Plating fog is often observed on the substrate when printed circuit boards are produced by photoadditive electroless plating. Thus unwanted metal is deposited on the unpatterned region, where there should be no plating activity, when a substrate with a catalytic plating pattern is immersed in plating solution. This metal deposition phenomenon observed on roughened resin substrates is examined in terms of (i) the physical state of substrate surface, (ii) the chemical state of substrate surface and (iii) the exposure and activation process.