Patent Document

FIELD OF THE INVENTION 
     This invention relates generally to machine vision systems for semiconductor chip bonding/attaching devices. More specifically, the present invention relates to an apparatus for providing different magnifications of an object based on the illumination color of the object. 
     BACKGROUND OF THE INVENTION 
     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. 
     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. 
     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 fiducals as possible, while a second measurement may require a high resolution to image fine details. 
     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 . 
     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 a drawback, however, in that it requires a separate camera for each level of magnification desired, thereby increasing size and cost. 
     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 ,  226  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. 
     Alternatively, 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 
     In view of the shortcomings of the prior art, it is an object of the present invention to provide one of multiple magnified views to an optical detector based on the wavelength of light illuminating the device being viewed. 
     The present invention is a vision system for use with a light source and providing a plurality of images of a device, the system comprises a first beamsplitter for receiving an image of the device illuminated by the light source, the beamsplitter providing a plurality of images of the device; a plurality of optical elements for receiving respective ones of the plural images of the device, each of the plurality of optical elements magnifying the image by a predetermined magnification factor to produce a plurality of magnified images; and a second beamsplitter for receiving the plurality of magnified images and filtering out all but one of the magnified images based on a wavelength of the light source. 
     According to another aspect of the invention, an optical detector receives the filtered magnified images from the second beamsplitter. 
     According to a further aspect of the invention, the optical detector is a camera. 
     According to still another aspect of the invention, the light has a wavelength in the visible spectrum. 
     According to yet another aspect of the present invention, the beamsplitters are dichroic splitters. 
     According to a further aspect of the invention, a first mirror is coupled between the first beam splitter and the second optical element and a second mirror is coupled between the second optical element and the second beam splitter. 
     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. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is schematic representation of a vision system according to the prior art; 
     FIGS. 2A and 2B are schematic representations of another vision system according to the prior art; 
     FIGS. 3A and 3B are schematic representations of a vision system according to a first exemplary embodiment of the present invention; and 
     FIG. 4 is a schematic representation of a vision system according to a second exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     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 . 
     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). 
     Referring now to FIG. 3B, device  302  is illuminated by a light source (not shown) having a predetermined wavelength different for the wavelength of light that illuminated device  302  as described above with respect to FIG.  3 A. 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  330  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 . 
     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 . 
     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 that 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×, 6×, and 8×, respectively. 
     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 that 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 . 
     As can be appreciated by one of skill in the art, this approach may be modified and expanded to use more than three light sources and magnification paths as desired. 
     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.

Technology Category: 3