gEDA-user: BGA package prototyping

[DJ Delorie]

It sounds like you want a fab with laser-drilled microvias.  That lets
you bring rows 3 and 4 out through the second signal layer, and
perhaps even allow via-in-pad without the wicking problem.

IIRC a bga ball is plain solder, it melts like everything else.
Otherwise, you'd need paste on the bga footprint.  Yes, PCB puts paste
there anyway, I think you *can* have paste (if you're careful), but
you don't *need* paste.

Most fabs can do 3/3 if you're willing to pay for it.

As for toaster ovens, I think the trick is alignment, not toasting.
BGAs might prefer the hotplate method, otherwise the soak needs to be
more tightly controlled.  Just guessing, of course.

Plus, of course, you can't inspect or repair a bad BGA reflow.