Flexible printed wiring board, electronic unit, electronic device, and method for manufacturing flexible printed wiring board

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

[Technical field]

[0001] The present invention relates to a flexible printed wiring board. [Background technology]

[0002] Electronic devices, such as mobile phones, smartphones, tablet terminals, and digital cameras, have flexible printed wiring boards that serve as a transmission path for digital signals. As electronic devices become more powerful and functional, the amount of data handled by the electronic devices has increased dramatically, and the transmission speed of digital signals passing through the flexible printed wiring board has also increased. Therefore, there is a risk that the quality of digital signals passing through the flexible printed wiring board will be degraded due to electromagnetic noise generated from the rigid printed wiring board or electronic components mounted on the rigid printed wiring board in the electronic device. There is also a risk that the electromagnetic noise radiated from the flexible printed wiring board will cause malfunction of surrounding semiconductor devices.

[0003] In response to this, Patent Document 1 discloses a flexible printed wiring board that includes a ground layer that has the function of blocking electromagnetic noise. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2000-077802 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is a demand for smaller electronic devices, and therefore there is a demand for flexible printed wiring boards to have high flexibility so that they can be stored in small spaces.

[0006] An object of the present invention is to provide a flexible printed wiring board that has both an electromagnetic noise shielding effect and high flexibility. [Means for solving the problem]

[0007] Books First aspect of the disclosure The semiconductor device includes an insulating body portion extending in a first direction, a signal line disposed inside the insulating body portion, a conductive layer disposed on a main surface of the insulating body portion and having a plurality of first openings, and an insulating layer disposed on the conductive layer and having a plurality of second openings. Two or more of the first openings are arranged at positions overlapping the insulating layer when viewed in a direction perpendicular to a main surface of the insulating body portion. The present invention is characterized in that Flexible printed wiring board . A second aspect of the present disclosure is a flexible printed wiring board comprising an insulator portion extending in a first direction, a signal line arranged inside the insulator portion, a conductive layer arranged on a main surface of the insulator portion and having a plurality of first openings, and an insulating layer arranged on the conductive layer and having a plurality of second openings, wherein two or more of the plurality of second openings are arranged in a position overlapping the conductive layer when viewed in a direction perpendicular to the main surface of the insulator portion.

[0008] Books Third aspect of disclosure preparing an insulating body having a signal line disposed therein; forming a conductive layer having a plurality of first openings on a main surface of the insulating body; and forming an insulating layer having a plurality of second openings on the conductive layer. A method for manufacturing a flexible printed circuit board . Effect of the Invention

[0009] According to the present invention, it is possible to provide a flexible printed wiring board that achieves both an electromagnetic noise shielding effect and high flexibility. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram of a digital camera that is an image capturing device as an example of an electronic device according to an embodiment. [Diagram 2] 1A is an explanatory diagram of an imaging unit according to an embodiment, and FIG. 1B is a cross-sectional view of a flexible printed wiring board taken along line IIB-IIB in FIG. [Diagram 3] 1 is an explanatory diagram of a flexible printed wiring board according to an embodiment, viewed from the main surface side of an insulating layer. FIG. [Figure 4] 1A is an explanatory diagram of a conductive layer according to an embodiment, and FIG. 1B is an explanatory diagram of an insulating layer according to an embodiment. [Diagram 5]5(a) to 5(c) are explanatory views showing an example of a method for manufacturing a flexible printed wiring board according to an embodiment. [Figure 6] 5(a) to 5(c) are explanatory views showing an example of a method for manufacturing a flexible printed wiring board according to an embodiment. [Figure 7] 1A is a schematic diagram of an apparatus used to evaluate the flexibility of the flexible printed wiring board of the embodiment and the flexible printed wiring board of the comparative example, and FIG. 1B is a schematic diagram of a system used to evaluate the transmission characteristics of the flexible printed wiring board of the embodiment and the flexible printed wiring board of the comparative example. [Figure 8] 1 is a table showing evaluation results in Examples 1 to 3 and Comparative Examples 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram of a digital camera 600, which is an imaging device as an example of an electronic device according to an embodiment. The digital camera 600 is a lens-interchangeable digital camera, and includes a camera body 601. A lens unit (lens barrel) 602 including a lens is detachably attached to the camera body 601. The camera body 601 includes a housing 611, an imaging unit 100, which is an example of an electronic unit, and a wireless communication unit 150. The imaging unit 100 and the wireless communication unit 150 are stored inside the housing 611.

[0012] The imaging unit 100 includes a printed circuit board 101, a printed circuit board 102, and a flexible printed wiring board 200 that electrically connects the printed circuit boards 101 and 102. The printed circuit board 101 is an example of a first electronic module. The printed circuit board 102 is an example of a second electronic module. By using the flexible printed wiring board 200 to connect the printed circuit boards 101 and 102, the wiring structure can be made lighter than a coaxial cable.

[0013] Printed circuit board 101 includes rigid printed wiring board 110 and semiconductor device 111 mounted on rigid printed wiring board 110. Printed circuit board 102 includes rigid printed wiring board 120 and semiconductor device 121 mounted on 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.

