Schematic Cleanup + PCB stackup considerations

[fabianmuehlberger]

Hi,

Since I am looking for a new keyboard, I came across this project. Looking at the board design files for the Corne chocolate from the main branch, I would suggest a rearrangement of the schematic symbols to a more functional layout.

The schematic should follow general guidelines like:

• Symbol naming/numbering from left top to right bottom,
• Upper left Power, IO
• right side MCU, peripherals (flash, crystal)
• do not cross lines if possible
• PWR labels always Up, GND labels always down
• labels on symbols should sit on the line

see example:

I have not checked if the left and right side have significant functional differences, if so, making hierarchical sheets for duplicates would be suggested too, e.g. keys, LEDs, MCU on separate sheets and references to them for left and right side if the components are the same.

Regarding the PCB, I would suggest switching to a 4 layer PCB. Since ground pour is only on the top side with a high number of traces on the top and bottom, as well as layer changes of signal lines, current return paths are VERY restricted. A 4 layer PCB with 2 ground inner layers would make routing easier and improve the board overall.

I made some example changes in the corne chocolate schematic on my fork Please let me know if you are interested in a redesign, if there is interest, I am happy to contribute.

Best Fabian

[foostan]

Thank you for your suggestion. Please provide evidence to evaluate the validity of your proposal. thank you.

[fabianmuehlberger]

What do you mean with validity? PCB design is mostly based on guild lines rather than fixed rules. The parts I mentioned are pretty basic and would apply to most simple PCBs with one populated side.

I found this guide with basic recommendations for the schematic.

Elegant schematics schematic checklist

A best practices regarding ground can be found here

[foostan]

Thank you for sharing. I'll confirm the guide and fix them.

About 4 layer, could you tell me your opinion more. Could you share Pros/Cons?

[fabianmuehlberger]

Hey, It's not about the guide, these enhancements can be separately applied.

1. Schematic rearrangement/refactor is to make it more concise. The goal is to make it easier to read and debug if there are problems. Following basic guidelines will help adapt and improve the design in the future and make it more portable.

2. PCB stackup is a big topic itself, and I am not an expert. But 4 layer PCBs are the norm nowadays and have gotten cheap to produce; therefore we can get the advantages over a 2 layer board with basically no downsides. I see no reason for not using a 4 layer board These are:

   • Inner ground layers: generally speaking, you want all traces separated by a ground layer. This helps with crosstalk and provides a solid current return path. With 2 layers, this is only possible when using one side for traces and the other for ground. Obviously, this can only be done on low density boards (low component count; space for routing).
   • Easier Routing: With a 4 layer board, it is much simpler since you can use the 2 inner layers for GND and the PWR bus and use the outer layers for the signal traces. This makes routing easier, since you simply have more space to do so.
   • EMI: For commercial products in the EU an EMI/EMC test is mandatory. So far, I have not produced a PCB for the market, but it's a big topic. Following the industry norm wherever you can helps comply with those standards. https://www.protoexpress.com/blog/7-pcb-design-tips-solve-emi-emc-issues/

Best

[foostan]

Thank you for sharing. I'll read the docs you shared.

[fabianmuehlberger]

From your answer, I assume that you are not interested in me contributing to the project. I close this issue then.