DIY PCB Copper Pour Questions

[otm]

Hi Guys,

Simple question really...

I am making a dual layer PCB (designspark) and I'm at the final stages, and want to add a ground plane, mainly to save copper so etching is quicker!

Is it OK to put a Ground pour on both sides of the board? I have a mix of SMD and through-hole, but I shouldn't think that makes a difference.

I'm not sure why I am second guessing myself..

Thanks for your help!

Owen.

 

[jpanhalt]

It is absolutely OK -- probably even preferred -- to put copper pour(s) on both sides of the board. Not all copper pours need to be ground. In fact, I will put several pours on the same side of a board. Each one can be a different signal.

What CAD program are you using?

John

 

[ronsimpson]

With through hole, most ground leads will connect the top ground to the bottom ground so they are the same.
With SMT it is harder to automatically connect top and bottom. Use many VIAs from ground to ground.

 

[otm]

Im Using DesignSpark (By RS components), I really like the model source library system which i find helps as I cant always be bothered to make new schematic symbols!

I do have a some vias, but luckily the through hole parts also act as vias which are being used to connect top and bottom Copper.

Just a thought how do PCB designers cope with Capacitance created on signal planes/tracks when using both Ground and power planes (multi layer boards)?


Owen.

 

[jpanhalt]

Sorry, I saw "designspark," but was thinking of SparkFun. I am not familiar with that piece of software per se, but I suspect you make a polygon around the area of the pour, assign it a rank along with setting some other variables, name it, and then pour. You can have overlapping polygons and use different ranks. That is a powerful tool. Thus, your power net and ground net can generally be taken care of with pours, but with different ranks, on the same side. As Ron says, if you are using through hole devices, connecting pours on different sides is not really a problem. For DIY, it is also easy to add your own vias, and just use a wire soldered to both sides.

John

 

[ronsimpson]

how do PCB designers cope with Capacitance created on signal planes/tracks when using both Ground and power planes (multi layer boards)?

Most of the time signals are slow enough that capacitance is not a problem. At RF and USB and DVI you make transmission lines where the L and C are known.
You can make the signal line thin to reduce the capacitance. Keep it short.
I often have a ground and power plane on the outside layers and the signals are on the inside layers. The power plains act as a shield, or box, to keep the noise from getting out.

 

[otm]

I often have a ground and power plane on the outside layers and the signals are on the inside layers. The power plains act as a shield, or box, to keep the noise from getting out.

Thats a neat idea

I must admit, I don't know why I second guessed myself...

Thanks you sooo much for your answers!

Owen.

 

[ronsimpson]

Ground/power top/bottom is good for through hole. It is harder for SMT.
For SMT there are not leads going through the board so putting the grounds and power inside is better. Signals go from part to part with out a via and "local ground" is with the parts but connects to the ground plain with vias. (example: the power supply cap connects from power pin of the IC to ground pin on the top side. All other grounds for that part connect to that ground. Some where near the ground pin there will be a good connection to the ground plain.

 

[DerStrom8]

Just a thought how do PCB designers cope with Capacitance created on signal planes/tracks when using both Ground and power planes (multi layer boards)?

If the top and bottom pours are on the same net (i.e. both are ground), you shouldn't have to worry too much about capacitance.

 

[William Salinas]

I use maximum amount of copper on every layer, because it minimizes the rate of using up etchant. If your volumes are not extremely high, it doesn't really make sense for you as the designer to worry about this.