Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Norm Carlberg" <normnet@...> wrote:
>
> I also would like to prototype BGA's.
> 
The problem with BGAs is there's no simple way to inspect the
soldering, and absolutely no way to correct a bad joint.  The pros use
soft X-ray machines to view the solder balls.  There are also some
exotic lenses that can look sideways under the chip for inspection. 
But, that just tells you is won't work, there's no way to repair one
bad connection under the BGA.  Even the pros send their chips out to
be reballed at $50 per chip.  Also, you end up having to use 6, 8 and
even more layers to get the signals out through the forest of vias
under the BGA.  Check the pricing on a 5-piece order of an 8-layer
board, it will run $1000 even with a very economical fabricator.  (Or,
do you already have multilayer PCB capability in your shop?)

You can get some fairly high pin-count chips in quad flat pack, 280
leads is quite standard, there may be some even a bit higher.  What
the HECK are you doing that needs more pins than that?  Also, the
high-end FPGAs get quite expensive.  Digi-Key has some $8000 chips
from Xilinx in their catalog!  Who the HELL can afford a SINGLE CHIP
that costs $8000?  Hmm, maybe the US government, but I can't imagine
too many others.

Jon