Residual stress and mechanical properties of polyimide thin films

Four different structure polyimide thin films based on 1,4-phenylene diamine (PDA) and 4,4'-oxydianiline (ODA) were synthesized by using two different dianhydrides, pyromellitic dianhydride (PMDA) and 3,3/,4,4/- biphenyltetracarboxylic dianhydride (BPDA), and their residual stress behavior and mechanical properties were investigated by using a thin film stress analyzer and nanoindentation method. The residual stress behavior and mechanical properties were correlated to the morphological structure in polyimide films. The morphological structure of polyimide thin films was characterized by X-ray diffraction patterns and refractive indices. The residual stress was in the range of -5 to 38 MPa and increased in the following order: PMDA-PDA < BPDA-PDA < PMDA- ODA < BPDA-ODA. The hardness of the polyimide films increased in the following order: PMDA-ODA < BPDA- ODA < PMDA-PDA < BPDA-PDA. The PDA-based polyimide films showed relatively lower residual stress and higher hardness than the corresponding ODA-based polyimide films. The in-plane orientation and molecularly ordered phase were enhanced with the increasing order as follows: PMDA-ODA < BPDA-ODA < BPDA-PDA PMDA-PDA. The PDA-based polyimides, having a rigid structure, showed relatively better-developed morphological structure than the corresponding ODA-based polyimides. The residual stress behavior and mechanical properties were correlated to the morphological structure in polyimide films.