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Board Level Hermeticity Testing of Assembled Modules using Optical Leak Testing: A New Model for Enhanced System Reliability
Keywords: Leak Test, Board Test , Hermeticity
A new inspection process, that is now approved under MIL STD 883, offers significant reliability enhancement of critical Hi-Rel electronic systems. Hermetic electronic packaging provides protection for electronic circuits from exposure to water, oxygen, hydrogen or other contaminates that may lead to corrosion and failure. Discrete components are tested to MIL STD 883 using a variety of leak test methods including perfluorocarbon gross leak testing, helium mass spectrometer fine leak testing or Optical Leak Test for both gross and fine leak test simultaneously. Until now, leak testing assembled modules on boards has not been performed because of helium absorption during bombing and release during mass spectroscopy leak testing may give false indications of leaks. However hermeticity testing at the device level does not insure hermeticity once assembly has been completed. The development and use of Optical Leak Testing as a reliable means for leak testing hermetic devices on assembled boards has revealed a formerly unknown failure mode in Hi-Rel electronics manufacturing. Electronic packages may develop thermal shock induced micro-cracks during assembly. These cracks may be induced by a wide range of causes not readily apparent during manufacturing including: elevated or non-uniform solder temperatures, further perpetuated by the use of lead free solders and other material and process issues. The authors team has successfully tested hundreds of production Hi-Rel circuit boards and modules and found the component population of assembled boards may have a loss of hermeticity rate of up to 100%. Optical Leak testing of assembled Hi-Rel electronic modules and boards will capture leaking hermetic devices that may otherwise fail in fielded weapon systems. This paper describes the implementation of board level optical leak testing and data for assembled production boards to show how this previously unknown failure mode may be avoided, substantially enhancing Hi-Rel electronic system reliability.
John W. Newman, President
NorCom Systems, Inc.
Norristown, PA
USA


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