Localization of defects in die-attach assembly by Continuous Wavelet Transform using Scanning Acoustic Microscopy

The main goal of this paper is to describe a new method based on Continuous Wavelet Transform (CWT) algorithm and successfully implemented in a Scanning Acoustic Microscope, developed at IXL Laboratory, for the measurement of Time Of Flight (TOF) between ultrasonic echoes and contribute to the help of defect diagnosis and failure analysis of a die-attach assembly. The paper is divided into three main parts. After a brief description of the different methods for the TOF measurement, we give the strong interest to use Wavelet Transform due to the nature of ultrasonic signals. The principle of the CWT algorithm and the TOF measurement method associated arc explained. The robustness of the CWT algorithm is evaluated to achieve information concerning its performances in presence of different signal parameters and SNR with a statistical treatment. In final, we propose an application of this algorithm to the help of acoustic images interpretation. This application concerns the detection and localization of defects into a die-attach assembly, specially the detection of fine crack. © 1999 Elsevier Science Ltd. All rights reserved.