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Effect of Cyclic Damage on the Constitutive Behavior & Microstructure of Sn3.0Ag0.5Cu (SAC305) Solder

Published online by Cambridge University Press:  31 January 2011

Gayatri Cuddalorepatta  and
Abhijit Dasgupta
Gayatri Cuddalorepatta
Affiliation:
[email protected], University of Maryland, Mechanical Engineering, College Park, Maryland, United States
Abhijit Dasgupta
Affiliation:
[email protected], University of Maryland, Mechanical Engineering, College Park, Maryland, United States
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Abstract

This study examines the effect of cyclic damage on the constitutive response and microstructural evolution of SAC305 solder. Cyclic damage is induced through isothermal, mechanical cycling tests at high strain rate and room temperature, using modified lap shear microscale specimens (180μm wide solder joint). The properties of interest are elastic, plastic, yield, and viscoplastic material constitutive behavior. In the current study, creep strain accumulation is accommodated when determining the constants, unlike those reported in prior studies [1]. Insights into the evolution of the measured properties are provided by correlating previously reported microstructural grain evolution of microscale SAC305 solder as a function of cyclic damage [2, 3].

The hysteresis response and the elastic, plastic and yield measurements from the initial cycles show significant piece-to-piece variability (similar to prior virgin state viscoplastic measurements [3]). The scatter arises since as-reflowed SAC solder joints at length scales of 200μm consist of only a few anisotropic Sn grains that make the joint mechanically inhomogeneous. However, when subject to mechanical cycling fatigue at room temperature these joints undergo grain homogenization due to recrystallization, which is a possible explanation to the drop in scatter with progressing damage. The observed grain evolution is similar to that seen in solder joints under life-cycle loading.

The elastic-plastic response and yield strength of SAC305 solder do not show significant contribution from creep deformations at the chosen load levels. The properties degrade with increasing accumulated cyclic damage, at a rate that is proportional to the severity of the cyclic load. The yield stress measurements suggest that SAC305 obeys an independent hardening rule, rather than isotropic or kinematic hardening. The performance of a continuum damage mechanics based model from prior studies in representing the measured degradation in elastic, plastic and yield properties is discussed [4,5].

Comparison of the creep behavior of cycled SAC305 specimens (at 50% load drop) with that of uncycled specimens shows that the effective creep compliance and effective secondary creep strain rate increase significantly. As a point of comparison, the creep resistance of cycled SAC305 specimens is even lower than that of as-reflowed Sn37Pb specimens. Similar changes are seen in the stress relaxation behavior. Challenges and limitations of the current studies are included.

Keywords

grain sizesolderingfatigue
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1158: Symposium F – Packaging, Chip-Package Interactions and Solder Materials Challenges , 2009 , 1158-F02-03
Copyright
Copyright © Materials Research Society 2009

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References

1 Cuddalorepatta, G. et al. , “Effect of Cyclic Fatigue Damage Accumulation on the Elastic-Plastic Properties of SAC305 Solders”, EuroSimE Proceedings 2009 Google Scholar
2 Holdermann, K. et al. , “Dynamic Recrystallization of Sn3.0Ag0.5Cu Pb-Free Alloy”, ASME IMECE Proceedings 2008 Google Scholar
3 Cuddalorepatta, G. et al. , “Viscoplastic Behavior of Hypo-Eutectic Sn3.0Ag0.5Cu Pb-Free Alloy Under Creep Loading Conditions”, ASME IMECE Proceedings 2007 Google Scholar
4 Kachanov, L. M. “Continuum Damage Mechanics”, Martinus Nijhoff Publishers, 1986 Google Scholar
5 Ladani, L. Dasgupta, A. International Journal of Fatigue, 31, 703, (2009)Google Scholar
6 Cuddalorepatta, G. et al. , “Isothermal Mechanical Durability of Hypoeutectic Sn3.0Ag0.5Cu”, ASME IMECE Proceedings, 2005 Google Scholar
7 Cuddalorepatta, G. et al. , “Optimization of Dwell Time for Accelerated Thermal Cycling of Sn3.0Ag0.5Cu Pb-Free Interconnects”, IC-ICAME Conference, IISc, India, 2008 Google Scholar
8 Cuddalorepatta, G. et.al, “Stress Relaxation Characterization of Hypoeutectic Sn3.0Ag0.5Cu Pb-free Solder: Experiment and Modeling”, EuroSimE Proceedings 2007 Google Scholar
9 Haswell, P. 2001, “Durability Assessment and Microstructural Observations of Selected Solder Alloys”, Ph.D. Dissertation, University of Maryland, College Park, MD, USA Google Scholar
10 Zhang, Q. 2004, “Isothermal Mechanical and Thermo-mechanical Durability Characterization of Selected Pb-Free Solders”, Ph.D. Dissertation, University of Maryland, College Park, MD, USA Google Scholar
11 Terashima, S. et al. , “Effect of Silver Content on Thermal Fatigue Life of Sn-xAg-0.5Cu Flip-Chip Interconnects,” J. of Elect. Mat., 32, 2, (2003)Google Scholar
12 Wiese, S. et al. , Microelectronics Reliability, 44, 1923, (2004)Google Scholar
13 Kang, S.K. et al. , “The Microstructure, Thermal Fatigue, and Failure Analysis of Near-Ternary Eutectic Sn-Ag-Cu Solder Joints”, Mater.Trans., 45, 3, (2004)Google Scholar
14 Sundelin, J. et al. , “Recrystallization Behavior of SnAgCu Solder Joints”, Mater. Sci. Eng. A., 474,(1-2), (2008)Google Scholar
15 Borgerson, P. et al. , “Pb-Free Solder: New Materials Considerations for Microelectronics Processing”, MRS Bulletin, (2007)Google Scholar
16 Zhao, J. et al. , International Journal of Fatigue, 22, 665,(2000)Google Scholar
17 Okura, J.H. Effects of temperature and moisture on durability of low cost flip chip on board (FCoB) Assemblies, 2001, Ph.D. Dissertation, University of Maryland, College Park, MD Google Scholar
18 Iosipescu, N. J. Materials, 2, 537, (1967)Google Scholar