Materials Letters, Volume 98, Pages 78-81, 1 May 2013

Effects of thermal cycling on rare earth (Pr)-induced Sn whisker/hillock growth

Huan Ye a,b,*, Songbai Xue a, Michael Pecht b
a College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
b Center for Advanced Life Cycle Engineering (CALCE), University of Maryland, College Park, MD 20740, USA


The addition of rare earth (RE) into Pb-free solders has been shown to induce spontaneous Sn whisker growth on RE-rich inter-metallics (IMCs). In this research, whisker growth behaviours under ambient and thermal cycling conditions were investigated to address the RE-induced Sn whisker growth mechanism. Unlike the needle-like whiskers grown mainly in ambience, it was found that coarse Sn hillocks were the dominant growth morphology under thermal cycling condition. It was discussed that the CTE mismatch between RE-rich PrSn3 IMCs and surrounding solder matrix induces compressive stress within the IMCs during thermal cycling, which contributes to the driving force for hillock growth.

Keywords : Metals and alloys, Micro-structure, Sn whisker/hillock, Rare earth.

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