Ni-Sn solid-liquid interdiffusion (SLID) bonding for thermo-electric elements in extreme environments — FEA of the joint stress

Ni-Sn solid-liquid interdiffusion (SLID) bonding was investigated for use in extreme thermal conditions. Energy harvesting by thermoelectrics push for utilization of ever increased temperature gradients to improve energy conversion efficiency. Exposure to large temperature gradients induce thermomechanical stress in joints that may lead to catastrophic device failure by fractures in the joint. Finite element analysis of skutterudite CoSb₃ joined by Ni-Sn SLID bonding to alumina substrates was performed. The bond structure was CoSb₃/ TiN/Ni /Ni₃Sn₄/Ni/Cu/Al₂O₃. Temperature gradients of up to ~100 °C/mm at temperatures up to 500 °C were employed. Two types of models were compared; (1) one element bonded to a substrate on one side and (2) one element symmetrically bonded to substrates on both sides. The results show that the stress field is dominated by the residual stress from the process, with limited contributions from external loads and system configuration.