A typical workflow for advanced package failure analysis usually focuses around two key sequential steps: defect localization and defect characterization. Defect localization can be achieved using a number of complementary techniques, but electro optical terahertz pulse reflectometry (EOTPR) has emerged as a powerful solution. This paper shows how the EOTPR approach can be extended to provide solutions for the growing complexity of advanced packages. First, it demonstrates how localization of defects can be performed in traces without an external connection, through the use of an innovative cross-sectional probing with EOTPR. Then, the paper shows that EOTPR simulation can be used to extract the interface resistance, granting an alternative way of quantitative defect characterization using EOTPR without the destructive physical analysis. These novel approaches showed the great potential of EOTPR in failure analysis and reliability analysis of advanced packaging.

We report the results of our studies on thermally induced surface topography changes in ultra-thinned silicon flip-chip packaged devices. Previous results showed that over polishing can result in bump topography on the ultra-thinned Si backside. The topographic bumps were found to form over the solder bump locations on the die. Our latest results show that heating exacerbates the topological variation, possibly due to underfill shrinkage caused by additional curing during heating, or plastic deformation caused by underfill and bump CTE mismatch. Our findings are relevant for Visible Light Probing because the induced topography can prevent Solid Immersion Lenses from making the intimate contact necessary for optimum performance.