Abstract
This article presents an optical technique for the three-dimensional (3D) shape inspection of micro-solder balls used in ball grid array (BGA) packaging, before attaching them to a board or film. This technique uses an optical source comprising spatially arranged light-emitting diodes (LEDs), and the results are derived based on the specular reflection characteristics of the BGA balls. A vision system is designed to acquire the reflected image from the micro-solder balls. For shape inspection, the locations of the LED point-light-source reflections are determined via image processing, and defects in 3D BGA shapes are detected using statistical information of the relative positions of multiple BGA balls captured in the images. Experiments were conducted to validate our proposed method, and the results revealed that it allows for simultaneous inspection of multiple BGA balls placed arbitrarily in a glass dish, without the need for precise ball-position control.
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