PCBA Design

PCBA stands for printed circuit board assembly. Examples of PCBA are computer motherboards or Arduino Unos. It works to connect together small electrical components into one compact board. Our CubeSat will consist of multiple different PCBAs connected and talking to each other.

https://www.youtube.com/watch?v=H9pGbLJknDk

Workflow Cycle

1. Project Scope

   After initial research is done and we have a high level idea of what we want to design, writing some documentation outlining the PCBs architecture and justification of design choices is very useful. Start a Notion page for your board in your subteam’s workspace using Board Project Scope Template.

   • Component Selection + Sourcing Spreadsheet for major components
     • Justification for Design Choices
     • Spreadsheet Calculator (if applicable to your board)
   • Review notes
   • Initial Test Plans
   • Project Completion Timeline (likely completed by your lead)

From this point forward you must work as quickly as possible, sadly in today's environment we have to move quickly or else you may be stuck in an infinite loop of re-sourcing parts that go out of stock )

1. Schematics

   Once we know what we want to create we can put it into a design. The schematic is intended to communicate all the electrical connections between components to other people or yourself a few weeks in the future. Make sure it is clear; include lots of notes and make sure things aren't cramped. During this process, you want to:

   1. Pick your parts
   2. Create/Import schematic symbol
   3. Create/Import footprint
   4. Add symbol and other circuitry to
   5. Clean up your schematic and prep it for design review

   Some design tips include:

   • Use a multi-page schematic if the design is complicated
   • Try to communicate information from left to right where possible
     • i.e. when designing a buck regulator, input on the left, output on the right
   • Feel free to use a library loader or similar to import components, but double check to make sure they are correct
   • Add lots of LEDs and test points for debugging
   • The symbol doesn't need to be physically accurate, feel free to move around pins on the symbol to make schematics more understandable
   • Include component information under properties for components as you go, will make generating BoM a lot easier
   • Don't assign IO for microcontrollers until you get to layout

2. Conduct Preliminary Schematic Review

   1. Internal design review (members, leads from our team) to review the schematic and make note of any issues
   2. How will we make notes btw? @Shreya Singh
      1. Separate sheets for separate boards (will have sourcing + reviews in one sheet)

3. Fix any issues with your schematic ASAP!

4. Conduct final review

   1. Advisor design review (smart people outside of the team + our team) to review the schematic and make note of any issues

5. Fix any issues with your schematic ASAP again!

6. Order the parts required for your board

Alright, now you can take a break knowing the parts you spent hours sourcing won't dissapear into thin air 🙂

1. Layout

   Now that the schematics are complete we can start designing the physical board layout. This is what we're actually getting made and assembled. It consists of pads for components to solder too and copper traces to connect the components together. Generally speaking 2 and 4 layer board are super cheap (under 100mm x 100mm).

   During this process, you want to:

   1. Review your footprints (just in case anything weird slipped through)
   2. Complete component placement
   3. Review your component placement with the team and fix any issues
   4. Complete routing
   5. Review routing with team (and maybe bring in advisors?) and fix any issues

   More design tips:

   • Spend a lot of time with component placement
     • Routing complexity is a function of good component placement, the better the placement the easier and better the routing
   • Don't be afraid to rip up your routing and start over
     • PCB design takes practice and your first few attempts will probably suck
   • Don't forget mounting holes
   • Manufacturer will sometime provide layout tips, follow them
   • Try to place as many components and do as many routes as possible on the top layer
     • Leave bottom layer for ground plane
     • May not be possible in later revisions depending on space constraints

2. Test Plans

   While waiting for your boards to arrive, flesh out your test plans. Make sure you're specific, include specific test point names, pictures, etc.

3. Bring up

   Once your board has arrived you can start assembling and (if applicable) flash some code onto it. Make sure you're using a good soldering iron, lots of flux and have good ventilation. Surface mount components can be tricky to get the hang of, but once you've gotten the first few down, it should be smooth sailing.

   When you first power up your board, chances are it won't work🙃. Make sure you have at least a multimeter handy, but a oscilloscope and logic analyzer (if applicable) might be handy depending on the issue you're encountering. Hopefully you including lots of test points and LEDs to help debug. Issues can range anywhere from poor soldering, to schematic/layout errors to poor initial design.

   Make sure you document all the issues you find with your board, so you or whoever takes on the next revision can improve on it.

4. Testing and Summary

   Now that your board works it's time to put it through its paces to make sure it meets all the design requirements. For a power regulator this includes cycle testing, measuring voltage ripple, measuring temperatures, measuring efficiency, etc. For a microcontroller this includes testing all peripherals, etc.

   Make sure you document all your testing results and summarize it into a report. Testing that isn't documented didn't happen😠. Use your testing results + any new external requirements from other subteams to improve your design and make a second revision.