Hyouk Chon Kwon

Fabrication of Copper Clad Aluminum Wire (CCAW) by Indirect Extrusion and Drawing

The optimized extrusion conditions from the present research were the extrusion temperature of 573~623K and the extrusion ratio(A0/A) of 21.39. Above the extrusion temperature of 623K, the fracture of sheath material was observed. It is due to the difference of flow stress between the sheath material and the core material during extrusion process. The bonding strength increased with increasing the extrusion temperature and the extrusion ratio. The bonding strength increased with increasing the annealing temperature. However, over 573K, it decreased abruptly since the thick and brittle intermetallic compounds of larger than 3µm were formed. The electricalconductivity of copper clad aluminum wire was about 70%IACS without annealing.

Effects of Core Material on Extrudability of Cu/Pure Al, Cu/Al3003 Clad Composites by Indirect Extrusion

We investigated about the effects of core material(Pure Al, Al3003) on extrudability such as the maximum extrusion ratio and the bonding strength of Copper Clad Aluminum(CCA) by indirect extrusion. As a results of this experiment, the maximum extrusion ratio of Cu/Al3003 was 38, which was larger than 21.39 of Cu/Al(Cu/pure Al). It was because that the difference of flow stress between copper as the sheath material and Al3003 as the core material was smaller than that of between copper and pure aluminum under the same extrusion temperature of 623K. The bonding strength gradually increased when the extrusion ratio increased, on the other hand, the bonding strength of Cu/Al3003 was higher than that of Cu/Al under same extrusion conditions. The diffusion layer thickness that affected bonding strength was not affected by the kind of core material, but it gradually increased when the extrusion ratio increased. It was thought that Cu/Al3003 had a more intimate diffusion layer than Cu/Al had because the extrusion pressure of Cu/Al3003 was higher than that of Cu/Al under the same extrusion conditions.

Fabrication and Properties of a Combined Structural Cu Sheet for Interconnect Material

In this study, it was aimed to develop a novel interconnect material simultaneously possessing high electrical conductivity and strength. Combined structural Cu sheets were fabricated by forming the high electrical conduction paths of Ag on the surface of high strength Cu alloy substrate by damascene electroplating. As a result, the electrical conductivity increased by 40%, while the ultimate tensile strength decreased by only 20%. When the depth of Ag conduction path was deep, fracture zone ratio as well as roll-over zone increased.

The Effect of Electromagnetic Stirring on the Semi-Solid Microstructure of High-Melting Alloys

Most of the work reported at this conference concerned the semi-solid processing of low melting point alloys, and in particular light alloys of aluminum and magnesium. It also can be true for the higher melting point alloys, such as Cu alloys. The purpose of this paper is to develop a semi-solid microstructure of Cu alloys using electromagnetic stirring applicable for squirrel cage rotor of induction motor. The size of primary solid particle and the degree of sphericity as a function of the variation in cooling rate, stirring speed, and holding time were observed. By applying electromagnetic stirring, primary solid particles became finer and rounder relative to as-cast sample. As the input Hz increased from 30Hz to 40Hz, particle size decreased. The size of primary solid particle was found to be decreased with increasing cooling rate. Also, it decreased with stirring up to 3 minutes but increased above that point. The degree of sphericity became closer to be 1 with hold time. Semi-solid microstructure of Cu alloys, one of the high melting point alloys, could be controlled by electromagnetic stirring.

Fabrication and Properties of TiB2 Reinforced Cu Composites by Electromagnetic Stirring

Cu-Ti and Cu-B alloys were separately cast in vacuum arc melting furnace for alloying. These alloys were added to the copper melt of 1500K in the induction furnace and performed electromagnetic stirring at 1000rpm. The cast ingot(dia : 70mm, length : 100mm) was hot extruded with the extrusion ratio of 13:1 after heating at 1073K for 1 hour. The TiB 2 precipitates were observed in the extruded materials and the mean size of TiB 2 precipitates was found to be about 1.5µm. The volume fraction of TiB 2 varies due to the density difference between the TiB2 and the copper melt. With the increasing of TiB2 contents from 3 to 8 vol.%, the hardness and the tensile strength increased from 951 to 140Hv and from 248 to 278MPa, respectively, and the electrical conductivity decreased from 82 to 70%IACS. However, the mean size of TiB 2 particle was not increased despite increasing an annealing temperature.

