Effects of Cu foam on microstructure and mechanical properties of SAC305 solder joints bonded with solid–liquid electromigration

Abstract

The effects of the addition of Cu foam on the microstructure and mechanical properties of Cu/Sn-3.0Ag-0.5Cu/Cu solder joints bonded with solid–liquid electromigration were investigated. Different bonding time (10, 30, 60 and 120 min) and current densities (0, 3.33 × 10² and 6.67 × 10² A/cm²) were applied to explore the optimal bonding conditions. The results indicated that the Cu foam as a barrier layer in the solder could effectively hinder the migration of Cu atoms. For the solder joints with Cu foam addition, the growth of the anodic intermetallic compounds (IMCs) became slow, the grains of the interfacial IMCs were apparently smaller, and the polarity effect was suppressed. The presence of Cu foam increased the tensile strength and improved the reliability of solder joints at the low current density (0 and 3.33 × 10² A/cm²). However, the tensile strength decreased sharply to 34.16 MPa after bonding for 120 min and the fracture mode changed from ductile fracture to brittle fracture at the high current density (6.67 × 10² A/cm²). Therefore, the addition of Cu foam was ineffective in improving the reliability at high current densities.