SOLDER PASTE INSPECTION BY SPECIAL LED LIGHTING FOR SMT MANUFACTURING OF PRINTED CIRCUIT BOARDS

Solder paste screen printing is the first and very critical stage of manufacturing in an SMT production line of printed circuit boards (PCBs). Many defects can be eliminated with proper paste inspection. Conventional inspection method would depend on an image acquired from a camera mounted from the top. This 2D inspection of solder paste based on images is fast but is limited to defect such as bridge or no solder. Defects related to the volume of the printed solder paste or unevenness of the paste cannot be treated from a top image. The proposed method of this paper would involve the use of special directional LED lighting from the side. A sequence of four images is acquired and image processing is carried out for the edge information of the printed solder paste. The proposed method can handle other types of defects that cannot be treated by conventional top lighting images.