Aqueous Sn(IV)sol containing Pd²⁺ was prepared from SnCl₄ and PdCl₂ as a pretreatment solution for use with electroless metal deposition. Under neutral conditions, the sol was stable for a long time without precipitation. Substrates of insulating materials such as glass and plastics were plated with Ni-P and Cu using electroless metal deposition after pretreatment with this sol instead of the sensitizer or catalyst. The gel film formed on the substrate from the sol consisted of tin compounds with dispersed Pd²⁺ and a rough surface. Before the electroless metal deposition, the substrate with the gel film was immersed in an aqueous sodium hypophosphite solution. Then Pd²⁺ in the gel film was reduced to metal Pd. After this process, the substrate was immersed in the Ni-P or Cu plating bath. Then the plating film was formed on the substrate. The Ni-P plating was bonded strongly to the substrate, but Cu plating was bonded weakly. It was exfoliated easily as the thickness increased. A part on the glass and alumina substrates was marked with the sol, similarly to ink of a pen, and was also plated selectively by the electroless metal deposition.

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We report a new patterning method to fabricate metal patterns on polyimide substrate with trench structure by combining imprint and electrochemical lithography. Using an ion-doped precursor polyimide films with trench structure prepared by imprint lithography, metal thin films can be successfully deposited at convex portion of trench structure through electrochemical and ion-exchange reactions, which resulted in the generation of metal patterns on polyimide films. The present process is quite simple, which can be performed without resist coating, exposure and etching. Therefore, the study provides effective methodology for fabrication of flexible printed circuit boards.

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