Influence of carbon nanotubes on the morphology of Cu6Sn5 in Cu/(Sn–Ag–Cu) solder joints

Abstract

This study delves into the intricate interaction between multi-walled carbon nanotubes (MWCNTs) and the Sn–Ag–Cu solder system, highlighting its relevance in lead-free soldering applications. Reflow and isothermal aging induce the formation of intermetallic layers at the joint interface, including Cu6Sn5, Cu3Sn, and irregularly shaped Ag3Sn particles. The addition of MWCNTs leads to the flattening of Cu6Sn5 grains, restraining their growth and potentially improving mechanical strength. Notably, MWCNTs exhibit a relatively high affinity with Ag3Sn. Grain size distribution analysis indicates that MWCNTs reduce particle size, effectively suppressing intermetallic compound growth. Over time, grain size increases due to simultaneous coarsening and growth during isothermal aging. In the growth kinetics analysis of intermetallic compounds in SAC305-MWCNTs solder joints, stable behavior is observed for Cu3Sn growth, driven by solid-state diffusion between Cu6Sn5 and Cu. In contrast, Cu6Sn5 exhibits significant variations in growth behavior with temperature changes. Furthermore, the evaluation of activation enthalpy for Cu3Sn growth in the Cu/(SAC305-MWCNTs) and Cu/SAC305 diffusion couples reveals similar n and k values of the power function for the layer growth, indicating a comparable rate-controlling process for Cu3Sn growth. The presence of MWCNTs in the solder does not significantly influence the rate-controlling process or activation enthalpy for Cu3Sn growth, contrasting with the observed effects on Cu6Sn5 growth. This study provides valuable insights into the interactions within the SAC305-MWCNTs solder system, offering significant implications for lead-free soldering applications.

Keywords

• Carbon nanotubes
• Intermetallic compound
• Sn–Ag–Cu alloys
• Rate-controlling process
• Cu6Sn5 morphology
• Grain boundary diffusion