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Acoustic micro-imaging based on high-frequency ultrasound has been widely and effectively used for microdefect detection in microelectronic packages. With the miniaturization of microelectronic devices and the reduction of defects, edge blurring occurs in high-frequency ultrasonic scanning and directly affects the detection accuracy and signal-to-noise ratio, especially in spherical structures, such as ball grid arrays, wafer-level chip-scale packaging, and flip-chip solder bumps. This paper depicts the ultrasound interaction behaviors and the edge blurring effects during microdefect imaging, which provide a theoretical basis for improving the defect detection accuracy in subsequent research. A microdefect finite-element model was developed to simulate scanning in acoustic microscopy imaging. C-lines and C-scans of microdefects of various sizes were obtained, which can identify the location and size of the defects more easily. Furthermore, an improved method to obtain the acoustic propagation path map was developed for analyzing the acoustic energy transmission during detection. Different energy consumption paths around the microdefect lead to differences among the C-lines. The different sizes of microdefects show different blurred edges in the C-scans. The experimental data and simulation show consistent results, which prove the credibility of the developed method.