WO2017212966A1

WO2017212966A1 - Flexible printed board

Info

Publication number: WO2017212966A1
Application number: PCT/JP2017/019859
Authority: WO
Inventors: 巧弥長峯; 北村　洋一
Original assignee: 三菱電機株式会社
Priority date: 2016-06-09
Filing date: 2017-05-29
Publication date: 2017-12-14
Also published as: GB201816765D0; JPWO2017212966A1; GB2565453A; GB2565453B; JP6563129B2

Abstract

According to the present invention, a base film (1) has a main surface (1a) and a back surface (1b), which are on opposite sides of each other, and is formed from an insulating material. A plurality of first conductors (2, 4, 6, 8) are formed on the main surface (1a) of the base film (1). A plurality of second conductors (3, 7, 9) are formed on the back surface (1b) of the base film (1). A plurality of connection conductors (5) penetrate through the base film (1) and electrically connect some of the first conductors (2, 4, 6, 8) and some of the second conductors (3, 7, 9) with each other. The film thicknesses of the plurality of second conductors (3, 7, 9) are thicker than the film thicknesses of the plurality of first conductors (2, 4, 6, 8).

Description

Flexible printed circuit board

The present invention relates to a flexible printed circuit board.

Wireless communication devices that transmit or receive radio waves via an antenna are roughly divided into an antenna, a high-frequency circuit, a control circuit, and a power supply circuit. The antenna converts high-frequency electrical signals into radio waves. The high frequency circuit is responsible for amplification, modulation and demodulation of the high frequency electric signal. The control circuit supplies an electrical signal for controlling the high-frequency circuit. The power supply circuit drives the high frequency circuit.

Generally, these electronic circuits are mounted on a printed circuit board for use. The printed circuit board is composed of an IC (Integrated Circuit), individual electronic components, and metal conductors connecting them. In some cases, the high-frequency circuit, the control circuit, and the power supply circuit are commonly mounted on a single printed circuit board. However, these circuits are often mounted and used on separate printed circuit boards from the viewpoint of circuit noise countermeasures.

In the latter case, connection wiring for electrically connecting printed circuit boards on which these circuits are mounted is necessary. For the connection wiring, generally, a wiring component that bundles a plurality of electric wires called a wire harness and a connector for the wire harness are used.

In recent years, in order to widely disseminate high-quality information communication, there has been a demand for smaller and thinner communication devices. However, the combined use of the wire harness and the wire harness connector has problems such as an increase in size and weight of the communication device itself. Therefore, in order to satisfy the demands for reducing the size and thickness of communication devices, it is conceivable to use a flexible printed circuit board for the connection wiring.

The flexible printed board is a board made of a flexible insulator and metal conductor. A flexible printed circuit board has a property of being thin and not bulky, lightweight and bendable. For this reason, the flexible printed circuit board is widely adopted for flat panel displays or small electronic devices.

Such a flexible printed circuit board is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-133660 (Patent Document 1). This publication describes that a part of an insulating layer in which a plurality of signal lines constituting a signal circuit part is formed is cut out, and a power supply circuit part is attached to the cut out part.

JP 2003-133660 A

However, in the flexible printed circuit board described in the above publication, in the process of laminating separately prepared circuits, misalignment between the circuits to be bonded occurs. If the positions of the circuits are shifted, a connection failure occurs, so that there is a problem that the circuits cannot be made dense.

Further, when trying to integrate separate parts by bonding, there is an increased concern about the protrusion of the adhesive and distortion or deformation of the flexible printed circuit board that occurs during the bonding process.

Also, it is necessary to prepare a separate insulator for each circuit to be applied, form a circuit, and further bond them together. Therefore, there exists a problem that the number of manufacturing processes and manufacturing cost increase.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a flexible printed circuit board having a plurality of electric circuits with different specifications and having high density, high accuracy, and low cost. is there.

The flexible printed board of the present invention includes a base film, a plurality of first conductors, a plurality of second conductors, and a plurality of connection conductors. The base film has a first surface and a second surface facing each other, and is made of an insulator. The plurality of first conductors are formed on the first surface of the base film. The plurality of second conductors are formed on the second surface of the base film. The plurality of connection conductors penetrate the base film and electrically connect a part of the plurality of first conductors and a part of the plurality of second conductors. Each of the plurality of second conductors is thicker than each of the plurality of first conductors.

As described above, according to the present invention, each of the plurality of second conductors is thicker than each of the plurality of first conductors. Therefore, an electric circuit that requires a thin film thickness can be formed with the first conductor, and an electric circuit that requires a thick film thickness can be formed with the second conductor. Accordingly, when a single flexible printed circuit board in which a plurality of electrical circuits that require different specifications are mixed is produced, a process that separately manufactures and bonds circuits that require different specifications is not necessary. Therefore, it is possible to realize a flexible printed board with high density, high accuracy, and low manufacturing cost.

FIG. 3 is a cross-sectional view showing the configuration of the flexible printed circuit board according to Embodiment 1 of the present invention, and is a cross-sectional view taken along the line II in FIGS. It is a top view which shows the structure of the flexible printed circuit board in Embodiment 1 of this invention. It is a rear view which shows the structure of the flexible printed circuit board in Embodiment 1 of this invention. FIG. 7 is a cross-sectional view showing a configuration of a flexible printed circuit board in Embodiment 2 of the present invention, and is a cross-sectional view taken along line IV-IV in FIGS. 5 and 6. It is a top view which shows the structure of the flexible printed circuit board in Embodiment 2 of this invention. It is a rear view which shows the structure of the flexible printed circuit board in Embodiment 2 of this invention. FIG. 11 is a cross-sectional view showing a configuration of a flexible printed circuit board according to Embodiment 3 of the present invention, and is a cross-sectional view taken along line VII-VII in FIGS. 9 and 10. FIG. 11 is a cross-sectional view showing a configuration of a flexible printed circuit board according to Embodiment 3 of the present invention, and is a cross-sectional view taken along the line VIII-VIII in FIGS. 9 and 10. It is a top view which shows the structure of the flexible printed circuit board in Embodiment 3 of this invention. It is a rear view which shows the structure of the flexible printed circuit board in Embodiment 3 of this invention. It is a top view which shows the structure of the other party printed circuit board to which the flexible printed circuit board in Embodiment 3 of this invention is connected. It is sectional drawing which shows the form which connected the flexible printed circuit board and printed circuit board in Embodiment 1 of this invention using the anisotropically conductive adhesive film. It is sectional drawing which shows the structure which added the protective layer to the flexible printed circuit board in Embodiment 1 of this invention. It is sectional drawing which shows the structure which added the protective layer to the flexible printed circuit board in Embodiment 1 of this invention, and is sectional drawing which shows the structure of the longitudinal direction of a power supply wiring and an auxiliary power supply circuit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
The configuration of flexible printed circuit board 100 according to Embodiment 1 of the present invention will be described with reference to FIGS.

