JP2022142966A - Wiring board, electronic unit, electronic device, and manufacturing method for wiring board - Google Patents

Abstract

To suppress radiation noise emitted from a wiring board and to improve the transmission characteristics of a signal transmitted over a signal line.SOLUTION: A wiring board 200 has an insulator portion 230 having a main surface 231 and a main surface 232, a signal line 22 disposed inside the insulator portion 230, a conductive layer 251 disposed on the main surface 231, and a conductive layer 252 disposed on the main surface 232. The main surface 232 is the opposite side surface of the main surface 231. The surface resistivity of the conductive layer 252 is greater than that of the conductive layer 251.SELECTED DRAWING: Figure 2

Description

The present invention relates to technology for countermeasures against electromagnetic noise.

Electronic devices such as mobile phones, smart phones, tablet terminals, and digital cameras have flexible printed wiring boards that serve as transmission paths for digital signals. As the functions of electronic devices have improved, the amount of data handled by the electronic devices has also increased, and the speed of digital signals passing through wiring boards has also increased. Due to the increase in the capacity and speed of data communication, there has been a tendency for the radiation noise from the printed circuit board to increase.

On the other hand, Patent Literature 1 discloses a flexible printed wiring board having an electromagnetic wave shield layer and a resistor layer arranged on one side of a signal line with an insulating layer interposed therebetween.

JP 2014-90162 A

However, in the flexible printed wiring board disclosed in Patent Document 1, signal transmission loss may increase when trying to suppress radiation noise.

An object of the present invention is to suppress radiation noise and improve signal transmission characteristics.

A wiring board according to the present invention includes an insulator portion having a first main surface and a second main surface opposite to the first main surface, a signal line disposed inside the insulator portion, and the second main surface. A first conductive layer disposed on one principal surface and a second conductive layer disposed on the second principal surface, wherein the surface resistivity of the second conductive layer is the surface resistivity of the first conductive layer characterized by being greater than

In the wiring board manufacturing method of the present invention, an insulator portion having a signal line disposed therein is prepared, a first conductive layer is formed on a first main surface of the insulator portion, and a first conductive layer is formed on the first main surface of the insulator portion. A second conductive layer having a surface resistivity higher than that of the first conductive layer is formed on each of the second main surfaces opposite to the surface.

According to the present invention, radiation noise can be suppressed and signal transmission characteristics can be improved.

1 is an explanatory diagram of a digital camera that is an imaging device as an example of an electronic device according to an embodiment; FIG. (a) is an explanatory diagram of an imaging unit according to the embodiment. (b) is a cross-sectional view of the wiring board taken along line IIB-IIB of (a). (a) to (d) are explanatory diagrams showing an example of a method for manufacturing a wiring board according to the embodiment. 1A is an explanatory diagram of a system for measuring radiation noise amounts of a wiring board of an example and a wiring board of a comparative example; FIG. (b) is a schematic diagram of a system used to evaluate the transmission characteristics of the wiring board of the example and the wiring board of the comparative example. 4 is a table showing layer structures of first conductive layers and second conductive layers in wiring boards of Examples and wiring boards of Comparative Examples; 4 is a table showing the configuration and evaluation of wiring boards of Examples. 4 is a table showing the configuration and evaluation of a wiring board of a comparative example; (a) is an explanatory diagram of a wiring board of Comparative Example 3. FIG. (b) is an explanatory diagram of a wiring board of Comparative Example 4;

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

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

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

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

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

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

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

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

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

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

FIG. 2(b) is a cross-sectional view of wiring board 200 taken along line IIB-IIB in FIG. 2(a). As shown in FIG. 2B, wiring board 200 has wiring board body 210 , conductive layer 251 , conductive layer 252 , insulating layer 243 , and insulating layer 244 . Wiring board body 210 includes an insulator portion 230 and a plurality of signal lines 22 described above.

The insulator portion 230 is made of an electrically insulating material. Each signal line 22 is made of a conductive material. The insulator portion 230 and the plurality of signal lines 22 are formed extending in the X direction. The plurality of signal lines 22 are arranged inside the insulator portion 230 at intervals in the Y direction. Note that FIG. 2B shows a pair of signal lines 22 out of the plurality of signal lines 22 . A pair of signal lines 22 constitute a differential signal line 220 . The insulator portion 230 is formed in a sheet shape and has a pair of main surfaces 231 and 232 . The principal surface 231 is an example of a first principal surface, and the principal surface 232 is an example of a second principal surface.

The insulator section 230 has an insulating layer 241 and an insulating layer 242 . The insulating layer 241 has a major surface 2411 and a major surface 2412 opposite to the major surface 2411 . A plurality of signal lines 22 are provided on the main surface 2411 of the insulating layer 241 .

The conductive layer 251 may not be electrically connected to any member, but is part of the ground line in this embodiment. That is, the conductive layer 251 is electrically connected to ground lines of the rigid printed wiring boards 110 and 120 . As a result, the return current of the signal passing through the signal line 22 flows through the conductive layer 251 . Similarly, conductive layer 252 may not be electrically connected to any member, but is part of the ground line in this embodiment. That is, the conductive layer 252 is electrically connected to the ground lines of the rigid printed wiring boards 110,120.

By the way, if the average length of the signal line that transmits the positive-phase signal and the signal line that transmits the negative-phase signal that are transmitted to the differential signal line is different, mode conversion occurs in which part of the differential signal changes to a common-mode signal. occurs and induces common mode noise. When common mode noise resonates on wiring board 200, large radiation noise occurs at the frequency of the common mode noise.

In addition, with the recent increase in the capacity of communication data, differential signals with a high transmission speed on the order of Gbps, such as 5 Gbps (Giga Bits Per Second) or higher, are transmitted to differential signal lines. A relationship of R=2f holds between the signal transmission speed R [bps] and the signal frequency f [Hz]. In general, the higher the frequency of the differential signal to be transmitted, the greater the amount of change over time in the current flowing through the transmission line, resulting in an increase in the amount of generated radiation noise. If the frequency of the generated radiation noise is close to the communication frequency band of the wireless communication device, the radiation noise will be superimposed on the communication data when the wireless communication IC performs wireless communication with an external device such as a PC or a wireless router through the antenna. Sometimes I end up doing it.

