High-speed drilling performance of coated micro-drills with Zr–C:H:Nx% coatings

A closed field unbalanced magnetron (CFUBM) sputtering system is used to deposit Zr–C:H:Nx% coatings with nitrogen contents ranging from 0 to 25 at.% on M2 steel disks and micro-drills. The microstructures of the various coatings are analyzed using Raman spectrometry, while the hardness and adhesion strength are measured by performing nanoindentation tests and scratch tests, respectively. The drilling performance of the coated micro-drills is evaluated by conducting high-speed through-hole drilling tests using printed circuit board (PCB) specimens. The service life of the coated micro-drills is assessed utilizing four different criteria, namely the nail head ratio and surface roughness of the drilled hole, and the corner wear and flank wear of the cutting edge, respectively. Overall, the results show that the Zr–C:H:N17% coating has the optimal high-speed machining performance, i.e. it extends the tool life by a factor of at least four compared to the uncoated micro-drill and yields a significant improvement in the machining quality.