Effects of wetting angle and loading direction on fatigue behavior of multi-copper column flip-chip interconnects

This paper describes a study of solder joint shape evolution and its effects on the fatigue behavior of multi-copper-column flip-chip interconnects. Surface evolver has been used for the solder joint prediction in terms of different solder-copper wetting angles and the number of copper column per interconnect. A systematic procedure has been developed to integrate the solder shape prediction with the stress/strain analysis of the interconnects, in which the solder surface geometry is first predicted and optimized by surface evolver, and then the key points and surfaces of the solder model are exported into ANSYS where the stress/strain behavior of the interconnect is investigated. A cyclic in-plane displacement loading is employed to simulate the interconnect deformation due to the thermal mismatch of chip and substrate. The effect of loading direction and solder-copper wetting angle on the plastic strain range within a single loading cycle was studied. It is found that for each multi-column interconnect, there exists an optimum orientation of the columns with respect to the package which would give the highest fatigue life