Failure mechanisms of microbolometer thermal imager sensors using chip-scale packaging

This paper analyzes relevant failure mechanisms for microbolometer thermal imager sensors that are assembled with a small size and low cost chip scale package. The analyses focus on device specific elements like the bolometer sensor structures, the longtime stability of the sensor and its performance, and the stability of the hermetic chip scale package. Executed reliability tests showed a high reliability of the sensor and the package without hard failures. The package survived harsh environmental accelerated stress tests and showed only a slight reduction of the shear strength through void formation and small cracks within the lead frame that could be verified through FEM simulations. The stress on the bolometers is investigated by thermomechanical FEM simulations. Executed reliability tests showed no enlargement in the number of defect pixel. The sensor performance showed a longtime drift and temperature dependence through outgassing processes inside the package leading to a significant performance reduction. Thus this effect is investigated more closely and possible countermeasures are proposed.