[0014] In this embodiment, the semiconductor device 111 is an image sensor. The image sensor is, for example, a complementary metal oxide semiconductor (CMOS) image sensor or a charge coupled device (CCD) image sensor. The image sensor has a function of converting light incident through the lens unit 602 into an electric signal. In this embodiment, the semiconductor device 121 is a digital signal processor. The digital signal processor has a function of acquiring an electric signal indicating image data from the semiconductor device 111, which is an image sensor, correcting the acquired electric signal, and generating corrected image data. In this embodiment, the imaging unit 100 has a camera shake correction function and includes a motor 160, which is an example of a drive source that drives 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 be flexible.

[0015] 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 disposed in 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 performing wireless communication with an external device such as a PC or a wireless router via the antenna. In this embodiment, the wireless communication IC 152 is capable of transmitting and receiving data via the antenna. Specifically, the wireless communication IC 152 modulates a digital signal indicating image data acquired from the semiconductor device 121 and transmits the modulated digital signal from the antenna as radio waves of a communication frequency of a wireless standard. The wireless communication IC 152 demodulates the radio waves received by the antenna into a digital signal indicating image data. The wireless communication IC 152 performs wireless communication with an external device in compliance with a standard such as Wi-Fi (registered trademark) or Bluetooth (registered trademark).

[0016] FIG. 2(a) is an explanatory diagram of an imaging unit 100 according to an embodiment. As shown in FIG. 2(a), 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. The 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 short side direction perpendicular to the X direction. The Y direction is an example of a second direction. The Z direction perpendicular to the X direction and the Y direction is the thickness direction of the flexible printed wiring board 200. The flexible printed wiring board 200 is flexible and can be bent and deformed.

[0017] The flexible printed wiring board 200 has an end 201 which is an example of a first end in the X direction, and an end 202 which is an example of a second end in the X direction. The end 202 is located on the opposite side of the flexible printed wiring board 200 to the end 201.

[0018] A connector 112 is mounted on 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 flexible printed wiring board 200 is attached to connector 112. As a result, end 201 of flexible printed wiring board 200 is electrically and mechanically connected to rigid printed wiring board 110.

[0019] A connector 122 is mounted on 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 flexible printed wiring board 200 is attached to connector 122. As a result, end 202 of flexible printed wiring board 200 is electrically and mechanically connected to rigid printed wiring board 120.

[0020] With the above configuration, semiconductor device 111 and semiconductor device 121 are electrically connected via rigid printed wiring board 110, flexible printed wiring board 200, and rigid printed wiring board 120 so as to be able to communicate with each other.

[0021] Fig. 2(b) is a cross-sectional view of the flexible printed wiring board 200 taken along the line IIB-IIB in Fig. 2(a). As shown in Fig. 2(b), the flexible printed wiring board 200 has a wiring board body 210 and a shielding member 220.

[0022] The wiring board body 210 has an insulator section 230 and the above-mentioned multiple signal lines 22. The insulator section 230 is made of a material having electrical insulation. Each signal line 22 is made of a material having electrical conductivity. The wiring board body 210, i.e., the insulator section 230 and the multiple signal lines 22 are formed to extend in the X direction. The multiple signal lines 22 are arranged inside the insulator section 230 at intervals in the Y direction. Note that FIG. 2(b) illustrates two of the multiple signal lines 22. The insulator section 230 is formed in a sheet shape and has a pair of main surfaces 231, 232. The shielding member 220 may be arranged on either one of the pair of main surfaces 231, 232, and is arranged on the main surface 231 in this embodiment. Note that the shielding member 220 may be arranged on each of the pair of main surfaces 231, 232.

[0023] The insulator portion 230 includes a plurality of insulating layers 240, 251, and 252. The plurality of insulating layers 240, 251, and 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. The plurality of signal lines 22 are disposed on the main surface 241. The insulating layer 251 is disposed on the main surface 241 and on the plurality of signal lines 22.

[0024] In this embodiment, the insulator section 230 has an insulating layer 252 disposed 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. Note that if the insulating layer 251 has an adhesive function, the insulating layer 252 may be omitted.

[0025] The insulating layer 240 will be described in detail below. The material of the insulating layer 240, which is an insulating substrate, is preferably a resin. Examples of the resin include polyimide-based resins such as polyimide, polyamide, and polyamideimide, thermosetting resins such as epoxy, and thermoplastic resins such as liquid crystal polymers. Among these, polyimide or liquid crystal polymers are preferable. Polyimide has excellent heat resistance and mechanical properties, and is easily available commercially. In addition, liquid crystal polymers have a low relative dielectric constant, making them suitable for high-speed signal transmission applications, and have low moisture absorption and excellent dimensional stability.

[0026] The thickness of the insulating layer 240 in the Z direction is preferably 10 μm or more and 100 μm or less. When 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 the surrounding electronic components can be secured, and changes in the characteristic impedance of the signal line 22 can be suppressed. Furthermore, when 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 sufficient flexibility can be obtained in the flexible printed wiring board 200. From the above viewpoints, the thickness of the insulating layer 240 in the Z direction is more preferably 12 μm or more and 75 μm or less.

[0027] Next, each signal line 22 will be described in detail. Each signal line 22 is a wiring that can be used to transmit digital data signals. As the amount of signal transmission increases, it is preferable to configure differential signal wiring in which a pair of signal lines 22 out of the multiple signal lines 22 is one set. Note that the multiple signal lines 22 may include wiring that transmits single-ended signals such as control signals and response signals. Furthermore, the flexible printed wiring board 200 may have a ground line (not shown) in addition to the signal lines 22.

