Optimized Viewing Techniques to Minimize Radiation Damage From X-ray Imaging Systems

• Published in: Journal of nondestructive evaluation Vol. 43; no. 2
• Main Authors: Pfeifer, Michael P., Simerl, Nathanael, Porter, John, McNeil, Walter J., Bahadori, Amir A.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.06.2024; Springer Nature B.V; Springer Nature
• Subjects: Ball grid array; Ball grid packaging; Characterization and Evaluation of Materials; Circuit boards; Classical Mechanics; Control; Cost function; Cracking (fracturing); Dynamical Systems; Electronics Inspection; Engineering; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; Ionizing radiation; Monte Carlo; Monte Carlo simulation; Non-destructive testing; Optimization; Radiation; Radiation damage; Radiation effects; Radiation sources; Semiconductor devices; Solid Mechanics; Trapped charge; Vibration; Viewing; X ray imagery; X ray inspection; X ray sources; X-ray system; Ball grid array; X-ray system; Non-destructive testing; Monte Carlo; Electronics Inspection
• ISSN: 0195-9298; 1573-4862
• DOI: 10.1007/s10921-024-01060-1

X-ray inspection of ball grid arrays (BGAs) is typically performed at one or more viewing angles to examine adhesion sites for errors such as voids, joint cracking, or head-in-pillow. During this inspection process, the circuit board assembly is subject to ionizing radiation exposure, which can cause trapped charge within oxide layers of semiconductor devices. Some x-ray machines allow for programmable inspection routines, which could be used to optimize radiation exposure to semiconductor components. Using Monte Carlo methods, x-ray inspection of a BGA was simulated to determine a range of acceptable viewing angles. Dose rates to circuit board components were estimated at each inspection angle to determine the view resulting in optimized radiation exposure. Results showed that for each BGA, the maximum unobstructed viewing times without exceeding a 5 Gy dose limit to a single part ranged from 82 to 94 min. Using a radiation cost function method, optimized viewing across all components was found. It was observed that for a consistent dose limit applied to silicon-based components, performing inspection with BGAs facing the x-ray source was optimal. A third method was applied, assigning individual dose limits based on empirical data from the NASA Goddard Space Flight Center radiation database. This method showed that optimized viewing maximizes the distance between the radiation source and highly sensitive components. It was also observed that cumulative effects from viewing two BGAs will influence viewing angles, causing the optimal view of one BGA to exist nearly 180 ∘ from the other.