Novel fabrication technologies for high performance electrical and optical chip-to-substrate input/output (I/O) interconnections were developed. This research is driven by the long term performance and integration requirements of high performance chip-to-substrate I/Os, as well as the package reliability demands from semiconductor manufacturing. An electroless copper plating and annealing process was developed to join copper structures to achieve chip-to-substrate assembly by all copper pillar interconnects. The developed copper pillar interconnects provide much higher current carrying capability for chip-to-substrate power/ground input/output distributions and have low electrical parasitic characteristics for high frequency electrical signal communications. This copper bonding process also demonstrates the capability to compensate for misalignments and height variations of bonded structures. A finite element generalized plane deformation model was employed to design fully compliant copper pillars to eliminate the need of underfill. Electrical parasitics of copper pillar chip-to-substrate interconnects were studied by the derived formulas for low parasitic requirements. An optimized dimension space for all the criteria was provided on the pillar dimension chart. A novel nanoimprint lithography was developed to combine with photolithography in one process to create high quality features on a macrostructure for chip-to-substrate optical I/O applications. This fabrication process also demonstrated the capability to produce off-angle complex structures.

It is projected by the Semiconductor Industry Association in their International Technology Roadmap for Semiconductors (ITRS) that by the year 2019, with the IC feature size shrinking to about 10nm, off-chip interconnects in an area array format will require a pitch of 95 µm. Also, as the industry adopts porous low-K dielectric materials, it is important to ensure that the stresses induced by the off-chip interconnects and the package do not crack or delaminate the low-K material. Compliant free-standing structures used as off-chip interconnects are a potential solution. However, there are several design, fabrication, assembly and integration research challenges and gaps with the current suite of compliant interconnects. Accordingly, as part of this research a unique parallel-path approach has been developed which enhances the mechanical compliance of the compliant interconnect without compromising the electrical parasitics. It also provides for redundancy and thus results in more reliable interconnects. Also, to meet both electrical and mechanical performance needs, as part of this research a variable compliance approach has been developed so that interconnects near the center of the die have lower electrical parasitics while the interconnects near the corner of the die have higher mechanical compliance. Furthermore, this work has developed a fabrication process which will facilitate cost-effective fabrication of free-standing compliant interconnects and investigated key factors which impact assembly yield of free-standing compliant interconnects. Ultimately the proposed approaches are demonstrated by developing an innovative compliant interconnect called FlexConnects. Hence, through this research it is expected that the developed compliant interconnect would address the needs of first level interconnects over the next decade and eliminate a bottleneck that threatens to impede the exponential growth in microprocessor performance. Also, the concepts developed in this research are generic in nature and can be extended to other aspects of electronic packaging.