Method for locating leaks in hermetically sealed container

Litant, I.

English

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USI/Sciantif i c  61 Teahrricrl InConnation Divimion 
Attantioat Mi88 Winnie Me Norgan 
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Patent Matters 
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U. 8. Patent No. 
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United States Patent Ofice Patented Dec, 3 548,636 22, 1970 
placed in a vacuum chamber which is evacuated. 13eIiurn 
3,548,636 leaking out of any leak in the sealed container is then de- 
'OR DETECmG IN WEmETP- tected by a specially modified mass spectronlcter. In an- GALLY SEALED CONTAPNERS 
bving Litant, Lexington, Mass., assignor to the other very similar method, a radioactive gas is used dur- 
states of ~ ~ ~ f i ~ ~  as represented by the ~ d ~ i ~ i ~ t ~ ~ t ~ ~  5 ing the pressurizing step and leaks are detected with a 
of the National Aeronautics and Space AdminisBration scintillation counter. 
Filed Sept. 30, 1968, Ser. No. 763,685 Another known method of leak dckction entails the sc- 
Int. 61. GOlm 3/06, 3/20 quential steps of weighing, pressurizing in an FC-75 Auo- 
U.S. CI. 73-40.7 11 Claims rocarbon and re-weighing a hermetically sealed container. 
10 A weight increase indicates that the container gossesscs 
a leak through which the fluorocarbon was forced during 
ABSmACT OF THE DHSCLOSmE the pressurization step. Still another leak detection method 
A leak detection method wherein the hermetically involves the use of fluorocarbons. )During this method, the 
sealed container is vacuum heated and then immersed in container is pressurized in Freon 113 before immersion 
a relatively cool bath of a detection fluid such as tri- 15 in a bath containing FC-75 fluorocarbon at about 70" @. 
chlorofluoromethane. Should leaks exist the detection fluid The appearance of bubbles in the fluorocarbon bath is an 
is drawn to the interior of the container by the resulting indication that Freon 113 first entered the container dur- 
reduction of pressure. After all traces of the fluid are ing the pressurizing step and is now escaping through a 
removed from the surface of the container, leaks are de- leak in the sealed container. 
tected by means of a halogen detector or by observance 20 The above described leak detection methods suffer from 
of bubbles when the container is immersed in a second a number of both common and independent disadvantages. 
liquid. For example, the range of leak sizes detected by indrvidual 
methods is relatively narrow so that separate tests must 
ORIGIN O F  THE INVENTION 
The invention described herein was made by an em- 
ployee of the United States Government and may be man- 
ufactured and used by or for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or therefor. 
be made to detect both gross and fine leaks. Also, most of 
the tests are cumbersome because of req~~ircments for ex- 
tensive periods of gas or liquid pressurization and pr3- 
cedural manipulations that are tedious and srrbjeci to OD- 
erator error. Still another problem is detection ineRciency 
which is particularly prevalent in the above described 
ethylene glycol test. Because that test relies ripon gas ex- 
BACKGROUND OF THE INVENTION pansion in the order of only 45 percent, many leaks are 
not detectable. Furthermore, in some instances a false 
This invention relates generally to a leak detection indication can result from the appearance in ?be liquid 
method and is especially suited for detecting leaks in bath of bubbles from a source dher  than leaks in the 
hermetically sealed containers. 35 sealed container being tested. 
Hermetically sealed containers are utilized in various The object of this invention, therefore, is to providc a 
fields to protect products from contamination resulting more efficient method for detecting and determining the 
from exposure to the atmosphere. This practice is particu- location of lealcs in hermetically sealed containers. 
larly common in the electronics industry wherein many qo 
components such as transistors, integrated circuits, relays, SUMMARY OF THE INVENTION 
etc. are protectively sealed in small metal cans. After hav- The invention is characterized by the provision of a 
ing been sealed, the gas tightness of these cans must be leak detection method wherein a detectron liquid i s  
tested to insure that the enclosed components will remain introduced into a hermetically sealed container thiough 
isolated from environmental conditions. 45 any leak therein, the introduced detection liquid i s  heated 
Various methods are now used to test hermetically and vaporized within the container, and resrrltant vapor 
sealed enclosures and, frequently different methods are re- escaping through the leak in the container is detected. 
