High contact density ball grid array package for flip-chips

A package for mounting a semiconductor device to a circuit board comprising:

• an insulating substrate having a substantially flat top surface and an opposing substantially flat bottom surface, and also having at least one rigid layer,
• a plurality of electrically conductive contacts disposed on the top surface of the substrate for receiving a semiconductor device and making electrical contact thereto,
• a plurality of electrically conductive through-holes extending from the top surface of the substrate to the bottom surface of the substrate, and disposed at a pitch one from the other,
• a plurality of electrically conductive traces for making electrical interconnections between the contacts and the through-holes,
• a z-conductive layer having a substantially flat top surface and an opposing substantially flat bottom surface, attached to the substrate and disposed such that the top surface of the z-conductive layer is adjacent to and planar with the bottom surface of the substrate, for providing electrical continuity between the bottom surface of the z-conductive layer and the through-holes, and
• a plurality of electrically conductive connectors, having a diameter that is greater than the pitch between the through-holes, attached to the bottom surface of the z-conductive layer and disposed so as to be in electrical contact through the z-conductive layer with no more than one through-hole, at least a portion of the connectors underlying the contacts.