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Mechanical deformation-induced Sn whiskers growth on electroplated films in the advanced flexible electronic packaging

Published online by Cambridge University Press:  31 January 2011

Shih-kang Lin ,
Yuhi Yorikado ,
Junxiang Jiang ,
Keun-Soo Kim ,
Katsuaki Suganuma ,
Sinn-wen Chen ,
Masanobu Tsujimoto  and
Isamu Yanada
Shih-kang Lin
Affiliation:
Department of Chemical Engineering, National Tsing Hua University, Hsin-chu 300, Taiwan; and Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
Yuhi Yorikado
Affiliation:
Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
Junxiang Jiang
Affiliation:
Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
Keun-Soo Kim
Affiliation:
Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
Katsuaki Suganuma*
Affiliation:
Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
Sinn-wen Chen*
Affiliation:
Department of Chemical Engineering, National Tsing Hua University, Hsin-chu 300, Taiwan
Masanobu Tsujimoto
Affiliation:
C. Uyemura & Co., Ltd., Osaka, Osaka, Japan
Isamu Yanada
Affiliation:
C. Uyemura & Co., Ltd., Osaka, Osaka, Japan
*
a)Address all correspondence to these authors. e-mail: suganuma@sanken.osaka-u.ac.jp
b) e-mail: swchen@mx.nthu.edu.tw
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Abstract

In this study, we investigated mechanical deformation-induced Sn whisker growth, which is frequently encountered in advanced flexible substrate packaging. Concentrated compressive stresses are introduced around the leads and solder surface finish joints connected by compression fixing. Six types of pure Sn thin films were electroplated on Ni-protected Cu substrates. These were 2- and 6-μm-thick Sn films electroplated with three different current densities: 2, 10, and 20 A/dm2. These films were compressed at room temperature and ambient humidity. The surface and cross-sectional grain morphologies of the films were examined by scanning electron microscopy and focused ion beam spectroscopy, respectively. The grain orientations of the electroplated Sn films were analyzed by x-ray diffraction and electron backscatter diffraction. After compression, nodule hillocks and whiskers were found around the indents. Beneath the indents, the original columnar Sn grains were deformed, and recovery and recrystallization processes occurred. Rapid whisker formation was observed. The whiskers induced by mechanical deformation are closely related to the grain microstructures, and the initial compression stresses are critical to the types and distribution of whiskers as well.

Keywords

JoiningMicrostructureSn
Type
Articles
Information
Journal of Materials Research , Volume 22 , Issue 7 , July 2007 , pp. 1975 - 1986
Copyright
Copyright © Materials Research Society 2007

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