GROUND plane or nor GROUND plane

[xnihilo]

This is probably not the right place for this question bu maybe someone might want to share what he knows.
My project is 95% finished but I still don't know if I should include a ground plane on one or both sides of my PCB and if yes, what area it should cover...

[Bruce]

I always include a ground plane with the bottom layer solid copper, and each ground connection from the upper layer connected directly to the plane.

Attached is an example of an RF transmitter board. The lower layer is all copper connected to ground.

[xnihilo]

I see.
I have a ground plane on both top and bottom layer. Is that right or wrong, is there a reason why not have a ground plane also on the top layer?
I thought ground plane was used for reducing noise and acting as a heatsink.
I heard also about loops that can increase capacitance...?

[mackrackit]

I would avoid a ground plane on the top and bottom, you can make a capacitor if you have one on both sides of the PCB.

[aratti]

You can keep the ground plane on both sides providing that the electrical connection between the two grounds is done in one unique point.

Al.

[Bruce]

I've seen valid arguments for both, but it totally depends on what you have on the board,
and how you're connecting entry points to your ground plane.

In my own opinion, dual ground planes aren't necessary. Unless you're trying to save on the
cost of etching boards.

I've had over 40 boards FCC certified with only a single ground plane on the lower layer.

Edit: What AL said is good info. If you DO include a ground plane on both sides of your board
(make sure you have only 1 entry point from your power supply input) to both planes.

I.E. the ground from your power supply input connects to the entry point of the plane. There
should be NO ground traces to anywhere else on your PCB. Each IC should have a very short
trace directly to a "via" that connects directly to your ground plane. A 4-spoke thermal connection
point like the one in the attached graphic works extremely well - with single or dual planes.

[Ioannis]

To add something so you can be more dizzy now, if you do have Ground planes on both sides (especially at RF designs) then you MUST have vias all over the place! You can't have only a single point, though true for DC power supply, but for the RF case vias must be there at distances less than 10mm.

Ioannis

[Melanie]

I support Ioannis on this one... I put via's linking Ground planes on a 5mm grid spacing (at frequencies 50MHz to 2.5GHz) and at 3mm above that. Doesn't mean your circuit isn't going to work if you don't... just different approaches and points of view. You don't have to do this for your entire board... just the RF sections.

[duncan303]

There is a book I have which is a very usefull basis for helping to understand ground planes amonst other things. It is written in very simple language well worth having as a reference book.

Henry W. Ott. Noise Reduction Techniques in Electronic Systems . its old and should be in every college library, if not snap up a second hand copy will only cost you the price of a beer:D

Placement and sizeing of ground planes and vias can get quite fancy, especially with multilayer boards, You can't just slap one on either side, it can do much much more harm than good, on a simple double sided board one only has to consider problems created by orphans (areas isolated by components).

Take a look also at ground planes around external timing crystals and "rings" you may get some extra marks.

______

[Acetronics2]

Hi,

I ALWAYS use Ground planes ... reason is very simple :

it uses MUCH less perchlorate or persulfate for engraving ...

Surprised ???

Alain

[duncan303]

Hi,
it uses MUCH less perchlorate or persulfate for engraving ...
Alain

and therefore [b]much[b/] more plating solution....:D

[Acetronics2]

And ... as plating thickness is much less than copper thickness ...

in the End ...

Alain

[duncan303]

And ... as plating thickness is much less than copper thickness ...

in the End ...

Alain

in the End ... depends on copper um/cost of etchant vs plating um/cost of solution

AND.... shelf lives of each solutions.....:D :D



_____

[xnihilo]

It helped a lot :) Now I still don't know if my ground plane on the bottom side is fine or not (i removed the top layer ground plane). there's a program called EAGLE that creates the plane once you draw a polygon and name it like the ground on the board. Does it do it right or not? Hell if I know.

A snapshot of the boards (when there were still a ground plane on both layers)
http://users.edpnet.be/charlesetchristelle/squadtag/tango%20starter%20kit%20pcb.jpg

By the way: I'm not using any RF device and my pic runs at 8MHz, 5V.

[duncan303]

It helped a lot :) there's a program called EAGLE that creates the plane once you draw a polygon and name it like the ground on the board. Does it do it right or not? Hell if I know.



looking good.. well done :)
turn off all the layers that you do not need to see and just leave bottom layer, then use the address label to "SHOW" your signal (whatever you have called it) and see the signal track it will shine brightly as a highlight, you will then see if the ground plane is cohesive. Its all down to wether when you created the polygon you used the setting "orphans", difficult for me to see in the jpg at the moment(on a mini machine) wether this is the case.

You are better not to have orphans using a single ground plane , unless you are running out of ethcant :D

cadsoft.de have a dedicated newsgroup, there is a lot there and they are very helpfull

[Ioannis]

If you have 1 layer board then you dont put Ground Plane on the other side.

