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Title: Micro-components evaluation using laser interferometry
Authors: Tay, C.J. 
Issue Date: 2008
Source: Tay, C.J. (2008). Micro-components evaluation using laser interferometry. New Trends in Lasers and Electro-Optics Research : 25-60. ScholarBank@NUS Repository.
Abstract: This work describes the use of optical interferometry techniques for non-destructive evaluation of micro-components. Various techniques using coherent interferometry techniques are developed. The techniques include, Optical Wedge Fringe Projection, Modified Michelson Interference, Laser Scattering Technique and Newton's Rings. In the optical wedge fringe projection technique a method for determining the deformation of a membrane in a miniature microphone is described. Using an optical fiber and an optical wedge a sinusoidal fringe pattern with a pitch of the order of microns can be readily generated. Subsequent image processing is carried out using a four frame phase-shifting technique. Results obtained suggest that the proposed setup is capable of measuring deformations on a miniature microphone in the sub-micron range. In the modified Michelson interference technique an optical method for the measurement of angular rotation of a micromirror driven by an electrostatic force is developed. To detect the rotation of the micromirror, a He-Ne laser probe with a collimated light beam of less than 50 μm in diameter is directed onto a micromirror with an achromatic lens. The laser beam reflected off the micromirror falls on the achromatic lens and is combined with another laser beam from a fixed reference mirror. The resulting interference fringe pattern is recorded and the angular rotation of the micromirror is determined from the change in pitch of the fringe pattern. In the laser scattering technique detection of cracks on the surface of a micro-chip solderball is carried out by capturing scattered light of a laser probe directed at the solderball. The technique is based on light scattering theory and uses conventional optical components to focus light beams emitted from a low-power He-Ne laser. The laser beam scans a test surface and when it encounters a surface defect, the scattered light intensity distribution is altered the scattering characteristic is dependent on the defect size. Test results on specimens with crack size ranging from 4 μm to 60 μm show that the proposed technique is suitable for crack detection of solderballs on a micro-chip. In the Newton's rings technique a collimated monochromatic light is directed onto an airwedge consisting of a reference surface (e.g. an optical flat or thin membrane) and an object. A long-working distance microscope with a CCD camera is utilized to capture the interference fringe pattern that results from a recombination of two beams reflected from the reference and the object. The resulting fringe patterns are analyzed by the use of Fast Fourier Transform (FFT) and deflections of the object are obtained and subsequently used to calculate the Young's modulus and deformation. By the use of monochromatic lights with different wavelengths, a method called multiple-wavelength interferometry is also developed to measure the deformation of an object. Different micro-components are used to validate the proposed technique. Experimental results show good agreement with that of the proposed technique. © 2008 by Nova Science Publishers, Inc. All rights reserved.
Source Title: New Trends in Lasers and Electro-Optics Research
ISBN: 1600214746
Appears in Collections:Staff Publications

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