Microstructure evolution and mechanical strength evaluation in Ag/Sn/Cu TLP bonding interconnection during aging test

In this study, the microstructure of Ag/Sn/Cu TLP bonding interconnections was investigated. No defects such as voids were observed at the interface between Ag-Sn IMCs and Cu-Sn IMCs in both as-reflowed and aged Ag/Sn/Cu TLP bondlines. Microstructure evolution and phase transformation during aging test were studied in detail to further evaluate the reliability of Ag/Sn/Cu TLP bondlines during long-term service in high temperature. The phase composition at the interface of as-reflowed interconnects was Ag/Ag3Sn/Cu6Sn5/Cu and transformed to Ag/(Ag)/ζ-Ag/Cu3Sn/Cu after aging test. Different characteristics of diffusion between Cu and Ag atoms were found in Cu/Ag/Sn TLP sample. The average shear strength of the as-reflowed and the aged Ag/Sn/Cu TLP bonding interconnections are 49.57 MPa and 50.03 MPa, respectively, and this indicated that almost no deterioration occurred during the aging test. The fracture surfaces of the aged Ag/Sn/Cu TLP bonding interconnections after shearing test were characterized in detail. The results show that the substitution of Cu for one side of Ag plates in traditional Ag-Sn TLP joint did not influence its strength and fracture mode. The Cu-rich structure at the fracture surfaces is always irregular while the Ag-rich phases are often accompanied by shear bands and dimples.