Over at Henrik Forstén's blog, he has a write-up of his very impressive project where he designed, assembled, soldered and installed an BGA (Ball Grid Arry) ARM based board from scratch.
He discusses board design challenges with a four-layered PCB, considerations with traces for DDR2 RAM, CPU, and three voltage supplies. There are many pictures showing the soldering process. His summary is: "Many people say that soldering BGAs is hard but based on this experience I can't agree. Maybe I just got lucky but I didn't have any problems with them."
Once the board is all put together, he goes on to boot Linux. That also proves somewhat tricky, and he ends up with a three-phase boot using an ARM bootloader, U-boot, and finally a custom built kernel.
He says, "I don't really care about the usefulness of the board and this whole project is more of a learning experience". Clearly it was a great success.