Effects of thermal curing on the structure of polyimide film

Abstract

The effects of thermal curing method on degree of imidization, molecular orientation, and chain ordering of the 4,4-oxydiphenylene pyromellitimide (PMDA-ODA) were investigated. Three different thermal curing methods were chosen in this study; two casts of polyamic acid on silicon wafer were isothermally cured at 200 degrees C for 3 h (I-200) and 300 degrees C for 3h(I-300) respectively, and the other one was cured in step manner(S-300): 100 degrees C for 1 h, 200 degrees C for 1 h, and finally 300 degrees C for 1 h. The degree of imidization was highest in the I-300 and lowest in the S-300, demonstrating that the amount of solvent and degree of imidization at each stage of the curing cycles significantly affect the final degree of imidization. The degree of in-plane orientation was found highest for the S-300 and lowest for the I-300. This suggests that the in-plane orientation decreases with increase of the chain immobilization. This chain ordering was found to be easily induced for the I-300 among the three cured films. In the I-300, the chains in the film are sparsely packed and ordering by the diffusion of polymer chians occurs most easily.