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76 DESIGN007 MAGAZINE I DECEMBER 2021 market, it has not been something truly avail- able for low-volume, high-mix applications. at has changed. Fabricators are installing the A-SAP™ process, which starts with a very thin electroless copper and uses semi-additive techniques to form traces much smaller than traditional subtractive-etch features. Fabrica- tors are also looking at mSAP, which is a semi- additive process that uses thin copper foil. ese new capabilities are exciting from a design perspective—and also challenging. is is a new design space that most of us are not used to or familiar with. Unlike someone new to flexible circuit design, who can easily rely on their fabricators knowledge to help guide them through the learning curve, in this case the fabricators are also going through a learn- ing curve. What a great opportunity to change the way we look at PCB design and fabrication. One of the first questions I am asked when talk- ing about SAP (semi-additive PCB processes) is design rules. at is industry default, and it is completely understandable that a PCB designer would want to understand the limita- tions as they start to think through how to best apply these new capabilities to their designs. I am advocating instead that we re-frame the typical communication cycle between PCB design and PCB fabricationl as one SAP expert has stated, let's design with manufac- turing, not for manufacturing. My opinion is that we as an industry would be remiss by putting parameters around these capabilities without fully understanding how they can be applied. We are just starting to scratch the surface of reviewing this for a wide variety of applications. Some designs will benefit most from miniaturization. Some designs will ben- efit most from reducing higher layer count and dependence on multiple lamination cycles to accomplish tight pitch BGAs. Some designs will benefit by shrinking the routing area and increasing hole size to eliminate microvias altogether. I am sure you get the point that ultra-high- density feature sizes can be used in so many different ways. is is the time for the PCB industry to challenge the creative side of PCB design to learn to identify all the different ways this technology can be used to solve today's packaging problems. At the same time, our le-brain traits must be put to full use. Here are few thought starter questions to help kick-start things: • How many layers could I eliminate with tighter pitch routing and what is the impact on impedance if I do that? • How can I combine SAP layers and subtractive etch layers to the greatest benefit? Is that using layer pairs of SAP to simplify for manufacturing? Or does it benefit the overall design to increase the cost and use subtractive etch on one side of the core and SAP on the other? • Do I use SAP layers or subtractive etch layers as outer layers? What are the benefits and drawbacks? e list could go on and we will keep address- ing these types of questions in future columns. What I want to close with today is a common message you oen read in my columns. I will always recommend strong communication between design and fabrication and as early in the design cycle as possible. is is going to be even more important as we all collectively move through this exciting learning curve. DESIGN007 Tara Dunn is the vice presi- dent of marketing and business development for Averatek. To read past columns or contact Dunn, click here. This is a new design space that most of us are not used to or familiar with.

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