Electromigration of 96.5Sn-3Ag-0.5Cu flip-chip solder bumps bonded on substrate pads of Au/Ni/Cu or Cu metallization

Designed experiments are conducted in this paper to study the effect of Au/Ni/Cu or Cu substrate pad metallization on the electromigration reliability of 96.5Sn-3Ag-0.5Cu flip-chip solder bumps with Ti/Ni(V)/Cu under bump metallurgy. Electromigration patterns are investigated in solder bumps under a current stressing condition with an average current density of about 5 kA/cm
²
at an ambient temperature at 150 degC. Experiments show that test vehicles with Cu metallization exhibit better electromigration reliability compared to those with Au/Ni/Cu metallization. Corresponding failure mechanisms are proposed based on the observations of microstructures inside current stressed solder bumps