As shown in FIG. 1, the flexible printed circuit board 100 of the present embodiment includes a base film 1, a plurality of

first conductors

2, 4, 6, 8, a plurality of

second conductors

3, 7, 9, It mainly has a connection conductor 5.

The base film 1 has a main surface (first surface) 1a and a back surface (second surface) 1b facing each other, and is made of an insulator. The base film 1 has a plurality of electric circuit forming regions having different specifications. The plurality of electric circuit formation regions include, for example, a high frequency circuit unit 20, a power supply circuit unit 30, and a control circuit unit 40.

Each of the plurality of

first conductors

2, 4, 6, 8 is formed on the main surface 1 a of the base film 1. The plurality of

first conductors

2, 4, 6, 8 include, for example, a center conductor 2, a ground conductor 4, a power supply circuit 6, and a control signal circuit 8.

Each of the plurality of

second conductors

3, 7, 9 is formed on the back surface 1 b of the base film 1. The plurality of

second conductors

3, 7, 9 have, for example, a back ground conductor 3, an auxiliary power supply circuit 7, and a dummy circuit 9.

Each of the plurality of connection conductors 5 penetrates the base film 1, and electrically connects a part of the plurality of

first conductors

2, 4, 6, 8 and a part of the plurality of

second conductors

3, 7, 9. Connected to. A through hole 5a is formed in the base film 1, and a connection conductor 5 is embedded in the through hole 5a.

The through hole 5a may penetrate not only the base film 1 but also each of the first conductor and the second conductor. In this case, the connection conductor 5 embedded in the through hole 5a also passes through the first conductor and the second conductor.

The plurality of connection conductors 5 include a high-frequency circuit connection conductor 5 formed in the high-frequency circuit unit 20 and a power supply circuit connection conductor 5 formed in the power supply circuit unit 30.

The film thickness T1 of each of the plurality of

second conductors

3, 7, 9 is set to be thicker than the film thickness T2 of each of the plurality of

first conductors

2, 4, 6, 8.

Hereinafter, the configuration of the flexible printed circuit board 100 of the present embodiment will be described more specifically.

As the base film 1, for example, a polymer film having excellent flexibility and heat resistance, such as a polyimide film having a thickness of 12.5 μm to 50 μm, and a low dielectric loss can be used.

Each of the plurality of thin

first conductors

2, 4, 6, 8 is composed of, for example, a copper thin film (copper foil), a nickel thin film, and a gold thin film. The copper foil is formed on the main surface 1a of the base film 1, and has a film thickness of, for example, 6 μm or more and 18 μm or less. The nickel thin film is formed on the surface of the copper foil, and has a film thickness of, for example, 3 μm or more and 5 μm or less. The gold thin film is formed on the surface of the nickel thin film, and has a thickness of about 0.01 μm, for example. The nickel thin film and the gold thin film on the surface of the copper foil are formed for the purpose of preventing oxidation of the thin conductor layer and improving solder wettability.

Each of the thick plurality of

second conductors

3, 7, 9 is composed of, for example, a copper foil, a nickel thin film, and a gold thin film. The copper foil is formed on the back surface 1b of the base film 1, and has a film thickness of, for example, 18 μm or more and 70 μm or less. The nickel thin film is formed on the surface of the copper foil, and has a film thickness of, for example, 3 μm or more and 5 μm or less. The gold thin film is formed on the surface of the nickel thin film, and has a thickness of about 0.01 μm, for example. Similar to the

first conductors

2, 4, 6, and 8, the nickel thin film and the gold thin film on the surface of the copper foil are formed for the purpose of preventing oxidation of the thin conductor layer and improving solder wettability.

The copper foil of each of the

first conductors

2, 4, 6, 8 and the

second conductors

3, 7, 9 and the polyimide film substrate of the base film 1 are made of an epoxy resin adhesive or an acrylic resin adhesive not shown. It is glued.

The copper foil and the polyimide base material may be connected to each other without using an adhesive, focusing on electric characteristics such as high-frequency characteristics. Specifically, the copper foil and the polyimide film substrate are formed by a method in which the copper foil is baked after being coated with the polyimide varnish, or a method in which a metal conductor layer is formed on the polyimide film substrate using sputtering and plating. May be connected.

It should be noted that the general flexible printed circuit board 100 is often provided with a protective film such as a component other than the above, for example, a solder resist or a coverlay. However, since these protective films are members not related to the present invention, description thereof is omitted.

Next, each component of the flexible printed circuit board 100 according to the present embodiment will be described from the electric circuit side with reference to FIGS.

As shown in FIGS. 1 to 3, the base film 1 has, for example, a high-frequency circuit unit 20, a power circuit unit 30, and a control circuit unit 40 as regions for forming a plurality of electric circuits having different specifications. is doing. Each of these

electric circuit portions

20, 30, 40 includes a

first conductor

2, 4, 6, 8 formed on the main surface 1a of the base film 1, and a

second conductor

3, 7, formed on the back surface 1b. 9 is configured to function as a single unit so that the circuit function is exhibited.