[0028] The method for forming the signal line 22 is not particularly limited, but the signal line 22 can be formed by, for example, laminating metal foil, metal plating, inkjet process, or the like. When using copper foil as the metal foil, a film laminated with an adhesive or the like can be used to form the required transmission line pattern by a photolithography / etching process. When using an inkjet process, the required pattern can be drawn with a polymer ink containing metal particles, and the pattern can be baked at a temperature equal to or lower than the glass transition point (Tg) of the insulating layer 240 to form the signal line 22. The thickness of the signal line 22 is not particularly limited, but is preferably, for example, 0.1 μm or more and 20 μm or less.

[0029] Next, the insulating layer 251 will be described in detail. Plastic and / or insulating resin can be used for the insulating layer 251. The plastic used for the insulating layer 251 includes so-called engineering plastic. That is, the plastic used for the insulating layer 251 includes, for example, polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyamide, polyimide, polyimideamide, and polyetherimide. The plastic used for the insulating layer 251 includes, for example, polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), and polyether ether ketone (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. When heat resistance is required, it is preferable to use an aramid film or a polyimide film.

[0030] The insulating resin used in the insulating layer 251 may be any resin having electrical insulation properties, such as a thermosetting resin or an ultraviolet curing resin. Examples of the thermosetting resin include phenolic resin, acrylic resin, epoxy resin, melamine resin, silicone resin, and acrylic-modified silicone resin. Examples of the ultraviolet curing resin include epoxy acrylate resin, polyester acrylate resin, and their methacrylate-modified products. The curing form may be any of heat curing, ultraviolet curing, and electron beam curing. In addition, other additives such as color pigments, flame retardants, antioxidants, lubricants, dust prevention agents, and curing accelerators may be blended as necessary.

[0031] The method of forming the insulating layer 251 is not particularly limited, but the following method can be used to coat the insulating resin on the plastic. For example, a solution obtained by dissolving the insulating resin in a solvent can be applied by a gravure coating method, a kiss coating method, a die coating method, a blade method, a roll coating method, a knife coating method, a spray coating method, a bar coating method, a spin coating method, or a dip coating method. The solvent can be appropriately selected depending on the type of resin used. For example, ketone-based solvents such as acetone, methyl ethyl ketone, and cyclohexanone, and alcohol-based solvents such as methanol, ethanol, propanol, ethylene glycol, glycerin, and propylene glycol monomethyl ether can be used. In addition, acids such as acetic acid, amide-based solvents such as formamide, dimethylacetamide, and N-methylpyrrolidone, nitrile-based solvents such as acetonitrile and propylonitrile, and ester-based solvents such as methyl acetate and ethyl acetate can be used. Carbonate-based solvents such as dimethyl carbonate and diethyl carbonate can also be used. When applying, a heating or drying process may be performed to volatilize the solvent as necessary. For heating and drying, a heating device and a drying device such as a hot air dryer or an infrared heater can be used, and the heating temperature, drying temperature, heating time, and drying time can be appropriately selected.

[0032] 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, sliding properties and bending properties are improved. From the above viewpoints, the thickness of the insulating layer 251 in the Z direction is more preferably 10 μm or more and 30 μm or less. Furthermore, the volume resistance value of the insulating layer 251 is preferably 10 9 Ω·cm or more is preferable, and 10 13 It is more preferable that the resistivity is Ω·cm or more.

[0033] 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 product of an adhesive. It is preferable that the insulating layer 252 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.

[0034] It is preferable that the insulating layer 252 is capable of sufficiently covering each signal line 22, which is a transmission line, and is smooth. Therefore, it is preferable that the thickness of the insulating layer 252 in the Z direction is 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 adhere more firmly. Furthermore, when the thickness of the insulating layer 252 is 50 μm or less, it is possible to suppress the adhesive from seeping out to the side from between the insulating layers 240 and 251. From the above viewpoints, 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.

[0035] The method for forming the insulating layer 252 is not particularly limited, but examples thereof include a method in which a sheet-like adhesive is bonded and cured, and a method in which a liquid adhesive is applied using a dispenser or printing method, etc., and then cured by heat or ultraviolet rays.

[0036] The wiring board main body 210 has been described above, but the shielding member 220 will be described in detail below. The shielding member 220 is a sheet-like member, and includes a conductive layer 221 and an insulating layer 222. The conductive layer 221 is disposed on the main surface 231 of the insulator portion 230. The insulating layer 222 is disposed on the conductive layer 221. The conductive layer 221 is a shielding layer that blocks electromagnetic noise, and is made of a conductive material. The insulating layer 222 is a protective layer that protects the conductive layer 221 from contact with the surrounding members of the flexible printed wiring board 200, and is made of an electrically insulating material.

[0037] Although the conductive layer 221 does not need to be electrically connected to any member, in this embodiment, it is used as a path for a return current of a signal passing through the signal line 22, and is a part of the ground line. That is, the conductive layer 221 is electrically connected to the ground lines of the rigid printed wiring boards 110 and 120.

[0038] Since the flexible printed wiring board 200 has the conductive layer 221, it is possible to ensure a shielding effect against electromagnetic noise radiated from the flexible printed wiring board 200 and external electromagnetic noise transmitted to the flexible printed wiring board 200. In this embodiment, the conductive layer 221 has a plurality of 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, it is possible to ensure the flexibility of the conductive layer 221, i.e., the flexibility of the flexible printed wiring board 200.