Therefore, in the present embodiment, the conductive layer 251 is arranged on the principal surface 231 of the insulator portion 230 and the conductive layer 252 is arranged on the principal surface 232 of the insulator portion 230 . That is, the plurality of signal lines 22 are sandwiched between the conductive layers 251 and 252 with the insulator portion 230 interposed therebetween. Also, the surface resistivity of the conductive layer 252 is higher than the surface resistivity of the conductive layer 251 . Further, each signal line 22 is wired so as to overlap with the conductive layers 251 and 252 when viewed in the Z direction. Note that the Z direction is also the direction perpendicular to the main surfaces 231 and 232 .

With the above configuration, during signal transmission, the return current of the signal can easily flow through the conductive layer 251 having a relatively low surface resistivity. Thus, the signal is less susceptible to resistive losses in conductive layer 252 . Therefore, the signal passing through wiring board 200 can exhibit good transmission characteristics.

On the other hand, when a noise current flows through the signal line 22, the noise current that cannot be canceled by the electromagnetic field generated by the return current of the conductive layer 251 also flows through the conductive layer 252, thereby directly attenuating the noise current of the signal line 22. It is possible to achieve a high noise suppression effect.

It is preferable that the spacing D1, which is the first spacing in the Z direction between the signal line 22 and the conductive layer 251, be narrower than the spacing D2, which is the second spacing in the Z direction between the signal line 22 and the conductive layer 252. As a result, more return current flows through the conductive layer 251 during signal transmission, and the signal is less susceptible to resistance loss of the conductive layer 252, so that excellent transmission characteristics can be exhibited.

Furthermore, if DD is the third distance between the pair of signal lines 22 in the differential signal line 220 in the Y direction, it is preferable that D1<DD<D2. That is, the Z-direction spacing D1 between the signal line 22 and the conductive layer 251 is preferably narrower than the Y-direction spacing DD between the pair of signal lines 22 in the differential signal line 220 . As a result, each signal line 22 is arranged close to the conductive layer 251, allowing more return current to flow through the conductive layer 251, thereby exhibiting better transmission characteristics.

Next, the insulating layer 241 will be described in detail. When wiring board 200 is a flexible wiring board, the material of insulating layer 241 is preferably resin. Examples of resins include polyimide-based resins such as polyimide, polyamide, and polyamide-imide, thermosetting resins such as epoxy, and thermoplastic resins such as liquid crystal polymers. Among these, polyimide or liquid crystal polymer is preferred. Polyimide has excellent heat resistance and mechanical properties, and is easily commercially available. Liquid crystal polymers are suitable for high-speed signal transmission applications because of their low relative permittivity, and their low hygroscopicity and excellent dimensional stability.

The thickness of the insulating layer 241 in the Z direction is preferably 10 μm or more and 100 μm or less. Since the thickness of the insulating layer 241 in the Z direction is 10 μm or more, the separation distance between the signal line 22 and the conductive layer 251 can be secured, and the characteristic impedance of the signal line 22 can be suppressed from being changed. can be done. Moreover, since the thickness of the insulating layer 241 in the Z direction is 100 μm or less, the rigidity of the insulating layer 241 can be reduced, and sufficient flexibility can be obtained in the flexible printed wiring board. From the above point of view, the thickness of the insulating layer 241 in the Z direction is more preferably 12 μm or more and 75 μm or less.

In addition, when wiring board 200 is a rigid wiring board, the material of insulating layer 241 is preferably a fiber base material. Examples of the fiber base material include glass fiber base materials such as glass woven fabric and glass non-woven fabric, and inorganic fiber base materials such as woven fabric or non-woven fabric containing an inorganic compound other than glass as a component. Examples of fiber base materials include organic fiber base materials composed of organic fibers such as aromatic polyamide, polyamide, aromatic polyester, polyester, polyimide, and fluororesin. Among these, glass fiber substrates are preferable from the viewpoint of excellent strength and low water absorption.

Next, each signal line 22 will be described in detail. A data signal, which is a digital signal representing image data, is transmitted to a differential signal line 220 formed by a pair of signal lines 22 . The method of manufacturing each signal line 22 is not particularly limited, but the signal line 22 can be formed by, for example, lamination of metal foil, metal plating, an inkjet process, or the like. When a copper foil is used as the metal foil, a film bonded with an adhesive or the like can be used, and the required transmission line pattern can be formed by a photolithographic etching process. In the case of using an inkjet process, polymer ink containing conductive metal particles is drawn in a required pattern, and the pattern can be formed by baking the pattern at a temperature below the glass transition point (Tg) of the insulating layer 241. . Although the thickness of each signal line 22 is not particularly limited, it is preferably 0.1 μm or more and 20 μm or less, for example.

Next, the insulating layer 242 will be described in detail. The insulating layer 242 is provided on the main surface 2411 of the insulating layer 241 and on the plurality of signal lines 22 . Insulating layer 242 includes adhesive portion 2421 and covering portion 2422 . The bonding portion 2421 and the covering portion 2422 are laminated in this order on the plurality of signal lines 22 .

It is preferable that the adhesive part 2421 has high electrical insulation. The adhesive portion 2421 is a hardened adhesive. Examples of adhesives used to form the adhesive portion 2421 include acrylonitrile-butadiene rubber (NBR)-based adhesives, polyamide-based adhesives, polyester-based adhesives, acrylic-based adhesives, polyester-polyurethane-based adhesives, and silicone-based adhesives. is mentioned.

Although the thickness of the bonding portion 2421 in the Z direction is not particularly limited, it is preferable that the bonding portion 2421 can sufficiently cover the signal lines 22 that are transmission lines and be smooth. Specifically, the thickness of the bonding portion 2421 in the Z direction is preferably 2 μm or more and 50 μm or less. When the thickness of the adhesive portion 2421 is 2 μm or more, the adhesive can be sufficiently embedded between the signal lines 22, and the adhesive portion 2421 can be firmly attached. Further, when the thickness of the adhesive part 2421 is 50 μm or less, it is possible to suppress the adhesive from seeping out from between the insulating layer 241 and the covering part 2422 to the side. From the above point of view, it is more preferable that the thickness of the bonding portion 2421 in the Z direction is 5 μm or more and 30 μm or less.

The method of forming the adhesive part 2421 is not particularly limited, but examples include a method of bonding sheet-like adhesives together and curing, a method of applying a liquid adhesive by a dispenser or a printing method, and a method of curing with heat or ultraviolet rays. be done.

