Method for Elucidating the Structural Evolution of a Nanoscale Release Layer in Double Copper Foils Under Thermal...

Double ultrathin copper foils (DTH), widely used for producing conductive tracks in electronics, consist of an ultrathin copper functional foil (FF), a nanometric release layer (RL), and an ultrathin copper carrier foil (CF). Achieving stable release strength of the CF during DTH lamination remains a key challenge, largely due to limited knowledge about the structure of the RL. In this study, a comprehensive characterization methodology is proposed to investigate the physico-chemical structure of a chromium-based RL, both before and after thermal exposure at 230 °C. Peel-off testing, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and transmission electron microscopy (TEM) were employed. The main structural transformation identified is the oxidation of the RL at the FF-RL interface, resulting in the formation of a chromium oxide layer. This transformation may underlie the significant increase in release strength, which rises from 5.9 N/m before thermal exposure to 163 N/m afterward.