Defect Detection of Gold-Plated Surfaces on PCBs Using Entropy Measures

Connector fingers are metallic pads at the edge of a printed circuit board (PCB). They must be inspected after plating to ensure that an adequate coating of gold has been applied. The gold-plated surface is not uniform, but produces a homogeneous texture in the image. In this paper, we propose two entropy measures of chromatic and structural regularities for the automatic defect inspection of gold-plated fingers (edge connectors) on PCBs. One entropy measure uses two chromatic features derived from the CIELUV colour space to detect colour anomalies, and the other measure uses edge angles to detect structural defects on gold-plated surfaces. Experimental results have shown that the proposed method is effective and efficient for detecting various defects such as pinholes, copper exposure, and nicks and roughness on gold-plated surfaces.