Electromigration-induced microstructure evolution and failure mechanism of sintered nano-Ag joint

Nanosized silver (nano-Ag) has been proposed as a flip-chip interconnection material owing to its low sintering temperature and impressive working performance. With ever-shrinking size of electronic devices, electromigration (EM) becomes an important reliability issue. However, the EM behavior of nano-Ag joints has rarely been investigated before. In this study, a flip-chip structured nano-Ag joint was examined at a current density of 1.0 x 104 A/cm2 at 150 degrees C and its microstructural change at different experimental times was analyzed. Severe delamination between the Cu substrate and sintered Ag occurred at the cathode, and the extent of delamination increased with increasing EM time. Fractured surfaces revealed the presence of a large number of whiskers on the opposite side of the cathode owing to stress release during the EM process. For comparison, a Sn-3Ag-0.5Cu solder joint was examined under identical experimental conditions. Although failure in both samples originated from the cathode, the failure mechanism was different. The root cause for the difference in the EM phenomenon observed in the two types of materials was determined in this study.