Wiring board, manufacturing method of the same, electronic module and electronic equipment

Abstract

To provide a wiring board having high flexibility.SOLUTION: A flexible wiring board comprises an insulation layer, a first conductive layer including a signal line provided inside the insulation layer, a second conductive layer provided on a portion of an upper layer of the insulation layer, and a coating layer coating the second conductive layer. The coating layer has a first part provided on the second conductive layer, and a second part provided on a portion of the insulation layer where the second conductive layer is not provided. In the thickness direction of the flexible wiring board, the thickness of the second part is less than the sum of the thickness of the first part and the thickness of the second conductive layer.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a wiring board, a method for manufacturing a wiring board, an electronic module, and an electronic device. [Background technology]

[0002] Flexible wiring boards that serve as signal transmission paths are used in electronic devices, such as mobile phones, smartphones, tablet terminals, and digital cameras. Flexible wiring boards are provided with conductive layers in addition to signal lines in order to improve electrical and / or mechanical functions.

[0003] Patent Document 1 discloses a flexible wiring board having signal wiring on one of opposing surfaces of an insulating layer and mesh wiring (conductive layer) having multiple openings on the other surface, the mesh wiring being covered with a covering layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-227211 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the embodiment of Patent Document 1, the mesh wiring is embedded in the covering layer, and the surface of the covering layer is a flat surface without any irregularities. However, if the surface of the covering layer is made flat, there is a risk that the flexibility of the wiring board may be impaired.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a wiring board with improved flexibility. [Means for solving the problem]

[0007] The means for solving the above problem is a flexible wiring board comprising an insulating layer, a first conductive layer having a signal line provided inside the insulating layer, a second conductive layer provided on a portion of an upper surface of the insulating layer, and a covering layer covering the second conductive layer, wherein the covering layer includes a first portion provided on the second conductive layer and a second portion provided on the insulating layer in a portion where the second conductive layer is not provided, and in the thickness direction of the flexible wiring board, a thickness of the second portion is smaller than the sum of the thicknesses of the first portion and the second conductive layer. Effect of the Invention

[0008] A technique is provided that is advantageous for improving the flexibility of a wiring board. [Brief description of the drawings]

[0009] [Figure 1] Fig. 1(a) is a perspective view of an electronic unit including a wiring board, and Fig. 1(b) is a plan view of the wiring board shown in Fig. 1(a). [Diagram 2] Fig. 2(a) is a cross-sectional view taken along line AA in Fig. 1(b), and Fig. 2(b) is an enlarged view of frame 400 in Fig. 2(a). [Diagram 3] Fig. 3(a) is an explanatory diagram showing only an insulating layer, a signal line, a conductive layer, and a ground line in a plan view of a wiring board according to a second embodiment from the main surface side of an insulator part. Fig. 3(b) is an explanatory diagram showing only a conductive layer according to the second embodiment. Fig. 3(c) is an explanatory diagram showing an enlarged view of at least a part of a conductive layer according to this embodiment. [Figure 4] FIG. 4(a) is a diagram showing a modification of the conductive layer shown in FIG. 3, and FIG. 4(b) is an enlarged view of a main part of FIG. 4(a). [Diagram 5] 5(a) is a schematic diagram of an apparatus used to evaluate the flexibility of the wiring board of the embodiment and the wiring board of the comparative example, and FIG. 5(b) is a schematic diagram of a system used to evaluate the transmission characteristics of the wiring board of the embodiment and the wiring board of the comparative example. [Figure 6]FIG. 6(a) is a schematic diagram of a wiring board according to a third embodiment, and FIG. 6(b) is a schematic diagram of a wiring board according to a fourth embodiment. [Figure 7] 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiment for carrying out the present invention will be described with reference to the drawings. However, the embodiment described below is one embodiment of the invention, and the present invention is not limited to this. Then, common configurations will be described with mutual reference to multiple drawings, and the description of configurations with common symbols will be omitted as appropriate. Items with the same name but different can be distinguished by adding "No. 0", such as the first item and the second item.

[0011] First Embodiment The configuration of a wiring board 200 according to this embodiment will be described with reference to Fig. 1(a) and Fig. 1(b). Fig. 1(a) is a perspective view of an electronic unit 100 including the wiring board 200. Fig. 1(b) is a plan view of the wiring board 200 shown in Fig. 1(a). The wiring board 200 is, for example, a flexible printed wiring board. Note that the method of forming the wiring on the wiring board 200 is not limited to printing, and it may be a pre-formed electric wire, and the wiring board 200 may be a flat cable.

[0012] The electronic unit 100 includes a circuit board 101, a circuit board 102, and a wiring board 200 that electrically connects the circuit board 101 and the circuit board 102. The circuit board 101 and the circuit board 102 are, for example, printed circuit boards. An article in which the wiring board 200 and at least one of the circuit boards 101 and 102 are connected to each other can be called an electronic module 10. For example, the electronic module 10 in which the wiring board 200 is connected to the circuit board 101 is prepared, and the wiring board 200 of the electronic module 10 is further connected to the circuit board 102, thereby forming the electronic unit 100. Also, an electronic device including the electronic unit 100 can be formed by mounting various devices on the circuit board 102.

[0013] As shown in FIG. 1, the wiring board 200 extends in the X direction, which is the longitudinal direction. The wiring board 200 has a wiring layer 149 including a plurality of signal lines 22 and ground lines 133, and each of the signal lines 22 and ground lines 133 extends in the X direction. The wiring layer 149 is, for example, a first conductive layer. The signal lines 22 and ground lines 133 are arranged at intervals in the Y direction, which is the short side direction perpendicular to the X direction. The Z direction perpendicular to the X direction and the Y direction is the thickness direction of the wiring board 200. The wiring board 200 is flexible and can be bent and deformed. Although only one ground line 133 is shown in FIG. 1(b), multiple ground lines may be used depending on the application.

[0014] In this embodiment, the signal lines 22 and ground lines 133 are all arranged in the Y direction when viewed from the Z direction (in a plan view). However, it is sufficient that at least some of the signal lines 22 and ground lines 133 are arranged in parallel in the Y direction when viewed in a plan view.

[0015] A connector 112 is mounted on wiring board 110 constituting circuit board 101. Connector 112 is electrically connected to semiconductor device 111 by a conductor pattern on wiring board 110. Similar to wiring board 110, a connector 122 is mounted on wiring board 120 constituting circuit board 102. Connector 122 is electrically connected to semiconductor device 121 by a conductor pattern on wiring board 120.

[0016] Wiring board 110 and wiring board 120 are, for example, rigid wiring boards, and may be printed wiring boards (rigid printed wiring boards) including a resin substrate or a ceramic substrate.

[0017] With the above configuration, semiconductor device 111 and semiconductor device 121 are electrically connected to each other so as to be able to communicate with each other via wiring board 110, wiring board 200, and wiring board 120. In this case, the connection to wiring boards 110 and 120 may be made by directly connecting wiring board 200 to wiring boards 110 and 120 by soldering, without going through connectors 112 and 122.

