Electroplated copper foil is used of printed circuit board as conducting wire. As electrics industry is developing, the circuit width becomes narrow and circuit density is on the increase. To make the high density electric circuit, ultra thin copper foil which the thickness is 3 ∼ 9 ㎛ is required. Carrier is used for UTC manufacture to support UTC because UTC is unable to support itself. Release layer is made to easily release between UTC and carrier. Release layer has an influence on copper nucleation and growth. In this study, the effects of the electroplated Cr layer on the Cu electrodeposit behavior were investigated by electrochemical method.
The electrochemical behavior of Cr reduction in the 1 M $CrO_3$ + 0.01 M $H_2SO_4$ solution was examined by potentiodynamic polarization test. Metal Cr was electroplated below -1.2 $V_{SCE}$. The surface morphologies of the electroplated Cr layer at -0.15 ∼ -0.8 A/㎠ for 2 ∼ 16 seconds were smooth. As current density of Cr electroplating increased, granular particles grew on the even Cr layer. As the Cr plating time increased, the deposit potential of Cu on Cr layer, which was plated at -0.15 A/㎠, became low. Moreover real overvoltage for Cu plating increased, the Cu nuclei density decreased, and the size of Cu nuclei increased. At the initiation of Cu nucleation, current density was linearly proportional to the $(t-t_0)^{\frac{3}{2}}$. It means that Cu did three-dimensional progressive nucleation.
It is a well known fact that cathode film was formed on the Cr plating layer in Cr plating. To clear the cathode film, -3.0 $V_{SCE}$ was applied to the Cr plating layer for 30 second in pH 14 buffer solution. The Cu nuclei density electrodeposited on cathodized Cr layer was higher than that electrodeposited on non-treated Cr layer. When +0.15 $V_{SCE}$ was applied to the Cr plating layer for 30 second in pH 14 buffer solution, the Cu nuclei density was drastically increased on anodized Cr layer. The cathodic treatment dissolved the cathode film formed while Cr plating. So the voltage did not drop at the cathode film. Non-voltage drop at cathode film induced real overvoltage high. Nuclei generation rate is related to the overvoltage through the equation N.R = $K_1exp(-\frac{K_2}{\eta^2}$). Accordingly, the Cu nuclei density decreased on cathodized Cr layer. At the anodic treatment, not only the cathode film, but also the Cr plating layer was dissolved. So the voltage drop at the anodized Cr plating layer was higher than that at the cathodized Cr plating layer. Therefore, Cu nuclei density on anodized Cr layer is exceedingly high.
