Key Engineering Materials Vols. 364-366

Abstract: This research first indicates the melt front delay of wedge-shaped lightguiding plate of backlight module on micro injection molding. This research fabricated the patterns of mold insert of lightguiding plate by photo etching process. The micro-facture of lightguiding plate was manufactured by micro injection molding. The lightguiding plate of backlight module was used for the PMMA material. The single parameter method was used to discuss the flatness and replication properties for different processing parameters (mold temperature, melt temperature, packing pressure, packing time and injection pressure). The results show that there are melt front delays due to the slow injection velocity, the low temperature induced by the little effect of shear heating, the high viscosity, the large flow resistance and the slow flow velocity. The mold temperature is the most important factor for the flatness and the replication of micro-feature of liughtguiding plate. Lower mold temperature induces better flatness properties. The surface roughness of micro-facture of lightguiding plate is 8.8 nm on micro injection molding for this work.

Abstract: Optical freeform surface requires submicrometer form accuracy and nanometer surface finish. Ultra-precision raster milling is an emerging technology in the fabrication of those surfaces in which the dynamics factors are vital to achieve the surface quality. This paper presents a theoretical dynamics model for ultra-precision raster milling. The cutting force is derived in the depth of cut (DOC) planes in the feed and raster directions. Hence, a 3D cutting force model is established. The cutting force induced deflection between tool and workpiece is determined which can be employed to analyze the influence of the deflection on the surface generation in raster milling. The dynamic model is useful for modeling of surface generation and further control of vibration between the tool and the workpiece.

Abstract: This paper describes a two-dimensional tool-path planning model for minimizing the regularly distributed errors or mid-frequency errors during computer controlled optical surfacing (CCOS) by optimally connecting different tool-path segments. The model was established based on a neuro-fuzzy algorithm, a path neighborhood function which is defined as a victorious output element calculated in a self-organization way, then, the optimum material removal function with a modified weight was derived. The material removal function was studied theoretically and the results of simulation present a Gaussian distribution feature. Discrete removal points and optimized tool-path grid were simulated. Finally, an experiment involving a parabolic mirror was performed for residual error removal and the two-dimensional tool-path planning algorithm was found to be valid.

Abstract: Nano-indentation of glass SF11 was performed for understanding the material deformation behavior in practical cutting process. Diamond cutting tests under different process conditions, i.e. conventional turning and ultrasonic vibration assisted cutting, were also carried out. Cleavage and microchipping appear to be the dominant tool wear mechanism based on the analytical results of wear zone microstructure and machined surface topography. The change in the tribology of the cutting process as well as the alteration of the deformation mechanism of the work material in the cutting zone might be responsible for the reduction in tool wear in vibration cutting.

Abstract: Focus detection method is one of non-contact profile measurement methods. However, the measurement accuracy of current focus detection method is limited by voice coil motor adopted by it. In this paper, based on an improved Foucault focus detection method, a new non-contact displacement sensor with diffraction grating metrology system is presented. Driven by a piezoelectric actuator instead of a voice coil motor, and a diffraction grating metrology system being with it, the sensor has high measurement accuracy. During surface profile sampling, according to focusing deviation signal, the focusing lens was driven to move vertically by the piezoelectric actuator so that its focus was always located on the workpiece surface, synchronously the vertical displacement of the focusing lens was obtained by the diffraction grating metrology system as the profile height of sampling points. The displacements of all sampling points gave the whole profile of the measured surface, which can be processed by a characterization software to obtain the measurement result. The resolution of the non-contact displacement sensor was 10 nm.

Abstract: White-light interferometric technique has been widely applied in the measurement of three-dimensional profiles and roughness with high-precision. Based on the characteristic of interferometric technique, a new method combined with image location and a three-dimensional stage is proposed to achieve the non-contact absolute shape measurement for aspheric and spherical surface in a slarge range. The interference fringes vary with the horizontal displacement of the measured surface, the surface information was obtained by locating the transformation of the maximal intensity in the interferograms. Two main influence factors are discussed; they are performance of the inerferimetric microscope and the stage. Since the performance of the stage directly determines the measurement precision, a three-dimensional displacement stage with a large range and a high precision was developed. Some experiments were carried out to verify the performance of the three-dimensional displacement stage and the validity of the new measurement method with satisfactory results.

