For signal circuits between the processor unit and connected components inside of computing systems, signal transmission acceleration is demanded. To reduce the transmission loss of substrates for semiconductor packages, the manufacturing process control must be considered, regarding factors such as the surface roughness of circuits and the dielectric loss tangent of the insulating resin.
An earlier study proposed conducting layer formation processes that maintain a smooth interface that provides good adhesion strength between liquid-crystal-polymer （LCP） film and the conducting layer. Atmospheric UV irradiation was used for electroless copper plating pretreatment, which creates a modified nanometer-scale layer including a hydrophilic rough surface on LCP film. This treatment can achieve both good adhesion strength and a smooth interface simultaneously between the conducting layer and the LCP film. Furthermore, the modified layer thickness increases with increasing UV irradiation, but the influence of the change of such modified layer states on the quality of high-speed signal transmission remains unclear.
This study investigated the influence of the modified layer on high-speed transmission characteristics. According to the results, no difference was found at each modified layer with various thicknesses in transmission characteristics （S parameter） up to 40 GHz. Results suggest that the modified layer has low electrical conductivity because of the discontinuous deposition of metal particles in the layer and suggest that almost no high-speed signals propagate to the modified layer.