A header assembly includes an insulative housing having a plurality of walls defining an interior cavity extending along a mating axis, and a plurality of contacts within the cavity and extending through one of the walls to an exterior of the housing for surface mounting to a circuit board. The insulative housing includes at least one alignment rib extending on an exterior surface thereof in a direction substantially perpendicular to the mating axis. The contacts are formed against and abutting the alignment rib, thereby ensuring coplanarity of the contacts for surface mounting to a circuit board.