Laser Based Ultrasound for Verification of Circuit Card Assemblies

Verification that equipment is authentic and not changed from a reference design and even at the circuit card assembly (CCA) level will likely be an important component of future arms control treaties. One approach is intrinsic unique identification (UID) of key hardware and its components to verify hardware integrity and authenticity. The effort described in this paper was an initial evaluation of the potential for laser-based ultrasound (LBU) as an inspection tool for UID of CCA boards and CCA components. The LBU system uses a laser pulse for ultrasound generation and an optical device for ultrasound detection to image subsurface structures without physical contact and in a dry state. This paper describes the selected CCA surrogate, CCA components that were examined, the laboratory-scale LBU system, LBU images of the CCA components, and initial development of UID algorithms. The database included repeat images of gull-wing connectors from a CCA board (match condition) and images from other CCA boards of the same model and batch (non-match condition). Database expansion included combinations of Gaussian noise added to the original images and image pixel shifts. For simplicity, a histogram was constructed of each image within the expanded database, and multiple metric algorithms were used to estimate either the difference or similarity between a reference and each histogram. Receiver operating characteristic (ROC) curves indicated good performance for both a Hellinger distance algorithm and a correlation algorithm as a potential means for UID of CCA boards and CCA components.