Electroless copper deposition has been widely used in the manufacture of printed circuit boards with plated through-holes. Intrinsic contaminants originating from the mixed PdCl2/SnCl2 catalyst may be present in the plating bath. In this study, the effects of Pd2+ and Sn4+ ions on the rate of copper deposition and the mechanical properties of the copper films were investigated. An excess of PdCl2 makes the bath unstable, leading to a reduction in the apparent deposition rate, but the appropriate amount of Pd2+ ions not only decreases lattice strain but also improves the elongation of the copper films. In the presence of both Pd2+ and Sn4+ ions, internal stress in the copper films was reduced, and the elongation of copper films was significantly improved by synergism between the two different ion species. Electrochemical analysis of electroless copper deposition elucidates that the presence of Pd2+ and Sn4+ ions not only decreases the amount of the methylene glycol anion adsorbed on the electrode surface but also prevents the inclusion of hydrogen into electroless copper films.
Electroless nickel plating on aluminum substrates utilizing a nickel displacement process has been investigated. A zincate process is in general use before electroless nickel plating on aluminum substrates. It has been confirmed, however, that the film of deposited nickel exhibits higher adhesion strength if a nickel displacement process is used instead of the zincate process, and that adhesion strength depends on the rate of the displacement reaction, which can be controlled by changing the kind of complexing agent and the plating conditions in the displacement bath. In addition, fine bumps are required in the TAB or flip chip bonding methods and straight-walled bumps approximately 20μm wide and 15μm high can be formed by electroless nickel deposition utilizing the displacement process.
The electrical contact properties of electroless deposits of Ni-Cu-P alloy containing metallic copper of low electrical resistance, and of Ni-Sn-P alloy containing metallic tin, which had aroused interest in the electrical resistance of its oxides, were investigated. The wear resistance of the deposits was also investigated using reed awitches.
Mechanical rubbing of polyimide (PI) films is used to homogeneously align liquid crystal molecules on the surface. The chemical structure of aromatic PI surfaces subjected to rubbing has been analyzed by X-ray photoelectron spectroscopy, and the frictional charging and surface states of the PI films have also been investigated by measurements of surface potential (SP) and photoelectric emission (PE). Six kinds of PI films were prepared by reacting two diamines containing CH3 and CF3 functional groups with three tetracarboxylic dianhydrides. Rubbing of the films caused the O content to increase, while the N and F contents decreased. The fraction of the two oxygen components (-O- and C=O) of the films was changed by the rubbing. The films with CF3 groups exhibited much more negative charging (negative SP) than those with CH3 groups. It is suggested that the order of the charging of the films with CF3 and CH3 groups closely depends on the ratio by which the F and N elements, respectively, were reduced by the rubbing. Both with and without rubbing, the films with CH2 groups gave a considerably larger PE level than those with CF3 groups. This suggests that the electron trap levels responsible for the negative charging in the latter films make virtually no contribution to PE.
Control of the crystal orientation of electroless-deposited CoNiReP/CoP double-layered (DL) film for perpendicular magnetic recording media was attempted in order to optimize the magnetic properties. The CoP single-layered (SL) film consists of c-axis longitudinally oriented hcp structure while the CoNiReP SL one consists of c-axis perpendicularly oriented hcp structure. The CoNiReP layer deposited directly onto the CoP layer grew epitaxially, however, resulting in deteriorated properties as a perpendicular recording medium. On the other hand, when the surface of the CoP layer was treated using a SnCl2/PdCl2 catalyzing process prior to CoNiReP deposition, the epitaxial growth was disturbed and a c-axis perpendicularly oriented hcp structure was formed, resulting in properties comparable to those of the CoNiReP SL film. It is suggested that such precise controllability of the crystal orientation (i.e., the magnetic properties) of the film will be very advantageous for the fabrication of multilayered devices with higher functional properties.
A new bromine-free solution consisting of colloidal silica, citric acid and hydrogen peroxide has been developed for the mirror-polishing of InP and InSb wafers. This paper describes the effects of the polishing pressure and pH value of the solution on surface quality. Use of the optimized solution reduced the surface roughness of the polished wafers to 15Å for InP and 30Å for InSb. There was no damage to the polished surfaces under the optimum conditions.
Tantalum oxide (Ta2O5) thin films were sputtered onto MOS structural diodes and MOS-FETs with Si wafer substrates by a number of methods, including RF reactive sputtering, RF reactive magnetron sputtering and ion beam sputtering, and the plasma-induced damage was evaluated by means of changes in flat-band potential in measurement of the capacitance-voltage (C-V) in the case of MOS diodes, and the change in transistor parameters in the case of MOS-FETs. (1) The most severe plasma-induced MOS damage occurred under ordinary RF sputtering conditions. The use of ion beam sputtering reduced the plasma-induced MOS damage compared from that in reactive RF sputtering. (2) The as-sputtered Ta2O5 films were all in amorphous structure with crystallization temperatures of about 730°C.
