Comparative study between the Sn–Ag–Cu/ENIG and Sn–Ag–Cu/ENEPIG solder joints under extreme temperature thermal shock

The interfacial reactions and the growth behavior of interfacial intermetallic compounds (IMCs), as well as their effects on the mechanical properties of the Sn-3.0Ag-0.5Cu (SAC305)/electroless nickel-electroless palladium-immersion gold (ENEPIG) solder joints under extreme temperature thermal shock between − 196 °C and + 150 °C were investigated, and compared with those of the SAC305/electroless nickel-immersion gold (ENIG) solder joints. The morphology of (Cu, Ni)₆Sn₅ IMCs formed at the SAC305/ENIG interface transformed from column-type to polygon-type during extreme temperature thermal shock, while the needle-type and thin-layer-type (Cu, Ni, Pd)₆Sn₅ IMCs at the SAC305/ENEPIG interface completely transformed to chunk-type. The growth rate of interfacial IMCs in the SAC305/ENEPIG joint was slower in contrast to that in the SAC305/ENIG joint, since the Pd(P) layer in the ENEPIG surface finish inhibited the formation and growth of interfacial IMCs. After thermal shock for 400 cycles, the shear force of the SAC305/ENIG and SAC305/ENEPIG joints decreased about 29.06% and 9.79%, respectively. Moreover, the shear force of the SAC305/ENEPIG joints was consistently higher than that of the SAC305/ENIG joints. The SAC305/ENEPIG joints always fractured in the solder matrix, regardless of thermal shock cycles, while the fracture location of the SAC305/ENIG joints transferred from inside the solder matrix to partially inside the solder matrix and partially at the solder/IMC layer interface with increasing thermal shock cycles.