GOALI: Understanding and Modeling Electromigration Induced Solder Degradation

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TECHNICAL SUMMARY:The goals of this research are (i) to gain a better understanding of the effect of microstructure on the driving forces and resulting mass diffusion processes associated with electromigration as well as stress and temperature driven diffusion processes in tin-based solder, and (ii) to develop validated predictive simulation tools to predict the lifetime of solder connections for given microstructural parameters. Electromigration is a mass diffusion process attributed to momentum transfer from conducting electrons to diffusing metal atoms, which, over time, may lead to degradation and device failure. With the conversion to tin-based solders and the continued miniaturization of microelectonic devices, reliability has become a major concern due to the complex behavior of tin-based solder subjected to increasing current densities that drive electromigration. This work involves an integrated effort involving experimentation, modeling, and simulation. The experimental work focuses on accelerated electromigration tests on chip scale package test structures and detailed materials characterization to investigate the effect microstructure has on degradation. This effort is closely coupled with the modeling and simulation work focused on developing a model for diffusion at the grain scale, considering the electrical, mechanical, and thermal driving forces. Both anisotropic lattice and grain boundary diffusion will be included in the model, as well as crystal plasticity in the mechanical response. The model will be implemented into a parallel, finite element simulation tool, which will be validated against experiments and used to predict time to failure for representative microstructures. This work is a collaborative effort with researchers at Fairchild Semiconductor, who will lead the experimental work, be involved in the development of simulation tools, and will use the tools developed in their future package design process.NON-TECHNICAL SUMMARY:This research addresses reliability issues associated with tin-based solders in microelectronic devices that are arising as devices become smaller in order to increase chip speed while reducing cost and power consumption. Due to environmental concerns, tin-based solders have now replaced lead-based solders used in microelectronic devices. When an electrical current is carried by a very small solder bump in a modern device, a process called electromigration occurs where the solder material actually migrates from one end of the solder bump to the other, driven by the electrons flowing through the solder. This migration of material may lead to failure, which is a major source of reliability concern in tin-based solders. Electromigration may be slowed or completely arrested through careful design and manufacture of the microelectronic device. In order to do this, a better understanding of electromigration in tin-based solder, and modeling and simulation tools based on that understanding must be developed, which is the focus of this research. Researchers at Fairchild Semiconductor, a US company and global provider of semiconductor solutions, are collaborators on this research. This project will impact Fairchild and its customers by developing the knowledge needed to more accurately predict the life and reliability of wafer level packaging and will provide a critical product design tool to shorten time to market and maintain a competitive advantage in the global market. This project will also train and equip undergraduate and graduate students involved in the research in new advanced methods for physics based modeling of materials and processes, computational engineering, and conducting fundamental interdisciplinary research to address emerging research needs in material processing and design.