Next, the covering portion 2422 will be described in detail. The covering portion 2422 is composed of a cover film made of electrically insulating and flexible plastic and a coating layer made of insulating resin.

A so-called engineering plastic is preferably used as the cover film. Examples of plastics used for the cover film include polypropylene, crosslinked polyethylene, polyester, polybenzimidazole, polyamide, polyimide, polyimideamide, and polyetherimide. Plastics used for cover films include, for example, polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), and polyetheretherketone (PEEK). From the viewpoint of low cost, a polyester film is preferred. From the viewpoint of excellent flame retardancy, it is preferable to use a polyphenylene sulfide film. If further heat resistance is required, it is preferable to use an aramid film or a polyimide film.

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

The method of forming the covering portion 2422 is not particularly limited, and the following method can be used when coating the insulating resin on the cover film. For example, a solution obtained by dissolving an insulating resin in a solvent is applied to gravure coating, kiss coating, die coating, blade coating, roll coating, knife coating, spray coating, bar coating, spin coating, and dip coating. can be coated with The solvent can be appropriately selected depending on the type of resin used. For example, ketone solvents such as acetone, methyl ethyl ketone and cyclohexanone, and alcohol solvents such as methanol, ethanol, propanol, ethylene glycol, glycerin and propylene glycol monomethyl ether can be used. Further, for example, acids such as acetic acid, amide solvents such as formamide, dimethylacetamide and N-methylpyrrolidone, nitrile solvents such as acetonitrile and propylonitrile, and ester solvents such as methyl acetate and ethyl acetate can be used. . Carbonate-based solvents such as dimethyl carbonate and diethyl carbonate can also be used. During coating, a heating step or a drying step may be provided for volatilizing the solvent, if necessary. For heating and drying, a heating device and a drying device such as a hot air dryer and an infrared heater can be used, and the heating temperature, drying temperature, heating time and drying time can be appropriately selected.

The Z-direction thickness of the covering portion 2422 is preferably 5 μm or more and 50 μm or less. When the Z-direction thickness of the covering portion 2422 is 5 μm or more, sufficient strength can be ensured in the covering portion 2422 . When the Z-direction thickness of the covering portion 2422 is 50 μm or less, slidability and flexibility are improved. From the above point of view, it is more preferable that the thickness of the covering portion 2422 in the Z direction is 10 μm or more and 30 μm or less. Moreover, the volume resistivity of the covering portion 2422 is preferably 10 ⁹ Ω·cm or more, more preferably 10 ¹³ Ω·cm or more. Note that if the covering portion 2422 has a function of adhering to the insulating layer 241 and the plurality of signal lines 22, the adhesion portion 2421 may be omitted.

Next, the conductive layer 251 will be described in detail. The conductive layer 251 can be formed by printing a conductive resin composition on the insulating layer 241 by the following printing method. Examples of printing methods include gravure printing, microgravure printing, flexographic printing, screen printing, inkjet printing, and dispenser printing. Other printing methods include, for example, spray coating, spin coating, die coating, lip coating, knife coating, dip coating, curtain coating, roll coating, and bar coating.

Note that examples of the metal forming the conductive layer 251 include copper, aluminum, nickel, iron, gold, silver, platinum, tungsten, chromium, titanium, tin, lead, and palladium. A combination may be used. Among these, silver or copper is preferable from the viewpoint of conductivity and low cost.

From the viewpoint of bending resistance, the thickness of the conductive layer 251 in the Z direction is preferably 1 μm or more, more preferably 5 μm or more.

The surface resistivity of the conductive layer 251 is preferably 1Ω/□ or less. When the surface resistivity of the conductive layer 251 is 1 Ω/□ or less, the resistance loss received by the return current during signal transmission is reduced, and the transmission characteristics are further improved. From the above point of view, the surface resistivity of the conductive layer 251 is preferably 0.1Ω/□ or less. The surface resistivity is also called sheet resistance.

Next, the conductive layer 252 will be described in detail. The conductive layer 252 is provided over the insulating layer 242 . The conductive layer 252 is made of a conductive resin composition in which a conductive filler is mixed with a binder resin composition.

Since the resin composition is required to have a function of containing a conductive filler and a function of being able to adhere to the insulating layer 242, a thermosetting resin and a UV curable resin are preferable. Thermosetting resins include, for example, epoxy resins, phenolic resins, amino resins, alkyd resins, urethane resins, synthetic rubbers, and UV curable acrylate resins. UV curable resins also include compounds having ethylenically unsaturated groups capable of free radical addition polymerization or crosslinkable. The compounds are monomers, oligomers, or polymers with terminal or side chain ethylenically unsaturated groups having one or more ethylenically unsaturated groups, such as vinyl or allyl groups. Examples of such compounds include acrylic acid and its salts, acrylic acid esters, acrylamides, methacrylic acid and its salts, methacrylic acid esters, methacrylamides, maleic anhydride and maleic acid esters. Examples of such compounds include itaconic acid esters, styrenes, vinyl ethers, vinyl esters, N-vinyl heterocycles, allyl ethers, and allyl esters. Further, examples of the compounds include derivatives thereof. In order to impart flexibility to the resin composition, the resin composition may contain a rubber component such as carboxyl-modified nitrile rubber, a tackifier, or the like. Moreover, in order to increase the strength of the resin composition, the resin composition may contain a cellulose resin or microfibrils (glass fiber or the like).

A conductive filler is a filler for imparting conductivity. Examples of conductive fillers include metals, conductive metal oxides, carbon materials, and the like, and one or a combination of two or more thereof may be used. Examples of metals include gold, nickel, tin, lead, zinc, titanium, bismuth, antimony, and metal powders obtained by alloying these. Examples of conductive metal oxides include zinc oxide, tin oxide, and indium oxide. Examples of carbon materials include carbon black, carbon fibers, carbon nanotubes, and carbon nanocoils.

The conductive layer 252 can be formed by printing a conductive resin composition on the insulating layer 242 by the following printing method. Examples of printing methods include gravure printing, microgravure printing, flexographic printing, screen printing, inkjet printing, and dispenser printing. Other printing methods include, for example, spray coating, spin coating, die coating, lip coating, knife coating, dip coating, curtain coating, roll coating, and bar coating.

