• KIEE International Transactions on Electrophysics and Applications
• /
• v.2C no.6
• /
• pp.309-313
• /
• 2002

In this paper, we have studied minimization of the kerf-width and surface burning, which occurred after the conventional singulation process of the multi-layer BGA board with copper, polyethylene and epoxy glass fiber. The high thermal energy of a pulsed Nd:YAG laser is used to cut the multi-layer board. The most considerable matter in the laser cutting of the multi-layer BGA boards is their different absorption coefficient to the laser beam and their different heat conductivity. The cut mechanism of a multi-layer BGA board using a 2$^{nd}$ harmonic Nd:YAG laser is the thermal vaporization by high temperature rise based on the Gaussian profile and copper melting point. In this experiment, we found that the sacrifice layer and Na blowing are effective in minimizing the surface burning by the reaction between oxygen in the air and the laser beam. In addition, N2 blowing reduces laser energy loss by debris and suppresses surface oxidation. Also, the beam incidence on the epoxy layer compared to polyimide was much more suitable to reduce damage to polyimide with copper wire for the multi layer BGA singulation. When the polyester double-sided tape is used as a sacrifice layer, surface carbonization becomes less. The SEM, non-contact 3D inspector and high-resolution microscope are used to measure cut line-width and surface morphology.

• Journal of Welding and Joining
• /
• v.17 no.1
• /
• pp.71-76
• /
• 1999

The real-time holographic interferometer with digital high-speed camera is applied to the experimental study of laser induced plasma/plume in pulsed Nd:YAG laser welding. A pulsed Nd:YAG laser with 1.2 kW average power is applied to generate laser induced plume. The recording speed of the high-speed camera is 3,000 f/s. The high speed photographs of weld plume without another visualization method, are compared with the visualization photographs with holographic interferometer. The radiation intensity from the laser induced plume is recorded by the high speed photographs, which fluctuated during laser radiation and disappeared after laser end. The density distribution of the plume is recorded by the holographic visualization method. The experimental results show the process of generation of the laser induced plasma/plume, and give the feasibility of quantitative measurement of laser induced plume in laser welding.

• Korean Journal of Optics and Photonics
• /
• v.10 no.1
• /
• pp.53-57
• /
• 1999

We established the laser oscillator using Nd:YAG crystal grown at Ssang Yong company in Korea and investigated the characteristics of oscillation, Q-switching and wave front of output beam. We measured the single pass gain by controlling the threshold input energy with two output couplers of different output reflectances. Moreover, we compared the gain measured by different output couplers with the gain directly measured by the laser amplifier. The peak power of Q-switching, the pulse width, and the single pass gain coefficient at the threshold energy were 1.5 MW, 30ns, and 0.0958 cm-$^1$ respectively and they were compared with those of the commercial Nd:YAG crystal. Our crystal was proved to be as good as the commercial crystal.

• Journal of Welding and Joining
• /
• v.25 no.4
• /
• pp.49-57
• /
• 2007

The optimization of the cladding parameters was studied to maximize the deposition efficiency in the laser cladding using a low power pulsed Nd:YAG laser. STS304 stainless steel plate and Co alloy powder were used as a substrate and powder for cladding, respectively. The six cladding parameters were selected through preliminary experiments and their effects on the deposition efficiency were analyzed statistically. Experiments were designed and carried out using the Taguchi experimental method using a L18 orthogonal array. It was found from the results of analysis of variance(ANOVA) that the powder feed position and powder feed angle had the most significant effects on the deposition efficiency, but the powder feed rate and laser focal position had nearly no effects. The deposition efficiency could be maximized at 0mm of the powder feed position and 50o of the powder feed angle in the experimental range. From this experimental analysis, a new laser cladding head with 20o of the powder feed angle was designed and manufactured. With a new laser cladding head, the highest deposition efficiency of 12.2% could be obtained.

• Proceedings of the KIEE Conference
• /
• 1996.07c
• /
• pp.1759-1761
• /
• 1996

Md:YAG laser has been used in many applications such as micromachining, nonlinear optical experiments, holography, and rangefinding. These applications quite often require operation of the laser at the $TEM_{00}$ mode since this mode produces the smallest beam divergence, the highest power density, and, hence, the highest brightness. In this study, a pinhole is put between a rod and a half mirror to make the $TEM_{00}$ mode, and then we measured the intensity distribution of the output beam as reducing the diameter of the pinhole from 6mm to 1.5mm. As a result, the optimum size of the pinhole fixed in a resonator to make the $TEM_{00}$ mode was obtained, and we found out that the output beam of the pulsed Nd:YAG laser with a single elliptical cavity has a Gaussian distribution.

