Researching Ground Plane is giving me a headache!

Hi all,

I'm an electronics Noob with a project that I'm ready to move to PCB.

I have a working Breadboard and also stripboard version.

Simple question with what appears to be no simple answer that I can find:

With a 2 layer PCB with through hole components should I have a ground plane on:

a) The same layer as the majority of the signal traces b) The opposite layer c) Both.

My project is quite simple with the following major components:

  1. Arduino Pro Mini 5v
  2. DS3231 RTC (I2c)
  3. 1602 LCD
  4. 3xAAA batteries.
  5. Momentary switch.

I use PWM and a capacitor instead of a pot to control contrast of the LCD. I mention this in case it would be classed as a mixed signal (digital and analog) situation.

I have read a lot but it seam the more I read the more complicated this subject gets. I suspect that my project would (and indeed it appears to) work perfectly well without a ground plane. But I would like my design to be close to best practice where appropriate.

Any help or pointers anyone has would be great.

If you were making the board , sounds like you could get away with no ground plane and just use SS PCB material. Depending on the noise environment, the frequencies on the the board, digital and analog components and complexity are some of the reasons to use a ground plane. If you were going to a board shop, the cost of a ground plane is very small if any. Usually the ground plane is on the top/component side of a board, however, some consider free space on both sides should be GND. Also, more ground plane less etching ;)

Don't make the noob mistake of allowing solder connects directly on the ground plane. Allow thermal isolation from the connects to the plane, so you won't go nuts hand soldering it (or reworking it, if it is ovened).

A mistake that many people who should know better, make.

Thermal relief.
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LarryD: Thermal relief. .

Language.

:art:

Thermal relief

LarryD: If you were making the board , sounds like you could get away with no ground plane and just use SS PCB material. Depending on the noise environment, the frequencies on the the board, digital and analog components and complexity are some of the reasons to use a ground plane. If you were going to a board shop, the cost of a ground plane is very small if any. Usually the ground plane is on the top/component side of a board, however, some consider free space on both sides should be GND. Also, more ground plane less etching ;)

Thanks.

I'll be getting the board produced by Elecrow, ITEAD or Sead.

I'd come across Thermal relief before and it looks like Fritzing provides thermal relief as standard on ground fill connections so I have that covered already.

It was my initial thinking to put a ground plane on the top/component layer as I can probably get away with only one or two small traces on the top layer giving a pretty much uninterrupted ground plane.

I keep coming across posts mentioning "high frequency" or "High speed" signals with regard to ground planes but no indication of what type of signal would be classed as such.

I think that most of the posts and articles that I'm reading refer to much more complex circuits than I'm likely to produce but I haven't found any simple 2 layer circuit examples/tutorials using ground planes.

High speed = modern CMOS logic (2 to 10ns rise times), or RF circuitry, or video.

For the logic signals that means of the order of 10^9 volts/second rates of change of voltage, which means stray capacitance and inductance become very important.

For RF circuitry you have gain at high frequencies, and the groundplane is the way to control the possible feedback paths by linking everything capacitively to ground, reducing unintended couplings between input and outputs of amplification blocks. You also find circuitry in metal boxes at RF to really prevent signal leakage between blocks.

One of the reasons a ground plane is good for logic signals is that the return path for a signal will follow any nearby wiring - another signal perhaps, so provide a groundplane to provide return paths for all signals - less cross-talk.

A ground plane also helps with electrostatic shielding, even for low frequency signals, and even though one side is exposed.

More important (not that one is more or less) always include decoupling/bypass capacitors in your circuit. https://en.wikipedia.org/wiki/Decoupling_capacitor https://en.wikipedia.org/wiki/Ground_plane

Don't forget: mounting holes, indicator LEDs, test points (including a ground terminal for testing), power and off board signal terminals, trace width requirement, component spacing, large enough pad sizes, heat sink areas, jumper options and maybe an area for unforeseen component additions. I am sure there are more. ;).

Watch out for component to chassis clearance.

If you think you might have to do some mods to your circuit afterwards, it's easier to cut and jumper when there's no ground plane. For what you are doing, electrically, it doesn't really matter whether you have one or not.

All of the non trace is etched away, so I do ground planes on most designs, so there is less copper dissolved away into god-knows-where. Greener.

If you think you might have to do some mods to your circuit afterwards, it’s easier to cut and jumper when there’s no ground plane.

You can also do this:

http://forum.arduino.cc/index.php?topic=346333.msg2387826#msg2387826

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