Volume displacement transducer for leak detection in hermetically sealed semiconductor device

Orner, J. W.

English

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3,559,460 United States Patent Oace 
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mation. The bubble method is almost entirely operator 3,559,460 
METHOD AND APPAWAmS FOR DEmGmG dependent, while the detergent system depends upon a 
GROSS LEAKS comparison of electrical measurements made before and john w. oFIPer, woburb M ~ ~ ~ . ,  to united after pressurization in the detergent solution. In acldition, 
States o f  America as represented by the Administrator it sometimes happens that a small amoullt of detergent 
of  the National Aeronanfics and Soace Administra~on solution enters the device through a relatively sn~ail eak 
Filed Feb. 24, 1969, Ser. N;. 801,660 
Int. C1. GOEm 3/36 
U.S. Cl. 73-49.3 7 Claims 
ABSTRACT OF THE DISCLOSURE 
The detection of gross leaks in hermetically sealed de- 
vices is accomplished by positioning a displacement trans- 
ducer on or near a metal surface of the device. The device 
is placed in a zone wherein the device is subjected to in- 
creased gas pressure thereby causing defiection of the 
surface being sensed by the displacement transducer. If 
there is a leak in the device, the device will become in- 
ternally pressurizcd thereby returning the deflected sur- 
face to its original condition. The displacement trans- 
ducer is employed to sense the deflection of the surface as 
it occurs. 
and does not come into direct contact with any of thc 
active electrical elements, thus the electrical performance 
of the device is not immediately affected, and the leak will 
not be detected. Furthermore, in such a case, Ihc deter- 
gent solution may eventually find its way on to the active 
elements, particularly under the influence of ~ibration 
during its normal service life and a f a i l ~ ~ r e  niay result. 
Furthermore these methods are essentially qualitative 
15 only, in that no quantitative measurement of leak rate 
can be made. 
It  will be appreciated that in accordance with the present 
invention gross leaks may be detected and measured in 
hermetically sealed devices in which the Beak rates are 
20 too large to be detected by the methods uscd for cietccling 
fine leaks, such as the helium mass spectronzeter method. 
BRIEF SUMMARY O F  INWNTION 
The ~resen t  leak testing method of the present Invca- 
The invention described herein was made by an em- 25 tion depends upon the fa; that when a sealed coniaincr 
ployee of the United States Government and may be is subjected to a change of ambient atmospheric pressure 
a mechanical displacement of the walls of the container 
manufactured and wed by Or for the Government for will take place. As the internal gas pressure in Ihe device governmental purposes without the payment of any royal- 
ties thereon or therefor. equalizes with the outside pressure, by reason of a gross 
sn leak. the disvlacement will recover at  an ezt~onentinl rate. 
" - 
BACKGROUND O F  THE INVENTION A deasurekent of the time constant of t i e  exponential 
Field of the invention recovery rate, in conjunction with the known intern21 
volume of the device, will enable calcrrlatiorr of the equivn- 
The invention relates to method and apparatus employ- lent leak rate. 
ing a displacement transducer to detect the presence of 35 
a gross leak in hermetically sealed semiconductor devices BRIEF DESCRIPTION OF THE DRAWINGS 
and is particularly applicable to detecting leaks in small In the drawings, wherein like reference chazacter s are 
electronic components such as transistors, sealed relays, used throughout to designate like parts: 
etc. FIG. 1 is a schematic of one embodiment of the inven- 
Description of the prior art 40 tion. 
FIG. 2 is a schematic of another embodiment oC the 
In this regard, present methods of fine leak detection invention. 
used for testing small sealed electronic components in- FIG. 3 is another embodiment employing a capacit- 
volving the use of helium have proved to be effective and ance system. 
adequate in the range from about to lo-" standard 45 FIG. 4 is the circuitry involved in carrying the method 
atm./cc. per second. They are inefficient and unreliable of FIG. 3. 
for leak rates larger than about 10-5 standard atm./cc. 
per second. Therefore, this invention pertains principally OF *IXE MVENmoN 
to these larger leak rates which are here defined as gross Now turning to a more detailed description of tlze 
leaks. invention taking into consideration FIG. 1, a test jig 111 
Prior art methods used for gross leak detection in small is positioned in a pressure chamber 10. As an example 
sealed electronic devices involve such tests as immersion of a device to be examined, a semiconduclor device I2 
in hot liquid while examining for the escape of gas bubbles is secured on the jig B l .  A displacement transdracer 13 
