U.S. patent application number 10/952953 was filed with the patent office on 2005-03-03 for multi-wavelength aperture and vision system.
Invention is credited to Beatson, David T., Hoffman, Christian.
Application Number | 20050046969 10/952953 |
Document ID | / |
Family ID | 29254311 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050046969 |
Kind Code |
A1 |
Beatson, David T. ; et
al. |
March 3, 2005 |
Multi-wavelength aperture and vision system
Abstract
A method and system for providing different images representing
plural depths of field of an electronic device. The vision system
has a beamsplitter for receiving an image of the device illuminated
by the at least one light source, the beamsplitter providing one of
the plurality of images of the device based in a wavelength of the
light source; an aperture having a plurality of effective diameters
based on the wavelength of light from the at least one light
source, the aperture determining a depth of field of the image of
the device; and an optical element for receiving the image of the
device, the optical element magnifying the image by a predetermined
magnification factor to produce a magnified image having the
determined depth of field.
Inventors: |
Beatson, David T.; (Kennett
Square, PA) ; Hoffman, Christian; (Willow Grove,
PA) |
Correspondence
Address: |
RATNERPRESTIA
P O BOX 980
VALLEY FORGE
PA
19482-0980
US
|
Family ID: |
29254311 |
Appl. No.: |
10/952953 |
Filed: |
September 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10952953 |
Sep 29, 2004 |
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10418803 |
Apr 18, 2003 |
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10418803 |
Apr 18, 2003 |
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10336458 |
Jan 3, 2003 |
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6760161 |
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10336458 |
Jan 3, 2003 |
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09961742 |
Sep 24, 2001 |
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6529333 |
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Current U.S.
Class: |
359/738 |
Current CPC
Class: |
G02B 27/1066 20130101;
G01N 2021/8845 20130101; G02B 27/145 20130101; G01N 21/8806
20130101 |
Class at
Publication: |
359/738 |
International
Class: |
G02B 027/10; G02B
009/00 |
Claims
What is claimed:
1. An aperture for use with a vision system and at least one light
source to view an object, comprising: a first region having a first
reactive property to a first wavelength of light from the at least
one light source, where the first reactive property provides a
first depth of field of the object; and a second region adjacent
the first region and having a second reactive property to a further
wavelength of light from the at least one light source, where the
second reactive property provides a second depth of field of the
object.
2. The aperture according to claim 1, wherein the first reactive
property results in a first effective diameter of the aperture and
the second reactive property results in a second effective diameter
of the aperture.
3. The aperture according to claim 1, further comprising a third
region absent a reactive property to any wavelength of light from
the at least one light source.
4. An aperture for use with a vision system and a light source for
viewing an object, the aperture comprising: a region having a
plurality of reactive properties based on a wavelength of light
from the light source, such that the plurality of reactive
properties provide a respective plurality of a depth of field of
the object based on the wavelength of light from the light source;
and a further region adjacent the first region and absent a
reactive property to any wavelength of light from the light source.
Description
[0001] This application is a Divisional application of pending
application Ser. No. 10/418,803 filed on Apr. 18, 2003 which is a
Continuation-in-Part of application Ser. No. 10/336,458 filed on
Jan. 3, 2003 and issued as U.S. Pat. No. 6,760,161 on Jul. 6, 2004
which is a Continuation of application Ser. No. 09/961,742 filed on
Sep. 24, 2001 and issued as U.S. Pat. No. 6,529,333 on Mar. 3,
2003.
FIELD OF THE INVENTION
[0002] This invention relates generally to machine vision systems
for semiconductor chip bonding/attaching devices. More
specifically, the present invention relates to a multi-wavelength
aperture providing different depths of field of an observed object
based on a wavelength of light and a system and method using such a
multi-wavelength aperture.
