Copper pour for dummies 101

[wblackledg]

Can somebody explain to me why or if I would want a copper pour on a simple circuit for a pcb board?

lets say a crystal radio pcb. something simple (that I understand, somewhat..  )

why have copper all over the board instead of on just the holes and the traces that connect the holes?

I must be missing something... 

thanks.

[T3sl4co1l]

Because, at higher frequencies, the flow of current in the conductor is almost immaterial, as much of the energy flows in the space around the conductor instead.  This space needs to be constrained (by pouring ground around the traces) to achieve consistent and useful transmission line impedances, and prevent the energy from crossing into every other single conductor on the board, and outside the board (radiated emissions).

Even at DC, you might still want the increased coverage due to costs (less etching to do -- however, less copper to recover from the etchant, so if this vanishingly small difference comes up in your cost analysis when it's time to order a million boards... maybe look into it), slightly improved strength and stiffness (especially for heavier boards), and much improved thermal conductivity (good for dissipating power on SMT designs, even when the copper isn't directly connected to the hot parts).

Although it helps to have a copper pour, it helps even more to stitch the copper.  Just because the copper is connected, through some roundabout path, back to ground, doesn't mean that any given point is locally grounded -- traces and pours exhibit inductance at higher frequencies.  Shorting across all of those paths, by pouring the top and bottom sides, and stitching with vias, is the best way to ensure solid performance.  A board made in this way can be almost as good as one with internal ground layers!

Tim

[wblackledg]

Because, at higher frequencies, the flow of current in the conductor is almost immaterial, as much of the energy flows in the space around the conductor instead.  This space needs to be constrained (by pouring ground around the traces) to achieve consistent and useful transmission line impedances, and prevent the energy from crossing into every other single conductor on the board, and outside the board (radiated emissions).

Even at DC, you might still want the increased coverage due to costs (less etching to do -- however, less copper to recover from the etchant, so if this vanishingly small difference comes up in your cost analysis when it's time to order a million boards... maybe look into it), slightly improved strength and stiffness (especially for heavier boards), and much improved thermal conductivity (good for dissipating power on SMT designs, even when the copper isn't directly connected to the hot parts).

Although it helps to have a copper pour, it helps even more to stitch the copper.  Just because the copper is connected, through some roundabout path, back to ground, doesn't mean that any given point is locally grounded -- traces and pours exhibit inductance at higher frequencies.  Shorting across all of those paths, by pouring the top and bottom sides, and stitching with vias, is the best way to ensure solid performance.  A board made in this way can be almost as good as one with internal ground layers!

Tim

thanks Tim.
I think I got now.  As you might have guessed I'm far from making a board. I'm just trying to understand the process as a hobbyist.

[tautech]

Incorporating a pour can also influence you layout.
Orientation of components in a way that make for easy connections to a GND pour.
In the Pour settings, you will need to specify the Net the pour is connected to.
You might not route the GND, the software will know to connect to the appropriate GND pins on components.

Be prepared to experiment, pour, un-pour, shift/rotate components, pour again and so on.

As Tim has explained, other than a better circuit the main advantage for hobbyists is the reduced amount of copper removed and etchant lasting longer. 

[TSL]

And if your going to pour to a net be sure to add "thermals" around those connections or you will have to put more heat than you want on them to get solder to flow.

"Thermals" are a stepping out the pad from the pour with 3 or 4 bridges connecting it to the pour. Since there is only small tracks connecting it to the pour the pad doesn't go cold as quickly with all that copper connected to it thus allowing you to solder your part without too much heat.

regards

Tim