• Smart Structures and Systems
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• v.1 no.2
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• pp.141-158
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• 2005

A new design of distributed crack sensors based on the topological change of transmission line cables is presented for the condition assessment of reinforced concrete (RC) structures during and immediately after an earthquake event. This study is primarily focused on the performance of cable sensors under dynamic loading, particularly a feature that allows for some "memory" of the crack history of an RC member. This feature enables the post-earthquake condition assessment of structural members such as RC columns, in which the earthquake-induced cracks are closed immediately after an earthquake event due to gravity loads, and are visually undetectable. Factors affecting the onset of the feature were investigated experimentally with small-scale RC beams under cyclic loading. Test results indicated that both crack width and the number of loading cycles were instrumental in the onset of the memory feature of cable sensors. Practical issues related to dynamic acquisition with the sensors are discussed. The sensors were proven to be fatigue resistant from shake table tests of RC columns. The sensors continued to show useful performance after the columns can no longer support additional loads.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.138-141
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• 2002

There are continuous efforts in the electronics industry to a reduced electronic package size. Reducing the size of electronic packages can be achieved by a variety of means, and for ball grid array(BGA) packages an effective method is to decrease the pitch between the individual balls. Chip scale package(CSP) and BGA are now one of the major package types. However, a reduced package size has the negative effect of reducing board-level reliability. The reliability concern is for the different thermal expansion rates of the two-substrate materials and how that coefficient CTE mismatch creates added stress to the BGA solder joint when thermal cycled. The point of thermal fatigue in a solder joint is an important factor of BGA packages and knowing at how many thermal cycles can be ran before failure in the solder BGA joint is a must for designing a reliable BGA package. Reliability of the package was one of main issues and underfill was required to improve board-level reliability. By filling between die and substrate, the underfill could enhance the reliability of the device. The effect of underfill on various thermomechanical reliability issues in $\mu$BGA packages is studied in this paper.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.217-220
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• 2000

The SrBi$_2$Ta$_2$O$\_$9/(SBT) thin films are deposited on Pt-coated electrode(Pt/TiO$_2$/SiO$_2$/Si) using RF sputtering method. The SBT thin films deposited on substrate at 400-500[$^{\circ}C$]. SBT thin film deposited on Pt-coated electrodes have the cubic perovskite structure and polycrystalline state. With increasing annealing temperature from 600[$^{\circ}C$] to 850[$^{\circ}C$], flourite phase was crystallized to 650[。 and Bi-layered perovskite phase was crystallize ed above 700[$^{\circ}C$]. The maximum remnant polarization and the coercive electric field is 11.73[${\mu}$C/$\textrm{cm}^2$], 85[kV/cm] respectively at annealing temperature of 750[$^{\circ}C$]. The fatigue characteristics of SBT thin films deposited on Pt/TiO$_2$/SiO$_2$/Si substrate did not change up to 10$\^$10/ switching cycles.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.2
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• pp.143-150
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• 2000

Ferroelectric SrxBi2+yTa2O9+$\alpha$ thin films with various compositions(x=0.7, 0.8, 1, y=0.3, 0.4) were prepared by sol-gel method. The film with moled ratio of 0.8:2.3:2.0 in Sr/Bi/Ta, which was deposited on Pt/SiO2/Si (100), showed better ferroelectric properties than other films. To investigate substrate effects, the same compositions were spin coated on Pt/Ti/SiO2/Si (100) substrates. At an applied voltage of 5V, the dielectric constant($\varepsilon$r), remanent polarization (2Pr) and coercive field (Ec) of the Sr0.8Bi2.3Ta2O9+$\alpha$ thin film prepared on Pt/Ti/SiO2/Si (100) were about 296, 24$\mu$C/$\textrm{cm}^2$ and Ec of 49kV/cm respectively. Both SBT films firred at 80$0^{\circ}C$ revealed no fatigue up to 1010 cycles. Retention characteristics of these capacitors showed no degradation up to 104 sec.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1999.05a
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• pp.171-176
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• 1999

Nondestructive inspection and accompanying life analysis based on fracture mechanics were the major conventional methods for evaluating remaining life of critical high temperature components in power plants. By using these conventional methods, it has been difficult to perform in-service inspection for life prediction. Also, quantitative damage evaluation due to unexpected abrupt changes in operating temperature was almost impossible. Thus, many efforts have been made for evaluating remaining life during operation of the plants and predicting real-time life usage values based on the shape of structures, operating history, and material properties. In this study, a core software for on-line life monitoring system which carries out real-time life evaluation of a critical component in power boiler(high temperature steam headers) is developed. The software is capable of evaluating creep and fatigue life usage from the real-time stress data calculated by using temperature/stress transfer Green functions derived for the specific headers and by counting transient cycles. The major benefits of the developed software lie in determining future operating schedule, inspection interval, and replacement plan by monitoring real-time life usage based on prior operating history.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.94-98
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• 2000

