Insights on interfacial IMCs growth and mechanical strength of asymmetrical Cu/SAC305/Cu-Co system

In this study, a Cu-50Co (50 wt% Co) dual-phase alloy substrate was prepared, which was used to fabricate a sandwich structure of Cu/SAC305/Cu-50Co solder joint. The interfacial microstructure evolution, the growth kinetics and activation energies of intermetallic compounds (IMCs) layer in Cu/SAC305/Cu-50Co solder joints during solid-state aging treatment at different temperatures (120 degrees C, 150 degrees C and 180 degrees C) for various time were investigated. After reflowing at 290 degrees C for 10 min, an uneven and jagged-shaped (Cu, Co)(6)Sn-5 IMC layer was observed at the SAC305/Cu-50Co interface while scallop-shaped Cu6Sn5 IMC was formed at the SAC305/Cu interface. The thickness of IMCs at both of SAC305/Cu and SAC305/Cu-50Co interfaces increased with increasing aging time and aging temperature during solid-state aging. A (Cu, Co)(3)Sn phase was formed between the (Cu, Co)(6)Sn-5 IMC and the Cu-50Co substrate, while Cu3Sn IMC layer was observed at the interface between the Cu6Sn5 layer and Cu substrate. After prolonged aging treatment, the higher the aging temperature, the earlier (Cu, Co)(3)Sn and Cu3Sn IMC appeared. During aging, the difference of the diffusion coefficient of IMCs for SAC305/Cu and SAC305/Cu-50Co interfaces was increasingly reduced, while the activation energies of the total IMC at SAC305/Cu and SAC305/Cu-50Co interfaces were 70.76 and 47.96 kJ/mol, respectively. The shear strength experiments regarding two kinds of as-reflowed solder joints (Cu/SAC305/Cu and Cu/SAC305/Cu-50Co) were carried out. The results showed that the shear strength of the Cu/SAC305/Cu solder joint (49.2 MPa) was slightly lower than that of the Cu/SAC305/Cu-50Co solder joint (61.25 MPa).