30 GHz Litz wires defined by ion track lithography

We have demonstrated the ability to combine microsystem technologies with sub-micron wire fabrication in polyimide based flexible printed circuitry board (PCB) laminates. Clusters of sub-micron wires in each via enables that no increase of resistance is shown for copper wires up to 30 GHz. A toroidal inductor is fabricated as an example of the application of ultra-high density via interconnects.

Introduction

Litz wires are multiple. interlaced thin wires woven together. The advantage of these is that AC-losses are reduced since the lateral surface to volume ratio is increased, suppressing the skin effect [1]. The large dimensions of vias in printed circuitboards (PCBs) make thern strongly affected by the reduced current density in the bulk wire at high frequencies, i.e. the skin effect.