Electrical connector assembly with high signal density

An electrical receptacle defining a bottom face to be mounted onto a horizontal host board and a horizontal slot opening forwardly to define a front-to-rear direction, a vertical direction, and a transverse direction, the electrical receptacle comprising:

• a transverse row of first mating contacts having contacting portions forwardly and downwardly protruding into said horizontal slot and terminating portions downwardly extending to be mounted to the host board, the contacting portions of the first mating contacts are disposed in a first transverse line;
• a transverse row of second mating contacts disposed below the horizontal slot and having contacting portions upwardly protruding into said horizontal slot and terminating portions downwardly extending to be mounted to the host board, the contacting portions of the second mating contacts are disposed in a second transverse line;
• a transverse row of third mating contacts disposed below the horizontal slot and having contacting portions upwardly protruding into said horizontal slot and terminating portions downwardly extending to be mounted to the host board, the contacting portions of the third mating contacts are disposed in a third transverse line before the second transverse line;
• an insulating housing having an upper wall and a lower wall defining the horizontal slot, the lower wall defining an lower cavity and a plurality of passageways communicating the lower cavity to the horizontal slot;
• and
• at least one plastic insert-molded with one or more of the third mating contacts, said at least one plastic being received in the lower cavity, each of the third mating contacts having a contacting portion extending through one of said passageways.