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8 April 1996 Laser hole drilling in thick polypropylene sheets for alignment sensors
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Laser micromachining of polypropylene for transducer applications has the advantage of creating small (< 100 micron) structures through very thick materials (> 400 micron). Normally translucent polypropylene formed using carbon as a dye is an excellent laser machining material having a high optical absorption, and a low thermal conductivity. For an optical alignment system a matrix of high aspect ratio holes of < 130 microns diameter with < 300 micron spacing was needed through thick (> 400 micron) sheets. This alignment sensor is to be used on the end of a robot arm and will aid in the manipulation of the arm. Using an argon ion laser focused through a 50 mm lens (5.2 micron R1/e2 spot, 55.2 micron focal depth), holes as small as 30 microns on 150 micron spacing were achieved in 400 - 500 micron thick black polypropylene sheets with consistent results. Best results currently are achieved with a laser power of only 0.3 W, using 10 - 100 pulse stream of 10 - 100 microsec pulses, and duty cycles of < 10%. Shorter duty cycles require more power, as do shorter pulse durations, and both result in larger holes at wider spacings. Minimum repeatable hole separation is controlled by the lip of material formed around the hole. These settings have achieved 41 X 29 (1189 hole) arrays on a sample, with a computer driven submicron XYZ positioning system. Commercially available opaque white polypropylene required 17 times the power, and achieved holes of only 127 microns, with 500 microns spacing in 500 micron thick material. Thicker (1 mm) black polypropylene produces 144 micron holes on 500 micron spacings due to the lip material, and required a 100 mm lens.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
D. E. Bergen, Glenn H. Chapman, Taranjit Singh Samra, and T. S. Weeks "Laser hole drilling in thick polypropylene sheets for alignment sensors", Proc. SPIE 2703, Lasers as Tools for Manufacturing of Durable Goods and Microelectronics, (8 April 1996);


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