Improvement in Intermetallic Thickness and Joint Strength in Carbon Nanotube Composite Sn-3.5Ag Lead-free Solder

The toxicity in the Sn-Pb solder has promoted the development of Pb-free solder in the electronics industries. Among the Pb-solders, the Sn-3.5Ag solder is considered a potential replacement and being studied by many researchers. Lately, nano material addition into the solder plays a significant role in the solder material in order to improve the joint reliability. In this study the influence of carbon nanotube (CNT) on the intermetallic formation and joint strength of Sn-3.5Ag solder under liquid state aging were investigated. The Sn-3.5Ag and Sn-3.5Ag-0.1CNT were prepared using the powder metallurgy method. The solders were soldered with Cu substrate at 250°C at different soldering time. The Cu6Sn5 and Cu3Sn intermetallics were observed under the scanning electron microscope with the Sn-3.5Ag-0.1CNT solder has a lower intermetallic thickness. The addition of CNT retarded the growth of Cu6Sn5 intermetallic from 1.69 x 10-10 to 1.02 x 10-10 cm2/s. Furthermore, CNT retarded the growth of Cu3Sn intermetallic from 4.9 x 10-11 to 2.5 x 10-11cm2/s. At the same time the Sn-3.5Ag-0.1CNT solder shows higher joint strength and lower ductility.