발간논문

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In the fifth part of this study, the ordered structure of Cr2N precipitate was investigated utilizing high-resolution neutron powder diffractometry (HRPD). Based on the Rietveld refinement of neutron diffraction patterns, the ordered Cr2N superstructure was confirmed to be an ordered h.c.p. or trigonal structure (space group: P(-)3 1m) with lattice parameter of a = 4.800 and c = 4.472 Å, as suggested in our previous TEM studies (part Ⅱ ~ Part Ⅳ). Even in perfect ordered state, a partial disordering of nitrogen atoms along caxis was detected, and the occupancies of nitrogen atoms in four different crystallographic position (l(a), 1(b), 2(d) and 2(c) Wyckoff sites) were determined to be 1.00(5), 0.0, 0.74(9) and 0.12(3), respectively. The accurate position of metal atoms was specified to be x = 0.346(8), y = 0 and z = 0.244(6), corresponding to deviation from ideal positions (x = 0.333, y = 0 and z = 0.250). This had a drastic effect on the scattering intensities of (11/33(0)) -type superlattice reflection, whereas the other two types of superlattice reflections were not significantly affected by deviation of metal atoms. The comparison between ideal and measured crystal structure of Cr2N was discussed using computer simulation of selected area diffraction (SAD) patterns.

keyword : Ordered structure, Partial disordering, Deviation of metal atoms, Neutron diffraction and Cr2N

The effects of microstructural variables, including DAS (dendrite arm spacing), the size of primary a phase, the size of eutectic Si particle and the thickness of eutectic structure, on tensile behavior of A356 cast aluminum alloy were quantitatively identified using linear regression analysis method. For systematic microstructural control in A356 alloy, directional solidification method was used with different solidification rates of 5, 25, 50 and 100 ㎛/s, respectively. The linear regression analysis suggests that both DAS and the size of primary a phase dominantly affect tensile strength of A356 cast aluminum alloy, while tensile ductility is most strongly dependent on the thickness of eutectic structure. The change in tensile behavior with varying microstructural variables in A356 alloy is discussed based on fracto graphic and micrographic observations.

keyword : A356 alloy, DAS, Eutectic Si, Tensile behavior, Linear regression analysis

The dry sliding wear tests were performed on A356-20 vol.% SiCp composites with and without surface coating. Thick alumina coatings were performed on A356-20 vol.% SiCp composites by micro-arc oxidation (MAO) process with different processing time. The samples were tested by pin-on-disc wear test equipment with different applied load and sliding velocity. It showed that MAO coated samples exhibited superior resistance to wear compared with uncoated samples in the severe wear conditions. Through the observations and analysis of the worn surface, worn subsurface, wear debris and variation of friction coefficient, the role of MAO coating layer is examined.

keyword : Micro-arc oxidation, Coating, Aluminum matrix composites, Dry sliding wear, MML

It is important to understand the relationship between processing and micro-structural characteristic of the Cu thin films to optimize those fabrication and use. The formation of twins, one of the significant factors for texture development decreases texture strength which depends on the twin boundary development of Cu films. Determination of grain growth and texture formation in the sputtered and electrodeposited Cu films during annealing was carried out for films of 100, 480, and 850 nm thickness deposited on a Ta(25 nm)/Si wafer. The grain growth and texture were analyzed by X-ray pole figure, EBSD (Electron backscatter diffraction). The annealing texture in connection with film thickness in the sputtered and electrodeposited Cu films is investigated and discussed.

keyword : Cu films, Grain growth, Twin, Texture

ITO thin films were deposited on corning 1737 glass using a D.C. magnetron sputtering. The morphology, the crystallinity and the electrical properties of ITO thin films were investigated by XRD, FESEM and 4 point probe system. The morphology of ITO particles changed from round island to polygonal shape as the O2 flow rate increased. In the first stage of the growth of ITO thin films, amorphous phase occurred. As O2 flow rate increased, ITO thin film grew to the crystalline with preferred orientation of (400) and (440). The sheet resistance of ITO thin films decreased to 9Ω/_ when the substrate temperature was 350℃. In this study, preferred orientation of (400) and coarse island particle of ITO thin films were critical factor.

keyword : ITO, Microstructure, Thin film, Sheet resistance, Preferred orientation

The electrical and the optical properties were investigated to find the optimum microstructure of ITO thin films deposited by D.C. magnetron sputtering. Carrier concentration and carrier mobility of ITO thin films were measured, the transmittance of them also was done. As O2 flow rate and substrate temperature increased, the transmittance of ITO thin film increased because ITO particles formed coarse and good crystalline. The sheet resistance was the minimum at O2 flow rate, 0.3 seem, and the minimum value was 9Ω/□ at substrate temperature, 350℃. The electrical and the optical properties of ITO thin film depended on the morphology and the crystallinity.

keyword : ITO, Thin film, Transmittance, Sheet resistance, Microstructure

The purpose of this study is to identify the effect of additives and current density on initial copper nucleation and growth during copper electrodeposition. Additives such as chloride ions, arabic gum were used in this study. An EG&G PAR model 273A potentiostat/galvanostat connected to a microcomputer with the M270 software was used for the electrochemical tests. Electrochemical experiments allied to SEM and image analysis were performed to characterize the nucleation and growth of copper in the presence of additives. In the higher current density, the copper foil had more uniform crystal size, higher surface covering and less needles shape crystals compared to lower current density. In the production of electrodeposited copper foil, grain size of the copper foil can be controlled by adding appropriate combination of additives.

keyword : Electrodeposition, Arabic gum, Chloride ions, Nucleation, Copper foil

The microstructural investigation and thermo-mechanical reliability evaluation of the conventional Sn-37Pb solder bumped flip chip package were carried out during the thermal shock test of the package. In the initial reaction, the reaction product between the solder and Cu mini bump of the chip side was Cu6Sn5 IMC layer, while a layer of Ni3Sn4 was formed between the solder and electroless Ni-P layer of the package side. The primary failure mechanism of the solder joints in this type of test method and package was confirmed to be thermally activated solder fatigue failure. The brittle interfacial failure mode was sometimes detected from the cross-sectional studies, but nearly whole of the failed packages showed the occurrence of the typical fatigue cracks.

keyword : Pb-bearing solder, Flip chip, Reliability, Fatigue

The microstructural investigation and thermo-mechanical reliability evaluation of the Sn-3.0Ag0.5Cu solder bumped flip chip package were carried out during the thermal shock test of the package. In the initial reaction, the reaction product between the solder and Cu mini bump of chip side was Cu6Sn5 IMC layer which has the same composition with that of Sn-37Pb case, while the two phases which were (Cu,Ni)6Sn5 and (Ni,CuhSn1 were formed between the solder and electroless Ni-P layer of the package side. The cracks were observed at the corner solder joints after the thermal shocks of 400 cycles. The primary failure mechanism of the Pb-free Sn-3.0Ag-0.5Cu solder joints in this type of package was also conftrmed to be thermally activated solder fatigue failure. The finite element analyses were conducted to interpret the failure mechanisms of the packages. The finite element analyses revealed that the cracks were induced by the accumulation of the plastic work and viscoplastic shear strains.

keyword : Pb-free solder, Flip chip, Reliability, Finite element analysis