U.S. patent application number 09/908218 was filed with the patent office on 2002-03-07 for probe station having multiple enclosures.
Invention is credited to Dougherty, R. Mark, Hawkins, Jeffrey A., Hayden, Leonard A., Peters, Ron A..
Application Number | 20020027442 09/908218 |
Document ID | / |
Family ID | 25355168 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020027442 |
Kind Code |
A1 |
Peters, Ron A. ; et
al. |
March 7, 2002 |
Probe station having multiple enclosures
Abstract
A probe station for probing a test device has a chuck element
for supporting the test device. An electrically conductive outer
shield enclosure at least partially encloses such chuck element to
provide EMI shielding therefor. An electrically conductive inner
shield enclosure is interposed between and insulated from the outer
shield enclosure and the chuck element, and at least partially
encloses the chuck element.
Inventors: |
Peters, Ron A.; (Tigard,
OR) ; Hayden, Leonard A.; (Beaverton, OR) ;
Hawkins, Jeffrey A.; (Portland, OR) ; Dougherty, R.
Mark; (Aloha, OR) |
Correspondence
Address: |
Jacob E. Vilhauer, Jr., Esq.
Chernoff, Vilhauer, McClung & Stenzel
1600 ODS Tower
601 S.W. Second Avenue
Portland
OR
97204
US
|
Family ID: |
25355168 |
Appl. No.: |
09/908218 |
Filed: |
July 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09908218 |
Jul 17, 2001 |
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09451698 |
Nov 30, 1999 |
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6288557 |
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09451698 |
Nov 30, 1999 |
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08870335 |
Jun 6, 1997 |
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6002263 |
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Current U.S.
Class: |
324/756.02 |
Current CPC
Class: |
G01R 31/2886 20130101;
G01R 31/286 20130101; G01R 1/04 20130101; G01R 1/18 20130101; G01R
31/2889 20130101; G01R 31/002 20130101; G01R 31/2808 20130101 |
Class at
Publication: |
324/754 |
International
Class: |
G01R 031/02 |
Claims
1. A probe station for probing a test device, said probe station
comprising: (a) a chuck assembly having a chuck assembly element
with a supporting surface for supporting said test device during
probing thereof; (b) an electrically conductive outer enclosure at
least partially enclosing said supporting surface and insulated
therefrom; (c) an electrically conductive inner enclosure
interposed between and insulated from said enclosure and said
supporting surface, and at least partially enclosing said
supporting surface; (d) respective electrical conductors connected
to said supporting surface and said inner enclosure, respectively,
causing said inner enclosure and said supporting surface to have
respective potentials independent of each other; and (e) a
selective connector either interconnecting or, alternatively,
disconnecting said inner enclosure and said outer enclosure
electrically with respect to each other.
Description
[0001] This application is a continuation of application Ser. No.
09/451,698, filed Nov. 30, 1999, which is a continuation of
application Ser. No. 08/870,335, filed Jun. 6, 1997, now U.S. Pat.
No. 6,002,263.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to probe stations, commonly
known as package or wafer probers, used manually, semiautomatically
or fully automatically to test semiconductor devices. More
particularly, the invention relates to such probe stations having
EMI shielded enclosures for substantially enclosing the test
devices, such as those probe stations shown in commonly-owned U.S.
Pat. Nos. 5,266,889 and 5,457,398 which are hereby incorporated by
reference.
[0003] The probe stations shown in the foregoing patents are
capable of performing both low-current and high-frequency
measurements within a single shielded enclosure. However, as
electrical test currents decrease, or as electrical test
frequencies increase, the use of merely a single EMI shielding
enclosure becomes less adequate. In the most sensitive of
measurements, and particularly (although not necessarily) when
guarding is employed for low current measurements as described in
U.S. Pat. No. 5,457,398, the choice of the shield potential is
critical. Reflecting such criticality, the single shield enclosures
shown in the foregoing patents have in the past been equipped with
selective connectors enabling the shield potential to match that of
the measurement instrumentation ground while being isolated from
other connectors, or alternatively to be biased by another
connector, or to be connected to AC earth ground. Usually the
measurement instrumentation ground is preferred since it provides a
"quiet" shield ideally having no electrical noise relative to the
measurement instrument. However, if the shielding enclosure is
exposed to EMI (such as electrostatic noise currents from its
external environment), its ideal "quiet" condition is not achieved,
resulting in unwanted spurious currents in the chuck assembly guard
element and/or the supporting element for the test device. The
effect of such currents is particularly harmful to the operation of
the guard element, where the spurious currents result in guard
potential errors causing leakage currents and resultant signal
errors in the chuck element which supports the test device.
