A circuit board includes an insulation part, a support layer disposed on the insulation part, a metal case disposed in the insulation part, a heat-exchanging fluid distributed within the enclosed space, and a first porous material distributed within the enclosed space. The metal case is thermally coupled to the support layer and includes a first inner surface, a second inner surface opposite to the first inner surface and positioned between the first inner surface and the support layer, a third inner surface connecting the first inner surface and the second inner surface, and an enclosed space surrounded by the first inner surface, the second inner surface and the third inner surface. The first porous material is disposed on the first inner surface.