[0039] 3 is an explanatory diagram of the flexible printed wiring board 200 viewed from the main surface 241 side of the 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 for convenience of explanation, the insulating layers 251 and 252 are omitted. Also, for convenience of explanation, the insulating layer 222 and a part of the conductive layer 221 are omitted. The Z direction is also a direction perpendicular to the main surface 231.

[0040] The following description focuses on one of the multiple signal lines 22. When viewed in the Z direction, two or more of the multiple openings 2210 are arranged at positions overlapping one signal line 22. Regarding these two or more openings 2210, the two or more openings 2210 are arranged opposite one signal line 22 such that a part or the whole of each of the two or more openings 2210 overlaps a part of one signal line 22 when viewed in the Z direction.

[0041] Fig. 4(a) is an explanatory diagram of the conductive layer 221 according to the embodiment. Fig. 4(a) illustrates a portion of the conductive layer 221 as viewed in the Z direction. From the viewpoint of ensuring high flexibility in the flexible printed wiring board 200, it is preferable that the multiple openings 2210 are arranged in a matrix. In this embodiment, the conductive layer 221 is formed in a mesh shape, and thereby the multiple openings 2210 are arranged in a matrix.

[0042] The shape of each opening 2210 can be set arbitrarily. The shape of each opening 2210 as viewed in the Z direction is preferably, for example, a rectangle, a polygon, a circle, an ellipse, or the like. Among polygons, a hexagon is preferable. Examples of rectangles include a trapezoid, a parallelogram, a rhombus, a rectangle, and a square.

[0043] Here, the length of each opening 2210 in the X direction is L1. The length of each opening 2210 in the Y direction is L2. It is preferable that each opening 2210 has a shape in which the length L1 in the X direction is longer than the length L2 in the Y direction. This makes it easier for a return current, which is a current that cancels out noise, to flow in the conductive layer 221, and makes it possible to suppress electromagnetic noise emitted from the flexible printed wiring board 200.

[0044] In particular, each opening 2210 is preferably rhombic in shape elongated in the X direction. Each of the lengths L1 and L2 is the length of a diagonal line passing through two mutually opposing interior angles among the four interior angles of the rhombus. That is, the diagonal line of the length L1 extends in the X direction, and the diagonal line of the length L2 extends in the Y direction. In addition, when each opening 2210 is rhombic, it becomes easier to arrange two or more openings 2210 along one signal line 22. By each opening 2210 being rhombic in shape elongated in the X direction, it becomes easier for a return current to flow in the conductive layer 221, and the electromagnetic noise emitted from the flexible printed wiring board 200 can be more effectively suppressed.

[0045] The method of forming the conductive layer 221 is not particularly limited, but the conductive layer 221 can be formed by the following method. 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 a subtractive method, an electroless plating method, an electrolytic plating method, or a physical vapor deposition method. Examples of physical vapor deposition methods include a vacuum deposition method and a sputtering method. In addition, a method of forming the conductive layer 221 by arranging a mask conforming to the shape of the opening on the main surface 231 side, forming a conductive film by a coating liquid coating method such as bar coating or slit coating, and then removing the mask, can be mentioned. In addition, a method of forming the conductive layer 221 by a screen printing method in which a conductive paste is printed using a screen plate having an opening pattern in advance, an inkjet method in which a coating liquid is discharged along a predetermined pattern, or a dot dispenser method can be mentioned.

[0046] 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 opening 2210 per unit area when the conductive layer 221 is viewed in the Z direction. The unit area includes a part of the conductive layer 221 and a part of the multiple openings 2210. When the aperture ratio of the conductive layer 221 is 40% or more, the aperture amplitude value of the eye pattern in the signal transmission can be sufficiently increased, and the transmission failure of the digital signal transmitted through the signal line 22 can be reduced. When the aperture ratio of the conductive layer 221 is 90% or less, the electromagnetic noise can be sufficiently shielded. Therefore, the electromagnetic noise radiated from the signal line 22, that is, the flexible printed wiring board 200, can be effectively reduced. That is, the electromagnetic noise affecting the wireless communication of the wireless communication unit 150 can be effectively reduced. From the above viewpoints, it is more preferable that the aperture ratio of the conductive layer 221 is 50% or more and 85% or less.

[0047] Moreover, in each opening 2210, the length L1 is preferably 1.5 times or more the length L2. Moreover, the length L1 is preferably 1.5 mm or less. When the major axis L1 is 1.5 mm or less, the effect of shielding the electromagnetic noise emitted from the signal line 22, i.e., the flexible printed wiring board 200, is enhanced. This makes it possible to effectively reduce the electromagnetic noise that affects the wireless communication of the wireless communication unit 150. From the above viewpoints, it is more preferable that the length L1 is 1.2 mm or less.

[0048] When the two signal lines 22 are differential signal lines, it is preferable that the length L2 of each opening 2210 is shorter than the distance between the two signal lines 22. This makes it possible to suppress the occurrence of common mode noise in the two signal lines 22, and thus to suppress the occurrence of defects in signal transmission.

[0049] Examples of the conductive material constituting the conductive layer 221 include metals such as gold, silver, copper, aluminum, and nickel. Examples of the conductive material constituting the conductive layer 221 include metal particles and metal fibers. Examples of the conductive material constituting the conductive layer 221 include, in addition to metals, conductive resin compositions such as carbon nanotubes in which a conductive filler is mixed with a resin, and conductive polymers such as polythiophene and polypyrrole.

