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Hermetic
seal testing is a crucial requirement for military,
space, as well as commercial hermetically sealed devices.
A lack of hermeticity is a reliability concern and may
allow moisture and contaminants to enter the internal
cavity, which could lead to premature failure. ORS performs
seal testing per Mil-Std 883 method 1014 conditions
A1 and C1, Mil-Std 750 method 1071 conditions H1 and
C, Mil-Std 202 Method 112 conditions C, D, A and E,
and client specific requirements. Testing is also performed
per Telcordia GR1221-CORE and GR-468-CORE for passive
and active devices.
Leak Site Identification
Helium spray sniff testing is a technique that can be
utilized to isolate hermetic leaks on open cavity packages
as well as packages subjected. Typically, a helium spray
creates a small envelope of helium in the proximity
of a leak site region would be measured and recorded.
Fluorescent
Dye Impregnation
Fluorescent dye impregnation is utilized to identify
leak site regions and characterize the physical attributes
of the ingress pathways to improve package sealing processes.
This technique also eliminates the problem of misinterpretation
when cross-sectioning fragile materials.
Fine Leak
Devices are typically preconditioned in a helium pressurized
chamber and, after the required conditions are met,
the helium leak rate is measured and recorded, applying
pass/fail criteria. Devices sealed with helium need
not be pressurized if requested.
Expanded Fine Leak for Other
Gases and Compounds
Specialized leak testing is available for determining
leak rates for gases other than helium. Leak rates of
various gases (i.e. Argon, CO2, Acetic Acid, Ethylene
Glycol, etc.) may be measured at low leak rates utilizing
a specialized mass spectrometer tuned for the particular
substance of interest. Applicable standards are normally
available in a wide range of leak rates.
Gross
Leak
A device with a gross leak could theoretically pass
the fine leak test. Therefore, this test is typically
performed after fine leak. Depending on the requirement
of the specification being followed, gross leak may
be performed by two different methods.
1. The device is submerged in an indicator fluid tank
at a specified high temperature of 125° C, and observed
for evidence of bubble stream emanating from a gross
leak site. A lower temperature may be used depending
on device material constraints.
2. The test may require preconditioning in a pressurized
chamber filled with an inert detector fluid that characteristically
has a low boiling point. After preconditioning, the
devices are submerged in an inert indicator fluid with
a higher boiling point. In theory, any detector fluid
located within the internal cavity of the package would
boil when exposed to the high temperature of the indicator
fluid, thus creating a bubble stream from the gross
leak site.
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