3D IC package with RDL interposer and related method

A 3D IC package includes a bottom die having a back interconnect side opposing a front device side, the back interconnect side having a plurality of bottom die interconnects extending thereto. A top die has a front device side opposing a back side, the front device side having a plurality of top die interconnects. An interposer includes a redistribution layer (RDL) between the bottom die and the top die, the RDL including a plurality of wiring layers extending from back side RDL interconnects thereof to front side RDL interconnects thereof. An under bump metallization (UBM) couples the back side RDL interconnects to the plurality of top die interconnects at a first location, and the front side RDL interconnects are coupled to the plurality of bottom die interconnects at a second location. The first location and second location may not overlap.