Helium Mass Spectrometry

Detection Principle

This technique relies on the unique properties of helium, which has a low molecular weight and behaves as an inert gas that does not react with cell components. Its small atomic size allows it to pass through minute physical defects that would block larger molecules. The mass spectrometer is tuned specifically to the mass-to-charge ratio of helium ions, ensuring high selectivity and preventing false positives from other atmospheric gases.

This selectivity allows the system to identify tiny micro-fissures in welds or polymer seals that would otherwise go unnoticed during visual or pressure-decay inspections.

Leak Quantification

The test is conducted by placing the sealed cell into a vacuum chamber connected to the mass spectrometer. If a leak exists, helium escapes from the pre-pressurized cell into the chamber, where it is ionized and detected. The amplitude of the ion current is proportional to the leak rate, allowing for precise quantification of the defect size.

This quantitative data allows manufacturers to establish clear pass or fail thresholds based on the expected lifetime of the cell. It ensures that the hermetic seals are capable of preventing moisture ingress over the target operational life.

Quality Control

Integrating this process into high-volume manufacturing lines requires rapid evacuation cycles and automated handling equipment. It is typically performed after the final sealing step or after the electrolyte filling and degassing phases. Catching seal defects at this stage prevents the assembly of cells that would fail prematurely due to electrolyte drying or internal corrosion.

The continuous monitoring of leak rates also provides feedback to the welding and sealing machinery, enabling prompt adjustment of process parameters when trends shift.