BACKGROUND OF THE INVENTION
[0003] Semiconductor devices, such as integrated circuit chips, are
electrically connected to leads on a lead frame by a process known
as wire bonding. The wire bonding operation involves placing and
connecting a wire to electrically connect a pad residing on a die
(semiconductor chip) to a lead in a lead frame. Once all the pads
and leads on the chip and lead frame have been wire bonded, it can
be packaged, often in ceramic or plastic, to form an integrated
circuit device. In a typical application, a die or chip may have
hundreds or thousands of pads and leads that need to be
connected.
[0004] There are many types of wire bonding equipment. Some use
thermal bonding, some use ultra-sonic bonding and some use a
combination of both. Prior to bonding, vision systems or image
processing systems (systems that capture images, digitize them and
use a computer to perform image analysis) are used on wire bonding
machines to align devices and guide the machine for correct bonding
placement.
[0005] Machine vision systems are generally used to inspect the
device before, during or after various steps in the fabrication
process. During such process steps, it may be necessary to obtain
multiple views of the device under different magnification levels
to determine whether the device meets predetermined quality
standards. One measurement may require a large field of view to
include as many fiducials as possible, while a second measurement
may require a high resolution to image fine details. Further, these
various measurements may need to narrow or expand the depth of
field of the observed object in order to view certain details.
[0006] In conventional systems, such multiple magnifications are
handled by having a separate camera for each desired magnification
level. Such a conventional device is shown in FIG. 1. In FIG. 1,
imaging device 100 includes objective lens 104, aperture 106, beam
splitter 108, mirror 110, relay lenses 112, 114, and cameras 116,
118. In operation an image of device 102 is transmitted through
object lens 104 as transmitted image 120 and in turn through
aperture 106 as image 122. Image 122 is incident on beam splitter
108, which in turn divides the light from image 122 into first
divided light rays 124 and second divided light rays 126. Divided
light rays 126 are then redirected by mirror 110 as divided light
128.
[0007] Relay lenses 112 and 114 are selected so as to provide the
desired magnification of divided light 124 and 128, respectively,
resulting in magnified images 130 and 132, which are incident on
cameras 116 and 118, respectively. This system has drawbacks,
however, in that it requires a separate camera for each level of
magnification desired, and also require that multiple apertures be
provided to handle different depths of field, thereby resulting in
greater complexity and increasing size and cost.
[0008] A second conventional system is shown in FIGS. 2A and 2B. In
FIGS. 2A and 2B, a shutter 218 is used in combination with a second
beam splitter 222 to receive two magnifications of device 202 with
a single camera 216. As shown in FIG. 2A, first beamsplitter 208
separates light rays 224 into light rays 226, 228, each being of
about equal illumination, that is each of light rays 226, 228 is
about half the illumination of light rays 224. When shutter 218 is
in a first position, light rays 226 are prevented from reaching
relay lens 214. On the other hand, light rays 228 are magnified by
relay lens 212 to become magnified light rays 230. In turn,
magnified light rays 230 are incident on second beamsplitter 222, a
portion (about 50%) of which is transmitted to camera 216 as light
rays 236. The remaining portion of magnified light rays 230,
however, is deflected by second beamsplitter 222 as lost light rays
234. As a result, only about 25% of the light used to illuminate
device 202 is actually received at camera 216. In addition, the
inclusion of shutter 218 increases the complexity and cost of this
system.
[0009] Alternatively, and as shown in FIG. 2B, when shutter is in a
second position, light rays 228 are prevented from reaching relay
lens 212, while light rays 226 are directed through relay lens 214
by mirrors 210, 220 as magnified light rays 232. Similar to FIG.
2A, a portion 236 of magnified light rays 232 are received by
camera 216 while remaining light rays 234 are lost. As is evident,
a large portion of the illumination available for imaging is
sacrificed due to the losses associated with first beam splitter
208 and second splitter 222. The light from a single channel hits
the second splitter and is split into a reflected portion 234 and
transmitted portion 236. Only one of these will be directed to
camera 216 while the other is lost. This approach can also have
reliability issues with respect to the moving shutter
mechanism.
