Lead free packaging of Pt micro-heater for high temperature gas sensors

Abstract

There is a continuing demand for the development of fast, sensitive and reliable sensors for applications in harsh industrial environments. Gas sensors are finding great importance in fuel and energy sectors. Monitoring and control of combustion related emissions result in efficient use of fuels and subsequent energy savings. Microelectronic gas sensors have advantages like small size, low power combustion, and possibility of in situ control and monitoring. These gas sensors are commonly employed in fire detectors, emission control system, CO2 operated enhanced geothermal system (EGS), supercritical water systems, organic rankine cycles used in binary power plants, high temperature gas-reactors in next-generation nuclear power plants and in gas processing. Packaging of microelectronic devices is equally important to the development practice. Input/Output connections are fabricated on these systems during this process. Thermo-mechanically strong lead attachments on sensor devices are necessary for high temperature applications. The conventional joining techniques like soldering, wire bonding, flip chip bonding and lead welding show failure in high temperature operative microelectronic systems. Present work is focused on the development and characterization of Pb free packaging of Pt micro-heaters, a main functionary of the gas sensors. Thick film Pt heater printed on ceramics substrate has been interconnected to Cu metal using Indium interlayer. The thermal and mechanical strengths of the interconnect specimen are determined and analyzed. The ultimate tensile strength (UTS) and ultimate shear strength (USS) values are plotted for different reaction parameters. The isothermal solidification morphology and crystallography are examined and discussed. The tests of thermal shock, pressure, operating life and vibration have been performed in an environmental lab to predict the compatibility of the packaging for deployment in harsh environments.