>Do you have any idea how hard it is to solder wires to germanium?
I've just soldered SOT-723 onto SOT-23 adapter board, I can solder anything to anything
This is about the material, not the size. If the solder just doesn't stick, it doesn't matter how big it is.
Common solder is, of course, designed to stick really well to copper. Which it does. To solder more exotic things, you probably need a completely different alloy.