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56 SMT007 MAGAZINE I SEPTEMBER 2026 However, certain semiconductor devices, including DRAM, flash memory, and other sensitive electronic components, may be susceptible to elevated or cumulative levels of ionizing radiation. When sensitive devices are present, users may need to consider the total radiation dose delivered during the inspection process. This is particularly important when an assembly requires extended inspection times, repeated inspection cycles, or high-magnification imaging. X-ray Fundamentals An X-ray inspection system functions as an X-ray shadow microscope. X-rays produced by an X-ray tube pass through the sample and are received by an image-capture device or image intensifier. Materials within the PCB absorb different amounts of X-ray radiation based primarily on their density, thickness, and atomic number. Materials that absorb more radiation create darker or more defined shadows on the detector, allowing internal features to be evaluated. Magnification is achieved by moving the sample closer to the X-ray tube's focal point. As the distance between the sample and the focal point decreases, the projected shadow increases in size. While this improves magnification, it can also significantly increase the radiation dose rate received by the sample. Factors affecting the radiation dose delivered during X-ray inspection include: • Distance between the sample and the X-ray source • X-ray tube voltage, measured in kilovolts • X-ray tube current and total tube power in watts • Length of exposure • Filtration placed between the X-ray source and sample • Number of repeated inspection cycles K N O C K I N G D OW N T H E B O N E P I L E Figure 1: Basic X-ray inspection geometry and the relationship between sample position, magnification, and dose rate.