MIL-STD-202H.pdf - 第86页
MI L - S TD - 202 - 112 4.3 Test condit ion B . 4.3 .1 Materia ls . 4.3 .1.1 Si licone oil . T he oi l u s ed f or t he bat h s ha l l be c l ear s i l i c o ne o i l hav i ng a v i s c os i t y o f 20 c entistokes at 25…
MIL-STD-202-112
Flexible method (IIIc). Part not filled with tracer gas. Force gas into leaks then detect its
escape. Then subject to test condition A, B or D (see 4.4.4.3.2.3 permitting use of water),
as applicable, to check for gross leaks.
Procedure IV - (For parts which are to be tested without breaking their seals.) Parts backfilled with tracer
gas as normally supplied.
Leak from inside of part to outside, then subject to test condition A, B or D (see 4.4.4.4
permitting use of water), as applicable, to check for gross leaks.
Test condition D (gross leak bubble test - Fluorocarbon liquid at 125°C ±5°C (257°F ±9°F). Use as an
alternate when test condition A is specified as a gross leak test.
Test condition E (bubble test - two fluorocarbon liquids - one at pressure followed by immersion in a second
liquid at 125°C ±5°C (257° ±9°F). Use when a nominal sensitivity of 10
-5
atm cm
3
/s is sufficient.
Test condition F (fluorocarbon vapor detection test). Use when a nominal sensitivity of 10
-5
atm cm
3
/s is
sufficient.
4.1.2 Substitution. The individual specification should specify the lowest sensitivity test condition which is
practical; a higher sensitivity test which can be calibrated shall be permitted, i.e., if a test is specified such as test
condition A requiring a sensitivity of 10
-5
atm cm
3
/s, test condition C may be used since it can be calibrated to read
this leakage rate. Substitution of test condition B or C should be made to test condition A when parts are rated at a
temperature lower than 130°C (266°F). Test condition D may be substituted for test condition A.
4.2. Test condition A.
4.2.1 Materials.
4.2.1.1 Mineral oil or peanut oil. The oil used for the bath shall be clear mineral oil or peanut oil having a universal
Saybolt viscosity of 175 to 190 seconds when tested at 38°C (100°F).
4.2.2 Apparatus.
4.2.2.1 Heated oil container. The container for the oil bath shall be of sufficient depth to immerse the uppermost
portion of the enclosure or seal to be tested to a depth of 1 inch (25.4 mm) below the surface of the bath. The
container shall be capable of maintaining the oil at the required temperature.
4.2.3 Precautions. This condition shall not be used for parts rated at a temperature lower than 130°C (266°F). It
shall not be used for parts which contain seals made of materials which will outgas due to the temperature of the
bath.
4.2.4 Preparation of specimens. Immediately before immersion it shall be determined that the specimen is at room
ambient temperature and free of any foreign (including labels) matter. If applicable, the critical side of the specimen
shall be determined. The critical side is defined as the side having the greatest number of seals or length of seal.
4.2.5 Procedure. This test consists of one immersion of the specimen or groups of specimens into a bath of clear
mineral oil or peanut oil (see 4.2.1.1) maintained at a temperature of 125°C ±3°C (257°F ±6°F). The specimen shall
be placed in the oil bath with the critical side (or side of special interest) in a horizontal position facing up. If the
specimen has no critical side, it shall be placed in the bath with its major axis in a horizontal position. The specimen
shall be completely submerged in the bath, with the uppermost portion of the enclosure or seal at a depth of 1 inch
(25.4 mm), and left in that position for a minimum duration of 1 minute. The specimen shall be carefully observed
during the entire duration of the immersion for indication of a poor seal as evidenced by a continuous stream of
bubbles emanating from the specimen. After the test is completed, the specimen shall be cleaned in a suitable
degreaser and permitted to dry thoroughly before any additional tests are performed.
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MIL-STD-202-112
4.3 Test condition B.
4.3.1 Materials.
4.3.1.1 Silicone oil. The oil used for the bath shall be clear silicone oil having a viscosity of 20 centistokes at 25°C
(77°F).
4.3.2 Apparatus.
4.3.2.1 Reduced pressure vessel. The vessel for the oil bath shall be of sufficient depth to immerse the uppermost
portion of the enclosure or seal to be tested to a depth of 1 inch (25.4 mm) below the surface of the bath, over which
can be drawn a vacuum resulting in an absolute pressure of not greater than 1.5 inches of mercury (not greater than
38.1 torr).
4.3.2.2 Vacuum pump. The vacuum pump shall be capable of evacuating and holding a vacuum resulting in an
absolute pressure of not greater than 1.5 inches of mercury (not greater than 38.1 torr) for a minimum duration of 1
minute in the reduced pressure vessel (see 4.3.2.1).
4.3.2.3 Degassing of silicone oil. The silicone oil shall be placed in the test fixture and a pressure of 1 inch (25.4
mm) of mercury or less attained over the fluid for as long as is necessary to degas the fluid. Such degassing is
complete when no further bubbling or frothing is present in the fluid. Throughout the test, components shall be
lowered gently in the fluid to prevent aeration of the fluid. The fluid shall not be poured from one container to another
without first being degassed again before testing.