[0004] For high-frequency measurements, guarding is typically not
employed. However, for the most sensitive of measurements, the
"quietness" of the shield is still critical. For this reason, it is
common practice to construct a fully shielded room, commonly known
as a screen room, large enough to contain a probe station with its
own separate shield enclosure, test equipment, and several
operators. However, screen rooms take up a large amount of space,
are expensive to build, and are ineffective with respect to noise
sources within the room.
[0005] The environmental influences which ordinarily compromise the
desired quiet condition of a shield are the motion of external
objects at constant potential which cause spurious shield currents
due to varying capacitance, and external AC voltages which cause
spurious shield currents via constant capacitance. For sensitive
measurements, what is needed is a truly quiet shield unaffected by
such environmental influences.
[0006] Also, to reduce the need for a screen room, and provide a
shield unaffected by closely adjacent environmental influences,
such quiet shield structure should be compact.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention satisfies the foregoing need by
providing a probe station having respective inner and outer
conductive shield enclosures insulated from each other, both
enclosures at least partially enclosing the chuck assembly element
which supports the test device, and also its associated guard
element if one is provided. The outer shield enclosure, which is
preferably connected either directly or indirectly to AC earth
ground, intercepts the external environmental noise, minimizing its
effects on the inner shield and on the chuck assembly elements
enclosed by the inner shield.
[0008] Such inner and outer shield enclosures are preferably built
integrally into the probe station and therefore are compact.
[0009] The foregoing and other objectives, features, and advantages
of the invention will be more readily understood upon consideration
of the following detailed description, taken in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a top view of an exemplary probe station in
accordance with the present invention, with the top of the station
partially removed to show interior structure.
[0011] FIG. 2 is a partially sectional, partially schematic view
taken along line 2-2 of FIG. 1.
[0012] FIG. 3 is a partially sectional, partially schematic view
taken along line 3-3 of FIG. 1.
[0013] FIG. 4 is an enlarged sectional view of a portion of a
flexible wall element of the embodiment of FIG. 1.
[0014] FIG. 5 is a partial top view of an alternative embodiment of
the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] An exemplary embodiment of a probe station in accordance
with the present invention, indicated generally as 10 in the
figures, has an electrically conductive outer enclosure 12
including a conductive raisable hinged lid 12a electrically
connected thereto. A chuck assembly 14 for supporting a test device
is laterally positionable by a chuck positioner assembly having
orthogonally arranged lateral X-axis and Y-axis positioners. A
lateral X-axis positioner 16 has a laterally extending positioning
screw (not shown) driven by an electric motor 18. The X-axis
positioner 16 is partially enclosed by a conductive housing 16a,
and optionally also by flexible pleated rubber boots 16b for
accommodating positioning movements while preventing the entry and
escape of dirt particles. The conductive housing 16a is insulated
from the outer enclosure 12 by respective dielectric anodized
coatings on both the exterior of the housing 16a and the interior
of the enclosure 12, and is indirectly connected electrically to AC
earth ground by means of conventional motor cabling and a grounded
motor power supply (not shown), represented schematically in FIG. 2
by a high-impedance electrical path 22. The X-axis positioner 16
selectively moves a Y-axis positioner 24, oriented perpendicularly
to the X-axis positioner 16, along the X-axis.
[0016] The lateral Y-axis positioner 24 is constructed similarly to
the X-axis positioner 16, and includes an outer conductive housing
24a with optional flexible pleated rubber boots 24b. The conductive
housing 24a is electrically connected to the housing 16a of the
X-axis positioner. The motor 26 of the Y-axis positioner 24 extends
through a horizontal slot 28 (FIG. 3) in the side of the enclosure
12, thereby permitting it to be moved freely along the X-axis by
the X-axis positioner 16. Alternatively, a larger enclosure 12
could eliminate the slot 28.
