Microscopic Study of a Ligand Induced Electroless Plating Process onto Polymers

The ligand induced electroless plating (LIEP) process was recently developed and thoroughly demonstrated with one of the most used polymers for plating processes acrylonitrile-butadiene-styrene (ABS). This generic process is based, thanks to the use of diazonium-salts as precursors on the covalent grafting of a thin layer of poly(acrylic acid) (PAA) acting as ligand for metallic salts onto pristine polymer surfaces. This strategy takes advantage of the PAA ion exchange properties. Indeed, carboxylated groups contained in PAA allow one to complex copper ions which are eventually reduced and used as catalysts of the metallic deposition. Essentially based on ABS, ABS-PC (ABS-polycarbonate) and PA (polyamide) substrates, the present paper focuses on the role of the polymer substrate and the relationships between the macroscopic properties and microscopic characterizations such as infrared (IR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The adhesion strength of the metal layers deposited via that LIEP process with the bulk polymer substrates was successfully compared with the adhesion of similar copper films deposited by the usual process based on chromic acid etching and palladium based seed layer by measuring the T-peel adhesion strength, and by carrying out the common industrial scotch tape test. Lastly, the electrical properties of the deposited layer were studied thanks to a four-point probe and scanning tunneling microscopy (STM) measurements.