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Design007-Jan2022

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68 DESIGN007 MAGAZINE I JANUARY 2022 Interview by the I-Connect007 Editorial Team Any discussion about high-speed PCB design techniques would be incomplete without con- sidering the properties and requirements of the materials. Your material selection drives much of your design strategy when you're operating at 28 gigabits per second or faster. We recently spoke with high-speed design expert Lee Ritchey of Speeding Edge, and electronic materials veteran Tarun Amla of Avishtech and intronics, about the relation- ship between advanced PCB materials and high-speed design techniques. ey discuss the challenges facing designers and engineers working with materials at speeds that were considered unreachable not long ago, and what designers need to know about material selec- tion as board speeds continue rising toward the stratosphere. Andy Shaughnessy: Would you set the stage by explaining the last few decades of materials that got us to where we are now and how designers are having to learn these EM properties? Lee Ritchey: I joined 3COM in 1996 where we were doing reasonably well making all the lengths work at 10 megabits per second. And then I got started working on 100 megabits, and that was thought to be pretty fast. At that point, the only thing we were worried about was reflections and crosstalk, which basically meant impedance. In the laminates, we worried about whether we could get repeatability on impedance with a cross-section. And by 1998, I helped a startup build us a product where we had the links leaving the box at a gigabit per second. at was thought to be magical, and of course it was, in that context. It wasn't very long before I went to a startup called Procket Networks, where all the inter- nal signals were 3.125 gigabits per second, and that was where we first started to worry about things like loss. Until then we hadn't worried much about any of those properties. We wor- ried about losses because the transceiver sets were not very good, so they couldn't toler- ate much. For example, a 10 dB loss was a big number, and so that's when we started driving the laminate manufacturers to reduce loss. At the time, the only material that was consid- Living in a Material World: High-Speed Design Strategies

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