High-aspect-ratio microdrilling of polymers with UV laser ablation: experiment with analytical model (original) (raw)
Related papers
2004
Laser drilling becomes of increasing importance when hole diameter is in the range of 10 to 50 mum, for which conventional alternative approaches are becoming difficult and cost inefficient. Furthermore, it is viewed as the technique of choice for a number of composite materials and hard materials which are not readily processed at the microscopic level by contact mechanical tools. We have demonstrated that suitable experimental conditions are capable of producing microholes with record aspect-ratio (up to 600) in pure polymers like PET, PI, PC, PS, PMMA, PEEK,... For example holes of diameter typically 30 mum can be as long as 18 mm, depth at which the drilling rate is getting nearly zero and the profile stationary. Other materials (metals, ceramics) which can be similarly laser microdrilled do not exhibit such very high aspect-ratio. The mechanisms of the drilling process have been studied in details and an original analytical model has been constructed recently. The various experimental results, obtained with the KrF laser, will be reviewed with emphasis on the parameters leading to formation of good holes with high aspect-ratio. For the application it is also important to note that such high values of aspect-ratio are obtained with regular configuration of the KrF laser giving a standard divergence of 3 mrad. However as shown by the model there is still room for improvement by using a beam with a lower divergence (theoretical limit is 0.2 mrad). Further experimental work is now in progress.
Effects of excimer laser illumination on microdrilling into an oblique polymer surface
Optics and Lasers in Engineering, 2006
In this work, we present the experimental results of micromachining into polymethymethacrylate exposed to oblique KrF excimer laser beams. The results of low-aspect-ratio ablations show that the ablation rate decreases monotonously with the increase of incident angle for various fluences. The ablation rate of high-aspect-ratio drilling with opening center on the focal plane is almost independent of incident angles and is less than that of low-aspectratio ablation. The results of high-aspect-ratio ablations show that the openings of the holes at a distance from the focal plane are enlarged and their edges are blurred. Besides, the depth of a hole in the samples oblique to the laser beam at a distance from the focal plane decreases with the increase of the distance from the focal plane. The number of deep holes generated by oblique laser beams through a matrix of apertures decreases with the increase of incident angle. Those phenomena reveal the influence of the local light intensity on microdrilling into an oblique surface.
Maskless 3D Ablation of Precise Microhole Structures in Plastics Using Femtosecond Laser Pulses
ACS Applied Materials & Interfaces, 2018
Femtosecond laser ablation is a robust tool for the fabrication of micro-hole structures. This technique has several advantages compared to other micro-fabrication strategies for reliably preparing micro-hole structures of high quality and low cost. However, few studies have explored the use of femtosecond laser ablation in plastic materials, due to the lack of controllability over the fabrication process in plastics. In particular, the depth profile of microhole structures prepared by conventional laser ablation techniques in plastics cannot be precisely and reproducibly controlled. In this paper, a novel, three-dimensional (3D), femtosecond laser ablation technique was developed, for the rapid fabrication of precise micro-hole structures in multiple plastics in air. Using a three-step fabrication scheme, micro-holes demonstrated extremely clean and sharp geometric features. This new technique also enables the precise creation of arbitrary shaped micro-well structures in plastic substrates through a rapid single-step ablation process, without the need for any masks. As a proof-of-concept for practical application, precise micro-hole structures prepared by this novel femtosecond laser ablation technique were exploited for robust resistive-pulse sensing of micro-particles.
