A receptacle connector includes an insulative housing equipped with a plurality of receptacle contacts and enclosed by a capsular metallic shield sub-assembly. An insulative holder encloses the shield sub-assembly with a deflectable latching structure thereon. The plug connector includes an insulative body equipped with a plurality of plug contacts. An internal PCB is located behind the housing and soldered with the corresponding contacts. A capsular metallic shell encloses the insulative body and adapted to be received within the metallic shield during mating. A cable is connected to the PCB. An insulative cover encloses the internal PCB, the rear portion of the insulative body and the front portion of the cable with a retaining structure to be coupled with the latching structure, and a sliding assurance structure ensuring the latching structure and the retaining structure to be securely engaged with each other for maintaining the reliable mating.