The thickness of the conductive layer 252 in the Z direction is preferably 0.1 μm or more and 100 μm or less. When the thickness of the conductive layer 252 in the Z direction is 0.1 μm or more, the durability against bending of the conductive layer 252 is improved, and the noise suppressing effect is further improved. Since the thickness of the conductive layer 252 in the Z direction is 100 μm or less, the wiring board 200 can be made thinner, and the flexibility of the wiring board 200 is further improved. From the above point of view, the thickness of the conductive layer 252 in the Z direction is preferably 1 μm or more and 50 μm or less.

The surface resistivity of the conductive layer 252 is preferably 10 Ω/□ or more and 10000 Ω/□ or less, more preferably 10 Ω/□ or more and 1000 Ω/□ or less so that noise current can be easily absorbed and attenuated inside the layer.

The insulating layers 243 and 244 are described in detail. An insulating layer 243 is provided over the conductive layer 251 . An insulating layer 244 is provided over the conductive layer 252 . The insulating layers 243 and 244 are for preventing the conductive layers 251 and 252 from conducting to other parts when the wiring board 200 comes into contact with other parts in the housing 611. It is composed of materials with properties. Since each insulating layer 243, 244 needs to have flexibility, it is preferable to be made of a resin material. In this embodiment, each of the insulating layers 243 and 244 is composed of an insulating resin and a coating layer provided on the insulating resin.

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

For the coating layer, for example, an insulating resin solution obtained by dissolving an insulating resin in a solvent can be applied by the following method. Examples thereof include gravure coating, kiss coating, die coating, lip coating, blade coating, roll coating, knife coating, spray coating, bar coating, spin coating and dip coating. A solvent for dissolving the insulating resin can be appropriately selected depending on the type of resin to be used. For example, ketone solvents such as acetone, methyl ethyl ketone and cyclohexanone, and alcohol solvents such as methanol, ethanol, propanol, ethylene glycol, glycerin and propylene glycol monomethyl ether can be used. Further, for example, acids such as acetic acid, amide solvents such as formamide, dimethylacetamide and N-methylpyrrolidone, nitrile solvents such as acetonitrile and propylonitrile, and ester solvents such as methyl acetate and ethyl acetate can be used. . Further, for example, carbonate-based solvents such as dimethyl carbonate and diethyl carbonate can be used. During coating, a heating step or a drying step may be provided for volatilizing the solvent, if necessary. For heating and drying, a heating device and a drying device such as a hot air dryer and an infrared heater can be used, and the heating temperature, drying temperature, heating time and drying time can be appropriately selected.

Although the thickness of the insulating layer 243 in the Z direction is not particularly limited, it is preferably 5 μm or more and 50 μm or less. When the thickness of the insulating layer 243 in the Z direction is 5 μm or more, sufficient strength can be secured in the insulating layer 243 . Moreover, when the thickness of the insulating layer 243 in the Z direction is 50 μm or less, the slidability and flexibility are improved. From the above point of view, it is more preferable that the thickness of the insulating layer 243 in the Z direction is 10 μm or more and 30 μm or less.

In addition, the volume resistance value of the insulating layer 243 is preferably 10 ⁹ Ω·cm or more, more preferably 10 ¹³ Ω·cm or more, from the viewpoint of enhancing the electrical insulation of the insulating layer 243 . Thereby, insulating layer 243 can effectively prevent conductive layer 251 from conducting to other parts when wiring board 200 contacts other parts in housing 611 . Therefore, even if wiring board 200 comes into contact with wireless communication unit 150, good communication is maintained in wireless communication unit 150. FIG.

The positional relationship between wireless communication unit 150 and each part of wiring board 200 in housing 611 will be described. The distance between the wireless communication unit 150 and the conductive layer 251 in the housing 611 is preferably shorter than the distance between the wireless communication unit 150 and each signal line 22 . That is, the conductive layer 251 is preferably arranged at a position closer to the wireless communication unit 150 than each signal line 22 . Since the conductive layer 251 is located closer to the wireless communication unit 150 than each signal line 22, radiation noise generated from each signal line 22 is suppressed from being superimposed on radio waves of wireless communication performed by the wireless communication unit 150. can be done.

A preferred example of a method for manufacturing wiring board 200 will be described in detail below. 3A to 3C are explanatory diagrams showing an example of a method for manufacturing the wiring board 200 according to the embodiment.

First, as shown in FIG. 3(a), an insulator portion 230 in which a plurality of signal lines 22 are arranged is prepared. That is, the wiring board main body 210 is prepared. Next, as shown in FIG. 3B, a conductive layer 251 is formed on the principal surface 231, which is the first principal surface of the insulator portion 230. Next, as shown in FIG. The method for forming the conductive layer 251 is as described above. Next, as shown in FIG. 3C, a conductive layer 252 is formed on the principal surface 232, which is the second principal surface of the insulator portion 230. Next, as shown in FIG. The order of forming the conductive layers 251 and 252 is not limited to this, and the order may be reversed. Next, as shown in FIG. 3D, an insulating layer 243 is formed over the conductive layer 251, and an insulating layer 244 is formed over the conductive layer 252. Then, as shown in FIG. Wiring board 200 is manufactured by the manufacturing method described above.

(Example)
Next, examples and comparative examples to be compared with the examples will be described. The wiring board of the example corresponds to the wiring board 200 of the above embodiment. The radiation noise and transmission characteristics of the wiring boards of the examples and the wiring boards of the comparative examples were evaluated below. The surface resistivity was measured according to JIS K7194 using Loresta-EP MCP-T360 (measuring probe MCP-TP03P) manufactured by Dia Instruments.

(1) Radiation Noise Measurement FIG. 4A is an explanatory diagram of a system 300 for measuring radiation noise amounts of the wiring board 200 of the example and the wiring board 200X of the comparative example. The amount of radiation noise of the wiring board 200 of the example and the wiring board 200X of the comparative example was evaluated using the system 300 shown in FIG. 4(a). The system 300 comprises a signal generator 31 , an oscilloscope 32 , a spectrum analyzer 33 , a near field probe 34 connected to the spectrum analyzer 33 and a pair of connection boards 35 . Each connection board 35 has a pair of terminals capable of inputting and outputting signals. As the signal generator 31, M8041A manufactured by Keysight was used. As the oscilloscope 32, 92504A manufactured by Agilent Technologies was used. E4440A manufactured by Keysight was used as the spectrum analyzer 33 . As the near field probe 34, a pen-shaped probe with a length of 110 mm manufactured by Electrometric was used.

