Electroless palladium plating solution

TABLE 25.2 Composition of a Typical Electroless Palladium Plating Solution... 

The ideal electroless solution deposits metal only on an immersed article, never as a film on the sides of the tank or as a fine powder. Room temperature electroless nickel baths closely approach this ideal electroless copper plating is beginning to approach this stabiHty when carefully controUed. Any metal that can be electroplated can theoretically also be deposited by electroless plating. Only a few metals, ie, nickel, copper, gold, palladium, and silver, are used on any significant commercial scale. 

The metal complexes are activated by reduction in hydrogen and then immersed into an electroless plating solution. The process has been using palladium(II)-hexafluoroacetylacetonate. The palladium complex can be activated in the absence of hydrogen. This reduces the risks of explosion in a technical process. 

With a conventional desktop ink-jet printer an aqueous palladium(II) solution is sprayed onto a surface-treated PI film. The palladium(II) is then reduced by treatment with sodium borohydride (NaBH ). Finally, a copper layer is deposited by electroless copper plating. The surface treatment of the PI, in order to accept the palladium(II) consists either of oxidation with alkaline KMNO4 at 80°C for 60 min or simply with NaOH at room temperature for 72 h. The latter treatment gives better results. Structures with dimensions down to 100 jum with good copper adhesion can be built. 

It was also reported that copper could be selectively formed on the pattern PPy electrode by electroless plating [124]. The PPy pattern, which was formed by the photolithographic patterning technique, was first immersed in acidic PdC solution, leading to selective adsorption of the palladium metal particles on the PPy pattern. The PPy pattern coated with palladium metal was then immersed in copper electroless plating solution, producing the selective copper-on-PPy pattern (Figure 8.78). 

A method used to ensure the complete filling of vias is electroless plating of nickel. Electroless plating is a process to plate metal without electrical current involved. As a result, it eliminates the seed layer needed in electroplating. To plate nickel on copper, the copper surface must first be activated in a palladium chloride solution. This activation treatment allows palladium to bond to copper at certain sites so that the subsequent nickel plating can nucleate. 

Combination with osmosis can improve the plating procedure and repair defects as described by Li et al. [408]. It was performed by feeding sodium chloride through the tube side of the membrane, which allowed the water of the electroless plating solution to diffuse through the membrane defects and increase the palladium concentration locally, and healed the defects. 

When using electroless metal plating, a tin(II) solution is applied to the liquid crystal polyester with an idea of using it as a treated liquid crystal polymer substrate. The application of a palladium (II)... 

Individual deposition of the Pd and Ag was also undertaken using an electroless method. By plating each metal individually the process can be controlled to obtain a range of different metal ratios. Again, the compositions of the plating solutions and the deposition methodology have been detailed elsewhere (Brown et al., 2010 Wu et al., 2010b). The components of the solutions were the same as the co-deposition solutions except for palladium where a chloride salt was used in place of the nitrate. Membranes that were coated with Pd only were used to compare with the bimetallic sample. Samples were also plated with Pd then sequentially with Ag as comparisons for the co-deposited samples. 

Acceleration modifies the surface layer of palladium nuclei, and stannous and stannic hydrous oxides and oxychlorides. Any acid or alkaline solution in which excess tin is appreciably soluble and catalytic palladium nuclei become exposed may be used. The activation or acceleration step is needed to remove excess tin from the catalyzed surface, which would inhibit electroless plating. This step also exposes the active palladium sites and removes loose palladium that can destabilize the bath. Accelerators can be any acidic or alkaline solution that solubilizes excess tin. 

Electroless plating — An autocatalytic process of metal deposition on a substrate by reduction of metal ions from solution without using an external source of electrons. It is promoted by specific reductants, namely formaldehyde, sodium hypophosphide, sodium boro-hydride, dialkylamine borane, and hydrazine. Electroless deposition has been used to produce different metal (e.g., nickel, cobalt, copper, gold, platinum, palladium, silver) and alloy coatings. It can be applied to any type of substrate including non-conductors. Some substrates are intrinsic catalytic for the electroless deposition other can be catalyzed usually by sensibilization followed by Pd nucleation also, in some non-catalytic metallic substrates the electroless process can be induced by an initial application of an appropriate potential pulse. In practical terms, the evaluation of the catalytic activity of a substrate for the electroless deposition of a given metal is... 

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