JP2022142965A - Flexible printed wiring board, electronic unit, electronic device, and manufacturing method for flexible printed wiring board - Google Patents

Abstract

To provide a flexible printed wiring board that can achieve both electromagnetic noise shielding effectiveness and high flexibility.SOLUTION: A flexible printed wiring board 200 includes an insulator portion 230 extending in the X direction, which is an example of a first direction, a signal line 22 disposed inside the insulator portion 230, a conductive layer 221 disposed on a main surface 231 of the insulator portion 230 and having a plurality of apertures 2210, and an insulating layer 222 disposed on the conductive layer 221 and having a plurality of apertures 2220.SELECTED DRAWING: Figure 2

Description

The present invention relates to flexible printed wiring boards.

Electronic devices such as mobile phones, smart phones, tablet terminals, and digital cameras have flexible printed wiring boards that serve as transmission paths for digital signals. As the performance and functions of electronic equipment have improved, the amount of data handled by the electronic equipment has increased dramatically, and the transmission speed of digital signals passing through flexible printed wiring boards has also increased. Therefore, there is a risk that electromagnetic wave noise generated from a rigid printed wiring board or electronic components mounted on the rigid printed wiring board in the electronic device may degrade the quality of digital signals passing through the flexible printed wiring board. In addition, there is a possibility that surrounding semiconductor devices may malfunction due to electromagnetic noise radiated from the flexible printed wiring board.

On the other hand, Patent Document 1 discloses a flexible printed wiring board provided with a ground layer having a function of shielding electromagnetic wave noise.

Japanese Patent Application Laid-Open No. 2000-077802

However, electronic devices are required to be downsized, and therefore flexible printed wiring boards are required to be highly flexible so that they can be accommodated in narrow spaces.

An object of the present invention is to achieve both an electromagnetic noise shielding effect and high flexibility in a flexible printed wiring board.

A flexible printed wiring board of the present invention includes an insulator portion extending in a first direction, a signal line arranged inside the insulator portion, and a plurality of first openings arranged on a main surface of the insulator portion. and an insulating layer disposed on the conductive layer and having a plurality of second openings.

A method for manufacturing a flexible printed wiring board according to the present invention includes preparing an insulator part having a signal line disposed therein, forming a conductive layer having a plurality of first openings on a main surface of the insulator part, An insulating layer having a plurality of second openings is formed on the conductive layer.

ADVANTAGE OF THE INVENTION According to this invention, the flexible printed wiring board which made the shielding effect of electromagnetic wave noise compatible with high flexibility can be provided.

1 is an explanatory diagram of a digital camera that is an imaging device as an example of an electronic device according to an embodiment; FIG. (a) is an explanatory diagram of an imaging unit according to the embodiment. (b) is a cross-sectional view of the flexible printed wiring board taken along line IIB-IIB in (a). FIG. 2 is an explanatory diagram of a flexible printed wiring board when the flexible printed wiring board is viewed from the main surface side of the insulating layer according to the embodiment; (a) is an explanatory diagram of a conductive layer according to the embodiment. (b) is an explanatory diagram of an insulating layer according to the embodiment. (a) to (c) are explanatory diagrams showing an example of a method for manufacturing a flexible printed wiring board according to the embodiment. (a) to (c) are explanatory diagrams showing an example of a method for manufacturing a flexible printed wiring board according to the embodiment. (a) is a schematic diagram of an apparatus used to evaluate flexibility of a flexible printed wiring board of an example and a flexible printed wiring board of a comparative example. (b) is a schematic diagram of a system used to evaluate the transmission characteristics of the flexible printed wiring board of the example and the flexible printed wiring board of the comparative example. 4 is a table showing evaluation results in Examples 1-3 and Comparative Examples 1-2.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram of a digital camera 600 that is an imaging device as an example of an electronic device according to an embodiment. A digital camera 600 is an interchangeable-lens digital camera and includes a camera body 601 . A camera body 601 is detachable with a lens unit (lens barrel) 602 including lenses. The camera body 601 includes a housing 611 , an imaging unit 100 that is an example of an electronic unit, and a wireless communication unit 150 . The imaging unit 100 and the wireless communication unit 150 are housed inside the housing 611 .

The imaging unit 100 includes a printed circuit board 101 , a printed circuit board 102 , and a flexible printed wiring board 200 electrically connecting the printed circuit boards 101 and 102 . Printed circuit board 101 is an example of a first electronic module. Printed circuit board 102 is an example of a second electronic module. By using the flexible printed wiring board 200 for connection between the printed circuit boards 101 and 102, the weight of the wiring structure can be reduced as compared with a coaxial cable.

The printed circuit board 101 includes a rigid printed wiring board 110 and a semiconductor device 111 mounted on the rigid printed wiring board 110 . The printed circuit board 102 includes a rigid printed wiring board 120 and a semiconductor device 121 mounted on the rigid printed wiring board 120 . Rigid printed wiring board 110 is an example of a first rigid printed wiring board. Semiconductor device 111 is an example of a first electronic component. Rigid printed wiring board 120 is an example of a second rigid printed wiring board. Semiconductor device 121 is an example of a second electronic component.

The semiconductor device 111 is an image sensor in this embodiment. The image sensor is, for example, a CMOS (Complementary Metal Oxide Semiconductor) image sensor or a CCD (Charge Coupled Device) image sensor. The image sensor has a function of converting light incident through the lens unit 602 into an electrical signal. The semiconductor device 121 is a digital signal processor in this embodiment. The digital signal processor has a function of acquiring an electrical signal representing image data from the semiconductor device 111, which is an image sensor, correcting the acquired electrical signal, and generating corrected image data. In this embodiment, the imaging unit 100 has a camera shake correction function and includes a motor 160 that is an example of a drive source for driving the printed circuit board 101 . Since the printed circuit board 101 is driven in this manner, the flexible printed wiring board 200 is required to have flexibility.

