• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.219-220
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• 2006

Laser surface hardening technologies have been used to improve characteristics of wear and to enhance the fatigue resistance for mold parts. The objective of this research work is to investigate the influence of the process parameters, such as power of laser and defocused spot position, on the characteristics of laser surface hardening for the case of SKD61 steel. CW Nd:YAG laser is selected as the heat source. The optical lens with the elliptical profile is designed to obtain a wide surface hardening area with a uniform hardness. From the results of the experiments, it has been shown that the maximum hardness is approximatly 740 Hv when the power, focal position and the travel of laser are 1,095 W, +1mm and 0.3 m/min, respectively. In addition, the hardening width using the elliptical lens was three time larger than that using the defocusing of laser beam.

• Journal of Periodontal and Implant Science
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• v.25 no.3
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• pp.614-622
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• 1995

Root caries is very frequently developed on exposed root surface after periodontal surgical treatment. In order to determine the anti-caries effect of Nd : YAG laser irradiation on periodontally exposed root surface, 40 mandibular molar teeth that had been extracted due to excessive periodontal destruction were used as the experimental teeth. All teeth were treated by the same procedure as conventional periodontal root treatment, ie thorough scaling, root planing and root conditioning with tetracycline HCl(100mg/ml, 5min.). Within middle one third of root, mesial half surface(20) or distal half surface(20) was randomly irradiated at various power of 1.0W, 2.0W, 3.0W and 4.0W for 60 seconds by non-contact(5mm) delivery of a pulsed Nd : YAG laser(EN.EL.EN060, Italy). The microhardness was measured by Vikers microhardness tester(Wilson, USA) at 2mm/second of jog speed under 100gm load. The difference of microhardness between irradiated side and non-irradiated side was statistically analyzed ANOVA and Duncan's method. Following results were obtained ; 1. The microhardness(Knoop hardness number) was significantly higher in laser irradiated surface than non-irradiated surface(p<0.05). 2. There was no significant difference in microhardness between experimental groups classified by different laser power(p>0.1). The results suggest that Nd : YAG laser irradiation on exposed root suface after periodontal therapy may inhibit the root caries development by enhancing surface microhardness.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.3
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• pp.181-188
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• 2010

Metal surface decontamination characteristics were investigated by using a laser ablation method. A second harmonic generation of a Q-switched Nd:YAG laser with a wave length of 532 nm, a pulse energy of 150 mJ and a pulse width of 5 ns was employed to assess the decontamination performance for metal surfaces contaminated with $CsNO_3$, $Co(NH_4)_2(SO_4)_2$, $Eu_2O_3$ and $CeO_2$. The ablation behavior was investigated for the decontamination variables such as a number of laser shots, laser fluence and an irradiation angle. Their optimum values were found to be 8, 13.3 J/$cm^2$ and $30^{\circ}$, respectively. The decontamination efficiency was different depending on the kinds of the contaminated ions, due to their different melting and boiling points and was in the order: $CsNO_3>Co(NH_4)_2(SO_4)_2>Eu_2O_3>CeO_2$. We also evaluated a correlation between the metal ablation thickness and the number of laser shots for the different laser fluences.

• Journal of Korean Neurosurgical Society
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• v.59 no.6
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• pp.559-563
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• 2016

Objective : Low back pain, caused intervertebral disc degeneration has been treated by thermal annuloplasty procedure, which is a non-surgical treatement. The theoretical backgrounds of the annuloplasty are thermal destruct of nociceptor and denaturization of collagen fiber to induce contraction, to shrink annulus and thus enhancing stability. This study is about temperature and its distribution during thermal annuloplasty using 1414 nm Nd : YAG laser. Methods : Thermal annuloplasty was performed on fresh human cadaveric lumbar spine with 20 intact intervertebral discs in a $37^{\circ}C$ circulating water bath using newly developed 1414 nm Nd : YAG laser. Five thermocouples were attached to different locations on the disc, and at the same time, temperature during annuloplasty was measured and analyzed. Results : Thermal probe's temperature was higher in locations closer to laser fiber tip and on lateral locations, rather than the in depth locations. In accordance with the laser fiber tip and the depth, temperatures above $45.0^{\circ}C$ was measured in 3.0 mm depth which trigger nociceptive ablation in 16 levels (80%), in accordance with the laser fiber end tip and laterality, every measurement had above $45.0^{\circ}C$, and also was measured temperature over $60.0^{\circ}C$, which can trigger collagen denaturation at 16 levels (80%). Conclusion : When thermal annuloplasty is needed in a selective lesion, annuloplasty using a 1414 nm Nd : YAG laser can be one of the treatment options.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.1056-1059
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• 2001

