Integrated Ultra Thin Flexible Inductors for Low Power Converters

The integration of passive components into the printed circuit board as embedded passives integrated circuits (emPIC) results in a higher power density of power converters. Here, we present ultra thin inductors that are integrated in a flexfoil printed circuit board, which results in flexible and bendable inductors of only 300 mum or even less thickness. This publication presents the manufacturing method, which is compatible to printed circuit board manufacturing processes. A number of various inductors ranging in their values from 1 muH to 2 mH and in their diameter from 4 mm to 30 mm are manufactured. The measurement results are discussed and compared to simulations with a good agreement. Using such an ultra thin inductor a low power boost converter was fabricated. The converter steps up the battery voltage of 3 V up to 15 V at 20 mA to drive a string of LEDs. The thin inductor fits underneath the conventional driver chip without significantly increasing the total building height. The total converter needs an area of 6 mm times 7 mm and would thus fit in a DIL6 package