Investigation of Interactions Between Co-fired LTCC Components

In spite of many advantages it offers for micro-electronic packaging, the low temperature co-fired ceramic (LTCC) technology has yet certain issues to be solved. Physical and chemical reactions, for instance, within and between the passive electronic components (thick film conductors, resistors –TFR) and the LTCC tapes (green sheets) during processing are one of the major challenges of this technology. This study aims to better understand and control the nature of such interactions, which have a direct effect on properties. The work is conducted on PTC (positive temperature coefficient) resistors, which are screen printed on (co-fired) and in (buried) LTCC sheets and fired at various temperatures. The final properties such as TCR (temperature coefficient of resistance) and sheet resistance are evaluated in terms of processing parameters using SEM (scanning electron microscopy), dilatometry and EDS (electro dispersive x-ray) analysis as characterization tools. The results show that the TFR properties of buried samples deviate more strongly from the expected values compared to those of co-fired ones. It is primarily related to the destroyed conductor and resistor lines, which is due to the entrapped gases in buried structures as a result of organic burnout of printed inks.