Browsing by Author "Wei, C. 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.
Performance Comparison of OFDM Signal and CAP Signal Over High Capacity RGB-LED-Based WDM Visible Light Communication
(2013-08-01)
Wu, F. M.
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Lin, C. T.
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Wei, C. C.
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Chen, C. W.
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Chen, Z. Y.
We experimentally demonstrate a visible light communication (VLC) system based on a single commercially available RGB-type LED. High spectrally efficient carrier-less amplitude and phase (CAP) modulation and orthogonal frequency-division multiplexing (OFDM) are adopted in the intensity-modulation and direct-detection VLC system of limited bandwidth. In order to achieve higher capacity of the uneven-frequency-response LED-based VLC system, OFDM signals are combined with the bit-and power-loading techniques, and CAP signals of various modulation are pre-emphasized to modulate one of the RGB chips. To reach the BER of less than 10(-3), CAP and OFDM signals demonstrate the maximum data rates of 1.32 and 1.08 Gb/s, respectively, employing the blue chip. In addition to spectrally efficient formats, the wavelength-division-multiplexing (WDM) scheme is applied to further increase the capacity. After individually optimizing RGB chips, the maximum aggregate data rates of CAP and OFDM are 3.22 and 2.93 Gb/s, respectively, in our RGB-LED-based WDM VLC system. Hence, compared with OFDM, the CAP scheme shows competitive performance and provides an alternative spectrally efficient modulation for next generation optical wireless networks.
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.
Theoretical investigation of polarization-insensitive data format conversion of RZ-OOK to RZ-BPSK in a nonlinear birefringent fiber
(2009-03-16)
Wei, C. C.
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Astar, W.
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Chen, J.
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Chen, Y. -J.
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Carter, G. M.
Polarization-insensitive conversion of return-to-zero (RZ) ON-OFF keying (RZ-OOK) to RZ binary phase-shift keying (RZ-BPSK) has been achieved by cross-phase modulation (XPM) in a nonlinear birefringent fiber. This work presents a theoretical analysis of the dependence of format conversion on pump-probe detuning, and the pump state-of-polarization (SOP) that can fluctuate unpredictably in a realistic system. An investigation of the impact of pump polarization fluctuation on receiver sensitivity and receiver optimal threshold for the converted RZ-BPSK probe is also carried out. It was found that although the desired XPM-induced pi phase shift can be achieved by launching both the RZ-OOK pump and the probe along the same birefringent axis of the fiber, the phase shift degrades to pi/3 the SOP of the RZ-OOK pump unpredictably switches to the other axis of the fiber, resulting in a large receiver sensitivity penalty fluctuation of 14 dB. By contrast, launching the probe at 45 degrees relative to the birefringent axes can reduce the polarization-dependent receiver sensitivity penalty fluctuation to about 2 dB as the SOP of the RZ-OOK pump is swept over the Poincare sphere. These conclusions are in good agreement with recently published experimental results. (C) 2009 Optical Society of America