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FEBRUARY 2021 I DESIGN007 MAGAZINE 39 Bubbling When solvents or air become trapped and can't escape the coating material, the chances of bubble formation are more than likely. Bubbles in a conformal coating can lead to product reliability issues further down the line and even possible failures. e IPC speci- fication allows a dry film thickness of 30–130 microns, the greater thickness being achieved by the application of multiple coating lay- ers. Trying to achieve a 130-micron dry film thickness from a single selective-coating pro- cess with a solvent-based acrylic material is a recipe for disaster and is likely to result in excessive bubble formation, film shrinkage, coating de-lamination and additional stress on components. e result is poorer protec- tion, rather than an improved overall level of circuit protection. Aiming for a uniform 30–50 microns and focusing on achieving perfect coverage at each application is a much better approach to improving the protection of electronic circuits. Achieving the correct coating thickness is important. Bear in mind that if the coating is too thick it can lead to entrapment of solvents in areas where the coating does not fully cure. Similarly, it can cause the coating to crack as it cures, as the result of changes in temperature, or due to mechanical shock and vibration. Conformal coatings protect electronic assemblies from harsh environments by seal- ing off the electronics from contaminants and environmental factors that can lead to reliabil- ity issues and failures. For coatings to be effec- tive, they need to uniformly cover the entire component without moisture, fluid, or outside impurities present. While it might be tempt- ing to use shortcuts either to reduce costs or to speed up production, there will inevitably be a price to pay. Know the limitations and/ or special properties of the materials you use to coat electronic assemblies and abide by the correct procedures. Still have doubts? ere are experts on hand at Electrolube who have seen it all before and who can steer you in the right direction. DESIGN007 Phil Kinner is the global business and technical director of confor- mal coatings at Electrolube. To read past columns or contact Kin- ner, click here. Download your free copy of Electrolube's book, The Printed Circuit Assembler's Guide to… Confor- mal Coatings for Harsh Environments, and watch the micro webinar series "Coatings Uncoated!" Detecting the presence of an unmanned underwater vehicle (UUV) is usually achieved by intercepting the noise radiated by its propeller. In a noisy harbor, this task is hindered because the acoustic signature of a UUV and the noise in the local environment often present too much signal complexity for current technologies to process. That may be about to change. Researchers at Draper, Massachusetts Institute of Technology (MIT) and Woods Hole Oceanographic Institute (WHOI) have developed an acoustic remote sensing method for high-precision propeller rotation and speed estimation of UUVs. A state-of-the-practice technique for identify- ing the presence of ships is by analyzing passive acoustic data with the Detection of Envelope Modulation on Noise (DEMON). In the study, the authors set out to isolate and characterize motor noise, so they focused on brushless DC (BLDC) motors because of their prevalence in UUV propulsion systems. In field experiments, the new method out- performed the DEMON algorithm. When boats passed by the UUV, the new method could detect the motor noise, but the DEMON spec- trum was dominated by the interfering boats' propeller noise. The new method can also apply to other robotic platforms that are powered by mass-produced BLDC motors. (Source: PRWEB) How Unmanned Underwater Vehicles Could Become Easier to Detect

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