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RESEARCH PAPERS

Experimental Observation of Correlation Between Creep and Uniaxial Ratchetting of Sn37Pb and Sn3Ag0.5Cu Solder Alloys

[+] Author and Article Information
Katsuhiko Sasaki

Division of Human Mechanical Systems and Design,  Hokkaido University, N13, W8, Kita-ku, Sapporo 060-8628, Japankatsu@eng.hokudai.ac.jp

Takuji Kobayashi

Division of Human Mechanical Systems and Design,  Hokkaido University, N13, W8, Kita-ku, Sapporo 060-8628, Japan

Ken-ichi Ohguchi

Department of Material Science and Engineering, Akita University, Tegatagakuen-cho 1-1, Akita 010-8502, Japan

J. Electron. Packag 129(1), 82-89 (May 21, 2006) (8 pages) doi:10.1115/1.2429714 History: Received December 06, 2005; Revised May 21, 2006

Time-dependent deformations such as creep and ratchetting of solder alloys are significant deformation phenomena that need to be understood to ensure the safety and reliability of solder joints in electronic packaging. There is much research on creep deformation of solder alloys, but ratchetting deformation, especially the correlation between creep and ratchetting deformation of solder alloys has not been investigated. This paper discusses the correlation between creep and uniaxial ratchetting deformation to establish the differences in the time-dependent deformation of lead-free and lead-containing solder alloys. Uniaxial ratchetting tests were conducted by cyclic tension–compression tests or cyclic tension–unloading tests at several ratios of the maximum to minimum stresses. Additional creep tests following the uniaxial ratchetting were also conducted to observe the effect of the uniaxial ratchetting on creep deformation. An empirical method to select an optimal lead-free solder alloy is discussed by defining a uniaxial ratchetting strain rate. The additional creep tests also show that the uniaxial ratchetting deformation has a strong correlation to the creep deformation and that the correlation is different for lead-free and lead-containing solder alloys.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 10

Curves of additional creep after the preloading (lead-free solder alloy, strain rate of preloading=0.04%∕s): (a) maximum stress=10MPa; (b) maximum stress=15MPa; and (c) maximum stress=17.5MPa

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Figure 11

Curves of additional creep after the preloading (lead-containing solder alloy, strain rate of preloading=0.04%∕s): (a) maximum stress=10MPa; (b) maximum stress=15MPa; and (c) maximum stress=17.5MPa

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Figure 1

Geometry of the specimens (unit: mm)

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Figure 2

Schematic outlines of uniaxial ratchetting and additional creep test: (a) uniaxial ratchetting tests; and (b) additional creep tests after the uniaxial ratchetting tests

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Figure 3

Stress–strain relations of pure tensile tests at the 0.04%/s strain rate for the lead-free and lead-containing solder alloys

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Figure 4

Creep curves of the lead-free and lead-containing solder alloys

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Figure 5

Stress–strain relation of the uniaxial ratchetting test at the −0.5 stress ratio for the maximum stress of 15MPa (lead-free solder alloy)

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Figure 6

Uniaxial ratchetting strain versus number of cycles (maximum stress=15MPa): (a) lead-free solder alloy; and (b) lead-containing solder alloy

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Figure 7

Uniaxial ratchetting strain versus time (maximum stress=15MPa): (a) lead-free solder alloy; and (b) lead-containing solder alloy

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Figure 8

Minimum uniaxial ratchetting strain rate versus stress ratio (maximum stress=15MPa)

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Figure 9

Ratchetting strain versus number of cycles due to the preloading (strain rate=0.04%∕s)

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Figure 12

Strain rate effect on the preloading for the maximum stress of 15MPa: (a) lead-free solder alloy; and (b) Lead-containing solder alloy

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Figure 13

Additional creep curves after the 50th cycle of preloading at a maximum stress of 15MPa: (a) lead-free solder alloy; and (b) lead-containing solder alloy

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