Scanning acoustic microscopy and shear wave imaging mode performances for failure detection in high-density microassembling technologies

This paper reports results on application of scanning acoustic microscopy (SAM) for analysis of high-density microassembling technologies such as BGA and TSV. We have demonstrated the interest of an original and dedicated model based on the calculations of the in-depth Point-Spread Function (namely PSF) corresponding to an extension of that of proposed in literature but restricted to the surface of an object. Our model includes the well-known decomposition of an acoustic wave into a solid specimen but also diffraction, calculations of geometrical aberrations and can predict the focal plane distribution (lateral resolution) at a specific focus depth according the Rayleigh diffraction theory. Specific test patterns have been used for metrology evaluation into different materials especially at high acoustic velocities. A specific attention is paid to the application of shear wave imaging capabilities in comparison of longitudinal wave imaging mode for the analysis of stress distribution along an interface from a qualitative point of view believing that one can provide complementary information on stress analysis in contrast of classical B or C-SCAN longitudinal imaging mode. Finally, some applications are given on the well-established Ball-Grid-Array (SBC-BGA) technology still remaining an interest in today's electronic packaging technology and then on a specific TSV design that is currently studied in the framework of the European "MASTER_3D" project. FEM modeling and analytical predictive stress model, implemented and reported in recent published papers, have been compared with SAM imaging results. Non-destructive micro-Raman spectroscopy is also considered to estimate the stress profile into the silicon wafer around circular TSVs by monitoring the wavelength shift of the Raman peak along the radial distance.