Advanced Materials Research Vols. 126-128

Abstract: For optical micro- machinery processing, nanosecond laser possess a special advantage in using it as a fabrication method of smaller hole subjected to the minimum thermal distortion. Thus it has become an effective and powerful tool widely used in drilling, cutting and welding process for micro-manufacturing field. To estimate the working performance of pulsed laser, an auxiliary method in numerical skill or semi-empirical technology is usually utilized, where the important parameters including energy intensity, duration and wavelength of laser beam will be taken into account. Nevertheless, several troubles, the unstable numerical iteration for phase change and precise calibration of sensor required in the measuring process, seem to be still inevitable, and which easily makes the numerical calculation become more complicated, even the global ablating behavior will be lost. To compensate the inadequacy mentioned above, an analytic model of optical ablation for pulsed laser, based on the evaporation effect responsible for penetration mechanism, is then derived in this study. Here the penetrating behavior, during the micro-machining process, can be clearly examined with the consideration of plasma absorption. After compared with experimental results made by Chen and Schmidt for copper drilling and steel ablation for Tim, a better agreement of analytic results identifies the accessibility of proposed model which also contributes to the future investigation on pico-or femto- laser material processing.

Abstract: Since the solder residue is essential in the semiconductor manufacturing process, it has great impact on the flip chip quality considerably. This paper intends to improve the flip chip quality and try to obtain an optimal solution for the system parameters in the flip chip manufacturing process. The SMT manufacturing process is studied for discussion. The amount of solder and the size of solder are selected as the two quality properties. During the flux cleaning process, many solders are left on the passive component side. The balling might flow into the chip. It will cause the bump short in the chip which will affect the quality of the flip chip severely. In this paper, response surface method is adopted as the design of experiments. The objective function and subjective constrained conditions are defined to formulate the optimization problem. The confirmation experimental results are also provided to prove the validity. It is believed that the optimization results are helpful to the improvement of the semiconductor manufacturing process.

Abstract: Recently, material removal utilising electrokinetic phenomenon was proposed as an alternative to create material removal at the nanometric level [1]. The concept of the introduced material removal process is to impinge particles contained in the slurry, under the influence of hydrodynamic and electrokinetic effects, onto the workpiece with a predetermined velocity to create material removal on the surface. The material removal process proved to be feasible where the material removal rate was reported to be in the range of a few hundred nm/hr with a surface roughness of a few nm (RMS). This paper aims to look into the effect of the electrochemical dissolution on the material removal process since high voltages are involved during the material removal process. During the experimental study, electrochemical dissolution was observed and it contributed a certain proportion of the material removal process. However, the main material removal mechanism still relies on the mechanical action of the abrasive particles on the surface of the workpiece to create material removal during the process.

Abstract: Nano structures such as CNTs were proposed to be directly used as cutting grains to fully utilize the nice mechanical and thermal properties for nano machining. To further understand the CNT abrasive tool, a theoretical study of the CNT uncut chip model was conducted together with preliminary experimental tests to investigate the chip generation in the nano machining process. We found that the CNT distribution was not even in the CNT layer of the wheel. Based this finding, a grain spacing model and a feed of workpiece per cutting edge model were developed. Theoretical results were all very small. It was also found that individual workpiece chips were difficult to find due to small sizes. Further work is necessary. Furthermore, Chip gelling effect was found. The reasons were due to agglomeration and epoxy melting. Experimental results were found agree with our theoretical results.

Abstract: This work is on the preparation of microelectrodes for μ-EDM operation using μ-WEDG process. Electrodes of Ø500 μm are fabricated with various discharge energy machining conditions. Effects of gap voltage, capacitance & feed rate on the surface finish of the electrodes and overcut of the thus produced micro holes are investigated. The profile of microelectrodes is measured using surface roughness tester with 2μm stylus interfaced with SURFPAK software. The study demonstrated that for brass electrodes an arithmetic average roughness value as low as 1.7μm and an overcut of 3 µm could be achieved. The significant machining parameters are found using ANOVA. Surface of the produced microelectrodes are examined using Scanning Electron Microscope. μ-WEDG process parameters could be adjusted to achieve good surface integrity on microelectrodes. Experimental results showed that the surface roughness of microelectrodes depended primarily on feed rate of the electrode. The observations showed the clear and quantitative correlation existing between the micrometer level surface quality and process parameters. The resulting microelectrodes are found to be of exceptionally high quality and could be used for μ- EDM operation on different types of work materials.

