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Review Article

A Review of Recent Research on the Mechanical Behavior of Lead-Free Solders

[+] Author and Article Information
Yao Yao

School of Mechanics and Civil Engineering,
Northwestern Polytechnical University,
Xi'an 710072, China
e-mail: yaoy@nwpu.edu.cn

Xu Long

School of Mechanics and Civil Engineering,
Northwestern Polytechnical University,
Xi'an 710072, China

Leon M. Keer

Department of Civil and
Environmental Engineering,
Northwestern University,
2145 Sheridan Road,
Evanston, IL 60208
e-mail: l-keer@northwestern.edu

1Corresponding authors.

Manuscript received February 16, 2017; final manuscript received July 18, 2017; published online August 16, 2017. Assoc. Editor: Rui Huang.

Appl. Mech. Rev 69(4), 040802 (Aug 16, 2017) (15 pages) Paper No: AMR-17-1013; doi: 10.1115/1.4037462 History: Received February 16, 2017; Revised July 18, 2017

Due to the restriction of lead-rich solder and the miniaturization of electronic packaging devices, lead-free solders have replaced lead-rich solders in the past decades; however, it also brings new technical problems. Reliability, fatigue, and drop resistance are of concern in the electronic industry. The paper provides a comprehensive survey of recent research on the methodologies to describe the mechanical behavior of lead-free solders. In order to understand the fundamental mechanical behavior of lead-free solders, the visco-plastic characteristics should be considered in the constitutive modeling. Under mechanical and thermal cycling, fatigue is related to the time to failure and can be predicted based on the analysis to strain, hysteresis energy, and damage accumulation. For electronic devices with potential drop impacts, drop resistance plays an essential role to assess the mechanical reliability of solder joints through experimental studies, establishing the rate-dependent material properties and proposing advanced numerical techniques to model the interconnect failure. The failure mechanisms of solder joints are complicated under coupled electrical-thermal-mechanical loadings, the increased current density can lead to electromigration around the current crowding zone. The induced void initiation and propagation have been investigated based on theoretical approaches to reveal the effects on the mechanical properties of solder joints. To elucidate the dominant mechanisms, the effects of current stressing and elevated temperature on mechanical behavior of lead-free solder have been reviewed. Potential directions for future research have been discussed.

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References

Figures

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Fig. 1

Comparison of experiments and predictions of original and modified Anand model for lead-free solder Sn–3.5Ag [28] (Copyright 2005 by IEEE): (a) original Anand model and (b) modified Anand model

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Fig. 2

Numerical and experimental stress–strain curves for the first two cycles for high lead solder Pb-3.5Sn [34] (Copyright 2004 by IEEE)

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Fig. 3

Relationship between time to failure and strain rate for various frequencies [55] (Copyright 2002 by Emerald Insight)

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Fig. 4

Predictions of equivalent stress and von Mises plastic strain in the joints with different standoff heights after 40 cycles [69] (Copyright 2014 by Elsevier)

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Fig. 5

Representative drop impact simulation of BGA packaging

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Fig. 6

Typical board level drop impact modeled by a two-spring system [99] (Copyright 2006 by Elsevier): (a) schematic of experimental system and (b) analytical model

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Fig. 7

Representative solder interconnect for 3D FE analysis

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Fig. 8

Simulation of the current crowding effect [110] (Copyright 2010 by Annual Reviews)

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Fig. 9

Schematic of experimental system under the combination of mechanical load and electric current [145] (Copyright 2011 by Elsevier)

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Fig. 10

Effect of electric current on the stress exponent n and activation energy Q [145] (Copyright 2011 by Elsevier)

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Fig. 11

Schematic of experimental system under controlled temperature, mechanical load, and electric current [130] (Copyright 2011 by Elsevier)

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Fig. 12

Effect of current density on the steady-state creep rate of Sn–3.8Ag–0.7Cu solder material [130] (Copyright 2011 by Elsevier)

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Fig. 13

Schematic of experiment system with coupled electrical-thermal-mechanical loads [150] (Copyright 2016 by Springer)

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Fig. 14

The effect of current stressing on the steady-state creep rate in Cu/SAC305/Cu joints under different tensile stresses and temperatures [150] (Copyright 2016 by Springer)

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