Low cost packaging for gas sensors

MEMS technologies have enabled the development of various sensors including gas sensors in a miniaturized and cost effective way. Sensor systems are being developed using these sensor chips where chip packaging is still a major cost due to special requirements. This paper focuses on the packaging needs of a MEMS based gas sensor. These gas sensors have various applications in safety systems for fire and harmful gases detectors for automobiles, home, offices, factories, environment, etc. A low cost packaging solution for MEMS based gas sensors is elaborated which is suitable for the trace level detection of various lethal gases like H₂S, PH₃, CO, CO₂, NH₃ etc. To enable the vast and multiple applications of these gas sensors it is important to provide a low cost sensor system which is low power and can be operated on battery. Standard semiconductor device packages like TO headers are costly and not suitable for low cost devices. Proposed packaging scheme uses printed circuit board (PCB) as substrate material (FR4) where reliable low resistance (1–2 ohm) interconnects are provided by conducting epoxy. PCB based packages add very little extra power (3–5 mW) to the power required for micro-heater that heats gas sensor film up to 300 °C. Packaged gas sensors were tested for their reliability in two different conditions i.e. 1 h ON reliability test and repetitive ON/OFF (100 times) test. These packages have additional advantages of being more mechanically stable than wire bonded packages and easy processing in comparison to Transistor Outline (TO) headers. Infrared imaging of the packaged device in forced condition shows the stability of the package.