Impact of different isothermal aging conditions on the IMC layer growth and shear strength of MWCNT-reinforced Sn–5Sb solder composites on Cu substrate

In this study, the effect of multi-walled carbon nanotubes (MWCNTs) reinforcement on the intermetallic compound (IMC) layer growth and shear strength of Sn–5Sb-xCNT/Cu composite solder joints subjected to different isothermal aging conditions has been investigated. A series of plain and composite lead-free solder systems (Sn–5Sb-xCNT; x = 0, 0.01, 0.05 and 0.1 wt%) was successfully developed through the powder metallurgy method. Isothermal aging process was performed on the solder/Cu joints at 120 °C, 150 °C and 170 °C temperatures in order to investigate the evolution of the interfacial IMC layers and the shear strength property. Experimental results showed that the thickness of the total IMC layer increased with rising aging temperature. While the Cu₃Sn IMC maintained a layer-type morphology for all aging conditions, morphology of the Cu₆Sn₅ IMC transformed from a scallop-type to a layer-type after aging at intermediate (150 °C) and high (170 °C) temperatures. Given the potential of MWCNTs as a reinforcement material, significant suppression in IMC layer growth was demonstrated by the composite solder joints relative to the plain counterpart. Comprehensive investigation on the growth kinetics showed that the presence of MWCNTs in the composite solder joints was effective in slowing down the diffusion mechanism responsible for IMC growth. Overall, the Sn–5Sb-0.05CNT composite solder joint exhibited the lowest diffusion coefficient within the range of 0.09 × 10⁻¹⁴- 1.03 × 10⁻¹⁴ cm²/s and 0.95 × 10⁻¹⁴- 9.8 × 10⁻¹⁴ cm²/s for Cu₆Sn₅ and Cu₃Sn IMC layers respectively. Moreover, the strengthening effect of the MWCNTs reinforcement was well marked in the composite solder joints as the maximum shear strength within a range of 24.2–15.2 MPa was exhibited by the Sn-0.01CNT/Cu composite solder joint subjected to reflow soldering and isothermal aging conditions.