulating layers than the signal line region 120. Therefore, the bending region 130 is less stressed when bending than the signal line region 120. Therefore, when the flexible circuit board 100 is incorporated into the housing of an electronic device such as a smartphone, it is easy to incorporate the flexible circuit board 100 in a bent state. Specifically, when the flexible circuit board 100 is incorporated into the housing in a bent state, the flexible circuit board 100 is bent in the bending region 130 and incorporated into the housing. At this time, the bending region 130, which has a relatively relaxed stress, can be bent relatively easily. This makes it easy to bend and incorporate the flexible circuit board 100 into the housing.

In addition, in the flexible circuit board 100, the analog signal lines are arranged on the wiring 22i, and the digital signal lines are arranged on the wiring 33i. In this way, both analog signal lines and digital signal lines are incorporated into the flexible circuit board 100. As a result, by using the flexible circuit board 100, both analog signal lines and digital signal lines can be arranged, thereby saving space within the housing of the electronic device.

In addition, the flexible circuit board 100 has a ground layer formed to cover the analog signal line through an insulating layer. Specifically, the ground layers 12b and 23b (wiring 12b and 23b) cover the wiring 22i of the analog signal line through an insulating layer. As shown in FIG. 3, a first insulating layer (adhesive layer 13 and insulating substrate 11) is laminated on the wiring 22i, and a ground layer 12b (wiring 12b) is formed on the first insulating layer. Similarly, a second insulating layer (insulating substrate 21) is laminated under the wiring 22i, and a ground layer 23b (wiring 23b) is laminated under the second insulating layer. In this way, the flexible circuit board 100 has ground layers 12b and 23b) formed to cover the analog signal line (wiring 22i) through the first and second insulating layers. That is, the flexible circuit board 100 has a three-layer stripline structure.

Interlayer connection paths electrically connected to analog or digital signal lines are provided in the connector region 110 of the flexible circuit board 100. These interlayer connection paths are provided in holes H1 to H4 of the connector region 110 shown in FIG. 3, and are electrically connected to the analog or digital signal lines. For example, the interlayer connection path provided in hole H2 is electrically connected to the analog signal line (wiring 22i). Also, the interlayer connection path provided in hole H4 is electrically connected to the digital signal line (wiring 33i).

The interlayer connection path of the connector region 110 may be formed by a plated through hole. More specifically, copper plating 61 is deposited on hole H2, and copper plating 62 is deposited on hole H4 to form a plated through hole. In this way, the interlayer connection path of the connector region 110 has a plated through hole (hole H2 or hole H4) connected to an analog signal line (wiring 22i) or a digital signal line (wiring 33i).

The interlayer connection path of the connector region 110 may be formed by a filled via. More specifically, the hole H1 is filled with a conductive paste to form a filled via. The filled via formed in the hole H1 is connected to the wiring 22i. Similarly, the hole H3 is filled with a conductive paste to form a filled via. The filled via formed in the hole H3 is connected to the receiving land 32a. The receiving land 32a is connected to the plated through hole of the hole H4. The interlayer connection path of the connector region 110 has a plated through hole and a filled via connected to the plated through hole via a conductive layer (receiving land 22a or 32a). The connector region 110 may be equipped with a connector component (not shown) electrically connected to the analog signal line and the digital signal line via the interlayer connection path.

The above describes the schematic configuration of the flexible circuit board 100 according to the first embodiment. According to the first embodiment, the bending region 130 of the flexible circuit board 100 has a reduced-layer structure with fewer wiring layers and insulating substrates than the signal line region 120. This reduces stress when bending the bending region 130. This makes it easy to bend and install the flexible circuit board 100 into the housing of an electronic device such as a smartphone.

The flexible circuit board 100 houses both analog and digital signal lines. This eliminates the need to place separate cables for the analog and digital signal lines inside the housing of the electronic device, making it possible to save space inside the housing of an electronic device such as a smartphone.

In addition, since the number of wiring layers and insulating layers is reduced in the bending region 130 compared to the signal line region 120, the amount of material for the wiring layers and insulating substrate required to manufacture the flexible circuit board 100 can be reduced, thereby reducing manufacturing costs.

<Method of 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 cross-sectional process views of FIGS.

First, as shown in FIG. 4(1), a single-sided metal foil laminate 10 is prepared. The single-sided metal foil laminate 10 has an insulating substrate 11, a metal foil 12 provided on the upper surface of the insulating substrate 11, and a protective film layer 14 provided on the lower surface of the insulating substrate 11 via an adhesive layer (weakly 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 substrate 11 may be, in addition to liquid crystal polymer (LCP), for example, polyimide (PI), modified polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluororesin (PFA, PTEE, etc.), and is not particularly limited.

The insulating substrate 11 has a thickness of, for example, 100 μm. The metal foil 12 is made of, for example, silver or aluminum, in addition to copper. The metal foil 12 has a thickness of, 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, for example, an insulating film such as PET (polyethylene terephthalate). The protective film layer 14 has a thickness of, for example, 10 μm. The adhesive layer 13 has a thickness of, for example, 10 μm.

Next, as shown in FIG. 4(2), the metal foil 12 of the single-sided metal foil laminate 10 is patterned by a known photofabrication method to form a first conductive pattern. This first conductive pattern includes a receiving land 12a and a wiring 12b. The diameter of the receiving land 12a is, for example, φ350 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 laser light to remove the protective film layer 14, the adhesive layer 13, and the insulating substrate 11, forming a bottomed hole H1 with the receiving land 12a exposed at the bottom. The diameter of the hole H1 is, for example, φ150 to 200 μm. More specifically, a carbon dioxide gas laser is used to irradiate a laser pulse onto a predetermined position of the protective film layer 14 to perforate it. The beam diameter of the infrared laser is set to 150 μm, which is the same as the diameter of the hole H1. The pulse width of the infrared laser is set to 10 μs, and the energy per pulse of the infrared laser is set to 5 mJ.

The protective film layer 14 is irradiated with five shots of the laser light of the infrared laser set as described above to obtain hole H1. As described above, the beam diameter of the infrared laser and the diameter of hole H1 are approximately the same. In other words, the beam diameter of the infrared laser can be adjusted to match the diameter of hole H1. For this reason, the infrared laser is suitable for forming hole H1 because it is easy to adjust the beam diameter. Note that the laser used to form hole H1 is not limited to the infrared laser, and a UV-YAG laser or the like may also be used.

