How to get a proper PCB ground pour?

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kk6gm
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Posted by kk6gm: Mon. Aug 25, 2014 - 10:34 PM
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OK, I'm really a software guy, but I dabble in some hardware design. One of the problems I often have is how to create a fully-connected ground pour on both sides of a 2-sided PCB. After configuring the pour to cover all of the top or bottom (less a little bit at the board edges), and after routing, when the pours are done I always get islands that are not connected. I generally fiddle with vias at this point to connect top and bottom regions until everything is connected, but it all feels very haphazard.

Perhaps I'm going about this all wrong, I wouldn't be surprised. How do you folks get a good ground pour on both sides of a PCB and with no isolated islands (really, with no isolated islands to which a ground connection has been made, e.g. an IC ground pin)? Thanks for any tips.

BTW, I'm using EasyPC v17.

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Learning and Information, General Electronics
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ka7ehk
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Posted by ka7ehk: Mon. Aug 25, 2014 - 11:56 PM
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On EAGLE, you draw a polygon on either side of the board, then assign it to one of the nets. Its usually ground on my boards but you could have a ground pour on one side and Vcc pour on the other.

As far as connected-ness, you need to insure that there is enough space for the pour fill to flow everywhere that it is needed., In EAGLE, that means setting an appropriate minimum spacing between conductors as that governs which spaces are too small.

Hope this helps
Jim

 

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valusoft
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Posted by valusoft: Tue. Aug 26, 2014 - 12:28 AM
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I don't think that the actual cad package used matters all that much. For what it is worth (information-wise), I use Eagle. And... I don't know that there is a strict rule governing the approach to be taken either. I would like to know it if there is. But... this is what I do. Laugh and discard as you wish.

- consider the natural flow of the signals: I usually draw my schematics from the left/input to the right/output taking into account any physical component placement requirements (eg, front panel layout)

- create the pcb external dimensions shape (usually rectangular) and place the mounting holes to suit the case (I have a number of cases that I use routinely and just reuse the result of this step)

- establish a ground plane polygon on both top and bottom sides of the board. (I almost always do a double sided design and minimise the amount of copper to be removed when I do a first etch prototype here)

- drag/drop any components that MUST be in particular positions (eg connectors on an edge, or encoders to match a front panel design)

- drag/drop remaining components to follow the left to right "rule"

- then I run the auto router just to see if the initial placement produces a 100% completion result. I NEVER use the auto router otherwise; always do manual routing myself. This will show breaks or islands in the ground planes.

- reposition parts to simplify/shorten trace lengths, reconnect ground planes and ease assembly. Having a "push & shove" capability is invaluable at this stage; I don't. :sad: Maybe run auto router again to complete the unrouted traces.

- rinse and repeat.

The board below was done using this method. Input on the left, output on the right. Daughter board top left. Four mounting holes in the corners. Central hole for a small cable tie to hold a battery that sits over the major blank area of the board. The component placement had to "flow" around the battery and under the daughter board.

Hope that helps.

Cheers,

Ross

Ross McKenzie, Melbourne Australia

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Bronze Markjs
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Posted by js: Tue. Aug 26, 2014 - 12:54 AM
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The package I use works best with a netlist from the schematic even though you can assign any copper pour to any net.

So draw a polygon, as other have said, assign it to a net and let the software do it for you. I have standard clearance of 20mils and track thickness of 10 mils but they can also be changed. The board below has several copper pours assigned to different nets, mostly GND.

Remember to remove isolated islands and stay away from the edges of the board by 25mils or more.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Torby
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Posted by Torby: Tue. Aug 26, 2014 - 01:59 AM
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Yea. I use freepcb. If I just put a copper area over the whole works, I get little bits of ground plane pinched off by traces. I don't know how harmful these are, but I can usually move vias enough to get them to connect. Unfortunately, freepcb won't show you where they're pinched off so I have to export to gerber files and use something like viewmate to examine the gerber looking for pinched places.

Maybe it's time I started using a big boy's layout program.

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mikech
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Posted by mikech: Tue. Aug 26, 2014 - 02:18 AM
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Altium (DXP or whatever they call it this year) lets you remove islands that are less than a specified area.

Does it really matter if there are isolated regions ?
I belong to the 'leave as much copper as possible' group.

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Bronze Markjs
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Posted by js: Tue. Aug 26, 2014 - 02:22 AM
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The package I use has a check box which tells it to remove (or not) isolated islands.

