[MechanicalTim]

I've never seen a curved rigid board and I'm having a hard time understanding how SMT would work. If you have examples I'd love to see them.

I've spent the last 15 years as a hardware design engineer in consumer electronics, 4 of those years were working on wrist worn wearables for one of the biggest players. Wearables utilize FPCs for curved sections. Sometimes sections the FPC will be stiffened with pieces of FR4 to support larger components, but the SoC, DDR, etc is always SMTd to flat rigid PCB. I've heard reports of rigid boards being bent if the stack up is only a few layers, but have never seen in a production product. Generally the traces and solder ball joints for the chips can't handle the strain.