After the hole H1 is drilled with an infrared laser, a desmear process is performed. In the desmear process, the resin residue (residual film) at the boundary between the insulating substrate 11 and the receiving land 12a and the back surface treatment film (Ni, Cr, etc.) of the receiving land 12a are removed.

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

4(4), the protective film layer 14 is peeled off from the adhesive layer 13. As a result, a part of the conductive paste 51 filled in the hole H1 protrudes, forming a protrusion 51a. The height of the protrusion 51a is approximately the same as the thickness of the protective film layer 14.
Through the above steps, wiring substrate 101 (first wiring substrate) is obtained.

Next, as shown in FIG. 5A (1), a double-sided metal foil clad laminate 20 is prepared. This double-sided metal foil clad laminate 20 has an insulating substrate 21, a metal foil 22 provided on the upper surface of this insulating substrate 21, and a metal foil 23 provided on the lower surface of this insulating substrate 21. The insulating substrate 21 may be, in addition to liquid crystal polymer (LCP), for example, polyimide (PI), modified polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluororesin (PFA, PTEE, etc.), and is not particularly limited.

The thickness of the insulating substrate 21 is, for example, 100 μm. The metal foil 22 and the metal foil 23 are made of, for example, silver or aluminum, in addition to copper. The thickness of the metal foil 22 and the metal foil 23 is, for example, 12 μm each. The metal foil 22 is formed on the insulating substrate 21 via a seed layer (not shown) formed on the upper surface of the insulating substrate 21. Similarly, the metal foil 23 is formed below the insulating substrate 21 via a seed layer (not shown) formed on the lower surface of the insulating substrate 21.

Next, as shown in FIG. 5A (2), the metal foil 22 of the double-sided metal foil laminate 20 is patterned by a known photofabrication method to form a second conductive pattern. This second conductive pattern includes a receiving land 22a and a wiring 22i. The diameter of the receiving land 22a is, for example, φ350 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 laminate 20 is patterned by a known photofabrication method to form a third conductive pattern. This third conductive pattern includes a receiving land 23a and a wiring 23b. The diameter of the receiving land 23a is, for example, φ350 μm. The wiring 23b functions as a ground layer in the flexible circuit board 100.

Next, as shown in FIG. 5A (4), the conformal mask of the receiving land 23a is irradiated with laser light to remove the insulating substrate 21, forming a bottomed hole H2 with the receiving land 22a exposed at the bottom. The diameter of the hole H2 is, for example, φ150 to 200 μm. Hereinafter, the formation of the hole H2 is similar to the formation of the hole H1. That is, an infrared laser, which is a carbon dioxide laser, is used to irradiate a laser pulse to a predetermined position of the receiving land 23a to drill the hole H2. The beam diameter of the infrared laser is set to 150 μm, the same as the diameter of the hole H2. The pulse width of the infrared laser is set to 10 μs, and the energy per pulse of the infrared laser is set to 5 mJ.

The laser beam from the infrared laser set as described above is irradiated five times to obtain hole H2. Note that the laser used to form hole H2 is not limited to infrared laser and may be a UV-YAG laser or the like.

After drilling hole H2 with an infrared laser, a desmear process is performed. In the desmear process, resin residue (residual film) at the boundary between the insulating substrate 21 and the receiving land 23a is removed. In addition, the back surface treatment film (Ni, Cr, etc.) of the receiving land 23a and the receiving land 22a is removed.

Next, as shown in FIG. 5A (5), a first metal plating 61 is deposited on the sidewalls and bottom surface of the hole H2. The first metal plating 61 is, for example, copper plating. The first metal plating 61 is deposited by partial plating or panel plating. The plating thickness of the first metal plating 61 is, for example, 16 μm.

Next, as shown in FIG. 5B (1), an adhesive layer 24 is formed so as to bury the third conductive pattern (receiving land 23a and wiring 23b) and the first metal plating 61 deposited in hole H2. This adhesive layer 24 is, for example, a weakly 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. For example, a liquid crystal polymer (LCP) or polyimide is used as the insulating resin film. The thickness of the cover material layer 71 is, for example, 12 μm.

Next, as shown in FIG. 5B (3), an adhesive layer 25 having an opening A1 is formed on the cover material layer 71. The adhesive layer 25 is, for example, a weakly adhesive layer having a thickness of 10 μm. Next, as shown in FIG. 5B (4), a protective film layer 26 is formed on the adhesive layer 25 so as to fill the opening A1 of the adhesive layer 25. The protective film layer 26 is, for example, a PET film with a weak adhesive having a thickness of 20 μm. The diameter of the opening A1 is, for example, 30 mm in the longitudinal direction and 2 mm in the lateral direction.

Next, as shown in FIG. 5C (1), the protective film layer 26 is irradiated with laser light to remove the protective film layer 26, the adhesive layer 25, the cover material layer 71, and the adhesive layer 24, and a bottomed hole H3 with the receiving land 23a exposed at the bottom is drilled. The diameter of the hole H3 is, for example, φ150 to 200 μm. Hereinafter, the formation of the hole H3 is similar to the formation of the hole H1. That is, an infrared laser, which is a carbon dioxide laser, is used to irradiate a laser pulse onto a predetermined position of the protective film layer 26 to drill a hole. The beam diameter of the infrared laser is set to 150 μm, the same as the diameter of the hole H3. The pulse width of the infrared laser is set to 10 μs, and the energy per pulse of the infrared laser is set to 5 mJ.

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

5C(3), the protective film layer 26 is peeled off from the adhesive layer 25 and the cover material layer 71. As a result, a part of the conductive paste 52 filled in the hole H3 protrudes, forming a protruding portion 52a. The height of the protruding portion 52a is approximately the same as the thickness of the protective film layer 26 formed on the adhesive layer 25.
Through the above steps, wiring substrate 102 (second wiring substrate) is obtained.

Next, as shown in FIG. 6 (1), a double-sided metal foil clad laminate 30 is prepared. This double-sided metal foil clad laminate 30 has an insulating substrate 31, a metal foil 32 provided on the upper surface of this insulating substrate 31, and a metal foil 33 provided on the lower surface of this insulating substrate 31. The insulating substrate 31 may be, in addition to liquid crystal polymer (LCP), for example, polyimide (PI), modified polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluororesin (PFA, PTEE, etc.), and is not particularly limited.

