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96 DESIGN007 MAGAZINE I APRIL 2021 Following these wet process steps, the semi-additive manufacturing panels will fol- low the same process flow that subtractive etch panels follow including solder mask, surface finish plating, electrical test, and inspection. Why Is This Important to PCB Design? Traditional subtractive etch processing, at least in the U.S., becomes very difficult for feature sizes below 3 mils (75 microns). As electronics packages shrink, this forces PCB designs to become much more complex— adding extra routing layers, adding micro- via layers, and increasing lamination cycles required, all which impact yield, reliability, and cost. e semi-additive process jumps this tech- nology curve. Within a few weeks, fabricators previously able to offer 3-mil line/space, can now offer 1-mil line/space and below. at is a complete game changer for PCB design. Some of the benefits are easily seen: • e ability to shrink the overall size of a circuit • e ability to route additional traces between pads can reduce the overall number of layers required for a design and subsequently the ability to reduce the number of stacked or staggered microvias Over the next few months, we will review use cases to help spur ideas. ere are also significant signal integrity benefits from semi-additive processing. ere is tighter line width control and straight con- ductor sidewalls greatly improve impedance control. Another feature to additive process- ing creating a buzz within the design commu- nity is the ability to create higher aspect ratio traces than available with subtractive etch or even mSAP options. We are just scratching the surface on how to best apply these new capabilities to PCB design, and I am looking forward to collabora- tive discussion and creativity. It is tempting to ask for "design rules" but in my opinion, that may limit the creativity in approaching design challenges in a new way and my hope is that we can develop a community of interest fol- lowed by a community of design expertise around this new technology. Please reach out to me with your questions and stay tuned as we start a deeper dive into this exciting tech- nology. DESIGN007 Tara Dunn is the vice president of marketing and business development for Averatek. To read past columns or contact Dunn, click here. Figure 2: Before and after etching the base copper layer. (Images courtesy of MEC Corporation)