Course Description (2hrs):
Constitutive and failure descriptions of SnAgCu solder alloys are of great interest at the present. Commonly, constitutive models that have been successfully used in the past for Sn-Pb solders are used to describe the behavior of SnAgCu solder alloys. Two issues in the characterization of lead-free solders demand careful attention: (i) Lead-free solders show significantly different creep strain evolution with time, stress and temperature and (ii) The building of valid constitutive models from test data derived from tests on solder joints must de-convolute the effects of joint geometry and its influence on stress heterogeneity. In the first part of the tutorial we will review the common approaches to modeling solder behavior, along with their limitations and then describe our efforts in developing constitutive models of SnAgCu solders that are valid across a wide range of strain rates.
The problem of solder joint fatigue is essentially one of fatigue crack growth. However, there is little work that has been done to arrive at fatigue life estimations by means of tracking of the crack front and its growth. Common fatigue life models such as the Coffin-Manson rule are empirical and therefore, limited in their applicability and in the insight they provide. There are several challenges to employing a fracture mechanics approach to accurately track the growth of a fatigue crack in a solder joint. Key among these, are the facts that the problem involves large-scale yielding, viscoplastic solder behavior and complex geometries. In the second part of the tutorial, we will describe the various approaches to modeling solder joint fatigue and present our efforts at developing Cohesive Zone Model inspired approaches to predicting crack propagation at solder interfaces.
Bio:
Ganesh Subbarayan is a Professor of Mechanical Engineering at Purdue University. He was previously at University of Colorado (1994-2002) and at IBM Corporation (1990-1993). He holds a B.Tech degree in Mechanical Engineering (1985) from the Indian Institute of Technology, Madras and a Ph. D. (1991, direct PhD program) degree in Mechanical Engineering from Cornell University. Dr. Subbarayan's research is broadly related to the reliability of Microelectronic Interconnects and Packages. Dr. Subbarayan is a recipient of the 2005 Mechanics Award from the ASME EPP Division, 2005 University Faculty Scholar Award from Purdue University, NSF CAREER award, the NSF Research Initiation Award, the 2003 Charles E. Ives Outstanding Paper Award from the Journal of Imaging Science and Technology, the 2002 Highly Commended Award from Soldering and Surface Mount Technology journal, the Itherm 2000 Best Paper Award, the 1996 Peter A. Engel Best Paper Award from ASME Journal of Electronic Packaging, and an IBM Invention Achievement Award. He is a Fellow of ASME and he currently serves as the Editor-in-Chief of IEEE Transactions on Advanced Packaging.
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