The wireless communication unit 150 performs wireless communication in the GHz band and is modularized. The wireless communication unit 150 has a rigid printed wiring board 151 including an antenna (not shown) and a wireless communication IC 152 mounted on the rigid printed wiring board 151 . The antenna is provided in the same plane as the wireless communication IC 152 and is arranged at a position close to the housing 611 so as to facilitate communication with the outside. The wireless communication IC 152 is preferably capable of transmitting and/or receiving image data by wirelessly communicating with an external device such as a PC or a wireless router via an antenna. In this embodiment, the wireless communication IC 152 can transmit and receive data via an antenna. Specifically, the wireless communication IC 152 modulates a digital signal representing image data acquired from the semiconductor device 121, and transmits the modulated signal from an antenna as a radio wave at a wireless standard communication frequency. Also, the wireless communication IC 152 demodulates radio waves received by the antenna into digital signals representing image data. The wireless communication IC 152 wirelessly communicates with external devices in compliance with standards such as Wi-Fi (registered trademark) and Bluetooth (registered trademark).

FIG. 2A is an explanatory diagram of the imaging unit 100 according to the embodiment. As shown in FIG. 2A, the flexible printed wiring board 200 extends in the X direction, which is the longitudinal direction. The X direction is an example of a first direction. A flexible printed wiring board 200 has a plurality of signal lines 22 . Each signal line 22 extends in the X direction. The X direction is also the wiring direction. The plurality of signal lines 22 are arranged at intervals in the Y direction, which is the lateral direction, perpendicular to the X direction. The Y direction is an example of a second direction. The Z direction orthogonal to the X and Y directions is the thickness direction of the flexible printed wiring board 200 . Flexible printed wiring board 200 is flexible and bendable.

The flexible printed wiring board 200 has an end 201 that is an example of a first end in the X direction and an end 202 that is an example of a second end in the X direction. End 202 is located on the opposite side of flexible printed wiring board 200 from end 201 .

A connector 112 is mounted on the rigid printed wiring board 110 . Connector 112 is electrically connected to semiconductor device 111 by a conductor included in rigid printed wiring board 110 . An end 201 of a flexible printed wiring board 200 is attached to the connector 112 . As a result, end 201 of flexible printed wiring board 200 is electrically and mechanically connected to rigid printed wiring board 110 .

A connector 122 is mounted on the rigid printed wiring board 120 . Connector 122 is electrically connected to semiconductor device 121 by a conductor included in rigid printed wiring board 120 . An end 202 of a flexible printed wiring board 200 is attached to the connector 122 . Thereby, the end 202 of the flexible printed wiring board 200 is electrically and mechanically connected to the rigid printed wiring board 120 .

With the above configuration, the semiconductor devices 111 and 121 are electrically connected to communicate with each other through the rigid printed wiring board 110, the flexible printed wiring board 200, and the rigid printed wiring board 120. FIG.

FIG. 2(b) is a cross-sectional view of the flexible printed wiring board 200 taken along line IIB-IIB in FIG. 2(a). As shown in FIG. 2B, flexible printed wiring board 200 has wiring board body 210 and shield member 220 .

Wiring board body 210 has insulator portion 230 and a plurality of signal lines 22 described above. The insulator portion 230 is made of an electrically insulating material. Each signal line 22 is made of a conductive material. The wiring board main body 210, that is, the insulator portion 230 and the plurality of signal lines 22 are formed extending in the X direction. The plurality of signal lines 22 are arranged inside the insulator portion 230 at intervals in the Y direction. Note that two of the plurality of signal lines 22 are shown in FIG. 2(b). The insulator portion 230 is formed in a sheet shape and has a pair of main surfaces 231 and 232 . The shield member 220 may be arranged on either one of the pair of main surfaces 231 and 232, and is arranged on the main surface 231 in this embodiment. In addition, the shield member 220 may be arranged on each of the pair of main surfaces 231 and 232 .

The insulator portion 230 includes a plurality of insulating layers 240 , 251 and 252 . The plurality of insulating layers 240, 251, 252 are in contact with each other. The insulating layer 240 is an insulating substrate and has a pair of main surfaces 241 and 242 . A plurality of signal lines 22 are arranged on the main surface 241 . The insulating layer 251 is arranged on the main surface 241 and on the plurality of signal lines 22 .

In this embodiment, the insulator section 230 has an insulating layer 252 arranged between the insulating layer 240 and the insulating layer 251 . The insulating layer 252 has a function of bonding the insulating layer 240 and the insulating layer 251 together. Note that the insulating layer 252 may be omitted if the insulating layer 251 has an adhesive function.

The insulating layer 240 will be described in detail below. The material of the insulating layer 240, which is an insulating substrate, is preferably resin. Examples of resins include polyimide-based resins such as polyimide, polyamide, and polyamide-imide, thermosetting resins such as epoxy, and thermoplastic resins such as liquid crystal polymers. Among these, polyimide or liquid crystal polymer is preferred. Polyimide has excellent heat resistance and mechanical properties, and is easily commercially available. Liquid crystal polymers are suitable for high-speed signal transmission applications because of their low relative permittivity, and their low hygroscopicity and excellent dimensional stability.

The thickness of the insulating layer 240 in the Z direction is preferably 10 μm or more and 100 μm or less. Since the thickness of the insulating layer 240 in the Z direction is 10 μm or more, the separation distance between the signal line 22 and surrounding electronic components can be ensured, and the characteristic impedance of the signal line 22 is suppressed from being changed. be able to. Moreover, since the thickness of the insulating layer 240 in the Z direction is 100 μm or less, the rigidity of the insulating layer 240 can be reduced, and the flexible printed wiring board 200 can obtain sufficient flexibility. From the above point of view, the thickness of the insulating layer 240 in the Z direction is more preferably 12 μm or more and 75 μm or less.

