This paper presents our design and experimental results of nickel microcantilevers, which were fabricated using a laser-LIGA process, based on KrF (248 nm) excimer laser micromachining. A chrome-on-quartz mask, containing the desired mask patterns was prepared for this work. The substrate of copper (30 μm thick) clad printed circuit board (PCB) was laminated with Laminar 5038 photopolymer to be laser patterned. Following laser patterning and laser cleaning, all the samples were electroformed with nickel on top of the copper layer. To release the Ni microcantilevers, the excimer laser was employed again to remove the polymer in the localised area to facilitate Cu selective etching. Here, copper acted as the sacrificial layer as well. The Cu selective etching was carried out with ~ 20 % (wt) aqueous solution of ammonium persulfate. Because the Cu selective etching is isotropic, some undercuts happened next to the anchor area. The samples were characterised using optical microscope, confocal laser scanning microscope and SEM, and some of Ni cantilevers were tested electro-thermally. Their performance was analyzed with respect to the simulation results.
This paper presents the results of our investigations on the laser micromachining of structures in a dry film photoresist polymer (Dynachem, Laminar AX dry film) laminated on a copper clad Printed Circuit Board (PCB) and (100) Silicon wafer coated with Ti (15nm)/Cu (100 to 4000 nm) and copper seed layers. This study concentrated on investigating and comparing the effect of laser fluence (0.01 to 2 J/cm2) and number of shots (1 to 1000) on the etch characteristics of the Laminar AX dry film on both substrates. The other important aspects that were studied include the minimum required seed layer thickness for electroplating. The removal of the residual polymer layer at the end of the laser micromachining process and its effect on plating characteristics has been studied. The surface quality and roughness of the laser micromachined sites and their effect on the plated Nickel structures were studied in detail. The laser fluence and the number of shots used at this stage affected the conditions of the seed layer, which in turn influenced the plated film growth kinetics. The seed layers with thicknesses less than or equal to 0.8 mm were completely removed when high fluence (> around 1 J/cm2) was used. The seed layer surface after micromachining was characterised using Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and profilometer. High Aspect Ratio Structures (HARS) of Nickel were fabricated using the Laminar AX moulds. The highest aspect ratio achieved so far in this work is 6. The characteristics of these structures are discussed in detail.
Laser light is used to investigate the surface texture of unsintered machined zirconia. Unsintered zirconia is a chalkylike material and when machined the resultant surface texture cannot be measured using conventional stylus techniques because the stylus damages the surface. Therefore the surface must be inspected in a noncontact fashion to reveal the surface texture. Laser scattering methods are well known to provide good surface texture characterisation so this approach was pursued. Zirconia samples were machined with varying feedrates and illuminated with a laser beam. The resultant scattering distributions for each of the surfaces did not differ in any significant way (regardless of the machining feedrate used) suggesting that the size of the microscopic irregularities of the surface are significantly greater than the illuminating wavelength. SEM photographs of the surfaces showed this to be true. Surface texture characterisation of unsintered machined zirconia using laser scattering was thus not possible. The properties of the material are such that the roughness of the machined zirconia is beyond the range measurable with most laser techniques.
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