A printed wiring board comprises a sheet-shaped core base material containing a magnetic material, a coil disposed inside the core base material, and an external circuit layer disposed on at least one of first and second surfaces of the core base material opposite to each other.

A printed wiring board includes: a first insulating layer having a first surface and a second surface opposite from the first surface; a second insulating layer stacked on the first surface of the first insulating layer; and a conductor wiring interposed between the first insulating layer and the second insulating layer. The first insulating layer contains a liquid crystal polymer. The second insulating layer contains a cured product of a thermosetting composition, containing an inorganic filler and a thermosetting component, and a fibrous base member. A temperature, at which a decrease in the mass of the second insulating layer that has had its temperature increased at a temperature increase rate of 10 C./min from an initial-state temperature of 25 C. reaches 5% of its initial-state mass, is equal to or higher than 355 C.

A printed wiring board comprises a sheet-shaped core base material containing a magnetic material, a coil disposed inside the core base material, and an external circuit layer disposed on at least one of first and second surfaces of the core base material opposite to each other.

A flexible circuit board includes a substrate including a base layer and a bonding layer formed on each of opposite sides of the base layer. Each of the two bonding layers is formed by coating a bonding solution and drying the bonding solution. The bonding solution is composed of an adhesive and a solvent. A viscosity of the adhesive is 5000 millipascal-seconds. The adhesive is composed of a precursor having a mass fraction of 35%-65%, carboxyl modified polyphenylene oxide having a mass fraction of 10%-15%, bisphenol-F-epoxy resin having a mass fraction of 10%-15%, a silane coupling agent having a mass fraction of 0%-1.5%, silica filler having a mass fraction of 5%-20%, and a flame retardant filler having a mass fraction of 10%-20%.

An organic insulator is composed an organic resin phase as a main component. The organic resin phase includes a weather-resistant stabilizer. The organic resin phase includes an inner region and a surface region formed in at least one surface of the inner region. The surface region has a higher content ratio of the weather-resistance stabilizer than the inner region. A metal-clad laminate includes the organic insulator and a metallic foil laminated on at least one surface of the organic insulator. A wiring board includes a plurality of insulating layers composed of the organic insulator, and a metallic foil disposed between the insulating layers.

A resin composition for a printed circuit board includes an epoxy resin; an active ester hardening agent configured to react with the epoxy resin; and a cyanate ester hardening agent.

A multilayer wiring board includes first and second insulating layers, a first conductive wiring layer on the first insulating layer, a second conductive wiring layer on a surface the second insulating layer facing the first insulating layer, an interlayer connection conductor including an intermetallic compound and penetrating through the first insulating layer to interconnect the first and second conductive wiring layers, a first intermetallic compound layer between the first conductive wiring layer and the interlayer connection conductor, and a second intermetallic compound layer between the second conductive wiring layer and the interlayer connection conductor, wherein the intermetallic compounds in the first and second intermetallic compound layers have a composition different from that of the intermetallic compound in the interlayer connection conductor, and the first intermetallic compound layer at a level different from a level of an interface between the first conductive wiring layer and the first insulating layer.

A wiring board includes a first insulating layer including a surface having unevenness, a second insulating layer including a surface having unevenness, laminated on the first insulating layer, and made of the same insulating material as that of the first insulating layer, insulating particles contained in the first and second insulating layers at rate of 40 to 80 wt %, a first wiring conductor on a first underlying metal layer surface, and a second wiring conductor on a second underlying metal layer surface. A second level difference of the unevenness in a surface region of the second insulating layer under the second wiring conductor is smaller than a first level difference of the unevenness in a surface region of the first insulating layer under the first wiring conductor, and the second level difference is not more than of an average particle size of the insulating particles.

There is provided an organic insulating body which contains a cyclic olefin copolymer as a main component and a peroxide having a benzene ring, and has such a property that a loss tangent peak appears at 120 C. or higher in a dynamic mechanical analysis.

A flexible circuit board includes a substrate including a base layer and a bonding layer formed on each of opposite sides of the base layer. Each of the two bonding layers is formed by coating a bonding solution and drying the bonding solution. The bonding solution is composed of an adhesive and a solvent. A viscosity of the adhesive is 5000 millipascal-seconds. The adhesive is composed of a precursor having a mass fraction of 35%-65%, carboxyl modified polyphenylene oxide having a mass fraction of 10%-15%, bisphenol-F-epoxy resin having a mass fraction of 10%-15%, a silane coupling agent having a mass fraction of 0%-1.5%, silica filler having a mass fraction of 5%-20%, and a flame retardant filler having a mass fraction of 10%-20%.