Fabrication Method and Characterization of Molded Interconnect Device Micro Transformer in Planar Form by Embedding Sintered Ferrite Cores

Abstract:
The rising demand for increasingly powerful hybrid and electric vehicles is driving the development of suitable charging technology. Here, the increase in switching frequency of over 500 kHz in GaN converters leads, among others, to a reduced core cross section for magnetic components. This reduced core cross section enables new fabrication methods for a planar integration. In this paper, a novel fabrication method for planar magnetics with a height of less than 2.5 mm is presented. A two-step injection molding process encapsulates multiple sintered ferrite cores simultaneously with polyether ether ketone (PEEK). The coils are produced on PEEK selectively by using a laser system and an electroless plating process. After the transformers are separated, they show an inductivity of up to 4.6 muH, which corresponds to an inductance density of 5.86 muH/cm2, and a coupling coefficient of 91 %. The less complicated winding process and the batch production of the molded interconnect device (MID) transformer allow higher production throughput compared to wire wound transformers.