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Evaluation of the microstructure and whisker growth in Sn–Zn–Ga solder with Pr content

Published online by Cambridge University Press:  24 May 2012

Huan Ye*
Affiliation:
College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China; and Center for Advanced Life Cycle Engineering, University of Maryland, College Park, Maryland 20742
Songbai Xue
Affiliation:
College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Michael Pecht
Affiliation:
Center for Advanced Life Cycle Engineering, University of Maryland, College Park, Maryland 20742
*
a)Address all correspondence to this author. e-mail: yeehoneum@gmail.com
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Abstract

In spite of previous reports documented that many beneficial effects can be obtained by adding rare earth (RE) elements to Pb-free solders, this paper presents the risk of Sn whisker growth in the Sn–9Zn–0.5Ga Pb-free solders due to the addition of RE Pr. Results showed that solder microstructures are refined with the addition of trace amount of Pr. However, excessive Pr addition led to the formation of Pr–Sn intermetallic compounds (IMCs) and spontaneous growth of Sn whiskers on the IMC surfaces. It was found that the IMC size has a dramatic impact on whisker growth. Sn whiskers grew in slow-cooled solder with larger IMC particles are much longer and more prolific than that in fast-cooled solder with smaller IMC size. It was proposed that the driving force for whisker growth is originated from the oxidation of the RE-rich Pr–Sn IMCs. Our results indicated that the effects of RE on Pb-free solders should be reevaluated.

Type
Articles
Copyright
Copyright © Materials Research Society 2012

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