Yutaka Fujiwara

Composite plating of Sn–Ag alloys for Pb-free soldering

Abstract The existence of Ag nanoparticles in the Sn–Ag composite plating electrolytes was confirmed from the UV–vis spectra using the surface plasmon peak. Wetting speed of the molten Sn–Ag solder to the Sn–Ag alloy-plated specimen by the composite plating was higher than that to the Sn-plated one. Solder bond strength of the Sn–Ag alloy-plated specimen was not decreased after the exposure to the humid environment, and was increased by the Ni underlayer.

Electrodeposition of Cu-Zn alloys from glucoheptonate baths

Abstract Cu-Zn alloy deposition processes from glucoheptonate baths have been studied by analysing the composition of deposits, measuring the current density-potential curves and measuring the absorption spectra of the bath. Alloying interactions during codeposition were discussed on the basis of partial current density-potential curves of each component and absorption spectra of the bath. Baths adjusted to pH 4.5 and 10.0 were studied. From the pH 4.5 bath, only copper was deposited at current densities below 0.5 A dm−2. At current densities above 0.5 A dm−2, however, the zinc content of deposits increased rapidly with increasing current density. The current density-potential curve of the pH 4.5 alloy bath was almost an algebraic sum of those of the individual baths and did not exhibit any alloying interactions. In contrast, the compositions of deposits from the pH 10.0 bath were almost constant over a wide range of current density from 0.5 to 2.0 A dm−2, and zinc was codeposited even at low current densities below 0.2 A dm−2. The partial current density-potential curve of copper exhibited a less noble (negative) shift with an addition of Zn2+. This less noble shift is attributed to the formation of a more stable Cu2+ complex species, on the basis of the change in the absorption spectra. However, the partial current density-potential curve of zinc was essentially unchanged in the presence of Cu2+ except that the limiting current was increased. The difference in the limiting current was ascribed to the difference in the rate of mass transfer due to H2 evolution.

Ag Nanoparticle Catalyst for Electroless Cu Deposition and Promotion of Its Adsorption onto Epoxy Substrate

Ag nanoparticle catalysts were prepared to replace the Pd/Sn catalysts for electroless Cu plating. Suspensions of Ag nanoparticles, of which the average diameter was 4.6 nm, were obtained instantaneously by mixing a AgNO 3 solution and a Sn(II)-citrate complex solution at a nearly neutral pH. The composition and electron diffraction patterns of the nanoparticle as well as a high stability of the suspensions suggested that the nanoparticles have the core-shell structure composed of the metallic Ag core surrounded by the SnO 2 shell. The adsorption of Ag nanoparticles onto the epoxy substrates was promoted by conditioning the substrate with alkyltrimethylammonium chloride (ATA) having an alkyl tail longer than C16. A small amount of Sn was also adsorbed. The promotion of the Ag nanoparticle adsorption can be accounted for by the large amount of adsorbed surfactant due to the hydrophobic interaction with the substrate. The positively charged ATA adsorbates acted as an electrostatic glue to adsorb the negatively charged Ag nanoparticles. Electroless Cu deposition was started at the epoxy substrates catalyzed with Ag nanoparticles.

Adsorption Promotion of Ag Nanoparticle Using Cationic Surfactants and Polyelectrolytes for Electroless Cu Plating Catalysts

