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Research Papers

Effect of Joint Size on Microstructure and Growth Kinetics of Intermetallic Compounds in Solid-Liquid Interdiffusion Sn3.5Ag/Cu-Substrate Solder Joints

[+] Author and Article Information
Ousama M. Abdelhadi

e-mail: omabdelhadi@crimson.ua.edu

Leila Ladani

e-mail: lladani@eng.ua.edu
Mechanical Engineering Department,
University of Alabama,
Tuscaloosa, AL 35401

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received July 11, 2012; final manuscript received February 19, 2013; published online March 28, 2013. Assoc. Editor: Jianmin Qu.

J. Electron. Packag 135(2), 021004 (Mar 28, 2013) (10 pages) Paper No: EP-12-1069; doi: 10.1115/1.4023846 History: Received July 11, 2012; Revised February 19, 2013

The effect of joint size on the interfacial reaction in the Sn3.5Ag/Cu-substrate soldering system was examined. An experiment was conducted in which parameters such as bonding time, temperature, and pressure were varied at multiple levels. The morphology and thickness of all intermetallic compounds (IMC) were analyzed using the scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) techniques. An examination of the microstructures of solder joints of different sizes revealed that the size of the solder joint has no effect on the type of IMCs formed during the process. It was found that the joint size significantly affected the thickness of the intermetallic layers. The Cu3Sn intermetallic layers formed in the smaller sized solder joints were found to be thicker than those in the larger sized solder joints. In all specimen sizes, the increase in the thickness of Cu3Sn intermetallic layers with soldering time was found to obey a parabolic relationship. Additionally, for the cases when eutectic solder is available in the joints, a similar soldering time and temperature dependency were found for the Cu6Sn5 IMC phase. The intermetallic growth of the Cu3Sn phase was under a volume-diffusion controlled mechanism. The growth rate constants and activation energies of intermetallic layers were also reported for different joint thicknesses. Furthermore, the growth rate constants of the Cu3Sn intermetallic layer were found to depend upon the size of the joints.

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Figures

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Fig. 1

(a) Actual specimen design (top) and schematic drawing (bottom) of the SS specimen. (b) Actual specimen design (top) and a schematic drawing (bottom) of the LS specimen. Dimensions are in mm.

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Fig. 2

SEM backscattered electron images illustrating the microstructure of Sn-3.5Ag/Cu solder joints of the SS2 specimen (25 μm-thick) fabricated at different temperatures for various soldering times

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Fig. 3

SEM backscattered electron images illustrating the microstructure of Sn-3.5Ag/Cu solder joints of the LS specimen (450 μm-thick) fabricated at different temperatures for various times

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Fig. 4

EDX analysis indicating the presence of (a) Cu3Sn (b) Cu6Sn5, and (c) Ag3Sn IMCs in the Sn-3.5Ag/Cu solder joints

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Fig. 5

Comparison of the IMC growth behavior in different specimen sizes at different soldering temperatures

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Fig. 6

Log-log plot of the growth rate constant versus the reciprocal of temperature: (a) for the Cu6Sn5 IMC layer and (b) for the Cu3Sn IMC layer in different specimen sizes

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