A printed circuit board includes a base, a signal layer lying on the base, and a number of pairs of differential signal traces positioned on the signal layer. The base is made of a grid of glass fiber bundles filled with epoxy resin. Each pair of differential signal traces includes a first signal trace and a second signal trace. Each of the first and second signal traces extends in a zigzag pattern. The first signal trace includes a number of wave crests and wave troughs. The wave crests define a reference straight line that connects all the wave crest of the first signal trace. The ratio of the distance from each wave crest to the reference straight line to the orthogonal distance between each wave crest and an adjacent wave trough along the reference straight line is 1:5.