Here, for reference, a wiring board (not shown) having no ground layer and including differential signal lines was prepared. A wiring board (not shown) was manufactured as follows. First, a 25 μm-thick polyimide film (Kapton 100H manufactured by Toray DuPont Co., Ltd.) was used as a substrate, and a 12 μm-thick copper foil was laminated as a wiring layer on one surface of the substrate. Thereafter, a differential transmission line having a line width of 140 μm, a line spacing of 55 μm, and a total length of 100 mm was fabricated by etching. Next, a 12.5 μm-thick polyimide film and a 15 μm-thick coverlay (CISV1215 manufactured by Nikkan Kogyo Co., Ltd.) were pasted on the differential transmission line to obtain a reference wiring board without a ground layer. .

Next, this wiring board (not shown) was connected to a pair of connection boards 35 . Using the signal generator 31, a signal having a data pattern of 5.3 Gbps as PRBS23 was sent to a wiring board (not shown). Then, the waveform of the common mode voltage was observed with an oscilloscope 32, and the input amplitude was adjusted so that the common mode voltage was 150 mV.

Next, the wiring board 200 to be measured was connected to the pair of connection boards 35 , and the signal generator 31 was used to send to the wiring board 200 a signal with a bit rate of 5.3 Gbps and a PRBS23 data pattern. Here, a signal was sent with an input amplitude adjusted using a reference wiring board without a conductive layer. 5 GHz radiation noise 36 generated from the wiring board 200 was detected by the near electric field probe 34 and the amount of radiation noise was measured by the spectrum analyzer 33 . Here, a method for measuring the amount of radiation noise will be described. First, the near field probe 34 was installed at a point 5 mm above the wiring board 200 . A plurality of points at intervals of 1 mm defined in the region where the conductive layer was formed was scanned five times with the near electric field probe 34, and the average value of all the data obtained from each point was taken as the amount of radiation noise.

The smaller the amount of radiation noise, the more shielding the radiation noise 36 has on the wiring board 200 . The radiation noise was measured in an atmosphere with a temperature of 25° C. and a relative humidity of 23 to 50% in a frequency range of 300 kHz to 20 GHz. The method for measuring the amount of radiation noise in wiring board 200 of the example was described above, and the amount of radiation noise was measured in the same manner for wiring board 200X of the comparative example.

The amount of radiation noise was evaluated in four stages of A, B, C, and D. A is less than 16 dBμV. B is greater than or equal to 16 dBμV and less than 18 dBμV. C is greater than or equal to 18 dBμV and less than 20 dBμV. D is 20 dBμV or more. The smaller the measured value, the smaller the amount of radiation noise. Therefore, C is superior to D, B is superior to C, and A is superior to B in terms of radiation noise amount.

(2) Transmission characteristics (eye pattern)
FIG. 4B is a schematic diagram of a system 400 used to evaluate the transmission characteristics of the wiring board 200 of the example and the wiring board 200X of the comparative example. This system 400 comprises an Agilent Technologies M8041A signal generator 41 , an Agilent Technologies 92504A oscilloscope 42 , and a pair of connection boards 35 . Using the system 400 configured as shown in FIG. 4B, the transmission characteristics of the wiring boards 200 and 200X, that is, the output waveform characteristics were evaluated. Each connection board 35 has a pair of terminals capable of inputting and outputting signals.

A wiring board 200 of the example and a wiring board 200X of the comparative example were connected between a pair of connection boards 35 in a state of being suspended in the air. Further, the signal generator 41 and one connection board 35 were connected, and a pseudo-random signal of PRBS 23 with a bit rate of 5.3 Gbps was input to one connection board 35 . The amplitude of the input signal to each terminal of one connection substrate 35 was set to 150 mV/side. That is, the amplitude of the differential signal input to the pair of terminals of one connection board 35 was set to 300 mV. An oscilloscope 42 was connected to the other connection board 35 . The oscilloscope 42 was used to observe the aperture amplitude of the eye pattern of the signal output from the other connection board 35 . The eye pattern aperture amplitude was measured in an atmosphere with a temperature of 25° C. and a relative humidity of 30 to 50%.

The transmission characteristics, that is, the aperture amplitude of the eye pattern were evaluated in four stages of A, B, C, and D below. A has an aperture amplitude of 120 mV or more. B is an aperture amplitude of 110 mV or more and less than 120 mV. C is an aperture amplitude of 100 mV or more and less than 110 mV. D is less than 100 mV aperture amplitude. C is superior to D, B is superior to C, and A is superior to B in transmission characteristics.

As examples, ten types of wiring boards 200 of Examples 1 to 10 were manufactured. As comparative examples, four types of wiring boards 200X of comparative examples 1 to 4 were manufactured. FIG. 5 is a table showing layer configurations of the first conductive layer and the second conductive layer in the wiring board 200 of the example and the wiring board 200X of the comparative example. FIG. 6 is a table showing the configuration and evaluation of the wiring board 200 of the example. FIG. 7 is a table showing the configuration and evaluation of a wiring board 200X of a comparative example.

The configuration of the wiring board 200 of each of Examples 1 to 10 will be described with reference to FIGS. 5 and 6. FIG.

(Example 1)
A polyimide film having a thickness of 25 μm was prepared as the insulating layer 241 . Kapton 100H manufactured by DuPont Toray Co., Ltd. was used for this polyimide film. A copper foil having a thickness of 12 μm was laminated on the main surface 2411 of the insulating layer 241, and a pair of signal lines 22 having a line width of 50 μm, a line interval of 140 μm, and a total length of 100 mm were produced by etching. Next, an insulating layer 242 was formed by attaching a 15 μm-thick coverlay with a 25 μm-thick adhesive onto the pair of signal lines 22 , that is, on the main surface 2411 of the insulating layer 241 . CEAM0525KA manufactured by Arisawa Seisakusho Co., Ltd. was used as the coverlay. Thus, a wiring board body 210 having a total thickness of 37.5 μm was obtained.

