Correlation Between Surface Morphology Evolution and Grain Structure: Whisker/Hillock Formation in Sn-Cu

被引:16
|
作者
Pei, Fei [1 ]
Jadhav, Nitin [1 ]
Chason, Eric [1 ]
机构
[1] Brown Univ, Sch Engn, Providence, RI 02912 USA
基金
美国国家科学基金会;
关键词
WHISKER GROWTH; TIN WHISKERS; SOLDER; FILMS; DIFFRACTION; MECHANISM;
D O I
10.1007/s11837-012-0442-x
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
Sn whisker and hillock formation is a reliability risk that has become increasingly important as the electronics industry has moved toward Pb-free manufacturing. To prevent them, we would like to understand what makes specific sites susceptible to deform into whiskers. We have used in situ scanning electron microscopy (SEM)/electron backscattering diffraction (EBSD) to monitor simultaneously the evolution of surface morphology and grain orientation in Sn surfaces in order to correlate whisker/hillock initiation with the underlying microstructure. Because rough films are difficult to measure with EBSD, we developed a unique procedure to make Sn-Cu samples with ultra-flat surfaces so that a large fraction of Sn grains can be indexed over repeated scans. We find that whiskers/hillocks grow from existing grains (not re-nucleated grains) with orientations close to (001). They often rotate from the as-deposited structure so that the orientation after growth does not indicate the orientation from which the whisker initiated. We measured the interface structure after removal of the Sn layer by chemical etching and found that there is no excessive accumulation of intermetallic compound around the whisker/hillock roots. Cross-sectional measurements revealed that a large fraction of the whiskers/hillocks have oblique boundaries underneath the surface, supporting the idea that these allow whiskers/hillocks to grow with lower stress.
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页码:1176 / 1183
页数:8
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