Hermeticity Testing (also known as Fine and Gross Leak) is used
to determine the effectiveness of the seal in microelectronic component packages.
If the package seal is damaged or defective, moisture and other contaminants
can enter into the package freely and degrade the long-term reliability.
To determine the size of the leak, the volume of air that passes
through the leak each second under a pressure difference of 1 atmosphere is
obtained. Leak rates greater than 1x10-5 atm-cc/sec are considered
gross leak rates; those smaller than 1x10-5 atm-cc/sec are considered
fine leak rates . Liquids are typically used to detect gross leaks,
while tracer gases are used for fine leak detection. SIX SIGMA performs gross
leak test using a perfluorocarbon fluid bubble detection system. Fine leak detection
is performed with industry-standard mass spectrometer helium leak detectors.
The methods used for gross leak test cannot be used for fine leak test and vice
Components cannot be constructed of organic materials to pass
hermetically tested. With the exception of ink marking, nearly all organic
materials will absorb enough helium to fail this test. Even bumper tape or part
number labels can cause a false failure, so they must be removed prior to testing.