Marco wrote:
> Hi all,
> as many of you may know after all my posts, I'm working with a Spartan3
> in the FT256 BGA package. Could anyone give me a link or something on
> documentation that may help me routing all those pins out in that kind
> of package with a 4-6 layer board. I'd like to get some examples or
> guidelines related to the most common approach adopted by experienced
> people.
> Thanks,
> Marco

I have been doing it last 6 years or so on 1.27 mm pitched BGAs
on two signal layers (top and bottom), planes as necessary (actually
6 in all cases so far), 3 lines between BGA pads, pitched 10 mils
(say, 5 mils trace and 5 mils gap, these may vary to 4-6 or 6-4).
Pad to gap is 5 or even 4 mil, drilling is 0.3mm or 0.2mm (I leave
this choice to the PCB house). I drill each BGA pad so I can have
access to all signals since my borads are typically expected
to begin to work and sell from revision 1; I have posted some
info before on how to avoid problems with the drilled BGA pads.

Dimiter

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Dimiter Popoff Transgalactic Instruments

http://www.tgi-sci.com
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