The effect of solvent absorption on the electrical and dielectric properties of polyimide films

A distinct difference in the solvent absorption behavior was observed in three types of polyimide films, the pyromellitic dianhydride–oxydianiline (PMDA‐ODA), the 3,3’,4,4’‐biphenyl tetracarboxylic diahydride‐p‐diaminophenyl (BPDA‐PDA) and the 3,3’,4,4’‐benzophenone tetracarboxylic dianhydride‐ 1,3‐bis(3‐aminophenoxy)benzene (BTDA‐APB), which is an isoimide film. All films were spin cast and imidized on silicon substrates to a peak temperature of 375 °C in nitrogen. In the BPDA‐PDA films, no solvent absorption was detected after immersion in n‐methyl‐2‐pyrrolidone (NMP) at temperatures up to 96 °C for 18 h. The PMDA‐ODA films exhibit a somewhat anisotropic solvent absorption mode, in which fast solvent diffusion and film swelling were observed in the direction normal to the film surface, while diffusion of solvent in the film plane (lateral direction) was much slower, especially at lower temperatures. However, as the temperature was raised higher (above ∼65 °C), a slow but measurable in‐plane solvent diff...