Feature extraction for fillet profile of Pb-free solder and its application to inspection

An image processing technique for characteristic extraction of microsoldering fillet pattern is discussed from the viewpoint of the external feature inspection system. The visual inspection system for the shape of Pb-free solder fillet aims to decrease the influence of surface roughness. When the surface roughness affects the luminance distribution of a solder fillet profile, two methods are proposed; binarization and band summation. In experiments, the two kinds of Pb-free solder are adopted (Sn-Ag-Cu and Sn-Ag-Bi-In systems). Images of solder fillets are observed by CCD digital microscope by changing the incident light angle and image processing is carried out. It is found that binarization and band-summation are useful for the characteristic extraction. The two methods decrease the influence of surface roughness and make the characteristics clear.