The effects of thermal cycling on electromigration behaviors in lead-free solder joints

With packaging density constantly increasing and the size of solder joints scaling down in microelectronic products, electromigration (EM) becomes serious reliability problem in interconnections which induced by the high current density. Currently, investigations on EM phenomenon mainly focus on microstructure evolution, the change of grain orientation and the dominant diffusion species, etc. Almost all these studies and EM damages are carried out under constant ambient temperature. However, electronic devices usually service in a non-equilibrium state environment in practical. The purpose of this research is investigating the EM behavior under the thermal cycling conditions and trying to understand the relationship between microstructure evolution and resistance change of the solder joints. The one-dimensional Cu/Sn3.0Ag0.5Cu/Cu linear solder joint was employed to study the EM behavior of Sn-3.0Ag-0.5Cu (SAC305) under combined conditions of cycling temperature ranges from -20 to 100 °C and a high current density of 10⁴A/cm². Resistance change and microstructure evolution were analyzed in this paper. Resistance and microstructure data was collected and observed by paperless recorder and scanning electron microscope (SEM), respectively. The results revealed that high current density can cause voids formation. The propagation of cracks was accelerated by cycling temperature due to the mismatch of coefficient of thermal (CTE) between solder matrix and Cu substrate. Moreover, the coupling effects of high density and cycling temperature can lead to a rapid failure when compare to the monolithic loading condition.