The possible problem with isolated island of copper is that they become little noise antennas and can help to spread noise to other parts of you circuit.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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kk6gm
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Posted by kk6gm: Tue. Aug 26, 2014 - 05:25 AM
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mikech wrote:
Altium (DXP or whatever they call it this year) lets you remove islands that are less than a specified area.

Does it really matter if there are isolated regions ?
I belong to the 'leave as much copper as possible' group.


Yeah, I don't mind leaving those alone. The problem is if an actual ground pin (IC or other component) connects to that little island, thinking that it has connected to ground, but of course it hasn't. Often this can be fixed with a via to the GND pour on the other side of the board, but as I said, it feels like a haphazard approach. And yet, with a little back and forth it does work. I was just wondering if there's some magical approach that I missed the memo on.

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ignoramus
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Posted by ignoramus: Tue. Aug 26, 2014 - 08:31 AM
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Run DRC check on allegedly finished board.
Look for open circuits in the form of partially routed nets.

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Torby
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Posted by Torby: Tue. Aug 26, 2014 - 11:33 AM
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js wrote:
The package I use has a check box which tells it to remove (or not) isolated islands.

The possible problem with isolated island of copper is that they become little noise antennas and can help to spread noise to other parts of you circuit.

So tell us what this miraculous package is!

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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kk6gm
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Posted by kk6gm: Tue. Aug 26, 2014 - 07:17 PM
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ignoramus wrote:
Run DRC check on allegedly finished board.
Look for open circuits in the form of partially routed nets.

Yes, this is how I find the islands that need to be connected, and connect them with a via if possible to a valid ground pour on the other side of the board.

Sometimes I need to run an explicit trace from the problematic component pin to a pin that I know will be connected to the ground pour (one that is "out of the clutter" so to speak), because there's no pour on the other side of the board to via to.

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Bronze Markjs
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Posted by js: Tue. Aug 26, 2014 - 09:36 PM
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Quote:
So tell us what this miraculous package is!
https://www.avrfreaks.net/index.p...

Unfortunately the author seems to have to greener pasture! The link there no longer works but it seems you can still buy the package from a Polish site. http://www.rimu.pl/hs/rimuuk.html

Don't know if the "support" is as bad as it was but the package works very well as long as the nut behind the keyboard doesn't get loose..... I have both schematic and pcb packages.

DocJC has the PCB package, I know he hates me now :lol: I can feel all those voodoo pins sticking into me...

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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kk6gm
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Posted by kk6gm: Tue. Aug 26, 2014 - 11:08 PM
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Torby wrote:
js wrote:
The package I use has a check box which tells it to remove (or not) isolated islands.

The possible problem with isolated island of copper is that they become little noise antennas and can help to spread noise to other parts of you circuit.

So tell us what this miraculous package is!


Just FYI, EasyPC lets you remove them or hilight them.

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Bronze Markjs
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Posted by js: Tue. Aug 26, 2014 - 11:32 PM
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Quote:
EasyPC
I have a demo version of it, one of my clients had the full package. It was pretty expensive from memory but very good.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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DocJC
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Posted by DocJC: Wed. Aug 27, 2014 - 01:14 AM
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Quote:
DocJC has the PCB package, I know he hates me now Laughing I can feel all those voodoo pins sticking into me...

Yup. Rimu has replaced ExpressPCB.

If I have time I can sent the Gerber files off to China for a very low price. Nice when it is a hobby project and not billed to an account.

I miss not being able to nudge a trace a smidgeon.

I did a large copy paste and I think it dropped the small ground plane under the Xtal, also. I had to try the copy / paste a few times, as I think there must be a limit on how many items it can hold in its list to transfer.

Still, I like it. It meets my needs.

JC

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kk6gm
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Posted by kk6gm: Wed. Aug 27, 2014 - 01:14 AM
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js wrote:
Quote:
EasyPC
I have a demo version of it, one of my clients had the full package. It was pretty expensive from memory but very good.

I've been using the 1000 pin limited version and that is $477.

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Bronze Markjs
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Posted by js: Wed. Aug 27, 2014 - 01:19 AM
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They had the full package, something like 2,300 POUNDS I think.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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fingar
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Posted by fingar: Wed. Aug 27, 2014 - 07:19 AM
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In Easy PC when you pour the copper there is a check box where you tick " Remove Isolated Islands"

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stevech
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Posted by stevech: Wed. Aug 27, 2014 - 08:17 PM
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software I used failed to detect/warn about copper islands.

In the fab, the isolation occurred whereas on the screen it was close but passed DRC. Took me quite a while to troubleshoot why the board didn't work right, then add one jumper.

lesson learned: don't cut it close.

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