Review of test methods used for the measurement of hermeticity in packages containing small cavities

A Miniaturized, Eye-Conformable, and Long-Term Reliable Retinal Prosthesis Using Monolithic Fabrication of Liquid Crystal Polymer (LCP)

“…One of the difficulties in demonstrating the reliability of polymer-based implants is a lack of general agreement on testing methods. The helium fine leak test is an industry standard for quantifying the hermeticity of metal or ceramic enclosures [61]. The leakage detected for helium can be simply converted into the leak rate L of another gas of interest, such as H 2 0, using L = √ ⁄ with M the molecular mass, as the leak rate depends only on the gas molecule size and the leak channel geometry [62].…”

“…However, the helium leak test can be misleading in the case of polymer packages because gas ingress does not only occur through fine leak channels (gas conduction) but also through the permeable polymer surface (gas diffusion) which depends on numerous variables such as the porosity of the material, size of the gas molecules and the chemical affinity with the materials [61,[63][64][65]. Helium absorbed onto the polymer surface during bombing will be gradually released leading to an inaccurate leak rate [66,67].…”

“…Helium absorbed onto the polymer surface during bombing will be gradually released leading to an inaccurate leak rate [66,67]. The small volume of the MEMS-based polymer package makes it more difficult to guarantee its hermeticity with the standard method due to the lowest detectable limits of helium detectors [55,61,62].…”

Integrated Devices for Micro-Package Integrity Monitoring in mm-Scale Neural Implants

“…Different methods have been developed over time to evaluate the hermeticity of micro-packages [11]. The military standard MIL-STD-883, Method 1014.10 describes various procedures to measure fine leaks [12].…”

“…The first relies on the optical absorption properties of a tracer gas; on the other hand the second uses the interaction between monochromatic light and phonons of the device under test to determine the type and the quantity of the gas inside the micro-package. The sensitivity of such tests can measure leakage in cavities down to 5 mm 3 , however they require the package to be transparent for the specific wavelengths used by each technique [11].…”