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I developed my project one more step and moved to the PCB stage.I will make a PCB for the first time with a microprocessor and SMD components.

I did my PCB design. Only the ground connections left. I am confused about GND polygon and ground traces.

I read on the forums that some people say form all your ground nets properly. How do you know the flood fill will connect all the grounds up?

Some people say make a polygon for certain GNDs and connect the rest yourself. I looked at commercial designs and I saw they all use polygons for GND.

I have a central GND pad microcontroller (RP2040.) I only left 104 GND wire connections.

Here is my RP2040:

I have ethernet (W5500.) I separated ethernet's (RJ 45's) ground with a ferrite bead. I have one RFID module. It uses 9V and requires a maximum of 120mA. I have an HX711 and I have 3 stepper motor signals. My system uses under 300mA current. On a breadboard, I can run them with one GND without problems.

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  • Should I connect GNDs with myself? If so, how can I decide on GND's width trace ?
  • Can I use the microcontroller's GND for everything? I only have DC power. Can I connect this GND to DC powers GND?
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  • \$\begingroup\$ Well, it depends. If MCU needs a cooler, GND traces are a good way to help with that either. 1) Yes, would be better to connect them but you don't have to if you have polygons. Traces depend on the current flow on it most of the time. You should know or guess which pin has a higher current. 2) Depends, if you need to care about EMI/EMC, you have to separate the high freq. lines and other grounds otherwise you can do it I think. Your DC Power is relative to its own ground. Different grounds may cause voltage differences either. Try to connect ground planes, polygons with vias to prevent it. \$\endgroup\$
    – OJazz
    Dec 30, 2021 at 12:18
  • \$\begingroup\$ Only ground connections left Oh boy! Grounds should go in first, or at least be planned first. Every high speed trace needs a ground running in parallel. Every high current trace with low voltage analogue circuits close to it needs serious planning of the current path, to inform your component placement, so that then the easiest route the ground current finds to take is a suitable one. \$\endgroup\$
    – Neil_UK
    Dec 30, 2021 at 12:42
  • \$\begingroup\$ @OJazz , I have ethernet (W5500) . I separate RJ 45's ground with ferrite beat. I have one RFID module. It is working with 9V and max 120mA requires. I have hx711 and I have 3 stepper motor signal. My sistem is working under 300mA . On breadboard, I can run them with 1 GND without problem. \$\endgroup\$ Dec 30, 2021 at 13:11
  • \$\begingroup\$ @Neil_UK , thank you. If I made new PCB , I will do that :) \$\endgroup\$ Dec 30, 2021 at 13:12
  • \$\begingroup\$ At this point the simplest way forward is to connect your gnd points to vias using the shortest, fattest tracks. Do a polygon pour on the bottom layer to connect all the ground points. Visualise where the current will flow - draw the loops on a printout. Also use fatter tracks for your power distribution. \$\endgroup\$
    – Kartman
    Dec 30, 2021 at 14:00

1 Answer 1

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That totally depends on what the purpose of a certain GND pin is:

  • digital return current
  • power return current
  • analog reference
  • charge dump for EMI related stuff

For 99% of projects the GND node is the most often used node throughput the project. As it it used across the board, its potential should be the same everywhere on the board at all frequencies.

The closest you can come to this ideal is a solid GND plane in a dedicated layer. But for a 2-layer board a patchy plane made up of top & bottom pours can also work.

This is what I recommend you to do in your board. It also avoids having to think about the purpose of each GND pin and connection for a while1. If you then end up in a situation where using the large global GND plane for a certain pin causes problems, you can then add additional GND traces for dedicated return currents.

1 Mindlessly connecting everything to the GND plane can created awkward current loops and cause EMI issues, especially in a 2-layer board. So if you must pass some EMI testing, it is adviced to understand return current loops and use that knowledge while placing and routing.

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