Reinforced performance of lead-free Sn-8Zn-3Bi solder with doping of 0.03 wt.% C60 on Cu pads

In this study, 0.03 wt.% C60 was doped into lead-free Sn-8Zn-3Bi solder by mechanically dispersing. The reinforced solder has been widely investigated under a current density of 3.5×103 A/cm2 at 100° for 180 hours. The interfacial morphologies and microstructures of the plain and doped Sn-8Zn-3Bi solder on Cu pads on daisy chain type ball grid array (BGA) substrates were systematically analyzed by SEM/EDX. It was found that C60 doped solder has well refined microstructure and the C60 dopant inhibited the Cu5Zn8 intermetallic compound (IMC) growth. Melting characteristic and mechanical property evaluation were also carried out. From differential scanning calorimetry (DSC) studies, the melting characteristic of the doped solders differed little from the plain solder. The shear strength and hardness of solder joints were substantially improved with the addition of C60. Moreover, shear fracture occurs at the IMC interfacial region during shear testing. The observed ductile fracture mode with a rough dimpled surface is attributed to a second phase dispersion strengthening mechanism.