A mobile phone circuit & a normal circuit both are parallel or same but a little difference is there, normally PCB (printed circuit board)& every other components which are fitted in a normal PCB all are fixed with the whole, it always comes in single layer pcb means one side where we can fit component leg in the pcb & fix it to the opposite side by solder wire ,
But mobile phone circuits are of multilayer, and the mobile phone components are different from the general components of the normal circuit. Those components are known as surface mount device (SMD ). They can be mounted over the surface of the PCB,
The surface mount device means the components mount on the surface only. The components which are soldered are called PCB; there are multiple layers with this too. That’s why it’s called multi-layer PCB, every mobile phone pcb are multilayer pcb. Now clear defiance between PCB and PBA.
Before the installation any component it’s called PCB (printed circuit Board).
After installation of components it’s called PBA (printed board assembly)
The technique of utilizing SMD components it’s called SMT (Surface Mount Technology), the components of SMD are used for several reasons like low wait , saving space, the size of mobile phone has been significantly reduced due to using smd components . It also consumes low current & works low voltage, the voltage loss of this components is very low.