In this study, three-dimensional finite elements were emplyed to study interfacial cracking problems encountered in electronic packaging. In the crack tip region, special elements were used that contain the correct 3-D crack tip singularity field with unknown stress intensity factors. These elements are usually designated as "enriched crack-tip elements". Using enriched elements, the elastic-plastic behavior of solder balls and interaction effects with nearby cracks in a semiconductor package were investigaed. Neglecting time dependent effects (creep, viscoplasticity), stress and fracture analyses were performed. Applying periodicty boundary conditions, a slice near the central region of a semiconductor device was considered. Two differently shaped interfacial cracks near the fillet region were considered. Including plasticity effects on the solder balls, the interaction between plastic deformation and fracture parameters was investigated (elastic crack tip behavior). The two interfacial crack configurations are; a vertical crack between the fillet and the chip, and an "L" shaped crack between the underfill material and the chip. The results from these calculations showed that plastic deformation, especially on the outermost solder ball, is affected by the presence of a crack in its vicinity and vice versa. It was observed that the plastic strains increase as the crack tip approaches the outermost solder ball. Depending on the type of crack under consideration, the fracture parameters can also vary significantly along the crack front even for the straight through cracks examined in this paper. This is attributled to the fact that there are two different materials (underfill material and solder) ahead of the crack front and that the solder deforms elasto-plastically. In studying the "L" shaped crack, it was concluded that inclusion of crack surface contact is critical for accurate determination of plastic strains and fracture parameters.
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