Next, each signal line 22 will be described in detail. Each signal line 22 is a wire that can be used to transmit a digital data signal. As the amount of signal transmission increases, it is preferable to construct a differential signal wiring in which a pair of signal lines 22 out of the plurality of signal lines 22 constitutes one set. Note that the plurality of signal lines 22 may include wiring for transmitting single-ended signals such as control signals and response signals. Also, the flexible printed wiring board 200 may have a ground line (not shown) in addition to the signal line 22 .

Although the method of forming the signal line 22 is not particularly limited, the signal line 22 can be formed by, for example, bonding of metal foil, metal plating, an inkjet process, or the like. When a copper foil is used as the metal foil, a film bonded with an adhesive or the like can be used, and the required transmission line pattern can be formed by a photolithographic etching process. Alternatively, when an inkjet process is used, a polymer ink containing metal particles is drawn in a required pattern, and the pattern is baked at a temperature below the glass transition point (Tg) of the insulating layer 240 to form the pattern. Although the thickness of the signal line 22 is not particularly limited, it is preferably 0.1 μm or more and 20 μm or less, for example.

Next, the insulating layer 251 will be described in detail. As the insulating layer 251, plastic and/or insulating resin can be used. Plastics used for the insulating layer 251 include so-called engineering plastics. Examples of plastics used for the insulating layer 251 include polypropylene, crosslinked polyethylene, polyester, polybenzimidazole, polyamide, polyimide, polyimideamide, and polyetherimide. Plastics used for the insulating layer 251 include, for example, polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), and polyetheretherketone (PEEK). From the viewpoint of low cost, it is preferable to use a polyester film. From the viewpoint of excellent flame retardancy, it is preferable to use a polyphenylene sulfide film. If further heat resistance is required, it is preferable to use an aramid film or a polyimide film.

The insulating resin used for the insulating layer 251 may be any resin having electrical insulating properties, such as a thermosetting resin or an ultraviolet curable resin. Thermosetting resins include phenol resins, acrylic resins, epoxy resins, melamine resins, silicone resins, and acrylic-modified silicone resins. Examples of ultraviolet curable resins include epoxy acrylate resins, polyester acrylate resins, and methacrylate-modified products thereof. The curing mode may be heat curing, ultraviolet curing, electron beam curing, or the like. Further, if necessary, other additives such as a coloring pigment, a flame retardant, an antioxidant, a lubricant, an antidust agent, and a curing accelerator may be blended.

Although the method for forming the insulating layer 251 is not particularly limited, the following method can be used when the insulating resin is coated on the plastic. For example, a solution obtained by dissolving an insulating resin in a solvent is applied to gravure coating, kiss coating, die coating, blade coating, roll coating, knife coating, spray coating, bar coating, spin coating, and dip coating. can be coated with The solvent can be appropriately selected depending on the type of resin used. For example, ketone solvents such as acetone, methyl ethyl ketone and cyclohexanone, and alcohol solvents such as methanol, ethanol, propanol, ethylene glycol, glycerin and propylene glycol monomethyl ether can be used. Acids such as acetic acid, amide solvents such as formamide, dimethylacetamide and N-methylpyrrolidone, nitrile solvents such as acetonitrile and propylonitrile, and ester solvents such as methyl acetate and ethyl acetate can also be used. Carbonate-based solvents such as dimethyl carbonate and diethyl carbonate can also be used. During coating, a heating or drying step may be provided for volatilizing the solvent, if necessary. For heating and drying, a heating device and a drying device such as a hot air dryer and an infrared heater can be used, and the heating temperature, drying temperature, heating time and drying time can be appropriately selected.

The thickness of the insulating layer 251 in the Z direction is preferably 5 μm or more and 50 μm or less. When the thickness of the insulating layer 251 in the Z direction is 5 μm or more, sufficient strength can be ensured in the insulating layer 251 . When the thickness of the insulating layer 251 in the Z direction is 50 μm or less, slidability and flexibility are improved. From the above point of view, it is more preferable that the thickness of the insulating layer 251 in the Z direction is 10 μm or more and 30 μm or less. Moreover, the volume resistance value of the insulating layer 251 is preferably 10 ⁹ Ω·cm or more, more preferably 10 ¹³ Ω·cm or more.

Next, the insulating layer 252 will be described in detail. The insulating layer 252 is an adhesive layer provided between the insulating layer 251 and the insulating layer 240 and the signal line 22 . That is, the insulating layer 252 is a cured adhesive. The insulating layer 252 preferably has high electrical insulation. Examples of adhesives used to form the insulating layer 252 include acrylonitrile-butadiene rubber (NBR)-based adhesives, polyamide-based adhesives, polyester-based adhesives, acrylic-based adhesives, polyester-polyurethane-based adhesives, and silicone-based adhesives. is mentioned.

It is preferable that the insulating layer 252 can sufficiently cover each signal line 22 that is a transmission line and be smooth. Therefore, the thickness of the insulating layer 252 in the Z direction is preferably 2 μm or more and 50 μm or less. When the thickness of the insulating layer 252 is 2 μm or more, the adhesive can be sufficiently embedded between the signal lines 22, and the insulating layer 252 can be firmly adhered. Further, when the thickness of the insulating layer 252 is 50 μm or less, it is possible to suppress the adhesive from seeping out from between the insulating layers 240 and 251 to the sides. From the above point of view, it is more preferable that the thickness of the insulating layer 252 in the Z direction is 5 μm or more and 30 μm or less.

The method of forming the insulating layer 252 is not particularly limited, but examples include a method of bonding sheet-like adhesives together and curing, a method of applying a liquid adhesive by a dispenser or a printing method, and a method of curing with heat or ultraviolet rays. be done.

The wiring board main body 210 has been described above, and the shield member 220 will be described in detail below. The shield member 220 is a sheet-like member and includes a conductive layer 221 and an insulating layer 222 . Conductive layer 221 is arranged on main surface 231 of insulator portion 230 . The insulating layer 222 is arranged on the conductive layer 221 . The conductive layer 221 is a shield layer that shields electromagnetic noise, and is made of a conductive member. Insulating layer 222 is a protective layer that protects conductive layer 221 from coming into contact with members surrounding flexible printed wiring board 200, and is made of a member having electrical insulation.

