RE: [oc] Multi-layer PCB boards, A REPLY to Jonathan

["Paul McFeeters" <paul.mcfeeters@ntlworld.com>]

Jonathan,

> That's a lot of pins.  You could be a little less ambitious to start.

At least its not a BG560, FG676 or FG680! lol  I am starting small, heck my
first project can even fit on a PQ208 board, I arranged this as it is
expected to be sold commercially (fingers crossed). I tend to look forward
to tomorrow rather constantly dwelling on today. Somebody once said "there
are no limitations for us except the limitations we place on ourselves".
Without forward vision nothing would ever get invented. I am getting round
the I/O limitation by connecting two B5-Spartan boards from Tony Burch. This
will do for the larger I/O projects until I can find a board manufacturer
who can make me a FG456 board. Maybe NuHorizon have one on their evaluation
board list? (Can always dream)

If we all weren't ambitious would we be bothering to develop cores and new
projects? Long live ambition.

> Help me out here.  What does mounting a BGA have to do with who fabs the
PCB?

Ever tried fabricating a board for BGAs? I imagine it would be many times
harder than for surface mounted devices. I believe (from what I've been told
by professionals) that a FG456 chip would need at least a 6 layer PCB to
mount it on (the FG456 pin layout looks like a bitch to fabricate). Alas the
PCB fabrication is still all new to me so for now I'll bow to the experts
but I won't admit defeat in proving them wrong in the future. Tomorrow is a
new day and something to look forward to. Maybe one day Xilinx will make the
456pin models as surface mount? (Just idle speculation not an excuse for an
entire message thread please)

Paul

PS Looking at the FG680 chip pin diagram this would actually be easier to
implement than a FG456! The FG680 pins are 5 rows deep whereas the FG456 has
7-10 rows (depending on how you count them). Plus the FG680 has a large
'hollow' core where wires could head to the centre, pass through to the
bottom of the board and then be routed wherever required. Alas even a cheap
FG680 package (XCV600-FG640C) is USD $1,350 so back to the FG456 (USD $50)
for me.




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