The effect of microstructure on the electromigration failure was studied in Al-2wt.%Cu conducting lines patterned from 4800Å-thick and l㎛ wide sputtered films. The grain structures of the lines are controlled by varying post-pattern annealing temperature and time to promote bamboo structures. The lines are subjected to a current density of 2.0×l0^6 A/㎠ at 225℃. Substantial lifetime improvement in post-pattern annealed samples is attributed to grain growth that induces near-bamboo structures. Failure kinetics is studied as a function of annealing time or temperature; the results suggest that, to improve the reliability, increasing annealing temperature is more effective than increasing annealing time.