Electromigration and thermal migration in Pb-free interconnects

A set of experiments designed to understand the evolution of electromigration damage in Pb-free interconnects was conducted. It is found that the degree of EM damage is higher with increasing stress current and stress duration, and dependent on the closeness of the c-axis of the Sn grain to current direction. Controlling the solder texture is one of the key elements in improving EM lifetime. The effect of thermal gradient on solder reliability is studied by applying heat to the chip side of the solder joint. No thermal gradient induced migration is observed in Sn bumps with temperature gradients as high as 6.8×10⁵ °C/m.