quired depending upon the sizes of the leaks being de- Because of the large pressure change that occurs witb:m 
tected. Leak sizes are empirically defined as gross or fine the container upon a change of state in the detectmn 
with a gross leak permitting passage of up to 1~ 10-5 50 liqiud, extremely small leaks can be easily detected by 
atmospheric cubic centimeters of air per second (std. this method. Furthermore, the method minimizes procc- 
cc./sec.) and a fine leak permitting air flow in the range dural requirements and is readily adapted to automation. 
between 1 x 10-5 and 1 x 10-8 std. cc./sec. per second. A feature of the invention is the provision of a leak 
According to one detection method, hermetically sealed detection method of the above type wherein the vapor 
electrical components are immersed in a detergent and 55 detection step entails immersing the container in a liquid 
water solution and pressurized to three or four atmos- bath and observing bubbles formed ihercin by vapor escap- 
pheres for a period of between four and sixteen hours. ing through the walls of the container. 'Phis method bas 
The components are then tested to determine whether any minimal equipment requirements and is sriitabie for detec- 
changes have occurred in their electrical characteristics. tion of gross leaks. 
Naturally, the existence of such a change indicates that 80 Another fcature of the invention is the provision of a 
the component has been contacted by solution that was leak detection method of the characterizez type -+vi~ercin 
forced through a leak in the sealed enclosure during the the detection liquid has a boiling temperature below 5 
pressurizing operation. Another leak detection method C. Use of a detection liquid with a reIativelig low boilin, 
entails the immersion of the sealed container in a bath of point greatly simplifies the procedural requireinents of the 
ethylene glycol heated to a temperature of between 125" (;5 method. 
and 150" C. The appearance of bubbles in the ethylene 
\\ 
Another feature of the invention is the prevision of a 
glycol bath indicates that expanding gas is escaping leak detection method of the above featured type wherein 
through a leak in the sealed container. the detection liquid comprises a halogen contdining com- 
According to another method, most commonly used to pound. Chemically inert, halogen containing liquids 
detect fine leaks, the sealed enclosure is pressurized with 70 possess various propzities that are uniqrxely suited to the 
helium gas at between three and four atmospheres for above described method. 
over one hour. The sealed component is subsequently Another feature of the invention is the grovisian of a 
3,548,636 
3 4 
Beak detection method of the above featured type wherein measured by the detector in this way can be related to 
the vapor detection step encompasses detection of the actual leaks by use of a factor dependent upon the 
escaping vapor w;ch a conventional halogen leak detector. properties of the detection liquid utilized. It  should be 
According to this method, leaks permitting gas flow rates noted that a needle probe is not necessary for detecting 
21s small as I x 10-10 std. cc./sec. can be detected. gross leaks. For these, positioning of the probe anywhere 
h o t h e r  feature of the invention is the provision of a near the device will give an indication of a leak. 
leak detection method of the above featured type wherein A preferred method for initially introducing the detec- 
the vapor detection step involves sniffing the outer surface tion liquid into the tested container involves a vacuum 
of the contaicer with a probe operatively connected to the heating process. According to this method the sealed con- 
PiiPogcn leak detector. By selectively moving the probe tainer is first heated in an evacuated oven resulting in 
about the outer surface of the container, the exact loca- the removal of air through any leak therein. The heated 
hens of detected lealis can be determined. container is then immersed in a bath of the detection 
~ ~ ~ ~ t h ~ ~  feature of &is invention is t e provision of a liquid which is preferably maintained at  a reduced tem- 
leak detecilol~ method of the above featured types wherein ~erature.  Responsive to the relatively cold environment 
the detection Liquid introduction step includes the steps of 15 provided by the liquid bath, the internal pressure of the 
first healrng an evacuated oven and then immersing container is quickly reduced to substantially less than 
the lieated contarner in a bath of the detection liquid. atmospheric. Because of this reduced pressure, the detec- 
During the vlccum heating operation, air is removed from tion liquid is readily drawn through the leaks in the con- 
the cantairier through any leak existing therein. sub- tainer's walls. The inherently low surface tension of the 
sequently, in ths ~elatively cold environment provided by 20 halogenated liquids employed permits them to penetrate 
the detecrlon liquid there is formed within the con- more easily into fine leaks. After removal from the bath, 
tainer a paitial vacuum that draws detection liquid into any detection liquid adhering to the outer surfaces of 
the contain-r through the existing leak. the container evaporates rapidly. Externally adhering liquid not removed could be detected during the subse- 
DESCRIPTION O F  THE DRAWING 25 quent detection step giving a false indication of a leak. 
