To Pour, Or Not To Pour. That Is The Question

Pcb w o pour Pcb w pourI know there are plenty of times when a copper-pour ground or power plane is a good idea, sometimes even a requirement. But, is it always so? Take a simple embedded microcontroller board. It has a 20MHz clock speed. Nothing too dramatic. No big power drains anywhere. Just milliamps going here and there.

Does it still help? What about the "greenness" of it? If more of the copper is etched off, more metal will be recovered from the fab company's chemical vats. Or does the additional etch time and and acid required for clearing the board of copper outweigh the benefits of the additional recovered copper?

Looking at all of the boards we get through our assembly lines here, I can't really tell a general industry preference. It's hard to detect an internal plane visually and surface pours don't seem to be any more popular then the lack of them. So, I don't know what the world says.

Any thoughts on this? Anyone? Anyone?

Duane Benson
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Comments

When home-etching, I tend to use pours, simply because it conserves the etchant.

But that is purely a pragmatic reason, not electrical or scientific.

I tend to add them, but I have to admit it's for poor reasons: I find it aesthetically more pleasing, and it saves me from having to route all of the GND traces since the GND pour usually takes care it them all.

I always use a GND copper pour on both sides. Whe I'm done routing I add about 10-20 redundant vias in different places of the PCB, just to make sure that electrical connection is really good (reduces risk of ground noise.)

The other advantage of using GND pour is that you do not need to route the GND trace. Just leave it unrouted, the copper pour takes care of it.

Internal planes are usually easy to detect by just holding the board up to a light.

I tend to add pours, with large isolations. The greeness is a good question - how green is photoresist? Is it better than using etchant?

with no hard data, i feel like pours increase the chance of shorts. copper splatters have more to hit in this case

For some reason I assumed that pours were more "green", because the copper isn't "going to waste". But if you extract it from the solution and re-use it, I guess it's actually more green to get rid of it. Odd.

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