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Research Papers

Development of the Damage State Variable for a Unified Creep Plasticity Damage Constitutive Model of the 95.5Sn–3.9Ag–0.6Cu Lead-Free Solder

[+] Author and Article Information
David M. Pierce1

Department of Mechanical Engineering,  Stanford University, Stanford, CA 94305

Sheri D. Sheppard

Department of Mechanical Engineering,  Stanford University, Stanford, CA 94305

Arlo F. Fossum, Paul T. Vianco, Mike K. Neilsen

 Sandia National Laboratories, Albuquerque, NM 87185

1

Corresponding author.

J. Electron. Packag 130(1), 011002 (Jan 31, 2008) (10 pages) doi:10.1115/1.2837513 History: Received September 27, 2006; Revised July 06, 2007; Published January 31, 2008

A unified creep plasticity damage (UCPD) constitutive model was developed to predict the fatigue of 95.5Sn–3.9Ag–0.6Cu solder joints. Compression, stress-strain and creep properties were generated in previous studies of this solder. Crack damage was reflected in a single state variable, Dω, in the model. Isothermal fatigue tests were performed at 25°C, 100°C, and 160°C using a double-lap shear test specimen. A new approach to fitting the revised damage model is proposed based on finite element analysis (FEA) simulation of the load decay of the fatigued solder material. Accurate predictions required that those parameters be temperature dependent. The UCPD constitutive model was successfully implemented as a subroutine in the commercial finite element code ANSYS ®. Consistent predictions were obtained as demonstrated by a comparison of results generated from FEA simulation of the test assembly against analogous experimental results.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 4

DLS full model with submodel cut-boundary outline and detail of full model solder array mesh density

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Figure 5

Submodel geometry and mesh, and submodel solder mesh density

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Figure 6

Hysteresis response at 100°C: FEA extracted data (Approach 1) versus original data

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Figure 7

Hysteresis response at 100°C: FEA extracted data (Approach 2) versus adjusted data

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Figure 8

Qualitative comparison of damage evolution in the DLS solder joint: (a) optical micrograph using bright field reveals the crack structures in the 95.5Sn–3.9Ag–0.6Cu Pb-free solder under isothermal mechanical fatigue conditions; (b) FEA contour plot of damage state variable (ω) for analogous simulation conditions

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Figure 9

Load decay comparison of FEA simulation and empirical data at 25°C

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Figure 10

Load decay comparison of FEA simulation and empirical data at 100°C

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Figure 11

Load decay comparison of FEA simulation and empirical data at 160°C

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Figure 3

DLS test assembly, edge and face views

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Figure 2

Optical micrographs using ((a) and (c)) bright field and ((b) and (d)) polarized light reveal the grain and crack structures in the 95.5Sn–3.9Ag–0.6Cu Pb-free solder under the following test conditions: ((a) and (b)) 25°C, Δε=0.10, 125cycles; ((c) and (d)) 25°C, Δε=0.05, 750cycles. In the latter case, arrows indicate the zone of recrystallization between two cracks (courtesy of Sandia National Laboratories and Cotts, Binghamton University).

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Figure 1

Optical micrographs that illustrate damage to a blind lap surface mount leaded solder joint caused by TMF. Note that under progressive TMF cycling, indicated by the arrows, the Pb-rich phase coarsening progresses and determines the fatigue crack path (courtesy of Sandia National Laboratories).

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