Electromigration in a Sn-3 wt.%Ag-0.5 wt.%Cu-3 wt.%Bi Solder Stripe Between Two Cu Electrodes Under Current Stressing

Abstract

The electromigration behavior of a Sn-3 wt.%Ag-0.5 wt.%Cu-3 wt.%Bi solder stripe between two Cu electrodes under current stressing at various densities has been investigated for a current stressing time of 72 h and a temperature of 120°C. After current stressing at a density of 1.0 × 104 A/cm2, the solder matrix exhibited a slight microstructural change as well as formation of a distributed Cu6Sn5 phase near the anode-side solder/Cu interface. Upon increasing the current density to 3.9 × 104 A/cm2 and 5.0 × 104 A/cm2, a high density of distributed Cu6Sn5 phase was formed across the entire solder stripe, resulting in pronounced microstructural change of the solder. Hillocks were also formed near the anode-side interface due to accumulation of a Sn-rich phase, a Bi-rich phase, and a distributed Cu6Sn5 phase, while voids were formed in the solder matrix and at the opposite cathode side. The mechanisms of formation of the distributed Cu6Sn5 phase and migration of Bi and Sn are discussed.