Yasuhiro Okamoto

Welding characteristics of aluminum alloy by pulsed nd: Yag laser with pre-and post-irradiation of superposed continuous diode laser

Authors developed the high-performance micro-welding of aluminum alloy, in which the superposition of continuous diode laser of wavelength 808nm and pulsed Nd:YAG laser of wavelength 1064nm could perform the high-processing speed, the deeper penetration depth and the wider bead width. However, the penetration depth at the beginning of laser scanning was insufficient, and the evaluation of cracks wasnot cleared yet. Therefore, in this study, the effects of pre-and post-heating with continuous diodelaser on welding phenomena of aluminum alloy were experimentally and numerically investigated. Thecombination of continuous diode laser and pre-heating pulse of Nd:YAG laser without melting of specimensurface could keep the high surface temperature, which led to the stable deeper penetration and widerbead width with smooth surface integrity even at the beginning of laser scanning. Moreover, it was confirmed that the superposition of continuous diode laser was effective to improve a welding quality of aluminum alloy, since the superposition of continuous diode laser prevented rapid heating and cooling of aluminum alloy. The post-heating with continuous diode laser kept the gentle temperature gradient at the laser spot, and the generation of crack could be decreased by appropriate power and irradiation time of continuous diode laser.Authors developed the high-performance micro-welding of aluminum alloy, in which the superposition of continuous diode laser of wavelength 808nm and pulsed Nd:YAG laser of wavelength 1064nm could perform the high-processing speed, the deeper penetration depth and the wider bead width. However, the penetration depth at the beginning of laser scanning was insufficient, and the evaluation of cracks wasnot cleared yet. Therefore, in this study, the effects of pre-and post-heating with continuous diodelaser on welding phenomena of aluminum alloy were experimentally and numerically investigated. Thecombination of continuous diode laser and pre-heating pulse of Nd:YAG laser without melting of specimensurface could keep the high surface temperature, which led to the stable deeper penetration and widerbead width with smooth surface integrity even at the beginning of laser scanning. Moreover, it was confirmed that the superposition of continuous diode laser was effective to improve a welding quality of aluminum all...

Micro-Welding of Super Thermal Conductive Composite by Pulsed Nd:YAG Laser

The diffusion of generated heat in the electronic devices is an important issue. The heat would be diffused from electronic devices by passive strategies, which would be carried out by the use of high thermal conductivity materials as a heat sink. The development of advanced materials with the superior high-thermal properties and the high strength-toweight ratio has led to new metal matrix composites (MMCs) as a great attractive material in the electrical and electronic industries. Aluminum and its alloys are widely used for the manufacturing of MMCs, which have reached the industrial stage in some areas (Barekar et al., 2009). In order to manufacture practical components from MMCs, a technique for joining MMCs to other similar composites or to monolithic materials is strongly required. Therefore, the development of reliable and economic joining technique is important for extending the applications of MMCs. It is well-known that laser welding is the most flexible and versatile welding technology, and it has succeeded in the welding of MMCs (Niu et al., 2006; Bassani et al., 2007).

Effect of laser wavelength on machining characteristics of aluminum nitride in micro-boring

Effect of wavelength on machining characteristics of aluminum nitride in micro-drilling using Q-switched YAG harmonics was experimentally investigated. The depth of drilled hole increases with the decrease of wavelength, since photon energy and absorptivity becomes higher with decreasing the wavelength of laser beam. Besides, the energy loss by the plasma in laser processing decreases with decreasing the wavelength. Therefore, shorter wavelength is more effective in order to drill the micro-hole with high aspect ratio, when micro hole of high aspect ratio is drilled. Moreover, it is made it clear that the drilled depth under vacuum condition is deeper than that under the atmosphere pressure condition, since the removal of debris is carried out more efficiently compared the atmosphere pressure and assist gas supplying condition.Effect of wavelength on machining characteristics of aluminum nitride in micro-drilling using Q-switched YAG harmonics was experimentally investigated. The depth of drilled hole increases with the decrease of wavelength, since photon energy and absorptivity becomes higher with decreasing the wavelength of laser beam. Besides, the energy loss by the plasma in laser processing decreases with decreasing the wavelength. Therefore, shorter wavelength is more effective in order to drill the micro-hole with high aspect ratio, when micro hole of high aspect ratio is drilled. Moreover, it is made it clear that the drilled depth under vacuum condition is deeper than that under the atmosphere pressure condition, since the removal of debris is carried out more efficiently compared the atmosphere pressure and assist gas supplying condition.

