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46 The PCB Magazine • March 2017 UNDERSTANDING DIMENSIONAL STABILITY IN FLEXIBLE CIRCUITS al analysis based on measuring these targets on the outside corners of the panel and then apply the proper X-Y and theta corrections for align- ment. • After the circuit image has been created, processing or dividing the panel into smaller "within panel" arrays is another strategy for handling dimensional changes. This approach looks at subsets of the panel, effectively gaining some of the advantages of smaller panel align- ment, without compromising the cost advan- tage of processing a larger panel of parts. Using optical targets to place SMT components on a smaller subset panel is a common compensa- tion for stencil registration. In another example, a hard tool die might cut four pieces at a time on an 80-piece panel. The panel could be cut into narrower strips and fed through the die. A primary difference between flexible and rigid circuitry is dimensional change which may need compensation. While the flexible circuit material change is generally less than one tenth of one percent, as measured across a dimen- sion of several inches, this can be significant. Compensating for the expected change can be a critical part of circuitry panelization and set up of a flexible circuit part number. This becomes a balancing act between maintaining dimension accuracy and tolerances, while maximizing pro- cessing efficiencies. The engineering team at the circuitry fabricator considers these options and tradeoffs when quoting a project and when specifying the process and panel layout. As al- ways, early consultation with a supplier is en- couraged to dodge avoidable problems. PCB References 1. DuPont Kapton HN datasheet. Dave Becker is vice president of sales and marketing at All Flex Flexible Circuits LLC. To contact Becker, or to read past columns, click here. Bats have long captured the imaginations of scientists and engineers with their unrivaled agility, but their complex wing motions pose significant technological challenges for those seeking to recreate their flight in a robot. The key flight mechanisms of bats now have been recreated with unprecedented fidelity in the Bat Bot—a self-contained robotic bat with soft, articulated wings, developed by researchers at Caltech and the University of Illinois at Urbana- Champaign (UIUC). "This robot design will help us build safer and more efficient flying robots, and give us more insight into the way bats fly," says Soon-Jo Chung, associate professor of aerospace and Bren Scholar in the Division of Engineering and Applied Science at Caltech, and Jet Propulsion Laboratory research scientist. (Caltech manages JPL for NASA.) Chung, who joined the Caltech faculty in August 2016, developed the robotic bat, along with postdoctoral associate Alireza Ramezani from UIUC, and Seth Hutchinson, a professor of electrical and computer engineering at the UIUC and Ramezani's co-advisor. Chung is the corresponding author of a paper describing the bat that was published on February 1 in Science Robotics, the newest member of the Science family of journals published by the American Association for the Advancement of Science. The Bat Bot weighs only 93 grams and is shaped like a bat with a roughly one-foot wingspan. It is capable of altering its wing shape by flexing, extending, and twisting at its shoulders, elbows, wrists, and legs. Engineers Build Robot Drone that Mimics Bat Flight

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