The thickness of the insulating substrate 31 is, for example, 50 μm. The metal foil 32 and the metal foil 33 are made of, for example, silver or aluminum, in addition to copper. The thickness of the metal foil 32 and the metal foil 33 is, for example, 12 μm each. The metal foil 32 is formed on the insulating substrate 31 via a seed layer (not shown) formed on the upper surface of the insulating substrate 31. Similarly, the metal foil 33 is formed below the insulating substrate 31 via a seed layer (not shown) formed on the lower surface of the insulating substrate 31.

By setting the thickness of the insulating substrate 31 to a relatively thin value of 50 μm, it is possible to narrow the line width of the signal line (wiring 33i) that matches the characteristic impedance expressed by Z ₀ =√(L/C), where L is the inductance per unit length and C is the capacitance between the lines. As a result, the line width of the signal line is narrowed, and the width of the flexible circuit board 100 can be narrowed, thereby saving space when the flexible circuit board 100 is incorporated into the housing of an electronic device such as a smartphone.

Next, as shown in FIG. 6(2), the metal foil 32 is patterned to form a fourth conductive pattern including the receiving land 32a, which is a conformal mask, and then, as shown in FIG. 6(3), the conformal mask is irradiated with laser light to remove the insulating substrate 31 to form a bottomed hole H4 with the receiving land 33a exposed at the bottom. The diameter of the hole H4 is, for example, φ150 to 200 μm. The hole H4 is formed in the same manner as the hole H1. That is, an infrared laser, which is a carbon dioxide laser, is used to irradiate a laser pulse onto the opening of the conformal mask to perforate the hole H4. The beam diameter of the infrared laser is set to 150 μm, which is the same as the diameter of the hole H4. Note that, as shown in FIG. 6(2), the metal foil 33 is patterned to form a fifth conductive pattern (the receiving land 33a and the wiring 33i). The diameter of the receiving land 33a is, for example, φ350 μm. Note that 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 drilling hole H4 with an infrared laser, a desmear process is performed. In the desmear process, resin residue (residual film) at the boundary between the receiving land 33a and the insulating base material 31 is removed. In addition, the back surface treatment film (Ni, Cr, etc.) of the receiving land 33a is removed.

Next, as shown in FIG. 6 (4), a second metal plating 62 is deposited on the sidewalls and bottom surface of the hole H4. The second metal plating 62 is, for example, copper plating. The second metal plating 62 is deposited by partial plating or panel plating. The plating thickness of the second metal plating 62 is, for example, 16 μm.

Next, as shown in Fig. 6 (5), a blade or the like is used to remove parts of the metal foil 32, the insulating base material 31, and the receiving land 33a to form a window W. The size of the window W is, for example, approximately the same as the size of the opening A1 of the adhesive layer 25 shown in Fig. 5B (3), and is, for example, 30 mm in the longitudinal direction and 2 mm in the lateral direction.
Through the above steps, wiring substrate 103 (third wiring substrate) is obtained.

In the above-mentioned process, the metal foil of each wiring substrate 101, 102, 103 may be subjected to a roughening treatment. The roughening treatment can improve the adhesive strength between the metal foil and the insulating substrate.

Below, with reference to Figure 7, we will explain the process of stacking the wiring substrate 101, wiring substrate 102, and wiring substrate 103 obtained in the above-mentioned process.

First, the wiring substrate 101 is laminated on the wiring substrate 102. Specifically, the conductive paste 51 is laminated so that the protruding portion 51a of the conductive paste 51 contacts the receiving land 22a.

Next, the laminate consisting of wiring substrate 101 and wiring substrate 102 obtained in the above process is laminated on wiring substrate 103. Specifically, the laminate is laminated so that protruding portion 52a of conductive paste 52 contacts receiving land 32a. In this way, wiring substrate 101, wiring substrate 102, and wiring substrate 103 are electrically connected to each other. Note that the stacking order of wiring substrates 101, 102, and 103 is not limited to the above.

In the lamination process for forming a laminate consisting of wiring substrate 101, wiring substrate 102, and wiring substrate 103, a vacuum press or vacuum laminator is used. The laminate is heated and pressurized by the vacuum press or vacuum laminator. For example, the laminate is heated to about 200°C and pressurized at a pressure of several MPa (for example, 2.0 MPa). The temperature to which flexible circuit board 100 is heated is, for example, at least about 50°C lower than the softening temperature of the liquid crystal polymer (LCP) that constitutes insulating substrates 11, 21, and 31.

When a vacuum press is used in the lamination process, the laminate is heated and pressurized for approximately 30 to 60 minutes under the above-mentioned conditions. Therefore, when the laminate is heated and pressurized by the vacuum press, the thermal curing of the adhesive layers 13, 24, and 25 is completed, and the thermal curing of the conductive pastes 51 and 52 is also completed.

On the other hand, when a vacuum laminator is used in the lamination process, the laminate is heated and pressurized for about several minutes under the above-mentioned conditions. Therefore, after the laminate is heated and pressurized by the vacuum laminator, it is moved to an oven device and a post-cure process is performed. In the post-cure process, for example, the laminate is heated at about 200°C for about 60 minutes. This post-cure process completes the thermal curing of the adhesive layers 13, 24, and 25, and also the thermal curing of the conductive pastes 51 and 52.

Next, as necessary, surface treatment and solder resist are applied to the first and fifth conductive patterns exposed to the outside, and then the exterior shape is processed.
Through the above steps, a flexible circuit board 100 having the cross-sectional structure shown in FIG. 3 is obtained.

As described above, according to the manufacturing method of the flexible circuit board according to the first embodiment, the bending region 130 has a reduced-layer structure in which the number of wiring layers and/or insulating layers is smaller than that of the signal line region 120. Therefore, the bending region 130 is subjected to less stress when bent than the signal line region 120, and the flexible circuit board 100 can be easily bent and assembled into the housing of an electronic device such as a smartphone.

Furthermore, in the flexible circuit board 100, the analog signal line is formed as wiring 22i, and the digital signal line is formed as wiring 33i. As shown in FIG. 3, the flexible circuit board 100 incorporates analog signal lines and digital signal lines. Therefore, by incorporating the flexible circuit board 100 into the housing of an electronic device such as a smartphone, it is possible to arrange an analog signal line that transmits an analog signal received by a wireless communication antenna and a digital signal line that transmits a digital signal received by a digital terminal such as a USB together at the same time. As a result, it is possible to save space inside the housing of an electronic device such as a smartphone.

