VEXTEC developed a probabilistic, material microstructural-based fatigue simulation approach for metallic life prediction. This methodology uses virtual testing to address real world variation in loading as well as the microscopic substructure of metals by modeling grain size, grain orientation, micro-applied stress and micro-yield strength as random variables. The fatigue simulation process is segregated into three phases: crack initiation, short crack growth and long crack growth. Global loading conditions, from finite element analyses, are translated to the local material microstructural level using 3-D Voronoi modeling. Although this technology was originally developed for lifing large structural aerospace components, it is now being used to predict fatigue response of electronic device interconnects. Electronic systems, such as circuit boards, are complex multilayered devices consisting of different materials with inherent variability. The electronics industry has extensively researched the root causes of lead solder failure. Thermal cycling causes global stresses across the devices which are translated to the stresses at the local solder material microstructure. Thermal cycling causes intermetallic shifting of the material microstructure that connects the metal to the board substrate. All of this, results in energy build up within solder material grains, which ultimately results in the initiation of a crack within the solder joint which grows to failure over time. Given the microstructural characteristics of lead-free solder, comparisons between these two types of materials can be made using this virtual simulation approach. Years of component or device fatigue testing can now evaluated based on near real time results from thousands or millions of virtual simulations.