Papers by Author: Hyouk Chon Kwon

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: The study on rheocasting has been conducted based on examination for destruction, growth, ripening of solid state in accordance with various changes in cooling. And flow characteristics of slurry for high liquid range rather than practical use has gotten attention. However, the characteristics of existing rheocasting and thixocasting are better mechanical property than competing process die casting but it’s competitiveness as automotive or electric electronic parts which cost of product is important. And productivity also has been decreased. Because die-casting techniques has been advanced such as vacuum, mold auto temperature control etc. 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. Therefore, the aim of this study is to devise the original strength of semi-solid process by sequential semi-solid process. 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. With this background, this research conducted electromagnetic stirring through slurry deliverance of sequential process through A356 alloy electromagnetic stirring pump (30Hz, 130A) with Sequential Semi-Solid Process device to assess the microstructures, primary particle size, degree of sphericity change in A356 alloy in accordance of solid-fraction, stirring speed, and stirring maintenance time.

Abstract: The μ-via in microelectronic substrate should have multiple purposes, one of them is to allow to the path of signal or current from electronic devices. The micro void can be easily formed in μ-via because μ-vias are filled with a screen printing process and the size of via is small. The residual void has been known as crack initiation of copper layer during a reliability test. The solder resist filling process and the behavior of a residual void in μ-vias were investigated. The void extraction process was very effective comparing with the conventional process to remove a residual void. As extracted with 1.5 atm for more than 30 sec, the residual void in μ-BVH was perfectly eliminated.

Abstract: Cu-Be alloy (C17200) rod having diameter of 23.5mm was produced by a vacuum continuous casting method at furnace temperature range of from 1240°C to 1260°C with casting speed range of from 35mm/min to 103mm/min. When the furnace temperature was 1240°C and 1250°C, Cu-Be alloy rod without fracture could successfully produced at high casting speed of 103mm/min. However, when the furnace temperature was 1260°C, the breakout occurred at casting speed faster than 78mm/min. Surface roughness (Ra) increased with increasing not only a furnace temperature but also a casting speed.

Abstract: This paper described extrudability and bonding strength of copper (TPC) clad aluminum alloy (pure Al, Al3003, Al5005, and Al7072) composites produced by indirect extrusion at 350°C with extrusion ratio of 21.39. Conical typed die with semi angle of 30°. Carbon oil was used to reduce the friction between billet/sleeve and billet/die. Maximum extrusion pressure was estimated to 491MPa for the Cu/Al, 714MPa for the Cu/Al3003, 820MPa for the Cu/Al5005, and 743MPa for the Cu/Al7072 alloy composites. No surface fracture was observed. From SEM observation, diffusion layer between the sheath material and the core material of extruded composites is observed and its thickness was measured to about 1.5㎛. The bonding strength was estimated to 65MPa for the Cu/Al, 89.3MPa for the Cu/Al3003, 70MPa for the Cu/Al5005, and 75MPa for the Cu/Al7072 alloy composites.

Abstract: The microstructures and mechanical properties of the bulk Al-Fe-(Mo, V, Zr) alloy produced by melt spinning process and subsequent hot extrusion at 693K in the extrusion ratio of 25 to 1 were investigated. TEM observation revealed an equiaxed grain structure with the average grain size of 200 nm for the extruded bulk alloy. Extremely fine dispersoids based on Al-Fe phases, Al-Fe-(Mo, V) phases and Al-Zr phases were observed to be distributed uniformly within grains and at grain boundaries. The size distribution of the binary Al-Fe and the Al-Fe-(Mo, V) phases were ranged from 20 nm to 50 nm, whereas the Al-Zr phase was less than 10 nm. The very high tensile strength of about 800MPa was achieved at room temperature for the extruded bulk alloy.

Abstract: In this study, rod type Cu54Ni6Zr22Ti18 bulk amorphous alloy fabricated by warm extrusion of amorphous powders was investigated. To get bulk type amorphous alloy, the Cu54Ni6Zr22Ti18 amorphous powders which has a particle size below 63( and wide supercooled liquid region of 53K were prepared by a high-pressure gas atomization method. The powders were filled in a Cu can with an inner dimension 20×2×50mm in air, evacuated, sealed and then precompacted in the press. Before extrusion, the billet was heated with heating rate of 50K/min and the holding time was about 5min. The extrusion temperature was 723K and the extrusion ratio was increased from 2 to 5. By warm extrusion of amorphous powders, a fully amorphous Cu54Ni6Zr22Ti18 bulk type alloys were successfully synthesized. The conditions for extrusion were decided based on the time-temperature-transformation curve and DSC analysis. Phase analysis was performed by XRD. The result of the phase analysis indicated that Cu54Ni6Zr22Ti18 bulk rod type samples having fully amorphous phase could be obtained until extrusion ratio of 4 at extrusion temperature of 723K, but partial crystalline phase would be observed in the bulk rod type alloy fabricated at extrusion ratio of 5.