On ultra-fine leak detection of hermitic wafer level packages

This paper describes the helium fine leak test for hermeticity detection and develops a methodology to infer the true leakage rate of a package from helium leak test data. The theoretical and practical limitations of the fine leak test are discussed when it is used for hermeticity detection of MEMS wafer level packages with volumes less than 10^-4 cc. An optical interferometry based hermeticity detection technique is also proposed to cope with the limitations of the fine leak test. The fundamentals of the proposed technique are presented and an experimental setup to implement the technique is described. The result of a preliminary experiment is also reported