gEDA-user: Making an odd-shaped PCB

[msokolov@xxxxxxxxxxxxxxx (Michael Sokolov)]

Hellow PCB developers and users,

As my design enters the pre-layout stage, I have a number of stupid
newbie questions about PCB.

Here is my first stupid newbie question.  The board that I need to make
is not rectangular, but has an odd shape.  (See my previous post about
copying someone else's form factor.)  How does one capture the odd shape
(cutouts and shaved corners) in PCB?

Let me break this question down into subquestions:

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?

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?)

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

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, or just the cutouts?  This question
   links back to question 2, and is best illustrated by an example.

Suppose my finished board needs to look like this:

  |<---------------------- 7672 mils ----------------------->|
 A|                                                          |B
--+-----------------------------------+----------------------+--
^ |                                   |   AC mains           | ^
| |                                   |   connector          | | 2040 mils
| |         This line is imaginary <--|                      | |
  |                                   |                      | V
6 |                                   +----------------------+--
5 |                                   |E  ^                  |F
6 |                                   |<--|-- 2600 mils ---->|
0 |                                   |   |
  |                                   |
m |                                   |   4
i |                                   |   5
l |                                   |   2
s |                                   |   0 mils
| |                                   |
| |                                   |   |
V |                                   |   V
--+-----------------------------------+----
 C|                                   |D
  |<----------- 5072 mils ----------->|

(This is actually a simplification, the real thing is even more complex!)

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?  Or should my outline layer depict just the DEF
cutout (i.e., consist of just two lines: DE and EF), with all other
edges and corners specified implicitly by the "total board size"
setting?

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

OK, this is enough stupid questions for me for today.  I hope that
someone will be kind enough to answer at least some of them. :-)

MS


_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user