MIL-STD-202H.pdf - 第91页
MI L - S TD - 202 - 112 4.4 .4.3.2. 3 Procedure I I I c . V a l ues f or b om b pr e s s ur e ex pos ur e t i m e and dw el l t i m e s hal l be chose n such that actual mea sured tracer g as l e ak r at e ( R 1 ) r e ad…
MIL-STD-202-112
4.4.4.3.2.2.4 Specific procedure IIIb. The devices shall be placed in radioactive tracer gas activation tank. The
activation chamber may be partially filled with inert material to reduce pumpdown time. The tank shall be evacuated
to 0.5 torr. The devices shall be subjected to a minimum of 2 atmospheres absolute pressure of krypton 85/dry
nitrogen mixture for the time necessary to satisfy the equation. Actual pressure and soak time shall be determined in
accordance with 4.4.4.3.2.2.1. The R value in counts per minute shall be not less than 600 above ambient
background. The krypton 85/dry nitrogen gas mixture shall be evacuated to storage until 0.5 torr vacuum exists in the
activation tank. This evacuation shall be completed within 3 minutes maximum. The activation tank shall then be
backfilled with air (air wash). The devices shall then be removed from the activation tank and leak tested within 1
hour after gas exposure with a scintillation-crystal-equipped counting station. Device encapsulations that come under
the requirements of 4.4.4.3.2.2.3 shall be exposed to ambient air for a time not less than the "wait time" determined
by 4.4.4.3.2.2.3. In no case will the time between removal from the activation chamber and test exceed 1 hour. This
exposure shall be performed after gas exposure but before determining leak rate with the counting station. Device
encapsulations that do not come under the requirements of 4.4.4.3.2.2.3 may be tested without a "wait time". (The
number of devices removed from pressurization for leak testing shall be limited such that the test of the last device
can be completed within 1 hour.) The actual leak rate of the component shall be calculated with the following
equation:
R
QXMINUTE
PERCOUNTSNETIN
READOUTACTUAL
Q
S
)(
=
Where Q = Actual leak rate in atm cm
3
/s, and Q
S
and R are defined in 4.4.4.3.2.2.1.
Unless otherwise specified, devices that exhibit a leak rate equal to or greater than 1 x 10
-8
atmospheric cubic
centimeters of krypton 85 per second shall be considered a failure.
Upon completion of this procedure, the specimen shall be checked for gross leaks by subjecting the specimen either
to test condition A, B, or D. Water, at room ambient temperature and a pressure of 2.5 inches (63.5 mm) of mercury,
may be used in place of silicone oil, if test condition B is used to verify gross leaks.
4.4.4.3.2.2.5 Personnel precautions. A Nuclear Regulatory Commission (NRC) license is necessary for
possession and use of the krypton 85 leak-test equipment. In the use of gas, code of Federal regulations Nuclear
Regulatory Commission Rules and Regulations, Title 10, Chapters 1, 20, 30, 31, and 32 should be followed and the
maximum permissible tolerance levels prescribed by the National Committee on Radiological Protection should be
observed.
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MIL-STD-202-112
4.4.4.3.2.3 Procedure IIIc. Values for bomb pressure exposure time and dwell time shall be chosen such that
actual measured tracer gas leak rate (R
1
) reading obtained for the device under test (if defective) will be greater than
the minimum detection sensitivity capability of the mass spectrometer. The devices shall be subjected to a minimum
of 2 atmospheres absolute of helium atmosphere. If the chosen dwell time (t
z
) is greater than 60 minutes, graphs
shall be plotted to determine an R1 value which will assure overlap with the selected gross leak test condition. The
chosen values, in conjunction with the value of the internal volume of the device package to be tested and the
maximum equivalent standard leak rate (L) limit (as shown below or as specified in the applicable procurement
document), shall be used to calculate the measured leak rate (R
1
) limit using the following formula:
e
-
e
-
- 1
M
M
A
1/2
P
LP
=
R
M
M
A
1/2
VP
o
Lt
2
M
M
A
1/2
VP
o
Lt
1
O
E
1
R
1
= The measured leak rate of tracer gas (He) through the leak in atm cm
3
/s He.
L = The equivalent standard leak rate in atm cm
3
/s air.
P
E
= The pressure of exposure in atmospheres absolute.
P
O
= The atmospheric pressure in atmospheres absolute (1 atmosphere).
M
A
= The molecular weight of air in grams (28.7 grams).
M = The molecular weight of the tracer gas (helium) in grams (4 grams).
t
1
= The time of exposure to P
E
in seconds.
t
2
= The dwell time between release of pressure and leak detection in seconds.
V = The internal volume of the device package cavity in cubic centimeters.
