Circuit board having selective vias filled with lossy plugs

An interconnect system comprising:

• a receptacle connector assembly having a first circuit board and a receptacle connector mounted to the first circuit board, the receptacle connector having a receiving cavity, the receptacle connector including an array of electrical contacts disposed within the receiving cavity, the electrical contacts include signal contacts and ground contacts, the first circuit board includes a first substrate and signal conductors and ground conductors routed on the first substrate, the signal contacts of the receptacle connector are terminated to corresponding signal conductors of the first circuit board and the ground contacts of the receptacle connector are terminated to corresponding ground conductors of the first circuit board, the first circuit board includes a plurality of plated ground vias extending at least partially through the first substrate being coupled to corresponding ground conductors, the plated ground vias including lossy plugs at least partially filling the plated ground vias, the lossy plugs being electrically coupled to the ground conductors, the lossy plugs being manufactured from lossy material capable of absorbing electrical resonance propagating through the substrate, wherein the lossy plugs are only coupled to the corresponding ground conductors and are not electrically coupled to the signal conductors;
• and
• a pluggable connector assembly configured to be inserted into the receiving cavity of the receptacle connector during a mating operation, the pluggable connector assembly including a second substrate having a first surface and a second surface opposite the first surface, the second substrate having a plurality of signal conductors and a plurality of ground conductors, the signal and ground conductors including respective contact pads in a mating area of the second substrate for engaging corresponding signal and ground contacts of the receptacle connector, and the second substrate having a plurality of plated ground vias extending at least partially through the second substrate between the first and second surfaces, the plated ground vias being coupled to corresponding ground conductors of the second substrate, the plated ground vias including lossy plugs at least partially filling the plated ground vias, the lossy plugs being electrically coupled to the ground conductors, the lossy plugs manufactured from lossy material absorbing electrical resonance propagating through the substrate, wherein the lossy plugs are only coupled to the corresponding ground conductors and are not electrically coupled to the signal conductors.