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copper pour on pwr and gnd plane

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deba_fire

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Hi Everyone,

I am designing a 4-layer PCB and have finished the routing stage.Now for better performance I have poured copper on top and bot routing layers.But when I pour copper on power(attach it to pwr) and on ground plane(attach it to gnd) I don't see the copper pour as I see it in top and bot layers.

Please someone help how to pour copper on split power and ground plane so that it beocmes visible in orcad layout.

Regards
DB
 

Are the inner layers positive (signal) or negative (power) layers?
Layer names of power and gnd would normally suggest they are negative.
 
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My layer stack is signal-->gnd-->pwr-->signal.My inner layers are negative.But when I draw a obstacle on the the negative layers and pour copper I am not able to see it in the layout window like what I see for the signal layers all filled up.
 

If the inner layers are negative, your question isn't quite understandable. You say, you want to draw a copper pour attached to the same net that's assigned to the power plane. That seems useless, because the power plane is already filled up with copper connected to this net. A different thing would be to draw polygons that define a cutout, or a power plane region connected to a different net. I don't know how these entities have to be defined in Orcad (I guess you're referring to Layout Plus?), but they are supported by most layout tools.
 
Yes my inner layers are negative(plane layers) and I have attached appropriate nets also to them.If I understand correctly you are saying that if any layer is defined as negative layer and then there is no need to pour copper on that layer.Yes I agree to your point but if its true then layout plus should show the copper filled area.I am not able to see that in the layout plus.I see just blank black screen with thermals around.How should I enable some setting which will show copper on the plane layer?
 

I don't use Orcad but if a layer is defined as negative (which power planes usually are) then you will not see copper - you will see the layer where the is NO copper. What you are seeing sounds correct. A report of unconnected nets should tell you that it is all connected.

Keith
 
Yes, it sounds like normal apearance of a power plane. The final proof will be a correct gerber output. It should consist of the antipads, possibly thermal relief and a thick board outline as a boundary.
 
Ok so it means if any layer is defined as plane(negative) then we will not see any visible copper on the screen.We will see copper only for positive(signal) layers only.I have competed the full layout and there are no unconnected nets.Its fully routed and on negative layers I can see thermal reliefs.
But I have one more question,I have power plane cuts.I have defined a copper pour area in power plane for a different net.I can see the obstacles in the power plane.And I can see the thermal around those particular nets.But how should I make sure there is copper??or it is just visible thermals in a negative layer make sure its a copper area.If I generate gerber will it make sure there is copper?
 

The basic point is to follow the method for creation of power plane sections, that is suggested in the tools manual. I don't know how it works with Orcad. But as I said, I would always check the the gerber output. It clearly shows the real design output.
 

Hi FvM,

Yes I have followed all the guidelines for split planes.But does orcad or any other layout tool gives any indication that copper is there on the plane layers?Like filled with some color or something like that??What I see is a complete black background and boundaries for my copper pours and respective thermals etc.Is it a standard that plane(negative layers) should have black background??
 

Yes, I use Eagle and that's exactly what power planes look like. If you prefer you can define them as signal layers then copper pour the plane. Then the layer will be a positive and you will be able to see it.

Keith
 
Thanks Keith and FvM I will get used to seeing planes as black background.As during manufacture they will be copper anyways.I will change my thinking style.
 

I would use positive planes, negative were only due to the limitations of early CAD and computer systems. You will get less errors with positive layers, especially when multiple voltages on a plane. Plus you can see what the plane looks like.
Last neg plane about 1990.
 

I would use positive planes, negative were only due to the limitations of early CAD and computer systems.
Click to expand...
It may be an easy way to create mixed power and signal planes without the need for combining two gerber files (positive and negative) assigned to one layer. But I see more limitations then possible benefit with most layout systems.
 

Sorry but I totaly disagree, positive copper pours for planes have been the norm since the 1990's.
Positive planes give you WYSWYG, DRC checking, True Connectivity, etc, you can split planes properly
I'd be interested in what the disagvantages are, as I dont actually know anyone these days that doe use negative planes.
 

I would like to here some opinions about this matter. I must confess, that I'm not aware of the features of all layout tools in this regard. If a tool can achieve anything on positive power planes, including auto routing of power wiring, I'll follow your view.
 

Negative power planes are the norm for most tools. They work fine and the DRC works fine. I cannot see any reason to avoid using them. I don't see how ""positive copper pours for planes have been the norm since the 1990's" when every CAD package I have used uses negative layers for plane layers. The only time I use copper pours are when I have multiple split planes in the same layer when it becomes easier to see what is going on with positive layers. Negative layers for power planes are simply "set & forget". Very easy.

Keith.
 

OK so in summary there are tools which show filled areas on plane layers.But as FvM and Keith told negative layers are just fine and they don't give DRC errors also.At the end I think it boils down to comfortableness of the guy using the software.
 

You dont have proper DRC with negative planes, All designers I know these days use positive planes for power planes due to the fact you can control the coipper much better. I dont kow what packages you have used but ALL packages I have used give you the choice. And with most boards these days you have more than one voltage, quite a lot more. In the days when all you had was mainly 5V, no problem. But today you want to avoid power plane slots, you quite often want to suppress inner layer pads on vias etc, avoid isolated copper and you can see what you are getting.
 

I have never used a negative plane, I never needed them.

I have used loads of positive ones though, I can control my positive poured planes extremely well, see exactly what I am getting and where I need to make changes (because I can see it).
They DRC fine, enable me to connect to them easily and see exactly where I need to pay attention to ensure maximum copper when I use
split planes etc.

However - its all down to an individual engineer how he (or she even) wants to use his CAD software, some of us do things certain ways because we have always done it
that way and the thought of changing methods is frowned upon. :)
 
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