Study on the electromigration-induced failure mechanism of Sn-3.0Ag-0.5Cu BGA solder balls

Abstract

The L-S electromigration (EM)-induced failure mechanism of Sn-3.0Ag-0.5Cu (SAC305) BGA solder balls was investigated. It is confirmed that temperature was becoming the most crucial factor to dominate the EM behavior. The high operation temperature caused the melting of the BGA solder balls in both the Cu/SAC305/Cu interconnects on PCB side and the Cu/SAC305/Ni interconnects on chip side. For the Cu/SAC305/Cu interconnects, an significant EM flux was induced under which the cathode Cu was excessively dissolved and a thick Cu-Sn IMC layer formed on the anode interface. For the Cu/SAC305/Ni interconnects, both Cu and Ni atoms could arrive to the opposite interface under concentration gradient and EM, resulting in the formation of Cu-Ni-Sn IMCs at both interfaces. However, the Ni UBM effectively inhibited the cathode consumption compared with the Cu UBM. The EM resistance of the Cu/SAC305/Ni interconnects is superior to that of the Cu/SAC305/Cu interconnects.