High-Contrast Laser Marking of Microelectronic Packaging Modules

Laser marking is an attractive technique allowing high-speed and high spatial resolution identification of materials, mechanical parts, tools or packaging modules for traceability, advertising, security or trademark protection reasons. The laser marking process, however, is very sensitive to the chemical composition, physical properties and texture of processed surfaces. We have investigated the role of surface chemistry and morphology of nickel-plated copper lids in achieving high optical contrast marking with a Q-switch Nd:YAG laser. Profilometry, scanning electron microscopy and xray photoelectron spectroscopy measurements have been carried out to characterize investigated samples. The results indicate that a low-contrast marking results from a poor ability of the laser to nanostructure the thermally unstable Ni(OH)2–rich surface. The primary mechanism of high-quality marking is related to laser-induced smoothing of the surface and not to the modification of the chemical composition of the irradiated material. However, thermal processing of the lids in air or N2 environments in the 300-350 °C range, before laser irradiation, has a pronounced effect on the chemical composition as well as on the color of the nickel-plated lids. Laser marking of such colormodified lids leads to drastically improved both resolution and contrast of the process.