The main reason I would like to use aluminum foil is because it is really easy to find. I don't know where to get copper foil, so I did a test to see how fast aluminum etches compared to copper.

Doesn't work too well, does it? Copper etches more slowly, I know this from *attempting* to etch my own PCB. You can see that aluminum reacts wildly to the acid and burns up very quickly.

Of course, a different etching solution could be used.

OK, my thoughts on the process

A sheet of foil would be stretched across a 3D printer bed as tight as possible. The 3d printer would print the board atop it. When the printing is done the board would be flipped over and placed on the bed again. The 3D printer then would print the mask, which could also work as a silkscreen after etching, and the board could be etched.

How do you solder this?

Still kinda figuring this out. I'm thinking about using a metal alloy that melts at a really low temp (like 150 Celsius) so that the board could be reflowed with something similar to solder paste. A low temp doesn't melt the board.