Detection and location of defects in electronic devices by means of scanning ultrasonic microscopy and the wavelet transform

In a highly competitive market, reliable techniques for manufacturing quality control of electronic devices are more and more demanded. In particular, scanning ultrasonic microscopy is nowadays showing itself a suitable, non-destructive tool for detecting and locating defects in a die-attach assembly of a wide range of components. Due to multiple reflections and scattering of the ultrasonic beam in multilayer die-attach assemblies, ultrasonic images can often appear very confused to be correctly interpreted, and the nature of defects very difficult to be pointed out. In the paper, the use of a digital signal-processing method, based on the Continuous Wavelet Transform, is suggested for automatically detecting and measuring the time-of-flight between ultrasonic echoes thus improving ultrasonic image understanding of complex structures. Methods performance is verified by means of numerical tests on several ultrasonic signals simulating different operating conditions; its reliability and efficacy come out from experiments on the die-attach assembly of actual electronic devices.