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40 DESIGN007 MAGAZINE I JUNE 2019 Johnson: Could you give some examples regarding how they're helping and contributing? Creeden: Absolutely. When I'm challenged with real estate and cannot put the required capaci- tors on the board because I have BGAs on both sides of a board, the team at Insulectro is a resource I can go to and ask for technology help. They suggested buried capacitance materials, which helps my power deliv- ery and filters out noise on the board. Another example is that we're seeing a lot more rigid and rigid-flex circuits. Insulec- tro has coached us to utilize materials that are appropriate for these types of boards, which has helped us grow in our understanding of rigid-flex development. Further, they point us toward their fabrica- tion partners, which is their customer base, and this helps us understand both the mate- rial and process. There's always a learning curve for designers when it comes to rigid and rigid-flex. Some of the Pyralux materials that DuPont brings have also been useful for us try- ing to get our product right from the begin- ning. Additionally, I'm seeing more microcir- cuitry and some very fine features that pose a challenge. Some of the dry-film materials that DuPont offers help us with circuits that require accuracy in the definition of microfeatures. Johnson: What's intriguing to me is that you're talking about materials early in the process. You're talking to materials experts as you're trying to figure out the layout of the board. When in the design cycle should PCB develop- ment people consider material selection? Creeden: That's a great question. It should be within the first days of starting your project because that's the best time to establish that things will be designed "correct by construc- tion." I do not want to design a product and then consult my fabricator in the last days of development. If the material is not in stock, we may be delaying the procure- ment of what is probably a late design, anyway. You'd want to make sure that it's in stock, and you'd also want the coach- ing from your fabricator and supply chain to make sure that you're making correct selec- tions. When you do this late in the process, selections may happen quickly, and there may not be enough time to ensure that it's an appropriate mate- rial selection. There's always a material technology decision, and it should be made early in the design pro- cess. The earlier, the better because this allows time to change it if that is required. Johnson: You're making the point that mate- rial is becoming increasingly important. With that in mind, and especially for anybody who's newer to this, why is material important? Creeden: If you've ever seen lightning strike in the air, you're probably seeing it from the cloud to the ground. Or if you've ever seen static elec- tricity, when the lights are low, you can see the spark fly. That's a good visualization to under- stand every time you're routing a trace. Histori- cally, circuitry traces were DC in nature, and their environment didn't matter as much. Now, you are managing an electromagnetic field. The field is capacitive, and that's best (high capaci - tive) when a trace is close to its return path. It's also magnetic, which is inductive. That is how a signal propagates (low inductance) down the line. You're also managing an EM energy field; you're not just connecting two points with a trace. The energy field is not in the trace. Rather, the trace and it's return path—typi - cally a GND plane—serve as reference points; thus, the energy exists in the dielectric material between them. Therefore, the material with all of its parameters are an integral part of the per - formance of the circuit. DESIGN007 To read this entire article, which appeared on Design007, click here. Mike Creeden

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