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48 DESIGN007 MAGAZINE I APRIL 2022 R/Flex Crystal and Jade materials all pro- viding low loss flexible materials of 1 mil thickness. 3. Unless all the routing is completed on the top (component) layer, breakout vias are still required—although the use of via-in-pad and blind vias dramatically reduce the real estate required. ere are also substantial signal integ- rity benefits from semi-additive processing. Tighter line width control and straight con- ductor sidewalls greatly improve impedance control. Also, the technology helps reduce parasitic inductance by reducing loop area, as well as increasing density. Fine-line precision RF features can also be realized with SAP tech- nology. 3D printing of multilayer PCBs is also an additive process. With its game-changing tech- nology, 3D printing allows free-form shapes, enabling you to find novel solutions to devel- opment challenges, thus enabling new devices and designs. It allows a seamless, one-step manufacturing process from digital design to functional devices. Plus, it enables printed 3D antennas/coils and eliminates loss-generators. Although 3D printing is currently limited to 3/4 mil trace/space construction, it has a huge advantage for prototype construction, of mul- tilayer boards in-house, within a matter of hours. Key Points: • Form factor-driven design pressures have been relieved, in part, by the increased use of high-density interconnects. • e traditional PCB subtractive etch processing becomes very difficult for feature sizes below 3 mil trace/space. • e thinner traces of HDIs can introduce an increased risk of signal degradation. • e SAP process is a production-proven method used on build-up materials that enable the manufacture of ultra-fine-line circuitry. • Fabricators previously only able to offer 3 mil trace/space, can now reliably produce 1 mil trace/space and below. • Further reductions required the adoption of various mSAP manufacturing processes. • SAP enables the printed circuit board fabricator to employ an additive screen process instead of an edge-removal, etched process. • SAP provides tighter line width control and straight conductor sidewalls greatly improving impedance control. • SAP provides tighter impedance tolerance than the traditional subtractive etch processes. • e SAP process promises greater routing density with six 1/1 mil trace/ space between lands. • Unintentional coupling of parallel segments is extremely strong between 1 mil spaced traces. • An extremely thin dielectric of 1 mil or less is required to maintain 50 ohms impedance with a 1 mil trace. • Breakout vias are still required with SAP–although via-in-pad dramatically reduces the real estate required. DESIGN007 Resources 1. Beyond Design: "Controlling the Beast" by Barry Olney 2. "SAP and mSAP in Flexible Circuit Fabrication" by Tara Dunn 3. "Achieving Fine Lines and Spaces Using mSAP" by Rich Bellemare and Jordan Kologe 4. "mSAP: The New PCB Manufacturing Impera- tive for 5G Smartphones" by Many Gantz 5. Nano Dimension, Dragonfly product datasheet Barry Olney is managing director of In-Circuit Design Pty Ltd (iCD), Australia, a PCB design service bureau that specializes in board- level simulation. The company developed the iCD Design Integ- rity software incorporating the iCD Stackup, PDN, and CPW Planner. The software can be downloaded at www.icd.com.au. To read past columns or contact Olney, click here.