Introduction of Professor Liming Chang
Prof. Liming Chang earned his B.S. degree in mechanical engineering from Drexel University in 1983 and M.S. and Ph.D. in mechanical engineering from the University of Illinois at Urbana-Champaign in 1985 and 1988. He then served as an assistant professor in mechanical engineering for four years at the Hartford Graduate Center, Rensselaer Polytechnic Institute. Prof. Chang joined the Pennsylvania State University in 1992 and was promoted to Associate Professor in 1996 and Professor in 2002.
Prof. Chang conducts research in engineering tribology. He develops mathematical models and conducts experiments to study problems in micro-elastohydrodynamic, mixed and boundary lubrication. He has published over fifty refereed journal papers in this area of research, primarily in ASME Journal of Tribology and STLE Tribology Transactions.
He has organized and chaired a number of technical sessions in STLE Annual Meetings and ASME/STLE Joint Tribology Conferences. Dr. Chang was the Vice Chair and Chair of STLE Gear Technical Committee and is currently a member of STLE Award Committee.
讲学题目：
1. Research on Thermal Shear Localization in Elastohydrodynamic Lubrication Films
2. On the Mechanisms of Material Removal in Chemical-Mechanical Planarization of Semiconductor Wafers
讲学时间、地点：
2007年7月16日上午 8：30~ 11：30
机械楼4017
讲学内容：
1．Research on Thermal Shear Localization in Elastohydrodynamic Lubrication Films
Experiments and computer simulations have revealed some unusual results of elastohydrodynamic lubrication (EHL) associated with a high degree of thermally induced inhomogeneous shear across the lubricant film, or thermal shear localization. The results include the development of a sizable film dimple in the central EHL region and a dramatic reduction in EHL traction. In this study, a theoretical analysis is carried out to determine the conditions under which the thermal shear localization may develop in EHL films. For a Newtonian lubricant obeying the Barus law of viscosity, a dimensionless group-parameter is identified that fully governs the degree of the thermal inhomogeneous shear. Results are presented that show the critical range of values of this parameter corresponding to the onset of the shear localization. The analysis is also extended to lubricants with non-Newtonian behavior. Results suggest that the same dimensionless group-parameter may be used to measure the degree of the shear localization when the lubricant viscosity in the parameter is replaced by an effective viscosity that accounts for the non-Newtonian effect.
2. On the Mechanisms of Material Removal in Chemical-Mechanical Planarization of Semiconductor Wafers
Understanding of the mechanisms of material removal is of fundamental importance in chemical-mechanical planarization of semiconductor wafers. A plausible mechanism at work is that the material is removed at the molecular scale by de-bonding the chemistry-weakened molecules at the wafer surface. A sequence of order-of-magnitude calculations is carried out to substantiate this mechanism of materials removal. The calculations reveal several interesting insights such as the small real area of pad/wafer contact, the large number of slurry particles participating in the removal process, and the high frequency of particle-action at a wafer surface point. The results lay further credence to the polishing mechanism in addition to its underlying theoretical foundation. Some modeling aspects based on this mechanism of materials removal are described.
国际合作处
2007年7月12日