Formulation, development, and characterization of magnetic pastes and epoxies for thick film inductors

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Virginia Tech


Inductors and transformers constitute two important magnetic components In RF and power hybrids electronic circuitry. Thick film inductors have been subject of extensive research in recent years because they significantly reduce the weight and size, and increase the frequency of operation of electronic circuits. The research work in this dissertation is aimed at the formulation of thick film ferrite pastes and ferrite epoxies and the design, construction, and evaluation of thick film spiral inductors. Wideband characterization (DC - 2GHz) of ferrite pastes, ferrite epoxies, and ferrite substrates is performed using two techniques. These techniques are based on current image and transmission line (coaxial cavity) concepts for low (DC-IOOMHz) and high (50MHz-2GHz) frequency regions, respectively. They are used to evaluate the permeability spectra of formulated and commercially available thick film magnetic materials in respective frequency ranges.

A method to numerically calculate the inductance of thick film circular spiral inductors based on modeling the spiral as concentric circles is presented. A novel method for fine as well as coarse tuning of thick film inductors is also introduced. The tunable inductors are constructed using formulated ferrite epoxies and magnetic cores. The method of analysis of variance is used to investigate the variation significance of tunable inductors. Finally, chemical and mechanical properties of developed magnetic materials are discussed. The studied properties include, glass transition temperature, degradation temperature, thermal coefficient of expansion, adhesion, particle-size distribution and particle densification , grain size, and compositional constituents of the magnetic materials.