Next, a conductive layer 251 is formed on the main surface 2412 of the insulating layer 241, that is, on the main surface 231 of the insulator section 230, and on the insulating layer 242, that is, on the main surface 232 of the insulator section 230. , a conductive layer 252 was formed. In Example 1, the conductive layer 251 contains Ag (silver) as a main component (50 wt % or more). A method for forming the conductive layers 251 and 252 will be described below.

A polyester urethane resin solution was used as a binder for forming the conductive layers 251 and 252 . As this polyester urethane resin solution, UR1400 manufactured by Toyobo Co., Ltd. having a solid content of 30 vol % was used.

Ag described in the layer structure (A) shown in FIG. 5 was used as the conductive filler forming the conductive layer 251 . Ag was added to the polyester urethane resin solution so that Ag was 92 wt % when the total of Ag and the solid content of the polyester urethane resin solution was 100 wt %. Then, the Ag-added polyester urethane resin solution was stirred at 15,000 rpm for 30 minutes using a homogenizer to disperse Ag, which is a conductive filler. This composition was applied onto main surface 231 of insulator portion 230 of wiring board main body 210 using an applicator, and then dried at 100° C. for 10 minutes. Thus, a conductive layer 251 containing 92 wt % Ag was formed. The thickness of the conductive layer 251 was 1 μm. The surface resistivity of the conductive layer 251 was 0.02Ω/□.

Ni described in the layer structure (E) shown in FIG. 5 was used as the conductive filler forming the conductive layer 252 . The conductive layer 252 was formed by a method similar to that of the conductive layer 251 . Thus, a conductive layer 252 containing 80 wt % Ni was formed. The thickness of the conductive layer 252 was 0.5 μm. The surface resistivity of the conductive layer 252 was 100Ω/□.

Next, a polyester urethane resin solution having the same composition as that used to form the conductive layers 251 and 252 is applied onto each of the conductive layers 251 and 252 using an applicator, and then dried at 100° C. for 10 minutes. An insulating layer 243 and an insulating layer 244 were formed. Thus, wiring board 200 of Example 1 was obtained. The thickness of the insulating layers 243 and 244 was 10 μm.

(Examples 2 to 9)
The layer structure, that is, the material, thickness and surface resistivity of the conductive layers 251 and 252 in each of Examples 2 to 9 were the conditions shown in FIG. Further, the layer structure, ie, the material and thickness of each insulating layer 243, 244 in each of Examples 2 to 9 was the same as in Example 1. The method of forming the wiring board 200 in each of Examples 2 to 9 was the same as in Example 1. FIG. Thus, wiring boards 200 of Examples 2 to 9 were obtained.

The conductive fillers forming the conductive layer 251 in the wiring board 200 of Example 2 are Ag (silver) and Cu (copper) described in the layer structure (B) shown in FIG. It contains 85 wt % of a conductive filler consisting of Ag and Cu as a main component. The thickness of the conductive layer 251 was 10 μm. The surface resistivity of the conductive layer 251 was 0.9Ω/□. The conductive filler constituting conductive layer 252 in wiring board 200 of Example 2 is Ni described in the layer structure (E) shown in FIG. 5, and conductive layer 252 contains 80 wt % of Ni. The thickness of the conductive layer 252 was 0.5 μm. The surface resistivity of the conductive layer 252 was 100Ω/□.

The conductive filler constituting conductive layer 251 in wiring board 200 of Example 3 is Ag described in the layer structure (A) shown in FIG. 5, and conductive layer 251 contains 92 wt % of Ag. The thickness of the conductive layer 251 was 1 μm. The surface resistivity of the conductive layer 251 was 0.02Ω/□. The conductive filler constituting conductive layer 252 in wiring board 200 of Example 3 is CB (carbon) described in the layer structure (F) shown in FIG. 5, and conductive layer 252 contains 15 wt % of CB. The thickness of the conductive layer 252 was 1 μm. The surface resistivity of the conductive layer 252 was 9100Ω/□.

The conductive filler constituting the conductive layer 251 in the wiring board 200 of Example 4 is Ag and Cu described in the layer structure (C) shown in FIG. It contains 80 wt % of conductive filler including Cu. The thickness of the conductive layer 251 was 2 μm. The surface resistivity of the conductive layer 251 was 2Ω/□. The conductive filler constituting conductive layer 252 in wiring board 200 of Example 4 is Ni described in the layer structure (E) shown in FIG. 5, and conductive layer 252 contains 80 wt % of Ni. The thickness of the conductive layer 252 was 0.5 μm. The surface resistivity of the conductive layer 252 was 100Ω/□.

The conductive filler constituting conductive layer 251 in wiring board 200 of Example 5 is Ag described in the layer structure (A) shown in FIG. 5, and conductive layer 251 contains 92 wt % of Ag. The thickness of the conductive layer 251 was 1 μm. The surface resistivity of the conductive layer 251 was 0.02Ω/□. The conductive filler constituting conductive layer 252 in wiring board 200 of Example 5 is CB (carbon) described in the layer structure (G) shown in FIG. 5, and conductive layer 252 contains 10 wt % of CB. The thickness of the conductive layer 252 was 0.1 μm. The surface resistivity of the conductive layer 252 was 22000Ω/□.

The conductive filler constituting conductive layer 251 in wiring board 200 of Example 6 is Ag described in the layer structure (A) shown in FIG. 5, and conductive layer 251 contains 92 wt % of Ag. The thickness of the conductive layer 251 was 1 μm. The surface resistivity of the conductive layer 251 was 0.02Ω/□. The conductive filler constituting conductive layer 252 in wiring board 200 of Example 6 is CB (carbon) described in the layer structure (H) shown in FIG. 5, and conductive layer 252 contains 10 wt % of CB. The thickness of the conductive layer 252 was 100 μm. The surface resistivity of the conductive layer 252 was 1200Ω/□.

The conductive filler constituting the conductive layer 251 in the wiring board 200 of Example 7 is Ag and Cu described in the layer structure (B) shown in FIG. It contains 85 wt % of conductive filler including Cu. The thickness of the conductive layer 251 was 10 μm. The surface resistivity of the conductive layer 251 was 0.9Ω/□. The conductive filler constituting the conductive layer 251 in the wiring board 200 of Example 7 is Ag and Cu described in the layer configuration (C) shown in FIG. It contains 80 wt% of filler. The thickness of the conductive layer 251 was 2 μm. The surface resistivity of the conductive layer 251 was 2Ω/□.