First, the high-frequency circuit unit 20 will be described.
As shown in FIG. 1, in the high-frequency circuit unit 20, transmission lines made of two kinds of conductors are formed on the main surface 1 a of the base film 1. That is, on the main surface 1 a of the flexible printed circuit board 100, the center conductor 2 and a pair of ground conductors 4 located on both sides of the center conductor 2 are formed. Each of the center conductor 2 and the pair of ground conductors 4 is a linear transmission line as shown in FIG. The central conductor 2 and each of the pair of ground conductors 4 are arranged so that the longitudinal direction of the central conductor 2 and the longitudinal direction of each of the pair of ground conductors 4 are parallel to each other.

In the high-frequency circuit unit 20, the back ground conductor 3 is formed on the back surface 1 b of the base film 1. Each of the pair of ground conductors 4 is electrically connected to one back ground conductor 3 by a high-frequency circuit connection conductor 5 that fills the through hole 5a.

In the high-frequency circuit unit 20 described above, the minimum transmission line configuration is a combination of the center conductor 2 and the ground conductor 4, and a coplanar structure is obtained by this combination. Another minimum transmission line configuration is a combination of the center conductor 2 and the back ground conductor 3, and a microstrip structure can be obtained by this combination.

However, by using a combination of the center conductor 2, the ground conductor 4, and the back ground conductor 3, a structure using both a coplanar structure and a microstrip structure can be obtained. With this combined structure, an effect of further reducing high-frequency transmission loss can be obtained.

The conductor dimensions, shape, and arrangement of the center conductor 2 are designed so that high-frequency signals can be transmitted most efficiently. Specifically, the conductor dimensions, shape, and arrangement of the center conductor 2 are such that the conductivity of the center conductor 2 that transmits signals and the base film 1 that separates the center conductor 2 (and the ground conductor 4) and the back ground conductor 3 from each other. What is necessary is just to obtain | require by performing electromagnetic field simulation based on the thickness and the dielectric constant of the base film 1.

Also, the conductor thickness of the center conductor 2 may be reduced to such an extent that there is no problem in manufacturing and use. That is, the conductor thickness of the center conductor 2 may be made as thin as possible as long as it is not affected by the skin effect known as a phenomenon that causes an increase in circuit resistance in the center conductor 2. As a result, the side etching phenomenon that the cross-sectional shape of the central conductor 2 becomes trapezoid in the etching during patterning of the central conductor 2 is minimized. Thereby, it is possible to manufacture a substrate in which the shape of the conductor obtained by the electromagnetic field simulation is reproduced with high accuracy. Specifically, the conductor thickness is desirably in the range of 6 μm to 18 μm.

On the other hand, it is not necessary to reduce the thickness of the conductor for the back ground conductor 3. This is because the characteristic required for the back ground conductor 3 is only the function as the ground conductor. That is, the back ground conductor 3 only needs to function as a ground conductor only at the portion in contact with the back surface 1b side of the base film 1, and the conductor acts as a ground conductor even if the conductor thickness is thin or thick. To do. Specifically, there is no problem if the conductor thickness of the back ground conductor 3 is thicker than the center conductor 2 and about 70 μm or less.

As shown in FIGS. 2 and 3, in the high-frequency circuit unit 20, the high-frequency circuit connection conductor 5 extends along the length direction of the flexible printed circuit board 100 (the extending direction of the ground conductor 4), and the center line of the ground conductor 4. It is arranged in the vicinity of a point sequence. The high-frequency circuit connection conductor 5 electromagnetically functions as a ground conductor (shield wall). The shortest distance S1 between two adjacent high-frequency circuit connection conductors 5 preferably satisfies the relationship S1 = λ / 4, where λ is the wavelength of the electromagnetic wave transmitted through the high-frequency circuit unit 20. It is more preferable that the shortest distance S1 satisfies the relationship of S1 ≦ λ / 8 if possible. The diameter of the high-frequency circuit connection conductor 5 is preferably 50 μm or more and 300 μm or less.

As described above, by designing a transmission circuit that is optimized according to the frequency used when designing the high-frequency circuit section 20, high-quality high-frequency signals can be transmitted even on the flexible printed circuit board 100.

Next, the power supply circuit unit 30 will be described.
As shown in FIGS. 1 to 3, in the power supply circuit unit 30, the power supply circuit 6 is provided on the main surface 1 a of the base film 1. In the power circuit 30, an auxiliary power circuit 7 is provided on the back surface 1 b of the base film 1. The auxiliary power circuit 7 is disposed at a position facing the power circuit 6 with the base film 1 interposed. The auxiliary power supply circuit 7 refers to a bypass circuit provided in association with the power supply circuit 6 in order to send a large current. That is, the thickness of the metal conductor of the auxiliary power circuit 7 is designed to be at least thicker than the power circuit 6, and a large current can be transmitted with the total current capacity of the power circuit 6 and the auxiliary power circuit 7. .

Each of the plurality of power supply circuits 6 is arranged so that the longitudinal directions of the plurality of power supply circuits 6 run parallel to each other. The center conductor 2 and each of the plurality of power supply circuits 6 are arranged so that the longitudinal direction of the center conductor 2 and each of the plurality of power supply circuits 6 run in parallel with each other. Each of the plurality of auxiliary power supply circuits 7 is arranged so that the longitudinal directions of the plurality of auxiliary power supply circuits 7 run in parallel with each other.

The power supply circuit 6 and the auxiliary power supply circuit 7 are electrically connected to each other by a power supply circuit connection conductor 5. A plurality of power supply circuit connection conductors 5 can be provided to secure a current capacity to be described later. The power supply circuit unit 30 is required to have a structure capable of supplying a large current in preparation for a case where power consumption of a circuit connected as a load is large.

To increase the current capacity of the circuit, it is necessary to increase the cross-sectional area of the conductor. However, the conductor thickness of the power supply circuit 6 is designed to be the same as the thickness of the first conductor formed on the main surface 1a, that is, the thickness of the conductor at which the center conductor 2 can transmit high frequency most efficiently. For this reason, the conductor thickness of the power supply circuit 6 cannot be increased in order to increase the current capacity. Further, the method of widening the power supply circuit 6 cannot be adopted from the viewpoint of miniaturization and space saving required for the flexible printed circuit board 100.

