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48 DESIGN007 MAGAZINE I NOVEMBER 2022 parts, their size and potential location, and we make decisions on where they could be placed, as well as how specific features of the product can be implemented and executed. We also have to ensure that board shape and size can house all the components and circuits that need to be implemented. In the meantime, I start working on board schematics and design validation. Physical strain on the PCB is another aspect of my job that involves physics. Engineers must select the optimal location for mounting and locator holes on the board. Mechanical engi- neers perform simulations to make sure that they aren't putting unnecessary strain on the board and ensure the board doesn't get dam- aged during assembly into the product. Once mounting hole locations are identified and the schematic is completed, an electrical/layout engineer can start working on layout. In layout, even more physics concepts come into play. Boards are getting more complex every day, and EDA tools continue to evolve as well. PCB designers are lucky that a lot of the design rules involving physics and calculations have already been set in pre-fixed rules. ese can be adjusted and changed, and absolutely should be tweaked in high-speed designs or specific signal designs. But as they are, any board designer should be able to design a good board without issues just by following these built-in specifications. e placement of components is critical when designing around a specific IC. Orienta- tion, distance from the part, ground planes and trace thickness all come into play. For optimal board design, a designer needs to make sure that the amount of current going through the signal can be supported by the trace width. To quote Eric Bogatin's best practices for laying out a 2-layer board, it is best to use 6-mil wide signal traces, 20-mil wide power traces, and 13-mil drilled diameter vias. ese guidelines can be applied in multilayer board designs, but note that a 6-mil trace can carry up to 1A of DC current, so if that's overkill for your own application, these parameters can be slightly adjusted to better suit your needs. Another important aspect of physics that we see when designing PCBs is heat transfer and thermal relief. If temperature guidelines are ignored, a board can overheat and damage the components on it, as well as start misbe- having, and nobody wants that in their prod- uct. An engineer must know where to place thermal relief on the board, as well as how to implement it properly. In addition, thermal relief can sometimes be a bit overdone, and this can drive up the cost of your project. I always spend a decent amount of time learning about the IC I am designing around, studying the datasheet, making sure I am implementing all the necessary subsystems and circuits, and ensuring that I am putting forward the most cost-optimized design. Certain circuit designs require physics laws and concepts, especially depending on what you're trying to implement. For example, in any RF design, an engineer must consider the specifics for the part that's being used, as well as how to properly ground and shield the part and place critical components around it. Moreover, many countries have electromag- netic compatibility (EMC) standards that mass-market electronics must pass in order to be sold in those countries, and EMC is firmly in the physics wheelhouse. e ability to understand mathematical calculations comes in handy when trying to achieve EMC and sig- nal integrity. Physics and electrical engineering both play a big role in a successful PCB design. Pru- dent designers will continue to learn about both disciplines—and how they can affect one another—throughout their careers. DESIGN007 Tamara Jovanovic is an electrical engineer with Happiest Baby, a smart bed manufacturer in Los Angeles. She is currently working on her MSEE.

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