Films with higher saturation magnetization are desired for improving the recording density of thin film magnetic recording heads. A study has been conducted on the effects of the magnetic properties of organic additives on the plating baths from which cobalt-iron films with a Bs greater than 1.5T were obtained. Film with a coercivity lower than 1 Oe was obtained from a bath containing 0.02mL/L of 2-propyn-1-ol (PPO) and 60g/L of naphthalene-1, 3, 6-trisulfonic trisodiumsalt (NTS). Internal stress decreased with the amount of NTS, and the sulfur content of the film correlated with internal stress and with coercivity. The effects of heat treatment on the soft magnetic properties of the films were also investigated. The anisotropic field Hk can be changed by the repeated heat treatment in a magnetic field directed along the hard axis. Films with a small anisitropy field (Hk<5 Oe) showed high permeability (μ>2000). Under this type of heat treatment, Hk was affected by direction of magnetic fields at three stages: (a) during deposition, (b) during initial heat treatment, and (c) during final heat treatment.
The effect of various additives on the electrodeposition of copper foil was investigated in order to produce copper foil for use on printed circuit boards. In the initial process of copper deposition, it was possible to evaluate the action mechanism of gelatin precisely using photoacoustic spectroscopy (PAS). At extremely low thiourea concentrations, the surface morphology of the copper deposits showed dendrites unaccompanied by degradation of thiourea complex. The presence of these additives also resulted in the copper deposits showing a (111) preferential orientation, which has excellent etching characteristics for copper foil for use on printed circuit boards.
Indium monoselenide (InSe) is a layer structure semiconductor, with interlayer bonding by van der Waals' force, and because of the small number of dangling bonds at layer cleavage planes. InSe is well suited to forming junction systems with different substances. Polyvinylidene-fluoride (PVDF) and vinylidene fluoride-tetrafluoroethylene copolymer [P(VDF·TFE)=β PVDF type], on the other hand, readily form ferroelectric thin films. The PVDF polarized in to flying clusters in the vacuum vapor deposition atmosphere, so that the probability of sticking differs depending on the kind of substrate. InSe single crystals prepared by the synthesis solute diffusion (SSD) method had n-type electric conduction, electric conductivity σ of 3.1×10-1S/cm, Hall mobillity μ of 200cm2/v·s, and a band gap of 1.1eV at room temperature. Thin films of PVDF were formed by vacuum vapor deposition on the InSe cleavage layer planes. The equivalent circuit of the PVDF/InSe junction system obtained was a parallel circuit consisting of a resistance and a condenser, and differences were observed in the capacity-voltage curve for the junction system due to polarization, according to whether the PVDF was α or β. The change in this curve becomes greater as the dielectric constant of the PVDF increases. In the PVDF/InSe junction system, a variation of the space-charge density were dependent on polarization voltage and molecule structure of the PVDF.
In studies of Co electrocrystallized on Pt (111) surfaces under electrode potential control, reflection electron microscopy (REM) has revealed a heteroepitaxial and simultaneous multinuclear multilayer growth in the range from 3 or 4 up to about 10 atomic layers. A Co/Pt multilayered structure, as evidenced by the presence of X-ray superlattice diffraction peaks, has been prepared by electrocrystallization, which depends upon the amount of polarization during Co electrocrystallization. The magnetic properties of the electrodeposited Co/Pt multilayers, which tend to exhibit in-plane anisotropy, depend upon the layered structure.
The correlation between the microstructure and the soft magnetic properties of electroless-deposited CoB films was investigated. Adding aminoacetic acid in various concentration to the CoB bath made it possible to control the coercivity of the films without changing their other magnetic properties such as saturation magnetization and squareness. Coercivity was also found to depend on film thickness. TEM observation demonstrated that the difference in coercivity is due to the microstructure, mostly the grain size in the initial deposition region. Films with low coercivity consisted of fine grains (about 10∼20nm in diameter), while those with high coercivity consisted of large grains (about 100nm in diameter). Although no clear differences in microstructure could be observed at the optimum film thickness of 0.5μm, it is suggested that films with low coercivity consist of fine grains from the initial deposition stage.
