Prediction of Delamination in Micro-electronic Packages

At present, a lot of delamination related reliability problems are observed in the micro-electronic industry. Examples are: die-lift; downbond stitch breaks associated with diepad delamination; passivation cracks related to interface delamination between chip and moulding compound. These reliability problems are driven by the mismatch between the different material properties, such as CTE, hygro-swelling, vapor pressure induced expansion, and degradation of the interfacial strength due to moisture absorption. The associated negative business consequence is significant. Clearly, the driving mechanisms of these delamination related problems should be explored before possible solutions can be found, such as expensive design changes and/or expensive material types to limit the delamination. This paper highlights our results to find the driving mechanisms for delamination-related reliability problems in micro-electronic packages using state-of-the-art virtual prototyping and/or qualification techniques. The numerical predictions are combined with novel interfacial adhesion test techniques able to measure the interfacial strength as functions of both temperature and moisture. As a typical example, delamination in the exposed pad package family is taken as a carrier. Novel numerical techniques are developed to predict the occurrence of interfacial delamination as function of manufacturing and testing conditions in micro-electronic packages. These techniques are improvements of well-known methods, such as virtual crack closure, J-integral, cohesive zone, and area release. The area release method does not require any presupposed position of any initial crack. Instead, at any desired positions within the specimen, an area energy release value is calculated which basically results from releasing an area (having a defined dimension) around each point in the specimen. Several reliable non-linear finite element models are developed to predict the moisture diffusion, deformation, stress, and interfacial energy history as functions of processes, temperature and moisture. Thus the effect of hygro-swelling, vapor pressure, interfacial degradation, and thermal expansion on delamination failures is predicted. Finally, by combining the models with simulation based optimization methods, design guidelines are derived for reducing reliability problems in microelectronic packages where the results provide us generic insight in the mechanisms of delamination-related problems