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

Furthermore, the flexible circuit board 100 is manufactured by laminating the wiring substrate 101, the wiring substrate 102, and the wiring substrate 103. That is, since the flexible circuit board 100 is manufactured by laminating three wiring substrates, the occurrence of misalignment between the wiring substrates is relatively suppressed. Therefore, the yield in the manufacturing process of the flexible circuit board 100 can be suppressed. In addition, the margin related to the above-mentioned misalignment can be relatively small, and the wiring structure in the wiring layer of the flexible circuit board 100 can be made denser.

Second Embodiment
<Structure of Flexible Circuit Board 100A>
Next, the structure of a flexible circuit board 100A according to the second embodiment will be described with reference to Fig. 8. The flexible circuit board 100 according to the first embodiment has a reduced-layer structure in the bending region 130, but the flexible circuit board 100A according to the second embodiment has a hollow structure in the bending region 130. The following description will focus on the differences from the first embodiment.

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

Specifically, in the bending region 130, a space HS is provided between the cover material layer 71 and the cover material layer 72. Therefore, the bending stress is reduced in the bending region 130 compared to the signal line region 120 when bending. Therefore, when the flexible circuit board 100A is incorporated into the housing of an electronic device such as a smartphone, it is easy to incorporate the flexible circuit board 100A in a bent state. Specifically, when the flexible circuit board 100A is incorporated into the housing in a bent state, the flexible circuit board 100A is bent in the bending region 130 and incorporated into the housing. At this time, the bending region 130, in which the stress is relatively reduced, can be bent relatively easily. This makes it easy to bend and incorporate the flexible circuit board 100A into the housing.

As in the first embodiment, in the flexible circuit board 100A, the analog signal lines are formed by wiring 22i, and the digital signal lines are formed by wiring 33i. In other words, the flexible circuit board 100A incorporates analog signal lines and digital signal lines, which can save space inside the housing.

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

Interlayer connection paths connected to analog signal lines or digital signal lines are provided in the connector region 110 of the flexible circuit board 100A. As in the first embodiment, these interlayer connection paths are provided in holes H1 to H4 of the connector region 110 shown in FIG. 8. The interlayer connection path provided in hole H2 is connected to the analog signal line (wiring 22i). The interlayer connection path provided in hole H4 is connected to the digital signal line (wiring 33i).

The interlayer connection path of the connector region 110 has a plated through hole connected to an analog signal line or a digital signal line. As in the first embodiment, the interlayer connection path of the connector region 110 has a plated through hole (hole H2 or hole H4) connected to an analog signal line (wiring 22i) or a digital signal line (wiring 33i).

The interlayer connection path of the connector region 110 may be formed by a filled via. More specifically, as in the first embodiment, holes H1, H3, and H5 are filled with conductive paste to form filled vias. Therefore, as described above, the interlayer connection path of the connector region 110 has a plated through hole and a filled via connected to the plated through hole via a conductive layer (receiving land 22a or 32a). Note that the connector region may also be equipped with a connector component (not shown) electrically connected to the analog signal line and the digital signal line via the interlayer connection path.

The above describes the conceptual configuration of the flexible circuit board 100A according to the second embodiment. According to the second embodiment, the bending region 130 of the flexible circuit board 100A has a hollow structure in which neither a wiring layer nor an insulating substrate is provided. This reduces the stress that occurs when bending the bending region 130. This makes it easy to bend and install the flexible circuit board 100A into the housing of an electronic device such as a smartphone.

The flexible circuit board 100A houses both analog and digital signal lines. This eliminates the need to place separate cables for the analog and digital signal lines inside the housing of the electronic device, making it possible to save space inside the housing of an electronic device such as a smartphone.

In addition, since the number of insulating layers is reduced in the bending region 130 compared to the signal line region 120, the amount of wiring layer and insulating substrate material required to manufacture the flexible circuit board 100A can be reduced, thereby reducing manufacturing costs.

<Method of 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 cross-sectional process views of FIGS. 9A to 10. FIG.

In the second embodiment, flexible circuit board 100A is also manufactured by laminating wiring substrate 101 (first wiring substrate), wiring substrate 102 (second wiring substrate), and wiring substrate 103A (third wiring substrate). The manufacturing methods of wiring substrate 101 and wiring substrate 102 are the same as those in the first embodiment. That is, the manufacturing method of wiring substrate 101 in the second embodiment is shown in FIG. 4, and the manufacturing method of wiring substrate 102 is shown in FIGS. 5A to 5C, so the description will be omitted. The manufacturing method of wiring substrate 103A will be described below.

As shown in FIG. 9A (1), a double-sided metal foil clad laminate 30 is prepared. This double-sided metal foil clad laminate 30 has an insulating substrate 31, a metal foil 32 provided on the upper surface of this insulating substrate 31, and a metal foil 33 provided on the lower surface of this insulating substrate 31. The insulating substrate 31 may be, in addition to liquid crystal polymer (LCP), for example, polyimide (PI), modified polyimide (MPI), polyethylene naphthalate (PEN), polyether ether ketone (PEEK), fluororesin (PFA, PTEE, etc.), and is not particularly limited.

The thickness of the insulating substrate 31 is, for example, 50 μm. The metal foil 32 and the metal foil 33 are, in addition to copper, for example, silver or aluminum. The thickness of the metal foil 32 and the metal foil 33 is, for example, 12 μm each. The metal foil 32 is formed on the insulating substrate 31 via a seed layer (not shown) formed on the upper surface of the insulating substrate 31. Similarly, the metal foil 33 is formed below the insulating substrate 31 via a seed layer (not shown) formed on the lower surface of the insulating substrate 31.

By setting the thickness of the insulating substrate 31 to a relatively thin value of 50 μm, it is possible to narrow the line width of the signal line (wiring 33i) that matches the characteristic impedance expressed by Z ₀ =√(L/C), where L is the inductance per unit length and C is the line capacitance. As a result, the line width of the signal line is narrowed, and the width of the flexible circuit board 100A can be narrowed, thereby saving space when the flexible circuit board 100A is incorporated into the housing of an electronic device such as a smartphone.

