A circuit board includes a signal layer and a power supply layer. The signal layer includes a first surface and a second surface opposite to the first surface. A number of pads are formed on the first surface for connecting to an electronic component. The power supply layer is formed on the second surface of the signal layer. The power supply layer includes an insulating substrate and at least one conductor formed on/in the insulating substrate. The conductor which is located under the pads defines a number of holes corresponding to the pads, each hole is substantially aligned with the corresponding pad, and the size of each hole is larger than the size of the corresponding pad.