Takuto Yamaguchi

Sintering Mechanism of Composite Ag Nanoparticles and its Application to Bonding Process-Effects of Ag2CO3 Contents on Bondability to Cu-

We have proposed a novel bonding process using composite Ag nanoparticles composed of Ag metallo-organic nanoparticles and Ag2CO3 for an application to the assembly of electronic devices. In this research, the sintering mechanisms of the composite Ag nanoparticles are discussed based on the results of the observation of the sintering behaviors and the investigation of the thermal characteristics. Moreover, Cu specimens were bonded using the composite Ag nanoparticles for measuring the bonding strengths. Based on the results, the effects of the Ag2CO3 contents in the composite Ag nanoparticles and the bonding conditions on the bondability were evaluated. As a result, it was found that the composite Ag nanoparticles were sintered rapidly because of the interaction between the Ag metallo-organic nanoparticles and Ag2CO3. Thereby, the bondability was improved by optimizing the contents of Ag2CO3 in the composite Ag nanoparticles.

Strengthening of Ceramic Coated Steel by Laser Quenching

In order to investigate the effectiveness of laser quenching for ceramic coated steels, 2 kinds of ceramic coated specimens of CrAlN and TiAlN were prepared, and the laser quenching experiments under various irradiation conditions were carried out. The influence of laser irradiation on the substrate hardness, film hardness and adhesive strength were investigated. Because of the high heat absorption of CrAlN and TiAlN films when compared to TiN, it was possible to quench the substrate effectively without any absorbent material for these specimens, although an absorbent was required for TiN coated specimen. The quenched area on the cross section of the substrate of CrAlN coated specimen was larger than that of TiAlN coated specimen. The difference of the quenched area could be explained by the difference of the heat absorption of these films. It was also possible to improve the adhesive strength of these films by laser irradiation. Although the film hardness decreased considerably by furnace quenching for ceramic coated steels, film hardness did not decrease by laser irradiation. It was concluded that the improvement of the adhesive strength and substrate hardness without the decrease of film hardness was achieved by laser quenching for CrAlN and TiAlN coated specimens.

Effects of laser heat treatment on mechanical properties of ceramic coated steels Part 1 – Laser irradiation conditions and mechanical properties of ceramic coated steels

Abstract In our previous study, we proposed a new surface modification technique by combination of ceramic coating and laser heat treatment. By applying laser heat treatment after coating, it was possible to improve the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness. In the present research, in order to quench a larger area of ceramic coated steel uniformly and efficiently, a high power diode laser equipped with a galvano-scanner was used in the laser heat treatment process. The scanning laser irradiation conditions to achieve uniformly quenched substrates without any surface damage were investigated for three kinds of ceramic coated steels: CrAlN, TiAlN and CrN. The film hardness and adhesive strength of the laser irradiated regions were evaluated. It is shown that scanning laser quenching after coating effectively improved the mechanical properties for larger area of ceramic coated steels.

Effects of laser heat treatment on mechanical properties of ceramic coated steelsPart 2 – Fracture strength of laser heat treated ceramic thin film

Abstract In our previous study, we proposed a new surface modification technique by combination of ceramic coating and laser heat treatment. By applying laser heat treatment after coating, it was possible to improve the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness. However, the effects of laser heat treatment on the fracture strength of ceramic thin films were not investigated yet. In the present research, in order to demonstrate further development of this method, the fracture strength of laser irradiated ceramic thin films (CrAlN, TiAlN and CrN) was investigated by sphere indentation testing. To prevent heat induced changes in the substrate hardness, a cemented carbide WC–Co rather than steel was used as substrate material. While the fracture strength of each film decreased significantly through furnace heat treatment, it remained almost unchanged in case of the laser irradiated films. The application of laser heat treatment for the substrate quenching after coating process can effectively prevent the fracture strength loss of ceramic thin film.

Quenching of Ceramic Coated Steels by Scanning Laser

In our previous study, it has been shown that improvement of the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness can be achieved by applying laser quenching. In the present research, in order to quench a larger area of ceramic coated steel uniformly and efficiently, a high power diode laser equipped with a galvano-scanner unit was used in the laser heat treatment process. The scanning laser irradiation conditions to achieve uniformly quenched substrates without any surface damage were investigated for 3 kinds of ceramic-coated steels: CrAlN, TiAlN and CrN. The film hardness and adhesive strength of the laser irradiated regions were evaluated. It is shown that scanning laser quenching after coating effectively improved the mechanical properties for larger area of ceramic-coated steels.

Heat dissipative Pb-free bonding technology using Al-rich Zn/Al/Zn clad solder

Abstract Al-rich Zn/Al/Zn clad solder were developed as Pb-free solder for a die-attachment. The Zn/Al/Zn clad solder was produced by clad rolling of Zn and Al strips in order to prevent Al from oxidation and improve wettability. The Zn/Al/Zn clad solder was melted at 382°C after solid-state interdiffusion of the Zn and Al layers. Bonding was successfully achieved with bonding pressure of a few kilopascals. Thermal cycle life of Invar-to-Cu substrate joint using the Zn/Al/Zn clad solder was longer than that of Pb-Sn-Ag solder. No Kirkendall voids were observed in the vicinity of the bonded interface after ageing at 250 °C for 1000 h.

Surface hardening of titanium by laser surface alloying using polyvinyl alcohol film

Laser surface alloying of commercial pure titanium pre-coated polyvinyl alcohol (PVA) film was carried out to improve wear resistance. The laser beam is absorbed at the surface of titanium substrate because the PVA film is transparent to the wavelength of a Yb-fiber laser. Thermal decomposition of the PVA occurred at the interface of the titanium substrate and PVA film. A crack free modified layer was obtained by the reaction of these thermal decomposition products and a titanium melt pool at the interface of the film and the substrate. A Ti(C,O) precipitation layer was formed on the surface layer of the laser alloyed zone. The laser alloyed zone exhibits superior wear resistance.Laser surface alloying of commercial pure titanium pre-coated polyvinyl alcohol (PVA) film was carried out to improve wear resistance. The laser beam is absorbed at the surface of titanium substrate because the PVA film is transparent to the wavelength of a Yb-fiber laser. Thermal decomposition of the PVA occurred at the interface of the titanium substrate and PVA film. A crack free modified layer was obtained by the reaction of these thermal decomposition products and a titanium melt pool at the interface of the film and the substrate. A Ti(C,O) precipitation layer was formed on the surface layer of the laser alloyed zone. The laser alloyed zone exhibits superior wear resistance.

Influence of Laser Heat Treatment on Fracture Strength of Ceramic Thin Film

In our previous study, it has been shown that improvement of the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness can be achieved by applying laser quenching. In the present research, in order to demonstrate further development of this method, the fracture strength of laser-irradiated ceramic thin films (CrAlN, TiAlN and CrN) was investigated by sphere indentation testing. To prevent heat-induced changes in the substrate hardness, a cemented carbide WC-Co rather than steel was used as substrate material. While the fracture strength of each film decreased significantly through furnace heat treatment, it remained almost unchanged in case of the laser irradiated films. Laser quenching has been shown to effectively reduce the fracture strength loss of the ceramic thin films in coated steels.