Flip-chip bonding alignment accuracy enhancement using self-aligned interconnection elements to realize low-temperature construction of ultrafine-pitch copper bump interconnections

In this paper, the integration accuracy of conventional flipchip bonding is effectively enhanced by means of automatically maintaining the alignment between the chip and substrate during the time that offsets may take place, i.e., bonding conditions applying period. The conventional bonding bump and pad elements have been appropriately modified to construct a concave-convex pair, i.e., self-aligned interconnection elements (SIEs). By this way, the post-bond offsets are determined by the SIEs, aiming at highly reproducible sub-micron range bonding precision. Moreover, because the post-bond offsets are guaranteed by the SIEs, ultrasonic assisted technique can be applied to make reliable bonds at acceptably low temperatures, while still maintaining the integration accuracy. Ultrafine-pitch (i.e. down to 10 μm) copper bump interconnections were realized using the proposed integration approach.