Automated Visual Inspection for Solder Joints of PCB Based on 3-D Image Analysis
Toshifumi Honda*, Hisae Yamamura*, Mineo Nomoto*, Takanori Ninomiya*, Tomoharu Horii** and Yoshio Miyawaki**
*Production Engineering Research Laboratory, Hitachi Ltd. 292 Yoshida-cho Totsuka-ku, Yokohama, 244-0817 Japan
**Telecommunications Division, Hitachi Ltd. 216 Totsuka-cho, Totsuka-ku, Yokohama, 244-8567, Japan
Automated visual solder inspection was studied for different printed circuit boards (PCBs) based on 3-D-image analysis. The optical 3-D scanner accurately detects height of a solder joint from differently focused images of a laser spot. Emitted laser light on the solder joint is detected simultaneously by plural sensors whose focal points are set at different height to realize high-speed height acquisition without secondary-reflection problems caused by the specular surface of the solder joint. An inspection algorithm was designed to recognize a solder joint using detected height and the intensity image so that different shapes of solder fillet do not affect inspection performance. A solder joint is classified based on extracted 3-D features of its fillet shape and 3-D location of the lead from its pad. Inspection parameters are automatically generated with inspection parameter autogeneration using electronic component and PCB design data. Evaluation showed the system gave 100% defect detection and very few false alarms (0.13%) using autogenerated inspection parameters. Results show the technique to be promising in actual production lines for different PCBs.
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