Different structures of the PCB board have different functions
Another kind of PCB will be the onboard SMD PCB or surface mounted device PCB. No have holes instead it's small conducting beds the location where the tiny SMD components are positioned and soldered using special equipments. It's got higher mechanical strength and either side can be used for components because there are no holes. Also as the SMD are very tiny that this circuits can be miniaturized.Specific information, you can contact a professional Printed circuit board company, you can get more information about the PCB board.