Flip-chip alignment with a dual imaging system using a visual servoing method

Abstract

IC chip has gradually become smaller and smaller, and thus it requires high packaging density. In chip packaging, accurate alignment of electronic components with respect to PCB is crucial for high quality packaging, especially in flipchip assembly. In this paper, vision system is used to provide relative pose information between flip-chip and substrate.Based on this information, these two parts are aligned accurately using visual servoing. In order to achieve high accuracy alignment, a dual imaging system (DIS) is introduced in this work, which is composed of zoom lenses, beam-splitter, mirror, CCD, and LED illumination. It can simultaneously observe the solder bumps on flip-chip and the pattern of pads on substrate using one camera. Once the image frame containing flip-chip and substrate is obtained, their features are extracted from the preprocessed image. Extraction of the features enables us to obtain the position and orientation errors between the chip and the substrate. On the base of the measured errors, visual servoing method can determine the instantaneous velocity input of flip-chip at each servoing time and control the relative position and orientation precisely in an on-line manner. We carry out a series of experiments for various magnifications in order to evaluate the performance of the dual imaging system and the visual servoing algorithm as well.