The Influence of Processing Conditions on the 3-D Interconnected Structure of Nanosilver Paste

Nanosilver paste is a promising material for power device interconnects. Interconnects are fabricated from nanosilver paste through a sintering process that drives off solvents and dispersants and fuses the silver particles. The integrity of the resulting interconnect is affected by the silver microstructure. This paper explored how sintering temperature, atmosphere, and time influenced microstructure as revealed by transmission electron microscopy and 3-D imaging via dual-beam serial sectioning. Nanosilver paste was sintered in combinations of the following parameters: a sintering atmosphere of air or nitrogen; temperatures of 120 °C or 255 °C; and sintering times of 5, 10, or 30 min. For the 255 °C temperature, oxygen in air facilitated removal of organic solvent and dispersant molecules and led to a microstructure with a coarser ligament network than samples sintered at the same temperature and times in nitrogen. The coarser ligament network was characterized by thick connected ligaments, large connected pores, and few isolated pores; this microstructure has been correlated with improved mechanical strength. Details of both 2-D and 3-D ligament network morphology, grain morphology, grain size, and the associated grain boundaries are discussed.