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SMT-July2016

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100 SMT Magazine • July 2016 Acknowledgements The author would like to acknowledge the images provided in the paper by LPKF USA and LPKF Laser & Electronics AG, Garbsen, Germany. SMT General References 1. "Laser Ablation—Cutting systems for the Electronics Industry," Ahne Oosterhof, Mark Hueske, Dieter Meier; Industrial Laser Solutions, June 2007. 2. "Flex Circuit Depaneling: How UV Lasers Meet Today's Trends," Shane Stafford, Industrial Laser Solutions, September 2012. 3. "Laser Cutting of Printed Circuit Boards: Evaluation of possible corrosive effects of re- siduals using SIR-test and optical inspection," Manfred Zäske, Siemens AG, CT RTC ELE EOM- DE, June 2013. Ahne Oosterhof currently consults for LPKF Laser & Electronics North America. An ultrathin film that is both transparent and highly conductive to electric current has been produced by a cheap and simple method de- vised by an international team of nanomaterials researchers from the Uni- versity of Illinois at Chica- go and Korea University. The film—a mat of tangled nanofiber, elec- troplated to form a "self- junctioned copper nano- chicken wire"—is also bendable and stretch- able, offering potential applications in roll-up touchscreen displays, wearable electronics, flex- ible solar cells and electronic skin. The new film establishes a "world-record com- bination of high transparency and low electrical resistance," the latter at least 10-fold greater than the previous existing record, said Sam Yoon, a pro- fessor of mechanical engineering at Korea Univer- sity and one of two corresponding authors on the publication. The film also retains its properties after repeated cycles of severe stretching or bending, according to Alexander Yarin, UIC Distinguished Professor of Mechanical Engineer- ing and one of the cor- responding authors. Manufacture begins by electrospinning a nanofiber mat of poly- acrylonitrile, or PAN. The fiber shoots out like a rapidly coiling noodle, which when deposited onto a surface intersects itself a million times. The naked PAN poly- mer doesn't conduct, so it must first be spatter- coated with a metal to attract metal ions. The fiber is then electroplated with copper—or silver, nickel or gold. "We can then take the metal-plated fibers and transfer to any surface—the skin of the hand, a leaf, or glass," Yarin said. An additional application may be as a nano-textured surface that dramati- cally increases cooling efficiency. Yoon said the "self-fusion" by electroplating at the fiber junctions "dramatically reduced the con- tact resistance." Yarin noted that the metal-plated junctions facilitated percolation of the electric cur- rent and also account for the nanomaterial's physi- cal resiliency. New Nanomaterial Offers Promise in Bendable, Wearable Electronic Devices MATERIAL EFFECTS OF LASER ENERGY

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