Next, as shown in FIG. 9A (2), the metal foil 32 is patterned to form a fourth conductive pattern including a receiving land 32a that functions as a conformal mask. Then, as shown in FIG. 9A (3), the metal foil 33 is patterned to form a fifth conductive pattern including a receiving land 33a and a wiring 33i. The diameter of the receiving land 33a is, for example, φ350 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.

Next, as shown in FIG. 9A (4), the insulating substrate 31 is removed by irradiating the receiving land 32a, which is a conformal mask, with laser light to form a hole H4 with the receiving land 33a exposed at the bottom. The diameter of the hole H4 is, for example, φ150 to 200 μm. The formation of the hole H4 is similar to the formation of the hole H1 in the first embodiment.

After penetrating the insulating substrate 31 with an infrared laser, a desmear process is performed. In the desmear process, the resin residue (residual film) at the boundary between the receiving land 33a and the insulating substrate 31 is removed. In addition, the back surface treatment film (Ni, Cr, etc.) of the receiving land 33a is removed.

Next, as shown in FIG. 9A (5), a second metal plating 62 is deposited on the sidewalls and bottom surface of the hole H4. The second metal plating 62 is, for example, copper plating. The second metal plating 62 is deposited by partial plating or panel plating. The plating thickness of the second metal plating 62 is, for example, 16 μm.

Next, as shown in FIG. 9B (1), an adhesive layer 34 is formed on the metal foil 32 so as to embed the fourth conductive pattern (receiving land 32a, wiring 32b) formed by patterning the metal foil 32 and the second metal plating 62 deposited in the hole H4. The thickness of the adhesive layer 34 is, for example, 10 μm. Next, as shown in FIG. 8B (2), a cover material layer 72 is formed on the adhesive layer 34. The cover material layer 72 is, for example, an insulating resin film. For example, a liquid crystal polymer (LCP) or polyimide is used as the insulating resin film. The thickness of the cover material layer 72 is, for example, 12 μm. Next, as shown in FIG. 8B (3), a protective film layer 35 is formed on the cover material layer 72. The thickness of the protective film layer 35 is, for example, 10 μm.

Next, as shown in FIG. 9C (1), the protective film layer 35 is irradiated with laser light to remove the protective film layer 35, the cover material layer 72, and the adhesive layer 34, and a bottomed hole H5 with the receiving land 32a exposed at the bottom is drilled. The diameter of the hole H5 is, for example, φ150 to 200 μm. Hereinafter, the formation of the hole H5 is the same as the formation of the hole H1 in the first embodiment. That is, an infrared laser, which is a carbon dioxide laser, is used to irradiate a laser pulse to a predetermined position of the protective film layer 35 to drill a hole. The beam diameter of the infrared laser is set to 150 μm, the same as the diameter of the hole H5. The pulse width of the infrared laser is set to 10 μs, and the energy per pulse of the infrared laser is set to 5 mJ.

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

9C(3), the protective film layer 35 is peeled off from the cover material layer 72. As a result, a part of the conductive paste 53 filled in the hole H5 protrudes, forming a protruding portion 53a. The height of the protruding portion 53a is approximately the same as the thickness of the protective film layer 35.
Through the above steps, wiring substrate 103A is obtained.

In the above-mentioned steps, the metal foil of each wiring substrate may be subjected to a roughening treatment, which can improve the adhesive strength between the metal foil and the insulating substrate.
Hereinafter, with reference to FIG. 10, a process of laminating wiring substrate 101, wiring substrate 102, and wiring substrate 103A obtained in the above-mentioned process will be described.

First, the wiring substrate 101 is laminated on the wiring substrate 102. Specifically, the conductive paste 51 is laminated so that the protruding portion 51a of the conductive paste 51 contacts the receiving land 22a.

Next, the laminate consisting of wiring substrate 101 and wiring substrate 102 obtained in the above process is laminated on wiring substrate 103A. Specifically, the laminate is laminated so that protruding portion 52a of conductive paste 52 contacts protruding portion 53a of conductive paste 53. In this way, wiring substrate 101, wiring substrate 102, and wiring substrate 103A are electrically connected to each other. Note that the stacking order of wiring substrates 101, 102, and 103A is not limited to the above.

In the lamination process for forming a laminate consisting of wiring substrate 101, wiring substrate 102, and wiring substrate 103A, a vacuum press or vacuum laminator is used as in the first embodiment. The laminate is heated and pressurized by this vacuum press or vacuum laminator. For example, the laminate is heated to about 200°C and pressed at a pressure of several MPa (for example, 2.0 MPa). The temperature at which the laminate is heated is, for example, about 50°C or more lower than the softening temperature of the liquid crystal polymer (LCP) of insulating substrates 11, 21, and 31.

When using a vacuum press in the lamination process, the laminate is heated and pressurized for approximately 30 to 60 minutes under the above-mentioned conditions. Therefore, when the laminate is heated and pressurized by the vacuum press, the thermal curing of the adhesive layers 13, 24, 25, and 34 is completed, and the thermal curing of the conductive pastes 51 and 52 is also completed.

On the other hand, when a vacuum laminator is used in the lamination process, the laminate is heated and pressurized for about several minutes under the above-mentioned conditions. Therefore, after the flexible circuit board 100A is heated and pressurized by the vacuum laminator, the laminate is moved to an oven device and a post-cure process is performed. In the post-cure process, for example, heating is performed at about 200°C for about 60 minutes. This post-cure process completes the thermal curing of the adhesive layers 13, 24, 25, and 34, and also the thermal curing of the conductive pastes 51 and 52.

Next, as necessary, surface treatment and solder resist are applied to the first and fifth conductive patterns exposed to the outside, and then the exterior shape is processed.
Through the above steps, a flexible circuit board 100A having the cross-sectional structure shown in FIG. 8 is obtained.

As described above, according to the manufacturing method of the flexible circuit board 100A of the second embodiment, the bending region 130 has a hollow structure in which neither a wiring layer nor an insulating layer is provided inside the bending region 130. Therefore, the bending region 130 is subjected to less stress when bent than the signal line region 120, and the flexible circuit board 100A can be easily bent and assembled into the housing of an electronic device such as a smartphone.

