Abstract: An electrical connector comprises an insulative housing, a number of contacts received in the housing and a pair of retention devices. The housing comprises an elongate base defining a slot for receiving an edge of a card therein and a pair of arms laterally extending from opposite ends of the base. Each arm comprises a spring cantilever and an aperture. Each retention device comprises a main portion, a spring arm and a horizontal solder pad for being soldered to a printed circuit board. The retention device is assembled to the corresponding arm with the main portion movably received in the aperture to ensure coplanarity between the horizontal solder pad and a bottom surface of the housing when the connector is mounted on a printed circuit board.