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Research Papers

Study of Solder/Copper Interface Behavior Under Varying Strain Rates

[+] Author and Article Information
Y. W. Kwon1

Department of Mechanical and Aerospace Engineering,  Naval Postgraduate School, Monterey, CA 93943

A. M. Luteran, J. M. Didoszak, A. S. Kwon

Department of Mechanical and Aerospace Engineering,  Naval Postgraduate School, Monterey, CA 93943

1

This material is declared a work of the US Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Electron. Packag 134(3), 031003 (Jul 18, 2012) (7 pages) doi:10.1115/1.4006862 History: Received June 02, 2011; Accepted April 16, 2012; Published July 18, 2012; Online July 18, 2012

This paper investigates the mechanical behavior of a copper–solder interface when subjected to varying strain rate loading between 0.05 s−1 and 10.0 s−1 . The copper is alloy 101, and the solder is lead-free type with a composition of 96% tin and 4% silver. Both uniform and nonuniform two-level strain rate loadings were applied. For the two-level strain rate loading, the strain rate was changed from one level to another during the loading process as a step change. The strain rate tests were performed at room temperature as well as at an elevated temperature of 65 °C. The test results showed significant effects of uniform and nonuniform strain rates as well as temperature on fracture surface, peak stress, fracture strain, modulus, and stored energy density until fracture. Generally, a higher strain rate increased the peak stress and fracture strain, but decreased the modulus. The heated specimens showed significantly reduced strength and fracture strain at high strain rates when compared to the specimens tested at room temperature. For the two-level strain rates, the sequence of the loading rates affected the material behavior significantly. The peak stress under the two-level strain rates might be located outside the range that was determined by the two individual uniform strain rates occurring in the two-level rates. On the other hand, the fracture strain under two-level strain rate loading always fell inside that range. An expression was proposed to predict the interface fracture strains for the case of a two-level strain rate loading based on the data of each respective single-level strain test. The prediction was reasonable when compared to the experimental data with an average absolute error of 10%.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Dimensions of the test specimens given in millimeters

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Figure 2

Aluminum cast with copper pieces

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Figure 3

SEM image of strain rate 0.1 s−1

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Figure 4

SEM image for strain rate 5.0 s−1

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Figure 5

Fixed support and applied displacement

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Figure 6

Cross section view of solder

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Figure 7

Plot of peak stress versus strain rate at room temperature. Circles are experimental data and the line is the curve-fit using the Cowper–Symonds equation.

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Figure 8

Plot of fracture strain versus strain rate at room or elevated temperature

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Figure 9

Plot of modulus versus strain rate at room or elevated temperature

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Figure 10

Plot of strain energy density at fracture versus strain rate at room or elevated temperature

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Figure 11

Comparison of peak stresses of heated and nonheated samples

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Figure 12

Fracture strain of single and multiple strain rates at a room temperature

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Figure 13

Fracture strain of single and multiple strain rates of heated specimens

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