New integrated planar magnetic cores for inductors and transformers fabricated in MCM-L technology

This paper discusses a new method for producing planar magnetic core structures around integrated winding layers in PCB technology. For open core structures, electroplated NiFe layers are used to form magnetic plates above and below internal layers of copper spiral turns. Closed cores are formed by interconnecting top and bottom magnetic plates by plated through-holes of NiFe. Issues relating to the fabrication of the core regions are described in detail. A significant advantage of the method is that the processes involved are similar to those used for defining copper tracks and plated through-holes in standard PCB technology. Initial prototypes have been produced with inductance values of up to 100 μH in a 1 cm² footprint.