1. A circuit board comprising at least two circuit board units, each of the circuit board units comprising:a baseboard having a conductive hole filled with an electrical conductor;
a cover layer arranged on the baseboard and defined at least one trench and at least one opening, wherein the at least one opening exposing out the electrical conductor; and
a circuit pattern embedded in the at least one trench and comprising a connecting portion, wherein the connecting portion is embedded in the opening and is electrically coupled to the electrical conductor; and
the at least two circuit board units are stacked, two sides of the at least one cover layer are respectively adhered to the corresponding baseboard, and two ends of the at least one connecting portion are respectively electrically coupled to the corresponding electrical conductor and electrically coupled the two adjacent circuit patterns.