Effect of focusing condition on micro-welding characteristic of glass by ps pulsed laser

An ultra-short pulse laser can make it possible to absorb laser energy at the focusing point inside a glass by non-linear absorption, and micro-welding of glass can be expected without an intermediate layer and adhesive. However molten area is greatly affected by its focusing condition, because one part of this process is related to non-liner phenomena, which can be generated at high-energy intensity condition. Therefore, in this study, effect of focusing condition on micro-welding of borosilicate glass (D263) were experimentally investigated using an ultra-shot pulsed laser of 12.5ps. Molten area was observed by a highspeed video camera, and breaking stress of the weld glasses was evaluated. Tear’s shape of molten area was created by the periodic movement of absorption point up and down in coaxial direction of laser beam. A usage of optical system with the spherical aberration correction made it possible to create a large volume weld joint even at the same pulse energy, because absorption rate of laser energy increased. Small pulse interval led to increasing the absorption rate, which could create a large molten area stably. An optical system with the spherical aberration correction led to stabilizing the shape of molten area, which resulted in the reliable joint.An ultra-short pulse laser can make it possible to absorb laser energy at the focusing point inside a glass by non-linear absorption, and micro-welding of glass can be expected without an intermediate layer and adhesive. However molten area is greatly affected by its focusing condition, because one part of this process is related to non-liner phenomena, which can be generated at high-energy intensity condition. Therefore, in this study, effect of focusing condition on micro-welding of borosilicate glass (D263) were experimentally investigated using an ultra-shot pulsed laser of 12.5ps. Molten area was observed by a highspeed video camera, and breaking stress of the weld glasses was evaluated. Tear’s shape of molten area was created by the periodic movement of absorption point up and down in coaxial direction of laser beam. A usage of optical system with the spherical aberration correction made it possible to create a large volume weld joint even at the same pulse energy, because absorption rate of laser e...

Characterization of Absorptivity in Micro-welding of Copper by Pulsed Green Nd:YAG Laser

The absorptivity to copper depended on the laser wavelength and welding mode, and absorptivity at 532nm was five times higher than that at 1064nm under no-melting condition. Absorptivity decreased with increasing penetration depth in the case of heat conduction welding, while absorptivity increased with increasing penetration depth in the case of key-hole welding. Deep penetration with the keyhole could be performed by a pulsed green Nd:YAG laser, while fundamental wavelength of Nd:YAG laser would result in almost no-melting even under the same condition. It was cleared that the effect of weld bead geometry was large, and the control of pulse waveform was effective for stable machining. The pulse waveform with maximum peak at the early period and a long pulse duration led to good results stabilizing the penetration depth with less porosity.The absorptivity to copper depended on the laser wavelength and welding mode, and absorptivity at 532nm was five times higher than that at 1064nm under no-melting condition. Absorptivity decreased with increasing penetration depth in the case of heat conduction welding, while absorptivity increased with increasing penetration depth in the case of key-hole welding. Deep penetration with the keyhole could be performed by a pulsed green Nd:YAG laser, while fundamental wavelength of Nd:YAG laser would result in almost no-melting even under the same condition. It was cleared that the effect of weld bead geometry was large, and the control of pulse waveform was effective for stable machining. The pulse waveform with maximum peak at the early period and a long pulse duration led to good results stabilizing the penetration depth with less porosity.

