Interfacial impedance method was applied to evaluate the interface stability of solder joints. Results showed that the surface treatment on rolled copper strongly influenced the solder joint interface structure. The composition and interfacial impedance between rolled copper and solder were also influenced by the surface treatment of the copper. Especially, a correlation was found between the surface treatment and time dependence of the interfacial impedance value. The admittance spectra of interfacial impedance between as-rolled copper and solder showed strain from the semicircular shape, although the plasma ashed copper or thermally oxidized copper showed no such strain over time. The strain probably represents solder joint instability. The interfacial impedance method can be useful for evaluation of the solid metal interface, not only the interface between the liquid and solid.

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Bright nitriding of SKD61 tool steel was conducted in electron-beam-excited plasma using neutral nitrogen species. In this study, particular attention was devoted to the effects of nitrogen species on the surface properties of treated samples. Interaction of the neutral species and the surface was obtained by repelling the positive ions. Thereby, the sample is controlled to have greater positive plasma potential. This paper describes nitriding with neutral nitrogen species and nitrogen ion, respectively designated as neutral and ion nitriding. The hardness, surface properties, and brilliance of the neutral nitrided samples were compared with those of samples treated by ion nitriding. The surface hardness of neutral and ion nitrided samples were more than twice those of the untreated samples. However, the ion-nitrided sample had markedly higher surface roughness with a thick compound layer. The surface of the neutral nitrided sample had a mirror finish resembling that of the untreated sample. These results show that neutral nitriding can be important for nitriding high-precision mechanical parts.

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Electroforming related to this study was conducted by varying conditions singly, such as the concentration of sodium lauryl sulfate (SLS) in the nickel sulfamate bath, the current density, or the plate thickness. The warp mechanism of electroformed plate was investigated by measuring the internal stress, the orientation using X-ray diffraction, and Vickers hardness. Results show that lowering the current density or the concentration of SLS, or increasing the electroformed plate thickness can minimize warping of the electroformed plate. When SLS was added to the nickel sulfamate bath, the surface tension decreased remarkably up to 0.01 g/dm³ (threshold, i.e., critical micelle concentration, cmc). Then it decreased only to a slight degree at concentrations higher than 0.01 g/dm³. On the other hand, the warp, Vickers hardness, and the orientation index of {220} of the electroformed plates increased remarkably up to 0.01 g/dm³. It scarcely increased at concentrations higher than 0.01 g/dm³. Therefore, it became apparent that structural changes of crystallites occurred in 0.01 g/dm³ (cmc) of the concentration of SLS as a border. Based on results of combustion analysis for the electroformed plates, atoms consisting of a single SLS, except the micelle, were incorporated in the crystallites, thereafter affecting various mechanical properties.

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Analysis of Cu(I) in copper sulfate electroplating solution was conducted by absorption of a chelate of Cu(I) with bathocuproinedisulfonic acid, disodium salt (BCS). Although the absorption of new copper sulfate electroplating solutions was negligible, the absorption of operating solutions was clear. The difference of new solutions and operating solutions was also verified using an electrochemical method for detection of Cu(I). We concluded that the Cu(I) ions are measurable using this chelate reagent. The absorption increased quickly in a few minutes after mixing with the chelate reagent and subsequently continued to increase slowly. To clarify this phenomenon, the organic compounds in the plating solutions were analyzed and Cu(I)-PEG (polyethylene glycol) complexes with different chain lengths were detected using MALDI-MS. Results show that Cu(I) ions exist in the plating solutions not only as small complexes with small organic compounds but also as large complexes with PEG. Small complexes of Cu(I) can react quickly with BCS and cause the rapid increase of the absorption in a few minutes after mixing. Cu(I)-PEG complexes prevent the chelating reaction of Cu(I) with BCS by steric hindrance of PEG, which explains the subsequent slow increase of the absorption. Using this chelate method, we monitored quantities of Cu(I) in copper sulfate electroplating production lines, detected the variation of Cu(I) quantities, and found the increase during the resting state of the lines.

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