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上田, 隆司 ; 三野, 大樹 ; 古本, 達明 ; 細川, 晃 ; 長友, 正平
概要:
CO2パルスレーザを用いて単結晶のサファイアウエハの熱応力割断を試みている．レーザ割断はサファイアウエハを分断する方法として有力な加工法である．パルスレーザを用いると，割断面には単結晶ウエハに特有な縞模様が形成される．曲線割断が可能であり，
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円弧状にサファイアウエハを割断できる．ウエハ上に加工された浅い溝の上をCO2パルスレーザでなぞることによって，ウエハを割断できる．Single-crystal sapphire wafers were cleaved by irradiation with a pulsed CO2 laser. Laser cleaving is a useful method to cut sapphire wafers. A striped pattern on the cleaved surface is observed when a pulsed laser is used. Laser cleaving makes it possible to cut the sapphire along the circular arc. Sapphire wafers can be cleaved by laser irradiating along a pre-made shallow groove.
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| 2.
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山田, 啓司 ; 西岡, 真吾 ; 細川, 晃 ; 上田, 隆司
概要:
Laser cleaving process is a prospective technique to divide a thin plate of brittle materials into small pieces, because of its high yield ratio and controllability. In addition, the process is carried out without coolant which
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causes the environmental pollution and the contamination of the electrical devices etched on the wafer. In this paper, laser cleaving of silicon wafer is conducted with pulsed Nd: YAG laser. The temperature of laser spot is measured by means of the two-color pyrometer with optical fiber and the acoustic emission caused by crack propagation is also observed. When the laser spot is scanned at the appropriate interval and velocity, the crack propagates in sequence by the corresponding laser irradiation. As a result, both high linearity of cleaved edge and fine fractured surface roughness are obtained. The thermal stress distribution induced by laser irradiation is analysed with FEM model, in which the stress intensity factor is calculated at the vicinity of the crack tip in order to clarify the criterion of crack propagation. The analysis and experiments reveal that the maximum tensile stress at the crack tip increases with temperature and the crack propagates when the stress intensity factor reaches the fracture toughness of the material.
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| 3.
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千徳, 英介 ; 上田, 隆司 ; 山田, 啓司 ; 細川, 晃
概要:
Laser forming of a sheet metal is the bending process caused by the thermal stresses which is produced in the sheet by l
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aser irradiation. Therefore, the temperature distribution in the sheet irradiated with laser beam is one of important factors to determine the bending angle of the sheet. In this study, the influence of temperature distribution and the experimental conditions like the diameter of laser beam and the thickness of a sheet on the bending angle is investigated experimentally. The temperatures of a surface irradiated with CO2 laser and its opposite surface are measured using an infrared radiation pyrometer with an optical fiber. As a result, the bending angle is directly proportional to the temperature Ts at the sheet surface irradiated with laser beam and the beam diameter D, and inversely proportional to the thickness h of the sheet. A parameter indicated by D1.41Ts1.5/h1.7 has high correlation with the all bending angles obtained under various experimental conditions. 様々な加工条件で板材のフォーミング加工を行い, 同時にレーザ照射部表面および裏面温度を測定し, 加工条件と照射温度の変形角への影響を調べた. その結果, 変形角はレーザビーム径の1.4乗に比例し, 照射温度の1.5乗に比例し, 加工物の板厚の1.7乗に反比例しており, これらの結果より導出した式は定性的に加工条件の変形角への影響を良く表している.
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| 4.
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上田, 隆司 ; 山田, 啓司 ; 及川, 志郎 ; 細川, 晃
概要:
Laser forming is the thermal process to deform a metal plate using the thermal stress produced by the rapid heating with the laser. In this study, the influence of irradiating conditions of CO2 laser on the bending angle of the
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workpiece is investigated. The temperature at the back surface of the workpiece irradiated with CO2 laser is measured using a two-color pyrometer with an optical fiber. The temperature distribution in the workpiece is calculated using the FEM thermal analysis. Simple bending experiments with one-way laser scanning are carried out. Stainless steel SUS304 of various thickness is used as work material. The results obtained are as follows. The bending angle is proportional to the temperature of the workpiece irradiated. The temperature of workpiece increases with the increase of laser power, the decrease of feed rate of the laser beam and the decrease of plate thickness. After all, the bending angle becomes larger with the increase of laser power, the decrease of the feed rate and the decrease of the thickness of the plate. The temperature of the workpiece can be used as a signal to control the deformation of the workpiece.
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千徳, 英介 ; 上田, 隆司 ; 細川, 晃
概要:
Laser leveling is an application of laser forming. Laser leveling of a sheet metal is a plastic process caused by therma
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l stresses which are produced in the sheet by laser irradiation. In this paper, a sphereical distortion on a sheet metal is leveled by laser irradiation. As a model of a circular distortion, the dsitortion is intentionally introduced on the sheet metal by pressing a steel ball of 25 mm radius against it. As work materials, steel sheet and stainless steel sheet whose thickness is 0.6mm are used. Laser beam is radially irradiated at the center of circular distortion for leveling the distorted sheet metal. Continuous CO2 laser beam is used and its power is changed at the range of 80W ∼ 200W under a constant scanning speed of 2mm/s. After laser irradiation, a distortion of about 400µm hight becomes almost flat without melting a sheet metal.
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| 6.
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山田, 啓司 ; 大礒, 桂一 ; 細川, 晃 ; 上田, 隆司
概要:
The thermal stress cleaving of silicon wafer with a laser beam is a prospective technique, which supersedes the mechanical dicing. This method makes it possible to cut a wafer at very high production rate in comparison with the diamond thin
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blade wheel and to protect the wafer from the contamination of cutting coolant and chips. In this paper, the cleaving mechanism of silicon wafer irradiated with the pulsed Nd:YAG laser is investigated. The temperature at the area irradiated with laser is measured using two-color pyrometer with an optical fiber. The acoustic emission is also measured to examine the mechanism of the crack propagation. In the process, the temperature at the area irradiated with laser should be controlled in order to reduce the thermal damages and to improve the cleaving accuracy.
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| 7.
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上田, 隆司 ; 田中, 邦茂 ; 西岡, 真吾 ; 山田, 啓司 ; 細川, 晃
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