Re: gEDA-user: gPCB Polygon Best Practices

[DJ Delorie <dj@xxxxxxxxxxx>]

> Tips like this really help cut down the learning curve.

The curve would be shorter if it just didn't do that, of course.

> So if I'm understanding this correctly let me re-summarize, inserting a 
> few more questions as we go.  The actual number of manufactured layers 
> is determined by the number of groups in use.

Mostly.  Actually, it's determined by how many of those groups you
send to the FAB :-) For example, I might add a few groups (as
individual layers) for other purposes, then just omit those files when
I send them off.

PCB produces one gerber (CAM) file per layer group.  It's up to you to
send the right ones to the fab.

> The buttons labeled "layers" in PCB is actually associated copper.

Think "drawing layers".  A layer group is the closest analog to
"copper layer".

> Each group of copper ["drawing layer"] be assigned different colors
> to help visualize the purpose of each set.

Yes.

> How do you communicate to the board house which group(manufactured
> layer) is the top or layer 1(top), 2,3, bottom? Perhaps it's not so
> much that there is a top an bottom as it is which copper is grouped
> with each other.

In nearly all cases, you have to tell them which is which via a README
or a web form.  When you export gerbers, it names the component-side
one and the solder-side ones appropriately, with the remaining copper
layers being numbered.  It's up to you to rename them, rearrange them,
document them, whatever, to tell the fab shop which is whick.

The exceptions are companies like PCB-Pool, which accept GC-Prevue
format, which allows you to import the gerbers and arrange and tag
them appropriately, then send the whole project to them as a single
file.

Note that PCB emits one gerber (or postscript print) for each layer
*group*, not for each *layer*.

> Is their a way to assign a "PCB layer" or set of copper to a
> specific net?  So for instance my GND plane or polygon would be
> assigned to the GND net.

Draw the polygon and tie it into the net with a thermal.  PCB should
figure the rest out from that.


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