Enhanced Electromigration Resistance of Pb-Free Solders by Using Cu/Sn Composite Structure

Abstract

This study employs a unique composite structure consisting of alternating Cu/Sn columns with different spacing to realize the electromigration resistance in Pb-free solders. Pure Sn and Cu/Sn composite structures were designed and current stressed by 1 × 104 A/cm2 at 80°C. The results show that the samples with a composite structure exhibited better electromigration resistance than those with a pure Sn structure. In addition, no void formation and no hillock appeared in the Cu/Sn composite structures with 20 μm of Cu column specimen after electromigration test for 1600 h. We proposed that this improved electromigration resistance in the composite samples is mainly because the current density in the current crowding region of Sn was reduced and the rate of void nucleation in the composite samples was effectively hindered by the introduction of Cu columns. Moreover, the void propagation rate was also lowered as a result of the better electromigration resistance of Cu columns.