Advances in Electronic Packaging and Integration Processes for Cryogenic and Superconductive Applications

Abstract

As superconducting electronics continue to mature, the need for more dense electronic packaging is critical for the scalability of cryogenic systems. This requires developments in flip chip processes, wire bond processes, and the introduction to new techniques that enable more flexible microelectronic fabrication of critical components. This work is best organized as two parts: 1) electronic packaging process development for cryogenic electronics and 2) fs-laser integration with superconductive thin films. Regarding electronic packaging process development: this dissertation details the development of indium-to-indium and indium-to-SAC low temperature flip-chip bonding processes now used routinely at Auburn University. In addition, a miniaturized flexible ribbon cable intended to act as a thermal break for cryogenic temperature stage spans was designed, fabricated, packaged, and tested. Lastly, these technologies were brought together to develop a potentially first of it's kind, multi-cable attachment process to a single MCM test vehicle. This bonding approach was verified as viable at cryogenic temperatures with both Cu and Nb cables, integrating cable technologies from previous students' work [1-4]. Regarding fs-laser integration with superconductive thin films: this dissertation explores modification mechanisms of fabricated Nb thin films (with conventional microelectronic fabrication processes) when irradiated in close proximity or directly on top of the film. Various conditions were explored, such as in atmosphere, in DI water, in vacuum as low as 2E-4 Torr, and in nitrogen backfilled environments. Modification was observed much below the ablation threshold of Nb, cautioning future integration engineers from assuming negligible effects on the thin films.