[0018] As shown in FIG. 1(b), the signal line 22 and the ground line 133 are provided so as to overlap the conductive layer 221 in a plan view. The conductive layer 221 is grounded by being connected to the ground line 133 at a portion thereof. Thereby, the conductive layer 221 can function as a shield layer that blocks electromagnetic noise. Hereinafter, the conductive layer 221 may also be referred to as a shield layer. The shield layer (conductive layer) 221 is, for example, a second conductive layer. The shield layer (conductive layer) 221 is used as a path for a return current of a signal passing through the signal line 22, and constitutes a part of the ground line. The shield layer (conductive layer) 221 may be disposed at least in a position facing the signal line 22 and the ground line 133, or in a position overlapping the signal line 22 and the ground line 133 in a plan view.

[0019] The shield layer (conductive layer) 221 includes a plurality of lines (linear conductive layer) 2211 extending in the Da direction intersecting with the X direction, which is the extension direction of the signal line 22, and a plurality of lines (linear conductive layer) 2212 extending in the Db direction intersecting with the Da direction and the X direction. The Da direction is, for example, a first direction, and the Db direction is, for example, a second direction. That is, in this embodiment, a part of the conductive layer 221 forms a lattice shape, and has a configuration (mesh structure) with diamond-shaped openings 2210 between the lattices. However, the shield layer (conductive layer) 221 of this embodiment is not limited to the above mesh structure, and may have a configuration with a plurality of openings in the shape of a circle, a triangle, a square, or another polygon, as long as the conductive layer 221 is not provided on the entire surface. It is preferable that the direction in which the line segment L1 and the line segment L2 that connect the intersections of the line 2211 and the line 2212 so as to straddle the openings 2210 extend is different from the X direction. This can suppress the variation in impedance between the signal lines 22, thereby reducing transmission failures of the digital signal to be transmitted. Line segment L2 intersects with line segment L1 and is shorter than line segment L1. Line segment L1 is preferably 1.5 times longer than line segment L2. Line segment L1 is preferably 1 mm or more and 5 mm or less. When line segment L1 is 1 mm or more or 5 mm or less, the shielding effect of electromagnetic noise radiated from signal line 22, i.e., wiring board 200, is enhanced. This can effectively reduce electromagnetic noise that affects wireless communication. From the above viewpoints, line segment L1 is preferably 1 mm or more and 5 mm or less.

[0020] In this embodiment, the first differential signal wiring 2201 and the second differential signal wiring 2202 are formed by two signal lines 22 each constituting a pair of differential signal wiring. In this case, the length of the line segment L2 of each opening 2210 is preferably shorter than the distance L3 between the first differential signal wiring 2201 and the second differential signal wiring 2202 adjacent thereto. Here, the distance between the first differential signal wiring 2201 and the second differential signal wiring 2202 is the distance between the differential signal wiring of the first differential signal wiring 2201 on the second differential signal wiring 2202 side and the differential signal wiring of the second differential signal wiring 2202 on the first differential signal wiring 2201 side. This makes it possible to suppress the occurrence of crosstalk noise between the two pairs of differential signal wiring, and to suppress the occurrence of defects in signal transmission.

[0021] When wiring board 200 is viewed in plan, the ratio of openings 2210 to the entire area of ​​wiring board 200 can be defined as the aperture ratio, and the aperture ratio is preferably 40% or more and 95% or less, and more preferably 50% or more and 90% or less. If the aperture ratio of shield layer (conductive layer) 221 is 40% or more, that is, the ratio of shield layer (conductive layer) 221 is less than 60%, the aperture amplitude value of the eye pattern in signal transmission can be sufficiently increased, and transmission failure of the digital signal transmitted through signal line 22 can be reduced. Also, if the aperture ratio of shield layer (conductive layer) 221 is more than 95%, that is, the ratio of shield layer (conductive layer) 221 is 5% or less, it is difficult to sufficiently shield radiation noise. By having the aperture ratio in this range, radiation noise radiated from wiring board 200 can be effectively reduced.

[0022] Next, the cross-sectional configuration of the wiring board 200 will be described with reference to FIG. 2(a) and FIG. 2(b). FIG. 2(a) is a cross-sectional view taken along line AA in FIG. 1(b). FIG. 2(b) is an enlarged view of the frame 400 in FIG. 2(a). The wiring board body 210 has an insulator section 230 and a wiring layer 149. The insulator section 230 is made of a material having electrical insulation. Each signal line 22 and ground line 133 are made of a material having electrical conductivity. The wiring board body 210, i.e., the insulator section 230, the multiple signal lines 22, and the ground line 133 are formed to extend in the X direction. The multiple signal lines 22 are arranged at intervals in the Y direction inside the insulator section 230, but are not necessarily required to be arranged inside the insulator section 230. Note that, although two of the multiple signal lines 22 are illustrated in FIG. 2(a), the number of signal lines in this embodiment is not limited to two, and the present invention is also applicable to three or more signal lines. The insulator part 230 is formed in a sheet shape and has a pair of main surfaces 231, 232 extending in the X direction. The insulator part 230 is composed of an insulating layer 252 in which the signal line 22 is embedded, and insulating layers 251 and 240 that sandwich the insulating layer 252. A shielding member 220 is disposed at a position in contact with one of the pair of main surfaces 231, 232 of the insulator part 230. In this embodiment, the signal line 22 is provided on one surface 251-2 of the insulating layer 251, and the shielding member 220 is provided on the other surface 251-1. In this embodiment, the other surface 251-1 of the insulating layer 251 coincides with one main surface 231 of the insulator part 230.

[0023] Each signal line 22 will be described in detail below. Each signal line 22 is a wiring that can be used to transmit digital data signals. With an increase in the amount of signal transmission, it is preferable to configure differential signal wiring in which a pair of signal lines 22 is one set among the multiple signal lines 22. The transmission direction of each signal line 22 is basically the same for all signal lines 22, but signal lines that transmit in different directions may be provided. Note that the multiple signal lines 22 may include wiring that transmits single-ended signals such as control signals and response signals. 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.

[0024] 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, etc. 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 baked at a temperature below the glass transition point (Tg) of the insulating layer 240 to form the pattern.

[0025] As described above, ground line 133 and shield layer (conductive layer) 221 are connected at connection portion 411, so that conductive layer 221 performs a shielding function. In the present embodiment, ground line 133 directly contacts shield layer (conductive layer) 221 through a through hole provided in insulating layer 251, so that connection portion 411 is formed. Furthermore, wiring board 200 has shield layer (conductive layer) 221, so that a shielding effect can be ensured against electromagnetic noise radiated from wiring board 200 and external electromagnetic noise transmitted to wiring board 200. In this way, conductive layer 221 can be given a shielding function by supplying a fixed potential to conductive layer 221. The fixed potential supplied to shield layer (conductive layer) 221 is, for example, a power supply potential or a ground potential (ground potential), but is not limited thereto. A conductive layer to which a ground potential is supplied can be called a ground layer.

[0026] In this embodiment, the shielding member 220 is disposed at a position in contact with the main surface 231. Note that the shielding member 220 may be disposed on each of the pair of main surfaces 231, 232.

