Re: gEDA-user: PCB suggestion

[Daniel Nilsson <daniel@xxxxxxxxxxxxxxx>]

On Fri, Jan 07, 2005 at 12:00:15AM +0000, Karel Kulhavy wrote:
> On Wed, Jan 05, 2005 at 09:14:08PM -0500, Daniel Nilsson wrote:
> > On Wed, Jan 05, 2005 at 07:10:34PM -0500, harry eaton wrote:
> > > 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!
> > 
> > Harry,
> > 
> > I think this brings up an interesting point, you need to use the right
> > tool for the job. With that I mean that there are "classes" of tools
> > for various complexity levels on a design. For the complexity levels
> > that I think the gEDA tools aim today I agree that more then 12 layers
> > should be very rare. But I can on the other hand say that at work we
> > have very few boards (if any) that would be routable on a 12 layer
> > PCB. I have worked on several designs that required 20 layers to be
> > routable for example. But that doesn't really matter because we would
> > not be able to use gEDA/PCB for layout work for so many other reasons
> > so I consider what we do at work as a different complexity level that
> > the gEDA tools currently don't aim for. But for my home projects PCB
> > is a great tool and exactly what I need to do the job, which is a job
> > of much lower complexity.
> 
> How many layers does a typical motherboard have?
> 
Well I'm not quite sure, but I do know there is a lot an work around
processor technology and the associated bus architectures to lower the
number of required layers on the PCB. This is since the PC marker is
so extremely cost sensitive at this point that adding another two
layers to a PCB could mean the processor requiring that is not a
success. So PC motherboards are not really high complexity designs
today from a PCB perspective.

I see information saying that the latest generation chip should be
routable on a 6-layer PCB for example. AMD also redesigned a socket
lately (I think it is socket 939) to allow fewer routing layers on the
PCB for this very reason.


-- 
Daniel Nilsson