geekanddadllc / pcb_tips

Making a PCB? What did you forget? Use this checklist before you order and save yourself some pain and money.

PCB_Tips

Making a PCB? What did you forget? Use this checklist before you order and save yourself some pain and money.

Some general thoughts and considerations before sending a PCB off to the fab house based on lessons learned, often the hard way, by myself and some of my friends:

General Tips:

• Use rounded corners and avoid sharp points
• Place your mounting holes, with screw head standoffs, BEFORE you route your traces
• Decoupling caps. You can probably use a few more
• Did you use protection diodes?
• Did you connect the programming port of the MCU to a programming header?
• Is everything labeled clearly on the silkscreen?
  • Polarities
    • LEDs
    • Diodes
    • Capacitors
    • ICs (add the notch)
    • Headers
  • Product Name
  • Company Name
  • Logos
  • URLs
  • Board version
  • Something fun, just for you
• Make sure all layers are visible before copying the board (for example making a panel)
• Do you have any high speed signals (usb 2 and up speed)? If so, make sure they don’t cross a break in the ground plane.
• Do you have any plated slots?
  • Did you draw them the way your PCB shop wants?
  • Did you make sure that their method doesn’t break your clearance checking?
• Footprints:
  • Did you print out the PCB on paper to check it against your actual parts?
  • No seriously; check those footprints against the datasheets one more time. Measure carefully!
  • Are those LEDs indicated correctly on the silkscreen? Check the datasheet again. Manufacturers aren’t consistent on marking even in the same product line sometimes
• Do you have test points? (Power rails, logic pins, I2C/SPI/UART lines, etc)
• Do you need a Reset or Boot pin broken out? Put the power or ground they need to be tied to next to them with a "do not populate" resistor footprint; trigger manually
• Did you remember to put a power or other indicator LEDs to help with debugging?
• Are your parts still available?
• Have you slept on it?

If you’re working on a prototype:

• Use more PCB space; it’s not too expensive to do a 4x4 inch board (check your board fab house)
• Modular design:
  • Break up the layout into modular sections:
    • Power
    • Signaling
    • Logic
    • Etc.
  • Separate parts and design it with 0 Ohm resistors or other easy ways to break things apart if these chunks don’t work
  • Use Test Points on the input and output of these modular sections
• Got any of those pesky RX/TX pairs? Lay them out in an easy to fix configuration such as this image or by using test points and cuttable traces:
  • 
• Break out unused GPIO to test pads “just in case”
• Use the most flexible options for I2C address setting that you can

If you’re working on a final version:

• Avoid ground loops; more vias!
• Design for manufacturing/assembly
  • Can you get those plugs in on an assembly line?
  • How hard is it to fix that in the device?
  • Tall components blocking access to things?
  • Use different plug types and pin counts to make it harder to plug the wrong thing in the wrong place
  • Don’t forget to account for the shroud sizes of headers and plugs; they can be bigger than you thought.
• This is the time for smaller/more compact designs
• Can you combine BOM items (e.g. do you need a 1.1K resistor and a 1K resistor or can they both be 1.1k?)
• What is the smallest component my assembly house will place before they start increasing the price?
• Is the meta-data cleaned up?
  • Is the BOM scrubbed for proper info?
  • Is extraneous info removed?
• Is the schematic cleaned up?
• Are there traces or planes that can be cleaned up?
  • e.g. a trace that jumped between layers to get around something, but that something is no longer there
  • In case you put some traces through some planes because you had to, does that perforate the plane too much?
  • Could that be avoided or mitigated somehow?
• Are there stray antenna-like features to the copper?
  • e.g. Planes that got sliced by a trace and have a connection only on one end

Special thanks to https://github.com/AlpenglowIndustries, https://github.com/jasoncoon, https://github.com/sethkaz, https://github.com/freemovers, https://github.com/SeanMollet, for their invaluable help in this guide.

Have some tips to share? Let me know!

Remember that you are loved. #MakeKindnessNormal