A Micromachined Wiring Board With Integrated Microinductor for Chip-Scale Power Conversion

This paper presents a multilayer wiring board that integrates a copper air-core microinductor to enable a highly compact, chip-scale power converter module. The wiring board is wafer-level fabricatedwith three 30-mu m-thick electroplated copper layers and is subsequently detached from the fabrication wafer to yield a board that is only 90 mu m thick for minimum overall module volume. Within this platform, a stacked-spiral air-core microinductor is designed for high-switching-frequency power conversion and yields high inductance density of 128 nH/mm(2) (100 nH/mm(3) by volume, including 600 mu m clearances both above and below the inductor to minimize coupling with external conductors). Although this technology is anticipated to be more appropriate for emerging, experimental converters with switching frequencies > 30 MHz, a proof-of-concept, ultraminiature (9 mm(2) footprint, 0.7 mm thick) power converter module is presented that utilizes the microinductor wiring board in conjunction with a commercially available surface-mount boost regulator (similar to 4 MHz switching frequency). The converter module yielded a maximum output power of 153 mW at 60% efficiency for a volumetric power density of 24 mW/mm(3) based on the physical volume occupied by themodule (13 mW/mm(3) based on the volume needing to be kept clear from external conductors).