A printed circuit board includes a signal plane and a reference plane. The signal plane includes a pad, a passive element mounted on the pad, and a signal transmission line electrically connected to the passive element via the pad. The reference plane provides a return path for a signal transmitted through the passive element and the signal transmission line. A void is defined in the reference plane corresponding to the passive element, to increase a length of the return path. A length of a first axis, perpendicular to the signal transmission line, of the void satisfies a following equation: W 1 ≈ 8  Wpad + 10  T 0.8  Wtrace + T , wherein Wpad is a width of the pad, Wtrace is a width of the transmission line, T is the height of the pad.