Well you'd be surprised that it all starts with a piece of material called Reinforced (fiberglass) epoxy resin.
This material will go a long...long way of brutal process
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Like any electronic device, it all starts with a pcb board which we call mother board. This board will go into a series of Sub processes in a Manufacturing plant. From Engineering which designs the patterns of the board to laminating (the green stuff or mat on a pcb) . Also holes are drilled into it according to design. This holes will be the insert point of the components that will be installed once the pcb if finished. After this, traces and lines will be available on the board but its just traces. For the lines to be conductive and inductive, it will go on to a process called electrolysis. And there's a lot of them, from CU plating(Cpper), NIAu plating (Nickle&Gold), and others. Once the traces are embedded thru electrolysis. A series of test will be conducted like OPEN/SHORT Test. This is to assure that the traces are under specifications. Note this traces are as thin as hair . So imagine one line is cut...this means a circuit is not complete. Once the pcb is complete it will go to the next process called SMT(Surface Mount Technology) , This is where they put the components on the pcb like resistors, regulators,etc...
This is where they get tricky...
There are several components that will be embedded on a PCB board and not all off them are made by the same manufacturer..
Example like SAMSUNG, this giant does not only produces devices, also components like smd's. This smd's are also sold in the market. I would not be surprised if one of these components are used in other brands. So if your asking about components on a smartphone... if they belong to a single manufacture? i would say not...
Now is our PCB finished? Nope...This PCB's are then shipped to different sub assembly plants where they install other components. LCD Screen, Battery, the enclosure, the buttons. When everything is complete a final test is done, then it will be packaged and finally to the distributors..which then shipped to different countries and different stores.
Please note this is only base on my knowledge, it may or may not be accurate. So i hope this help.