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High density perforation of thin Al-foils with ultra short pulse lasers in dependence on the repetition rate

: Hambach, N.; Hartmann, C.; Keller, S.; Gillner, A.

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Journal of Laser Micro/Nanoengineering. Online journal 11 (2016), Nr.2, S.192-198
ISSN: 1880-0688
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer ILT ()

Medical devices and engineering products need an increasing number of micro scaled–features, such as holes for filtration, separation and ventilation or small structures e.g. for hydrophobic effects. The size of these structures is often in the range of 20 μm and below while the structured areas grow at the same time. Therefore the factors influencing the drilling process are becoming more and more important and used to generate high process stability during the laser process. This paper investigates the process limits as well as the factors influencing the application of perforation with laser radiation of a 15 μm thick aluminum foil with UV ps-pulses. The pitch of the holes within the drilling pattern is varied as is the repetition rate used for the percussion drilling of each of the holes. The holes are evaluated by means of their diameter and shape. The precision of the hole shape is examined for two characteristics: circularity and ellipticity. Holes with a diameter of < 10 μm are drilled with pitches between 14 μm and 25 μm. Depending on the repetition rate three different drilling regimes are identified: 1. thermal drilling with increasing surface-oxidation, 2. thermal drilling with decreasing surface-oxidation and 3. shadowing of laser radiation.