when is a ground plane neccesary and when is it detrimental?

Usually when I make a pcb I always have a ground plane throughout the whole board, but my next project is working with higher frequencies maybe just under 1Mhz, and I know the ground plane basically works like a capacitor at that frequency so would put a draw on those fast frequencies, but without it I imagine it would cause more interference right? Is it best to just leave it out under the high frequency traces or to have it no matter what? Or something else? The datasheet for the ic(hip4081a) doesn't mention anthing other than the bootstrap capacitor placement and nothing about ground planes

http://www.elmac.co.uk/pdfs/Lord_of_the_board.pdf

higher frequencies maybe just under 1Mhz,

There is nothing remotely high about 1MHz. Capacitance on a ground plane are negligible at these frequencies.

Use the biggest ground plane you can support with board size and component spacing. Ground plane capacity and transmission line effects don't come in to play until you are handling 1. Long high speed (> 50 Mhz) clock, serial data and parallel data. 2. you are working with controlled impedance or higher power RF devices (>100 mW & 50 Mhz). Use trace width's as wide as possible ESPECIALLY for Vcc. Unless you are building a really high density board small traces are more expensive to produce than narrow (they are easier to silk screen and screening last time I checked was cheaper to produce than Photographic techniques especially in smaller batches although that information may well be out of date as the industry was in the process of changing when I retired. There is NO advantage really from an electronic sense to use small width's except for clearance between IC and component pads and it is a poor idea to route wires between the pads of a component.

Doc

That article is a well written and valuable piece of knowledge but nearly worthless except the comment about"Lord of the Board" at 10's to 100's of kilohertz the ONLY thing that is applicable is pulse Rise time and for anything that could be done with an Arduino Never an issue as that is a frequency related thing. There is Nothing on or connected to an arduino that could benefit from a few nS less rise time except RF stuff and that type of PC design is a whole different world. The clock period is 62.5 nS (1/16,000,000) or 0.0000000625 S and although that number is rather small you won't see anything nearly that fast by several orders of magnitude.

Doc

Oh ok, for me 1Mhz is pretty fast, I guess just because I've never had to do anything remotely as fast so definetly safe doing the usual?

for me 1Mhz is pretty fast, I guess just because I've never had to do anything remotely as fast

Arduino is clocked at 16MHz.

Lol I know, but I've never had to route traces that are going at that speed lol

Oh ok, for me 1Mhz is pretty fast, I guess just because I've never had to do anything remotely as fast so definetly safe doing the usual?

Yes.

Doc

Thanks for the replies, much appreciated

I know the ground plane basically works like a capacitor at that frequency so would put a draw on those fast frequencies

Actually the way to get capacitance is with lots of bypass capacitors at critical positions, eg, on v.reg and microcontroller Vdd pins.

Personally, I think the "Lord of the Board" pdf provides a lot of very useful basic information, for use as a guideline for pcb layout.

The most pertinent comment as regards ground planes is "Keeping the signal and 0V paths adjacent along their length – and therefore maximizing their mutual inductance – will ensure not only minimum coupling with the magnetic fields around the PCB, but also minimum impedance of the return path and therefore minimum noise voltage developed along it. This will keep down the “noisiness” of the whole board, which is mostly what is responsible for common mode RF emissions".

The critical word in the quote is "adjacent", and the good and bad situations are adequately shown in Fig 2. The ground plane maximizes the "paths adjacent" effect and minimizes loop-inductance which leads to EMI generation. That's the primary purpose.

On typical microcontroller bds like Arduino, most signals aren't going to be fast enough to generate a huge amount fo EMI, I think, except possibly for the crystal connections, so you need to keep those traces as short as possible. On my pcbs, I put a ground trace "island" around the crystal layout and separate it from the rest of the grounds.

You might also go to microchip.com and download pdf file "Analog and Interface Guide Volume 1".