Anomaly detection and fault-mode isolation for prognostics health monitoring of electronics subjected to drop and shock

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In this paper, a new technique has been developed for health monitoring and failure mode classification based on measured damage pre-cursors. A feature extraction technique in the joint-time frequency domain has been developed along with pattern classifiers for fault diagnosis of electronics at product-level. The Karhunen Loeve transform (KLT) has been used for feature reduction and de-correlation of the feature vectors for fault mode classification in electronic assemblies. Euclidean, and Mahalanobis, and Bayesian distance classifiers based on joint-time frequency analysis, have been used for classification of the resulting feature space. Presently, failures in electronics subjected to shock and vibration are typically diagnosed using the built-in self test (BIST) or using continuity monitoring of daisy-chained packages. The BIST which is extensively used for diagnostics or identification of failure, is focused on reactive failure detection and provides limited insight into reliability and residual life. Previously, the authors have developed damage pre-cursors based on time and spectral techniques for health monitoring of electronics without reliance on continuity data from daisy-chained packages. Identification of specific failure modes reported in this paper is new. Various fault modes such as solder inter-connect failure, inter-connect missing, chip delamination chip cracking in packaging architectures have been classified by de-correlating the feature space and identifying dominant directions to describe the space, eliminating directions that encode little useful information about the features. Several chip-scale packages have been studied, with leadfree second-level interconnects including SAC105, SAC305 alloys. Transient strain has been measured during the drop-event using digital image correlation and high-speed cameras operating at 50,000 fps. Continuity has been monitored simultaneously for failure identification. In addition, explicit finite element models have been developed and various kinds of failure modes. The clustered damage pre-cursors have been correlated with underlying damage.