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OCTOBER 2022 I DESIGN007 MAGAZINE 35 terintuitive, but it is rare that costs are compared as apples to apples. I oen see designs reduce layer count, reduce lami- nations, and shrink overall size. All these things simplify the design, improve yield, and reduce costs. • Biocompatibility: I don't think I men- tioned earlier, but the A-SAP process begins by completely removing the copper foil and a thin layer of electroless copper is added to the dielectric. But this process is not limited to only copper. I have seen several applications where gold and platinum are used as the conductive metal. is, done with polyimide or LCP, provides a much more biocompatible solution for medical applications. Q: What are some of the hurdles facing design- ers—and fabricators—who work on UHDI boards? A: In my mind, the biggest hurdle is the learn- ing curve that both designers and fabricators need to go through. Fabricators are learning a new process, and while that process of cre- ating the traces is not difficult, it does need to mesh with other processes. For example, what is the new process for via-in-pad-plated over or what thickness of copper can be plated in the hole? ere may be different approaches based on customer design. Fabri- cators are well-versed in using various tech- niques to meet customer needs and this is no different, but it does require thought and experience. From a design perspective, as we mentioned earlier, there are a lot of questions. How do you design with controlled impedance at these fine lines? ere are white papers, by the way, to help with that. What materials are compatible with this process? Where does it make sense to use subtractive etch vs. SAP layers? Is there reliability data? ese are a few of the common initial questions. Q: Are there any resources—books, websites, instr uctor s, etc.—for UHDI design tech- n i q u e s? I i m ag i n e p e o p l e a r e c o m i ng to Averatek with questions. A: Yes, we do field a number of questions, which is one of the best parts of my role at Averatek, and along with the work we are doing, we are also working with a number of PCB design- ers who are interested in really understand- ing how to apply these fine features. These designers are starting education programs, writing papers, presenting at conferences, and are available to assist as others go through this learning curve. A good place to start is the Info Center on Averatek's website, where we have compiled a number of white papers and articles address- ing the subject. I also believe most of the PCB- focused trade shows are now offering tracks about SAP and I have seen several webinars available as well, both from fabricators and from equipment suppliers such as Orbotech. Q: What advice would you give designers who are considering moving into UHDI? A: It is the same advice I give to anyone new to designing with HDI, new to designing with flex or rigid-flex, and now new to designing with ultra HDI: Work closely with your fabricator. Learn to understand their capabilities and let them help guide you through the design. ey have the experience of building many designs with these technologies and are always happy to help PCB designers design a manufactur- able part. DESIGN007 Tara Dunn is the vice president of marketing and business development for Averatek and an I-Connect007 columnist. To read past columns, click here.

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