due to the thermal expansion of the internal air, or alterna- is affixed to an external surface portion 14 of the device 
tively, the device is pressurized in an aqueous solution 55 12 so that as the surface is flexed by variations of the 
of detergent followed by a functional test of its electrical internal pressure of the device 12, the tr~nsducer 13 i s  
characteristics. Any penetration of the detergent solution subjected to compression. When the pressure ckanlbcr 10 
will degrade the normal electrical performance of the is pressurized, the resultant differential pressrrre across 
device thereby indicating a gross leak in the sealed en- the walls of the device 12 causes the sn~facc portion 14  
closure. 60 to flex inwardly thereby subjecting the transducer to 
These methods of detecting gross lealcs in small sealed compression to decrease the resistance of the transducer. 
devices have a number of disadvantages which not only In pressurizing the chamber B0, it will be particularly 
add to the difficulty of testing, but also give rise to un- useful to rapidly increase the pressure to a desired level, 
certainties and lack of reliability. For example, none of thereby achieving greatest deflection of the surfaces isf 
the methods in current use are readily adaptable to auto- the device undergoing testing. Obviously, pressurization 
3,559,460 
3 4 
in gradual increments permits the device to present nor- circuit from high frequency generator (G).  Diode recti- 
mal surface& as the pressure both inside and outside the fiers (dl and dz) are so connected as to  charge C1 and 
devace 12 reach equilibrium. Equilibrium js a function CZ to opposite polarities and thus R3 can be adjusted for 
of the snze of the ieak to pressure differential with time zero voltage output. Any changs in capacitance of either 
period of ach~eving maximum desired pressurization being Cl or Cz will then cause a voltage to appear across the 
a variable factor. In the instant embodiment, the size of output te~minals. 
the leak 1s not important other than to note that the A rapid change in the gas pressure within the pressure 
leak is a grors leak; therefore, pressurization must not vessel 47 will cause an equally rapid physical displace- 
be in small increments so that a time factor ensues for ment of the relay case wall adjacent to plate 42 thus 
equilibrium to take place. altering the thickness of the air gap, changing the ca- 
The pressurization is accomplished by feeding the cham- pacitance between the relay case 41 and the flat plate 42, 
bcs 10, whrch is of only relatively small volume, from a and causing a voltage to appear across the comparator 
suitable source of gas such as contained in a cylinder 20. circuit output terminals. If a gross leak in the sealed en- 
The preisurizing gas is preferably helium. The transducer closure of the relay exists, an exponential recovery will 
13 has suitable leads 28 connected to it, with a pair of con- 15 occur at a rate which is proportional to the size of the 
ductc-rs 22 in t l ~ e  wall of the chamber 10. A pair of leads leak. Thus, if the output voltage is monitored, as for ex- 
23 then go la a transducer amplifier indicator 17. The ample by a strip chart recorder, the gross leak can be 
output tkcrcfrern may go to an amplifier indicator 25 by readily detected and measured. 
means of a pair oi leads 24. An X-Y Recorder 30 may Several types of displacement transducers are com- 
then be fed trom the amplifier 25 for purposes of achiev- 20 mercially obtainable. Some require direct contact, while 
in2 a permanent record, as desired. some do not. A good example of a non-contacting dis- 
In the second embodiment, as can be seen from FIG. 2, placement transducer is the Aero-Vit System manufac- 
a test jig 31 has rnouilted thereon a direct reading dial tured by the Kaman Nuclear Division of Kaman Corpora- 
indicator 35 for measuring the deflection of the wall on tion. 
the device 41. The linkage in this arrangement is me- 25 While there have been shown and described particular 
chanical la natt~re. Since the dial indicator 35, the jig 31 embodiments of the invention, it will be obvious to those 
and thc senrico~lductor device 41 must all be positioned in skilled in the art that various changes and modifications 
the cban~ber 110, the chamber 1b)  must be provided with may be made therein without departing from the inven- 
viewing means such as a port and suitable lighting means tion, and, therefore, it is aimed to cover all such changes 
(not illastrared) for viewing the indicator 35 in real time 30 and modifications as fall within the spirit and scope of 
tvhiie it is an the chamber 10. the invention. 
Itl co~junction with the above embodiment, the device What is claimed is: 
41 1.s placed in the jig 31. The direct dial device 35 1. A method for detecting gross leaks in hermetically 
