[dragontamer]

I'm looking into maybe doing a BGA / MPU through KiCAD soon. Not that I'm confident in my abilities at all, but it'd be a challenge that I'd like to succeed in.

Yeah, you've listed off ~100 nets vs 1000s+ nets. But...

Many MPUs are BGA200 to BGA400 in size, and seemingly designed for 4-layer to 6-layer boards (available from OSHPark). Which means I expect around... maybe 200 nets or so in practice (a lot of the pins are either power-or-ground. But many other pins would be in fact connected to "something" and be their own net). More than your first number, less than your second number.

In your opinion, is that still within the feasibility of a hobbyist laying things out by hand? A lot of SiP MPUs have "internal DDR2" in sufficient quantities to boot Linux, although I'm also thinking about routing my own RAM for maximum flexibility.

[xw3099]

It’s definitely doable in one off quantities. And in fact people do it. Probably the most annoying thing would be dealing with length matching but honestly modern interfaces are much more tolerant than the specs imply. Power delivery could also be a sore point. So again, if you just looking to get a prototype working, it’s workable. But in volume. I wouldn’t go this route. This presentation lists some important things that are lacking in KiCAD when you really need to know the answer. https://archive.fosdem.org/2022/schedule/event/advanced_sim/...