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Research Papers

Modified Constitutive Creep Laws With Micromechanical Modeling of Pb-Free Solder Alloys

[+] Author and Article Information
Joel Thambi

Innovation Center for Advanced Electronics,
Continental Automotive GmbH,
Regensburg 93055, Germany
e-mails: luthersjoel@gmail.com;
joel.thambi@sabic.com

Andreas Schiessl

Innovation Center for Advanced Electronics,
Continental Automotive GmbH,
Regensburg 93055, Germany
e-mail: andreas.schiessl@continental-corporation.com

Manuela Waltz

Faculty of Mechanical Engineering,
Technische Hochschule Ingolstadt,
Esplanade 10,
Ingolstadt 85049, Germany
e-mail: Manuela.Waltz@thi.de

Klaus-Dieter Lang

Faculty of Electrical Engineering and
Computer Science,
Technische Universität Berlin,
Berlin 10623, Germany
e-mail: klaus-dieter.lang@izm.fraunhofer.de

Ulrich Tetzlaff

Faculty of Mechanical Engineering,
Technische Hochschule Ingolstadt,
Esplanade 10,
Ingolstadt 85049, Germany
e-mail: Ulrich.Tetzlaff@thi.de

1Present address: Application Technology, SABIC, Plasticslaan 1, Bergen Op Zoom 4612 PX, The Netherlands.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received May 18, 2016; final manuscript received January 3, 2017; published online June 14, 2017. Assoc. Editor: Toru Ikeda.

J. Electron. Packag 139(3), 031002 (Jun 14, 2017) (10 pages) Paper No: EP-16-1064; doi: 10.1115/1.4035850 History: Received May 18, 2016; Revised January 03, 2017

This paper explicitly establishes a modified creep model of a Sn–3.8Ag–0.7Cu alloy using a physical-based micromechanical modeling technique. Through experimentation and reformulation, steady-state creep behavior is analyzed with minimum strain rates for different temperatures 35 °C, 80 °C, and 125 °C. The new modified physical creep model is proposed, by understanding the respective precipitate strengthened deformation mechanism, seeing the dependency of the activation energy over the temperature along with stress and, finally, by integrating the subgrain-size dependency λss. The new model is found to accurately model the creep behavior of lead-free solder alloy by combining the physical state variables. The features of the creep model can be explored further by changing the physical variable such as subgrain size to establish a structure–property relationship for a better solder joint reliability performance.

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References

Figures

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Fig. 1

(a) View of the cast die after solidification of solder material and (b) manufactured creep specimen taken out from the aluminum die

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Fig. 2

Creep behavior of precipitate strengthened materials (only schematics). The stress is given in units of the classical Orowan stress [16].

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Fig. 3

SEM micrographs showing microstructure of the solder alloy with the intermetallic (Ag-3Sn and Cu-6Sn-5) and the β-Sn matrix

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Fig. 4

Distribution of Ag-3Sn intermetallic precipitates analyzed for the volume fraction studies from eutectic region, from pre-experimental selected samples

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Fig. 5

Threshold line calculated from Table 2 incorporated into Norton plot to differentiate the low stress and HSR

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Fig. 6

(a) Stress exponent of LSR and HSR showing steady relationship temperature and (b) stress exponent plotted versus σ/RT for different temperatures

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Fig. 7

Isostress lines plotted for creep strain versus reciprocal of temperature for the activation energy Q calculation

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Fig. 8

Activation energy Q plotted against the normalized stress for high-temperature range and low-temperature range

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Fig. 9

Investigations of the substructure formation of a creep specimen: (a) EBSD images showing subgrain distribution on a necking region, (b) EBCC image showing subgrain between dendrites on non-necking region, and (c) corresponding measurement of subgrain size measured qualitatively from random samples

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Fig. 10

Creep equation with subgrain-size state variable: (a) comparison on creep strain rate obtained from the experimental results optimized with the new modified creep model and (b) predicted versus the actual creep strain rate

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