Research Papers

Individual Phase Mechanical Properties at Different Temperatures of Sn–Ag–Cu Lead-Free Solders Incorporating Special Pileup Effects Using Nanoindentation

[+] Author and Article Information
Muhammad Sadiq

University of Engineering &
Technology Peshawar,
Peshawar 25000 KPK, Pakistan
e-mail: msadiq3@gatech.edu

Jean-Sebastien Lecomte

ENSAM-Arts et Métiers ParisTech,
4 rue Augustin Fresnel,
Metz 57078, France

Mohammed Cherkaoui

George W. Woodruff School
of Mechanical Engineering,
Georgia Institute of Technology,
801 Ferst Drive NW,
Atlanta, GA 30332

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received December 12, 2013; final manuscript received October 10, 2014; published online April 17, 2015. Assoc. Editor: Tong Cui.

J. Electron. Packag 137(3), 031005 (Sep 01, 2015) (5 pages) Paper No: EP-13-1135; doi: 10.1115/1.4029836 History: Received December 12, 2013; Revised October 10, 2014; Online April 17, 2015

Sn–Ag–Cu (SAC) alloys are considered as good replacements of Sn–Pb alloys which are banned due to the toxic nature of Pb. But, SAC alloys have a coarse microstructure that consists of β-Sn rich and eutectic phases. Nanoindentation is a useful technique to evaluate the mechanical properties at very small length scale. In this work, continuous stiffness measurement (CSM) nanoindentation setup (CSM Instruments SA, Peseux, Switzerland) is used to determine the individual phase mechanical properties like Young's modulus and hardness at high temperatures. It is demonstrated that these properties are a function of temperature for both β-Sn rich and eutectic phases. Loadings starting from 500 μN up to 5000 μN are used with 500 μN steps and average values are presented for Young's modulus and hardness. The loading rates applied are twice that of the loadings. High temperatures result in a higher creep deformation and therefore, to avoid it, different dwell times are used at peak loads. The special pileup effect, which is more significant at elevated temperatures, is determined and incorporated into the results. A better agreement is found with the previous studies.

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Fig. 1

(a) SEM and (b) OM micrographs before nanoindentation

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Fig. 2

Load–displacement curves with no holding time

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Fig. 3

Load–displacement curves for eutectic and β-Sn phases at 20 °C

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Fig. 4

Load–displacement curves for eutectic and β-Sn phases at 45 °C

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Fig. 5

Load–displacement curves for eutectic and β-Sn phases at 85 °C

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Fig. 6

AFM image after nanoindentation. (a) 3 × 3 indentation array and (b) indentation over eutectic zone.

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Fig. 7

(a) Pileup schematic and (b) equilateral triangles after testing. (c) Pileup profiles for equilateral triangles.

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Fig. 8

AFM image for nanoindentation over IMCs




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