On Hermeticity Detection of Wafer Level Packages for MEMS Devices

Wafer level packaging has emerged as one of the promising solutions for hermetic packaging of MEMS devices. Detection of the level of hermeticity of the package is essential for reliability and design assessment of the devices. Traditionally, hermeticity has been tested using Helium based fine leak testing. However, there are limitations when this technique is used for the hermeticity detection of small volumes (< 10⁻³ cc) that are typical in wafer level packages. This paper reviews the helium fine leak test, its limitations and the influence of the different test parameters on leakage rate measurement are analyzed for wafer level packages with small cavity volumes. The results indicate a need for development of a new hermeticity measurement technique to achieve the measurement sensitivity required for wafer level packages.