Laser removal of oxides from a copper substrate using Q-switched Nd:YAG radiation at 1064, 532 and 266 nm

The objective of the work reported is to study the effect of wavelength and the material removal mechanisms of a laser process for removing copper oxide from copper. The removal of copper oxide is necessary in electronics device fabrication in order to improve the surface wetability and so achieve a good quality solder joint. Such a laser cleaning process could be incorporated into an existing laser soldering process. The effect of Q-switched Nd:YAG radiation at 1064, 532 and 266 nm (the first, second and fourth Nd:YAG harmonics) on the oxidised surface of a copper alloy foil was studied with increasing fluence. The laser-treated surfaces were characterised using optical microscopy, scanning electron microscopy (SEM), and static secondary ion mass spectroscopy (SSIMS). Successful oxide removal was achieved at all wavelengths above certain thresholds that defined the lower end of the process operating window for single-pulse operation. The ablation mechanisms involved in the removal of copper oxide from copper at 1064, 532 and 266 nm were found to combine both thermal and mechanical effects, the surface melting first occurring at fluences lower than those at which cleaning is initialised.