[0050] When forming the conductive layer 221 by coating, it is preferable to use a silver paste containing highly conductive silver particles and a resin binder as the conductive material. In addition to the silver paste, a gold paste, a copper paste, a carbon paste, etc. may also be used.

[0051] The electrical resistance value of the conductive layer 221 is preferably 0.01 Ω or more and 5 Ω or less, and more preferably 0.01 Ω or more and 1 Ω or less, from the viewpoint of electromagnetic noise shielding capability.

[0052] 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, when common mode noise occurs, a return current flows more easily through the conductive layer 221, and the amount of radiated 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 viewpoints, the thickness of the conductive layer 221 in the Z direction is more preferably 2 μm or more and 10 μm or less.

[0053] Fig. 4(b) is an explanatory diagram of the insulating layer 222 according to the embodiment. Fig. 4(b) illustrates a portion of the insulating layer 222 viewed in the Z direction. In this embodiment, the insulating layer 222 has a plurality of openings 2220. Each opening 2220 is a second opening. Each opening 2220 is a through hole. By having the insulating layer 222 have a plurality of openings 2220, it is possible to ensure higher flexibility in the flexible printed wiring board 200.

[0054] Further, when viewed in the Z direction, two or more of the multiple openings 2220 are arranged at positions overlapping one signal line 22. To explain these two or more openings 2220, the two or more openings 2220 are arranged facing one signal line 22 so that a part or the whole of each of the two or more openings 2220 overlaps a part of one signal line 22 when viewed in the Z direction.

[0055] From the viewpoint of ensuring high flexibility in the flexible printed wiring board 200, it is preferable that the multiple openings 2220 are arranged in a matrix. In this embodiment, the insulating layer 222 is formed in a mesh shape, and thereby the multiple openings 2220 are arranged in a matrix. By arranging the multiple openings 2220 in a matrix, it is possible to suppress plastic deformation of the insulating layer 222 due to deformation stress, that is, curling of the flexible printed wiring board 200.

[0056] When viewed in the Z direction, the area of ​​one of the multiple openings 2210 is defined as S1. The one opening 2210 has the smallest area among the multiple openings 2210. When viewed in the Z direction, the area of ​​one of the multiple openings 2220 is defined as S2. The one opening 2220 has the largest area among the multiple openings 2220.

[0057] As viewed in the Z direction, the area S2 of the opening 2220 of the insulating layer 222 is preferably smaller than the area S1 of the opening 2210 of the conductive layer 221. This makes it possible to effectively prevent the conductive layer 221 located below the insulating layer 222 from contacting members arranged around the flexible printed wiring board 200.

[0058] The shape of each opening 2220 can be set arbitrarily. The shape of each opening 2220 as viewed in the Z direction is preferably, for example, a rectangle, a polygon, a circle, an ellipse, or the like. Among polygons, a hexagon is preferable. Examples of rectangles include a trapezoid, a parallelogram, a rhombus, a rectangle, and a square. Considering the flexibility of the flexible printed wiring board 200, the shape of each opening 2220 as viewed in the Z direction is preferably a rectangle.

[0059] The insulating resin used in the insulating layer 222 may be any resin having electrical insulation properties, and examples thereof include thermosetting resin, ultraviolet curing resin, and a coating agent made of a resin solution in which a cured film component is dispersed in a solvent. Examples of the thermosetting resin include phenol resin, acrylic resin, epoxy resin, polyamide resin, polyamideimide resin, polyimide resin, melamine resin, silicone resin, and acrylic modified silicone resin. Examples of the ultraviolet curing resin include epoxy acrylate resin, polyester acrylate resin, and their methacrylate modified products. Examples of the resin solution include polyester urethane resin and polyamideimide resin dissolved in an organic solvent. In addition, if necessary, color pigments, flame retardants, antioxidants, lubricants, plasticizers, viscosity adjusters, dust prevention agents, curing accelerators, inorganic fillers such as silica and carbon black, organic fillers such as silicone particles and polyester particles, and other additives may be blended. As the insulating resin of the insulating layer 222, it is preferable to use a coating agent made of a resin solution in which a cured film component is dispersed in a solvent. By using this coating agent as the insulating resin of the insulating layer 222, shrinkage due to a curing reaction is small, and it is possible to suppress warping of the flexible printed wiring board 200. Furthermore, it is more preferable to use, as the insulating resin of the insulating layer 222, a coating agent in which a polyamide-imide resin having flexibility and heat resistance is dissolved in a solvent.

[0060] The insulating layer 222 can be formed by the following methods. For example, a mask conforming to the shape of the opening 2220 is placed on the conductive layer 221, an insulating film is formed by a coating liquid coating method such as bar coating or slit coating, and then the mask is removed to form the insulating layer 222. 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 an inkjet method or a dot dispenser method in which a coating liquid is ejected along a predetermined pattern to form the insulating layer 222.

[0061] The thickness of the insulating layer 222 in the Z direction is preferably thicker than the thickness of the conductive layer 221 in the Z direction from the viewpoint of preventing the conductive layer 221 from contacting the peripheral members of the flexible printed wiring board 200. The thickness of the insulating layer 222 in the Z direction is preferably 5 μm or more and 20 μm or less. When the thickness of the insulating layer 222 in the Z direction is 5 μm or more, the conductive layer 221 can be effectively prevented from contacting the peripheral members of the flexible printed wiring board 200. When 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 more effectively increased. From the above viewpoints, the thickness of the insulating layer 222 in the Z direction is more preferably 6 μm or more and 10 μm or less.

