A manufacturing method of a double layer circuit board comprises forming at least one connecting pillar on a first circuit, wherein the at least one connecting pillar comprises a first end, connected to the first circuit, and a second end, opposite to the first end; forming a substrate on the first circuit and the at least one connecting pillar; drilling the substrate to expose a portion of the second end of the at least one connecting pillar, wherein the other portion of the second end of the at least one connecting pillar is covered by the substrate; and forming a second circuit on the substrate and the portion of the second end of the at least one connecting pillar, wherein an area of the first end connected to the first circuit layer is greater than an area of the portion of the second end connected to the second circuit layer.