Mechanisms of Sn Hillock Growth in Vacuum by In Situ Nanoindentation in a Scanning Electron Microscope (SEM)

摘要

Nanoindentation is an excellent technique to quantitatively probe the Sn film surface and to introduce controlled compressive stresses. In this work, we have conducted a long-term study of whisker growth in Sn films plated on Cu. In situ indentations were conducted in a scanning electron microscope under vacuum, to elucidate the effect of whiskering without significant oxidation. The evolution of whisker growth up to 1500 h was studied. Measurements of whisker height and width were used to determine the relationship between nodule volume and time. Extensive nodule growth was observed at indentations. Competing mass flow between indentations was observed, with some indentations exhibiting extensive growth, while the growth of others arrested within 100 h. It can be postulated that, when stresses are relieved slowly, hillock heights grow nearly linearly over time. When stress is relieved quickly, a sigmoidal-type curve (arresting growth) is predicted.