1. A printed circuit board, comprising:a substrate having a top surface and a bottom surface;
a first signal net and a second signal net being in close proximity to each other and disposed within a specific region on the top surface of the substrate;
an outermost insulating layer disposed on the top surface of the substrate to cover the substrate, the first signal net and the second signal net, wherein the outmost insulating layer comprises a plurality of openings which expose at least a top portion of the second signal net from the outmost insulating layer, the openings arranged along a lengthwise direction of the second signal net with a first pitch, wherein the first pitch is equal to or smaller than 20 mm;
a reference plane disposed underneath the bottom surface of the substrate and underlying the first signal net and the second signal net, wherein the reference plane is electrically connected to the second signal net through a plurality of via holes formed underneath a bottom portion of the second signal net and disposed in the substrate, the via holes arranged along the lengthwise direction of the second signal net with a second pitch, wherein the second pitch is equal to or smaller than 20 mm; and
a conductive layer disposed in the openings to electrically connect to the second signal net, and the conductive layer further disposed on the outermost insulating layer corresponding to the specific region in which the first signal net is arranged such that the conductive layer overlaps with the first signal net,
wherein positions of the via holes underneath the second signal net interleave with positions of the openings on top of the second signal net along the lengthwise direction of the second signal net.