Planar inductors and method of manufacturing thereof

Abstract

A printed circuit board has two layers of printed circuit board dielectric material; a core made of ferromagnetic material between the two layers; and conductive leads on the opposite side of each dielectric layer from the core connected by via holes through both dielectric layers to form a conducting coil around the core. The conductive leads can form two separate coils around the core to form a transformer. A planar conducing sheet can be placed on or between one or more of the printed circuit board's dielectric layers to shield other circuitry on the printed circuit board from magnetic fields generated around the core. The core can be formed at least in part by electroless plating. Electroplating can be used to add a thicker layer of less conductive ferromagnetic material. Ferromagnetic inductive cores can be formed on the surface of a dielectric material by: dipping the surface of the dielectric in a solution containing catalytic metal particles having a slight dipole; and placing the dielectric in a metal salt to cause a layer containing metal to be electrolessly plated upon the dielectric. Plasma etching or other technique can be used before the dipping process to roughen the dielectric's surface to help attract the catalytic particles. This method can be used to form an inductor core on or between one or more dielectric layers of a printed circuit board, of a multichip module, of an integrated circuit, or of a micro-electromechanical device.