Modeling and Simulation - The Effects of Grain Coarsening on Local Stresses and Strains in Solder Microstructure
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.
- Research Organization:
- Sandia National Laboratories (SNL), Albuquerque, NM, and Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 3288
- Report Number(s):
- SAND99-0149C; ON: DE00003288
- Resource Relation:
- Conference: International Symposium on Advanced Packaging Materials - Processes, Properties and Interfaces; Braselton, GA; 03/14-17/1999
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COMPUTERS
INFORMATION SCIENCE
MANAGEMENT
LAW
MISCELLANEOUS
36 MATERIALS SCIENCE
42 ENGINEERING NOT INCLUDED IN OTHER CATEGORIES
Soldered Joints
Electronic Equipment
Grain Size
Aging
Thermal Cycling
Thermal Fatigue
Fractures
Cracks
Strains
Stresses
Lead
Tin
Eutectics
Computer Calculations