In-situ SEM and XRM studies of fully embedded via/line interconnect structures allow imaging of the time-dependent void evolution in inlaid copper interconnects. It is shown that void formation, growth and movement, and consequently degradation, depend on interface bonding and copper microstructure. Specific experiments were designed to study reliability-limiting degradation mechanisms in on-chip interconnects. In this paper, the challenges of copper microstructure monitoring and the study of degradation mechanisms, related to the reliability of the copper inlaid structures, are discussed. In particular, in-situ experiments to visualize mass transport and degradation in fully embedded copper via/line test structures are described. A model for void formation, growth and movement, and consequently interconnect degradation, is proposed. Electromigration lifetime can be drastically increased by changing or modifying the copper/capping layer interface.