Hermeticity Assessment of MEMS Micro Packages: Leak Rate Measurements Based on Infrared Spectroscopy

This paper presents an alternative method for the hermeticity assessment of MEMS micro-packages, and the first experiments performed using this technique. The method consists in monitoring the internal gas pressure of the cavity by Fourier Transform Infra Red (FTIR) spectroscopy. The package’s hermeticity is then deduced from the pressure variations. In order to carry out the IR transmission measurements, nitrous oxide was chosen as bombing gas due to its excellent absorption properties for mid-IR radiations. The method was applied to BCB-sealed silicon micro-packages and allowed to study the influence of different parameters like the sealing ring dimensions or the internal volume on their hermeticity. Additional measurements were carried out on hermetic packages, with an additional organic coating. These experiments validated the method for micro-packages with a volume of 5 mm³ or more.