Multiscale Modeling of the Effect of Micro-alloying Mn and Sb on the Viscoplastic Response of SAC105 Solder

This study investigates the time-dependent viscoplastic response of two relatively new SAC105-X solders—SAC105-05Mn (Sn 1.0 Ag 0.5 Cu (SAC105) doped with 0.05 wt.% Mn), and SAC105-55Sb (SAC105 doped with 0.55 wt.% Sb). The results showed that the addition of Mn or Sb increases the creep resistance of SAC105 solder by one to two orders of magnitude at the tested stress levels of 2–20 MPa. The addition of Mn as a fourth alloying element promotes homogeneous distribution of micron-scale Cu 6 Sn 5 intermetallic compounds (IMCs), thereby reducing their interparticle spacing as compared to that of SAC105. On the other hand, addition of Sb does not change the spacing of the Cu 6 Sn 5 particle, but promotes the formation of uniformly sized Sn dendritic lobes, homogeneously distributed in the whole solder joint. Moreover, Sb also forms a solid solution with Sn and strengthens the Sn matrix in SAC105-55Sb itself. The effects of these microstructural changes (obtained using image processing) on the secondary creep constitutive response of SAC105 solder interconnects were then modeled using a mechanistic multiscale creep model. The mechanistic model was able to accurately capture the trends in the secondary creep constitutive response of the alloys and to explain the improvement in creep resistance of SAC105 due to the addition of Mn and Sb.