SUMMARY OF THE INVENTION
[0010] In view of the shortcomings of the prior art, the present
invention is directed to an aperture having different effective
diameters based on a wavelength of light passing therethrough to
provide one of multiple depths of field of the device being
viewed.
[0011] The present invention is a vision system for use with at
least one light source and providing a plurality of images
representing plural depths of field of a device. The system
comprises a beamsplitter for receiving an image of the device
illuminated by the at least one light source, the beamsplitter
providing one of the plurality of images of the device based in a
wavelength of the light source; an aperture having a plurality of
effective diameters based on the wavelength of light from the at
least one light source, the aperture determining a depth of field
of the image of the device; and an optical element for receiving
the image of the device, the optical element magnifying the image
by a predetermined magnification factor to produce a magnified
image having the determined depth of field.
[0012] According to another aspect of the invention, the aperture
is a dichroic aperture.
[0013] According to a further aspect of the invention, the optical
detector is a camera.
[0014] According to still another aspect of the invention, the
light has a wavelength in the visible spectrum.
[0015] According to yet another aspect of the present invention,
the beamsplitters are dichroic splitters.
[0016] According to a further aspect of the invention, the aperture
comprises a first region having a first reactive property to a
first wavelength of light from the at least one light source; and a
second region adjacent the first region and having a second
reactive property to a further wavelength of light from the at
least one light source, such that the first reactive property
provides a first depth of field of the object and the second
reactive property provides a second depth of field of the
object.
[0017] According to still a further aspect of the invention, the
first reactive property results in a first effective diameter of
the aperture and the second reactive property results in a second
effective diameter of the aperture.
[0018] According to yet a further aspect of the invention, the
aperture comprises a region having a plurality of reactive
properties based on a wavelength of light from the light source;
and a further region adjacent the first region and absent a
reactive property to any wavelength of light from the light source,
such that the plurality of reactive properties provide a respective
plurality of a depth of field of the object based on the wavelength
of light from the light source.
[0019] These and other aspects of the invention are set forth below
with reference to the drawings and the description of exemplary
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The invention is best understood from the following detailed
description when read in connection with the accompanying drawing.
It is emphasized that, according to common practice, the various
features of the drawing are not to scale. On the contrary, the
dimensions of the various features are arbitrarily expanded or
reduced for clarity. Included in the drawing are the following
Figures:
[0021] FIG. 1 is schematic representation of a vision system
according to the prior art;
[0022] FIGS. 2A and 2B are schematic representations of another
vision system according to the prior art;
[0023] FIGS. 3A and 3B are schematic representations of a vision
system according to a first exemplary embodiment of the present
invention;
[0024] FIG. 4 is a schematic representation of a vision system
according to a second exemplary embodiment of the present
invention;
[0025] FIGS. 5A-5C are views of a dichroic aperture according to an
exemplary embodiment of the present invention;
[0026] FIG. 5D is a plan view of a dichroic aperture according to
another exemplary embodiment of the present invention;
[0027] FIG. 6 is a schematic representation of a vision system
according to an exemplary embodiment of the present invention
utilizing an exemplary dichroic aperture; and
[0028] FIGS. 7A-7B are a schematic representations of vision
systems according to another exemplary embodiment of the present
invention utilizing an exemplary dichroic aperture.
DETAILED DESCRIPTION
[0029] Referring to FIGS. 3A and 3B, an exemplary embodiment of the
present invention is shown. In FIG. 3A, device 302 is illuminated
by a light source (not shown) having a predetermined wavelength. In
a preferred embodiment, this wavelength is within either the
visible spectrum of light or ultraviolet spectrum of light. Light
rays 330, representing an image of device 302, emerges from lens
304 and aperture 306. Light rays 330 are incident on dichroic
splitter 308, which in turn reflects a substantial portion of light
rays 330 as reflected light rays 332, based on properties of
splitter 308 which are dependant upon the wavelength of light
illuminating device 302. As dichroic splitters are not 100%
efficient, a small portion of light rays 330 will pass through
dichroic splitter 308 as light rays 334. Light rays 332 are then
reflected by mirror 310, such as a planar mirror, as light rays 336
so as to allow them to be magnified by optical relay 314. In an
exemplary embodiment, optical relay 314 is a doublet type lens
assembly having a predetermined magnification factor. Based on this
magnification factor, light rays 336 are magnified and emerge from
optical relay 314 as magnified light rays 338. As is understood by
those of skill in the art, magnified light rays 338 represent an
enlarged image of device 302.
