3D interconnection and packaging: impending reality or still a dream?

Traditional interconnect schemes are basically two-dimensional. It has long been a dream for system designers to be able to combine multiple integrated circuits by connecting them in the third dimension. Three approaches to the 3D interconnect problem are described: system in a package (3D-SiP), system on a chip (3D-SoC) and 3D integrated circuits (3D-IC).