1. A membrane circuit structure with function expandability, the membrane circuit structure comprising:a substrate comprising a first region and at least one second region, wherein the at least one second region is arranged near the first region;
a lower circuit layer printed on the first region, wherein the lower circuit layer is made of a first conductive material; and
a covering layer electroplated on a portion of a surface of the lower circuit layer, wherein the covering layer is made of a second conductive material and in contact with the lower circuit layer so as to enhance the electrical conductivity of the lower circuit layer,
wherein at least one expansion line is welded on the corresponding second region, and electrically connected with the covering layer and a corresponding function-expanding unit.