Copper induced direct CO2 laser drilling blind hole with the aid of brown oxidation for PCB CCL

CO2 laser drilling of blind hole is the necessary process to obtain high-density connection between different conductive layers for printed circuit board (PCB). A copper induced direct CO2 laser drilling blind hole was proposed to simplify the working process and enhance hole alignment with the aid of copper brown oxidation. Brown oxidized copper holding a roughened surface to extend the laser route in its surface and copper oxidation of CuO with a high laser absorptivity were investigated by scanning electron microscopy (SEM), 3D microscope, X-ray photoelectron spectroscopy (XPS), infrared thermal camera, and metallographic microscopy. It therefore breaks the limitation of pure copper stripped by CO2 laser. Example for CCL of top copper with thickness of 18 μm and dielectric resin with thickness of 80 μm realized the qualified Φ100 μm blind hole under 45 mL/L brown oxidation solution for 90 s.