FIG, 1 is a flow diagram illustrating a preferred em- For this operation also, detection liquid with a relatively 
bodiment of the invention; and low boiling temperature of, for example, less than 50" 
FIG. 2 1s a graph having curves representing leaks C. are highly desirable. Complete evaporation removal of 
detected accoiding the invention. Leak rates in standard such liquids from the container's outer surface is quickly 
ciihlc centin~elcrs per second are plotted vs. time in 30 and easily accomplished at room temperature with a 
minutes. simple blowing operation. 
DESCRIPTION OF THE INVENTION In a specific example of the invention, an integrated 
electronic circuit enclosed within a 0.220" by 0.220" 
Acc~rdlng 10 the present invention, a suitable detection hermetically sealed can was heated in a vacuum oven at  
llquid is in2oduced through any leak existing is a 35 about 125" C. for ten minutes. Next, the can was re- 
l.ermellcally sealed container being tested. The introduced moved from the oven and immersed in a bath of tri- 
detec'ilon Ilquid Is then permitted to vaporize. Because chlorofluoromethane which was maintained at a tempera- 
of the the s~lbsiantially increased internal vapor pres- ture between 0" and 5" C. After one hour in the cold 
sune p~oduced by the change of state in the detection detection liquid, the can was removed and quickly blown 
Irquid, the resultant vapor escapes through the leak in 40 dry with nitrogen to remove any detection liquid still 
the contames's kvalls at an elevated rate that is readily adhering to its outer surfaces. Finally, a hyperdermic 
detectable. needle probe connected to a conventional halogen leak 
Hlghly preferred detection liquids include chemically detector was moved slowly about the surface of the can 
inell, halogen-containing liquids with relatively low boil- and four distinct leaks were located and measured. A 
ing points. Such liquids are easily vaporized and experience 45 flow diagram illustrating these steps is shown in FIG. 1. 
during a change from a liquid to vapor state volume The four curves 11-14 in FIG. 2 represents the meas- 
increases of as much as 130 times. In addition, the ured leaks with time in minutes plotted as the abscissa 
pieferled halogen containing liquids have extraordinarily and leak rate in standard cubic centimeters per second 
low suiface tensions enabling them to penetrate extremely plotted as the ordinate. This example illustrates the ease 
\mall 0riSces. These properties are obviously quite 50 with which extremely small hermetically sealed containers 
bewficiai to the practice of the described leak detection can be accurately leak checked. The plotted curves also 
method. Ha!ogen-containing liquids found particularly indicate the extensive time periods over which existing 
u~efu l  ale trLchlorofluoromethane, CCLsF with a boiling leaks are detectable. As shown the four leaks were ob- 
pollll of 24. i " C. and a fully fluorinated material marketed served over a period of 75 minutes during which the 
by the Minnesota ~ m i n g ,  and Machinery CO. under the 55 measured leaks fell from values in the 10-6 std. cc./sec. 
trade name FG-32 and having a boiling point of 32" C. range to the 10-8 cc./sec. range. 
Both oi these detection liquids have the above noted 
~~~~~d~~~ to another method embodiment of the in- 
elesirable prcpert~es and a relatively inexpensive. 
vention, a detection liquid is first introduced into a her- 
Another advantage of halogen-containing detection metically sealed container &rough any leaks therein as 
l ~ ~ l d s  IS that they permit the use of conventional halogen 60 described above. Next, the container is submerged in a 
detectors for detecting vapor discharged through a leak suitable test liquid maintained above the boiling tempera- 
the con~ainer being tested. Generally, halogen leak ture of the detection liquid. The appearance of bubbles 
oeteclors ~nc l t~de  a vacuum pump that draws air from a on the surface of the submerged container indicates the 
s-nsmg probe 10 a detector elenlent consisting of a heated, existence and location of openings through which vapor- 
rositnvely charged, platinum emitter within a cylindrical 65 ized detection liquid is escaping. Since this method does 
collector. The detector responds to the presence of halogen not utilize a b a k  detection instrument, this method has 
vzpo; with an increase of current between the emitter and the advantage of minimal required equipment costs. Mow- 
collector electrodes. Such instruments have sensitivities ever, only leaks in the gross leak range can be readily 
capable of deteclingleaks 8, small as 1X 10-lo std. cc./sec. detected in this manner. 
