Abstract: The present invention provides a core piece and a reactor that have excellent bondability to a resin portion and are capable of reducing the generation of eddy currents. The core piece is a core piece that constitutes a magnetic core disposed within or outside a coil formed of a wound wire, the core piece including an end surface that is orthogonal to a magnetic flux flowing through the coil and to which a resin portion is bonded, wherein the end surface has an intersecting groove in which a plurality of grooves intersect without forming a loop. The core piece may be, for example, a powder compact made of metal particles and an insulating material present between the metal particles. The core piece may constitute, for example, a portion of the magnetic core, the portion being disposed within the coil.

Abstract: A wiring board sheet which enables the miniaturization of a wiring board by mounting electric components (10) in an insulation layer (4) to increase the quantity of mounting electric components, has a high reliability, and undergoes a complicated manufacturing process, and a method for manufacturing the wiring board sheet A multilayer board which is mannufactured from this wiring board sheet, eliminates a difference in thermal histories during molding in each layer, simplifies the manufacturing process, and realize miniaturization by the scale-down and high-density of a conductor circuit and an improvement in reliability, and a method for manufacturing the multilayer board.

Abstract: A wiring board sheet which enables the miniaturization of a wiring board by mounting electric components (10) in an insulation layer (4) to increase the quantity of mounting electric components, has a high reliability, and undergoes a complicated manufacturing process, and a method for manufacturing the wiring board sheet A multilayer board which is manufactured from this wiring board sheet, eliminates a difference in thermal histories during molding in each layer, simplifies the manufacturing process, and realize miniaturization by the scale-down and high-density of a conductor circuit and an improvement in reliability, and a method for manufacturing the multilayer board.