Electromigration Damage Characterization in Sn-3.9Ag-0.7Cu and Sn-3.9Ag-0.7Cu-0.5Ce Solder Joints by Three-Dimensional X-ray Tomography and Scanning Electron Microscopy H.X. XIE, 1 D. FRIEDMAN, 2 K. MIRPURI, 2 and N. CHAWLA 1,3 1.—Materials Science and Engineering, Arizona State University, Tempe, AZ 85287-6106, USA. 2.—Assembly Test and Technology Development, Intel Corporation, Chandler, AZ 85226, USA. 3.—e-mail: nchawla@asu.edu Cerium (Ce)-containing Sn-3.9Ag-0.7Cu alloy exhibits desirable attributes of microstructural refinement, increased ductility, and mechanical shock per- formance, while possessing better oxidation resistance than other rare-earth- containing solders. In addition to the beneficial mechanical properties, it is imperative to study the reliability performance of novel solder alloys in the form of electromigration experiments, in comparison with Sn-3.9Ag-0.7Cu. In this study, electromigration tests were conducted on solder joints at elevated temperature with a constant current using a V-groove testing methodology. The microstructural change of solder joints during electromigration was investigated by scanning electron microscopy, and the void growth was mon- itored utilizing the three-dimensional (3D) x-ray microtomography imaging technique. The current density inside the solder matrix was determined by 3D microstructure-based finite-element modeling. Finally, the product of diffu- sivity and effective charge number of solder joints during electromigration was calculated from both marker displacement and 3D void growth. It was found that electromigration-induced Cu diffusion in Sn-3.9Ag-0.7Cu-0.5Ce alloy was greatly accelerated, and void formation at the cathode side was retarded as a result of finer microstructure and existence of CeSn 3 intermetallic particles. Key words: Rare earth, cerium, lead-free solder, electromigration, x-ray tomography INTRODUCTION The shift in semiconductor manufacturing from Pb-based to Pb-free solder has caused reliability concerns for future electronic packaging platforms, due to the low ductility and poor mechanical shock resistance of Sn-Ag-Cu solder alloys. 1–3 Recently, a series of rare-earth-containing Sn-3.9Ag-0.7Cu Pb- free solders have been proposed as high-ductility alternatives. 4–6 It has been shown that the addition of a trace amount of rare-earth elements can refine the microstructure, reduce the interfacial interme- tallic layer thickness, and, most importantly, increase the ductility and shock performance of solder joints. 4–8 Oxidation behavior studies on rare- earth-containing solder indicate that Ce-based sol- der alloy possesses the best oxidation resistance 7 and thermal stability 8 among several rare-earth- containing solders. Previous studies have established the feasibility of a Ce-based solder alloy as a replacement for conventional SAC alloys. Nevertheless, the electro- migration behavior of Ce-containing solder still needs to be investigated. 9 The electromigration behavior of Sn-Ag-Cu lead-free solder has been studied and compared with conventional Sn-Pb solder. 10–13 Generally, Sn-Ag-Cu solder has much better electromigration performance, owing to the lower homologous temperature and higher Young’s modulus. However, very few studies have been carried out on the electromigration behavior of rare (Received April 10, 2013; accepted June 17, 2013) Journal of ELECTRONIC MATERIALS DOI: 10.1007/s11664-013-2667-z Ó 2013 TMS