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AUGUST 2024 I DESIGN007 MAGAZINE 75 copper is in contact with the catalyst. Get- ting the hole wet once is good, but you need to replenish that action. Mechanical processes are used to get fluid through the holes numer- ous times to produce a thick enough coating. e copper needs to be thick enough to sur- vive the pre-clean processes and the initial dunking of panels into a sulfuric acid bath, which happens later in the manufacturing process. Portions of the pre-clean process will etch copper away if uninhibited. Enough copper must remain aer those processes to ensure adequate electrical conduction for electroplating. Electroless Copper Design Considerations If the electroless copper deposit goes wrong, voids in through-holes could cause manufac- tured PCBs to end up in the scrap heap. Luck- ily, designers can consider this possibility when designing for the reality of manufactur- ing. To avoid problems during this process, use the largest vias possible. While there are some- times good reasons to use micro-vias and high aspect ratio holes, aim for a 10:1 aspect ratio or smaller. e smaller the aspect ratio, the better the chances the boards will be reliable long- term and properly yielded to minimize costs. To learn more about designing for the reality of the PCB manufacturing process, check out more episodes of On the Line with…. DESIGN007 Matt Stevenson is vice presi- dent and general manager of ASC Sunstone Circuits. To read past columns, click here. Download Matt's book, The Printed Circuit Designer's Guide to… Designing for Reality and listen to the podcast here. Northwestern University engineers have devel- oped a new soft, flexible device that makes robots move by expanding and contracting—just like a human muscle. To demonstrate their new device, called an actuator, the researchers used it to create a cylin- drical, worm-like soft robot and an artificial bicep. In experiments, the cylindrical soft robot navi- gated the tight, hairpin curves of a narrow pipe- like environment, and the bicep was able to lift a 500-gram weight 5,000 times in a row without failing. Because the researchers 3D-printed the body of the soft actuator using a common rubber, the resulting robots cost about $3 in materials, excluding the small motor that drives the actua- tor's shape change. That sharply contrasts typical stiff, rigid actuators used in robotics, which often cost hundreds to thousands of dollars. "Roboticists have been motivated by a long- standing goal to make robots safer," said North- western's Ryan Truby, who led the study. "If a soft robot hit a person, it would not hurt nearly as much as getting hit with a rigid, hard robot." Taekyoung Kim, a postdoctoral scholar in Truby's lab and first author on the paper, led the research. Pranav Kaarthik, a Ph.D. candidate in mechanical engineering, also contributed to the work. (Source: Northwestern University) Creating Artificial 'Muscles' for Safer, Softer Robots