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I'm designing a simple PCB for GPS signal control. The frequency is below 5Hz, supply voltage is 9V and converted to 5V. This print will be screwed in a plastic housing with four M3 mounting holes at the corner which can be see in the picture. I have tried to route most of the trace on the Top signal layer.

My question is:

  1. Is it a good idea to pour the entire bottom layer as GND? Or it can be on the Top layer too?

  2. Should I connect the GND pour with the mounting holes? I saw a term called Chassis Grounding which makes use of screw for external grounding connection. I don't really understand this technique clearly, so I would like to have some advice on it.

Thank you!

Top Layer

Top layer

Bottom Layer with GND pour

Bottom layer

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  • \$\begingroup\$ I'm far from an expert, but what I saw so far, it's normally a good idea to use one layer for GND, typically the lower layer, and also use the unused (big) areas of the upper layer as GND and connect them with enough vias (connections). I don't see any reason to connect GND to the screws since plastic does not pass electricity. But I upvote your question to learn some more about what pros have to say about it. \$\endgroup\$ – Michel Keijzers Sep 18 '19 at 10:50
  • \$\begingroup\$ Take a look at any old floppy or CD PCB and tell me if you see a gnd plane. What is the highest impedance and smallest signal. \$\endgroup\$ – Tony Stewart EE75 Sep 18 '19 at 11:12
  • \$\begingroup\$ The max control signal BW is not the rep. Rate but rather the 0.35/risetime. With low impedance logic their is not much current or EMI to worry about interference with GHZ GPS so grounding is not an issue. What may be an issue however is the CM ripple from any SMPS that supplies power to the control signal interface. Thus this needs to be defined. \$\endgroup\$ – Tony Stewart EE75 Sep 18 '19 at 14:05
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Is it a good idea to pour the entire bottom layer as GND? Or it can be on the Top layer too?

It's usually a good idea to fully pour the bottom layer and, you can optionally try to flood the top layer too and connect it to the bottom full pour with vias every centimetre or inch (not critical on this design by the sounds of it).

I would also suggest you apply at least a 20 thou (mil) clearance to the flood so that it doesn't encroach to closely with the top copper tracks. Most PCB tools allow you to set this up.

Power tracks should be appropriately thick and it might be worth adding decoupling capacitors in a few places (your call because I can only guess what interconnections you have).

I'd also add a few test pads so that if needed, you can probe on various nodes.

Should I connect the GND pour with the mounting holes?

I'd use an 0603 resistor to connect each mounting hole to the ground plane then you have the option of both scenarios. There usually isn't a best-answer that suits all scenarios on this question.

Add a silk screen with written details and rev number on and I think you are good to go.

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