Papers by Author: Seung Boo Jung

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Authors: J.K. Choi, H.B. Kang, J.W. Lee, Seung Boo Jung, Cheol Woong Yang
Abstract: Interfacial reaction between electroless plated Ni-P/Au UBM(Under Bump Metallization and eutectic Sn-58mass%Bi solder was studied by using AEM(Analytical Electron Microscopy). UBM is prepared by the electroless plating of Au (0.15μm ) / Ni-15at%P (7 μm ) on bare Cu substrate, and then it is reacted with Sn-58Bi solder at 220°C for 1 min. The chemical analysis using AEM provided us very consequential information about microstructure of the interface and phases formed. CBED(Convergent Beam Electron Diffraction) technique is used for phase identification of intermetallic compounds. In this study, the AEM results indicate that Ni3Sn is formed at the P-rich Ni layer/Ni3Sn4 interface by crystallographic analysis. The measured primitive cell volume(104.10 Å3)of this phase is close to the Ni3Sn(103.19 Å3) rather than Ni2SnP(235.24 Å3).
Authors: Jong Woong Kim, Sun Kyu Park, Seung Boo Jung
Abstract: Ball shear test was investigated in terms of effects of important test parameters, i.e. shear height and shear speed, with an experimental and non-linear finite element analysis for evaluating the solder joint integrity of area array packages. A Pb-free solder composition was examined in this work: Sn-3Ag-6Bi-2In. The substrate was a common SMD (Solder Mask Defined) type with solder bond pad openings of 460㎛ in diameter. It could be observed that increasing shear height, at fixed shear speed, has the effect of decreasing shear force, while the shear force increased with increasing shear speed at fixed shear height. Too high shear height could cause some bad effects on the test results such as unexpected high standard deviation values or shear tip sliding from the solder ball surface. The low shear height conditions were favorable for screening the type of brittle interfacial failures or the degraded layers in the interfaces.
Authors: Jong Woong Kim, Hyun Suk Chun, Sang Su Ha, Jong Hyuck Chae, Jin Ho Joo, Young Eui Shin, Seung Boo Jung
Abstract: Board-level reliability of conventional Sn-37Pb and Pb-free Sn-3.0Ag-0.5Cu solder joints was evaluated using thermal shock testing. In the microstructural investigation of the solder joints, the formation of Cu6Sn5 intermetallic compound (IMC) layer was observed between both solders and Cu lead frame, but any crack or newly introduced defect cannot be found even after 2000 cycles of thermal shocks. Shear test of the multi layer ceramic capacitor (MLCC) joints were also conducted to investigate the effect of microstructural variations on the bonding strength of the solder joints. Shear forces of the both solder joints decreased with increasing thermal shock cycles. The reason to the decrease in shear force was discussed with fracture surfaces of the shear tested solder joints.
Authors: S.G. Kim, Seung Boo Jung, Ji Hun Oh, H.J. Kim, Yong Hyeon Shin
Abstract: Polycrystalline ZnO thin films were for the first time deposited on SiO2/Si (100) substrate using 2-step deposition; atomic layer deposition (ALD) and RF magnetron sputtering, for Film Bulk Acoustic Resonator (FBAR) applications. The film deposition performed in this study was composed of following two procedures; the 1st deposition was using ALD method and 2nd deposition was using RF magnetron sputtering. The ZnO buffer layer ALD films were deposited using alternating diethylzinc (DEZn)/H2O exposures and ultrahigh purity argon gas for purging. Exposure time of 1 sec and purge time of 23 sec yielded an ALD cycle time. Two-step deposited ZnO films revealed stronger c-axis preferred-orientation than one-step deposited. Therefore, this method could be applied to the FBAR applications, since FBAR devices require high quality of thin films.
Authors: Seung Boo Jung, Yoritoshi Minamino, Hideki Araki, Toshimi Yamane, Kiyoshi Hirao, S. Saji
Authors: Yoritoshi Minamino, Hidehiro Yoshida, Seung Boo Jung, Kiyoshi Hirao, Toshimi Yamane
Authors: Won Bae Lee, Hyung Sun Jang, Yun Mo Yeon, Seung Boo Jung
Abstract: The hardness distribution related to the precipitates behaviors as friction stir welded and PWHT (post weld heat treated) 6061 Al alloy have been investigated. Frictional heat and plastic flow during friction stir welding created a fine, eqiuaxed and elongated microstructure near the weld zone due to dynamic recovery and recrystallization. A softened region which had been formed near the weld zone couldn't be avoidable due to the dissolution and coarsening of the strengthening precipitates. PWHT (SHT+ Aging) homogeneously recovered the hardness distribution over that of the base metal without softening region, resulted from non-homogeneously distributed hardness only aging treated. 36ks aging followed by SHT gave a higher hardness overall weld than that of the base metal due to a higher density of the spherical shaped precipitate.;
Authors: Jong Woong Kim, Seung Boo Jung
Abstract: The effects of void formation on the joint strength and failure mode of the solder joints were examined. A computational modeling technique, i.e., finite element modeling, was employed to investigate the effects. The effects of location, size and number of void were also investigated and compared with the case that has no void in the solder ball. When there was 1 or more voids in the solder ball, the joint strength decreased regardless of the location, size, and number of voids. Especially, the shear force of the joints decreased about 50% when 3 voids were formed in the solder ball. From the stress analyses, the possibility of preliminary brittle interfacial failure should be lower when voids were formed in the solder ball.
Authors: Chang Yong Lee, Won Bae Lee, Yun Mo Yeon, Seung Boo Jung
Abstract: Friction stir welding of dissimilar formed Mg alloys(AZ31/AZ91) was successfully carried out at the limited welding conditions. In a sound joint, SZ was mainly consisted of AZ31 Mg alloy which was located the retreating side. Dynamic recrystallization and grain growth occurred and β intermetallic compounds of AZ 91 Mg alloy was not observed in SZ. BM had a higher hardness than that of the weld zone. The fracture location was not weld zone but BM of the AZ91 Mg alloy in tensile test.
Authors: Won Bae Lee, Chang Yong Lee, Yun Mo Yeon, Jong Bong Lee, Shur Chang Chae, Seung Boo Jung
Abstract: The grain growth behavior and mechanical properties in the friction stir weld zone after post weld heat treatment (PWHT) have been investigated. As PWHT temperature increased, a normal grain growth of as-welded equaxied grains ceased and abnormally grown grains with elongated shape coarsened. Huge elongated grains changed into smaller equaxied grains at 500°C. In case of lower heat input condition, abnormal grain growth initiated faster due to smaller initial grain size. The weld zone with bigger initial grains had advantages to maintain the thermal stability at high temperature. The hardness near the weld zone was almost recovered to the 95% of the unaffected base metal at 500 °C and the weld zone under lower heat input condition resulted in the homogeneous recovery through the whole weld zone.
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