Performance transformation of Co-added Sn58Bi solder joints under thermal shock conditions for interconnection packaging

Investigating solder joint stability in electronic packaging under extreme temperature fluctuations holds significant importance. In this experiment, the stability of Co particle-reinforced Sn58Bi/Cu solder joints was studied during the thermal shock process from −55 °C to 125 °C. By comparing the Sn58Bi-xCo (x = 0, 0.3)/Cu solder joints subjected to thermal shocks(from the 200th to 1200th cycle), it was found that adding Co effectively inhibited the Bi phase coarsening in the joint. Adding Co led to the transformation of the Cu₆Sn₅ intermetallic compound (IMC) layer into the (Cu, Co)₆Sn₅ IMC layer, resulting in an increase in the growth rate of the (Cu, Co)₆Sn₅ layer and a decrease in the growth rate of the Cu₃Sn layer. During the thermal shock process, adding Co led to the refinement of the IMC grains and the enhancement of the stability of the IMC layer. This, in turn, resulted in the inhibition of crack propagation and the delay of the occurrence of brittle fracture. The shear strength of the Co-added solder joints was consistently higher than that of the Sn58Bi solder joints.