Estimated reading time: 6 minutes

Elementary, Mr. Watson: PCB Routing: The Art—and Science—of Connection

Many people who design circuit boards love the routing part of the design. This is partially because we want to stop looking at the annoying rat's nest of connections, which seem to have no rhyme or reason at first glance. We want to get to something more exciting.

Routing is the ultimate part of solving the puzzle. You take all the messy lines from the schematic and turn them into neat, organized paths. For many designers, this is the job's most exciting part. It looks cool, feels like progress, and makes the board come to life. But (I can’t lie, it’s a big “but”) sometimes, designers focus too much on routing and forget something important: Good routing starts with good planning. Routing actually begins all the way back in your stackup and, even more importantly, the component placement.

The rat's nest is the primary tool for component placement. The messy tangle of lines connecting pins all over the board shows where every electrical connection needs to be made. This jumble can feel overwhelming, but it's a helpful guide: It tells you exactly which points need to be connected. I like watching students make their first push into the PCB and their reactions. They think that they did something wrong, which, depending on my frame of mind, I sometimes play along with.

In the 1993 movie, “Searching for Bobby Fischer,” there's a powerful scene where Ben Kingsley, the chess instructor, helps a young chess prodigy understand how to see the whole game. Kingsley's character clears all the pieces off the chessboard during a lesson, leaving it empty. He does this to show that sometimes, when you're stuck or can't find the right move, you must take a step back and look at the situation without all the distractions. By clearing the board, he helps the boy see the bigger picture, when all the pieces before had cluttered his mind, and he now finds the hidden solution. This is the “Bobby Fischer Trick.” This moment teaches that sometimes simplifying and focusing on the essentials can unlock the best moves in chess and life. That also goes for your component placement and what will become your routing.

Use the Bobby Fischer Trick in your PCB design: Clear your board, much like you would a chessboard. When you turn off everything on your PCB design except the rat's nest, you see a web of thin lines connecting pins all over the board. These lines show all the electrical connections that you need to route. Looking at this messy tangle, you can spot problems immediately: long lines stretching across the board and many lines crossing each other. Long lines can cause signal delays or interference, and crossed lines mean traces will have to jump over each other using vias or complicated routing paths. This view helps designers understand where routing will be most challenging and shows which areas need better component placement or special attention during routing. It's like seeing the puzzle pieces before you start putting them together, helping you plan how to make the connections clean and efficient. The quality of your routing is only as strong as the thoughtfulness of your placement; every smooth connection begins with smart decisions.

The layer stackup is one of the most essential parts of solving the puzzle, having good routing, and a successful PCB design. It defines how the layers in the board are arranged: where the signal layers are placed, where the power and ground planes go, and how everything works together to support the routing. A well-planned stackup makes routing easier, cleaner, and more reliable.

One of the key connections between the stackup and routing is the use of layer pairs, which in this case refers to pairs of signal layers used to manage routing directions. Designers often plan these signal layer pairs so that one handles traces going horizontally, or East and West, and the other handles traces going vertically, North and South. These routing strategies help reduce the possibility of routing congestion and make it easier to route escape pins on complex parts like BGAs (which will be discussed on another day). Following such a strict rule results in your PCB design developing routing channels.

For example, in a six-layer board, the layer pairs you have decided on are that layer 1 is paired with layer 6. Layer one will go North and South, and layer six will go East and West. These two layers become a routing pair that supports efficient signal flow.

One solid practice I should mention here is that each signal layer in the stackup should sit next to a solid reference plane, usually a ground or power plane. That ensures every trace has a clean return path, essential for signal integrity and noise control. This type of pairing—signal next to plane—is essential for maintaining impedance and reducing EMI. The stackup also affects how and when vias are used during routing. Vias connect traces between different 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 published interview, technologists at OKI Circuits 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. The rat's nest shows which pins need to be connected. These 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. The line from the rat's nest disappears as you finish each trace. That is how you know you are making progress. It's essential to keep checking that your traces follow 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. The 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 completed 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 resounding “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. This 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. There is a lot of enjoyment 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.

This column originally appeared in the June 2025 issue of Design007 Magazine.