Fatigue and Bridging Study of High-Aspect-Ratio Multicopper-Column Flip-Chip Interconnects Through Solder Joint Shape Modeling

This paper addresses fatigue and bridging issues by numerical analysis for an ultra-fine-pitch flip-chip interconnect that consists of multiple copper columns (MCC) and a solder joint. First, the processing flow is briefly presented, which enables prototyping of high-aspect-ratio (~6) copper columns, and hence, enhanced thermomechanical reliability of the interconnects. A public software, Surface Evolver (SE), has been used through this work to predict the solder joint geometry evolution. By integrating SE solder joint shape modeling, stress/strain analysis within ANSYS, and design of experiment (DoE) techniques as well, detailed numerical analysis has been conducted on the solder joint fatigue response to various factors such as the Cu-Solder wetting angle, loading direction, and solder geometry parameters. Finally, by applying the DoE techniques and the most updated features of SE, bridging risks of this interconnect with a fine pitch of 40mum is investigated, in which critical solder volume is calculated as a function of the interconnect geometry parameters. Based on these results, a solid basis for the design and processing of this advanced flip-chip interconnect has been established