[0027] The shielding member 220 will be described in detail below. The shielding member 220 is a sheet-like member, and includes a shielding layer (conductive layer) 221 and a covering layer 222 having the shielding layer (conductive layer) 221 provided therein. The shielding layer (conductive layer) 221 is disposed at a position in contact with the main surface 231 of the insulator part 230, and may be disposed at least at a position facing the signal line 22 or at a position overlapping with the signal line 22 in a plan view. The covering layer 222 functions as a protective layer surrounding the shielding layer (conductive layer) 221 so that the shielding layer (conductive layer) 221 does not come into contact with the surrounding members of the wiring board 200, and is composed of a member having electrical insulation. Hereinafter, the covering layer 222 may be referred to as a protective layer.

[0028] 2, the surface of covering layer (protective layer) 222 of this embodiment is not flat, but has an uneven structure. This allows wiring board 200 to have both flexibility and shielding properties. The specific configuration is shown below.

[0029] The shield layer (conductive layer) 221 has a plurality of openings 2210 as described in FIG. 1(b), and has, for example, a mesh structure. In other words, the shield layer (conductive layer) 221 is provided on a part of the surface 251-1 (one of the main surfaces 231 of the insulator part 230) of the insulating layer 251. On the other hand, the covering layer (protective layer) 222 has a first part 11 provided on the shield layer (conductive layer) 221 and a second part 21 provided on the insulating layer 251 in a part where the shield layer (conductive layer) 221 is not provided. In this embodiment, the first part 11 is provided directly on the shield layer (conductive layer) 221. Also, the second part 21 is provided directly on the insulating layer 251 in a part where the shield layer (conductive layer) 221 is not provided. The first part 11 of the covering layer 222 can be called a first protective layer, and the second part 21 can be called a second protective layer.

[0030] The sum of thickness D11 of covering layer 222 and height (thickness) H of shield layer (conductive layer) 221 in first portion 11 is greater than thickness D21 of covering layer 222 in second portion 21. That is, the thickness of shield member 220 in a portion where shield layer (conductive layer) 221 is provided is greater than the thickness of shield member 220 in a portion where shield layer (conductive layer) 221 is not provided. With this configuration, wiring board 200 that achieves both flexibility and shielding properties can be obtained. In this embodiment, even in portions other than connection portion 411, the sum of thickness D11 of covering layer 222 and height (thickness) H of shield layer (conductive layer) 221 in first portion 11 is greater than thickness D21 of covering layer 222 in second portion 21.

[0031] Furthermore, the lowest point of the recess 413 among the unevenness on the surface of the coating layer 222 is provided on the wiring layer 149 side from the main surface 412 of the shield layer (conductive layer) 221, thereby improving the flexibility. The height of the protrusion 414 does not need to be uniform at all points, and may be different heights as shown in FIG. 2(b). The thicknesses D11 and D21 of the coating layer 222 may be uniform or one of them may be formed thicker, but it is preferable that the thickness D21 is greater than the thickness D11 because this makes it easier to form the coating layer 222. It is preferable that the shield layer (conductive layer) 221 is not provided below the lowest point of the recess 413 (on the wiring layer 149 side), and it is preferable that the protrusion 414 is provided on the opposite side of the shield layer (conductive layer) 221 from the wiring layer 149.

[0032] The depth d from the convex portion 414 to the concave portion 413 on the surface of the coating layer 222 is preferably in the range of 5 μm to 20 μm. If the depth d of the concave portion is less than 5 μm, the improvement of the flexibility is limited. If the depth d of the concave portion is more than 20 μm, the coating of the side surface of the shield layer (conductive layer) 211 by the coating layer 222 becomes thin, which may cause breakage or powder fall during stable use for a long time, which may cause problems in use. As described above, the portion where the shield layer (conductive layer) 221 is not provided corresponds to the opening 2210 shown in FIG. 1(b). Therefore, the shape of the concave portion in a plan view can be a circle, a triangle, a square, a diamond, or other polygon depending on the shape of the opening 2210. Also, the shorter the period in which the concave portions 413 exist, in other words, the greater the number of the concave portions 413, the more the flexibility is improved compared to the case where the concave portions 413 are not formed.

[0033] Here, the height (thickness) of wiring board 200, that is, the distance from main surface 232 to convex portion 414, can be adjusted by signal line 22 and shield layer (conductive layer) 221. Specifically, when signal line 22 and shield layer (conductive layer) 221 are provided overlapping in the Z direction, the height of wiring board 200 in the overlapping portion can be formed higher than the other portions. Conversely, the height of wiring board 200 in the portion where neither signal line 22 nor shield layer (conductive layer) 221 is provided is formed lower than the other portions. Even when only signal line 22 or only conductive layer 221 is provided, the height of wiring board 200 can be changed, and it is preferable that the height of wiring board 200 when only conductive layer 221 is provided is formed higher than the height of wiring board 200 when only signal line 22 is provided. By adjusting the height of wiring board 200 in this manner, desired flexibility and shielding properties can be obtained.

[0034] The thicknesses D11 and D12 are preferably in the range of 2 μm or more and 5 μm or less. If the thickness is 2 μm or more and 5 μm or less, it is possible to effectively prevent the shield layer (conductive layer) 221 from contacting the surrounding members of the wiring board 200. In this embodiment, the surface of the covering layer 222 has a recess surrounded by the shield layer (conductive layer) 221, so that the covering layer 222 can exhibit flexibility that is not oriented in a specific direction. In addition, it is preferable that the thicknesses D21 and D22 are 4 μm or more and 6 μm or less, so that the shield layer (conductive layer) 221 can be effectively prevented from contacting the surrounding members of the wiring board 200.

[0035] The method of forming the shield layer (conductive layer) 221 is not particularly limited. For example, methods of forming the shield layer (conductive layer) 221 on the main surface 231 of the insulator part 230 shown in FIG. 1(b) include subtractive method, electroless plating method, electrolytic plating method, and physical vapor deposition methods such as vacuum deposition and sputtering method. Also, known coating film forming means such as bar coating, slit coating, and screen printing method can be adopted. Among these, as a means of forming a patterned shield layer (conductive layer) 221 on the main surface 231 of the insulator part 230, it is preferable to use screen printing, which can apply a conductive material in a pattern under normal temperature and pressure. The conductive material formed by screen printing is dried and coated by heating, and the shield layer (conductive layer) is manufactured.

[0036] Materials constituting the shield layer (conductive layer) 221 include metal materials such as gold, silver, copper, aluminum, and nickel, conductive resin compositions in which conductive fillers such as metal particles, metal fibers, and carbon nanotubes are mixed with resin, and conductive polymers such as polythiophene and polypyrrole. Of these, silver paste made of silver particles with high conductivity and a resin binder is particularly suitable as a material for forming a coating film. In addition to silver paste, gold paste, copper paste, carbon paste, and the like may also be used.

[0037] When the shield layer (conductive layer) 221 is formed with silver paste, the viscosity of the silver paste is preferably 1 Pa·s or more and 500 Pa·s or less at a shear rate of 10 / s. When the viscosity is 1 Pa·s or more, the line width of the shield layer (conductive layer) 221 does not change after formation, and a shield layer (conductive layer) 221 of stable quality can be obtained. When the viscosity is 500 Pa·s or less, the shield layer (conductive layer) 221 can be formed without interruption of the line. From the above viewpoints, the viscosity of the silver paste is more preferably 5 to 100 Pa·s at a shear rate of 10 / s. From the viewpoint of electromagnetic wave noise shielding ability, the electrical resistivity of the shield layer (conductive layer) 221 is preferably 1×10 Ω·cm or less, and more preferably 1×10 -5 Ω·cm or less is more preferable.

