1. An IC package comprising: a. a printed wiring board (PWB) having an upper major surface and a lower major surface, and at least one quadrilateral cavity formed in said upper major surface and extending through said PWB to said lower major surface, b. a first array of interconnection sites on said upper major surface of said PWB along at least one edge of said cavity, c. an intermediate interconnection substrate (IIS) attached to said printed wiring board and substantially covering said cavity, said IIS having an upper major surface and a lower major surface, d. a second array of interconnection sites on the lower major surface of said IIS, with said second array of interconnection sites attached to said first array of interconnection sites on said PWB, e. at least one IC chip attached to said second major surface of said IIS with said at least one IC chip extending into said cavity, f. an interlevel interconnection between a first site on said upper major surface of said PWB and a second site on said lower surface of said PWB, said interconnection comprising a conductive runner extending from said first site along the upper surface of said PWB to the edge of said cavity, along the edge of said cavity, and from the edge of said cavity along the lower surface of said PWB to said second site.