The determination of stresses and material properties of polyimide coatings and films using real time holographic interferometry/

Abstract

This dissertation presents a new technique for determining the residual stresses and material properties of polyimide coatings. The primary materials studied are polyimides, pyromellitic dianhydride-oxydianiline (PMDA-ODA) and poly (N,N\sp\prime(phenylene)-3,3\sp\prime4,4\sp\prime-biphenyl tetracarboxylic diimide) (BPDA-PDA). The determination of the internal stresses which develop during processing in these coatings is critical for reliability prediction and material selection for the microelectronics industry. For any given coating on a rigid substrate, the shear and normal tractions between the two materials goes to zero away from the edges. A portion of the substrate can therefore be removed leaving a simply supported membrane (coating) with its original state of stress intact. Classical vibration theory states that the square of the resonant frequency of a membrane is proportional to its biaxial stress. Real-time holographic interferometry is used to identify the resonant modes of vibration. It is also shown that using this technique the orthotropic axes of polymer films can be identified, thus simplifying the determination of all nine orthotropic elasticity coefficients