edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 26 NO. 3 14 ASSESSING COMPATIBILITY OF ADVANCED IC PACKAGES TO X-RAY BASED PHYSICAL INSPECTION M. Shafkat M. Khan, Chengjie Xi, Nitin Varshney, Aslam A. Khan, Hamed Dalir, and Navid Asadizanjani University of Florida, Gainesville, Florida m.khan3@ufl.edu EDFAAO (2024) 3:14-24 1537-0755/$19.00 ©ASM International® INTRODUCTION X-ray imaging has become a crucial method for postsilicon validation, offering a closer look into the internal structures and ensuring the integrity of integrated circuits (IC) and advanced packaging systems.[1,2] This technique involves capturing x-ray images from various angles to create three-dimensional models of IC devices or packages. X-ray laminography and tomography are particularly important in this process. The nondestructive nature of x-ray imaging and its ability to reveal intricate details within complex assemblies are its primary benefits. High-resolution x-ray systems enable the visualization of the complex internal structures found in advanced IC packages,[3] such as diverse system in packages (SIP) that contain multiple dies in a single package.[4] X-ray imaging facilitates fault isolation, measures the dimensions of inner circuit layers, inspects the alignment of stacked components, and evaluates the overall assembly’s integrity.[5,6] The efficiency of x-ray inspection in revealing features within ICs is largely dependent on the size of these features and the overall complexity of the design. Advanced IC packaging, characterized by its densely packed compo- nents and noise-generating elements, poses significant challenges in both the image acquisition and reconstruction phases when using x-ray tomography or laminography. The trend toward miniaturization and the high-density integration in these packaging technologies leads to reduced feature sizes and a tighter arrangement of components. Such conditions often result in overlapping or unclear details, complicating the analysis of x-ray inspection data. Moreover, factors that contribute to noise, like scattered x-ray radiation or artifacts from material interfaces, can further hinder the image acquisition process.[7] These elements can add undesired signals or distortions, impeding the precise detection and localization of defects or faults in the IC package. A notable example of this can be seen in Fig. 1, where the difference in the visibility of redistribution layers (RDL) with discernible feature sizes and those too small to resolve is evident. The development of a new metric, specifically designed for assessing x-ray inspection compatibility in semiconductor packaging design and manufacturing, marks a significant advancement in the field.[8] This metric, referred to as CMx-ray, is fashioned to be instrumental in providing designers with a concrete measure of how visible Fig. 1 Observability of fine-pitched features is influenced by the specifications of their size, dimension, and material composition. (a) (b) (c)
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