I make most of the electrical and electronic things I create by hand, because they’re usually one-offs, so it doesn’t make sense to design them for automated manufacture. However, once you move beyond an early prototype, almost everything these days is designed to be mass produced or at least manufactured using automatic processes. Even for one-off designs, the fact that it’s now easy to 3D print, laser cut, etc. means that I don’t do a lot of mechanical fabrication by hand. I still build things out of foam board and cardboard to experiment with different shapes and structures, but that more like sketching in 3D than actually making a real system. Physical parts I usually make on the laser cutter, which means that I draw them on my laptop using Inkscape and then a machine cuts them out of a sheet of acrylic or wood.
It really depends on the level the project is at, and the complexity of the circuit.
The circuit boards get made by companies that specialise in making them. For prototypes circuits, we will solder on all of the components by hand. It’s a nice change from our normal work.
For production, the components are placed by a pick-and-place machine and go through a special oven for soldering.
For the latest components, it is not possible to build the circuits by hand, as all the connections are under the components and really close together.