[0017] A conventional Z-axis positioner 30, having a conductive
housing 30a electrically connected to the housing 24a, is movable
along the Y-axis by the Y-axis positioner 24. The Z-axis positioner
30 includes respective internal electric motors (not shown) which
selectively reciprocate a plunger assembly 30b vertically and
rotate it through a limited range about a vertical axis in a known
manner.
[0018] The outer conductive enclosure 12 is connected by a
low-impedance path 32 (FIG. 2) directly to AC ground. Collectively,
the outer enclosure 12, 12a and the positioner housings 16a, 24a,
and 30a cooperate to provide an electrically conductive outer
shield enclosure which separates the remainder of the probe station
from environmental noise sources, whether located externally of the
enclosure 12 or internally thereof inside the positioner housings.
Such noise sources include the electric motors 18 and 26, and those
motors within the Z-axis positioner 30, as well as other electrical
components such as cables, thermal heaters, encoders, switches,
sensors, etc.
[0019] Mounted atop the plunger assembly 30b and electrically
insulated therefrom by dielectric spacers 34 is a square-shaped
conductive chuck shield 36 having a downwardly depending conductive
cylindrical skirt 36a. Mounted atop the chuck shield 36 and
electrically insulated therefrom by dielectric spacers 38 is a
conductive chuck guard element 40, which includes a peripheral
cylindrical conductive guard skirt 40a. The guard skirt 40a
peripherally surrounds a conductive chuck element 42 in spaced
relation thereto. The chuck element 42 is insulated from the guard
element 40 and guard skirt 40a by dielectric spacers 44 and has a
supporting surface 42a thereon for supporting a test device during
probing. Probes (not shown) are mounted on a probe ring 46, or
other suitable type of probe holder, for contacting the test device
when the Z-axis positioner 30 raises the supporting surface 42a
upwardly into probing position.
[0020] As shown schematically in FIG. 2, the chuck shield 36 is
electrically connected to the shield of a triaxial cable 37
interconnected with the measurement instrumentation. The guard
element 40, together with the guard skirt 40a, is connected to the
guard conductor of the triaxial cable, and the chuck element 42 is
connected to the center or signal conductor of the triaxial cable
37. Preferably a further guard element in the form of a conductive
plate 48, also electrically connected to the guard conductor of the
triaxial cable and insulated from the remainder of the probe
station by dielectric spacers 50, is suspended in opposed
relationship to the supporting surface 42a. The conductive plate 48
also provides a connection to a guard element on the bottom of a
probe card (not shown). Further details of the electrical
connections, and of the dielectric spacers utilized to insulate the
chuck elements from each other, are explained in U.S. Pat. No.
5,457,398 which is incorporated herein by reference. As explained
in such patent, the connections to the chuck elements 40 and 42
cause such elements to have substantially equal potentials to
minimize leakage currents therebetween.
[0021] An electrically conductive inner shield enclosure 52, which
also preferably acts as the probe station's environment control
enclosure not only for purposes of EMI shielding but also for
purposes of maintaining a dry and/or dark environment, is mounted
by dielectric spacers 54 to the interior of the outer enclosure 12
so as to be interposed between and insulated from the outer
enclosure 12 and the chuck elements 40 and 42. Like the chuck
shield 36, the enclosure 52 is connected to the shield of the
triaxial cable 37 associated with the measurement instrumentation.
A selective connector mechanism, schematically illustrated as a
three-way switch 56 in FIG. 2, enables respective different
potentials to be selectively established on the enclosure 52.
Normally the selective mechanism 56 would be in the "float"
position whereby the potential of the enclosure 52 depends on the
triaxial shield associated with the measurement instrumentation.
However the enclosure 52 can alternatively be electrically biased
by the selective connector mechanism 56, or interconnected with the
outer enclosure 12 if desired for particular applications. In the
normal situation where the inner enclosure 52 is not electrically
connected to the outer enclosure 12, the outer shield components
12, 12a, 16a, 24a, and 30a protect the inner shield 52 from
external noise sources, so that the inner shield in turn can
minimize noise-induced spurious currents affecting the chuck
elements 40 and/or 42 and thereby maximize the accuracy of the test
measurements.
