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Prof. Marc Desmulliez, MISEC, Heriot-Watt University Link to Survey The limitations of the standard helium leak test in conjunction with a gross leak test, such as the bubble test, when applied to microcavities are well documented. MIL-STD-883G gives standards for the use of the helium leak test to detect leaks in packages under 0.05cm3 although no specific values for micro-scale cavities are listed. The sensitivity of the mass spectrometer used means the minimum leak rate that can be detected is of the order 10-11atm.cm3.s-1. A microsystems device may be adversely affected by leak rates as a low as 6e-18 atm.cm3.s-1. A gap in the detectable range of the helium leak test and the chosen gross leak test develops in cavities less than 10mm3. As the cavity size reduces, any helium in the package after bombing can escape before the sample is transferred from the bombing chamber to the mass spectrometer. The maximum leak rate detectable using the helium leak test drops to below the minimum leak rate detectable using the gross leak test, leaving a misleading gap in the detectable range. An adequately sensitive alternative test method for small volume packages has yet to be developed. We are conducting research to develop such a test along with a model to predict the leak rate of packages sealed using organic materials. This has the potential to provide some users with a less costly packaging method should the predicted leak rate suit the expected lifetime of the device. To make our research relevant to industry it is essential to discover how hermeticity testing is currently being conducted and if there is a demand for a more accurate and sensitive testing method. I hope that you will be able to take a few minutes to complete the market survey and return to the address below or by email. Contributors will receive a summary of results! ------------------------------------------ |