Modeling and Experimental Behavior Studies on Tin Whiskers
Type of DegreePhD Dissertation
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The spontaneous growth of tin whiskers can occur under room temperature conditions. However, under more extreme external conditions (e.g., high temperature, high humidity, or thermal cycling), the rate of such growth tends to accelerate, longer whisker lengths, resulting in a larger possibility to decrease the reliability of electronic devices. Most research has not focused on internal conditions, such as the microstructure and internal stress distribution. Researchers have gained knowledge on factors that drive the tin whisker growth rate, but there is no general consensus on the internal mechanisms and key factors of whisker growth. Here, it is proposed to study the behavior of whisker formation from tin depositions on silicon substrates with different dimensions and applied stress. A model for the whisker growth mechanism is presented, which applies the influence of internal stress release and atomics diffusion in a finite element formation, based on the existing DRX model for tin whisker growth. The process of whisker formation of samples under controlled possible influencing factors is studied with the goal of developing a deeper understanding of the critical factors that drive whisker growth. In the experiments, reasonable controls on background Ar pressure, sputtering duration, thermal cycling temperature, and duties will be applied, and the comparison and analysis between the computational and experimental results will be made. The expected experimental results will serve to validate and provide insight to enhance the model’s predictive capability. The resulting model for whisker growth will illustrate whisker growth mechanisms using a DRX-based model, and provide insight into the influence of internal stress among metal layers, which would in turn provide input to the manufacturing process of electronics devices for the decrease whisker occurrences in future uses. Further, with TEM meshed grids, we confine volume of deposition material in both thickness and areal dimensions. On limited depositions, the whisker production is reduced by more than 86% comparing to controlling specimens without volume limitation. The experimental results also reveal the existence of volume threshold, below which whisker incubation is completely ceased. Such suppression effect of whiskering is also speculated to be governed by the spacings induced during deposition, which are considered as a powerful method to drain large amount of in-layer stress and affected the whiskering process.