Thick-film resistors with low and high TCRs on LTCC substrates

Low-Temperature Co-fired Ceramic (LTCC) materials, which are sintered at the low temperatures typically used for thick-film processing, i.e., around 850 degrees C, are widely used for ceramic multi-chip modules (MCM-C). Thick-film resistors with low TCRs (Du Pont, 2041, nominal sheet resistivity 10 kohm/sq.) and thick-film NTC thermistors with high negative TCRs (EMCA-Remex, 4993, nominal resistivity 1 kohm/sq.) which were developed for alumina substrates, were evaluated on glassy LTCC substrates, The electrical and microstrutural characteristics of films fired on alumina or co-fired on "green" LTCC substrates were compared, The electrical characteristics (TCRs, sheet resistivities and noise indices) of 2041 resistors fired on both substrates are similar indicating that the resistors are compatible with the LTCC material. In the case of the NTC 4993 thermistors; the resistivities, beta factors and noise indices of the thermistors fired on LTCC substrates significantly increased, indicating the interactions between the thermistor layers and the LTCC substrates. The changes in the electrical parameters were attributed to the diffusion of a silica-rich phase from the LTCC into the thermistor films.