The effect of curing history on the residual stress behavior of polyimide thin films

Abstract

ABSTRACT:The effect of curing history on the residual stress behaviors in semiflexible structure poly(4,4Ј-oxydiphenylene pyromellitimide) (PMDA-ODA) and rigid structure poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) polyimide was investigated. Depending upon the curing history and different structures of polyimide, the residual stress behaviors and the morphology of polyimide thin films were detected in situ by using a wafer bending technique and wide angle X-ray diffraction (WAXD), respectively. For the rigid structure BPDA-PDA polyimide, the residual stress and the slope decreased from 11.7 MPa and 0.058 MPa/°C to 4.2 MPa and 0.007 MPa/°C as the curing temperature increased, and the annealing process is done. However, for the semiflexible structure PMDA-ODA, the change of the residual stress and the slope was relatively not significant. In addition, it was found that the cured polyimide prepared at a higher temperature with a multistep curing process showed a higher order of chain in-plain orientation and packing order than does the polyimide film prepared at a lower temperature with a one-step curing process. These residual stress behaviors of polyimide thin films show good agreement with WAXD results, such as polyimide chain order, orientation, and intermolecular packing order, due to curing history. Specifically, it shows that the effect of curing history on residual stress as well as morphological change was significant in rigid BPDA-PDA polyimide but, not in semiflexible PMDA-ODA polyimide. Therefore, it suggests that the morphological structure depends upon curing history, and the polyimide backbone structure might be one of important factors to lead the low residual stress in polyimide thin films.

Stress behaviors and thermal properties of polyimide thin films depending on the different curing process

“…Here, curing processes were performed with the following cure schedules (illustrated in Table I): cure A: heated to 400°C at 30°C/min, and held at 400°C for 60 min, then cooled to 25°C; cure B: heated to 400°C at 2°C/min, held at 400°C for 60 min, and cooled to 25°C at 1°C/min; cure C: heated to 150°C for 30 min, 230°C for 30 min, 300°C for 30 min, and 400°C for 60 min, ramping rate at each step was 2°C/min, cooled to 1.0°C/min. The schematic bending apparatus, TFSA, [13][14][15][16][17] was used for the film stress measurements. The thickness of polyimide films was controlled to minimize the effect of thickness deviation.…”

Molecular structure and thickness dependence of chain orientation in aromatic polyimide films

“…32 According to the previous studies, the degrees of chain orientation in PI films are higher for the PIs having rigid molecular structures than those having flexible molecular structures or bulky side groups. 11,[15][16][17][18][19][20]26,31 Furthermore, the preparation conditions of PI films such as film thickness, [13][14][15][16][17][21][22][23][24]27,30 thermal history, 15,17,25,33 and precursors of PIs 24,26 also affect the degrees of chain orientation. In the present study, we investigate the molecular structure dependence of the chain orientation and the rotational orientation of five-membered imide planes in aromatic PI films prepared by spin-coating onto substrates.…”

“…There have been a number of studies for investigating chain orientation and anisotropy in their properties such as coefficient of thermal expansion [11][12][13] (CTE), elastic modulus, 11,12 and refractive index. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] The magnitude of anisotropies in these properties basically depends on two factors: the intrinsic anisotropy and the degree of orientation of polymers. For instance, anisotropy in refractive index, namely birefringence Dn, in a rotationally symmetrical system can be expressed as:…”

“…Polarized Fourier transform infrared (FT-IR) spectroscopy is frequently employed for quantitative investigation of molecular orientation of stretched films, however this method does not provide information perpendicular to the film planes as long as using normally incident light into film plane. Therefore, in-plane/out-of-plane birefringence, 13,16,18,[29][30][31] wide angle X-ray diffraction (WAXD) measurement, 18,19,21,25,26,28 and anisotropy in the absorbance of dichroic dye 17,24 have been widely used for investigating the chain orientations in the thickness direction (TD) of spin-coated PI films. However, birefringence does not provide structure-independent investigations without the knowledge of Dn 0 , and WAXD measurement is insensitive to the orientation in the amorphous domains.…”