Improvement of Gas Shielding Effect in Vertical-position Laser Micro-welding of Titanium Alloy

High brightness lasers enable an efficient processing of wide area with high processing speed, but there are few effective supplying method of shielding gas for a wide area. It is difficult to fill up a wide processing area with a shielding gas, and the usage of shielding box might deteriorate the flexibility of remote laser welding method. In the case of titanium alloy, the oxidation and nitriding of weld area must be prevented due to the risk of strength reduction. In addition, for large and long size components, welding parts may be located in a vertical wall, which makes it difficult to keep a shielding gas at a processing area. Therefore, a proper shielding method of argon gas at a wide area is required in a vertical-position remote laser welding of titanium alloy for large size components.The shielding gas flow was numerically analyzed by computer fluid dynamics (CFD) method, and some shapes of ring-type shielding gas nozzle were investigated. Shielding gas flows from two layers of injection ports could increase the mass fraction of argon gas, and higher of ring-type nozzle led to the higher mass fraction. Moreover, it was suggested that a tilting of injection port against the center of ring-type nozzle was effective to keep the argon gas at a processing area, and the proper balance of flow rate between two layers could improve the mass fraction of argon gas. Laser irradiation experiments indicated similar effects of ring-type shielding gas nozzle shape, and the atomic percent of oxygen in vertical-position laser micro-welding of titanium alloy could be decreased by the newly designed nozzle shape.High brightness lasers enable an efficient processing of wide area with high processing speed, but there are few effective supplying method of shielding gas for a wide area. It is difficult to fill up a wide processing area with a shielding gas, and the usage of shielding box might deteriorate the flexibility of remote laser welding method. In the case of titanium alloy, the oxidation and nitriding of weld area must be prevented due to the risk of strength reduction. In addition, for large and long size components, welding parts may be located in a vertical wall, which makes it difficult to keep a shielding gas at a processing area. Therefore, a proper shielding method of argon gas at a wide area is required in a vertical-position remote laser welding of titanium alloy for large size components.The shielding gas flow was numerically analyzed by computer fluid dynamics (CFD) method, and some shapes of ring-type shielding gas nozzle were investigated. Shielding gas flows from two layers of injection ports c...

A009 Investigation of Micro-drilling Characteristics for SiC by Harmonics of YAG Laser

Micro-drilling characteristics of SiC by harmonics of Nd:YAG laser were experimentally investigated in the viewpoints of wavelength and the surrounding gas type condition. Moreover, plasma and processing behavior were observed to discuss micro-drilling characteristics of SiC. The debris was removed away in the opposite direction of laser beam along the flow field generated by laser irradiation. The behavior, the spectrum and the intensity of laser induced plasma were influenced by the surrounding gas condition. The appearance of plasma affected the surface integrity at the circumference of drilled hole, and the surface integrity could be improved under the reduced pressure condition.

Singulation of semiconductor package by superposition of pulsed fiber laser and green yag laser

The application of laser beam processing has been expected in the field of semiconductor devices because of its flexible cutting line and narrow kerf width. However, the deterioration of cutting quality would occur in the case of themosensitive materials due to the thermal damage, since the laser beam processing is mainly thermal process. Therefore, the laser singulation method by the superposition of pulsed fiber laser and green YAG laser was proposed to perform the high-quality processing for the semiconductor package, which is consisted of thermosetting epoxy-resin with silica for molding compounds and glass epoxy board for semiconductor package with insulator coatings. The superposition of pulsed fiber laser and green YAG laser with high pulse repetition rates led to a straighter kerf shape with smaller kerf width under the same pulse energy condition. The smaller kerf width could be achieved by controlling the time delay between both laser pulses compared with synchronized laser pulses. The heat affected zone in singulation process could be reduced by the superposition of pulsed fiber laser and green YAG laser. Moreover, the synchronized laser pulses could lead to the smaller heat affected zone compared with unsynchronized one.The application of laser beam processing has been expected in the field of semiconductor devices because of its flexible cutting line and narrow kerf width. However, the deterioration of cutting quality would occur in the case of themosensitive materials due to the thermal damage, since the laser beam processing is mainly thermal process. Therefore, the laser singulation method by the superposition of pulsed fiber laser and green YAG laser was proposed to perform the high-quality processing for the semiconductor package, which is consisted of thermosetting epoxy-resin with silica for molding compounds and glass epoxy board for semiconductor package with insulator coatings. The superposition of pulsed fiber laser and green YAG laser with high pulse repetition rates led to a straighter kerf shape with smaller kerf width under the same pulse energy condition. The smaller kerf width could be achieved by controlling the time delay between both laser pulses compared with synchronized laser pulses. The heat affe...

