MS&E Colloquium - Chason
Date: October 24, 2008 from 2:00 pm to 3:00 pm EDT
Location: 214 S. W. Mudd
Contact: For further information regarding this event, please contact Chad Gurley by sending email to .
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How non-equilibrium thin film conditions affect residual stress

and morphology evolution



Eric Chason


Brown University

Division of Engineering

Providence, RI


Thin films are often not in their equilibrium state, which is a driving force for their properties to change with time.  In this talk, we will discuss results of two different studies in which the non-equilibrium conditions modify the stress and microstructural evolution: 1) stress generation in polycrystalline films and 2) whisker formation in Sn coatings on Cu.  In the case of polycrystalline films, we will review experimental results of stress evolution under a variety of growth conditions.  We will describe a simple kinetic model of competition between different mechanisms of stress generation and relaxation to explain the results.  In this picture, tensile stress is created as the grain boundary is formed and compressive stress is generated by atoms inserting themselves into the growing grain boundary.  This simple model is shown to describe a large number of observations and predict the effect on stress of changing the growth conditions.  In the case of whisker formation, we will show how an interfacial reaction between the Sn and Cu creates stress which acts as a driving force to extrude the whisker from the surface.  These whiskers are a major reliability concern in Pb-free electronics manufacturing, and we will also describe how the presence of Pb prevents whiskers form forming.  In both cases, the studies are aided by the use of real-time in situ diagnostics that enable the kinetic evolution of the stress and morphology to be studied.