The conductive layer 221 does not have to be electrically connected to any member, but in this embodiment, it is used as a path for the return current of the signal passing through the signal line 22 and is part of the ground line. there is That is, the conductive layer 221 is electrically connected to ground lines of the rigid printed wiring boards 110 and 120 .

Since flexible printed wiring board 200 has conductive layer 221 , it is possible to secure a shielding effect against electromagnetic noise radiated from flexible printed wiring board 200 and external electromagnetic noise transmitted to flexible printed wiring board 200 . In this embodiment, the conductive layer 221 has multiple openings 2210 . Each opening 2210 is a first opening. Each opening 2210 is a through hole. Since the conductive layer 221 has a plurality of openings 2210, the flexibility of the conductive layer 221, that is, the flexibility of the flexible printed wiring board 200 can be ensured.

FIG. 3 is an explanatory diagram of flexible printed wiring board 200 viewed from main surface 241 side of insulating layer 240 according to the embodiment. In FIG. 3, the insulating layer 222, the conductive layer 221, the signal line 22, and the insulating layer 240 are illustrated, and the insulating layers 251 and 252 are omitted for convenience of explanation. Also, for convenience of explanation, part of the insulating layer 222 and the conductive layer 221 are omitted. The Z direction is also the direction perpendicular to the main surface 231 .

One signal line 22 out of the plurality of signal lines 22 will be focused on and explained. Two or more openings 2210 among the plurality of openings 2210 are arranged at positions overlapping one signal line 22 when viewed in the Z direction. These two or more openings 2210 will be described. Two or more openings 2210 are formed such that each of the two or more openings 2210 partially or entirely overlaps with one signal line 22 when viewed in the Z direction. It is arranged to face one signal line 22 .

FIG. 4A is an explanatory diagram of the conductive layer 221 according to the embodiment. FIG. 4A shows a portion of the conductive layer 221 viewed in the Z direction. From the viewpoint of ensuring high flexibility in flexible printed wiring board 200, it is preferable that a plurality of openings 2210 be arranged in a matrix. In this embodiment, a plurality of openings 2210 are arranged in a matrix by forming the conductive layer 221 in a mesh shape.

The shape of each opening 2210 can be set arbitrarily. The shape of each opening 2210 viewed in the Z direction is preferably rectangular, polygonal, circular, elliptical, or the like. A hexagon is preferable among polygons. Rectangles include, for example, trapezoids, parallelograms, rhombuses, rectangles, and squares.

Here, the length of each opening 2210 in the X direction is L1. Let L2 be the length of each opening 2210 in the Y direction. Each opening 2210 preferably has a shape in which the length L1 in the X direction is longer than the length L2 in the Y direction. As a result, a return current, which is a current that cancels out noise, flows easily in conductive layer 221, and electromagnetic wave noise radiated from flexible printed wiring board 200 can be suppressed.

In particular, each opening 2210 preferably has a rhombic shape extending in the X direction. Each of the lengths L1 and L2 is the length of a diagonal line passing through two of the four interior angles of the rhombus that face each other. That is, the direction in which the diagonal line of length L1 extends is the X direction, and the direction in which the diagonal line of length L2 extends is the Y direction. Further, when each opening 2210 is diamond-shaped, it becomes easier to arrange two or more openings 2210 along one signal line 22 . Since each opening 2210 has a rhombic shape extending in the X direction, return current flows more easily in conductive layer 221, and electromagnetic noise radiated from flexible printed wiring board 200 can be more effectively suppressed.

A method for forming the conductive layer 221 is not particularly limited; however, the conductive layer 221 can be formed by the following method. For example, a method of placing a mask conforming to the shape of the opening on the main surface 231 side and forming the conductive layer 221 by a subtractive method, an electroless plating method, an electrolytic plating method, or a physical vapor deposition method can be used. Examples of the physical vapor deposition method include a vacuum vapor deposition method and a sputtering method. Alternatively, for example, a mask conforming to the shape of the opening is arranged on the main surface 231 side, and the conductive layer 221 is formed by removing the mask after forming the conductive film by a coating liquid coating method such as bar coating or slit coating. method. Other examples include a screen printing method in which a conductive paste is printed using a screen plate having an opening pattern in advance, and a method in which the conductive layer 221 is formed by an inkjet method or a dot dispenser method in which a coating liquid is discharged along a predetermined pattern. .

The aperture ratio of the conductive layer 221 is preferably 40% or more and 90% or less. The aperture ratio of the conductive layer 221 is the ratio of the area of the openings 2210 per unit area when the conductive layer 221 is viewed in the Z direction. A unit area includes a portion of the conductive layer 221 and a portion of the plurality of openings 2210 . When the aperture ratio of the conductive layer 221 is 40% or more, the aperture amplitude value of the eye pattern in signal transmission can be sufficiently increased, and the transmission failure of the digital signal transmitted through the signal line 22 can be reduced. . Further, when the aperture ratio of the conductive layer 221 is 90% or less, electromagnetic noise can be sufficiently shielded. Therefore, the electromagnetic wave noise radiated from the signal line 22, that is, the flexible printed wiring board 200 can be effectively reduced. That is, it is possible to effectively reduce electromagnetic noise that affects wireless communication of the wireless communication unit 150 . From the above point of view, the aperture ratio of the conductive layer 221 is more preferably 50% or more and 85% or less.

Also, in each opening 2210, the length L1 is preferably 1.5 times or more the length L2. Also, the length L1 is preferably 1.5 mm or less. When the length L1 is 1.5 mm or less, the effect of shielding electromagnetic noise emitted from the signal line 22, that is, the flexible printed wiring board 200 is enhanced. As a result, electromagnetic noise that affects the wireless communication of the wireless communication unit 150 can be effectively reduced. From the above point of view, it is more preferable that the length L1 is 1.2 mm or less.