Therefore, in the first embodiment, the auxiliary power circuit 7 is provided on the back surface 1b so as to face the power circuit 6 formed on the main surface 1a, and the power circuit 6 and the auxiliary power circuit 7 are connected to the power circuit connecting conductor. 5 is electrically connected. Thus, since the auxiliary power circuit 7 is arranged at a position facing the power circuit 6 with the base film 1 interposed therebetween, the conductor width of the auxiliary power circuit 7 is equal to the conductor width of the power circuit 6. For this reason, even if the auxiliary power supply circuit 7 is provided, the width of the power supply circuit section 30 does not increase.

Further, since the auxiliary power circuit 7 is formed on the back surface 1b of the base film 1, there is no restriction on the manufacturing process that the same thickness as that of the central conductor 2 formed on the main surface 1a is required. Therefore, the auxiliary power supply circuit 7 can be formed with the same thick conductor thickness as that of the back ground conductor 3 without being restricted by the manufacturing process.

With this structure, the cross-sectional area of the conductor necessary for energizing a large current can be secured by the combined cross-sectional area of the power supply circuit 6 and the auxiliary power supply circuit 7. Thereby, since the subject that the cross-sectional area of the conductor mentioned above is insufficient can be solved, the degree of freedom in design can be greatly improved.

The number of power supply circuit connection conductors 5 in the power supply circuit unit 30 may be set based on the cross-sectional area of the auxiliary power supply circuit 7. That is, the cross-sectional area when the power supply circuit connection conductor 5 is cut and the integrated value of the number of the power supply circuit connection conductors 5 may be designed to be equal to or larger than the cross-sectional area of the auxiliary power supply circuit 7.

With the structure as described above, a large current can be transmitted in the power supply circuit unit 30 of the flexible printed circuit board 100 in the present embodiment.

Next, the control circuit unit 40 will be described.
As shown in FIGS. 1 to 3, the control signal circuit 8 is provided on the main surface 1 a of the base film 1 in the control circuit unit 40. In the control circuit unit 40, a dummy circuit 9 is provided on the back surface 1 b of the base film 1.

Each of the plurality of control signal circuits 8 is arranged so that the longitudinal directions of the plurality of control signal circuits 8 run parallel to each other. Further, each of the plurality of control signal circuits 8 and each of the plurality of power supply circuits 6 are arranged so that the longitudinal direction of each of the plurality of control signal circuits 8 and each longitudinal direction of the plurality of power supply circuits 6 run in parallel with each other. It is out.

The control signal circuit 8 is a digital circuit. For this reason, the control signal circuit 8 is different from the high-frequency circuit unit 20 of an analog circuit that is easily affected by noise or the power supply circuit unit 30 that has to examine the problem of heat generation, even if no special consideration is required in terms of electrical circuit. Can be operated. Therefore, the control signal circuits 8 can be arranged as densely as possible in terms of manufacturing.

Such high-density wiring is expressed in line and space. In the line and space, the conductor width of the wiring is called a line, and the interval between adjacent wirings (or the distance between the wiring and the conductor pad) is called a space.

In this embodiment, the conductor thickness of the control signal circuit 8 is formed to be equal to the conductor thickness of the center conductor 2. Therefore, the conductor thickness of the control signal circuit 8 is designed in the range of 6 μm or more and 18 μm or less, which is a design guideline for the center conductor 2 thinned to the limit in manufacturing and use. Thereby, also in the control signal circuit 8, the side etching phenomenon is minimized.

Therefore, it is possible to form a sufficiently high density circuit wiring in line and space. Specifically, the line and space of the control signal circuit 8 in the first embodiment is 50 μm (line) / 50 μm (space) to 150 μm (line) / 150 μm (space).

The dummy circuit 9 is a circuit having a conductor thickness equal to that of the circuit on the back surface 1 b other than the control circuit unit 40, that is, the back surface ground conductor 3 and the auxiliary power supply circuit 7. The dummy circuit 9 allows the thickness in the control circuit unit 40 (the total of the thickness of the base film 1, the thickness of the control signal circuit 8 and the thickness of the dummy circuit 9) to be the thickness of the high-frequency circuit unit 20 (the thickness of the base film 1). And the thickness of the central conductor 2 and the thickness of the back ground conductor 3) and the thickness in the power supply circuit section 30 (the sum of the thickness of the base film 1, the power supply circuit 6, and the auxiliary power supply circuit 7). can do. The dummy circuit 9 may be omitted if it is determined that it is not necessary to provide the dummy circuit 9 by considering the rigidity, thickness, and handling of the flexible printed circuit board 100 as a whole. Although the dummy circuit 9 in the flexible printed circuit board 100 is floating, when the control signal circuit 8 is easily affected by noise, it can be electrically connected to the ground conductor as necessary.

Next, a connection form when using the flexible printed circuit board 100 in the present embodiment will be described.

For example, a form of electrically connecting printed boards using a flexible printed board (printed board-flexible printed board-printed board) includes the following connected forms.

First, the connection with the connector will be described. Unlike a connector for a wire harness, a flexible printed circuit board connector has a metal terminal provided inside a flat resin connector. After the flexible printed board is inserted into the connector, the resin cover is closed. As a result, the terminals of the flexible printed circuit board are mechanically pressed against the terminals inside the connector, whereby the two are electrically connected.

In the case of such a connection method, if the thickness is different in the plane of the flexible printed circuit board, the load applied to the flexible printed circuit board when the connector cover is closed becomes uneven. Thereby, there exists a possibility of producing a conduction defect between the terminal of a flexible printed circuit board, and the terminal inside a connector.

On the other hand, in the flexible printed circuit board 100 according to the present embodiment, as described above, the thickness of the control circuit unit 40 can be made equal to the thickness of the high-frequency circuit unit 20 and the thickness of the power supply circuit unit 30. For this reason, in the connection by the said connector, it is suppressed that a load becomes nonuniform between the terminal of the flexible printed circuit board 100, and the terminal inside a connector. As a result, poor conduction is unlikely to occur between the terminals of the flexible printed circuit board 100 and the terminals inside the connector, and a highly reliable connector connection is possible.

