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APRIL 2022 I DESIGN007 MAGAZINE 11 In a conversation with Dave Torp, he dis- cusses additive design techniques and why the design cycle is similar to traditional design, but in a different order. Cherie Litson walks us through the steps in additive and semi-addi- tive design, including DFM and signal integ- rity considerations. Luca Gautero explains how solder mask is applied during additive processes, and how this affects the design rule check guidelines. Columnist Tara Dunn answers some of the many questions design- ers have about designing boards made with semi-additive (SAP) processes. Tomas Ches- ter addresses designing PCBs with additive traces. Columnist Barry Olney discusses a typi- cal SAP design process, its benefits and challenges, and why SAP may be part of a natural manufacturing evolution as lines and spaces grow increasingly denser. Dave Wiens explains how today's EDA tools will have to adapt to optimize the design cycle for additive and semi-additive PCBs, and Calu- met's Todd Brassard and Meredith LaBeau detail some of the hurdles facing designers who move into additive PCBs, and why a little competition here would help get this technol- ogy standardized. We also have columns from our regular con- tributors Matt Stevenson, Martyn Gaudion, John Coonrod, Vern Solberg, Kelly Dack, Beth Turner, and Joe Fjelstad. Finally, we have a review of e Printed Circuit Designer's Guide to… Stackups: e Design within the Design by Skyler Sopp, and an article by Anaya Vardya. Additive and semi-additive processes are microcosms of the industry—there's a lot of innovation going on. And we'll keep bringing you the design information you need to know. See you next month! DESIGN007 Andy Shaughnessy is managing editor of Design007 Magazine. He has been covering PCB design for 20 years. He can be reached by clicking here. but the interest is there. If your company's high-density boards have pushed traditional subtractive etch fabrication to its practical lim- its, you're probably already researching addi- tive and semi-additive processes. Defense and aerospace contractors are very interested in additive. NASA is doing an addi- tive happy dance, and so are consumer device makers who are on the leading edge of min- iaturization, in the arena of ultra-HDI. If you need spaces and traces below 1 mil, additive is an attractive option. It's not that subtractive etch can't go below 1 mil spaces and traces. Traditional fabrication processes can go below 1 mil, but the boards become burdensomely complex, which is going to cost you—in extra routing and via layers, and increased lamination cycles, which drive up cost and drive down reliability and yield. Additive and semi-additive processes seem to be a better way, at least so far. Additive can produce spaces and traces 0.5 mils wide and smaller, and the laminate itself can be thinner, too. And the additive traces are beautiful, with straight walls—not trapezoidal. For 60 years, fabricators and designers have wondered what it would be like to have perfectly straight- walled traces, and now we can find out. But there are plenty of potential pitfalls. In fact, we don't even know what we don't know, as Pentagon spokesmen like to say. How does a designer get involved in designing additive PCBs? What resources are available? When does it makes sense to use additive or semi- additive vs. traditional? How are signal integ- rity, crosstalk, and impedance affected by these new constructions? Where is the sweet spot? Do today's EDA tools support additive and semi-additive? is month's issue of Design007 Magazine will focus on how readers can get started designing additive and semi-additive PCBs, and how the design process for additive tech- nology differs from that of traditional subtrac- tive processes.

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