Well, your advices where stright forward.
The FPGA is 1 mm pitch with square distribution, I've guess will be
more than 200 routes. I've already done such designs on 12 layers (0.5
and 0.4 mm pitch) but the price for PCB manufacturing was huge so my
intention is to avoid blind microvia and if possible buried too... I'm
wondering how can be done.
About the picture, forget it!
:)

greetings,
Vasile

On 6/11/07, M. Adam Davis <stienman@gmail.com> wrote:
> Well, if you only have to route 200 wires away from the chip, and the
> rest go to power, ground, or caps on the opposite side of the PCB,
> then you can do it with very few layers.
>
> Alternately, I've seen 26 layer boards that hold dozens of huge
> interconnected FPGAs.
>
> It also depends on the distribution of the balls, where the wires are
> going, how more board space is immediately outside the chip, and other
> circuit constraints (ie, you may need to keep all the lines in a given
> data bus to the same length).
>
> Lastly, there's a tradeoff between the cost of extra layers and blind
> and buried vias.  Chances are you cannot complete the routing of such
> a huge chip without blind vias, and perhaps not without buried vias.
> If you go very small in drill size and trace/space, you may be able to
> eliminate a layer or two that you might otherwise have to add.
>
> So, in short, there's no rule of thumb I'm aware of that'll go from
> number of balls to layers of board.
>
> But if you decide to dead bug mount it for prototyping, be sure to
> send pictures to the list!  :-P
>
> -Adam
>
> On 6/11/07, Vasile Surducan <piclist9@gmail.com> wrote:
> > I've guess there are people here which already did it.
> > The question is which is the minimum number of layers for routing an
> > 1738 balls FPGA witha couple of 3.1Gbps transcievers inside ?
> >
> > thx,
> > Vasile
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