Furthermore, as in the first embodiment, in the flexible circuit board 100A, the analog signal line is formed as wiring 22i, and the digital signal line is formed as wiring 33i. As shown in FIG. 8, the flexible circuit board 100A incorporates analog signal lines and digital signal lines. Therefore, by incorporating the flexible circuit board 100A into the housing of a smartphone or the like, it is possible to arrange the analog signal line that transmits the analog signal received by the wireless communication antenna and the digital signal line that transmits the digital signal received by a digital terminal such as a USB together at the same time. As a result, it is possible to save space inside the housing of an electronic device such as a smartphone.

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

Furthermore, flexible circuit board 100A is manufactured by laminating wiring substrate 101, wiring substrate 102, and wiring substrate 103A. That is, flexible circuit board 100A is manufactured by laminating three wiring substrates, so the occurrence of misalignment between the wiring substrates is relatively suppressed. This makes it possible to suppress the yield in the manufacturing process of flexible circuit board 100A. In addition, the margin related to the above-mentioned misalignment can be relatively small, and the wiring structure in the wiring layer of flexible circuit board 100A can be made denser.

Third Embodiment
Next, a flexible circuit board 100B according to a third embodiment will be described with reference to Fig. 11A. Similar to the flexible circuit board 100A according to the second embodiment, the flexible circuit board 100B has a hollow structure in the bending region 130. In addition, the flexible circuit board 100B has a notch on one side of the bending region 130 (the lower side in Fig. 11A). The following mainly describes the differences from the second embodiment.

Figure 11A is a schematic perspective view showing the bending region 130 of the flexible circuit board 100B. This Figure 11A is a schematic perspective view of region C in Figure 2, and shows a part of the connector region 110, a part of the signal line region 120, and the bending region 130.

More specifically, the bending region 130 of the flexible circuit board 100B has a space HS in which neither a wiring layer nor an insulating layer is provided. That is, the bending region 130 has a hollow structure. In other words, a space HS, which is 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.

11A, the lower surface 130b of the bending region 130 is provided with slits ST1 and ST2, which are cuts. Specifically, the slits ST1 and ST2 are provided in a region on one side of the space HS in the thickness direction of the flexible circuit board 100B. 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. The slits ST1 and ST2 are provided along a width direction perpendicular to the longitudinal direction of the signal line region 120. However, this is not limited to this, and the slits ST1 and ST2 may be provided along a direction intersecting the width direction of the bending region 130. Generally speaking, the slits ST1 and ST2 are provided so as to have a width direction component perpendicular to the longitudinal direction of the signal line region 120 of the flexible circuit board 100B.

Other structures of the flexible circuit board 100B are similar to those of the flexible circuit board 100A according to the second embodiment, and therefore will not be described. The manufacturing method of the flexible circuit board 100B is also similar to that of the flexible circuit board 100A according to the second embodiment, and therefore will not be described. The wiring 22i, 33i is formed by coasting so as to avoid the slits ST1, ST2.

As described above, the bending region 130 of the flexible circuit board 100B has a space HS where neither a wiring layer nor an insulating layer is provided, and further has slits ST1 and ST2 on the lower surface 130b of the bending region 130. Therefore, the bending region 130 is more resistant to bending stress than the signal line region 120, and the flexible circuit board 100B can be more easily bent and installed inside the housing of a smartphone or the like.

As in the second embodiment, analog signal lines and digital signal lines are incorporated in the flexible circuit board 100B. This allows analog signal lines and digital signal lines to be arranged together at once by arranging the flexible circuit board 100B, thereby saving space within the housing of a smartphone or the like.

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

Furthermore, flexible circuit board 100B is manufactured by laminating wiring substrate 101 (first wiring substrate), wiring substrate 102 (second wiring substrate), and wiring substrate 103A (third wiring substrate). That is, flexible circuit board 100B is manufactured by laminating three wiring substrates, so that the occurrence of misalignment between the wiring substrates is relatively suppressed. Therefore, the yield in the manufacturing process of flexible circuit board 100B can be suppressed. In addition, the margin related to the above-mentioned misalignment can be relatively small, and the wiring structure in the wiring layer of flexible circuit board 100B can be made dense.

(Fourth embodiment)
Next, a flexible circuit board 100C according to a fourth embodiment will be described with reference to Figures 11B and 11C. Similar to the flexible circuit board 100A according to the second embodiment, the flexible circuit board 100C has a hollow structure in the bending region 130. In addition, one side of the bending region 130 of the flexible circuit board 100C (the lower surface side in Figures 11B and 11C) is provided in a meandering or crank shape. The following description will focus on the differences from the second embodiment.

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

More specifically, the bending region 130 of the flexible circuit board 100C has a space HS in which neither a wiring layer nor an insulating layer is provided, i.e., the bending region 130 has a hollow structure. In other words, there is a space HS between the upper surface 130a in the bending region 130 and the lower surface 130b in the bending region 130.

First, as shown in FIG. 11B, the lower surface 130b of the bending region 130 has a meandering shape. Specifically, the lower surface 130b of the bending region 130 is provided in a meandering shape when the flexible circuit board 100C is viewed in a plan view. In other words, this meandering lower surface 130b is provided in an area on one side of the space HS in the thickness direction of the flexible circuit board 100C. Note that the upper surface 130a and the lower surface 130b, which are both sides of the bending region 130, may also be provided in a meandering shape.

On the other hand, as shown in FIG. 11C, the lower surface 130b of the bending region 130 may have a crank shape. Specifically, the lower surface 130b of the bending region 130 is provided in a crank shape when the flexible circuit board 100C is viewed in a plan view. In other words, this crank-shaped lower surface 130b is provided in an area on one side of the space HS in the thickness direction of the flexible circuit board 100C. Note that the upper surface 130a and the lower surface 130b, which are both sides of the bending region 130, may be provided in a crank shape.

Other structures of the flexible circuit board 100C are similar to those of the flexible circuit board 100A according to the second embodiment, and therefore a description thereof will be omitted. In addition, the manufacturing method of the flexible circuit board 100C is also similar to that of the flexible circuit board 100A according to the second embodiment, and therefore a description thereof will be omitted. The wiring 22i, 33i is formed along a meander shape or a crank shape.

As described above, the bending region 130 of the flexible circuit board 100C has a space HS where neither a wiring layer nor an insulating layer is provided, and further, the lower surface 130b of the bending region 130 is provided in a meandering or crank shape. Therefore, the bending region 130 is more resistant to bending stress than the signal line region 120, and the flexible circuit board 100C can be more easily bent and installed inside the housing of a smartphone or the like.

