Micro-scale plasticity effects in microvia reliability analysis

Microvias play a key role in high density wiring substrates. To theoretically predict the fatigue life of the microvias, accurate estimation of plastic strain evolution in microvias is critical. Due to the temperature-dependent material properties and high cyclic strains induced due to thermal excursions in electronic packaging interconnects and components, plasticity theories are extensively used to predict the low-cycle fatigue life. Experimental evidence indicates that plastic deformation in metals and polymers at small scales depends not only on the state variables of stress and strain, but also on their higher order gradients. As the diameter of the microvia reduces, the wall thickness correspondingly reduces and hence the minimum feature size reduces to the order of microns, where scale effects in plasticity are predominant. A plastic strain gradient-based computational algorithm is employed in this work to study the thermo-mechanical deformation of microvia structure. The thermo-mechanical reliability analysis demonstrates the influence of incorporating strain gradient effects in predicting the evolution of plastic deformation in microvia structures.