shows a parametric image of the thicknesses of the sinter layers between the die metallization and the Cu bond buffer [5]. The values displayed in the parametric image were obtained by analyzing the differences in phase of the die echoes. Due to the relatively long ultrasonic pulses a strong overlap between the entrance-and exiting echo of the sinter layer occurs resulting in a low accuracy of the estimates. An alternative approach is the analysis of the shift of the power spectral maxima of the acoustic signals. Spectral analysis is particular sensitive to temporal separation and thus the physical distance that correspond to time shifts in the echo signals. Further work will be required to increase the accuracy and robustness of this approach to be applicable with sufficient reliability. The results presented in fig 5 and 6 are preliminary to illustrate the potential of the acoustic signal analysis for the derivation of additional 2 nd order quality parameters of power electronic devices.