Electromigration reliability of Sn-3.0Ag-0.5Cu/Cu-Zn solder joints

Abstract

The electromigration reliability and failure modes of Sn-3.0Ag-0.5Cu (SAC)/Cu-Zn solder joints were investigated at 146 degrees C and a current density of 1.1x10(4)A/cm(2). After aging at 146 degrees C for 150h without electric current, typical bi-layers of Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) were formed in the SAC/Cu joints, whereas a single Cu-6(Sn, Zn)(5) phase was observed in the SAC/Cu-Zn joint. The total thickness of the IMC layer in the SAC/Cu-Zn specimen was thinner than that in the SAC/Cu specimen. After current stressing for 150h on the anode side, the total thickness of the IMC layers of both types of solder joints was thicker than that without electric current. On the cathode side, the IMCs, Cu6Sn5 of SAC/Cu and Cu-6(Sn, Zn)(5) of SAC/Cu-Zn joints dissolved, and voids induced by electromigration propagated along the solder/IMC interfaces. Suppressed void formation was observed at the SAC/Cu-Zn interface when compared to the SAC/Cu interface. Further, electric current was applied to the solder joints until failure and the electromigration lifetime was plotted as a function of the Weibull cumulative distribution to examine the electromigration reliability of the solder joints. The mean time-to-failure of the SAC/Cu-Zn joint was two times longer than that of the SAC/Cu joint. Owing to the anisotropic behavior of Sn, two failure modes, the dissolution of the Cu pad (mode 1) and void propagation at the solder/IMC interface (mode 2) were observed in the SAC/Cu and SAC/Cu-Zn joints. In both specimens, the failure time of mode 2 was longer than that of mode 1. However, the main failure type was mode 1 in SAC/Cu joints and mode 2 in SAC/Cu-Zn joints. For both failure modes, the lifetime of Cu-Zn specimens was longer than that of Cu specimens. The electromigration reliability of the SAC/Cu-Zn joint was found to be superior to that of the SAC/Cu joint because the occurrence of failure mode 1 was suppressed and the lifetime of the SAC/Cu joint in both failure modes was longer.