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22 DESIGN007 MAGAZINE I SEPTEMBER 2022 In a previous column, I deliberated on why the 2D field solver is an essential tool for all high-speed PCB designers. But like all tools, one needs to know how best to apply its unique features to enhance your design pro- cess. Obviously, calculating transmission line impedance, in its various forms, is the prime function but field solvers can also provide additional information to ensure good design practice long before the layout begins. Many PCB designers believe that it is the fab- rication shop's role to calculate all the required impedances at the end of the process to best suit the materials that they stock. But by then, it's too late; the horse has already bolted. It is difficult and time-consuming to go back and change the constraints once the board is complete. So, where do we start to build the perfect stackup for our project? Initially, virtual mate- rials are used to get the rough numbers. en the impedance is fine-tuned once the actual materials are substituted. Every digital board will require 50-ohm impedance and generally a 100-ohm differential pair. is is our target impedance. However, multiple technologies are oen used on complex designs which need to be accommodated on the same layer. Utilizing a Field Solver for Stackup Planning Beyond Design by Barry Olney, IN-CIRCUIT DESIGN PTY LTD / AUSTRALIA