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

Abstract

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 fabricated with three 30-μm-thick electroplated copper layers and is subsequently detached from the fabrication wafer to yield a board that is only 90 μm 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (100 nH/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> by volume, including 600 μm 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 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 (~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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> based on the physical volume occupied by the module (13 mW/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> based on the volume needing to be kept clear from external conductors).