ULTRA-Miniaturized power converter modules using micromachined copper scaffolds

Abstract

This paper presents ultra-miniature (<2 mm3) power converter modules with high power density (77 W/cm3) enabled by micromachined 3D copper scaffolds containing high-inductancedensity (130 nH/mm2) air-core power inductors. The scaffolds are formed by electroplating multiple, 30-!m-thick layers of copper within patterned photoresist molds, yielding freestanding copper traces with >10:1 aspect ratios. After backfilling with a chemically-resistant polymer, the scaffolds are then fully detached from the silicon fabrication wafer by wet-etching an underlying oxide layer. Surface-mount switch/controller chips and capacitors are attached by solder reflow to the copper scaffolds, forming selfcontained converter modules.