Next, connection by an anisotropic conductive adhesive film (hereinafter also referred to as ACF) will be described.
As shown in FIG. 12, flexible printed circuit board 100 and printed circuit board 200 in the present embodiment are connected using, for example, ACF. The ACF includes conductive particles 12 having a diameter of several μm to several tens of μm in a resin 11 serving as a binder. For the conductive particles 12, nickel particles or resin particles plated with metal are often used.

In the connection by ACF, the conductive particles 12 of ACF are sandwiched between the

pad electrodes

202, 204, 206, 208 on the printed circuit board 200 and the

terminals

2, 4, 6, 8 of the flexible printed circuit board 100. A proper load is applied. As a result, electrical conduction is obtained between the

pad electrodes

202, 204, 206, 208 of the printed circuit board 200 and the

terminals

2, 4, 6, 8 of the flexible printed circuit board 100.

In the case of such a connection method, if the thickness is different in the plane of the flexible printed board 100, a load for capturing the conductive particles 12 is applied unevenly in the plane of the flexible printed board 100. As a result, there is a concern that poor conduction may occur due to the

terminals

2, 4, 6, and 8 in which the conductive particles 12 of the ACF are not sufficiently captured.

On the other hand, in the flexible printed circuit board 100 according to the present embodiment, as described above, the thickness of the control circuit unit 40 can be made equal to the thickness of the high-frequency circuit unit 20 and the thickness of the power supply circuit unit 30. For this reason, a load necessary for capturing the conductive particles 12 of ACF is evenly applied in the plane of the flexible printed circuit board 100. Thereby, since it becomes possible to pinch | interpose the electrically-conductive particle 12 by all the

terminals

2, 4, 6, and 8 of the flexible printed circuit board 100, highly reliable conduction | electrical_connection can be obtained.

Next, connection using solder will be described. If there is a step on the surface of the conductor in the surface of the flexible printed circuit board, there is a possibility that a conductor that contacts the molten solder and a conductor that does not contact may come out during soldering. .

On the other hand, in the flexible printed circuit board 100 according to the present embodiment, as described above, the thickness of the control circuit unit 40 can be made equal to the thickness of the high-frequency circuit unit 20 and the thickness of the power supply circuit unit 30. For this reason, highly reliable conduction can be obtained without problems even in solder.

Next, the operational effects of the present embodiment will be described in comparison with the problems of each circuit section.

First, problems specific to high-frequency circuits will be described. When transmitting a high-frequency signal, if the characteristic impedance of the circuit that transmits the high frequency is different from the impedance of the load or circuit that is the transmission destination, the high-frequency signal is not transmitted well, and the transmission efficiency decreases. Such a decrease in efficiency is called reflection loss and is often negligible for low-frequency signals, but it becomes apparent when the frequency is increased. In order to efficiently transmit a high-frequency signal with reduced reflection loss, it is necessary to match the characteristic impedance of the high-frequency circuit with the impedance of the load or circuit that is transmitted.

The characteristic impedance of the flexible printed circuit board is determined by the thickness of the substrate material, the dielectric constant of the substrate material, the thickness of the metal conductor, and the width of the metal conductor. For this reason, it is possible to match the characteristic impedance by properly designing them and manufacturing the substrate with high accuracy.

However, in the case of the etching method (subtractive method) used for circuit formation of a conductor in a general printed circuit board or a flexible printed circuit board, a side etching phenomenon caused by a chemical solution traveling in the in-plane direction of the substrate in the etching process Thus, the cross-sectional shape of the conductor becomes a trapezoid. For this reason, a difference occurs between the design and the actual performance, resulting in a difference in characteristic impedance, which affects the circuit characteristics. In order to reduce the difference from the design value due to such a side etching phenomenon as much as possible, it is effective to reduce the thickness of the conductor and reduce the difference between the trapezoidal upper and lower bases of the conductor cross section.

From the above, in order to form an efficient high-frequency circuit, it is required to reduce the conductor thickness of the signal line.

Next, problems specific to the power supply circuit will be described. In a power supply circuit, it is required to secure a sufficient current capacity in order to cope with various circuit loads. In order to satisfy this requirement, it is necessary to increase the cross-sectional area of the metal conductor. In order to increase the cross-sectional area of the metal conductor, for example, it is necessary to increase the thickness of the metal conductor or increase the width of the metal conductor.

Next, problems specific to the control circuit will be described. In the control circuit, digital signal transmission is fundamental in recent years, and the current capacity required by the handled pulse signal is very small. For this reason, special consideration is not necessary for the cross-sectional area of the metal conductor.

However, in order to reduce the size of a multifunctional device, it is necessary to arrange many control signals in a narrow space, so it is necessary to arrange metal conductors at high density. In order to arrange the metal conductors at a high density, it is effective to minimize the above-mentioned side etching phenomenon and to narrow the line and space described later to the maximum.

Next, the problem when the above high frequency circuit, power supply circuit and control circuit are mixedly mounted will be described. As described above, in order to efficiently transmit a high-frequency signal, it is required to reduce the thickness of the metal conductor. However, if the thickness of the metal conductor is reduced, the cross-sectional area is reduced, and a large current cannot flow through the same metal conductor. There is also a method of ensuring current capacity by increasing the cross-sectional area by widening the width of the metal conductor. However, this method not only eliminates a space for providing a control circuit that requires a large number of wirings, but also cannot apply this method to a narrow space inside a small device.

As described above, the characteristics of the metal conductor required for each circuit of the high-frequency circuit that efficiently transmits high-frequency, the power supply circuit that sends a large current, and the control circuit that requires high-density wiring are contradictory. For this reason, it was difficult to integrate each circuit compactly.

