Copper was deposited by sputtering on two types of polyimide (PI) films. one:is fabricated by ionized cluster beam deposition (ICBD) and the other is Kapton, commercially available from DuPont. Diffusion properties of copper into these two polyimide films were investigated by x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. In addition, the packing densities of these PI films were measured by a rotational analyzer type ellipsometer.:We found that PI films deposited by ICED (ICB-PI) have a higher packing density than Kapton. We also found that less; copper is diffused into ICE-PI than into Kapton, that is, PI by the ICE method blocks Cu diffusion into PI. The diffusion coefficient of Cu/ICB-PI is 2.45 X 10(-17) - 2.8 X 10(-15) cm(2)/s at 300-390 degrees C; the activation energy of Cu diffusion into ICE-PI is 1.75 eV and Do for ICE-PI is 1.92 X 10(-1) cm(2)/s. The Cu atoms diffuse into PI as a form of clusters.