If the two signal lines 22 are differential signal wirings, the length L2 of each opening 2210 is preferably shorter than the distance between the two signal lines 22 . As a result, the occurrence of common mode noise in the two signal lines 22 can be suppressed, and the occurrence of defects in signal transmission can be suppressed.

Materials of the conductive material forming the conductive layer 221 include metals such as gold, silver, copper, aluminum, and nickel. Also, examples of the conductive material forming the conductive layer 221 include metal particles and metal fibers. In addition to metal, the material of the conductive material that constitutes the conductive layer 221 includes a conductive resin composition such as carbon nanotube in which a conductive filler is mixed with resin, and a conductive polymer such as polythiophene and polypyrrole. be done.

When the conductive layer 221 is formed as a coating film, it is preferable to use silver paste containing highly conductive silver particles and a resin binder as the conductive material. Other than silver paste, gold paste, copper paste, carbon paste, or the like may be used.

The electrical resistance value of the conductive layer 221 is preferably 0.01Ω or more and 5Ω or less, more preferably 0.01Ω or more and 1Ω or less, from the viewpoint of shielding ability against electromagnetic wave noise.

The thickness of the conductive layer 221 in the Z direction is preferably 1 μm or more and 20 μm or less. When the thickness of the conductive layer 221 is 1 μm or more, the electrical resistance value of the conductive layer 221 can be reduced. Therefore, the return current when common mode noise occurs easily flows through the conductive layer 221, and the amount of radiation noise can be reduced. When the thickness of the conductive layer 221 in the Z direction is 20 μm or less, the surface can be made smooth. From the above point of view, it is more preferable that the thickness of the conductive layer 221 in the Z direction is 2 μm or more and 10 μm or less.

FIG. 4B is an explanatory diagram of the insulating layer 222 according to the embodiment. FIG. 4B illustrates a portion of the insulating layer 222 viewed in the Z direction. In this embodiment, insulating layer 222 has a plurality of openings 2220 . Each opening 2220 is a second opening. Each opening 2220 is a through hole. Having a plurality of openings 2220 in insulating layer 222 ensures higher flexibility in flexible printed wiring board 200 .

Two or more openings 2220 among the plurality of openings 2220 are arranged at positions overlapping with one signal line 22 when viewed in the Z direction. These two or more openings 2220 will be described. Two or more openings 2220 are formed so that each of the two or more openings 2220 partially or entirely overlaps with one signal line 22 when viewed in the Z direction. It is arranged to face one signal line 22 .

From the viewpoint of ensuring high flexibility in flexible printed wiring board 200, it is preferable that a plurality of openings 2220 be arranged in a matrix. In this embodiment, a plurality of openings 2220 are arranged in a matrix by forming the insulating layer 222 in a mesh shape. By arranging the plurality of openings 2220 in a matrix, it is possible to suppress the plastic deformation of the insulating layer 222 due to deformation stress, that is, the curling of the flexible printed wiring board 200 .

Let S1 be the area of one of the plurality of openings 2210 when viewed in the Z direction. One opening 2210 has the smallest area among the plurality of openings 2210 . Also, the area of one opening 2220 out of the plurality of openings 2220 when viewed in the Z direction is S2. One opening 2220 has the largest area among the plurality of openings 2220 .

The area S2 of the opening 2220 in the insulating layer 222 is preferably smaller than the area S1 of the opening 2210 in the conductive layer 221 when viewed in the Z direction. This can effectively prevent conductive layer 221 positioned below insulating layer 222 from coming into contact with members arranged around flexible printed wiring board 200 .

The shape of each opening 2220 can be set arbitrarily. The shape of each opening 2220 viewed in the Z direction is preferably rectangular, polygonal, circular, elliptical, or the like. A hexagon is preferable among polygons. Rectangles include, for example, trapezoids, parallelograms, rhombuses, rectangles, and squares. Considering the bendability of flexible printed wiring board 200, the shape of each opening 2220 when viewed in the Z direction is preferably rectangular.

The insulating resin used for the insulating layer 222 may be any resin having electrical insulating properties, such as a thermosetting resin, an ultraviolet curable resin, a coating agent made of a resin solution in which cured film components are dispersed in a solvent, and the like. is mentioned. Thermosetting resins include phenol resins, acrylic resins, epoxy resins, polyamide resins, polyamide-imide resins, polyimide resins, melamine resins, silicone resins, and acrylic-modified silicone resins. Examples of ultraviolet curable resins include epoxy acrylate resins, polyester acrylate resins, and methacrylate-modified products thereof. Examples of resin solutions include those obtained by dissolving polyester urethane resins and polyamideimide resins in organic solvents. In addition, if necessary, coloring pigments, flame retardants, antioxidants, lubricants, plasticizers, viscosity modifiers, anti-dust agents, curing accelerators, inorganic fillers such as silica and carbon black, silicone particles and polyester Organic fillers such as particles and other additives may be blended. As the insulating resin for the insulating layer 222, it is preferable to use a coating agent composed of a resin solution in which cured film components are dispersed in a solvent. By using this coating agent as the insulating resin for insulating layer 222 , shrinkage due to curing reaction is small, and warping of flexible printed wiring board 200 can be suppressed. Furthermore, as the insulating resin for the insulating layer 222, it is more preferable to use a coating agent in which a flexible and heat-resistant polyamide-imide resin is dissolved in a solvent.

Methods for forming the insulating layer 222 include the following methods. For example, a method of forming the insulating layer 222 by placing a mask that conforms to the shape of the opening 2220 on the conductive layer 221, forming an insulating film by a coating liquid coating method such as bar coating or slit coating, and then removing the mask. is mentioned. Other examples include a screen printing method in which an insulating paste is printed using a screen plate having an opening pattern in advance, and a method in which the insulating layer 222 is formed by an inkjet method or a dot dispenser method in which a coating liquid is discharged along a predetermined pattern. .