As in the second embodiment, analog signal lines and digital signal lines are incorporated in the flexible circuit board 100C. This allows analog signal lines and digital signal lines to be arranged together at once by arranging the flexible circuit board 100C, thereby saving space within the housing of a smartphone or the like.

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

Furthermore, the flexible circuit board 100C is manufactured by laminating the wiring substrate 101 (first wiring substrate), the wiring substrate 102 (second wiring substrate), and the wiring substrate 103A (third wiring substrate). That is, since the flexible circuit board 100C is manufactured by laminating three wiring substrates, the occurrence of misalignment between the wiring substrates is relatively suppressed. Therefore, the yield in the manufacturing process of the flexible circuit board 100C can be suppressed. In addition, the margin related to the above-mentioned misalignment can be relatively small, and the wiring structure in the wiring layer of the flexible circuit board 100C can be made dense.

(Modification)
Next, the structure of a flexible circuit board 100D according to a modified example will be described with reference to Fig. 12. The flexible circuit board 100 according to the first embodiment has a reduced-layer structure in the bending region 130, but the flexible circuit board 100D according to the modified example also has a reduced-layer structure in the connector region 110A. The following description will focus on the differences from the first embodiment.

Figure 12 is a schematic plan view of a modified flexible circuit board 100D. As shown in Figure 12, the modified flexible circuit board 100D includes connector regions 110 and 110A, a signal line region 120, and a bend region 130. Note that Figure 12 shows a state in which a connector part 111 is mounted in the connector region 110A.

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

In the modified example, the connector region 110A also has a reduced-layer structure. That is, the connector region 110A has a reduced-layer structure with fewer wiring layers and/or insulating layers than the signal line region 120. The cross-sectional structure of the connector region 110A may be the same as that of the bending region 130. That is, the cross-sectional structure of the connector region 110A may be the same as that of the bending region 130 shown in FIG. 3. In the flexible circuit board 100D shown in FIG. 12, one of the connector regions is shown as the connector region 110A having a reduced-layer structure. In the flexible circuit board 100D according to the modified example, both connector regions may have the connector region 110A having a reduced-layer structure.

The other structures of the flexible circuit board 100D are similar to those of the flexible circuit board 100 according to the first embodiment. The manufacturing method of the flexible circuit board 100D is also similar to that of the flexible circuit board 100 according to the first embodiment. That is, in the manufacturing method of the flexible circuit board 100D, the process for forming the reduced layer structure of the bending region 130 can be applied to the process for forming the reduced layer structure of the connector region 110A.

As described above, according to the modified flexible circuit board 100D, the connector region 110A, in addition to the bending region 130, has a reduced-layer structure with fewer wiring layers and/or insulating layers than the signal line region 120. This allows for a further reduction in the amount of wiring layers and insulating substrate material required for the flexible circuit board 100D, thereby further reducing manufacturing costs.

The connector region 110A and the bending region 130 are subjected to less stress when bent than the signal line region 120. Therefore, similar to the flexible circuit board 100 according to the first embodiment, the flexible circuit board 100D can be easily bent and assembled into the housing of a smartphone or the like.

Furthermore, analog signal lines and digital signal lines are incorporated into the flexible circuit board 100D. As a result, by arranging the flexible circuit board 100D, the analog signal lines and digital signal lines can be arranged together at once, thereby saving space within the housing of a smartphone or the like.

Furthermore, the flexible circuit board 100D is manufactured by laminating the wiring substrate 101 (first wiring substrate), the wiring substrate 102 (second wiring substrate), and the wiring substrate 103 (third wiring substrate). That is, since the flexible circuit board 100D is manufactured by laminating three wiring substrates, the occurrence of misalignment between the wiring substrates is relatively suppressed. Therefore, the yield in the manufacturing process of the flexible circuit board 100D can be suppressed. In addition, the margin related to the above-mentioned misalignment can be relatively small, and the wiring structure in the wiring layer of the flexible circuit board 100D can be made denser.

<Electronic devices incorporating flexible circuit boards>
Fifth Embodiment
Next, an embodiment of an electronic device incorporating the flexible circuit board 100 according to the first to fourth embodiments or the modified examples will be described with reference to Fig. 13A. In the electronic device according to this embodiment, the flexible circuit board 100 is bent and incorporated into a side surface inside the housing of the electronic device.

The right and center diagrams of FIG. 13A are diagrams that show the state of the flexible circuit board 100 before and after bending. As shown in the right and center diagrams of FIG. 13A, when the flexible circuit board 100 is assembled into the housing of an electronic device, the bending region 130 of the flexible circuit board 100 is bent into a desired shape and assembled. The flexible circuit board 100 is assembled on the side of the housing of the electronic device. Therefore, from a state in which the connector region 110a and the bending region 130 stand upright on the signal line region 120 as shown in the right diagram of FIG. 13A, the bending region 130 is bent forward so that the connector region 110b falls forward as shown in the center diagram of FIG. 13A.

The diagram on the left side of FIG. 13A is a diagram that shows a schematic diagram of an electronic device UE incorporating a flexible circuit board 100. In the electronic device UE, the flexible circuit board 100 and other electronic components are incorporated in a housing 500. Specifically, this electronic device UE includes a housing 500, and a flexible circuit board 100 according to the above-mentioned embodiment or modification arranged in the housing 500. Furthermore, a first module 200 and a second module 300 are arranged inside the housing 500, and a battery 400 is arranged between the first module 200 and the second module 300.

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

The first module 200 is provided with a connector part 220. The first module 200 and the connector region 110a are electrically connected via this connector part 220. Meanwhile, the second module 300 is also provided with a connector part 310. The second module 300 and the connector region 110b are electrically connected via this connector part 310. This electrically connects the first module 200 and the second module 300 via 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 this embodiment, the flexible circuit board 100 is incorporated along the side surface inside the housing 500 of the electronic device UE. That is, the bending region 130 is bent so that the connector part 220 and the connector part 310 fit into the first module 200 and the second module 300, respectively, and the flexible circuit board 100 is incorporated into the housing 500 so that the signal line region 120 fits along the side surface inside the housing 500.

