Thin films of polyimide were prepared by spin coating the poly(amide–acid) precursor onto copper and aluminum substrates, followed by the usual heat treatment to promote imidization (curing) of the film. Films prepared on aluminum substrates were completely cured during the heat treatment, as shown by x-ray photoelectron spectroscopy and infrared measurements. On copper substrates, the thinnest films (2000 Å or less) showed considerable intermixing of copper ions in the polymer layer. This prevented the films from curing completely during heat treatment. The formation of a copper carboxylate at the acid site in the polyimide precursor is postulated.
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Burrell et al. (1989) studied this question.