Couple of PCB copper pour questions

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kk6gm
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Posted by kk6gm: Fri. Jul 29, 2011 - 02:58 PM
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I'm a software guy but I do an occasional PCB design as well. I'm doing a 2-sided 6" x 6" design now that will be sparsely populated (more connectors than anything else, something of a motherboard that will connect some digital modules). My questions are about copper pours.

1) What is the advantage, if any, of using a cross-hatched pour over a solid pour?

2) On a 2-sided design, is it better to pour a ground plane on both sides, or to pour ground on one side and Vcc on the other?

EDIT:
3) If you're planning to pour a ground plane, what do you do about routing the ground net? The issue here is that in the normal sequence, you'll route the board and presumably your ground net will be fairly wide traces, which take up room that other traces could use. Then you pour a ground plane which makes those wide traces irrelevant, at least on the side where the plane is, and it would have been better to make them thin or not route them at all. Is there a common approach to this inefficiency?

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Learning and Information, General Electronics
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ka7ehk
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Posted by ka7ehk: Fri. Jul 29, 2011 - 03:21 PM
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I have always been puzzled about the cross-hatched pour. There may be fewer thermal (soldering) problems if you don't have thermal reliefs. I've never felt a compelling reason to use the hatched pour.

I tend to do Vcc on one side and ground on the other, but, I'm generally pretty pragmatic about the whole thing. Some circuits esp switch-mode power supplies require a degree of paranoia about grounding, (also audio and video) but generally, its not THAT big a deal. Important, yes, but the big thing is just having a good ground.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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leon_heller
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Posted by leon_heller: Fri. Jul 29, 2011 - 04:28 PM
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I used to use cross-hatched copper pour with my home-made PCBs when I used a laser printer for the artwork, as laser printers don't work very very well with large black areas. Now that I use an inkjet, I use the ordinary copper pour if it's required. Most of the time it isn't necessary.

Cross-hatching is advantageous for large-scale PCB production as it uses less expensive copper, which can be reclaimed from the spent etchant.

I don't route the ground or power nets if I'm using copper pour, the software automatically connects everything that it can. If any pins aren't connected, I move things around and modify the routing until they are connected.

Leon Heller G1HSM

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ganeshskandha
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Posted by ganeshskandha: Fri. Jul 29, 2011 - 06:37 PM
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Ground planes helps you to reduce noise. It also helps in heat dissipation.. The larger and continuous the ground plane the better.
If you have some analog components you should have separate ground for analog and digital circuits..

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leon_heller
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Posted by leon_heller: Fri. Jul 29, 2011 - 07:00 PM
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You seem to be confusing a ground plane with copper pour, they are quite different.

Leon Heller G1HSM

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Someguy22
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Posted by Someguy22: Fri. Jul 29, 2011 - 08:33 PM
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Cross hatching prevents uneven etching during production and board warping after production.

Google: "pcb warping, uneven copper"

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frankvh
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Posted by frankvh: Sat. Jul 30, 2011 - 02:52 AM
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My 2 cents:

1) None that I've personally experienced. I use solid pours and planes on all my PCBs.

2) I like to route VCC with traces (as thick as is appropriate for their needs), and pour ground top and bottom (and internal layers as well in the case of a multilayer layer board).

3) I don't generally route the gnd net - that remains as a ratsnest until the ground pours are done. Then I look at the pours (either in the PCB program or in the gerbers) to check for problem areas, ie, areas where components or vias may break up the gnd pours resulting in less-than-desired gnd connectivity (or even a complete break in the gnd). Also, I scatter plenty of gnd vias around the board to firmly connect the ground pours top and bottom.

http://www.frankvh.com

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kk6gm
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Posted by kk6gm: Sat. Jul 30, 2011 - 09:28 PM
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frankvh wrote:

2) I like to route VCC with traces (as thick as is appropriate for their needs), and pour ground top and bottom (and internal layers as well in the case of a multilayer layer board).

3) I don't generally route the gnd net - that remains as a ratsnest until the ground pours are done. Then I look at the pours (either in the PCB program or in the gerbers) to check for problem areas, ie, areas where components or vias may break up the gnd pours resulting in less-than-desired gnd connectivity (or even a complete break in the gnd). Also, I scatter plenty of gnd vias around the board to firmly connect the ground pours top and bottom.


I have to say that this is my inclination too. By pouring ground both top and bottom I'm more likely to get all the ground pins connected to a low-impedance ground without extra fuss. But I'll play with both approaches and see what comes out better.

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alank2
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Posted by alank2: Sun. Jul 31, 2011 - 01:27 AM
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Hi,

frankvh wrote:
My 2 cents:

1) None that I've personally experienced. I use solid pours and planes on all my PCBs.

2) I like to route VCC with traces (as thick as is appropriate for their needs), and pour ground top and bottom (and internal layers as well in the case of a multilayer layer board).

3) I don't generally route the gnd net - that remains as a ratsnest until the ground pours are done. Then I look at the pours (either in the PCB program or in the gerbers) to check for problem areas, ie, areas where components or vias may break up the gnd pours resulting in less-than-desired gnd connectivity (or even a complete break in the gnd). Also, I scatter plenty of gnd vias around the board to firmly connect the ground pours top and bottom.

This is what I do as well.

Thanks,

Alan

Autoprogrammer:

https://www.avrfreaks.net/forum/wts-standalone-pdiisp-auto-programmers

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