As described above, according to this embodiment, the first module 200 and the second module 300 can be electrically connected by the flexible circuit board 100. This allows space to be saved inside the housing of the electronic device UE, and enables the battery 400 to be made larger. In addition, since the flexible circuit board 100 can be placed without straddling the battery 400, a coil used for wireless power supply, etc., can be placed on the top 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 will be described with reference to Fig. 13B. In this embodiment, the flexible circuit board 100 is incorporated into the bottom surface of the housing of the electronic device with the bending region 130 bent. The following description will focus on the differences from the fifth embodiment.

Figure 13B is a diagram showing an electronic device UE incorporating a flexible circuit board 100. Figure 13B (1) is a schematic cross-sectional view of the electronic device UE in plan, and Figure 13B (2) is a schematic cross-sectional view of the side of the electronic device UE. As shown in Figures 13B (1) and (2), the electronic device UE incorporates the flexible circuit board 100 and other electronic components in a housing 500. Specifically, the electronic device UE includes a housing 500 and a flexible circuit board 100 according to the above-mentioned embodiment or modification within the housing 500. Furthermore, a first module 200 and a second module 300 are arranged inside the housing 500, and a battery 400 is arranged between the first module 200 and the second module 300.

Figure 13B (3) shows an oblique image of the flexible circuit board 100 incorporated in the housing 500. As shown in this Figure 13B (3), the flexible circuit board 100 has bending region 130B bent at P1 and P2, and bending region 130A bent at P3 and P4. In other words, bending region 130A and bending region 130B are each bent at two locations. That is, in the flexible circuit boards 100 according to the first to fourth embodiments or modifications, the stress when bending the bending region 130 is reduced, so that it is possible to bend the bending region 130 at two locations as in this embodiment.

As in the fifth embodiment, the first module 200 and the second module 300 can be electrically connected by the flexible circuit board 100. This allows space to be saved inside the housing of the electronic device UE, and allows the battery 400 to be made larger. In addition, since the flexible circuit board 100 can be arranged without spanning the top surface of the battery 400, a coil used for wireless power supply, etc. can be arranged on the top surface of the battery.

Based on the above description, a person skilled in the art may be able to conceive additional effects and various modifications of the present invention, but the aspects of the present invention are not limited to the individual embodiments described above. Components from different embodiments may be combined as appropriate. Various additions, modifications, and partial deletions are possible within the scope that does not deviate from the conceptual idea and intent of the present invention derived from the contents defined in the claims and their equivalents.

10 Single-sided metal foil clad laminate 20, 30 Double-sided metal foil clad laminate 11, 21, 31 Insulating substrate 12, 22, 23, 32, 33 Metal foil 13, 24, 25, 34 Adhesive layer 14, 26, 35 Protective film layer 12a, 22a, 23a, 32a, 33a Receiving land 12b, 23b Ground layer (wiring)
22i Wiring (analog signal line)
32b Wiring 33i Wiring (digital signal line)
51, 52, 53 Conductive paste 61, 62 Metal plating 71, 72 Cover material layer 100 Flexible circuit board 101, 102, 103 Wiring substrate 110, 110A Connector region 120 Signal line region 130, 130A, 130B Bending region 200 First module 300 Second module 400 Battery 500 Housing A1 Openings H1, H2, H3, H4, H5 Hole HS Space ST1, ST2 Slit W Window opening UE Electronic device

Claims (11)

A flexible circuit board for electrically connecting a first module having a wireless communication antenna for receiving an analog signal and a digital terminal for receiving a digital signal to a second module for performing signal processing of the analog signal and the digital signal, the flexible circuit board being provided with a signal line region, a connector region, and a bending region for connecting the signal line region and the connector region;
one or more analog signal lines extending in a longitudinal direction of the signal line region and transmitting analog signals received from the wireless communication antenna;
one or more digital signal lines extending in the longitudinal direction of the signal line region and transmitting digital signals received from the digital terminals;
a ground layer formed so as to cover the analog signal line via an insulating layer;
Equipped with
The bent region has a reduced-layer structure in which the number of wiring layers and/or insulating layers is smaller than that in the signal line region.
Flexible circuit board. The flexible circuit board according to claim 1, characterized in that the connector region also has a reduced-layer structure in which the number of wiring layers and/or insulating layers is smaller than that of the signal line region. A flexible circuit board for electrically connecting a first module having a wireless communication antenna for receiving an analog signal and a digital terminal for receiving a digital signal to a second module for performing signal processing of the analog signal and the digital signal, the flexible circuit board being provided with a signal line region, a connector region, and a bending region for connecting the signal line region and the connector region;
one or more analog signal lines extending in a longitudinal direction of the signal line region and transmitting analog signals received from the wireless communication antenna;
one or more digital signal lines extending in the longitudinal direction of the signal line region and transmitting digital signals received from the digital terminals;
a ground layer formed so as to cover the analog signal line via an insulating layer;
Equipped with
the bending region has a hollow structure in which a hollow region is provided inside in which neither a wiring layer nor an insulating layer is provided;
Flexible circuit board. The flexible circuit board according to claim 3, characterized in that a cut having a width component perpendicular to the longitudinal direction of the signal line region is provided in one or both sides of the hollow region in the thickness direction of the flexible circuit board. The flexible circuit board according to claim 3, characterized in that the area on one or both sides of the hollow area in the thickness direction of the flexible circuit board is formed in a meander shape or crank shape when the flexible circuit board is viewed in a plan view. The flexible circuit board according to any one of claims 1 to 5, characterized in that the connector region is provided with an interlayer connection path connected to the analog signal line or the digital signal line. The flexible circuit board according to claim 6, characterized in that the interlayer connection path has a plated through hole connected to the analog signal line or the digital signal line, and a filled via connected to the plated through hole via a conductive layer. a connector part electrically connected to the analog signal line and the digital signal line via the interlayer connection path is mounted in the connector region,
The flexible circuit board according to claim 6 or 7. A housing and
The flexible circuit board according to claim 1 , which is disposed in the housing; and
the first module disposed within the housing;
the second module disposed within the housing;
a battery disposed within the housing between the first module and the second module;
Equipped with
Electronic devices. The electronic device according to claim 9, characterized in that the flexible circuit board is arranged to pass between the side surface of the housing and the battery. The electronic device according to claim 9, characterized in that the flexible circuit board is arranged to pass between the rear or front surface of the housing and the battery.

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