Ablation debris control by means of closed thick film filtered water immersion

2010-06-24T11:35:44Z (GMT) by Colin F. Dowding Jonathan Lawrence
The performance of laser-ablation-generated debris control by means of open immersion techniques has been shown to be limited by flow surface ripple effects on the beam and the action of ablation plume pressure loss by splashing of the immersion fluid. To eradicate these issues a closed technique has been developed which ensures a controlled geometry for both of the optical interfaces of the flowing liquid film. This has the action of preventing splashing, ensuring repeatable machining conditions, and allows for control of liquid flow velocity. To investigate the performance benefits of this closed immersion technique bisphenol A polycarbonate samples have been machined using filtered water at a number of flow velocities. The results demonstrate the efficacy of the closed immersion technique: a 93 per cent decrease in debris is produced when machining under closed filtered water immersion; the average debris particle size becomes larger, with an equal proportion of small and medium-sized debris being produced when laser machining under closed flowing filtered water immersion; large-sized debris is shown to be displaced further by a given flow velocity than smaller-sized debris, showing that the action of flow turbulence in the duct has more impact on smaller-sized debris. Low flow velocities were found to be less effective at controlling the positional trend of deposition of laser-ablation-generated debris than high flow velocities; but, use of excessive flow velocities resulted in turbulence motivated deposition. This work is of interest to the laser micromachining community and may aid in the manufacture of 2.5 dimensional laser-etched patterns covering large area wafers and could be applied to a range of wavelengths and laser types.