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 subjec ted to thermal loads during manufacturing processes, stresses can be p roduced 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 ques tion of whether cross-sectioning these structures to examine the inter ior for such defects as interfacial de-adhesion or delamination may ch ange the stress distribution and actually generate flaws, thereby defe ating the purpose of the cross-sectioning, In this paper, thermally in duced stresses are evaluated for laminated thin-film Kapton(R) on alum ina structures, taking into account creep deformation and stress relax ation of the Kapton(R) layer, After experimentation temperature and st ress-dependent creep-strain constitutive models were developed; the pr operties of nonlinear temperature-dependent elastic-plastic and the co efficient of thermal expansion were also described, Stress analysis wa s performed, using plane-strain finite element analysis, It was found that sufficient stress relaxation can occur to arrest interface peelin g and delamination at the free edge.,