Evaluation of Thick-Film Materials for High-Temperature Packaging

High-temperature electronics are required for applications such as automotive, down-hole drilling for oil and geothermal energy, aircraft, and space exploration. SiC and GaN devices are capable of operating in these high-temperature environments and challenging the packaging materials and technology to be compatible with these environments. Thick-film materials and technology have the potential of building reliable interconnections at high temperatures. This paper investigated the electrical reliability of two thick-film conductors (PtPdAu, Au) and two dielectrics at 300 °C. Test vehicles were fabricated with thick-film materials as capacitor and interdigitated finger test structures. For the test vehicles with PtPdAu thick-film, the leakage current of the capacitor structures with thin multilayer dielectrics increased in a short time during 300 °C aging with a 100-V bias, while the leakage current of capacitor structures with thick dielectrics had only a slight increase or remained constant during 300 °C aging with bias. Cross-sectional scanning electron microscopy and energy dispersive spectroscopy analysis showed that bismuth (Bi) in the PtPdAu paste diffused into the dielectrics from both the top and bottom conductors during the high-temperature firing steps in fabrication. If the Bi was continuous through the thin dielectric, the leakage current increased during aging with bias. The leakage current of the Au conductor in capacitor and interdigitated finger structures (both thick and thin dielectrics) did not increase with biased aging in high temperature. The Au conductor did not contain Bi.