J
John Larkin
- Jan 1, 1970
- 0
It's just 4 layers. Where would you need more layers for? Most of the
chips are surface mounted on one side. There is no sense in using more
layers because you have no space to put the via's.
If you look carefully at a modern motherboard, you'll find most of the
signals are routed on the component side. This means the 2 inner
layers and most of the solder side can be used for power.
I recently did a couple of boards using some fine-pitch 456-ball BGAs,
Xilinx FPGAs. We needed 8 layers, 6 mil traces, and 10 mil via drills
to get all the signals out. It might have been possible in 6 layers,
if the Vcc-io and Vcc-core had shared a layer and we'd worked at it a
lot longer, but it would have been really nasty.
John