A circuit board includes at least two circuit board units stacked together. Each circuit board unit includes a substrate and a circuit layer. The substrate defines a conductive hole penetrating therethrough. The conductive hole provided with a conductor therein. One side of the substrate further defines a groove, the groove including a concave portion aligned with the conductive hole. The circuit layer includes a connection pad located in the concave portion. The connection pad is shaped as a conductive protrusion, which surrounds and is electrically connected to the conductor. The circuit layer is located in the groove, and the conductive hole is electrically connecting the circuit layers of the circuit board units.