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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 B1 & B2, Mil-Std 750 method 1071 conditions H1 and
G1 & G2, 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
to IVA testing. Devices are fixtured so as to draw a vacuum from the internal cavity into the leak detector through the open cavity or through
a puncture site of the IVA test site. Typically, a helium spray creates a small envelope of helium in the proximity of a leak site region. The
helium is drawn through the leak site and into the instrument giving an indication of the leak site location. Readings would be measured and
recorded. This method works well with hermetic leak failures in the 10-4 to 10-8 atm cc/sec range.
Leak Site Identification is also available through the Kr85 hermeticity testing. Once a non hermetic package has been identified through Kr85
testing, a hand held gamma detector can be used to find radiation escaping through the leak site region. Readings are 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.
Helium or Krypton 85 Fine Leak
Devices are typically preconditioned in a pressurized chamber and, after the required conditions are met, the leak rate is measured and
recorded, applying pass/fail criteria. Devices sealed with helium and undergoing helium leak testing 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.
Helium 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.
Kr85 Gross Leak
A device with a gross leak could theoretically pass the fine leak test. Therefore, this test is typically performed prior to Fine Leak testing
as a method of eliminating failures that would other wise trap large amounts of radioactive Kr85 through longer term Fine leak
pressurization.
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