Polycrystalline SBTN ferroelectric thin films were prepared by sol-gel method with various Nb mole ratios on Pt/ $SiO_2$/Si (100) substrates. The films were annealed at different temperatures and characterized in terms of phase and microstructure. Relatively a well saturated hysteresis pattern was obtained at x =0.2 in S $r_{0.8}$B $i_{2.3}$(T $a_{1-x}$ N $b_{x}$)$_2$ $O_{9+}$$\alpha$/ thin films. At an applied voltage of 5V, the dielectric constant ($\varepsilon$$_{r}$) and dissipation factor (tan $\delta$) of typical S $r_{0.8}$B $i_{2.3}$(T $a_{1-x}$ N $b_{x}$)$_2$ $O_{9+}$$\alpha$/ thin film (x=0.2) were about 236.2 and 0.034. Measured remanent polarization (2Pr) and coercive field (Ec) were 4.28C/c $m_2$, and 38.88kv/cm respectively. No fatigue was observed up to 6$\times$10$_{10}$ switching cycles at 5V and the normalized polarization reduced by a factor of only 4%.%. 4%.%. 4%.%.%.%.%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.12-13
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• 2006

Ferroelectric Cerium-substituted $Bi_4Ti_3O_{12}$ thin films with a thickness of 200 nm were deposited using the liquid delivery metal organic chemical vapor deposition process onto a Pt(111)/Ti/$SiO_2$/Si(100) substrate. At annealing temperature above $600^{\circ}C$, the BCT thin films became crystallized and exhibited a polycrystalline structure. The BCT thin film annealed at $720^{\circ}C$ showed a large remanent polarization ($2P_r$) of $44.56\;{\mu}C/cm^2$ at an applied voltage of 5V. The BCT thin film exhibits a good fatigue resistance up to $1{\times}10^{11}$ switching cycles at a frequency of 1 MHz with applied electric field of ${\pm}5\;V$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.290-291
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• 2006

The effect of praseodymium substitution on the ferroelectric properties of $Bi_4Ti_3O_{12}$ thin films have been investigated. Ferroelectric Pr-substituted $Bi_4Ti_3O_{12}$ thin films were fabricated by chemical solution deposition onto Pt/Ti/$SiO_2$/Si substrates. The structure and morphology of the films were analyzed using Xray diffraction, and scanning electron microscopy, respectively. About 200-nm-thick BPT films grown at $720^{\circ}C$ exhibited a polycrystalline structure and showed excellent ferroelectric properties with a remanent polarization ($2P_r$) of $28.21\;{\mu}C/cm^2$ at an applied voltage of 5 V. The films a1so demonstrate fatigue-free behavior up to $10^{11}$ read/write switching cycles with 1 MHz bipolar pulses at an electric field of ${\pm}5\;V$.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.67-71
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• 2000

The wear behaviors of ultrahigh molecular weight polyethylene pins against titanium alloy and stainless steel disks moving in two different kinematic motion were investigated by conducting repeat pass rotational sliding and linear reciprocal sliding wear tests. Linear reciprocal motion wore more the polyethylene pin than did repeat pass rotational motion for both disk materials. It means that the repeated directional change of contact stresses generates more wear debris in polyethylene. For the linear reciprocal sliding tests, titanium alloy disks were damaged with some scratches after one million cycles but no surface damage was observed on the polyethylene pins. On the other hand, for the repeat pass rotational sliding tests, all titanium alloy disks were severely abraded on the entire region of sliding track. This phenomenon can be interpreted by that stress fatigue under repeated sliding contact initiated titanium oxide layer wear particles from disk surface, and these hard particles were embedded into polyethylene pin and then they severely abraded the disk surface. From these results it can be concluded that the kinematic motion in pin-on-disk wear tests play a crucial role on the wear behaviors of UHMWPE pins against titanium alloy and stainless steel disks.

• Korean Journal of Materials Research
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• v.19 no.6
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• pp.337-343
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• 2009

In this study, we optimized Pb-free Sn/Ni plating thickness and conditions were optimized to counteract the environmental regulations, such as RoHS and ELV(End-of Life Vehicles). The $B_{10}$ life verification method was also suggested to have been successful when used with the accelerated life test(ALT) for assessing Pb-free solder joint life of piezoelectric (PZT) ceramic resonator. In order to evaluate the solder joint life, a modified Norris-Landzberg equation and a Coffin-Manson equation were utilized. Test vehicles that were composed of 2520 PZT ceramic resonator on FR-4 PCB with Sn-3.0Ag-0.5Cu for ALT were manufactured as well. Thermal shock test was conducted with 1,500 cycles from $(-40{\pm}2)^{\circ}C$ to $(120{\pm}2)^{\circ}C$, and 30 minutes dwell time at each temperature, respectively. It was discovered that the thermal shock test is a very useful method in introducing the CTE mismatch caused by thermo-mechanical stress at the solder joints. The resonance frequency of test components was measured and observed the microsection views were also observed to confirm the crack generation of the solder joints.