Daisuke Wakuda

Room-Temperature Sintering Process of Ag Nanoparticle Paste

Recently, the authors developed a novel room-temperature wiring method using Ag nanoparticle paste. In this paper, the sintering mechanism of the Ag nanoparticle paste was clarified through examination of the adsorption stability and the removal of the dispersant from the Ag nanoparticles. The Ag nanoparticles in the paste are protected by dodecylamine as a dispersant. This paste possesses substantially long shelf life and thermo stability at room temperature. When the printed line of the Ag nanoparticle paste is dipped in a methanol bath, methanol effectively dissolves and removes the dispersant from the nanoparticles. Ag nanoparticles are sintered within a short period. The sintering of Ag nanoparticles is not uniform. Some Ag nanoparticles quickly grow and form a network by sintering (necking). The others maintain a nanometer scale. Large Ag particles and an Ag skeleton continue to grow by absorbing very small nanoparticles. In addition, the use of ethanol and isopropanol as the treatment agent is shown for the first time.

Ag Nanoparticle Paste Synthesis for Room Temperature Bonding

Time-dependent sintering properties of an Ag nanoparticle paste for room temperature bonding were investigated. Ag nanoparticle paste with a small amount of dodecylamine dispersant can sinter at room temperature by the evaporation of toluene solvent. When the solvent evaporates, sintering with neck growth and the coalescence of particles is initiated within half an hour and the Ag grain continues to grow gradually for hours. Furthermore, a time-dependent change in the shear strength is demonstrated using a bonding test with Cu plates at room temperature. Bonding between the Ag paste and a Cu plate is favorable and fracturing occurs within the sintered Ag body. The strength of sintered Ag increases with sintering time due to neck growth and the coalescence of particles. The shear strength is more than 8 MPa after 6 h and 12 h of drying.

Ink-jet Printing of Nano Materials and Processes for Electronics Applications

Ag metallic particles from nano-scale to submicron-scale are combined with organic solvent to provide fine circuits and interconnection. Ag nanoparticle pastes have been successfully adopted to ink-jet wiring and the multilayered circuit layers in a SiP structure. Ink-jet printing with Ag nano particle pastes demonstrated the potentials of the new printed electronics technology. Lowering process temperature for Ag nanoparticle pastes finally reached room temperature wiring in air atmosphere.

Stretchable fine fiber with high conductivity fabricated by injection forming

Stretchable conductors are necessary to realize soft and rubbery electronics. A stretchable fine fiber with high conductivity was fabricated by a injection forming. The fiber is made of silicone series conductive adhesive containing Ag flake fillers. The fiber has uniform diameter without any substrate and has very long length by the injection forming method. The diameters can be controlled by changing the bore diameter of the injection needle. Furthermore, the fine fiber, 230 μm in diameter, maintains excellent conductivity under cyclic tensile stress. The conductivity is approximately 470 S/cm without tensile stress and maintains over 90 S/cm under cyclic tensile test which is stretched up to 10% strain. The result exhibits a great potential of the conductive fine fiber as a stretchable conductor.

Room temperature sintering mechanism of Ag nanoparticle paste

Recently, the authors have developed a novel room temperature wiring method with Ag nanoparticle paste. In the present work, the sintering mechanism of Ag nanoparticle paste was clarified through analysis of the adsorption stability and the removal of the dispersant from the Ag nanoparticles. The Ag nanoparticles in the paste are protected by dodecylamine as a dispersant. This paste possesses a substantially long shelf life. When a printed line of Ag nanoparticle paste is dipped in a methanol bath, the methanol dissolves the dispersant allowing it to be removed from the nanoparticles, effectively. Ag nanoparticles are sintered within a short period, although the sintering is not uniform. Some Ag nanoparticles grow quickly and form networks by sintering necking. The other nanoparticles remain on the nano-meter scale. Large Ag particles and Ag skeletons continue to grow by absorbing very small nanoparticles. In addition, the effect of ethanol and isopropanol as treatment agents is found.

Low-Temperature Wiring with Ag Nanoinks [Nanopackaging]

In this article, the mechanisms of these low-temperature curable inks are briefly reviewed. The dispersant removal by washing in alcohols for the nanoparticle ink and the decomposition behavior of the β-ketocarboxylate ink were clarified by thermal and microstructural analyses. The sintering and growth behaviors were also examined.

Novel Room Temperature Wiring Process of Ag Nanoparticle Paste

Ag nanoparticles protected by dodecylamine were formed into paste and successfully sintered at room temperature in air atmosphere. In order to remove the dodecylamine dispersant, Ag nanoparticles printed as lines on glass substrates were dipped in methanol for 10 s to 7200 s. As a result, the sintered wires possess excellent low resistivity, 7.3times10-7 Omegam after 7200 s dipping. From in-situ electrical resistance measurement, the electrical resistance of Ag nanoparticles becomes smaller as sintering time increases. Microstructural observation on room temperature sintering revealed that, as dipping time increases, Ag nanoparticles agglomerate to be coarsened, and connection among particles becomes clearer. Thus, a novel room temperature wiring method for Ag nanoparticles has been successfully developed in air atmosphere.

Room temperature sintering of ag nano-scale particles with drying of the solvent

We successfully developed a new Ag nanoparticle paste which can sinter at room temperature simply by drying solvent of the paste. Very small amount of alkylamine was incorporated into the Ag nanoparticles paste to protect the nanoparticles. By drying at room temperature, Ag nanoparticles are sintered resulting in low resistivity of 4.9times10-6 Omegam. Necking and coalescence of Ag nanoparticles occur only for a few minutes after drying the solvent. At room temperature, grain of Ag nanoparticles grows gradually for a few days. Heat treatment of the paste can reduce the resistivity effectively. The Ag nanoparticle paste was printed on glass substrates and was heated at 50degC, 100degC and 150degC for various times, respectively. Sintering of nanoparticles was promoted by this heat-treatment. It was observed that Ag nanoparticles grow by absorbing smaller nanoparticles during sintering. By this sintering mechanism, nanoparticles can grow much bigger than uniform sintering mechanism. Since the new paste can be sintered even at room temperature without heat treatment, the paste can expand the versatility of its applications for electronics wiring.

Properties of Ag nanoparticle paste for room temperature bonding

Time-dependent sintering properties of Ag nanoparticle paste for room temperature bonding were investigated. The Ag nanoparticle paste with very small amount of alkylamine dispersant can sinter at room temperature by drying toluene solvent. When the solvent evaporates, sintering with necking growth and coalescence of particles is provoked at least within half an hour and the Ag grain continues to grow gradually for hours. Time-dependent alteration of the shear strength is demonstrated through bonding test at room temperature using Cu plates. Bonding between Ag paste and Cu plate is favorable and breaking occurs inside sintered Ag body. The strength of Ag increases with the progress of sintering at room temperature. The shear strength reaches over 8 MPa after 6 and 12 h drying process.