Electromigration Performance of Cu Bumps in Various Configurations

To investigate the effect of bump structure on electromigration (EM) performance, four bump structures were designed: Cu/solder/OSP, Cu/Ni/solder/OSP, Cu/solder/ENEPIG, and Cu/Ni/solder/ENEPIG. The EM test results show that the EM performance of Cu bumps is significantly affected by the bump scheme and the direction of electron flow. The early failure rate is higher when the electron flow originates from the Ni-rich barrier side. Furthermore, the Cu/Ni/solder/ENEPIG system shows the highest early failure rate due to its single Sn grain structure. This study challenges the previous belief regarding the Ni barrier, suggesting that the inclusion of a Ni-rich barrier may necessarily have a detrimental impact on the EM performance of Cu bumps.