The initial growth stage of etch pits in high-purity aluminum was examined in 3.6%HCl solution by applying galvanostatic pulse of 0.5A/cm2 for 10-2s, with the off time between pulses varied from 10-3 to 1s. The morphology of the etched aluminum surface was found to depend markedly on the off time. At off time longer than 0.1s, hemispherical pits composed of large numbers of minute hemispherical pits, were formed on the etched surfaces. These small pits were covered with a non-uniform fibrillar layer of etching products, which are thought to be deposits of aluminum hydroxide. The effect of the off time on pit morphology was examined further by measurement of potential changes and polarization curves. At longer off times, the electrode potential of the specimens shifted to the repassivation potential. An overshoot always occurred in the galvanostatic potential transients at application of the current pulses, suggesting the formation of an anodic film. This was supported by measurements of the polarization curves.
Ru II (NH3)6Cl2 was dissolved in aerated distilled water to a concentration of 3×10-2mol/L, and the solution was then aged in contact with the atmosphere for 24 hours at 25°C. ITO glass substrates were then immersed in the aged solution for 72 hours, taken out, and dried. A uniform, blue-colored thin film was obtained. Electrochemical measurements were performed in 0.01mol/L H2SO4 electrolyte, using SCE as the reference electrode. The surface morphology of the ruthenium compound film showed many granular deposits, indicating a relatively large surface area. TEM and electron diffraction observations showed that the film was composed of grains of various sizes and was amorphous. The electrochromic bohavior showed reversible color change of 104 times, being almost colorless at an applied potential of +100mV vs SCE and blue at +900mV. In the cyclic voltammograms, two redox peaks were observed, corresponding to the coloration and bleaching respectively. The main coloration reaction occurred at +300mV, and bleaching occurred at +230mV. However, the relation between the injected charge and the optical density was not proportional, because there was a two-step coloration/bleaching reaction. The coloration efficiency calculated from these data was ca. 80cm2/C, which is comparable to that of WO3.
The effects of phosphorus codeposition on the morphology, internal stress and corrosion resistance of electroplated Pd-Ni-P alloy films were investigated. The alloy films obtained were shown to have nearly the same composition ratio as the molar ratio of Pd2+/Ni2+ in the bath. The phosphorus content of the alloy films increased with an increase in phosphonic acid concentration. Phosphorus codeposition was found to decrease tensile stress and suppress the formation of cracks, resulting in an increase in corrosion resistance.
When palladium-plated lead frames are used for ICs, solder bridging and silver migration do not occur. In this report, palladium plated lead frames were studied for such characteristics as solderability and wire-bondability after thermal treatment to simulate IC assembly. Their corrosion resistance was also studied. The following results were obtained. (1) Solderability of 0.05μm-thick palladium plating was virtually as good as that of 5μm-thick Sn 90wt% solder plating. (2) Palladium-plated lead frames had excellent solderability and gold wire-bondability even after heating at 300°C for about 1min. (3) The corrosion resistance of the palladium plating on copper alloy substrates was relatively good, but on ferro-alloy substrates, considerable pitting corrosion occured due to the difference in natural electrode potential between the palladium and the substrate.
The higherdensities and fine pitch patters of recent printed circuit boards market, it is troublesome to prepare an adequate solder layer using such conventional mounting technologies as hot air leveling and solder paste treatment. Thus a new displacement-type plating process have been developed apply a thick layer of Pb-Sn alloy on PCBs having fine pitch patterns, as thicknesses of 10μm have been deposited within ca. 13 minutes The new deposit was resistant to oxidation, and its solderability after heattreatment at 200°C for 10 minutes was superior to that of layers made by conventional technique.
A new potentio-galvanostat has been developed to study the anodic oxidation behavior of Al at potentials of -1∼200V. Cyclic voltammograms obtained in adipate solution showed several current peaks at higher anodic potentials than 30V vs. Ag/AgCl, and these are thought to be significant in anodic film formation.
The effects of the addition to organic acid baths for displacement solder plating of surfactants used as leveling agents and oxidation inhibitors used as bath stabilizers were investigated. The most effective surfactants were found to be isolated systems of Triton X-100 and laurylpyridinium chloride for the hydrophile-lipophile balance of the surfactants and a mixture of laurylamine and Triton X-100 for a decrease in foaming. o-Aminophenol and o-phenylenediamine, which are conjugated-system compounds of 1, 2-substituted benzenes and have moderate reducing power, showed good properties as oxidation inhibitors.
The solderability and electric contact resistance of chemically deposited Pd-P alloy using phosphite as reducing agent was investigated. From the experimental results, it is suggested that electroless palladium plating can be utilized as alternative both to the gold plating on electrical contacts and to soldering or preflux coating to retain good solderability.