Development of multi-wire EDM slicing method for silicon ingot
INSTRUCTIONS The diameter of silicon wafer becomes larger in order to increase the number of chips per one wafer. For such a larger diameter silicon ingot is mainly sliced by using multi-wire method, in which a long thin wire is used with slurry. In this method, several hundreds of wafers could be sliced at the same time. However there are still problems remained, such as large cracks, slurry treatment, contamination and so on. Therefore, we proposed a new slicing method of monocrystalline silicon ingot using wire electrical discharge machining (wire-EDM), and showed the possibility of wire EDM slicing for monocrystalline silicon ingot [1]. However, the efficiency of wafer slicing by the commerciallyavailable wire-EDM compared to multi-wire saw method is very low, because the number of sliced wafer was only one per one process in the conventional wire-EDM method. Therefore, a multi-wire EDM slicing equipment was newly developed with a single wire and a multi-EDM power supply unit in order to increase the efficiency of wafer slicing [2-4]. In this report, machining characteristics for mono-crystalline silicon ingot using this newly developed multiwire EDM slicing equipment was discussed. Besides, the possibility of applying this technique to silicon ingot for solar cell was also investigated.
Control of Kerf Width in Multi-wire EDM Slicing of Semiconductors with Circular Section
Abstract Multi-wire EDM slicing method have been developed to overcome problems of conventional multi-wire saw method, and high-efficient and high-accurate slicing could be expected compared with a single-wire EDM technologies. Recently, a group power supplying method was newly proposed to satisfy both processing efficiency and simplification of slicing equipment, and it can supply sufficient discharge energy to multiple processing wire electrodes only using one conductivity piece set with one EDM power unit. Input energies were almost constant at each processing wire electrode, and electrical discharge pulses could be homogeneously distributed to each processing point without the wire breakage even by using only one conductivity piece set in the group power supplying method. This multi-wire EDM slicing method with the group power supplying can slice materials into many wafers of a certain thickness according to the pitch distance of processing wire electrode. In this method, it is important to perform the uniform kerf width in order to achieve a constant thickness of wafer. However, the cutting width of workpiece always varies in the case of silicon and silicon carbide ingots with circular cross section. Therefore, influence of cutting width of workpiece on slicing characteristics was experimentally investigated to achieve the uniform kerf width. The maximum feed rate of workpiece had a great influence on the kerf width with different cutting width of workpiece, and a larger kerf width was obtained with decreasing the cutting width of workpiece under a constant maximum feed rate condition. A uniform kerf width could be obtained by setting a half and quarter maximum feed rate of workpiece, although the cutting width of workpiece increased by twice or four times.
High-frequency hearing thresholds: effects of age, occupational ultrasound and noise exposure
AbstractPurpose
It has been suggested that high-frequency audiometry (HFA) could represent a useful preventive measure in exposed workers. The aim was to investigate the effects of age, ultrasound and noise on high-frequency hearing thresholds.MethodsWe tested 24 industrial ultrasound-exposed subjects, 113 industrial noise-exposed subjects and 148 non-exposed subjects. Each subject was tested with both conventional-frequency (0.125–8 kHz) and high-frequency (9–18 kHz) audiometry.ResultsThe hearing threshold at high frequency deteriorated as a function of age, especially in subjects more than 30 years old. The ultrasound-exposed subjects had significantly higher hearing thresholds than the non-exposed ones at the high frequencies, being greatest from 10 to 14 kHz. This hearing loss was already significantly evident in subjects with exposure <5 years and increased with years of exposure and advancing age. The noise exposure group had significantly higher hearing thresholds than the non-exposed group at the conventional frequencies 4 and 6 kHz and at the high frequency of 14 kHz. After stratification for age, there was a significant difference between the two groups at 9–10 and 14–15 kHz only for those under 30 years of age.ConclusionMultivariate analysis indicated that age was the primary predictor, and noise and ultrasound exposure the secondary predictors of hearing thresholds in the high-frequency range. The results suggest that HFA could be useful in the early diagnosis of noise-induced hearing loss in younger groups of workers (under 30 years of age).
