Surface morphology and underlying mechanisms of HVLP copper foils with different additives

Hyper Very Low Profile (HVLP) copper foil has found extensive applications in high-speed and high-frequency circuit boards. The primary challenge lies in the additives, which are required to strike a balance between the mutually restrictive relationship of the low roughness and high peel strength of copper foil, ensuring low signal loss and high transmission stability. This research explores the impacts of 2,3-dimercapto-1-propanesulfonate (DMPS) and collagen concentrations on the surface morphology, roughness, and peel strength of HVLP copper foil. The findings reveal that both additives refine the grain structures and augment the peel strength: at a concentration of 10 mg/L, collagen reduces surface roughness to 0.91 μm and increases peel strength to 0.64 N/mm, while DMPS at 15 mg/L results in a roughness of 0.9 μm and a peel strength of 0.55 N/mm. When investigating the mechanism and nucleation behavior of DMSP and collagen during the electroplating-roughening process, it was found that DMSP promotes copper deposition by virtue of its thiol and sulfonate groups, while collagen inhibits copper deposition by its amino group (-NH₂). Significantly, neither additive modifies the three-dimensional instantaneous nucleation characteristics of copper ions during the roughening process. By establishing correlations among density-functional theory (DFT) calculations, UV–Vis absorption spectroscopy, and electrochemical testing, the adsorption-desorption behaviors of additives on the copper foil surface are investigated. The findings disclose that DMPS establishes robust covalent bonds with copper, allowing for extended adsorption and efficient grain refinement even at elevated concentrations. Conversely, collagen demonstrates relatively weak adsorption as a result of electrostatic interactions, restricting its grain-refining capacity to lower concentrations.