Papers by Keyword: Phase Shifting Method

Abstract: In recent years optical disks have been very popular and in manufacturing process error detection in optical disks becomes very important, especially for the defects whose size of a few millimeters in length and several hundred nanometers in depth. The authors have developed a new system to measure the defects of disk substrates using a Mach-Zehnder interferometer with a phase shifting method. But it was found that optical disks had undulation of the optical thickness and it disturbed the detection of defects. To solve the problem moving-average method was developed and introduced in data processing to distinguish the defect from the undulation, and with modified unwrapping program the defect was visualized by binary image processing.

Abstract: The measurement principle where in a high-NA (Numerical Aperture) surface, for which the degree of the angle of surface inclination exceeds π/3 radians, could be evaluated with high precision and high speed is proposed. This is based on the stitching method, where aspherical surface measurement becomes possible by dividing the surface of the sample into a range so that measurements can be made with an interferometer and finally combined. We examine the method of applying an interferometer to the condition in which the sample is rotated on an air spindle at a constant speed. It is not necessary in this method to make the sample static. Therefore, the vibration of the servo motor and any location errors can be eliminated. Moreover, the measurement time does not depend on the number of divided areas which are necessary for the stitching method, allowing for high-speed measurement. The principle behind this technique is expanded first, and an experiment system based on it was constructed. The principle proposed was evaluated, and its effectiveness was confirmed.

Abstract: A hybrid stress determination around circular and elliptical holes utilizing photoelastic phase-shifting and nonlinear least-squares methods is presented. The method was demonstrated by calculating fringe orders of distant points along straight lines using 8-step phase-shifting method. The data was used to evaluate the coefficients in the complex stress functions for hybrid analysis. Tangential stresses around the boundary of the holes were obtained using conformal mapping technique. Different number of terms in a power-series representation of the complex type stress function was tested to qualitatively observe the effects of varying stress field. Actual fringes were related with the reconstructed and sharpened fringes along with the change in the number of terms, m. Good agreement was obtained when m in stress functions was equal to nine. At high stress concentration, the result obtained from the hybrid method agrees with FEM by two and five percent for circular and elliptical hole, respectively. The results show that the established numericalexperimental method for stress analysis is considerably reliable.

Abstract: Thermal deformation behaviors of electronic packages, stacked-MCP (multi chip package) and SOJ (small outline J-leaded package) were measured by phase-shifting moiré interferometry. This method was developed using a wedged glass plate as a phase shifter to obtain displacement fields with a sensitivity of nanometer scale. Digital image processing was also introduced to determine the strain distributions quantitatively. In stacked-MCP, thermal loading was applied from room temperature 25°C to two elevated temperatures (75 and 100°C), and thermal strains were then examined at these two elevated temperatures. The results showed that the normal strain εxx concentrated at the ends of two silicon chips, and the transverse strain εyy increased between the two silicon chips. The shear strain γxy increased at the end of the lower silicon chip to 0.30% from 0.17% when the temperature increased by 25°C. In SOJ, the thermal strains were investigated with the two packages before and after mounted on PWB (printed wiring board). The results showed that the strains increased by about 50% when the SOJ was mounted on the PWB.

Abstract: Speckle interferometry with phase shifting method is used to measure in-plane displacements of a steel plate with a partly through-thickness circular hole and a steel plate with a through-thickness circular hole. The circular hole of steel plate with a partly through-thickness circular hole is cut on the rear side of the plate, so that it is not visible during experiment. The speckle noises of fringe patterns acquired by optical experiment are processed with image processing algorithm of Gaussian blur and the in-plane displacements of the two specimens are obtained by use of the processed fringe patterns. Also the in-plane displacements of the two specimens are calculated by use of ANSYS. The results of optical experiments are quite comparable to those of calculation with ANSYS.