A printed circuit board includes a signal layer, an insulation layer, and a reference layer. A transmission line is located on the signal layer. A probing pad is located on the transmission line. Two aligned slots defined in opposite sides of the reference layer leaving a connecting portion. The slots and the connecting portion are in vertical alignment with the probing pad. The signal layer, the insulation layer, and the reference layer are configured in a cascading order. An arrangement of the signal layer in relation to the reference layer including the slots and the connecting portion reduces a capacitance effect caused by the probing pad.