The Tungsten Carbide Drilling and Routing Session

Notable amid the vast array of information and knowledge shared at the 13th Electronic Circuits World Convention in Nuremberg, Germany, was the highly-informative session on advances in drilling and routing, with a focus on the technology of tungsten carbide cutting tools. The session was introduced and moderated by EIPC Technical Director Michael Weinhold.

Growth in applications of high-power LEDs had created an increasing demand for substrates with high thermal conductivity, and resulted in the development of a wide range of insulated metal substrates heavily loaded with ceramic fillers in the dielectric. Consequently, the dielectric layer of these composite laminates tended to be very abrasive, causing rapid wear of conventional tungsten carbide routing cutters. Johann Schmidt of CGT GmbH discussed how diamond coated tools could significantly increase dimensional accuracy and reduce production cost.

Schmidt described a proprietary process for diamond coating of tungsten carbide drills and routers, based on hot-filament chemical vapour deposition. A particular feature of this proprietary coating was that it was built up as a multilayered combination of different crystalline and nano-crystalline layers. Typical coating thickness was 12 microns, although this could be varied depending on tool geometry and diameter. The multilayered structure gave the benefit of resistance to crack propagation, a major limitation of single-layer coatings, and a very smooth surface with low friction and excellent chip-removal characteristics. Hardness of the coating was approximately 9000VPN, compared with about 2100VPN for standard tungsten carbide grades, and coated tools could be used at higher feeds and speeds.

Schmidt showed many comparative examples: On a typical IMS substrate, routing feed could be increased from 4 mm per second to 15mm per second with tool life extended from 7.5 metres to 60 metres. And a coated drill could complete 1,000 hits with no clogging, whereas a conventional drill was clogged with aluminium swarf after only 150 hits.

Diamond-coated tools offered greater dimensional accuracy and cost and productivity benefits from increased production speeds and significantly improved tool life resulting in less machine down-time for tool changing. Clearly, even with the most advanced cutter technology, good tool management, machine maintenance and operating discipline were essential, with minimal spindle run-out, rigid fixturing of the work and powerful vacuum extraction if the best results were to be realised. Some applications, such as using a 2-flute end-mill on IMS, benefited from wet lubrication.


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