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The demand for optical waveguides integrated into Printed Circuit Boards (PCBs) is increasing as the limitations of copper interconnects for greater than 10 Gb/s data rates are being reached. Optical polymer materials offer a good solution due to their relatively low cost and compatibility with traditional PCB manufacturing processes. Laser ablation is one method of manufacture, for which excimer lasers have been used, but UV Nd:YAG (Neodymium-doped Yttrium Aluminium Garnet) lasers are an attractive alternative due to their widespread use within the PCB industry for drilling vias. In this paper, 355 nm, 60 ns pulse length UV Nd:YAG laser ablation of Truemode™ acrylate-based optical polymer was investigated. The UV Nd:YAG laser was found to be able to ablate the polymer efficiently and the effects of laser ablation power and pulse repetition frequency (PRF) on depth of ablation were studied and used to determine preferred settings. 45 μm × 45 μm multimode optical waveguides were fabricated to demonstrate the process and optical loss measurements were carried out. These measurements demonstrated that the structures were able to transmit light at the data communications wavelength of 850 nm (NIR), but further work is required to reduce the level of loss. The use of UV Nd:YAG as a possible alternative to excimer for laser micromachining would facilitate the rapid deployment of the optical technology within the PCB industry.
Date of Publication: Dec.1, 2011