[0038] The thickness of the shield layer (conductive layer) 221 in the Z direction is preferably in the range of 1 μm or more and 20 μm or less. If the thickness is 1 μm or more, the electrical resistance of the shield layer (conductive layer) 221 can be sufficiently reduced, so that the opening 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. Furthermore, if the thickness is 20 μm or less, the combined thickness of the shield layer (conductive layer) 221 and the covering layer 222 can also be reduced, so that a wiring board with higher flexibility can be provided. From the above viewpoints, the thickness of the shield layer (conductive layer) 221 in the Z direction is more preferably in the range of 2 μm or more and 15 μm or less.

[0039] The insulating layer 240, the insulating layer 251, the insulating layer 252, and the covering layer 222 shown in FIG. 2(a) will be described in detail below.

[0040] First, the insulating layer 240 will be described in detail. 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.

[0041] The thickness of insulating layer 240 in the Z direction is preferably, for example, 10 μm or more and 100 μm or less. When the thickness of insulating layer 240 in the Z direction is 10 μm or more, a separation distance between signal line 22 and surrounding electronic components can be ensured, and fluctuations in the characteristic impedance of signal line 22 can be suppressed. Furthermore, when the thickness of insulating layer 240 in the Z direction is 100 μm or less, the rigidity of insulating layer 240 can be reduced, and sufficient flexibility can be obtained in wiring board 200. From the above viewpoints, the thickness of insulating layer 240 in the Z direction is more preferably 12 μm or more and 75 μm or less.

[0042] 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.

[0043] 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.

[0044] The method of forming the insulating layer 251 is not particularly limited, but in this embodiment, the insulating layer 251 is formed by bonding a flexible insulating layer (insulating resin substrate) 251 formed in advance in a plate shape to an insulating layer (insulating substrate) 240 on which the signal line 22 is formed, with an insulating layer (adhesive layer) 252, as described later. Alternatively, the insulating layer 251 can be formed by coating an insulating resin on the insulating layer 252. Here, the coating can be performed by the following method. For example, a solution in which an insulating resin is dissolved 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, a ketone-based solvent such as acetone, methyl ethyl ketone, or cyclohexanone, or an alcohol-based solvent such as methanol, ethanol, propanol, ethylene glycol, glycerin, or 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 coating, a heating or drying step may be provided to volatilize the solvent as 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.

[0045] 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 resistivity of the insulating layer 251 is preferably 10 9 Ω·cm or more is preferable, and 10 13It is more preferable that the resistivity is Ω·cm or more.

[0046] Next, the insulating layer 252 will be described in detail. In this embodiment, 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.

[0047] 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.

[0048] 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.

[0049] In this embodiment, insulating layer 252 is an adhesive layer that bonds insulating layer 240 and insulating layer 251, but insulating layer 252 and insulating layer 251 may be formed by coating. In this case, these insulating layers may be formed separately, or insulating layer 252 and insulating layer 251 may be formed of the same material. In this way, when insulating layer 252 and insulating layer 251 are formed integrally, it can be considered as a configuration in which either insulating layer 252 or insulating layer 251 is not provided.

[0050] Next, the coating layer 222 will be described in detail. The insulating resin used in the coating layer 222 may be any resin having insulating properties, and examples thereof include thermosetting resins, ultraviolet curing resins, and coating agents made of resin solutions in which hardened film components are dispersed in a solvent. Examples of thermosetting resins include phenolic resins, acrylic resins, epoxy resins, polyamide resins, polyamideimide resins, polyimide resins, melamine resins, silicone resins, and acrylic-modified silicone resins. Examples of ultraviolet curing resins include epoxy acrylate resins, polyester acrylate resins, and their methacrylate-modified products. Examples of resin solutions include polyester urethane resins and polyamideimide resins dissolved in organic solvents. In addition, color pigments, flame retardants, antioxidants, lubricants, plasticizers, viscosity adjusters, dust-removing inhibitors, hardening accelerators, inorganic fillers such as silica and carbon black, organic fillers such as silicone particles and polyester particles, and other known additives may be added as necessary. Among these, a coating agent made of a resin solution in which a cured film component is dispersed in a solvent is preferred because it shrinks little due to the curing reaction and can suppress warping.Moreover, a coating agent in which a flexible and heat-resistant polyamide-imide resin is dissolved in a solvent is more preferred.

[0051] A known method can be selected as a method for forming the coating layer 222. For example, a method can be used in which a liquid resin composition is applied as a coating film to form a cured film, such as bar coating, slit coating, spray coating, dot dispenser, or screen printing. A method can also be used in which an adhesive component is applied onto a plastic film, and the plastic film is attached onto the shield layer (conductive layer) 221 via an adhesive component layer. A method for forming a cured film after the coating film is formed can be appropriately selected according to the material, such as heat curing, ultraviolet curing, electron beam curing, heat drying, or vacuum drying.

[0052] From the viewpoint of preventing shield layer (conductive layer) 221 from contacting with the surrounding members of wiring board 200, the thickness of covering layer 222 in the Z direction is preferably greater than the thickness of shield layer (conductive layer) 221. The thickness of covering layer 222 in the Z direction from main surface 412 of shield layer (conductive layer) 221 is preferably in the range of 2 μm to 10 μm. By having a thickness of 2 μm or more, it is possible to effectively prevent shield layer (conductive layer) 221 from contacting with the surrounding members of wiring board 200. Furthermore, by having a thickness of covering layer 222 in the Z direction from main surface 412 of shield layer (conductive layer) 221 of 10 μm or less, it is possible to more effectively increase the flexibility of wiring board 200. Furthermore, from the viewpoint above, it is more preferable that the thickness of covering layer 222 in the Z direction from main surface 412 of shield layer (conductive layer) 221 is 3 μm to 7 μm.

[0053] <Second embodiment> Next, a wiring board 200 according to a second embodiment will be described with reference to FIG. 3. The cross-sectional shape of the wiring board 200 according to this embodiment is the same as that of the first embodiment shown in FIG. 2(a). FIG. 3(a) is an explanatory diagram showing only the insulating layer 240, the signal line 22, the shield layer (conductive layer) 221, and the ground line 133 in a plan view of the wiring board 200 according to this embodiment from the main surface 231 side of the insulator part 230. FIG. 3(b) is an explanatory diagram showing only the shield layer (conductive layer) 221 according to this embodiment. FIG. 3(c) is an explanatory diagram showing at least a part of the shield layer (conductive layer) 221 according to this embodiment in an enlarged manner.

[0054] In wiring board 200 of the present embodiment, shield layer (conductive layer) 221 has thick line portion 2214 extending in Da direction intersecting with X direction in which signal line 22 extends, and thick line portion 2215 extending in Db direction intersecting with Da direction. Also, this embodiment differs from the first embodiment in that thick line portion 2214 is connected to thin line portion 2216 having a smaller line width than thick line portion 2214, and thick line portion 2215 is connected to thin line portion 2217 having a smaller line width than thick line portion 2215. In this embodiment, thin line portion 2216 extends in the Da direction, and thin line portion 2217 extends in the Db direction.

