gEDA-user: Design with a 144 pin QFP

[Daniel O'Connor]

On Mon, 4 Feb 2008, Larry Doolittle wrote:
> On Sun, Feb 03, 2008 at 01:26:40PM +0000, ST de Feber wrote:
> > The device in mind is an Altera Cyclone-3 FPGA.
> > Most probably the ep3c5.
>
> FPGAs are the easiest chips to lay out, as long as you keep
> an open mind about pin assignments until you're halfway
> through the layout.  Unless there is some other complex
> part of the board, four layers is probably enough.
> One for power, one for ground, and the top layer has
> most of the routing away from the FPGA to its peripherals.
> That leaves one layer for anything that doesn't quite
> fit on the other three.

A little while ago I laid out a QFP144 Spartan 3 on a 2 layer board 
without too much difficulty.

The bypass network underneath was a bit of a hassle but it didn't take 
that long.

Recently it got redesigned so that the top and bottom layers were 
covered with ground polys, again not too difficulty.

I imagine 4 layers would be "better" but if you're on a budget 2 layers 
might be worth it :)

-- 
Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
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