Impact of surface treatment on high frequency signal loss characteristics

In multi-layer printed circuit board (PCB) manufacturing, adhesion promoters are applied between the inner layer copper surface and prepreg resin to ensure superior bonding reliability. Traditional adhesion promoters used over the last decade include processes such as black oxide and oxide replacement processes. Both inner layer bonding enhancement processes apply a coating or chemically etch the copper surface to create certain amount of roughness and provide mechanical bonding. Most oxide replacement processes also cover the roughened surface with organic coatings that further improves the inner layer adhesion through chemical bonding as well.