On the applicability of MIL-Spec-based helium fine leak test to packages with sub-micro liter cavity volumes

The MIL-Spec-based helium fine leak test (test condition A1 and test condition A2) is reviewed for its applicability to packages with sub-micro liter cavity volumes. The existing gas conduction models are utilized to investigate the validity of the criteria defined in the test guidelines in terms of true leak rates. The application domains valid under the current guidelines are determined as a function of the internal cavity volume. The results show that the test is valid only for a finite domain of true leak rates when the volume is smaller than 10−2 cm3 and the invalid domain increases as the cavity volume decreases.