Home/Technical Glossary/Fine Leak Fine Leak Fine leak is a term used in microelectronic package hermetic leak testing. A hermetically sealed package is pressurized with helium or sealed with a helium trace gas inside the package. The sealed package is subjected to a vacuum chamber connected to a mass spectrometer and the rate of helium leak is measured in atm-cc/sec. Military standard allowable leak rate for a hermetically sealed package is less than or equal to 5 x 10-8 atm-cc/sec.