Product Code: ICA12_M1102

Real Time Surface Tracking System in Laser Microprocessing
Ville Hautala, Department of Production Engineering, Tampere Univ. of Technology; Tampere Finland
Antti Määttänen, Primoceler Inc.; Tampere Finland
Jorma Vihinen, Department of Production Engineering, Tampere Univ. of Technology; Tampere Finland
Presented at ICALEO 2012

In many micromachining applications, precise laser height focus control is essential for process success. Often workpiece surface changes are significantly greater than the laser"s depth of focus, which leads to uneven machining quality or the failure of the machining process. To resolve this problem, we have developed a surface tracking system that measures the workpiece surface in real time and changes the focusing optic position according to the measurement results. The system is designed for planar workpieces which surface variation is below 400 "m. There are no limitations for other dimensions. Machining paths are restricted for straight lines. Confocal point sensors are used for the surface measurement and piezoelectric actuator is used for displacement of the optics. Preliminary tests were made using 150 mm diameter silicon wafers and 50 mm diameter sapphire wafers that were slightly tilted. Machining speeds varied from 100 mm/s up to 1700 mm/s and the surface variance was over 300 "m. In tests, the laser focus height variance was maintained under 10 "m range. The Laser processing was successful despite of the large surface variance and even without tilting wafers there was a clear improvement in machining quality compared to machining done without surface tracking.

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