Capabilities of normal metal electrical interconnections for 3D MCM electronic packaging

The rapid increases in IC chip performance have made increasing demands on electronic packaging technology in order to achieve the improvements in system performance that the IC speeds promise. An exciting approach to reducing the signal latency in electronic systems is to go to 3-D packaging, in which closely stacked boards are coupled with large numbers of vertical interconnects distributed over the area of the boards. In part because of a perception that electrical Z interconnect approaches such as `fuzz buttons' would seriously compromise signal performance due to parasitic lumped inductance effects, optical inter-board interconnect approaches have been proposed for this application. This paper examines the capabilities of normal metal electronic interconnects in meeting the requirements for 2-D and 3-D MCM applications, and to elucidate the areas in which more exotic approaches such as superconducting or optical interconnects offer significant potential advantages. It is pointed out that for short interconnects, such as those inside of a 2-D or 3-D MCM, normal metal interconnects can be designed to give excellent performance for digital signal frequencies up to at least 5 GHz.