Partially imidized polyamic

The coating must be prebaked to remove solvent and in the process the polyamic acid coating is partially imidized. The degree of this bake determines the conditions for etching and stripping. 

In thermal treatment of the partially crosslinked polyamic acid ester, the conversion of the amide structures to imide structures starts at about 100°C. This conversion was investigated by means of FT-IR spectroscopy (Bruker IFS 85, reflexion measurement) on annealed films on Al-wafers, where the amide-carbonyl stretching vibrations at 1680 cm- and 1540 cm- and the corresponding imide band at 1780 cm- were quantitatively evaluated. 

Table II shows comparisons of data for several cured PI5878 samples. For the KOH treated sample that had no acetic acid rinse, bulk gotassium diffused to the surface on direct heat curing to 280 C. Though the data given reflect in situ results, the same phenomenon occurred in air or nitrogen ambients with virtually no change in the carbonyl binding energies for the sample. By contrast, the non-KOH treated sample and the treated surface that had a 5 minute acetic acid rinse showed identical C Is features - imide and "partially oxidized" carbon functionalities. The results demonstrate that potassium incorporated in the polyamic acid matrix prevents the imidization process.

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