Hole qualities in laser trepanning of polymeric materials
Optics and Lasers in Engineering, 2012
The present study focuses the effect of four input controllable laser cutting variables on the hole taper and hole circularity in laser trepan drilling of polymeric materials. Experiments have been conducted on acrylonitrile butadiene styrene (ABS) and polymethyl methacrylate (PMMA) polymer sheets. Laser power, assist gas pressure, cutting speed and stand-off distance were selected as independent process variables. Three different holes of diameters 2 mm, 4 mm and 6 mm were drilled in these work materials of 5 mm thickness. A Taguchi L9 orthogonal array with four factors and three levels of each factor was used to plan and conduct the experiments in order to obtain required information with reduced number of experiments. The process performance was ascertained in terms of hole taper and hole circularity. Initial analysis involved in determining the effect of the four process variables on hole taper and circularity for these two polymers at three different hole diameters. From ANOVA analysis, the optimum levels of the four process variables with respect to materials and hole diameters were evaluated. As it was found that the optimum levels of four process variables were different for different hole size and materials, additional analysis was conducted to incorporate the effect of material and hole diameter on the hole taper. From the analysis, the optimum combinations were obtained at compressed air pressure of 2.0 bar, laser power of 500 W, cutting speed of 0.6 m/min, stand-off distance of 5.0 mm, hole diameter of 2.0 mm and material of PMMA. These combinations produced the minimum taper in the hole. The circularity of the hole was more at the entrance than the exit when ABS polymer was laser drilled while in PMMA, the hole was more circular at the exit than the entrance.
Controlled process for polymer micromachining using designed pulse trains of a UV solid state laser
Applied Surface Science, 2007
A flexible workstation equipped with a solid state laser operating at 266 nm wavelength was used to machine holes in polyethylene terephthalate, polyimide and polycarbonate. An optical pulse picker was employed to reduce the high repetition rates of the laser, while a breakthrough sensor was used to avoid over-drilling of through holes. For each material, different repetition rates and designed pulse trains were tested to improve feature quality and process efficiency. Although the three polymers had very different reactions at this wavelength they all showed an improvement in feature quality with decreasing repetition rate due to a reduction in thermal effects. Up to 10 kHz the average depth per pulse remained unchanged and afterwards a slight increase was observed but this was accompanied by large uncertainties. Bursts of pulses at 40 kHz inserted inside the low repetition rate pulse train reduced the drilling time and the amount of debris redeposited without affecting the feature quality. It was found that a number of cleaning pulses after perforation eliminates the heat affected zone around exits. Holes with entrance diameters below 20 mm and exit diameters as small as 2 mm were obtained with high repeatability.
High aspect-ratio micromachining of polymers with an ultrafast laser
Applied Surface Science, 2002
Laser ablation of various polymers has been studied using a beam of 100 fs laser pulses at a wavelength of 800 nm. For a beam focussed by a plano-convex lens, high-quality machining of holes with diameters 20±40 mm and depths 300±400 mm (aspect ratio greater than 10) has been achieved. When projection patterning is carried out with a rectangular pinhole, arrays of micro-strings have been observed deep in the bulk of the sample. The micro-strings have diameters as small as 2 mm (about three times the wavelength) and lengths greater than 10 mm (aspect ratio 5000). The achievement of the high aspect ratios and the formation of the arrays of micro-strings are discussed. #
Study on laser micro-drilling process
2011
There are many situations when a classic drilling process is not worth to be used-even the material to be machined is too hard, or the geometrical precision conditions for the required whole are too high. As laser technology has known an impressive development, the laser does represent the solution for the mentioned situations. This paper presents some experimental research done in order to determine optimum process parameters for obtaining micro-holes by using the laser beam.
IOP Conference Series: Materials Science and Engineering
Micromachining techniques are being used regularly in various engineering and production sectors such as Micro Electromechanical Systems, Aerospace, Automotive, Electronics and Biomedical industries. For Laser Beam Micromachining, highly energized laser beam is focused on a small region of the workpiece surface. As a result, it is heated up rapidly to sufficiently high temperatures, then the material starts to melt and/or vaporize from the surface. This phenomenon of material removal is called laser ablation. The holes that are produced by one-dimensional laser beam drilling (LBD) can come with defects like taper, heat affected zone (HAZ) and Recast Layer. On the other hand, LBD process offers high control, high efficiency, precision, and production rate, particularly for drilling microscopic holes in a variety of materials. LBD performance is measured on different parameters such as taper and recast layer of the machined holes. Previous studies report many observations regarding th...