Recent Progress in Metallurgical Bonding Mechanisms at the Liquid/Solid Interface of Dissimilar Metals Investigated via in situ X-ray Imaging Technologies

The liquid/solid (L/S) interface of dissimilar metals is critical to the microstructure, mechanical strength, and structural integrity of interconnects in many important applications such as electronics, automotive, aeronautics, and astronautics, and therefore has drawn increasing research interests. To design preferential microstructure and optimize mechanical properties of the interconnects, it is crucial to understand the formation and growth mechanisms of diversified structures at the L/S interface during interconnecting. In situ synchrotron radiation or tube-generated X-ray radiography and tomography technologies make it possible to observe the evolution of the L/S interface directly and therefore have greatly propelled the research in this field. Here, we review the recent progress in understanding the L/S interface behaviors using advanced in situ X-ray imaging techniques with a particular focus on the following two issues: (1) interface behaviors in the solder joints for microelectronic packaging including the intermetallic compounds (IMCs) during reflow, Sn dendrites, and IMCs during solidification and reflow porosities and (2) growth characteristics and morphological transition of IMCs in the interconnect of dissimilar metals at high temperature. Furthermore, the main achievements and future research perspectives in terms of metallurgical bonding mechanisms under complex conditions with improved X-ray sources and detectors are remarked and discussed.