Statistical Analysis of Plating Variable Effects on the Electrical Conductivity of Electroless Copper Patterns on Paper

We describe a process for selective metallization of paper substrates bearing inkjet printed patterns of a commercial Pd/Sn colloidal catalyst ink plated using a commercial electroless Cu bath. The electrical conductivity of the Cu films is analyzed as a function of feature geometry (line dimensions (L) and spacing (S)), type of paper (P), age of the Pd/Sn patterns (A), plating time (T), and plating temperature (H) using a two-level factorial design. Conductivity is influenced predominantly by the P, T, and H factors, with lesser contributions attributed to pair-wise interactions among several of the variables studied. Increases in T and/or H enhance conductivity of the Cu films, whereas increases in P, corresponding to the use of rougher, more porous, paper substrates, yield Cu films exhibiting decreased conductivity. Our analysis leads to a model that predicts Cu film conductivity well over the ranges of variables examined, provides guidelines for identification of optimum conditions for plating highly conductive Cu films, and identifies areas for further process improvement.