When we design circuit boards, we view them in extreme zoom and it’s hard to keep the actual scale in mind. And we’ve all experienced “blind spots” after staring at them for a long time. I’ve developed a process that brings back the scale to my mind and helps me discover problems. I print the design twice when I think it’s ready to be manufactured.
  • Print #1: A scaled-up version of the design, to A4 or A3 paper size, with only the outline and copper features, nothing else. Every physical layer gets its own distinct color with some opacity so that I can see the overlaps between layers.
  • Print #2: One-to-one scale print in black with the outline, footprint pads (but not the routing!), and a large feature with a known size in both the X and Y directions. (I use my outline dimension arrows.)

Print #1 is for finding functional issues. I sit somewhere away from my computer with that print, the printed schematic, and highlighter pens and trace every track and tick it off on both documents. It allows me to catch tracks going where they shouldn’t, and also notice microcontroller pads with no connection: a red flag.

I use Print #2 to get the scale back to the fore and to verify the footprints. I do my best to have samples of all the components at this stage. I verify all of them because you never know. But first I measure that “large feature” in both X and Y dimensions. This is important because of annoyingly covert printer scaling; measuring that feature lets me know that I’m indeed working with a true 1:1 print.
Circuit Shorts: print is not dead

For extra assurance, I ask another person, if one is around and willing, to go through the same process with my design. Another set of eyes for some sanity-checks and questions is a good thing.

The process of setting everything up can be annoying, but it sure ain’t as annoying as getting a board back with the wrong footprint! I also don’t like printing waste — both prints can be on the same piece of paper — but if it means avoiding a scrapped board rev, I think it’s probably worth it.

What techniques do you use to make sure everything is as correct as possible with your PCB before pressing the button for manufacturing?

Additional Resources About Circuit Design

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