Guided wave based inspection of integrated circuit packages using the time-frequency synchrosqueezing transform

Ultrasonic guided waves have the potential to inspect integrated circuit (IC) packages using wave based techniques due to excellent sub surface penetration through metallic as well as dielectric material. Guided waves in a heterogeneous composite assembly such as an IC package have modes with complex dispersion characteristics due to multiple layers of material with intricate geometry. No analytical solution exists for predicting dispersion in highly anisotropic composites. Numerical methods, such as the finite element method, have been used to model dispersion in composites, however these methods are computationally intensive and not feasible for predicting dispersion in IC packages. In this paper, the time-frequency characteristics of guided waves propagating through a complex IC are studied using the synchrosqueezing transform (SST). This is a transform that has been shown to be robust to bounded signal perturbations, to provide highly localized time and frequency information for highly nonlinear modes, and to reconstruct the signal corresponding to each mode. Reference ultrasonic guided wave signals are collected for the IC package in its healthy and damaged states using piezoelectric transducers to characterize the dispersion modes in the excitation region. Initial results demonstrate that the dispersive mode information from the extracted SST ridges provide an effective damage indicator for IC packaging.