Novel fusion welding technology of Si/glass using ultrashort laser pulses with high pulse repetition rates

Using ps laser pulses with high pulse repetition rates, novel fusion welding technique of Si/glass material combination has been developed, which can overcome the most problems encountered in existing anodic bonding, providing excellent joint strength and throughput. Our technique allows welding of Si/glass without pre-and post-heating at high spatial resolution down to 10µm at maximum joint strength of 80MPa, and is shown to provide much better performance than ns laser pulses based on the analysis of laser-matter interaction. No defects are found by cutting using standard blade dicer and accelerated life test (500 cycles: -40˚C∼85˚C) of the laser-welded joint, demonstrating the welding technique has excellent performance for applications to wafer-level packaging and hermetic sealing.Using ps laser pulses with high pulse repetition rates, novel fusion welding technique of Si/glass material combination has been developed, which can overcome the most problems encountered in existing anodic bonding, providing excellent joint strength and throughput. Our technique allows welding of Si/glass without pre-and post-heating at high spatial resolution down to 10µm at maximum joint strength of 80MPa, and is shown to provide much better performance than ns laser pulses based on the analysis of laser-matter interaction. No defects are found by cutting using standard blade dicer and accelerated life test (500 cycles: -40˚C∼85˚C) of the laser-welded joint, demonstrating the welding technique has excellent performance for applications to wafer-level packaging and hermetic sealing.

Singulation of sapphire substrate with high aspect ratio internal modification by sub-nanosecond pulsed fiber laser

Sapphire has been widely used for a substrate of high brightness LED, and it is important to reduce the edge damage in the singulation process of sapphire substrate for the high quality product and the cost reduction. In this study, the internal modification technique of sapphire substrate by a sub-nanosecond pulsed fiber laser of 180ps was experimentally investigated with a normal achromatic focusing lens of 20mm in focal length, and the possibility of singulation method with this internal modification technique was discussed. The laser beam of 180ps and 1060nm was focused in sapphire substrate of 0.4mm thickness by passing through the epitaxial layer grown on the top side, and the internal modification zone was generated from the satin-finished surface as the bottom side of sapphire substrate. A high aspect ratio modified line such as 5–10u2005µm width and 200u2005µm height was successfully performed by the laser irradiation from the epitaxial layer side. A sapphire wafer of 0.4mm thickness could be broken from the internal modified line with less damage of the epitaxial layer by sufficient smaller stress compared with the tensile strength of sapphire. The breaking strength and its dispersion became smaller with increasing the number of laser scanning.Sapphire has been widely used for a substrate of high brightness LED, and it is important to reduce the edge damage in the singulation process of sapphire substrate for the high quality product and the cost reduction. In this study, the internal modification technique of sapphire substrate by a sub-nanosecond pulsed fiber laser of 180ps was experimentally investigated with a normal achromatic focusing lens of 20mm in focal length, and the possibility of singulation method with this internal modification technique was discussed. The laser beam of 180ps and 1060nm was focused in sapphire substrate of 0.4mm thickness by passing through the epitaxial layer grown on the top side, and the internal modification zone was generated from the satin-finished surface as the bottom side of sapphire substrate. A high aspect ratio modified line such as 5–10u2005µm width and 200u2005µm height was successfully performed by the laser irradiation from the epitaxial layer side. A sapphire wafer of 0.4mm thickness could be broken from...