발간논문

Home > KJMM 논문 > 발간논문

Alloy deposits of Sn-Bi, were electroplated on a Cu plate from an organic sulfonate bath using direct or pulsed currents, and the effects of the plating parameters on the composition and the microstructure of the electrodeposits were investigated. In addition, the effects of alloy composition of the electrodeposits on the formation kinetics of intermetallic compounds were examined. Addition of grain refiner to the bath increased the cathodic polarization, and reduced the difference of the deposit potential between Sn and Bi. Thus, Sn-Bi alloy can be electrodeposited with fine and rounded grains in bath with the additive. The Sn content in the deposits was increased with an increase of Sn content in the bath. The preferred deposition trend of Sn was stronger than that of Bi, because the deposit potential of Sn was more positive than that of Bi in the bath with the additive. The Sn content in the deposits was decreased with an increase of current density, and the grains of deposit became finer because of the increased cathodic overpotential. When Sn-Bi alloy was electrodeposited using pulse current at 4 A/d㎡ peak current density, the Sn content in the deposit was increased with increasing the pulse frequency and decreasing the duty cycle. The morphology of Sn-Bi deposits became finer with decreasing pulse frequency and increasing duty cycle. When the depostis of Sn-Bi alloy were aged at 80℃, the growth of Cu-Sn intermetallic compound layer [ε(Cu_3Sn) +η`(Cu_6Sn_5)] showed a parabolic time dependence, and the growth rate of that depended significantly on the composition of Sn-Bi electrodeposits. The apparent activation energy for the growth of intermetallic compound in 42Sn-58Bi electrodeposit was 52.48 kJ/㏖, that in 70Sn-30Bi elecrodeposit was 43.32 kJ/㏖, and that in 90Sn-10Bi was 41.35 kJ/mol.

keyword :

To reduce the occurrence of defects on both galvanized and galvannealed sheet steels in industrial continuous galvanizing line, the morphology and formation mechanism of surface defects have been investigated by optical microscopy, scanning electron microscopy and roughness profiler. It is obvious that both removal of oxides on steel surface and cleanness of the continuous galvanizing line are essential to produce defect-free galvanized and galvannealed coatings. In galvannealed steel, the existence of thin oxides at the interface between coating and substrate causes the inhibition of the Fe-Zn reaction and, thus, results in the under-alloying; some parts of coatings are still remained as pure-Zn. On the other hand, in galvanized steel, Mn-containing oxides account for the poor wettability of molten Zn and the formation of dross-like defect. Some of the steel fragments and/or fines observed on the surface of galvannealed coating are considered to be an origin of the spot defects. It was also concluded that the defects generally considered as dross are mostly not the case.

keyword :

The size distribution of Ti_2O_3 inclusion during solidification of low carbon steel has been calculated using reactive diffusion equations, which take account of the nucleation and growth of inclusion as well as solidification. The calculated results were compared to experimental observations. And the effect of various parameters such as cooling rate, chemical composition of steel, on the inclusion size distribution were studied.

keyword :

The fracture of eutectic Sn-Ag solder joint by thermal aging was investigated through a pull test and microstructural observation. The joint strength in the pull test decreased with increasing aging time and was saturated for aging time more than 25 hours. The change in joint strength was explained not only by such metallurgical factors as grain growth and intermetallics formation, but also by the mechanical factor of strength mismatch between solder and intermetallics. For aging time less than 25 hours, Cu_6Sn_5 intermetallics formed. Strength mismatch between solder and Cu_6Sn_5 intermetallics reduces joint strength by causing stress concentrations around the intermetallics. Joint strength decreased with the Hall-Petch relationship as solder grains become coarsened with increasing aging time. For aging time above 25 hours, Cu_3Sn intermetallics formation was confirmed. During Cu_3Sn intermetallics formation, voids generally formed. They play an important role in determining the primary failure site. The present study shows that an extended aging time reduces the joint strength and then saturates because all solder joint failure is more strongly determined by local stress concentration around voids than by the stress concentration caused by strength mismatch.

keyword :

The fabrication of Sn-Pb and Sn-Ag solder bump (150 ㎛ diameter, 250 ㎛ pitch) by electroplating was studied for flip chip package. As a preliminary experiment, the effect of current density and plating time on Sn-Pb and Sn-Ag deposit was investigated. The eutectic compositions of Sn-Pb and Sn-Ag were controlled and the Sn-37 wt.%Pb and Sn-3.5 wt.%Ag solder bumps were fabricated in optimal condition of 6A/d㎡, 4hr and 6A/d㎡, 1.5hr, respectively. The shape of humps was observed by SEM and ball shear test after reflow was performed to measure adhesion strength between solder bump and UBM(Under Bump Metallurgy). The shear strength of Sn-Ag bump fabricated by electroplating was higher than that of Sn-Pb.

keyword :

The distribution ratio of zinc between Ag-Zn and Fe-C-Zn alloys was measured to clarify the thermodynamic behavior of zinc in Fe-C melt at high temperatures. The activity coefficient of zinc in Ag-Zn alloy was preliminarily measured as a fundamental thermodynamic data for the activity of zinc in Fe-C melt. From the dependence of activity coefficient of zinc in Fe-C melt on temperature and carbon content, the following equation could be obtained at 1573-1623K: 1nγ_zn^Fe-C= {35.1-(42200/T)}+20.9(X_c-X_c^satd) (1573 K≤T≤1623 K) X_c^satd= {3610+14.2T(K)/123000+11.1T(K)}

keyword :

A study has been made on the recovery of nitric acid and valuable metals such as Cu, Sn and Pb from the spent nitric etching solutions. The nitric acid was extracted effectively by TBP but the heavy metals such as Fe, Cu, Sn and Pb were not extracted by TBP from the spent nitric etching solutions. From the experimental results, 95% of nitric acid in spent etching solution was extracted at O:A ratio of 3:1 in five stages by 60% TBP, and 98% of nitric acid was stripped from the loaded organic phase at O:A ratio of 1:1 in four stages by distilled water. After extraction of nitric acid, Cu was effectively recovered as a metal by electrowinning and Sn was successfully removed by precipitation methode as the form of hydroxide or hydrated oxide by adjusting pH of the raffinate solution. Finally, Pb was recovered by cementation with iron scrap at above 65℃. Parameters controlling the cementation process, such as temperature, pH and the effect of the additives were investigated.

keyword :

The characteristics of mold level fluctuation were investigated using FFT(Fast Fourier Transformation) analysis of mold level and measuring strand bulging in thin slab casting. The special frequency of periodic mold level fluctuation, which was amplified with casting time and sometimes made breakout of solidified shell, was coincided with that of strand bulging and pinch roll speed. The unsteady bulging of strand was the main cause of this kind of mold level fluctuation.

keyword :