Platinum Metals Rev., 1970, 14, (2), 53
Palladium-Silver Resistor Pastes
Effect of Firing Conditions on Electrical Performance
Complex reactions occur when silver-palladium resistor pastes are fired in the preparation of thick film circuits. Some light was shed on these in a paper by P. H. Krahl and A. F. Bogenschütz of the Research Institute of Allgemeinen Electricitätsgesellschaft, AEG-Telefunken, Ulm (Metall, 1968, 22, (10), 988) and reviewed in Platinum Metals Review, 1968, 13, (1), 30. The same authors have now investigated the effect of firing conditions on the electrical properties of the resistors (Metall, 1970, 24, (2), 118-122).
The authors used two Du Pont pastes based on silver-palladium and silver-palladium oxide, and a three-zone kiln with independent zone control. The effects of firing time and temperature were investigated independently using controlled atmospheres of air and oxygen.
Their results show that the firing temperature, cycle and atmosphere strongly influence the electrical properties of the resistors, mainly because of variations in the degree of oxidation of Pd and reduction of PdO, and in the degree of fusion of the glass frit vehicle in which the metal and oxide powders are dispersed. Under no single set of conditions were optimum values obtained for all of: reproducibility of resistance values, temperature coefficient of resistance, low electrical noise, and long-term stability.
The authors recommend that because it is difficult to predict the behaviour of the pastes, firing tests should always be carried out to establish the most suitable conditions. They obtained their most favourable results using a 30 to 40 minute cycle, and temperatures of 680°C and 780°C respectively for the Pd and PdO based resistors, claiming reproducible resistances with a scatter of ± 10 per cent of the mean values by rigid adherence to these conditions.