Effect of Novel SAC-Bi Solder Joints on Electromigration Reliability for Wafer Level Chip Scale Packages

Abstract The Sn-4Ag-0.5Cu base solder adding 3 wt.% bismuth (SAC-3Bi) has better drop and thermal cycling performance than due the excellent mechanical properties in previous study. Therefore, SAC-3Bi applied joints of wafer level chip scale packaging (WLCSP) recent year. In this study, was used on WLCSP device to evaluate electromigration reliability. A specially designed test vehicle for balls with 200μm diameter Ti/Cu/Cu UBM have been investigated experimentally. behavior terms electrical resistance change, mechanism also explored by microstructure evolutions. experiment conducted continuously at 1.2 1.6 under 170 °C 185 condition. monitored according Kelvin structure. An EM prediction model built based Black-type time failure equation, followed JEDEC five conditions. activation energy is 0.80 eV ± 0.02 eV, coinciding SAC alloy (0.72 ~ 0.89 eV). using a scanning electron microscope (SEM) accompanying energy-dispersive X-ray spectroscopy (EDS) backscatter diffraction (EBSD) behaviors phase characterization. There were intermetallic compounds Cu3Sn Cu6Sn5 interface copper solder. We observed two modes during current stressing, fracture occurred UBM/solder ball Cu redistribution layer (RDL), respectively. mechanisms detail from analysis.