Modeling and Simulation - The Effects of Grain Coarsening on Local Stresses and Strains in Solder Microstructure

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A critical issue in the long-term reliability of solder connections used in electronic packages is the joint failure during thermal cycling. Presently in most finite element analysis to predict the solder joint fatigue failures, solder is assumed as a homogeneous single-phase metal. However in the last decade, several metallurgical studies have shown that solder microstructure may have a role in early solder joint failures (ref 1). Investigators have observed (ref 1) that solder microstructure coarsens in local bands during aging and during thermal cycle fatigue. In a failed solder joint, the fatigue cracks are found in these bands of coarse ... continued below

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Chanchani, R. January 21, 1999.

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  • Sandia National Laboratories
    Publisher Info: Sandia National Laboratories, Albuquerque, NM, and Livermore, CA
    Place of Publication: Albuquerque, New Mexico

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A critical issue in the long-term reliability of solder connections used in electronic packages is the joint failure during thermal cycling. Presently in most finite element analysis to predict the solder joint fatigue failures, solder is assumed as a homogeneous single-phase metal. However in the last decade, several metallurgical studies have shown that solder microstructure may have a role in early solder joint failures (ref 1). Investigators have observed (ref 1) that solder microstructure coarsens in local bands during aging and during thermal cycle fatigue. In a failed solder joint, the fatigue cracks are found in these bands of coarse grains. It is speculated that the grain coarsening increases the local strains within the microstructure, thereby increasing the likelihood for a crack to initiate. The objective of this study is to model and simulate the effect of grain coarsening on local stresses and strains. During solidification of eutectic Pb/Sn solder, two types of microstructure form, namely lamellar and equiaxed. In this study, I have developed a computer code to generate both types of microstructures of varying grain coarseness. This code is incorporated into the finite element (FE) code that analyzes the local stresses and strains within the computer-generated microstructure. The FE code, specifically developed for this study, uses an algorithm involving the sparse matrix and iterative solver. This code on a typical single-processor machine will allow the analyst to use over 1 million degrees of freedom. For higher number of degrees of freedom, we have also developed a code to run on a parallel machine using message passing interface. The data reported in this paper were obtained using the single-processor code. The solder microstructure, if assumed to be homogeneous single phase, has gradual variation in local stresses and strains. In 2-phase solder, von mises stresses and strains are heterogeneously distributed. In general, the maximum von mises stress in 2-phase solder case are higher than in 1-phase solder. In lamellar microstructure of 2-phase solder, the maximum von mises stress in the microstructure gradually increases with grain coarseness. In equiaxed microstructure of 2-phase solder, the maximum von mises stress does not follow a general trend, increasing or decreasing, with increasing grain coarseness.

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  • International Symposium on Advanced Packaging Materials - Processes, Properties and Interfaces; Braselton, GA; 03/14-17/1999

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  • Other: DE00003288
  • Report No.: SAND99-0149C
  • Grant Number: AC04-94AL85000
  • Office of Scientific & Technical Information Report Number: 3288
  • Archival Resource Key: ark:/67531/metadc688967

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • January 21, 1999

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  • July 25, 2015, 2:20 a.m.

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  • Nov. 29, 2016, 8:19 p.m.

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Chanchani, R. Modeling and Simulation - The Effects of Grain Coarsening on Local Stresses and Strains in Solder Microstructure, article, January 21, 1999; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc688967/: accessed December 12, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.