[0055] The linear portion 2221 extending in the Da direction of the shield layer (conductive layer) 221 is configured by alternately arranging thick line portions 2214 and thin line portions 2216, and a plurality of linear portions 2221 extending in the Da direction are arranged in the Db direction. The linear portion 2222 extending in the Db direction of the shield layer (conductive layer) 221 is configured by alternately arranging thick line portions 2215 and thin line portions 2217, and a plurality of linear portions 2222 extending in the Db direction are arranged in the Da direction. The plurality of linear portions 2221 extending in the Da direction and the plurality of linear portions 2222 extending in the Db direction intersect at a plurality of points in the thin line portions 2216 and the thin line portions 2217, thereby forming a mesh-like (also called a lattice-like or mesh structure) shield layer (conductive layer) 221. The thick line portion 2214 is, for example, a first line portion, and the thick line portion 2215 is, for example, a third line portion. The thin line portion 2216 is, for example, the second line portion, and the thin line portion 2217 is, for example, the fourth line portion.

[0056] In this embodiment, all of the linear portions 2221 having a smaller line width than the thick line portion 2214 are defined as thin line portions 2216, but each of the thin line portions 2216 can be called a first thin line portion 2216 or a second thin line portion 2216. Furthermore, all of the linear portions 2222 having a smaller line width than the thick line portion 2215 are defined as thin line portions 2217, but each of the thin line portions 2217 can be called a first thin line portion 2217 or a second thin line portion 2217. Furthermore, the linear portion 2221 can be defined as a first linear portion, and the linear portion 2222 can be defined as a second linear portion.

[0057] As shown in FIG. 3(c), shield layer (conductive layer) 221 has thick line portion 2214 extending in the Da direction and thick line portion 2215 extending in the Db direction intersecting with the Da direction and the X direction. Shield layer (conductive layer) 221 also has thin line portion 2216 and thin line portion 2217 having a smaller line width than thick line portion 2214 and thick line portion 2215. Thick line portion 2214 and thick line portion 2215 are connected to thin line portion 2216 and thin line portion 2217. Thin line portion 2216 and thin line portion 2217 having a smaller line width intersect with each other, thereby improving the flexibility of wiring board 200. When wiring board 200 is composed of only thick line portion 2214 and thick line portion 2215, thick line portion 2214 and thick line portion 2215 intersect with each other. When thick line portions intersect with each other, the area of ​​the intersecting region becomes large.

[0058] In contrast, by having the thin wire portions cross each other, the area of ​​the crossing region is reduced, and flexibility can be improved without causing transmission failure. By forming shield layer (conductive layer) 221 in a mesh shape and having the thin wire portions cross each other, it is possible to improve the flexibility of wiring board 200 while reducing transmission failure of the digital signal transmitted through signal line 22. In other words, it is possible to improve the functionality of wiring board 200. Here, the crossing region is crossing region 2000 surrounded by the dotted line in FIG. 2(c).

[0059] At this time, the line widths W1 and W3 of the thick line portion 2214 and the thick line portion 2215 are not particularly limited, but are preferably 50 μm or more and 200 μm or less. If W1 and W3 are 50 μm or more, the effect of suppressing electromagnetic noise in a higher frequency band can be exhibited, and malfunction of surrounding semiconductor devices can be suppressed. Furthermore, if W1 and W3 are 200 μm or less, the area in which the shield layer (conductive layer) 221 covers the signal lines 22 can be made uniform in the X direction in which each signal line 22 extends. Therefore, the variation in impedance between each signal line 22 can be suppressed, and transmission failure of the transmitted digital signal can be reduced.

[0060] The line widths W2 and W4 of the thin line portion 2216 or the thin line portion 2217 are not particularly limited, but are preferably 10 μm or more and less than 50 μm. When W2 and W4 are 10 μm or more, the electrical conduction of the shield layer (conductive layer) 221 can be sufficiently increased, so that the opening 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. Furthermore, when W2 and W4 are 50 μm or less, the area of ​​the intersection region 2000 where the thin line portion 2216 and the thin line portion 2217 intersect can be reduced within a range that does not cause a transmission failure, so that higher flexibility can be ensured. From the above viewpoint, it is more preferable that the line widths W2 and W4 of the thin line portion 2216 and the thin line portion 2217 are 15 μm or more and 40 μm or less. However, the line widths W2 and W4 only need to be smaller than W1 and W3, and are not limited to the above range.

[0061] It is preferable that the acute angle θa formed by the Da direction and the X direction is greater than 0 degrees and smaller than the acute angle formed by the De direction and the Da direction in which the line segment L1 extends. Alternatively, it is preferable that the acute angle θb formed by the Db direction and the X direction is greater than 0 degrees and smaller than the acute angle formed by the De direction and the Db direction in which the line segment L1 extends. It is also more preferable that the acute angles θa and θb are greater than 0 degrees and smaller than 1 / 2 of the acute angle formed by the De direction and the Da direction in which the line segment L1 extends, or the De direction and the Db direction. The acute angles θa and θb may be the same or different.

[0062] In this embodiment, the thick line portion 2214, the thick line portion 2215, the thin line portion 2216, and the thin line portion 2217 are formed collectively by screen printing.

[0063] <Third embodiment> Next, a wiring board 200 according to a third embodiment will be described with reference to Fig. 4. Fig. 4(a) is a diagram showing a modification of the shield layer (conductive layer) 221 shown in Fig. 3, and Fig. 4(b) is an enlarged diagram of a main part of Fig. 4(a). The shield layer (conductive layer) 221 of this embodiment differs from the shield layer (conductive layer) 221 of the second embodiment in the shape near the intersection region 2000 where the thin line portion 2216 and the thin line portion 2217 intersect.

[0064] That is, in the shield layer (conductive layer) 221 according to the present embodiment, the thin wire portion 2216 and the thin wire portion 2217 of the shield layer (conductive layer) 221 according to the second embodiment extend in a direction different from the Da direction and the Db direction.

[0065] The thick line portion 2214 is connected to a thin line portion 2216 extending in the Dc direction. The thick line portion 2215 is connected to a thin line portion 2217 extending in the Dd direction. The acute angle formed by the Dc direction and the X direction is larger than the acute angle formed by the Da direction and the X direction. The acute angle formed by the Dd direction and the X direction is larger than the acute angle formed by the Db direction and the X direction. The acute angles formed by the X direction and the Dc direction, and the X direction and the Dd direction are preferably, for example, 30° or more, and more preferably 40° or more. The acute angles formed by the X direction and the Dc direction, and the X direction and the Dd direction are preferably, for example, 60° or less, and more preferably 50° or less. More preferably, the acute angles formed by the X direction and the Dc direction, and the X direction and the Dd direction are 45°, but it is preferable that the Dc direction and the Dd direction are perpendicular to each other. The Dc direction is, for example, the third direction, and the De direction is, for example, the fourth direction.

[0066] If the acute angle between the thin wire portion 2216 and the thin wire portion 2217 is within the above range, it is possible to reduce transmission failures of the digital signal transmitted through the signal line 22. Here, the case where the acute angle or right angle between the Dc direction and the Dd direction is larger than the acute angle or right angle between the Da direction and the Db direction has been described. However, it is sufficient that the acute angle or right angle between the Dc direction and the Dd direction is different from the acute angle or right angle between the Da direction and the Db direction.