[0030] Magnified light rays 338 are again redirected by mirror 320
as magnified light rays 342 to be incident on a surface of dichroic
splitter 322. In addition, light rays 334, having been magnified by
a predetermined magnification factor by optical relay 312, are
incident on an opposite surface of dichroic splitter 322 from that
of magnified light rays 342. In an exemplary embodiment, the
magnification factors of optical relays 312 and 314 are different
from one another. Dichroic splitter 322 has properties, based on
the wavelength of light illuminating device 302, such that the
undesired image rays 340 do not pass through splitter 322, but
rather are reflected away as discarded light 344. In this way
multiple images are not provided to optical detector 316. On the
other hand, dichroic splitter 322 has properties, based on the
wavelength of light illuminating device 302, allowing magnified
light rays 342 to be directed toward optical detector 316 as image
rays 346. As a result, optical detector 316 "sees" only a single
magnified image of device 302. In a preferred embodiment of the
present invention optical detector 316 may be a camera, such as a
CCD or CMOS camera, or a position sensitive detector (PSD).
[0031] Referring now to FIG. 3B, device 302 is illuminated by a
light source (not shown) having a predetermined wavelength
different from the wavelength of light that illuminated device 302
as described above with respect to FIG. 3A. In a preferred
embodiment, this wavelength is within the visible spectrum of
light. In FIG. 3B, light rays 350, representing another image of
device 302, emerges from lens 304 and aperture 306. Light rays 350
are incident on dichroic splitter 308, which in turn passes a
substantial portion of light rays 350 as light rays 352, based on
properties of splitter 308 which depend upon the wavelength of
light illuminating device 302. Once again, as dichroic splitters as
not 100% efficient, a small portion of light rays 350 will be
reflected by dichroic splitter 308 as reflected light rays 354.
These light rays will in turn be redirected by mirror 310 as light
rays 356, which will in turn be magnified by optical relay 314 as
magnified light rays 358, which are then redirected toward dichroic
splitter 322 by mirror 320 as reflected light 360.
[0032] Light rays 352 that emerge from dichroic splitter 308, pass
through and are magnified by optical relay 312 to become magnified
light rays 362. As a result, magnified light rays 362 are incident
on dichroic splitter 322. As discussed above with respect to FIG.
3A, dichroic splitter 322 has properties, based on the wavelength
of light illuminating device 302, such that undesired light rays
360 pass through splitter 322, and thus are directed away from
optical detector 316 as discarded light 364. On the other hand,
dichroic splitter 322 has properties, based on the wavelength of
light illuminating device 302, allowing magnified light rays 362 to
pass through splitter 322 as image rays 366. It is image rays 366
which are now "seen" by optical detector 316. In this way multiple
images are not provided to optical detector 316 and different
magnifications of device 302 may be provided merely by changing the
wavelength of light that illuminates device 302.
[0033] FIG. 4 illustrates a second exemplary embodiment of the
present invention in which more that two light sources are used to
illuminate device 302 and provide more than two different
magnifications of device 302. In FIG. 4, device 302 is illuminated
by one of light sources 406, 416, 428, each having a different
wavelength. In a preferred embodiment, these wavelengths are within
either the visible spectrum of light or ultraviolet spectrum of
light. Illumination emitted by each of light sources is directed
toward device 302 though a series of dichroic splitters 404, 418,
420, and 430. In the exemplary embodiment, only one light source is
used to illuminate device 302 depending on the magnification
desired. In the example illustrated in FIG. 4, light source 406 is
used to provide magnification of device 302 through lens 412, light
source 416 is used to provide magnification of device 302 through
lens 424, and light source 428 is used to provide magnification of
device 302 through lens 434. The magnification factor of each of
lenses 412, 424, 434 is selected as desired. In a preferred
embodiment of the present invention the magnification factor of
lenses 412, 424, 434 is 2.times., 6.times., and 8.times.,
respectively.
