Influence of the preparing conditions on the physicochemical characteristics of glasses for thick film hybrid microelect
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G. Guizzetti Department of Physics, "A. Volta", University ofPavia, Via A. Bassi 6, 27100, Pavia, Italy (Received 26 January 1993; accepted 18 April 1994)
Seven batches of a high-lead glass were used for the preparation of RuO2-based thick film resistors. Investigation of their electrical properties showed a lack of reproducibility of results whose origin was related to changes of the physicochemical properties of the glassy matrix. A systematic investigation of the glass batches, both in form of frit powders and screen printed and fired layers, was carried out with several spectroscopies to detect changes in composition and structure. The spectroscopic methods included x-ray Energy Dispersive Fluorescence (EDS), Scanning Electron Microscopy (SEM), Atomic Absorption (AA), diffuse optical reflection of the powders and specular reflection of the layers, optical transmission, and other complementary methods. The dissolution of Al, due to interaction between the glasses and the alumina substrate, as well as the diffusivity and solubility of Ag due to interaction with the Ag-bearing terminations were measured. The results demonstrated that, apart from small compositional differences, the various batches were characterized by differences in residual stresses, redox reactions, and "microstructure." The latter was responsible for very notable differences in the optical properties of the glasses, which in turn are closely related with the difference in atomic solubility and diffusivity. Optical spectroscopies have been found to be a suitable means for testing reproducible preparation methods of glass frits for thick-film hybrid microelectronics.
I. INTRODUCTION Thick film materials are prepared by screen printing and firing on a suitable substrate. Generally, the pastes (or inks) contain a glass constituent in the form of frit, consisting of micrometric glass particles.1 This constituent accomplishes different functions, according to the nature of the layer. Glass is present in minor quantities in conductive layers where it promotes adhesion with the ceramic substrate and the sintering of the conductive grains. In dielectrics it improves density, dielectric strength, adhesion, and provides passivation, while in resistive pastes it plays a vital role as dielectric matrix of the cermet structure and determines the electrical properties (mainly resistivity and its temperature coefficient).2'3 Reproducible properties of these components require, of course, reproducibility in the properties of the glass frit which consists of a high lead glass for most of the air-fireable thick-films.4'5 This work was motivated by problems faced during studies of model resistive systems, where we observed that pastes prepared from different batches resulted in resistors with sheet 2304 http://journals.cambridge.org
J. Mater. Res,, Vol. 9, No. 9, Sep 1994 Downloaded: 20 Mar 2015
resistance values different up to 100% and temperature coefficient of resistance (TCR) not only different in values but also in sign. After accurate tests which ruled
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