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Research Papers

Damage Evolution in Lead Free Solder Joints in Isothermal Fatigue

[+] Author and Article Information
Awni Qasaimeh

Department of Manufacturing and
Engineering Technology,
Tennessee Tech University,
1 William L. Jones Drive,
Cookeville, TN 38505
e-mail: aqasaimeh@tntech.edu

Sa’d Hamasha, Peter Borgesen

Department of Systems Science and
Industrial Engineering,
Binghamton University,
P.O. Box 6000,
Binghamton, NY 13902

Younis Jaradat

Department of Systems Science and Industrial Engineering,
Binghamton University,
P.O. Box 6000,
Binghamton, NY 13902

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received September 4, 2014; final manuscript received December 8, 2014; published online January 21, 2015. Assoc. Editor: Eric Wong.

J. Electron. Packag 137(2), 021012 (Jun 01, 2015) (8 pages) Paper No: EP-14-1077; doi: 10.1115/1.4029441 History: Received September 04, 2014; Revised December 08, 2014; Online January 21, 2015

The extrapolation and generalization of accelerated test results for lead free solder joints require the identification of a damage function that can be counted on to apply beyond the region of the test. Individual ball grid array (BGA) scale Sn3Ag0.5Cu (SAC305) solder joints were subjected to isothermal shear fatigue testing at room temperature and 65 °C. The resulting mechanical response degradation and crack behavior, including strain hardening, crack initiation, and propagation, were correlated with the inelastic work and effective stiffness derived from load–displacement hysteresis loops. Crack initiation was found to scale with the accumulated work, independently of cycling amplitude and strain rate. The subsequent damage rate varied slightly with amplitude.

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References

Figures

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Fig. 1

Schematic showing shear fatigue testing of individual bump. Solder diameter = 30 mil, pad diameter = 22 mil, fixture opening = 40 mil, and fixture offset from the pad = 6 mil.

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Fig. 2

Instron machine and sample setup during the test

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Fig. 3

Load–displacement relation illustrating loading slope and inelastic work calculations

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Fig. 4

Loading slopes versus cycles in load controlled test for SAC305 solder under 400 gf peak load at room temperature

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Fig. 5

Loading slopes versus cycles in load controlled test for three SAC305 solder joints. Peak load is 500 gf at room temperature.

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Fig. 6

Cross polarizer image of cross section of 30 mil SAC305 BGA joint showing beach ball structure [19]

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Fig. 7

Loading slope (effective stiffness) with cycling in displacement controlled mode. Peak displacement is 20 μm at room temperature.

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Fig. 8

Initial loading slopes for different cycling peak loads (SAC305) at room temperature (median is shown). Sample size is 12.

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Fig. 9

The effective stiffness of the lead free alloys as a function of the stress amplitude [21]

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Fig. 10

Loading slopes behavior in variable loading amplitude: mild cycling (100 cycles at 300 gf) interrupted by harsh (100 cycles at 500 gf, dotted red line) followed by another 100 cycles at 300 gf at room temperature

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Fig. 11

Number of fatigue cycles to reach maximum stiffness for different peak loads at room temperature. Sample size is 9.

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Fig. 12

Work progression with cycling under load controlled test (400 gf peak load)

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Fig. 13

Work per cycle versus number of fatigue cycles for different peak loads

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Fig. 14

Comparison of work progression in load controlled testing at room temperature and 65 °C (500 gf peak load)

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Fig. 15

Weibull probability plots of the fatigue life of SAC305 alloy at 600 gf cyclic load and different loading rate at room temperature

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Fig. 16

Box plot of work deposition per cycle of SAC305 at different loading rate. Sample size is 10.

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Fig. 17

Total work to failure versus cumulative failure % for different loading rates: 600 gf peak load

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Fig. 18

Examples of dye penetration in the cracked area after 300 cycles (load controlled: 500 gf peak load): accumulated work is 0.005 J (left) and 450 cycles—accumulated work is 0.018 J (right)

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Fig. 19

Examples of cracked area after 2000 cycles (displacement control: 25 μm peak displacement): accumulated work is 0.0125 J (left): and 3000 cycles—accumulated work is 0.0089 J (right)

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Fig. 20

Loading slope drop and crack area in load controlled test for different peak loads

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Fig. 21

Loading slope drop versus crack area under displacement controlled test of 25 μm peak displacement

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Fig. 22

Slope variation versus accumulated work indicating crack initiation and propagation parts. Cycling at room temperature.

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Fig. 23

Work deposition for crack initiation at different cycling peak loads

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Fig. 24

Boxplots for the prefactor (left) and the exponent (right) in the equation under different cycling amplitudes

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