Abstract: This study presents an enhanced common path interference system designed to measure the refractive index of crystal optical components. The proposed system is based on the classic Michelson interferometer and comprises a frequency stabilized helium-neon (He-Ne) laser, a beam splitter, a fixed mirror, an adjustable mirror, and a light detection system. The waveplate of interest was clamped to a rotatory motor and positioned between the beam splitter and the fixed mirror. The refractive index of the waveplate was then derived from the change in rotational angle of the waveplate as it moved from one position of minimum interference to the next. The measurement system proposed in this study is simple in construction, straightforward in operation, and robust to the effects of experimental noise. Furthermore, the system is a non-contact measurement system, and hence does not damage the optical component of interest. The experimental results are found to be in good agreement with the theoretical results. Therefore, the proposed system provides a viable means for the rapid experimental evaluation of the optical characteristics of quartz components.

Abstract: In this study, the back-propagation neural network technology (BPN) is utilized to identify the shape of the defective solder ball of ball grid array (BGA) so as to promote the accuracy of the optical inspection and measurement. The two dimensional BGA optical inspecting system is implemented by Visual Basic as the developing tool incorporated with the Halcon’s function which is the database of the image processing on Windows operation system. For the development of the processing procedure of the automatic optical inspecting system, the precise geometrical information of the solder ball is evaluated by the sub-pixel method to identify the shape of solder ball and its location which are acquired to classify the defects of solder ball including the ball offset, the ball over scale, the ball absence, and the ball shape under the BGA board is offset and rotated at any angle. From the experimental results, the back-propagation neural network technology is proved to properly identify and classify the shape defects, especially for the ball deformation and the ball bridging of the solder ball which can achieve and contribute the requirements for the automatic inspection and the high identification efficiency.

Abstract: Using TracePro® Monte-Carlo ray-tracing simulations, this paper investigates the improved light extraction efficiency (LEE) obtained by patterning the surface and/or substrate of GaN LEDs with unique three-dimensional micro-cavity patterns. The simulations commence by considering the case of a sapphire-based GaN LED. The effects on the LEE of the micro-cavity dimensions, the absorption coefficient of the active layer, the point source location, and the chip dimensions are systematically examined. Subsequently, the LEE performance of the sapphire-based GaN LED is compared with that of a thin-GaN LED for various surface texturing strategies. In general, the results show that patterning either the surface or the substrate of the LED structure provides an effective improvement in the LEE of both the sapphire-based GaN LED and the thin- GaN LED. For both LED structures, the maximum LEE enhancement is obtained by patterning both the upper surface of the LED and the substrate surface. However, the simulation results indicate that the improvement obtained in the LEE is the result primarily of pattering the upper surface of the LED.

Abstract: A new dry cleaning methodology named laser shock cleaning and optical inspection technique has been applied not only to remove the particles from the surfaces of image sensors but also to inspect the surfaces automatically before or after the cleaning. In the packaging of CMOS and CCD image sensing modules, the particles generated during the assembly process should be removed from the surfaces of image sensors in order to ensure clear image as well as to enhance the yield. The different kinds of particles were removed from the surfaces by the laser shock cleaning technique which utilizes the airborne shock wave induced by intense laser pulse. For the quantitative evaluation of cleaning performance, number, shape and size of the particles on the surfaces of image sensors were measured by vision inspection technique before and after cleaning. It was found that most particles on the surfaces were successfully removed after the treatment of laser-induced shock waves. The average removal efficiency of the particles was over 95 %. It is interestingly found that the remaining particles after the cleaning are based on organics, which are probably attached during the bonding process.