gEDA-user: Re: Making an odd-shaped PCB

[Kai-Martin Knaak <kmk@xxxxxxxxxxxxxxx>]

On Sun, 04 Feb 2007 23:27:47 +0000, Michael Sokolov wrote:

> 1. How are odd-shaped boards generally made?  Does the PCB manufacturer
>    make a rectangular board first and then cut/shave/file it down as
>    necessary?

No. They arrange the ordered boards to minimize the waste. PCB estate is
valuable. Cutting is generally done by milling along the borders as
defined by the layout. 


> 2. In the .pcb file there is a PCB() or PCB[] record specifying the
>    board size.  Should I set it to the size that the rectangular board
>    would have had if the answer to Q1 was 'yes', or something different?
>    (A little larger?)

Make it a little larger. I got segfaults with lineout lines slightly
beyond the board size window.


> 3. In this mailing list traffic I have overheard something called the
>    outline or fab layer.  What exactly is it and how does it work? 

It is a layer like all the others. The only distinctive detail is the
special name "outline". You have to add it to the layer stack in the
preferences dialog. Make sure, the layer is neither in the component side
group nor part of the solder side group. 

Gerber output will produce a special file 
	boardname.fab.gbr
that contains just the lines of the lineout layer plus whatever holes the
design might contain. You may explicitely tell the fab about this file, as
there is no standard file name for the lineout file.

>    first of all, are "outline layer" and "fab layer" two different terms
>    for the same thing, or are they two different things?

Both are the same.


> 4. What should the outline layer look like?  Is it a set of lines and
>    arcs forming a closed path that encircles the complete shape of the
>    finished PCB, however odd it is,

yes.


> Here's what my question boils down to: should I make the "total board
> size" as reckoned by PCB 7672 x 6560 mils (7672 mils = AB distance, 6560
> = AC distance), or something larger?  If I choose the exact ABxAC
> dimensions as my PCB size, that'll be the hard boundary of the "world"
> within which PCB will allow me to draw on any layer, right?  In that
> case how would I draw the whole ACDEFB shape on the outline layer?  Or
> can one have lines on a layer that run exactly along the edge of the
> drawable universe?

Yes.

>  Or should my outline layer depict just the DEF
> cutout (i.e., consist of just two lines: DE and EF), 

No.


> with all other edges and corners specified implicitly by the "total board
> size" setting?

The fab won't care fore the board size setting if you tell them to use the
lines in the *.fab.gbr file as outline pattern.


> 5. Is the fab/outline layer identified by a special magic layer name in
>    PCB?  Is it "fab" or "outline" or what?

It is
	outline

Time for a more explicit wiki entry?

---<(kaimartin)>---
-- 
Kai-Martin Knaak
http://lilalaser.de/blog



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