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Design007-Nov2021

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76 DESIGN007 MAGAZINE I NOVEMBER 2021 Article by Pete Starkey I-CONNECT007 In the second of a series of three RealTime with... inter views, I-Connect007 managing editor Nolan Johnson received knowledgeable and informative answers from John Bushie, director of technology at American Standard Circuits, and Anaya Vardya, president and CEO, to his questions on the unique challenges of RF and microwave PCBs. Asked by Johnson for a definition of what was currently considered RF, Bushie responded that there was no clear boundary. But as data rates continued to increase, high-speed and ultra-high-speed digital circuits progressively took on analogue properties so that they began to require performance characteristics tradi- tionally associated with RF and microwave circuitry. Referring to observations noted in their recent book, Johnson remarked that designers had appeared more concerned about material selection than considerations of manufactur- ability. Bushie's comment was that in reality the performance achieved resulted from a combi- nation of material factors with fabrication tech- niques and tolerances, and it was a challenge for designers to find a r e a l i s t i c b a l a n c e b e t w e e n c o s t a n d per formance. Atti- tudes toward mate- rial cost ranged from "performance at any price" to "cost is everything." At the latter end of this spectrum there was potential for using lower-loss variants of more traditional mate- rials. And properties like mechanical strength and dimensional stability were other factors to be taken into account. Bushie stressed the importance of getting the fabricator involved as early as possible in the design process to help optimise the balance between material selection and design for manufacturability, in order to achieve cost-effective and functional designs which might combine different mate- rial types. An example was a multilayer stack- up using a core of FR-4 laminates and prepregs in combination with PTFE outer layers. Anaya Vardya added that some of the rigid-flex designs discussed in the previous session could incorporate RF materials: constructions were becoming increasingly hybridised. ere were no actual boundar- ies, but it remained critical to be aware of the processing require- ments of the different materi- American Standard Circuits on the Fundamentals of RF and Microwave PCBs

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