Semiconductor device lead inspection system

An inspection system utilizes an image doubler design that includes a plurality of mirrors that effectively folds the object distance by reflecting the image along a folded path. Strobed illumination is used in conjunction with a shutterless camera. Increased image resolution results from an optional anamorphic lens with vertical magnification. The lens assembly includes concentric toroidal lens that are produced from a single piece of machineable optical material.

FIELD OF THE INVENTION 
This invention relates to semiconductor devices, and more particularly to 
an improved image system used in inspecting the leads on semiconductor 
devices. 
BACKGROUND OF THE INVENTION 
In testing and mounting semiconductor devices, it is necessary that the 
leads of the device be correctly positioned and that the ends of leads lie 
in a common plane. This is particularly true for surface-mount devices. 
The leads of the semiconductor device may be bent sideways, out, in or 
down, thereby moving the end of the pin from a plane common with the ends 
of the other pins. In some instances, one or more pins may have a greater 
height than the others. 
Existing planarity inspection equipment is either not cost-effective or 
performs the inspection "off-line" as in a quality control operation. The 
hardware required for off-line inspection is inexpensive, however, the 
inspection is done manually, lead-by lead, making 100% inspection 
time-consuming as, well as labor cost prohibitive. Automatic equipment 
which can be used for on-line inspection is actually stand-alone equipment 
integrated with the other processing equipment. 
SUMMARY OF THE INVENTION 
An inspection system utilizes an image doubler design that includes a 
plurality of mirrors that effectively folds the object distance by 
reflecting the image along a folded path. Increased image resolution 
results from an optional anamorphic lens assembly including concentric 
toroidal lens that is produced from a single piece of machinable optical 
material. The optional lens provides a greater vertical magnification 
while maintaining the same horizontal size. 
The split image is produce on a shutterless full frame, high resolution 
camera by attenuating background illumination and strobing a light 
emitting diode illuminator. The duration of the strobe is controlled by a 
vision computer on which the viewed object is displayed. 
The inspection system is usable for inspecting leads on semiconductor 
devices, and includes an inspection station for holding a device to be 
inspected, a strobed source of illumination adjacent to said device being 
inspected for illuminating the device, a shutterless viewing camera for 
receiving an image of the device being inspected, an optical system having 
a folded optical path on a side of said device opposite said source of 
illumination for directing a split image of the device being inspected to 
said viewing camera, and a display device for displaying the split image 
of said device being inspected. 
The optional concentric toroidal anamorphic lens system has four aspheric 
surfaces forming two lenses and a support member holding said two lenses 
in spaced apart positions. In one plane, the first of said two lenses has 
two concave surfaces and a second of said two lenses has a concave surface 
and a convex surface. The lens assembly is concentric in the other 
(orthogonal) plane, that is the four surfaces of the two lenses are cut on 
the radii extending from a common axis. This allows the system to be 
easily fabricated out of one piece of machinable optical material on a 
diamond point turning lathe with one setup. In addition, because of the 
concentric design, multiple systems can be recut at the same time with one 
setup. 
The technical advance represented by the invention, as well as the objects 
thereof, will become apparent from the following description of a 
preferred embodiment of the invention when considered in conjunction with 
the accompanying drawings, and the novel features set forth in the 
appended claims.

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 shows the optical path and components for the component lead 
inspection system. A semiconductor device 10 having body 11 and a 
plurality of leads is placed in front of an illumination system 13. The 
illuminated image is viewed by camera 31 along path 14, to mirror assembly 
17, is reflected back along path 15 to mirror 16 and reflected at a 
45-degree angle along path 20 to mirror/beam splitter 21. 
When the image impinges on mirror/beam splitter 21, the image is reflected 
via path 24 to reflector 22, and back along path 25, through mirror/beam 
splitter 21, along path 28 to lens assembly 30, and then to camera 31. 
The image passes through mirror/beam splitter 21, along path 26 to 
reflector 23, back along path 27 to mirror/beam splitter 21 and is 
reflected along path 29 to lens assembly 30 where it is focused on camera 
31. It should be noted that during the splitting of the image at 
mirror/beam splitter 21, the two duplicate images are formed by splitter 
21 are separated vertically such that image 32 and image 33 are vertically 
and horizontally spaced and horizontally shifted from each other at camera 
31. Mirrors 22, 23 are adjustably tiltable mirrors, and vertical and 
horizontal spacing of the two images is controlled by tilting mirrors 22, 
23 relative to the split optical beam paths. 
An optional lens 30a may be used to provide better resolution at a greater 
vertical magnification. Lens 30a is described in more detail with 
reference to FIG. 4. 
Camera 31 is, for example, a full frame high resolution type camera such as 
the Kodak "MegaPlus" camera, having improved reliability with the shutter 
removed. There is no need for an electro-mechanical shutter since the 
illumination source 13 is strobed at a rate to match that of the computer 
controlled image display system, presenting a continuous image of the 
device 10. Camera 31 is connected to a computer controlled viewing device 
34. Camera 31 has a known scanning and frame rate, and source 13 is 
synchronized with the camera scanning and frame rate to provide a stable 
image in the viewing device. 
FIG. 2 is a top view of the optical path represented by paths 14 and 15, 
and mirror assembly 17. Device 10 is in front of illumination source 13. 
An image of device 10 is directed along path 14 to mirror assembly 17. 
Mirror assembly 17 includes two mirrors 18 and 19 positioned at a 
90-degree angle with respect to each other, to redirect the image of 
device 10 through a 180-degree angle. The image impinges on mirror 19, is 
reflected to mirror 18, and in turn is reflected along path 15 to mirror 
16. Mirror 16 is positioned at a 45-degree angle from the horizontal 
plane, as illustrated in FIG. 1. 
FIG. 3 represents the image of the semiconductor device being inspected, as 
displayed on a video monitor. The image is split and the two parts are 
vertically displaced from each other as described with reference to FIG. 
2. Actually, the two images present the opposite ends, 11a and 11b, of one 
side of the semiconductor device 11. There is overlap of contacts 12 in 
the two images, but by splitting the image into two parts, a larger and 
clearer image of the leads 12 is possible. Using the split image allows 
better utilization of the high resolution camera imager which normally has 
a 3:4 or square aspect ratio. As pointed out above, additional vertical 
resolution may be obtained using optional lens 30a. As an example of an 
improper length lead, lead 12a is shown longer than the other leads. Lead 
12c is shown bent outward so that it is not in line with the other leads 
along the side of the semiconductor device. The inspection will show bent 
leads, leads that are too short, too long, or otherwise improperly 
positioned. 
FIG. 4 is a side view of lens assembly 30a. Lens assembly 30a is a 
concentric toroidal anamorphic lens that utilizes aspheric surfaces to 
form two spaced apart lens 40 and 41. Lenses 40 has two concave surfaces 
40a and 40b in the same plane. Lens 41 has a concave surface 41a and a 
convex surface 41b. The two lenses are spaced apart by support member 44. 
Lens assembly 30a is a single piece of acrylic plastic. The lens assembly 
is concentric in the other (orthogonal) plane about an axis perpendicular 
to this plane and lends itself to Diamond Point fabrication processes. The 
four surfaces of the two lenses are cut on the radii A, B, C and D from 
point 46. FIG. 5 shows the radii A, B, C and D and point 46.