Typically BGAs have a central square of balls which are all connected
to ground. What is the best way to hookup the PCB tracking for
the central ground matrix.

The simplest, and lowest inductance, seems to be to put down a solid
square
of copper covering the central ground ball pads, and pepper the square
with
ground vias. But will this cause a soldering problem with the
manufacturer

sjones@scannex.co.uk wrote:
should be adaptable to other devices. (Sorry, I don't have the exact
link to hand).
Generally, don't expect to solder direct to a big square of copper:
you'll never get it hot enough. The preferred way is to use a
proper-size pad for each ball, with vias in the diagonal spaces between
those pads (there is room: the package designers made sure of that You
can use X-shaped runners between the pads & vias.
Your solid square of copper lives on a lower plane, & extends at least
to the outside of the BGA. Decoupling caps. (plenty of them) are
commonly put on the backside of the PCB, as close as possible to the
power pins.
Of course, a multi-layer PCB is essential: you won't get the signal
lines out on a 2-layer, even if you could make the grounding work.

On Thu, 25 Jan 2007 09:32:54 -0800, sjones wrote:

The manufacturer of the device you are using probably has a document that
describes what you need to do. But generally, you have a pad that the ball
connects too, and then there is a short track to a via to an internal
plane. Between the pad and via you need solder mask, otherwise during
soldering the solder ball can melt and disappear down the via !! and you
end up with an open circuit. Browse the applications section of the
manufacturer's web site of your part - a detailed document is probably
there somewhere.

On 25 Jan 2007 09:32:54 -0800, sjones@scannex.co.uk wrote:

Just use the standard dog-bone shaped pad, ball on one end and
groundplane via on the other, like any other bga connection. Works
fine.

John