Adhesion durability of de magnetron sputtered tantalum to in situ radio frequency (rf) plasma treated biphenyl tetracarboxylic acid dianhydride-para phenylene diamine (BPDA-PDA) polyimide films was determined as a function of repeated 400 degrees C thermal exposure cycles and 85 degrees C/80% temperature/humidity (T/H) exposures. rf plasma treatments in Ar, oxygen and a sequential combination of oxygen followed by Ar were evaluated. Using 90 degrees peel testing, it was found that all the plasma treatments resulted in high peel strengths (greater than 60 g/mm) initially and after high temperature thermal exposures, but structures fabricated with rf oxygen plasma treatment rapidly degraded in peel strength during T/H exposure. It is proposed that this hydrothermal degradation is a result of the instability of the nonstoichiometric tantalum oxide present at the metal/polyimide interface which transforms to stoichiometric Ta2O5, during the T/H exposure. Supporting evidence for this model is presented based on failure analysis of peeled strips by Auger electron spectroscopy as well as in situ x-ray photoelectron spectroscopy observations of the Ta bonding chemistry to the rf plasma treated polyimide.