A system for detecting failed electronics using acoustics

Abstract

Industry-produced printed circuit boards (PCBs) used by the U.S. Department of Defense are typically coated with a layer of “conformal coating” made of silicone or polyurethane in order to protect the board. Conformal coating has to be removed every time board troubleshooting and maintenance are performed and must be reapplied after board maintenance is complete. This can be an expensive and time-consuming process. This paper describes an effort to develop a non-contact solution to detect failed components on a PCB without having first to remove the conformal coating [1]. This technique detects density changes in the physical makeup of circuit board components due to failure. By analyzing ultrasonic reflections from components at 2 megahertz (MHz), the authors were able to distinguish between working components and failed components with varying degrees of accuracy. The authors applied this technique to 1 KΩ resistors and three types of transistor-to-transistor logic (TTL) integrated circuits (ICs). Over-voltage faults were induced in these components in order to generate observable density changes. Reflections were processed for time-domain and frequency-domain features, which were used to train neural networks to distinguish between working components and failed components. For 1 KΩm resistors, the system has demonstrated 70% to 80% accuracy in distinguishing components with over-voltage faults. For two of the TTL IC types, 80% to 85% percent accuracy has been achieved. For one IC type, a 55% percent accuracy was measured. The authors have demonstrated that low-cost acoustic measurements in the megahertz range can be used to detect failures in ICs and other common circuit board components.