On the other hand, in the present embodiment, as shown in FIG. 1, the thickness of each of the plurality of

second conductors

3, 7, 9 is the same as that of each of the plurality of

first conductors

2, 4, 6, 8. Thicker than film thickness. Therefore, an electric circuit that requires a thin film thickness can be formed with the first conductor, and an electric circuit that requires a thick film thickness can be formed with the second conductor.

Specifically, in the high-frequency circuit section 20, the thickness of the central conductor 2 can be reduced to a level that does not cause a problem in manufacturing and use. Thereby, the side etching phenomenon that the cross-sectional shape of the center conductor 2 becomes trapezoid in the etching at the time of patterning of the center conductor 2 is minimized. Thereby, the board | substrate which reproduced the shape of the conductor calculated | required by said electromagnetic field simulation with high precision can be manufactured.

In addition, since the auxiliary power circuit 7 is formed on the back surface 1b in the power circuit section 30, there is no manufacturing process restriction that the thickness must be the same as that of the center conductor 2 formed on the main surface 1a. Therefore, the auxiliary power supply circuit 7 can be formed with the same thick conductor thickness as that of the back ground conductor 3 without being restricted by the manufacturing process. As a result, the cross-sectional area of the conductor necessary for energizing a large current can be obtained by the cross-sectional area of the auxiliary power supply circuit 7. Thereby, since the subject that the cross-sectional area of the conductor mentioned above is insufficient can be solved, the degree of freedom in design can be greatly improved.

Also, in the control circuit section 40, the conductor thickness of the control signal circuit 8 can be reduced to the extent that there is no problem in manufacturing and use, like the central conductor 2. As a result, the side etching phenomenon that the cross-sectional shape of the control signal circuit 8 becomes trapezoid in the etching during patterning of the control signal circuit 8 is minimized. As a result, the control signal circuits 8 can be arranged with high density.

As described above, a plurality of

electrical circuit units

20, 30, 40 that require different specifications can be formed on one flexible printed circuit board 100 while satisfying different specifications of the plurality of

electrical circuit units

20, 30, 40. it can. This eliminates the need for separately manufacturing and bonding a plurality of electrical circuits that require different specifications. Therefore, it is possible to realize a flexible printed board with high density, high accuracy, and low manufacturing cost.

Further, as shown in FIGS. 13 and 14, a protective layer 13a may be provided on the main surface 1a of the flexible printed circuit board 100, and a protective layer 13b may be provided on the back surface 1b. For each of the

protective layers

13a and 13b, a flexible film such as polyimide or a photosensitive resin such as a solder resist can be used. Each of the

protective layers

13a and 13b is bonded and fixed to each of the main surface 1a and the back surface 1b of the flexible printed circuit board 100 with an adhesive (not shown) to protect the conductor surface from corrosion and oxidation. Thereby, environmental resistance can be improved.

When the

protective layers

13a and 13b are provided, it is necessary to design the

protective layers

13a and 13b so as not to affect the electrical connection with the printed circuit board 200 on the main surface 1a and the back surface 1b. For example, when conductive particles having a diameter of several μm to several tens of μm are sandwiched between wirings, such as ACF, it is necessary to design the protective layer 13a so as not to prevent the capturing of the conductive particles between the wirings. .

Embodiment 2. FIG.
As shown in FIGS. 4 to 6, the flexible printed circuit board 100 according to the second embodiment is replaced with the power supply circuit unit 30, the control circuit unit 40, and the power supply circuit unit 30 and the control circuit unit 40 according to the first embodiment. Is different from the configuration of the first embodiment in that it has a composite circuit unit 50 in which is combined.

The composite circuit unit 50 is a circuit unit in which the power supply circuit unit 30 and the control circuit unit 40 are combined, and includes the power supply circuit 6, the auxiliary power supply circuit 7, the control signal circuit 8, and the power supply circuit connection conductor 5. Have.

The auxiliary power circuit 7 is formed on the back surface 1 b so as to face not only the power circuit 6 but also the control signal circuit 8. That is, the dummy circuit 9 in the first embodiment is omitted, and the conductor width of the auxiliary power circuit 7 is extended to the back side of the control signal circuit 8.

The auxiliary power circuit 7 is electrically connected to the power circuit 6 by a power circuit connecting conductor 5 that fills the through hole 5a.

Since the configuration of the present embodiment other than the above is substantially the same as the configuration of the first embodiment, the same elements are denoted by the same reference numerals and description thereof is not repeated.

In the present embodiment, the dummy circuit 9 is omitted, and the conductor width of the auxiliary power circuit 7 is extended to the back side of the control signal circuit 8. As a result of such a structure, the auxiliary power circuit 7 can have a larger cross-sectional area than that of the first embodiment. Thereby, the flexible printed circuit board 100 which further improved the heat dissipation characteristic can be realized.

Generally, the temperature rise of the wiring related to the power supply circuit is caused by heat generation due to Joule heat caused by the current value and resistance value of the circuit. However, the temperature of the member constituting the circuit depends on the environment in which the member is placed, that is, the outside air temperature around the member and the heat dissipation, and therefore varies depending on the part. Since the heat escapes quickly in the part with good heat dissipation of the circuit, the temperature is kept low. On the other hand, the temperature of the portion where the heat dissipation property of the circuit is bad increases because heat accumulates.

When wiring in the air for the purpose of connecting between printed circuit boards, such as a flexible printed circuit board, heat dissipation is performed near both ends of the flexible printed circuit board directly connected to the printed circuit board and in the air. Therefore, the temperature during energization is different. The temperature is low in the vicinity of both ends of the flexible printed circuit board connected to the printed circuit board, and the temperature is high in the portion suspended in the air.

In the portion connected to the printed circuit board, the heat generated by the flexible printed circuit board is quickly radiated to a metal casing or the like outside the printed circuit board through a metal part such as a pad electrode or a through hole of the printed circuit board. On the other hand, in the part suspended in the air, the periphery of the flexible printed circuit board is air which is a thermal insulator. Moreover, since the members constituting the flexible printed circuit board are composed of the polyimide film base and the epoxy resin adhesive or the acrylic resin adhesive as described above except for the metal wiring portion, the thermal conductivity is significantly low (both Both are about 0.2W / mK). For this reason, as a heat dissipation path, the heat is transmitted to the printed circuit board through the metal conductor on the flexible printed circuit board. However, in this case, since the heat transfer distance becomes long, the thermal resistance becomes large and the heat radiation performance is often insufficient.

