Printed circuit boards (PCBs) have required higher density and more integration, since many electronic devices have become downsized and multi-functionalized. For higher density, PCBs should have enough adhesion between the substrate and the conductive layer, maintaining a smooth surface for finer patterning. Newly developed surface modifications using TiO2 powder as a photocatalyst and UV irradiation has achieved excellent adhesion strength of 1.15kN/m without increasing the roughness of the substrate. This paper reported a mechanism of excellent adhesion and fabrication of fine patterns on PCBs with lines and spaces of 10μm/10μm. A modified surface of PCBs in a depth of 30-50nm was created by the irradiation of UV light under the presence of TiO2 as a photocatalyst. Moreover, it is confirmed that palladium (Pd) and tin (Sn) as the catalysts penetrated into the surface modified layer, and electroless copper (Cu) plating was initiated at the bottom of this layer. Therefore, it is suggested that the excellent adhesion was originated from the nano-level anchor effect by the formation of a co-existed layer between the PCBs and the deposited copper. Accordingly, fine patterns with line and space of 10μm/10μm were actually fabricated by using the new surface modification in place of etching and followed by conventional pre-treatment. By introducing the new surface modification, fine line circuits were formed without roughening the surface of the PCB, and no extraneous deposition was observed between the lines in contrast to the conventional method. It is concluded that this new method has an intrinsic advantage for the formation of finer patterned PCBs.