The conductive filler constituting conductive layer 251 in wiring board 200 of Example 8 is Ag described in the layer structure (A) shown in FIG. 5, and conductive layer 251 contains 92 wt % of Ag. The thickness of the conductive layer 251 was 1 μm. The surface resistivity of the conductive layer 251 was 0.02Ω/□. The conductive filler constituting conductive layer 252 in wiring board 200 of Example 8 is Ni described in the layer structure (E) shown in FIG. 5, and conductive layer 252 contains 80 wt % of Ni. The thickness of the conductive layer 252 was 0.5 μm. The surface resistivity of the conductive layer 252 was 100Ω/□.

The conductive filler constituting the conductive layer 251 in the wiring board 200 of Example 9 is Ag and Cu described in the layer structure (D) shown in FIG. It contains 75 wt % of conductive filler including Cu. The thickness of the conductive layer 251 was 5 μm. The surface resistivity of the conductive layer 251 was 3Ω/□. The conductive filler constituting conductive layer 252 in wiring board 200 of Example 9 is Ni described in the layer structure (E) shown in FIG. 5, and conductive layer 252 contains 80 wt % of Ni. The thickness of the conductive layer 252 was 0.5 μm. The surface resistivity of the conductive layer 252 was 100Ω/□.

(Example 10)
In Example 10, the thickness of the insulating layer 241 was changed to 50 μm.

The conductive filler constituting conductive layer 251 in wiring board 200 of Example 10 is Ag described in the layer structure (A) shown in FIG. 5, and conductive layer 251 contains 92 wt % of Ag. The thickness of the conductive layer 251 was 1 μm. The surface resistivity of the conductive layer 251 was 0.02Ω/□. The conductive filler constituting conductive layer 252 in wiring board 200 of Example 10 is Ni described in the layer structure (E) shown in FIG. 5, and conductive layer 252 contains 80 wt % of Ni. The thickness of the conductive layer 252 was 0.5 μm. The surface resistivity of the conductive layer 252 was 100Ω/□.

(Comparative Example 1 and Comparative Example 2)
The layer structure, ie, the material, thickness and surface resistivity of the conductive layers 251 and 252 in each of Comparative Examples 1 and 2 were the conditions shown in FIG. The layer structure, ie, the material and thickness of each insulating layer 243 and 244 in each of Comparative Examples 1 and 2 was the same as in Example 1. The method of forming the wiring board 200X in each of Comparative Examples 1 and 2 was the same as in Example 1. As a result, wiring boards 200X of Comparative Examples 1 and 2 were obtained.

The conductive filler constituting each of the conductive layers 251 and 252 in the wiring board 200X of Comparative Example 1 is Ag described in the layer structure (A) shown in FIG. contains. The thickness of each conductive layer 251, 252 was 1 μm. The surface resistivities of the conductive layers 251 and 252 were both the same, 0.02Ω/□.

The conductive filler constituting each of the conductive layers 251 and 252 in the wiring board 200X of Comparative Example 2 is Ni described in the layer structure (E) shown in FIG. contains. The thickness of each conductive layer 251, 252 was 0.5 μm. The surface resistivity of each conductive layer 251, 252 was 100Ω/□.

That is, in Comparative Examples 1 and 2, the surface resistivity of the conductive layer 251 is set to the same value as the surface resistivity of the conductive layer 252 .

(Comparative Example 3)
FIG. 8A is an explanatory diagram of a wiring board 200X3 of Comparative Example _3. FIG. In addition, in FIG. 8A, the same reference numerals are given to the same configurations as in the embodiment. In Comparative Example 3, in the same manner as in Example 1, after manufacturing wiring board body 210 , conductive layer 251 , insulating layer 243 , conductive layer 252 , and insulating layer 244 were applied in this order on main surface 2412 of insulating layer 241 . A wiring board 200X3 was manufactured by forming the wiring board _200X3 . The material and thickness of the insulating layers 243 and 244 were the same as in the first embodiment.

The conductive filler constituting the conductive layer 251 in the wiring board 200X3 of Comparative Example ₃ is Ag described in the layer structure (A) shown in FIG. 5, and the conductive layer 251 contains 92 wt % of Ag. The thickness of the conductive layer 251 was 1 μm. The surface resistivity of the conductive layer 251 was 0.02Ω/□. The conductive filler constituting the conductive layer 252 in the wiring board 200X3 of Comparative Example ₃ is Ni described in the layer structure (E) shown in FIG. 5, and the conductive layer 252 contains 80 wt % of Ni. The thickness of the conductive layer 252 was 0.5 μm. The surface resistivity of the conductive layer 252 was 100Ω/□.

(Comparative Example 4)
FIG. 8B is an explanatory diagram of a wiring board 200X4 of Comparative Example _4. FIG. In addition, in FIG.8(b), the same code|symbol is attached|subjected about the structure similar to embodiment. In Comparative Example 4, in the same manner as in Example 1, after manufacturing wiring board body 210 , conductive layer 252 , insulating layer 244 , conductive layer 251 , and insulating layer 243 were applied in this order on main surface 2412 of insulating layer 241 . A wiring board 200X4 was manufactured by forming the wiring board _200X4 . The material and thickness of the insulating layers 243 and 244 were the same as in the first embodiment.

The conductive filler constituting the conductive layer 251 in the wiring board 200X4 of Comparative Example ₄ is Ag described in the layer structure (A) shown in FIG. 5, and the conductive layer 251 contains 92 wt % of Ag. The thickness of the conductive layer 251 was 1 μm. The surface resistivity of the conductive layer 251 was 0.02Ω/□. The conductive filler constituting the conductive layer 252 in the wiring board 200X4 of Comparative Example ₄ is Ni described in the layer structure (E) shown in FIG. 5, and the conductive layer 252 contains 80 wt % of Ni. The thickness of the conductive layer 252 was 0.5 μm. The surface resistivity of the conductive layer 252 was 100Ω/□.

That is, in Comparative Examples 3 and 4, the configuration of each of the conductive layers 251 and 252 was the same as in Example 1, but the arrangement of the conductive layers 251 and 252 was different from that in Examples 1-10.

6 and 7 show the evaluation results of the above (1) and (2) for the wiring boards of these examples and the wiring boards of the comparative examples.

As shown in FIG. 6, in the wiring boards 200 of Examples 1 to 10, the amount of radiation noise at 5 GHz is small, and the aperture amplitudes of the eye patterns are all C-rank or higher, which is good.

