Researchers from the Fraunhofer Institute for Microstructure of Materials and Systems, Germany, discussed a study in which machine learning was used for signal analysis of acoustic signals to improve defect identification, at the ASM International EDFAS 2019 conference in Portland, Oregon.
Signal processing and data interpretation in scanning acoustic microscopy are often challenging, and are based on the subjective decisions of the operator, making the defect classification results susceptible to human error. The aim of this work was to combine unsupervised and supervised machine learning techniques for feature extraction and image segmentation that allows automated classification and predictive failure analysis on scanning acoustic microscopy (SAM) data.
In the first part, conspicuous signal components of the time-domain echo signals and their weighting matrices were extracted using independent component analysis. The applicability was shown by the assisted separation of signal patterns to intact and defective bumps from a dataset of a CPU-device manufactured in flip-chip technology. The high success rate was verified by physical cross-sectioning and high-resolution imaging.
In the second part, the signal separation used in the first part was employed to generate a labeled dataset for training and fine tuning of a classification model based on a one-dimensional convolutional neural network. The learning model was sensitive to critical features of the given task without human intervention for classification between intact bumps, defective bumps, and background.
This approach was evaluated on two individual test samples that contained multiple defects in the solder bumps and has been verified by physical inspection. The verification of the classification model reached an accuracy of more than 97% and was successfully applied to an unknown sample. This demonstrates the high potential of machine learning concepts for further developments in assisted failure analysis.
Paper title: Machine learning-assisted signal analysis in acoustic microscopy for defect identification
Authors: Michael Kögel, Sebastian Brand, Frank Altmann
Fraunhofer Institute for Microstructure of Materials and Systems, IMWS, Halle, Germany