4.3.3 Preparation of specimens. As specified in 4.2.4.
4.3.4 Procedure. This test consists of one immersion of the specimen or group of specimens into a bath of clear
silicone oil (see 4.3.1.1) maintained at room ambient temperature. The specimen shall be placed in the oil bath with
the critical side (or side of special interest) in a horizontal position facing up. If the specimen has no critical side, it
shall be placed in the bath with its major axis in a horizontal position. The specimen shall be completely submerged
in the bath with the uppermost portion of the enclosure or seal at a depth of 1 inch (25.4 mm). A vacuum resulting in
an absolute pressure of not greater than 1.5 inches of mercury (not greater than 38.1 torr) shall be drawn and held
over the bath for a minimum duration of 1 minute. The specimen shall be carefully observed during the entire
duration of the immersion for indication of a poor seal as evidenced by a continuous stream of bubbles emanating
from the specimen. After the test is completed, the specimen shall be cleaned in a suitable degreaser and permitted
to dry thoroughly before any additional tests are performed.
4.3.5 Precaution. This test condition should not be used either as a separate test or a gross leak test for
component parts which are to be subsequently attached to printed circuit board assemblies. Since complete removal
of silicone oil residues is difficult, the oil will be transferred unknowingly to other parts during assembly processes.
Traces of silicone can result in poor solder wettability of component part leads, poor adhesion to sealants, and
mealing of the conformal coating on the printed circuit board.
4.4 Test condition C.
4.4.1 Materials.
4.4.1.1 Tracer gases. When performing tests in accordance with procedures I, II, and IV of this condition, tracer
gases, i.e., helium, argon, or other rare gas, or a mixture of a gas with nitrogen (such as 90 percent nitrogen and 10
percent helium) shall be used. The tracer gas used in procedures IIIa and IIIc shall be helium. The tracer gas used
in procedure IIIb shall be the radioactive gas, krypton 85.
4.4.2 Apparatus. For all the procedures of this test condition, the test apparatus, exclusive of pressurization
equipment, shall be calibrated using a diffusion type calibrated standard leak at least once each working shift.
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MIL-STD-202-112
4.4.2.1 Mass-spectrometer-type leak detector. For procedures I, II, IIIa, IIIc, and IV of this test condition, a
commercially available mass-spectrometer-type leak detector, preset to read a tracer-gas content, shall be used to
measure the leakage rate of gas through a faulty seal. Another instrument may be used if it can be demonstrated to
the Government that the instrument, properly calibrated to read tracer-gas content, has the required
leakage-detection sensitivity (see 4.1.1).
4.4.2.1.1 Chambers. Depending on which procedure is used (see 4.4.4), suitable pressure or vacuum chambers
are required.
4.4.2.1.2 Pumps. Depending on which procedure is used (see 4.4.4), suitable pressure or vacuum pumps are
required.
4.4.2.2 Radioactive-gas detection apparatus. Apparatus for procedure IIIb shall consist of:
a. Radioactive tracer gas activation console.
b. Counting equipment consisting of a scintillation crystal, photomultiplier tube, preamplifier, ratemeter, and
krypton 85 reference standards. The counting station shall be of sufficient sensitivity to determine through
the device wall the radiation level of any krypton 85 tracer gas present within the device. The counting
station shall have a minimum sensitivity, in c/m per µCi, corresponding to a leak rate of 10
-9
atm cm
3
/ s of
krypton 85 and shall be calibrated at least once every working shift using krypton 85 reference standards
and following the equipment manufacturer's instruction.
c. A tracer gas consisting of a mixture of krypton 85 and dry nitrogen. The concentration of krypton 85 in dry
nitrogen shall be no less than 100 microcuries per atmospheric cubic centimeter. This value shall be
determined at least once each 30 days and recorded in accordance with the calibration requirements of this
standard.
4.4.3 Supplementary tests. When parts to be tested are normally evacuated through a tube and are sealed in
some manner prior to delivery, procedures I and II (see 4.4.4.1 and 4.4.4.2) will require a separate verification of the
seal of the evacuation tube in conjunction with this test method, using the mass-spectrometer-type leak detector (see
4.4.2.1). The verification may be accomplished by backfilling the specimen with air or gas at a specified pressure and
then submitting the specimen to either procedure IIIa, IIIb, IIIc, or IV.
4.4.4 Procedures. This test condition consists of five procedures (see 4.4.4.1 to 4.4.4.4, inclusive), the choice of
which must be specified in the individual specification. Procedure IV is the preferred method of performing this test
for parts that are not evacuated.
4.4.4.1 Procedure I. The mass-spectrometer-type leak detector shall be coupled to the unsealed evacuation tube
of the specimen, and a vacuum created within the specimen. It is extremely important that the coupling connections
between the specimen and the leak detector be perfectly sealed. The specimen shall then be subjected to a gas
atmosphere either by surrounding the specimen with the gas or by spraying the specimen thoroughly with a jet of the
gas. If a defect exists in the specimen, an amount of gas that depends upon the size of the defect will be drawn
through it and passed into the leak detector, which will read the leakage rate. When this portion of the procedure is
completed, the specimen shall be filled with air or gas at a specified pressure and having a known percentage of
tracer gas. The evacuation tube shall then be pinched off and sealed. After sealing, the seal of the tube shall be
verified by either procedure IIIa, IIIb, IIIc or IV, if filled with tracer gas.
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