The Z-direction thickness of insulating layer 222 is preferably greater than the Z-direction thickness of conductive layer 221 from the viewpoint of preventing conductive layer 221 from coming into contact with members surrounding flexible printed wiring board 200 . Also, the thickness of the insulating layer 222 in the Z direction is preferably 5 μm or more and 20 μm or less. Since the thickness of the insulating layer 222 in the Z direction is 5 μm or more, it is possible to effectively prevent the conductive layer 221 from coming into contact with the surrounding members of the flexible printed wiring board 200 . Moreover, since the thickness of the insulating layer 222 in the Z direction is 20 μm or less, the flexibility of the flexible printed wiring board 200 can be enhanced more effectively. From the above point of view, it is more preferable that the thickness of the insulating layer 222 in the Z direction is 6 μm or more and 10 μm or less.

A preferred example of the method for manufacturing the flexible printed wiring board 200 will be described in detail below. As a method for forming the conductive layer 221 and the insulating layer 222 on the insulator portion 230, a screen printing method that can be formed at normal temperature and normal pressure is preferable. 5(a) to 5(c) and 6(a) to 6(c) are explanatory diagrams showing an example of a method for manufacturing the flexible printed wiring board 200 according to the embodiment.

First, as shown in FIG. 5A, a wiring board body 210 is prepared. The wiring board body 210 includes an insulator portion 230 and a plurality of signal lines 22 arranged inside the insulator portion 230, as shown in FIG. 2(b). A screen plate 301 is arranged on the main surface 231 that is the main surface of the insulator portion 230 . The screen plate 301 is formed with an opening pattern in the shape of the conductive layer 221 to be formed. A conductive paste P<b>1 as a material for the conductive layer 221 is placed on the screen plate 301 .

Next, as shown in FIG. 5B, the scraper 302 spreads the conductive paste P1 on the screen plate 301 to a predetermined thickness. Next, as shown in FIG. 5C, the conductive paste P1 is transferred onto the main surface 231 by the squeegee rubber 303. Next, as shown in FIG. A conductive layer 221 is formed on the main surface 231 by solidifying the conductive paste P1 transferred onto the main surface 231 .

Next, as shown in FIG. 6A, a screen plate 311 is arranged on the conductive layer 221, which is on the conductive layer. The screen plate 311 is formed with an opening pattern in the shape of the insulating layer 222 to be formed. An insulating paste P2 as a material for the insulating layer 222 is placed on the screen plate 311 .

Next, as shown in FIG. 6B, the scraper 312 spreads the insulating paste P2 on the screen plate 311 to a predetermined thickness. Next, as shown in FIG. 6C, the insulating paste P2 is transferred onto the conductive layer 221 by a squeegee rubber 313. Then, as shown in FIG. An insulating layer 222 is formed on the conductive layer 221 by solidifying the insulating paste P2 transferred onto the conductive layer 221 .

According to the manufacturing method described above, the conductive layer 221 and the insulating layer 222 can be easily formed, and the manufacturing time can be shortened.

(Example)
Next, examples and comparative examples to be compared with the examples will be described. The flexible printed wiring board of the example corresponds to the flexible printed wiring board 200 of the above embodiment. The flexibility and transmission characteristics of the flexible printed wiring boards of Examples and the flexible printed wiring boards of Comparative Examples are evaluated below.

For each of the examples and comparative examples, a single-sided flexible printed wiring board having a length of 150 mm in the X direction and a width of 20 mm in the Y direction and having 20 sets of differential signal wiring was used.

Hereinafter, methods for evaluating flexible printed wiring boards according to examples and comparative examples will be described.

(1) Bending load Flexibility of each of the flexible printed wiring boards of the examples and the flexible printed wiring boards of the comparative examples was evaluated by the repulsive load when the flexible printed wiring boards of the comparative examples were bent.

FIG. 7A is a schematic diagram of an apparatus used to evaluate the flexibility of the flexible printed wiring board 200 of the example and the flexible printed wiring board 200X of the comparative example. A flexible printed wiring board 200 of the embodiment has a wiring board body 210 and a shield member 220 . A flexible printed wiring board 200X of the comparative example has a wiring board body 210 and a shield member 220X.

As shown in FIG. 7(a), the flexible printed wiring boards 200, 200X are arranged horizontally so that the shield members 220, 220X are inside. When one end of the flexible printed wiring boards 200 and 200X in the longitudinal direction is bent 180 degrees with a curvature of 3 mm, the repulsive force in the vertical direction at one end is measured using a digital force gauge 41 of "ZTA-2N" manufactured by Imada Co., Ltd. evaluated.

The bending load is an index for quantitatively judging the flexibility of the flexible printed wiring board. In general, the greater the bending load of the flexible printed wiring board, the lower the flexibility of the flexible printed wiring board, that is, the harder and stiffer the flexible printed wiring board. Moreover, generally, the lower the flexibility of the flexible printed wiring board, the more difficult it becomes to attach the flexible printed wiring board to the electronic module. In addition, when the flexible printed wiring board is connected to two electronic modules, when one electronic module is driven relative to the other electronic module, it becomes a factor that impedes the driving.

The bending load was evaluated in three stages of A, B, and C below. A has a bending load of less than 200 mN. B has a bending load of 200 mN or more and less than 300 mN. C has a bending load of 300 mN or more. B is superior to C, and A is superior to B, in terms of bending load.

(2) Transmission characteristics (eye pattern)
FIG. 7B is a schematic diagram of a system 500 used to evaluate the transmission characteristics of the flexible printed wiring board 200 of the example and the flexible printed wiring board 200X of the comparative example. This system 500 comprises a signal generator 51 of M8041A manufactured by Agilent Technologies, an oscilloscope 52 of 92504A manufactured by Agilent Technologies, and a pair of connection boards 53 . Each connection board 53 has a pair of terminals capable of inputting and outputting signals.

