Laser processing plays a key role in the industrial manufacture. The transparent material processing with a visible nanosecond laser based on a tripartite-interaction procedure has proven to be an effective method, which has the advantages of low cost, high efficiency, and simplicity over the traditional direct processing by using a femtosecond laser. In our pre-study, by using an assisted metal foil attached to the rear surface of a transparent glass sheet, some holes can be drilled on the glass sheet with a visible nanosecond laser. Such a physical mechanism is based on the heat conduction, generation of stress and ablation among the laser beam, the glass sheet and the metal foil. However, the processing quality of the glass sheet during the previous process is still dissatisfied and remains to be improved. In this study, we demonstrated a new tripartite-interaction procedure among the laser beam, glass sheet and copper foil, i.e. attaching an assisted copper foil on the front surface of the glass sheet, to further improve the processing quality of the hybrid tripartite-interaction processing. The experimental results are compared with those of our previous work, indicating that drilled holes and grooves with less crack and better quality can be obtained by using the new procedure. Moreover, to analyze the reasons of obtaining less cracks and better quality, we have carried out a series of theoretical studies on simulating such a new tripartite-interaction process. According to some specific simulation results of the temperature and density variations in the glass and copper, we can analyze that the reduction of thermal damage on the glass sheet and the improvement on processing quality might be attributed to the thermal transfer induced by attenuated laser energy in such a configuration. Our results could be useful for the development of visible nanosecond laser processing in industrial applications.
Silicon is one of the most important semiconductor materials and the basic material in the field of modern microelectronics, and it has been widely used in microelectronics and photovoltaic industries which are closely related to our daily life. Because the traditional silicon wafer cutting technology has some serious problems such as insufficient cutting accuracy, low efficiency, and serious pollution, the laser processing has been paid more and more attention in silicon wafer cutting applications in about recent fifteen years. Therefore, it is extremely important to develop the laser silicon wafer cutting procedure for the improvement of the laser silicon wafer processing technology. An algorithm named as constrained interpolation profile has been invented in computational fluid dynamics. It is actually a semi-Lagrangian method to solve hyperbolic partial differential equations, and has the advantages of the stable results, compact process, and low dissipation, etc. Focused Gaussian laser beams with the same energy of 200 μJ and pulse widths of 100 fs, 20 ps, and 0.5 ns, respectively, were irradiated on the surface of a silicon wafer. The physical properties of density, temperature, and pressure in both time and space domains were obtained by means of the algorithm of constrained interpolation profile in the laser processing simulation. The mechanisms of laser silicon wafer processing were studied in detail by analyzing the changes in physical properties of silicon material. The conclusions of this paper might be useful in the optimization of a silicon wafer cutting process by the use of a pulsed laser.
Laser processing plays a key role in treating a lot of materials. The mechanism of laser stealth dicing (SD) is based on irradiation of a laser beam which is focused inside the brittle material. The laser beam scans along the predetermined path, so that the characteristics of the interior brittle material can be changed, the stress layer can be therefore formed. Finally, an external force is applied to separate the brittle material. Since only the limited interior region of a wafer is processed by the laser irradiation, the damages and debris contaminants can be avoided during the SD process. SD has the advantages of a high speed for thinner wafers without any chipping, the smooth section without dust and slag, and completely dry process, which has been widely used in large scale integrated circuits and microelectronic manufacturing systems. However, further studies on the simulation analyze and parameter optimization have kept to be rear for SD so far. In this study, an approach named as constrained interpolation profile (CIP) was adopted, which has the advantages of compactness, stability, and low dissipation in computational fluid dynamics compared with other simulation procedures. We have finished a theoretical simulation to obtain the physical features of the temperature, pressure, density of the silicon substrate at different focal depth where a nanosecond pulsed laser is irradiated, then we found a suitable focal depth with a good dicing quality by analyzing these physical features.
Laser drilling has been more and more widely used in laser machining process. Therefore, optimizing the quality of laser drilling becomes extremely important. We know that laser drilling can be achieved by using high power density of a laser. As light waves with different waveforms represent the different energy distributions in time domain, we believe that the quality of laser drilling should be related to the laser waveform. At present, a laser used in the laser processing usually hasthe waveform with a Gaussian or a Lorentzian distribution. In this study, we numerically simulated the punching quality of a pulsed laser with the Gaussian distribution and a pulsed laser with the top-flat distribution (we called it as a square-shaped laser pulse) at the same energy. It mainly refers to the changes of density, temperature, and pressure of the target materials under the same energy for different waveforms. The constrained interpolation profile algorithm has been used to simulate the machining process. Until now, there are few studies on the features of laser drilling with different waveforms in time domain. This paper provides a new method to optimize the quality of laser drilling.
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