NEW OPTICAL MEASURING SYSTEM FOR SOLDER JOINT INSPECTION

Due to specularity and complex 3D geometry, the visual inspection of s older joints has been regarded as one of the most difficult tasks and thus has not guaranteed accurate inspection results. This paper deals with art optical sensing system designed to inspect solder joints auto matically. Taking into account a specular characteristic, a new optica l solder joint inspection system is proposed to obtain the external pr ofile of solder joints accurately. A laser scanning unit scans the are a of solder joint and observes the angle of the reflected beam. To rea lize this measuring principle, the system is so composed that a galvan ometer steers the direction of laser beam to a point to be measured, a mirror unit (a parabolic and a conic mirror) gathers the specular com ponents of the reflected beam toward its center and a beam-receiving u nit positioned along the mirror unit's center line detects the reflect ed beam. To classify the defects of solder joint, a statistical patter n recognition method is utilized. To verify the validity of the develo ped system, a series of experiments was performed for SOPs and QFPs in insufficient, normal and excess soldering condition. Based upon obser vation of the experimental results, the proposed system is found to sh ow good performance for inspection of solder joint defects. Copyright (C) 1996 Elsevier Science Ltd.