Practical aspects and limitations of hermeticity testing of micro-encapsulations using cumulative helium leak detection for miniaturized implantable medical devices

Hermeticity of an electronic package defines its effectiveness to seal and protect the encapsulated electronics from the ingress of contaminants, gases, and moisture, as well as helping avoid toxic materials from inside the capsule contacting tissue. Using accelerated testing by methods of leak detection analysis, the theoretical limit of the lifetime due to water ingress of an encapsulated device can be estimated. However, classical methods are not sufficient for microencapsulations and exhibit limitations due to the resolution of the detection mechanisms required for such small cavities. With the availability of cumulative helium leak detection (CHLD), the detection limits can be extended by several magnitudes of resolution. However, limitations due to the physics of leakage apply. This article discusses the limitations concerning the ability for combined gross and fine leak testing in combination with outgassing effects using CHLD for miniaturized implantable medical devices. Practical aspects are evaluated regarding the applicability of CHLD for such microencapsulations at the example of an AuSn-sealed alumina package.