Microstructural Evolution and Some Unusual Effects During Thermo-Mechanical Cycling of Sn-Ag-Cu Alloys

Kumar, P and Talenbanpour, B and Sahaym, U and Wen, CH and Dutta, I (2012) Microstructural Evolution and Some Unusual Effects During Thermo-Mechanical Cycling of Sn-Ag-Cu Alloys. In: 13th IEEE InterSociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm) , MAY 30-JUN 01, 2012 , San Diego, CA , pp. 880-887.

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Abstract

Sn-Ag-Cu (SAC) solders are susceptible to appreciable microstructural coarsening during storage or service. This results in evolution of joint properties over time, and thereby influences the long-term reliability of microelectronic packages. Accurate prediction of this aging behavior is therefore critical for joint reliability predictions. Here, we study the precipitate coarsening behavior in two Sn-Ag-Cu (SAC) alloys, namely Sn-3.0Ag-0.5Cu and Sn-1.0Cu-0.5Cu, under different thermo-mechanical excursions, including isothermal aging at 150 degrees C for various lengths of time and thermo-mechanical cycling between -25 degrees C and 125 degrees C, with an imposed shear strain of similar to 19.6% per cycle, for different number of cycles. During isothermal aging and the thermo-mechanical cycling up to 200 cycles, Ag3Sn precipitates undergo rapid, monotonous coarsening. However, high number of thermo-mechanical cycling, usually between 200 and 600 cycles, causes dissolution and re-precipitation of precipitates, resulting in a fine and even distribution. Also, recrystallization of Sn-grains near precipitate clusters was observed during severe isothermal aging. Such responses are quite unusual for SAC solder alloys. In the regime of usual precipitate coarsening in these SAC alloys, an explicit parameter, which captures the thermo-mechanical history dependence of Ag3Sn particle size, was defined. Brief mechanistic description for the recrystallization of Sn grains during isothermal aging and reprecipitation of the Ag3Sn due to high number of thermo-mechanical cycles are also presented.

Item Type:	Conference Paper
Series.:	InterSociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems
Publisher:	IEEE
Additional Information:	Copy right for this article belongs to IEEE,NEW YORK,
Keywords:	Sn-Ag-Cu;lead-free solder;Ag3Sn;microstructural coarsening;recrystallization
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	11 Feb 2013 11:04
Last Modified:	11 Feb 2013 11:04
URI:	http://eprints.iisc.ac.in/id/eprint/45747

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