A receptacle connector includes a contact assembly having a dielectric carrier holding contacts, which may be overmolded by the dielectric carrier. The receptacle connector includes a housing holding the contact assembly having a mating end mated with a plug connector and a mounting end mounted to the circuit board. The housing has first and second side walls and first and second end walls. The housing has a card slot open at the top for receiving the plug connector and a contact assembly cavity open at the bottom for receiving the contact assembly. The housing may have positioning ribs extending from the first and second side walls to position the contact assembly within the cavity and/or strengthening ribs extending across the cavity to connect the side walls at a location remote from the end walls.