Thermal stress singularities in microelectronics

A method of stress analysis for problems found in the packaging of electronic devices is presented. The objective is to determine the strength of the singularity and the associated stress intensity factor at the end of a bonded interface between dissimilar materials. The basis of the method is to use values of the stress components as functions of position from a finite-element analysis as input to a curve fitting program. It is necessary to restrict the curve fitting to a range of positions close enough to the singularity so that the asymptotic form of the singularity is valid and far enough away that the finite-element results are accurate. An automatic method to select the best range is used. Plane stress, plane strain and axisymmetric cases involving a flat interface between two materials are solved as examples. The geometry close to the singularity is that of two 90° wedges bonded together. Of particular interest in the geometry analyzed are the maximum shear and normal stresses along the interface of the two materials