The flexible printed wiring board 200 of the example and the flexible printed wiring board 200X of the comparative example were connected between a pair of connection boards 53 while floating in the air. Further, the signal generator 51 and one connection board 53 were connected, and a pseudo-random signal of PRBS23 with a bit rate of 5.3 Gbps was input to one connection board 53 . The amplitude of the input signal to each terminal of one connection substrate 53 was set to 150 mV/side. That is, the amplitude of the differential signal input to the pair of terminals of one connection board 53 was set to 300 mV. An oscilloscope 52 was connected to the other connection board 53 . The aperture amplitude of the eye pattern of the signal output from the other connection substrate 53 was observed by the oscilloscope 52 . The eye pattern aperture amplitude was measured in an atmosphere with a temperature of 25° C. and a relative humidity of 30 to 50%.

Below, the transmission characteristics, that is, the aperture amplitude of the eye pattern were evaluated in three stages of A, B, and C. A has an aperture amplitude of 110 mV or more. B is an aperture amplitude of 100 mV or more and less than 110 mV. C is less than 100 mV aperture amplitude. B is superior to C and A is superior to B in terms of transmission characteristics.

(3) Area of opening 2220 in insulating layer 222 and area of opening 2210 in conductive layer 221 The area of each opening 2220 in the insulating layer 222 and the area of each opening 2210 in each conductive layer 221 are measured by the following method, for example. be able to. Measurement can be performed using an image captured by an optical microscope, a scanning white interference microscope, a laser microscope, a scanning electron microscope (SEM), or the like from the Z direction perpendicular to the main surface 231 of the insulator portion 230. can. The area of the captured image is 25 mm ² .

It is possible to binarize the acquired rectangular captured image, extract each aperture 2210 and each aperture 2220, and obtain the area of each aperture 2210 and the area of each aperture 2220 based on the number of pixels. Then, the minimum area can be obtained from the areas of the openings 2210 and the maximum area can be obtained from the areas of the openings 2210 .

In addition, since the conductive layer 221 is located under the insulating layer 222, it may not be observed by an optical measuring instrument when the insulating layer 222 is colored. In that case, the area of each opening 2210 of the conductive layer 221 can be obtained by obtaining a three-dimensional image by, for example, 3D micro X-ray CT and performing the above-described image analysis on the conductive layer 221 .

Here, as the wiring board main body 210, a single-sided flexible printed wiring board manufactured by Nippon Mektron Co., Ltd. was used. The dimensions of the wiring board main body 210 were 20 mm in width and 150 mm in length. The insulating layer 240, which is the insulating substrate of the wiring board main body 210, was a polyimide film with a thickness of 12.5 μm. A copper foil having a thickness of 12 μm was formed as each signal line 22 on the main surface 241 of the insulating layer 240 . A pair of signal lines 22 constitutes one set of differential signal wirings, and 20 sets of operating signal wirings are formed on the main surface 241 . An insulating layer 252 that is an adhesive layer with a thickness of 15 μm and an insulating layer 251 with a thickness of 12.5 μm are disposed on the plurality of signal lines 22 . The insulating layer 251 was composed of a coverlay made of a polyimide film. With the above configuration, the thickness of wiring board main body 210 was 52 μm.

As examples, three kinds of flexible printed wiring boards 200 of Example 1, Example 2, and Example 3 were manufactured.

(Example 1)
A conductive layer 221 as an electromagnetic wave noise shielding layer was formed on the insulating layer 251 of the wiring board main body 210 . The conductive layer 221 is formed by applying a silver paste (product name: DD-1630L-245) manufactured by Kyoto Elex Co., Ltd. with a screen printer (manufactured by Micro Tech Co., Ltd.: MT-320T) to a thickness of 3 to 3. It was formed by printing on the insulating layer 251 under the condition of 5 μm.

The conductive layer 221 of Example 1 was a mesh-like conductor pattern with a line width of 50 μm. Each opening 2210 formed in the conductive layer 221 had a rhombic shape in which the diagonal line extending in the X direction was longer than the diagonal line extending in the Y direction. Each opening 2210 had a diagonal length extending in the Y direction of 500 μm and a diagonal length extending in the X direction of 2000 μm. The aperture ratio of the conductive layer 221 was 81%. The minimum area of each opening 2210 in the conductive layer 221 was 0.5 mm ² . The thickness of the conductive layer 221 was 4 μm.

An insulating layer 222 was formed over the conductive layer 221 . The insulating layer 222 was formed by using a screen printer (MT-320T manufactured by Micro Tech Co., Ltd.) using a polyamide-imide resin solution coating agent manufactured by Toyobo Co., Ltd. (product name: HR-16NN).

The insulating layer 222 of Example 1 was a mesh resin pattern with a line width of 50 μm. Each opening 2220 formed in the insulating layer 222 had a square shape with a pair of sides extending in the X direction and a pair of sides extending in the Y direction. Each side of each opening 2220 was 0.7 mm. A plurality of openings 2220 were arranged in a square lattice in the X and Y directions. The maximum area of the openings 2220 in the insulating layer 222 was 0.49 mm ² . The thickness of the insulating layer 222 was 6 μm.

(Example 2)
The wiring board main body 210 and the conductive layer 221 in Example 2 used those having the same configurations as those in Example 1. FIG.

The insulating layer 222 was formed using the same material and the same equipment as in Example 1. The insulating layer 222 in Example 2 was a mesh-like resin pattern. Each opening 2220 formed in the insulating layer 222 had a rhombic shape in which the diagonal line extending in the X direction was longer than the diagonal line extending in the Y direction. Each opening 2220 had a diagonal length extending in the Y direction of 600 μm and a diagonal length extending in the X direction of 1200 μm. The maximum area of the openings 2220 in the insulating layer 222 was 0.36 mm ² . The thickness of the insulating layer 222 was 7 μm.

