Low cycle fatigue crack growth in nanostructure copper

ITRS has predicted that integrated chip (IC) packages will have interconnections with I/O pitch of 90 nm by the year 2018. Lead-based solder materials in flip chip technology will not be able to satisfy the thermal mechanical requirement these fine pitches. Of all the known interconnect technologies, nanostructure interconnects such as nanocrystalline Cu are the most promising technology to meet the high mechanical reliability and electrical requirements of next generation devices. However, there is a need to fully characterize their fatigue properties. In this research, numerical analysis has been employed to study the semi-elliptical crack growth and shape evolution in nanostructured interconnects subject to uniaxial fatigue loading. The results indicate that nanocrystalline copper is in fact a suitable candidate for ultra-fine pitch interconnects applications. This study also predicts that crack growth is a relatively small portion of the total fatigue life of interconnects under LCF conditions. Hence, crack initiation life is the main factor in determining the fatigue life of interconnects.