Meaning
Pressurized tracer gas injection exposes sealed electronic components or battery cells to high concentrations of helium to detect leaks through mass spectrometry. This technique is used for parts that are hermetically sealed and do not have a port for direct internal pressurization. During the helium bombing process, the items are placed in a pressure vessel filled with helium for a specific period of time.
If a leak exists, the gas is forced through the defect into the interior of the part. This procedure is the standard method for verifying the seal integrity of small prismatic cells and sensors.
Pressure Soak
Components are subjected to several atmospheres of pressure to ensure that the tracer gas can penetrate even the smallest microscopic cracks. The effectiveness of the helium bombing process depends on the pressure level and the amount of time the parts spend in the chamber. High pressure increases the driving force, making it easier for the gas to enter a leaking volume.
This stage must be carefully managed to avoid crushing delicate parts or causing mechanical deformation of the cell casing. Engineers calculate the required pressure based on the internal volume of the item being tested.
Dwell Duration
Time spent under pressure determines the amount of helium that will accumulate inside a defective part. A long dwell in the helium bombing process is necessary for detecting very small leaks, as the flow rate through a tiny orifice is extremely low. Once the pressure is released, the parts are removed from the chamber and the exterior is cleaned of residual gas.
Any helium that was forced inside will now begin to leak back out, where it can be measured by a mass spectrometer. This return flow is what the detector actually sees during the final inspection step.
Signal Detection
Mass spectrometers are tuned to recognize the specific atomic mass of helium to provide a sensitive and accurate reading. Because helium is rare in the atmosphere, the presence of a signal is a clear indication that the helium bombing process was successful in finding a leak. The rate of the returning gas is measured and compared to a pass or fail threshold established by the quality department.
Rapid testing is required after the soak to ensure the gas does not all escape before the part reaches the detector. This method is highly reliable for identifying manufacturing defects in sealed energy storage devices.
