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Research Papers

Strain Rate Effects and Rate-Dependent Constitutive Models of Lead-Based and Lead-Free Solders

[+] Author and Article Information
Fei Qin

College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing 100124, P R Chinaqfei@bjut.edu.cn

Tong An, Na Chen

College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing 100124, P R China

J. Appl. Mech 77(1), 011008 (Sep 30, 2009) (11 pages) doi:10.1115/1.3168600 History: Received July 22, 2008; Revised March 13, 2009; Published September 30, 2009

As traditional lead-based solders are banned and replaced by lead-free solders, the drop impact reliability is becoming increasingly crucial because there is little understanding of mechanical behaviors of these lead-free solders at high strain rates. In this paper, mechanical properties of one lead-based solder, Sn37Pb, and two lead-free solders, Sn3.5Ag and Sn3.0Ag0.5Cu, were investigated at strain rates that ranged from 600s1 to 2200s1 by the split Hopkinson pressure and tensile bar technique. At high strain rates, tensile strengths of lead-free solders are about 1.5 times greater than that of the Sn37Pb solder, and also their ductility are significantly greater than that of the Sn37Pb. Based on the experimental data, strain rate dependent Johnson–Cook models for the three solders were derived and employed to predict behaviors of solder joints in a board level electronic package subjected to standard drop impact load. Results indicate that for the drop impact analysis of lead-free solder joints, the strain rate effect must be considered and rate-dependent material models of lead-free solders are indispensable.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) Specimen and its sizes for the split Hopkinson tensile bar (SHTB) tests, (b) schematic setup of the separated sleeve SHTB testing and (c) raw signals of the incident and transmitted pulses

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Figure 2

True stress-strain curves at strain rate of 0.001 s−1: (a) compressive and (b) tensile

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Figure 3

Compressive true stress-strain curves at high strain rates: (a) Sn37Pb, (b) Sn3.5Ag, and (c) Sn3.0Ag0.5Cu

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Figure 4

Relations between the flow stresses at 2% strain and strain rates in log-log scale. The lead-free solders are more sensitive to strain rate than Sn37Pb.

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Figure 5

Tensile true stress-strain curves at high strain rates: (a) Sn37Pb, (b) Sn3.5Ag, and (c) Sn3.0Ag0.5Cu

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Figure 6

Specimens after the SHTB tests. The two lead-free solders experienced greater plastic deformation before broken than Sn37Pb did.

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Figure 7

Ultimate tensile stresses of solders at various strain rates: (a) Sn37Pb, (b) SnAg, and (c) SnAgCu and SnCu

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Figure 8

Compressive true stress-strain curves of Sn37Pb at strain rates of (a) 600 s−1, (b) 1200 s−1, and (c) 2200 s−1

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Figure 9

Tensile true stress-strain curves of Sn37Pb at strain rates of (a) 600 s−1, (b) 1200 s−1, and (c) 1800 s−1

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Figure 17

(a) The peeling stress, (b) the true strain, and (c) the equivalent plastic strain predicted by different constitutive models

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Figure 16

Distributions of (a) maximum principal stress and (b) maximum principal strain rate in a solder joint at 0.42 ms, computed by the Johnson–Cook model. Strain rate of 103 s−1 was observed.

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Figure 15

Finite element model

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Figure 14

(a) Schematic setup for the board level drop impact testing. (b) The input-G model. (c) The sliced double cantilever beam model.

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Figure 13

Tensile true stress-strain curves of Sn3.0Ag0.5Cu at strain rates of (a) 600 s−1, (b) 1200 s−1, and (c) 1800 s−1

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Figure 12

Compressive true stress-strain curves of Sn3.0Ag0.5Cu at strain rates of (a) 600 s−1, (b) 1200 s−1, and (c) 2200 s−1

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Figure 11

Tensile true stress-strain curves of Sn3.5Ag at strain rates of (a) 600 s−1, (b) 1200 s−1, and (c) 1800 s−1

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Figure 10

Compressive true stress-strain curves of Sn3.5Ag at strain rates of (a) 600 s−1, (b) 1200 s−1, and (c) 2200 s−1

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