4.3.4  Summary and Conclusion

Within this section, FEM elastic thermal-mechanical simulations were performed with the purpose of analysing the stress behavior along the via and in the surrounding silicon. Critical stress points on the metal layer at the top and bottom of the TSV were identified by means of FEM simulations. It was also shown how the stress develops in the bulk Si, and it was demonstrated that the stress drops in proportion to the squared distance from the via border. A method for calculating the exact stress in the middle region of an unfilled TSV was also presented. The results were successfully used to predict the points of minimal stress in the arrangement of TSVs, explaining how the spacing and the pattern in which the TSVs are laid out support high mechanical stability and reliability of the entire structure. The same procedure can be used for other via geometries and via placements in order to study the mechanical stability.