OEM and ODM 4 Layer PCB Board Multilayer Circuit Board Assembly OEM and ODM 4 Layer PCB Board Multilayer Circuit Board Assembly What's 4 Layer PCB? A 4-layer PCB is a type of multilayer printed circuit board that consists of four conductive copper layers laminated together with insulating material (typically FR-4). These layers are interconnected through vias (plated holes) to form a complete circuit. Structure of a 4-Layer PCB: A standard 4-layer PCB stack-up usually