3D Inspection of Electronic Boards

When inspecting electronic boards for missing or misaligned components 2D image-based inspection is often suggested as the adequate means to an end. However, in this particular inspection task a straightforward 2D approach proved difficult due to the presence of labels and text on the electronic components which could change from board to board. Furthermore, an occasional exchange occured between components, such as e.g. capacitors, with the same shape and functionality but with a different color appearance.

To tackle this problem a 3D approach was adopted in which an inline 3D laser-scanner based on the Ranger camera series from Sick was chosen as the 3D recording platform. This scanner platform was calibrated in order to capture the metric 3D shape of the electronic boards as they passed
by under the scanner on a transport line. The speed and accuracy of the laser system were the key element to deliver precise 3D models of the boards at a fast rate while being insensitive to the presence of labels and text on components or a change in their color appearance.

The recorded 3D models could then be compared to a 3D recording of a correctly assembled board. As the electronic boards did not always appear at the same place or in the same orientation under the laser-scanner, dedicated registration software was developed which computes the displacement required to overlay the recorded 3D model on the ideal 3D model in real-time. After registration the missing components such as capacitors, jumper caps, etc .. and misaligned components such as badly soldered resistors, etc.. could be detected with very high accuracy. Given a user interface, operators are able to indicate the allowed metric deviations of each component on the board, leading to a highly effective
and tunable 3D Quality Control system for electronic boards.