A novel X-ray diffraction -based technique for complete stress state mapping of packaged silicon dies

Fundamental understanding of the silicon stresses and their changes with traditional wire-bonded and flip chip packages is critical to address the performance and reliability improvements in new technologies. Recently we have developed a novel technique for non-destructive measurements of complete strain state (and thereby the stress state) of the single crystal (bulk Si) by tracing the relative change in direction of an x-ray beam diffracted from a stressed crystal. This is based on the relationship between the stress state in a crystal and the local lattice plane orientation. Experimentally, this can be achieved by using a large area synchrotron white beam in conjunction with a precision grid of x-ray absorbing material placed in the path of the beam. The grid breaks the X-ray beam into an array of micro-beams that are diffracted by the single crystal sample to produce an integrated x-ray topograph on which the inverse grid image is distorted due to changes in the paths of diffracted microbeams i.e. an x-ray reticulograph is created. The distortions are a result of the variations in the diffracting lattice plane orientation produced by strain present in the crystal. By measuring this distortion on multiple topographs through the electronic package and applying the ray tracing principle, the entire strain state of the silicon can be calculated and mapped for the entire sample. We have carried out stress mapping of the silicon device in the package by applying this non-destructive and non-invasive technique.