Investigation of a low-temperature-dominant HFCVD composite process for high-toughness diamond coated milling cutters in 5G-PCB applications

During the milling of ceramic-filled printed circuit boards (PCBs) for 5G communications, diamond-coated cemented carbide tools fabricated using conventional hot filament chemical vapor deposition (HFCVD) processes frequently experience premature fracture due to insufficient fracture toughness, thereby impeding the full utilization of the exceptional wear resistance of diamond coatings. This study proposes a novel approach aimed at enhancing the toughness of the cemented carbide by minimizing cobalt removal, while simultaneously employing a low-temperature-dominant HFCVD composite diamond coating deposition process to mitigate excessive cobalt diffusion resulting from increased cobalt content in the substrate, thereby ensuring the high-quality diamond growth. The specific design of the composite process parameters is guided by a coupling model that establishes the relationship between the performance characteristics of coated tools (diamond quality, tool toughness, and film-substrate adhesion strength), the inherent cobalt distribution within coated tools, and critical preparation parameters (substrate temperature Ts, cobalt removal depth D, grain size of diamond coatings G, and coating thickness h). A three-step diamond deposition process is developed, with the initial two steps utilizing low-temperature deposition, to balance and optimize the performance characteristics of the substrate, interface, and coating within the coated tools. The resulting coated milling cutter demonstrates excellent performance when applied to the machining of 5G-PCB materials. It resolves the issue of premature tool fracture, exhibits superior film-substrate adhesion strength and wear resistance, and has a service life approximately eight times longer than uncoated milling cutters and three times longer than tools produced using a single deposition process.