[0062] A preferred example of a method for manufacturing the flexible printed wiring board 200 will be described in detail below. A screen printing method that can form the conductive layer 221 and the insulating layer 222 on the insulator part 230 at room temperature and normal pressure is preferred. Figures 5(a) to 5(c) and 6(a) to 6(c) are explanatory views showing an example of a method for manufacturing the flexible printed wiring board 200 according to an embodiment.

[0063] First, a wiring board main body 210 is prepared as shown in Fig. 5(a). As shown in Fig. 2(b), the wiring board main body 210 includes an insulator section 230 and a plurality of signal lines 22 arranged inside the insulator section 230. A screen plate 301 is arranged on a main surface 231 that is the main surface of the insulator section 230. An opening pattern having a shape of the conductive layer 221 to be formed is formed on the screen plate 301. A conductive paste P1, which is the material of the conductive layer 221, is arranged on the screen plate 301.

[0064] Next, as shown in Fig. 5(b), the conductive paste P1 is spread to a predetermined thickness on the screen plate 301 by a scraper 302. Next, as shown in Fig. 5(c), the conductive paste P1 is transferred onto the main surface 231 by a rubber squeegee 303. The conductive paste P1 transferred onto the main surface 231 is solidified, thereby forming a conductive layer 221 on the main surface 231.

[0065] 6(a), a screen plate 311 is placed on the conductive layer 221, which is on the conductive layer. An opening pattern having a shape of the insulating layer 222 to be formed is formed in the screen plate 311. An insulating paste P2, which is the material of the insulating layer 222, is placed on the screen plate 311.

[0066] Next, as shown in Fig. 6(b), the insulating paste P2 is spread to a predetermined thickness on the screen plate 311 by a scraper 312. Next, as shown in Fig. 6(c), the insulating paste P2 is transferred onto the conductive layer 221 by a rubber squeegee 313. The insulating paste P2 transferred onto the conductive layer 221 is solidified, thereby forming an insulating layer 222 on the conductive layer 221.

[0067] According to the above manufacturing method, the conductive layer 221 and the insulating layer 222 can be easily formed, and the manufacturing time can be shortened.

[0068] (Example) Next, an example and a comparative example to be compared with the example 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 board of the example and the flexible printed wiring board of the comparative example will be evaluated below.

[0069] For each of the example and comparative example, 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 pairs of differential signal wiring was used.

[0070] The evaluation methods for the flexible printed wiring boards according to the examples and comparative examples will be described below.

[0071] (1) Bending load The flexible printed wiring boards of the examples and the flexible printed wiring boards of the comparative examples were each bent and the flexibility thereof was evaluated based on the rebound load.

[0072] 7(a) is a schematic diagram of an apparatus used to evaluate the flexibility of the flexible printed wiring board 200 of the embodiment and the flexible printed wiring board 200X of the comparative example. The flexible printed wiring board 200 of the embodiment has a wiring board main body 210 and a shielding member 220. The flexible printed wiring board 200X of the comparative example has a wiring board main body 210 and a shielding member 220X.

[0073] 7(a), the flexible printed wiring boards 200, 200X are arranged horizontally so that the shielding members 220, 220X are on the inside. The vertical repulsive force of one end of the flexible printed wiring boards 200, 200X when the end is bent 180 degrees with a curvature of 3 mm was evaluated using a digital force gauge 41, "ZTA-2N" manufactured by Imada Co., Ltd.

[0074] The bending load is an index for quantitatively judging the flexibility of a flexible printed wiring board. Generally, the greater the bending load of a flexible printed wiring board, the lower the flexibility of the flexible printed wiring board, i.e., the harder and stiffer the flexible printed wiring board is. Generally, the lower the flexibility of a flexible printed wiring board, the more difficult it is to attach the flexible printed wiring board to an electronic module. Furthermore, when a flexible printed wiring board is connected to two electronic modules, this can cause a factor in impeding the driving of one electronic module when it is driven relative to the other electronic module.

[0075] The bending load was evaluated in three stages: A, B, and C. A is a bending load less than 200 mN. B is a bending load between 200 mN and 300 mN. C is a bending load of 300 mN or more. In terms of bending load, B is better than C, and A is better than B.

[0076] (2) Transmission characteristics (eye pattern) 7(b) is a schematic diagram of a system 500 used to evaluate the transmission characteristics of the flexible printed wiring board 200 of the embodiment and the flexible printed wiring board 200X of the comparative example. This system 500 is composed of a signal generator 51, M8041A manufactured by Agilent Technologies, an oscilloscope 52, 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.

[0077] Flexible printed wiring board 200 of the embodiment and flexible printed wiring board 200X of the comparative example were connected between a pair of connection boards 53 in a suspended state. Signal generator 51 was connected to one of the connection boards 53, and a pseudo-random signal of PRBS23 with a bit rate of 5.3 Gbps was input to one of the connection boards 53. The amplitude of the input signal to each terminal of one of the connection boards 53 was 150 mV / side. That is, the amplitude of the differential signal input to the pair of terminals of one of the connection boards 53 was 300 mV. An oscilloscope 52 was connected to the other of the connection boards 53. The oscilloscope 52 was used to observe the opening amplitude of the eye pattern of the signal output from the other of the connection boards 53. The opening amplitude of the eye pattern was measured in an atmosphere with a temperature of 25° C. and a relative humidity of 30 to 50%.

