A Study of the Thermal Characteristics of NiCuZn Ferrite Chip Inductors

Abstract

Like other electrical components, the characteristics of magnetic components are significantly affected by not only magnetic fields, but also ambient temperature and inner/outer stress. In order to understand the nature of inductance shift of NiCuZn ferrite after thermal treatments, in this work we measured and analyzed the inductance shift of inductors which were treated separately by reflow and temperature cycling conditions. The results reveal that the inductance shift comes from not only residual stress release, which causes an increase in inductance during the cooling stage, but also the change in magnetic status by the peak temperature, which also causes an increase in inductance. Nevertheless, this magnetic status would be affected by the magnetic field to form a remanence that causes a fall in inductance later on, and this remanence level can be reduced under subzero temperature conditions. Comparing the construction of components for multilayer chips made of pure ferrite with those made of wound coil, this complex relation between heat, stress and the magnetic field of chip inductors are caused by the cofiring of ferrite and conductor material during the manufacturing process of chip inductors.