Kinetics of Liquid Spreading and Penetration with Application to RuO2−Glass Thick-Film Resistors

The rate of spreading of a spherical liquid droplet on a flat substrate is analyzed using the time-dependent contact angle approach. The constants in the contact angle development equation are explicitly related to physical parameters. Normalized rate of spreading is shown to be independent of the volume of the liquid droplet. A general capillary flow equation incorporating the time-dependent contact angle is used to analyze the kinetics of infiltration of the glass phase into the conductive phase in RuO₂/lead-horosilicate-glass thick-film resistors. The dependence of the kinetics on temperature, interparticle separation, and dissolved alumina content of the glass are discussed with reference to microstructure development in these resistors.