These days, as dynamic function and special properties to compare traditional material, $Al_20_3$ ceramic use all over the industry. But it is very difficult to process because of high hardness and brittleness. Therefore, in this paper, it was investigated that laser process parameter which can produce appropriate quality of $Al_20_3$ ceramic microhole machining.

• Proceedings of the Optical Society of Korea Conference
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• 2008.02a
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• pp.211-212
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• 2008

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1849-1851
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• 1999

The PDP(Plasma Display Panel) barrier rib was fabricated by focused $Ar^+$ laser ($\lambda$=514nm) and Nd:YAG($\lambda$=532, 266 nm) laser irradiation. The depth of the etched groove increases with increasing a laser fluence. and decreasing a scan speed. Using the second harmonic of the Nd:YAG laser, the threshold laser fluence was $6.5mJ/cm^2$ for the sample of PDP barrier rib dried at $120^{\circ}C$. The thickness of $150{\mu}m$ of the sample on the glass was etched without any damage on the glass substrate by fluence of $19.5J/cm^2$. The barrier rib sample on hot plate was etched by Nd:YAG laser(532 nm) as increasing a temperature of the sample. In this case, the etch rate was $95{\mu}m/s$, $190{\mu}m/s$ at room temperature, $175^{\circ}C$ respectively.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.2
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• pp.106-113
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• 2002

Stencil is used normally as a mask for seeder pasting on pad of PCB. The objective of this study is to develop stencil cutting system and determine optimal conditions which make good-quality stencil by using a Nd:YAG laser. The effects of process parameters such as laser power, type of mask, gas pressure, cutting speed and pulse width old the cut edge quality were investigated. In order to analyse fille cut surface characteristics(roughness, kerf width, dross) optical microscopy, SEM photography and roughness test were used. As a result, the optimal conditions of process parameters were determined, and the practical feasibility of the proposed system is also examined by using a commercial Gerber file for PCB stencil manufacturing.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.4 no.3
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• pp.317-321
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• 2003

A conventional typewriter types letters by hammering a carbon ribbon which is attached at a paper. The laser typing process which write a micro pattern of Chrome on a silicon wafer has been developed. A glass that is coated with 100 nm Chrome (Carbon ribbon) is attached on a silicon wafer (paper). An Nd-Yag laser (hammer) is irradiated on the glass, and the Chrome is transferred on the silicon wafer. Micro patterns are made by controlling laser beam trajectory. The suggested micro pattering can be used at the high density data storage of TeraBit/in$^2$ or at the improvement of productivity of semiconductor manufacturing procedure.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.652-655
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• 2001

In this paper, I have studied minimization of the kerf-width and surface burning which are occurred after the singulation process of multi layer $\mu$-BGA( thickness 1.1 mm, 0.9 mm) with a pulsed Nd:YAG( = 532 nm, repetition rate = 10 Hz) laser. The thermal energy of a pulsed Nd:YAG laser is used to cut the copper layer. I have studied are minimization of the surface burning and kerf-width using a photo resist, $N_2$blowing and polyester double sided tape as a cutting parameter. The $N_2$blowing reduces a laser energy loss by debris and suppresses a surface carbonization. Also, I have studied characters of cutting with a choice of side of laser beam incidence. The SEM(Scanning Electron Microscope), non-contact 3D inspector and high-resolution microscope are used to measure kerf width and surface state. The optimum value of 1.1 mm $\mu$-BGA singulation is 524 $\mu$m that is reduced kerf width of 60 % with $N_2$blowing. And I obtained reduction of carbonization of 68 % with a polyester double side tape in 0.9 mm $\mu$-BGA. I used laser intensity of 1.91$\times$10$^{6}$ / $\textrm{cm}^2$ in this study.