Wired:

At least two dozen primary suppliers on three continents and two islands (Japan and Taiwan) provide these parts.

The transportation complexity is magnified further because many components do not move in a simple path from supplier to final assembly. Some go on a hopscotching world tour from one country to the next and back again as one piece is joined to another to create an assembly, which is then moved elsewhere in the world for another part to be inserted or attached.

The phone’s innards are put together much as a cook assembles ingredients for a dish that becomes, in turn, a component of another chef’s course, which is then incorporated by someone else into a larger meal.

Few of us give much thought to the innards of our electronics but the supply chain process of getting all that stuff into your hands is remarkable. It’s also why we see so many rumors of individual components. The devices have become far too complex for Apple to keep a lid on everything.