Current-induced interfacial reactions in Ni/Sn–3Ag–0.5Cu/Au/Pd(P)/Ni–P flip chip interconnect

The current-induced interfacial reactions in the Ni/Sn-3.0Ag-0.5Cu/Au/Pd(P)/Ni–P (ENEPIG) flip chip interconnects and the failure mechanism during electromigration (EM) were reported. When ENEPIG was the cathode, EM significantly enhanced the consumption of Ni–P leaving a Ni3P layer; once the Ni–P was completely consumed, the growth of Ni2SnP was accelerated. The dissolved Ni atoms from the Ni–P and the interfacial intermetallic compounds (IMCs) were driven toward the anode upon electron current stressing and precipitated as large (Ni,Cu)3Sn4IMCs. The excessive consumption of Ni–P and the formation of voids were responsible for the EM-induced failures. When Ni was the cathode, the rapid localized dissolutions of Ni under bump metallization (UBM) and Cu pad in the current crowding region resulted in a two-stage transformation of interfacial IMCs at the opposite Ni–P/solder interface. The localized dissolutions of Ni UBM and Cu pad on chip, as well as the formation of voids, were responsible for the EM-induced failures.