Grain Size Dependence of Tensile Properties in Cu-Sn Thin Foils (Experimental Study)

This study was carried out to investigate the effects of grain size on mechanical properties in Cu-Sn foil with a thickness of 30 um. The grain size was varied from approximately 7 um to 50 um using heat treatment at 773 K for 2 h to 24 h in a vacuum atmosphere. Tensile test was carried out at room temperature with strain rate of 1mm/min. Typical yield drop phenomenon was observed. Mechanical properties were found to be strongly affected by microstructural features including grain size. The yield strength and tensile strength gradually decreased with increasing the grain size. The strain to fracture also decreased by grain growth. These results could be explained by not only the grain size dependence of yield strength but also the ratio of thickness to grain size dependence of yield strength.

Process Dependence of Microstructure and Mechanical Properties for Al-Fe Based Bulk Alloys

In this work, a comparative study of the microstructure and mechanical properties of Al-8Fe based bulk alloys fabricated by three different rapid solidification methods and subsequent hot extrusion was carried out. Spray forming, gas atomization, and melt spinning methods were used as techniques for rapid solidification having various cooling rates. Equiaxed grains containing Al-Fe, Al-Fe-(Mo, V), and Al-Zr phase particles were characterized. The yield strength of the melt spun and extruded specimen was estimated to approximately 800 MPa at room temperature, a value which is roughly 1.5 times higher than that obtained for the atomized and extruded specimen and roughly 2.5 times higher than for the spray formed and extruded specimen. The higher strength of the melt spun and extruded specimen originated from a finer microstructure compared to the atomized and extruded specimen and the spray formed and extruded specimen.

Tensile Behavior of Rolled and Annealed Copper Thin Foils

Tensile properties of rolled and annealed copper thin foils were investigated based on the grain size and thickness. Yield strength was higher in the thinner foil than in the thicker foil at as-rolled state. Difference of yield strength between the thinner foil and the thicker foil becomes small at annealed state. Tensile strength was higher in the thinner foil than in the thicker foil at as-rolled state, but it was reversed at annealed state. Strain to fracture or elongation increased with increasing thickness in the annealed state. A knife edge type of fracture was characterized in both the as-rolled state and the annealed state. A higher tensile strength and strain to fracture of the annealed thicker foil was attributed to the higher number of grains per thickness. From this work, it was concluded that mechanical properties of thin foils were dependent upon the number of grains per thickness.

Effectiveness of Residual Stress on Forming Copper Patterns of Printed Circuit Board

The effectiveness of residual stress on forming copper patterns of printed circuit board was investigated during applied thermal conditions. Generally, the electrolytic copper foil showed a compressive residual stress about -54MPa as received, which easily caused to form copper patterns irregularly. We verified the compressive residual stress was relaxed with applying thermal conditions under 200°C for a few hours. And also, we observed that the compressive residual stress of copper foil tended to be relaxed, constant, and compressive again during heating times at each temperature. The relationships between residual stress and etching factor of copper pattern were analyzed in this works.

The Effects of Heat Treatment on the Bonding Strength of Surface-Activated Bonding (SAB)-Treated Copper-Nickel Fine Clad Metals

Surface activated bonding (SAB) is a novel method for the precise joining of dissimilar materials. It is based on the concept that two atomically clean solid surfaces can develop a strong adhesive force between them when they are brought into contact at high vacuum condition without high deformation at a 40~90%. With this SAB process, the effects of heat treatment on the bonding strength of surface-activated bonding (SAB)-treated copper-nickel fine clad metals were investigated. An increase in the SAB rolling load of the copper-nickel fine clad metals increased the peel strength after heat treatment, indicating that increases in the SAB rolling load decreased the interface voids formed by initial micro-range surface roughness between the clad materials in the SAB cladding process. Unlike conventional cold rolling, outstanding interface diffusion between the clad materials was not observed after heat treatment. In addition, the peel strength increase of the clad metals compare with initial peel strength increased with SAB rolling load (<1% reduction ratio at a roll load of 5000 kgf ) up to 3.99 N/mm after heat treatment.