A socket (female connector) used for a connector assembly includes a film substrate constituted by a flexible thin board made of insulation material. The film substrate is provided with connection through holes adapted to be inserted therein connection posts of a header (male connector). Connection pads are formed on a first surface of the film substrate around respective connection through holes. The connection pads include a first pad and a second pad. The film substrate is provided on the first surface with a first patterned conductor connected to the first pad and a third patterned conductor connected to the second pad. The third patterned conductor is connected to a second patterned conductor formed on a second surface of the film substrate by means of a blind via that is formed by boring the film substrate from the second surface so as to reach the third patterned conductor.