Circuit Board, Method for Fabricating the Same and Semiconductor Package Using the Same

A circuit board is provided including a core insulation film having a thickness and including a first surface and an opposite second surface, an upper stack structure and a lower stack structure. The upper stack structure has a thickness and has an upper conductive pattern having a thickness and an overlying upper insulation film stacked on the first surface of the core insulation film. The lower stack structure has a thickness and has a lower conductive pattern having a thickness and an overlying lower insulation film stacked on the second surface of the core insulation film. A ratio P of a sum of the thicknesses of the upper conductive pattern and the lower conductive pattern to a sum of the thicknesses of the core insulation film, the upper stack structure and the lower stack structure is in a range from about 0.05 to about 0.2.