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JULY 2021 I DESIGN007 MAGAZINE 71 you almost never need more than one ground plane. Carl Schattke: Engineer a return path for the best results. Quite a few in-depth articles are available on this topic. Cherie Litson: Number one, take Rick Hart- ley's class. Number two, make sure you group components over the appropriate power and ground references and treat power as a fat sig- nal trace, not a plane. Number three, don't run traces over gaps in your planes. Lee Ritchey: Yes, with the multiple voltages found in most modern designs, it is a tough job assigning power and ground layers. ere is no simple answer to how to do this. My lat- est design has 29 power rails in a 22-layer stackup. It took almost a month to get the power part of the design right, and it only took two days to develop the design rules. Welcome to the 21st century. Heidi Barnes: I would take a look at the advan- tage of thin dielectrics to lower the path induc- tance and the loop inductance of power and ground vias. is should make it possible to do more of a wide trace power rail routing instead of trying to use a whole plane layer. e lower path inductance also allows all but the smallest capacitors to be placed further from the load so that there is less congestion when routing multiple rails into a BGA-type device. Eric Bogatin: Keep the same return plan adja- cent to signal layers so you can add a return via when the signal transitions. Keep power and ground on adjacent layers with as thin a dielec- tric as possible. Use a power-power plane pair for dielectric fill. DESIGN007 In a new study, North Carolina State University researchers demonstrated they could print layers of electrically conductive ink on polyester fabric to make an e-textile that could be used in the design of future wearable devices. In addition, researchers said the findings suggest they could extend tech- niques common in the flexible electronic industry to textile manufacturing. They reported their findings in the journal ACS Applied Materials & Interfaces. In the study, researchers described how they used a FUJIFILM Dimatix inkjet printer to create a durable and flexible e-textile material, what they did to reliably create the e-textile, and its properties. Part of their challenge was to find the right compo- sition of materials so the liquid ink would not seep through the porous surface of the textile materials and lose its ability to conduct electricity. They created the e-textile by printing layers of electrically conductive silver ink like a sandwich around layers of two liquid materials, which acted as insulators. They found that the chemical proper- ties of the insulating materials, as well as of the tex- tile yarns, were important to maintaining the ability of the liquid silver ink to conduct electricity, and pre- vent it from penetrating through the porous fabric. "We wanted a robust insulation layer in the mid- dle, but we wanted to keep it as thin as possible to have the entire structure thin, and have the electric performance as high as possible," Kim said. "Also, if they are too bulky, people will not want to wear them." (Source: North Carolina State University) Inkjet Printing Shows Promise as New Strategy for Making E-Textiles

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