• Laser Solutions
• /
• v.7 no.1
• /
• pp.37-47
• /
• 2004

Laser-assisted selective infiltration is a new method of building metal layers to make metal parts layer by layer, in which superheated microscopic metal droplets are infiltrated into a laser-preheated layer of microscopic metal powders. In this work, the selective infiltration of a low melting-point metal, Sn-37Pb wt%, was conducted to investigate the effects of such dominant parameters as superheating temperature, Nd:YAG laser power for preheating, substrate temperature, etc. The optimal conditions for successful selective infiltration of a single layer of microscopic metal powder were experimentally obtained

• Maxillofacial Plastic and Reconstructive Surgery
• /
• v.22 no.1
• /
• pp.33-42
• /
• 2000

The purpose of this study was to compare the wound healing process after skin incision using scalpel, $CO_2$ laser and pulsed Nd:YAG laser in rats. After skin on the back was incised 3 cm long, rats were sacrificed at 1, 3, 7, 14, 21 and 28 days. Macroscopic, histologic and immunohistochemical examinations using the collagen type IV and the CD34 antibodies which are necessary to the forming process of new capillary were performed. Results obtained were as follows ; Macroscopically the initial wound healing of the laser group was about $1{\sim}2$ weeks slower than that of the scalpel group. There weren't however any remarkable differences in all groups in 4 weeks after incision. By histologic finding, acute inflammatory cells were more prominent during the initial wound healing in the scalpel group than in the other groups. Epithelialization started in the order of scalpel, $CO_2$ and Nd:YAG laser group after skin incision. By the Masson's trichrome stain, collagen synthesis in the Nd:YAG laser group was more slowly initiated than in the other groups. But it was completed at the $3{\sim}4$ weeks in all groups. Immunohistochemically, collagen type IV and CD34 expression were markedly increased at 2 weeks in the scalpel and $CO_2$ laser group. Meanwhile, in the Nd:YAG laser group, these reactions were observed later tan the other groups. Collagen type IV and CD34 expression were decreased in all groups after 4 weeks. These results suggest that $CO_2$ and Nd:YAG laser showed similar healing process compared with scalpel and a potential substitute for scalpel in skin incision.

• Journal of Oral Medicine and Pain
• /
• v.21 no.1
• /
• pp.183-196
• /
• 1996

The author examined the clinical and histological changes on the dorsal tongue mucosa of adult Sprague-Dawley rats after lasing by pulsed Nd:YAG laser. The dorsal tongue was lased for 3 seconds by 1.5, 2.0, 2.5, 3.0, 3.5, 4.0W and 10, 15, 20, 20pps. After tissue changes were observed clinically, the excised samples were observed histologically and the width of tissue destruction was analyzed quantitatively under the Confocal laser microscope respectively. The following results were obtained : 1. Whitening of peripheral tissue was observed more as increasing pulsed per second (Hz) below power 2.5W and observed at all parameters above power 3.0W. 2. Charring of mucosal surface was observed at all parameters but mild at parameters below power 2.0W. 3. The destruction of epithelium was observed at all parameters and tissue destruction was extended to lamina propria at higher pulses per second. 4. The width of tissue destruction was more widening as increasing energies per pulse (p<0.001) and the narrowest at 20Hz than 10Hz, 15Hz and 30Hz(p<0.05). As the above results, author suggests power below-3.5W and 20Hz as the lasing parameters for oral soft tissue therapy.

• Journal of the Korea Computer Industry Society
• /
• v.2 no.3
• /
• pp.369-376
• /
• 2001

The optimization of resonator and laser power supply has been considered to be significant for improving the efficiency of a pulsed Nd:YAG laser system. We have proposed a new method of 3-mesh parallel sequential charge and discharge circuit as a laser power supply; more compact than conventional power supply, competitive in price, easy to control the laser power density according to various material processing, and equipped with the optimum reflectivity of output coupler. In this study, we could find that the maximum laser output was obtained by using 85% of reflectivity in the case of 50[W]-class. In addition using the power supply of new method, it's possible to charge each capacitor bank with a higher energy within the given charging time adopted a new method mentioned above; namely, we can allow each capacitor to have much more charging time and storage energy. So, higher laser output was obtained than conventional power supply.

• Proceedings of the KIEE Conference
• /
• 1998.07e
• /
• pp.1696-1698
• /
• 1998

Pulsed Nd:YAG laser using Nd:YAG crystal operates stably in the thermal conductivity, mechanical, optical condition. That is used broadly in material processings because of easy reaction to the materials, and the maintenance is very easy because of lamp excitation. In these material processings, power dinsity control is very important to improve processing technology. Power density is controled by inductance and capacitance or repetition rate. Therefore we are going to control laser power density as One-Chip Microprocessor(PIC16C55) and 8051. We have been experimented at the pulse repetition rate range of 10pps to 60pps(pulse per second).