An assessment of change in stress due to cross-sectioning in moire´ interferometric characterization of electronic packages

Cross-sectional moire´ interferometry technique is a very commonly applied one for the characterization of electronic packages. While the technique is popular, its use has not been accompanied by rigorous evaluation of its measurement accuracy. Such an evaluation, necessary because the cross-sectioning destructively modifies the original geometry, is the goal of the current paper. In the present study, a five-layer specimen with intact axi-symmetry as well as one in which the symmetry is destroyed through cross-sectioning are chosen as the vehicles for developing an understanding of the effect of cross-sectioning. We present a rigorous validation of an analytical elasticity model of axi-symmetric package-like structures in which the model prediction is shown to be accurate to within 1% of experimental measurement. The validated analytical model is used to estimate a reduction in radial stress of approximately 40% due to the cross-sectioning of the circular specimens, while the radial strains were virtually unaffected by cross-sectioning. These results suggest that cross-sectional moire´ interferometry is likely to yield accurate strains, but not stresses. Since damage under cyclic loading is a function of both stress and strain, the use of moire´ interferometry for studying the evolution of strains in packages under cyclic loading is likely to be grossly in error.