If you want fast etching then use as much as possible Ground Plane.

If you want to protect against EMI then use as much as possible Ground Plane.

If you have double sided PCB, then
If you want all the above then
use as much as possible Ground Plane.
Endif
Endif

If you have RF then use as much as possible as much (again) Ground Plane

If you have double sided PCB, then
If you want all the above then
use as much as possible Ground Plane and
connect with vias as many times as possible.
Endif
Endif


Conclusion:

Always use as much as possible Ground Plane!

Ioannis

[duncan303]

Good Post Ioannis....:D

______

[xnihilo]

looking good.. well done :)
turn off all the layers that you do not need to see and just leave bottom layer, then use the address label to "SHOW" your signal (whatever you have called it) and see the signal track it will shine brightly as a highlight, you will then see if the ground plane is cohesive. Its all down to wether when you created the polygon you used the setting "orphans", difficult for me to see in the jpg at the moment(on a mini machine) wether this is the case.

You are better not to have orphans using a single ground plane , unless you are running out of ethcant :D

cadsoft.de have a dedicated newsgroup, there is a lot there and they are very helpfull

Yes, thanks :)

[xnihilo]

If you want fast etching then use as much as possible Ground Plane.

"etching"???

If you have RF then use as much as possible as much (again) Ground Plane

No rf used.

Always use as much as possible Ground Plane!

Well, I think I'm safe, I'm using a nice GND plane on BOTTOM side.

Thanks.

[ralfmayr]

Always use as much as possible Ground Plane!
If you have only GND Plane at the Bottom, and you forget to connect top layer assembled SMT components with their ground pad to the bottom layer, than you have a problem later...
Best is always using GND Planes on top and bottom, reduces EMI, reduces the problem described above and it is more easy to use SMT components like QFN components with heatsink/gnd pad in the middle. You only need to make some more extra gnd vias along the board outlines, thats important not to get later some dirty effects (More important in rf layouts). Keep attention not to get isolated areas also!
Regards,
Ralf

[xnihilo]

Well, EAGLE cad automatically AUTOroutes the tracks so I guess this program does the job pretty well or should I check everything once it has autorouted the tracks?

[ralfmayr]

I don't know Eagle, we work with Zuken-Cadstar.
But i would never let the Autorouter doing the GND routing job!

[Bronurstomp]

I think what some of the older guys are talking about (And you know who you are) is "etching" your own PCB versus sending off the Gerber plots to a fab house and having a PCB done. Not many of us do that anymore, as having a PCB fabbed is pretty cheap compared to all the muss and fuss of having all those chemicals and having to cut the raw copper clad board IMHO.
Anyway, what I like to do on my PCBs is use the top and bottom layers as VCC and Ground reflowed polygons once the board is 100% routed. (I use Protel98, I'm just learning Eagle.)
That does 2 things:
1) you get some intergral capacitance on the VCC-Ground polygons, which you want for decoupling(Use .1uF around your chips anyway) purposes, and 2) it tends to balance out your copper across the whole board. If the copper is not balanced across the whole board, if you should ever want to do something like wave reflow of your board, the heat will curl your board up like a potato chip if the copper is heaver in one area. The temperature expansion coefficient of copper is much different that of the PCB material like FR4. It's more important the bigger your board gets.
Just try to be aware of isoloated islands if your using the polygons as connections to your power connector. Keep it in mind as you do your routing.
So after all that, to answer your question: Having a "ground Plane" on both the top and bottom won't hurt anything for your application, but it WILL make it harder to modify if you need to change it someday.

[mackrackit]

I think what some of the older guys are talking about (And you know who you are)
Hey, I resemble that!!! :D


is "etching" your own PCB versus sending off the Gerber plots to a fab house and having a PCB done. Not many of us do that anymore, as having a PCB fabbed is pretty cheap compared to all the muss and fuss of having all those chemicals and having to cut the raw copper clad board IMHO.
Having the ability to roll your own is great for prototyping or that one of a kind project. :)

[Ioannis]

If you want fast etching then use as much as possible Ground Plane.

"etching"???

If you have RF then use as much as possible as much (again) Ground Plane

No rf used.

Always use as much as possible Ground Plane!

Well, I think I'm safe, I'm using a nice GND plane on BOTTOM side.

Thanks.

OK, OK, I know. I am not fluent in English. Sorry.

Ioannis

[Archangel]

OK, OK, I know. I am not fluent in English. Sorry.

Ioannis I disagree, I think you are, "etching" is very likely the word I would have used, but then of course, I speak an American dialect of English, not exactly fish and chips. :D

Hey, I resemble that!!! :DAs do many of us !


Having the ability to <font color=blue><b>roll your own</b></font color> is great for prototyping or that one of a kind project. :)
More evidence of our generation ! BUT Yes, it sure does, and a heck of a lot cheaper!