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Fabrication of a Low Profile Planar Transformer Using Molded Interconnect Device Technology

The need for high frequency charging technology for hybrid and electric cars as well as any kind of handheld devices is increasing steadily. Furthermore, frequencies of 500 kHz and above as well as new GaN converters allow a decrease in components size and footprint of the power devices. In this work a novel fabrication method for planar transformer with a height of less than 2.5 mm is presented. The transformers are produced inside a PEEK substrate by utilizing injection molding, laser structuring and electroless plating. The magnetic core consists of multiple laser-cut ferrite sheets. The transformers show results of up to 27 μH in a frequency range from 1 kHz to 1 MHz, which corresponds to 4.5μ H/cm2, and a coupling factor of over 95%. In comparison to wire wound transformers, multiple complex process as the winding itself can be replaced by less complex process like laser structuring and electroless plating. These processes allow the production in batch, which can lower the cost in an industrial production below of wire wound transformers.