Browsing by Author "Liu, P. C."

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Electromigration in Sn-Cu intermetallic compounds
(2009-01-15)
Wei, C. C.
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Chen, C. F.
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Liu, P. C.
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Chen, Chih
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材料科學與工程學系
As the shrinking in bump size continues, the effect of intermetallic compounds (IMCs) on electromigration becomes more pronounced. Electromigration in Sn-Cu intermetallic compounds was examined using edge displacement method. It was found that Cu(6)Sn(5) compounds are more susceptible to electromigration than Cu(3)Sn compounds. The lower solidus temperature and higher resistivity of the Cu(6)Sn(5) IMCs are responsible for its higher electromigration rate. Length-dependent electromigration behavior was found in the stripes of various lengths and the critical length was determined to be between 5 and 10 mu m at 225 degrees C, which corresponded to a critical product between 2.5 and 5 A/cm. Furthermore, the Sn-Cu compounds were proven to have better electromigration resistance than eutectic SnAgCu solder.
Electromigration-induced Pb and Sn whisker growth in SnPb solder stripes
(2008-07-01)
Wei, C. C.
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Liu, P. C.
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Chen, Chih
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Tu, K. N.
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材料科學與工程學系
Electromigration at 5 x 10(4) A/cm(2) and 100 degrees C was conducted to grow composite Pb/Sn whiskers from SnPb solders, in which a Pb whisker grows first and then a whisker of Sn grows. In some cases, small Sn islands are embedded in Pb whiskers. The diameter of a composite whisker is < 1 mu m, which is much smaller than that of spontaneous Sn whisker growth on leadframes. The growth orientation of Pb whiskers was in the [110], [111], and [112] directions. This investigation proposes that compressive stress generated by electromigration at the anode provides the force driving whisker growth. Therefore, accelerated tests of whisker growth at higher temperatures using electromigration are feasible.
Relieving Sn whisker growth driven by oxidation on Cu leadframe by annealing and reflowing treatments
(2007-08-15)
Wei, C. C.
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Liu, P. C.
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Chen, Chih
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Lee, Jeffrey C. B.
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Wang, I. Ping
Owing to environmental concern, Pb-free solders are replacing eutectic tin lead in electronic packaging industry. Thus, whisker growth becomes a serious reliability issue for Sn finishes. In this study, the mechanism of whisker growth from Sn finish on Cu leadframe was investigated under the temperature/humidity storage test. It is found that oxidation of the Sn finish was the driving force behind the whisker growth. Thermal treatments including annealing at 220 degrees C and reflowing at 260 degrees C were employed to mitigate the whisker growth. It is found that both heat treatments can significantly reduce the whisker growth rate. It is speculated that the heat treatments can relieve the residual stress in the Sn finishes and can modify their grain structure, resulting in a slower oxidation rate. Thus, they can slow down the grow rate of Sn whiskers. In addition, reflowing treatment can change the columnar grain structure of the Sn film to the equiaxed grain structure in some of its regions, resulting in a lower grain boundary diffusion rate of Sn. Therefore, the reflowed sample had the lowest growth rate of Sn whiskers. (c) 2007 American Institute of Physics.