[0022] Movement of the chuck assembly 14 laterally by the X-axis
and Y-axis positioners 16 and 24, respectively, is accomplished
with the Z-axis positioner retracted in order to position the test
device with respect to the probe or probes. During such movement,
the environmental integrity of the inner enclosure 52 is maintained
by means of an electrically conductive flexible wall assembly
indicated generally as 58. The wall assembly 58 includes a pair of
flexibly extensible and retractable pleated wall elements 58a which
are extensible and retractable along the X-axis, and a further pair
of such wall elements 58b which are flexibly extensible and
retractable along the Y-axis. The outermost ends of the wall
elements 58a are electrically connected to the inner surfaces of
the inner enclosure 52 by screws (not shown). The innermost ends of
the wall elements 58a are similarly connected to a rectangular
metal frame 60 supported by the Y-axis positioner housing 24a by
means of brackets 62 (FIG. 3) and dielectric spacers 64 which
insulate the frame 60 from the Y-axis positioner housing 24a. The
outermost ends of the flexible wall elements 58b, on the other
hand, are electrically connected to the inner surfaces of the ends
of the frame 60 by screws (not shown), while their innermost ends
are similarly connected to respective conductive bars 66
insulatively supported by dielectric brackets 68 atop the Z-axis
positioner housing 30a. Conductive plates 70 are electrically
connected to the bars 66 and surround the chuck shield skirt 36a in
spaced relation thereto.
[0023] As the X-axis positioner 16 moves the Y-axis positioner 24
and chuck assembly along the X-axis, it likewise moves the frame 60
and its enclosed wall elements 58b along the X-axis as the wall
elements 58a extend and retract. Conversely, as the Y-axis
positioner 24 moves the Z-axis positioner and chuck assembly along
the Y-axis, the wall elements 58b similarly extend and retract
along the Y-axis.
[0024] With reference to FIG. 4, a cross-section of an exemplary
pleat 72 of the flexible wall elements 58a and 58b is shown. The
electrically conductive core 74 of the pleated material is a fine
mesh polyester, chemically coated with copper and nickel. The core
74 is sandwiched between respective layers 76 which are nylon
fabric with a PVC stiffener. The respective layers 76 in turn are
covered by respective outer layers 78 of polyurethane. The pleated
material is preferably fluid-impervious and opaque so that the
inner enclosure 52 can serve as a dry and/or dark environment
control chamber, as well as an EMI shield. However, if the inner
enclosure 52 were merely intended to serve as a shield, the pleated
material need not be fluid-impervious or opaque. Conversely, if the
inner enclosure 52 were intended to serve merely as an environment
control chamber for dry and/or dark purposes, without EMI
shielding, the pleated material's conductive core 74 could be
eliminated. Also, alternative pleated materials of other
compositions, such as thin, highly flexible stainless steel or
other all-metal sheet material, could be used.
[0025] As a further alternative, a one-piece flexible wall assembly
80 (FIG. 5) having circular or oblate curved rings of pleats 82
surrounding the chuck assembly 14 could be provided in place of the
wall assembly 58 to permit flexible extension and retraction in
radial X and Y directions. The outer extremity of the wall assembly
80 is electrically connected by a curved conductive frame 84 to the
inner shield enclosure 52. The inner extremity of the wall assembly
80 is supported by a circular conductive ring 86, and an underlying
circular dielectric bracket (not shown) comparable to bracket 68,
upon the Z-axis positioner housing 30a.
[0026] As a further alternative, the inner enclosure 52 could
utilize conductive or nonconductive sliding plates, such as those
shown in U.S. Pat. No. 5,457,398 incorporated herein by reference,
in place of the flexible wall assembly 58 if the more desirable
characteristics of the flexible wall assembly are not needed. As a
still further alternative, unpleated flexibly extensible and
retractable material could be used instead of pleated material in
the wall assembly 58.
[0027] The terms and expressions which have been employed in the
foregoing specification are used therein as terms of description
and not of limitation, and there is no intention, in the use of
such terms and expressions, of excluding equivalents of the
features shown and described or portions thereof, it being
recognized that the scope of the invention is defined and limited
only by the claims which follow.
* * * * *