Re: gEDA-user: PCB suggestion

[Egil Kvaleberg <egil@xxxxxxxxxxxx>]

harry eaton wrote:

> I wonder why they get so hot that they need
> fans when there are no power connections.  My point is it's usually possible
> to route a board with far fewer layers than are actually used.
The world has changed quite a bit since the birth of 'pcb': With very 
high density, very high pin count chips, it is simply topologically 
impossible, even with micro-vias, to fit all the necessary connections 
into less then 4 or perhaps 6 inner routing layers, no matter how much 
you try and how much routing space you can 'waste' on the outside. Add 
to that 2 power planes and 2 outer layers (which on very high density 
SMT is pretty useless for routing, anyway), you quickly end up with a 
total of 10 copper layers.

Commericial products like high-end PC graphics boards routinely use 10 
layers now-a-days.

Another issue is that from an economical point-of.view, it makes total 
sense in many low volume applications to spend less time doing smart 
routing, and instead go for 2 more layers. 10 and to a certain extent 12 
layer PCBs have now become common and economical (from a total economy 
point of view). Of  course, the possibility/necessity of more ground 
planes and better signal integrity is another argument for more layers 
in certain applications.

> Since I now know there
> are some fairly high-end-complexity users out there I will extend the copper
> layer support to 16 soon
16 layers should be "enough for everyone" for some definition of  'the 
future'.

Egil