PCB Friday: Two-Layer PCB Routing Strategies and Tips

Roughly five years ago, I took a class on KiCad at MakerFX in Orlando, taught by Anool J M. This got me through the initial steps of setting it up, understanding how programs in the software suite work together, and making my first KiCad design.

How to sensibly route traces, however, took a bit of time to grasp. While I'm still no expert, the following tips are meant to help you progress from total n00b to a nominal level of confidence. If you've been designing PCBs for a while, much of this will be old hat, but maybe you'll still find a helpful tidbit or two.

Strategy #0: Lots of fun, get started now!

Arguably not a strategy per se, but I want to put this out there off the bat. When you decide you want to start designing PCBs, just do it — as Nike would implore you. Design something, get to a point where you reasonably think it will work, and put in the order. Make your mistakes and try again.

Once you get a few boards back and work the kinks out of your designs, you'll be ready to make your actual killer product. My first PCB worked as designed, but there were several things I could have done better. It was the start of a learning process that continues to this day.

Though you can learn on your own, I highly recommend taking an in-person class as I did. At the same time, don't be afraid to start using the software before you have official instruction!

Strategy #1: Fill THEN route

Just about every component on a PCB needs to connect to ground (GND), and as it just so happens, you can make the front and/or back of your PCB one big ground plane with the Draw Filled Zones tool. This allows you to define the connection area, and what network (net) it should be connected to (this is often GND, but doesn't have to be).

Draw the area to be filled with a ground (or other) plane. If your parts are on the same side, all of a sudden many component connections will be taken care of. If the filled area is on the other side, just pop in a via👇 to easily connect.

Strategy #2: Vias!

In the context of a two-layer board, vias are electrical connections between one side and the other. If you want to route a trace from point A to point B and there is another trace in-between, pop in a via with the v KiCad shortcut and it ducks onto the other side to continue it's path unimpeded.

Routing tracks via... vias is a bit of a balance. I try to mostly avoid them when practical. However, if using a via will save a significant amount of snaking around your board (or make a design possible), don't be afraid to bob and weave from side to side like an electrical engineering boxer.

If both sides are filled with connections to the same net (e.g. GND), you can connect these areas with free-standing vias. This is used to avoid isolation of different areas and/or to provide a more expedient path for electrons.

Strategy #3: Rotate and position to minimize rats nest

When you update your PCB from the schematic, you'll be presented with a "rats nest" of components and to-be-connected white lines. While the ultimate arrangement of tracks and filled areas used to connect these lines will vary from design to design, broadly speaking, it is a good idea to separate out the components, then rotate them as needed to minimize how often the lines cross.

Strategy #4: Configure schematic for PCB routing

In some designs, you have a choice of several pins to use for a specific purpose. Often these choices are made arbitrarily, then passed along to the PCB Editor for routing.

This often works fine, but sometimes you're left with a challenging scenario. Rather than fighting sub-optimal choices from the PCB layout phase, consider revising your schematic to make routing easier. Better yet, consider routing in the schematic phase!

Strategy #5: Functional sections

While not appropriate for every design, dividing your PCB into functional blocks can be helpful for PCB layout and troubleshooting. I haven't personally used this technique, but here's a synth example that you may find instructive.

Strategy #6: Power side, communication side

Consider placing all of your components on one side, along with the tracks that carry signals from one component to another. Power (positive busses and ground planes) can then be situated primarily on the opposite side.

Strategy #7: F Power routing

Rather than having your power bus immediately branching off or snaking around your board, it can be helpful to design this in a (very) rough "F" shape. Here the vertical section of the F represents the main backbone of the network, with the horizontal sections branching off to reach individual components.

On my RP2040 Basic board shown above, the 3.3V track starts in the upper-left corner and travels to the right while branching off in a sort-of, tipped-over F shape. You could also think of this as a river, with tributaries combining from right to left until finally reaching the 3.3V supply.

Note that the rest of this side is filled as a ground plane, and the yellow dots are vias that connect both sides together.

Strategy #X: Moar layers!

I've yet to reach the level where I need more than two layers. However, if things get too tight, or if you need to deal with EMI issues, four or more layers can be extremely helpful. Consider that when using a four-layer board, you can run signals on the top and bottom layers, then reserve the inner two layers for ground and VCC planes.

Of course, four layer service will typically cost more than the two-layer equivalent — OSH Park, for example charges $10/in^2 for four-layer service, versus $5/in^2 for two-layer boards — which seems fair since you're getting twice the conductive surface area.

Happy making

Hopefully you found these strategies and tips helpful, though I'm still learning and am certainly open to feedback and new ideas on the subject. Feel free contact me with your thoughts!

Thanks for reading!

Thanks for reading my biweekly PCB Friday column! I'm looking forward to sharing more PCB-related knowledge and insights here, and I hope you'll follow along for the journey. You can see more of my hacking/DIY exploits on the Jeremy Cook DIY YouTube page, read my semi-technical musings at TechAdjacent.io, or email me: hi@jeremyscook.com!

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