Femtosecond Laser Machining Of Drilled Holes In Silicon Nitride

In this study, the laser drilling parameters of a Nd:YAG ultrashort pulsed laser are evaluated to produce zero taper through holes on silicon nitride ceramics. Manufacturing of ceramics is expensive and difficult because of the mechanical and thermal properties of ceramics, limiting applications. Additionally, the high level hardness of the ceramic can affect the ceramic and the manufacturing tool. There is a need to explore non-contact machining such as laser machining to expand the uses of ceramics in industry applications.In order to accomplish this goal, understanding of the physical mechanisms that occurs while laser ablation is needed. Furthermore, the minimum energy needed for ablation of silicon nitride must be established as well as the energy for drilling. With that data, initial drilling matrix can be determined with the specific parameters (hatch spacing, scanning speed, percent power). Then, each parameter can be individually examined to determine the influence on the drilling operation and optimize the parameters. The drilled holes will be characterized by the cylindricity, taper, and taper angle. Utilizing a laser system in the femtosecond pulse width will allow drilling of holes with minimal heat affected zone and stress build up. An issue seen throughout the drilling operation is the formation of a shear lip at the entrance of the hole. The shear lip distorts the entrance hole and appears larger than it is. Experimental studies are performed on silicon nitride disks, in specific drilling operations to examine drilling parameters that will achieve a zero taper through hole