To cut or not to cut: a thermomechanical stress analysis of polyimide thin-film on ceramic structures

When thin-film polyimide-on-ceramic multilayered structures are subjected to thermal loads during manufacturing processes, stresses can be produced at the interface of the film and ceramic due to a mismatch in the coefficients of thermal expansion of the materials. These stresses, which may cause delamination and peeling of the films, are typically largest near the free edge of the structure. This has raised the question of whether cross-sectioning these structures to examine the interior for such defects as interfacial de-adhesion or delamination may change the stress distribution and actually generate flaws, thereby defeating the purpose of the cross-sectioning. In this paper, thermally induced stresses are evaluated for laminated thin-film Kapton on alumina structures, taking into account creep deformation and stress relaxation of the Kapton layer. After experimentation temperature and stress-dependent creep-strain constitutive models were developed; the properties of nonlinear temperature-dependent elastic-plastic and the coefficient of thermal expansion were also described. Stress analysis was performed, using plane-strain finite element analysis. It was found that sufficient stress relaxation can occur to arrest interface peeling and delamination at the free edge