Flexible PCBs look pretty cool, for sure - I saw some sheets made of copper-clad Kapton on Amazon, but they were pricey. Still, I think that's what all those TFT ribbon circuits are made of. I once tried soldering little wires to one of those, and I was amazed at how good the tiny gaps between the contacts were at repelling solder and preventing it from bridging.

the dynamics of solder is quite funny, when you look at all the guys soldering chips with pin gap of 0.1mm; solder paste aggregating on metal contacts and leaving the pcb clear all on itself ..