Provided is a circuit device having conductive patterns which are equally spaced apart and a manufacturing method thereof. A method for manufacturing a circuit device of the present invention includes the steps of: preparing a conductive foil; forming conductive patterns, which are included in a unit having at least regions for mounting circuit elements, by forming isolation trenches having a uniform width in the conductive foil; electrically connecting the conductive patterns to the circuit elements; sealing with a sealing resin so as to cover the circuit elements and to be filled in the isolation trenches; and removing the conductive foil in its thickness portions where no isolation trenches are provided.