Direct laser marking on ROM media for identification

摘要

In order to attempt the direct laser marking for ROM media like a compact disk for identification, various laser heating was carried out against a thin metallic film in the transparent medium. As heat sources for the processing, a semiconductor laser excitation YAG laser (532 nm wavelength of second harmonic, max 150 mW), semiconductor lasers (780 nm, up to 2 W), and an Ar ion laser (514.5 nm, max 2000 mW), etc. were used. The media under consideration on laser marking is an aluminum thin film reflector layer, which was sandwiched between a polycarbonate (PC) of 1.2 mm and a protection film of 5 μm thickness. The aluminum thin film (Al) is 100 nm in thickness. The obtained laser marking sizes were less than 1 μm and were evaluated using SEM and AFM. The observation samples inside a transparency resin were obtained by tearing off a protection film, and the surfaces of the bared PC and protection film were examined. The surface conditions and cross sections of laser-marking area were observed. It seems that the heated aluminum thin film were melted and a hole arose. Then a cavity was not observed from SEM cross-section observation in the marking area. It became clear that the holes were filled with PC by SEM and AFM observation. These results indicate the possibility of heat localization at the Al-PC interface and also significant heat penetration into the PC substrate itself.