Browsing by Author "Wu, W. C."

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An alternative method for measuring the index profile of a gradient-index lens
(2011)
Hsieh, H. C.
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Wu, W. C.
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Chang, W. Y.
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Hsu, F. S.
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Su, D. C.
An alternative method for measuring the index profile of the GRIN lens is proposed based on Fresnel's equations and the common-path phase-shifting interfermetry. A light beam composing of the right- nd the left- ircularly polarized components is obliquely incident on the tested GRIN lens and the reflected light passes through an analyzer. The light is collected and imaged by an imaging lens to a CMOS camera. Four interferograms under different additional phases are taken and Carre's phase-shifting method is used to calculate the full-field phase distribution. Next, the estimated data are substituted into the special equations derived from the Fresnel's equations, and the index profile of the GRIN lens can be obtained. Its validity has been demonstrated. It has both merits of the common-path interferemetry and the phase-shifting interferemetry.
Coaxial transitions for CPW-to-CPW flip chip interconnects
(2007-08-16)
Wu, W. C.
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Chang, E. Y.
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Huang, C. H.
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Hsu, L. H.
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Starski, J. P.
A novel coaxial transition for CPW-to-CPW flip chip interconnect is presented and experimentally demonstrated. To realise the coaxial transition on the CPW circuit, benzocyclobutene was used as the interlayer dielectric between the vertical coaxial transition and the CPW circuit. The coaxial interconnect structure was successfully fabricated and RF characterised to 67 GHz. The structure showed excellent interconnect performance from DC up to 55 GHz with low return loss below 20 dB and low insertion loss less than 0.5 dB even when the underfill was applied to the structure.
Investigation of electroless Co(W,P) thin film as the diffusion barrier of underbump metallurgy
(2008)
Wu, W. C.
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Hsieh, Tsung-Eong
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Pan, Hung-Chun
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材料科學與工程學系
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Department of Materials Science and Engineering
The plating characteristics of an electroless cobalt-tungsten-phosphorus [Co(W,P)] layer and its capability to serve as a diffusion barrier of underbump metallurgy (UBM) for flip-chip Cu-IC are investigated. Increasing the pH of the plating solution in a range of 7.6-9.0 decreased the rate of deposition, increased the phosphorus content, altered the structure from polycrystalline to amorphous, and decreased the surface roughness of Co(W,P) films. The barrier capability of Co(W,P) to eutectic PbSn solder was evaluated by means of liquid- and solid-state aging tests. In specimens subjected to tests of these two types, a P-rich layer presented in between solder and unreacted Co(W,P), demonstrating the sacrificial barrier behavior of Co(W,P). Transmission electron microscopy (TEM) analysis of specimens subjected to liquid-state aging indicated the supersaturated P atoms, and the Co2P consequently formed, might aggregate at grain boundaries of the P-rich layer, thus enabling the stuffed-type barrier capability of the Co(W,P) layer. TEM, scanning electron microscopy, and energy-dispersive spectrometer characterizations of specimens subjected to solid-state aging revealed that the reaction of solder and Co(W,P) implies a formation of CoSn2 and CoSn3 intermetallic compounds (IMCs) and a mixture of various IMCs in P-rich layer. Our experimental results demonstrated a satisfactory barrier property of electroless Co(W,P), heralding promising applications in UBM structures for flip-chip Cu-IC. (C) 2008 The Electrochemical Society.