Abstract: Indentations on the three main crystallographic planes (100), (110), and(111) of CaF2 were analyzed. Appropriate material parameters were obtained by experimental load-displacement curves. The results show a value in the range of 70–110 MPa for the initial shear yield strength. The submicron-level orthogonal cutting process of CaF2 had been investigated by the finite element approach, and the effects of tool rake angle on cutting stress and chip formation were investigated. The results indicate that increasing the tool rake angle causes a significant increase in stress and a decrease in chip thickness. The simulation results from the present study show the optimal tool rake angle to the ultra-precision cutting of CaF2 is -20°.

Abstract: This paper investigates the surface integrity of Ti-6Al-4V in conventional grinding using SiC abrasive, it includes surface roughness, surface topography, surface residual stress and metallurgical structure alteration. The experiment result indicated that grinding depth and feed rate have significant effect on surface roughness. Workpiece ground surface was free of crack, but severe plastic deformation layer and light burn appeared because of chemical reactions and mechanical factors. Ground surface was in a state of high tensile residual stress, thermal cycling of surface layer had the greatest effect. The machined surface experienced microstructure alteration on the top layer of ground surface, a heat-affected zone (HAZ) was observed.

Abstract: Dry sliding wear properties of aluminum nitride (AlN) reinforced aluminum silicon (Al-Si) alloy were investigated by using a pin-on-disc configuration tester. In this work, different weight percentages (5 and 10 wt%) of AlN was added into the Al-Si alloys. The samples were prepared by a stir casting process via a bottom pour technique which was then aged with a T6 condition prior to the wear test. Detailed analyses on the morphologies were conducted using scanning electron microscope (SEM) with the aid of an energy dispersive x-ray analyser (EDX). Prior to the heat treatment, the distribution of hard aluminum nitride particles that surrounded the Si phase had improved the hardness of the composites by 15%. The hardness value was found to be significantly increased about 80% for aged samples compared to un-aged samples. This was mainly contributed from precipitations of Si grain and intermetallic compounds; Mg2Si and FeSiAl5 formation in the alloys. Thus, a significant increased in wear resistance up to 56% was also observed especially at the highest applied load of 70N. Surface investigation by a scanning electron microscope (SEM) revealed that a combination of abrasion and adhesion wear mechanism was dominant for both un-aged and aged samples.

Abstract: In this paper, Taguchi method was applied to design the cutting experiments when end milling Inconel 718 with the TiAlN-TiN coated carbide inserts. The signal-to-noise (S/N) ratio are employed to study the effects of cutting parameters (cutting speed, feed per tooth, radial depth of cut, and axial depth of cut) on surface roughness, and the optimal combination of the cutting parameters for the desired surface roughness is obtained. An exponential regression model for the surface roughness is formulated based on the experimental results. Finally, the verification tests show that surface roughness generated by the optimal cutting parameters is really the minimum value, and there is a good agreement between the predictive results and experimental measurements.

Abstract: Hard disk substrates play a key role in the data storage process of magnetic storage hard disk drives (HDDs). However, a potential failure mode exists with the head clearance requirements caused by surface variation which is induced by substrate nano-asperities. Consequently, developing a polish process to eliminate surface asperities and residual surface defects in the glass substrate disks process is therefore a necessity to meet the challenges of future technology. Currently, the leading candidate utilizes nano cluster diamond (NCD) abrasive which is a synthetic diamond created in a controlled explosion process. A great effort is now underway to modify these NCD clusters to reduce light scratches and asperities in the perpendicular magnetic recording media polish process. Three distinct diamond types of NCD-90, NCD-80 and NCD-70 were utilized in this study. The major difference among these three distinct cluster diamond types is the diamond percentage amounts. Because of the differing diamond percentage content, one achieves a different structure which changes the polish properties. HRTEM, XPS, Raman, BET, AFM, Optical Surface Analyzer and disk defect testers were used for the diamond particles, polished substrate and disk analysis. The detail shall be discussed in this study.