Effects of Water-Based and Underwater Assistance Methods on the Hole Quality of Silicon Nitride Ceramics Using a Picosecond Laser

This study investigated the effects of water-based and underwater assistance methods on the quality of picosecond laser-drilled microholes in silicon nitride ceramics, analyzing the influence of laser power variations in air and aqueous environments on entrance/exit diameters, taper angles, internal wall morphology, surface roughness, and oxygen content. Water-based assistance involved submerging the workpiece's lower surface while keeping the upper surface in the air, whereas underwater processing involved fully immersing the specimen. The experimental results demonstrated that both aqueous environments effectively improved microhole quality compared to air processing. The water-assisted methods significantly enhanced the entrance/exit morphology by reducing ablation traces and slag deposits. The aqueous medium increased the entrance/exit diameters while decreasing the taper angles and effectively removing debris, thereby reducing internal wall roughness. Underwater processing achieved lower roughness at the hole entrances and middle sections compared to water-based assistance. Both water-assisted methods produced superior internal wall morphology to air processing, with comparable performance. These findings provide valuable references for optimizing water-assisted picosecond laser drilling processes.