Effect of pre-annealing of Au metallization structure on the bonding performance with low temperature pressureless sintering Ag

Au metallization is the inevitable choice for many device applications which require a multiple reflow processes. This research focuses on revealing the effect of pre-annealing of Au metallization structure using an electro-less plating process on the bonding performance with sintered microporous Ag. The pre-annealing temperature was investigated from 150 °C ~ 350 °C. Compared with the Au metallization structure without pre-annealing, the shear strength of interface between Au metallization structure and sintered microporous Ag increased from 15 MPa to 25 MPa when the structure pre-annealed at 250°C. The mechanism of pre-annealing on the Au metallization structure was discussed by SEM, EDS and XRD analysis. It was revealed that pre-annealing at the temperature of 250 1 effectively prevented the diffusion of Ni-P layer from the underneath of the Au metallization layer into the sintered microporous Ag as well as the formation of Ag-Au solid solution during the sintering process. The pre-annealing treatment can largely improve the bonding quality for Au metallization structure by using the sintered Ag technology.