Low temperature bonding of 30um pitch micro bump interconnection for 3D IC stacking using non-conductive adhesive

For evaluating the feasibility of adhesive bonding by NCF (non-conductive film) in micro bump joints, three types of micro joints were adopted in this study. The structure of the type I micro joints was Cu/Ni/Au while that of the type II micro joints was Cu/Ni/Au micro bump joined with Cu/Sn solder micro bump. Both the type I and type II micro joint were bonded by using NCF. The structure of the type III micro joints were the same, but the type III micro joints were produced by eutectic bonding. For the type III micro joints, the micro gap between chips was wrapped by a capillary underfill. The bonding results revealed that the contact resistance of the NCF joints was in the range of 100 Ωm ~ 400 Ωm which was higher than that of eutectic joints. Electrical continuity of micro bump interconnection was monitored by measuring the contact resistance of four-point Kelvin structure and daisy chain during reliability test. Thermal cycling test and thermal humidity storage test were conducted to evaluate the reliability performance of these three types of micro interconnections. The reliability test displayed that the reliability performance of eutectic joints was better than that of the NCF joints. The study showed that NCF joints have great potential to be applied in low temperature bonding of fine pitch 3D IC stacking.