Pd nanocubes enclosed by {100} facets for activating electroless Cu deposition on liquid crystal polymer substrates with strong adhesion strength

Abstract

In this study, we investigate the catalytic performance of palladium (Pd) nanocatalysts with different surface atomic structures for activating electroless copper (Cu) deposition on liquid crystal polymer (LCP) substrates. These nanocatalysts include Pd nanocubes featuring {100} facets of square atomic arrangement as their predominant surface structure and Pd spherical nanoparticles characterized by random atomic arrangements, synthesized using an aqueous method. Our electrochemical measurements reveal that the induction time for the growth of Cu films is significantly shorter when utilizing Pd nanocubes compared to Pd nanospheres. This shorter induction time signifies a quicker initiation of Cu growth, primarily due to the presence of Pd {100} facets. Furthermore, we also develop a surface modification approach involving a crosslinking reaction that utilizes the highly branched polyethylenimine and linear polyvinylpyrrolidone on the Pd nanocubes. This method not only facilitates the adsorption of Pd nanocubes onto the LCP substrates but also achieves a robust peel adhesion strength (630 gf/cm) of the resulting Cu films, exceeding the industrial adhesion goal of 500 gf/cm. Moreover, in-depth synchrotron X-ray photoelectron spectroscopy analysis provides valuable insights into the depth-dependent chemical changes within the Cu films and proves the removal of Cu oxides after the acid treatment.