I'm just a hobbyist, so regarding spending, the ever-popular "as little as possible" is close to my heart, given that each penny comes from my own pocket... I

I'm just a hobbyist, so regarding spending, the ever-popular "as little as possible" is close to my heart, given that each penny comes from my own pocket... I try to keep my BGAs limited to 256 pins if I can, but sometimes it will go higher - I'm looking at using an I.MXRT1176 for example, and that's 289 balls at 0.8mm pitch. I've also used Efinix FPGAs at 0.8mm pitch/256 balls. I've gone as low as 0.65mm pitch, but that is pushing the limits of where I want to be... It's fairly common to see 3.5mil as space/trace minimums nowadays (again in the cheap(er) Chinese PCB houses). That's still not quite enough to escape two traces between each outer ball on a 0.8mm grid - though reducing the solder pad and ignoring the warnings from the board-house has worked before :) I've never done blind/buried vias, they always seem to be a lot more expensive than the 6- or 8-layer boards I can get done for cheap at nextpcb or jlpcb. Maybe I ought to ask again... Things like FPGAs, DDR/HyperRAM ram, etc. used to be outside the province of hobbyists, but given the packaging for those high-frequency-capable pins, BGAs are ever-more common, and with them come the layout issues.