The MIDI router/processor I'm designing will likely >> go to 4 layers. > I usually just start with 4 layers to begin with. The pricing is not all that great anymore (not like it was 15 years ago). My last job (cell phones) we were laying out 18 to 22 layer boards all the time. And they were only 0.040 thick. And had 750 passive components :) Paul S.