(FIG. 2 )  1s gut into operative abutment therewith. The sealed devices containing a quantity of free internal 
jig 31 ir placed in the pressure chamber 10 or is already 35 volume comprising: 
sn the cliarnber lbB prior to positioning of the device there- positioning deflection detecting means in operative re- 
in. 111 the usual circumstances the chamber 10 will be of lationship with respect to an external surface por- 
relatively small dimensions, so for ease of operation the tion of said device, 
electronic device is mounted on the jig 31 before placing inserting said device in a pressure changing zone, 
it in the chamber 80. The chamber 10 is then closed. The 40 rapidly increasing the differential pressure across said 
pressure is then rapidly raised by the gas from the cylin- surface portion by varying the fluid pressure in said 
der 20 t ~ r ~ t ~ i  at least double atmospheric pressure is at- zone, 
t m e d  in the chanlbeir 10. Under the aegis of the increased detecting an initial deflection of said surface produced 
pseqsure the wall of the device will deflect. by an increase in said differential pressure, 
Naturally, the degree of permissible pressurization will 45 waiting for a reduction in said differential pressure pro- 
be somewhat limited as the pressure should not be so great duced by a net fluid %w through a leakage path in 
to effect thc strocturd capabilities of the device itself. One said sealed device, and 
would not desire to collapse the device or cause a com- detecting a second deflection of said surface produced 
pressive failure of the device. by said decrease in differential pressure. 
In the foregoing the method of the present invention 60 2. The method of claim 1 wherein the variation of 
hds been directed to the concept of increased pressuriza- pressure is accomplished by increasing the pressure in 
tion, so t h ~ t  when there is a gross leak externally sup- said zone by introducing a pressurizing gas, such as air. 
piled gas enters the device. However, the present inven- 3. The method of claim 2 wherein the pressurizing gas 
lion includes the further concept of rapidly reducing the is helium. 
pressure in the chamber PO to thereby achieve an outward 65 4. The method of claim 1 wherein the sensing means 
deflection of the surfoces of the device until the gas in is a displacement transducer which supplies a signal 
the device escapes through a leak if one is present. In when said external surface portion of the device is de- 
this embod?ment, tbe walls of the device are deflected out- flected. 
wardiy to actuate the displacement transducer. 5. A gross leak tester for hermetically sealed devices 
For further purposes of illustration, attention is directed 60 comprising: 
to FECS. 3 and 4. Demonstrated in the concept of test work holder means for said devices, 
the hormetic scaP of a relay 41 of square cross section. The deflection sensing means in operative relationship with 
relay 41 under test is placed upon a flat plate 42 upon an external surface portion of said device so as to 
whlck two strips of tape 43 and 44 have been placed directly sense deflections thereof produced by dif- 
in such a manner as to electrically insulate the case of 65 ferential pressure across the walls of said device, 
the relay from lhe plate 42, but to leave a small air gap a chamber capable of relative gas pressure change 
between the relay and the plate 42. Thc relay case is retaining said work holder means, said device and said 
ebctricaily connected by means of lead 45 to feed through deflection sensing means, 
terminal 46 tl~rough the bottom plate of a pressure vessel said sensing means being adapted to be connected to in- 
47. Thus, the relay 41 and the flat plate 42 form the two 70 dicating means to indicate the degree of deflection of 
plaies oi a cendenser. said surface portion as the pressure in said cham- 
The external circuitry is shown in FIG. 4. It  is a ca- ber is varied. 
pacitance comparator circuit in which C1 is the capaci- 6. The leak tester of claim 5 including a source of 
tsncc just described and Cz is a standard capacitance of pressuriziug gas and said chamber is in communication 
appioxirnately the same value. Power is applied to the 75 with said source of gas. 
3,559,460 
5 6 
7. The leak tester of claim 6 wherein the source of pres- 2,754,677 7/1956 New ---------------_- 73-37 
surizing gas is helium. OTHER REFERENCES 
References Cited IBM Technical Disclosure Bulletin, Gross Leak De- 
UNITED STATES PATENTS tection, by J. J. Kennedy, vol. 5, No. 1, June 1962. 5 
2,453,338 1'1/1948 Pajak -------------- 73-52 X LOUIS R. PRINCE, Primary Examiner 
2,658,819 11/1953 Fbrmwalt ----------- 73-52 X W. A. HENRY n[, Assistant Examiner 


Method and apparatus for detecting gross leaks Patent

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