Modeling of Intergranular Mechanical Fatigue of a Sintered Nanosilver Die Attachment for Power Electronics

As a novel promising die-attach material, sintered nanosilver had been widely studied in electronic packaging, especially in applications with high power density. The increased power density, as well as a significant reduction in the solder joint size, could cause considerable thermomechanical stresses in the die attachment and the dies. It should be critical to predict the stress-strain response and the lifetime of the die attachment precisely in order to optimize the reliability of power devices. Instead of the conventional macroscopic constitutive models, e.g., Anand model, OW-AF model, and so on, a crystal plasticity finite-element (CPFE) method, which can involve the effects of grain size, orientation, shape, distribution, and so on, was proposed to predict both the macro- and micromechanical deformation behaviors of the sintered nanosilver. The parameters of the CPFE model of the sintered nanosilver were determined. The simulation results indicated that stress concentration could be present in or among the grains of the sintered nanosilver, locally. The nonuniform stress distribution should be critical to determine the crack initiation of the sintered die attachment. Consequently, the fatigue lifetime could be predicted more accurately using the CPFE model rather than the conventional OW-AF model, especially for the sintered nanosilver with porous microstructures.