Re: gEDA-user: Can't route

[Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx>]

Ben,

I think you have the correct idea.

I would hand route the traces from under the fpga and perhaps around the
other major periferal chips. Then i would sort out the rats nest by
swapping io pins. After that I would let the autorouter take a shot at
the layout.

As a explination/warning about the bga image and via in pads. First via
in pad isn't necessary you can have vias off to the side of each pad but
this costs you the use of the top layer. Second, these vias can behave
like chimnies and transport heat up through them wicking the solder back
down. To avoid this the assembly shop/ fab shop coated the back side
with an epoxy ressin. Always always always review your design with both
the fab shop and assembly shop before starting manufacturing. Third,
these boards have to be flat otherwise the bga won't adhear to the pads
or will puddle shorting pads... probably will do both.

One last note, this was done on a much earlier version of pcb and was
only an 8 layer board.

Steve Meier





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