Papers by Author: Jae Ho Lee

Abstract: The codeposition behavior of submicron sized diamond with nickel from nickel electrolytes has been investigated. Electroplating of diamond dispersed nickel composites was carried out on a rotating disk electrode (RDE). The effects of current type and current density on the electrodeposited Ni-diamond composite coating were investigated. The effects of pH and surfactants on the composite coating were also investigated. The hardness of coating was measured with varying electroplating conditions. As diamond was incorporated into the coating, the hardness of coating as well as the wear resistance was improved. The surface morphologies of the Ni-diamond composite coatings were observed using FESEM.

Abstract: In Ni-SiC composite coating, the SiC content is dependent on the surface properties of SiC particles. As sulfuric acid has a strong dehydration force, addition of sulfuric acid in the Ni sulfamate bath changed the surface properties of SiC particles, affecting the codeposition behavior of SiC particles. Also the additives such as SDS affect the electrodeposition behavior of the Ni-SiC composite coating. In this study, effects of the HSO4 ‾ and the current density on the electrodeposition behavior of the Ni-SiC composite coating have been investigated. The Ni-SiC composite coatings were electrodeposited at current densities of 50~200mA/cm2. The surface and cross-sectional morphologies of the Ni-SiC composite coatings were observed using SEM, and their mechanical properties were characterized with micro-Vikers hardness.

Abstract: Ceramic coatings were synthesized on pure Mg and binary Mg-7.1wt%Al alloy by plasma electrolytic oxidation (PEO) technique, and the effect of current ratio, C2/C1, ranging from 0.2 to 0.85 on their mechanical and electrochemical properties was investigated. As the C2/C1 ratio increased, the thickness of the coating layer increased, while surface roughness was almost unchanged. The hardness and wear resistance had a marked tendency to increase with increasing C2/C1 ratio and Mg-Al alloy showed higher hardness and wear resistance at all C2/C1 ratios compared to pure Mg. The weight loss of the pure Mg and Mg-Al alloy in 3.5%NaCl solution was reduced by coatings. However, it had no dependence on the C2/C1 ratio. The wear resistance of the coated Mg-Al alloy was better than that of the coated pure Mg.

Abstract: Nickel tungsten (Ni-W) alloy coating was electroplated to increase its mechanical properties. Tungsten cannot be electroplated by itself, however, it is codeposited with other iron group metals especially with nickel. The morphologies of nickel tungsten coating were varied with current density. To eliminate the formation of cracks, pulse plating was employed. Crackless nickel tungsten alloy were obtained in pulse reverse electroplating. Hardness of nickel tungsten coating has twice higher compared to the normal electroplated nickel.

Abstract: The dishing phenomena of soft materials in chemical mechanical polishing (CMP) process were problematic in delineating inlaid metal patterns. The inlaid copper structures were fabricated on Si wafer where SiO2 was thermally grown. Seed layer was deposited by thermal evaporate method followed by copper electrodeposition. Copper was electrodeposited with IBM paddle type electroplating machine to obtain uniform thickness of coating. The dishing amounts were measured at various current density and current type. The dishing amounts with pattern density and line width were also measured. The losses of copper were not sensitively dependent on current density however those were dependent on current type. The dishing amount of copper was decreased at high pattern density especially over 50% and increased with line width. Surface topology and grain size of coating were investigated with surface profilometer and FESEM.

Abstract: Electroplating of copper in via filling is very important in 3D SiP (System in Packaging). Defect free via filling can be obtained through additive in the electrolyte and current type control. Via in Si wafer were formed by RIE method with 170 &m depth and 50 &m in diameter. Seed layers were deposited by ionized metal plasma (IMP) sputtering; Ta for diffusion barrier, Cu for conductive layer. Via was filled with copper by electroplating method. Different types of additives were used in via filling; PEG, SPS, Cl- and JGB. Defects in via were controlled and eliminated by precise monitoring of additive concentration and input current. The optimum condition of electroplating was determined by getting cross-sectional images of filled vias and by determining the degree of via filling.

Abstract: As electronic devices are getting smaller and lighter, the density of copper lines on flexible printed circuit board (FPCB) is getting higher. Conventionally, subtractive method was used for copper line on a flexible films, however, as the line pitch is getting smaller, the lateral etching of copper cause serious problem. To replace the subtractive method, semi-additive method was used for fine pitch copper line fabrication. In semi additive process, sputtered layer for the electroplating copper was required. The feasibility of electroless plating to replace high cost sputtered copper seed layer was investigated. Electroless depositions of copper were conducted on different substrate to find optimum conditions of electroless copper plating. To find optimum conditions, the effects and selectivity of activation method on several substrates were also investigated. The adhesion strength between polyimide and copper was improved by treating the polyimide surface with butylamines. Pretreatment prior to electroless plating is very sensitive and surface dependent. Surface morphologies were investigated with FESEM.

Abstract: Ceramic coatings were synthesized on pure magnesium, binary Mg-Al and Mg-Zn alloys by plasma electrolytic oxidation (PEO) technique, and their mechanical and electrochemical properties were investigated. The coatings showed porous microstructure and some volcano top-like pores on the surface. The coatings on Mg-Al alloys consisted of MgO, MgAl2O4 and Al2O3. In the coatings on Mg-Zn alloys, MgO and ZnO were detected. The hardness and wear resistance showed slight dependence on Al content but no tendency to increase with increasing Zn content. The coated Mg alloys with Al, Zn showed better corrosion resistance in 3.5%NaCl solution but poor corrosion resistance in methyl alcohol, compared to the coated pure Mg.

Abstract: The research conducted was focused primarily on the development of a process for obtaining silver-coated tungsten powders for applications related to electrical-conducting devices. Particles of high strength material when coated with silver offer a means of obtaining desirable electrical properties and high strength. The coating process employed aqueous ammoniacal silvernitrate electrolytes with a formaldehyde solution as the reductant. Modifying additives were also applied. The reduction and subsequent deposition of silver occurred selectively on the surface of the tungsten particles. The morphologies of the coated particles were assessed by SEM imaging. The silver was uniformed coated on tungsten powder and its thickness was estimated to be approximately 100nm on the basis of a mass account.

Abstract: Copper via filling is an important factor in 3D stacking interconnection of SiP (system in package). As the packaging density is getting higher, the size of via is getting smaller. When DC electroplating is applied, a defect-free hole cannot be obtained in a small size hole. To prevent the defects in holes, pulse and pulse reverse current was applied in copper via filling. The size of 50, 70, 100
in diameter and 100
in height. The holes were prepared by DRIE method. TaN and Ta was sputtered for copper diffusion barrier. Via specimen were filled by DC, pulse and pulse-reverse current electroplating methods. The effects of additives and current types on copper deposits were investigated. Vertical and horizontal cross section of the via were observed by SEM to find the defects in via. When pulse-reverse electroplating method was used, defect free via were uccessfully obtained.