The reliability of Al-Cu interconnects is a strong function of both grain structure and the Cu content and distribution. Because pre-patteming and post-patterning grain growth are affected by the presence of Al2Cu precipitates, the effects of grain structure and Cu distribution are interrelated. We have studied the effect of Al2Cu precipitate spacing on interconnect reliability independent of grain size effects. This was accomplished by varying the thermal history of the continuous films to produce samples with identical grain structures, but different precipitate spacings. The precipitate spacing in continuous films was varied by an order of magnitude, from 2.6 μm to 25. pm. Lines were then patterned from each sample and tested. Lifetime testing results show that the reliability of lines with smaller precipitate spacings can be roughly an order of magnitude higher than that of lines with a larger precipitate spacing. We have also qualitatively studied the effects of Cu distribution on post-patterning grain growth. We found that precipitates retard post-patterning grain evolution, leading to reduced reliability. These results suggest strategies for developing thermal histories which will lead to optimal reliability.