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.
ABS resin has been widely applied as a plating substrate for plastics in applications such as the parts of vehicles and electrical devices. Hexavalent chromium has been applied as an etchant of plating on ABS resin. However, it is required to eliminate hexavalent chromium from the pretreatment process, since the prohibition of these treatments was determined by the EU directive on the End of Life Vehicles (ELV) from July, 2007. Therefore, alternative etching without hexavalent chromium has been investigated by using ultra violet irradiation (UV) and titanium oxide (TiO2) as a photocatalyst. We already achieved adhesion with the strength of about 1.0kNm−1 between ABS resin and deposited metal without hexavalent chromic acid etching. In this study, the mechanism of adhesion strength improvement with photocatalysts has been investigated using ABS specimens and rubber related ABS resin. As the results, the 1,2-polybutadiene distributed in the AS matrix was preferentially reformed and induced hydrophilicity on the reformed surface with the remaining network structure by cross-linking. In addition, we found that the reformed layer was composed a few μm thick and the catalyst penetrated into 30-40nm from the surface. It was concluded that the good adhesion strength between the deposited metal and resin was derived from the nano-anchor effect by the deposition of metal from the inside of 30-40nm of reformed resin.
The effects of the bath composition and the plating conditions of gold plating using 5,5-dimethylhydantoin-gold complex on deposition were investigated. High current efficiency and bright films were obtained from the bath containing phosphate buffer in a wide range of current density in comparison with the citrate bath. In terms of the plating conditions, the plating temperature should be 60ºC to deposit with high current efficiency. The optimum pH value was 8.0 to increase the current efficiency to almost 100% in a wide range of current density. The optimum composition to obtain a bright yellow deposit film was 0.04mol/L of gold ion and 6 times that concentration of 5,5-dimethylhydantoin, even though the gold complex has four ligands in its molecular structure. Addition of thallium ion shifted the deposition potential to positive direction and increased current density, and accelerated depositing. Thallium played an important role to make deposited grains uniform, refine and dense. As a result, the appearances of the deposited films were bright yellow.