报告题目：Modeling of tin whisker growth

报告人:                                  Prof. Fuqian Yang

Department of Chemical and Materials Engineering

University of Kentucky, Lexington, KY 40506

时间：2015年7月15日(周三)  09: 30         

地点：中国科学院力学研究所主楼344会议室

报告摘要：

Whisker growth on beta-tin (b-Sn) is a phenomenon associated with stress relaxation. The growth of Sn-whiskers has been observed extensively in various environments, which appears to be a local response to external loading, including compressive stress, electric field, electric current, resonance vibration, temperature cycling, and humidity.  The use of pure Sn and Sn-based Pb-free alloys in microelectronics devices and systems has raised reliability concerns pertaining to the formation and growth of Sn-whiskers, particularly among high-reliability product communities such as the aerospace, biomedical, and military industries.

Based on the concept of the flow of the grain boundary fluid proposed by Yang, a nonlinear viscous model was proposed in analyzing the growth of a whisker.  This model consists of two units; one is linear flow and the other is power-law flow. Closed-form solution was derived for the growth rate of a whisker as a function of the pressure difference, which reduced to the result given by Tu and Li. Using this result and assuming the whisker growth as the mechanism for stress relaxation, two special cases were analyzed. For the linear flow, both the whisker growth and the stress relaxation associated with the whisker growth are an exponential function of time, and the characteristic time controlling the temporal evolution of the whisker length is proportional to the ratio of the viscosity of the grain boundary fluid to the biaxial modulus of the film. For the power-law flow, both the whisker growth and the stress relaxation associated with the whisker growth are a power function of time. The final length of the whisker for time approaching infinity, which is independent of the rheological properties of the grain boundary fluid, is proportional to the initial pressure and the film thickness and inversely proportional to the biaxial modulus of the film and the square of the whisker radius. The stress state in the film plays an important role in controlling the whisker growth.

报告人简介：

Dr. Fuqian Yang received his B.S. in Engineering Physics from Tsinghua University, M.S. in Mechanical Engineering and Ph.D. in Materials Science and Engineering from the University of Rochester. He is a full professor in the Department of Chemical and Materials Engineering at the University of Kentucky. He is a member of editorial board for Materials Science and Engineering A, Materials and Metallurgical Transaction A, Smart Grid and Renewable Energy and Annals of Materials Science & Engineering. He and Professor J.C.M. Li of the University of Rochester recently co-edited a book “Micro and Nano Mechanical Testing of Materials and Devices”, which was published by Springer in 2008. Dr. Yang’s research focuses on electrical-chemical-mechanical behavior of advanced materials, including creep behavior of materials, adhesive deformation of materials, electromechanical interaction of materials, stress-diffusion interaction, and fluid flow.

报告联系人：沈楠  (office@lnm.imech.ac.cn 82543935)