Hong Kee Lee

A Kinetic Study on the Electrodeposition of Ni-Cr Alloy on Copper for Embedded Resister Layer in PCB

The thin film resistors such as Ni-Cr alloy could be formed by the electrodeposition method for embedded passive device in printed circuit board. A kinetic study on the electrodeposition of nickel-chromium alloy on copper has been performed using a rotating disk geometry. Activation energies of nickel and chromium in the temperature range between 15°C and 35°C were 8.9kcal/mole and 3.5kcal/mole, respectively. The electrodeposition rate of nickel seems to be controlled partly by electrochemical reaction and partly by mass transport, namely mixed controlled. However, that of chromium seems to be controlled by mass transport. As the amount of chromium in deposit increased, the electric resistance of deposit surface increased. The maximum electric resistance of nickel-chromium alloy deposit was 78.6Ω /□.

Effect of Alkali Surface Modification on Adhesion Strength between Electroless-Plated Cu and Polyimide Films

The effects of the alkali surface modification process on the adhesion strength between electroless-plated Cu and polyimide films were investigated. The polyimide surfaces were effectively modified by alkali surface treatments from the hydrophobic to the hydrophilic states, and it was confirmed by the results of the contact angle measurement. The surface roughness increased by alkali surface treatments and the adhesion strength was proportional to the surface roughness. The adhesion strength of Cu/polyimide interface treated by KOH + EDA (Ethylenediamine) was 874 gf/cm which is better than that treated by KOH and KOH + . The results of XPS spectra revealed that the alkali treatment formed oxygen functional groups such as carboxyl and amide groups on the polyimide films which is closely related to the interfacial bonding mechanism between electroless-plated Cu and polyimide films. It could be suggested that the species and contents of functional group on polyimide films, surface roughness and contact angle were related with the adhesion strength of Cu/polyimide in combination.

Effect of Additional Electrical Current on Adhesion Strength between Copper and Polyimide Films

The effect of the additionally applied electrical current on the adhesion strength between electroless Cu and polyimide films was investigated. Peel tests were performed after applying electrical current within the range from 0.1 to 100 mA for the duration from 1 to 30 minutes. Sample with more than 1 mA of additional electrical current for 1 minute showed higher adhesion strength than that without additional electrical current. However, samples with 10 mA of additional electrical current for more than 10 miniutes showed the degradation of adhesion strength. Ra and RMS values of the peeled polyimide surface were proportional to the adhesion strength though there were no significant changes in the morphology of the peeled surfaces with varied amount and time-length of additional electrical current. Applying electrical current could increase the density of chemical bonding, which results in increase of the adhesion strength between copper and polyimide. However, in the case of applying additional electrical current for excessive amount or time, the degradation of the adhesion strength owing to the formation of copper oxide at the interface could occur.

Diffusion barrier properties of atomic layer deposited iridium thin films on the Cu/Ir/Si structure

We have investigated diffusion barrier properties of atomic layer deposited iridium (Ir) thin film as a function of thermal treatment temperature. Up to the temperature of 500°C, Ir thin film maintaind its initial stage without penetration of Cu layer into Si through Ir layer. Thermal stability of Ir layer up to 500°C was supported by HR-TEM and XRD measurement results. On the other hand, Ir layer was thermally annealed at 600°C, Cu-silicide was formed and interdiffusion of Cu and Ir was observed.

Residual Stress Characterization of Electroformed Ni-Base Alloy for μ-Gear Mold

The micro gear molds for powder injection molding were fabricated by electroforming process of Ni-Fe alloys. The residual stress at interface between electrodeposit and substrate was important for micro electroforming. Addition of 6 g/L saccharin lowered residual stress from 466.3 MPa up to 32.8 MPa and increase of Fe content resulted in increase of residual stress. Electrodeposition by pulse current decreased residual stress in deposit although Fe content was increased. These results reveal clearly that decrease of residual stress due to pulse current is larger than increase of residual stress due to higher Fe content. The micro electroformed gear molds with 550 μm and 2,525 μm in outer diameter and 400 μm in height were fabricated by micro electroforming and 316L feedstock was injection-molded into micro molds. As a result, it is suggested strongly that micro electroforming is very useful process to manufacture micro mold with high dimensional accuracy for micro PIM.

Manufacturing Technology of μ-Gear and Mold by Fe-Ni Alloy Electroforming

The micro parts were fabricated by electroforming process of Fe-Ni alloy. Reaction mechanism of Fe-Ni alloy electrodeposition process was investigated using rotating disk electrode. To clarify the rate determining step, the activation energies of iron and nickel elements were calculated from the Arrhenius plot in the temperature range of 308K~328K. The reaction rate of iron in electrodeposition of Fe-Ni alloy was controlled by chemical reaction at temperature range of 308K~318K, while at range of 318K~328K, it was controlled by mass transport. The reaction rate of nickel was controlled by chemical reaction at 308K~318K and by a mixed mechanism of chemical reaction and mass transfer at 318K~328K. For alloy electroforming of micro gears and a mold for powder injection molding, the mandrels of micro gear (1.7mm in diameter and 600 μm in height) and micro mold (550 μm in diameter and 600 μm in height) were prepared by UV-lithography using SU-8 photoresist. Subsequently, Fe-Ni alloy micro gear mold were electroformed with high hardness (490 Hv) and very good surface roughness (Ra 37.5 nm).

Characteristics of Silver Electrodeposition Solution and Silver Film Fabricated by Electrodeposition with Additives for Interconnection

As the electrodeposition reaction is a heterogeneous reaction including both material transfer and electrochemical reaction, this study tries to find out the reaction mechanism about Ag electrodepostion used as semiconductor interconnection using rotating disk electrode system (RDE system). Considering the environmental problem, non-cyanide Ag electrodeposition solution has been carried out. With varying the process conditions of a certain range including the rotating speed of RDE, applied voltage, and temperature etc., obtained the electrodeposition rate of Ag according to the reaction time. The rate determining step was clarified with the activation energy(Ea) of the electrodeposition reactions for the each process conditions estimated from Arrhenius Plot. Activation energy of Ag in the temperature range between 18°C and 32°C was 3.2kcal/mole. The electrodeposition rate of Ag seems to be controlled mass transport. With the electrodepositon solution mentioned above, the characteristics of silver thin film and bottom-up filling capability were investigated by DC or pulsed electrodeposition method. Especially, the effects of additives on the properties of bottom-up filling of Ag were studied.