[0034] To illustrate how the second exemplary embodiment functions,
a specific example is now discussed. If for example, it is desired
to magnify an image of device 302 by a specific magnification
factor achieved through lens 434, light source 428 is activated and
the remaining light sources 406, 416 are deactivated. Light rays
444 pass through dichroic splitters 430, 420 and 418 and are
reflected by dichroic splitter 404 based on the wavelength of the
light rays. These light rays are then re-directed by mirror 402 to
illuminate device 302. In turn, light rays 440, representing an
image of device 302, emerges from lens 304, are reflected by mirror
402 as reflected light rays 442 and directed toward dichroic
splitter 404. As mentioned above, the wavelength of the light rays
446 are such that they are reflected by splitter 404 and pass
through splitters 418, 420. The bottom surface of splitter 430 has
different properties than that of the top surface of splitter 430.
As a result, light ray 446 are reflected by splitter 430 rather
than passing through it. These reflected rays 448 pass through
aperture 432 and are in turn magnified by lens 434. Light rays 450,
representing the magnified image of a portion of device 302 are
next redirected by mirror 436 as reflected light rays 452, which in
turn, based on the wavelength of the light rays, pass through
dichroic splitters 426 and 414, and are received by detector 316,
such as a CCD or CMOS camera, or a position sensitive detector
(PSD). As such, detector 316 received a magnified image of device
302 based on the wavelength of the light used to illuminate the
device. Similarly, the path of light used to illuminate device 302
and its reflected image is based on the wavelength of light sources
406 and 416.
[0035] Referring now to FIGS. 5A-5C, an exemplary dichroic aperture
500 has various regions 502, 504 and 506. As shown in FIG. 5A, in
aperture 500, region 502 represents a portion of the aperture where
no light can penetrate, region 504 has a diameter d1 and represents
a portion where light having a first wavelength .lambda.1 can
penetrate, and region 506 has a diameter d2 smaller than d1 and
represents a portion where light having a second wavelength
.lambda.2 can penetrate. With respect to region 506, light having
the first wavelength will also pass through this region. As is
known to those skilled in the optical arts, the diameter of an
optical aperture affects the depth of field (DOF) and Modulation
Transfer Function (MTF) (or optical resolution) of the object being
observed. Therefore, as a result of illuminating the object to be
observed by light having different wavelengths (in this example
.lambda.1 or .lambda.2), the DOF and MTF may be controlled. For
example, and as shown in FIGS. 5B and 5C, if light having
wavelength .lambda.1 is used, aperture 500 has diameter d1
resulting in a short DOF 510 and a greater MTF. On the other hand,
if light having a wavelength .lambda.2 is used, aperture 500 has a
diameter d2 resulting in a greater DOF 512 and lower MTF. Although
not shown in FIG. 5C, the portion of light having wavelength
.lambda.2 that does not pass through aperture 500 is reflected.
[0036] Dichroic aperture 500 may be formed using well-known thin
film coating and masking techniques, for example. Although the
exemplary dichroic aperture 500 is illustrated with two regions
(504, 506), the invention is not so limited. As shown in FIG. 5D,
for example, it is contemplated that any number of regions may
510a, 510b, . . . 510n be provided, each tuned to a different
wavelength of light, to provide a variety of Depths of Field, as
desired.
