Stereophotogrammetry in Microassembly

Hybrid microsystems are preferably assembled serially by robots, which place the individual components successively in their intended locations. Microassembly processes are subject to various influences, which often consume a considerable part of the specified tolerance. Acceptable quality and economical yield can be achieved, if sensors are employed to detect and immediately correct deviations arising in the assembly process. This chapter describes a camera sensor for direct integration into robots for microassembly. The sensor uses beam-splitting mirror optics to record two images of the process from the top-left and the top-right with a single camera. It measures the spatial location of flat components in real-time by stereophotogrammetric evaluation of the two images. The parts are detected by means of circular marks or other features, which are deposited by electroplating or are made of fluorescent resist. Two arrays of light-emitting diodes on the sides of the mirror optics provide a constant dark-field illumination throughout the entire assembly process. The sensor uses fast methods for the evaluation of the images in order to meet the demanding real-time requirements of assembly. The compact design makes the sensor promising also for other applications such as the optical inspection of ball-grid array (BGA) packages on printed circuit boards (PCB).