A printed circuit board includes a motherboard and a daughterboard. The motherboard includes at least one first signal pad and defines at least one via under the at least one first signal pad. The daughterboard includes at least one second signal pad and defines at least one via under the at least one second signal pad. The at least one first signal pad and the at least one second signal pad are sucked into the respective vias on the motherboard and the daughterboard according to siphon principle to allow each of the first signal pads and the second signal pads to form uneven top surfaces, the uneven top surfaces of the at least one first signal pads and the at least one second signal pads are connected to each other for electronically connecting the daughterboard to the motherboard.