[0067] In this embodiment, the line width W1 of the thick line portion 2214 is made larger than the line width W2 of the thin line portion 2216. Moreover, the line width W3 of the thick line portion 2215 is made larger than the line width W4 of the thin line portion 2217. However, as long as the acute angles between the X direction and the Dc direction, and between the X direction and the Dd direction, are within the above ranges, transmission failures can be reduced.

[0068] <Example> Next, examples and comparative examples will be described. The flexible printed wiring board of the example corresponds to 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 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. Wiring board 200 of the example has wiring board body 210 and shielding member 220. Wiring board 200X of the comparative example has wiring board body 210 and shielding member 220X (see FIG. 5(a)).

[0070] The wiring board body 210 was fabricated as follows. A 12 μm thick copper foil was laminated as a wiring layer on one side of a 25 μm thick polyimide film (Kapton 100H, manufactured by DuPont-Toray Co., Ltd.). After that, an etching technique was used to pattern the wiring layer to a line width of 140 μm, line spacing of 55 μm, and total length of 120 mm, to fabricate a wiring layer capable of differential transmission. Next, a 12.5 μm thick polyimide film and a 15 μm thick coverlay (CISV1215, manufactured by Nikkan Industries Co., Ltd.) were attached on top of the wiring layer, to obtain the wiring board body 210.

[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] FIG. 5(a) is a schematic diagram of an apparatus used to evaluate the flexibility of wiring board 200 of the example and wiring board 200X of the comparative example.

[0073] 5(a), wiring boards 200, 200X are arranged horizontally with shielding members 220, 220X on the inside. One end of wiring boards 200, 200X in the longitudinal direction was bent 180 degrees with a curvature of 3 mm, and the vertical repulsive force of one end was evaluated using 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 a rigid printed wiring board. Furthermore, when a flexible printed wiring board is connected to two circuit boards (rigid printed wiring boards), this becomes a factor that hinders the movement of one circuit board (rigid printed wiring board) when it is moved relative to the other circuit board.

[0075] (2) Transmission characteristics (eye pattern) 5(b) is a schematic diagram of system 500 used to evaluate the transmission characteristics of wiring board 200 of the example and wiring board 200X of the comparative example. This system 500 is composed of signal generator 51, M8041A manufactured by Agilent Technologies, 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.

[0076] Between a pair of connection boards 53, wiring board 200 of the embodiment and wiring board 200X of the comparative example were connected in a state of being suspended in the air. Moreover, 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 set to 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 set to 300 mV. Moreover, oscilloscope 52 was connected to the other of the connection boards 53. The opening amplitude of the eye pattern of the signal output from the other of the connection boards 53 was observed by oscilloscope 52. 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%.

[0077] Example 1 A shield layer (conductive layer) 221, which is a radiation noise shielding layer, is formed on insulating layer 251 of wiring board body 210. A screen plate having the conductive layer pattern (line width 65 μm, aperture ratio 81%) of FIG. 1(b) was prepared, and silver paste (product name: DD-1630L-245, manufactured by Kyoto Elex Co., Ltd.) was used as shield layer (conductive layer) 221. The printing conditions of a screen printer (MT-320T, manufactured by Micro-Tec Co., Ltd.) and the paste viscosity were adjusted to form shield layer (conductive layer) 221 on main surface 231 of insulating layer 251 (see FIG. 2(a)).

[0078] Next, the covering layer 222 is formed on the shield layer (conductive layer) 221. A slit nozzle having a discharge port of 0.4 mm x 20 mm was prepared, and a polyamideimide resin dissolving coating agent (product name: HR-16NN, manufactured by Toyobo Co., Ltd.) was used as the covering layer 222. A coating film was formed on the main surface 412 of the shield layer (conductive layer) 221 using a slit coater (SHOTMASTER 300ΩX, manufactured by Musashi Engineering Co., Ltd.). After being quickly provisionally cured, it was fully cured in a drying furnace at 200°C in the atmosphere for 30 minutes to form the covering layer 222 (see FIG. 2(a)).

[0079] Example 2 The wiring board body 210 in Example 2 had the same configuration as in Example 1. In addition, the shield layer (conductive layer) 221 was formed by preparing a screen plate having the conductive layer pattern (line width W1=65 μm, W2=35 μm, aperture ratio 82%) shown in FIG. 3(a) and using the same material and the same device conditions as in Example 1.

[0080] Next, the covering layer 222 is formed on the shield layer (conductive layer) 221. A slit nozzle having a discharge port of 0.4 mm x 20 mm was prepared, and a polyamideimide resin dissolving coating agent (product name: HR-16NN, manufactured by Toyobo Co., Ltd.) was used as the covering layer 222. A coating film was formed on the main surface 412 of the shield layer (conductive layer) 221 using a slit coater (SHOTMASTER 300ΩX, manufactured by Musashi Engineering Co., Ltd.). After being quickly provisionally cured, it was fully cured in a drying furnace at 200°C in the atmosphere for 30 minutes to form the covering layer 222 (see FIG. 2(a)).

[0081] Example 3 The wiring board body 210 in Example 3 has the same configuration as that in Example 1. A screen plate having the conductive layer pattern (line width 70 μm, aperture ratio 78%) shown in FIG. 6(a) was prepared, and a shield layer (conductive layer) 221 was formed using the same material and the same device as in Example 1. The cross-sectional structure of the wiring board 200 is similar to that of the first embodiment shown in FIG. 2(a).

[0082] Next, the covering layer 222 is formed on the shield layer (conductive layer) 221. A slit nozzle having a discharge port of 0.3 mm x 20 mm was prepared, and a polyamideimide resin dissolving coating agent (product name: HR-12N2, manufactured by Toyobo Co., Ltd.) was used as the covering layer 222. A coating film was formed on the main surface 412 of the shield layer (conductive layer) 221 using a slit coater (SHOTMASTER 300ΩX, manufactured by Musashi Engineering Co., Ltd.). After being provisionally cured immediately, the coating layer 222 was fully cured in a drying furnace at 200°C in the atmosphere for 30 minutes to form the covering layer 222 (see FIG. 2(a)).

[0083] Example 4 The wiring board body 210 in Example 4 has the same configuration as that in Example 1. A screen plate having a conductive layer pattern (line width 60 μm, aperture ratio 83%) in FIG. 6(b) was prepared, and a shield layer (conductive layer) 221 was formed using the same material and the same device as in Example 1. The cross-sectional structure of the wiring board 200 is the same as that of the first embodiment shown in FIG. 2(a).

[0084] Next, the covering layer 222 is formed on the shield layer (conductive layer) 221. A slit nozzle having a discharge port of 0.3 mm x 20 mm was prepared, and a polyamideimide resin dissolving coating agent (product name: HR-12N2, manufactured by Toyobo Co., Ltd.) was used as the covering layer 222. A coating film was formed on the main surface 412 of the shield layer (conductive layer) 221 using a slit coater (SHOTMASTER 300ΩX, manufactured by Musashi Engineering Co., Ltd.). After being provisionally cured immediately, the coating layer 222 was fully cured in a drying furnace at 200°C in the atmosphere for 30 minutes to form the covering layer 222 (see FIG. 2(a)).

