PWB-Embeddable Lateral Ferrite Core Inductor and Method of Forming Thereof
Original Publication Date: 2001-Oct-09
Included in the Prior Art Database: 2001-Oct-09
This document describes an embedded inductor for printed wiring board (PWB) substrates including a ferrite core and a potential process for fabricating it. Inductors fabricated according to this method could potentially have inductance values in the hundreds of nanohenries to low microhenry values. For many electrical designs, values of inductors up in the microhenry range are required. For good RF performance, spiral inductors may be necessary, but for cases such as switching power supplies, a multi-turn inductor may be used. Good performance for this type of design can be obtained into the 300 kHz range. For potential cost and area savings, a PWB-embeddable solution is desired. However, there is no PWB embeddable component of this type in Motorola's technology base. The device disclosed is a PWB-embeddable inductor that is produced with a ferrite core. The magnetic field direction in the device is parallel to the substrate surface (coil center is lateral). Magnetic shielding at the ends of the coils may be required. The core can be created in toroidal shape, for transformer applications within the plane, or stacked for multilayer HDI to minimize board surface area. Alternatively, plated through holes can connect ferrite layers on opposite side of the FR-4 core layers, allowing a loop of ferrite material, which is useful in building transformers from one side of the board to the other or adding two inductors in series on opposite sides of the board.