(Example 3)
The wiring board main body 210 in Example 3 had the same configuration as in Example 1. FIG.

The conductive layer 221 was formed using the same material and the same equipment as in Example 1. FIG. The conductive layer 221 of Example 3 was a mesh-like conductor pattern with a line width of 60 μm. Each opening 2210 formed in the conductive layer 221 had a rhombic shape in which the diagonal line extending in the X direction was longer than the diagonal line extending in the Y direction. Each opening 2210 had a diagonal length of 260 μm extending in the Y direction and a diagonal length of 1500 μm extending in the X direction. The aperture ratio of the conductive layer 221 was 66%. The minimum area of each opening 2210 in the conductive layer 221 was 0.2 mm ² . The thickness of the conductive layer 221 was 7 μm.

The insulating layer 222 was formed using the same material and the same equipment as in Example 1. The insulating layer 222 in Example 3 was a mesh-like resin pattern. Each opening 2220 formed in the insulating layer 222 had a rhombic shape in which the diagonal line extending in the X direction was longer than the diagonal line extending in the Y direction. Each opening 2220 had a diagonal length extending in the Y direction of 190 μm and a diagonal length extending in the X direction of 850 μm. The maximum area of the openings 2220 in the insulating layer 222 was 0.08 mm ² . The thickness of the insulating layer 222 was 10 μm.

As comparative examples, two types of flexible printed wiring boards 200X of comparative examples 1 and 2 were manufactured.

(Comparative example 1)
In Comparative Example 1, the configuration was the same as in Example 1, except that the conductive layer in the shield member 220X was a solid pattern with a thickness of 5 μm without openings.

(Comparative example 2)
In Comparative Example 2, the configuration was the same as in Example 1, except that the insulating layer in the shield member 220X was a solid pattern with a thickness of 8 μm without openings.

(Evaluation results)

FIG. 8 is a table showing evaluation results in Examples 1-3 and Comparative Examples 1-2.

In Comparative Example 1, since the conductive layer in the shield member 220X is a solid pattern, the electric capacity is large, and the transmission characteristics at a bit rate of 5.3 Gbps are significantly impaired compared to Examples 1 to 3. was done. In the case of Comparative Example 1, frequent occurrence of communication errors may prevent proper data communication.

In Comparative Example 2, since the insulating layer in the shield member 220X is a solid pattern, the rigidity of the flexible printed wiring board 200X increases, resulting in loss of bending load, that is, flexibility.

On the other hand, in Examples 1 to 3, the bending load of the flexible printed wiring board 200 was small, and the transmission characteristics at the bit rate of 5.3 Gbps were good.

The present invention is not limited to the embodiments described above, and many modifications are possible within the technical concept of the present invention. Moreover, the effects described in the embodiments are merely enumerations of the most suitable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments.

22... Signal line 200... Flexible printed wiring board 221... Conductive layer 222... Insulating layer 230... Insulator part 2210... Opening (first opening) 2220... Opening (second opening)

Claims (17)

an insulator portion extending in a first direction;
a signal line arranged inside the insulator;
a conductive layer disposed on the main surface of the insulator portion and having a plurality of first openings;
an insulating layer disposed on the conductive layer and having a plurality of second openings;
A flexible printed wiring board characterized by: Two or more first openings among the plurality of first openings are arranged at positions overlapping with the signal line when viewed in a direction perpendicular to the main surface of the insulator portion,
The flexible printed wiring board according to claim 1, characterized in that: Each of the plurality of first openings has a length in the first direction longer than a length in a second direction perpendicular to the first direction,
The flexible printed wiring board according to claim 1 or 2, characterized in that: each of the plurality of first openings is rhomboid-shaped;
The flexible printed wiring board according to claim 3, characterized in that: The plurality of first openings are arranged in a matrix,
The flexible printed wiring board according to any one of claims 1 to 4, characterized in that: The conductive layer is mesh-like,
The flexible printed wiring board according to any one of claims 1 to 5, characterized in that: Two or more second openings among the plurality of second openings are arranged at a position overlapping with the signal line when viewed in a direction perpendicular to the main surface of the insulator part,
The flexible printed wiring board according to any one of claims 1 to 6, characterized in that: each of the plurality of second openings has a rectangular shape,
The flexible printed wiring board according to any one of claims 1 to 7, characterized in that: The plurality of second openings are arranged in a matrix,
The flexible printed wiring board according to any one of claims 1 to 8, characterized in that: The insulating layer is mesh-like,
The flexible printed wiring board according to any one of claims 1 to 9, characterized in that: The area of one of the plurality of second openings is smaller than the area of one of the plurality of first openings when viewed in a direction perpendicular to the main surface of the insulator portion. ,
The flexible printed wiring board according to any one of claims 1 to 10, characterized in that: The one first opening has the smallest area among the plurality of first openings,
The one second opening has the largest area among the plurality of second openings,
The flexible printed wiring board according to claim 11, characterized in that: The aperture ratio of the conductive layer is 40% or more and 90% or less.
The flexible printed wiring board according to any one of claims 1 to 12, characterized in that: A flexible printed wiring board according to any one of claims 1 to 13;
a first rigid printed wiring board to which a first end in the first direction of the flexible printed wiring board is connected;
a first electronic component mounted on the first rigid printed wiring board;
An electronic unit characterized by: a second rigid printed wiring board to which a second end in the first direction of the flexible printed wiring board is connected;
a second electronic component mounted on the second rigid printed wiring board;
15. The electronic unit according to claim 14, characterized in that: an electronic unit according to claim 14 or 15;
a housing in which the electronic unit is housed,
An electronic device characterized by: Prepare an insulator part inside which the signal line is arranged,
forming a conductive layer having a plurality of first openings on the main surface of the insulator section;
forming an insulating layer having a plurality of second openings on the conductive layer;
A method for manufacturing a flexible printed wiring board, characterized by:

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