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JUNE 2025 I DESIGN007 MAGAZINE 21 layers, and the stackup determines whether they are through-hole, blind, or buried. Too many vias or poor via planning can add cost and affect performance. Good layout techniques work in even the highest layer-count boards. In a recently pub- lished inter view, technologists at OKI Cir- cuits discussed their 124-layer PCB, breaking their previous record of 108 layers. We might find this amazing and wonder how we could ever possibly route a complex PCB design. But the basic principles mentioned here are exactly what designers use in complex designs, regardless of the layer count. Always have a GND or pour reference plane for each signal layer. Pair them up from there with the remaining layers, and decide which direction, North and South or East and West, the traces will align on each layer. Follow the rat's nest. Routing using the rat's nest is like following the map. e rat's nest shows which pins need to be connected. ese lines help guide you as you draw real copper traces on the board. When you start routing, pick one line at a time and try to follow it with your trace. If the line is short and straight, your trace will be too. If the lines are crossing or looping around, that's a sign you might want to move your parts again. e line from the rat's nest disappears as you finish each trace. at is how you know you are making progress. It's essential to keep checking that your traces fol- low the rat's nest and don't take long, Route in one direction on a specific layer, like the top layer (i.e., East and West), and the other on another (like up and down) to keep things neat. e rat's nest will follow as you go in a single direction on a specific layer. As the rat's nest becomes a right angle to your com- pleted route, you change directions to its layer pair and go opposite like layer 6 (i.e., North and South). You now have a roadmap for designing any PCB, no matter the complexity level. I would be remiss if I did not share my two cents on autorouting vs. manual routing. Many times I have asked my class attendees if they use autorouters, and I always get a resound- ing "no." I have investigated this over the years, and I believe it's due to the unique relationship between the designer and the creative process. is is the foundation of why we do what we do in the first place: the enjoyment of solving a puzzle. We enjoy the artistic problem-solving side of designing a PCB, and participating in the creative process. ere is a lot of enjoy- ment there. In my 24 years of designing PCBs, I have never autorouted one. Great designs are shaped by the hands and minds of those who choose to create, not by clicking a button. DESIGN007 John Watson is a professor at Palomar College, San Marcos, California. To read past columns, click here.