Electromigration reliability of flip-chip bonded Sn-3.5Ag-0.5Cu solder bumps on thick Cu and thin Ni(V)/Cu under bump metallurgies

Abstract

Electromigration reliability of flip-chip bonded Sn-3.5Ag-0.5Cu solder bumps on 10-μm-thick Cu UBM and 0.4-μm Ni(V)/0.4-μm Cu UBM was characterized by measuring mean-time-to-failure with current densities of 3-4 × 10 4 A/cm 2 at 130-185°C. Microstructural analysis of the solder bumps clearly revealed that electromigration failure of the solder bumps occurred with UBM consumption and void formation at the cathode side of the solder bump. Activation energies for solder electromigration, evaluated with the calibrated test temperature which was obtained by adding the temperature increment by Joule heating to the apparent test temperature, were 0.9 eV/atom on 10-μm-thick Cu UBM and 1.3 eV/atom on 0.4-μm Ni(V)/0.4-μm Cu UBM at current densities of 3-4 × 10 4 A/cm 2.