Furlheirnore, wiih hyperdelmic needle type probes, the 70 In a specific example of this type a 0.220" x 0.220" x 
precise loc,~tioii of existing leaks can be established for 0.050" hermetically sealed can was heated in a vacuum 
even vcry sn~all containers. Leak location is determined oven at about 125" C. for ten minutes. Next, the heated 
by rfieiely moving the probe slowly over the surface of can was removed from the oven and submerged in a bath 
the sealed contalnea until the presence of halogen is of trichlorofluoromethane which was maintained at a 
irldrcated by tlie detector instrument. The specific leaks 75 temperature between 0" and 5" C. After one hour in 
5; 
the cold detection liquid, the can was removed and 
quickly blown dry with nitrogen to remove adhering de- 
tection liquid. Finally, the dry can was immersed in a 
bath of ethylene glycol maintained at  about 125-150" C. 
The existence and location of several gross leaks were 
indicated by escaping vapor bubbles formed on the sur- 
face of the submerged can. 
Obviously, many modifications and variations of the 
present invention are possible in light of the above teach- 
ings. For example only, detection liquids other than both 
specifically mentioned can be desirable for leak detec- 
tion. It is to be understood, therefore, that within the 
scope of the appended claims the invention can be prac- 
ticed otherwise than as specifically described. 
What is claimed is: 15 
1. A method for detecting a leak in a hermetically 
sealed enclosure comprising the steps of introducing a 
detection liquid into the enclosure through any leak there- 
in, said introducing step accomplished by heating the en- 
closure and immersing the heated enclosure in a bath of 20 
detection liquid having a boiling temperature below 50 
degrees C., vaporizing the detection liquid introduced into 
the enclosure, and, detecting vapor generated during said 
vaporizing step and escaping through any leak in the 
enclosure. 25 
2. A method according to claim 1 wherein said en- 
closure heating step comprises heating the enclosure in 
an evacuated oven. 
3. A method according to claim 2 wherein the detec- 
tion liquid comprises a halogen containing compound. 30 
4. A method according to claim 3 wherein said detect- 
ing step comprises detecting the escaping vapor with a 
halogen detector. 
5. A method according to claim 4 wherein said detect- 
6 
ing step con~prises positioning adjacent the enclosure a. 
probe connected to the halogen detector. 
6. A method according to claim 2 wherein said detect- 
ing step comprises immersing the enclosure in a liquid 
bath and observing bubbles formed by the escaping vapor. 
7. A method according to claim 1 including the step 
of removing externally adhering detection iiqrnid from the 
enclosure after said immersing step and beforc s a d  de- 
tection step. 
8. A method according to claim 7 wherein the detec- 
tion liquid comprises a halogen containing compound. 
9. A method according to claim 8 wherein said detect- 
ing step comprises detecting the escaping vapor with a 
halogen detector. 
18. A method according to claim 9 wherein said detect- 
ing step comprises positioning adjacent the enclosure a 
probe connected to the halogen detector. 
11. A method according to claim 7 wherein said de- 
tecting step comprises immersing the enclosure in a liquid 
bath and observing bubbles formed by the escaping vapor. 
References Cited 
UNITED STATES PATENTS 
2,550,498 4/1951 Rice -------------- 73-40.7X 
1,995,699 3/1935 Baker -------------- 7 3 4 5 . 5  
FOREIGN PATENTS 
944,402 12/1963 Great Britain ------.- 73-40.7 
S .  C L E M E N T  S W I S H E R ,  Primary Examiner 
U.S. CI. X.R. 


Method for detecting leaks in hermetically sealed containers Patent

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