Therefore, in the present embodiment, the generation of Joule heat is suppressed by increasing the cross-sectional area of the auxiliary power circuit 7. Further, by increasing the surface area of the auxiliary power circuit 7 and causing the auxiliary power circuit 7 to function as a heat sink, heat dissipation into the air is facilitated. Thereby, the temperature rise of the whole flexible printed circuit board 100 is reduced.

Note that the conductor width of the power supply circuit 6 only needs to have a minimum width necessary to connect the power supply circuit connection conductor 5. Further, the power supply circuit 6 can increase the connection area with the printed circuit board in the longitudinal direction of the power supply circuit 6 if necessary, so that the high-density wiring area of the control signal circuit 8 is not hindered.

With the structure as shown in this embodiment, it is possible to realize the flexible printed circuit board 100 that can secure a large current capacity while maintaining high reliability by suppressing the temperature rise low.

Further, the flexible printed circuit board 100 in the present embodiment has a uniform thickness in the plane of the flexible printed circuit board 100 as in the cross-sectional structure of the flexible printed circuit board 100 shown in FIG. Therefore, also in the present embodiment, as in the first embodiment, a highly reliable connection can be obtained in the connection using the connector, the ACF, or the solder.

Embodiment 3 FIG.
As shown in FIGS. 7 to 10, the flexible printed circuit board 100 in the present embodiment is a composite in which a power supply circuit unit 30 and a control circuit unit 40 are combined instead of the control circuit unit 40 in the first embodiment. The configuration differs from that of the first embodiment in that the circuit portion 60 is provided.

In the composite circuit section 60, a plurality of control signal circuits 8 and a plurality of power circuit terminals 10 are formed on the main surface 1 a of the base film 1. In the composite circuit unit 60, the auxiliary power circuit 7 is formed on the back surface 1 b of the base film 1.

The plurality of control signal circuits 8 linearly extend on the main surface 1a so that the longitudinal directions of the plurality of control signal circuits 8 run in parallel with each other. The plurality of power supply circuit terminals 10 are located on an extension line in the longitudinal direction of the control signal circuit 8 on the main surface 1a, and are arranged on both one side and the other side in the longitudinal direction of the control signal circuit 8. . The plurality of auxiliary power supply circuits 7 in the composite circuit unit 60 extend linearly so as to run parallel to each other on the back surface 1b. Each of the plurality of power supply circuits 6 is electrically connected to the auxiliary power supply circuit 7 by a power supply circuit connection conductor 5.

Each of the plurality of power supply circuit connection conductors 5 is formed so as to embed a through hole 5a formed in the base film 1.

The composite circuit section 60 is provided when the current capacity of the power supply circuit section 30 is insufficient with respect to the current capacity required for the flexible printed circuit board 100. Also in the present embodiment, the power supply circuit unit 30 bears most of the current capacity of the flexible printed circuit board 100. However, the current capacity of the power supply circuit unit 30 can be supplementarily increased by the additional structure provided in the composite circuit unit 60.

Unlike the function of the auxiliary power supply circuit 7 described in the second embodiment, the configuration of the present embodiment is a structure that is purely intended to increase the contact area of the connection portion.

A connection configuration that requires such a structure is caused by Joule heat generated at the connection portion when the resistance of the connection portion rises to about several Ω when a circuit is connected using, for example, ACF, and a large current is applied. Effective when heat generation cannot be ignored. Moreover, the connection form which requires such a structure is effective even in an analog circuit in which a problem occurs in a circuit unless the connection portion is connected with low impedance.

Here, an example in which the flexible printed circuit board 100 (FIGS. 7 to 10) and the printed circuit board 200 (FIG. 11) are connected using an ACF will be described with reference to FIGS. 9 and 11. FIG. A dotted line in FIG. 11 represents a portion where the flexible printed circuit board 100 overlaps the printed circuit board 200 when the flexible printed circuit board 100 and the printed circuit board 200 are connected.

As shown in FIG. 11, the printed circuit board 200 includes a substrate 201, a center conductor 202, a ground conductor 204, a power supply circuit 206, a control circuit terminal 208, a power supply circuit terminal 210, and a lower layer wiring 215. It mainly has a conductor 205.

The substrate 201 has a plurality of electric circuit formation regions having different specifications. The plurality of electric circuit formation regions include, for example, a high-frequency circuit unit 220, a power supply circuit unit 230, and a composite circuit unit 260.

In the high-frequency circuit unit 220, a center conductor 202 and a ground conductor 204 are formed on the surface of the substrate 201. For example, two ground conductors 204 sandwich one central conductor 202. The center conductor 202 and the two ground conductors 204 extend linearly so as to run in parallel with each other.

In the power supply circuit unit 230, a plurality of power supply circuits 206 are formed on the surface of the substrate 201. Each of the plurality of power supply circuits 206 extends linearly so as to run in parallel with each other. Each of the plurality of power supply circuits 206 is parallel to the center conductor 202 and the ground conductor 204.

In the composite circuit section 260, a plurality of control circuit terminals 208 and a plurality of power supply circuit terminals 210 are formed on the surface of the substrate 201. The plurality of control circuit terminals 208 are arranged side by side in the same direction as the direction in which the plurality of power supply circuits 206 are arranged. The plurality of power supply circuit terminals 210 are arranged side by side in the same direction as the direction in which the plurality of power supply circuits 206 are arranged.

Each of the plurality of power supply circuit terminals 210 is electrically connected to each of the power supply circuits 206 by a lower layer wiring 215. Each of the plurality of lower layer wirings 215 extends from the power supply circuit unit 230 to the composite circuit unit 260 on the back surface of the substrate 201. The lower layer wiring 215 is electrically connected to the power supply circuit 206 by the connection conductor 205. The lower layer wiring 215 is electrically connected to the power supply circuit terminal 210 by the connection conductor 205.