[0085] In addition, for the shield layer (conductive layer) 221 in Examples 1 to 4, the heights before and after the formation of the shield layer (conductive layer) 221 were compared using a length measuring machine (MF-1001; Nikon Corporation), and the height H of the shield layer (conductive layer) shown in Table 1 was obtained. In addition, for the covering layer 222, the heights before and after the formation of the covering layer 222 were compared using a length measuring machine, and the thicknesses D11 and D21 of the covering layer shown in Table 1 were obtained. As a result, the depth d of the recess became the value shown in Table 1.

[0086] Comparative Example 1 Comparative Example 1 had the same structure as Example 1, except that the surface of the coating layer 222 did not have an uneven structure.

[0087] [Table 1]

[0088] (Evaluation Results) Table 1 shows the evaluation results of Examples 1 to 4 and Comparative Example 1. In Examples 1 to 4, the amount of radiation noise emitted from wiring board 200 was small, and the bending load also showed a good value. On the other hand, in Comparative Example 1, although a sufficient radiation noise shielding effect was obtained, the bending load was large due to the stiffness when bent.

[0089] <Fourth embodiment> Next, with reference to FIG. 7, a digital camera 600, which is an imaging device, will be described as an example of an electronic device using any of wiring boards 200 shown in the first to third embodiments.

[0090] 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 electronic unit 100, and a wireless communication unit 150. The electronic unit 100 and the wireless communication unit 150 are stored inside the housing 611. In the case of an imaging device such as that of this embodiment, the electronic unit 100 is an imaging unit.

[0091] Electronic unit 100 includes circuit board 101, circuit board 102, and wiring board 200 that electrically connects circuit board 101 and circuit board 102. Circuit board 101 is an example of a first circuit board. Circuit board 102 is an example of a second circuit board. By using wiring board 200 to connect circuit board 101 and circuit board 102, the wiring structure can be made lighter than a coaxial cable. Here, any of the wiring boards previously described in the first to third embodiments is used as wiring board 200.

[0092] Circuit board 101 includes wiring board 110 and semiconductor device 111 mounted on wiring board 110. Circuit board 102 includes wiring board 120 and semiconductor device 121 mounted on wiring board 120. Semiconductor device 111 and semiconductor device 121 are examples of electronic components mounted on wiring boards 110 and 120. The electronic components mounted on wiring boards 110 and 120 may be an imaging device, a computing device, a display device, a communication device, a storage device, a power supply device, or a computing device. The electronic components mounted on wiring boards 110 and 120 are not limited to active components, and may be passive components.

[0093] In this embodiment, the semiconductor device 111 is an image sensor (imaging device). 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 electric signal. In this embodiment, the semiconductor device 121 is a processor (arithmetic device) such as a digital signal processor or an image signal processor. The image signal processor has a function of acquiring an electric signal indicating image data from the semiconductor device 111, which is an image sensor (imaging device), correcting the acquired electric signal, and generating and outputting the corrected image data. An article in which the circuit board 101 connected to the wiring board 200 includes an image sensor in this way can be called an imaging module or an imaging unit. The imaging module is an example of an electronic module, and the imaging unit is an example of the electronic unit 100.

[0094] In this embodiment, electronic unit 100 includes driving device 160 that moves circuit board 101 (wiring board 110 and semiconductor device 111). Driving device 160 includes a motor, which is an example of a driving source. In digital camera 600 including electronic unit 100 including driving device 160, moving semiconductor device 111 via circuit board 101 can achieve a camera shake correction (anti-shake) function. The driving source in driving device 160 is not limited to an electromagnetic motor, but may be a piezoelectric motor such as an ultrasonic motor, or an electrostatic motor. Since wiring board 200 is connected to circuit board 101 that is moved in this way, wiring board 200 is required to be flexible.

[0095] It should be noted that instead of electronic unit 100 having wiring board 200, circuit board 101, and circuit board 102, an article having either circuit board 101 or circuit board 102, and further having driving device 160 and other components, can also be referred to as an electronic unit.

[0096] In this embodiment, wiring board 200 is mounted on digital camera 600 in a bent state, and is arranged so that shield layer (conductive layer) 221 is on the outer side of the curved surface. That is, shield layer (conductive layer) 221 corresponds to the surface of wiring board 200 on the housing 611 side.

[0097] The wireless communication unit 150 performs wireless communication in the GHz band and is modularized. The wireless communication unit 150 has a rigid wiring board, which is an example of the wiring board 151 including an antenna (not shown), and a wireless communication IC 152 mounted on the 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). In electronic unit 100 as an imaging unit, if shield layer (conductive layer) 221 provided on wiring board 200 is used as an electromagnetic shield, it is possible to prevent electromagnetic waves emitted from wireless communication unit 150 from generating noise in electronic unit 100. Note that wiring board 200 can also be used to connect wiring board 151 to another wiring board.

[0098] The above-described embodiment can be modified as appropriate without departing from the technical concept.

[0099] Furthermore, a plurality of embodiments may be combined, and part of at least one embodiment may be deleted or replaced.

[0100] In addition, new matters may be added to at least one embodiment. The disclosure of this specification includes not only what is explicitly described in this specification, but also all matters that can be understood from this specification and the drawings attached to this specification.

[0101] Furthermore, the disclosure of this specification includes the complement of each concept described in this specification. In other words, if this specification contains a statement that "A is greater than B," for example, even if the statement that "A is not greater than B" is omitted, this specification can be said to disclose that "A is not greater than B." This is because when a statement that "A is greater than B" is made, it is assumed that the case in which "A is not greater than B" is taken into consideration.

[0102] The disclosure of the present invention is given below.

[0103] (Configuration 1) A flexible wiring board comprising an insulating layer, a first conductive layer having a signal line provided inside the insulating layer, a second conductive layer provided on a portion of an upper surface of the insulating layer, and a covering layer covering the second conductive layer, wherein the covering layer includes a first portion provided on the second conductive layer and a second portion provided on the insulating layer in a portion where the second conductive layer is not provided, and the thickness of the second portion in a thickness direction of the flexible wiring board is smaller than the sum of the thicknesses of the first portion and the second conductive layer.

[0104] (Configuration 2) The flexible wiring board described in configuration 1, characterized in that the first conductive layer includes a ground line, and the ground line is electrically connected to the second conductive layer at a connection portion through a through hole provided in the insulating layer.

[0105] (Configuration 3) A flexible wiring board as described in configuration 1 or 2, characterized in that, of the covering layers of the first portion, the thickness of the covering layer provided on a certain portion of the second conductive layer is different from the thickness of the covering layer provided on a portion other than the certain portion of the second conductive layer.

[0106] (Configuration 4) The flexible wiring board according to any one of configurations 1 to 3, characterized in that the surface of the coating layer has an uneven portion, and the lowest point of the concave portion of the uneven portion is located on the side of the first conductive layer rather than the upper surface of the second conductive layer.

[0107] (Configuration 5) 5. The flexible wiring board according to configuration 4, wherein the lowest point is surrounded by the second conductive layer.

[0108] (Configuration 6) 6. The flexible wiring board according to configuration 4 or 5, wherein the second conductive layer is not provided on the side of the recess facing the first conductive layer.