[0078] Below, the transmission characteristics, i.e., the opening amplitude of the eye pattern, were evaluated into three levels: A, B, and C. A is an opening amplitude of 110mV or more. B is an opening amplitude of 100mV or more but less than 110mV. C is an opening amplitude of less than 100mV. In terms of transmission characteristics, B is better than C, and A is better than B.

[0079] (3) Area of ​​the opening 2220 in the insulating layer 222 and area of ​​the opening 2210 in the conductive layer 221 The area of ​​each opening 2220 in the insulating layer 222 and the area of ​​the opening 2210 in each conductive layer 221 can be measured, for example, by the following method. The area can be measured using an image captured by an optical microscope, a scanning white light interference microscope, a laser microscope, a scanning electron microscope (SEM), or the like in the Z direction perpendicular to the main surface 231 of the insulator part 230. The area of ​​the captured image is 25 mm 2 Let us assume that.

[0080] The acquired rectangular captured image is binarized to extract each opening 2210 and each opening 2220, and the area of ​​each opening 2210 and each opening 2220 can be calculated based on the number of pixels. Then, the minimum area can be calculated from the areas of each opening 2210, and the maximum area can be calculated from the areas of each opening 2210.

[0081] In addition, since the conductive layer 221 is located under the insulating layer 222, it may not be possible to observe the conductive layer 221 with an optical measuring device when the insulating layer 222 is colored, etc. In that case, a three-dimensional image is obtained by, for example, a 3D micro X-ray CT, and the above-mentioned image analysis is performed on the conductive layer 221, whereby the area of ​​each opening 2210 of the conductive layer 221 can be obtained.

[0082] Here, a single-sided flexible printed wiring board manufactured by Nippon Mektron Co., Ltd. was used as the wiring board body 210. The dimensions of the wiring board body 210 were width 20 mm and length 150 mm. The insulating layer 240, which is an insulating substrate of the wiring board body 210, was a polyimide film having a thickness of 12.5 μm. On the main surface 241 of this insulating layer 240, copper foil having a thickness of 12 μm was formed as each signal line 22. A pair of signal lines 22 constituted one set of differential signal wiring, and 20 sets of differential signal wiring were formed on the main surface 241. On the multiple signal lines 22, an insulating layer 252, which was an adhesive layer having a thickness of 15 μm, and an insulating layer 251 having a thickness of 12.5 μm were arranged. The insulating layer 251 was composed of a coverlay made of a polyimide film. With the above configuration, the thickness of the wiring board body 210 was 52 μm.

[0083] As examples, three types of flexible printed wiring boards 200, namely, Example 1, Example 2, and Example 3, were manufactured.

[0084] Example 1 Conductive layer 221, which is an electromagnetic noise shielding layer, was formed on insulating layer 251 of wiring board body 210. Conductive layer 221 was formed by printing silver paste (product name: DD-1630L-245) manufactured by Kyoto Elex Co., Ltd. on insulating layer 251 using a screen printer (MT-320T manufactured by Micro-Tec Co., Ltd.) under conditions such that the thickness would be 3 to 5 μm.

[0085] 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 was a rhombus with a diagonal line extending in the X direction longer than a diagonal line extending in the Y direction. Each opening 2210 had a diagonal line extending in the Y direction with a length of 500 μm and a diagonal line extending in the X direction with a length 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 conductive layer 221 had a thickness of 4 μm.

[0086] An insulating layer 222 was formed on the conductive layer 221. The insulating layer 222 was formed by using a polyamideimide resin soluble coating agent (product name: HR-16NN) manufactured by Toyobo Co., Ltd., using a screen printing machine (MT-320T manufactured by Micro-Tech Co., Ltd.).

[0087] The insulating layer 222 in Example 1 was a mesh-like resin pattern with a line width of 50 μm. Each opening 2220 formed in the insulating layer 222 was a square having 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. The multiple openings 2220 were arranged in a square lattice pattern in the X direction and Y direction. The maximum area of ​​each opening 2220 in the insulating layer 222 was 0.49 mm. 2 The insulating layer 222 had a thickness of 6 μm.

[0088] Example 2 In the second embodiment, wiring board body 210 and conductive layer 221 had the same configuration as in the first embodiment.

[0089] The insulating layer 222 was formed using the same material and the same device 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 was a rhombus with a diagonal line extending in the X direction longer than a diagonal line extending in the Y direction. Each opening 2220 had a diagonal line extending in the Y direction with a length of 600 μm and a diagonal line extending in the X direction with a length of 1200 μm. The maximum area of ​​each opening 2220 in the insulating layer 222 was 0.36 mm 2 The insulating layer 222 had a thickness of 7 μm.

[0090] Example 3 The wiring board body 210 in the third embodiment had the same configuration as that in the first embodiment.

[0091] The conductive layer 221 was formed using the same material and the same device as in Example 1. The conductive layer 221 in Example 3 was a mesh-like conductor pattern with a line width of 60 μm. Each opening 2210 formed in the conductive layer 221 was a rhombus with a diagonal line extending in the X direction longer than a diagonal line extending in the Y direction. Each opening 2210 had a diagonal line extending in the Y direction with a length of 260 μm and a diagonal line extending in the X direction with a length of 1500 μm. 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 conductive layer 221 had a thickness of 7 μm.

