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Development of High Permeability Core Materials for Embeddable Inductors in Flexible Organic Substrates

Published online by Cambridge University Press:  15 February 2011

C. K. Liu ,
P. L. Cheng ,
S. Y. Y. Leung ,
T. W. Law  and
D. C. C. Lam
C. K. Liu
Affiliation:
Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay Road, Kowloon, Hong Kong SAR, China
P. L. Cheng
Affiliation:
Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay Road, Kowloon, Hong Kong SAR, China
S. Y. Y. Leung
Affiliation:
Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay Road, Kowloon, Hong Kong SAR, China
T. W. Law
Affiliation:
Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay Road, Kowloon, Hong Kong SAR, China
D. C. C. Lam
Affiliation:
Department of Mechanical Engineering, Hong Kong University of Science and Technology, Clear Water Bay Road, Kowloon, Hong Kong SAR, China
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Abstract

Capacitors, resistors and inductors are surface mounted components on circuit boards, which occupy up to 70% of the circuit board area. For selected applications, these passives are packaged inside green ceramic tape substrates and sintered at temperatures over 700°C in a co-fired process. These high temperature processes are incompatible with organic substrates, and low temperature processes are needed if passives are to be embedded into organic substrates. A new high permeability dual-phase Nickel Zinc Ferrite (DP NZF) core fabricated using a low temperature sol-gel route was developed for use in embedded inductors in organic substrates. Crystalline NZF powder was added to the sol-gel precursor of NZF. The solution was deposited onto the substrates as thin films and heat-treated at different temperatures. The changes in the microstructures were characterized using XRD and SEM. Results showed that addition of NZF powder induced low temperature transformation of the sol-gel NZF phase to high permeability phase at 250°C, which is approximately 350°C lower than transformation temperature for pure NZF sol gel films. Electrical measurements of DP NZF cored two-layered spiral inductors indicated that the inductance increased by three times compared to inductors without the DP NZF cores. From microstructural observations, the increase is correlated with the changes in microstructural connectivity of the powder phase.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 769: Symposium H – Flexible Electronics - Materials and Device Technology , 2003 , H10.10
Copyright
Copyright © Materials Research Society 2003

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