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The integration of passive components into the printed circuit board (PCB) as embedded passives integrated circuits (emPIC) results in a higher power density of power converters. To achieve a highly automated, low cost, integral manufacturing, the devices are constructed layer wise. Materials and processes necessary for the manufacturing of such circuits are described in this publication. Especially for magnetic components like inductors and transformers the design of such thin components is challenge. Because of the high aspect ratio, traditionally used models lead to a high calculation effort or use nonappropriate approximations. This contribution presents an analytic approach for the design. The model considers the magnetic flux distribution in the core and in the winding area and therefore allows a precise calculation of the inductivity as well as the losses in the device and their distribution. It is very well suited for a parametric analysis and thus for the synthesis of thin planar magnetic components. Material technologies for the construction of the capacitive layers and the magnetic cores are investigated. A ferrite polymer compound is adapted to be compatible with the PCB laminating process. Accordingly a 60-W offline converter was designed and fabricated using the new technology. Its transformer is entirely integrated in the PCB as well as 11 capacitors. Standard PCB lamination processes are used for the layerwise integration of the components. The circuit needs an area of the size of a credit card with a PCB thickness of 4 mm. Up to 82% efficiency could be demonstrated.
Date of Publication: May 2005