[0092] The insulating layer 222 was formed using the same material and the same device 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 was a rhombus with a diagonal line extending in the X direction longer than a diagonal line extending in the Y direction. Each opening 2220 had a diagonal line extending in the Y direction with a length of 190 μm and a diagonal line extending in the X direction with a length of 850 μm. The maximum area of ​​each opening 2220 in the insulating layer 222 was 0.08 mm2 The insulating layer 222 had a thickness of 10 μm.

[0093] As comparative examples, two types of flexible printed wiring boards 200X, Comparative Example 1 and Comparative Example 2, were manufactured.

[0094] Comparative Example 1 Comparative Example 1 had the same configuration as Example 1, except that the conductive layer in the shield member 220X was a solid pattern with a thickness of 5 μm that had no openings.

[0095] Comparative Example 2 Comparative Example 2 had the same configuration as Example 1, except that the insulating layer in the shielding member 220X was a solid pattern with a thickness of 8 μm and no openings.

[0096] (Evaluation Results)

[0097] FIG. 8 is a table showing the evaluation results in Examples 1 to 3 and Comparative Examples 1 and 2.

[0098] In Comparative Example 1, since the conductive layer in the shielding 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. In the case of Comparative Example 1, there is a risk that proper data communication cannot be performed due to frequent occurrence of communication errors.

[0099] In Comparative Example 2, the insulating layer of the shielding member 220X was a solid pattern, and as a result, the rigidity of the flexible printed wiring board 200X was large, resulting in a loss of bending load, that is, flexibility.

[0100] In contrast to this, in Examples 1 to 3, the bending load of the flexible printed wiring board 200 was small, and the transmission characteristics at a bit rate of 5.3 Gbps were also good.

[0101] The present invention is not limited to the above-described embodiments, and many modifications are possible within the technical concept of the present invention. Furthermore, the effects described in the embodiments are merely a list of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments. [Explanation of symbols]

[0102] 22...signal line, 200...flexible printed wiring board, 221...conductive layer, 222...insulating layer, 230...insulating body portion, 2210...opening (first opening), 2220...opening (second opening)

Claims

1. An insulator portion extending in a first direction; A signal line disposed inside the insulator portion; a conductive layer disposed on a major 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; Two or more of the first openings are arranged at positions overlapping the insulating layer when viewed in a direction perpendicular to a main surface of the insulator portion. A flexible printed wiring board comprising:

2. An insulating portion extending in a first direction; A signal line disposed inside the insulator portion; a conductive layer disposed on a major 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; Two or more of the second openings are arranged at positions overlapping the conductive layer when viewed in a direction perpendicular to a main surface of the insulator portion. A flexible printed wiring board comprising:

3. Two or more of the plurality of first openings are arranged at positions overlapping the signal line when viewed in a direction perpendicular to a main surface of the insulating body portion.

3. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is a flexible printed wiring board having a thickness of

4. Each of the plurality of first openings has a length in the first direction that is longer than a length in a second direction perpendicular to the first direction.

4. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is a flexible printed wiring board having a thickness of

5. Each of the plurality of first openings is rhomboidal.

5. The flexible printed wiring board according to claim 4.

6. The plurality of first openings are arranged in a matrix.

6. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is a flexible printed wiring board having a thickness of 100 nm or less.

7. The conductive layer is mesh-like.

7. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is a flexible printed wiring board having a thickness of

8. When viewed in a direction perpendicular to a main surface of the insulating body portion, two or more of the second openings are arranged at positions overlapping the signal line.

8. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is a flexible printed wiring board having a thickness of 100 nm or less.

9. Each of the plurality of second openings is rectangular in shape.

9. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is a flexible printed wiring board having a thickness of 100 nm or less.

10. The plurality of second openings are arranged in a matrix.

10. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is a flexible printed wiring board having a thickness of 100 nm or less.

11. The insulating layer is mesh-like.

11. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is a flexible printed circuit board.

12. When viewed in a direction perpendicular to a main surface of the insulator portion, an area of ​​one of the second openings is smaller than an area of ​​one of the first openings.

12. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is a flexible printed wiring board having a thickness of 100 nm or less.

13. the one first opening has a smallest area among the plurality of first openings, The one second opening has a largest area among the plurality of second openings.

13. The flexible printed wiring board according to claim 12.

14. The aperture ratio of the conductive layer is 40% or more and 90% or less.

14. The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is a flexible printed wiring board having a thickness of 100 nm or less.

15. A flexible printed wiring board according to any one of claims 1 to 14, a first rigid printed wiring board to which a first end of the flexible printed wiring board in the first direction is connected; a first electronic component mounted on the first rigid printed wiring board; An electronic unit characterized by:

16. a second rigid printed wiring board to which a second end of the flexible printed wiring board in the first direction is connected; a second electronic component mounted on the second rigid printed wiring board; 16. Electronic unit according to claim 15.

17. An electronic unit according to claim 15 or 16; A housing in which the electronic unit is housed.

1. An electronic device comprising:

18. An insulator part with a signal line disposed therein is prepared, forming a conductive layer having a plurality of first openings on a main surface of the insulator portion; forming an insulating layer on the conductive layer, the insulating layer having a plurality of second openings; A method for producing a flexible printed wiring board comprising the steps of:

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