[0109] (Configuration 7) 7. The flexible wiring board according to any one of configurations 1 to 6, wherein the second conductive layer has a mesh structure.

[0110] (Configuration 8) The flexible wiring board according to any one of configurations 1 to 7, characterized in that the second conductive layer has a first linear portion and a second linear portion, the first linear portion having a plurality of first linear portions extending in a first direction and a second linear portion having a smaller line width than the plurality of first linear portions and provided between the plurality of first linear portions so as to connect the plurality of first linear portions, the second linear portion having a plurality of third linear portions extending in a second direction intersecting the first direction and a fourth linear portion having a smaller line width than the plurality of third linear portions and provided between the plurality of third linear portions so as to connect the plurality of third linear portions, and the third linear portion and the fourth linear portion intersect with each other.

[0111] (Configuration 9) The flexible wiring board of configuration 8, characterized in that the third line portion extends in a third direction different from the first direction and the second direction, the fourth line portion extends in a fourth direction different from the first direction, the second direction, and the third direction, and an acute angle or right angle formed by the third direction and the fourth direction is different from an acute angle or right angle formed by the first direction and the second direction.

[0112] (Configuration 10) The flexible wiring board of configuration 9, wherein the acute angle or right angle formed between the third direction and the fourth direction is larger than the acute angle or right angle formed between the first direction and the second direction.

[0113] (Method 1) 11. A method for manufacturing a flexible wiring board according to any one of configurations 1 to 10, wherein the second conductive layer is formed by screen printing.

[0114] (Module 1) 11. An electronic module comprising: a flexible wiring board according to any one of configurations 1 to 10; a rigid wiring board to which an end of the flexible wiring board is connected; and an electronic component mounted on the rigid wiring board.

[0115] (Module 2) The electronic module described in Module 1, characterized in that the electronic components include an image sensor.

[0116] (Module 3) An electronic unit comprising: an electronic module according to module 1 or 2; and a drive device that moves the rigid wiring board.

[0117] (Module 4) An electronic device comprising: an electronic module according to any one of modules 1 to 3; and a circuit board to which an end of the flexible wiring board other than the end is connected, wherein a processor is mounted on the circuit board for processing signals output from the electronic component.

[0118] (Equipment 1) 5. An electronic device comprising: the electronic module according to any one of Modules 1 to 4; and a housing that houses the electronic module, wherein the flexible wiring board is housed in the housing in a bent state; and the second conductive layer is provided on an outer surface of the bent surfaces of the flexible wiring board. [Explanation of symbols]

[0119] 11 Part 1 21 Part 2 22 Signal Line 149 First conductive layer 200 Flexible wiring board 221 Second conductive layer 222 Covering layer 240, 251, 252 Insulating layer D11 Thickness of first part D21 Thickness of second part H Thickness of the second conductive layer

Claims

1. A flexible wiring board comprising an insulator portion, a first conductive layer having a signal line provided inside the insulator portion, a second conductive layer provided on a portion of the upper surface of the insulator portion, and a covering layer covering the second conductive layer, the covering layer includes a first portion that overlaps the second conductive layer in a thickness direction of the flexible wiring board, and a second portion that is provided on the insulator portion and does not overlap the second conductive layer in the thickness direction of the flexible wiring board, the second conductive layer includes a third portion that overlaps the first conductive layer in a thickness direction of the flexible wiring board and a fourth portion that does not overlap the first conductive layer in the thickness direction of the flexible wiring board, A flexible wiring board, characterized in that, in the thickness direction of the flexible wiring board, the thickness of the second portion is smaller than the sum of the thickness of the first portion and the thickness of the second conductive layer.

2. A flexible wiring board as described in Claim 1, characterized in that a portion of the second part overlaps the first conductive layer in the thickness direction of the flexible wiring board.

3. A flexible wiring board as described in claim 1, characterized in that the thickness of the second part is greater than the thickness of the first part.

4. A flexible wiring board as described in Claim 1, characterized in that the surface of the coating layer has an uneven portion, and the depth of the recesses in the uneven portion is smaller than the thickness of the second conductive layer.

5. A flexible wiring board as described in claim 1, characterized in that the thickness of the first part is 2 μm or more and 5 μm or less, and / or the thickness of the second part is 4 μm or more and 6 μm or less.

6. The flexible wiring board according to claim 1, characterized in that the surface of the coating layer has an uneven portion, and the lowest point of the concave portion of the uneven portion is located closer to the insulator portion than the upper surface of the second conductive layer.

7. A flexible wiring board as described in Claim 1, characterized in that the surface of the coating layer has an uneven portion, and the lowest point of the concave portion of the uneven portion is surrounded by the second conductive layer.

8. 2. The flexible wiring board according to claim 1, wherein the first conductive layer includes a ground line, and the ground line is electrically connected to the second conductive layer at a connection portion through a hole provided in the insulator portion.

9. A flexible wiring board as described in claim 1, characterized in that the thickness of the coating layer provided on the first location of the second conductive layer and the thickness of the coating layer provided on the second location of the second conductive layer are different from each other.

10. The flexible wiring board according to claim 1 , wherein the second conductive layer has a mesh structure.

11. the second conductive layer has a first linear portion and a second linear portion, the first linear portion includes a plurality of first line portions extending in a first direction, and second line portions having a line width smaller than that of the plurality of first line portions and provided between the plurality of first line portions so as to connect the plurality of first line portions; the second linear portion includes a plurality of third line portions extending in a second direction intersecting the first direction, and a fourth line portion having a line width smaller than that of the third line portions and provided between the third line portions so as to connect the third line portions; 2. The flexible wiring board according to claim 1, wherein the third line portion and the fourth line portion intersect with each other.

12. the third line portion extends in a third direction different from the first direction and the second direction, the fourth line portion extends in a fourth direction different from the first direction, the second direction, and the third direction; 12. The flexible wiring board according to claim 11, wherein the acute angle or right angle formed between the third direction and the fourth direction is different from the acute angle or right angle formed between the first direction and the second direction.

13. 13. The flexible wiring board according to claim 12, wherein the acute angle or right angle formed between the third direction and the fourth direction is larger than the acute angle or right angle formed between the first direction and the second direction.

14. 14. The method for manufacturing a wiring board according to claim 1, wherein the second conductive layer is formed by screen printing.

15. The flexible wiring board according to any one of claims 1 to 13, a rigid wiring board to which an end of the flexible wiring board is connected; and an electronic component mounted on the rigid wiring board.

16. 16. The electronic module of claim 15, wherein the electronic component includes an image sensor.

17. an electronic module according to claim 15; a drive device that moves the rigid wiring board.

18. an electronic module according to claim 15; a circuit board to which an end portion of the flexible wiring board different from the end portion is connected, The electronic device is characterized in that a processor that processes signals output from the electronic components is mounted on the circuit board.

19. an electronic module according to claim 15; a housing that houses the electronic module, the flexible wiring board is accommodated in the housing in a bent state, The electronic device is characterized in that the second conductive layer is provided on an outer surface of the bending surface of the flexible wiring board.

20. A housing that houses the electronic module, the flexible wiring board is accommodated in the housing in a bent state, 20. The electronic device according to claim 18, wherein the electronic component includes an image sensor.

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