Re: gEDA-user: PCB suggestion

["harry eaton" <bumpelo@xxxxxxxxxxx>]

It's not true that pcb has a "fundamental" limit of 8 layers. There are 8
copper layers. There are TWO silkscreen layers IN ADDITIONto the 8 COPPER
LAYERS. You can draw lines, arcs and polygons on the silk layers. It's
fairly straightforward to add several non-copper layers for things like
keep-outs, outline, or the mask layers. The hard part is implementing the
functionality associated with those layers. It's more of a "fundamental"
limit to go beyond 8 copper layers but then nobody has ever, to my
knowledge, built an 8 layer board with pcb. I know of a few 6 layer boards,
many 4 layer boards, tons of double-sided boards and few single-sided boards
but nothing beyond 6 layers.  It is rare indeed that more than 8 copper
layers are required. Usually when 10 and 12 layer boards are made it is
because the designers are lazy.

The Pentium processor chip has only 7 wiring layers; it must be of "medium
to low" complexity!

Eight copper layers is not presently a serious limitation to users; Even so,
storing the PIP/Thermal flags separately from the main "flag" variable would
quickly allow expansion to 16 copper layers, but it'll be a pain to handle
the grouping dialog, on/off and layer naming for them.

harry

----- Original Message -----
From: "DJ Delorie" <dj@xxxxxxxxxxx>
To: <geda-user@xxxxxxxx>
Sent: Wednesday, January 05, 2005 1:17 PM
Subject: Re: gEDA-user: PCB suggestion


> <snip>
>
> PCB at the moment has a fundamental limit of 8 layers, and assumes all
> eight layers are copper.  The rest of the layers are deduced from
> those.  Changing its internals to have a virtually unlimited number of
> layers, and explicit layers for such annotations, is a technical
> problem, not an interface problem.