Comparing Examples 1, 8 and 10, it can be seen that the signal transmission characteristics are improved as the interval D1 is narrower than the interval D2, ie, (D2-D1) is larger.

Comparing Examples 1, 2, 4, and 9, it can be seen that the higher the Ag and Cu contents in the conductive layer 251 and the lower the surface resistivity of the conductive layer 251, the better the signal transmission characteristics.

That is, it is preferable that the surface resistivity of the conductive layer 251 is 3Ω/□ or less. Moreover, it is more preferable that the surface resistivity of the conductive layer 251 is 1 Ω/□ or less. Further, it is more preferable that the surface resistivity of the conductive layer 251 is 0.1Ω/□ or less.

In addition, the conductive layer 251 preferably contains 75 wt % or more of metal filler made of Ag and Cu. In addition, the conductive layer 251 more preferably contains 80 wt % or more of metal filler made of Ag and Cu. In addition, the conductive layer 251 more preferably contains 85 wt % or more of metal filler made of Ag and Cu. Moreover, it is more preferable that the conductive layer 251 contains 92 wt % or more of a metal filler made of Ag.

Comparing Examples 1, 3, 5, 6, and 7, it can be seen that a high noise suppression effect is obtained when the surface resistivity of the conductive layer 251 is 2 Ω/□ or more and 22000 Ω/□ or less. From this point of view, the surface resistivity of the conductive layer 251 is preferably 10 Ω/square or more and 10000 Ω/square or less, and more preferably 10 Ω/square or more and 1000 Ω/square or less.

Further, when comparing Examples 1 to 10, it is preferable that the thickness of the conductive layer 252 is 0.1 μm or more and 100 μm or less.

On the other hand, as shown in FIG. 7, in the wiring board 200X of Comparative Example 1, both the conductive layers 251 and 252 have low surface resistivities, and the noise current attenuation effect due to the resistance loss cannot be obtained. Noise suppression effect cannot be obtained. In the wiring board 200X of Comparative Example 2, both the conductive layers 251 and 252 have high surface resistivities, and the return current of the signal current is attenuated due to resistance loss, and good signal transmission characteristics cannot be obtained. In the wiring board 200X3 of Comparative Example ₃ , almost no noise current flows through the conductive layer 252 that plays the role of radiation noise suppression, and a sufficient noise suppression effect cannot be obtained. In the wiring board 200X4 of Comparative Example ₄ , most of the return current of the signal current flows through the conductive layer 252 with large resistance loss, and good transmission characteristics cannot be obtained.

As described above, according to Examples 1 to 10, compared with Comparative Examples 1 to 4, the radiation noise radiated from the wiring board 200 can be suppressed, and the signal transmitted through the signal line 22 can be suppressed. Transmission characteristics can be improved.

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

22 Signal line 200 Wiring board 230 Insulator portion 231 Main surface (first main surface) 232 Main surface (second main surface) 251 Conductive layer (first conductive layer) 252 ... conductive layer (second conductive layer)

Claims (20)

an insulator portion having a first principal surface and a second principal surface opposite to the first principal surface;
a signal line arranged inside the insulator;
a first conductive layer disposed on the first main surface;
a second conductive layer disposed on the second main surface;
the surface resistivity of the second conductive layer is greater than the surface resistivity of the first conductive layer;
A wiring board characterized by: a first spacing between the signal line and the first conductive layer is narrower than a second spacing between the signal line and the second conductive layer;
The wiring board according to claim 1, characterized in that: comprising a plurality of the signal lines,
A pair of signal lines adjacent to each other among the plurality of signal lines constitutes a differential signal line through which a differential signal is transmitted,
the first spacing is narrower than the third spacing between the pair of signal lines;
The wiring board according to claim 2, characterized in that: When viewed in a direction perpendicular to the first main surface, the signal line overlaps the first conductive layer and the second conductive layer,
The wiring board according to any one of claims 1 to 3, characterized in that: The first conductive layer has a surface resistivity of 3 Ω/□ or less.
The wiring board according to any one of claims 1 to 4, characterized in that: The first conductive layer has a surface resistivity of 1 Ω/□ or less.
The wiring board according to any one of claims 1 to 4, characterized in that: The first conductive layer has a surface resistivity of 0.1 Ω/□ or less.
The wiring board according to any one of claims 1 to 4, characterized in that: The first conductive layer contains Ag as a main component,
The wiring board according to any one of claims 1 to 7, characterized in that: The first conductive layer contains 92 wt% or more of Ag,
The wiring board according to any one of claims 1 to 8, characterized in that: The first conductive layer contains a total of 75 wt% or more of Ag and Cu,
The wiring board according to any one of claims 1 to 8, characterized in that: The first conductive layer contains a total of 80 wt% or more of Ag and Cu,
The wiring board according to any one of claims 1 to 8, characterized in that: The first conductive layer contains 85 wt% or more of Ag and Cu in total.
The wiring board according to any one of claims 1 to 8, characterized in that: The second conductive layer has a surface resistivity of 2 Ω/□ or more and 22000 Ω/□ or less.
The wiring board according to any one of claims 1 to 12, characterized in that: The second conductive layer has a surface resistivity of 10 Ω/□ or more and 10000 Ω/□ or less.
The wiring board according to any one of claims 1 to 12, characterized in that: The second conductive layer has a surface resistivity of 10 Ω/□ or more and 1000 Ω/□ or less.
The wiring board according to any one of claims 1 to 12, characterized in that: The thickness of the second conductive layer is 0.1 μm or more and 100 μm or less,
The wiring board according to any one of claims 1 to 15, characterized in that: The wiring board is a flexible printed wiring board,
The wiring board according to any one of claims 1 to 16, characterized in that: A wiring board according to any one of claims 1 to 17;
an electronic component electrically connected to the wiring board;
An electronic unit characterized by: an electronic unit according to claim 18;
a housing in which the electronic unit is housed,
An electronic device characterized by: Prepare an insulator part inside which the signal line is arranged,
A first conductive layer is formed on the first main surface of the insulator portion, and a surface resistance higher than the surface resistivity of the first conductive layer is formed on the second main surface of the insulator portion opposite to the first main surface. each forming a second conductive layer of
A wiring board manufacturing method characterized by:

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