The degradation process of the crystallinity of electroplated copper thin films, which are used for interconnections and micro bumps for 3D integration, during electromigration and stress-induced migration tests was observed clearly by applying an EBSD method. The grain boundary diffusion was the main reason for the degradation of the crystallographic quality in both grain boundaries and grains. The reliability of the interconnections was improved drastically by minimizing the lattice mismatch between the electroplated copper and its base material for electroplating. The large mismatch deteriorated the crystallographic quality of the electroplated copper thin films and thus, increased the shrinkage rate of the films caused by the annealing. The electronic resistivity of the crystallinity-controlled films decreases effectively, and their lives during electromigration test improved drastically. In addition, the residuals stress in the films annealed at 400°C decreased to the stress lower than their yielding stress, and therefore, no stress-induced migration was observed. These results clearly indicate that the control of the crystallinity of metallic interconnectionis indispensable for assuring their long-life reliability.