AbstractDurability of metal/polyimide (PI) interfaces is essential for the long term reliability of advanced microelectronics packages. In earlier work, we showed that water absorbed by the PI can affect durability because, at high temperatures, it migrates to the interface and oxidizes the metal. In this study, we have investigated water transport through PMDA-ODA and BPDA-PDA polyimides as a function of ion beam treatment. Thermal desorption mass spectrometry (TDS) and gravimetric water uptake measurements were correlated with XPS spectra obtained from modified films. Transport through films with unmodified surfaces is rapid as shown by water uptake, however uptake is slowed considerably by surface modification. Additionally, only modified films exhibit peaks in TDS spectra–the peak temperature and intensity scale with dose. High resolution XPS spectra taken after modification suggest a graphitic-like surface region independent of dose. However, the extent of this “damaged” region scales with the dose. From the TDS spectra, we determine that the activation energy for water diffusion through this layer is 12–15 kcal/mol.