Interfacial intermetallic growth and shear strength of lead-free composite solder joints

In the present study, varying weight percentages of carbon nanotubes (CNTs) were incorporated into Sn–Ag–Cu solder matrix, to form composite solders. Isothermal aging study was performed on solder joints, to investigate the formation and growth of the intermetallic compound (IMC) layer at the solder/metallization interface. Shear tests were also conducted on as-soldered and aged solder joints. Results revealed that after soldering, the initial interfacial IMC thickness of the unreinforced solder joint was comparable to that of the composite solder joints. However, after aging, the interfacial IMC layer of the unreinforced solder joint was observed to grow more significantly than that of the composite solder joints. Moreover, the composite solder joints also exhibited lower diffusion coefficient and this signified that the presence of CNTs was effective in retarding the growth of the IMC layer. Shear tests results revealed that as-soldered and aged composite solder joints had better shear strength than their monolithic counterparts and the shear strength of all aged solder joints decreased with increasing aging time.