Table design is just one element to accurate positioning; software is the other. So says systems integrator Jim Saudargas. His company, Concepts in Computing, South Beloit, IL, writes the source code that ties together all elements necessary for wafer fabrication: the vision system camera and lens; frame-grabber cards that convert camera output into digital data the computer can manipulate; X-Y table drives that position the camera and wire bonder; and the software platform, be it Windows 95 or NT. Saudargas notes there are many ways to accomplish precise positioning. In one scenario, the semiconductor manufacturer may opt for a medium-range positioning system "just to get in the general vicinity of the fiducials, or reference marks on the wafer." From there, the manufacturer may employ the vision system to move in closer, making relative measurements from the fiducials. "Suppose a vision system provides a quarter-pixel resolution," Saudargas speculates. "If the field of view is 300 microns and it is 480 pixels high, that equates to about 0.6 microns per pixel. One fourth of that allows submicron readings, even though the stage and scale itself are not that accurate." Regardless of positioning scenario, Saudargas claims software is the key. "You can have the best hardware positioning solutions available," he says, "but it will not be helpful unless you have the right software driving it."
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