Ag nanoparticles were adsorbed onto epoxy and fluorine-doped tin oxide (FTO) glass substrates by dipping them into a Ag nanoparticle colloidal solution to catalyze the substrate for electroless Cu plating. Before the Ag nanoparticle adsorption, the substrates were conditioned with either a cationic surfactant, stearyltrimethylammonium chloride (STAC), or a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA), both having quaternary amine headgroups. The adsorbed Ag nanoparticles catalyzed the HCHO oxidation reaction, thereby allowing the electroless Cu deposition reaction to start. For both the epoxy and the FTO glass substrates, conditioning with the concentrated PDDA solution having a 100 × 10 -3 mol L -1 quaternary amine concentration was the most effective in producing the largest amounts of Ag nanoparticles to be adsorbed and in providing the fastest initial deposition rate of the electroless Cu plating. When the diluted conditioners were used, a comparison between the diluted STAC and PDDA showed that STAC was the more effective conditioner for the epoxy substrates, while PDDA was more effective for the FTO glass substrates. The effectiveness of STAC was attributed to the strong hydrophobic interaction with the epoxy substrate surface. However, the effectiveness of PDDA was attributed to the strong electrostatic interaction with the FTO glass surface.

Characterization of Cu-Zn alloy deposits from glucoheptonate baths

Abstract The surface morphology, phase structure and colour of Cu-Zn deposits from pH 10.0 glucoheptonate baths have been studied as a function of current density. Smooth and dense deposits were obtained at 2.0 A dm−2 or below, whereas granular deposits were obtained at higher current densities. The deposits obtained at current densities below 1.0 A dm−2 contained a significant quantity of “unalloyed” zinc inclusion in an ionic state. This unalloyed zinc inclusion caused an increase in the lattice “irregularities” and a decrease in the overall reflectance of deposits. The colour of the deposits was affected by both the features of the diffuse reflection spectra and the overall reflectance. Since the overall reflectance of the deposits obtained at current densities below 1.0 A dm−2 was lowered by the unalloyed zinc inclusion, these deposits did not have the characteristic appearance of yellow brass, whereas the features of the diffuse reflectance spectra were similar to those of a Cu70%-Zn30% brass. However, the deposits obtained at 1.0 A dm−2 or above, which did not contain the unalloyed zinc inclusion, exhibited the colour characteristic of yellow brass.

Martensitic Iron-Carbon-Boron Alloy Electrodeposit with Improved Mechanical Properties

Iron-carbon-boron (Fe-C-B) alloy films have been prepared by cathodic deposition from an aqueous solution containing iron(II) chloride hydrate, malic acid, and dimethylamineborane (DMAB). Effects of DMAB concentration on the structural and mechanical characteristics were investigated with an analysis of evolved gas, X-ray diffraction, X-ray photoelectron spectroscopy, and measurements of Vickers hardness number, fracture toughness, and wear volume. The Fe-C-B alloy films had a martensitic structure with body-centered tetragonal lattice with interstitial carbon and boron atoms, and showed high Vickers hardness number of around 700 by solid solution hardening, irrespective of DMAB concentration. The Fe-0.96 mol % C-0.64 mol % B alloy film showed excellent fracture toughness and decreased wear volume, compared with those for Fe-C alloy films. The improvement in fracture toughness and wear resistance was achieved by decreasing the content of oxygen impurity in the films.

Mechanisms of the Action of Histidine in the Deposition of Cu-Zn Alloys from Pyrophosphate Baths

Measurements of current density-potential (I-E) curves and AC impedance during electrodeposition of Cu-Zn alloys showed that Zn was codeposited only under conditions of diffusion-limited Cu deposition in the case of baths without histidine. This was confirmed by the characteristics of the I-E curves and by the characteristic Warburg impedance behavior. In the case of the baths containing histidine, on the other hand, Zn was codeposited under conditions where Cu deposition was not diffusion-controlled. I-E curves and double layer capacitances suggest that the adsorbed histidine suppressed Cu deposition and markedly increased the surface concentration of Cu+ adions. The adsorbed histidine suppressed Cu deposition even at negative potentials sufficient for Zn codeposition in the alloy baths Therefore, the rate of Cu deposition in the alloy baths was so small that it did not exceed the diffusion limited current of Cu2+ ion at negative potentials sufficient for Zn codeposition and this resulted in the smooth Cu-Zn alloy deposits. Data from AC impedance measurements suggest that an adsorbed intermediate plays an important role in alloy deposition processes from the baths containing histidine.