Synthesis and evaluation of high-performance diamond films with multilayer structure on printed circuit board drills

Abstract

Printed Circuit Board (PCB) filled with a large amount of Alumina ceramics has broad application prospects in the fifth-generation industry but is hard to drill. This work focuses on high-performance diamond films to improve the working life of drilling tools and holes quality of products. By utilizing hot filament chemical vapor deposition (HFCVD) methods, the monolayer microcrystalline diamond (MCD), bilayer micro-nanocrystalline diamond (MNCD), and four-layer diamond (MNMNCD) are coated on commercial PCB drills (WC-6% Co). Solid particle erosion tests are conducted to study erosive wear mechanism of diamond films impacted by ceramic powders/particles. Besides, cutting performances of diamond coated drilling tools are evaluated by performing high-speed drilling tests with PCB as workpieces. In Erosion tests, the monolayer MCD film presents intergranular fracture and shows the lowest erosive resistance. The MNCD and MNMNCD films have similar fracture forms, where curved boundaries and steps between layers indicate their discontinuous fracture, and minor deep cone holes on the surfaces demonstrate their high resistance to crack growth. Moreover, only one minor deep cone hole is observed on the four-layer film which indicates it has the best resistance to particle impinging. In drilling tests, the number of holes drilled by the diamond coated tools before failure is regarded as criteria of working life. Then surface and sectional morphologies of holes are also observed to evaluate the quality of products. The results indicate the number of holes machined by the four-layer MNMNCD coated drills reaches 10,000, while that of the monolayer and the bilayer MNCD ones are 3000– 4000 and 6000 respectively. More importantly, different from the other two types of diamond coated tools, almost no burrs with a height of over 20 μm are observed on the hole entrance using the four-layer diamond coated tools. Therefore, considering both the working life and holes quality, the MNMNCD films excel in the cutting performance of the new type of PCB drilling.