Electrical and microstructure evolution of thick film lead-free resistors after various temperature treatments

The series of lead-free thick film resistors were elaborated by Institute of Electronic Materials Technology (ITME) in Warsaw. The paper presents investigations of two pastes: R-100 with resistivity 100 Omega/square and R-100 k with resistivity 100 kOmega/square The pastes were screen printed on alumina substrate with AgPd lead-free terminations. Then fired at several temperatures in the range 750-950degC for 10 minutes and 6 hours at highest temperature. Sheet resistivity and thermal coefficient of resistance (TCR) were measured. X-ray diffractograms were taken. The conductive phase that was RuO₂ maintained initial crystal structure regardless firing conditions. No devitrification was observed in lead-free resistors glasses. The lattice constants of RuO₂ were uniform at temperatures over 800degC. The resistors matched the desired resistivity and the TCR was least temperature dependent at the firing temperatures around 850degC.