[0037] Referring now to FIG. 6, an exemplary embodiment of a vision
system 600 using dichroic aperture 500 is illustrated. In FIG. 6,
device 302 is illuminated by light source 602 having light rays 604
of a predetermined wavelength and/or light sources 406 or 428 also
having a wavelength equal to that of light source 602. Light source
602 may be capable of providing illumination in one or more
discrete wavelengths as desired. Further light source 602 may be
combined with either light source 406 or 428 to provide both
oblique and perpendicular illumination to device 302. Those of
skill in the art understand that, although it is desirable for the
wavelength of light source 406 or 428 to be equal to that of light
source 602, due to manufacturing tolerances the wavelengths may
vary slightly. Similar to the embodiment described above,
illumination for light sources 406, 428 are incident on device 302
via dichroic splitters 404, 408.
[0038] Light rays 330, representing an image of device 302, emerge
from lens 304, such as an achromatic or chromatic lens as desired.
Light rays 330 are incident on dichroic splitters 404, 408, which
in turn reflect a portion of light rays 330 as reflected light rays
(not shown), based on properties of splitter 308 which are
dependent upon the wavelength of light source 602. The remaining
light is incident on dichroic aperture 500. Based on the wavelength
of the light, dichroic aperture 500 adjusts its effective diameter
as discussed above and passes the light onto relay lens 412, such
as an achromatic lens having a predetermined magnification factor,
either positive or negative. This resultant image is incident on
optical detector 316. Because of the reaction of dichroic aperture
to the wavelength of light from light sources 602, 406, 428 on
device 302, the depth of field may be either narrow 608 or deep
610.
[0039] In another exemplary embodiment, light source 602 may have a
variable wavelength to adjust the DOF of the object being observed,
as desired.
[0040] Although the exemplary embodiment illustrates three light
sources 602, 406, 428, the invention is not so limited. It is also
possible to add additional light sources similar to those of 406,
428 with appropriate dichroic splitters as desired. Of course, as
the number of available wavelengths increase, the number of active
areas in dichroic aperture 500 should also increase by a like
number.
[0041] FIGS. 7A-7B illustrate other exemplary embodiments of the
present invention in which dichroic aperture 500 is incorporated
into the embodiment described above with respect to FIG. 4. In an
effort to provide a more concise representation, however, this
exemplary embodiment addresses only two magnification paths, rather
that the three magnification paths of FIG. 4. The invention is not
so limited and it is contemplated that the invention may be used
with any number of light sources (including variable wavelength
light sources) and magnification paths, as desired.
[0042] As shown in FIG. 7A, device 302, disposed on substrate 301
for example, is illuminated by one of light sources 406, 428, each
having a different wavelength. In a preferred embodiment, these
wavelengths are within either the visible spectrum of light or
ultraviolet spectrum of light. Illumination emitted by each of
light sources is directed toward device 302 though a series of
dichroic splitters 404, 408, and 430 and dichroic aperture 500.
Light for the one active light source 406, 428 changes the
effective diameter of dichroic aperture 500, thereby adjusting the
DOF of observed device 302.
[0043] In the exemplary embodiment of FIG. 7, only one light source
at a time is used to illuminate device 302 depending on the desired
magnification and DOF. For example, light source 406 is used to
provide magnification of device 302 through lens 412 at a first
DOF, and light source 428 is used to provide magnification of
device 302 through lens 434 at a second DOF. The magnification
factor of each of lenses 412, 434 is selected as desired, as is the
DOF. In a non-limiting exemplary embodiment of the present
invention, the magnification factor of lenses 412, 434 is 2.times.,
and 8.times., respectively. Furthermore, filters 706, 710 may be
added to respective magnification paths as desired to eliminate
cross coupling between the wavelengths of light by removing any
remaining undesired wavelengths of light that may have passed
through dichroic splitters 404, 406, and 430. Additionally, and as
shown in FIG. 7B, achromatic apertures 708, 712 may also be added
to eliminate stray light that may be present in light rays 702, 704
respectively.
[0044] As can be appreciated by one of skill in the art, this
approach may be modified and expanded to use more than two light
sources and magnification paths as desired.
[0045] Although the invention has been described with reference to
exemplary embodiments, it is not limited thereto. Rather, the
appended claims should be construed to include other variants and
embodiments of the invention which may be made by those skilled in
the art without departing from the true spirit and scope of the
present invention.
* * * * *