MIL-STD-202H.pdf - 第85页
MI L - S TD - 202 - 112 F l ex i bl e m et ho d ( I I I c ) . P ar t no t f i l l ed w i t h t r a c er ga s . F or c e g as i n to leaks then detect its es c ape. T hen s ubj ec t t o t e s t c ondi t i on A , B or D ( …
MIL-STD-202-112
4. GENERAL REQUIReMENTS
4.1. Test conditions.
4.1.1 Selection. There are six test conditions (A, B, C, D, E, and F) in this method. Test conditions A and B utilize
oil as a means to detect gross leaks by the observation of bubbles. Both of these tests will detect leaks of a nominal
value of 10
-5
atm cm
3
/s. Test condition B is used to test parts which will not withstand the temperature required in
test condition A. Test condition C detects fine leaks by using a tracer gas and apparatus to measure a leakage rate
(R
1
) to a nominal of 10
-8
atm cm
3
/s. The apparatus can be calibrated for any leakage rate within its range. Test
condition D utilizes a fluorocarbon liquid at 125°C ±5°C (257°F ±9°F) at ambient pressure and detects gross leaks by
the observation of bubbles. This latter test condition provides an alternate gross leak test to test condition A. Test
condition E utilizes two fluorocarbon liquids; one under pressure followed by the other at 125°C ±5°C (257°F ±9°F) at
room ambient pressure and detects gross leaks by the observation of bubbles. This test condition provides a
measure of leakage rate of a nominal value of 10
-5
atm cm
3
/s. Test condition F utilizes a fluorocarbon liquid and a
fluorocarbon vapor detector to detect gross leaks. Test condition F provides a measure of leakage rate of a nominal
value of 10
-5
atm cm
3
/s. Both test conditions C and F require more expensive commercial equipment and trained
personnel, but the equipment provides automatic and quantitative readings. The selection of a test condition to
perform the seal test depends on the state of the art of component part manufacturing, the leakage rate which can be
tolerated for the desired reliability, the frequency of testing, range of test conditions, cavity size, and whether the
testing is to be on a 100 percent production or on a periodic basis. The individual specification shall specify the test
condition letter required. When test condition C is specified, the procedure number (see 4.4.4) and the degree of
leakage rate sensitivity required shall be included. The following is included as a sensitivity and applicability guide:
Test condition A (bubble test - mineral oil or peanut oil at 125°C ±3°C (257°F ±6°F)). Use when a nominal
sensitivity of 10
-5
atm cm
3
/s is sufficient.
Test condition B (bubble test - silicone oil at room ambient temperature 25°C ±2°C (77°F ±3.6°F), with a vacuum
resulting in an absolute pressure of not greater than 1.5 inches of mercury (not greater than 38.1 torr). Use to
test parts which cannot withstand the temperature of test condition A, and when a nominal sensitivity of 10
-5
atm
cm
3
/s is sufficient.
Test condition C (tracer gas test). Use when a nominal sensitivity of 10
-8
atm cm
3
/s is sufficient.
Procedure I - (For parts having an evacuation tube which is unsealed and is to be connected to the leak
detector for test purposes.)
Leak from outside of part to inside. Check the seal of evacuation tube by backfilling with
air or gas. Then subject to procedure IIIa, IIIb, IIIc or IV.
Procedure II - (For parts having an evacuation tube which is unsealed to permit pressurizing with a
tracer gas.)
Leak from inside of part to outside. Check the seal of evacuation tube by backfilling with
air or gas. Then subject to procedure IIIa, IIIb, IIIc, or IV.
Procedure III - (For parts which are to be tested without breaking their seals.)
Fixed method (IIIa) - Part not filled with tracer gas. Force gas into leaks, then detect its
escape. Then subject to test condition A, B or D (see 4.4.4.3.2.1 permitting use of water),
as applicable, to check for gross leaks.
IIIb - Part not filled with tracer gas. Force radioactive gas into leaks, then use a
radioactivity counter to determine gas that has entered part. Then subject to test condition
A, B, or D (see 4.4.4.3.2.2.4 permitting use of water), as applicable, to check for gross
leaks.
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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.
3
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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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联系方式：xuyj@beice-sh.com 13917165676