Microstructure evolution and shear fracture behavior of aged Sn3Ag0.5Cu/Cu solder joints

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2016-09, Vol.673, p.167-177
• Main Authors: Hu, Xiaowu, Xu, Tao, Keer, Leon M., Li, Yulong, Jiang, Xiongxin
• Format: Article
• Language: English
• Subjects: Aging; Copper; Fracture; Fracture mechanics; Intermetallic compound; Intermetallic compounds; Intermetallics; Microstructure; Shear; Shear strength; Solders
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2016.07.071

The effect of isothermal aging on the microstructure and shear strength of Sn3Ag0.5Cu/Cu (SAC305/Cu) solder joints were studied systematically. The single-lap shear samples of SAC305/Cu solder joint were prepared and aged up to 456h at 150 and 180°C, respectively. The interfacial intermetallic compound layer of the aged solder joint gradually thickened with increasing both aging time and aging temperature, while, the interfacial intermetallic compound layer morphology transformed from scallop-type to layer-type after the aging treatment. The growth of the interfacial Cu-Sn interfacial intermetallic compounds layer of aged SAC305/Cu solder joints exhibited a linear function of the square root of aging time, indicating that the formation of the interfacial Cu-Sn interfacial intermetallic compounds during aging treatment was mainly controlled by the diffusion mechanism. The diffusion coefficient (D) values of interfacial intermetallic compound layer were 4.64×10−17 and 1.06×10−16m2s−1 for aging temperatures of 150°C and 180°C, respectively. Single-lap shear tests results revealed that the shear strength of SAC305/Cu solder joints decreased continuously with an increase in interfacial intermetallic compound layer thickness and aging time. The main reason for these characteristics was the excessive increase in the interfacial intermetallic compound thickness of solder joints, causing a change in the stress concentration of the shear load from the protruding region to the inside of the interfacial intermetallic compound layer at the same tested condition. In addition, the shear fractures in as-reflowed and short time aged solder joints were shown to be ductile in nature and confined in the bulk solder rather than through the interfacial intermetallic compound layer. However, the shear fracture locations transferred from the solder bulk to the interfacial Cu-Sn interfacial intermetallic compound layer, and finally to the Cu3Sn/Cu interface with increasing aging time.