12 layer board...1000+ pin BGA chip...400mm by 300mm
Unbelievable, makes my little board look pretty simple.
I guess one "problem" with SMDs is that you are tempted to pack lots in because the chips fit, but there's still the same number (and often a lot more) of traces to run and a lot of the board is out of bounds because you can't run traces between pins.
For example a 28-pin dip is ~1.3" long and in that space you can run about 26 traces between pins. The TSSOP28 is only about .35" long but you can't run a single trace through it.
Net result, less real estate for traces if you pack the chips in.
So as I see it you have to start leaving more space around chips or go to four layers.
After doing this board four layers definitely gets my vote.
I can pit the crystal,caps, and a few resistors under the socket,
You can of course do this with SMD as well, just put them on the other side of the board. I did a small PCB a while back with a tiny85, rs485 transceiver and a few small components, all up about 1/2" square and that's using SIOCs that are relative large by SMD standards.
Rob