Metal Removal Mechanism from Optical Discs Using Pulsed Power

The phenomenon of metal removal from the optical discs under pulsed power application has been investigated. Pulsed power with 35.3 J/pulse was applied to concentric ring electrodes placed on the optical discs. The protective layer containing the metal layer was completely separated from the plastic substrate by about 30 shots of pulsed power. In order to clarify the mechanism of the metal removal, discharges and shock waves were observed with a high-speed camera and a pulse-laser Schlieren system, respectively. As a result, a fan-shape discharge was observed after a breakdown took place between the electrode and the metal layer at the first shot. The fan-shape discharge expanded until the current reached a peak, and then it gradually disappeared. The protective layer around the fan-shape discharge region was separated from the plastic substrate. At the second and the following shots, similar discharges appeared until the metal layer around the high voltage electrode was completely separated. Then, the fan-shape discharge appeared at the tip of a surface discharge which bridged the high voltage electrode and the isolated metal layer. On the other hand, the shock wave was mainly observed around the discharge between the electrode and the metal layer. The fragments of the protective layer containing the metal layer were observed to spread so as to follow the shock wave propagation. The distance and the speed of the shock wave propagation were analyzed by an image analyzing software. From the above, it was revealed that the fan-shape discharge and the shock wave affected the metal separation from the optical discs.