In this study the effect of X-ray irradiation on demineralization of bovine dental enamel in vitro was investigated. Enamel specimens were irradiated with 72 Gy and subsequently demineralized (140 h) under reproducible constant composition conditions at pH = 5 in the presence of methylhydroxydiphosphonate (MHDP). Microhardness measurements after demineralization without MHDP showed significant differences (p < 0.001) between irradiated and nonirradiated enamel specimens; no significant differences were found in the presence of MHDP. Quantitative microradiography showed that both mineral loss and lesion depth were significantly lower (p < 0.001) for the irradiated enamel specimens compared with the nonirradiated ones. Surface layer formation was observed in irradiated enamel demineralized in a solution without MHDP. It was shown that X-ray irradiation decreased the enamel acid solubility in vitro.
Over the past two decades, globalized outsourcing in the semiconductor supply chain has lowered manufacturing costs and shortened the time-to-market for original equipment manufacturers (OEMs). However, such outsourcing has rendered the printed circuit boards (PCBs) vulnerable to malicious activities and alterations on a global scale. In this article, we take an in-depth look into one such attack, called the “Big Hack,” that was recently reported by Bloomberg Buisnessweek. The article provides background on the Big Hack from three perspectives: an attacker, a security investigator, and the societal impacts. This study provides details on vulnerabilities in the modern PCB supply chain, the possible attacks, and the existing and emerging countermeasures. The necessity for novel visual inspection techniques for PCB assurance is emphasized throughout the article. Further, a review of various imaging modalities, image analysis algorithms, and open research challenges are provided for automated visual inspection.
Globalization and complexity of the PCB supply chain has made hardware assurance a challenging task. An automated system to extract the Bill of Materials (BoM) can save time and resources during the authentication process, however, there are numerous imaging modalities and image analysis techniques that can be used to create such a system. In this paper we review different imaging modalities and their pros and cons for automatic PCB inspection. In addition, image analysis techniques commonly used for such images are reviewed in a systematic way to provide a direction for future research in this area.
Index Terms—Component Detection, PCB, Authentication, Image Analysis, Machine Learning
Electronic assemblies such as printed circuit boards (PCBs) and integrated circuits (ICs) require precise fabrication and process control of the electrical and mechanical properties. Microelectronic fabrication is a combination of additive methods, such as deposition of metal layers [18]; or subtractive, such as etching or milling [19]. This stack of layers in PCB or IC design creates the connectivity required for each device to operate functionally within a range of design specifications such as electrical resistance or impedance. The non-destructive verification of final assembled devices has become widespread with access to highenergy metrology equipment, demand for trusted devices [13], and to mitigate the complex defect-prone multilayer designs in PCB ( >8 Layer Lay-up) and IC (2.5D & 3D). Volumetric tools such as X-ray Micro Computed Tomography CT and Nano CT [9] are used to analyze the internal features of PCBs [5] and ICs [10] non-destructively. The automated quantification of these internal structures requires highresolution data to provide enough spatial resolution throughout the sample's "sliced" volume. Each slice's resolution in the volume represents the spatial resolution of the X-ray scan collection. To quantify internal structures such as signal traces or via connections the internal feature must be processed to separate or segment individual components enabling automated dimensional analysis or material property characterization. As the miniaturization of device geometries and the density of components increases, the labor resources required for manual segmentation of layered volumetric data becomes impossible.
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