The heat resistance of gold or silver that was plated on SUS 430 stainless steel with various underlayers was examined by evaluating the solderability and the wire bonderability of the plated surface subjected to aging in air at 460°C. It was found that heat resistance improved if suitable underlayers were provided. In terms of providing heat resistance as an intermediate layer on the Ni activation layer, Ag or Ni-Co was preferred for Au plating, while Pd-Ni, Ni-P or Au was preferred for Ag plating.
The Ni-Co activation layer without an intermediate layer was excellent, especially for Au plating. Surface analysis by X-ray photoelectron spectroscopy and Auger electron spectroscopy suggest that a thin 0.02μm of Ni-Co activation layer is more effective than a one of Ni as a diffusion barrier layer against Fe-diffusion. The oxidation of the underlayer in the Ag-plated sample was confirmed.

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A new type of electroless gold plating bath has been developed using tetracyanoaurate (III). The trivalent gold bath showd excellent stability even in the absence of KCN because the tetracyanoaurate (III) was reduced to monovalence by BH₄^- liberating the cyanide ions. The deposition rate of gold was increased by a factor of 8 to 9 with the addition of trace amounts of PbCl₂ or TlCl. This enhancement of electroless gold deposition can be explained by a model for the catalytic action of adsorbed heavy metal atoms proposed by McIntyre. The adsorbed foreign atoms seemed to influence the crystallographic orientation of the gold deposits. In the initial stage of the deposition of gold on the base metal, displacement and autocatalytic reactions may occur in parallel, but the displacement reaction diminished and the deposition rate decreased significantly when the substrate was completely covered with gold film. The autocatalytic deposition of gold is enhanced by the forced convection of the plating solution, so that the rate of deposition of gold was increased markably by stirring the solution. The stirring also enhanced the incorporation of oxygen into the solution, and this improved the stability of the electroless gold plating bath. In contrast, it was confirmed that excessive agitation of air inhibited the deposition of gold. The stability of the electroless gold plating bath was markedly reduced by introducing a trace amount of nickel ion. It is, therefore, essential in the heavy deposition of electroless gold for nickel substrates to be pretreated by displacement gold plating.

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The bipolar couple-electrode method, in which the potential difference between a pair tiny electrodes placed on the cathode surface is measured, was investigated as a means of determining current density distribution in plating baths of Cu, Ni, Zn and Cr. The potential difference showed good linearity with the current density calculated from the thickness of the deposits by using two electrodes made of the same metal as the deposits in the solution. No linearity was found in systems which used platinum electrodes.

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Pure aluminum specimens were covered with hydrous oxide films by immersion in boiling distilled water and then anodized galvanostatically in a neutral borate solution at different temperatures to form composite oxide films. The formation behavior of the hydrous oxide and composite oxide films was examined by gravimetry, XPS, chemical analysis and electron microscopy.
It was found that the hydrous oxide films consist of two layers; a fibrous outer layer (thickness δ_h.o) and a dense inner layer (δ_h.i). The thickness of the outer layer, δ_h.o, increased rapidly with time to reach a steady value of ca. 0.3μm but that of the inner layer, δ_h.i, continued to increase gradually after a rapid increase. The hydrous oxide had a chemical composition of Al₂O₃⋅2.7H₂O and a density of ca. 2.3g/cm³, both of which did not change with immersion time.
The composite oxide films consisted of two layers; an outer crystalline oxide layer (thickness δ_o) and an inner amorphous oxide layer (δ_i). During anodizing, δ_h.i decreased linearly, and the total thickness, δ_o+δ_i, increased linearly with t_a. The δ_h.i vs. t_a and δ_o+δ_i vs. t_a curves were independent of anodizing temperature, T_a. The outer layer thickness, δ_o, increased with t_a, at a rate increasing with t_a. This behavior was pronounced at higher T_a. The rate of increase in δ_i decreased with t_a, and this also became more pronounced at higher T_a. The electric field supported by δ_i+δ_o was found to increase with t_a from 7.7 to 10.3×10⁶V/cm. This is explained as being due to the formation of the crystalline oxide layer capable of supporting higher electrical field and to the increase in δ_o/(δ_i+δ_o).

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