Unless otherwise specified, devices with an internal cavity volume of 0.01 cm
3
or less shall be rejected if the
equivalent standard leak rate (L) exceeds 5 x 10
-8
atm cm
3
/s. Devices with an internal cavity volume greater than
0.01 cm
3
and equal to or less than 0.4 cm
3
shall be rejected if the equivalent standard leak rate (L) exceeds 1 x 10
-7
atm cm
3
/s. Devices with an internal cavity volume greater than 0.4 cm
3
shall be rejected if the equivalent standard
leak rate (L) exceeds 1 x 10
-6
atm cm
3
/s.
Upon completion of this procedure, the specimen shall be checked for gross leaks by subjecting the specimen either
to test condition A, B, or D. Water, at room ambient temperature and a pressure of 2.5 inches of mercury, may be
used in place of silicone oil, if test condition B is used to verify gross leaks.
4.4.4.4 Procedure IV. The specimen, which is backfilled and sealed during production with a known percentage of
tracer gas, shall be placed in a chamber connected to the mass-spectrometer-type leak detector, and the chamber
evacuated. The internal pressure of the specimen shall be one atmosphere or greater. If a leak exists, the gas
passes through the specimen into the chamber and then into the leak detector which will read the leakage rate. If
specified, the specimen shall be perforated to determine if a gas is actually present. Upon completion of this
procedure, the specimen shall be checked for gross leaks by subjecting the specimen either to test condition A, B, or
D. Water, at room ambient temperature and a pressure of 2.5 inches (63.5 mm) of mercury, may be used in place of
silicone oil, if test condition B is used to verify gross leaks.
4.5. Test condition D.
4.5.1 Materials.
4.5.1.1 Fluorocarbon liquid. The fluid shall be D02, D02-TS, D03, FC-40 1/ or FC-43 2/.
4.5.2 Apparatus.
4.5.2.1 Heated fluid container. The container for the fluid shall be made of pyrex glass and shall be sufficient size
to hold the test specimen in the fluid and to maintain a temperature of 125°C ±5°C (257°F ±9°F).
1/ D02, D02-TS, and D03 are the registered trade mark of Ausimont (Division of Montedison).
2/ Minnesota Mining Co. (3M) registered trade name.
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MIL-STD-202-112
4.5.2.2 Filter. A filter shall be used which is capable of removing particles greater than 1 micron in size from the
fluid.
4.5.2.3 Magnifier. A 3X minimum magnifier or a stereo zoom microscope shall be used for observation of bubbles
emanating from the test specimens when immersed in the indicator fluid.
4.5.3 Precautions. The following precautions shall be observed:
a. Fluorocarbon liquids shall be filtered as specified in 4.5.2.2. Bulk filtering and storage is permissible. Leak
indicator fluids, which have accumulated observable quantities of particulate matter during use, shall be
discarded or reclaimed by filtration for reuse. Leak detecting fluids shall not be used for more than one
eight-hour shift without being refiltered.
b. The observation container shall contain sufficient fluid to assure coverage of the test specimen to a
minimum depth of two inches.
c. Illumination shall be a lighting source capable of providing at least 15,000 foot candles at the test specimen
position. The lighting source shall not require calibration but the light level shall be verified at the test
specimen position. The background behind the glass observation container should be a dull, non-reflective
black material.
d. The observation container should be covered at all times when not in use to minimize evaporation losses
and moisture adsorption.
e. Test specimens to be tested should be free from foreign material on the surface, including conformal
coatings and markings which may contribute to erroneous test results.
4.5.4 Procedure. The test specimens, mounted on specified fixtures to hold them in the fluid, shall be immersed,
with the uppermost portion at the minimum depth of 2 inches below the surface of the fluid, lid downward, one at a
time (or in such a configuration that a single bubble from a single specimen out of a group under observation may be
clearly observed as to its occurrence and source). The fluid shall be maintained at a temperature of 125°C ±5°C
(257°F ±9°F). The specimens shall be observed against a dull non-reflective black background through the magnifier
(see 4.5.2.3) from the instant of immersion until 20 seconds after immersion. Leakers will be identified by a single
bubble or a stream of bubbles. Specimens from which a single bubble is observed is considered to be a reject.
4.6. Test condition E.
4.6.1 Materials.
4.6.1.1 Fluorocarbon liquid. The fluids shall be D/80, FC-72 or PP-1 fluorocarbon detector fluids, and D02,
D02-TS, D03, FC-40, FC-43, PP-7 or PP-9 fluorocarbon indicator fluids.
4.6.2 Apparatus.
4.6.2.1 Heated fluid container. The container for the fluid shall be made of pyrex glass and shall be of sufficient
size to hold the test specimen in the fluid and to maintain a temperature of 125°C ±5°C (257°F ±9°F).
4.6.2.2 Filter. A filter shall be used which is capable of removing particles greater than 1 micron in size from the
fluid.
4.6.2.3 Magnifier. A magnifier with a magnification in the range between 3X to 30X for observation of bubbles
emanating from devices when immersed in the indicator fluid.
4.6.2.4 Chamber. A vacuum/pressure chamber for the evacuation and subsequent pressure bombing of device up
to 75 lbf/in
2
up to 10 hours.
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