Interactions between alumina and high lead glasses for hybrid components

Kinetics of dissolution of alumina substrates in 7 compositions of high lead glasses have been studied. The dissolution process is controlled by the correlated diffusion of Al and Pb (and/or B), with interdiffusion coefficients D, at 850°C, 10 min, in the range from 10-10 to 10-6 cm s-1, according to the different compositions Al solubility ranges from about 10 to 20%. The diffusivity and solubility increase by increasing the content of B and Pb. The reactivity of alumina substrates with the glassy component of thick-film resistors greatly affects their microstructure and electrical properties. Some consequences of these interactions have been evidenced: change in electrical resistivity and its dependence on the resistor thickness, changes in the sintering process and grain growth of RuO2 grains, and a catalytic effect on phase transformations of pyrochlore ruthenates in rutile RuO2 in the glassy matrix of resistors. Al dissolution moreover gives rise to a recession of the buried glass /substrate interface, which can easily be measured. When alumina is concerned, this measurement gives insight into the sum of twoprocesses: Al dissolution in the glass layer and grain-boundary diffusion of glass into the substrate itself.