The control circuit terminal 208 is electrically connected to a lower layer wiring (not shown) formed on the back surface of the substrate 201 by a connection conductor 205.

The connection conductor 205 is formed so as to be embedded in the through hole 205a provided in the substrate 201.

The power supply circuit 6 (FIG. 9) is electrically connected by sandwiching conductive particles of ACF between the power supply circuit 206 (FIG. 11) facing the power supply circuit 6 (FIG. 9). In order to increase the connection area between the opposing circuits, there is a method of increasing the conductor width of each of the opposing circuits. However, in this case, the widths of the flexible printed circuit board 100 and the printed circuit board 200 are increased, which is a factor that hinders downsizing of the entire product.

7 to 10, the flexible printed circuit board 100 is provided with a composite circuit portion 60, and the printed circuit board 200 corresponds to the pattern of the main surface 1 a of the composite circuit portion 60 as shown in FIG. 11. A control circuit terminal 208 and a power circuit terminal 210 are provided. The power supply circuit terminal 210 is electrically connected to the lower layer wiring 215 by the connection conductor 205, and the lower layer wiring 215 is electrically connected to the power supply circuit 206 by the connection conductor 205. As a result, the power supply circuit terminal 210 is electrically connected to the power supply circuit 206. The control circuit terminal 208 is also wired in the plane of the printed circuit board 200 by the connection conductor 205 and a lower layer wiring (not shown).

With the above structure, the current flowing through the power supply circuit 206 of the printed circuit board 200 is divided into the following two paths. That is, a path for energizing the composite circuit unit 60 of the flexible printed circuit board 100 through the connection conductor 205, the lower layer wiring 215, and the power circuit terminal 210, and a power circuit 206 for the printed circuit board 200 and the power circuit unit 30 of the flexible printed circuit board 100 are energized. It is a route.

As a result, since the flexible printed circuit board 100 according to the present embodiment can increase the area of the ACF connection portion, the resistance of the connection portion can be reduced.

Also, by distributing the path through which the current passes, the power supply circuit 6 of the power supply circuit unit 30 on the main surface 1a can be used as a redundant circuit even when conduction failure occurs for some reason. Therefore, also in the present embodiment, as in the first embodiment, a highly reliable connection can be obtained in the connection using the connector, the ACF, or the solder.

In addition, the flexible printed circuit board 100 in the present embodiment has a uniform thickness in the surface of the flexible printed circuit board as in the cross-sectional structure of the flexible printed circuit board 100 shown in FIG. Therefore, also in the present embodiment, as in the first embodiment, a highly reliable connection can be obtained in the connection using the connector, the ACF, or the solder.

The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Base film, 1a main surface, 1b back surface, 2,202 center conductor, 3 back ground conductor, 4,204 ground conductor, 5,205 connecting conductor, 5a through hole, 6,206 power circuit, 7 auxiliary power circuit, 8 Control signal circuit, 9 dummy circuit, 10, 210 power circuit terminal, 11 resin, 12 conductive particles, 13a, 13b protective layer, 20, 220 high frequency circuit section, 30, 230 power circuit section, 40 control circuit section, 50, 60 , 260 composite circuit section, 100 flexible printed circuit board, 200 printed circuit board, 201 circuit board, 208 control circuit terminal, 215 lower layer wiring.

Claims

A base film having a first surface and a second surface facing each other and made of an insulator;
A plurality of first conductors formed on the first surface of the base film;
A plurality of second conductors formed on the second surface of the base film;
A plurality of connection conductors penetrating the base film and electrically connecting each of the plurality of first conductors and each of the plurality of second conductors;
The flexible printed circuit board, wherein each of the plurality of second conductors is thicker than each of the plurality of first conductors.
The flexible printed circuit board according to claim 1, wherein the plurality of first conductors and the plurality of second conductors constitute a high-frequency circuit unit, a power supply circuit unit, and a control circuit unit.
The high-frequency circuit unit includes a center conductor,
The power supply circuit unit includes a power supply circuit and an auxiliary power supply circuit,
The plurality of first conductors include the center conductor and the power supply circuit,
The flexible printed circuit board according to claim 2, wherein the plurality of second conductors include the auxiliary power supply circuit.
The total film thickness of the first conductor, the second conductor, and the base film in the high-frequency circuit section is the thickness of the first conductor in the power circuit section, the second Equal to the total film thickness of the conductor and the base film, and the total thickness of the first conductor, the second conductor and the base film in the control circuit unit. The flexible printed circuit board of Claim 2 equal to a film thickness.
The plurality of connection conductors include two high-frequency circuit connection conductors adjacent to each other in the high-frequency circuit unit,
The flexible printed circuit board according to claim 2, wherein a shortest distance between the connection conductors for the two high-frequency circuits is equal to or less than a quarter of a wavelength of an electromagnetic wave transmitted through the high-frequency circuit unit.
The plurality of connection conductors include a power supply circuit connection conductor for electrically connecting the power supply circuit and the auxiliary power supply circuit in the power supply circuit unit,
The flexible printed circuit board according to claim 3, wherein a cross-sectional area of the connection conductor for power supply circuit is equal to or greater than a cross-sectional area of the auxiliary power supply circuit.
The control circuit unit includes a control signal circuit,
The power supply circuit unit includes a power supply circuit and an auxiliary power supply circuit,
The plurality of first conductors includes the control signal circuit and the power supply circuit,
The plurality of second conductors include the auxiliary power supply circuit,
The flexible printed circuit board according to claim 2, wherein the auxiliary power supply circuit faces both the power supply circuit and the control signal circuit.
The flexible printed circuit board according to claim 7, wherein the power supply circuit and the control signal circuit are arranged so that a longitudinal direction of the power supply circuit and a longitudinal direction of the control signal circuit run in parallel with each other.
The flexible printed circuit board according to claim 7, wherein the power supply circuit is located on an extension line in a longitudinal direction of the control signal circuit.